Alkali Granites with Pan-African Affinities from Kerala, S. India
Alkali Granites with Pan-African Affinities from Kerala, S. India
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来自印度南部喀拉拉邦的具有泛非亲缘关系的碱性花岗岩
DOI：
10.1086/629257
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
S. Drury
中科院分区：
文献类型：
--
作者：
M. Santosh;S. Drury
在印度南部的喀拉拉邦地区，侵入了前寒武纪紫苏花岗岩和混合岩，年龄在550 ~ 740 Ma之间。所有这些都与区域断层线性构造在空间上有关。它们的地球化学特征类似于非洲-阿拉伯地盾的泛非后运动学岩体。岩石成分为花岗质-二长花岗岩质，富SiO2、K2 O（高达12%）和Na 2 O，低CaO、FeO和MgO。它们的主量元素组成以及其中一个岩体的低$^{87}Sr/^{86}Sr_{I}$（0.703）表明它们具有A型亲合性。然而，当地的紫苏花岗岩具有如此低的Rb和放射成因的$^{87}Sr$，花岗岩可能是由地壳熔融形成的。它们的总体微量元素特征一般是典型的碱性花岗岩，但细节表明，大多数类似于最近的火山弧花岗岩，一个岩体是典型的板内环境。富CO2流体包裹体的存在支持了稀土和高场强元素的富集与岩浆演化过程中碳流体的高通量有关的观点。岩体沿着与裂谷有关的断层的情况表明，岩浆活动表现出与印度大陆和超大陆的前裂谷构造有关的伸展阶段，在泛非期间，印度大陆是超大陆的一部分。
In the Kerala region of the south Indian shield alkali-granite plutons ranging in age from 550 to 740 Ma intrude Precambrian charnockites and migmatites. All of them are spatially related to regional fault-lineaments. Their geochemistry is similar to Pan-African post-kinematic plutons from the Afro-Arabian shield. They are of granitic to adamellitic composition, with high $SiO_{2}, K_{2}O$ (up to 12%), and $Na_{2}O$, and low CaO, FeO, and MgO. Their major element composition, together with a low $^{87}Sr/^{86}Sr_{I}$ (0.703) from one pluton, denote A-type affinities. However, local charnockites have such low Rb and radiogenic $^{87}Sr$ that the granites could have formed by crustal melting. Their overall trace element characteristics are typical of alkaline granites in general, but the details show that most resemble more recent volcanic-arc granites, and one pluton is typical of a within-plate setting. The presence of $CO_{2}$-rich fluid inclusions supports the notion that the enrichment of rare-earth and high field strength elements is related to high fluxes of carbonic fluids during the magma evolution. The situation of the plutons along rift-related faults suggests that the magma-tism manifests an extensional phase associated with the pre-rift tectonics of the Indian continent and the supercontinent of which it was a part during the Pan-African.