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Synorogenic foreland basin fill of the south central Pyrenees preserves the eroded remnants of the early stages of Pyrenean fold-thrust belt evolution and topographic growth. Detailed isotopic provenance analysis allows for the reconstruction of sediment sources and boundary conditions of sediment routing systems. Detrital zircon (DZ) (U-Th)/(Pb-He) double-dating of foreland basin sediment is a powerful tool for sedimentary provenance analysis and constraining the exhumational history of mountain belts. This study integrates published structural, stratigraphic, and petrologic data, with new geochronometric and thermochronometric data in a four dimensional source-to-sink approach to decipher provenance and thermal evolution during Pyrenean orogenesis. The Ainsa Basin within the south Pyrenean foreland basin system contains the Hecho Group, a succession of turbiditic channels and levees deposited in the transition zone between the fluvial-deltaic systems of the Tremp-Graus-Ager basin in the east to the submarine fan complex of the Jaca basin in the west. This study presents 2175 new DZ U-Pb ages and 246 new DZ (U-Th)/(Pb-He) double-dated ages from 20 samples collected from the Eocene Hecho group turbidites and the overlying Sobrarbe-Escanilla fluvio-deltatic sandstone in the Ainsa Basin of the south central Pyrenees. These data along with previous DZ U-Pb studies indicate a progressive shift in sediment provenance during orogenesis. The basin was initially being fed by Cadomian/Caledonian plutonic and metamorphic rocks exposed in the eastern Pyrenees with minor sediment contribution from sources located to the south and south east of the basin. Progressive westward exhumation of the Pyrenean Axial Zone promoted a shift in the dominant sediment source to subsequently exhumed Variscan plutons and recycled Mesozoic deposits in the central Pyrenean Axial Zone. Based on DZ (U-Th)/He results, four main cooling events are identified: Pyrenean orogenesis (~56 Ma), initial inversion (~80 Ma), Cretaceous rifting (~100 Ma), and pre-Mesozoic cooling ages related to earlier tectonic phases. This study imposes new constraints on the paleogeographic evolution of the Pyrenees and illustrates that active contractional structures are the dominant control on sediment routing evolution by introducing new sources and controlling sediment pathways during orogenesis.
Detrital zircon U-Pb geochronology and thin-section petrology of core samples taken from onshore Alabama and offshore federal lease blocks, including Destin Dome, Pensacola, and Mobile, constrain sediment provenance for the Upper Jurassic Norphlet Formation in the eastern Gulf of Mexico. Previous research of the Norphlet Fm. in onshore Alabama suggests that sediments near onshore areas of Alabama originated from metamorphic rocks of the Talladega slate belt and Piedmont. This study provides evidence that the Gondwanan Suwannee terrane is another potential source for the Norphlet Fm. in the EGOM. This study determined U-Pb ages for 1111 detrital zircons from 13 Norphlet Fm. core and cutting samples were determined using LA-ICPMS. The Norphlet Fm. yields four major U-Pb age ranges: 197.9 - 350 Ma, 350 - 770 Ma, 800 - 1650 Ma, and 1650 - 3390 Ma. These ages correspond with known U-Pb ages of source terranes common to Laurentia, including the Grenville (950 - 1300 Ma), (Granite-Rhyolite (1350 - 1550 Ma), Yavapai-Matzatzal (1650 - 1750 Ma), Penokean (1800 - 1900 Ma), and Superior Provinces (>2500 Ma). U-Pb ages also reveal sourcing from the Gondwanan Suwannee Terrane (540 - 580 Ma and 2000 - 2200 Ma). This study establishes four geochronologic source terranes: the ancient Appalachian Mountains, the Appalachian foreland basin, Mesozoic rift basins, and the Suwannee Terrane. Ten samples from onshore Alabama yield detrital zircon U-Pb ages characteristic of Laurentian sources (Appalachian mountains and Appalachian foreland basin), whereas two offshore samples yield characteristic Gondwanan (Suwannee Terrane) ages. Four samples located adjacent to the Mesozoic rift basin reveal ages characteristic of both Laurentia and Gondwana - indicating an area of sediment mixing during the late Jurassic. Twelve thin-sections taken from 9 cores in the onshore and state waters areas were point counted for 400 grains each for compositional analysis. Petrolographic analyses reveal plagioclase and potassium feldspars, polycrystalline quartz, metamorphic and volcanic lithic fragments as dominant grain types. Petrologic data corroborate that onshore Alabama samples were sourced by recycled orogenic and cratonic rocks of Laurentia and southern samples were sourced by less mature sources characteristic of a rift basin (Mesozoic rift basins). A paleogeographic reconstruction illustrates sediment being distributed from Laurentian and Gondwanan sources via alluvial, fluvial, eolian, and marine depositional environments.
The Fish Creek-Vallecito Basin exposes an archive of sediment related to early rifting of the Gulf of California beginning at 8.0 Ma followed by Colorado River delta progradation from 5.3-3.0 Ma. Mio-Pliocene deposits from the Fish Creek-Vallecito Basin of southern California and a sample from the modern Colorado River delta were analyzed through detrital zircon U-Pb (n=1996) and (U-Th)/He (n=280) double-dating in order to better constrain sediment provenance, hinterland exhumation, and Colorado River evolution. Coupling this dataset with outcrop study of the first Colorado River-sourced turbidites into the basin at 5.3 Ma, allows for evolution of the Colorado River system to be viewed from a source-to-sink perspective. Detrital zircon U-Pb and (U-Th)/He (ZHe) ages obtained in this study suggest earliest derivation of sediment was from the Peninsular Ranges followed by more distant sediment sourcing from the Colorado River. Initial Colorado River-sourced deposits show Yavapai-Mazatzal U-Pb ages with Laramide ZHe ages suggesting that the river was sourcing from Laramide basement cored uplifts at the onset of deposition into the Gulf of California, supporting a top-down model of river evolution. An increased percentage of Grenville U-Pb age grains as well as a wider range of ZHe ages associated with western US basement-derived zircon from a modern Colorado River delta sample indicate erosion into older stratigraphic units through time which is consistent with deep erosion on the Colorado Plateau since ̃6 Ma. Vertically measured sedimentology logs through the Wind Caves Member, the first Colorado River-sourced unit deposited, were used to determine slope and basin floor architecture as the Colorado River and delta dispersed subaqueous sediment gravity flows into the marine Gulf. Measured sections arrayed along depositional strike show a 4.5 km wide pod of sand-rich turbidites that were delivered through a broad Fish Creek exit point from the paleo-Colorado shelf. The vertical sedimentation trend is one showing thick bedded, amalgamated channelized and sheet-like sandstones initially, shifting to thinner-bedded sheets and more isolated channels higher in the increasingly muddy section. The facies variability up section is interpreted as a change from a submarine basin floor fan to a lower slope environment as the Colorado River prograded its delta into the Gulf.
Direct constraints on processes associated with rifting and mantle exhumation are necessary to understand the thermal and structural evolution of continental rift systems, and the role of pre-existing crustal architecture on orogenesis and foreland basin development. This work constrains the Early Cretaceous hyperextension history along the Iberia-European margin and how rift inheritance affected the structural and foreland basin evolution of the Late Cretaceous-Oligocene Pyrenean orogeny. Chapters 1 and 2 aim to understand the thermal and structural evolution of the North Pyrenean basement massifs during Early Cretaceous rifting and hyperextension using multi-mineral thermochronometry. These chapters integrate zircon, apatite, and rutile U‐Pb ages from the Agly and Saint Barthélémy massifs that provide new constraints to understand the decoupled versus coupled extensional evolution, exhumation timing of the middle‐lower crust, and the age of juxtaposition of the upper crust granitic pluton with middle crustal gneisses, and fluid-rock interactions along a detachment fault. Novel method integration and approaches using apatite were developed and implemented in these chapters to best interpret the apatite U-Pb ages to gain the most insight into thermal, structural, and fault zone processes in the Early Cretaceous rift system’s distal margin. Chapters 3 and 4 use the sedimentary record in the pro-wedge foreland basins of inversion and orogenesis to understand the provenance, hinterland evolution, and the role of extensional inheritance on the orogenic phase of the margin. This work shows that the eastern Pyrenean foreland basin deposits were sourced from Corsica-Sardinia and the Catalan Coastal Ranges during the Late Cretaceous-Paleocene, and the Pyrenees beginning in the Eocene. Detrital mineral trends across the basins suggest that the pro-wedge foreland basin developed and remained segmented throughout the Late Cretaceous-Oligocene. The results from these chapters highlight the dominant control of inherited structures and rift basins on controlling the sediment provenance and foreland basin architecture in inverted rift systems. The dissertation aims to show the structural evolution of the Early Cretaceous rifting and thermal and structural processes that were operating within the continental crust at the rift margin, and how this inherited rift architecture affected the orogenic evolution and foreland basin development during the Pyrenean orogeny. These results add to our overall understanding of the structural and thermal evolution during rifting and continental break-up and role of rift inheritance in the evolution of superimposed orogenic systems and their associated foreland basins
Despite several decades of evolving concepts for thrust belt mechanics and foreland basin evolution, an in-depth understanding of key process linkages and dynamic connectivity between foreland basins and thrust belts remain elusive. In particular, temporal aspects of thrust deformation, detrital provenance, flexural basin subsidence, and stratigraphic architecture, remain debated. This study provides an unprecedented systematic U-Pb and (U-Th)/He (He) detrital zircon (DZ) double dating provenance record for the classic Sevier fold-thrust belt (SFTB) and foreland basin in north-central Utah, to elucidate the temporal linkage between thrust deformation, hinterland unroofing and foreland basin sedimentation through improved isotopic provenance analysis. The zircon (U-Th)/(He-Pb) data in the SFTB and foreland basin allowed constraining distinct episodes of cooling, indicative of major Cenomanian and Campanian thrusting and denudation in the SFTB. The temporal synchronicity between deformation, exhumation and coarse clastic strata indicates that rapid hinterland deformation triggers episodes of major coarse clastic sedimentation and dispersal beyond the proximal foreland basin margin. Moreover, DZHe depositional lag time and DZ U-Pb provenance analyses at the one-myr chronostratigraphic resolution strongly suggest that discrepancies in stacking pattern, shoreline trajectory and progradation rates in the foreland basin can in fact be explained by distinct episodes of major hinterland exhumation. This high-density DZ data set, additionally establish an unequivocal temporal link between major retroarc shortening and voluminous arc magmatism, challenging current conceptual Cordilleran orogenic models that invoke temporal delays between retroarc shortening and voluminous arc magma generation. Both arc magmatic fluxes and retroarc shortening episodes appear to be driven by plate boundary convergence rates. Hence, this study proposes a new model where rate increases in subduction and/or overriding plate motion control both retroarc contraction and arc-magma cyclicity. Other aspects of this investigation explore the influenced of tectonics on continental-scale drainage reorganization in western North America and the Neuquén Basin, Argentina. In summary, the integration of these zircon geo-thermochronometric data in the proper SFTB and foreland basin architectural context helped improve (1) conceptual models that relate temporal, thermal, and spatial aspects of thrust activity to sediment dispersal patterns and (2) shed light into the spatiotemporal feedbacks between upper-crustal deformation and convergent-margin magmatism in Cordilleran orogenic systems.
"The Condrey Mountain Schist (CMS) of the Klamath Mountains (northern California and southern Oregon) represent low grade oceanic and terrigenous sediments thrust beneath higher grade ophiolitic rocks of the Rattlesnake Creek Terrane (RCT). This study presents new U-Pb detrital zircon dates from the CMS, and from the possibly correlative basin rocks of the Galice Formation and accretionary rocks of the South Fork Mountain Schist. The Galice Formation yields a maximum depositional age of ca. 152 Ma with prominent date distributions of ca. 150-200 Ma (39% of analyzed grains), 200-600 Ma (1%), 600 - 1000 Ma (2%), and 1000-3200 Ma (58%). The South Fork Mountain Schist yields a detrital zircon age spectrum with a maximum depositional age of ca. 135 Ma, and prominent age distributions of ca. 120-200 Ma (28.5% of analyzed grains), 200-600 Ma (24%), 600-1000 (8.5%), and 1000-2850 (39%). An interior unit of the CMS has a maximum depositional age of ca. 136 Ma and contains detrital zircon age distributions within 136 to 200 Ma (24% of analyzed grains), 200 to 600 Ma (27.5%), 600 to 1000 Ma (10%), 1000 to 2300 Ma (38.5%). Structural, petrographic, and detrital zircon geochronologic similarities between the CMS and SFMS suggest a common provenance. Kinematic indicators within the Condrey Mountain shear zone, a shallowly dipping ductile structure separating the CMS from the RCT, suggest that the CMS was transported eastward during prograde metamorphism and exhumed during top-to-the-east normal faulting. A tonalitic intrusion from the exterior unit of the CMS yields an inferred igneous emplacement age of ca. 172 Ma. These relations indicate that the exterior CMS was tectonically emplaced at least 37 Myr prior to deposition of the interior CMS"--Abstract, page iii.
Provenance study is a fundamental element of basin analysis, where understanding of sedimentation patterns and their driving mechanisms often requires information about the source of basin sediments. Many recent studies have turned to the geochronology (particularly single detrital zircon ages) and isotope geochemistry in sedimentary rocks to derive detailed information about sediment sources. This dissertation applies geochronology and isotope geochemistry to provenance questions in different settings, utilizing zircon U/Pb ages, feldspar common Pb isotope ratios, and carbonate 87Sr/86Sr ratios to gain new insights into provenance in three well-studied sedimentary systems. The first chapter, set in the Gualala Basin of northern California, provides an example of how conventional provenance indicators, detailed study of conglomerate clasts, U/Pb zircon ages, and common Pb isotope ratios of feldspar from the sand-sized fraction can all provide useful information. Combined, these different data types can produce a more complete picture of sedimentary source areas than any of them would be able to alone. In a continued investigation of applications for detrital zircon ages in provenance study, the second chapter develops a new "Confidence Envelope" method for comparing age distributions. The method developed here is based on characterizing the expected range of variability in samples drawn from the age distribution of a proposed sediment source area, and testing whether a sample of unknown provenance falls within that range. Using the uniquely well-constrained setting of the Green River Formation in Wyoming, the last two chapters investigate paleo-water provenance using an unprecedented dataset of 87Sr/86Sr ratios and Sr concentrations, compiled from both new data and data collected from previous studies. These data demonstrate that isotopic ratios in the Green River Formation lacustrine system changed rapidly, therefore lacustrine sediments were an extremely high-resolution recorder of lacustrine Sr evolution
This dissertation contains studies that use various geochronometric and thermochronometric techniques to better understand the post-magmatic evolution of Sierra Nevada, California. (U-Th)/He ages in apatite and zircon from Sierran batholithic rocks are used to constrain the Cenozoic exhumation of the northern part of the range. Zircon and apatite ages determined from the same samples revealed relatively rapid cooling and exhumation rates (0.2 - 0.8 km/My) from ̃90 to 60 Ma, followed by tectonic quiescence and slow exhumation (0.02 - 0.04 km/My) from the late Paleocene to present. In addition to the thermochronology of basement lithologies, the detrital zircon geochronology of grains from preserved Eocene fluvial sediments in the central and northern Sierra Nevada was performed. U-Pb ages of detrital zircons from the deposits were found to have distributions closely matching age-area estimates of Mesozoic plutons in the Sierra Nevada, suggesting that Eocene river systems were draining local Sierran catchments and likely had steeper axial gradients than has been proposed. Provenance analysis of the Eocene sediments is used to provide constraints on the paleotopography of the Sierra Nevada and inferred range-wide Cenozoic uplift. In addition to the Sierra Nevada work, this dissertation also contains studies that focus on the development of the K-Ca system as a geochronometric technique suitable for dating the deposition of sedimentary sequences. We present a new method for measuring Ca isotopic ratios using a multi-collector ICP-MS equipped with a hexapole collision cell. Isobaric argon interferences are minimized via gas phase reactions in the collision cell. The reproducibility of Ca ratio measurements is found to be ̃0.02 % (RSD), which is comparable to high precision TIMS techniques and an order of magnitude improvement over single collector ICP-MS techniques using a similar reaction cell method. K-Ca ages of glauconite and K-rich evaporites are determined in order to evaluate the usefulness of the K-Ca system as a sedimentary geochronometer. K-Ca ages in both glauconite and K-salts are found to be variable and significantly younger than documented depositional ages. Reported ages, however, are thought to be recording important basinal thermal histories and recrystallization events.
The Vindhyan Supergroup, located in central peninsular India, is one of the largest and thickest Precambrian sedimentary successions of the world, outcropping over an area of over 104,000 km2. The Vindhyan is the largest of the so-called ... Purana ... basins in India. Split into the upper Vindhyan and the lower Vindhyan, the age of the Upper Vindhyan sedimentary sequence is the subject of considerable controversy. This study seeks to determine if the Vindhyan Basin is much older in age than a previously assigned Neoproterozoic age, the age of basin closure, source of sediments, and to discuss the nearby ... Trans-Aravalli Vindhyans ... or Marwar basin, and its relationship to the Vindhyan Basin. Multiple hypotheses have been forwarded concerning basin closure: some argue for an early Neoproterozoic to late Mesoproterozoic closure (... 1050 Ma) of Upper Vindhyan sedimentation whereas others argue for an Ediacaran-Cambrian age. U-Pb dating of detrital zircons from upper Vindhyan sedimentary rocks of the Son Valley sector, purported U-Pb detrital zircon from the Rajasthan sector of the basin and paleomagnetic data from the Majhgawan kimberlite indicates a Mesoproterozoic age for the upper Vindhyans and supports the hypothesis that the Vindhyan and Marwar basin do not share a co-evolutionary history. However, Hf isotopic data show that the Vindhyan and Marwar shared similar sources, most likely from the Aravalli region. U-Pb data corroborates other provenances that provided detritus to the Vindhyan and Marwar basins. Paleographical implications can also be made from these detrital zircon age populations.