FRICTIONAL SLIDING OF PLAGIOCLASE GOUGE UNDER LOWER-CRUST TEMPERATURE AND RELATIVELY LOW EFFECTIVE NORMAL STRESS

doi:10.3969/j.issn.0253-4967.2016.02.005

Abstract

Abstract:

The discovery of tremors on the lower crust portion of the San Andreas Fault has attracted more attention on the mechanical properties of the lower crust in recent years, and some experimental studies have been carried out to understand the mechanical behavior. Previous experiments under effective normal stresses of 200MPa have shown that pyroxene and plagioclase mineral separated from the gabbro and their mixtures all show velocity weakening in the lower-crust temperature range, which results in unstable slip when frictional sliding is the dominant deformation mechanism. This work is to examine whether the velocity-weakening behavior of plagioclase gouge also applies to relatively lower effective normal stress. Our experiments were performed under effective normal stress of about 100MPa, with a constant confining pressure control, with pore pressure of 30MPa and temperature of 100℃ to 600℃. We found that the frictional sliding of plagioclase are basically the same with the previous results obtained under effective normal stress of 200MPa, both of which show velocity weakening over the entire temperature range. The only difference is the out-of-trend drop of constitutive parameter a at 600℃ for the lower effective normal stress of 100MPa. It is thus concluded that reducing the effective normal stress has little effect on the sliding stability of plagioclase, and the previous conclusion made for mechanical behavior of the lower crust that unstable slips are possible therein also applies to the lower effective normal stress of 100MPa.

Key words: low effective normal stress, plagioclase, velocity weakening, sliding instability, lower crust

摘要：

近年来圣安德烈斯断层在下地壳深度上震颤的发现使其力学性质引起了更多的关注。文中对斜长石断层泥在低正应力条件下的摩擦滑动性质进行了实验。实验条件为有效正应力100MPa，采用围压控制，温度100～600℃，孔隙水压30MPa。通过对比有效正应力为200MPa，其他条件都相同时的实验结果发现，斜长石的摩擦滑动力学行为基本一致，仅在本构参数a值随温度的变化规律上略有差异，但在整个温度范围均呈速度弱化。由此可见，有效正应力的降低对斜长石的摩擦滑动行为影响不大，因而在下地壳可以产生不稳定滑动的结论仍然成立。

关键词: 较低正应力, 斜长石, 速度弱化, 不稳定滑动, 下地壳

CLC Number:

P315.2

YAO Sheng-nan, HE Chang-rong. FRICTIONAL SLIDING OF PLAGIOCLASE GOUGE UNDER LOWER-CRUST TEMPERATURE AND RELATIVELY LOW EFFECTIVE NORMAL STRESS[J]. SEISMOLOGY AND GEOLOGY, 2016, 38(2): 290-302.

姚胜楠, 何昌荣. 斜长石在下地壳温度及较低有效压力条件下的摩擦滑动[J]. 地震地质, 2016, 38(2): 290-302.

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