The Tora Tigga Complex, Southern Dir, NW Pakistan, An Example of Mafic-Ultramafic Rocks in The Bottom of an Island Arc
Abstract
The Tora Tigga complex comprises dunite, peridotites and pyroxenites (± hornblende), hornblendites, metagabbros and plagiogranite covering over 6 km2 area. It is located in the north of the Indus-Zangbo suture, in an extensive terrain of amphibolites that form the southern part of the Cretaceous Kohistan island arc. The ultramafic rocks are closer to those found in stratiform complexes than to oceanic peridotites and the metagabbros are calc-alkaline island arc-type. Chemical variation suggests that the rocks are magmatically related. They probably represent amphibolite facies metamorphosed cumulates in a magma chamber of the Kohistan arc. The hornblendites are medium-grained to pegmatitic, and range from small dykes, patches and pools to large bodies over 2.5 km in length. There are gradational lithologies to pyroxenites and peridotites in which hornblende is replacive in texture; however, chemical data do not support a metasomatic origin for such rocks and the hornblendites.
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