THE DISRUPTION OF A DIORITE MAGMA POOL BY INTRUDING GRANITE - THE SOBU BODY, LADAKH BATHOLITH, INDIAN HIMALAYAS

Most examples of magma mingling described in the literature result fro m the intrusion of hot mafic magma into colder felsic magma. This pape r describes a small body (100 x 30 m) in the Ladakhi Himalayas, northw est India, where mingling occurred when granite magma intruded and dis rupted a pool of partially molten quartz-diorite that formed fine-grai ned pillow-like enclaves. The mingled body is surrounded by coarse-gra ined quartz-diorite that was effectively solid during granite emplacem ent and, within a short distance from the body, was brecciated by the granite. Because the enclaves are virtually in situ, their shapes reta in details related to their disruption and to the relative motion betw een the two magmas. Whereas this seems to be a rare description of min gling and formation of mafic enclaves by intrusion of felsic into mafi c magma, this paper argues that, because many batholiths evolve from m afic to felsic, this may be more common in nature than generally reali zed and not simply an extraordinary feature of that particular localit y in the Himalayas.