Dissertations / Theses on the topic 'Arc Crust'
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Edwards, Caroline Marion Hawkey. "A comparison of arc evolution on continental and oceanic crust, Sunda Arc, Indonesia." Thesis, Royal Holloway, University of London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361452.
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Mercer, Celestine Nicole. "Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust /." Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2009. http://hdl.handle.net/1794/10250.
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Mercer, Celestine Nicole 1979. "Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust." Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10250.
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xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.This dissertation explores several important consequences of H 2 O-rich fluids in magmatic and ore-forming systems within continental arc crust. North Sister, a stratovolcano in the Oregon High Cascades, provides a window into magma generation processes in the deep crust. Eruption of a remarkably limited basaltic andesite composition over the lifespan of this volcano may reflect last equilibration of mantle derived magma within a deep crustal hot zone. High pressure, water-undersaturated phase equilibrium experiments show that an anhydrous, augite-rich gabbro at ∼12 kbar (40 km depth) and ∼ 1175°C is the most probable lithology with which North Sister basaltic andesite with ∼3.5 wt% H 2 O last equilibrated within the deep crust before erupting. While magma often erupts at the planets surface as at North Sister, a greater volume never reaches the surface and solidifies within the upper crust. Exsolution of magmatic fluids is an inevitable consequence of crystallization of hydrous crustal magmas. The fate of these fluids is the focus of the remainder of this dissertation. Modeling of CO 2 and H 2 O variations during crystallization of granitic magma reveals that exsolution of a large mass of fluid occurs only after CO 2 is largely degassed, creating ideal conditions for hydrofracturing and formation of porphyry copper deposits. CO 2 and H 2 O solubility relations suggest that H 2 O-rich magma was required to produce the porphyry-Cu-Mo deposit at Butte, Montana, which may explain its distinctively deep generation. Electron microprobe analyses of Ti in quartz and Zr in rutile in samples from Butte yield porphyry magma temperatures (630-770°C) that overlap substantially with hydrothermal vein temperatures (<430-750°C). Veins display large temperature ranges (50-250°C) that signify variable degrees of cooling of hot magmatic fluids upon contact with cooler wall rock during vein growth. Modeling of Ti diffusion in quartz suggests that individual dikes and veins likely cooled over short timescales (10s-1000s years), indicating that porphyry systems may evolve by episodic magmatic fluid injections with discrete thermal spikes. Modeling of Ti diffusion in quartz combined with electron backscatter diffraction maps show that small hydrothermal quartz veins likely formed by epitaxial growth. This dissertation includes co-authored material both previously published and in preparation for submission.
Committee in charge: A. Dana Johnston, Chairperson, Geological Sciences; Mark Reed, Member, Geological Sciences; Paul Wallace, Member, Geological Sciences; Richard P. Taylor, Outside Member, Physics
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Freymuth, Heye. "The role of the oceanic crust in the genesis of volcanic arc magmas." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.684749.
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Volcanic arc magmas are usually thought to receive components from three different sources: the subarc mantle, fluids derived from the subducted oceanic crust and lithospheric mantle, and melts derived from subducted sediments. This thesis re-evaluates this model based on isotopic data for magmas from the Izu, New Britain and Mariana arcs. High (230Th/232Th) ratios of up to 2.5 and U excess over Th in samples from the Izu and New Britain arcs are shown to be inconsistent with a derivation from subducted sediments or the sub-arc mantle and are instead argued to reflect a contribution of a melt of the mafic oceanic crust. In addition to Th, the magmas require a number of incompatible elements to be added to the sub-arc mantle. Many of these elements have traditionally been interpreted to be derived from a melt of subducted sediments. Yet, radiogenic Nd and Hf isotopes in these samples do not indicate the presence of a sediment melt. In order to explain this discrepancy, a model is presented in which the component previously identified as sediment melt is a mixture of a sediment melt and a melt of the mafic oceanic crust. Mo isotopes are suggested as a novel tracer for subduction components in volcanic arc magmas and a potential tracer for deep recycling of material transported into the mantle beyond subduction zones. Mo isotope ratios are presented for samples from oceanic sediments, the altered top part of the mafic oceanic crust, and volcanic arc magmas from the Mariana arc, thus defining input and output parameters for a subduction zone. Mo is shown to be preferentially transported in an isotopically distinct fluid derived from the subducted slab. Fluid addition leads to values of 0'98Mo in the Mariana arc lavas ~0.1-0.3 %0 higher than in MORB.
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Alvarado, Patricia Monica. "Crustal Seismicity in the Back-Arc Region of the Southern Central Andes from Historic to Modern Times." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/195537.
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The western margin of South America between 30ºS and 36ºS is seismically active. While the largest magnitude earthquakes are the interplate subduction zone events, the historically most devastating earthquakes have been the moderate-to-large magnitude earthquakes with depths < 35 km in the Andean back-arc. This region is characterized by accreted terranes later reactivated during Mesozoic extensional processes. Crustal seismicity in the back-arc is related to the thin-skinned Precordillera (PC) fold-thrust belt and the thick-skinned Sierras Pampeanas (SP) basement-cored uplifts overlying the flat slab segment. South of 33ºS, the active volcanic arc above the normally dipping subducted plate is also seismically active at crustal depths. In this study we combined historical and regional broadband seismic data to characterize moderate-to-large earthquakes and the crustal structure in this region. We have digitized and modeled teleseismic records of the 1944 and 1952 San Juan, Argentina PC earthquakes. Both events have shallow source depths, short duration of the source time functions with a thrusting focal solution for the 1944 (Mw 7.0) earthquake and a major strike-slip component in the 1952 (Mw 6.8) earthquake solution. By modeling regional broadband waveforms collected during the CHile-ARgentina Geophysical Experiment (CHARGE) during 2000 and 2002 we constrained the seismic moment tensor and improved focal depths for 27 crustal (3.5 < Mw < 5.1) earthquakes. We found predominantly thrust-fault focal mechanisms and focal depths of 10-26 km for earthquakes over the flat slab region; the eastern SP and active arc have earthquakes with strike-slip focal mechanisms and shallower depths. We used these same earthquakes to determine the crustal structure using raypaths that sample different geologic terranes. Our results indicate high Vp, low Vs for the northern Cordillera, PC and western SP thicker crust; low Vp, low Vs and a thinner crust beneath the arc (south of 33°S) consistent with a mafic composition and partial melt. The eastern SP basement shows low Vp, low Vs and thinner crust consistent with a more quartz-rich composition. These differences have an important control on the present day Andean earthquake deformation and the high seismic hazard posed in this region.
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Jolis, Ester M. "Magma-Crust Interaction at Subduction Zone Volcanoes." Doctoral thesis, Uppsala universitet, Berggrundsgeologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-198085.
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The focus of this work is magma-crust interaction processes and associated crustal volatile release in subduction zone volcanoes, drawing on rock, mineral, and gas geochemistry as well as experimental petrology. Understanding the multitude of differentiation processes that modify an original magma during ascent to the surface is vital to unravel the contributions of the various sources that contribute to the final magmas erupted at volcanoes. In particular, magma-crust interaction (MCI) processes have been investigated at a variety of scales, from a local scale in the Vesuvius, Merapi, and Kelut studies, to a regional scale, in the Java to Bali segment of the Sunda Arc. The role of crustal influences is still not well constrained in subduction systems, particulary in terms of the compositional impact of direct magma crust interplay. To address this shortcoming, we studied marble and calc-silicate (skarn) xenoliths, and used high resolution short timescale experimental petrology at Vesuvius volcano. The marbles and calc-silicates help to identify different mechanisms of magma-carbonate and magma-xenolith interaction, and the subsequent effects of volatile release on potential eruptive behaviour, while sequential short-duration experiments simulate the actual processes of carbonate assimilation employing natural materials and controlled magmatic conditions. The experiments highlight the efficiency of carbonate assimilation and associated carbonate-derived CO2 liberated over short timescales. The findings at Merapi and Kelut demonstrate a complex magmatic plumbing system underneath these volcanoes with magma residing at different depths, spanning from the mantle-crust boundary to the upper crust. The erupted products and volcanic gas emissions enable us to shed light on MCI-processes and associated volatile release in these systems. The knowledge gained from studying individual volcanoes (e.g., Merapi and Kelut) is then tested on a regional scale and applied to the entire Java and Bali arc segment. An attempt is presented to distinguish the extent of source versus crustal influences and establish a quantitative model of late stage crustal influence in this arc segment. This thesis therefore hopes to contribute to our knowledge of magma genesis and magma-crust interaction (MCI) processes that likely operate in subduction zone systems worldwide.
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Klein, Benjamin Zachary. "Processes and rates of arc crust growth and differentiation in the Southern Sierra Nevada crustal section." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121759.
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Thesis: Ph. D. in Geology, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019Cataloged from PDF version of thesis.
Includes bibliographical references.
This thesis presents a multidisciplinary investigation of the processes and timescales for the construction of arc crust, with a focus on the exposed crustal section in the southernmost Sierra Nevada Batholith, California. This section exposes plutons that were emplaced at pressures ranging from 3-10 kbars, as well as metamorphic wall rocks. Chapters 1 and 2 represent focused studies of the Bear Valley Intrusive Suite (BVIS), the dominant igneous component of the crustal section. Chapter 1 presents new magmatic structural data and whole rock geochemical data that highlight a discontinuity in the BVIS between a lower crust dominated by originally shallowly lying mafic cumulates and an upper crust dominated by steeply oriented felsic intrusives. These observations are used to constrain the thermal state of the arc during the emplacement of the BVIS. Chapter 2 is a high-precision CA-ID-TIMS U/Pb zircon geochronology study of the BVIS.
This study shows that the entire BVIS was emplaced within 1.1 million years, and thus represents the highest documented (intrusive) subduction zone magmatic flux. Chapter 3 focuses on the contribution of the metamorphic wall-rocks to the observed crustal section. Using detrital zircon geochronology, I argue that these wall-rocks preserve an inverted stratigraphy that is most easily explained if these sediments were first subducted and subsequently returned as relaminated material, which would make these materials the first in situ example of relaminated sediments. Chapters 4 and 5 present broader studies of subduction zone processes in space and time. In Chapter 4, I present a study based on a global compilation of modern arc lavas.
This study develops new proxies that use distinctive major element trends produced by fractionating magmas to qualitatively constrain the hydration state and initial fractionation pressure of differentiating magmas, and finds that magmas in continental arcs typically evolve at wetter and higher-pressure conditions compared to island arcs. Finally, Chapter 5 investigates the dynamics of subducted slabs through Earth's history and finds that, based on anticipated higher mantle temperatures and concomitant thicker, more mafic oceanic crust, subducted slabs in the Archean are unlikely to have stagnated within or immediately below the mantle transition zone.
by Benjamin Zachary Klein.
Ph. D. in Geology
Ph.D.inGeology Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences
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Jones, Rosemary Ellen. "Subduction zone processes and continental crust formation in the southern Central Andes : insights from geochemistry and geochronology." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9672.
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Subduction zones, such as the Andean convergent margin, are the sites at which new continental crust is generated, and where subducting material is either recycled to the crust via arc magmatism or transferred to the deep mantle. The composition of arc magmas and associated new continental crust reflects variable contributions from mantle, crustal and subducted reservoirs. Insights into crustal growth and recycling processes in the southern Central Andes, specifically in the Pampean flat-slab segment, have been gained by utilising a range of petrological, geochronological and geochemical techniques. These techniques have been applied to a suite of Late Cretaceous (~73 Ma) to Late Miocene (~6 Ma) intrusive (granitoids) and extrusive (basalts to rhyolites) arc rocks collected from an east - west transect across the Andean Cordillera. The oxygen and hafnium isotopic composition of the accessory mineral zircon allows mantle-derived melts contaminated with older, upper continental crustal to be identified. Boron isotopic compositions of melt inclusions, combined with concentrations of certain incompatible trace elements, can be used to assess the source and influence of fluids derived from subducting material on the melt source region. The southern Central Andes provides a particularly interesting area to study these processes as the thickness of the continental crust has increased significantly over the course of the Cenozoic (from ~35 km to >50 km) and the angle of the subducting Nazca plate has shallowed since ~18 Ma, causing the position of the volcanic arc to migrate to the east. In order to unravel the complexities involved with constraining the contributions to arc magmas at an active continental margin, a range of geochronological, geochemical, and geothermobarometric techniques, including high resolution, micro-analysis of mineral phases and melt inclusions, have been applied. High resolution, U-Pb dating of magmatic zircon has improved regional stratigraphy in the Pampean flat-slab segment (between ~29 and 32 °S) and provided an accurate temporal constraint for geochemical and geothermobarometric data. The results of in-situ O and Lu-Hf isotope analysis of zircon show both distinct temporal and spatial variations across the Andean arc. The observed isotopic variability is attributed to variable contamination of mantle-derived melts with distinct Andean basement terranes, which vary east – west in composition and age. ‘Mantle-like’ δ18O(zircon) values, juvenile initial ƐHf(zircon) values and a lack of inherited, xenocrystic zircon cores, suggests the Late Cretaceous (~73 Ma) to Eocene (~39 Ma) plutons located in the Principal Cordillera of Chile, experienced very little interaction with the upper continental crust. Amphibole – plagioclase geothermobarometry indicates these calc-alkaline granitoids, which form extensive north – south trending belts, were emplaced at shallow depths in the crust (~4 – 5 km). Therefore the Late Cretaceous to Late Eocene is interpreted as a period of significant upper crustal growth. The isotopic variability in the Late Oligocene (~26 Ma) to Late Miocene (~6 Ma) arc magmatic rocks demonstrates that during thickening of the continental crust and migration of the Andean arc to the east, arc magmas assimilated Late Paleozoic to Early Mesozoic basement. In addition, arc magmas erupted/emplaced in the Argentinean Precordillera (i.e. farthest east from the trench) assimilated a Grenville-aged (~ 1330 – 1030 Ma) basement. The youngest arc magmas (~6 Ma) erupted in the Frontal Cordillera also show evidence for the assimilation of this ancient basement terrane, potentially signalling under-thrusting beneath the Frontal Cordillera. Overall, the later part of the Cenozoic represents a period of crustal reworking. Boron concentrations and isotope ratios measured in pyroxene hosted melt inclusions and for the first time in zircon hosted melt inclusions, are higher than the values expected for the mantle wedge and show significant variations with time. The source of the Paleocene (~61 Ma) arc magmas were influenced by fluids primarily derived from altered oceanic crust. Lower δ11B values and boron concentrations obtained for Oligocene (25 – 23 Ma) arc magmatic rocks reflects a diminished influence of slab-derived fluids reflecting a greater depth to the top of the slab. Fluids derived from serpentinite influenced the source of the arc magmas after ~19.5 Ma. This has been linked with the intersection of the Juan Fernández Ridge, a volcanic seamount chain associated with hydrated and serpentinised oceanic lithosphere.
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Pfänder, Jörg A. "Oceanic crust and island arc formation in Central Asia during late Neoproterozoic times evidence from petrological and geochemical studies /." [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2002/0051/diss.pdf.
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Moyer, Griffin Amoss. "Strain Accommodation, Metamorphic Evolution, And 3d Kinematics Of Transpressional Flow Within The Lower Crust Of A Cretaceous Magmatic Arc In Fiordland, New Zealand." ScholarWorks @ UVM, 2019. https://scholarworks.uvm.edu/graddis/1110.
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The George Sound Shear Zone (GSSZ) exposed in Bligh Sound within Fiordland, New Zealand allowed us to reconstruct the kinematics of transpressive flow in >100 km2 of exhumed Cretaceous lower crust. We compare the three-dimensional characteristics of the deformation to theoretical models of transpression that assume steady-state flow in a homogeneous medium. This assumption is rarely the case for shear zones that experience metamorphism during deformation. We determined the three-dimensional kinematics of the GSSZ and evaluated the effects of metamorphism on strain accommodation and structural fabric evolution in the GSSZ to determine if metamorphism is an important parameter that transpressional models should account for. We found that metamorphism aided strain localization within the GSSZ and resulted in a style of structural fabric development that deviates from predictions made by theoretical models.
We used foliation and lineation orientation data and field observations to determine GSSZ kinematics. Asymmetric pyroxene σ-porphyroclasts and hornblende fish show top-down-to-the-SW apparent normal shear sense with a sinistral component. The Z-axes of oblate SPO ellipsoids define the vorticity normal section and the moderately WNW-plunging vorticity vector. Foliation deflections relative to the shear zone boundaries yielded a vorticity magnitude (Wk) of ≥0.8. Our kinematic results suggest that the GSSZ records inclined, triclinic transpression with sinistral, top-down-to-the-SW simple shear-dominated flow.
We used finite strain analysis and petrographic analysis to determine that metamorphism influences strain accommodation. Finite strain analyses were performed in 3D on 16 samples using the Rf/ɸ, Fry, and Intercept methods to determine the SPO fabric ellipsoids at different stages of deformation. Petrographic analysis was performed to identify metamorphic reactions using syn-kinematic minerals and constrain deformational temperatures using deformation mechanisms of plagioclase. Early deformation formed a ~13 km wide prolate fabric at granulite facies. Deformation later localized into a ~2-4.6 km wide oblate, mylonitic fabric at upper amphibolite facies. This fabric cross-cuts the prolate fabric and is characterized by metamorphic hornblende and biotite produced from retrogressive hydration reactions. Samples with syn-kinematic biotite contain more shear bands and display more grain size reduction of plagioclase than samples without this phase, suggesting these samples may have accommodated more strain. Changes in syn-kinematic metamorphic minerals were accompanied by steepening of stretching lineations and by changes in foliation orientation.
Our analyses show that retrogressive hydration metamorphism aided strain localization within a cross-cutting oblate fabric, and the uneven distribution of biotite within this domain potentially influenced along strike variation in strain magnitude and fabric ellipsoid symmetry. Our results highlight the influence of fluid-induced metamorphism on shear zone evolution and call for new transpressional models to incorporate changes in rheology due to syn-kinematic metamorphism.
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Johnson, Julie A. "A Geochemical Study of Crustal Plutonic Rocks from the Southern Mariana Trench Forearc: Relationship to Volcanic Rocks Erupted during Subduction Initiation." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1249.
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Two suites of intermediate-felsic plutonic rocks were recovered by dredges RD63 and RD64 (R/V KK81-06-26) from the northern wall of the Mariana trench near Guam, which is located in the southern part of the Izu-Bonin-Mariana (IBM) island arc system. The locations of the dredges are significant as the area contains volcanic rocks (forearc basalts and boninites) that have been pivotal in explaining processes that occur when one lithospheric plate initially begins to subduct beneath another. The plutonic rocks have been classified based on petrologic and geochemical analyses, which provides insight to their origin and evolution in context of the surrounding Mariana trench.
Based on whole rock geochemistry, these rocks (SiO2: 49-78 wt%) have island arc trace element signatures (Ba, Sr, Rb enrichment, Nb-Ta negative anomalies, U/Th enrichment), consistent with the adjacent IBM volcanics. Depletion of rare earth elements (REEs) relative to primitive mantle and excess Zr and Hf compared to the middle REEs indicate that the source of the plutonic rocks is similar to boninites and transitional boninites. Early IBM volcanic rocks define isotopic fields (Sr, Pb, Nd and Hf-isotopes) that represent different aspects of the subduction process (e.g., sediment influence, mantle provenance). The southern Mariana plutonic rocks overlap these fields, but show a clear distinction between RD63 and RD64. Modeling of the REEs, Zr and Hf shows that the plutonic suites formed via melting of boninite crust or by crystallization from a boninite-like magma rather than other sources that are found in the IBM system.
The data presented support the hypothesis that the plutonic rocks from RD63 and RD64 are products of subduction initiation and are likely pieces of middle crust in the forearc exposed at the surface by faulting and serpentine mudvolcanoes. Their existence shows that intermediate-felsic crust may form very early in the history of an intra-oceanic island arc system. Plutonic rocks with similar formation histories may exist in obducted suprasubduction zone ophiolites and would be evidence that felsic-intermediate forearc plutonics are eventually accreted to the continents.
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Holbik, Sven P. "Arc Crust-Magma Interaction in the Andean Southern Volcanic Zone from Thermobarometry, Mineral Composition, Radiogenic Isotope and Rare Earth Element Systematics of the Azufre-Planchon-Peteroa Volcanic Complex, Chile." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1524.
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The Andean Southern Volcanic Zone (SVZ) is a vast and complex continental arc that has been studied extensively to provide an understanding of arc-magma genesis, the origin and chemical evolution of the continental crust, and geochemical compositions of volcanic products. The present study focuses on distinguishing the magma/sub-arc crustal interaction of eruptive products from the Azufre-Planchon-Peteroa (APP 35°15’S) volcanic center and other major centers in the Central SVZ (CSVZ 37°S - 42°S), Transitional SVZ (TSVZ 34.3-37.0°S), and Northern SVZ (NSVZ 33°S - 34°30’S). New Hf and Nd isotopic and trace element data for SVZ centers are consistent with former studies that these magmas experienced variable depths of crystal fractionation, and that crustal assimilation is restricted to the lower crustal depths with an apparent role of garnet. Thermobarometric calculations applied to magma compositions constrain the depth of magma separation from mantle sources in all segments of the SVZ to(70-90 km). Magmatic separation at the APP complex occurs at an average depth of ~50 km which is confined to the mantle lithosphere and the base of the crust suggesting localized thermal abrasion both reservoirs. Thermobarometric calculations indicate that CSVZ primary magmas arise from a similar average depth of (~54 km) which confines magma separation to the asthenospheric mantle. The northwards along-arc Sr-Nd-Hf isotopic data and LREE enrichment accompanied with HREE depletion of SVZ mafic magmas correlates well with northward increasing crustal thickness and decreasing primary melt separation from mantle source regions indicating an increased involvement of lower crustal components in SVZ magma petrogenesis.
The study concludes that the development of mature subduction zones over millions of years of continuous magmatism requires that mafic arc derived melts stagnate at lower crustal levels due to density similarities and emplace at lower crustal depths. Basaltic underplating creates localized hot zone environments below major magmatic centers. These regions of high temperature/partial melting, and equilibration with underplated mafic rocks provides the mechanism that controls trace element and isotopic variability of primary magmas of the TSVZ and NSVZ from their baseline CSVZ-like precursors.
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Roell, Jennifer L. "Geochemical evidence for incremental emplacement of Palms pluton, southern California." Thesis, Connect to resource online, 2009. http://hdl.handle.net/1805/2061.
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Thesis (M.S.)--Indiana University, 2009.Title from screen (viewed on February 2, 2010). Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Andrew P. Barth, Gabriel M. Filippelli, Kathy Licht. Includes vitae. Includes bibliographical references (leaves 102-110).
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Zelt, Colin Andrew. "Seismic structure of the crust and upper mantle in the Peace River Arch region." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/29327.
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The Peace River Arch (PRA) is a regional ~E-W trending geological structure within the Western Canada Sedimentary Basin whose Phanerozoic history of vertical movements is anomalous with respect to the basin as a whole. Four intersecting ~300-km-long reversed refraction lines within the PRA region in northwestern Alberta and northeastern British Columbia have been interpreted for crustal and upper mantle P-wave velocity structure. The data have been analyzed using a new two-dimensional ray-trace forward modelling algorithm to match travel times and amplitudes of first and coherent later arrivals. An inversion of first arrival travel times along a fan shot profile has been performed to constrain crustal thickness northwest of the arch in a region not sampled by the in-line profiles. 5-waves and the observed spectra of the refraction data have been analyzed to infer a regional Poisson's ratio and Q structure, respectively. The consistency of the seismic models with the observed Bouguer gravity data was studied.
The new algorithm for tracing rays and calculating amplitudes in two-dimensional media is based on a simple, layered, large-block velocity model parameterization in which velocity is an analytic function of position. This allows for computationally efficient ray tracing. The user's ability to specify kinematically-similar ray families permits practical and rapid forward modelling of refraction data. In addition, the routine allows for 5-wave propagation, converted phases, multiple and surface reflections, approximate attenuation, head waves, a simulation of smooth layer boundaries, and a reverse ray-direction amplitude calculation. Amplitude calculations are based on zero- and first-order asymptotic ray theory. The main attributes of the routine are illustrated with several examples.
The major features of the interpreted structural model of the PRA region are (1)
weak to moderate lateral variations in crustal structure with no evidence of significant layering or thick low-velocity zones within the crust, (2) an average sub-basement RMS crustal velocity of 6.6 km/s, average upper mantle velocity of 8.25 km/s and average crustal thickness of 40 km, (3) a high-velocity (> 7.0 km/s) lower crust of 5 to 10 km thickness, (4) westward crustal thinning north of the arch, (5) regional variations in structure that appear related to the N-S Precambrian trends as revealed by aeromagnetic data, including crustal thickness, upper crustal and upper mantle velocities and P[sub m]P character, and (6) subtle variations in structure that may be associated with the E-W trending Devonian axis of the PRA, including a shallowing of high lower-crustal velocities, thickening of the crust, and an anisotropic P[sub m]P character beneath the arch and along-axis low-amplitude P[sub n] arrivals. A high-velocity lower crust and localized shallowing of high lower-crustal velocities are commonly observed in continental rift zones. These features and the ~E-W trend of the arch perpendicular to the ancient western margin suggest that the PRA originated as a Paleozoic failed-rift.
The results of supplementary studies show (1) an average crustal Poisson's ratio of 0.25, (2) Q increases with depth from ~500 to ~1000 in the crust and is ~1000 in the upper mantle, and (3) a seismic-gravity relationship that suggests that localized velocity anomalies of the refraction models are not associated with density anomalies. Also, extended-listen-time processing of a 10-km-long industry Vibroseis reflection line coincident with one of the refraction lines shows prominent dipping events that correlate with the zero-offset two-way travel time of a strong intracrustal reflector and the crust-mantle boundary of the refraction model. A series of reflections over 1.5 s terminating at the refraction Moho indicates a complex, possibly layered crust-mantle transition zone of 5 km thickness.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Desmet, Alain. "Ophiolites et séries basaltiques crétacées des régions caraïbes et nordandines : bassins marginaux, dorsales ou plateaux océaniques ?" Nancy 1, 1994. http://www.theses.fr/1994NAN10313.
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Les régions caraïbes et nordandines comportent, au crétacé, des séries magmatiques basiques, volcaniques ou ophiolitiques. L'étude petrologique analytique (majeurs, traces, terres rares, microsonde) de quelques séries du Costa Rica, de Colombie et d'Équateur, a permis leur identification magmatique et dynamique. La comparaison des laves à certaines séries volcaniques océaniques actuelles a conduit à une réinterprétation magmatique et géodynamique globale. Au Costa Rica, la péninsule de Santa Elena est formée d'une large nappe ophiolitique tholeiitique avec péridotites, cumulats gabbroiques et dolerites diverses (n-morb). Les iles Murcielago sont couvertes de ferrobasaltes t-morb. Santa Elena représente un témoin de croute océanique crétacée mis en place vers 70 ma et Murcielago un lambeau de plateau océanique soudé à l'Amérique centrale. La Colombie offre, au crétacé, et du nord au sud de la cordillère occidentale, un large éventail de formations océaniques: la série du Boqueron de Toyo, à volcanisme basaltique et intrusions diorito-tonalitiques (92 ma) témoigne du fonctionnement d'un arc insulaire immature. La série d'Altamira, a cumulats gabbroiques et basaltes primitifs illustre l'ouverture vers 80 ma d'un bassin en arrière de l'arc précédent. Le massif de Bolivar, correspond, avec ses cumulats tholeiitiques (i ou iia), a la croute océanique. La coupe de Buenaventura a Buga, avec ses nappes empilées riches en sédiments océaniques et en basaltes de type t-morb évoque des terrains constitués en plateau océanique et accrétés à la marge sud-américaine. En Équateur, le crétacé supérieur de la cordillère occidentale offre une situation analogue: des lambeaux de croute océanique sont dispersés le long d'une grande suture ophiolitique oblitérée par l'arc volcanique de Macuchi. La série de la Quebrada San Juan est l'équivalent de celle de Bolivar. Les basaltes (t-morb) du Grupo Pinon de la cote correspondent aussi à du matériel de plateau océanique accrété au bâti sud-américain
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Losa, Llabata Marta. "Gene regulation in embryonic development." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/gene-regulation-in-embryonic-development(8a9efb79-1ca9-409e-89b9-9d66213e593f).html.
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Branchial arches (BAs) are a series of transient structures that develop on the ventro-lateral surface of the head in vertebrate embryos. BAs initially appear as a series of similar segments; as development proceeds each BA will contribute to different structures. Here, it was investigated the transcriptional mechanisms that instruct the different fates of the BAs in development. Initially, each BA contains a blood vessel, known as aortic arch (AA) artery, that connects the dorsal aorta with the heart. Remodelling of the AAs is crucial to form the adult heart circulation. This process leads to regression of the anterior AAs, running though the first and second BAs (BA1 and BA2), and persistence of the AAs contained in more posterior BAs (PBA). To identify the mechanisms that control remodelling of the AAs, we compared the transcriptomes and epigenomic landscapes of different BAs. Using RNA-seq and H3K27Ac ChIP-seq, we uncovered the activation of a vascular smooth muscle cell (VSMC) differentiation transcriptional program exclusively in the PBAs (and not in BA1/BA2). In support of this finding, we show that VSMC differentiation occurs specifically in the PBAs, but not BA1-2 in mouse embryonic development. Despite the absence of VSMC differentiation in developing BA1-2, cells harvested from these tissues reveal a spontaneous tendency to differentiate towards VSMC fate when grown in vitro, and activate several VSMC-specific genes (Myocd, Acta2, Tagln, Jag1). Together, our results suggest that forming VSMCs is a key process for the persistence of AAs. We also showed that cells derived from all BAs have the potential to differentiate to VSMCs in vitro. However, only cells in the PBAs differentiate to VSMCs in vivo, resulting in the maintenance of posterior AAs. In this study, we also uncovered a novel transcriptional principle that specifies the fate of BA2. Using ChIP-seq, we found that binding of Meis transcription factors establish a ground pattern in the BAs. Hoxa2, which specifies BA2 identity, selects a subset of Meis-bound sites. Meis binding is strongly increased at these sites, which coincide with active enhancers, linked to genes highly expressed in the BA2 and regulated by Hoxa2. Thus, Hoxa2 modifies a ground state binding of Meis to instruct segment-specific transcriptional programs.
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Turmina, Leonardo Balbinot. "O livre-arb?trio no pensamento de Tom?s de Aquino." Pontif?cia Universidade Cat?lica do Rio Grande do Sul, 2014. http://tede2.pucrs.br/tede2/handle/tede/5880.
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Previous issue date: 2014-03-25This dissertation intends to investigates the arguments that the Saint and Doctor of the Roman Catholic Church, Thomas Aquinas introduces in his thinking concerning of free will and the way that he envisages the Divine Providence. It analyzes the development of these issues over the course of patristic, as well as some of the main ideas of the thinkers who were the pillars of the catholic saint. With reference to his magnum opus, the Summa Theologica, this dissertation looks for the dimension of free will that humans have in front of the divine will in many issues of his work.
A presente disserta??o procura investigar os argumentos que o santo e doutor da Igreja Cat?lica Apost?lica Romana, Tom?s de Aquino, apresenta no seu pensamento referente ao livre-arb?trio e como este encontra espa?o perante a Divina Provid?ncia. Para tanto, analisa-se o desenvolvimento dessas quest?es ao decorrer da patr?stica, bem como as principais ideias de alguns dos pensadores que foram pilares do pensamento do santo cat?lico. Tendo como refer?ncia sua obra m?xima, a Suma Teol?gica, a disserta??o procura em diversas quest?es da obra a dimens?o do livre-arb?trio que o ser humano possui perante a vontade divina.
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Jeannolin, François. "Sédimentologie et hydrogéologie du néogène de l'Est valentinois et du bassin de Crest, Drome, France." Grenoble : ANRT, 1985. http://catalogue.bnf.fr/ark:/12148/cb37594829z.
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Wang, Jianhua. "Contribution à la connaissance sédimentologique des formations miocènes marines de deux bassins du sud-est de la France Sommières (Gard), Crest (Drôme) /." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb376017863.
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Larocque, Jeffrey Paul. "The role of amphibole in the evolution of arc magmas and crust: the case from the Jurassic Bonanza arc section, Vancouver Island, Canada." Thesis, 2008. http://hdl.handle.net/1828/1309.
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Exposed on Vancouver Island, British Columbia, the Jurassic Bonanza arc is believed to represent the southerly continuation of the Talkeetna arc. Small bodies of mafic and ultramafic cumulates within deeper plutonic levels of the arc constrain the fractionation pathways leading from high-MgO basalt to andesite-dacite compositions. The removal of amphibole from the most primitive non-cumulate compositions controls the compositions of mafic plutons and volcanics until the onset of plagioclase crystallization. This removal is accomplished by the intercumulus crystallization of large amphibole oikocrysts in primitive olivine hornblendite cumulates. Experimental hornblende compositions that crystallize from high-MgO basalts similar to primitive basalts from the Bonanza arc show a good correlation between octahedral Al in hornblende and pressure, and provide a means of estimating crystallization pressures during differentiation of primitive arc basalt. Application of an empirical barometer derived from experimental amphibole data (P = Al(6)/0.056 – 0.143; r2 = 0.923) to natural hornblendes from this study suggests that crystallization of primitive basalts took place at 470-880 MPa. Two-pyroxene thermometry gives a result of 1058 +/- 91 ºC for the only olivine hornblendite sample with both pyroxenes. Lever rule calculations require the removal of 30-45 % hornblende from the most primitive basalt compositions to generate basaltic andesite, and a further 48% crystallization of hornblende gabbro to generate dacitic compositions. Hornblende removal is more efficient at generating intermediate compositions than anhydrous gabbroic fractionating assemblages, which require up to 70% crystallization to reach basaltic andesite from similar starting compositions. There are no magmatic analogues to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will push the bulk arc composition to high-Mg# andesite. Garnet removal appears to be a key factor in producing bulk continental crust.
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Wang, Yu-Ju, and 王郁如. "Three dimensional S-wave attenuation model of the crust and uppermost mantle beneath arc-continent collision, Taiwan." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/32439179268305476460.
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碩士國立中央大學
地球物理研究所
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The S-wave attenuation structures (Qs) of Taiwan are imaged using the S-wave data from the dense deployed strong motion network of Taiwan. The image of 3-D Qs is essential in Taiwan because Qs is sensitivity to localized permeability and heterogeneity, which are important characters for interpreting active tectonic regions as Taiwan. The attenuation images of S-wave are obtained using t* values measured from S-wave spectra from Taiwan strong motion network for moderate size earthquakes (ML4.5-5.5) to avoid the source complexity. The time period used in this study is from 1993-1998. Over 2000 velocity spectra of S wave arrivals from 173 earthquakes were analyzed. A non-linear least square technique is applied to the spectra for t* by assuming a ��-2 model for the frequency band of 1-20Hz. A frequency-independent Qs was assumed in this study. Combined the existed three-dimensional S-wave velocity model, the three-dimensional Qs images were obtained. The Qs-tomography shows general consistent feature to geological structure. At shallow depth (4~9km), the Qs tomography separated the western Taiwan into high Qs and low Qs images to the north and south, respectively, along latitude of 23.5∘N. The low Qs image within southwestern Taiwan is related to its thicker sediment; while the high Qs image within northwestern Taiwan is related to the formation of foreland sequence. The image also reveals the variation across Longitudinal Valley, which is the suture zone of the arc-continent collision. At deeper depth, 27-38 km, a high Qs images extended from latitude of 24∘N to 25∘N, which is related to the subduting slab. A relative low Qs zone beneath the Central Range was found in the depths of 30-40 km. This low Qs zone is consistent with the low velocity zone obtained in Vp and Vs velocity images. The profile across the Chi-Chi hypocenter shows clear variation on Qs image across the ruptured Chelungpu fault. Our results show that the Qs images provide significant information for further understanding the tectonic structure of Taiwan.
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Chan, Christine F. "Constructing a sheeted magmatic complex within the lower arc crust : insights from the Tenpeak pluton, North Cascades, Washington." Thesis, 2012. http://hdl.handle.net/1957/36070.
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The sheeted complex of the ~92 Ma Tenpeak pluton, in the Northern Washington Cascades crystalline core, forms a <1.5-km wide zone with a moderate, NE-dip at the SW margin of the pluton. Sheeted magmatic complexes, such as the one in the Tenpeak pluton, are common in plutons and represent examples of incremental growth of plutons. Though it is widely accepted that plutons are constructed incrementally over prolonged timescales of several million years, it is not clear if and to what degree individual batches of magma interact, the timing and size of each magma pulse, and the role, timing, and location of magmatic differentiation.
This project uses a combination of field evidence, bulk rock chemistry, and mineral geochemistry to address the (1) role of magma mixing and fractionation, (2) constraints on the relative timing of magma differentiation, (3) diversity of mixing styles
preserved, and (4) physical properties that dictate how individual batches of magma interact within this sheeted complex. Rock samples were collected throughout the complex from mafic, felsic, dioritic, thinly-banded, and gradational sheets. Field evidence shows a range of sheet contacts that vary from sharp to diffuse, strong prevalence of mafic enclaves, and localized cases of mechanical mixing in which plagioclase feldspars from a felsic sheet are incorporated into a mafic sheet. In general, sheet thickness increases farther from the contact with the White River shear zone.
The bulk rock and mineral chemistry suggests that the felsic magmas in sheets formed independently from the more mafic and hybridized sheets. The composition of the felsic sheets cannot be modeling by binary mixing processes involving mafic and felsic magmas or result from fractionating the most mafic magmas. However, mass-balance calculations using a linear least-squares mass balance calculation and Rayleigh fractionation models indicate that it is possible to explain the range of felsic compositions by internal, crystal fractionation driven mostly by plagioclase crystallization (~40-58%). Negative Eu anomalies in amphiboles from the felsic sheets imply that plagioclase fractionation commenced prior to the onset of amphibole crystallization.
With the exception of the most primitive mafic sheet sampled, the mafic and hybridized sheets represent variable proportions of the mafic parental magma and the range of felsic differentiated magmas. Efficient mixing that resulted in these mafic to hybridized magmas must also have occurred prior to mineral growth as the mineral chemistry reflects intermediate, mixed compositions. The bulk rock and mineral chemistry of the most primitive, mafic sheet suggest that it did not mix with any felsic magmas. However there is evidence that the mafic sheet underwent plagioclase fractionation prior to emplacement. This is evident by lower bulk rock Sr/Ba relative to calculated Sr/Bamelt of plagioclase that cannot be reconciled without removing ~40-58% plagioclase. In contrast to the felsic sheets, the amphiboles from this mafic sheet lack Eu anomalies implying that amphibole crystallization occurred prior to major plagioclase fractionation.
Chemical evidence reveals that magma mixing played an important role in controlling the chemical composition of individual sheets and field observations suggesting that there was a range of mixing styles. Throughout the sheeted complex, there are localized sites of mechanical mixing where plagioclase phenocrysts from adjacent felsic sheets are mechanically mixed into mafic sheets. Evidence for mechanical mixing is present across both sharp and gradational contacts. This implies varying rheological and viscosity contrasts between different sheets, though in both cases crystallinity and viscosity appears sufficiently low to allow crystals to migrate across sheet contacts.
Variability in sheet thickness and contact type suggests that the physical parameters (i.e. temperature, viscosity, rheology, and magma flux) of the system continue to evolve throughout the formation of the sheeted complex. Near the White River, sheets are thin and more heterogeneous but become progressively thicker (>302 m) and more felsic in composition up-section. The composition of plagioclase and amphibole is remarkably uniform in all of the felsic sheets suggesting that each sheet formed from an array of felsic parental magmas. Thicker, felsic sheets most likely reflect hotter conditions where larger magma fluxes could be accommodated or viscosity-temperature contrasts that were low enough to allow for efficient mixing between two adjacent sheets and therefore erase sheet contacts.Graduation Date: 2013
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Pfänder, Jörg A. [Verfasser]. "Oceanic crust and island arc formation in Central Asia during late Neoproterozoic times : evidence from petrological and geochemical studies / Jörg A. Pfänder." 2001. http://d-nb.info/963931210/34.
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吳燕明. "Mineralogy and petrology of the rocks in the continental margin arc-oceanic crust contact zone in a backarc basin:as exemplified by the Laohushan raea, Eastern North Qilian Orogenic belt, NW China." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/32230691737276439714.
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Ivey, Kathryn Nicole. "Transcriptional regulation of neural crest-derived pharyngeal arch artery development." 2004. http://edissertations.library.swmed.edu/pdf/IveyK121504/IveyKathryn.pdf.
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Tumbleson, Danika M. "Treatment and genetic analysis of craniofacial deficits associated with down syndrome." Thesis, 2014. http://hdl.handle.net/1805/6432.
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Indiana University-Purdue University Indianapolis (IUPUI)Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21) and occurs in ~1 of every 700 live births. Individuals with DS present craniofacial abnormalities, specifically an undersized, dysmorphic mandible which may lead to difficulty with eating, breathing, and speech. Using the Ts65Dn DS mouse model, which mirrors these phenotypes and contains three copies of ~50% Hsa21 homologues, our lab has traced the mandibular deficit to a neural crest cell (NCC) deficiency in the first pharyngeal arch (PA1 or mandibular precursor) at embryonic day 9.5 (E9.5). At E9.5, the PA1 is reduced in size and contains fewer cells due to fewer NCC populating the PA1 from the neural tube (NT) as well as reduced cellular proliferation in the PA1. We hypothesize that both the deficits in NCC migration and proliferation may cause the reduction in size of the PA1. To identify potential genetic mechanisms responsible for trisomic PA1 deficits, we generated RNA-sequence (RNA-seq) data from euploid and trisomic E9.25 NT and E9.5 PA1 (time points occurring before and after observed deficits) using a next-generation sequencing platform. Analysis of RNA-seq data revealed differential trisomic expression of 53 genes from E9.25 NT and 364 genes from E9.5 PA1, five of which are present in three copies in Ts65Dn. We also further analyzed the data to find that fewer alternative splicing events occur in trisomic tissues compared to euploid tissues and in PA1 tissue compared to NT tissue. In a subsequent study, to test gene-specific treatments to rescue PA1 deficits, we targeted Dyrk1A, an overexpressed DS candidate gene implicated in many DS phenotypes and predicted to cause the NCC and PA1 deficiencies. We hypothesize that treatment of pregnant Ts65Dn mothers with Epigallocatechin gallate (EGCG), a known Dyrk1A inhibitor, will correct NCC deficits and rescue the undersized PA1 in trisomic E9.5 embryos. To test our hypothesis, we treated pregnant Ts65Dn mothers with EGCG from either gestational day 7 (G7) to G8 or G0 to G9.5. Our study found an increase in PA1 volume and NCC number in trisomic E9.5 embryos after treatment on G7 and G8, but observed no significant improvements in NCC deficits following G0-G9.5 treatment. We also observed a developmental delay of embryos from trisomic mothers treated with EGCG from G0-G9.5. Together, these data show that timing and sufficient dosage of EGCG treatment is most effective during the developmental window the few days before NCC deficits arise, during G7 and G8, and may be ineffective or harmful when administered at earlier developmental time points. Together, the findings of both studies offer a better understanding of potential mechanisms altered by trisomy as well as preclinical evidence for EGCG as a potential prenatal therapy for craniofacial disorders linked to DS.