Paleogeodynamic settings of ophiolite formation in Kuznetsk Alatau

Complex studies of rocks from the ophiolites of Kuznetsk Alatau provided ne w data on the petrochemistry and geochemistry of trace and rare-earth eleme nts and mineralogy and thermobarogeochemistry of melt inclusions. This perm itted reconstruction of the paleogeodynamic settings of ophiolite formation in this region. Among the ancient ophiolites, subalkalic series ABABB (ano maly back-are basin basalts), typical of modern back-are basins of the west ern Pacific, have been first revealed. It is shown that the Kuznetsk Alatau ophiolites formed in the paleogeodynamic setting of a developing island-ar e system, with a successive change of their magmatic series: tholeiitic --> calc-alkalic --> K-Na subalkalic (ABABB). Formation of these specific suba lkalic series indicates splitting of the paleoisland are and beginning of f ormation of a back-are basin.