The charnockite-anorthosite suite of rocks exposed in central Dronning Maud Land, East Antarctica: a study on fluid-rock interactions, and post-entrapment change of metamorphic fluid inclusions

• Main Author: Kleinefeld, B.
• Format: Thesis
• Language: unknown
• Published: 2003
• Subjects: Antarc*; Antarctica; Dronning Maud Land; East Antarctica
• Online Access: https://epic.awi.de/id/eprint/16323/; https://epic.awi.de/id/eprint/16323/1/Kle2003d.pdf; https://hdl.handle.net/10013/epic.26278; https://hdl.handle.net/10013/epic.26278.d001

The study area of central Dronning Maud Land, East Antarctica is a typical example of a granulite facies Precambrian terrane that was exposed to substantial polymetamorphism during the late Neoproterozoic/early Palaeozoic. Fluid inclusion studies from typical representatives of the charnockite-anorthosite suite of rocks, associated gneisses and syenitic intrusives give new constraints on both peak metamorphic conditions and post-peak metamorphic processes during retrograde uplift. Detailed petrographical studies were supported by Electron Microprobe techniques and combined with microthermometry and Raman spectrometry data.Three distinct fluid phases, either consisting of CO2±N2, H2O-salt or CO2±N2±H2O- salt were differentiated. All fluid inclusion types are hosted by plagioclase, quartz and garnet and display textural relationships indicative for a primary (metamorphic or magmatic) origin. The CO2±N2 fluid is most abundant, and it is assumed that it played an important role during metamorphic charnockite formation and anorthosite emplacement. However, evidence of post-entrapment change reveals that a largenumber of inclusions were subjected to profound reequilibration processes that resulted in a modification of original fluid properties, often accompanied by the partial to complete loss of an aqueous component.An important indicator for the residual character of some CO2±N2 fluid inclusions was the frequent observation of sheet silicate and carbonate microcrystals that were produced by a micro-chemical reaction of an originally CO2-H2O±N2 fluid with its plagioclase host. These observations from the anorthosite complex were used to model the fluid-host interaction with consideration of different original fluid compositions. Compared to an actual fluid inclusion it is obvious, that volume estimations of solid phases can be used as a starting point to reverse the retrograde reaction and recalculate the compositional and volumetrical properties of the original fluid. Isochores for an unmodified inclusion can thus ...