Petrography, geochemistry, and geochronology of the Kohistan Batholith granitoids from the Central Kohistan Magmatic Arc, Northern Swat, Pakistan

• Applicant: Professorin Dr. Kirsten Drüppel
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527791139

The Kohistan terrain comprises a Cretaceous intra-oceanic arc which became an Andean-type margin after collision with the Karakoram block in the Late Cretaceous. During collision, Kohistan was obducted, so a uniquely complete section of the arc is now exposed from mafic-ultramafic base to volcanic and granitic rocks at the top. The Kohistan batholith constitutes the major unit of the arc and comprises a range of granitoids and minor gabbro and diorite associated with volcanic and metamorphic rocks. The research area in Northern Swat, Pakistan, contains plutonic bodies of gneissose quartz diorite, tonalite, diorite (sanukitoids and adakites?), granite, plugs of gabbronorite, and a small diorite intrusion. These rocks are spatially associated with minor volcanics as well as migmatitic metasediments and amphibolites. The Swat valley was mapped in detail and sampled in 2021. As part of the project, the petrological characteristics of all rock units exposed will be investigated in detail, using electron microscopy and electron microprobe analysis. Major and trace element compositions of the different granitoids and the associated mafic, volcanic, and metamorphic rocks will be determined using X-ray fluorescence and ICP-MS analysis. In-situ U-Pb dating of minerals such as zircon, apatite, titanite, and monazite will help to elucidate the onset of arc-related magmatism and age relationships between quartz diorite, granite, tonalite, younger leucogranite sheets and gabbroic plugs, the volcanics and the presumably older metasediments and amphibolites. In-situ Hf isotope of zircon will help to resolve the sources of the different igneous suites, whereas the morphology and trace element composition of zircon will allow to calculate its crystallization temperatures. The composition of amphibole in the plutonic rocks will be used to determine their emplacement depths.Whilst granitoids in the eastern part of the Kohistan Batholith have been studied in some detail, petrological, geochemical, isotopic, and age data are largely missing for those exposed in northern Swat Kohistan. All the above-mentioned analytical techniques combined with mapping and interpreting GIS data will be used to understand the petrogenesis and evolution of the granitoids and to unravel their geodynamic setting and relationship to associated volcanic and metamorphic rocks.

• DFG Programme: Research Grants
• International Connection: Pakistan, USA
• Co-Investigators: Dr. Axel Gerdes; Professor Dr. Armin Zeh
• Cooperation Partners: Professor Dr. Oliver Jagoutz; Professor Dr. Muhammad Qasim Jan; Muhammad Sajid