Browsing by Subject "Tectonics"
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Item An analysis of subduction related tectonics offshore southern and eastern Taiwan(2014-12) Eakin, Daniel Hoyt, Jr.; Lavier, Luc Louis; McIntosh, Kirk D.Arc-continent collision is associated with vigorous mountain building and terrane accretion on relatively short (<10 Ma) geologic timescales. It is believed to be an important mechanism for the growth of continents. Taiwan represents one of the few active examples of this process. As such, is the perfect natural laboratory to investigate the nature of the continent ocean boundary and the uncertain behavior of the accretionary prism and extended, transitional rifted margin crust during the collision process. Taiwan also provides a unique opportunity to investigate structures in the backarc, yielding key insights into the still controversial tectonic conditions that were responsible for the unique subduction-collision system observed today. The obliquity of the collision between the North Luzon Arc and the Chinese rifted margin allows for examination of different temporal stages of collision at different locations. Recently acquired seismic reflection and wide-angle seismic refraction data, offshore Taiwan, document the crustal structure of the incipient mountain belt and of the Philippine Sea Plate in the backarc domain to the east. Geophysical profiles offshore southern Taiwan show evidence for a transition from the subduction of ocean crust to highly extended, transitional continental crust of the northern South China Sea distal margin. During oceanic subduction, accretion and underplating of thick sedimentary cover sequences create a large 13-15 km thick accretionary prism. Prior to the encroachment of the continental shelf, there is evidence for further underplating of transitional distal margin crust to the base of the prism. These findings support a multi-phase collisional model in which early growth of the mountain belt is driven by structural underplating of the previously sedimentary-only accretionary prism with blocks of transitional crust from the distal rifted margin. Geophysical profiles offshore eastern Taiwan show evidence for asymmetric crustal thickening, from 12-18 km, along the entire length of the Gagua Ridge suggesting the West Philippine Basin oceanic crust is underthust beneath that of the Huatung Basin. In this interpretation, the Gagua Ridge was the result of a failed subduction initiation event during the early Miocene that may have existed simultaneously and, for a short time, competed with the Manila subduction zone in accommodating convergence between the Eurasia and Philippine Sea plates.Item Arc-related Mesozoic basins of northern Mexico : their origin, tectonic inversion and influence on ore localization(2016-05) Lyons, James Irwin, 1948-; Kyle, J. Richard; Lawton, Timothy Frost; Cloos, Mark; Horton, Brian K; Elliott, BrentNew structural mapping and radiometric dating in northern Mexico integrated with previous studies indicate the need for revision of current regional tectonic models. The Mezcalera Marginal Basin, an autochthonous Jurassic-Lower Cretaceous basin exposed from southern Arizona to Guerrero replaces accreted terrane models. The lack of significant documentable offsets of this marginal basin provides evidence that contradict proposed major Mexican transform faults in northern Mexico. A left-lateral Cenomanian transpressional fault along which the Caborca and related terranes and offset Bisbee Group strata were displaced is documented by east-directed thrusting of the translated basement and supracrustal strata over the autochthonous Mezcalera Basin strata. Oxfordian (149 Ma) submarine volcanic domes at Batopilas, Chihuahua indicates the Nazas arc of central Mexico migrated across the Mezcalera Marginal Basin, and 124 to 138 Ma dates on Bisbee Group Morita Formation tuffs indicate Alisitos arc volcanism to the west. The well documented Late Cretaceous through Miocene arc migration can thus be projected to the Early Jurassic. Oceanic plate rollback toward the Pacific from the Jurassic through the Early Cretaceous explains the observed arc migration as well as the resulting extension of the Mexican continent. A previously unrecognized intracratonic basin, the Carrizal Basin, a probable northern extension of the Mexican Basin, is documented west of the Chihuahua Basin. The older usage Aldama Platform is divided into the Casas Grandes Platform to the west and the Florida-Aldama Ridge to the east of the Carrizal Basin. Basin inversion as defined by mapping of bivergent out-of-the-basin thrusting along both sides of both the Carrizal and Mexican Intracratonic Basins suggests inversion as the principal tectonic process that produced the Sierra Madre Oriental fold belts. Stratigraphic relationships document the inception of tectonic shortening as Late Cenomanian and a folded 43.7 Ma rhyolite flow at Division de Norte, Chihuahua documents continuing basin inversion well into the Eocene. Previous observations of spatial correlations between structurally complex basin margins and numerous major Cretaceous through Miocene mineral deposits are enhanced by the discovery of the large Cinco de Mayo polymetallic carbonate deposit hosted in stacked west-directed out-of-the-basin thrusting on the west margin of the Carrizal Basin.Item Cenozoic deformation history of the Andean plateau in southern Peru : stratigraphic, structural, and geochronologic constraints(2015-08) Perez, Nicholas David; Horton, Brian K., 1970; Gulick, Sean; McQuarrie, Nadine; Steel, Ron; Stockli, Daniel FCenozoic shortening in the central Andes of southern Peru was accommodated by thin- and thick-skinned deformation that governed hinterland/foreland basin dynamics, the timing and location of exhumation, and development of modern high topography. A new line length balanced cross section estimates 130 km of shortening (38%) across the Eastern Cordillera and Subandean Zone. I propose the location of a pre-Andean graben in the Eastern Cordillera, and a kinematic model that links selectively inverted basement-involved normal faults to shallow detachments that accommodate thin-skinned deformation across the orogen. New U-Pb zircon geochronology from synrift deposits establishes Triassic age deposition, and suggests compartmentalized rift basins were filled with local Eastern Cordillera sediment sources. Eocene exhumation in the Eastern Cordillera represents reactivation of Triassic normal faults and the onset of Andean deformation. In-sequence deformation was transferred from the Eastern Cordillera to the Altiplano by the thin-skinned Central Andean Backthrust Belt and induced flexural subsidence in the Ayaviri hinterland basin beginning at ~30 Ma. Facies analyses, sediment provenance, geochronology, and structural mapping define multiple phases of basin reorganization that are temporally correlative with motion along basin margin thrust faults. Major middle Miocene reorganization of the Ayaviri basin is linked to ~17 Ma out-of-sequence thrust fault motion in the Western Cordillera. Oligocene-Miocene hinterland basin evolution in the northern Altiplano was driven by thrust tectonics. U-Pb detrital zircon geochronology from Cretaceous through Cenozoic stratigraphy in hinterland and foreland basins record distinct provenance differences since the Cretaceous. This is the detrital record of either an inherited structural high in the Eastern Cordillera that predated Eocene shortening and created two depocenters with distinct provenance, or lateral provenance variations across a large retroarc foreland basin. Existing K/Ar, ⁴⁰Ar/³⁹Ar, and new zircon (U-Th)/He thermochronology suggest Eocene-Oligocene exhumation in the Eastern Cordillera was synchronous ~400 km along strike. New apatite (U-Th)/He data from the Eastern Cordillera demonstrate a change to localized, diachronous exhumation and uplift events in the Miocene-Pliocene. Apatite (U-Th)/He thermochronology demonstrates onset of deformation in the Subandean Zone by ~15 Ma, after shortening and exhumation in the Eastern and Western Cordillera ceased.Item Cenozoic evolution of a fragmented foreland basin, Altiplano plateau, southern Peru(2012-05) Fitch, Justin David; Horton, Brian K., 1970-Debate persists on the timing, magnitude and style of crustal shortening, uplift and basin evolution in the Andes. Many studies suggest that the central Andes, including the Altiplano plateau, were gradually uplifted as a result of protracted Cenozoic retroarc shortening. However, recent isotopic studies conclude that the Andes instead rose in pulses, with the most significant event occurring at 10-6 Ma. Many researchers attribute these rapid pulses of uplift to lower lithosphere delamination events. A better understanding of the history of Cenozoic crustal shortening is essential for determination of the mechanism(s) of Andean uplift. The well-exposed Cenozoic San Jerónimo Group was studied in the Ayaviri basin of the northern Altiplano in southern Peru. The 3-5 km-thick succession is situated at 3900-4800 m elevation, between the Western Cordillera magmatic arc and the Eastern Cordillera fold-thrust-belt. New detrital zircon U-Pb geochronological results from four sandstones and one reworked tuff in the San Jerónimo succession show large age populations indicative of syndepositional volcanism between approximately 38 and 27 Ma. A 1600-m-thick magnetostratigraphic section further constrains the depositional timing and accumulation rate of the upper portion of the succession. Sedimentological observations show a rapid transition from cross-stratified braided-fluvial sandstones to proximal channel-fill and alluvial-fan conglomerates at ~30 Ma. Paleocurrent measurements show important temporal and spatial variations in sediment dispersal patterns while conglomerate clast counts show an upsection transition from almost exclusively volcanic input to increasing contributions of clastic, quartzite, and limestone detritus. The corresponding shifts in depositional environment and sediment provenance are attributed to the activation of new thrust structures in close proximity to the basin, namely the Pucapuca-Sorapata fault system, indicating the presence of an eastward advancing fold-thrust belt dating to at least 38 Ma and reaching the Ayaviri basin within the northern Altiplano plateau at ~30 Ma.Item Detrital zircon (U-Th)/(Pb-He) geo- and thermo-chronometric constraints on provenance and foreland basin evolution of the Ainsa Basin, south-central Pyrenees, Spain(2016-08) Thomson, Kelly David; Stockli, Daniel F.; Horton, Brian K; Clark, Julian DSynorogenic 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.Item Exhumation of the Lesser Himalaya of Northwest India : Zircon U-Pb and (U-Th)/He constraints and implications for the Neogene seawater evolution(2016-08) Colleps, Cody Lee; Stockli, Daniel F.; Horton, Brian K.; McKenzie, N. RyanThe kinematic and exhumational evolution of the Lesser Himalayan (LH) of Northwest India remains a topic of debate; the resolution of which may provide insight into the relationship between the weathering of chemically distinct Himalayan source rocks and observed shifts in global seawater chemistry. Two contrasting models have been proposed to explain the origin of the now southward dipping Tons Thrust, which separates the LH into the inner Lesser Himalaya (iLH) of late Paleo-Mesoproterozoic rocks and the younger outer Lesser Himalaya (oLH) of low grade Cryogenian to Cambrian metasedimentary rocks. The initial exhumation of Cambrian black shales of the oLH anomalously enriched in 187Os has been proposed to drive a rapid increase in global seawater 187Os/188Os at ~16 Ma, thus testing these contrasting tectonic models is critical to elucidate this proposed relationship. While one model suggests that the Tons Thrust shared an original decollement with the South Tibetan Fault System and that the oLH is a far-traveled klippe emplaced against the iLH during the Eocene-Oligocene prior to out-of-sequence activation of the Main Central Thrust (MCT), a second model suggests that the oLH is a short-traveled, in sequence thrust sheet emplaced in the Late Miocene, post-dating movement along the MCT. Given the temporal discrepancy for oLH emplacement of at least 14 Myrs and broad constraints on the thermal history of the oLH, iLH, and MCT hanging wall, zircon (U-Th)/He (ZHe) thermochronology can effectively be used to test these hypotheses and reconstruct the exhumational evolution of the LH. New bedrock and foreland basin ZHe data support the short-traveled oLH model and provide direct evidence for rapid exhumation and southward advancement of thrusting away from the Main Central Thrust (MCT) to the Tons Thrust starting at ~16 Ma, resulting in a shift in exhumation to LH strata highly enriched in Os and relatively less in Sr compared to MCT hanging-wall rocks. This shift in exhumation directly corresponds to coeval shifts in global 187Os/188Os and 87Sr/86Sr seawater records. While these seawater records are commonly utilized as deep-time proxies to track global silicate weathering intensity responsible for CO2 drawdown and climatic cooling, our data, coupled with mass balance box-modeling, indicates that regional weathering of isotopically unique source rocks can drive these seawater records independently from shifts in global-scale weathering rates, consequently hindering this utility of these records.Item Geochemical and thermal insights into caldera-forming "super-eruptions"(2013-05) Lake, Ethan Taliaferro; Cloos, MarkExplosive, caldera forming "super-eruptions" (an eruption of VEI 8 or larger, resulting in 1000+ km³ of volcanic ejecta in ignimbrite sheets) are the single most destructive natural disaster native to Earth. Super-eruptions require three elements to occur: 1-crustal magmatic fluxes above background solidification rates, 2-growth of a batholith scale magma chamber, and 3-an eruption trigger. This study addresses these requirements with new petrographic and geochemical analyses and numerical simulations of crustal magma bodies. Crustal magmatic fluxes up to 10x steady-state arc rates are required to form volcanic provinces that host super-eruptions. Super-eruptions can occur in continental hot-spots or rift environments. Why arcs "flare-up" is the subject of active debate. Arcs may follow a regular cycle of lithospheric thickening, delamination, and asthenospheric upwelling (the Andean cycle); alternatively fertilized lithospheric mantle may undergo rapid melting. Targeted sampling (n = 165) of mapped but unsampled mafic and lamprophyric magmas in the San Juan magmatic locus of Colorado, an archetypical ignimbrite province, over three years identified both the lithospheric mantle reservoir and the most primitive San Juan magmas using optical petrography, whole rock geochemistry (n = 50) and Pb, Sr, and Nd isotope geochemistry (n = 32). These mafic magmas more closely resemble the continental lithosphere geochemically. Mixing models based on Energy Constrained Assimilation/Fractional-Crystallization (EC-AFC) indicate that the San Juan magmatism is the product of lithospheric melts and 30-40% crustal assimilation rather than asthenospheric upwelling. The Farallon flat-slab "pre-fluxed" and refrigerated the Colorado lithospheric mantle; removal of that slab at around 40 Ma triggered the SJVF "flare-up." Numerical simulations of crustal magma chamber growth indicate giant magma chambers form when high magma fluxes raise upper crustal temperatures to 300-400 °C at 5-10 km depth. These simulations focus on chamber growth, convection, and cooling at the expense of geometry or chamber mechanical failure with realistic sill-like geometry at the expense of thermal modeling. New 3D finite difference simulations emphasize the importance of geometry on chamber lifespan and crustal heating. A spherical chamber (i.e. model construct) requires 10x the cooling time of a 2km caldera footprint sill of same volume. Increasing sill thickness by 1km can double chamber longevity. Focused intrusions (i.e. 1D modeling) locally produce higher thermal gradients and preserve larger primary basalt volumes. Random intrusions in 3D yield basalt to crust ratios of 3-4:1 (required in the EC-AFC models). Random intrusion in 3D into the upper crust at "flare-up" fluxes ([greater than or equal to]10 km³ per k.y.) elevate average crustal geotherms by 10 °C / km, allowing for growth of batholithic scale magma chambers a wider footprint. Once situated in the upper crust, sub-caldera magma chambers cool inward forming moving crystallization and fluid saturation fronts. If the saturation front propagates faster than the crystallization front, nucleating fluid bubbles have the opportunity to grow, ascend, and collect at the chamber roof. New 2D finite difference models couple magma chamber cooling to fluid production to explore the conditions of fluid escape and collection. Less silicic magma composition, equant geometry, high ambient thermal gradient, and a stock all aid in fluid pocket growth by slowing the advance of the crystallization front (a fluid trap) and triggering saturation at lower fluid concentrations. Fluid pockets that grow to certain sizes ( > 500 m hemispherical bubble) have the potential to trigger an eruption by propagation of a fluid fracture to the surface. This mechanism possibly triggered the eruption of the 5000+ km³ Fish Canyon Tuff as well as smaller, recent eruptions (Pinatubo, El Chichón). Caldera forming super-eruptions occur in regions that meet these three requirements: 1-high magmatic flux, 2-rapid growth to batholithic size, and 3-a delayed eruption trigger. For the SJVF of Colorado melting of the "pre-fluxed" lithosphere provided the magmatic pulse which melted and heated the crust, forming a broad batholith. As magmatism peaked and began to wane, upper crustal magma chambers started to crystallize, exsolving fluids. These fluids ascended, collected, and fractured their way to the surface, triggering the Fish Canyon Tuff and other eruptions.Item The impact of climate and tectonics on sedimentary and deformational processes, Gulf of Alaska(2012-12) Reece, Robert Sherman; Gulick, Sean P. S.Collision of the Yakutat Terrane with North America in southern Alaska has driven growth of the Chugach-St. Elias orogen. Glaciation of the St. Elias Range has periodically increased since the Miocene, but began dominating erosion and spurred enhanced exhumation since the mid-Pleistocene transition at ~1 Ma. Ice associated with this glacial intensification carved cross-shelf sea valleys that connect the St. Elias Range to the deep-sea Surveyor Fan. A newly increased terrigenous sediment flux into the fan triggered the formation and growth of the Surveyor Channel. The change in geomorphology observed throughout Fan sequences allows us to characterize the influence that a glaciated orogen can have in shaping margin processes and the sediment pathways from source to sink. Seismic data also reveal an isolated, large, short runout, mass-transport deposit (MTD) buried in the Surveyor Fan. The MTD geometry, size and location on a convergent margin lend support to recent studies suggesting seismic strengthening and infrequent sediment failure on active margins. This study provides insight into the magnitude and scope of events required to cause submarine mega-slides and overcome higher than normal sediment shear strength, including the influence of climate and sea level change. Beneath the Surveyor Fan, integrated geophysical data reveals massive intraplate shearing, and a lack of oceanic crust magnetic lineaments in regions of Pacific Plate crust. We argue that stress from the Yakutat-North America collision transferred outboard to the Pacific Plate is the major driver for the deformation causing these features. This stress would have resulted in significant strain in the NE corner of the Pacific Plate, creating pathways for sill formation in the crust and Surveyor Fan. The collision further intensified as the thickest Yakutat portion began to subduct during the Pleistocene, possibly providing the impetus for the creation of the Gulf of Alaska Shear Zone, a >200 km zone of shear extending out into the Pacific Plate. This study highlights the importance of farfield stress from complex tectonic regimes in consideration of large-scale oceanic intraplate deformation.Item Paleogene sedimentation patterns and basin evolution during Andean orogenesis, Middle Magdalena Valley basin, Colombia(2010-08) Moreno, Christopher John; Horton, Brian K., 1970-; Steel, Ronald J.; Milliken, Kitty L.The Central Cordillera and Eastern Cordillera of the northern Andes form the western and eastern flanks of the north-trending Middle Magdalena Valley basin. Previous estimates for the timing of initial exhumation of the two cordilleras range from ~100 to ~10 Ma. Accurately constraining the spatial and temporal distribution of deformation in Colombia has implications for the shortening history of the Andean convergent margin and the prediction of rapid lateral facies changes in sedimentary basins in close proximity to sediment sources. This study applies sandstone petrographic point counts, field sedimentological analyses of basin fill, and paleocurrent measurements of trough cross-stratification, clast imbrication, and flute casts to provide new insights into the tectonic history of the flanks of the Middle Magdalena Valley basin. Between the lower and upper Paleocene strata of the Lisama Formation, paleocurrent orientations show a shift from northward to eastward transport. This change in sediment dispersal coincides with a shift from a cratonic (Amazonian) to orogenic (Andean) sediment source, as recorded by published U-Pb detrital zircon geochronological results (Nie et al. 2010), suggesting initial uplift of the Central Cordillera by mid-Paleocene time. Later in the basin’s history, establishment of an alluvial-plain system with meandering-channel deposits is recorded in lower–middle Eocene strata of the lower La Paz Formation. Consistent eastward paleocurrents characterize mid-Paleocene through uppermost Eocene strata, indicating a continuous influence of western sediment source areas. However, within the upper middle Eocene succession (~40 Ma), at the boundary between the lower and upper La Paz Formation, sandstone compositions show a dramatic decrease in lithic content. This compositional change is accompanied by a facies shift to amalgamated fluvial channels, reflecting changes in both the composition and proximity of the western sediment source. We attribute these changes to the growing influence of the exhumed La Cira/Infantas paleohighs off the western flank of the present-day Nuevo Mundo syncline. In the uppermost Eocene strata of the Esmeraldas Formation, paleocurrents show a switch to dominantly westward transport that persisted through the Neogene. In addition, deposits show a contemporaneous decrease in the amount of coarse-grained channel deposits. These changes are interpreted to reflect the onset of exhumation in the Eastern Cordillera. The lack of a significant change in sandstone compositions at this boundary suggests a compositional similarity between strata uplifted by the Lisama structure and the Eastern Cordillera. These data support and further refine previous thermochronologic and provenance studies which suggest that uplift-induced exhumation of the Central Cordillera and Eastern Cordillera commenced by mid-Paleocene and late Eocene–early Miocene time, respectively.Item Sedimentary, structural, and provenance record of the Cianzo basin, Puna plateau-Eastern Cordillera boundary, NW Argentina(2011-05) Siks, Benjamin Charles; Horton, Brian K., 1970-; Steel, Ronald J.; Milliken, Kitty L.The fault-bounded Cianzo basin represents a Cenozoic intermontane depocenter between the Puna plateau and Eastern Cordillera of the central Andean fold-thrust belt in northern Argentina. New characterizations of fold-thrust structure, nonmarine sedimentation, and sediment provenance for the shortening-induced Cianzo basin at 23°S help constrain the origin, interconnectedness, and subsequent uplift and exhumation of the basin, which may serve as an analogue for other intermontane hinterland basins in the Andes. Structural mapping of the Cianzo basin reveals SW and NE-plunging synclines within the >6000 m-thick, upsection coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth stratal relationships within upper Miocene levels of the succession indicate syncontractional sedimentation directly adjacent to the Hornocal fault. Measured stratigraphic sections and clastic sedimentary lithofacies of Cenozoic basin-fill deposits show upsection changes from (1) a distal fluvial system recorded by vi fine-grained, paleosol-rich, heavily bioturbated sandstones and mudstones (Paleocene‒Eocene Santa Bárbara Subgroup, ~400 m), to (2) a braided fluvial system represented by cross-stratified sandstones and interbedded mudstones with 0.3 to 8 m upsection-fining sequences (Upper Eocene–Oligocene Casa Grande Formation, ~1400 m), to (3) a distributary fluvial system in the distal sectors of a distributary fluvial megafan represented by structureless sheetflood sandstones, stratified pebble conglomerates and sandstones, and interbedded overbank mudstones (Miocene Río Grande Formation, ~3300 m), to (4) a proximal alluvial fan system with thick conglomerates interbedded with thin discontinuous sandstone lenses (upper Miocene Pisungo Formation, ~1600 m). New 40Ar/39Ar geochronological results for five interbedded volcanic tuffs indicate distributary fluvial deposition of the uppermost Río Grande Formation from 16.31 ± 0.6 Ma to 9.69 ± 0.05 Ma. Sandstone petrographic results show distinct upsection trends in lithic and feldspar content in the Casa Grande, Río Grande, and Pisungo formations, potentially distinguishing western magmatic arc (Western Cordillera) sediment sources from evolving eastern thrust-belt sources (Puna‒Eastern Cordillera). In addition to growth stratal relationships and 40Ar/39Ar constraints, conglomerate clast compositions reflect distinct lithologic differences, constraining the activation of the Cianzo thrust and coeval movement on the reactivated Hornocal fault. Finally, U-Pb geochronological analyses of sandstone detrital zircon populations in conjunction with paleocurrent data and depositional facies patterns help distinguish localized sources from more distal sources west of the basin, revealing a systematic eastward advance of Eocene to Miocene fold-thrust deformation in the central Andes of northern Argentina.Item The southeastern Caribbean subduction to strikeslip transition zone: a study of the effects on lithospheric structures and overlying clastic basin evolution and fill(2014-12) Alvarez, Tricia Grier; Wood, Lesli J.; Mann, Paul, 1956-The formation and evolution of sedimentary basins are best understood within the context of prevailing tectonic conditions. This dissertation presents an integrated geologic and geophysical study of the southeast Caribbean–northeast South American margin which is characterized by a 300-km-long curved transition from subduction to strike-slip plate boundary interaction. Tomography models are generated to image the geometry and orientation of the subducting slab and associated upper mantle structures, and integrated with observations made from gravity, magnetic and seismicity data. The plate boundary interaction changes laterally from: (1) direct subduction where oceanic South American lithosphere dips towards the west at up to 65° beneath the Caribbean plate; to (2) collision where South American transitional-continental type lithosphere dips 44°–24° beneath the Caribbean plate; to (3) east-west oriented strike-slip interaction where the slab is detached from the South American continent. A tectonostratigraphic framework based on the interpretation of ~10,000 km of 2-D seismic and abundant well data is used to study the evolution of the structures and basin fill of the margin. The basins are characterized by composite and superimposed structural styles which differ from basins formed in pure strike-slip or convergent margins. A NW–SE oriented tear fault aligned with the South American continent-ocean-boundary defines the boundary between different contractional styles in the sedimentary succession of the subduction and collision provinces. An examination of bathymetric conditions and the upper Pleistocene succession of the continental shelf suggest a bimodal sediment transport process, linked to shoreline changes. Current-driven, strike-parallel sediment distribution systems dominate during highstand, generating unique shelf-bound channels and fills. Lowstand across the area is characterized by dip-directed, sediment distribution systems with SW–NE oriented channels that direct sediments to the shelf edge and deep basin environments. The results of this study illustrate that plate boundary conditions and associated lithospheric arrangement at depth, play a significant role in influencing the form of shallow structures, basins and surface geomorphology. Crustal-scale structures; influenced by deeper lithospheric-scale configuration, act over longer time-scales to create and deform depocenters; while sea-level stand exerts significant control on the timing and location of sedimentation over shorter time periods.Item Structural and stratigraphic evolution of Shira Mountains, central Ucayali Basin, Peru?(2009-05-15) Sanchez Alvarez, Jaime OrlandoThe Ucayali Basin is a Peruvian sub-Andean basin that initially formed during the extensive tectonics of the Early Paleozoic. Originally, the Ucayali Basin was part of a larger basin that extended east of the current Andean chain along the Peruvian territory. Subsequently, this large basin was divided into many smaller sub-Basins during the Andean Orogeny. Today, the basin covers an area of about 140,000 km2, and it is morphologically defined by two well-differentiated structural features: the sub- Andean fold and thrust belt (SFTB) to the west and the Amazon plain and Brazilian shield to the east. It is limited to the north and south by the Contaya and Fitzcarrald Arches respectively, the Andes to the west and the Brazilian Shield to the east. These structural features acted as favorable elements to add sediments and to contribute to the structural development of this basin. The sedimentary section of the basin varies in thickness from 1 to 10 km, with ages of strata ranging from the Paleozoic to Quaternary. The strata were deposited in deep and shallow marine as well as transitional and fluvial continental environments. The most important phase of marine sedimentation was initiated with the transgression of the Cretaceous sea (Aptian ?Albian) over the irregular paleogeography defined by morphologic highs and peneplains. Tectonic features of the basin show structural deformations parallel to the Andean front, where overturned structures are observed. These are commonly cut by thrusts and laterally displaced by strike-slip faults. To better understand the development of the Shira Mountains in the central part of the Ucayali Basin, the structural and stratigraphic relationships were mapped out using a dense grid of 2D seismic reflection data and well log control. Three regional EW cross sections were constructed and restored to the top of the Cretaceous to determine the nature of deformation and faulting during the Paleozoic and Mesozoic. The reconstructions show that Shira Mountains fault was initially a major normal fault bounding a half graben. The fault was reactivated by later compression as a thick-skinned thrust fault that detaches between 21 and 24 km depth. Reactivation occurred during Upper Miocene between 7.2 and 5.3 Ma, corresponding to the Quechua 3 compressive phase of Andean Orogeny. The shortening of the central Ucayali Basin determined by the reconstructed cross sections ranges between 3 and 5.5%.Item Structural controls on evaporite paleokarst development : Mississippian Madison Formation, Bighorn Canyon Recreation Area, Wyoming and Montana(2012-05) Eldam, Nabiel S.; Kerans, C. (Charles), 1954-; Zahm, Christopher Kent; Steel, RonThis study provides new insights on the mechanisms that controlled the development of solution-enhanced fractures and suprastratal deformation associated with the Mississippian Madison Sequence IV evaporite paleokarst complex. Based on detailed field mapping utilizing LiDAR, GPS, and field observations, we document a paleostructural high (oriented 145º) associated with the Ancestral Rockies uplift within the study area. One hundred twenty-one sediment-filled, solution-enhanced fractures within the Seq. IV cave roof were mapped and characterized by their dominant fill type (Amsden or Madison) and vertical extent. Spatial analysis reveals minimum spacing of these features occurs in areas uplifted during the Late Paleozoic suggesting a link between paleostructural position and solution feature spacing. Shape analysis of these solution features also supports structural position during the Late Paleozoic acted as a dominant control on fracture morphology: (1) downward tapering and fully penetrative features concentrate in areas that experienced uplift; (2) upward tapering concentrate in areas that were undeformed. Mapping of Seq. IV cave roof strata demonstrates vertical collapse variability exceeds 22 m and fault intensity increases in areas of increased collapse. These findings have significant implications for prediction and characterization of solution-enhanced fractures and suprastratal deformation within evaporite paleokarst systems.Item Structural framework and its influence on the Quaternary-age sequence architecture of the northern shelf of Trinidad and Tobago(2010-08) Punnette, Stefan Wayne; Wood, Lesli J.; Mann, Paul, 1956-; Tatham, Robert; Steel, Ronald J.The North Coast Marine Area (NCMA) extends across ~7000 km2 of the northern Trinidad and Tobago shelf in water depths between 50 to 200 meters. In 2009 the NCMA had two exploration blocks under active oil and gas exploration with gas production from the NCMA totaling ~ 1.1 tcf since 2002. All natural gas discovered to date in the NCMA has been interpreted as biogenic although one previous worker has speculated that a minor component of thermogenic gas is also present. The NCMA is located within a complex tectonic environment characterized by oblique strike-slip displacements between the Caribbean and South American plates at a rate of about 20 mm/yr. The main faults of the 200-km-wide plate boundary zone include: 1) the El Pilar right-lateral strike-slip fault zone to the south on the island of Trinidad and the Gulf of Paria which GPS results indicate to be largely inactive; 2) the North Coast fault zone (NCFZ) which coincides with the southern boundary of the Tobago basement terrane and appears to be slightly active with down-to-the-north, Miocene to recent oblique-slip movements on the NCFZ producing accommodation space for deposition of sediments along the northern shelf of Trinidad and Tobago; and 3) the Hinge Line fault zone (HLFZ) crossing through the NCMA and forming the focus of Chapter 2 of this thesis. The ~120 km long Hinge Line fault zone has an average east-northeast strike approximately parallel to the GPS-derived plate motion direction (080°), and is a subvertical, thick-skinned right-lateral strike-slip fault. Localized zones of transpression and transtension form locally where the trace of the fault deviates from the 080° direction of pure, right-lateral shear and these localized areas of complex faulting and folding provide important structural traps for Pliocene and Miocene gas reservoirs in the NCMA north of the HLFZ. Growth sequences along the HLFZ indicate that the fault activated in Miocene time and continues to up to the late Pleistocene (~500 k.y.) and in some areas forms active scarps on the seafloor. Structural maps and isochron maps were made for four horizons underlying the northern shelf of Trinidad including top Mesozoic basement, top Miocene, top Pliocene and seafloor. These maps support a change in terrigenous source area for the northern shelf of Trinidad: during the Miocene and early Pliocene, terrigenous sources were coming from the southeast through the Atlantic Ocean; during the mid-Pliocene to present the source area changed to the southeast through the Gulf of Paria. The shallow seismic stratigraphic study of Chapter 3 analysed two Pleistocene fourth-order shelf and shelf-edge stratigraphic sequences deposited over the past ~500 k.y in the western part of the NCMA. New micropaleontologic data tied to a well through the two sequences B and C constrain the initial deposition of each sequence ~450 k.y (Sequence B) and ~260 k.y. (Sequence C). The lithologic well log shows that the sequences are sand, shale, and thin limestone. Seismic interpretation allows division of sequences B and C into eight system tracts which include: 1) lowstand system tracts, 2) transgressive system tracts, 3) highstand system tracts and 4) falling stage system tracts. Two lowstand systems tracts in sequences B and C are characterized by delta plain deposition of the Orinoco Delta with a north-eastward terrigenous source direction coming from the western side of Trinidad, through the Gulf of Paria. The falling stage systems tract of sequence C consists of a suite of ~20 – 45-m-high, 0.1° – 0.25°-inclined, and north-eastward-prograding muddy, shelf deltaic clinoforms marking the paleo-shelf edge. Fault controls penetrate into Sequence B and may have produced accommodation space but do not penetrate into overlying Sequence C which therefore must have been eustatically controlled. These Pleistocene sequences may provide a more recent analog for Miocene and Pliocene age sequences and reservoirs that form the highly productive horizons of the NCMA gas field.Item Tectonics and sequence stratigraphy of the Venezuelan Basin, Caribbean Sea(2007-12) Kroehler, Margaret Emily; Mann, Paul, 1956-; Christeson, Gail L.The central core of the Caribbean plate is the 3-4-km-deep Venezuelan Basin that is underlain by late Cretaceous oceanic plateau and oceanic crust. The Venezuelan Basin is obliquely subducted to the east-southeast beneath the continental South American plate at the east-west-trending South Caribbean deformed belt (SCDB), a 50-100-km-wide wedge of accreted sedimentary rocks. I have mapped the structure and sequence stratigraphy of five late Cretaceous to recent sedimentary sequences overlying a 230,000 km² area of the Venezuelan Basin. The dataset includes ~5900 km of 2D seismic reflection data acquired during five separate surveys from 1974-2004; these seismic data are tied to DSDP drill sites 146/149 and 150 which provide age and lithologic control on the interpreted sequences. I use these data to document older Cretaceous faults formed soon after the formation of the plateau and oceanic crust; to explain the along-strike variations in structural style of the actively subducting Caribbean plate; and to constrain the age and tectonic mechanism for the initiation of subduction along the SCDB. The earliest set of faults are normal faults, only affect rocks of Late Cretaceous age, and approximately parallel a set of seafloor-spreading magnetic anomalies described by previous workers. These normal faults are widely spaced in the area of smooth-topped lava flows making up the 15-km-thick oceanic plateau, but they are much more densely distributed in the area of abnormally thin (3-5-km-thick), rough-surfaced, oceanic crust in the eastern Venezuelan Basin. The faults are interpreted as the result of back-arc extension behind the Aves volcanic arc during the late Early to Late Cretaceous. Selective reactivation of inherited faults and new bending-related faults affecting late Cretaceous to recent sedimentary sequences strike east-west and parallel the trend of the SCDB. The age of the initiation of subduction at the SCDB has been determined based on the age of onlapping, wedge-shaped, sedimentary sequences in the Venezuelan Basin. Subduction began in the western Venezuelan Basin in the middle Eocene in the western study area, in the early Miocene in the central study area, and in the post-early Miocene-Recent in the eastern study area. The ages of subduction agree with a similar eastward younging in the age of folding and thrusting in northern South America. From this observation I infer that subduction of the Caribbean plate beneath the SCDB initiated as a backthrust response to collision between the Caribbean arc and the South American continent that began in the early Eocene and youngs in an eastward direction.Item The effects of lateral tectonics on a fluvio-deltaic system : an application to the Ganges Brahmaputra Delta(2013-05) Kopp, Jessica Ann; Kim, Wonsuck; Mohrig, David; Hickson, ThomasDeltaic systems have long been recognized for their socioeconomic impacts as well as their high potential to trap and store hydrocarbons. The Sediment Transport and Earth-surface Process (STEP) basin at the University of Texas at Austin has the ability to create large 3D physical experiments, designed for nurturing new understanding of these systems and the parameters that influence their evolution. We explored how a laterally tilting basin influenced a prograding fluvio-deltaic system. The tilting occurs along a rotational axis, bisecting the model’s basement and allowing the delta to experience uplift in one half of basin and subsidence in the opposite half. After six experiments with a range of tilting rates, we observed that varying rates of tilting changed progradation patterns as well as the resultant stratigraphy. The tectonic tilting forced a continuous change in topset slope, which accounts for the evolving behavior of the fluvial system with regards to channel occupation and thus shoreline asymmetry. When slow tilting was applied, the delta advanced faster in the direction of uplift due to the relative decline in basin water depth. This created truncated stratigraphic intervals dominated by active channel cut and fill with thin but laterally linked channel bodies depositing finer material. Behavior was significantly different on the subsidence side of the delta; shoreline migration was stunted while the delta became primarily aggradational, depositing thicker, alternating packages of sands. During higher rates of tilting, deposition at the uplift end was quickly abandoned and instead focused on stacking conformable sequences of delta lobes in the area of increased subsidence, resulting in a complete lack of progradation in any direction. Progressively greater rates of tilting yielded more dramatic steering of channelized flow toward the area of greatest subsidence. Comparing characteristic tectonic and channel timescales proves to be a good predictor of shoreline symmetry along with sediment distribution due to differential subsidence. In this study, we tested the hypothesis that differential subsidence acting on the Ganges-Brahmaputra (G-B) system is responsible for delta asymmetry. The asymmetry in planform shoreline geometry and subsurface stratigraphy of the G-B delta system are extensively similar to the experimental results.Item The tectonostratigraphy of the Cycladic Blueschist Unit and new garnet geo/thermochronology techniques(2016-12) Seman, Spencer Mark; Stockli, Daniel F.; Barnes, Jaime; Cloos, Mark; Baxter, Ethan; Soukis, KonstantinosDue to deformation and recrystallization at high-pressure low-temperature metamorphic conditions, blueschist and eclogite-facies rocks typically lack primary sedimentary features or fossils to constrain depositional age. Without this information, it is difficult to describe how these rocks evolved structurally through time and, therefore, to infer the processes at work during the exhumation. This work defines the tectonostratigraphy of the Cycladic Blueschist Unit (CBU) of Greece using detrital zircon geochronology, to correlate metasediments based on their provenance and estimate maximum depositional age. Two distinct types of metasediments are present within the CBU: those derived from the northern rifted margin of Gondwana and deposited during the Triassic-Early Jurassic, and flysch sourced from the Internal Hellenides deposited during the Late Jurassic-Late Cretaceous. In the Western Cyclades, younger flysch sediments are still found overlying older rift margin sediments. This is a primary depositional relationship at the scale of ~500 meters preserved through the subduction and exhumation process. On Syros Island, composed of a structural section of CBU ~12 km in thickness, I employ detrital zircon geochronology to define repetitions of tectonostratigraphy. Based on repeated Triassic volcanics, Syros is composed of thrust sheets ~3 km in thickness. Next, I use combination of detrital zircon geochronology and (U-Th)/He thermochronology to refine the tectonostratigrapy of southern Attica, specifically Hymittos Mountain and the Lavrion Peninsula. This work shows that two distinct low-angle normal fault systems are present in Attica, one active in the Middle Miocene and the other in the Late Miocene. Garnet is a common rock-forming mineral in both high-pressure low-temperature metamorphic rocks and magmatic-hydrothermal skarn. I have developed a garnet-based (U-Th)/He thermchronometric technique to constrain the timing of cooling of high-pressure low-temperature metamorphic rocks. This work shows that He diffusion in garnet is sensitive to temperatures between 200-300˚C at geologic timescales and characterizes a series of potential standards of grossular-andradite composition. Finally, in order to better understand the temporal evolution of magmatic-hydrothermal systems, I created a new U-Pb based technique to date the growth of grossular-andradite garnet. I characterize four different potential reference standards and apply to technique to hydrothermal skarn on Serifos Island, Greece.Item Uplift and exhumation of the Eastern Cordillera of Colombia and its interactions with climate(2015-05) Anderson, Veronica Jacqueline; Horton, Brian K., 1970-; Ketcham, Richard A; Stockli, Daniel F; Shanahan, Timothy M; Garzione, Carmala NRecent breakthroughs in assessing past elevation using stable isotopes of sedimentary materials have provided important constraints on the timing and geodynamics of surface uplift in various orogenic systems. These advances in paleoaltimetry have enabled discrimination between competing models of topographic development in the Tibetan plateau, have provided constraints on the longevity of the Sierra Nevada as a major topographic feature in western North America, and have highlighted the possible role of lower lithospheric delamination in the central Andes of South America. However, there remains considerable debate over the geodynamic mechanisms involved in Andean uplift, as most available estimates on the timing and pace of past elevation gain show an irregular spatial and temporal distribution. In particular, uncertainty persists over the timing of surface uplift of the Eastern Cordillera in the tropical northern Andes of Colombia. Although changes in sediment accumulation, provenance, and thermochronometric estimates of bedrock exhumation suggest Andean shortening in the Eastern Cordillera since late Eocene-Oligocene time, the rise of the ~2600-m-high Bogotá plateau (Sabana de Bogotá), a intermontane hinterland basin appears to have significantly lagged the onset of shortening in the fold-thrust belt. In addition, there is dramatic variation in structural style along strike within the Eastern Cordillera, making it unclear whether a major basement-involved topographic high (the Garzón Massif) at the southern end of the range was contemporaneous with the rest of the Eastern Cordillera. Studies of pollen assemblages in clastic sedimentary fill of the Bogotá plateau suggest that it may have risen rapidly from ~6-3 Ma and has maintained the same elevation thereafter. However, this scenario of rapid latest Miocene-Pliocene uplift followed by post-3 Ma stasis appears inconsistent with the structural geologic record, as more than half of the total shortening along the eastern Andean flank has occurred since ~3 Ma. We investigate the elevation history of the Bogotá plateau using novel lipid biomarker proxies for past surface temperature and isotopic composition of precipitation, and update the geochronologic framework of this basin using a refined magnetic polarity stratigraphy. We also utilize a multidisciplinary approach to determine the timing of uplift-induced exhumation of the Garzón Massif, employing U-Pb detrital zircon geochronological and sandstone petrographic results as tracers of sedimentary provenance, apatite fission track (AFT) thermochronometry to constrain exhumation, and the isotopic composition and elemental composition of paleosols and carbonate nodules to track climatic shifts associated with the uplift of the Garzón Massif. These approaches indicate that (1) the Bogotá Plateau had likely been partialy elevated prior to the late Miocene (~7.5 Ma) and has been uplifting continuously since then, (2) and that while the timing onset of exhumation of the Garzón Massif is similar to other parts of the Eastern Cordillera, it did not begin to build substantial topography until ~ 6 Ma. These results imply that the Eastern Cordillera did not become a contiguous topographic barrier, until late Miocene-Pliocene time, providing new constraints on the establishment of the Magdalena River, a northward-draining system that contributes an enormous sediment load to the Caribbean Sea, as a discrete system fully separated from the Amazon basin.