Geochronological research about the relation of Proterozoic rocks, western of Kolkata, with 1700Ma rocks in Nepal.

在印度半岛，存在大面积的元古代熔岩。用K-Ar和Rb-Sr测年法测定了这些岩石的年龄为1500-1600 Ma，我们以前报道了这些岩石与位于北400公里的亚喜马拉雅Siwalik的Dwar Khola白云岩（1600-1800Ma， 40Ar-39Ar年龄）的关系。我们于2003年收集了这些样品，并在本文中报告了40Ar-39Ar的年龄结果。这些火山岩位于元古代变质岩和花岗质岩中，分为4部分（Dalma， Dhanjori和Jagarnathpur， Ongabila）。高原年龄约为1700-1800 Ma，尼泊尔白云岩的年龄无法得到。所有年龄谱均表现为变质扰动型或过量氩型。根据这些结果，我们得出了这些火山岩的5个年龄。1) 1800 - 2000马;原始年龄与尼泊尔白云岩相同。2)1550 ~ 1670ma；原始年龄或变质年龄3)1400Ma；变质年龄4)950 ~ 1050ma；南极Napier杂岩的变质年龄(5)450-550Ma；与泛非变质作用相对应的变质时代。

In peninsular India, there are Proterozoic Lavas extending large area. The ages of these rocks are reported 1500-1600 Ma by K-Ar and Rb-Sr dating methods and we have reported the relation of these rocks to the Dwar Khola dolerite (1600-1800Ma 40Ar-39Ar ages) from Siwalik of Sub-Himalaya, situated about 400km north, before. We have collected these samples in 2003 and report 40Ar-39Ar age results in this paper.These volcanic rocks are situated in the Proterozoic metamorphic and granitic rocks and divided 4 parts ((Dalma, Dhanjori and Jagarnathpur, Ongabila). Plateau ages about 1700-1800 Ma as those of Nepal dolerites cannot be obtained.All age spectrum show disturbed pattern by metamorphism or excess Ar pattern.From these results, we conclude 5 ages for these volcanic rocks.1)1800-2000Ma ; original age same as those of Nepal Dolerites.2)1550-1670Ma ; original age or metamorphic age3)1400Ma ; metamorphic age4)950-1050Ma ; metamorphic age which is recognized in intruded rocks in Napier Complex, Antarctica.5)450-550Ma ; metamorphic age corresponding to the Pan African Metamorphism.