Paleo-tethyan Tectonic Evolution Along The Middle-southern Segment Of The Ailaoshan Suture Zone: Structural Deformation

The AilaoShan tectonic belt is a multi-stage tectonic superimposed composite orogenic belt,mainly experienced the evolution of Tethys and the effect of IndiaEurasia collision.There arecurrentlynot enough evidences for the subduction,closure of the Ailaoshan ocean.Our study area lie in the western of Ailaoshan-Honghe shear zone and include the low metamorphic belt and the non-metamorphic belt.In this paper,we observe in detail the deformation features of each unit,divide the differencesbetween the Silurian-Permian and the Late Triassic-Cretaceous,which are carried out to remove the new generation superposition deformation structure.Otherwise,LA-ICP-MS zircon U-Pb chronology analysis of deformed or undeformed granitic intrusive rock are used to preciselydefine the time of relevant tectonic deformation.The Ailaoshan suture is an accretionaryorogenic belt formed by the westward subduction of Ailaoshan ocean and the accretion to Yangtze block,which separatesthe northeastern of Yangtze block and the southweatern of Indosinian block.It consists of Silurian-Devonian deep-sea flysch,ophiolite,Carboniferous-Lower Permian marine carbonate,island arc magma,Permianback-arc basin turbidite.The structural deformation of the Paleo Tethys in Ailaoshan suture underwent two stages.(1)Thrusting shearing during the subduction,it formed penetrating cleavage(S1)which was parallel to the axial direction of horizontal fold-inclined horizontal fold(f1),NE-SW stretching lineation(L1),several phyllonite belts indeep structure level,and developedNE-SW bedding shear zone,thrust faults and related foldsin lower structure level.When thrusting process was blocked,the recoil occurred and there formed the horizontal fold-inclined horizontal fold whose axial inclined toward to east.(2)Contraction deformation in collision stage.Under the E-W compression,theredeveloped nearly S-N tight inclined fold,plunging vertical fold,crenulation lineation(f2)and crenulation cleavage(S2)in the shallow level.Since the Cenozoic,due to the collision of the Indian-Eurasian continent,it has been affected by superimposed tectonic influences,such as thrust nappe structure,strike-slip shear zone,graben and semi-graben basin.