| Quructagh block is located in the Northeast of Tarim block,and located at the junction between the south Tianshan and the Tarim Craton,is the important window to research the evolution of the south tianshan paleo-ocean. We have done many detailed geology surveying in the western segment of Quructagh block depend on the 1:50000 regional geological survey base on the previous studies,and conduct the systematic research on the tectonic deformation characteristics of Quructagh block,discussed the formation mechanism and the geological significance of Paleozoic tectonic deformation combine with the regional geological background of the western segment of Quructagh block and previous studies materials and carry out a preliminary discussion of the geological evolution process from the Middle-Late Neoproterozoic to Late Paleozoic and got some understanding in the following passage:(1)Confirmed the Paleozoic compressional structures represented by Xinger shear zone. We find a shear zone develops in the Middle-Late Neoproterozoic’s rocks of the middle area of our researched region,which extend in near EW direction and dextral shear,is a general ductile shear zone formed in SN direct principalcompressive stress and the EW direct maxium shear stress.And it is matching lots of flaser structures widely distributed in the researched region,showing the regional stress field formed by the SN north-south-trending compressional stress.The U-Pb isotope test show that the gabbro dike that occurred deformation by dextral shear stess in the shear zone was formed in 415.93 ±0.91 Ma,which can limite the main deformation time should after early Devonian,matching the regional tectonic-magmatic hydrothermal events relate to the compression system,could represent the main deformati- on period of this tectonic events.(2)We found two extensional structures developed in the researched region at least. The early extensional structure developed in the early-middle Neoproterozoic stratums, marked by the slip-detachment fault developed between the bottom of Qingbaikou Sy- stem and the basin composed of Paleoproterozoic monzonite granite and Xingditag Gr. and a serial of extension- al tectonic assemblage direct NW-SE,depend on the structure intersections and the results of isotopic test, we deduced that the period of this extension structures formed between 841.0~738.9Ma. The late extension structures was marked by the microgranular mafic cluster developed widely、vertical and parallel. Depend on the previous studiesp,the late extensional tectonics were formed between 820Ma~650Ma,who continued the early extensional tectonic framework.(3)We offers that it have twice transition of structural stress field at least from Neoproterozoic to late Paleozoic. The first was happened between 738.9Ma~650Ma, the maximum regional extensional orientation was transformed from NW to NE,and with near EW directed sinistral shear.The second happended between 650Ma~458Ma, the tectonic stress field was transformed from NE or NW directed minimum principal compression stress to SN directed the maximal principle stress,and finished the transition of extensional structure tocompressional structure.(4)Defined the tectonic deformation sequence of the western segment of Quructagh block.We divide it into four tectonic generation from middle-late Neoproterozoic to late Paleozoic: middle-late Neoproterozoic, middle-late Neoproterozoic to early Paleozoic, early-middle Paleozoic, late Paleozoic.(5)Base on the basic theory of plate tectonics,take the ocean-continent conversion as the thread,we explored the process ofstructural evolution of the north margin of Tarim slab.In a word,in this article we mainly focus on the deformational characteristics of the western segment of Quructagh block formed in Paleozoic.Depend on a lot of systematic field geological survey and analysis of micro-structures,we defined the structural deformation sequence from Neoproterozoic to late Paleozoic,determined the transition of tectonic and dynamic regime from extensional tectonic framework to compressional tectonic framework,limited the phases of the deformation of each of the tectonic stages combine with isotope chronology data and previous studies and deduce the variations characteristics of palaeotectonic stress field when the south tianshan paleo-ocean transformed from expanding to contracting between the late neoproterozoic to early period of Paleozoic.It provided systemed and detailed data and information for discussing the geological tectonicevolution and the characters of geodynamics of the north margin of Tarim slab. |
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