Mesoproterozoic Picrite–Picrobasalt Volcanism of the Ishimba–Tatarka Suture Zone: Petrogeochemistry, Metamorphism of the Rocks, and Rb–Sr and 147Sm–143Nd ID-TIMS Systematics

Abstract

The Early Mesoproterozoic (1370 Ma) age is substantiated for the picrite–picrobasaltic volcanism associated with the formation of the riftogenic Ishimba–Tatarka suture zone (paleorift) in the southwestern Siberian craton. First Rb–Sr and ¹⁴⁷Sm–¹⁴³Nd data are presented on the late Precambrian metavolcanogenic-sedimentary rocks ascribed to the Rybinsk–Panimba volcanic belt in the central part of the northern Yenisei Ridge. According to petrogeochemical composition, the protoliths of the metavolcanic rocks correspond to picrobasalts and basalts, more rarely, to picrites. The volcanogenic-sedimentary sequence in different areas rests on the same marker horizon of carbonaceous shales, which allows us to correlate the age of the Panimba volcanogenic sequence with the Korda Formation, regarding these formations at the Early Mesoproterozoic stratolevel. Geothermobarometry and analysis of features of regional metamorphism of volcanogenic-sedimentary rocks in the reference areas show uneven P–T conditions of transformation of the initial rocks: 4.8–4.9 kbar/527–549°C for picrobasaltic metatuffites; 5.0–5.8 kbar/543–612°C for metamafic rocks; and 3.5–4.6 kbar/522–636°C for metapelites. Based on the age (1056–996 Ma), the metamorphism is close to the Grenville tectonic epoch. The established age of picrite–picrobasalt volcanism in the Precambrian of the Yenisei Ridge correlates with the time of manifestation of trondhjemites of the Nemtikha complex and with the reference Mashak plume magmatism in the South Urals, which were formed in an intracontinental extensional geodynamic setting during the breakup of the Nuna supercontinent.