Metamorphic and melt-migration history of midcrustal migmatitic gneisses from Nupskapa, The Maud Belt, Antarctica
Includes bibliographical references. Melt migration is an important process in the crust that causes significant mass transport, as well as differentiation and stabilisation of continental crust. Melt migration near the source occurs pervasively, through interconnected networks of melt-bearing struc...
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| Other Authors: | , |
| Format: | Master Thesis |
| Language: | English |
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University of Cape Town
2014
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| Online Access: | http://hdl.handle.net/11427/13277 https://open.uct.ac.za/bitstream/11427/13277/1/thesis_sci_2014_thomas_s.pdf |
| Summary: | Includes bibliographical references. Melt migration is an important process in the crust that causes significant mass transport, as well as differentiation and stabilisation of continental crust. Melt migration near the source occurs pervasively, through interconnected networks of melt-bearing structures. This style is restricted to the suprasolidus mid- to lower crust, while focused migration and ascent of magma occurs in isolated dykelike structures under subsolidus conditions, generally in the upper crust where brittle fracturing of rocks can occur. The details of how and when melt migration changes from a pervasive to focused style are poorly understood, particularly the temperature, pressure and deformation conditions which allow the transition to occur. The Nupskapa nunatak, in Dronning Maud Land of East Antarctica, exposes large cliffs that record evidence of multiple episodes of melt movement, in the form of pervasive leucogranite vein networks cross-cut by larger leucogranite dykes. Mineral equilibria modelling with THERMOCALC and comparison of results with previous work indicates that the Nupskapa nunatak records both Grenvillian and Pan-African metamorphism. Coarse-grained peak assemblages in samples from the Nupskapa area record conditions of 820-880 C at 9.5-11.6 kbar, while post-tectonic retrograde assemblages record late Pan-African conditions of 555- 595 C at 3.2{4.8 kbar. These later conditions lie between the wet solidus and the brittle-viscous transition and are inferred to represent the conditions of intrusion for post-tectonic composite dykes. Small-scale leucosomes predominantly lie parallel to the gneissic host rock fabric and define a pervasive network across the Nupskapa cliff. These leucosomes exhibit diffuse feathery boundaries and are inferred to represent in situ melting and melt segregation during M1 granulite facies peak metamorphism. Composite leucogranitic dykes cross-cut both the early leucosome phase and Pan-African shear zones in the field area. These north-trending, ... |
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