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Tectonics, Structures and FT Thermochronology

Structural Geology and Tectonics

Structural geology is the study in theory, in the laboratory and in the field of mineral and rock deformation at scales ranging from intracrystalline to continental. Tectonics is the study of the construction of the Earth - how large-scale processes of rock formation and deformation interact to create the planet. Research at Penn focuses on regional aspects of these sciences. Emphasis is placed on field study and laboratory analysis to develop regional deformational histories to aid in understanding the assembly of geologic regions. Investigations examine settings as varied as modem and ancient convergent plate boundaries (the Mariana forearc and the California Coast Ranges) and intracontinental deformation belts (basement uplifts in Iberia and in the Rocky Mountains). Within these regions, inquiries have included experimental deformation of serpentinite muds, studies of basalt geochemistry, fission-track analysis of basement and cover rocks, and seismic and gravity interpretation.

Extensive collaboration with colleagues from other leading research institutions provide our students with access to a wide range of expertise, equipment and perspectives. Among others, these institutions include the Lamont-Doherty Earth Observatory, the Smithsonian Institution, the University of Hawaii and the University of Lisbon.

FT Thermochronology

Fission-track thermochronology is one of the newest and most powerful tools geologists use to reconstruct tectonic and thermal histories of diverse geologic terranes. The method has been applied to many fields of geology, thus enhancing positive interactions between scientists in different disciplines of earth and planetary sciences. Research in this program involves the deciphering of tectonic and thermal histories of rift margins and basins, orogenic belts and sedimentary basins, and dating of meteorite impact events

Current Research

Structural Geology and Tectonics

1. Intracontinental Deformation: Spain, Portugal and the midcontinental U.S. Comparative investigation of the intracontinental consequences of collisional orogeny at continental margins. Such collisions produce deformation far into the continent when basement blocks are shifted along old faults, commonly those related to failed rifts.

2. Late Mesozoic Paleogeography of the U.S. Pacific Coast: California & Oregon. Current models do not explain the presence of a previously unmapped ophiolitic milange unit lying within the forearc of the Franciscan subduction complex but outside the complex itself. The modern Mariana subduction zone appears be a good actualistic analogue for many aspects of the fossil Late Mesozoic one along the U.S. Pacific coast. Investigations at Penn focus on testing this comparative model, and currently include several field projects along a spectacular section of the coast in southwestern Oregon.

3. Tectonics of the California Coast Ranges: Compressional stresses between the Pacific and North American plates that are not resolved by transcurrent motion along faults of the San Andreas system are being taken up by active thrust faulting and related folding, forming a variant of Valley-and-Ridge geometry containing exotic rock types such as ophiolites and forearc-basin subsea-fan rocks. Work in this area includes fission-track studies (in collaboration with Dr. Omar) and studies of fault geometry and timing.

Dr. Omar uses FT and thermal modeling to reconstruct tectonic and thermal histories of the following geologic terranes:

1. The Red Sea Rift: Timing, geometry, and extent of rift flank uplift and its relationship to subsidence history of the rift basin. Ultimate objective is to obtain a greater understanding of the interaction of tectonics, geologic structure and erosion at the Red Sea rift margin.

2. Atlantic Margin Rift Basins: Newark and Taylorsville basins. Evaluation of the timing, spatial distribution, and migration of crustal-scale fluid-flow, a poorly understood phenomenon, the effects of which are only now becoming apparent.

3. Southeast Brazil: The goal of this project is to allow definitive limits to be placed on the timing of uplift and denudation of the southeast Brazilian topography and mechanisms for their formation.

4. Rocky Mountains: the main objective of this project is to determine the tectono-thermal history of individual basement blocks and intervening sedimentary basins in order to decipher the tectonic and deformation history of the western USA.

Faculty

Gomaa I. Omar

Phipps, Steve

Department of Earth and Environmental Science / University of Pennsylvania, 251 Hayden Hall, 240 South 33rd Street, Philadelphia, PA 19104-6316