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首页> 外文期刊>Contributions to Mineralogy and Petrology >Origin of the Powai ankaramite, and the composition, P-T conditions of equilibration and evolution of the primary magmas of the Deccan tholeiites
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Origin of the Powai ankaramite, and the composition, P-T conditions of equilibration and evolution of the primary magmas of the Deccan tholeiites

机译：Powai钙铁矿的起源，Deccan硬质岩原岩浆的组成，平衡和演化的P-T条件

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摘要

The Powai ankaramite flow from Mumbai, western Deccan Traps, contains abundant crystals of augite (En(59-47)Fs(10-14)Wo(27-42), 22-40 modal %, 3-5 mm) and olivine (Fo(84-74), 11-16 modal %, 1-2 mm), and minor plagioclase (An(71), similar to 0.5 mm) embedded in a fine-grained matrix. Minor orthopyroxene (En(79-77)Fs(16-19)Wo(5-4)) with irregular and embayed margins is mantled by thick augite overgrowth rims. The Fe-Mg distribution between the large crystals and bulk rock shows disequilibrium, indicating that the ankaramite is a cumulate rock. The ankaramite probably formed by the intrusion of tholeiitic melt into a cumulate pile with olivine, augite, and orthopyroxene left by the crystallization of earlier magmas, resulting in orthopyroxene dissolution and subsequent precipitation of augite. Olivine-hosted melt inclusions and melts represented by the ankaramite groundmass and some associated tholeiitic dikes are multiply saturated with olivine + plagioclase + clinopyroxene at <= 6 kb according to phase equilibrium constraints. Calculations involving incremental addition of equilibrium phases to these melts and to the common aphyric tholeiites of the voluminous Ambenali and Mahabaleshwar Formations show that their primary magmas (wt% SiO2: 48-50, MgO: 9.8-11.8, and FeO: 7.2-7.9, and Mg# 70-74) last equilibrated with spinel lherzolite at similar to 8-13 kb (similar to 30-49 km depths) and similar to 1268-1332 degrees C, and trace element considerations indicate <= 15 % batch melting of mantle. These tholeiitic primary magmas then underwent olivine gabbro fractionation in upper crustal magma chambers at depths <= 23 km. The minimum depth of equilibration of the primary magmas is shallower than the present-day Moho in the Mumbai area based on seismological data, indicating localized mantle upwelling and lower crustal interactions previously inferred from the Nd-Sr isotopic ratios and other geochemical characteristics of the ankara-mite and associated tholeiites.
机译：来自Deccan Trap西部孟买的Powai安卡拉母岩流含有丰富的闪锌矿晶体（En（59-47）Fs（10-14）Wo（27-42），22-40 modal％，3-5 mm）和橄榄石（ Fo（84-74），11-16模态％，1-2毫米）和次要斜长石（An（71），类似于0.5毫米）嵌入细颗粒基质中。边缘不规则和隐伏的次生邻苯二甲烯（En（79-77）Fs（16-19）Wo（5-4））由厚的闪长岩过度生长的边缘覆盖。大晶体与块状岩石之间的铁镁分布显示出不平衡状态，这表明安卡拉石是块状岩石。蓝kara石可能是由于早熔岩的结晶而留下的橄榄岩，奥古石和邻苯二酚渗透到堆积成堆的堆积物中而形成的，从而使邻苯二甲dissolution溶解并随后沉淀成块。根据相平衡约束条件，以橄榄石+斜长石+斜柏油为代表的以橄榄石为基质的熔体包裹体和以南高岭石地层为代表的熔体以及一些相关的堤防堤以= 6 kb的橄榄石+斜长石+ clinopyroxene饱和。涉及向这些熔体以及大量的Ambenali和Mahabaleshwar地层的常见无水生硫铁素体中逐渐添加平衡相的计算表明，它们的主要岩浆（重量％SiO2：48-50，MgO：9.8-11.8，FeO：7.2-7.9， Mg＃70-74（Mg＃70-74）最后以约8-13 kb（类似于30-49 km的深度）和1268-1332摄氏度与尖晶石锂沸石平衡，并且痕量元素的考虑表明<= 15％批地幔熔融。然后，这些高渗原岩浆在深度小于等于23 km的上地壳岩浆室内经历了橄榄石辉长岩分级。根据地震数据，主要岩浆的最小平衡深度比今天的孟买地区的莫霍面浅，表明先前由Nd-Sr同位素比和安卡拉的其他地球化学特征推断出的局部地幔上升流和下地壳相互作用螨和相关的tholeiite。

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