The Cretaceous volcanism of the Songliao Basin: Mantle sources, magma evolution processes and implications for the NE China geodynamics - A review

Abstract

Continental rifts result from the simultaneous action of shallow processes such as the thinning of the lithosphere, and deeper processes related to the dynamics of the mantle. The role of these deeper processes may change over time as a function of the type of rifting, e.g., subduction-related rift vs plume-related rifts, and the pre-rift geodynamics. During the Cretaceous, the Songliao Basin (NE China) was affected by continental rifting accompanied by discontinuous stages of volcanism. The relative role of the asthenospheric and lithospheric mantle associated with the Songliao Basin rift volcanism, its evolution with time, and the origin of the felsic rocks are still debated problems due to the lack of comprehensive studies. Here, we present a critical review of the available geochronological and geochemical data (major, trace elements, and Sr-Nd isotopes) and show that the Songliao rift Cretaceous volcanism developed between 133 Ma and 102 Ma in five main stages: Stage I (133–129 Ma), Stage II (124–118 Ma), Stage III (117–113 Ma), Stage IV (115–106 Ma), and Stage V (105–102 Ma). While magmas with an alkaline, intraplate affinity characterize all the Stages, magmas with a subalkaline (calc-alkaline) signature erupted in Stages II and III. Mafic and intermediate rocks are always present, whereas felsic magmas have been found in the last three Stages. Based on the major, trace elements and Nd-Sr isotopic compositions, the general evolution of volcanism is dominated by crystal fractionation processes. Evidence of assimilation of upper crust material is restricted to the more evolved rocks (SiO2 > 57 wt%). The alkaline mafic rocks derived from a veined asthenospheric mantle modified by melts deriving from the sediments of the Paleo- Pacific slab or associated with pre-rifting, Jurassic, collisional subduction processes related to the closing of the Mongol–Okhotsk Ocean. The source of the Songliao rift subalkaline rocks is the sub-continental lithospheric mantle metasomatized by fluids released from the dehydration of the subducting Paleo-Pacific slab. The release of fluids from the sediments subducted during the Jurassic Mongol–Okhotsk collision may also have played a role. The Songliao Basin Cretaceous rift may be classified as a subduction-related rift caused by the eastward rollback of the west-dipping Paleo-Pacific slab, a process initiated after the Jurassic collisional phase in NE China. Within the wider geodynamic frame of the eastern Asian block, the 133–102 Ma volcanism of the Songliao rift suggests a transition from a lithospheric mantle responsible for the pre-140 Ma NE China, Mongolia, and Russia volcanism to an asthenospheric mantle source of the post-107 Ma magmatism. This is also suggested by the fact that the Songliao rift magmatism shows compositional features consistent with the contribution of both the lithospheric and asthenospheric mantle. The Songliao rift volcanism would be therefore associated with a passive rifting process, where the progressive removal of the lithosphere below East Asia, which is due to eastward rollback of the Pacific oceanic plate, caused an upwelling of asthenospheric material, finally involved in the post- 102 Ma magmatism in the NE China block.