Geology of the Mt Falconer Pluton, Lower Taylor Valley, South Victoria Land, Antarctica

Abstract

The pre-Beacon Group rocks of the Mt Falconer area (about 77° 30'S, 163° E), Antarctica, consist of, in decreasing order of age: (a) Skelton Group metasedimentary rocks (amphibolite facies); (b) granodiorite gneiss; (c) diorite “hybrid”, microdiorite, and granophyre dikes; (d) Mt Falconer epizonal quartz monzonite pluton (about 2 square miles in outcrop area); and (e) camptonite dikes. The pluton and the dikes of units (c) and (e) cut off the foliation and gneissosity of units (a) and (b) rocks, but there is no apparent deflection of the earlier structural trends. Dikes of unit (c) are cut off at a low angle by the pluton, which is in turn cut by dikes of unit (e) along the same structural trend as the earlier dikes. It is thought that the dikes of units (c) and (e) and the Mt Falconer pluton were passively emplaced along joints normal to fold axes in the Skelton Group rocks. The maximum depth of emplacement was probably no greater than 8–10 km. Textural and field relationships and the lack of correlation between anorthite content of plagioclase and modal abundance of orthoclase perthite and quartz suggest late stage, non-uniform introduction of K, Na, and Si during the crystallisation of the dioritic rocks of unit (c). This metasomatism is thought to be associated with the emplacement of the Mt Falconer pluton.