Highly heterogeneous lithospheric mantle beneath the Central Zone of the North China Craton evolved from Archean mantle through diverse melt refertilization

摘要

High-Mg# peridotite xenoliths in the Cenozoic Hebi basalts from the North China Craton have refractory mineral compositions (Fo>91.5) and highly heterogeneous Sr-Nd isotopic compositions (~(87)Sr/ ~(86)Sr=0.7031-0.7048, ~(143)Nd/ ~(144)Nd=0.5130-0.5118) ranging from MORB-like to EM1-type mantle, which are similar to those of peridotites from Archean cratons. Thus, the high-Mg# peridotites may represent relics of the ancient lithospheric mantle. Published Re-Os isotopic data for Cenozoic basalt-borne xenoliths show T _(RD) ages of 3.0-1.5Ga for the peridotites from Hebi (the center of the craton), 2.2-0Ga for those from Hannuoba and Jining (north margin of the craton), and 2.6-0Ga for those from Fanshi and Yangyuan (midway between the center and north margin of the craton). In situ Re-Os data of sulfides in Hannuoba peridotites suggest that whole-rock Re-Os model ages represent mixtures of multiple generations of sulfides with varying Os isotopic compositions. These observations indicate that initial lithospheric mantle beneath the Central Zone of the North China Craton formed during the Archean and was refertilized by multiple melt additions after its formation. The refertilization became more intensive from the interior to the margin of the craton, leading to the high heterogeneity of the lithospheric mantle: more ancient and refractory peridotites with highly variable Sr-Nd isotopic compositions in the interior, and more young and fertile peridotites with depleted Sr-Nd isotopic composition in the margin. Our data, coupled with published petrological and geochemical data of peridotites from the Central Zone of the North China Craton, suggest that the lithospheric mantle beneath this region is highly heterogeneous, likely produced by refertilization of Archean mantle via multiple additions of melts/fluids, which were closely related to the Paleoproterozoic collision between the Eastern and the Western Blocks and subsequent circum-craton subduction events.