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Zircon U-Pb Dating of the Paleoproterozoic Tuffs from the Nsama Formation in Northeastern Zambia: Records of the Assemblage Event of the Columbia Supercontinent

2022; RELX Group (Netherlands); Linguagem: Inglês

10.2139/ssrn.4151520

1556-5068

Junping Ren,

earthquake and tectonic studies

The study of the LA–MC–ICP–MS zircon U-Pb geochronology and geochemistry of tuffs from the Nsama Formation of the Mporokoso Group in the Muva Supergroup is of great importance for the Bangweulu Block in northeastern Zambia, as there has been no precise dating reported so far. The Block mainly consists of the Paleoproterozoic basement and the sedimentary Muva Supergroup as the younger cover out of which three (3) fresh tuff samples from the Nsama Formation were dated by using LA–MC–ICP–MS zircon U–Pb, producing a weighted mean of 1791 ± 5 Ma. Furthermore, it was determined that the tuffs belonged to a high-K calc-alkaline series, characterized by enrichment of LREE relative to HREE and Rb and Th (U), and depletion of Ba, Nb, Sr, P, and Ti. In addition, the tuff samples displayed ε Hf (t) values ranging from -2.6 to +4.7, among which twenty (20) analyses yielded values of negative ε Hf (t) corresponding to T DM2 of 2211–2543 Ma, while forty-one (41) analyses yielded values of positive ε Hf (t) corresponding to T DM1 of 2034–2219 Ma. Lu–Hf isotopic data suggested that the Paleoproterozoic and Archaen crusts existed in the Block and that the protolith was most likely derived from a hybrid source of both old crust and depleted mantle materials. Based on the aforementioned, it is concluded that the Nsama Formation formed in a granitic volcanic arc along an active continental margin, which may be responded to the assemblage of the Columbia Supercontinent in Africa.