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KINEMATIC STUDY OF THE NORTHERN MARGINAL FAULT Z0NE OF WUYISHAN, S0UTH CHINA

Shu liang-shu1, Lu Hua-fu1, Charvet J2, Fauve M2   

  1. 1. Department of Earth Sciences, Nanjing University, Nanjing, 210093; 2. Department of Earth Sciences, Orleans University, 45067 Orleans, France
  • Received:1997-09-20 Revised:1997-09-20 Online:1997-09-20 Published:1997-09-20

Abstract: Wuyishan is an important tectonic domain which connects the late Proterozoic Jiangnan belt to the north with the Mesozoic-Cenozoic southeastern China Coastal zone to the south. Its northern boundary is the Dongxiang-Jiangshan-Shaoxing fault zone with 20- 50km wide, more than 800 km long along a NEE-NE direction. The ductile shear rocks and pre-Cambrian schist, gneiss, orthogneiss and migmatite occur in this zone, accompanied with serpentinized mafic-ultra- mafic blocks around 900 Ma. The kinematic analysis of the fault zone and neighbouring area to the south reveals polyphase tectonic deformation as follows: 1. The 1ate Proterozoic collision between Jiangnan arc and Southeastern China Precambrian metamorphic terrane took place during the interval of 800-9O0 Ma, accompanied with the formation of the Chencai-Longyou tectonic melange zone and a regional metamorphism of greenschist to amphibolite facies, strong folding with an axial plane dipping to southeast, and ductile deformation with a southeastward sense of shear. 2. The early Paleozoic thrusting deformation resulted in a progressive metamorphism and my1onitization. The biotite flakes of micasehist were replaced by hairy sillimanite; the mylonitic foliation and stretching lineation developed well and crosscut previous schistosities and fold. This thrusting made the metamorphic rocks refolded. An analysis of the non-coaxal ductile deformational indicators shows a sense of shear from north to south. Its geodynamic mechanism is likely related to the early Paleozoic amalgamation and accretion of the southeastern Fujian terrane along the Zhenghe-Dapu zone in the southern margin of Wuyishan toward the northwestern Fujian volcanic arc that developed on the Southeastern China metamorphic basement. The Sm- Nd isochron age of 399±8 Ma on gabbro and the 40Ar/39Ar age of 421±8 Ma on biotite grains of mylonitized micaschist recorded this geological-thermal event. This event also affected the southern margin of the Jiulingshan of the Jiangnan belt to the northwest. 3. The Indosinian sinistral brittle shear deformation occurred in a high tectonic leve1. This is an intracontinental deformation resulted from 1ate Triassic collision between Yangzi and North China plates. The sinistral brittle strike-slip deformation caused 1ate Paleozoic and the older rocks fractured and sheared displacement along NEE-NE direction; the Dongxing-Jiangshan-Shaoxing fault zone was finally placed.