平南幔源包体中橄榄石的显微构造研究及其意义

孔华; 马芳; 金振民; 欧新功

平南幔源包体中橄榄石的显微构造研究及其意义

孔华^{1, 2},
马芳³,
金振民²,
欧新功¹

1.
中南工业大学地质系, 长沙 410083
2.
中国地质大学地球科学学院, 武汉 430074
3.
北京大学地质学系, 北京 100871

基金项目:

原地质矿产部项目 9501109

国家自然科学基金项目 40002018

详细信息

作者简介:
孔华, 男, 副教授, 1968年生, 1996年毕业于中南工业大学, 获博士学位, 现从事岩石学及显微构造研究

中图分类号: P588.1;P542⁺.5
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出版历程
- 收稿日期: 2000-05-11
- 刊出日期: 2001-01-25

OLIVINE MICROSTRUCTURES FROM MANTLE-DERIVED XENOLITH IN PINGNAN COUNTY, GUANGXI

1.
Department ofGeology, Central-South University of Technology, Changsha 410083, Chin
2.
Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
3.
Department of Geology, Peking University, Beijing 100871, China

摘要

摘要: 平南玄武岩中的尖晶石二辉橄榄岩包体的平衡温度为930~980℃, 平衡深度为59~74km, 包体中橄榄石的扭折带滑移系多为(010) [100], 但也有(001) [100]的滑移系类型; 斜方辉石的滑移系为(100) [001], 它们均为高温低应变速率下的滑移系, 说明该区的上地幔主要是在高温低应变速率条件下经历了塑性变形作用.橄榄石位错组态多样, 有自由位错、位错壁、位错弓弯、缠结、{110}滑移带, 反映了上地幔的塑性变形特征.根据位错壁的大小估算, 上地幔差异流动应力为24.5~42.1MPa, 流动速率为2.93×10^-17~8.36×10^-16s^-1, 有效粘度为1.72×10²³~2.80×10²⁴ Pa·s, 特征与中国东部新生代上地幔较为一致, 反映同处于拉张环境.
- 尖晶石二辉橄榄岩包体 /
- 上地幔 /
- 位错 /
- 平南
Abstract: The equilibrium temperature of the mantle-derived spinel lherzolite xenolith in the basalt in Pingnan County, Guangxi lies between 930 and 980 ℃, and its corresponding equilibrium depth between 59 and 74 km. The kink-band sliding system of the olivine in the mantle-derived xenolith is often (010) [100], but sometimes (001) [100]. However, the kink-band sliding system of orthopyroxene is (100) [001]. All these sliding systems occurred both at the high temperature and at the low strain rate, indicating that the upper mantle of the region experienced the plastic deformation both at the high temperature and at the low strain rate. Varieties of dislocations are present in the olivine, such as free dislocation, dislocation wall, dislocation bow, tangle, and (110) sliding system, indicating the plastic deformation features of the upper mantle. The size of the dislocation is used to estimate the following features of the upper mantle: the differential flow stress 24.5-42.1 MPa, the flow rate 2.93×10^-17 -8.36×10^-16s^-1, the effective viscosity η 1.72×10²³-2.80×10²⁴ Pa·s. All these upper-mantle features are in agreement with those in the Cenozoic eastern China, showing that they both occurred in the same tensile environment.
- spinel lherzolite xenolith /
- upper mantle /
- dislocation /
- Pingnan

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图 1 橄榄石和斜方辉石的滑移系

a.橄榄石的扭折带滑移系; b.橄榄石的扭折带滑移系; c.辉石的扭折带滑移系

Fig. 1. Measured slip system of olivine and orthopyroxene

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图 2 尖晶石二辉橄榄岩中橄榄石的优选方位

下半球投影, 等值线: 1%-3%-5%-7%, Mf5.90颗; Ml-2f2.85颗; Mf2.100颗.L.线理

Fig. 2. Preferred orientation of olivine [100], [010], [001] in spinel lherzolite

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表 1 橄榄岩包体的矿物化学成分

Table 1. Minerals' chemical composition of lherzolite xenolith

表 2 二辉橄榄岩的平衡温度、压力、平衡深度

Table 2. Balanced temperature, pressure and depth of lherzolite

表 3 平南新生代上地幔流动应力估算

Table 3. Calculation of differential flow stress

表 4 平南新生代上地幔流变学参数

Table 4. Rheological parameters of upper mantle beneath Pingnan area

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