Дисертації з теми "Detrital Provenance"

Detrital zircon U-Pb geochronology is a useful tool for analyzing provenance in the sedimentary record. Differentiating recycled and first cycle populations in the detrital record, however, is not a straightforward process. A second potential problem in using detrital signatures to determine provenance of sediment lies in the assumption that detrital signatures of modern rivers reflect input from each exposed unit in the catchment boundaries. To investigate each of these problems, I present U-Pb analysis of detrital zircon (DZ) from modern river sand collected from 20 watersheds, 6 detrital apatite (DA) signatures from modern river sand, and 6 DA signatures from exposed strata, all within the Talkeetna Mountains (south-central Alaska). DA rarely survives past the first cycle of erosion and deposition due to its inability to survive chemical weathering, and thus dominantly represent igneous input in detrital signatures, whereas zircon can be of igneous origin or can survive multiple cycles of erosion and deposition. By comparing the DA signatures with the DZ signatures, I present a method to better differentiate first cycle, igneous sediment contributions from recycled populations within a detrital signature. The results of these comparisons show that DA signatures provide ages of igneous input into the detrital record; these ages are also reflected in the DZ signature, thus signaling these DZ populations as igneous in origin. This study also investigates the potential for DA recycling and DA input from recycled strata. To address the second problem, I present a method using GIS software and the most recent map of Alaska to create simulated signatures that records input on a scale proportionate to the exposed surface area of each bedrock unit. In ~35% of the watersheds tested, the simulated signatures predict trends similar to the DZ signatures from the modern river sands, in 55% of the watersheds tested the simulated signatures missed one or more populations present in the DZ signature, and in 10% of watersheds tested, the simulated signature predicted trends very different from the DZ signatures. In cases where the DZ and simulated signatures do not match, I believe this represents influences of climate and relief and zircon fertility.

The Alleghanian orogeny was a collision between the Gondwanan and Laurentian continents that produced the Pangean supercontinent. Mechanical and kinematic models of collisional orogens are believed to follow a critical taper geometry, where the tectonic imbrication of continental crust begins nearest to the edge of continental plate and advances toward the craton in a break- forward sequence. Studies of shear zones within the Alleghanian collisional orogen, however, suggest that most of the early deformation was translational. Propagation of craton-directed thrusts into the foreland did not occur until the latest Pennsylvanian in the southern Appalachians, and the middle-late Permian in the central Appalachians. Radiometric sedimentary provenance proxies have been applied to the late Mississippian-early Permian strata within the Appalachian foreland basin to determine the crustal composition and structural evolution of the orogen during the continental collision. U-Pb ages of detrital zircons from the early to middle Pennsylvanian sandstones suggest that most of the detritus within the Appalachian basin was recycled from Mesoproterozoic basement and Paleozoic strata of the Laurentian margin. The presence of Archean and late Paleoproterozoic age detrital zircons is cited as evidence of recycling of the Laurentian syn-rift and passive-margin sandstones. Detrital zircon ages from early-middle Permian-age sandstones of the Dunkard Group do not contain any Archean or Paleoproterozoic detrital-zircon ages, implying a source of sediment with a much more restricted age population, possibly the igneous and metamorphic internides or middle Paleozoic sandstones from the Appalachian basin. The persistance of 360-400 Ma K/Ar ages of detrital white mica suggest that the sediment was supplied from a source that was exhumed during the Devonian Acadian orogeny. Detrital-zircon and detrital-white-mica ages from Pennsylvanian-age sandstones indicate that the late Paleozoic orogen did not incorporate any significant synorogenic juvenile crust. The 87Sr/86Sr ratios of middle Pennsylvanian-early Permian lacustrine limestones within the Appalachian basin show a slight enrichment through time, suggesting that labile 87Sr-rich minerals in the Alleghanian hinterland are being exposed. Stable isotopic data from the lacustrine limestones also corroborates that the Appalachian basin became much more arid through time.

The Wrangellia composite terrane is one of the largest fragments of juvenile crust added to the North American continent since Mesozoic time, and refining its accretionary history has important implications for understanding how continents grow. New U-Pb geochronology and Hf isotopes of detrital zircons from Late Jurassic-Late Cretaceous strata from the forearc of the Wrangellia composite terrane allows more insight on the tectonic and paleogeographic history of the terrane. Our stratigraphically oldest samples from the Late Jurassic Naknek Formation have a detrital zircon U-Pb signature dominated by Early and Late Jurassic grains (195-190 Ma; 153-147 Ma). Hf isotopic compositions of these grains are juvenile to intermediate (εHf(t)=4.5-14.7). Disconformably above the Naknek Formation are two poorly understood units Ks and Kc. The Ks unit is dominated by Early to Late Jurassic grains (159-154 Ma) with a few Paleozoic grains (347-340 Ma). Hf isotopic compositions of Carboniferous-Jurassic grains are juvenile to intermediate (εHf(t)=6.0-18.8). The overlying Kc unit has Late to Early Jurassic zircons (198-161 Ma), and an increase in Paleozoic ages (374-323 Ma). Hf isotopic compositions of these grains are juvenile to intermediate (εHf(t)=4.5-14.7). Samples from the Matanuska Formation have major Late Cretaceous grains (90-71 Ma), and minor Early Cretaceous (137-106 Ma), Late to Early Jurassic (200-153 Ma), Paleozoic (367-277 Ma), and Precambrian grains (2597-1037 Ma). Hf compositions have a wider range from both the Late Cretaceous grains (εHf(t)=-1.5-14.9) and Paleozoic-Precambrian grains (εHf(t)=-23.7-16.3). Our results suggest an evolving provenance from Late Jurassic to Late Cretaceous time for the Wrangellia composite terrane forearc basin. The Late Jurassic Naknek Formation samples were dominantly derived from a juvenile to intermediate Jurassic igneous sediment source. During Early Cretaceous time, there is a slight increase in the number of Paleozoic grains in the Ks and Kc unit samples. The Early Cretaceous sediments have a mostly positive Hf isotopic compositions suggesting exhumation of Jurassic and Paleozoic juvenile igneous sediment sources. By Late Cretaceous time, our data illustrates another increase in Paleozoic grain abundances, in addition to the introduction of Precambrian grains, all with widely variable Hf isotopic compositions. We interpret this to reflect a larger sediment flux from the interior of Alaska where more evolved igneous rocks of that age are found.

Originally mapped as Precambrian and uppermost Ocoee Supergroup (OS), recent discoveries of Paleozoic microfossils have placed the Walden Creek Group (WCG), eastern Tennessee, into a younger depositional framework (Silurian or younger). In this study, monazite geochronology using SIMs, detrital zircon U-Pb geochronology determined by LA-ICP-MS, feldspar compositions determined by microprobe, zircon-tourmaline-rutile (ZTR) indices, and framework mineral modes were used to characterize provenance of sandstones of the WCG. Monazite ages cluster at 450 and 1050 Ma. All Ordovician ages are from grains that, in BSE images, have inclusion-rich microtextures interpreted as diagenetic and/or metamorphic, thus requiring that the WCG was deposited prior to Taconic metamorphism. The WCG heavy mineral suite is similar to the OS in its low modal abundance of monazite, but contains a slightly higher ZTR index. WCG Feldspar compositions are sodium poor-Kfs and sodic plagioclase, like the OS. Detrital zircon U-Pb ages for three formations of the WCG (seven samples total, n = 620) match the Ocoee signature. The dominant age modes are at ca. 1000 and 1150 Ma, with smaller modes at 1450 and 650 Ma. The monazite ages and supporting observations prove the WCG is not Paleozoic and its source rock signature matches the underlying OS.

Tectonic development of the Andean Cordillera has profoundly changed the topography, climate, and vegetation patterns of the southern central Andes. The Cenozoic Bermejo Basin in Argentina (30 degrees S) provides a key record of thrust belt kinematics and paleoclimate south of the high-elevation Puna Plateau. Ongoing debate regarding the timing of initiation of upper plate shortening and Andean uplift persists, precluding a thorough understanding of the earlier tectonic and climatic controls on basin evolution. We present new sedimentology, detrital geochronology, sandstone petrography, and subsidence analysis from the Bermejo Basin that reveal siliciclastic-evaporative fluvial and lacustrine environments prior to the main documented phase of Oligocene-Miocene shortening of the Frontal Cordillera and Argentine Precordillera. We report the first radiometric dates from detrital zircons collected in the Cienaga del Rio Huaco Formation, previously mapped as Permian, that constrain a Late Cretaceous (95-93Ma) maximum depositional age. Provenance and paleocurrent data from these strata indicate that detritus was derived from dissected arc and cratonic sources in the north and northeast. Detrital zircon U-Pb ages of 37Ma from the overlying red beds suggest that foredeep sedimentation began by at least the late Eocene. At this time, sediment dispersal shifted from axial southward to transversal eastward from the Andean Arc and Frontal Cordillera. Subsidence analysis of the basin fill is compatible with increasing tectonic deformation beginning in Eocene time, suggesting that a distal foredeep maintained fluvial connectivity to the hinterland during topographic uplift and unroofing of the Frontal Cordillera, prior to Oligocene-Miocene deformation across the Precordillera.

Thesis (M.S. in geology)--Washington State University, May 2009.
Title from PDF title page (viewed on July 15, 2009). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 76-83).

Strata in the Cook Inlet forearc basin in south-central Alaska record the effects of tectonic events related to normal subduction and two flat-slab subduction events. Through detrital zircon geochronology we track provenance changes of strata deposited in a forearc basin in conjunction with these different subduction processes. Our data from strata deposited concurrent with normal subduction help to confirm previous provenance models of forearc basins that suggest provenance is sourced primarily from a proximal, coeval arc. However, compared to these models, our data from strata deposited coincident to flat-slab events show markedly different provenance signatures dependent upon: (1) geographic position relative to the flat-slab event; (2) pre-established, or lack thereof, topography; and (3) type of flat-slab event. Detrital zircon signatures of strata deposited in the Cook Inlet after flat-slab subduction of a mid-ocean ridge diversify to include older detritus found in the distal inboard region. This distal signature is then incrementally cut-off in younger strata due to deformation of the upper-plate from progressive insertion of a shallowly subducted oceanic plateau. Detrital zircon signatures for strata associated with each flat-slab event are largely older than depositional age due to the lack of coeval arc activity. Our data may help to improve the ability to recognize other flat-slab events through detrital zircon geochronology. In particular, changes in detrital zircon signatures found in strata deposited during flat-slab subduction of an oceanic plateau correlate well with the exhumation of rocks associated with the propagation of deformation in the over-riding plate due to plate coupling.

Thesis advisor: J. Christopher Hepburn
The Nashoba terrane of SE New England is one of three peri-Gondwanan tectonic blocks caught between Laurentia and Gondwana during the closure of the Iapetus Ocean in the early to mid- Paleozoic. U-Pb analyses (LA-ICP-MS) were carried out on zircon suites from the meta-sedimentary rocks of the Nashoba terrane. The youngest detrital zircons in the meta-sedimentary rocks of the Nashoba terrane are Ordovician in age. There is no significant difference in age between meta-sedimentary units of the Nashoba terrane across the Assabet River Fault Zone, a major fault zone that bisects the NT in a SE and a NW par. Zircon in meta-sedimentary rocks in the Marlboro Fm., the oldest unit of the Nashoba terrane, is rare, which may reflect the basaltic nature of the source material, and is commonly metamict. The Marlboro Fm. contained the oldest detrital grain of all the analyzed samples, with a core of ~3.3 Ga and rim of ~2.6 Ga indicating that it was sourced from Archaen crustal material. Detrital zircons from the Nashoba terrane show a complete age record between the Paleoproterozoic and Paleozoic that strongly supports a provenance from the Oaxiqua margin of Amazonia. The detrital zircon suite of the Nashoba terrane is distinct from both Avalonia and the Merrimack belt; however, they resemble zircon suites from Ganderia. This study proposes that the Nashoba terrane of Massachusetts correlates with the passive trailing edge of Ganderia. Finally, metamorphic zircon analyses of the terrane show that the Nashoba terrane experienced a peak in hydrothermal fluid infiltration during the Neoacadian orogeny
Thesis (MS) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences

The Taimyr Peninsula is a key element in the circum-Arctic region and represents thenorthern margin of the Siberian Craton. The Taimyr Peninsula is a late Paleozoic fold andthrust belt and preserves late Paleozoic through Mesozoic siliciclastic sedimentarysuccessions and providing an ideal location to investigate the Paleozoic to Mesozoictectonic evolution associated with the Uralian orogeny, the Siberian Trap magmatism andopening of Amerasia Basin within a circum-Arctic framework. Multiple methods areadopted, including petrography, heavy mineral analysis and detrital zircon U-Pbgeochronology for provenance investigation, apatite fission track dating for revealingthermal history and balanced cross section for understanding the deformation style ofTaimyr.The results of this thesis indicate that the Late Carboniferous to Permian sediments ofsouthern Taimyr were deposited in a pro-foreland basin of the Uralian orogen during theUralian orogeny. In the Triassic, the siliciclastic deposits still show a strong Uraliansignature but the initiation of Siberian Trap-related input begins to be significant. Erosionof the Uralian orogen has reached a deep metamorphic level. By Late Jurassic andCretaceous time, the deposition setting of southern Taimyr is an intracratonic basin.Erosion and input from Uralian sources waned while greater input from SiberianTrap-related rocks of the Taimyr region dominated. The Taimyr Peninsula underwent atleast three cooling and uplifting episodes: 280 Ma, 250 Ma and 220 Ma, corresponding tothe Uralian orogeny, the Siberian Traps and the late Triassic transpression.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: In press. Paper 3: Manuscript. Paper 4: Manuscript.

This thesis greatly enhanced our understanding of the continental-scale links between sedimentary basins and far-field tectonic processes. A novel, multi-method approach was used to reveal a previously unknown, major mountain building event in southwest Queensland that fundamentally altered the history of the Drummond Basin in central Queensland. An unusually large river system was identified, which transported the gravel and sand across the basin from a distant source region. This thesis has provided new insights into the mid-Paleozoic geological history of the Australian continent, established new approaches to tracing the origin of sediment and resolving the complex histories of sedimentary basins.

The Andes Mountains provide an ideal natural laboratory to analyze the relationship between the tectonic evolution of a subduction margin, retroarc shortening, basin morphology, and volcanic activity. Timing of initial shortening and foreland basin development in Argentina is diachronous along strike, with ages varying by 20-30 million years. The Neuquén Basin (32°S-40°S) of southern-central Argentina sits in a retroarc position and provides a geological record of sedimentation in variable tectonic settings from the Late Triassic to the early Cenozoic including: 1.) active extension and deposition in isolated rift basins in the Late Triassic-Early Jurassic; 2.) post-rift back-arc basin from Late Jurassic-Late Cretaceous; 3.) foreland basin from Late Cretaceous to Oligocene; and 4.) variable extension and contraction along-strike from Oligocene to present. The goal of this study is to determine the timing of the transition from post-rift thermal subsidence to foreland basin deposition in the northern Neuquén Basin and then assess volcanic activity and composition during various tectonic regimes. The Aconcagua and Malargüe areas (32°S and 35°S) are located in the northern segment of the Neuquén Basin and preserve Upper Jurassic to Miocene sedimentary rocks, which record the earliest phase of shortening at this latitude. This study presents new sedimentological and detrital zircon U-Pb data from the Jurassic to latest Cretaceous sedimentary strata to determine depositional environments, stratigraphic relations, provenance, and maximum depositional ages of these units and ultimately evaluate the role of tectonics on sedimentation in this segment of the Andes. The combination of provenance, basin, and subsidence analysis shows that the initiation of foreland basin deposition occurred at ~100 Ma with the deposition of the Huitrín Formation, which recorded an episode of erosion marking the passage of the flexural forebulge. This was followed by an increase in tectonic subsidence, along with the appearance of recycled sedimentary detritus, recorded in petrographic and detrital zircons analyses, as well development of an axial drainage pattern, consistent with deposition in the flexural forebulge between 95 and 80 Ma. By ca. 70 Ma the volcanic arc migrated eastward and was a primary local source for detritus. Growth structures recorded in latest Cretaceous units very near both the Aconcagua and Malargüe study areas imply 35-40 km and 80-125 km of foreland migration between 95 and 60 Ma in the Aconcagua and Malargüe areas, respectively. Strata ranging in age from Middle Jurassic to Neogene were analyzed to determine their detrital zircon U-Pb age spectra and Hf isotopic composition to determine the relationship between magmatic output rate, tectonic regime, and crustal evolution. When all detrital zircon data are combined, significant pulses in magmatic activity occur from 190-145 Ma, and at 128 Ma, 110 Ma, 69 Ma, 16 Ma, and 7 Ma. The duration of magmatic lulls increased markedly from 10-30 million years during back-arc deposition (190-100 Ma) to ~40-50 million years during foreland basin deposition (100-~30 Ma). The long duration of magmatic lulls during foreland basin deposition could be caused by flat-slab subduction events during the Late Cretaceous and Cenozoic or by long magmatic recharge events. There are three major shifts towards positive Hf isotopic values and all are associated with regional extension events whereas compression seems to lead to more evolved isotopic values.

The Middle Ordovician Ancell Group, including the St. Peter Sandstone, Glenwood Shale and Starved Rock Formation, records intracontinental basin development during eustatic sea level changes in Iowa and Illinois. The St. Peter Sandstone overlies the Prairie du Chien Group across an erosional unconformity that marks a major sequence boundary, whereas upper contact of the St. Peter Sandstone with the Glenwood Shale also is a second sequence boundary. Data from 80 wells, selected well logs, and 20 cores were integrated to refine the high-resolution sequence stratigraphy of the Ancell Group. Two main sequences bounded by three sequence boundaries are interpreted to represent 3rd order sequences. Distinctive shallowing-upward parasequences bounded by flooding surfaces in many cores record higher frequency relative sea level fluctuations in the Ancell Group, but these cannot presently be correlated regionally. Facies variations define an aggradational transgressive systems tract TST), a prograding highstand systems tract (HST) and down stepping falling stage system tract (FSST) in both the St. Peter Sandstone and the Glenwood Shale-Starved Rock Formation units. The St. Peter Sandstone thickens towards the northeast and thins to the northwest and southwest in Iowa. In contrast, the St. Peter Sandstone in Illinois thickens to the south likely recording a prolonged FSST incised valley or channel fill. Detrital zircon geochronology of 13 samples from the St. Peter Sandstone and Starved Rock Formation define common peaks at 1100-1500 Ma and 2500-2700 Ma with minor components at 1670-1750 Ma and 3000-3600 Ma. The detrital zircon signature is dominated by Archean, and Grenville (1000-1300 Ma) ages. The detrital zircon geochronology indicates that the Ancell Group was sourced directly from the Archean Superior Province to the north and Grenville Province to the northeast, although recycling of Archean grains from the Paleoproterozoic Huron Basin cannot be ruled out. The near complete lack of 1800-1900 Ma ages argues against derivation of detritus from the Trans-Hudson or Penokean Orogens. The Transcontinental Arch northwest of the Iowa Basin acted as a barrier to sediment transport from the Trans-Hudson Orogen. Basement rocks of the Penokean Orogen are inferred to have been covered by water or younger sediments southeast of the Iowa Basin. CIA analyses of Ordovician shale samples from around the Transcontinental Arch indicate that the climate condition during Middle Ordovician time was warm and humid. This is consistent with a paleoclimate interpretation where mechanical erosion and chemical weathering yielded first cycle mature quartz arenites (Witzke, 1980).

Detrital monazite Th-Pb and detrital zircon U-Pb and U-Th/He double-dating coupled with sandstone petrography and exhumation rates can be used to test for sediment recycling in Pennsylvanian sandstones within the Alleghenian clastic wedge. The Alleghenian clastic wedge is a logical system in which to test for sediment recycling as four major collisional events (Grenville, Taconic, Acadian and Alleghenian orogenies) likely reworked the continental margin and recycled siliciclastic sediment. The combination of these geochronologic and thermochronologic methods provide a more accurate assessment of the proportion of recycled sediment in the Grundy Formation (sublitharenite) and the Corbin Sandstone (quartz arenite), which past studies and the use of standard zircon U-Pb alone could not distinguish. Recognition of sediment recycling is thus critical for sedimentary provenance studies, which assume a direct path from sediment source to depositional basin. Zircon U-Pb age modes for both formations include the dominant “Grenville doublet” along with a lesser component of Granite-Rhyolite and Taconic age modes. The Corbin Sandstone is temporally more expansive, with age modes associated with the Yavapai-Mazatzal and Kenoran orogenies not present in the Grundy Formation. Monazite Th-Pb age modes are younger than zircon U-Pb for both samples, with dominant modes in the Taconic, Acadian, and Alleghenian, and only minor age modes associated with the Grenville Orogeny. The extent of sediment recycling was quantified by the difference in crystallization ages and exhumation/cooling ages of detrital zircon. This difference in time (∆t) becomes higher in the case of recycling (> ~300 Ma). A median 288 Ma ∆t cutoff value between first-cycle and multi-cycle Grenville aged zircons was calculated using post-Grenville exhumation rates. Furthermore, “detrital diagenetic monazite” grains older than the 312 Ma age of deposition are present in both the Grundy Formation and Corbin Sandstone and proves the occurrence of sediment recycling. In conclusion, most detrital grains of Grenville origin and older are likely multi-cycle, while detrital grains associated with the Taconic, Acadian, Neo-Acadian, and Alleghenian orogenies are likely first-cycle in origin.

O Sistema de Nappes Carrancas compõe um sistema de nappes que circunda ao sul o Cráton do São Francisco e é formado pela Unidade Biotita Xisto e pelas formações Campestre e São Tomé das Letras do Grupo Carrancas. A Unidade Biotita Xisto contém veios de quartzo e xistosidade anastomosada e é formada por quartzo, biotita, muscovita, clorita e, localmente plagioclásio, carbonato e granada. A Formação Campestre é formada por quartzitos intercalados a filitos/xistos que variam de cloritóide filitos grafitosos, com muscovita, quartzo e turmalina e, localmente, granada a xistos com granada, estaurolita e cianita. A investigação da Unidade Biotita Xisto como autóctone em relação ao Cráton do São Francisco, seu potencial agrupamento com o Grupo Carrancas em uma megassequência deposicional, bem como sua comparação com a unidadealóctone Xisto Santo Antônio (Nappe Andrelândia) constituem parte dos objetivos deste estudo. Para tal, foram feitas análises químicas e isotópicas (Sr e Nd) em rocha total e geocronologia U-Pb em cristais de zircão detríticos, tanto na Unidade Biotita Xisto como na Formação Campestre, com intuito de elucidar a relação entre as mesmas e compará-las com dados da literatura disponíveis para o Xisto Santo Antônio. A Unidade Biotita Xisto apresenta características químicas compatíveis com sedimentos que sofreram intemperismo químico de intensidade e período de tempo moderados, depositados em ambientes de colisão continental, com área-fontecomposta essencialmente por rochas félsicas. Assinaturas de elementos traço e isotópicas de Sr ( \'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' entre 0,713 e 0,715) e Nd (\'\'épsilon\' IND.Nd\' entre -6 e -5) indicam contribuição de arco magmático e crosta continental e diferem, portanto, daquelas esperadas em ambientes de margempassiva. A mesma contribuição é observada para o Xisto Santo Antônio, cuja área fonte registra importante assinatura de material juvenil. As idades U-Pb LA-MC-ICP MS obtidas em cristais de zircão mostram contribuição principal de rochas do final do Criogeniano e contribuição secundária do Riaciano. A classe modal ao redor de 665 Ma é comparável com a idade cristais de zircão detrítico do Xisto Santo Antônio, o que aponta parauma mesma área-fonte principal para ambas unidades. A deposição dos sedimentos precursores da Unidade Biotita Xisto ocorreu entre 630-611 Ma, sendo as fontes principais os granulitos cálcio-alcalinos e rochas vulcânicas co-genéticas, além de granitos sin-colisionais da Nappe Socorro-Guaxupé. A pouca representatividade de idades paleoproterozóicas e a ausência de assinaturas químicas de margem passiva, inviabilizam as rochas do Cráton doSão Francisco como parte da área-fonte. Desta forma, a Unidade Biotita Xisto não é autóctone em relação ao Cráton do São Francisco, sendo, potencialmente, a unidade que compõe a frente da Nappe Andrelândia. Por outro lado, a Formação Campestre possui assinatura geoquímica de sedimentos que sofreram uma intensa reciclagem e alteração da composição do sedimento original. As assinaturas químicas de elementos traço e isotópicas Sr e Nd indicam contribuição de crosta continental superior, com componente de crosta antiga e sem afinidade com sedimentos depositados em margem passiva (\'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' entre 0,74 e 0,76; \'\'épsilon IND.Nd\' entre -18 e -15). Os zircões detríticos analisados forneceram idades U-Pb LA-MC-ICP-MS variadas, do Toniano ao Mesoarqueano, correlacionáveis com rochas vulcânicas e plutônicas do Cráton do São Francisco, com as faixas marginais do Cráton de Angola e/ou faixas orogênicas do Cráton Amazônico e com rochas dos arcos Mara Rosa e Goiás.A abrangência das idades U-Pb da Formação Campestre e das formações Chapada dos Pilões e Paracatu, permite a correlação, no Orógeno Brasília, entre os Grupos Carrancas e Canastra. A paleogeografia mais provável é a de um ambiente de rifte, antecessor à deriva e aoestabelecimento de uma margem continental passiva.
The Carrancas Nappe System composes a system of nappes that surround the southern margin of the São Francisco Craton and is formed by the Biotite Schist Unit and by the Campestre and São Tomé das Letras formations of the CarrancasGroup. The Biotite Schist Unit encompass quartz veins and anastomosed schistosity and is formed by quartz, biotite, muscovite, chlorite and, locally plagioclase, carbonate and garnet. The Campestre Formation is composed by interleaved quartzites and phyllite/schist that varies from graphite-chloritoid phyllites, with muscovite, quartz, tourmaline and garnet, and locally garnet schists and schists with garnet, staurolite and kyanite. The investigation of the Biotite Schist Unit as authochtonous in relation to the São Francisco Craton, it´s potencial grouping with the Carrancas Group in a deposicional megassequence, as well as it´s comparison with the allochthonous Santo Antônio Schist (Andrelândia Nappe) is part of the goals of this study. For this purpose, chemical and isotopic (Sr and Nd) whole rock analysis were obtained, along with U-Pb detrital zircon data, in the Biotite Schist Unit and also in the Campestre Formation, in order to elucidate the relationship between these units and compare them with literature data available for theSanto Antônio Schist. The Biotite Schist Unit show chemical characteristics compatible with sediments that underwent chemical weathering of moderate intensityand time, deposited in continental collision setting, with source region composed essentially by felsic rocks. Trace elements and Sr isotopic signatures ( \'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' between 0,713 and 0,715) and Nd (\'\'épsilon IND.Nd\' between -6 and -5) points to contribution from magmatic arc and continental crust, and are different from the expected for passive margin settings. The same contribution is observed in the Santo Antônio Schist, which source area registers an important juvenile material signature. The U-Pb LA-MC-ICP MS zircon data show major contribution from rocks of the later Cryogenian and minor contribution from the Ryacian. The modal class around 655 Ma is comparable with the U-Pb detrital zircon data from the Santo Antônio Schist, pointing to the same source area for both units. The deposition of the precursors sediment of the Biotite Schist Unit occurred between 630 - 611 Ma, and the main sources were the calk-alcaline granulites and co-genetic volcanic rocks, besides the Socorro-Guaxupé Nappe sin-collisional granites. The low representation of Paleoproterozoic ages and the absence of passive margin chemical signatures preclude the rocks of the São Francisco Craton as part of the source area. Thus, Biotite Schist Unit is not an autochthonous unit in relation to the São Francisco Craton, and is, potentially, the unit that composes the Andrelândia Nappe front. On the other hand, the Campestre Formation has geochemical signatures of sediments that underwent intense recycling and alteration of the original sediment. The trace element and Sr and Nd isotopic signatures indicates upper continental crust contribution, with older crust component and no affinity with passive margin sediments ( \'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' between 0,74 and 0,76; \'épsilon\' IND.Nd\' between -18 and -15). The U-Pb LA-MC-ICP MS detrital zircon data provide varied ages, from the Tonian to the Mesoarchean, correlated withvolcanic and plutonic rocks of the São Francisco Craton, with the marginal belts of the Angola Craton, and/or orogenic belts of the Amazonian Craton and with the Mara Rosa and Goiás magmatic arcs. The range of the U-Pb ages of the Campestre Formation and the Chapada dosPilões and Paracatu formations, allows the correlation, in the Brasília Orogen, of the Campestre and Canastra groups. The most likely paleogeography is that of a rift setting, before the continental drift and the establishment of a passive continental margin.

第19回名古屋大学年代測定総合研究センターシンポジウム平成18(2006)年度報告 Proceedings of the 19th symposiumon on Chronological Studies at the Nagoya University Center for Chronological Research in 2006 日時:平成19 (2007)年1月15日(月)～17日(水) 会場:名古屋大学シンポジオン Date:January15th-17th, 2007 Venue:Nagoya Uhiversity Symposion Hall

Arc–continent collision is a significant plate boundary process that results in crustal growth. Since the early stages of evolution are often obscured in mature orogens, more complete understanding of the processes involved in arc–continent collision require study of young, active collision settings. The Banda Arc presents an exceptional opportunity to study a young arc–continent collision zone. This thesis presents aspects of the geology and geochronology of Ataúro and the Aileu Complex of Timor-Leste, and the tectonics of the Banda Arc.
U–Pb dating of detrital zircons from the Aileu Complex by LA-ICPMS show major age modes at 270–440 Ma, 860–1240 Ma and 1460–1870 Ma. The youngest zircon populations indicate a maximum depositional age of 270 Ma. The detrital zircon age populations and evidence for juvenile sediments within the sequence favours a synorogenic setting of deposition of sediments sourced from an East Malaya – Indochina terrane.
Previous uncertainty in aspects of the cooling history for the Aileu Complex is resolved with 39Ar/40Ar geochronology of hornblende. Cooling ages of 6–10 Ma are established, with the highest metamorphic grade parts of the Complex yielding the older ages. Cooling ages of 10 Ma imply that metamorphism of the Aileu Complex must have commenced by at least ~12 Ma. Metamorphism at this time is attributed to an arc setting rather than the direct result of collision of the Australian continent with the Banda Arc, an interpretation consistent with the new provenance data.
Geological mapping of Ataúro, an island in the volcanic Banda Arc north of Timor, reveals a volcanic history of bi-modal subaqueous volcanism. 39Ar/40Ar geochronology of hornblende from dacitic lavas confirms that volcanism ceased by ~3 Ma. Following the cessation of volcanism, coral reef marine terraces have been uplifted to elevations of 700 m above sea level. Continuity of the terraces at constant elevations around the island reflects regional-scale uplift most likely linked to sublithospheric processes such as slab detachment.
North of Timor, the near complete absence of intermediate depth seismicity beneath the inactive segment of the arc is attributed to a slab window that has opened in the collision zone and extends to 350 km below the surface. Differences in seismic moment release around this slab window indicate asymmetric rupture, propagating to the east at a much faster rate than to the west. If the lower boundary of this seismic gap signifies the original slab rupture then the slab window represents ~4 m.y. of subsequent subduction and implies that collision preceded the end of volcanism by at least 1 m.y.
Variations in seismic moment release and stress state across the transition from subduction of oceanic crust to arc–continent collision in the Banda Arc are investigated using earthquake catalogues. It is shown that the slab under the western Savu Sea is unusual in that intermediate depth (70–300 km) events indicate that the slab is largely in down-dip compression at this depth range, beneath a region of the arc that has the closest spacing of volcanoes in the Sunda–Banda arc system. This unusual state of stress is attributed to subduction of a northern extension of the Scott Plateau. Present day deformation in the Savu Sea region may be analogous with the earliest stages of collision north of Timor.

Dados isotópicos U-Pb, Hf e de O foram obtidos em zircões detríticos das unidades do final do Paleozoico e início do Mesozoico da Bacia do Paraná, sudeste do Brasil, com o objetivo de determinar a proveniência dos sedimentos, assim como contribuir para o entendimento da evolução tectônica da bacia. Assinaturas isotópicas Sm-Nd e Pb-Pb em amostras de rocha-total também foram obtidas com o intuito de auxiliar na interpretação sobre as áreas fontes. A seção estudada, Coluna White em Santa Catarina, inclui rochas de 11 unidades estratigráficas (da base para o topo): Formação Rio do Sul, Formação Rio Bonito, incluindo os membros Triunfo, Paraguaçu e Siderópolis, Formação Palermo, Formação Irati, Formação Serra Alta, Formação Teresina, Formação Rio do Rasto, subdividida nos membros Serrinha e Morro Pelado, e Formação Botucatu, Idades U-Pb foram obtidas em 1941 grãos de zircão detrítico e variam de 242 Ma a 3,4 Ga. Todas as unidades sedimentares apresentam quatro grupos principais de zircões detríticos, Neoarqueano (2,7-2.5 Ga), Paleoproterozoico Médio (2,0-1,8 Ga), Grenviliano (1,1-0,9 Ga) e Brasiliano (850-490 Ma), refletindo a importância do embasamento Pr-e-Cambriano que bordeja a parte leste da bacia como áreas fontes, tais como as Faixas Dom Feliciano, Kaoko e Namaqua-Natal, incluindo o embasamento local datado em 584 Ma. O Membro Siderópolis apresenta uma importante mudança nas fontes dos sedimentos que preencheram a Bacia do Paraná, pois é a partir dessa unidade que o pico de idade permiana (266 a 290 Ma) é observado. Esse pico persiste até o topo da seção, a Formação Botucatu. As assinaturas isotópicas de O e Hf dos zircões detríticos mostram que parte dos grãos do Paleoproterozoico Médio é provavelmente de rochas do embasamento atualmente recoberto, que estava exposto até a deposição da Formação Rio Bonito. Os isotópos de Hf e O também mostram que parte dos zircões com idade grenviliana é proveniente de rochas argentinas, o que implica em longas distâncias de transporte. As assinaturas isotópicas de parte dos grãos permianos os ligam a fontes da Argentina e Chile, sendo que parte desses grãos possui forma mais arredondada, o que sugere que eles alcançaram a bacia pelo transporte em ambientes subaquáticos e não somente pelo ar (quedas de cinzas vulcânicas) como é comumente apontado. Outros picos de idade mais jovens (Ordoviciano ao Carbonífero), observados a partir da Formação Palermo e nas unidades superiores, também são provenientes de fontes argentinas e chilenas, mostrando a importância dos detritos de fontes distantes durante o preenchimento da bacia. Os dados Sm-Nd e Pb-Pb em rocha total mostram que os sedimentos da Bacia do Paraná apresentam predominância de fontes de origem crustal. As assinaturas são semelhantes aos granitoides de Santa Catarina, rochas da Faixa Ribeira, do Escufo Brasileiro, das Faixas Namaqua-Natal e Kaoko, Terreno Arequipa-Antofalla (embasamento dos Andes) e granitoides do Norte da Patagônia. Esses dados corroboram os padrões de zircões detríticos observados, que apontam para áreas fontes tanto proximais quanto distais. Além disso, as idades modelo Sm-Nd (\'T IND. DM\') obtidas são mais antigas que 1,4 Ga e mais negativas (-10 a -15) nas unidades inferiores (Formação Rio do Sul até o Membro Paraguaçu), enquanto que as unidades superiores apresentam valores de \'\'épsilon\' IND.Nd(0) entre -6 a -12 e idades modelo \'T IND.DM\' mais jovens que 1,5 Ga, sugerindo a participação de uma fonte mais jovem a partir da deposição do Membro Siderópolis, conforme foi observado pelos dados de zircão detrítico (pico de idade permiana)
U-Pb, Hf and O isotope data were obtained from detrital zircons from late Paleozoic-early Mesozoic units from Paraná Basin, southeastern Brazil, in order to constain the provenance of the sediments, as well as to contribute to the understanding of the tectonic evolution of the basin. Whole rock Sm-Nd and Pb-Pb isotopic signatures were also taken in order to help the interpretation. The studied section, White Column in Santa Catarina state, includes rocks from 11 stratigraphic units (from base to top): Rio do Sul Formation, Rio Bonito Formation (Triunfo, Paraguaçu and Siderópolis members), Palermo Formation, Irati Formation, Serra Alta Formation, Teresina Formation, and Rio do Rasto Formation (Serrinha and Morro Pelado members) and Botucatu Formation. U-Pb ages were obtained on 1941 detrital zircons and range from 242 Ma to 3400 Ma. All sedimentary units show four main detrital age groups, Neoarchean (2700-2500 Ma), mid-Paleoproterozoic (2000-1800 Ma), Grenvillian (1100-900 Ma) and Brasiliano (850-490 Ma), reflecting the importance of the Precambrian basement bordering the east side of the basin, such as Dom Feliciano, Kaoko and Namaque-Natal Belts as source areas, including the local basement that was dated at 584 Ma. The Siderópolis Member shows an important change in the source of sediments with a Permian age-peak (266 to 290 Ma). This age-peak persists towards the top of the section until the Botucatu Formation. O and Hf isotopic signatures from the detrital zircons show that a portion of the mid-Paleoproterozoic grains is probably from rocks of the presently covered basement, which was exposed until the deposition of the Rio Bonito Formation. O and Hf isotopes also show that some Grenvillian aged zircons are from Argentinian rocks, which implies a long transport distance. Isotopic signatures of part of the Permian grains also link them to sources from Argentina and Chile, and part of these grains has more rounded shapes, suggesting that they reached the basin after long distance traveling on subaquatic environment and nor only through the air (ash falls) as it is commonly accepted. Other younger age peaks (Ordovician to Carboniferous) found from Palermo Formation upsection are also linked to Argentinian and Chilean sources, showing the importance of distant sources during the filling of the basin. The Sm-Nd and Pb-Pb data on whole rocks show that the sediments from the Paraná Basin present predominance of sources with crustal origin. Osotopic signatures are similar to granitoid rocks from Santa Catarina, Ribeira Belt, Brazilian Shield, Namaqua-Natal and Kaoko Belts, as well as the Arequipa-Antofalla terranes (Andes basement) and granitoids from North Patagonia. These data corroborate the observed detrital zircon patterns thar point to both proximal and distal source areas. \'T IND.DM\' model ages older than 1.4 Ga and more negative (-10 to -15) epsilon values were observed in the lower units (Rio do Sul Formation to Paraguaçu Member), while the upper units show \'\'épsilos\' IND.Nd(0)\' values ranging from -6 to -12 and \'T IND. DM\' model ages younger than 1.5 Ga, corroborating the addition of a younger source starting from the Siderópolis Member deposition upwards, as noted by detrital zircon data (Permian age-peak).

It is now accepted that the last British-Irish Ice Sheet (BIIS) was highly dynamic and drained by numerous fast flowing ice streams. This dynamic nature combined with its maritime location made the BIIS sensitive to the rapid climate change that characterised the Last Glacial Interglacial Transition. Gaining an understanding of the behaviour of the BIIS at this time is important to explore the nature of forcing between ice sheets and climate. This thesis presents new chronological data relating to the deglaciation of the northwest sector of the BIIS (NW-BIIS) from onshore dating of moraines using cosmogenic exposure dating. This improved chronological framework is supported by offshore data in the form of a newly constructed Ice Rafted Detritus (IRD) record from the offshore sediment core MD95-2007. These data suggest that deglaciation commenced sometime after 18 ka and that the NW-BIIS was located close to the present day shoreline by 16 ka. Further provenance analysis of the IRD using U-Pb dating of detrital minerals demonstrates that during the Last Glacial-Interglacial Transition MD95-2007 was being supplied distal IRD from a source(s) to the west. The absence of diagnostic Scottish material suggests that after retreat to the coastline at 16 ka calving margins were not re-established during Greenland Interstadial 1. By combining these results with existing data relating to the deglaciation of the NW-BIIS it is possible to summarise the deglaciation history of the NW-BIIS from the continental shelf to mountainous source regions and compare this to numerical models of BIIS behaviour during this time. With a better understanding of the chronology of NW-BIIS retreat it is possible to relate the timing of initial deglaciation to possible forcing factors and gain a better understanding of the response of a marine based sector of an ice sheet to rapid climate change.

This item is only available electronically.
The Amadeus Basin is a Late Proterozoic to early Phanerozoic basin in central Australia, which records a complex sedimentation and thermal history throughout the basin. This study presents new analysis of zircon and apatite samples for detrital provenance and thermal evolution, focused in the southern Amadeus Basin (KULGERA). While the thermal history and provenance are well constrained for the north, such data for the southern region of the basin are lacking. Nineteen outcrop samples are analysed for detrital zircon U-Pb and provenance and one BR05DD01 drill-core sample is analysed for the AUPb and AFT ages. All sampled zircons share a similar prominent peak at ca. 1086 – 1163 Ma and a second prominent peak at ca. 1554 – 1791 Ma. However, all formations do not share a similar provenance due to the major tectonic events from the Musgrave Province and Arunta Region influencing sedimentation and architecture in the Amadeus Basin. Two age peaks derived in the AFT plot at114 +/- 11 Ma and 223 +/- 13 Ma suggest an extensive thermal history in the apatite partial annealing zone. Due to the insufficient number of analysed apatite grains, this hinders the identification of age populations and more detailed age calculations. More data would be required for the apatite analysis in order to conclude a specified age population and age calculation.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR

This item is only available electronically.
Despite the prolific hydrocarbon and geothermal potential within the Cooper-Eromanga Basin, the thermal history of the region has largely remained elusive. This study presents new fission track, U-Pb and rare earth geochemical data for apatite samples from five wells within the Cooper-Eromanga Basin. Based on these data, thermal history models were constructed and an apatite provenance study was carried out. The apatite samples taken from the upper Eromanga Basin sediments (Winton, Mackunda and Cadna Owie Formations) yielded a dominant population of early Cretaceous and minor population of late Permian – Triassic apatite ages that are (within error) equivalent to corresponding fission track age populations. Furthermore, the obtained Cretaceous apatite ages correlate well with the stratigraphic ages for each analysed formation, suggesting (1) little time lag between apatite exposure in the source region and sediment deposition; and (2) that no significant (>~100oC) reheating occurred after deposition. The apatites were likely distally sourced from an eastern Australian volcanic arc, (e.g. the Whitsunday Igneous Association), mixed with sediment sources from the New England and/or Mossman Orogens. Deeper samples (>2000m) from within the Cooper Basin (Toolachee Formation) yielded (partial) reset fission track ages, indicating heating to temperatures exceeding ~80-100oC after deposition. The associated thermal history models are broadly consistent with previous studies and suggest that maximum temperatures were reached at ~95-70 Ma as a result of progressive heating by sedimentary burial and/or radiogenic basement heat loss. The interpretation of subsequent late Cretaceous – Palaeogene cooling remains more enigmatic and may be related with enhanced thermal conductivity as a response to aquifer flow and/or cementation. Four of the five wells recorded a Neogene heating event: however, more data would be required to assess the significance of this more recent thermal perturbation.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2017

The Neoproterozoic (1000–538 Ma) was a period of some of the most significant changes to Earth’s systems throughout its c. 4.5-billion-year history. The tectonic system drove the final amalgamation of Rodinia, subsequent breakup coinciding with the emplacement of numerous large igneous provinces, and the initial stages of Gondwana amalgamation during the late Ediacaran. Current evidence suggests two long lived global glacial events occurred, the Sturtian and Marinoan glaciations, with both thought to be Snowball Earth events. These significant changes driven by Earth’s systems appear to have culminated in a nutrient rich ocean, a progressive rise in atmospheric oxygen concentration, the proliferation of eukaryotic and metazoan life, and the evolution of the earliest confirmed animalia, the Ediacaran fauna. The Neoproterozoic–Cambrian rocks of the redefined Adelaide Superbasin (formerly Adelaide Geosyncline) hold one of the most complete records of this pivotal time in Earth’s history. These records include key sequences of the Cryogenian global glaciations, the Ediacaran Acraman bolide ejecta layer, the eponymous Ediacaran fauna, and the global boundary stratotype section and point (GSSP) for the base of the Ediacaran. Despite the important record the Adelaide Superbasin holds, our knowledge of the chronology and tectonic evolution of it is still a hindrance to the calibration of other investigative techniques like chemostratigraphy, and for the development of global correlation frameworks for these Earth system events and stratigraphic sequences. While a significant corpus of research has been done to address these same issues around the globe, particularly in Canada, China, Ethiopia, Namibia, Scotland, and Svalbard, geochronology of Neoproterozoic sequences remains a significant challenge due to the fragmented, eroded, and commonly deformed stratigraphic record of the Neoproterozoic. The primary purpose of this research is to address the knowledge gap in the detrital zircon record of the Adelaide Superbasin to refine the chronostratigraphic framework, and to revise the tectonic and palaeogeographic model for the Adelaide Superbasin within the Neoproterozoic. This thesis presents over 6,500 new detrital zircon data from a significantly greater spatial and temporal diversity of samples from the Neoproterozoic of the Adelaide Superbasin—this is approximately half of the now available detrital zircon data for the basin. The research presented here suggests that deposition in the Adelaide Superbasin began between c. 890 Ma and 830 Ma, in half-graben depocentres resultant from far-field extensional forces. The rift system propagated along existing crustal weaknesses in an overall southerly direction, with major extensional pulses c. 830 Ma, c. 790 Ma (north), and c. 750–730 Ma (south) reflected by abrupt changes in zircon provenance. The northern region of the Adelaide Superbasin became an aulacogen with the opening of the proto-Pacific likely developing in the southern regions of the basin, heading northeast around the Curnamona Province. Detrital zircon spectra show a return to predominantly local sediment derivation during deposition of the Yudnamutana Subgroup, representative of the Sturtian glaciation. This is attributed to both glacial scouring of the surrounding region and disruption in sediment supply from distal sources due to the widespread nature of the glaciation. Beyond this time, derivation from distal sources became increasingly prevalent as the basin continued to develop through sag phases, with overall sedimentation becoming gradually shallower through the Neoproterozoic as the basin filled. This research has also led to a suggestion that an unrecognised Stenian–Tonian zircon source lay to the north/northeast of the basin. Finally, the rocks characterised by thick glaciogenic diamictite in the Yudnamutana Subgroup are all redefined as the Sturt Formation, resolving years of conjecture.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2022

碩士
臺灣大學
地質科學研究所
96
High sedimentation rates (50-500cm/kyr) in the South Okinawa Trough (SOT) provide high resolution records for reconstructing millennial or centennial paleo-environment changes. This research analyzes the grain size distribution , clay mineral assemblage and major elements of the IMAGE Core MD012403 retrieved from the Southern Okinawa Trough. The medians of grain size in MD012403 varied from 7.3 Φ to 7.8 Φ during 32.6 ka-20 ka and showed a coarsening trend during 21 ka-10.1 ka. After 10.1 ka, the grain sizes increased to 6.6-7.1 Φ were more stable in association with poor sorting. High content of sortable silt also occurred at this period, indicating the intensity of Kuroshio current was enhanced. The average chlorite / kaolinite ratio of detrital sediments from Taiwan (5.0) is much higher than that from the East China Sea Continental (ECS) Shelf (<2.0). The ratio of chlorite / kaolinite in Core MD012403 shows high values (2-6) during 0 ka-12 ka and maintains low (0.5) between 12 ka-21 ka. This suggests that the ECS may be the major sedimentary provenance during 12 ka-21 ka. Concentrations of MnO、CaO、MgO、ΣFe2O3 in sediment increase with depth but Na2O displays an opposite trend. Aoki and Oinuma(1974) documented that the sediments come from East China Shelf have a significantly low K/Ti ratio. In this study, the ratios of K/Ti drop down during 12 ka-21 ka indicating sources of sediments were mainly from ECS shelf. This interpretation is consistent with evidence also supports the inference derived from clay mineral assemblage.

博士
國立臺灣大學
地質科學研究所
102
Tibetan plateau is one of the most phenomenal orogens in the world. The spectacular landscape provides the opportunity to understand the fundamental mechanisms of mountain building process from varied disciplines such as geomorphology, geochemistry, and geophysics. Like many other orogenic belts around the world, the expedition into the plateau can be hampered by the inaccessibility of intended outcrops. These rough terrains, however, are often the most crucial outcrops to reveal the tectonic picture of the regime. Alternatively, sediments collected from the downstream of selected watershed can reflect a synthetic picture and provide integrated information in a catchment scale. With appropriate strategies and targets, we can therefore establish a comprehensive understanding toward the aimed tributaries and distinguish the veiled governing forces. In this study, we used multiple thermo-chronometers to detect the provenance of modern sediments from two tributaries of Yarlung-Tsangpo River, southeast Tibet. Results from zircon fission track (ZFT), apatite fissiontrack (AFT), Ar-Ar single grain analysis on K-feldspar and U/Pb-ZFT double dating all indicate the occurrence of grains with young thermal ages prevailing in the Lhasa River. This remarkable young population is not significantly detected in the Nyang River, another tributary east of Lhasa River. The discrepancy of age population between the two catchments suggests that the fundamental surface process must be different. Zircon U/Pb and fission track double dating suggests that the young age component represent the recent exhumation episode in Lhasa River. Comparisons between downstream, upstream sediments and in situ rock samples inside Lhasa River explicate that the provenance of the young grains is related to the major structure, Gulu Rifting belt. The high percentage of these young grains suggests a focused denudation in a restricted area of the Lhasa River, mostly along the Nyainqentanglha range.

The Middle-Late Ordovician Eureka Quartzite in south-central Nevada and eastern California is a supermature quartz arenite that was deposited along the Lower Paleozoic western passive margin of Laurentia. Measured section descriptions and facies stacking patterns indicate that the Eureka Quartzite represents a 3rd-order sequence and contains three ~2-4 m.y. sequences and many small parasequences. Detrital zircon analysis of eight samples from the base and top of four locations contains three main populations of ~1.8-2.0 Ga, ~2.6-2.8 Ga, and ~2.0-2.3 Ga, and a smaller infrequent population of ~1.6-1.8 Ga grains. These peaks are interpreted to represent sediment sourced from exposed proximal basement to the east, likely from the Yavapai and Mazatzal Provinces (~1.6-1.7 Ga), the Trans-Hudson Orogen (~1.8-1.9 Ga), Paleoproterozoic crusts (~2.0-2.3 Ga), and underlying or proximal Archean (~2.6-2.8 Ga) sources. Sediment likely was transported to the shoreline and across Archean basement by rivers draining the Transcontinental Arch. Long-shore currents played an important role in deposition and likely account for the similarity of Middle-Late Ordovician, supermature, quartz arenite deposits on western Laurentia. Although the Peace River Arch likely provided some sediment for the Eureka Quartzite, it is apparent its provenance was mostly Trans-Hudson Orogen and Archean basement. Temporal and spatial provenance changes are inferred from probability-density plots of the detrital zircon analyses to indicate sea-level changes covered or exposed possible sediment sources during deposition.

The southernmost portion of the Indian subcontinent, the Southern Granulite Terrane of India, holds a pivotal role in the reconstructions of the Ediacaran-Cambrian supercontinent Gondwana. Bound to the west by Madagascar and the East African continental fragments and to the east by Sri Lanka and Antarctica, this terrane offers a breadth of information regarding across terrane correlations and palaeotectonic settings, Arguably, within the Southern Granulite Tenane, the most debated issue of all is the existence of a late Neoproterozoic (ca. 550 - 500 Ma) suture zone between the Salem and Madurai Blocks, termed the Palghat Cauvery ShearZone (or alternatively, the Cauvery Shear Zone). The U-Pb zircon geochronology of the orthopyroxene-bearing orthogneisses (charnockites) in the northern part of Madurai Block yielded Neoarchaean and Cryogenian (ca.2.7 - 2.5 Ga and 795 ± 17 Ma) crystallization ages with metamorphic overprinting at ca. 535 Ma. Their Nd and Sr isotopic ratios (εNd₍τ₎ = -16.9 and +4.55, ⁸⁷Sr/⁸⁶Sr = 0.7017 - 0.7567) suggest they were generated by variable mixing of mantle-derived magmas with the older Archaean crust. The charnockites and garnet-biotite bearing granitoids in the southern part of the Madurai Block yielded much younger crystallization (1007 ± 23 Ma and 784 ± 18Ma) and Nd depleted mantle model ages ranging between 1.69 Ga and 1.38 Ga with low initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7054 - 0.7084, suggesting that the Madurai Block is not a uniform crustal domain, The age of metamorphism in this southern part of the Madurai Block is similar to that further north and indicates isotopic disturbance and zircon growth during the Ediacaran-Cambrian metamorphism. The coupled U-Pb and Lu-Hf isotopic study of the metasedimentary rock packages from the Salem Block mainly yielded late Archaean to early Palaeoproterozoic (ca. 2.7 - 2.45 Ga) detrital zircon ages with εHf values between +0.3 and +8.8, suggesting derivation from largely juvenile sources. ln contrast, the metasedimentary rocks from the Madurai Block are dominated by Mesoarchean to Palaeoproterozoic detrital zircon ages (ca. 3.2 Ga and 1.7 Ga) to the north and Mesoproterozoic to Neoproterozoic (ca. 1.5 - 0.65 Ga) detrital zircon ages in the south. Collectively, the Hf isotopic signatures of detrital zircons from the Madurai Block suggest they were derived from variably mixed reworked Archaean and Palaeoproterozoic sources, with additional input from the juvenile Palaeoproterozoic, late Mesoproterozoic and evolved Neoproterozoic sources. When compared to the metasedimentary rock packages from adjacent tenanes in Gondwana, the Madurai Block metasedimentary rock units correlate best with the basement sources derived from East Africa. The disparity between the delrital signatures from the Salem and Madurai Block suggest they had dissimilar depositional histories until the latest Neoproterozoic, The Palghat Cauvery Shear System (PCSS) at the southernmost margin of the Salem Block, represents a network of anastomosing crustal-scale shear zones with a largely dextral offset. The careful structural field observations coupled with U-Pb zircon geochronology of cross-cutting pegmatites, leucosomes and deformed basement gneisses show that the deformation in the Palghat Cauvery Shear System (southern Salem Block) is not a result of a single deformational event. Rather, the E-W and NE-SW trending fabrics that characterize much of the northern portion of the PCSS formed during an early Palaeoproierozoic (ca. 2.5 - 2.48 Ga) metamorphic event associated with largely dextral strike-slip motion. This deformation is overprinted by the E-W and ESE-WSW trending fabrics in the southern part of the PCSS (the Cauvery Shear zone) associated largely with dip-slip and minor dextral strike-slip contractional deformation suggesting dextral transpression. This latest deformation is loosely constrained to ca. 740 - 550 Ma. The Madurai Block deformational events (D₁– D₄) are different in character to those further north and are constrained to ca. 550 - 500 Ma. The latest Neoproterozoic event (ca. 550 - 500 Ma) appears to have affected both the southern portion of the Salem Block and all of the Madurai Block and is most likely linked to the final stages of Gondwana amalgamation. This study also suggest that care should be taken when regarding the regional-scale structural fabrics of the PCSS as being associated with the latest Neoproterozoic metamorphism. The Southern Granulite Terrane records two major episodes of magmatism at ca. 2.7 - 2.43 Ga and 0.83 - 0.75 Ga. ln the Salem Block, the ca. 2.7 – 2.5 Ga magmatism is associated with production of tonalitic-trondhjemitic-granitic (TTG) magmas during partial melting of basaltic/amphibolitic sources with limited contributions directly from the mantle, similar to the "typical" Archaean TTG provinces worldwide. Somewhat younger (ca. 2.54 - 2.43 Ga) basement rocks in the Madurai Block also show some similarities to the Archean TTG rocks further north. However, a large portion of the gneisses also show higher K₂O/Na₂O ratios, Ni and Cr concentrations and Mg numbers (molar ratio of MgO/(MgO + FeO)) suggesting higher inputs from the mantle during their genesis. The Cryogenian aged magmatism (ca. 0.8 - 0.75 Ga) in the Salem Block is associated with production of highly alkaline magmas (syenites/carbonitites/ultramafics), while in the Madurai Block similarly aged magmas are calc-alkaline, largely granitic to granodioritic, with high LILE/HFSE and LREE/HFSE ratios, low Ni and Cr concentrations typical of magmas generated above a subduction-zone. The differences in the structural character, age and geochemistry of the basement gneissic rocks as well as the differences in the depositional histories of the metasedimentary rock units between the Salem and Madurai Blocks suggests these two domains underwent widely different tectonothermal histories prior to the latest Neoproterozoic orogeny associated with the amalgamation of Gondwana. This study strongly supports a presence of a terrane boundary (a suture zone) between the Salem and Madurai Blocks.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2014

Thesis (M.S.)--University of Wisconsin--Madison, 2004.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 63-75).

Jurassic-Cretaceous tectonics, paleogeography and sedimentary provenance of central Africa are poorly constrained and continue to be debated. The lack of constraints on the timing and controls on late Mesozoic sedimentary basin development, drainage evolution and paleoenvironments is problematic because central Africa is well endowed with natural resources, and good understanding of these issues is fundamental to a better assessment of hydrocarbon and alluvial diamond exploration targeting. Moreover, by improving our understanding of Mesozoic strata across this vast region, we can also help to contextualise the ecological and evolutionary relationships of floras and faunas from central Africa with contemporary floras and faunas from different parts of Africa and throughout Gondwana. In particular, refining the depositional age of late Mesozoic units is key to understanding and reconstructing regional paleogeography and drainage patterns during this poorly resolved time period in Africa, which also furthers our understanding of the origins and dispersal pathways for Mesozoic, Cenozoic and modern African floras and faunas, as well as economically significant alluvial mineral resources, such as diamonds, that are important to the economies of this part of the world. To address these issues a detailed and multifaceted sedimentary provenance analysis of 14 late Mesozoic units from seven sedimentary basins across central Africa (spanning seven different countries) was conducted. This integrated sedimentological approach incorporated sandstone petrography, paleocurrent analysis, U-Pb detrital zircon geochronology, Lu-Hf isotope and trace element geochemistry to investigate Jurassic and Cretaceous continental deposits from central Africa. The main objective was to investigate late Mesozoic sedimentary basin development, drainage evolution and provide constraints on the age of deposition, sediment source and paleofluvial drainage patterns, using core and outcrop samples from across the region; including Democratic Republic of Congo (DRC), Kenya, Angola, Sudan, Tanzania, Zimbabwe and Malawi. Sandstone petrography and paleocurrent data indicate mixed sediment sources mainly to the south of study areas. Maximum depositional age analyses performed on U-Pb detrital zircon sample results demonstrate that most of the late Mesozoic units in central Africa are younger than previously accepted. Detrital zircon provenance analysis points to primary contributions from Neoproterozoic Pan-African Mobile Belts (e.g., Mozambique and Zambezi belts), which were probably exposed at this time are the dominant (>75%). The Lu-Hf isotope geochemistry results also show a mixed sediment provenance consisting of juvenile mantle and reworked crustal sources, which corroborates the sandstone petrography results. Western areas of central Africa (e.g. DRC and Angola) are dominated by sediments from reworked crustal sources, whereas eastern parts of central Africa (e.g. Sudan, Kenya and Tanzania) are dominated by sediments of juvenile mantle sources. The results further suggest a pattern of large ephemeral lakes in the Middle Jurassic to Early Cretaceous in the Congo and Zambezi basins, followed by the development of a large, dominantly north directed fluvial systems across central Africa in the middle Cretaceous. The results are supportive of a uniform northward continental drainage pattern throughout late Mesozoic, which supports the assertion that the paleo-Congo drainage system was likely north flowing, rather than east flowing out of the Congo Basin and into Indian Ocean as previously suggested. The results of this thesis are also supportive of the hypothesis of a major drainage divide between southern and central Africa during the late Mesozoic and the concept of a major NW trending fluvial drainage pattern into the shear zones within the Central African Rift System, although the ultimate depocentre still remains uncertain. The maximum depositional age of three Cretaceous sedimentary units, including the dinosaur-bearing Wadi Milk Formation of Sudan has been constrained. The new ages shows a generally much younger age of deposition than previous assignations, calling into question the reliability of these overly broad biostratigraphic age for these important sedimentary units.

This thesis results from a pilot study which, driven by repeatedly surprising results, opens up a reliable method of geochronology for Quaternary research. There have been repeated attempts to expand the limits of normal use of U-Pb dating. Geologists typically use U-Pb dating on detrital zircons (DZ) for dating and provenance studies on rocks older than the Cenozoic era. We tested several tephra layers in Utah and New Mexico, USA, with published 40 Ar/ 39 Ar ages between 1.3 and 1.6 Ma and found that the ages derived from clustered U-Pb dating are reliable, even though they were discordant. We used one of these tephra layers in the La Sal Mountains, Utah, to assign a minimum age to slope deposit layers (cover beds) underlying the tephra bed. In doing so, we discovered that we could not only identify unconformities between layers by means of palaeopedology. But that - although they were similar to one another regarding physical and chemical properties - they were not the same at all in terms of the provenance of their aeolian matter as derived from U-Pb analysis of detrital zircons, as one could actually assume. The source of aeolian matter mixed to these layers has changed decisively from layer to layer. The findings also allowed tentatively assigning palpable source areas for each layer. Since this had demonstrated the feasibility of a provenance approach, we then extended our study regionally to cover beds of the central Great Basin (GB) and the northern Colorado Plateau (CP). Using a published sequence-stratigraphic approach based upon stratigraphically consistent phases of soil development, we attempted to study cover beds from the same two Upper Quaternary time slices. We expanded our range of methods by end-member modelling analyzes (EMMA) and the analysis of surface and shape of detrital zircons. We used statistical methods such as multidimensional scaling (MDS) and density functions (probability density functions and kernel density estimations) to visualize similarities and distances of age distributions. The MDS and the density functions showed very clearly that the patterns of ages between the GB and the CP can be divided into two groups that differ from one another. This is probably due to different transport cascades of the zircons to and within both areas. Due to the lack of databases on the morphology of in-situ zirconia, it is not yet possible to draw precise conclusions about transport routes from them, although we have probably been able to identify traces of several stages of aeolian transport on many zircons. Conclusions can also be drawn about detrital zircons that were transported to the sampling point purely by the kinetic energy of volcanic eruptions during the Cretaceous (Cordilleran magmatic arc) and the Paleogene (strong volcanism within the study area). Moreover, we can show main similarities of the layers across the CP. Although they are separated spatially and temporally, they have a similar age distribution. The only exception here is the upper La Sal Mountains profile, for which I have several assumptions as to why this is so. We did not have enough conclusions for the reconstruction of the palaeoenvironmental conditions during the layer and soil formation phases; further investigations will have to follow. However, we show that a provenance study on Quaternary layers and further conclusions from the results are possible and would like to condense this approach for the study area in the future, but also try to transfer it to other study areas.:Abstract .......................................................................................................................3 Kurzfassung ................................................................................................................5 Contents ......................................................................................................................7 List of figures ............................................................................................................ 11 List of tables ............................................................................................................. 13 List of abbreviations and units .................................................................................. 14 1 Introduction ........................................................................................................... 16 1.1 Research questions ........................................................................................... 16 1.2 Cover beds ......................................................................................................... 17 1.3 Palaeosols .......................................................................................................... 17 1.4 Study area .......................................................................................................... 18 1.5 Zircons ............................................................................................................... 21 1.6 Thesis format ...................................................................................................... 23 2 Capability of U-Pb dating of zircons from Quaternary tephra: Jemez Mountains, NM, and La Sal Mountains, UT, USA ....................................................................... 24 2.1 Abstract .............................................................................................................. 25 2.2 Kurzfassung ....................................................................................................... 25 2.3 Introduction ........................................................................................................ 26 2.4 Geological setting ............................................................................................... 27 2.4.1 Jemez Mountains, New Mexico ...................................................................... 27 2.4.2 La Sal Mountains, Utah ................................................................................... 30 2.5 Methods ............................................................................................................. 30 2.6 Results and discussion ..................................................................................... 33 2.6 Conclusions ........................................................................................................ 38 Data availability ........................................................................................................ 38 Competing interests.................................................................................................. 38 Acknowledgements .................................................................................................. 38 2.7 References ......................................................................................................... 39 3 Cover beds older than the mid-Pleistocene revolution and the provenance of their aeolian components, La Sal Mountains, Utah, USA ........................................ 42 3.1 Abstract .............................................................................................................. 43 3.2 Introduction ........................................................................................................ 43 3.3 Material and methods ........................................................................................ 44 3.3.1 The La Sal Mountains tephra layer ................................................................. 44 3.3.2 Cover beds and palaeosols............................................................................. 45 3.3.3 Samples and analyses .................................................................................... 46 3.4 Results and discussion ...................................................................................... 49 3.5 Conclusions ....................................................................................................... 56 Acknowledgments ................................................................................................... 58 Summary information A. Supplementary data ......................................................... 58 3.6 References ........................................................................................................ 58 4 Zircon provenance of Quaternary cover beds using U-Pb dating: regional differences in the south-western USA ...................................................................... 63 4.1 Abstract .............................................................................................................. 64 4.2 Introduction ........................................................................................................ 65 4.3 Materials ............................................................................................................. 66 4.3.1 Study areas ..................................................................................................... 66 4.3.2 Stratigraphy and sampling sites ...................................................................... 68 4.3.3 Palaeolake deposits ........................................................................................ 71 4.3.4 Potential sources of detrital zircons ................................................................ 71 4.4 Methods ............................................................................................................. 75 4.4.1 End-member modelling of grainsize composition ........................................... 75 4.4.2 U-Pb dating ..................................................................................................... 75 4.4.3 Zircon dimensions and surfaces ..................................................................... 77 4.4.4 Statistical and graphical representations ........................................................ 78 4.5 Results and discussion ...................................................................................... 79 4.5.1 Aeolian contribution to cover beds .................................................................. 79 4.5.2 Zircon morphology .......................................................................................... 82 4.5.3 Age distributions of detrital zircons ................................................................. 88 4.5.4 Multidimensional scaling (MDS) ..................................................................... 94 4.6 Conclusions ....................................................................................................... 98 Appendix ................................................................................................................ 102 Acknowledgements ................................................................................................ 102 4.7 References ....................................................................................................... 103 5 Extended summary .............................................................................................. 118 5.1 Synthesis .......................................................................................................... 118 5.2 Regional differences and similarities ................................................................ 123 5.3 Outlook ............................................................................................................. 128 6 Supplementary Information ................................................................................. 130 6.1 Supplementary material chapter ‘Capability of U-Pb dating of zircons from Quaternary tephra: Jemez Mountains, NM, and La Sal Mountains, UT, USA’........ 130 6.1.1 Raw data electron microprobe analyses of glass shards from tephra layers .131 6.1.2 Raw data U-Pb ratios and calculated ages for all samples ............................137 6.2 Supplementary material chapter 3 ‘Cover beds older than the mid-Pleistocene revolution and the provenance of their eolian components, La Sal Mountains, Utah, USA’ .............................................................................................................. 160 6.3 Supplementary material chapter 4 ................................................................... 175 6.3.1 SI1 Raw U-Pb ratios and calculated ages ......................................................175 6.3.2 SI 3 Grainsize diagrams of samples of the present study (except for PL)......266 6.3.3 SI 4 Zircon morphology data .........................................................................269 6.3.3.1 Great Basin .................................................................................................269 6.3.3.2 Colorado Plateau ........................................................................................289 7 References (excluding chapters 2, 3 and 4) ....................................................... 308 8 Acknowledgements ............................................................................................. 312
Diese Arbeit ist das Ergebnis einer Pilotstudie, die aufgrund immer wieder neuer, unerwarteter Ergebnisse eine zuverlässige geochronologische Methode für die Quartärforschung eröffnet. Es wurde mehrfach versucht, die üblichen Grenzen der Verwendung der U-Pb-Datierung zu erweitern. In der Geologie wird die U-Pb-Datierung an detritischen Zirkonen (DZ) normalerweise für Datierungs- und Provenienzstudien an Gesteinen, die älter als das Känozoikum sind, eingesetzt. Wir haben mehrere Tephra-Schichten in Utah und New Mexico, USA, mit veröffentlichten 40 Ar/ 39 Ar-Altern zwischen 1.3 und 1.6 Ma getestet und festgestellt, dass die Alter, die aus den Clustern der U-Pb-Datierungen abgeleitet wurden, zuverlässig sind, obwohl sie diskordant waren. Wir haben eine dieser Tephra-Schichten in den La Sal Mountains, Utah, verwendet, umlagernden Deckschichten ein Mindestalter zuzuweisen. Dabei stellten wir fest, dass wir nicht nur mittels Paläopädologie Schichtgrenzen zwischen Schichten ausweisen konnten. Sondern dass sie sich, obwohl sie sich in Bezug auf physikalische und chemische Eigenschaften ähneln, in Bezug auch auf die Herkunft ihres äolischen Materials (abgeleitet aus der U-Pb-Analyse der DZ) überhaupt nicht glichen, wie man eigentlich annehmen könnte. Die Herkunft des eingemischten äolischen Materials hat sich von Schicht zu Schicht entscheidend verändert. Die Ergebnisse ermöglichten es auch, jeder Schicht konkrete wahrscheinliche Liefergebiete zuzuweisen. Da dies die Möglichkeit einer Provenienz-Analyse belegt hatte, erweiterten wir unsere Studie regional auf Deckschichten des zentralen Great Basin (GB) und des nördlichen Colorado Plateaus (CP). Unter Verwendung eines publizierten sequenz-stratigraphischen Ansatzes, der auf stratigraphisch konsistenten Phasen der Bodenentwicklung basiert, haben wir versucht, Deckschichten aus denselben beiden oberen quartären Zeitscheiben zu untersuchen. Wir erweiterten unser Methodenspektrum um End Member-Modellierung (EMMA) und die Analyse der Oberfläche und Form von DZ. Wir verwendeten statistische Methoden wie mehrdimensionale Skalierung (MDS) und Dichtefunktionen (Wahrscheinlichkeitsdichtefunktionen und Kerndichteschätzungen), um Ähnlichkeiten und Abstände von Altersverteilungen zu visualisieren. MDS und Dichtefunktionen zeigten deutlich, dass GB und CP unterschiedliche Altersspektren aufweisen. Dies ist wahrscheinlich auf unterschiedliche Transportkaskaden der Zirkone in beide und innerhalb beider Gebiete zurückzuführen. Aufgrund des Fehlens von Datenbanken zur Morphologie von gesteinsbürtigen Zirkonen kann man daraus noch keine genauen Rückschlüsse über Transportwege ziehen, obwohl wir wahrscheinlich an vielen Zirkonen Spuren mehrerer Schritte des äolischen Transports identifizieren konnten. Es liegen auch DZ vor, die vermutlich ausschließlich durch die kinetische Energie von Vulkanausbrüchen während der Kreidezeit (Cordilleran Magmatic Arc) und des Paläogens (starker Vulkanismus innerhalb des Untersuchungsgebiets) zum Probenahmepunkt transportiert wurden. Darüber hinaus können wir Ähnlichkeiten zwischen den verschiedenen Schichten im CP zeigen. Obwohl sie räumlich und zeitlich getrennt sind, haben sie eine ähnliche Altersverteilung. Die einzige Ausnahme hiervon ist das Profil der höheren La Sal Mountains, wofür es mehrere mögliche Gründe gibt. Wir konnten nicht genügend Erkenntnisse für die Rekonstruktion der paläoökologischen Bedingungen während der Schicht- und Bodenbildungsphasen gewinnen; weitere Untersuchungen müssen folgen. Wir zeigen jedoch, dass eine Provenienzstudie an quartären Schichten und weiterreichende Schlussfolgerungen möglich sind, und möchten diesen Ansatz für das Untersuchungsgebiet in Zukunft verdichten, aber auch versuchen, ihn auf andere Untersuchungsgebiete zu übertragen.:Abstract .......................................................................................................................3 Kurzfassung ................................................................................................................5 Contents ......................................................................................................................7 List of figures ............................................................................................................ 11 List of tables ............................................................................................................. 13 List of abbreviations and units .................................................................................. 14 1 Introduction ........................................................................................................... 16 1.1 Research questions ........................................................................................... 16 1.2 Cover beds ......................................................................................................... 17 1.3 Palaeosols .......................................................................................................... 17 1.4 Study area .......................................................................................................... 18 1.5 Zircons ............................................................................................................... 21 1.6 Thesis format ...................................................................................................... 23 2 Capability of U-Pb dating of zircons from Quaternary tephra: Jemez Mountains, NM, and La Sal Mountains, UT, USA ....................................................................... 24 2.1 Abstract .............................................................................................................. 25 2.2 Kurzfassung ....................................................................................................... 25 2.3 Introduction ........................................................................................................ 26 2.4 Geological setting ............................................................................................... 27 2.4.1 Jemez Mountains, New Mexico ...................................................................... 27 2.4.2 La Sal Mountains, Utah ................................................................................... 30 2.5 Methods ............................................................................................................. 30 2.6 Results and discussion ..................................................................................... 33 2.6 Conclusions ........................................................................................................ 38 Data availability ........................................................................................................ 38 Competing interests.................................................................................................. 38 Acknowledgements .................................................................................................. 38 2.7 References ......................................................................................................... 39 3 Cover beds older than the mid-Pleistocene revolution and the provenance of their aeolian components, La Sal Mountains, Utah, USA ........................................ 42 3.1 Abstract .............................................................................................................. 43 3.2 Introduction ........................................................................................................ 43 3.3 Material and methods ........................................................................................ 44 3.3.1 The La Sal Mountains tephra layer ................................................................. 44 3.3.2 Cover beds and palaeosols............................................................................. 45 3.3.3 Samples and analyses .................................................................................... 46 3.4 Results and discussion ...................................................................................... 49 3.5 Conclusions ....................................................................................................... 56 Acknowledgments ................................................................................................... 58 Summary information A. Supplementary data ......................................................... 58 3.6 References ........................................................................................................ 58 4 Zircon provenance of Quaternary cover beds using U-Pb dating: regional differences in the south-western USA ...................................................................... 63 4.1 Abstract .............................................................................................................. 64 4.2 Introduction ........................................................................................................ 65 4.3 Materials ............................................................................................................. 66 4.3.1 Study areas ..................................................................................................... 66 4.3.2 Stratigraphy and sampling sites ...................................................................... 68 4.3.3 Palaeolake deposits ........................................................................................ 71 4.3.4 Potential sources of detrital zircons ................................................................ 71 4.4 Methods ............................................................................................................. 75 4.4.1 End-member modelling of grainsize composition ........................................... 75 4.4.2 U-Pb dating ..................................................................................................... 75 4.4.3 Zircon dimensions and surfaces ..................................................................... 77 4.4.4 Statistical and graphical representations ........................................................ 78 4.5 Results and discussion ...................................................................................... 79 4.5.1 Aeolian contribution to cover beds .................................................................. 79 4.5.2 Zircon morphology .......................................................................................... 82 4.5.3 Age distributions of detrital zircons ................................................................. 88 4.5.4 Multidimensional scaling (MDS) ..................................................................... 94 4.6 Conclusions ....................................................................................................... 98 Appendix ................................................................................................................ 102 Acknowledgements ................................................................................................ 102 4.7 References ....................................................................................................... 103 5 Extended summary .............................................................................................. 118 5.1 Synthesis .......................................................................................................... 118 5.2 Regional differences and similarities ................................................................ 123 5.3 Outlook ............................................................................................................. 128 6 Supplementary Information ................................................................................. 130 6.1 Supplementary material chapter ‘Capability of U-Pb dating of zircons from Quaternary tephra: Jemez Mountains, NM, and La Sal Mountains, UT, USA’........ 130 6.1.1 Raw data electron microprobe analyses of glass shards from tephra layers .131 6.1.2 Raw data U-Pb ratios and calculated ages for all samples ............................137 6.2 Supplementary material chapter 3 ‘Cover beds older than the mid-Pleistocene revolution and the provenance of their eolian components, La Sal Mountains, Utah, USA’ .............................................................................................................. 160 6.3 Supplementary material chapter 4 ................................................................... 175 6.3.1 SI1 Raw U-Pb ratios and calculated ages ......................................................175 6.3.2 SI 3 Grainsize diagrams of samples of the present study (except for PL)......266 6.3.3 SI 4 Zircon morphology data .........................................................................269 6.3.3.1 Great Basin .................................................................................................269 6.3.3.2 Colorado Plateau ........................................................................................289 7 References (excluding chapters 2, 3 and 4) ....................................................... 308 8 Acknowledgements ............................................................................................. 312

碩士
國立中正大學
應用地球物理研究所
104
In this study we analysis the detrital zircon U-Pb ages from Late Triassic to Eocene strata of Sichuan basin and Songpan-Ganze folded belt in eastern Tibet to discuss possible sediment provenance. The Songpan-Ganze folded belt, comprised of 5-15km thickness of late Triassic flysch deposit, was deformed by Mesozoic and Cenozoic events which formed 3-5km high plateau. It connects with Sichuan basin by Longmenshan orogenic belt. In the Sichuan basin it comprised of shallow marine deposit since Mesozoic and become foreland basin deposit after the Cenozoic. We collected samples from Triassic to Eocene strata in SW Sichuan basin and Songpan-Ganze folded belt in different age strata and we also combined with previous studies to analysis the possible sediment provenance. In the Songpan-Ganze folded belt we obtained more comprehensive age spectrums in Devonian strata. Previous study show the age spectrum concentrates on 970 Ma and 440 Ma and we observed there exists many 2.4-2.6 Ga grains. The Triassic strata are similar with previous studies which ages concentrate on ca. 1.8Ga, 790Ma and some grains are 260-300Ma and 410-470Ma. In Sichuan basin the preliminary data show there are quite different age spectrums from Triassic to Jurrassic. The Triassic to Jurassic strata show the age spectrums concentrate on 270Ma, 450Ma, 800Ma, and few 1800Ma. But in Jurassic strata most of grain ages concentrate on 1800Ma. In the Cretaceous strata we started to observed ca. 215 Ma peak and some on 770Ma which infer the sediments could come from Songpan-Ganze folded belt. In Eocene strata the age spectrums concentrate on 1800 Ma and 270 Ma which infers the sediments different source from Cretaceous to Eocene.

碩士
國立臺灣大學
地質科學研究所
107
The Kenting and Lichi Mélanges formed at the subduction system of Eurasian plate and Philippine Sea plate, located in Hengchun Peninsula and southern Coastal Range, respectively. Mélange is a body of rock characterized by exotic blocks, contained in a fine-grained deformed matrix. The purpose of this study is to analyse provenance of the sandstone blocks on the Mélanges, by using detrital zircon U-Pb dating, petrography, nannofossil biostratigraphy, and Hf isotope analysis. In addiction, in order to understand the sources of ophiolite, and the sandstone blocks of the Kenting and Lichi Mélanges, this study also collected samples from Eastern Taiwan Ophiolite and Miocene strata of Hengchun Peninsula. We analysed 7 Miocene strata samples from Hengchun Peninsula, 28 sandstone blocks from the Mélanges and 4 Eastern Taiwan Ophiolite. According to U-Pb age assemblage analysis, Lilungshan Formation and Shimen Formation have the same character with Central and Norther Taiwan Miocene Strata, but Loshui Formation has a different character. According to paleocurrent data and petrography results, contains argillite, quazite, and ophiolitic lithics, the provenance of Lilungshan Formation and Shimen Formation is the old accretionary wedge. According to U-Pb age assemblage analysis and petrography results, the provenance of Loshui Formation is the Cathaysia. According to zircon U-Pb age assemblage and petrography results, we classified sandstone blocks of the Mélanges into four types. Type 1 sandstone has the same character with Lilungshan Formation and Shimen Formation, the provenance of Type 1 sandstone represent the old accretionary wedge. Type 2 sandstone has the same character with Loshui Formation, the provenance of Type 2 sandstone is the Cathaysia. The provenance of Type 3 ophiolitic sandstone is the old accretionary wedge. The young zircon age population of Type 3 is derived from South China Sea oceanic crust, which been scratched and uplifted by the subduction system, and the old zircons are from continental material. The provenance of Type 4 volcanic lithics sandstone is volcano arc. The young zircon age population of Type 4 is from the volcanic arc, and the old zircons are captured from sedimentary strata, when the original magma upwelling. The Lichi Mélange contains Type 1, Type 2, Type 3 and Type 4 sandstone blocks. The Kenting Mélange contains Type 1 and Type 3 sandsone blocks. The zircon U-Pb age of Eastern Taiwan Ophiolite of the Lichi Mélange, include two age populations (1)17.4~16.3 Ma, and (2)14.8~13.9 Ma, which zircon Hf isotopic data indicated the magmas are from depleted mantal.

Indiana University-Purdue University Indianapolis (IUPUI)
A broad range of samples were collected from the Huron-Erie Lobe, Lake Michigan Lobe, Saginaw Lobe, and Tipton Till Plain of northern Indiana to determine the provenance of Laurentide Ice Sheet till in the Midwest U.S. during the Illinoian and Wisconsinan glaciations. U-Pb age distributions from approximately 300 detrital zircons (DZ) were used as provenance indicators for each till sample. Till from the Lake Michigan Lobe and was found to be largely homogenized. The distinct lobe DZ age distributions are the Lake Michigan Lobe till with a dominant ~1465 Ma peak, the northern Huron-Erie Lobe till with a dominant ~1060 Ma and a secondary peak at ~1450 Ma, the southern Huron-Erie Lobe till with nearly equal peaks at ~1435 Ma, ~1175 Ma, and ~1065 Ma, and the southern Saginaw Lobe till with a dominant peak at ~1095 Ma. Those four DZ age distributions were treated as endmembers in a nonlinear least-squares mixing model to calculate the contribution of each lobe to till in the Tipton Till Plain. Huron-Erie and Saginaw lobe tills were found to be the primary components of the Tipton Till Plain, and Lake Michigan Lobe till was only found in the western Tipton Till Plain. Zircons from the Saginaw Lobe till increased 39 % in the eastern Tipton Till Plain between the Illinoisan and Wisconsinan glaciations. The mixing model was also applied to relate the DZ age distributions of the lobes to bedrock within and near their flow paths. When comparing nearby bedrock to each lobe’s till, mixing model results, yield an approximate maximum transport distance between 500 and 630 kilometers for the matrix vii fraction of till in the Lake Michigan, Huron-Erie, and Saginaw lobes. Samples for the southern Huron-Erie Lobe indicate that the most of the zircon ages within the southern Huron-Erie Lobe till in Indiana were specifically entrained between Niagara County, New York and east-central Indiana. Within the model’s error, 93 – 100 % of the detrital zircons in each of the three lobes are relatable to nearby Paleozoic and Precambrian sedimentary and metamorphic bedrock formations.

Indiana University-Purdue University Indianapolis (IUPUI)
Tills for this study were analyzed from sites in East Antarctica (EA), West Antarctica (WA) and along a transect in the Ross Sea. Particle size, sand petrography, and detrital zircons were used to provide new information on the subglacial geology of Antarctica, as well as assisting in the reconstruction of Last Glacial Maximum (LGM) ice flow paths. Statistical analyses using the Kolmogorov-Smirnov (K-S test) reveal that EA and WA zircon age distributions are distinct at a P-value <0.05. This makes it possible to trace the unique signatures from EA and WA into the Ross Sea.

Indiana University-Purdue University Indianapolis (IUPUI)
Tills from major ice streams (Institute, Foundation, Academy, Recovery, and Slessor) of the Weddell Sea Embayment contain detrital zircons with distinct U-Pb age populations that can be used as a provenance tool to better understand ice stream dynamics. U-Pb ages of detrital zircons were measured in 21 samples of onshore till, erratics, and bedrock of potential source rocks, and 12 samples of offshore till. Grains were analyzed by LA-ICPMS at the University of Arizona (n=5447). Relative probability U-Pb age density plots of till in moraines along the Institute Ice Stream have dominant Grenville (1070 Ma) and secondary Ross/Pan-African peaks (560 Ma, 630 Ma). The Foundation and Academy show prominent Ross/Pan-African peaks (500-530 Ma and 615-650 Ma). The Recovery transports zircons with prominent 530 Ma and 635 Ma peaks along the southern margin, and 1610 and 1770 Ma along the northern margin. The Slessor carries zircons with prominent populations at 1710 Ma and secondary 2260-2420 Ma. U-Pb ages in zircons from offshore till samples show a general trend of fewer Mesozoic ages from west to east. The western most core, PS 1423, has dominant Jurassic populations while cores 1197 and 1278 have a high proportion of early Ross/Pan-African ages relative to Grenville ages. The similar zircon age distributions between PS 1278 and the Foundation Ice Stream tills suggest that the Foundation switched to an easterly flow path around Berkner Island (BI) at some point during the LGM. In the eastern Weddell Sea (PS 1400), there was a near absence of Proterozoic zircon age populations carried by the Slessor and northern side of the Recovery. Another unexpected find was a lack of Grenville ages in PS 1423 relative to the Institute tills. The U-Pb data in this study provides a basis for two possible LGM ice flow reconstructions. In the first, the Institute flowed west around the unnamed isolated bedrock highs, deposited tills between PS 1423 and PS 1197, providing a westerly flow path around BI for the Foundation. In the second, the Institute flows over the subglacial topography and deposited till closer to PS 1197, forcing the Foundation east around BI.

This item is only available electronically.
Detrital zircon ages obtained from the Corny Point Paragneiss and the Massena Bay Gneiss in the southeastern Gawler Craton, Australia, constrain their deposition to the interval ca. <1880 Ma. The presence of 2020 Ma, 2450 Ma and 2520 Ma detrital zircons within the Corny Point Paragneiss constrains the source region for the sedimentary protoliths to three possible domains within Australia; the Gawler Craton, the Glenburgh Orogen in the Western Australian Proterozoic, and the North Australian Craton, all of which contain rock systems with similar ages. Whole rock εNd (1850Ma) values from the Corny Point Paragneiss range from -1 to -5. These values potentially preclude the Late Archaean to mid Proterozoic crust of the Gawler Craton as a sole or major source region due to its highly evolved average εNd (1850Ma) of around -10. Preclusion of the Gawler Craton as a source is apparently confirmed by Hf isotopic compositions of 2020 Ma detrital zircons from the Corny Point Paragneiss, which have εHf (2020Ma) ranging between +3 to +7. This compares with εHf (2020Ma) of -1 to -4 for zircons from the 2020 Ma Miltalie Gneiss in the Gawler Craton. Available Nd isotopic data suggests that the Glenburgh Orogen is too crustally evolved to have provided the majority of sediment into the Corny Point Paragneiss protolith. The 2020 Ma detrital Hf isotopic compositions of the Corny Point Paragneiss are similar to the 2020 Ma Wildman Siltstone (εHf (2020Ma) +2 to +7) in the Pine Creek Orogen in the North Australian Craton. Two possible scenarios can be extrapolated from the detrital zircon and Nd isotopic data; (1) the Corny Point Paragneiss sediment was derived from a source region within the North Australian Craton and could share source regions with the Wildman Siltstone, or (2) the sediments were derived from a Gawler Craton source region that included a dominant juvenile component of the 2020 Ma Miltalie Gneiss in the adjacent Gawler Craton which has since been eroded. In the first scenario, the absence of connection to the Gawler Craton allows for the Betts and Giles (2006) plate reconstruction model, which proposes that the Corny Point Paragneiss formed part of the North Australia Craton, and was sutured to the Proto Gawler Craton at 1730-1700 Ma. The second scenario highlights a significant limitation in evaluating the significance of provenance data, particularly when considering old potential source terrains that have undergone significant levels of denudation. The proximity of the Corny Point Paragneiss to the rifted southern and eastern margins of the Australian Proterozoic means a thorough evaluation of the palaeogeographic significance of the Corny Point Paragneiss detrital signature requires corresponding datasets from regions such as Antarctica which were formerly contiguous with the Gawler Craton.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2006

This item is only available electronically.
The Heavitree Formation of the Amadeus Basin, central Australia, is thought to correlate with a number of similar formations in the Officer, Ngalia, Georgina and Murraba Basins that formed the Centralian Superbasin. The Jasper Gorge Formation of the Victoria Basin and Jamison Sandstone of the Beetaloo Sub-basin are also thought to be corollaries. These formations are all constrained to being younger than ca. 1.0 Ga by U-Pb detrital zircon studies. However, in all cases, this is suspected to considerably pre-date the timing of deposition. Here, we present new U-Pb and Hf data from seven samples of the Amadeus Basin Heavitree Formation to a) better constrain the age of the Heavitree Formation, b) investigate the spatial variation in provenance of the Heavitree Formation, and, c) compare it with other ‘Supersequence 1’ quartzites from the wider Centralian Superbasin.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2018

碩士
國立臺灣大學
地質科學研究所
101
Detrital zircons collected from sedimentary rocks can find out exhumation history for the U-Pb dating. This study aims to reconstruct the Eocene–Miocene exhumation history of the southeast China by using U-Pb detrital zircon geochronology. The samples were collected from the Eocene-Miocene formation along the Beigang river and the upper Miocene formation from the Daan river. Each sample contains about 80-100 zircons U-Pb dating data with LA-ICPMS. Zircon formed from igneous activity or metamorphism of the source province. U-Pb dates are distributed to several groups according to the major geological movement in southeast China, (1) Wutai orogeny (2400-2600 Ma) (2) Luliang orogeny (1700-1900 Ma) (3) Sibao orogeny (930-1000 Ma) (4) Jinning orogeny (700-850 Ma) (5) Caledonian orogeny (400-450) (6) Indosinian orogeny (200-250 Ma) (7) Early Yanshanian orogeny (200-145) (8) Late Yanshanian orogeny (Ⅰ) (100-145 Ma) and (9) Late Yanshanian orogeny (Ⅱ) (100-65 Ma) (10) continental rifting period (65-8Ma). Age spectrum analyses of the Eocene formation indicates that the major proportion is the Late Yanshanian orogenyⅠgroup, about 12%－22%； the major proportion of the Oligocene formation is the Late Yanshanian orogenyⅠgroup, about 23%－36%； the major proportion of the Miocene formation is the Luliang movement group about 10%－23%. The Major proportion of Yanshanian orogeny (Ⅰ) group shows the increasing in the Eocene to the Oligocene formations, but the decreasing in the Miocene formation means that Late Yanshanian orogeny (Ⅰ) period rock eroded and reduced the exposed area during the Miocene period； The Luliang movement group proportion of Miocene formation data is increasing, and it means that the younger rocks eroded causes older rocks exposed. The youngest zircon age can be a corroboration of sedimentary age of sedimentary rock, 39.3±0.8 Ma of the Eocene formation, 27.4±0.6 Ma of the Oligocene formation, 26.7±0.6 Ma of the Miocene formation that confirms the previous reports of the age of sedimentary rocks. Keywords: Central Taiwan, detrital zircon, U-Pb datimg

The Western European Variscan orogenic belt is thought to represent the final in a series of Paleozoic continental collisions that culminated with the amalgamation of the supercontinent Pangea. The Iberian segment of the Variscan belt is characterized by Cantabrian orocline, which is 180º and convex toward the west. Several lines of evidence are at odds with classical interpretation of the Cantabrian orocline as the core of the much larger ‘Ibero-Armorican’ arc, suggesting instead that it is structurally continuous with a second more southerly and complimentary orocline. Paleocurrent data collected from the Lower Ordovician Armorican Quartzite of the deformed Iberian Paleozoic passive margin sequence confirm the existence of the so-called Central Iberian orocline. Structural continuity between the Cantabrian and Central Iberian oroclines suggests that they formed contemporaneously and in the same fashion. Mesoscale vertical-axis folds deforming slaty cleavage and shear fabric within the Ediacaran Narcea Slates have a dominant vergence toward the hinge of the Cantabrian orocline, suggesting that its formation was in part accommodated by a mechanism of flexural shear during buckling of a linear belt in response to an orogen parallel principle compressive stress. The Cantabrian-Central Iberian coupled oroclines therefore palinspastically restore to an originally linear belt 2300 km in length. Provenance analysis of detrital zircons sampled from the Armorican Quartzite along a 1500-km-long segment of the palinplastically restored Iberian passive margin indicate that it originated in a paleogeographic position stretching east-west along the northern limits of north African Gondwana, from the Arabian-Nubian Shield to the Saharan hinterland. Paleomagnetic data and the distribution of Variscan ophiolites support a model of mid-Paleozoic separation of the Variscan autochthon (Armorican continental ribbon) from north Gondwana preceding or in conjunction with a 90º rotation required to reorient the ribbon to a Late Carboniferous north-south trend. Formation of the Iberian coupled oroclines accommodated 1100 km of orogen parallel shortening. The Western European Variscan belt, North American Cordillera, and Eastern European Alpine system are orogens similarly characterized by both coupled oroclines and paleomagnetic inclinations that are significantly shallower than cratonic reference values. Palinspastic restoration of the Alaskan and Carpathian–Balkan coupled oroclines fully resolves inclination anomalies within the Cordillera and Eastern Alpine system, respectively. Inclination anomalies within the Iberian Variscan belt are only partially resolved through palinspastic restoration of the Iberian coupled oroclines, but the sinuous geometry of the belt is not yet fully deciphered. Oroclines within the Western European Variscan belt, not the orogen itself, provide the true record of Pangean amalgamation.
Graduate

This item is only available electronically.
The Beetaloo Basin of the ‘greater McArthur Basin’, is a 15,000km2 Palaeoproterozoic depocenter which hosts shallow water, dominantly marine, clastic sedimentary rocks and is a large hydrocarbon reserve. Here I present LA-ICP-MS detrital zircon U-Pb age data, Rare Earth Elemental zircon and illite crystallinity XRD results and compare with existing studies to explore the variation in provenance throughout the basin and to better understand its temperature history as much of the basins’ history is still unknown. Nine sandstone and seventeen shale core samples were analysed. New constraints were placed on the depositional age for the Corcoran Formation to between 1390 ± 27 Ma and 1324 ± 4 Ma. The Velkerri Formation, Moroak Sandstone and Kyalla Formation of the Maiwok Sub-group all largely supported the results of previous studies yielding comparable maximum depositional ages. Zircon phosphorous concentrations revealed a largely I-type granitic source rock indicating the granites were formed in arc related settings. Detrital zircon age data revealed possible origins of sediments showing that the Corcoran Formation has a major source of ca. 1600 Ma zircons which are not unlike rocks from Eastern Queensland orogens. The Velkerri Formations’ main age peak falls at ca. 1765 Ma which shows a change to older detrital source rocks with more similarities to the Arunta and Kathleen and Western Orogenies. Moving up-section to the Moroak Sandstone and Kyalla Formations, samples shift to younger ca. 1560 Ma peak ages at the base of the Moroak followed by a gradual increase in age with younger sequences where a maximum peak age of ca. 1795 Ma is found in the mid Kyalla Formation. This gradual increase shows a gradual shift in sediment source from E/SE sources to southern source regions. Illite crystallinity data show that the shales within the Beetaloo Basin have experienced much greater temperatures than at present. Altree 2 has an XRD calculated bottom-hole temperature of 155°C at1647m depth, the Jamison records 156°C at 1695m with the Elliot being the hottest at 194°C at 1697 deep. These values were then used to calculate the amount of cover removed from present day. Altree 2 returned an estimate of 2050m of cover removed, Jamison 1769m and Elliot with the most cover removed at 2680m showing that the southern region of the Beetaloo Basin has experienced the greatest uplift since maximum subsidence followed by the northern Altree 2.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2017

This item is only available electronically.
The Chewings Range Quartzite is a meta-sedimentary cover sequence located in the Warumpi Province of the Arunta Region. U-Pb detrital Zircon analysis of the Chewings Range Quartzite indicates a minimum depositional age of ~ 1640Ma, with the main population of zircons residing within a range of 1700 – 1800Ma. Evidence from Sm-Nd isotopic data suggests that a series of Staurolite Garnet Schists, often grouped with the Chewings Range Quartzite, has a significantly more juvenile character. This suggests that it may represent a new unit with a significantly differing provenance to that of the Chewings Range Quartzite. Combined REE, geochemistry and detrital zircon dating suggests that the Chewings Range Quartzite was derived primarily off the Arunta Region and North Australian Craton, while the Stauralite Garnet Schists holds more affinity with juvenile Musgrave Province to the south.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010

Sandstone modal compositions and detrital zircon U-Pb analysis of the Paleocene-Eocene Wilcox Group of the southern Gulf Coast of Texas indicate long-distance sediment transport primarily from volcanic and basement sources to the west, northwest and southwest. The Wilcox Group of south Texas represents the earliest series of major post-Cretaceous pulses of sand deposition along the western margin of the Gulf of Mexico (GoM). Laramide basement uplifts have long been held to be the provenance of the Wilcox Group, implying that initiation of basement uplifts was the driving factor for this transition from carbonate sedimentation to clastic deposition. To determine the provenance of the Wilcox Group and test this conventional hypothesis, 40 thin sections were point-counted using the Gazzi-Dickinson method to determine sandstone composition and 10 detrital zircon samples were analyzed by LA-ICP-MS to determine U-Pb age spectra for each of the sampled areas. Modal data for sand grain populations suggest mixed sources including basement rocks, magmatic arc rocks and subordinate sedimentary rocks for the Wilcox Group. Zircon age spectra for these sandstones reveal a complex grain assemblage derived from older sediments and crystalline rocks ranging in age from Archean to Cenozoic. Sediment was primarily derived from Laramide uplifted crystalline blocks of the central and southern Rocky Mountains, the Cordilleran arc of western North America, and arc related extrusive and intrusive igneous rock of northern Mexico. Comparisons of Upper and Lower Wilcox zircon age spectra show that more arc related material was deposited in the Lower Wilcox, whereas more basement material was deposited in the Upper Wilcox.
text