Late Cretaceous mud volcanism in the southwestern Songliao basin records slab rollback of the subducted paleo-Pacific Plate underneath NE China

We present a new seismic reflection dataset and use it to characterize fossil mud volcanoes in the southwestern Songliao graben basin in northeastern China. The results reveal a link between mud volcanism and slab rollback along the eastern Asian margin. This study focuses on the upper 3 km of the Lujiapu sub-basin, which lies in the southwestern Songliao basin. The base of the sequence consists of Lower Cretaceous siliciclastic deposits that are penetrated by mud volcano fluidization pipes. These deposits are overlain by Upper Cretaceous strata that have been deformed by the mud volcanoes. The sequence is capped by undeformed Neogene-Quaternary sediments. These observations constrain the timing of mud volcanism to the Santonian-Campanian (similar to 87-72 Ma). During Late Cretaceous diapirism, normal faulting at the tops of the mud volcanoes formed horsts and grabens. Surface anticlines and inversion structures near the mud volcano source layer indicate that basin inversion occurred during deposition of the Sifangtai and Mingshui formations (Campanian). Similar structures are also identified in the central Songliao basin. Thus, we propose that slab flattening to deepening during paleo-Pacific Plate sub-duction led to basin inversion. This process triggered the migration of high-pressure fluids and brecciated plastic rocks along pre-existing normal faults, which in turn produced the mud volcano system.