Type of Document Master's Thesis Author Blevins, Michael URN etd-06272008-114733 Title Deciphering Controls on Polyphase Intraplate Deformation in the Ertomiao Region, Lang Shan, North-Central China Degree Master of Science (M.S.) Department Geology & Geophysics Advisory Committee
Advisor Name Title Brian J. Darby Committee Co-Chair Gary R. Byerly Committee Co-Chair Michael D. Blum Committee Member Keywords
- metamorphic core complex
- low-angle normal fault
- Lang Shan
- intraplate deformation
- structural geology
Date of Defense 2008-06-02 Availability unrestricted AbstractThe Ertomiao region of the Lang Shan, China, is located approximately 700 km west of Beijing, in the north-central portion of the North China block. This area is characterized by multiple periods of deformation, including periods of extension and contraction, spanning from Permian through Cenozoic time. This setting provides the structural relationships necessary to decipher the controls of polyphase crustal deformation.
During fieldwork key structural observations and crosscutting relationships were established. Beginning with a period of contraction, northeast striking post Jurassic, pre Early Cretaceous (123 ma) thrust faults place Precambrian gneiss (unit PCB) onto Jurassic/Cretaceous sandstone and conglomerate (unit Jr/K). Additionally, folds with northeast trending axial hinges developed in unit Jr/K and mylonite units. The next period of deformation was Early Cretaceous, pre Eocene high-strain extension notable for the development of the Ertomiao metamorphic core complex (Emcc). A northeast extending low-angle normal fault developed with an upper plate of unit Jr/K and a lower plate of granitic mylonite (units K1 and K2). Following extension this area underwent a significant amount of erosion, reducing the upper and lower plates of the Emcc to the same topographic elevation. Eocene/Oligocene sandstone and conglomerates were deposited on top of the erosional surface as subhorizontal beds. Deformation continued with post Eocene, pre Miocene northeast trending left-lateral strike-slip faulting. Final deformation recorded in the Ertomiao region is along the active northeast striking range front normal fault.
It is thought that each of the structures observed is controlled by far-field tectonic stresses. Post Jurassic, pre Early Cretaceous (123 ma) contraction is related to collision of the South China block with the North China block. The first period of extension and development of the Emcc is associated with back-arc extension of the Pacific subduction zone. Later strike-slip faulting and extension are linked to the collision of India to Asia. The polyphase history of this area offers insights into the deformation of continental crust as a product of far-field tectonic influence.
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