Geology, Petrographic Characteristics and Tectonic Structure of Paleoproterozoic Basement of Kabul Block (north Eastern Afghanistan), Initial Findings

Abstract

The Paleoproterozoic basement of Kabul Block is a cratonic basement in north eastern Afghanistan. Precambrian Kabul Block including metamorphic rocks only takes place at the base of the study area. The Neo-Proterozoic Welayati formation overlies the Paleo-Proterozoic Sherdarwaza formation with a tectonic contact, and they both overlay Khair Khana formation. In the region, Alghoi meta granitoid intruded into both Khair Khana and Sherdarwaza formations. The Khair Khana formation contains of granulites, granitic gneisses ve amphibolites. The mineral assemblages of granulites are plagioclase + quartz + K-feldspar + orthopyroxene + clinopyroxene (diopside/augite). Granitic gneisses are observed as hornblende gneiss, garnet-biotite gneiss and pyroxene-gneiss. Hornblende-gneisses include hornblende + quartz + K-feldspar mineral assemblage, garnet-biotite gneisses are evident with plagioclase + quartz + K-feldspar + biotite (red) + garnet mineral assemblage, and pyroxene gneisses include quartz + plagioclase + biotite + clinopyroxene mineral assemblage. Amphibolites consist of hornblende + plagioclase + quartz ± zoisite ± sphene ± ilmenite ± apatite mineral assemblage. The Sherdarwaza formation contains marbles, amphibolites, biotite gneisses, micaschists and migmatites. Marbles consist of calcites ± quartz ± apatite. In amphibolites, harnblende + plagioclase + quartz ± epidote ± zoisite ± garnet mineral assemblage are observed. Biotite gneisses include plagioclase + quartz + microcline + biotite ± sphene ± apatite ± zircon mineral assemblage. Micachists consist of quartz + plagioclase + microcline + biotite ± sphene ± apatite mineral assemblage. Migmatites include plagioclase + quartz + microcline +biotite ± sphene ± apatite mineral assemblage. Alghoi meta granitoid is generally observed as stocks and small masses, and sometimes it shows foliation. It consists mainly of meta granites. The meta granites that show granular texture include plagioclase + quartz + K-feldspar + biotite + hornblende. The Welayeti formation contains quartzite, kyanitegarnet-staurolite schist, garnet-mica schist, kyanite-garnet-mica schist and garnet-muscovite schist. Quartzite include quartz ± muscovite ± biotite. They are observed hornblende + quartz + plagioclase ± garnet ± epidote ± zoisite ± rutile ± magnetite in amphibolites. Kyanite-garnet-staurolite schists are evident with staurolite + kyanite + garnet + mica + biotite + quartz + plagioclase ± apatite ± epidote ± ilmenite ± monazite mineral assemblage. Garnet-mica schists and kyanite-garnet-mica schists include quartz + plagioclase + biotite + muscovite + kyanite + garnet ± chlorite ± apatite ± tourmaline ± sphene ± rutile. In garnet-muscovite schists, muscovite + quartz + plagioclase + garnet ± tourmaline ± apatite ± zircon are observed. The granulites in Kabul Block are together with granite gneisses, and they can be separated under one formation. Granulites show different mineral compositions, Usually, they are without garnet, in some cases they include garnet. The amount of plagioclase is higher in them according to other rocks. In some cases, the composition of granulitesis very similar to that of quartz mangarites that indicates high temperature and pressure of the metamorphism process and shows that this block is related to a segment of Columbia and Rodinia supercontinents during Paleoproterozoic collisional events.