Late Pan-African Fluid Infiltration in the Mühlig-Hofmann- and Filchnerfjella of Central Dronning Maud Land, East Antarctica

Abstract

The nunataks of Muhlig-Hofmannfjella and Filchnerfjella in central Dronning Maud Land, East Antarctica, comprise a deep-seated metamorphic-plutonic rock complex, dominated by a dark colour due to dark feldspar and containing granulite facies minerals including perthite, plagioclase, orthopyroxene and garnet. The area was affected by a late Pan-African fluid infiltration outcropping as conspicuous light alteration zones restricted to halos around thin granitoid veins. The veins were formed during infiltration of volatile-rich melts, probably originating from underlying magma-chambers. The alteration halos were formed by CO2-H2O-Volatiles emanating from the veins into the host rock causing hydration of the granulite facies assemblages. The alteration involves a breakdown of orthopyroxene to biotite and sericitisation of plagioclase at crustal conditions around 350-400 degrees C and 2 kbar. The marked colour change is caused by transformation of feldspars, spread of dusty micas, opaques and fluid inclusions in addition to replacement of coarse to finer grains. The process is locally penetrative indicating that fluid infiltration can affect large rock volumes. The frequent distribution of alteration zones throughout the mountain range independent of lithological variations shows that the fluid infiltration is regionally extensive.