Chemical composition and genetic relations of the Matchless amphibolite (Damara orogenic belt)

Ten widely spaced samples of the Matchless and neighbouring amphibolites have been analysed for major and 24 minor elements (including Rare Earths). The mafic rock is of uniform character and occurs almost continuously over a 350 km distance within a thick sequence of clastic sediments. The mafic rocks were probably deposited on a sialic crust and they have the typical composition of an ocean-ridge tholeiite. The geologic evidence for an origin at diverging or converging plate boundaries is not convincing. An explanation of these rocks as indicators of abnormal heat flow in a chemically normal mantle under a thin crust (>= 30 km) is in accordance with petrologic experiments