Field relations and structural constraints for the Teru volcanic formation, northern Kohistan Terrane, Pakistani Himalayas

Abstract

The products of Late Cretaceous–Paleogene Andean style magmatism along the southern margin of Asia are preserved in the 2500km long Trans-Himalayan (Kohistan–Ladakh–Gangdese) granitoid batholith, together with scattered volcanic outcrops (basalts, andesites, rhyolites and pyroclastics). Andean–type magmatism began in northern Pakistan as early as Late Cretaceous and lasted until terminal collision with India at about 45Ma. We present new field and structural data for the Teru volcanic formation (previously known as the Shamran volcanics) exposed west of Gilgit in the Kohistan terrane of the Pakistani Himalayas. The Teru volcanic formation comprises a 3-km thick sequence of subaerially-erupted mafic to felsic lavas and associated volcaniclastic rocks. The Kohistan batholith bounds this sequence to the south and the sequence is overthrust to the north by the mid-Cretaceous Chalt volcanic group (intra-oceanic arc phase) along the south-verging Ghizer thrust. These volcanics are lithologically comparable to similar-age suites elsewhere in the Himalayas. This suggests that the paleogeography of southern Asia at this time was dominated by an extensive convergent-margin province prior to collision with India. After India collided with Asia, the Kohistan terrane was uplifted and eroded, which removed most of the Andean margin phase volcanics.