Geodynamic models for collisional orogeny are commonly based on the Himalayan orogenic belt. Surprisingly little detailed information is available about the timing of emplacement of major thrust faults in the Himalaya, particularly in the region between the Main Central thrust and the front of the thrust belt. The goal of this research is to document the early Miocene to present history of thrusting in Nepal. This involves documentation of slip timing for all the major thrust faults south of the Main Central thrust, including the Ramgarh, Main Boundary, and Main Frontal thrusts, as well as several major thrusts in the frontal imbricate zone
and within a regional-scale antiformal duplex. Bedrock and detrital geo-thermochronology will be combined in a multi-dating approach on zircon and apatite crystals/grains. The U-Pb system will be used on apatite and zircon (bedrock and detrital), the 40Ar/39Ar system on white micas (detrital), the fission track method on apatites (bedrock and detrital), and the (U-Th)/He method on apatite and zircon (bedrock and detrital). Double dates (U-Pb and (U-Th)/He) will be acquired
from zircons, and triple dates (U-Pb, (U-Th)/He, and fission track) will be acquired from apatites. In the detrital samples, U-Pb age data will constrain detrital grain provenance, and the thermochronological methods will provide information on cooling history. Bedrock samples will be collected from proximal thrust fault positions along previously mapped regional traverses across the Subhimalayan and Lesser Himalayan zones, and detrital samples will be collected from lower Miocene-Pleistocene foreland basin deposits. Paleomagnetic stratigraphy will provide chronological control on the foreland basin record. Combination of chronostratigraphy with
cooling ages from detrital grains will allow calculation of lag times between exhumation and deposition, and assessment of regional erosional history in the thrust belt. Together these data should provide a detailed chronology of thrusting in the southern part of the Himalaya, and allow refinement and/or rejection of recently proposed geodynamic models. The data will also be relevant for assessing relationships between climate and geodynamics in the Himalaya.
Collaborators: Peter G. DeCelles, Tank Ojia (UA)
Funding: NSF Tectonics
Current student: Edward Albert Cross
Some of the most fundamental scientific questions in tectonics include: "what are the processes responsible for the present day thickness of continental crust observed in continental plateaus and what is the response at the surface to such processes?" Whereas we tend to have a qualitative understanding of these processes, our understanding of the magnitude and timing of surficial effects is still limited. One popular model often invoked to explain the present day crustal structure and elevation of the Central Andean Plateau, including the Argentinean Puna and the Bolivian Altiplano, is lithospheric "delamination". Full, convective removal of eclogitized lower crust and lithospheric root and subsequent rebound in the Altiplano of Bolivia is proposed to explain paleoaltimetric evidence for high magnitude (> 2km) surface uplift. However, the region of geophysically defined thinnest crust and lithosphere and of basaltic volcanism originally argued to be the site of lithospheric removal is located to the south in the Puna Plateau of Argentina. Moreover, new geochemical data suggest the presence of Ordovician lithosphere beneath the Puna, arguing against complete lithospheric removal. Therefore, there is a clear need for a comprehensive, interdisciplinary study to reconcile surficial data with geophysical data, targeted in the area of "thin crust and mantle lithosphere" in the Puna Plateau. This project involves a multidisciplinary investigation including structural geology, sedimentology and stratigraphy, geochronology, thermochronology, geochemistry and paleontology, targeting the thinned region in order to constrain (1) the history of horizontal shortening and extension, (2) basin evolution and incision (3) magma geochemistry and (4) paleo-environment in the mid-late Cenozoic. These comprehensive new data will then be used as input parameters in a novel, combined numerical-physical, model that will test a set of hypotheses, including full, partial and small-scale convective removal of mantle lithosphere, delamination and back-arc extesion, to explain the present crustal configuration of the Plateau. The goal of this research is to constrain the connection between mantle processes on surficial deformation, uplift, subsidence and magmatism within the Puna Plateau, a natural laboratory that will serve as an example for other geodynamically similar regions on Earth.
Collaborators: Lindsay Schoenbhom & Russell Pysklywec (U Toronto), Mark Clementz (University of Wyoming), Mihai Ducea & Jay Quade (U Arizona).
Funding: NSF Tectonics, ExxonMobil
Graduated students: John Boyd & Robin Canavan (U Wyoming)
The nature of the stratigraphic signature of orogeny continues to be a subject of debate, and in many cases stratigraphic estimates for the onset of orogeny lag significantly behind estimates based on structural, metamorphic, and geochronological data. The Andean orogenic belt is the type-example of a high-elevation retroarc thrust belt, and models based on the Andes are regularly exported to retroarc orogenic belts around the globe. Nevertheless, a fundamental aspect of Andean orogeny—the timing of initial mountain building owing to crustal shortening and thickening—remains controversial. Recent studies in the southern Andes and Bolivian central Andes demonstrate Late Cretaceous to late Paleocene foreland basin development and, by logical inference, initial crustal shortening and thickening. In contrast, many workers interpret the stratigraphic record of northern and central Argentina to reflect Late Cretaceous-Paleogene extension and post-rift thermal subsidence, followed much later by crustal shortening during the Neogene. However, Paleogene basin models in NW Argentina are not based on comprehensive regional data sets including sedimentary provenance, paleocurrent and thickness patterns, chronostratigraphy, and paleoaltimetry.
The goal of this project is to implement a regional study of Paleogene sedimentary rocks in NW Argentina, with the aim of establishing the tectonic setting of deposition in this important region of the central Andes during the transition from regional extension to shortening. Three models for basin evolution will be tested: (1) post-rift thermal subsidence, (2) foreland basin subsidence, and (3) intermontane basin development during tectonic disruption of the Andean foreland. Each model makes specific predictions about depositional environments, sediment distribution patterns, provenance, basin architecture, subsidence and thermal history, and paleoelevation. In order to reconstruct basin evolution during the Paleogene in NW Argentina, we propose to collect sedimentological (lithofacies, thickness,
paleocurrent directions, provenance data), chronological (40Ar/39Ar tuff ages, palynology, U-Pb zircon ages, and apatite fission track ages), and oxygen isotopic data from well exposed Paleogene strata in a roughly 30,000 km2 region. Our preliminary U-Pb and apatite fission track studies have yielded exciting results that promise new insights into the timing and nature of orogeny in the central Andes. Expected products of the research include a comprehensive dataset on the Paleogene stratigraphy of NW Argentina, and a concerted application of two new methods (detrital zircon U-Pb geochronology and oxygen isotopic
paleoaltimetry) to early Cenozoic tectonic problems in the central Andes. Moreover, our results will directly address the issue of how to read orogenic signatures in the stratigraphic record.
Collaborators: Peter DeCelles & Jay Quade (U Arizona), Brian Horton (UT Austin), Daniel Stark (Tectpetrol).
Graduated students: Sharon Bywater & John Trimble (U Wyoming)
Funding: NSF Tectonics, ExxonMobil
The Pamir Mountains of Central Asia are among the highest mountains on Earth, which, together with the Himalaya and Tibet, are the result of Indo-Asia continent-continent collision. High mountainous regions are the product of tectonic forces that build topography and erosional processes that destroy it. Moreover geographically extensive high elevation regions can influence climate over tens of millions of years, potentially causing global cooling and driving the monsoons. Therefore, if we want to understand the relationships between tectonics and climate we need to know how and when mountains grow. While data from the Tibetan Plateau and its eastern (west-central China and Sichuan) and southern (Himalayan) margins has been collected over the last few decades, there is virtually no data from the western regions of Pakistan, Afghanistan, Tajikistan and Kyrgyzstan. The past record of mountain building is partially erased in the mountains by erosion but it is recorded by the material eroded and deposited in nearby basins. The Tajik depression and Peter the First Range in Tajikistan and Tarim basin in China, located just west north and east of the Pamir Mountains, has accumulated such a record over the last 60 million years. The origin and age of both the material that was removed from the mountains and of the associated sedimentary record preserved in the foreland region can be used to determine when mountains first began to grow (through shortening and crustal thickening) and how they evolved over time. This research a multi-disciplinary approach (detrital geo-thermochronology) applied to syn- orogenic sedimentary rocks and modern river sands. The goal of this project is to unravel the dynamics of collision and climate-tectonic interactions in this part of the world and the results can be extrapolated to other regions.
Collaborators: Lindsay Schoenbhom (U Toronto), Ed Sobel (U Potsdam), Brad Singer (U Wisconsin), Mike Cosca (USGS Denver) and Chen Jie (Institute of Geology, Beijin)
Students: Claire Lukens (U Wyoming), Fariq Shazanee Mustapha Kamil (U Arizona)
Funding: National Geographic
The goal of this research is to constrain the tectonic and thermal evolution of the Sevier fold-and-thrust belt of southeastern Idaho, southwestern Wyoming, and northern Utah and its relationship with the Laramide. In order to constrain this tectonic and thermal history, proposed research activities include detrital U-Pb
geochronology, fission track thermochronology and (U-Th-Sm)/He thermochronology. These analytical techniques will be performed on apatite and zircon obtained from both pre-orogenic and syn-orogenic strata sampled from the southern half of the fold-and-thrust belt. The resulting datasets will provide constraints on the depositional age and sediment provenance of synorogenic strata as well as resolve the timing and rates of cooling (exhumation) and/or thermal
perturbations within the fold-and-thrust belt. To examine the relationship between the thermal history and thrust tectonics, these constraints will be combined with existing structural, stratigraphic, and geophysical datasets to develop a thermo-kinematic model of the ID-WY-UT fold-and-thrust belt. This combined with thermochronology in the Laramide region will be able to test various models proposed for Laramide deformation and help understand the overall behaviour of the foreland basin system. This research will (1) test and refine existing hypotheses for the evolution of the Sevier fold-and-thrust belt, (2) constrain the timing of individual thrust faults along the oil-rich Utah-Wyoming portion of the Sevier belt, and (3) strongly impact petroleum research by constraining the timing of hydrocarbon thermal maturation with respect to thrust fault generated deformation.
Collaborators: Peter DeCelles (U Arizona) & Majie Fan (U Wyoming)
Students: Clay Painter (U Arizona)
The current depositional analog for most interpretations of the Canadian heavy oil sand stratigraphy is based upon the "incised valley" model. Incised valleys form when there is a drop in relative sea level. During the falling stage and subsequent low stand, rivers actively erode and incise into older deposits. During the subsequent rise of relative sealevel, the valleys fill. If the river deposition cannot keep pace with the rate of sea level rise, the valley is drowned by the sea and forms an estuary and/or bay (i.e. Galveston Bay). The deepest portion of incised valleys fill with fluvial deposits and the upper portions can fill with estuarine deposits. The stratigraphy of incised valley deposits as seen in outcrops suggests that the various reservoir units have limited lateral extent due to the confined nature of valleys and the scale of depositional features within the estuary.
In contrast, new analysis of previous work and outcrops suggest an alternate depositional model. It appears that significant tidal facies are deposited in an inter-deltaic setting where the dominant source of sand is along strike, from the nearby wave dominated deltaic headland. Tidal facies deposited in this setting appear to have subtle sedimentologic differences from the incised valley model. More importantly, there appears to be a predicable up-dip to down-dip facies track. Reservoirs deposited in this setting seem to be dominated by large flood tidal deltas, barrier islands/spits, tidal inlet channels and tidal flats that have been extensively reworked by tidal inlets. In general, the scale of these depositional features is much larger than reservoirs facies in an incised valley. It is very important to evaluate this new tidal model in order to build accurate reservoir models capable of predicting fluid flow.
Collaborators: Mike Boyle (Shell International, Calgari)
Graduated student: Carly York (U Wyoming)
Current student: Clay Painter (U Arizona)
Funding: Shell International
The suturing of continental fragments following the subduction of intervening oceanic lithosphere is a fundamental process in lithospheric dynamics and the shaping and growth of Earth's continents. However, our understanding of this fundamental process remains limited. Can we use geological observations in some particularly well-exposed suture zones to make general statements about how landscapes and sedimentary basins evolve during suturing? What geodynamic processes lead to
decreases in plate convergence rate? Are Mediterranean-style rollback of remnant oceanic lithosphere and opening of marginal oceanic basins characteristic of all or most pre-climax collision zones? Do presuturing ophiolite obduction and intraoceanic arc–continental margin interactions leave predictable signatures in suture zones? How is the upper continental plate preconditioned by pre-suturing tectonism and how does the upper plate evolve during the transition from oceanic to continental subduction? Is there a predictable mode of deformation in the downgoing continental plate? And what do we expect the balance to be among continental subduction and erosive removal of mass from a collisional orogenic system? This project has the goal to investigate the archetypal India–Asia collision zone (IACZ) in southern Tibet. Techniques employed in this reasearch include structural geology, stratigraphy, geochronology, thermochronology, stable and radiogenic isotope geochemistry, igneous and metamorphic petrology, paleomagnetism, and geodynamical modeling. We aim to determine the: (1) evolution of paleogeography and paleoelevation during the transition from oceanic subduction to mature continental collision; (2) geodynamic processes that caused marked decreases in India–Asia convergence rate; (3) role of Mediterranean-style opening and closing of marginal basins prior to terminal collision; (4) metamorphic evolution of lower-plate (Indian) rocks in response to ophiolite emplacement, possible intra-oceanic arc
collision, and continent collision; (5) role of pre-collisional Andean-style magmatism and deformation in preconditioning the upper-plate lithosphere and how this Andean-style system evolved during continent collision; (6) paleogeography of the Neo-Tethys margins and the history of subduction, exhumation, thickening, and underthrusting/rollback of Greater Indian continental lithosphere; and (7) spatial pattern, magnitude, and history of erosion and sediment dispersal.
UA Collaborators: Paul Kapp, Petre DeCelles, Mihai Ducea, Jay Quade, George Gerhels.
Funding: NSF-Continental dynamics
Current student: Devon Orme
and several other students from the UA