上地壳环境中的流体作用与灰岩的脆—韧性转变

对取自西南非纳米比亚Damara造山带Waterberg断层带中的细粒灰岩的变形结构与亚微结构开展的多方面综合研究 ,揭示出在流体相遍布的上部地壳环境中 ,细粒灰岩的变形属性具有双重性 :脆性与晶质塑性。这种双重性突出表现在破裂与微破裂构造的广泛发育 ,以及细粒动态重结晶颗粒沿着破裂带 (面 )的出现。导致这种双重过程的主要因素在于岩石变形作用过程中流体相的介入。破裂与微破裂的出现 ,为流体相介入岩石变形提供了通道 ,使得流体相能够弥散于高应变带及高应变晶体内。水解弱化是流体相影响岩石变形的重要机理。流体相促进位错滑移与攀移 ,并加速应变颗粒的恢复作用 ,以协调破裂过程。

FLUID FLOW AND BRITTLE TO DUCTILE TRANSITION OF LIMESTONE UNDER THE UPPER CRUSTAL CONDITIONS

The synthetical analysis of faulted limestone from the Waterberg fault zone in the Damara Orogen, Namibia, Southwest Africa indicates a duplicity of the deformation of the limestone: brittle and crystalline plasticity. The duplicity is shown by the co-existence of fractures and microfractures, and dynamically recrystallized grains distributing along the fractures. The major factor leading to the duplicity is attributed to the involvement of fluid phases (dominated with water) in the deformation of the rocks. The occurrence of fractures and microfractures provides fluid-passes for the involvement of fluid in the deformation, which makes the fluids dissipated in highly strained grains and along high strain zones in the fault zone. Hydrolytic weakening is the dominant mechanism effective during the fluid-involved deformation. Fluid enhances dislocation glide and climb, increases the rate of recovery of strained grains and accommodates the fracturing.