Mafic to hybrid microgranular enclaves in the Ladakh batholith, northwest Himalaya: Implications on calc-alkaline magma chamber processes

摘要: Felsic magmatisms in the north of Indus-Tsangpo Suture Zone (ITSZ) Ladakh range northwest Indian Himalaya, referred herein granitoids (LG), and associated magmatic rocks constitute bulk batholith. They have been characterized as Andean-type, calc-alkaline, largely metaluminous (I-type) to a few peraluminous (S-type) derived from partial melting subducting materials. The LG can be broadly classified into coarsegrained facies with abundant mafics (hbl-bt), medium-grained low content mafics, fine-grained leucocratic very amount mafics. Mesocratic melanocratic, rounded elliptical, fine medium grained, mafic hybrid microgranular enclaves (ME) are ubiquitous coarse-grained LG. ME absent or rare variety In this paper different types ME, their field relation microstructures respect felsic host documented northwestern, central, southeastern parts Rounded elongate variable sizes (a cm metres across, mostly d<30 cm) commonly having sharp, crenulate, occasionally diffuse contacts suggest that several pulses crystal-charged magmas coexisted, hybridized, co-mingled subvolcanic settings. Occurrence composite (several small enclosed large porphyritic ME) strongly point multiple magma intrusions partly crystalline chambers. Synplutonic dykes disrupted form subrounded angular (brecciated) swarms disposed strike-length injections at waning stage evolution rheological contrasts. Pillowing melt against (aplitic) residual suggests intrusion nearly-crystallized condition pluton. Although common mineral asemblages (hblbt-pl-kfs-qtz-ap-zrn-mt±ilm) (diorite, quartzdiorite) (granodiorite, monzogranite) may relate cogenetic relation, grained (hybrid) nature lack cumulate texture oppose cognate origin for ME. Presence plagioclase xenocrysts, quartz ocelli accicular apatite indicate mingling undercooling hybridized globules relatively cooler magma. Grain size differences some except those ones, appear related varying degrees most likely controlled by sizes. Several smaller however, chilled margin probably because disaggregation during course progressive hybridization (mingling mixing) leaving behind trails schlieren. Field microstructural evidences least products multistage mixing processes concomitant fractional differentiation batches formed open chamber(s) subduction setting.