辽西医巫闾山地区晚中生代伸展变形事件识别及其构造意义

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中图分类号：P548 文献标志码：A

Abstract： The Yiwulüshan area in western Liaoning constitutes a key Late Mesozoic deformational tectonic unit in the northeastern segment of the North China craton （NCC）.Its multi-stage deformation events preserve critical information regarding the transition of the regional tectonic regime. Through systematic analysis of the macro- and microstructural characteristics of strongly deformed rocks in Yiwulüshan metamorphic core complex，combined with quartz EBSD fabric analysis， this study identifies two distinct phases of extensional ductile shearing events： i.e.，Late Jurassic high-temperature （550-650° ） ductile shearing （under low amphibolite facies conditions） and Early Cretaceous lowtemperature （400-500° ） ductile shearing （under greenschist facies conditions）. The early-stage deformation is characterized by LS-type tectonites dominated by dextral shearing，exhibiting prominent simple shear properties. In contrast，the late-stage deformation forms L=S type tectonites with sinistral shearing behavior，where the contributions of simple shear and pure shear are comparable. Zircon U-Pb geochronological constraints indicate that these two phases of events occurred during 156.9-146.7Mi H （Late Jurassic） and 132.6-126.8Ma （Early Cretaceous），respectively. Analysis of the recrystallized grain size of quartz reveals that the high-temperature shear zone was associated with lower differential stress （20.53-22.16MPa） ） and higher strain rate （8.41×10-13-5.56×10-11s-1） ，whereas the lowtemperature shear zone showed the relative slower strain rate （differential stress： strain rate： 1.34×10-15-9.69×10-13s-1） . The early high-temperature extensional deformation is linked to the transition of the tectonic regime in the northeastern NCC—from the north-southward closure of the Mongol - Okhotsk Ocean to the subduction of the Paleo-Pacific plate. The late low-temperature extensional deformation is related to the roll-back of the subducting Paleo-Pacific plate.

Key words： Yiwulushan； metamorphic core complex； quartz EBSD fabric； Zircon U - Pbgeochronology;ductile shear zone;extensional deformation

0 引言

作为中国最古老的克拉通之一，华北克拉通有着复杂的演化历程，其晚古生代一中生代发生了复杂的构造演化，经历了与周边块体的碰撞、俯冲，以及后续的伸展作用[1-3]。（剩余36264字）