NAPPE STRUCTURE IN THE MAOSHAN AREA AND ITS GEOLOGICAL SIGNIFICANCE

The Maoshan area is located in the eastern part of the Central China diwa (geodepression) region. Maoshan mountain of south Jiangsu stretches in NE direction into south Anhui,appearing as a S-type. It is a nappe zone, a zone of thrust sheets composed of platform aud diwa struct ural layers. The zone extends northeastward from Baituzhen, Funiushan and Zhenjian to Taizhou. A Mesozoic-Cenozoic rift zone lies to the sou theast of the Maoshan nappe zone (Fig,1). The behaviour and deformation of the thrust sheet front, especially the mingling puddingstones in the nappe zone and the autochthonous rocks during the thrusting process have been observed and studied. Hence the nappe structure is divided into several structural facies zones on the basis of the model given by the authors (1982): (1) The zone of thrustaccumulated mingling puddingstone is developed in the upper part of the thrust fault zone, and mixed with heterogeneous material and allochthonous mass; sometimes allochthonous mass is embedded in the thrust sheet by compressional movement. (2) The zone of flattened and ground puddingstone and highly dynamometamorphic rocks (schist, phyllite, phyllonite and mylonite) is a plastic deformation zone. (3) The zone of breccia-puddingstone and gently minor folds ot schistosity is a sliding zone of thrusting. (4) The minor structures on the thrust sheet front and the gentle folds and reverse faults in the foreland were elucidated previ ously by the authors (1982).The structural facies zones are consistentwith the optic elastic test (Figs 7 and 8)The Maoshan nappe structure was formed and developed in five stages: (1) the NE 30-50° trending group of folds and reverse faults formed in a time span trom Indosinian to early Yanshanian age (T_3—J_2), during which the slip-off planes Were formed by strong folding. (2) In middle Yanshanian age (J_3—K_1), the nappe structure was strongly developed, givng tise to a series of overithrusts, imbricate structures, klippen and olistoliths, trending NE 30°. (3) In the late Cretaceous, normal faulting occurred, controlling the deposition of the Pukou and Chishan Formations. (4)From end of late Cretaceous to Paleocene, strike-slip-thrust faults appeared again. (5)Inthe Eocene and Oligocene, normal faults were renewed, controlling the deposition of the Funing Group. After the Indosininan movement the Maoshan area evolved into the diwa stage. It showed strong horizontal (folding and thrnsting) and vertical (normal faulting) movements, with a thrusting slip and subsiding amplitude of more than 10 km and 4 km respectively.Research on the nappe structure in the Maoshan area is of great significance for the study of regional geology, ore deposits, coal,petroleum exploration and recent seismic activity.