Abstract

The rocks of Raialo Group in the Alwar sub-basin of North Delhi Fold Belt were investigated with a focus on meta-basic lava flows of the Tehla Formation. The basaltic rocks, now occurring as amphibolites, are medium- to fine-grained and show evidence of greenschist to lower amphibolite facies metamorphism, characterized by dominant plagioclase, hornblende, actinolite, chlorite, and minor, epidote, opaque, and Fe–Ti oxide mineral assemblage. The presence of amygdules and vesicles, well preserved primary igneous texture, and relict pyroxenes, at places, confirm their basaltic lineage. In a single outcrop, located to the northeast of Tehla village, well-preserved pillow structures have been discovered. The pillow structures vary in size (few cm to >1 m) and shape (spheroid, elongate and kidney-shaped), and inter-pillow spaces are filled up with chert, at places. This is the first report of pillow basalt occurrence from the North Delhi Fold Belt. In addition to offering evidence of submarine basaltic volcanism, the mega-pillows, gabbroic lenses, and presence of ultramafic rocks in the region suggest a possible ophiolite setting that needs a detailed petrographic and geochemical evaluation.

Research highlights

• First report of pillow structures from North Delhi Fold Belt.

• Identification of mafic- ultramafic association and possibility of an ophiolite setting.

中文翻译：

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Alwar 子盆地 Tehla 地区 Raialo Group 的基性火山岩：印度西北部北德里褶皱带枕状熔岩的首次报告

摘要

对北德里褶皱带 Alwar 次盆地 Raialo 群的岩石进行了研究，重点研究了 Tehla 组的变基性熔岩流。现在以角闪石形式出现的玄武岩为中至细粒，并显示出绿片岩至下角闪石相变质作用的证据，其特征是占优势的斜长石、角闪石、阳起石、绿泥石和少量、绿帘石、不透明和 Fe-Ti 氧化物矿物组合。杏仁核和囊泡的存在、保存完好的原生火成岩结构和残余辉石，在某些地方证实了它们的玄武岩谱系。在位于 Tehla 村东北部的一个露头中，发现了保存完好的枕状结构。枕头结构的大小（几厘米到 > 1 m）和形状（球形、细长形和肾形）各不相同，枕头间的空间在某些地方充满了燧石。这是北德里褶皱带出现枕状玄武岩的第一份报告。除了提供海底玄武岩火山作用的证据外，该地区的巨型枕状结构、辉长岩透镜和超基性岩的存在表明可能存在蛇绿岩环境，需要进行详细的岩石学和地球化学评估。

研究亮点

• 北德里褶皱带枕头结构的第一份报告。

• 确定镁铁质-超镁铁质协会和蛇绿岩环境的可能性。