Home – Home – Jornals – Russian Geology and Geophysics 2006 number 2

The Keping basalts occur on the western margin of the Tarim plate and are confined to the Kupukuziman and Kaipaizileike Formations of Early Permian age. They are enriched in Fe₂O₃, TiO₂, and P₂O₅ and are undersaturated in SiO₂. The overwhelming majority of the explored specimens belong to the alkali basalt series, and only one specimen, to the tholeiite series. Rare-earth and trace elements are geochemical signatures of the basalts that appeared under the conditions of within-plate extension. They have the following characteristics: ε _Nd ( T ) from -1.73 to -3.69, ε _Sr ( T ) from +27.56 to +56.87; ²⁰⁶Pb/²⁰⁴Pb = 17.87-18.02, ²⁰⁷Pb/²⁰⁴Pb = 15.45-15.53, ²⁰⁸Pb/²⁰⁴Pb = 38.22-38.49. Nd, Sr and Pb isotopic compositions suggest that the Keping basalts have been derived from the Precambrian enriched-type continental lithospheric mantle. This is also typical of the mafic igneous rocks, which are the most abundant in the Tarim basin and on its margin. For this reason, the Xinjiang Uigur Autonomous Region is divided into two obviously different geochemical provinces, southern and northern. The southern and northern provinces are characterized by isotopic compositions of enriched and depleted mantle, respectively. The Late Paleozoic igneous rocks in these two provinces seem to be produced by different geologic processes.