Ultramafic xenoliths in Mesozoic diorite in west Shandong Province

摘要

Ultramafic xenoliths are common in Tietonggou intrusion, Laiwu, Shandong Province. Peridotite xenoliths develop two-stage metasomatism popularly: (i) The early metasomatism is characterized by intergranular clinopyroxene and phlogopite; (ii) The later metasomatism is characterized by orthopyroxene veins with a few plagioclases and amphiboles. These ultramafic xenoliths are thought to be mostly from the crust-mantle transitional zone on the basis of their combination, mineral chemistry, equilibrium temperature, and metasomatic characteristics. Major elements, rare earth elements, and Sr-Nd isotopic composition of the ultramafic xenoliths indicate that there is a petrogenetic relationship between the silica-enriched xenoliths and their host diorites. We propose that such silica enrichment might be an indicator of melt-rock interactions in the Mesozoic lithosphere beneath western Shandong.