Basin Compartmentalization in the Foreland: El Cajon Basin, Southwestern Argentina

Shell Oil Corp

Cenozoic tectonic and geomorphic evolution of the Red River Region, Yunnan Province, China

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004.Some pages folded.Includes bibliographical references.(cont.) Xianshuihe-Xiaojiang fault system during growth of the southeast plateau margin. Cosmogenic ²⁶A1 and ¹⁰Be basin-wide erosion rate and burial ages indicate a background incision rate of [approximately] 0.05 to 0.10 mm/a, lower than the long-term incision rate minimum of [approximately] 0.26 mm/a. Cosmogenically-determined incision rate approximately doubles to [approximately] 0.20 mm/a in the region of maximum dip-slip displacement on the Red River fault. This thesis also develops a new cosmogenic tool for quantitative landscape analysis: using depth dependence data for multiple cosmogenic nuclides from a single site to constrain an erosion history. This method is applied in the Dry Valleys region of Antarctica.This thesis outlines the Cenozoic development of the Red River region, exploring regional landscape evolution and tectonic accommodation of the India-Eurasia collision, focusing on the Oligo-Miocene, left-lateral Ailao Shan shear zone and the active, right-lateral Red River fault on the northeast margin of the shear zone, along which the Red River has incised a deep valley. Oligo-Miocene fluvial and alluvial conglomerates in the valley record shear zone unroofing: pervasive, syn-depositional shortening indicates transpressional exhumation. A low-relief landscape, developed in Late Miocene time, was probably uplifted in Pliocene time, triggering the incision of the Red River and isolating the low-relief landscape from modem base level. On the basis of stratigraphic data, river incision began in Pliocene time or later. Tributary longitudinal profiles indicate two-phase incision, the result of pulsed plateau growth or trunk channel adjustments to changing climate conditions. Paleo-Red River reconstruction indicates [approximately] 1400 m river incision, 1400-1500 m surface uplift and 750 m vertical displacement across the northern part of the Red River fault. Minimum right-lateral displacement on the fault is 40 km, 15-16 km of which predates river incision, plateau growth and development of other regional fault systems. Long term average slip-rate is a minimum of [approximately] 5 mm/yr. Rotation of a crustal fragment around the eastern Himalayan syntaxis, bounded on the east by the Xianshuihe-Xiaojiang fault system, causes deflection of the Red River fault, accommodated by distributed shear along strike of the Xianshuihe-Xiaojiang fault system. The Red River fault has decreased in regional importance since the initiation of theby Lindsay M. Schoenbohm.Ph.D

Recent, slow normal and strike-slip faulting in the Pasto Ventura region of the southern Puna Plateau, NW Argentina

Recent normal and strike-slip faulting on the Puna Plateau of NW Argentina has been linked to lithospheric foundering, gravitational spreading, plate boundary forces and a decrease in crustal shortening from north to south. However, the timing, kinematics and rate of extension remain poorly constrained. We focus on the Pasto Ventura region (NW Argentina) located on the southern Puna Plateau and recent deformation

Late Cenozoic tectonic evolution of the Ailao Shan-Red River fault (SE Tibet): implications for kinematic change during plateau growth

Surface uplift, river incision, shear zone exhumation, and displacement along active faults have all interacted to shape the modern landscape in the southeastern margin of the Tibetan Plateau. The Ailao Shan-Red River fault, a major structure in the tectonic evolution of southeastern Asia, is an excellent recorder of these processes. We present new stratigraphic, structural, and low-temperature thermochronologic data to explore its late Cenozoic tectonic and geomorphic evolution. The stratigraphic and structural observations indicate that the major bend in the fault was a releasing bend with significant Miocene sedimentation in the early–middle Miocene but became a restraining bend with abundant shortening structures developed after the late Miocene reversal of displacement. We also document exhumation of the shear zone from two low-temperature thermochronologic transects. New apatite (U-Th)/He(AHe) data and published thermochronologic results reveal two accelerated cooling episodes, backed by stratigraphic and geomorphic observations. The first rapid cooling phase occurred from ca. 27 to 17 Ma with removal of cover rocks and exhumation of the shear zone. The second accelerated cooling episode revealed by our AHe data commenced at 14–13 Ma, lasting 2–3 Myr. The Ailao Shan range may have risen to its modern elevation with high-relief topography developing due to river incision. We interpret the onset of this rapid exhumation to reflect renewed plateau growth associated with lower crustal flow

Late Quaternary Activity of the La Rinconada Fault Zone, San Juan, Argentina

Most of the permanent deformation in the Pampean Flat slab segment of the central Andes is taken up at the Andean Orogenic Front in Argentina, a narrow zone between the Eastern Precordillera and Sierras Pampeanas that comprises one of the world's most seismically active thrust zones. Active faults and folds in the region have been extensively mapped but still largely lack information on style and rates of deformation, which is essential for understanding the distribution of regional strain and estimating the seismic potential of individual faults. Structural, geomorphic, and 36Cl cosmogenic radionuclide surface exposure age methods are used to focus on key sites along the 30-km-long La Rinconada Fault Zone in this region of west-central Argentina, which is ~15 km away from the highly populated (~500,000) city of San Juan, to define a late Quaternary average shortening rate of 0.41 ± 0.01 mm/year. This slip rate is the same order of magnitude, but slightly lower than nearby similar east dipping Eastern Precordillera faults including the La Laja and Las Tapias Faults. Relatively low slip rates are interpreted as being a consequence of distributed deformation between the latitude of the La Rinconada Fault Zone (31 and 32°S), as compared to between latitudes 32 to 33°S where deformation appears to be focused on fewer structures, including the Las Peñas and La Cal Thrust Faults. The La Rinconada Fault Zone is capable of generating earthquakes of Mw 6.6–7.2, but further investigations are required to determine timing and recurrence intervals of discrete events.Fil: Rimando, Jeremy. University of Toronto; CanadáFil: Schoenbohm, Lindsay. University of Toronto; CanadáFil: Costa, Carlos Horacio. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Owen, Lewis. University of Cincinnati; Estados UnidosFil: Cesta, Jason M.. University of Cincinnati; Estados UnidosFil: Richard, Andrés David. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Gardini, Carlos Enrique. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentin

Late Quaternary intraplate deformation defined by the Las Chacras Fault Zone, West‐Central Argentina

Several major (up to MW 7.5) earthquakes over the past 320 years have shaken the thick-skinned Sierras Pampeanas region of Argentina, despite exhibiting much lower GPS-shortening rates than across the thin-skinned Precordillera region to its west. Whether geodetic shortening rates indicate an actual long-term shortening gradient, and whether shortening rates translate to higher uplift rates due to steeper faults in the Sierras Pampeanas, remain uncertain due to the limited spatio-temporal coverage and the inherently large error in the vertical component of deformation of GPS measurements. We measure geomorphic offsets and use 10Be terrestrial cosmogenic nuclide surface exposure dating to determine slip rates on the Las Chacras Fault Zone (LCFZ)—an ∼30 km long, NNW-trending, steeply dipping (55–65°E) reverse fault that branches off of the longest, westernmost, thick-skinned Valle Fértil range-front fault in the western Sierras Pampeanas. Average shortening and uplift rates measured on the LCFZ are ∼0.2 and ∼0.3–0.4 mm/yr, respectively. Despite an uplift rate similar to most other faults in the region, the LCFZ shortening rate is lower than faults to its west; this is in agreement with the inferred west-east decrease in shortening rates from GPS data, indicating consistent regional deformation patterns since the Late Pleistocene. The decrease in shortening to the east coincides spatially with the termination of the flat portion of the subducted Nazca plate between 67 and 68°W. From scaling relationships among magnitude, slip rate, and fault length, the LCFZ is capable of generating earthquakes of MW 6.7–7.1.Fil: Rimando, Jeremy. University of Toronto; CanadáFil: Schoenbohm, Lindsay. University of Toronto; CanadáFil: Ortiz, Gustavo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Alvarado, Patricia Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Venerdini, Agostina Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Owen, Lewis. North Carolina State University; Estados UnidosFil: Seagren, Erin. University of Toronto; CanadáFil: Marques Figueiredo, Paula. North Carolina State University; Estados UnidosFil: Hammer, Sarah. University of Cincinnati; Estados Unido

Two-phase exhumation along major shear zones in the SE Tibetan Plateau in the late Cenozoic

Three continent-scale shear zones are arguably the most outstanding structural features in the southeastern Tibetan Plateau, and therefore, their tectonic and landscape evolution have significant implications for understanding the history and mechanisms of intracontinental mountain building and plateau growth. This study presents low-temperature thermochronology from the Gaoligong and Chongshan shear zones (GLSZ and CSSZ) and quantitative analyses of fluvial longitudinal profiles of tributaries in the Salween drainage, which lies between the shear zones. Apatite and zircon (U-Th)/He data reveal a two-stage exhumation history for both shear zones: rapid and prominent cooling in the middle Miocene followed by a second, lower magnitude cooling event in the late Miocene to early Pliocene. Ductile transpressional shearing is inferred to have caused the first cooling, continuing until ~11\ua0Ma. The northward migration of the tectonic events along the Mogok metamorphic belt and GLSZ and synchronous dextral displacement along the Jiali fault indicate the dominant role of the north advancing eastern Himalayan syntaxis on the surrounding structures. Increased river incision is identified in the middle Salween drainage, leading to two-segment river profiles and further exhumation along the GLSZ and CSSZ. The tributary transient response could result from temporal changes in uplift or adjustments of the trunk channel to climatic change. Furthermore, glaciers play an important role in shaping the landscape of the upper reaches of catchments in the northern segment of the shear zones. Different drivers for the two exhumation events may reflect distinct stages of plateau growth characterized by different crustal deformation patterns

Late Miocene upper-crustal deformation within the interior of the southern puna plateau, central Andes

The origin and evolution of the central Andes, a noncollisional orogenic system, have been hypothesized to evolve as a result of several dynamic processes, including formation of an eastward-propagating orogenic wedge, segmentation into rhomb-shaped basins as a result of N-S gradients in crustal shortening, reactivation of inherited deep structures, and lithospheric foundering. How these proposed processes dominate the orogen spatially and temporally is uncertain; however, constraining the timing of upper-crustal deformation is critical for investigating these models. We document the formation and deformation of the Pasto Ventura basin (NW Argentina) in the southern Puna Plateau. Through field mapping, deformation analysis, secondary ion mass spectrometry U-Pb dating of zircon from interbedded volcanic ashes, and Ar/Ar geochronology of volcanics, we show that major basin formation started ca. 11.7-10.5 Ma and continued until at least ca. 7.8 Ma. The basin underwent syndepositional faulting and folding from ca. 10 to 8 Ma. Contractional deformation in the Pasto Ventura basin ended between ca. 7.3 and 4 Ma, based on the onset of regional horizontal extension. Data from the Pasto Ventura region allow us to bridge existing data and complete a regional compilation of upper-crustal deformation for the Puna Plateau. Our analysis shows that late Miocene formation and deformation of the Pasto Ventura basin represent an important out-of-sequence contractional event in the southern Puna Plateau. While a number of geodynamic processes likely shape the evolution of the southern Puna, multidisciplinary data sets, including deformation in the Pasto Ventura basin studied here, highlight the role of the formation and detachment of a late Miocene lithospheric drip in causing the upper-crustal deformation on the southern Puna Plateau since the mid-late Miocene

Diverse Styles of Lithospheric Dripping: Synthesizing Gravitational Instability Models, Continental Tectonics, and Geologic Observations

Abstract Density instabilities in the lithosphere can founder gravitationally via viscous dripping and decoupling from overlying crust. The lithospheric dripping concept has been invoked across the globe, but the diversity of crustal effects, observable evidence, and tectonic settings involved in dripping remain underexplored. Here, we synthesize numerical and analogue modeling studies and geologic data from the literature, including all proposed lithospheric dripping events to‐date. We argue that two distinct styles of dripping can occur depending on crustal strength (relative to that of the mantle lithosphere). Near‐surface contraction and subsidence of strong crusts contrasts with near‐surface extension and uplift of weak crusts. We discuss these events in terms of tectonic setting, timing, size, and the main types of data associated with each event. We also find that lithospheric dripping is associated with a distinct suite of geological observations including sedimentological, structural, volcanic, and geophysical data, which can be used to distinguish strong crusts from weak crusts. We find 27 events for which lithospheric dripping is a key hypothesis, including 9 with clear evidence for strong‐crust dripping and 3 with clear evidence of weak‐crust dripping. We review emerging research methods have the potential to detect the signals of dripping in the geologic and geophysical record, and we suggest additional techniques in light of our strong‐crust versus weak‐crust framework. The diverse tectonic settings and inferred consequences of these lithospheric drips, if confirmed, would demand a shift in our understanding of continental geology to emphasize the role of vertical removal of continental lithosphere

View to the U: An eye on UTM research

This is an audio recording from the podcast series "View to the U: An eye on UTM research".Professor Lindsay Schoenbohm talks about her work that uses the landscape to read tectonics, with tectonics being the process that affect the properties and the structure of the Earth’s crust and its evolution over time. We also cover some of the faraway locales she has travelled to in order to conduct her fieldwork – venturing most commonly to ‘seismically active parts of the world,’ where earthquakes can occur – as well as some of the more exciting and memorable trips that have occurred over the course of her academic career. With this second season of the podcast focused on Women in Academia, Lindsay also discusses the associated challenges and frustrations for women in the work environment but she sees hope on the horizon with the open dialogue and debates that have been sparked over the past year or so. Lindsay is an Associate Professor and an Associate Chair in the Department of Chemical & Physical Sciences at the University of Toronto Mississauga. Her research explores Tectonic Geomorphology, which is the study of the surface of the earth and the forces that are involved in shaping it – both the constructive agents that build features like mountains and continents, but also the destructive elements like erosion caused by rivers, landslides and glaciers