{"title":"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","authors":"R. Rajani","doi":"10.1344/geologicaacta2022.20.11","DOIUrl":null,"url":null,"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.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":null,"pages":null},"PeriodicalIF":1.3000,"publicationDate":"2022-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Geochemistry of Khandadharpahar-Thakuranipahar metabasites from the western Singhbhum Craton, eastern India: implications for subduction-zone tectonics and mantle-wedge metasomatism\",\"authors\":\"R. Rajani\",\"doi\":\"10.1344/geologicaacta2022.20.11\",\"DOIUrl\":null,\"url\":null,\"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.\",\"PeriodicalId\":55107,\"journal\":{\"name\":\"Geologica Acta\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":1.3000,\"publicationDate\":\"2022-09-16\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Geologica Acta\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://doi.org/10.1344/geologicaacta2022.20.11\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOLOGY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Geologica Acta","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1344/geologicaacta2022.20.11","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOLOGY","Score":null,"Total":0}
Geochemistry of Khandadharpahar-Thakuranipahar metabasites from the western Singhbhum Craton, eastern India: implications for subduction-zone tectonics and mantle-wedge metasomatism
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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