Remagnetization of igneous rocks in Gupis area of Kohistan arc, northern Pakistan

The Kohistan are was formed due to subduction of neo-Tethyan oceanic crust beneath Asia. The are is comprised of volcanic, plutonic and sedimentary ro cks of Mesozoic to Tertiary age, formed prior and after the suturing of the Indian and Asian continents. Paleomagnetic investigations have been carrie d out on Paleocene volcanic and plutonic rocks exposed in the northern part of the are. A total of 110 samples from 16 sites were drilled. According t o rock-magnetic studies the main magnetic carrier is magnetite. Optical mic roscopy study reveals that low-grade metamorphism have effected all rocks. Magnetite is found as both a primary magmatic mineral and secondary alterat ion product in all samples. Samples of volcanics yield post tilting charact eristic remanent magnetizations (ChRM). The in situ mean direction of the C hRMs of the intrusives is similar to the in situ mean direction of volcanic s. The presence of secondary magnetite in plutons, the similarity of in sit u mean ChRM of plutons with that of post-tilting ChRMs of similar age volca nics and dissimilarity of the mean ChRM of plutons from expected directions at the time of formation of plutons support a secondary origin for the ChR M of plutons. As the ChRM directions of the volcanics and intrusives are th e same, it implies that both ChRMs were acquired during the same remagnetiz ation event. Comparing the mean paleolatitude (25 +/- 6 degreesN) from Gupi s area with those from Indian APWP and considering the fact that there was prevailing heating event in Lower Tertiary in the area, the acquisition age of this secondary remanent magnetization can be bracketed between 50 and 3 5 Ma.