Babusar Amphibolites, Arc Tholeiites from the Southern Kohistan Arc, N. Pakistan
Abstract
An imbricate sequence of amphibolites, apparently in the form of a linear belt, occurs in the hanging wall of the Indus Suture at Babusar Pass (SE Kohistan). Major-, trace- and a limited rare-earth element data classifies them to be arc tholeiite in composition, in contrast to the bulk of the Kohistan arc which is predominantly calc-alkaline. Models are discussed about their position with respect to the rest of the Kohistan magmatic sequence. Whereas there is a possibility that they represent early tholeiite phases of arc magmatism, a model is presented which considers them (together with a conformable basal ultramafic unit) as crust of a tholeiitic island arc, formed as a separate entity from a predominantly calc-alkaline Kohistan arc to the north.
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