Compositional variations of chromiferous spinel in Mg-rich rocks of the Deccan Traps, India

Journal of Earth system science

Roberto De’ Gennaro2¹  Ivana Rocco1²  Leone Melluso1² 

[1] Centro Interdipartimentale Strumentazioni per Analisi Geomineralogiche (C.I.S.A.G.), Universit`a di Napoli Federico II, via Mezzocannone 8, 80134 Napoli, Italy.$$;Dipartimento di Scienze della Terra Universit`a di Napoli Federico II, via Mezzocannone 8, 80134 Napoli, Italy.$$

关键词: Chromiferous spinel;    pyroxene inclusions;    Large Igneous Provinces;    Deccan Traps;    India.;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

Composition of chromiferous spinel included in olivines of Mg-rich basalts and gabbros of the Deccan Traps (Gujarat and Western Ghats) are reported here. They vary from Al-rich compositions [Al2O3 = 53wt.%; Cr#, 100Cr/(Cr + Al) = 12] to Cr-rich compositions [Cr2O3 = 51wt.%; Cr#= 84], and from Cr-Al rich compositions towards Cr-rich Ti-magnetite (TiO2 up to 23 wt.%, ulvöspinel up to 67mol.%). The Mg#[100Mg/(Mg + Fe2+)] of spinel decreases from 81 to nearly zero. The highest Cr#has been found in the Bushe Fm., Thakurvadi Fm., and some high-Ti basalts of the Pavagadh section, whereas some of the low-Ti basalts of Saurashtra have Al-rich compositions typical of spinels found in mid-ocean ridge basalts. The chemical composition of the Deccan Trap spinels is completely different compared to that observed in mantle spinel suites, with very few exceptions. The decreasing Al and increasing Fe and Ti of spinel seems to be mainly the result of decrease of Mg in the locally coexisting melts and favourable cationic substitutions in the lattice. There is barely any evidence of general relationships between the composition of the Deccan spinels and inferred mantle sources of the host magmas. Pyroxene inclusions in spinels may witness a high-pressure stage of crystallization, but the possibility of non-equilibrium crystallization, or even magma mixing, cannot be ruled out. Overall, the compositional ranges of chromiferous spinel in the Deccan Traps closely match those observed in the other Large Igneous Provinces having mafic/ultramafic intrusions and mafic magma compositions (e.g., Siberian Traps, Karoo, Emeishan).

【 授权许可】

Unknown