Geochemical Features of Bellara Trap Volcanic Rocks of Chitradurga Greenstone Belt, Western Dharwar Craton, India: Insights into MORB-BABB Association from a Neoarchean Back-Arc Basin  

作　　者：Chakravadhanula Manikyamba Sohini Ganguly Arijit Pahari 

机构地区：[1]CSIR-National Geophysical Research Institute,Hyderabad,500007,India [2]School of Earth,Ocean and Atmospheric Sciences,Goa University,Taleigao Plateau,Goa,403206,India

出　　处：《Journal of Earth Science》2021年第6期1528-1544,共17页地球科学学刊（英文版）

基　　金：supported by the projects of the CSIR-Emeritus Scientist;INDEX Project from the Council of Scientific and Industrial Research (CSIR) to the National Geophysical Research Institute to Chakravadhanula Manikyamba;the SERB-Research Scientist Project (No. SB/SRS/2019-20/27/EA) to Sohini Ganguly;the DST INSPIRE fellowship for pursuing the Ph.D. programm at NGRI to Arijit Pahari。

摘　　要：This study presents a comprehensive account of the petrogenetic and geodynamic evolution of the Bellara Trap volcanic rocks from the Ingaldhal Formation, Chitradurga Group, western Dharwar Craton(WDC). Geochemical attributes of these rocks are consistent with two groups with distinct evolutionary trends: one comprising tholeiitic, MORB(mid-ocean ridge basalt) type basalts(BTB) and the other corresponding to calc-alkaline andesites(BTA). Basalts are essentially composed of clinopyroxene and plagioclase whereas the andesites are porphyritic with phenocrysts of plagioclase, clinopyroxene and polycrystalline quartz embedded in a groundmass of K-feldspar, quartz and opaques. Primary igneous mineralogy is overprinted by greenschist facies metamorphism resulting in chlorite-actinolite-plagioclase assemblage. The BTB samples reflect nearly flat REE patterns with weak LREE enrichment in contrast to pronounced LREE enhancement over HREE discernible for BTA. Tectonically, the BTB samples correspond to an active mid-oceanic ridge-rift setting with a MORB composition, whereas a back-arc basin(BAB) regime is corroborated for the BTA samples fractionating from back-arc basin basalts. Geochemical imprints of subduction input are more pronounced in BTA compared to BTB as mirrored by their elevated abundances of incompatible fluid mobile elements like Ba, Th, U and LREE. The BTB is endowed with an N-to E-MORB signature attributable to minor contributions from subduction-related components at the inception of a back-arc basin in the vicinity of an active subduction system. The BTA derived through differentiation of a basaltic magma with BABB(back-arc basin basalt) affinity compositionally akin to a heterogeneous source mantle carrying depleted MORB-type and enriched arc-type components inducted with progressive subduction. The BABB-type andesites and MORB-type basalts from Bellara Traps record a compositional heterogeneity of mantle in an intraoceanic arc-back arc system. Mantle processes invoke a BABB-MORB spectrum with a MORB-lik

关 键 词：western Dharwar Craton Chitradurga Group Bellara Traps back-arc basin Neoarchean MORB-BABB 

分 类 号：P534.2[天文地球—古生物学与地层学] P588.14[天文地球—地质学] P597.3