Mesoproterozoic (ca. 1.26 Ga) Srednecheremshansk mafic–ultramafic intrusion in the southern Siberia: Signature of the Mackenzie event in Siberia

Abstract

Several published Mesoproterozoic paleogeographic reconstructions suggest proximity of northern Laurentia and southern Siberia. However, the apparent absence of the traces of the ca. 1.27 Ga giant Mackenzie magmatic event in southern Siberia was somewhat contradictory to this hypothesis. Here we present geochronological, mineralogical, geochemical, Nd isotopic, and paleomagnetic data from the Srednecheremshansk dyke-shaped intrusion, which was recently found in the Sharyzhalgay uplift of the southern part of the Siberian craton and which can be related to the Mackenzie event. The plagioclase-bearing peridotite of this intrusion yielded U-Pb (ID-TIMS) baddeleyite concordia age of 1260 ± 3 Ma, which is interpreted as the time of their emplacement. This age is close to the previously published baddeleyite age of gabbro from the same intrusion (1258 ± 5 Ma). The Srednecheremshansk intrusion is composed of ultramafic and mafic rocks. The main rock-forming minerals of the intrusion are olivine, orthopyroxene, clinopyroxene, phlogopite, and plagioclase in various proportions. Sulfide mineralization of the intrusion is represented by pentlandite nodules. The chemical composition of Srednecheremshansk ultramafic and mafic rocks correspond to subalkaline peridotite gabbro and gabbro. These rocks are characterized by negative ɛNd(t) values range from −6.3 to −6.9. Ultramafic and mafic rocks have similar geochemical and isotopic characteristics, indicating their generation from a single subcontinental lithospheric mantle source. The chemical composition of the Srednecheremshansk intrusion is similar to those of the ca. 1.27 Ga Muskox mafic–ultramafic intrusion of the Mackenzie Large Igneous Province in northern Laurentia. Paleomagnetic data permit a variety of possible Laurentia-Siberia reconstructions in Mesoproterozoic. The combination of geochronological, geochemical, and paleomagnetic data allows the relation of the Srednecheremshansk intrusion with the Mackenzie magmatic event.