EXCESS ARGON IN AMPHIBOLES LINKED TO GREENSCHIST FACIES ALTERATION INTHE KAMILA-AMPHIBOLITE BELT, KOHISTAN ISLAND-ARC SYSTEM, NORTHERN PAKISTAN - INSIGHTS FROM AR-40 AR-39 STEP-HEATING AND ACID LEACHING EXPERIMENTS/

A mineralogical and Ar-40/Ar-39 study of 13 amphibole samples in the K amila Amphibolite Belt and Kamila Shear Zone in northern Pakistan has found a correlation between the degree of greenschist facies alteratio n and quantity of excess Ar-40. Additionally, there is a north-south d ivide with amphibole samples from the northern region showing larger d egrees of greenschist facies alteration, brittle deformation, and exce ss Ar-40 incorporation compared to the predominantly plastically defor med, less altered, amphibole samples from the Kamila Shear Zone in the south. Acid leaching of two amphiboles from the Kamila Amphibolite Be lt indicates that a large proportion of the excess Ar-40 is correlated with later greenschist facies alteration phases, and can be easily re moved by acid etching, thus revealing acceptable regional Ar-40/Ar-39 plateau ages.