Field Observations of Dykes and Geometry of Igneous Enclaves in Ladakh Batholith Granitoids Around Taru, Leh, Ladakh, North India
摘要
The Ladakh Batholith is part of Andean-type Trans-Himalaya (Gangdese) plutonic belt that extends for 2500 km from Afghanistan in the west to east of Lhasa in Tibet. Dykes of varied composition e.g. doleritic, andesitic, basaltic andesite with 24–54 Ma age intrude Ladakh batholith along the southern margin at a number of places like Taru, Umla, Saboo, Thikse, Hemis-Shangpuchan etc. Ladakh batholith is also intruded by pegmatitic and aplite veins throughout its length and breadth. In the present work, dykes intruding Ladakh batholith at Taru village of Leh district of the Union Territory Ladakh have been studied to understand their mineralogical characteristics and stress regimes. The studied dykes are post-plutonic and extend from a few metres to several metres along with 1–3 m width. Nine dykes exist within ~5 km2 area around Taru. Mostly these are composed of plagioclase, pyroxenes, hornblende, k-feldspars, quartz and biotite. The phenocrysts have sizes between 1 to 10 mm. The studied dykes around Taru village have dominant NE-SW trend. Rose diagram of joints of the studied dykes shows that NE is the dominant trend of joints followed by NW, SW and SE as the other trends. The dominant strikes of the studied dykes and those of the joints is NE-SW. Igneous enclaves occur at places as grey to blackish blobs in the Ladakh granitoids around the study area. These enclaves are mafic, felsic and hybrid, fine to medium grained, melanocratic to mesocratic, without or with phenocrysts and vary in size significantly. The enclaves have varied shapes like schlieren, spindle, star, batman, tear drop, elongated, fish etc. The presences of these igneous enclaves indicate that the mingling process of mafic and felsic composition magmas had occurred within these granitic plutons present around Taru village.