Pan-African Tectonism in the Western Maud Belt: P-T-t Path for High-grade Gneisses in the H.U. Sverdrupfjella, East Antarctica

• Main Authors: Board, W.S., Frimmel, H E, Armstrong, Richard
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Oxford University Press 2015
• Subjects: Keywords: deformation; metamorphic rock; P-T-t path; Proterozoic; tectonic evolution; Antarctica; Arctic and Antarctic; East Antarctica; Queen Maud Land; World; Archaea; Laurentia East Antarctica; Geochronology; Maud Belt; Pan-African orogeny; Antarctic; Arctic; Dronning Maud Land; Grunehogna; Sverdrupfjella; Antarc*
• Online Access: http://hdl.handle.net/1885/79206

Extensive high-grade polydeformed metamorphic provinces surrounding Archaean cratonic nuclei in the East Antarctic Shield record two tectono-thermal episodes in late Mesoproterozoic and late Neoproterozoic-Cambrian times. In Western Dronning Maud Land, the high-grade Mesoproterozoic Maud Belt is juxtaposed against the Archaean Grunehogna Province and has traditionally been interpreted as a Grenvillian mobile belt that was thermally overprinted during the Early Palaeozoic. Integration of new U-Pb sensitive high-resolution ion microprobe and conventional single zircon and monazite age data, and Ar-Ar data on hornblende and biotite, with thermobarometric calculations on rocks from the H.U. Sverdrupfjella, northern Maud Belt, resulted in a more complex P-T-t evolution than previousyl assumed. A c. 540 Ma monazite, hosted by an upper ampibolite-facies mineral assemblage defining a regionally dominant top-to-NW shear fabric, provides strong evidence for the penetrative deformation in the area being of Pan-African age and not of Grenvillian age as previously reported. Relics of an eclogite-facies garnet-omphacite assemblage within strain-protected mafic boudins indicate that the peak metamorphic conditions recorded by most rocks in the area (T = 687-758°C, P = 9·4-11·3 kbar) were attained subsequent to decompression from P > 12·9 kbar. By analogy with limited U-Pb single zircon age data and on circumstantial textural grounds, this earlier eclogite-facies metamorphism is ascribed to subduction and accretion around 565 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions is ascribed to the intrusion of post-orogenic granite at c. 480 Ma. The recognition of extensive Pan-African tectonism in the Maud Belt casts doubts on previous Rodinia reconstructions, in which this belt takes a pivotal position between East Antarctica, the Kalahari Craton and Laurentia. Evidence of late Mesoproterozoic high-grade metamorphism during the formation of the Maud Belt exists in the form of c. 1035 Ma zircon overgrowths that are probably related to relics of granulite-facies metamorphism recorded from other parts of the Maud Belt. The polymetamorphic rocks are largely derived from a c. 1140 Ma volcanic arc and 1072 ± 10 Ma granite.