TECTONIC SIGNIFICANCE OF 24 MA CRUSTAL MELTING IN THE EASTERN HINDU-KUSH, PAKISTAN

Northward-directed subduction has continued beneath the Hindu Rush fro m the Mesozoic, when the region formed part of the southern margin of Asia, until today. The Kohistan are was accreted at ca, 100 Ma, follow ed by the Indian plate at 54-50 Ma. After the India-Asia collision, a regional crustal-melting event occurred at ca, 25-21 Ma to the east of the Hindu Rush in the Karakoram Range, producing the Baltoro pluton. In the eastern Hindu Rush Range, most of the granitoids appear to be s ubduction-related plutons that predate the India-Asia collision, Howev er, the Gharam Chasma pluton is a two-mica (+/- garnet +/- tourmaline) leucogranite that has intruded into staurolite-grade schists and (sil limanite +/- K-feldspar)-grade migmatites, U-Pb ages on monazite, xeno time, and uraninite from undeformed samples of the Gharam Chasma pluto n and a leucogranite dike that crosscuts the migmatites indicate that crustal melting occurred at ca, 24 Ma, synchronous with the Baltoro me lting event. This age also provides an upper limit on the age of the r egional staurolite-grade metamorphism in the eastern Hindu Kush.