地壳深部“重力-构造力复合压力状态”研究和大别-苏鲁超高压变质形成深度的测算

摘要

讨论了地壳深部岩石处于“重力-构造力复合的静水压力模型”.此模型的基本认识为,地壳深部压力是由重力应力和构造应力引起的两部分各向等应力合成的,构造应力场的静水压力部分被称为“构造附加静水压力”.遵循这一认识,需要从总静水压力中先去掉构造附加静水压力,进而用构造校正[深度=重力引起压力/(总压力-构造附加的压力)]的方法,进行形成深度的测算.考虑岩石作为黏弹性体的应力-应变关系,作者用黏弹性本构方程,获得大别地区英山县含柯石英榴辉岩的成岩深度≥30 km,安徽岳西碧溪岭地区含柯石英榴辉岩深度为23～53 km,河南新县地区的含柯石英榴辉岩成岩深度为36～40 km.再进一步用变质深度的流变学公式,在黏性系数0.2×1023条件下,推算出超高压变质岩形成深度约50～55 km.可见,大别超高压变质岩形成深度介于23～55 km,而不是前人认为的超过100 km甚至更深,由此,“深俯冲-折返”模式需要科学的论证.本研究为高压-超高压变质的“构造增压壳内成因”提供了一些依据.%In this paper,we put forth a discussion about the deep crustal "gravity-tectonic force composite hydrostatic pressure model".The basic understanding of this model is that the deep crustal pressure is composed of two equal parts:gravity and tectonic stress where the tectonic stress field is called "the tectonic additional static pressure".According to this model,it is necessary to remove the tectonic additional static pressure from the total pressure,and then use the structural correction method[depth =gravity induced pressure/(total pressure-additional structural pressure)] to calculate the formation depth.Considering the stress-strain relationship of viscoelastic rock,authors used viscoelastic constitutive equation and obtained the diagenesis depth of coesite-bearing eclogites of ≥30 km in Dabie region Yingshan County,23-53 km in Anhui Yuexi Bixiling region,and 36-40 km in Henan Xinxian region,respectively.Furthermore,using rheology formula for the metamorphic depth calculation,and shear viscosity value of 0.2 × 1023,the formation depth of UHPM rocks was found to be about 50-55 km.Obviously,the formation depth of the Dabie UHPM rocks is between 23-55 km,rather than the previous view of more than 100 km or deeper.Thus,the "deep subduction-reentry" model requires a scientific proof.This research provides some evidence on the high-and ultrahigh-pressure metamorphism by "tectonic pressure shell causes".