湘西通道地区新元古代长界橄榄辉石岩中单斜辉石矿物学特征及其板内裂谷成因论证

发布时间：2018-01-26 00:50

本文关键词： 长界橄榄辉石岩单斜辉石拉斑玄武质岩浆软流圈物质上涌板内裂谷环境江南造山带　出处：《地质论评》2017年04期 　论文类型：期刊论文

【摘要】：湘西通道地区长界橄榄辉石岩主要组成矿物为单斜辉石、橄榄石和斜长石,还具有少量的Ti—Fe氧化物。本文利用电子探针对江南造山带西段湘西通道地区长界橄榄辉石岩单斜辉石进行了详细的矿物学研究,研究结果表明单斜辉石属于顽透辉石和普通辉石。长界橄榄辉石岩单斜辉石较富镁而贫铁,并且还具有高硅、贫碱、低钙的特征,其母岩浆属于拉斑玄武系列。单斜辉石温压计算结果显示,橄榄辉石岩的形成温度为1260～1383℃,压力为1.5～2.6GPa,深度为50～86km,平均深度为73km。整体来看,长界橄榄辉石岩形成的温度基本与软流圈地幔的温度(1280～1350℃)相当,其形成深度为约73km的地幔深处,且在这种温压条件下,软流圈地幔可以发生减压熔融。单斜辉石的成分特征显示示长界橄榄辉石岩是板内拉斑玄武岩,指示其构造背景为裂谷环境。另外,单斜辉石具低的Al_2O_3(0.02%～5.51%)、TiO_2(0～0.46%)和Na_2O(0.01%～1.44%)的特征,这可能是单斜辉石寄主岩石岩浆源区受到俯冲熔体/流体的交代改造作用所导致。结合作者和前人的研究结果,我们推测长界橄榄辉石岩源区为软流圈地幔,其形成可能与裂谷作用导致软流圈物质上涌并发生熔融有关,且在形成长界橄榄辉石岩之前,软流圈地幔已经遭受过俯冲熔体/流体的交代改造作用。
[Abstract]:Xiangxi channel area long circle olivine pyroxenite consisting mainly of clinopyroxene, olivine and plagioclase, also has Ti Fe a small amount of oxide. In this paper, by means of electron probe of mineral detailed study of Jiangnan orogenic belt in Xiangxi area long channel circles olivine pyroxenite clinopyroxene, the results of the study show that clinopyroxene belongs to the coercivity of penetration diopside and augite. Long circle olivine pyroxenite clinopyroxene is rich in magnesium and iron poor, and also has the characteristics of high silicon, low alkali, low calcium, its parent magma belongs to tholeiitic series. The clinopyroxene temperature and pressure calculation results show that the formation of the olive pyroxenite temperature is 1260 to 1383 DEG C, pressure the depth of 1.5 ~ 2.6GPa, 50 ~ 86km, the average depth is 73km. overall, long circle olivine pyroxenite formation temperature and asthenosphere mantle temperature (1280 ~ 1350 DEG C), the formation depth is about 73km deep mantle In this place, and the temperature and pressure conditions, asthenospheric mantle can occur. Decompression melting composition characteristics of clinopyroxene showing long circle olivine pyroxenite is plate tholeiite, indicating its tectonic background for the rift. In addition, clinopyroxene with low Al_2O_3 (0.02% ~ 5.51%), TiO_2 (from 0 to 0.46%) and Na_2O (0.01% ~ 1.44%) features, which may be clinopyroxene host rock magma source region by subduction metasomatic alteration fluid / melt caused. Combined with the research results and the author of previous studies, we hypothesized that long circle olivine pyroxene rocks as asthenospheric mantle, its formation may be related to the rifting caused upwelling of the asthenosphere and melt, and before the formation of long circle olivine pyroxenite, asthenospheric mantle metasomatism has suffered the transformation of subduction melts / fluids.

【作者单位】：中国地质科学院地质研究所;广西壮族自治区地质调查院;
【基金】：国家自然科学基金资助项目(编号:41402052) 基本科研业务费资助项目(编号:J1602) 中国地质调查项目(编号:1212011120117和1212011120115)~~
【分类号】：P588.125
【正文快照】： 注:本文为国家自然科学基金资助项目(编号:41402052)、基本科研业务费资助项目(编号:J1602)和中国地质调查项目(编号:1212011120117和1212011120115)的成果。江南造山带构造岩浆活动非常复杂,一直以来是学界研究的热点及重点地区。前人研究基本查明江南造山带形成于新元古代时

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