Study On Upper Mantle Temperature Structure Beneath North China And Northeast China

We investigate three-dimensional(3-D)temperature distribution of the upper mantle at depths of 50–200 km and the thickness of thermal lithosphere beneath North China and Northeast China using high-resolution seismic velocity models as well as mineral physics and geothermal data and methods.Some small-scale temperature structure and thermal lithosphere thickness variations between many different tectonic blocks have been obtained thanks to the seismic velocity models we use have higher resolution than previous studies.The tectonic evolution process of the lithosphere below the North China Craton as well as Northeast China and the dynamic mechanism beneath the Cenozoic volcanic groups in the Northeast China are discussed in detail.The velocity structure and temperature structure of the upper mantle beneath different tectonic blocks of North China Craton and its adjacent areas are quite different.The Qilian orogen,the Shanxi rift system and the Tanlu fault system are characterized by lower seismic velocity,higher temperature and thinner thermal lithosphere,indicating that these areas may be mechanically weak zones,which may be related to subductions of the Indian plate and the(Paleo-)Pacific plate beneath the Eurasian continent,resulting in upwelling of hot asthenospheric materials.In addition,these mechanically weak zones may provide channels for the upwelling of the asthenospheric materials and play an important role in the Cenozoic partial destruction of the lithosphere beneath the North China Craton.The Ordos block exhibits higher seismic velocity,lower temperature and thicker thermal lithosphere,suggesting that the western part of the North China Craton has suffered from less damage and still kept a remanent Archean lithospheric keel.The upper mantle beneath Northeast China shows strong lateral heterogeneity.There are significant differences in the temperature structure under both sides of the Daxing'anling gravity lineament.The western side exhibits the high temperature zone as a whole,and the eastern side shows an alternate distribution pattern between high and low temperature zones.In addition,the thermal lithosphere thickness on both sides has changed dramatically.The Changbai volcanic group and central area of the Songliao Basin in the eastern side of the Daxing'anling gravity lineament exhibit lower seismic velocity,higher temperature and thinner thermal lithosphere,which may be related to the subduction of the Pacific plate beneath the Eurasian continent,resulting in upwelling of hot and wet asthenospheric materials associated with stagnant Pacific slab dehydration in mantle transition zone.The thermo-chemical erosion of the upwelling asthenospheric materials may induce the delamination of partial lithosphere beneath the Songliao Basin.The edge of the Songliao Basin is characterized by higher seismic velocity,lower temperature and thicker thermal lithosphere,which may indicate the ancient lithosphere that has not been delaminated.This feature also reveals the lateral heterogeneity of the upper mantle beneath the Songliao Basin.The Halaha volcanic group and the Abaga volcanic group in the western side of the Daxing'anling gravity lineament exhibit lower seismic velocity,higher temperature and thinner thermal lithosphere,which may be related to the small-scale upwelling of hot asthenospheric materials associated with the delamination of partial lithosphere beneath the Songliao Basin.