The shield is very depressed in the centre of Antarctica. Here, it carries the bulk of the Antarctic ice sheet. Large areas lie deeper than 1, m below sea level. Why live in Antarctica? How many people? Nations of the Antarctic Treaty system agreed in to put a halt to the exploitation of minerals when they signed the….
This content was last updated 1 year ago on 27 October Back to About Antarctica. The Transantarctic Mountains, depicted here, started growing about 50 million years ago, and represent the shoulders of the rift zone now occupied by the Ross Sea. The oldest rocks that form the core of this range are metamorphic rocks that were deformed during the Early Palaeozoic Ross Orogeny. A Weddell seal lies on the sea ice in the foreground.
A grounded iceberg, incorporating sea-floor sediment lies across the sea ice in the background. The crystalline texture of this Ross Orogeny granite shows alignment of white feldspar crystals, indicating deformation during or after intrusion on a small island in Granite Harbour, Western Ross Sea.
Granite from the Ross Orogeny, in this case showing an undeformed texture and the characteristic light-coloured minerals of quartz grey and feldspar white and pink. Large volumes of magma intruded the gneisses during this period. The magma solidified to form new rocks like granite, charnockite and syenite. These intrusions? Another characteristic feature of the granitoid rocks in Dronning Maud Land is the dark-brown weathering colour, which often makes them recognisable at a long distance.
Towards the end of the pan-African orogeny, the thickened crust became unstable. Extension of the crust in Dronning Maud Land led to rocks from a deeper level in the crust being carried to higher levels. The extension stretching continually occurred from deeper crustal levels, where ductile plastic deformation of the rock mass takes place, towards higher crustal levels, where the crust deforms in a brittle fashion.
Structures formed at the different crustal levels can be observed as folds, shear zones and faults. Brown rocks characterise large parts of Dronning Maud Land.
You can often see light-coloured zones and stripes on the cliffs. These stripes are caused by fluids which have transformed, bleached, the dark rocks. Crystalline rocks originating at great crustal depths are basically compact and impermeable.
Fluids can, however, invade the rock along fractures which occur as veins in the centre of the light stripes. The marked colour change arose when the fluids flooded along the microfractures in the country rock, transforming the original minerals into new, hydrous minerals.
Analyses of fluid inclusions preserved in the minerals show that they consisted of water, carbon dioxide and small amounts of nitrogen. Fluid infiltration in the bedrock of Dronning Maud Land is far-reaching and shows regional distribution.
Their significance in geological processes has been an important research topic in recent years. Owing to the good exposure where the mountains breach the Antarctic ice cap, Dronning Maud Land is a unique laboratory for studying just such processes.
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