Nature and evolution of Mesozoic-Cenozoic lithospheric mantle beneath the Cathaysia block,SE China

摘要

Mantle-derived garnet and spinel peridotite xenoliths and xenocrysts from the Daoxian basalts (151-131 Ma) and the Anyuan lamprophyres (approx44 Ma) provide insights into the nature and evolution of subcontinental lithospheric mantle beneath the Cathaysia block,SE China.The Daoxian area lies astride the translithospheric Ningyuan-Jianghua fault zone in western Cathaysia,whereas the Anyuan area lies east of the fault zone.The peridotite xenoliths from both localities have experienced melt extraction (generally 3-10% fractional or batch melting) and subsequent silicate melt metasomatism.Depleted coarse-textured spinel peridotites from Anyuan and localities in East Cathaysia have relatively magnesian olivine (Mg~#>=91) and may be relics of the Proterozoic lithospheric upper mantle,preserved locally at shallow levels away from the translithospheric fault.At Daoxian coarse-textured xenoliths are absent,and some xenoliths have sheared microstructures.The minerals of the Daoxian xenoliths have lower Cr~# and Mg~# than those from Auyuan.The Daoxian xenoliths also have higher bulk CaO+A1_2O_3 contents and FeO/MgO,suggesting more pronounced metasomatism.The differences between the Daoxian and Anyuan xenolith suites reflect their spatial relationship to the translithospheric Ningyuan-Jianghua fault zone,which played an important role in the Mesozoic replacement of Proterozoic lithospheric mantle.The lithospheric mantle information from these localities is combined with published data from other localities to provide the first comprehensive survey of the evolution of the lithospheric mantle beneath the Cathaysia block.The xenolith suites of West and East Cathaysia are interpreted as sampling mixtures of older and newly accreted lithospheric mantle that replaced the Proterozoic lithosphere through extension,thermal erosion and melt metasomatism.