Abstract
Diorites, granites, and associated magmatic enclaves and dykes constitute the bulk of the Ladakh Batholith, which is an integral part of the Trans-Himalayan magmatic arc system. In this paper, geometry of microgranular enclaves hosted in the granites has been examined from the Leh-Sabu-Chang La and surrounding regions of the eastern Ladakh Batholith to infer the mechanism and schedule of mafic to hybrid magma injections into evolving felsic magma chambers and the resultant enclave geometry. Mafic and/or hybrid magmas injected into felsic magma at low volume fraction ( 0.65) of crystals. A large rheological difference between coeval felsic and mafic magmas inhibits much interaction. Mafic magma progressively crystallizes and evolves while minimizing thermal and rheological differences. Consequently, the felsic-mafic magma interaction process gradually becomes more efficient causing dispersion of enclave magma globules and undercooling into the partly crystalline felsic host magma. Thus, the evolution of the Ladakh Batholith should be viewed as multistage interactions of mafic to hybrid magmas coeval with felsic magma pulses in plutonic conditions from its initial to waning stages of evolution.
Highlights
Granites may contain any type of lithic inclusion or fragment, which is commonly referred to as enclave
Some favor the cogenetic relation between the enclave and host granites (e.g., Pin et al, 1990; Shellnut et al, 2010) whereas some argue their derivation from common crustal sources (e.g., Güraslan and Altunkaynak, 2019; Lu et al, 2020); and some advocate mafic-felsic magma mixing, mingling, chemical modification, and isotopic re-equilibration at varying degrees responsible for their partial to nearly equivocal chemical and isotopic features (e.g., Holden et al, 1987; Eberz and Nicholls, 1990; Elburg, 1996; Kumar and Rino, 2006; Adam et al, 2019)
It is likely that the Neo-Tethyan oceanic subduction-related magmatism may have been initiated with the emplacement of diorite followed by profuse granite magmatism in the Ladakh Himalaya
Summary
Granites (sensu lato) may contain any type of lithic inclusion or fragment, which is commonly referred to as enclave (a French term, Lacroix, 1890 in Didier, 1973). New spectacular field and petrographic features of microgranular enclaves, and dyke- and sheet-like enclave swarms, referred as synplutonic dykes, hosted in the granites exposed in and around Leh, Sabu, and Chang La regions of Ladakh Batholith have been documented and examined in order to understand the style and schedule of mafic to hybrid magma injections into felsic magma chambers from its initial to waning stages of evolution (i.e., with increasing crystallinity and rheology). From the granites of western (1.44–2.19), central (1.31–1.90), and eastern (1.71–2.63) parts suggests the contribution of dominant calc-alkaline, metaluminous (I-type), and subordinate amount of peraluminous (S-type) felsic magmas in the evolution of Ladakh Batholith. Kumar and Singh (2008) suggest that the enclaves and host granites are largely as calc-alkaline, mildly to strongly metaluminous (molar Al2O3/CaO + Na2O + K2O 0.9–1.05), which are compositionally different from diorite, gabbro, and mafic dykes. In and around the Leh and Sabu regions, stock-like dioritic bodies are found as pre-existing older lithological units as compared to the granites (Kumar et al, 2016; Weinberg, 1997)
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