The geological evolution of the Mawson Coast/Framnes Mountains

Brief description

Metadata record for data from ASAC Project 177
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From the abstracts of some of the referenced papers:

The high-grade metamorphic rocks of the Colbeck Archipelago comprise granulite facies metasedimentary gneisses and charnockitic gneisses of three ages. A suite of rocks previously mapped as the Colbeck Gneiss is shown to be composite in age and origin, consisting of metasedimentary and orthogneiss that are intruded by granitic gneiss and charnockitic gneiss. An (?) Archaean granulite facies S1 gneissosity is preserved in the metadsedimentary gneisses and early orthogneiss; the development of S1 was followed by isobaric cooling from peak metamorphic conditions of T greater than or equal to 750 degrees C and P equal to 5.1 plus or minus 0.8 kbar. Younger intrusions cut rocks containing S1 structures, but were deformed by an approximate 1200 Ma granulite facies D2 event that resulted in reclined, isoclinal F2 folds oriented parallel to a pervasive east-trending L2 mineral and stretching lineation. Rocks bearing S2 structures are cut by the areally extensive ~ 960 Ma Mawson Charnockite, which was affected by two upright folding events D3 and D4 at ~ 920 Ma. Events D2-4 comprise the Proterozoic Rayner Structural Episode, which is characterised regionally by the retrogression of Archaean assemblages. The two pulses of extensive intermediate to felsic magmatism accompanied or immediately preceded the Proterozoic orogenies evident as D2-4, and it is tempting to infer casual links. However, field relationships are consistent with intrusion having been contemporary with anomalously high conductive heat fluxes, which could be due to advective heating from larger intrusions are not exposed at the present structural level. The formation of extensional, granulite facies D5 ultramylonite plus or minus pseudotachylite zones is the last deformation event in the area.

The high-grade metamorphic rocks exposed along the MacRobertson and east Kemp Land coasts consist of, in the west, Archaean gneisses reworked during a ductile mid-Proterozoic deformation, and in the east, foliated Proterozoic charnockite gneiss containing large remnants of gneiss of probable Archaean age. Evidence for three folding events is recognised in the reworked gneisses. An early recumbent terrain is deformed by two upright events possessing near-vertical axial surfaces. The charnockite gneiss preserves evidence of only the final event. These three events comprise the Rayner Structural Episode, which was a consequence of the ductile thrusting of Archaean gneiss westward toward a stable Archaean block, the Napier Complex. Kinematic indicators are consistent with the formation of the Proterozoic recumbent terrain by dominantly shear deformation. Dissection of both the Rayner and Napier Complexes by retrograde shear zones and mylonite-pseudotachylite zones was a consequence of the northward thrusting of the two complexes during the Cambrian.