Origin Of Cenozoic Lithospheric Mantle In Several Areas Of Eastern China

Major and trace elements of mantle peridotitic xenoliths entrained by Cenozoic basalts from Hannuoba, Nushan, Panshishan and Fangshan are analyzed. Systematic geochemical comparisons of characteristics for Palaeozoic and Cenozoic peridotites from eastern China, oceanic lithospheric mantle and Archean Craton are drawn, combined with published data of the mantle peridotitic xenoliths. Major elements for Cenozoic peridotitic xenoliths in eastern China share similar fertile signature to the abyssal peridotitic and show a distinctive dissimilarity from Archean Craton and refractory Palaeozoic lithospheric mantle in eastern China. Further partial melting modeling of the major-trace elements reveals that lithospheric mantle for Archean Craton need a higher degree of melting (~15%) than Cenozoic lithosperic mantle in eastern China and the oceanic lithospheric mantle, the latter could be well matched by lower degree fractional melting from DMM (~5%). Although a few samples from Nushan and Panshishan indicate considerable melting extents which are analogous to that of Archean Cratonic lithospheric mantle, their depleted isotopic evidence argue that they are not residual of an old lithospheric mantle. Compared with extreme negative Ti anormaly in spider-diagram for Palaeozoic lithospheric mantle from eastern China, simples from Hannuoba, Nushan, Panshishan and Fangshan and abyssal peridotites share a moderate negative Ti anormaly, which is analogous to DMM end-member. Metasomatic modeling of possible melts over Palaeozoic enriched lithospheric mantle excludes the possibility that Cenozoic lithospheric mantle inherits from Archean Cratonic lithospheric mantle. Commonly, depleted-LREE patterns are expected after lower degree partial melting. While considerable samples from Hannuoba, Nushan, Panshishan and Fangshan exhibit various patterns, like"scoop","scoop-inverted", and enriched LREE types, which are due to metasomatism of OIB-like silica-enriched melts. Cryptical metasomatism is responsible for geochemical characteristics of lithospheric mantle in Nushan, Panshishan and Fangshan area, while Cenozoic lithospheric mantle in Hannuoba area underwent predominately modal metasomatism—silica-enriched Melt+Ol→Opx+silica-depleted Melt—which is supported by evidence from petrography and correlations between major-trace elements and mineral modes and which is responsible for refertilization of Nb and U. Combined with published data, results of equilibration temperatures for mineral compositions indicate a thermal state heterogeneity for eastern China, i.e., the central part is hotter than the southern and the northern flank.