Petrogenesis of late cenozoic basaltic complexes in the southern Baikal and southern Khangai volcanic areas in central Asia: Evidence from melt inclusions

摘要

Data on melt inclusions in minerals provide direct information on the physicochemical petrogenetic parameters of Late Cenozoic basaltic complexes in the Southern Baikal and Southern Khangai Volcanic Areas (SBVA and SKVA, respectively) in Central Asia. Newly obtained data on inclusions in olivine reveal differences between the temperatures of the magmatic systems that produced basalts in SBVA and SKVA. The comparison of the experimentally determined homogenization temperatures and parameters calculated from data on the composition of glasses in the melt inclusions allowed us to realistically evaluate the temperatures of the petrogenetic processes that generated Late Cenozoic basaltic complexes in SBVA (1130-1160°C and 1175-1250°C) and SKVA (1145-1185°C, 1210-1270, and about 1300-1310°C). The analysis of fluid phases in the inclusions testifies that basaltic melts in SBVA were rich in carbon dioxide, which ensured elevated pressures (up to 5-6.6 kbar) during the crystallization of the minerals. Data on the composition of inclusions in the olivine highlight differences between the chemistries of magmatic systems in the two territories: elevated TiO_2, Al_2O_3, and CaO concentrations at relatively low FeO and MgO contents in the SBVA melts as compared to analogous concentrations in the SKVA basaltic magmas. The petrochemical and geochemical parameters of the primary melt inclusions and the composition of the olivine generally testify that deep plume magmatic processes were actively involved in the generation of basalts in both SBVA and SKVA. Data on melt inclusions in olivine and the composition of the clinopyroxene reveal similarities between the geochemistry, mineralogy, and crystallization parameters of Late Cenozoic basalts in both SBVA and SKVA and Cretaceous-Paleogene basalts in the Tien Shan and their certain differences from the plume-related systems of the OIB type. These data suggest that the geodynamic environment of the Cenozoic and Late Mesozoic intraplate plume magmatism in Central Asia were different from the geodynamic environment of typical long-lived mantle plumes like that at Hawaii.