Cretaceous-Paleogene within-plate magmatism in Central Asia: data from the Tien Shan basalts

Abstract

We investigated local geology of Meso-Cenozoic basalt complexes in the Tien Shan and collected the first samples that represent nearly the entire area of within-plate basaltic magmatism in Central Asia (over 285,000 km 2). According to their 40Ar/ 39Ar ages, the Tien Shan basalts erupted for a relatively short time span between 61 and 76 Ma, in the Late Cretaceous-Paleogene. The trace- and rare-earth-element compositions of rocks show that most of the studied basaltic series in the Tien Shan formed in within-plate magmatic systems related to mantle plume sources. Some melts bear evidence of crustal contamination. The compositions of melt inclusions and patterns of trace and rare-earth elements in them are consistent with the plume origin of the melts and with the evolution of magmatic systems toward an increase in K, Al, and Fe contents. The melt inclusion data show a direct dependence of the crystallization temperatures of parental melts of the Meso-Cenozoic Tien Shan basalts on their Mg#: 1220–1250 °C for picrite basalts of the Uchkuduk site, 1175–1215 °C for basalts of the Tekelik, and 1145–1170 °C for andesite basalts of the Alakol' site.