Paleoproterozoic collisional and intraplate granitoids of the southwest margin of the Siberian craton: Petrogeochemical features and U-Pb geochronological and Sm-Nd isotopic data

Abstract

Accretion of the Archean blocks of the continental crust 1.95-1.90 Ga ago that caused the formation of the Paleoproterozoic supercontinent Pangea I (1) was accompanied by metamorphism and intensive granite formation in collisional orogenes. Paleoproterozoic collisional granitoids are widely represented in the uplifts of the Eurasian platform basement: on the Ukrainian, Anabar, and AldanoStanovoi shields as well as along the southwestern margin of the Siberian craton. They form extended belts consisting of domi� nating posttectonic microcline granites with minor tonalities, granodiorites and quartz syenites predomi� nantly of sodium-potassium calcalkaline magmatic series. Their characteristic feature is enrichment by largeionic and high field strength elements, light lan� thanoids, uranium, and especially thorium (2). Fur� ther sialization of the crust and increasing of the degree of its geochemical differentiation (maturity) were important consequences of this powerful process of granite formation. The extended belt of the Paleoproterozoic grani� toids marks uplifts of the Siberian craton basement along the modern southwestern and southern margins tracing in the structures of the Yenisey ridge, Prisaya� nie, Pribaikalie, and AldanoStanovoi shield. Forma� tion of the belt was accompanied by the first occur� rence of sodiumpotassium granitoid magmatism, which was the most powerful for this segment of the Earth and occurred in the interval 1.90-1.75 Ga ago. Granite formation was caused by accretioncollisional and, as was established recently (3), subsequent intra� plate processes. In the present work by the example of the investiga� tion of the Taraka massif of the south Yenisey Ridge, the multistage character of the rock associations com� posing the massif varying in age as well as in composi� tion was proved. For the first time, the results of the petrogeochemical and isotopegeochronological investigations of the intraplate (anorogenic) granites were presented. These granites were distinguished by the authors within this massif due to their enrichment in thorium and rare earth elements. The variety of geo� dynamic conditions of granitoid formation and pro� longed multistage evolution of the Paleoproterozoic granite formation were noted. Wider development of anorogenic granites within the mentioned belt was shown.