Doctor of Philosophy
Geological structures occur on a vast range of scales in Earth’s lithosphere. Because Earth’s lithosphere is rheologically heterogeneous, a multiscale approach is necessary to relate these structures to the tectonic history of orogens. One such approach, called the multi-order power-law approach (MOPLA), has been developed recently. In this study, MOPLA is applied to the Shangdan tectonic zone (SDTZ) in the Qinling orogenic belt (QOB). The kinematics of the SDTZ and its relation to the country rock deformation are crucial questions for Qinling tectonics, having both been the subject of debate for decades. Detailed work is conducted along the SDTZ to address these two fundamental questions.
MOPLA treats a heterogeneous material as a continuum of rheologically distinct elements. The rheological properties of the material and the mechanical fields of the constituent elements are computed by solving the partitioning and homogenization equations self-consistently. The computation is based heavily on the numerical evaluation of Eshelby tensors. This thesis develops an optimal scheme for evaluating Eshelby tensors and implements the scheme in MATLAB to improve the computational efficiency of MOPLA.
Multiscale structural analysis is performed along the SDTZ. Three deformation events are identified in the SDTZ and its adjacent areas. D1 deformation is a NE-SW shortening deformation and occurred between ca.385-355Ma. D1 deformation is only observed to the north of the SDTZ in western Qinling. D2 deformation is a strike-slip dominant deformation and occurred between ca.227-201Ma. In western Qinling, D2 deformation is a dextral strike-slip along the SDTZ. In eastern Qinling, D2 deformation is a sinistral strike-slip along the SDTZ and N-S shortening deformation in the Liuling Group that is south of the SDTZ. D3 deformation is an along-orogen extension and occurred between ca.140-135Ma. D3 deformation is only observed in the Liuling Group in eastern Qinling. D2 deformation, the opposite shearing along the SDTZ and the N-S shortening deformation in the Liuling Group, was a response to the oblique convergence between the South China Block and the North China Block. The convergence angle is constrained to 20°~40° using MOPLA. The tectonic evolution of the QOB from the late Paleozoic to early Mesozoic is illustrated.
Qu, Mengmeng, "Analysis and Tectonic Synthesis of the Multiscale Structures along the Shangdan Tectonic Zone in the Qinling Orogenic Belt, China" (2018). Electronic Thesis and Dissertation Repository. 5383.