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Grun, Rainer Wolfgang. "Contributions to quaternary geochronology." Phd thesis, Canberra, ACT : The Australian National University, 1995. http://hdl.handle.net/1885/145307.
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Marshall, William Alderman. "Geochronology of salt-marsh sediments." Thesis, University of Plymouth, 2007. http://hdl.handle.net/10026.1/2826.
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Salt-marsh sediments can provide important achives of past sea levels if they can be securely dated. This thesis investigates eight methods for dating salt-marsh sediments. These include traditional and established dating methods (¹⁴C dating and the radionuclides ¹³⁷Cs and ²¹ºPb) and more novel approaches to dating the deposition of salt-marsh sediments (palaeomagnetic dating, the use of' atmospheric stable lead deposition, tephra chronologies, pollen markers, SCP analysis and the use of atmospheric ¹⁴C 'bomb spike' and high-precision AMS ¹⁴C measurements). Sites were selected to provide contrasting sediment sequences that differed both in lithology and accumulation rates and included salt marshes from the Taf estuary (southwest Wales), the Arne Peninsula (southern England) and Vioarholmi (western Iceland). The investigations in the Taf estuary produced the first palaeomagnetic chronology from a salt marsh. From the Arne Peninsula this thesis reports the first successful use of bomb-spike calibrated ¹⁴C analyses in a salt marsh as well as high-precision AMS ¹⁴C ages for the 'problem' period AD 1700-1950. Stable Pb analysis at all three sites produced a number of chronological markers that signalled the timing of increases in industrial Pb emissions, and the later use of Pb petrol additives during the 20th century. In addition, a unique isotopic signal, attributed to the working of Pb metal during the height of the Roman Empire in Europe, was found in the Icelandic sediments. The radionuclides ²¹ºPb and ¹³⁷Cs produced precise chronologies for the last 100 yr in the Taf estuary. However, post-depositional mobility of ¹³⁷Cs on the Arne Peninsula and low ²¹ºPb concentrations at Vioarholmi prevents the construction of reliable ²¹ºPb and ¹³⁷Cs chronologies. In contrast, the use of tephra at Vioarholmi, and pollen and spheroidal carbonaceous particle markers on the Arne Peninsula, showed great potential as independent unique-event dating tools that could be used to constrain conventional ¹⁴C calibrations. Finally, the chronological information produced by all the individual methods was combined to construct an integrated chronology for each site. This approach significantly reduced age uncertainties and produced higher resolution, and more robust, salt-marsh sedimentation histories
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Heim, Sabine. "Geochronology of anthropogenic contaminants in fluvial sediments /." Aachen : Shaker, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014779100&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Simonetti, Antonio. "The geochronology of acadian plutonism in Southern Quebec /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61761.
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Lawley, Christopher J. M. "Geochronology and structure of the Lupa Goldfield, Tanzania." Thesis, Durham University, 2012. http://etheses.dur.ac.uk/5906/.
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Gold occurrences in the Lupa goldfield, SW Tanzania, are typical of the orogenic Au deposit type. Auriferous quartz veins and mylonitic shear zones cross cut Archean granitoids (ca. 2740 Ma) and Paleoproterozoic felsic-mafic intrusions (1960–1880 Ma) comprising a Paleoproterozoic magmatic arc at the Tanzanian cratonic margin. Lu-Hf zircon results provide evidence for ca. 3.1 Ga basement beneath the Lupa goldfield and imply significant portions of the Ubendian Belt represent re-worked Archean crust. A greenschist facies metamorphic mineral assemblage overprints all of the magmatic phases and U-Pb dating of syn-metamorphic titanite hosted by a foliated Archean granitoid at ca. 1950 Ma suggests the onset of this tectonothermal episode occurred during the Paleoproterozoic. The majority of mineralization is hosted by a network of brittle-ductile and mylonitic shear zones, which record evidence for transpressional deformation of triclinic, or lower order, symmetry. Relacement of igneous feldspar (plagioclase and K feldspar) with intrinsically weaker phyllosilicates, during sericitization of the granitic wall rock, created the ideal conditions for strain localization and locally may have led to the onset of crystal plastic deformation processes. Continued feedback between fluid, rock and deformation generated interconnected networks of weak mylonitic shear zones that are subject to reactivation. Quartz veins are the other significant host for Au and possess geometries that imply mineralization occurred concurrently with episodic fluid pressure fluctuations. Re-Os molybdenite, pyrite and chalcopyrite geochronology ages record a protracted metallogenic history and provide evidence for at least two mineralizing events at ca. 1940 and 1885 Ma. Each metallogenic event is represented in detail by a hydrothermal history that occurred at a time scale less than the resolution of the Re-Os method. High precision U-Pb zircon ages for the Saza Granodiorite overlap with Re-Os ages and provide unequivocal evidence for magmatism concomitant with sulphidation, however the wide range of Re-Os sulphide ages precludes a genetic relationship between any individual intrusion and Au. The goldfield-wide metallogenic event at ca. 1885 Ma occurred concurrently with eclogite facies metamorphism elsewhere in the Ubendian Belt and provides one of Earth’s earliest examples of subduction processes temporally linked to orogenic Au deposit formation. Mesoproterozoic Re-Os ages (ca. 1125 Ma) correlated to the Kibaran/Irumide Orogenies and compatible with inferred Pb loss events provide evidence for sulphidation during at least two discrete orogenic cycles and suggest mid-crustal mylonitic shear zones represent long-lived zones of structural weakness.
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Sahy, Claudia Diana. "Geochronology and chronostratigraphy of the Eocene-Oligocene transition." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/28952.
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This thesis integrates high-precision (<0.2%, 2σ) [superscript 206]Pb/[superscript 238]U dating of zircons from volcanic tuffs intercalated in key Late Eocene-Oligocene marine and terrestrial sedimentary successions, with high-resolution biostratigraphic and magnetostratigraphic data sets in order to critically examine the accuracy and precision of the numerical age calibration of the Eocene – Oligocene transition (EOT). Weighted mean [superscript 206]Pb/[superscript 238]U ages from the Italian Umbria-Marche and North American White River Group (WRG) sedimentary successions are 0.4-1.0 Myr younger than legacy [superscript 40]Ar/[superscript 39]Ar biotite and sanidine data from the same tuffs (calibrated relative to Fish Canyon sanidine at 28.201 Ma). [superscript 206]Pb/[superscript 238]U calibrated age-depth models were used to constrain the age of magnetic reversals between 26.5-36 Ma (C8r-C16n.2n). Interpolated magnetic reversal ages are consistent with relatively constant seafloor spreading rates, and provide a fully integrated and robust chronostratigraphic framework for the EOT, as shown by mutual consistency of chron boundary ages from the Umbria-Marche basin and the WRG between 31-36 Ma. These data effectively eliminate the discrepancies between astronomically tuned and radio-isotopically calibrated time scales of the EOT. An evaluation of the fidelity of planktonic foraminifer bioevent based chronostratigraphy across the EOT indicates that the last occurrence of hantkeninids and the last common occurrence of Chiloguembelina cubensis which mark the Eocene-Oligocene (34.090 ± 0.074 Ma) and Rupelian – Chattian (28.126 ± 0.175 Ma) boundaries are not timetransgressive across oceanic basins. However, other Oligocene planktonic foraminifer bioevents occur 0.4-0.8 Myr later in the western Tethys than in tropical and subtropical open ocean settings. In the WRG sedimentary succession, the first and last appearance datums of key Late Eocene mammal taxa show diachroneity of ca. 1 Myr over a distance of 400 km. Long-term aridification recorded by the WRG appears to be time-transgressive, and progressed gradually from west to east, while abrupt Early Oligocene cooling reported from WRG outcrops in NE Nebraska was synchronous with Early Oligocene glaciation of Antarctica.
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Rushworth, Elisabeth. "Carbonates from Olduvai Gorge, Tanzania : palaeohydrology and geochronology." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/10193/.
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Carbonates are abundant in the Pleistocene sedimentary sequence at Olduvai Gorge, Tanzania. This study reports their potential for investigating palaeoenvironments and for radiometric dating using U-Pb geochronology. Using their textural characteristics the, commonly nodular, terrestrial carbonates have been placed in one of five groups. By using multiple textural and geochemical analytical techniques, the palaeohydrological origin of each group has been proposed. When referenced to the geographical and stratigraphic framework at the eastern lake margin, the carbonates have been used to identify the palaeohydrological conditions beneath specific land surfaces and how it changed through time. The results identify the onset of synsedimentary faulting below Tuff IB, the palaeohydrological significance of fault control in landscape development, and the persistence of water in discrete settings. This helps to explain why hominin activity is located in certain areas in a fault compartment. The study has proved that detailed investigation of carbonates offers an effective method for understanding the wider palaeohydrology at exposure surfaces and the factors influencing hominin exploitation at particular locations and has the potential to provide a predictive tool for future archaeological investigations. Two types of dolomite are found at different stratigraphic levels, identifying episodes of high Mg/Ca ratios in the lake, and dolomite precipitation occurring in both a basinal and a lake marginal setting. Sand-sized calcite crystals formed in the shallow sub-surface sediments on the lake floor and lake margins under anoxic to sub-oxic conditions. 238U - 206Pb dating of these zoned calcite crystals using Laser Ablation MC-ICP-MS and has produced dates only a little older than those using 40Ar/39Ar on tuffs in the same stratigraphic intervals. 234U/238U activity ratios of the Pleistocene crystals indicate that different levels are more affected by open system behaviour than others. Early-diagenetic, authigenic calcite crystals show exciting promise for directly dating saline, alkaline lake sediments which may be useful in similar hominin sites where geochronology is less well constrained.
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Rooney, Alan. "Re-Os geochronology and geochemistry of Proterozoic sedimentary successions." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/621/.
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The Re-Os organic-rich sedimentary rocks (ORS) geochronometer has the potential to provide precise depositional ages and vital information on the Os isotope composition of palaeo-seawater. This thesis presents new geochronology data from Proterozoic sedimentary successions and insights into Re-Os systematics of organic-rich sedimentary rocks and petroleum products such as bitumen and oil. New Re-Os ORS geochronology from two drill cores indicate that the Proterozoic Atar Group of the Taoudeni basin, Mauritania is ~200 Ma older than previous estimates (1107 ± 12 Ma, 1109 ± 22 Ma and 1105 ± 37 Ma). Furthermore, this data also provides precise Re-Os geochronology data from sedimentary rocks that have experienced flash pyrolysis and demonstrate that the Re-Os systematics are not disturbed by the effects of very rapid heating. Coupled with palaeomagnetic data the Re-Os geochronology suggests that a reassessment of the role of the West African craton during the assembly of Rodinia is required. New Re-Os geochronology for the Ballachulish Slate Formation of the Dalradian Supergroup, Scotland yields a depositional age of 659.6 ± 9.6 Ma. The Re-Os age represents a maximum age for the glaciogenic Port Askaig Formation and represents the first successful application of the Re-Os geochronometer in sedimentary rocks with low Re and Os abundances (<1 ppb and <50 ppt, respectively). This new age suggests that the Port Askaig Formation may be correlative with Sturtian glaciations rather than middle Cryogenian events. Laboratory-based hydrous pyrolysis experiments were employed to evaluate the complexation of Re and Os in ORS and their transfer behaviour into petroleum. The findings from these experiments demonstrate that the Re-Os geochronometer is not disturbed by thermal maturation of whole rocks. Furthermore, the data support the hypothesis that the isotope composition of oils and bitumens can be used to fingerprint petroleum to specific source rocks.
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Heim, Sabine [Verfasser]. "Geochronology of Anthropogenic Contaminants in Fluvial Sediments / Sabine Heim." Aachen : Shaker, 2005. http://d-nb.info/118658825X/34.
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Schneider, Albrecht. "Eruptive processes, mineralization and isotopic evolution of the Los Frailes Karikari region, Bolivia." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37847.
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Li, Shenghua. "Development and application of stimulated luminescence dating methods for sediments." Thesis, Aberystwyth University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281880.
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Landon-Browne, Ayesha. "Combined Short-lived (182W, 142Nd) and Long-lived (147Sm-143Nd) Isotope Study on Rocks from the Pulpwood-Playter Harbour Sequence (Wawa Subprovince): Constraints on the Mantle Source of Neoarchean Ferropicrites." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39573.
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Short-lived isotope systems can be utilized to track differentiation processes that had occurred during Earth’s early history. Both the 182Hf-182W and 146Sm-142Nd systems are sensitive to silicate fractionation events due to differing parent-daughter incompatibilities. The 182Hf-182W system is also affected by metal-silicate fractionation events due to the siderophile nature of W. An increasing number of mantle-derived rocks, mainly formed during the Archean (4.0-2.5 Ga), have presented variable anomalies in the daughter products of both systems, indicating their sources contain isotope signatures established shortly after the formation of the Earth.
Some Archean Fe-rich primitive magmas known as ferropicrites, have been suggested to derive from mantle domains that differentiated after the crystallization of a Hadean (>4.0 Ga) magma ocean. In order to investigate the potential involvement of a Hadean source in the petrogenesis of Archean ferropicrites, we have studied the Nd and W isotopic compositions of rocks from the Pulpwood-Playter Harbour sequence in the Wawa subprovince, Ontario, Canada. This sequence is composed of ferropicritic intrusive rocks and lavas in association with tholeiitic mafic lavas. A 147Sm-143Nd isochron including all lithologies yields an age of 2681±51 Ma (MSWD =6.6) with an initial 143Nd of +2.5. This Nd initial isotopic composition indicates the rocks were derived from a long-term incompatible-element depleted mantle source. Both the ferropicritic and the tholeiitic rocks plot on the same isochron, suggesting they derived from the same mantle source, despite their different geochemical compositions. Negative 142Nd anomalies compared to the Nd terrestrial standard were found in the majority of the rocks studied here, yielding an average μ142Nd value of -2.0±3.9. Although not resolvable from the terrestrial standard given
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the current analytical precision, the fact that almost all analysed samples exhibit negative μ142Nd values could suggest the influence of a Hadean source in their formation. If this is the case, a single early silicate fractionation event occurring between 4.56 and 4.47 Ga could explain both the ε143Nd and μ142Nd values obtained for the studied rocks. Alternatively, the involvement of eclogitic material, with a Hadean basaltic protolith, interacting with Archean peridotitic mantle could explain the Nd isotopic composition of the ferropicrites, but this would not account for the identical isotopic composition of the tholeiites – thus rendering a garnet pyroxenite source improbable. One intrusive ferropicritic sample yielded a resolvable 182W excess of +14.1 ±6.7 ppm. If this excess 182W is characteristic of the Pulpwood-Playter Harbour sequence, it indicates the decoupling of 182Hf-182W and 146Sm-142Nd systems. This decoupling could be explained by early metal-silicate fractionation recorded in the Hf-W systematics of these rocks or the contribution of Fe-rich meteoritic material into the source of ferropicrites.
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Eikenberg, Jost. "Radium isotope systematics in nature: applications in geochronology and hydrogeochemistry." Villigen : Division for Radiation Protection and Safety, Paul Scherrer Institute Villigen (PSI), 2002. http://e-collection.ethbib.ethz.ch/show?type=habil&nr=10.
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Jurkowski, Jacek. "U-Pb geochronology study of Lynn Lake greenstone belt, Manitoba." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0011/MQ52583.pdf.
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La, Rocque Cynthia A. "Geochronology and petrology of north-central Gaspe igneous rocks, Quebec." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65499.
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Lifton, Zachery Meyer. "Understanding an evolving diffuse plate boundary with geodesy and geochronology." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50316.
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Understanding spatial and temporal variations in strain accumulation and release along plate boundaries is a fundamental problem in tectonics. Short-term and long-term slip rates are expected to be equal if the regional stress field remains unchanged over time, yet discrepancies between modern geodetic (decadal time scale) slip rates and long-term geologic (10^3 to 10^6 years) slip rates have been observed on parts of the Pacific-North American plate boundary system. Contemporary geodetic slip rates are observed to be ~2 times greater than late Pleistocene geologic slip rates across the southern Walker Lane. I use a combination of GPS geodesy, detailed field geologic mapping, high-resolution LiDAR geodetic imaging, and terrestrial cosmogenic nuclide geochronology to investigate the observed discrepancy between long- and short-term slip rates. I find that the present day slip rate derived from GPS geodesy across the Walker Lane at ~37.5°N is 10.6 ± 0.5 mm/yr. GPS data suggest that much of the observed discrepancy occurs west of the White Mountains fault zone. New dextral slip rates on the White Mountains fault zone of 1.1 ± 0.1 mm/yr since 755 ka, 1.9 +0.5/-0.4 mm/yr since 75-115 ka, 1.9 +0.5/-0.4 mm/yr since 38.4 ± 9.0 ka, and 1.8 +2.8/-0.7 mm/yr since 6.2 ± 3.8 ka are significantly faster than previous estimates and suggest that slip rates there have remained constant since the middle Pleistocene. On the Lone Mountain fault I calculate slip rates of 0.8 ± 0.1 mm/yr since 14.6 ± 1.0 ka and 0.7 ± 0.1 mm/yr since 8.0 ± 0.5 ka, which suggest that extension in the Silver Peak-Lone Mountain extensional complex has increased dramatically since the late Pleistocene.
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Roberts, Hazel Jane. "An investigation of a polymetamorphic terrain using ⁴⁰Ar-³⁹Ar geochronology." Thesis, Open University, 1999. http://oro.open.ac.uk/54421/.
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This research is an exploration both of the Precambrian metamorphic geology of south-western Montana and the Wlaser ablation microprobe 4OAt-39At geochronological technique. Using the high spatial resolution of the UV laser microprobe it has been possible to produce systematic 4OAt-39Ar ages within individual mica grains. Further, the UV laser has been used to drill into biotite inclusions within garnet to look at the shielding effect of the garnet lattice, and to drill depth profiles into garnet to measure helium diffusion in laboratory experiments. The south-western Montana region of the Precambrian Wyoming Province was believed to have undergone at least three separate periods of metamorphism: M1- granulite facies in the Archaean, M2 - amphibolite facies in the Early Proterozoic, and M3 - greenschist to epidote-amphibolite facies in the Mid-Proterozoic. Because of the relatively low blocking temperature of the 40Ar- 39Ar geochronological system in mica (c.300-350 °C), it is readily reset by regional metamorphic events and previous K-Ar and 4OAr_38 Atgeochronology had found that the Early Proterozoic event dominated the ages obtained. UV laser 40Ar-39At dating of the matrix mica constrained the timing of cooling from the Early Proterozoic metamorphic event to between 1780 to 1740 Ma with a cooling rate between 1 and 8 °C/m.y. 4OAr_39Ar analyses of individual biotite inclusions in garnet also produced similar ages. However, Pb-Pb step leach dating of a small subset of garnet yielded ages between 1808 and 1765 Ma, demonstrating that the garnet did not grow during an Archaean event but, rather, during the Early Proterozoic metamorphic event. Thus, the shielding properties of garnet on biotite inclusions could not be easily assessed in these samples. However, where matrix biotite had been partially reset by the Cretaceous plutons, there was some evidence to suggest that a minority of the biotite inclusions in the same sample had been shielded from resetting. The influence of fractures, defects and other fast diffusion paths is believed to have prevented most of the inclusions from being shielded. No evidence was found to show that the rocks in south-western Montana were metamorphosed during the Archaean and it seems likely that the M1 and M2 events were not greatly separated in time and were both Early ProterozoiC in age. The high spatial resolution of the UV laser microprobe was used in order to date highly altered biotite within rocks that had undergone later (M3) greenschist metamorphism. Biotite was interlayered with chlorite, clinozoisite and prehnite but using the UV laser it was possible to separately analyse areas of unaltered biotite and areas of alteration within a single mineral and produce ages from both. It was thus possible to measure two ages from one sample: an unaltered age consistent with the timing of the Early Proterozoic metamorphism, and a younger age that could be linked to the c.1500-1360 Ma timing of Belt basin formation to the north and west of the region. This technique therefore was able to overcome the difficulties associated with producing meaningful ages from altered samples whilst constraining the timing of the M3 metamorphic event.
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Neace, Erika R. "Zircon LA-ICPMS Geochronology of the Cornubian Batholith, SW England." Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1448912006.
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Copeland, Audrey Elizabeth, Jay Quade, James Watson, Brett McLaurin, and Elisa Villalpando. "Stratigraphy and Geochronology of La Playa Archaeological Site, Sonora, Mexico." Thesis, The University of Arizona, 2011. http://hdl.handle.net/10150/229791.
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The current study examines the stratigraphy, geochronology, and paleoecology of La Playa, an Early Agricultural period archaeological site (3600-1800 BP) located in northern Sonora, Mexico. We distinguished seven stratigraphic units ranging in age from >44,570 to 680 cal yr BP. All of the cultural remains are contained in Unit B, which spans from 4700-1580 BP. Deposits from Unit B represent overbank deposition from the nearby Rio Boquillas. The majority of cultural materials come from Units B4 and B5, which correspond to the Cienega phase (2800-1800 BP) of the Early Agricultural period. This period coincides with the first sedentary agricultural populations in the region and is marked by thousands of archaeological features including roasting pits, human burials, and extensive canal systems at La Playa. The presence of semi-aquatic and aquatic snails demonstrates that water was present year round in the canal system. The stable and radiometric isotopic evidence suggests that the early agriculturalists diverted ground water, likely from the nearby Rio Boquillas. Cultural remains from Unit C spanning the period <1580-680 BP are rare, suggesting major population decline during this time. There is little to no evidence of bioturbation in Unit C, suggesting that the landscape was thinly vegetated at this time. La Playa has experienced up to five meters of erosion during historic times, exposing a complex alluvial stratigraphy and numerous cultural features, which has greatly complicated archaeological interpretations at the site.
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Newberry, Tundi Lee. "Weathering geochemistry and geochronology of the Australian sedimentary-hosted opal deposits /." [St. Lucia, Qld.], 2005. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18612.pdf.
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Cohen, Barbara Anne, and Barbara Anne Cohen. "Geochemistry and 40AR - 39AR geochronology of lunar meteorite impact melt clasts." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/625905.
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Placzek, Christa. "Stratigraphy, Geochronology and Geochemistry of Paleolakes on the Southern Bolivian Altiplano." Tucson, Arizona : University of Arizona, 2006. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1401%5F1%5Fm.pdf&type=application/pdf.
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Pietsch, Timothy J. "Fluvial geomorphology and late quaternary geochronology of the Gwydir fan-plain." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060720.153247/index.html.
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Al-Jawadi, A. F. "Minor igneous intrusions of the Lake District : geochronology, geochemistry and petrology." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376308.
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Horstwood, Matthew Simon Anthony. "Stratigraphy, geochemistry and zircon geochronology of the Midlands Greenstone Belt, Zimbabwe." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246222.
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Safipour, Roxana G. "U-Pb geochronology of the Acasta Gneiss Complex in Northwest Canada." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/114375.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 58-59).
The Acasta Gneiss Complex in Northwest Canada contains the oldest dated rocks in the world. The gneisses range in age from 4.03-3.6 Ga, as determined by U-Pb dating of zircons (Bowring and Williams 1999). U-Pb dating of xenocrystic cores in these zircons indicates a cryptic record of continental crust older than 4.0 Ga. In this study, zircons were selected and characterized from thirteen samples of Acasta Gneisses. Many of the zircons contain xenocrystic cores mantled by younger domains. U-Pb geochronological data were collected using laser ablation inductively coupled plasma mass spectrometery (LA-ICPMS). Twelve of the samples show evidence for two distinct crystallization events, one which formed the cores and another in which the mantle domain overgrew the cores. The oldest cores were dated at >4.0 Ga. This provides additional evidence for pre-4.0 Ga crust formation in the late Hadean.
by Roxana G. Safipour.
S.B.
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Brook, Edward J. "Surface exposure geochronology using cosmogenic nuclides : applications in Antarctic glacial geology." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/51532.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution, 1994.Vita.
Includes bibliographical references (leaves 224-227).
by Edward Jeremy Brook.
Ph.D.
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Placzek, Christa. "Stratigraphy, Geochronology and Geochemistry of Paleolakes on the Southern Bolivian Altiplano." Diss., The University of Arizona, 2005. http://hdl.handle.net/10150/194352.
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Precise chronologies of climate events in the tropics are rare yet essential for understanding how tropical climate relates to global climate at millennial to longer time scales. An increasingly important area for understanding these interactions is the southern Bolivian Altiplano (15-22oS) which represents the waning and southeastern end of the South American Monsoon, a system that is, today, modulated by regional upper-air circulation anomalies under the influence of tropical Pacific sea-surface temperature gradients associated with El Niño/Southern Oscillation (ENSO). Mechanisms of summer rainfall variations on millennial and longer time scales are less well understood, despite well-established evidence for profound changes in hydrologic budgets on the southern Bolivian Altiplano. Large shifts in effective moisture on the southern Bolivian Altiplano produced deep lakes in the Poopo, Coipasa, and Uyuni basins, basins that are currently occupied by salt pans or very shallow lakes. We mapped shoreline stratigraphy and sampled carbonates for over 170 uranium-thorium (U-Th) and radiocarbon (14C) dates to refine paleolake history of the Southern Bolivian Altiplano. As part of this dissertation work, I helped assemble a U-Th dating facility at the University of Arizona and obtained over 90 uranium-thorium (U-Th) dates from paleolake carbonates. Carbonate textures were evaluated for potential diagenetic effects, but the principal consideration in dating such carbonates is the isotopic composition and quantity of initial Th incorporated into the carbonate. We establish criteria for statigraphically meaningful dates and strategies for successful U-Th dating of paleolake carbonates. The stable isotope, 87-strontium/86-strontium (87Sr/86Sr), and 234U/238U ratios of modern surface waters and of paleolake carbonates can be used as tracers of the region's various lake cycles and provides a test hydrologic models of these lake cycles.Volcanic tuffs provide important stratigraphic markers for paleolimnologic, geomorphic, and archeological studies. Despite the widespread occurrence of late Quaternary tuffs on the Bolivian Altiplano, few of these deposits have been previously recognized either from natural exposures or in paleolake sediment cores. We document the presence of 38 distal tuffs in Quaternary lacustrine and alluvial deposits, and determine the composition of glass and phenocrysts by electron microprobe analyses.
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Mitchell, Ruairidh J. "UHT metamorphism. Can integrated thermobarometry and geochronology quantify lower crustal processes?" Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/80609.
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The Eastern Ghats Province cooled at 0.34 ± 0.09 °C/Ma from ~6.8–8.3 kbar, 1000°C between c. 1000–880 Ma, and was reheated to >900 °C at c. 550–500 Ma. This reflects a period of burial in the deep crust of an orogen with high radiogenic heat production and slow rates of erosion. Additionally, local equilibrium can persist in metamorphic rocks at >900 °C, should solid phases be chemically and physically isolated from melt.
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Lion, Allan. "Thermochronologic and Geochronologic Investigations of the Pre-Volcanic Crystalline Basement of Thera (Santorini), Greece: Determining the Tectonostratigraphy and Deformational History of the Metamorphic Core." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38605.
Full textAbstract:
The cores of most Cycladic Islands are formed as consequences of early Paleogene high-pressure subduction processes of the African plate beneath Europe, and Miocene extensional exhumation of the subduction trench. The island of Thera (Santorini) resides in the Hellenic Volcanic Arc, and is dominated by Quaternary eruptive volcanic material atop a pre-volcanic basement. The position of the island has led to debate as to the nature of the pre-volcanic basement, with connections drawn to either the Cycladic Blueschist Unit (CBU) or the Phyllite-Quartzite Unit (PQU). Field observations, which document a top-to-SSE detachment, in conjunction with geochronological techniques have been applied to assess the tectonostratigraphy of the pre-volcanic basement. The results resolve the pre-volcanic basement as belonging to the CBU which has been juxtaposed against Sub-Pelogonian marble by the SSE directed detachment. This firmly establishes Thera within the Cycladic realm, documents Miocene deformation, and changes the geologic map of the Hellenides.
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Parsons, Kelli Joanne. "Spatial and temporal patterns of land-use induced sedimentation in Clear Creek Basin, Iowa." Thesis, University of Iowa, 2018. https://ir.uiowa.edu/etd/6245.
Full textAbstract:
This study is centered around the spatial distribution and age structure of PSA in a section of floodplain in the upper reaches of Clear Creek Watershed in east central Iowa. The study area topography, climate, soil, and pre-settlement tallgrass prairie landcover are representative of the headwaters of many Midwest watersheds, making the findings applicable in other parts of the region. Through this investigation, I aim to further understand the volume and age structure of PSA sediments deposited on the floodplain after Euroamerican settlement. This will be done through multiple methods: the collection and measurement of PSA in soil cores, visual and spatial analysis of land use and stream channel morphology, PSA volume calculations, and isotope geochemistry. Using 210Lead (Pb) and 137Cesium (Cs) isotope geochemistry to calculate age structures of the PSA will provide a more detailed, temporal resolution of physical data than erosion and deposition model predictions can generate. A detailed land use history will further facilitate the understanding of depositional processes that have occurred in the study area and region. By understanding the age structure of the sediment on the floodplain, as well as sediment volumes that are stored in floodplain headwaters, tangible connections can be made between agricultural land use and floodplain sedimentation rates and the impact (if any) assessed of potential conservation practices. This research is supported by the Intensively Managed Landscape Critical Zone Observatory (IML-CZO) of the National Science Foundation’s CZO network, which aims to understand how land use changes affect the long-term resilience of the critical zone, where water, atmosphere, ecosystems, soil, and bedrock interact.
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Downey, Matthew. "The Structural Geology, Kinematics and Timing of Deformation at the Superior craton margin, Gull Rapids, Manitoba." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1258.
Full textAbstract:
The Gull Rapids area, Manitoba, lies on the Superior craton margin and forms part of the Superior Boundary Zone (SBZ), a major collisional zone between the Archean Superior craton and the adjacent Paleoproterozoic Trans-Hudson Orogen. There are two main rock assemblages at Gull Rapids: orthogneisses (of possible Split Lake Block origin) and supracrustal rocks (metavolcanic and metasedimentary). Late, crosscutting felsic and mafic intrusive bodies (mostly dykes and sills) are used to constrain the relative and absolute timing of deformation and metamorphism. The Gull Rapids area records a complex tectonic history. The area experienced four generations of Neoarchean ductile and brittle deformation (G1 ? G4) and one of Paleoproterozoic ductile-brittle deformation (G5). G1 deformation produced the main foliation in the map area, as well as local isoclinal folding which may be related to an early shearing event. M1a prograde mid-amphibolite facies metamorphism is contemporaneous with the early stages of G1. Widespread, tight to isoclinal sheath folding during G2 was recorded in the supracrustal assemblage, and is the result of southwest-side-up, dextral shearing during the early shearing event. A ca. 2. 68 Ga widespread phase of granitoid intrusion was emplaced late-G1 to early-G2, and is rich in metamorphic minerals that record conditions of M1b upper-amphibolite facies peak metamorphism. M1b metamorphism, late-G1 to early-G2 deformation, and intrusion of this felsic phase are contemporaneous. M2 retrograde metamorphism to mid-amphibolite facies was recorded sometime after M1b. G1 and G2 structures were re-folded during G3, which was then followed by G4 southwest-side-up, dextral and sinistral shearing, contemporaneous with late pegmatite intrusion at ca. 2. 61 Ga. This was followed by mafic dyke emplacement at ca. 2. 10 Ga, and then by G5 sinistral and dextral shearing and M3 greenschist facies metamorphism or hydrothermal alteration at ca. 1. 80 Ga.
Deformation and metamorphism at Gull Rapids post-dates emplacement and deposition of gneissic and supracrustal rocks, respectively. This deformation and metamorphism, except for G5 and M3, is Neoarchean (ca. 2. 68?2. 61 Ga), and represents a significant movement of crustal blocks: km-scale shearing of the supracrustal assemblage and consequent uplift of the Split Lake Block. Late deformation and metamorphism (G5, M3) may be related to the Paleoproterozoic Trans-Hudson orogeny. The Neoarchean and Paleoproterozoic zircon populations in the geochronological data suggest that the Gull Rapids area largely experienced Neoarchean deformation and metamorphism with a weak Paleoproterozoic overprint. All of the evidence presented above suggests that the Gull Rapids area lies in a part of the Superior Boundary Zone, yet does not lie at the exact margin of the Superior craton, and therefore does not mark the Archean-Proterozoic boundary proper in northeastern Manitoba.
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Smith, Martin Lancaster, and martin smith@anu edu au. "Towards a Geochronology for Long-term Landscape Evolution, Northwestern New South Wales." The Australian National University. Research School of Earth Sciences, 2006. http://thesis.anu.edu.au./public/adt-ANU20061026.141414.
Full textAbstract:
The study area extends from west of the Great Divide to the Broken Hill and Tibooburra regions of far western New South Wales, encompassing several important mining districts that not only include the famous Broken Hill lodes (Pb-Zn-Ag), but also Parkes (Cu-Au), Peak Hill (Au), Cobar (Cu-Au-Zn) and White Cliffs (opal). The area is generally semi-arid to arid undulating to flat terrain covered by sparse vegetation.
¶
During the Cretaceous, an extensive sea retreated across vast plains, with rivers draining from the south and east. After the uplift of the Great Divide associated with opening of the Tasman Sea in the Late Cretaceous, drainage swung to the west, cutting across the Darling River Lineament. The Murray-Darling Basin depression developed as a depocentre during the Paleogene. Climates also underwent dramatic change during the Cenozoic, from warm-humid to cooler, more seasonal climates, to the arid conditions prevalent today. Up until now, there has been very little temporal constraint on the development of this landscape over this time period. This study seeks to address the timing of various weathering and landscape evolution events in northwestern New South Wales.
¶
The application of various regolith dating methods was undertaken. Palaeomagnetic dating, clay δ18O dating, (U+Th)/He and U-Pb dating were all investigated. Palaeomagnetic and clay dating methods have been well established in Australian regolith studies for the last 30 years. More recently, (U+Th)/He dating has been successfully trialled both overseas and in Australia. U-Pb dating of regolith materials has not been undertaken. Each method dates different regolith forming processes and materials. Palaeomagnetic and clay dating were both successfully carried out for sites across northwestern New South Wales, providing a multi-technique approach to resolving the timing of weathering events. Although (U+Th)/He dating was unsuccessful, there is scope for further refinement of the technique, and its application to regolith dating. U-Pb dating was also unsuccessfully applied to late-stage anatase, which is a cement in many Australian silcretes.
¶
Results from this study indicate that the landscape evolution and weathering history of northwestern New South Wales dates back at least 60 million years, probably 100 million years, and perhaps even as far back as 180 million years. The results imply that northwestern New South Wales was continuously sub-aerially exposed for the last 100 Ma, indicating that marine sedimentation in the Murray-Darling and Eromanga-Surat Basins was separated by this exposed region. The ages also provide further evidence for episodic deep chemical weathering under certain climatic conditions across the region, and add to the data from across Australia for similar events. In particular, the palaeomagnetic ages, which cluster at ~60 ± 10 Ma and 15 ± 10 Ma, are recorded in other palaeomagnetic dating studies of Australian regolith. The clay ages are more continuous across the field area, but show older clays in the Eromanga Basin sediments at White Cliffs and Lightning Ridge, Eocene clays in the Cobar region, and Oligocene Miocene clays in the Broken Hill region, indicating progressively younger clay formation from east to west across northwestern New South Wales, in broad agreement with previously published clay weathering ages from around Australia.
¶
These weathering ages can be reconciled with reconstructions of Australian climates from previously published work, which show a cooling trend over the last 40 Ma, following an extended period of high mean annual temperatures in the Paleocene and Eocene. In conjunction with this cooling, total precipitation decreased, and rainfall became more seasonal. The weathering ages fall within periods of wetness (clay formation), the onset of seasonal climate (clay formation and palaeomagnetic weathering ages) and the initiation of aridity in the late Miocene (palaeomagnetic weathering ages).
¶
This study provides initial weathering ages for northwestern New South Wales, and, a broad geochronology for the development of the landscape of the region. Building on the results of this study, there is much scope for further geochronological work in the region.
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Ely, Kim Susan. "Geochronology of Timor-Leste and seismo-tectonics of the southern Banda Arc." Connect to thesis, 2009. http://repository.unimelb.edu.au/10187/7063.
Full textAbstract:
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.
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Noyes, Andrea K. "A feasibility study of U-Pb ilmenite geochronology, Monastery kimberlite, South Africa." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0010/MQ60161.pdf.
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Leslie, Christopher Dean. "Detrital zircon geochronology and rift-related magmatism : central Mackenzie Mountains, Northwest Territories." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/7109.
Full textAbstract:
Neoproterozoic to Cretaceous age strata in the Mackenzie Mountains of the northern Canadian Cordillera record many geological events that affected the western margin of Ancestral North America. Two of these events that are the focus of this study are; (1) the development of a thick long-lived passive margin sequence of sedimentary rocks; and (2) continental rifting of this passive margin in Ordovician time that was accompanied with alkaline volcanism of the Marmot Formation.
Sedimentary units from throughout the Mackenzie Mountains stratigraphy contain ubiquitous detrital zircons with U-Pb ages of 2800 – 2415 Ma and 2080 – 1700 Ma; these reflect a component of sediment derived from basement sources of western Laurentia. More surprising is the abundance of “anomalous” detrital zircons ages (e.g., 1800 – 1000 Ma) in these units that cannot be linked to known local sources. The most likely source for detrital zircons of these ages are felsic igneous rocks now exposed in southern and eastern North America. We therefore speculate that in the Neoproterozoic sediments were dispersed from these distal sources across the North American Craton. Reworking and recycling of these older sediments is evident in most of the younger investigated strata. In Carboniferous and younger strata there is also a major influence from sources exposed in the Canadian Arctic and possibly along Alaskan margin as evidenced by detrital zircons with Lower Paleozoic ages (e.g., 477 – 392 Ma).
Continental extension of the western margin of Laurentia in Early to Middle Cambrian and again in Middle Ordovician time formed a rifted sedimentary basin termed the Misty Creek Embayment. Alkaline mafic magmatism associated with the Middle Ordovician rifting event (460 – 444 Ma) comprises massive mafic volcanic rocks (MFV and MFX suites), intrusive dykes and sills, volcaniclastic and epiclastic rocks and volcaniclastic filled diatremes (DVI suite). Petrographic studies together with whole rock, mineral chemistry and Nd isotopic studies indicate that the MFV and MFX suites were likely generated by small degrees of partial melting at the base of the subcontinental lithosphere with a minor asthenospheric input. The DVI parental magmas were also generated by small degrees of partial melting primarily in metasomatized subcontinental lithosphere.
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Tafti, Reza. "Metallogeny, geochronology and tectonic setting of the Gangdese belt, southern Tibet, China." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37070.
Full textAbstract:
The Gangdese belt in southern Tibet forms the eastern section of the Trans-
Himalayan magmatic belt. Until recently, the timing of magmatism in the Gangdese belt was
poorly known due to the limited number of geochronological studies. Results of this study
provide new insights into both the tectonomagmatic and metallogenic evolution of the
southern Tibet.
Six major magmatic events (Triassic and older, Early-Middle Jurassic, Late Jurassic,
middle Cretaceous, latest Cretaceous-Eocene, and Oligocene-Miocene) are recognized within
the southern Gangdese belt, each reflecting a specific paleotectonic setting. Early-Middle
Jurassic magmatism occurred in a continental marginal arc tectonic setting, with magmatism
related to south-dipping subduction of the Paleo-Tethys beneath the Lhasa terrane. Late
Jurassic magmas were derived from a mixed magma source in an extensional magmatic arc
setting, possibly during rollback of the Paleo-Tethyan slab and opening of the Neo-Tethys to
the south of the Lhasa terrane. Continental arc magmatism, dominated by widespread and
voluminous plutonism (Gangdese) and volcanism (Linzizong), began in Early Cretaceous
time due to the onset of the north-dipping subduction of Neo-Tethys oceanic slab under the
southern edge of the Lhasa terrane. This phase of subduction ended after the middle Eocene
collision of the Indian and Eurasia continental plates. An apparent increase in magmatic
activity around 50 Ma is attributed to the possible Neo-Tethyan slab rollback and breakoff.
Cretaceous-Eocene magmatism includes a hiatus of magmatic activity from 80 Ma to 68 Ma.
Miocene magmatism is post-collisional with adakite-like compositions possibly generated
from partial melting of an enriched lower crust due to delamination of the thickened
lithospheric mantle and asthenospheric upwelling after the collision. At least three major metallogenic epochs (Early-Middle Jurassic, Cretaceous-Eocene
and Miocene) within the belt have been recognized, including the world-class Jurassic
Xietongmen Cu-Au and Miocene Qulong Cu-Mo porphyry deposits. The Early-Middle
Jurassic event includes formation of two major porphyry Cu-Au deposits (Xietongmen and
Newtongmen) in the Xietongmen district, reflecting a major but previously unrecognized
metallogenic event. This has global economic importance because the rate of new
discoveries of large deposits within better explored belts elsewhere in the world has
decreased significantly in the last few decades.
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Rohde, Joana Kristin [Verfasser]. "Geochronology and Geochemistry of the Tristan-Gough Hotspot Track / Joana Kristin Rohde." Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1137509643/34.
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Bakhsh, Rami A. M. "Granites from the midyan terrain, NW Saudi Arabia: petrology, geochemistry and geochronology." Thesis, University of London, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589422.
Full textAbstract:
Granites from the Midyan terrain, NW Saudi Arabia: Petrology, geochemistry and geochronology Five, Neoproterozoic, poorly-studied felsic intrusives from NW Saudi Arabia have been subjected to a detailed geological study to understand their characteristics, evolutionary history, tectonic setting, ages and economical potential for rare metal mineralization. The work has utilized field observations, mappmg, mineralogy, petrography, geochemistry (ICP-AES and MS, XRF, scanning electron microscopy and microprobe) and geochronology (Rb/Sr whole rock isochrons and U-Pb zircon analysis). The results have indicated that the individual plutons in the region are each quite different. This is mainly displayed by the existence of different types of granites, based on chemistry and petrography (peralkaline, alkaline and calc-alkaline) and mineralogy (particularly the presence of different types of amphibole, both sodicand calcic). The plutons probably formed at low crystallizaton pressures (~ 1.2 to 3.4 Kbar) and at shallow (~4 to 12 km ±O.5 km) depths, but seem to have been derived from similar source regions. The granites were most likely derived by low-pressure, partial melting of crustal rocks with possible crustal contamination, followed by fractional crystallization and later sub-solidus alteration by fluids. The plutons' ages span a range from 630Ma (Cryogenian) to 554Ma (Ediacaran). The geochemical differences between the granites could be related to their formation during different stages of the region's evolution. A gradual change in tectonic setting is indicated, from island arc accretion in the middle stages of the Panafrican orogen, to a post-collisional setting in the early stages of the Panafrican event. Economically, the granites contain relatively high contents of rare earths elements (REEs) and rare-metals (RMs), mostly hosted by phosphates (monazite-Ce and xenotime), Nb-oxide (fergusonite- Y) and possible rare earth carbonates (synchysite). These elevated REEs and Nb contents and their mineralogical forms highlight the presence of suitable exploration targets for rare earth elements late stage deposits. xiii
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Wilkinson, Camilla M. "Understanding extraneous argon in silicic volcanic products using 4oAr/39Ar laserprobe geochronology." Thesis, Open University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593909.
Full textAbstract:
The Ar-Ar dating technique is one of the most widely applied geochronological techniques to products of silicic volcanism, which represent geologically instantaneous events, and have been used to calibrate the geological timescale, correlate stratigraphy and biostratigraphy over large areas, and assess the impact of explosive volcanic eruptions. Recent advances (e.g., improved instrument precision and recalibration of the K-Ar decay scheme), are now making it possible to obtain increasingly precise and accurate ages for young volcanic eruptions, K-poor minerals, and even discrete parts of single crystals. These advances have highlighted the realisation that relatively small levels of Ar contamination (e.g., extraneous Ar, either excess Ard, or inherited Ar), previously assumed to be minor, may now have a considerable effect on the accuracy of ages detennined using the Ar·Ar technique. To assess the issue of extraneous Ar, this study applied the Ar·Ar technique to a range of minerals (including sanidine, plagioclase and biotite), and glass separated from the products of large volume silicic magma systems, which have undergone repeated cycles of crystallisation and rejuvenation. The in situ Ar·Ar laserprobe technique was applied to dacite of the Fish Canyon magmatic system (erupted at - 28 Ma; Colorado, USA), and the single grain fusion Ar·Ar laser melting technique was applied to rhyolitic pumice (from explosive ignimbrite and ash fall, and effusive dome building events) of the Yellowstone Plateau Volcanic Field (2.1 Ma; Idaho, Wyoming, USA), and the Bishop Tuff (erupted at - 0.76 Ma; California, USA).
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Heri, Alexandra Regina. "Geochemistry, geochronology and isotope geochemistry of eocene dykes intruding the Ladakh batholith." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B50899624.
Full textAbstract:
Eocene dykes intruding the Ladakh batholith were sampled along the southern margin of the Trans-himalayan plutonic arc in Ladakh, NW-India. Approximately 30 dykes were encountered in the 40 km trail between Leh and Hemis Shugpachan. The dykes in the east of the field are trending E to NE and those in the west trending N to NW, exhibiting sub-parallel orientations within each area. Eighteen dykes were sampled (two of them multiple times) and subjected to petrographic, geochemical and isotopic analyses. They exhibit various degrees of differentiation from basaltic to rhyolitic compositions and are mainly composed of plagioclase, quartz, hornblende (s.l.) and/or biotite and magnetite. Furthermore, dykes in the eastern part of the field area contain quartz xenocrysts resulting from crustal assimilation, while no relict quartz was found in the west. The dykes exhibit alteration phases and features suggesting that they underwent autometamorphism, i.e. hydration reactions due to igneous cooling. Whereas the dykes in the east of the field area record low-T alteration, the mineral parageneses in the west are typical for alteration at elevated temperatures typical for greenschist metamorphic facies. Al-in-hornblende barometry performed on Magnesio-hornblende and Tschermakitic-hornblende phenocrysts of the least altered dyke indicates formation in upper-amphibolite metamorphic facies conditions and pressures of about 6 kbar corresponding to an intrusion depth of approximately 20 km.
Major and trace element analyses and Rb-Sr and Sm-Nd isotope analyses revealed a stunning variability in geochemistry and isotopic composition amongst the coeval dykes. All dykes exhibit LREE enrichment and HREE depletion as well as negative Tb and Nb anomalies characteristic for subduction-related intrusives and extrusives. Their REE patterns support a clear subdivision into chemically distinct groups. The group hypothesis was further tested and found valid using statistical tools designed to assess similarity/dissimilarity amongst individuals of a group with a common ancestor, such as hierarchical cluster analysis and multidimensional scaling. The dykes are cogenetic, but clearly not consanguineous, i.e. have not formed from one, progressively differentiating magma chamber.
The variability observed in Sr-Nd isotopes can be explained by the dykes having undergone differing degrees of crustal assimilation. In particular the dykes in the east containing quartz xenocrysts show negative iiNd) and positive N(Sr) values caused by crustal assimilation, whereas the dykes in the west with no quartz xenocrysts exhibit positive qqNd) and N(Sr) near zero. 39Ar-40Ar dating by incremental heating of several hornblende-bearing dykes revealed crystallization ages between 50 and 54 Ma, whereas two biotite-bearing dykes gave ages of 45 and 37 Ma, likely to be cooling or recrystallisation ages.
The combination of structural field evidence with petrographic, petrologic, geochemical, isotopic and geochronological analyses demonstrates that the dykes, although sharing a common origin, i.e. having formed in the same tectonic setting at roughly the same time, have undergone further geological processes leading to an unexpected diversification of the dykes. These findings provide ample scope for further in-depth and breadth investigations on “late-magmatic dykes” in the future.published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy
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Dalsin, Mallory Linda. "The mineralogy, geochemistry and geochronology of the Wicheeda Carbonatite Complex, British Columbia." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45393.
Full textAbstract:
Carbonatites are rare magmatic rocks composed of greater than 50% carbonate minerals. They are generally associated with continental rift-related tectonic settings and are commonly enriched in rare earth elements (REE), Nb, and P. The Wicheeda carbonatite complex, located 80 km northeast of Prince George in British Columbia, Canada, has been historically explored for its REE potential, but until recently there has been very little scientific study. The purpose of this study was to explore the geology, mineralogy, geochemistry, and geochronology of the Wicheeda Carbonatite Complex.
The complex consists of a carbonatite plug with a number of carbonatite and potassic-syenite dykes and sills emplaced into the sedimentary rocks of the upper Cambrian and lower Ordovician Kechika Group. Sodic-fenitization is common around the carbonatites and the degree of alteration and abundance of syenite outcrops increases away from the carbonatite plug. The complex was mapped over an area of 1.45 km². The REE mineralogy of the Wicheeda carbonatite was defined through optical petrography (86 thin sections), scanning electron microscopy, electron probe microanalysis (371 points on 14 mineral species), and single-crystal X-ray diffraction (7 samples). The REE mineralogy is complex, with multiple stages of primary, late-stage, rapidly cooling crystallization. It consists of Ca-REE-fluorocarbonates, Ba-REE-fluorocarbonates, ancylite-(Ce), monazite-(Ce), euxenite-(Y), and allanite-(Ce); the majority of these minerals are LREE rich. Whole rock isotopic analysis was completed for the Rb-Sr and Sm-Nd systems. An isochron age of 316 ± 36 Ma was determined using the Sm-Nd system, giving values for εNdT and ⁸⁷Sr/⁸⁶SrT that range from -0.5 to 0.5 and 0.70526 to 0.70659, respectively. Evidence from the Wicheeda Carbonatite Complex along with comparisons with other worldwide carbonatites, suggests that the complex formed from a dominantly silicate, parental, mantle melt emplaced into the continental lithosphere. The lithosphere underwent metasomatism and, potentially, low degrees of partial melting and/or the incorporation of previously subducted sediments for carbonatite generation.
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Brewer, T. S. "Geochemistry, geochronology and tectonic setting of the proterozoic Telemark supracrustals, Southern Norway." Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303806.
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Liu, Junjie. "Re-Os systematics of crude oil and Re-Os petroleum system geochronology." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12296/.
Full textAbstract:
Re and Os are present in many crude oils in measurable abundances. The Re-Os geochronometer has successfully constrained the timing of oil generation, thermochemical sulphate reduction and thermal alteration of crude oil for petroleum systems worldwide. The Os isotope composition has also been used as an oil-source correlation tool. This thesis firstly presents two petroleum matrix-matched Re-Os measurement reference materials: the RM8505 crude oil and ~ 90 g homogeneous asphaltene powder isolated from the RM8505 crude oil. The Re-Os data are from the repeated measurements of these samples via the Carius Tube - Isotope Dilution - Negative Thermal Ionization Mass Spectrometry methodology. The normal distribution and low relative standard deviation of the abundance and isotopic data ensure them to be appropriate petroleum matrix-matched reference materials for Re-Os measurements. A Re-Os age of 66 ± 31 Ma was defined by the Duvernay-sourced oil asphaltene fractions from Western Canada sedimentary basin. This age is in excellent agreement with the main-stage hydrocarbon generation of Duvernay Formation based on basin modelling. Further, this study supports Os isotope composition as a valid oil-source tracer and the hypothesis that the oil 187Os/188Os composition is inherited from the source unit during oil generation. This study shows limited or no influence of the Re-Os systematics of crude oil through the interaction of basinal fluids. The progressively precipitated asphaltene fractions of six oil samples exhibit a decrease in Re and Os abundance, and diverse 187Re/188Os and 187Os/188Os patterns. This study proposes that Re and Os in crude oil are to be bound in multiple free compounds and such molecules occluded/absorbed in the asphaltene aggregate structure. No combination of the fractions of a crude oil can consistently yield geologically meaningful Re-Os age for all of the six oil samples, either the progressively precipitated asphaltene fractions or the asphaltenes and maltenes separated by n-alkanes. As such, obtaining geologically meaningful Re-Os dates from a single oil may not be viable for many oils.
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Page, Laurence M. (Laurence Michael). "Structure, metamorphism, and geochronology of the Singis-Nikkaluokta region, Arctic Scandinavian Caledonides." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/60420.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.1 folded map in pocket.
Includes bibliographical references (leaves 190-196).
by Laurence M. Page.
Ph.D.
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Tilke, Peter Gerhard. "Caledonian structure, metamorphism, geochronology, and tectonics of the Sitas-Singis area, Sweden." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/40348.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN.
8 maps in pocket of volume 1.
Bibliography: leaves 215-223.
by Peter Gerhard Tilke.
Ph.D.
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Cumming, Vivien Mary. "Rhenium-osmium geochronology and geochemistry of ancient lacustrine sedimentary and petroleum systems." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/6945/.
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The Re-Os geochronometer is a valuable tool able to provide precise depositional ages of marine organic-rich sedimentary rocks as well as the generation age of hydrocarbons. In addition, Os isotopes afford vital insights into seawater Os fluctuations and provide the ability to fingerprinting hydrocarbons to their source. This thesis presents new research on extending the Re-Os geochronometer to lacustrine sedimentary and petroleum systems, which provide exceptionally high-resolution records of continental geological processes as well as significant hydrocarbons sources. Lacustrine organic-rich sedimentary rocks possess similar Re and Os abundances to those found in marine successions. New Re-Os depositional dates from the Eocene Green River Formation are in agreement with Ar-Ar and U-Pb ages of intercalated tuff horizons. As also documented in marine systems, precision is controlled by the variation in initial 187Os/188Os and the range of 187Re/188Os ratios, which are controlled by depositional setting and type of organic matter. The Os isotope composition of lake water at the time of deposition suggests the lake was dominated by inputs from continental runoff, giving insights into continental weathering. The Green River Formation is the source rock for the Green River petroleum system in the Uinta Basin. Three types of hydrocarbons are derived from this petroleum system; oils, tar sands and gilsonite. Re-Os geochronology of these different hydrocarbon phases broadly agrees with previous generation models. Hydrous pyrolysis experiments yield similar Re and Os transfer systematics to the natural system observed and importantly reinforce that Os isotope compositions are directly transferred from source to hydrocarbon, providing a powerful correlation tool. Lacustrine units are also important records of Earth’s climate system. New geochemical and Re-Os data from the late Mesoproterozoic Nonesuch Formation yield a Re-Os depositional age of 1078 ± 24 Ma, while Os isotope compositions strongly support existing evidence for a lacustrine setting. Fe-S-C systematics suggest that the Nonesuch Formation was deposited from an anoxic Fe-rich water column.
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Leich, Alexander. "Eudialyte Geochronology: Investigating the Timing of REE Mineralization in the Grenville Province." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:109026.
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Thesis advisor: Ethan F. BaxterThe Proterozoic Kipawa Syenite Complex and Red Wine Intrusive Suite have both been explored as potential REE ore bodies and are a heretofore unexploited REE resource. This study improves upon the internal-isochron eudialyte geochronology method developed by Sjöqvist et al. (2020) through the addition of Electron Microprobe mapping prior to precise MicroMill sampling to build Sm/Nd internal mineral isochrons to directly date this potential rare earth element ore mineral. We show that Nb and Ta concentrations correlate well with Sm/Nd ratios in zoned eudialyte crystals, providing a qualitative map to guide microsampling. At the Kipawa Syenite Complex two internal eudialyte isochrons yield ages of 1066±56 Ma (MSWD=1.7) and 1109±53 Ma (MSWD=1.2) while a multi-sample eudialyte bulk isochron produces an age of 1092±53 Ma (MWSD= 1.5). The weighted average of the three isochrons is 1090±31 Ma, and gives the age of eudialyte formation across the Kipawa Syenite Complex. Nd model ages confirm derivation from older continental crust with TDM=2.28. At the Red Wine Intrusive Suite single internal eudialyte isochron yields an age of 765±240 Ma (MSWD=3.7) while the high-Nb sector of this crystal yields an age of 704±120 Ma (MSWD=1.6). A multi-sample eudialyte and mosandrite bulk isochron produces an age of 989± 150 Ma (MSWD=15). The latter age reflects original Grenvillian crystallization of REE ore-minerals, while the age of the high-Nb zone reflects a younger, heretofore unrecognized recrystallization event. Nd model ages suggest derivation from the Proterozoic crust with TDM=1.80. Examination of Nd model ages and geochemical data from five agpaitic deposits (Red Wine, Kipawa, Ilímaussaq, Norra Kärr, Lovozero) reveals three distinct deposit types identified as the Lovozero type, the Grenville type, and the Kipawa type
Thesis (MS) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences
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Rohde, Joana [Verfasser]. "Geochronology and Geochemistry of the Tristan-Gough Hotspot Track / Joana Kristin Rohde." Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1137509643/34.
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Yamasaki, Seiko. "Isotopic geochemistry and K-Ar geochronology for submarine lavas of Hawaiian volcanoes." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124432.
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