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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Bimodal tholeiitic and mildly alkalic basalts from Bhir area, central Deccan Volcanic Province, India: Geochemistry and petrogenesis
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Bimodal tholeiitic and mildly alkalic basalts from Bhir area, central Deccan Volcanic Province, India: Geochemistry and petrogenesis

机译：印度德干火山省中部比尔地区的双峰型温和碱性玄武岩：地球化学和岩石成因

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摘要

Bimodal tholeiitic and mildly alkalic basalts occur near Bhir, in the central part of Deccan Volcanic Province (DVP). Major and trace element concentrations show that, of the ten flows, nine are tholeiitic and one is an alkalic basalt. The Bhir basalts have a wide range of chemical composition. Geochemical variations in the stratigraphic section define three distinct phases of evolution (zones 1 to 3). Crystal fractionation of plagio-clase, clinopyroxene, olivine and Fe-Ti oxide expanded the compositional range. Low Mg#s (39-55), low concentrations of Ni and Cr and high Zr suggest the evolved nature of the Bhir basalts. Fractionation modeling suggests about 42% fractional crystallization.rnIn spite of the dominant role of fractional crystallization in the evolution of Bhir basalts, some other processes must be sought to explain the chemical variations. Crustal contamination, magma mixing and degree of partial melting are suggested to explain the observed chemical variations. Resorption, reverse zoning and compositional bimodality in plagioclase phenocrysts indicate magma mixing. Samples of flows one and four suspected of being contaminated all have enriched SiO_2 and LILE (K, Rb, and Ba) contents and depletion in Ti and P, believed to be due to 'granitic' crustal contamination.rnAs compared to tholeiitic basalts, the alkalic basalts are characterized by low SiO_2 and high TiO_2, Na_2O, K_2O and P_2O_5. Alkalic basalts are richer in LILE (Rb and Ba), HFSE (Nb, Zr, and Y) and REE than the tholeiitic basalts. The alkalic basalt occurrence is important from a petrogenetic point of view and also suggests that the sources of alkalic basalt magmas may be of variable ages under different parts of the DVP. Based on major, trace and rare earth element distributions it is suggested that asthenospheric mantle having affinities with the source of OIB was the source material of the magmas and the range in the composition of tholeiitic and alkalic basalts was probably controlled by different degrees of melting and/or inhomogeneities in the mantle source.
机译：在Deccan火山省（DVP）的中部Bhir附近发生了双峰型和弱碱性玄武岩。主要元素和痕量元素的浓度表明，在十个流中，九个为疏松岩，一个为碱性玄武岩。 Bhir玄武岩具有广泛的化学组成。地层剖面中的地球化学变化定义了三个不同的演化阶段（1-3区）。斜长石，斜辉石，橄榄石和Fe-Ti氧化物的晶体分级扩大了组成范围。 Mg＃s（39-55）低，Ni和Cr浓度低以及Zr高表明Bhir玄武岩的演化性质。分馏模型表明大约有42％的分馏结晶。尽管分馏结晶在Bhir玄武岩的演化中起主要作用，但仍必须寻求其他方法来解释化学变化。建议使用地壳污染，岩浆混合和部分熔融程度来解释观察到的化学变化。斜长石斑晶中的吸收，反向带化和成分双峰表明岩浆混合。怀疑受到污染的流1和4的样品都富含SiO_2和LILE（K，Rb和Ba）含量以及Ti和P中的贫化，据信这是由于“粒状”地壳污染所致。碱性玄武岩的特征是低SiO_2和高TiO_2，Na_2O，K_2O和P_2O_5。碱性玄武岩比起玄武岩，其LILE（Rb和Ba），HFSE（Nb，Zr和Y）和REE含量更高。从岩石成因的角度来看，碱性玄武岩的发生很重要，并且还暗示了碱性玄武岩岩浆的来源在DVP的不同部分可能具有不同的年龄。根据主要，痕量和稀土元素分布，建议与OIB来源具有亲合力的软流圈地幔是岩浆的来源，而高渗玄武岩和碱性玄武岩的组成范围可能受不同程度的融化和控制。 /或地幔源中的不均匀性。

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