Cooling history of the NW Himalaya, Pakistan

Abstract

Fission‐track and 40Ar/39Ar cooling ages indicate that the late‐Tertiary cooling history of the Himalayan ranges of northern Pakistan is largely a function of uplift and erosion. Interpretation of cooling ages which range from under 0.5 Ma to over 80 Ma suggests that during the late Tertiary, long‐term uplift rates at least doubled, from under 0.2 mm/yr to in some cases well over 0.5 mm/yr. Uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions. The association of very rapid uplift and erosion with the Nanga Parbat‐Haramosh Massif can be explained by a locally vigorous collision of India with Eurasia near a promontory of Indian crust. The resultant rapid uplift of the Nanga Parbat‐Haramosh Massif reactivated the Main Mantle Thrust melange zone with a reversed sense of motion. Discontinuities in the coolingage distribution along the Main Mantle Thrust in the southern Swat‐Hazara region may be the result of the thermal effects of overthrusting.