Abstract Along continental margins with rapid sedimentation, overpressure may build up in porous and compressible sediments. Large-scale release of such overpressure has major implications for fluid migration and slope stability. Here, we study if the widespread crater-mound-shaped structures in the subsurface along the mid-Norwegian continental margin are caused by overpressure that accumulated within high-compressibility oozes sealed by low-permeability glacial muds. We interpret 56 000 km 2 of 3D and 150 000 km 2 of 2D-cubed seismic data in the Norwegian Sea, combining horizon picking, well ties and seismic geomorphological analyses of the crater-mound landforms. Along the mid-Norwegian margin, the base of the glacially influenced sediments abruptly deepens to form 28 craters with typical depths of c. 100 m, areal extents of up to 5130 km 2 and volumes of up to 820 km 3 . Mounds are observed in the vicinity of the craters at several stratigraphic levels above the craters. We present a new model for the formation of the craters and mounds where the mounds consist of remobilized oozes evacuated from the craters. In our model, repeated and overpressure-driven sediment failure is interpreted to cause the crater-mound structures, as opposed to erosive megaslides. Seismic geomorphological analyses suggest that ooze remobilization occurred as an abrupt energetic and extrusive process. The results also suggest that rapidly deposited, low-permeability and low-porosity glacial sediments seal overpressure that originated from fluids being expelled from the underlying high-permeability and high-compressibility biosiliceous oozes.

Abstract The Longgang volcanic field (LVF) is a monogenetic volcanic field in China that erupted in the Quaternary, forming more than 100 scoria cones and maars in an area of over 1500 km 2 . The most recent eruption occurred c. 1500–1700 years ago. By summarizing the results of previous and recent research, this paper reviews the geological background, volcano distribution, eruption history, typical volcanoes and geochemical characteristics of the LVF. The volcanic activities in the LVF were structurally controlled by near-EW-, NW- and NE-trending faults. An analysis of typical volcanic edifices reveals that at least two eruptive episodes occurred in the Holocene, and most of the maars in the LVF have characteristics of multiple eruptive styles. It is concluded that the eruption types included effusive eruptions, magma explosive eruptions and phreatomagmatic eruptions. The results of geochemical studies of LVF eruptive products show that most of the rock is trachybasalt and that the magma rarely interacts with crustal rocks. Compared with the previous results for the neighbouring Changbaishan polygenetic volcanic field, the probable origins of their differences in volcanism are discussed.

Abstract The Halaha River–Chaoer River (HC) volcanic field in the Greater Hinggan Mountain Range (NE China) consists of at least 41 monogenetic basaltic volcanoes. Strombolian, violent Strombolian and phreatomagmatic eruptions, as well as the transitional eruptions, generated simple volcanic cones (single vent) and composite volcanic cones (multiple vents). The simple elongated cone is the most abundant geomorphology type. By analysing the elongated crater and coalescent aligned circular crater, cone breaching and depression, and aligned vents, we identified a number of magma-feeding fissures. The majority of these fissures strike NE–ENE. Accordingly, we infer that the regional stress field affected volcanism in the HC field. The lavas in this field are alkali basalts that are enriched in light rare earth elements (La/Yb N = 7.9–24.5). Their ocean island basalt-like rare earth element and spider-diagram patterns, high Nb/U ratios and high TiO 2 contents (>2 wt%) indicate that the basalts were derived from the asthenosphere mantle. Both the asthenosphere upwelling and the tectonic forces are the key controlling factors of the volcanism in the HC field.