Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Geology

Supervisor

Dr. Dazhi Jiang

Abstract

The Qinling Orogenic Belt (QOB), located between the North China Block and the South China Block, has been considered as a key factor in understanding the collision between these two blocks. Although several models for the evolution of the QOB have been proposed, the controversies on those models have yet to be resolved. The Liuling group, located in the south of the ShangdanSuture whichseparates the QOB into the South Qinling Belt and the North Qinling Belt,isan important window to reconstruct theevolutionhistory of the QOB since late Paleozoic. The subject of this thesis focuses onanalysingoutcrop scale structures to establish the deformation history of the Liuling group in the Danfeng Region and then uses the deformation history to place constraints on the regional tectonics and to discriminate existing models.

Detailed structural analysis reveals that the Liuling group has undergone two generations of deformation. The first generation (D1) produced NWW-SEE (orogen-parallel) shortening structures such as isoclinal folds and a transposition foliation in the whole study area. It also caused NWW-SEE (orogen-parallel) sinistral shearing in the adjacent Mianyuzui high strain zone. The second generation (D2) leads to the development of the extensional structures, for example, recumbent folding and L-tectonite. In addition, U/Pb zircons from four pegmatite dikes that cross-cut the first generation of deformation have been dated. However, all zircons are interpreted as inherited zircons, which are captured from the host rocks. Although thegeochronogicaldata cannot be used to limit the absolute ages of the deformation, their deformation timingare discussedin regional context. It is likely that D1 deformation has occurred between 250Ma and 200Ma due to active mountain building that was caused by the convergence between South Qinling Belt and North South China Block. D2 took place betweenca. 150-100Ma, reflecting the along-strike extension and vertical thinning of the QOB.


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