Late Paleozoic–Cenozoic intra-plate continental basaltic magmatism of the Tienshan–Junggar region in the SW Central Asian Orogenic Belt

Abstract

This paper reviews previously published and presents new geochemical (bulk rock), petrologic (phenocrysts and their hosted melt inclusions) and geochronological (Ar–Ar) data from Late Paleozoic to Cenozoic volcanic rocks from the Tienshan–Junggar region cropping out in the territories of Kyrgyzstan, Kazakhstan, and China. The mafic volcanic rocks are surrounded by continental sedimentary rocks. They are mainly alkaline basalts. The Late Cretaceous–Paleocene basalts of the Central Tienshan (Group 1), and the Early Jurassic (Group 2) and Early Permian (Group 3) volcanic rocks of the Junggar Basin are geochemically similar to intra-plate basalts of the Hawaiian hotspot, Siberian and Ontong-Java LIPs, and Central Mongolia, origin of which is commonly attributed to mantle plumes. The Late Carboniferous basalts (Group 4) of NW Junggar are less enriched in the LREE and moderately depleted in the HFSE (Ti, Nb, Y, Zr) resembling crustally contaminated lavas of the Kerguelen hot spot. Melt inclusions hosted by phenocrysts from Group 1 basalts homogenized at relatively high temperatures, from 1175 to 1250°С. The composition of the melt inclusions suggests that the basalts were derived from Ti-Nb-LREE enriched mafic melts. Based on geological, geochronological, petrologic and geochemical data we recognize four periods of intra-plate volcanism: Late Carboniferous, Early Permian, Early Jurassic, and Late Cretaceous–Paleocene. The data from the plume-type intra-plate basalts suggest their relation to the action of three mantle plumes: i) Tarim (Early Permian), ii) Junggar (Early Jurassic), and iii) Tienshan (Late Cretaceous–Paleocene).