CAJ | 학술논문

大别杂岩主要由早白垩世侵入岩和三叠纪变质岩组成。它的四周是四条区域性韧性剪切带：郯城-庐江断裂,商城-麻城断裂,襄樊-广济断裂和晓天-磨子潭断裂。其中,晓天-磨子潭断裂和襄樊-广济断裂在早白垩世具有相反的走滑剪切方向：北侧的边界断裂(晓天-磨子潭断裂)是一个左行剪切断裂,而南侧的边界断裂(襄樊-广济断裂)是一个右行剪切断裂。在大别杂岩内部,早白垩世低角度剪切面理的倾伏向以 SE向或 NW向为主。这些晚期剪切面理上的拉伸线理的倾伏向同样为 SE或 NW向。大别杂岩总体具有朝 SE 向挤出和顶部相对朝 NW向剪切的构造特征。这些表明晚中生代是该杂岩演化的重要阶段。该杂岩的边界断裂和内部构造特征指示其晚期抬升是沿造山带方向(SE-NW)以低角度方式进行的。这一过程直接导致高压-超高压变质岩和同构造岩浆岩被抬升至近地表。同时,年代学研究表明：大别杂岩(扬子板块东北缘地壳)在晚侏罗世-早白垩世经历大规模混合岩化的时间为145~135 Ma,同造山岩浆作用的时间为145~135 Ma,后造山火山-岩浆活动的时间为135~120 Ma。因此,该杂岩中三叠纪高压-超高压变质岩所记录的早白垩世抬升过程不是印支事件的后续,而是燕山期陆内造山及随后发生的伸展过程有关。尽管这一陆内造山事件的起始时间至今仍不确定,但大别山未变形岩体(130~120 Ma)的年代学研究结果和我们新测得的同构造伟晶岩脉的锆石U-Pb年龄(130 Ma)为早白垩地壳变形提供了良好的上限制约。这样,大别山经历了三叠纪碰撞造山和伸展,晚侏罗世-早白垩世陆内造山-伸展二次过程。
대별잡암주요유조백성세침입암화삼첩기변질암조성。타적사주시사조구역성인성전절대：담성-려강단렬,상성-마성단렬,양번-엄제단렬화효천-마자담단렬。기중,효천-마자담단렬화양번-엄제단렬재조백성세구유상반적주활전절방향：북측적변계단렬(효천-마자담단렬)시일개좌행전절단렬,이남측적변계단렬(양번-엄제단렬)시일개우행전절단렬。재대별잡암내부,조백성세저각도전절면리적경복향이 SE향혹 NW향위주。저사만기전절면리상적랍신선리적경복향동양위 SE혹 NW향。대별잡암총체구유조 SE 향제출화정부상대조 NW향전절적구조특정。저사표명만중생대시해잡암연화적중요계단。해잡암적변계단렬화내부구조특정지시기만기태승시연조산대방향(SE-NW)이저각도방식진행적。저일과정직접도치고압-초고압변질암화동구조암장암피태승지근지표。동시,년대학연구표명：대별잡암(양자판괴동북연지각)재만주라세-조백성세경력대규모혼합암화적시간위145~135 Ma,동조산암장작용적시간위145~135 Ma,후조산화산-암장활동적시간위135~120 Ma。인차,해잡암중삼첩기고압-초고압변질암소기록적조백성세태승과정불시인지사건적후속,이시연산기륙내조산급수후발생적신전과정유관。진관저일륙내조산사건적기시시간지금잉불학정,단대별산미변형암체(130~120 Ma)적년대학연구결과화아문신측득적동구조위정암맥적고석U-Pb년령(130 Ma)위조백성지각변형제공료량호적상한제약。저양,대별산경력료삼첩기팽당조산화신전,만주라세-조백성세륙내조산-신전이차과정。
The Dabie complex is mainly composed of Early Cretaceous intrusive rocks and Triassic metamorphic rocks. On the four sides of the complex, there are four regional shearing belts: the Tancheng-Lujiang Fault, the Shangcheng-Macheng Fault, the Xiangfan-Guangji Fault and the Xiaotian-Mozitan Fault. Among them, the strike-slip directions of the Xiangfan-Guangji Fault and Xiaotian-Mozitan Fault were opposite in Early Cretaceous. The northern boundary (Xiaotian-Mozitan Fault) is a sinistral ductile shear zone, and the southern boundary (Xiangfan-Guangji Fault) is a dextral ductile one. In the inner part of the Dabie complex, low-angle mylonitic foliations, which were formed in Early Cretaceous, mostly dip toward SE or NW. Lineations on these later foliations also plunge toward SE or NW. Generally, the Dabie complex is characterized by southeastward extrusion and top-to-NW shearing along the orogen. These structures indicate that Late Mesozoic tectonic processes were very important for the later evolution of the complex. The deformation characteristics in the shear zone and the inner part of the Dabie complex suggest a low-angle exhumation along the orogen (SE-NW), which led to the exhumation of the HP/UHP metamorphic rocks and the synkinematic magmatic rocks to the Earth’s surface. Meanwhile, geochronological data indicate that, during Late Jurrassic-Early Cretaceous, the Dabie complex (or the northeastern margin of the Yangtze plate) underwent large-scale migmatization in 145~135 Ma, synkinematic magmatism in 145~135 Ma, and post-orogenic magmatism in 135~120 Ma. Therefore, Early Cretaceous exhumation recorded in the Triassic metamorphic rocks from the Dabie complex is not the continuation of the Endosinian event, but associated with the Yanshanian intraland orogeny and the subsequent extension. Though the starting time of the orogeny remains unclear, the available dating results for the undeformed plutons (130~120 Ma) and the new zircon U-Pb age of the synkinematic pegmatite dyke obtained by the authors provide better timing constraints on the end of the crustal deformation in Early Cretaceous along the Dabie orogen. In conclusion, the Dabie complex underwent Triassic collisional orogeny-extension, and Late Jurrassic-Early Cretaceous interland orogeny-extension two processes.