Geochemistry of Khandadharpahar-Thakuranipahar metabasites from the western Singhbhum Craton, eastern India: implications for subduction-zone tectonics and mantle-wedge metasomatism

IF 1.3 4区地球科学 Q2 GEOLOGY

Geologica Acta Pub Date : 2022-09-16 DOI:10.1344/geologicaacta2022.20.11

R. Rajani

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Abstract

The identification of new rock types in the volcano-sedimentary sequences of the Singhbhum Craton has attractedmuch attention in recent years. The present study deals on newly identified Nb-Enriched Basalts (NEB) from theKhandadharpahar-Kadakala-Thakuranipahar (KKT) section, western Singhbhum Craton, which is comparablein composition to basalts-basaltic andesites and calk-alkaline in character. These metabasites have a porphyritictexture with phenocrysts of pyroxene and plagioclase, as well as a groundmass that has metamorphosed to thegreenschist facies. High Nb contents (7.5-22.8ppm) combined with high (Nb/Th)PM (0.28-0.59), (Nb/La)PM (0.40-0.69) and Nb/U (11.7-34.4) ratios, compared to arc basalts ((Nb/Th)PM= 0.10-1.19; (Nb/La)PMn 0.17-0.99, Nb/U<10), characterized them as NEB. Negative Nb, Zr, Hf and Ti anomalies, and Nb/Th vs La/Nb and Th/Nb vs. La/Sm relationships, collectively indicate typical arc volcanics. The available geochemical parameters suggest a genesisof KKT metabasites through i) slab melt migration from the downgoing oceanic crust, ii) low-degree melting ofthe garnet-bearing peridotite in the mantle wedge metasomatized by the slab melts, iii) slab melt - peridotiteinteraction triggering increasing Nb concentrations and iv) NEB generation in an arc-related environment. Thediscovery of KKT NEB sheds new information on Paleoproterozoic subduction-zone processes and crustal growthin the Singhbhum craton.

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印度东部Singhbhum克拉通西部Khandadharpahar Thakuranipahar变质玄武岩的地球化学：对俯冲带构造和地幔楔交代作用的影响

近年来，在Singhbhum火山口火山沉积序列中识别新的岩石类型引起了人们的广泛关注。本研究对Singhbhum克拉通西部Khandadharpahar Kadakala Thakuranipahar（KKT）剖面新发现的富铌玄武岩（NEB）进行了研究，其成分与玄武岩、玄武岩、安山岩和钙碱性玄武岩相当。这些变质玄武岩具有含辉石和斜长石斑晶的斑状结构，以及变质为绿片岩相的岩体。高Nb含量（7.5-22.8ppm）与高（Nb/Th）PM（0.28-0.59）、（Nb/La）PM（0.40-0.69）和Nb/U（11.7-34.4）比率相结合，与弧玄武岩（（Nb/Th）PM=0.10-1.19）相比；（Nb/La）PMn 0.17-0.99，Nb/U<10），将其表征为NEB。Nb、Zr、Hf和Ti负异常，以及Nb/Th与La/Nb和Th/Nb与La/Sm的关系，共同表明了典型的弧火山岩。可用的地球化学参数表明，KKT变基岩的成因是通过i）来自下行海洋地壳的板状熔体迁移，ii）由板状熔体交代的地幔楔中含石榴石的橄榄岩的低温熔融，iii）板状熔体-橄榄岩的相互作用触发Nb浓度的增加，以及iv）在与电弧相关的环境中产生NEB。KKT NEB的发现为Singhbhum克拉通古元古代俯冲带过程和地壳生长提供了新的信息。

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来源期刊

Geologica Acta 地学-地质学

CiteScore

2.50

自引率

6.70%

发文量

审稿时长

>12 weeks

期刊介绍： - Relevant conceptual developments in any area of the Earth Sciences. - Studies presenting regional synthesis. - Thematic issues or monographic volumes presenting the results from one or more research groups. - Short papers reflecting interesting results or works in progress. - Contributions and results from Research Projects, Workshops, Symposiums, Congresses and any relevant scientific activity related to Earth Sciences. - Geologica Acta aims to stimulate rapid diffusion of results and efficient exchange of ideas between the widespread communities of Earth Science researchers (with special emphasis on Latinamerica, the Caribbean, Europe, the Mediterranean