Zircon U-Pb Age, Geochemistry and Geological Significance of the Basic-Acidic Rocks in the Ubendian Belt, Tanzania

The Ubendian Belt, which is situated on Tanzania’s southwest border, has undergone a multi-stage tectonic evolution history. Compared with other stages, there has been comparatively little research on the Mesoproterozoic Mag Matism, which restricts the study on the Mesoproterozoic tectonic evolution history of Ubendian Belt. Based on this, the Mesoproterozoic gabbro and syenite are selected for petrological, geochronology and geochemistry studies. The results show that the crystallization ages of the gabbro and syenogranite are (1433±9) Ma and (1428±11) Ma, respectively, indicating they are Mesoproterozoic. The gabbro is characterized by high content of TiO₂(2.6%) and Ti/Y ratio (601), enriched in LREE with (La/Yb)_N of 4.85, and slightly positive Eu ano Malies (δEu=1.02). The LILEs (Rb, Ba, Sr, K) are enriched and HFSEs (Nb, Ta, Zr) are depleted, the geochemical features of the gabbro are consistent with continental flood basalts (CFB), indicating that it May be the production of a low degree partial melting of the enriched continental lithospheric Mantle. The syenites have high contents of SiO₂ (71.59%～75.08%), they are characterized by enrichment in LREE with (La/Yb)_N of 22.86～28.51, significant negative Eu ano Malies (δEu=0.12～0.34). Their values of Ga/Al are high (Ga/Al×104=2.98～3.11) and the content of Zr+Nb+Ce+Y is much larger than 350×10⁻⁶, indicating that they are A-type granites. The lower Mg^# values (6～10) and Sr/Y ratios (0.17～0.65), indicating that they are the production of partial melting of basaltic rocks in the middle-lower crust. Both of the gabbro and syenite originated within an intra-plate rifting enviroment, which is consistent with the global tectonic regime of the Columbia Supercontinent rifting event.