流体孔隙剪切变形与岩石圈层状运动机理  

Fluid Pore Shearing Strain and the Mechanism of Layered Lithosphere Motion

作　　者：张永北[1,2,3,4] 毕华 余龙师 孙世华[4] 邱家骧[3] 王人镜[3] 

机构地区：[1]海南省农垦科学院,海口570206 [2]海南省师范大学资源环境与旅游学院,海口570207 [3]中国地质大学(武汉)地球科学学院,武汉430074 [4]中国科学院地质与地球物理研究所,北京100101

出　　处：《地质论评》2012年第5期801-808,共8页Geological Review

摘　　要：在岩石圈层状滑移系统中,如大陆地壳俯冲叠置构造、逆冲推覆断层、拆离断层、滑坡等系统,近于水平的断裂带上存在许多有一定压力的流体孔隙。如果这些流体孔隙是密闭的,便可看成液压千斤顶的液缸。那么,断层面以上滑移体的重量S_T不仅被断裂带上的固体支撑,也受孔隙液体举托力F_f支撑。设F_f与S_T之比为R,那么R就是一个描述滑移体滑移运动难易程度的重要参数。R值越大,滑移体越容易被移动(推动)。而岩石圈中层状滑移系统滑脱面的剪切变形可以显著地改变该参数的大小,从而对层状滑移运动产生深刻的影响。设剪切面上孔隙流体平均压强初始值为P_0,剪切角为α,剪切变形后的平均压强为P(α),R(α)-α间存在下式的函数关系:R(α)=(R_0P(α))/(P_0cosα)由此可见,R(α)与P(α)正相关,与剪切角α也正相关。P(α)与剪切角α的函数关系目前还难以给出,但剪切过程中,流体孔隙压强保持不变的恒压过程是常见的,即P(α)=P_0。将该等式代入上式(1),即可获得下式:R(α)=(R_0)/(cosα),[P(α)=P_0,即恒压过程]由此作出恒压剪切过程的R(α)-α图解。从而发现,恒压剪切过程中,只要滑脱面上密闭流体孔隙存在初始压强,即R_0>0,那么,R(α)随α增长,当剪切角α达到一定程度,R(α)迅速超过1;R_0越大,实现R(α)>1所需的α值越小;反之,所需的α值越大。由此证明,密闭流体孔隙经过恒压剪切变形,导致R(α)>1的基本规律。非恒压过程总体规律不变。R(α)>1意味着层状滑移体完全被孔隙流体的浮托力支持。从而揭示岩石圈俯冲——推覆体及拆离机理和滑坡爆发的可能机制。In a layered lithosphere slipping system,there are many pores filled of fluid with a certain pressure. Supposing the floating force caused by the pore fluid pressure in the slipping plane is Ff,the loading weight of bedding slipping block is ST,then a new index of R,the ratio of Ff to ST,can be given,that is very important to describe the layered slipping motion of lithosphere being easy or difficult.Actually,shearing strain in lithosphere can outstandingly change the value of R.In this paper the authors try to derive a dynamic equation in order to describe the relationship between R and the shearing angle（α） as formula（1）： R（α） =R0P（α）/P0cosα（1） According above formula（1）,R（α） is positive correlation with P（α）,and also is positive correlation with shearing angleα.Now,it is difficult to give the formula to describe the relationship between P（α） andα,but the pore fluid keeping at a constant pressure is common case in the shearing strain process,that is P（α） = P0. Therefore,replacing P（α） with P0 of above formula（1）,the following formula（2） can be gotten： R（α）=R0/cosα------,[P（α） = P0,constant pressure]（2） and then R（α）-—αdiagram of constant pressure shearing process can be drawn,in which the regularity can be discovered as follows：in the shearing strain process of constant pressure,if R0〉0,R（α） is increasing withα;as the shearing angleαgoing up at a certain value,R（α） runs up its value exceed 1 rapidly;and the more R0 is,the less theαis for R（α）〉1;otherwise,the more theαis.The case of R（α）〉1 means that the bedding slipping block is totally supported by pore fluid pressure.This regularity reveals a possible outbreaking mechanism of subduction—thrust nappe or detachment structure or landslide in lithosphere.

关 键 词：流体孔隙 构造物理 构造 大陆动力学 岩石圈运动 大陆深俯冲 滑坡 剪切增浮原理 

分 类 号：P584[天文地球—岩石学]