|
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.CLICK ON ANY PHOTO FOR HIGH RESOLUTION VERSION |
Cumulates
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. |