Data for: Syncollisional Gabbro in the Irtysh Shear Zone, Eastern Kazakhstan: Compositions, Geochronology, and Geodynamic Implications
Description
Petrographical, mineralogical, geochemical, and geochronological studies reveal three mineralogically and chemically different types of gabbro intrusions in the Irtysh shear zone in Eastern Kazakhstan: (1) gabbrodolerite and dolerite, (2) enriched biotite-bearing gabbro, and (3) layered peridotite-gabbro (largest intrusion). The rocks formed by fractional crystallization from two types of parent magmas, with their compositions (a) similar to tholeiitic subalkaline basalt (gabbro of types 1 and 2) and (b) intermediate between tholeiitic and calc-alkaline series being relatively depleted and more magnesian (type 3 gabbro). Geochemical and isotopic data indicate a sublithospheric subduction-related mantle source for the two types of primary magmas, which were produced, respectively, by low- and high-degree partial melting of depleted mantle material (spinel lherzolite). The obtained U-Pb and Ar-Ar ages of the gabbro samples (317-313 Ma) fall within the time of a collisional orogenic event. As predicted by geodynamic models, ascending mafic melts from a mantle wedge may intrude through windows in the sublithospheric mantle in the presence of slab discontinuity at the transform boundary of colliding plates along the Irtysh shear zone.