| 桐柏地区高压变质地体在地壳中的抬升机制 |
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| 引用本文： | 崔建军,胡健民,刘晓春.桐柏地区高压变质地体在地壳中的抬升机制[J].岩石学报,2009,25(9):2165-2176. |
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| 作者姓名： | 崔建军 胡健民 刘晓春 |
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| 作者单位： | 中国地质科学院地质力学研究所,北京,100081 |
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| 基金项目： | 国家自然科学基金项目，国土资源大调查项目，国家973项目 |
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| 摘 要： | 桐柏杂岩位于秦岭与大别造山带之间,南北两侧为NWW-SEE向延伸的含榴辉岩高压变质地体,其构造就位过程及其与高压变质地体的构造关系为地质学家们所关注.本文研究表明,所谓的桐柏杂岩实际上是一个早白垩世花岗质片麻岩杂岩体,其内包裹一定数量的三叠纪中高级变质岩石.桐柏杂岩南北两条边界韧性剪切带具有相反的运动学指向,分别为大型右行和左行韧性剪切带,其形成时代为131Ma.这两条韧性剪切带中的剪切面理分别朝SSW和NNE向倾斜,韧性剪切带及杂岩体内部发育的拉伸线理均稳定地朝SEE方向缓倾伏.而在杂岩体的东端发育低角度近南北向韧性剪切变形带,其糜棱面理朝SEE方向低角度缓倾斜,矿物拉伸线理也朝SEE方向低角度缓倾伏,运动学标志指示东侧地质体朝295°～310°的方向逆冲.因此,桐柏杂岩实际上被一个顺造山带的韧性剪切带所围限,这个韧性剪切带及杂岩体内部韧性变形运动学指示了一个早白垩世由东向西的低角度抬升过程,而这一过程直接导致了含榴辉岩高压变质地体沿着造山带的方向从地壳深部抬升到近地表.这一研究结果对理解和认识桐柏-大别-苏鲁地区高压一超高压变质地体的晚期抬升过程具有重要意义.
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| 关 键 词： | 桐柏杂岩 韧性剪切带 高压变质地体 抬升机制 |
| 收稿时间： | 2008/11/18 0:00:00 |
| 修稿时间： | 2/9/2009 12:00:00 AM |
Exhumation of high-pressure metamorphic terrane at the crustal levels in the Tongbai area, central China |
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| CUI JianJun,HU JianMin and LIU XiaoChun.Exhumation of high-pressure metamorphic terrane at the crustal levels in the Tongbai area, central China[J].Acta Petrologica Sinica,2009,25(9):2165-2176. |
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| Authors: | CUI JianJun HU JianMin and LIU XiaoChun |
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| Institution: | Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China |
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| Abstract: | The Tongbai complex is situated at the junction between the Qinling and Dabie orogens. On the two sides of the complex, there are two eclogite-bearing high-pressure ( HP) metamorphic belts stretching from NWW to SEE. The issue concerning formation process and special structural relationship between the Tongbai complex and HP metamorphic belts have a strong appeal to geologists. This paper demonstrates that the so-called ' Tongbai complex' is dominated by Early Cretaceous granitic gneisses, with a number of Triassic medium- to high-grade metamorphic rocks. Two ductile shear zones, which formed at 131 Ma, occur alone the southern and northern boundaries of the complex. The strike-slip directions of the shear zones are opposite; the southern boundary is a dextral ductile shear zone, and the northern boundary is a sinistral ductile one. The mylonitic foliations dip to NNE in the northern shear zone, and to SSW in the southern shear zone. In the ductile shear zones as well as the inner part of the Tongbai complex, the stretching lineations invariably dip toward SEE. On the eastern end of the complex, a south-north stretching thrust ductile shear zone occurs, in which low-angle mylonitic foliations dip toward SEE and lineations on the foliations also plunge toward SEE. These dynamic features indicate that the eastern metamorphic terrane thrusted onto the Tongbai complex with a direction of about 295° ～310°. Therefore, the Tongbai complex is actually surrounded by a huge ductile shear zone streching alone the orogen. The deformation characteristics in the shear zone and the inner part of the Tongbai complex suggest a low-angle exhumation for the HP metamorphic terrane from the east to the west along the orogen during the Early Cretaceous, which led to the HP metamorphic rocks being exhumed to the Earth' s surface from the crustal levels. Thus, the present structural observation is very important for understanding the mechanism of late exhumation of the HP/ UHP metamorphic terrane from the Tongbai-Dabie-Sulu region. |
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| Keywords: | Tongbai complex Ductile shear zone HP metamorphic terrane Exhumation mechanism |
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