Geology of northern Jetty Peninsula, MacRobertson Land, Antarctica

Northern Jetty Peninsula, incorporating Else Platform (~140 km2) and Kamenistaja Platform (~15 km2), represents a mostly ice-free low-lying region located on the western flanks of the Lambert Graben. The region is underlain by granulite-facies Proterozoic gneisses and unmetamorphosed Permian sediments. Metamorphic rock types include quartzo-feldspathic, pelitic and semi-pelitic metasedimentary rocks of probable Mesoproterozoic age (Kamenistaja Paragneiss and Else Gneiss). Minor intercalated ultramafic and calc-silicate bodies are also present. Neoproterozoic (ca. 940-1000 Ma) syn-tectonic felsic intrusives (megacrystic Chistoe Granite, Melkoe Granite and Soyuz Leucogranite) are also widespread. Proterozoic rocks are subsequently intruded by Paleozoic Jetty Granite Dykes and felsic Stagnant Pegmatites (ca. 500 Ma), alkaline mafic dykes (ca. 308-320 Ma) and Mesozoic alkaline stocks and pipes (ca. 130-150 Ma). The Toploje Member of the Amery Group (a sequence of Permo-Triassic fluvial siliciclastic rocks, which outcrop extensively on the southern and western flanks of Beaver Lake) is exposed on southwestern Kamenistaja Platform and appears fault-bounded against the high-grade Proterozoic rocks. Together with adjacent high-grade rocks in Kemp and Mac.Robertson Lands to the west, the rocks of northern Jetty Peninsula form part of an extensive Meso-Neoproterozoic high-grade mobile belt (the 'Rayner Orogeny'; ca. 900-1100 Ma). During this event, on Else Platform, peak metamorphic conditions reached pressures as much as ~6.5 to 7.5 kbar at temperatures ~ 800º C and resulted in the development of a pervasive gneissosity (the dominant form surface, S1). Localized high-strain zones (S2) developed during latter stages of the high-grade metamorphic evolution, conditions during which are estimated at ~5 to 6 kbar at temperatures ~ 700º C. The intrusion of north-trending Jetty Granite Dykes (and their subsequent deformation) at ca. 500 Ma occurred at probable upper amphibolite-facies, indicating that an early Palaeozoic event (which reached granulite-facies in Prydz Bay, ~ 200-300 km to the northeast) significantly affected the Jetty Peninsula region. Minor northwest-trending steeping dipping mylonites and vertical north-trending brittle faults cut all rock types, except the massive quartz 'blows' and veins. These quartz pods are locally abundant (e.g. near Soyuz station), and, together with the late brittle faults, are thought to be related to incipient rifting of the Lambert Graben during the breakup of Gondwana.