The Precambrian basement in the northwest Bengal basin is concealed under mainly Tertiary and in places overlain by Gondwana sediments in the half graben basins. The present work reports the study of the petrographic and geochemical investigations of the basement of Barapukuria, one of the major Gondwana coal basins, for the first time. The basement at the Barapukuria, encountered at a depth of ∼200 to 656 m in several drill holes, comprises of tonalite, granodiorite, and leucogranite, which are primarily composed of the variable amounts of plagioclase, quartz, biotite, and amphibole with accessory leucoxene, calcite, epidote, muscovite, and allanite. The lower part of the felsic sequence in the drill hole GDH 43 was dissected by a hornblendite dike. The tonalite and granodiorites have likely chemical composition with silica, which varies within a moderate range from ∼54 to 63 wt% and ∼64 to 68 wt%, respectively. Both tonalite and granodiorites have high iron content ranging from ∼9 to 16 wt% and ∼6 to 12 wt% respectively. Leucogranite, on the other hand, is siliceous (70.32 to 72.10 wt%) and relatively iron rich (4.91 to 6.89 wt%). Collectively, the felsic rocks mostly show a calc-alkaline, I-type character and a moderate degree [(La/Yb) CN = 17] of LREEs enrichment. The Barapukuria basement rocks share similar petrographic and geochemical signatures to the nearby (∼14km east) ∼1.72 Ga felsic basement in Maddhapara. The scarcity of data on the Gondwana coal basin basement from the northeastern Indian shield, however, precludes a comparison between these basements in northeast India and Barapukuria in northwest Bangladesh.

中文翻译：

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揭示 Barapukuria 的基底：对孟加拉国西北部冈瓦纳盆地基底的地球化学研究

孟加拉盆地西北部的前寒武纪基底主要隐藏在第三纪之下，在半地堑盆地中被冈瓦纳沉积物覆盖的地方。目前的工作首次报告了对冈瓦纳主要煤盆地之一巴拉普库利亚基底的岩石学和地球化学调查研究。Barapukuria 基底在 200 至 656 m 深的几个钻孔中遇到，由闪长岩、花岗闪长岩和白花岗岩组成，主要由数量不等的斜长石、石英、黑云母和角闪石组成、方解石、绿帘石、白云母和allanite。钻孔 GDH 43 中长英质层序的下部被角闪石岩脉解剖。闪长岩和花岗闪长岩的化学成分可能与二氧化硅，分别在约 54 至 63 重量％和约 64 至 68 重量％的中等范围内变化。闪长岩和花岗闪长岩的铁含量都很高，分别为约 9 至 16 重量％和约 6 至 12 重量％。另一方面，无色花岗岩是硅质的（70.32 至 72.10 重量％）并且相对富含铁（4.91 至 6.89 重量％）。总体上，长英质岩大多表现出钙碱性、I型特征和中等程度的轻稀土元素富集[(La/Yb) CN = 17]。Barapukuria 基底岩石与 Maddhapara 附近（约 14 公里以东）约 1.72 Ga 长英质基底具有相似的岩石学和地球化学特征。然而，由于印度地盾东北部冈瓦纳煤盆地基底的数据稀缺，因此无法将印度东北部的这些基底与孟加拉国西北部的 Barapukuria 进行比较。