Layered Cumulates in Granitoids, Leh Pluton, Ladakh Batholith, NW India

Roberto Weinberg, Monash University, Australia



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Cumulates are common in granitic bodies. The question of how crystals accumulate in such viscous melts is currently being discussed. This page illustrates a 40x30 m cumulate area within the granodiorite band of the Leh Pluton of the Ladakh Batholith (Weinberg and Dunlap, 2000, J. Geol. 108, 303-320). The upper contact of the Leh Pluton strikes N70W dipping 70o N and is comprised of granite, almost free of mafic. Southwards, mosl likely downwards into the pluton, enclaves become more common into a granodiorite band and even more common within the diorite in the deepest exposed portion. This cumulate zone within the granodiorite has numerous layers, and these are folded magmatically, possibly as a result of relative movement between the cumulate zone and the surrounding layer.






The eastern side of the cumulate zone within granodiorite. Base of cumulate is at the lower right of photo. Scale: the photograph covers ~20m in the horizontal direction

The western side of the cumulate zone. Cumulate bands dip 60-70o NNE


Cumulate bands. Looking west.

Cumulate bands. Looking west.


Base of the eastern cumulate area

Irregular lower contact between hornblendite at the base of eastern region and the surrounding granodiorite

Hornblendite at the base of the eastern region


Layering within cumulate


Sharp/gradual boundaries between cumulate layers and magmatic shear zone

Sharp mafic and felsic bands in block

Gradual decrease in mafic grains to the right

Magmatic shear band: a possible interstitial melt escape path


Mafic Enclaves

In general, there are few microgranular mafic enclaves in this cumulate zone. This is an angular mafic enclave surrounded by felsic granitic rock forming an elliptical composite enclave within layered cumulate

This block shows the accumulation of enclaves with long hornblende laths and plagioclase.