藏东南措美大火成岩省含水火成杂岩体成因
发布时间：2019-01-05 02:16
【摘要】：大火成岩省一般以大面积近同期喷发的玄武质岩石为主,含少量长英质岩石,并具有高的地幔潜温和低的水含量。但出露于青藏高原东南部特提斯喜马拉雅带东段的措美大火成岩省,却具有多样化的岩石类型,包括玄武岩、辉绿岩墙/岩床、辉长岩侵入体和少量层状苦橄玢岩、辉石岩、闪长质岩墙/岩床和酸性火山岩。这种多样化的岩石类型使措美大火成岩省成为研究大火成岩省中成分多样性的原因和准确刻画岩浆过程的理想研究对象。早期研究主要聚焦在分布范围、区域年代学格架、玄武质岩石的源区和成因等方面,并不清楚苦橄玢岩、辉石岩和闪长质岩石的原始岩浆成分、熔融条件(包括温度、压力和含水性)和岩浆演化过程,直接限制了对措美大火成岩省岩浆成因机制的理解。因此,本论文选取措美大火成岩省东部错那地区的苦橄玢岩和相关玄武岩、中部哲古措地区的辉石岩-辉长岩-闪长质侵入杂岩为研究对象,复原原始岩浆成分和熔融条件,分析岩浆演化过程和岩石成因,约束不同岩性之间的成因关联,为刻画大火成岩省岩浆成分多样性的原因提供研究实例。本论文获得的主要结论如下:(1)错那地区苦橄玢岩的母岩浆的MgO为约20 wt.%,对应的地幔潜温1550℃。为措美大火成岩省地幔柱成因提供了关键性的约束。错那苦橄玢岩和共生玄武岩具有平行的微量元素分布型式和相似的Nd和Os同位素组成表明两者来自同一地幔源区。(2)哲古措地区发育有橄榄二辉岩、辉长岩、角闪辉长岩、辉绿岩、闪长岩、石英闪长岩和英云闪长岩岩脉或岩墙,构成一套成分连续且多样的侵入杂岩。两件闪长质岩石样品的锆石U-Pb年龄均为约133 Ma,与措美大火成岩省主要岩浆作用时限一致。根据其Nd同位素特征共分为两个系列:辉石岩和组I辉长岩系列和组II辉长质岩石和闪长质岩石系列。辉石岩和组I辉长岩具有负的εNd(t)值,微量元素和同位素模拟表明两者为原始岩浆经历地壳混染作用和橄榄石-辉石结晶分异作用的结果。组II辉长质岩石和闪长质岩石具有与措美大火成岩省主体玄武质岩石一致的正εNd(t)值,为一套完整的分离结晶序列。(3)上述岩浆杂岩的单斜辉石-熔体平衡温压计和角闪石单矿物温压计和湿度计计算结果表明措美大火成岩省存在多层次的岩浆房。原始岩浆在约20~30 km的下地壳岩浆房发生橄榄石-辉石结晶分异和/或地壳混染形成了错那苦橄玢岩和分异的玄武质岩浆以及哲古措辉石岩和组I辉长岩。而分异的玄武质岩浆在上地壳约6 km的岩浆房发生单斜辉石、角闪石、斜长石和榍石的分离结晶形成哲古措组II辉长质岩石和闪长质岩石。水含量是玄武质岩浆结晶分异形成中性岩的重要控制因素。
[Abstract]:In the major igneous provinces, Black Tortoise rocks erupting in a large area at the same time mainly contain a small amount of feldspathic rocks and have high mantle potential and low water content. However, the Tom 茅 great igneous province, which is exposed to the eastern segment of the Tethys Himalayan belt in the southeast of the Qinghai-Tibet Plateau, has a variety of rock types, including basalt, diabase dikes / beds, gabbro intrusions and a small amount of layered picrite porphyrite, pyroxenite, and pyroxenite. Diorite dykes / beds and acid volcanic rocks. This diverse rock type makes the province of igneous rocks in Thumei an ideal research object for studying the causes of composition diversity and accurately depicting magmatic processes in the major igneous provinces. Early studies focused on distribution, regional chronological framework, provenance and genesis of Black Tortoise rocks. It was not clear that the primitive magmatic composition, melting conditions (including temperature) of picrite porphyrite, pyroxenite and diorite, Pressure and water-bearing) and magmatic evolution process directly limit the understanding of magmatic genesis mechanism in Tomai great igneous province. Therefore, this paper selects picrite porphyrite and related basalts in Moena area, eastern part of Cumei igneous province, and pyroxenite-gabbro diorite intrusive complex in the central Zegusuo area as the research object, and recovers the original magmatic composition and melting conditions. By analyzing the evolution process of magma and the origin of rocks, the genetic correlation between different lithology is restricted, which provides an example for the study of the reasons for the diversity of magma composition in the great igneous province. The main conclusions obtained in this paper are as follows: (1) the MgO of the parent magma of picrite porphyrite in Sona area is about 20 wt.%, corresponding to the mantle latent temperature of 1550 鈩，
本文编号：2401127
[Abstract]:In the major igneous provinces, Black Tortoise rocks erupting in a large area at the same time mainly contain a small amount of feldspathic rocks and have high mantle potential and low water content. However, the Tom 茅 great igneous province, which is exposed to the eastern segment of the Tethys Himalayan belt in the southeast of the Qinghai-Tibet Plateau, has a variety of rock types, including basalt, diabase dikes / beds, gabbro intrusions and a small amount of layered picrite porphyrite, pyroxenite, and pyroxenite. Diorite dykes / beds and acid volcanic rocks. This diverse rock type makes the province of igneous rocks in Thumei an ideal research object for studying the causes of composition diversity and accurately depicting magmatic processes in the major igneous provinces. Early studies focused on distribution, regional chronological framework, provenance and genesis of Black Tortoise rocks. It was not clear that the primitive magmatic composition, melting conditions (including temperature) of picrite porphyrite, pyroxenite and diorite, Pressure and water-bearing) and magmatic evolution process directly limit the understanding of magmatic genesis mechanism in Tomai great igneous province. Therefore, this paper selects picrite porphyrite and related basalts in Moena area, eastern part of Cumei igneous province, and pyroxenite-gabbro diorite intrusive complex in the central Zegusuo area as the research object, and recovers the original magmatic composition and melting conditions. By analyzing the evolution process of magma and the origin of rocks, the genetic correlation between different lithology is restricted, which provides an example for the study of the reasons for the diversity of magma composition in the great igneous province. The main conclusions obtained in this paper are as follows: (1) the MgO of the parent magma of picrite porphyrite in Sona area is about 20 wt.%, corresponding to the mantle latent temperature of 1550 鈩，
本文编号：2401127
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