Garnet bearing granite (Grt granite) and high grade pelitic gneisses occur in the Kannak Complex, southern Kontum Massif, central Vietnam. Electron microprobe (EMP) dating of monazite in Grt granite and garnet orthopyroxene gneiss (Grt Opx gneiss) gave ages of ca. 260 Ma from cores and ca. 230 Ma from thin rims. Since most monazite grains are predominately of core composition, the ca. 260 Ma age indicates the timing of high temperature metamorphism and the formation of Grt granite. Grt granite is locally accompanied by coeval intrusions of fine grained gabbro, which is a candidate for the heat source leading to high grade metamorphism and partial melting of the crust during the Late Permian.
SUMMARYThe prohibition of commercial mineral resource extraction through the Antarctic Treaty System has removed one significant source of potential damage to Antarctica's geological and geomorphological values. However, given the on-going increase in Antarctic tourism and scientific footprint, some high-quality geological features may be vulnerable to human impact, such as damage due to the construction of logistical facilities, unregulated collection of geological specimens or oversampling for scientific purposes. The Protocol on Environmental Protection to the Antarctic Treaty puts in place a framework for the protection of Antarctica's environmental, scientific, historic, wilderness and aesthetic values. However, the Antarctic Protected Area system is still immature and further implementation of existing management tools may be required to protect the diverse range of vulnerabilities, qualities and spatial scales represented in the geology and geomorphology of the continent. At sites where high-quality mineralogical or palaeontological specimens exist in limited quantities, considerations of how best to prevent oversampling and manage access to remaining material may be supported by assessment of cumulative impacts. Examination of the level of Antarctic specimen loans from a selection of national geological collections suggested that existing publically accessible geological collections could be better utilized, which could reduce environmental impact and oversampling at vulnerable Antarctic sites.
This paper first reports the counter-clockwise pressure-temperature (P-T) path for the Lützow-Holm Complex in East Antarctica. The metamorphic textures of kyanite-bearing pelitic gneisses from Tenmondai Rock including earlier spinel and ilmenite inclusions, geothermobarometric data, and pseudosection modeling indicate that the pressure increases prior to the peak metamorphic conditions at around 9 ± 0.5 kbar and 770-820 °C, followed by cooling to kyanitestability field. We conclude that these gneisses, underwent granulite-facies metamorphism with a counter-clockwise P-T path, but this contrasts with the widely recognized clockwise P-T path of the Lützow-Holm Complex basement rocks in general. One plausible hypothesis we proposed could be that this counter-clockwise P-T path originated from magmatism with late compression and the rocks of the different structural levels are juxtaposed, while acknowledging that this hypothesis conflicts with previous studies and that further work is needed to clarify these issues.
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