Post-collisional magmatism of 1.88–1.84 Ga in the southern Siberian Craton: An overview

Abstract

The paper presents an overview of geological, geochronological, geochemical, and isotopic data on 1.88–1.84 Ga igneous rocks from the South Siberian post-collisional magmatic belt that records the final event of craton assembly. The belt consists mainly of granitoids and coeval felsic volcanics, less abundant mafic rocks, and sporadic carbonatites. In spite of the chronological and geodynamic proximity, the igneous rocks from different parts of the belt have dissimilar chemical and isotopic signatures, which are well consistent with the events that preceded the final assembly of the craton. Samples from the southwestern part of the belt show the greatest diversity, with an affinity of granitoids and felsic volcanics to different granite types (I-, S-, and A), and large εNd(T) ranges from positive to strongly negative for both felsic and mafic rocks. The compositional diversity of post-collisional igneous rocks here may be due to their origin shortly after the collisional events (1.90–1.87 Ga) during the orogen collapse. The diversity can have different explanations for felsic and mafic rocks: melting of heterogeneous sources assembled in the thickened orogen, as well as lithospheric delamination and asthenospheric upwelling, respectively. In the latter case, a source for mafic melts can be both asthenospheric material and subcontinental lithospheric mantle. The rocks of the southeastern belt segment are less diverse. Almost all granitoids and felsic volcanics have ferroan compositions, A-type granite affinity, and variable negative εNd(T) values similar to those in mafic rocks and in the Aldan shield carbonatites. The granitoids and volcanics here have compositions that commonly form in within-plate extension settings, which correlate with the 2.00–1.90 Ga age of collisional events in the area prior to the belt formation. The cessation of collisional movements in the southwestern craton part led to extension throughout its southern (and southeastern) areas. The ensuing melting of continental crust and subcontinental lithospheric mantle produced, respectively, felsic and mafic melts. The igneous rocks of the easternmost part of the South Siberian belt include also alkaline carbonatites and host diverse mineral deposits indicates that this part of the craton may have been exposed to the effect of a hot spot.