Evidence of the latest Paleoproterozoic (~1615 Ma) mafic magmatism the southern Siberia: Extensional environments in Nuna supercontinent

Abstract

The paper presents a new geological, geochronological, geochemical and Nd isotopic data on the latest Paleoproterozoic dolerite sills, exposed in the Biryusa inlier of the southern Siberian craton among the sandstones of sedimentary sequence traditionally suggested as Neoproterozoic. One dolerite sill yielded U-Pb (ID-TIMS) baddeleyite concordia age of 1613 ± 5 Ma, which interpreted as time of their emplacement. New geochronological data allow reconsider previously reported Neoproterozoic age of sedimentary sequence hosting dolerite sills studied and suggest for them at least Paleoproterozoic age. The dolerites correspond to subalkaline and alkaline tholeiitic basalts and less often subalkaline tholeiitic basaltic andesite according to their major-element compositions with lower to moderate mg#, varying from 26 to 58. All dolerites demonstrate a similar slightly negative ɛNd(t) values range from −2.2 to −2.5. Geological, geochemical and Nd isotopic data suggest that mafic melts responsible for genesis of the dolerites were generated in an intracontinental extensional setting from homogeneous mantle source produced by interaction between OIB and ACR-like magmas. Geochemical features of the studied dolerites together with geological observations, namely – a presence of coeval rift-related sedimentary strata in the neighboring Urik-Iya graben (paleorift), suggest an overall extensional tectonic environments in the southern part of the Siberian Craton at 1.65–1.60 Ga. Synthesis of data on ca. 1.65–1.58 Ga magmatism around the world showed that the spatial distribution of various ca. 1.65–1.58 Ga mafic and felsic intrusions, including dyke swarms, anorogenic granites, as well as intracontinental basins within Nuna supercontinent suggest the overall extensional tectonic environments, probably related to the retreat of subduction slabs surrounded the supercontinent.