Petrography, geochemistry and petrogenesis of the intrusive rocks in the Leh (Ladakh batholith) region, Trans-Himalaya (India)

The Ladakh Batholith ia a part of the Trans-Himalayan Plutonic Belt located in Jammu & Kashmir (India), which represents subduction-related And-type magmatism, intruding an island arc setting. The Shyok tectonic zone lies to the north and Indus suture zone to the south of the Ladakh batholith that extends with WNW-ESE direction having ~600 km in length, 30-80 km in width and 3 km in thickness. The intrusive rocks of the Basgo, Nimu, Umla, and Taru regions of the Ladakh batholith and its surroundings show different compositions ranging from medium-coarse-grained to generally grayish colored monzodiorite to granitic rocks. These rocks are having common mafic magmatic enclaves and dykes that cut these rocks in different directions. The intrusive rocks of Basgo, Nimu, Umla and Taru region are medium to coarse grained with having common holocrystalline and hypidiomorphic granular texture. The main minerals of these rocks are K-feldspar, plagioclase, quartz, biotite, hornblende; sphene, apatite, zircon, Fe-Ti oxide forms accessory minerals. Petrographically, they are fine to medium grained monzonite, monzodiorite, diorite, granodiorite and granite rocks. They consist of plagioclase (An55-99), K-feldspar (Or85-99). Amphiboles are mainly Edenite, Magnesio-Hornblende and Hastingsite in composition. In terms of Al-Mg-Fe(t) content, all samples are plotted in field of annite have relatively more Fe content than Mg. Biotites from all granitoids were accompanied with amphibole group of minerals, which is a typical characteristic of calc-alkaline subduction related metaluminous (I-type) granitoids. Fe-Ti oxide with poikilitic, perthitic, myrmekitic textures and graphic textures. The geothermobarometry results of intrusive rocks have crystallization temperatures ranging from 452 to 628°C and pressures ranging from 2.3 to 3.9 kbar. Al-in-hornblende barometry indicates the depth of crystallization for the diorite to be 12.8 km and granodiorite to be around 8.3 km. The calc-alkaline rocks are metaluminous/peraluminous I-to S-type of pluton ranging from monzodiorite to granite. A/CNK (0.87-1.31) indicating I-type parental magma for most of the samples, whereas some samples shows transition between I & S- type granitoids. SiO2 values of Ladakh Batholith samples are vary between 51.8% and 75.8%. Binary Harker diagrams show a strong negative correlation when Al2O3, TiO2, Fe2O3t, MgO, CaO, Na2O, P2O5 are plotted against the increasing amount of silica, while K2O values have strong positive correlation. Chondrite-normalized REE patterns of intrusive rocks shows enrichment in LREE pattern whereas depletion in HREE pattern. They have total REE content of 20–181 ppm, and are moderately to highly LREE enrichment, with (La/Yb)N = 3.75–45.95. These granites show prominently negative Eu anomalies (Eu/Eu*=0.35–4.97) and moderately HREE fractionation with (Gd/Yb)N = 0.83–4.40. Sr-Nd isotope analyses of the Ladakh intrusive rocks fall within a narrow range for initial 87Sr/86Sr(i) (0.70414 to 0.70544) and 143Nd/144Nd(i) (0.512647 to 0.512695) ratios with slightly positive εNd(t) values (+1.68 to +2.62), similar to I-type granites generated in an arc setting. In the Sri-Ndi diagram, samples are located in the low Sr and high Nd area, while some granodiorite composition samples are located in the area representing the high Sr and high Nd area. Petrography, rock and isotope geochemistry shows the fractional crystallization and magma mixing / mingling processes are effective in the formation of Ladakh intrusive rocks. KEYWORDS: Jammu and Kashmir, India, Trans-Himalaya, Ladakh Batholith, Intrusive Rock, Mineral Chemistry, Geochemistry, Radiogenic Isotope Geochemistry, Petrogenesis, Fractional Crystallization, Magma Mixing/Mingling