TECTONIC IMPLICATIONS OF NEW ISOTOPIC AGES FOR ROCKS FROM THE PESHAWAR PLAIN OF PAKISTAN INCLUDING A U/PB AGE FOR THE FIRST REPORTED CENOZOIC VOLCANIC ROCKS IN THE LESSER HIMALAYA

New U/Pb ages confirm: (i) that Lesser Himalayan thrust slices expose Precambrian basement with the ~ 800 Ma ages characteristic only of the NW part of then Indian continent on which the Malani Andean-type volcanic arc, and its possible correlative arc rocks in Oman, Dhofar, the Seychelles and Madagascar were constructed (ii) the occurrence of granitic gneisses yielding the enigmatic Ordovician ages now widely recognized in the NW Himalaya (iii) Permian ages for the intrusion of granitic rocks of the Peshawar Plain Alkaline Igneous Province (PPAIP). PPAIP outcrops are all within Lesser Himalayan thrust slices. For that reason we suggest that all earlier reported Late Cretaceous and Cenozoic ages on rocks of the PPAIP are metamorphic ages and are related to Himalayan tectonics. Surprising to us was the discovery that volcanic rocks (rhyodacitic ignimbrites ?) at Gohati (34.17N72.41E), previously thought to be part of a Permian alkaline complex yielded a ²⁰⁶Pb/²³⁸U age of 26.6 +/- 1.3 Ma (MSWD= 1.6). Cenozoic, mainly granitic, intrusions are common in the Himalaya. In the NW Himalaya Cenozoic ages have been reported from the High Himalayas in the Nanga Parbat Haramosh province , in Kohistan/ Ladakh and in the Karakorum but Cenozoic volcanic rocks have not been reported from the Himalaya although they are widely distributed in Tibet. Perhaps the Gohati volcanic rocks were erupted above a crack that propagated into the Indian continent much as the newer Harrats of Arabia are being erupted above cracks extending into the Arabian continent from the Zagros collision zone.