Schedule of Mafic to Hybrid Magma Injections Into Crystallizing Felsic Magma Chambers and Resultant Geometry of Enclaves in Granites: New Field and Petrographic Observations From Ladakh Batholith, Trans-Himalaya, India

Santosh Kumar
2020 Frontiers in Earth Science  
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.
more » ... or hybrid magmas inject into felsic magma at low volume fraction (<0.35) of crystals and form the rounded to elongated microgranular enclaves in the Ladakh Batholith. Angular to subangular (brecciated), rounded to elongated pillow-like microgranular enclave swarms can also be documented as disrupted synplutonic mafic to hybrid dykes and sheets, when intruding the felsic magma with high 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 the 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. FIGURE 2 | (A) Panoramic view of diorite and granite-leucogranite-pegmatite hills near Sabu, showing the intrusive relationships between them. (B) Diorite is dismembered as xenoliths and partially assimilated by the intruding granite-leucogranite-pegmatite system. (C) Modally graded crude igneous layering shown by alternate bands of mafic and felsic minerals in the granite. (D) Biotite granite contains elongated mesocratic fine grained facies with diffused boundaries. FIGURE 6 | (A) Hillock showing disrupted mafic to hybrid synplutonic dykes and sheets injected into most crystallized granite. Note that synplutonic dykes and sheets are discontinuous and have got disrupted appearing pillowed but they broadly follow the same strike direction (NE-SE). (B) There are numerous mafic to hybrid enclave globules that are offset from dykes and sheets. (C) Closer view of part of mafic and hybrid synplutonic dykes. (D) Closer view of parts of hybrid synplutonic dykes. Note the sharp contact and straight contact outline of dyke with host granite, and felsic (quartz and K-feldspar) phenocrysts (xenocrysts) present in the hybrid synplutonic dyke. FIGURE 9 | (A) Plagioclase xenocryst (Pl-xn) in the porphyritic (hybrid) enclave. Note the sericitization along the plane of corrosion shown by a white arrow. Crossed polar. (B) Plagioclase xenocryst (Pl-xn) in porphyritic (hybrid) enclave showing patchy zoned core, corroded margin with the growth of An-rich plagioclase (bright gray) and albite rim. Crossed polar. The base of the photograph equals 2.5 mm. (C) Predominating amphibole and subordinate biotite show subpoikilitic relation with plagioclase laths in mafic synplutonic dyke. Note the quartz rinds in the center surrounded by minute dusty mafic grains. Plane Polarized. (D) Crossed polar view of the same as (C). The base of the photograph equals 2.5 mm.
doi:10.3389/feart.2020.551097 fatcat:mobsa26nhzhg3inmijx4omo3tq