大别——苏鲁高压-超高压变质带的“构造增压壳内成因”研究

发布时间：2018-06-08 22:52

  本文选题：大别超高压变质带 + 重力-构造力复合压力　； 参考：《地学前缘》2017年02期

【摘要】：研究发现,高压-超高压变质岩基本都发育于全球或区域规模的大型构造带,产于强烈构造变形带中相对较弱应变的部位。苏鲁—大别超高压变质岩具有明显的构造变形,这成为追索构造应力-应变作用和探讨形成构造环境与演化过程的重要线索。本研究用成岩成矿深度的"构造校正测算方法",进行野外观察、岩石变形-应力测算及构造校正测算。其结果显示,超高压变质岩形成深度在23~55km之间。大别—苏鲁超高压变质岩的锆石SHRIMP年龄显示,具有环带的内核高压矿物年龄大于680 Ma,而其含柯石英幔圈里超高压变质矿物在(231±4)Ma形成,角闪岩相等退变质矿物形成在(211±4)Ma,可见超高压变质发生在陆缘和陆内的地质环境。综合研究其岩石矿物的Sr-Nd、O和He同位素含量,有力证明了岩石的壳内成因特征。深钻孔岩心的岩石矿物学系统显示,超高压变质岩及其几公里宽范围里的各类围岩普遍含有柯石英等高压-超高压矿物包体。上述实际资料,用超高压变质的"深俯冲-折返"模式已经不能得到科学的解释。本文提出大别—苏鲁超高压变质岩"构造增压壳内成因模式",认为这些超高压变质作用可能发育在陆内地块之间的强烈构造挤压环境。在230Ma左右,由于构造压力与重力压力叠加致使局部达到超高压及相应温度等条件,特别是当p≥2.8GPa时,变质的物理化学条件得到满足,可以在23~55km深处发生超高压变质作用,之后经应力松弛和拆离构造,岩石又逐步抬升并发生退变质作用。也可以说,该超高压变质岩具有构造物理化学成因。
[Abstract]:It is found that the high-pressure ultrahigh pressure metamorphic rocks are mainly developed in large tectonic zones on a global or regional scale, and occur in the relatively weak strain areas of the strong tectonic deformation zones. The ultrahigh pressure metamorphic rocks of Sulu-Dabie have obvious tectonic deformation, which is an important clue for tracing tectonic stress-strain action and exploring the tectonic environment and evolution process. In this study, the "structural correction method" of diagenetic metallogenic depth was used to carry out field observation, rock deformation-stress calculation and structural correction calculation. The results show that the formation depth of UHP metamorphic rocks is between 23~55km. The zircon shrimp age of the Dabie Sulu ultrahigh pressure metamorphic rocks shows that the core high pressure mineral age of the annular zone is greater than 680 Ma, while the ultrahigh pressure metamorphic minerals in the coesite mantle circle were formed at 231 卤4 Ma. The equivalent retrograde metamorphic minerals of amphibolite were formed at 211 卤4 Ma, indicating that the ultrahigh pressure metamorphism occurred in the continental margin and within the continental geological environment. A comprehensive study of the Sr-NdN _ O and he isotopic contents of its rock minerals shows that the genetic characteristics of the rocks in the crust are proved. The petro-mineralogical system of the deep-drilled core shows that the ultrahigh pressure metamorphic rocks and their surrounding rocks in a wide range of several kilometers generally contain high-pressure and ultra-high pressure mineral inclusions such as coesite. The above data can not be explained scientifically by using the "deep subduction-reentrant" model of ultrahigh pressure metamorphism. In this paper, the authors put forward the "genetic model of tectonic pressurized crust" of the Dabie Sulu ultrahigh pressure metamorphic rocks, and considered that these ultrahigh pressure metamorphic processes may have developed in a strong tectonic compression environment between the continental blocks. At 230 Ma or so, the superposition of tectonic pressure and gravity pressure resulted in local ultra-high pressure and corresponding temperature, especially when p 鈮，

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