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

科希斯坦地体由白垩纪大洋内弧组成，在晚白垩世与喀喇昆仑地块碰撞后形成安第斯型边缘。在碰撞期间，科希斯坦被遮挡，所以现在从镁铁质-超镁铁质底部到顶部的火山岩和花岗岩，暴露了一段独特的完整的弧形。科希斯坦岩基构成了弧形的主要单位，由一系列花岗岩和与火山岩和变质岩伴生的次要辉长岩和闪长岩组成。巴基斯坦斯瓦特北部的研究区包括片麻状石英闪长岩、英云闪长岩、闪长岩(闪长岩和埃达克岩？)、花岗岩、辉长闪长岩栓和一个小的闪长岩侵入体。这些岩石在空间上与次要火山岩以及混合岩质变质岩和角闪岩有关。2021年，对斯瓦特山谷进行了详细测绘和采样。作为该项目的一部分，将使用电子显微镜和电子探针分析详细调查所有暴露的岩石单元的岩石学特征。不同花岗岩类及其伴生的镁铁质、火山岩和变质岩的主量元素和微量元素成分将通过X射线荧光和电感耦合等离子体质谱分析确定。锆石、磷灰石、钛铁矿、独居石等矿物的原位U-Pb定年将有助于阐明弧型岩浆作用的开始，以及石英闪长岩、花岗岩、英云闪长岩、年轻的淡花岗岩片和辉长岩塞、火山岩和可能较老的变质岩和角闪岩之间的年龄关系。锆石的原位Hf同位素有助于分辨不同火成岩套的来源，而锆石的形态和微量元素组成将有助于计算其结晶温度。深成岩中角闪石的成分将被用来确定它们的侵位深度。虽然对科希斯坦岩基东部的花岗岩类进行了较详细的研究，但在科希斯坦北部出露的花岗岩类大多缺乏岩石学、地球化学、同位素和年龄数据。所有上述分析技术，结合制图和解译地理信息系统数据，将被用来了解花岗岩类的岩石成因和演化，并揭示它们的地球动力学背景及其与伴生的火山和变质岩的关系。

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.