Abstract
Chemical analyses for 21 elements together with physical data are presented for 38 amphiboles (34 of them new) from garnet granulites, pyroxene granulites, amphibolites, and quartz diorites constituting the southern half of the Kohistan Cretaceous–Early Tertiary arc. The metamorphic hornblendes are rich in alumina and some of them have high Alvi/Aliv ratios. The elements in the amphiboles are studied in relation to each other and to those of their host rocks. The Mg/Fe ratio is strongly dependent, and Fe3+ and K partly dependent upon bulk chemistry, whereas Ca and Na are relatively independent of the chemistry of the host rock. The amounts of Al, Ti, and Na are controlled to a large extent by bulk mineralogy and to a lesser extent by bulk composition. The influence of metamorphic conditions is not important except on A-site occupancy and, possibly, on Ti and Mn contents. Other factors having variable influence on these components are also discussed. Refractive indices, birefringence, and density display a systematic increase (and 2V a decrease) with decrease in the ratio (Mg + Alvi)/(Mg + Aliv + Alvi + Ti + Fe3+ + Fe2+ + Mn). Pleochroic colors and amount of absorption are controlled by Fe3+, Ti, Fe3+/Ti, and Mg/Fe2+, while Z:c appears to increase with Fe3+ + Ca.