Abstract:

There was a gravity-magnetic abnormal belt traversing the middle part of Tarim Basin. The igneous rocks in ages of Proterozoic and Paleozoic outcropped only in the Bachu area, western Xinjiang, with the Jinningian(the latest Mesoproterozoic-Early Neoproterozoic)one being characterized by deformation and metamorphism. The FeO*/MgO vs.TiO₂  diagram, MnO-TiO₂-P₂O₅, Zr-Nb-Y and Th-Hf-Ta triangular diagrams showed the tectonic setting of the Jinningian volcanic rocks being oceanic island.The REE features and trace element spidergrams indicated further that the oceanic island volcanic rocks could be divided into two groups: the alkaline basalt being a record of Azores-type oceanic island, and the tholeiite(as well as subordinate weakly alkaline basalt)interlayered with andesite(or andesitic basalt)being a record of Hawaii-type one, which reflected varied evolution phases of an oceanic basin. One sample of ultramafic rock seemed to be a product of Jinningian island arc, which was discovered by drilling in central Tarim. Both the igneous rocks of oceanic islands and island arc meant that there might be a Jinningian fossil suture in the middle part of Tarim Basin. In other words, the Tarim plate(craton)might be amalgamated by two originally separated blocks and become a part of the Rodinia supercontinent in the Jinningian orogeny. The fossil suture activated repeatedly and became a pathway of magmatism in Sinian.Paleozoic, especially, the basalt eruption and alkalic rock intrusion during Early Permian(the Cisuralian). Based on it, the implications of the Jinningian tectono-magmatism in basement structural pattern,tectonic evolution and oil-gas potentials in the Tarim Basin were discussed.

Key words: oceanic islands of Azores-type and Hawaii-type, petrochemistry of volcanic rocks, the Jinningian, the Bachu area in Xinjiang