Interaction between deformation and charnockite emplacement in the Bunger Hills, East Antarctica
Abstract
The Bunger Hills, East Antarctica, have been metamorphosed at granulite facies and variably deformed by three deformation phases, as well as having been intruded by a number of dyke generations and large pyroxene-bearing intrusive bodies. The multiple intrusion and the conspicuous pattern of the major structural features around the intrusive bodies allows a detailed relative timing history of the events to be established. A layered and a massive gneiss series can be distinguished. The layered gneiss series consists of metapelitic, psammitic, intermediate and meta-basic gneisses that are interlayered on all scales. The massive gneiss series is, in part, identical in bulk composition and has been interpreted as an intrusive equivalent to the layered series. The first deformation phase, D1, caused recumbent folding of both series and boudinage of an early set of mafic dykes. The metamorphic temperature peak was reached during this deformation. A northern charnockite body (Fishtail Bay body) was intruded during D1 and was partially deformed by it. D2 occurred subsequently and is the major shortening deformation. The transition from D1 to D2 is marked by intrusion of mafic dykes that are metamorphosed and folded but not boudinaged. The regional orientation of the F2 axes is extremely variable over the extent of the Bunger Hills. The F2 axes appear to wrap around the northern charnockite body. This may be explained by a competency contrast between the rigid charnockite and the surrounding partially molten gneiss sequence during deformation in a dextral shear environment. A large southern intrusive body (Lake Figurnoe charnockite) was intruded towards the end of this deformation phase. This body is much coarser grained, is undeformed and has a contact metamorphic halo around it. The metamorphic pressure peak was reached at this time. Strong asymmetric D3 doming and late brittle fracturing occurred during subsequent cooling of the Bunger Hills.
- Publication:
-
Journal of Structural Geology
- Pub Date:
- 1990
- DOI:
- 10.1016/0191-8141(90)90088-G
- Bibcode:
- 1990JSG....12..767S