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 from the intrusion of hot mafic magma into colder felsic magma. This paper describes a small body (100 X 30 m) in the Ladakhi Himalayas, northwest India, where mingling occurred when granite magma intruded and disrupted a pool of partially molten quartz-diorite that formed fine-grained pillow-like enclaves. The mingled body is surrounded by coarse-grained quartz-diorite that was effectively solid during granite emplacement and, within a short distance from the body, was brecciated by the granite. Because the enclaves are virtually in situ, their shapes retain details related to their disruption and to the relative motion between the two magmas. Whereas this seems to be a rare description of mingling and formation of mafic enclaves by intrusion of felsic into mafic magma, this paper argues that, because many batholiths evolve from mafic to felsic, this may be more common in nature than generally realized and not simply an extraordinary feature of that particular locality in the Himalayas.