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

Abstract

The Kohistan arc was formed due to subduction of neo-Tethyan oceanic crust beneath Asia. The arc is comprised of volcanic, plutonic and sedimentary rocks of Mesozoic to Tertiary age, formed prior and after the suturing of the Indian and Asian continents. Paleomagnetic investigations have been carried out on Paleocene volcanic and plutonic rocks exposed in the northern part of the arc. A total of 110 samples from 16 sites were drilled. According to rock-magnetic studies the main magnetic carrier is magnetite. Optical microscopy study reveals that low-grade metamorphism have effected all rocks. Magnetite is found as both a primary magmatic mineral and secondary alteration product in all samples. Samples of volcanics yield post tilting characteristic remanent magnetizations (ChRM). The in situ mean direction of the ChRMs of the intrusives is similar to the in situ mean direction of volcanics. The presence of secondary magnetite in plutons, the similarity of in situ mean ChRM of plutons with that of post-tilting ChRMs of similar age volcanics and dissimilarity of the mean ChRM of plutons from expected directions at the time of formation of plutons support a secondary origin for the ChRM of plutons. As the ChRM directions of the volcanics and intrusives are the same, it implies that both ChRMs were acquired during the same remagnetization event. Comparing the mean paleolatitude (25 ± 6• N) from Gupis 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 35 Ma.

Paleomagnetism of the Crocker Formation, northwest Borneo: Implications for late Cenozoic tectonics

“…Because the onset temperature for annealing zircon (~200 °C) is lower than the Curie temperature of magnetite (580 °C), remagnetization of the Nakan area must be the result of a diagenetic (chemical) event rather than a thermal event. Chemical remagnetization of igneous rocks can be associated with low-grade metamorphism (Ahmad et al, 2001;Yo-ichero et al, 2000). Thin sections of the Nakan samples, however, show little to no alteration to support the hypothesis of a diagenetic and/or epithermal event (Lumadyo et al, 1993).…”

Magnetomineralogical changes along the Kohistan-Karakoram collision zone inNorth Pakistan: implications for variable thermochemical activities

“…The The areas within rectangles, located around the towns of Drosh and Gupis, are investigated in this study. The study area of Ahmad et al (2001) is also marked by a small rectangle. Detailed geological maps of the Yasin-Gupis and Drosh areas are shown in Figures 2 and 3.…”

Timing of collision of the Kohistan–Ladakh Arc with India and Asia: Debate

“…Ahmed et al . (2001) also reported rock‐magnetic and paleomagnetic results of the Paleogene volcanic (Teru Volcanic Formation) and plutonic rocks exposed in the northern part of the KLA (Fig.…”

“…The plutonic rocks also showed the same directions. Therefore, the volcanics were remagnetized at the time of intrusive activity or both volcanic and intrusive rocks have suffered the same remagnetization (Ahmed et al . 2001).…”

“…2005), and the Lhasa block and KLA were located at paleolatitudes of 21–27°N (Tan et al . 2010) and 12°N (the Utror Volcanic Formation; Ahmed et al . 2001) respectively.…”