Lithogeochemistry, geochronology and geodynamic setting of the Lupa Terrane, Tanzania: Implications for the extent of the Archean Tanzanian Craton

Abstract

Herein we provide new zircon U–Pb ID-TIMS, U–Pb LA-MC-ICP-MS and Lu–Hf LA-MC-ICP-MS results from the Lupa Terrane, SW Tanzania, and demonstrate that previously considered Paleoproterozoic granites comprising the Paleoproterozoic Ubendian Belt are in fact Archean (ca. 2.74Ga). Disparately older inherited zircons (ca. 2.85Ga) and Lu–Hf zircon model ages (≥3.1Ga) suggest that these Archean granites likely interacted with substantially older crust underlying the Lupa Terrane at the Tanzanian cratonic margin. Foliated Archean granites are in turn cut by non-foliated, voluminous and greenschist facies granitic-gabbroic intrusions (1.96–1.88Ga), which are broadly concomitant with granulite- to amphibolites-facies rocks that characterize the other lithotectonic terranes comprising the Ubendian Belt. New geochemical results suggest that these Paleoproterozoic intrusive phases possess trace element compositions that are typical of continental magmatic arcs, which is consistent with the crust-magma interaction inferred from field relationships and inherited Archean zircons within Paleoproterozoic granitic intrusions. Together the available field and geochemical evidence suggest that the Lupa Terrane was a continental cratonic margin during the Paleoproterozoic onto which the other Ubendian lithotectonic terranes were accreted and implies at least a 150km southwest extension of the currently accepted position of the Tanzanian craton margin. These new results are consistent with re-worked Archean crust reported in other metamorphic belts enveloping the Tanzanian Craton and seismic tomography studies that suggest significant portions of the Ubendian Belt represent re-worked Archean lithosphere.