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首页> 外文期刊>Journal of the Geological Society of India >Mineralogical study of gabbro-anorthosite from Dumka, Chhotanagpur Gneissic Complex, Eastern Indian Shield
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Mineralogical study of gabbro-anorthosite from Dumka, Chhotanagpur Gneissic Complex, Eastern Indian Shield

机译：印度东部盾构乔丹纳格普尔片麻岩复合体Dumka辉长岩钙长石的矿物学研究

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摘要

The Chhotanagpur Gneissic Complex (CGC), bearing imprints of widespread high grade metamorphic and magmatic history since Palaeoproterozoic, represents an integral crustal segment of Eastern Indian Shield. The gabbroanorthosite intrusives constitute a part of mafic-ultramafic magmatism in the CGC. The study area around Dumka (24°16′ to 24°20′N: 87°13′ to 87°22′E) predominantly comprises of granite gneiss and charnockitic country rocks within which gabbro-anorthosite intrusions occur as lenses. Field relations and structural studies reveal that the country rocks of Dumka have suffered three phases of deformation represented by F1, F2 and F3 folds. The gabbro-anorthosite intrusives maintain a sharp contact with the host rocks, deformed and metamorphosed. Relict igneous layering or primary igneous foliation (Sig) is recorded where metamorphic overprint is minimal. Mineral phases of gabbro-anorthosite rocks suggest that clinopyroxene compositions from gabrro correspond to diopside and clinoferrosilite, while those from anorthosite are clinoferrosilite. Amphiboles from the gabbro-anorthosite rocks are calcic, and range from ferroan pargasite in gabbro to ferroan pargasitic hornblende in anorthosite. Plagioclase from gabbro and anorthosite belong to bytownite and andesine respectively. Chemical composition of garnet in gabbro is almandine. Thermobarometric estimates for Dumka gabbroanorthosites correspond to 511°C to 915°C and 5.0–7.5 kb pressure, comparable to that estimated for Bengal Anorthosite (593–795°C, 4.1–7.3 kb). Fractionation trend of plagioclase substantiates a single parental magma in the evolution of Dumka gabbro-anorthosite intrusives.
机译：自古元古代以来，Chhotanagpur片麻岩复合体（CGC）拥有广泛的高级变质和岩浆历史印记，是东印度盾构不可分割的地壳部分。辉长岩原位侵入体构成了CGC中镁铁质-超岩浆岩浆作用的一部分。杜姆卡周围的研究区域（北纬24°16′至24°20′：东经87°13′至87°22′）主要由花岗岩片麻岩和夏尼特岩质岩构成，其中辉长岩-钙长石侵入物以透镜的形式出现。现场关系和结构研究表明，Dumka的乡村岩石经历了三个变形阶段，分别以F1 ，F2 和F3 褶皱为代表。辉长岩-钙长石侵入体与宿主岩保持着剧烈的接触，发生了变形和变质。在变质叠印极少的情况下记录了遗留火成岩层或主火成岩（Sig ）。辉长岩-钙长石岩石的矿物相表明，辉石的斜辉石成分对应于透辉石和斜铁硅铝石，而斜长石的斜辉石成分则为斜铁硅铝石。辉长岩-钙长石岩石的闪石是钙质的，范围从辉长岩中的铁锰铁辉石到钙长石中的铁辉石胃角闪石。辉长岩和钙长石的斜长石分别属于bytownite和andesine。辉长岩中石榴石的化学成分是金刚烷胺。 Dumka gabbroanorsitesites的热压估算值对应于511°C至915°C和5.0–7.5 kb的压力，与孟加拉孟加拉钙铁原石的估算值（593–795°C，4.1–7.3 kb）相当。斜长石馏分的趋势证实了Dumka gabbro-无钙铁矿侵入体演化过程中的单个父母岩浆。

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