Lateral Extrusion Tectonics Of Nonrestrictive Block

The Qinling orogenic belt,an intracontinental belt,was resulted from the collision between the North China and the Yangtze blocks.It has a significance on understanding of the formation and tectonic evolution of the continental crust in China.The Qinling orogenic belt has experienced a long-term and complicated geological evolution and reworking.It has undertaken different deformations and orogenesis in various time intervals.Not only do the non-uniform tectonic features form,but also extremely complicated material compositions and space compound of the tectonic frameworks form.Although some researches have been complished on the Qinling orogenic belt during last decades,some geological issues are still unresolved,particularly in the East Qinling area on the late Mesozoic strike-slip motions,relative to the magmatic intrusions and their forming mechanism.Principally,the kinematic features of the strike-slip motions and their correlation with the granitic emplacement in the southern margin and the North China Craton and the eastern extending of the Qinling orogenic belt,are still in debate.This paper did detailed field investigations on the southern side of the North China Carton and the eastern extending of the North Qingling orogenic belt.Detailed system analysis have done on the tectonic relationship between the Late Mesozoic granites origin and the strike-slip faults.Furthermore,this paper also did geometric and kinematic analysis on the kinematic characteristics and genetic mechanism of the northern East Qinling according to the experimental principle of the sandbox model.Though comparing the result of model experiment with the field structures,some conclusions are as follows:(1)The sedimentary cover exposed in the northern part of the East Qinling and characterized by high S-dipping angle are mainly limestone,dolomitic limestone and sandstone in Cambrian and Sinian.The layers around the strike-slip fault zone have undertaken the strong schistosity and the volcanic rocks exposed in the Lower Proterozoic seriously fragment.Concluded,the strike-slip faults in the northern East Qinling have a convergent distribution from east to west and all formed in the Late Mesozoic about 126-120 Ma when the strike-slip faults show sinistral slip.(2)The granites exposed in the northern area along the strike of the main faults show a zonal distribution and the formation time is about 130-110 Ma belonging to the Late Mesozoic the same as the formation time of the strike-slip faults in the study area.(3)Through analyzing the experiment results of the sandbox model,it is indicated that the kinematic and genetic mechanism of the northern area of the East Qingling in the Late Mesozoic accord with the tectonic features of the lateral extrusion of the nonrestrictive block.(4)The Late Mesozoic granites exposed in the northern East Qinling and the genetic mechanism of the sinistral strike-slip faults are both caused by the three-dimensional inhomogeneity the lithosphere and the east-direction escape of the block resulted from the lateral extrusion tectonism of the nonrestrictive block.(5)The lateral extrusion tectonism of the nonrestrictive block not only can result in the lithosphere instability giving rise to the large-scale strike-slip faults,but also can result in the formation of the massive magmatism through disturbing the deep crust.