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The blanketting effect of greenstones cover ... |
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Most Archaean crusts are composed of granitoid rocks overlain by a 5 to 15 km thick greenstones cover made of mafic volcanics. These mafic rocks were extracted form a hot (~1700ºC) mantle plume that spread at the base of the lithosphere. The greenstone covers acted as a blanket preventing the heat produced in the crust to escape and consequently producing a warmer geotherm. The graph on the left shows the very weak thermal impact of a hot plume emplaced at that base of a 140 km thick lithosphere. In contrast the graph on the right shows how significant is the thermal impact of the emplacement of a thick greenstone cover. Following the emplacement of a 10km thick greenstone cover TMoho rises by nearly 300ºC in less than 50Ma! |
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