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首页> 外文期刊>Journal of Asian earth sciences >Clinopyroxene compositions in the Deccan and Rajmahal Traps and their bearing on magma types and evolution
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Clinopyroxene compositions in the Deccan and Rajmahal Traps and their bearing on magma types and evolution

机译：Deccan和Rajmahal圈闭中的斜辉石成分及其对岩浆类型和演化的影响

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摘要

Electron probe analyses of clinopyroxenes from several areas of the Deccan and Rajmahal Traps consisting mostly of subalkalic and alkalic basalts, picritic basalts and a few dolerite dykes have been obtained. Evaluation of the data indicate the absence of pigeonite from subalkalic basalts that occur in close spatial association with mild or strongly alkalic basalts in areas such as Rajpipla, Navagam and central Kachchh. Co-existence of augite and pigeonite, however, has been noticed in subalkalic basalts/dykes and picritic basalts from a number of Deccan localities such as Sagar, Igatpuri, Kalsubai, Triambak, Pavagarh and Gir-nar besides the one sample from Rajmahal. Diopside, salite, and wollastonite-rich compositions dominate the basanites and foidites of Kachchh whereas chrome-diopside and salite are the main types in the picrite basalt samples from Anila, Botad and Paliyad in Saurashtra akin to those found in contiguous areas in the east from borehole flows at Dhandhuka and Wadhwan studied in detail previously. Compositional variations in zoned clinopyroxenes indicate differentiation of the parental magma and also mixing of different magma types (subalkalic and alkalic) from areas such as Igatpuri, Rajpipla and Kachchh. Based on host-rock chemistry, total alkalis-silica plot, CIPW norms, estimated temperatures of eruption and augite - pigeonite thermometry, it has been inferred that clinopyroxene compositions, especially the incidence of pigeonite, appear to be very sensitive to bulk chemistry of host rocks, especially their Na_2O, K_2O, SiO_2, total iron and TiO_2 contents. Non-quadrilateral cationic components in the clinopyroxenes, such as Al in tetrahedral and octahedral positions together with Si, Na, Ti and Cr abundances have been found to be useful to discriminate clinopyroxenes from alkalic and subalkalic basalt types besides inferences on the ferric iron component in them. Evaluation of host-rock compositions in the ternary olivine-clinopy-roxene-quartz plot indicate polybaric conditions of crystallization and evolution especially in samples that are picritic (e.g. Pavagarh, Anila and Kachchh) and which could also breach the olivine-clinopyrox-ene-plagioclase thermal divide that exists in part between alkalic and subalkalic basalts under atmospheric conditions.
机译：电子探针分析了Deccan和Rajmahal陷阱几个地区的斜辉石，主要由次碱性和碱性玄武岩，云母玄武岩和一些白云石脉组成。数据评估表明，在Rajpipla，Navagam和Kachchh中部地区，与弱或强碱玄武岩在空间上紧密相关的次碱玄武岩中没有皂石。然而，除了来自拉贾马勒的一个样本外，在许多德干地区（如萨加尔，伊加普里，卡尔苏拜，特里安巴克，帕瓦加尔和吉尔纳尔）的次碱性玄武岩/堤坝和野餐级玄武岩中，还发现了辉石和贝南石并存。透辉石，硅藻土和硅灰石含量较高，主要构成了Kachchh的玄武岩和钠闪石，而铬透辉石和硅藻土是索拉什特拉邦阿尼拉，博塔德和帕里亚德的玄武岩玄武岩样品中的主要类型，类似于东部东部连续地区发现的这些类型。先前已对Dhandhuka和Wadhwan的井眼流量进行了详细研究。分区的斜向辉石的成分变化表明母岩浆的分化，也表明来自Igatpuri，Rajpipla和Kachchh地区的不同岩浆类型（次碱性和碱性）混合。根据基质-岩石化学，总碱-二氧化硅图，CIPW规范，火山喷发的估计温度和闪锌矿-石棉的测温法，可以推断出斜辉石的组成，特别是对斑铝石的发生率，似乎对基质的本体化学非常敏感。岩石，尤其是Na_2O，K_2O，SiO_2，总铁和TiO_2含量。已发现斜生辉石中的非四方阳离子组分，例如四面体和八面体位置的Al以及Si，Na，Ti和Cr的丰度，可用于区分斜生辉石与碱性和亚碱性玄武岩类型，除了推断铁中的铁成分他们。在三元橄榄石-斜辉石-环氧-石英图中评估主岩成分表明，结晶和演化的多重条件，特别是在轻度样品（例如Pavagarh，Anila和Kachchh）中，也可能会破坏橄榄石-斜辉石-烯-斜长石热分界在大气条件下部分存在于碱性玄武岩和次碱性玄武岩之间。

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