印度西达尔瓦克拉通西南部梅尔卡拉剪切带(MSZ)钙碱性花岗岩的岩石学、地球化学和岩石成因:大陆弧岩浆活动和深地壳熔融的迹象

IF 1.3 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Prantick Santra, Rigzin Norboo, Anindya Bhattacharya
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引用次数: 0

摘要

梅卡拉剪切带(MSZ)是西达尔瓦克拉通(WDC)和库尔格地块(CB)之间并列的一个强烈变形、弯曲、绵延的区域。在马迪凯里镇附近,MSZ 露出了许多花岗岩级元超硬岩和黑云母花岗岩的带状和飞地,这些花岗岩寄生在黑云母或长英质正长片麻岩(后退黑云母)中。随后,该地区被剪切带中轴线上的花岗岩侵入,没有变质特征。关于该剪切带的花岗岩级岩石的起源和形成时间,目前尚无明确的观点,而未变质的花岗岩群也未根据地形的演变进行详细研究。为了解决这个问题,我们对来自澳门特别行政区的未变质花岗岩组进行了实地关系、岩石学和大块岩石地球化学研究。岩石学和地球化学数据表明,这些花岗岩属于I型。痕量元素和稀土元素(REE)模式表明岩浆弧背景。岩石是钙碱性的,稀土元素模式是分馏的,富含 Ba、Sr,而 Nb、Ta 和 Ti 等高场强元素则是贫化的,几乎没有明显的负 Eu 异常。这些特征表明,在熔体的生成过程中,地壳的参与比地幔占主导地位。研究样品显示出 "类似阿达克岩 "的地球化学特征(高 Sr/Y、La/Yb),但并非典型的板块熔融产物。本研究表明,花岗岩来自厚地壳源,是在 941-985°C 和 10-12.5 千巴压力(相当于 30-40 千米深度)的氧化条件(fO2 介于 NNO 和 HM 缓冲之间)下部分熔化而成的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Petrography, geochemistry and petrogenesis of calc-alkaline granitoids from the Mercara Shear Zone (MSZ), southwest of West Dharwar Craton, India: Indication of continental arc magmatism and deep-crustal melting

Petrography, geochemistry and petrogenesis of calc-alkaline granitoids from the Mercara Shear Zone (MSZ), southwest of West Dharwar Craton, India: Indication of continental arc magmatism and deep-crustal melting

The Mercara Shear Zone (MSZ) is an intensely deformed, curvilinear, mylonitised zone juxtaposed between the Western Dharwar Craton (WDC) and the Coorg Block (CB). In the vicinity of Madikeri town, the MSZ exposes many bands and enclaves of granulite-grade meta-supracrustals and mafic granulites hosted within charnockite or felsic orthogneiss (retrogressed charnockite). Subsequently, the area is intruded by a suite of granitoids along the mid-axis of the shear zone, showing no signature of metamorphism. Views on the origin and timing of the formation of the granulite-grade rocks of the MSZ are not streamlined, and the unmetamorphosed suite of granitoids has not been studied in detail in light of the evolution of the terrain. The field relationship, petrography and bulk rock geochemistry of the suite of unmetamorphosed granitoids from the MSZ were carried out to address this issue. Petrological and geochemical data indicate an I-type affinity of the granitoids. Trace and rare earth element (REE) patterns suggest a magmatic arc setting. The rocks are calc-alkaline, and the REE pattern is fractionated, enriched in Ba, Sr, and depleted in high field strength elements like Nb, Ta, and Ti with almost no significant negative Eu anomaly. These characteristics indicate the dominance of crustal involvement over the mantle in the generation of melt. Studied samples show ‘adakite-like’ geochemical characteristics (high Sr/Y, La/Yb) but are not the product of typical slab melting. The present study indicates that the granitoids were derived from a thick crustal source by partial melting in an oxidized condition (fO2 between NNO and HM buffer) at 941–985°C and 10–12.5 kbar pressure (corresponding to 30–40 km depth).

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来源期刊
Journal of Earth System Science
Journal of Earth System Science Earth and Planetary Sciences-General Earth and Planetary Sciences
CiteScore
3.20
自引率
5.30%
发文量
226
期刊介绍: The Journal of Earth System Science, an International Journal, was earlier a part of the Proceedings of the Indian Academy of Sciences – Section A begun in 1934, and later split in 1978 into theme journals. This journal was published as Proceedings – Earth and Planetary Sciences since 1978, and in 2005 was renamed ‘Journal of Earth System Science’. The journal is highly inter-disciplinary and publishes scholarly research – new data, ideas, and conceptual advances – in Earth System Science. The focus is on the evolution of the Earth as a system: manuscripts describing changes of anthropogenic origin in a limited region are not considered unless they go beyond describing the changes to include an analysis of earth-system processes. The journal''s scope includes the solid earth (geosphere), the atmosphere, the hydrosphere (including cryosphere), and the biosphere; it also addresses related aspects of planetary and space sciences. Contributions pertaining to the Indian sub- continent and the surrounding Indian-Ocean region are particularly welcome. Given that a large number of manuscripts report either observations or model results for a limited domain, manuscripts intended for publication in JESS are expected to fulfill at least one of the following three criteria. The data should be of relevance and should be of statistically significant size and from a region from where such data are sparse. If the data are from a well-sampled region, the data size should be considerable and advance our knowledge of the region. A model study is carried out to explain observations reported either in the same manuscript or in the literature. The analysis, whether of data or with models, is novel and the inferences advance the current knowledge.
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