The post-Pan-African thermal and extensional history of crystalline basement rocks in eastern Tanzania

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Apatite fission track thermochronology from basement rocks in eastern Tanzania reveals a protracted history of denudation, uplift and extensional tectonism for the region after Carboniferous time. The data show that post-Pan-African development of eastern Tanzania was characterised by long periods of slow cooling punctuated by at least three relatively rapid cooling events, during the Early Cretaceous, Late Cretaceous-Early Palaeogene and Late Eocene-Early Oligocene. The relatively rapid cooling resulted from episodes of increased denudation rates related to the formation and reactivation of high-angle block faults that moved in response to intraplate stress. The episodes of denudation are manifested as packages of clastic sedimentary rocks in East African basins. Abrupt offsets in the trends of the apatite fission track data at major faults is consistent with development of a nascent rift valley within the broad region of previously block faulted and mildly extended crust, during Neogene time. The nascent rift valley was focused within a zone of weakness, associated with reactivation of favourably orientated regional-scale Proterozoic structures. This is particularly true of the subsurface boundary between the thick lithosphere of the Tanzanian Craton and the relatively thinner lithosphere of the Proterozoic Mozambique Belt.