Subduction and continental collision in the Lufilian Arc-Zambesi Belt orogen : A petrological, geochemical, and geochronological study of eclogites and whiteschists (Zambia)
Mountain building processes are often the consequence of colliding continental plates which were usually separated by an ocean basin with basaltic crust. I investigated the relation between the Congo and the Kalahari cratons during the formation of the supercontinent Gondwana and the possibility of an ocean basin formerly existing between the two cratons. Eclogites are rocks with a basaltic composition which have undergone the high-pressure / low-temperature metamorphism typical of subduction zones where dense oceanic plates sink under less dense continental plates. Other potentially subduction related rocks beside eclogites are whiteschists (talc-kyanite schists). Whiteschists and eclogites occur in an orogenic belt situated between the Congo and the Kalahari cratons in Zambia. I studied the pressure-temperature evolution and the chemical composition of the eclogites and whiteschists. The results of the study show that the eclogites of Zambia represent former oceanic crust and that the ocean basin was relatively large. The age of the eclogite facies metamorphism is ca. 600 Ma. However, the whiteschists experienced peak metamorphic conditions only reaching the high-pressure amphibolite facies. Their formation is related to a crustal thickening event that affected the whole Lufilian Arc-Zambesi Belt orogen almost simultaneously at ca. 530 Ma. Thus, the conclusion is that the ocean basin was subducted ca. 600 Ma ago leading to the formation of eclogites and the whiteschists were formed ca. 70 my later during final collision of the Congo and the Kalahari craton during the Gondwana assembly.
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