PATTERN ANALYSES AND GENETIC INTERPRETATION ABOUT THE GEOTECTONICS OF YUDONG (EAST CHONGQING)
XU Zhengyu1, LI Dacheng1, LU Wenzhong1, LIN Ge2 and LIU Chiyang3 (1. Hangzhou Institute of Petroleum Geology, PetroChina Company Limited, Hangz hou 310023, China; 2. Guangzhou Institute of Geochemistry, Chinese Academy of Sc iences, Guangzhou 510640, China; 3. Department of Geology, Northwest University, Xi’an 710069, China)
Derailed structural analyses and interpretations indicate that Yud on g area has undergone three development stages from weak orogeny and stable crato nic basin during Late Proterozoic-Paleozoic, strong orogeny and peripheral fore land basin during Mesozoic to post-orogenic and residual basin during Cenozoic, and the modern structural pattern and mode are actually resulted from compound, association and superposition of multiple stages of tectonic deformations. As a whole, the study area can be divided into three structural layers. The regional tectonic morphology is in a thin-skin structural pattern of advance propagatio n-type thrust nappe, and the local tectonics occurs in seven variant patterns. Here in the lower structural layer occur duplex structures and fault-bend folds , in the middle structural layer occur fault-bend folds and fault-propagation folds, while in the upper structural layer mainly occur surge folds, fault-prop agation folds and pop-up structures. Formation of these structures involves thr ee stages from Late Yanshanian, Early Himalayan and Late Himalayan. Generally, t he west-thrusting and NE-trending thrust structure system was formed earliest, the SE-thrusting and NEE-trending thrust fold system was formed secondly, and the east-thrusting and NNE-SN-trending thrust fold system was formed last. T he structure in the north of the study area was formed earlier than that the mid dle and south. The NWW-EW-trending nappe fold system in the north end actually disturbed and constrained the northward extension of the NE-NEE-trending thru st nappe system in the middle-north, while the transform (regulation) zone as d eveloped in the middle has obvious accommodation effect.