SM-ND AGE OF THE GARHWAL-BHOWALI VOLCANICS, WESTERN HIMALAYAS - VESTIGES OF THE LATE ARCHEAN RAMPUR FLOOD-BASALT PROVINCE OF THE NORTHERN INDIAN CRATON

Whole rock Sm-Nd isotope dating of the Garhwal and Bhowali mafic volca nics of the Kumaun Lesser Himalayan sector yield an age of 2.51 +/- 0. 08 Ga and an initial epsilon(Nd) =5.1 +/- 0.5. This age and initial ep silon(Nd) are the same as that of the Rampur-Mandi volcanics, which oc cur to the west in the Lesser Himalayas. In addition to confirming the widespread presence of the Late Archaean crustal elements in the Hima layas, these data constrain the age of the oldest rifting event and de position of supracrustal sediments in the Himalayas and set at rest th e long standing controversy about the age and inter-relationship of th ese mafic volcanics. Despite their present-day disparate occurrence as a result of the post-eruption deformation, the area covered by these mafic volcanics is large enough to classify them as flood basalts, the Rampur flood basalt (RFB) province. Rift-related volcanism of the sam e age is known from the contiguous Aravalli region of the NW Indian Sh ield. The orientation of the rifts in the two regions suggests the pos sibility of a mantle plume setting for the RFB. (C) 1998 Elsevier Scie nce B.V.