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

Abstract

Abstract. The nunataks of Mühlig-Hofmannfjella and Filchnerfjella in central Dronning Maud Land, East Antarctica, comprise a deepseated 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 magmachambers. The alteration halos were formed by CO 2 -H 2 O-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°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.

Fluid infiltration, heat transport, and healing of microcracks in the damage zone of magmatic veins: Numerical modeling

“…The quartz syenite is mostly coarse grained and contains megacrysts of mesoperthitic K feldspar with minor quartz and plagioclase. A proportion of 5 -10% of mafic minerals comprises orthopyroxene, grunerite, hastingsite, biotite, and locally fayalite [Engvik and Elvevold, 2006]. The syenites of central Dronning Maud Land (11°E) are dated as 520-510 Ma [Mikhalsky et al, 1997;Paulsson, 2003].…”