Detailed seismic stratigraphic analysis of 2D seismic data over the Faroe-Shetland Escarpment has identi¢ed 13 seismic re£ection units that record lava-fed delta deposition during discrete periods of volcanism. Deposition was dominated by progradation, during which the time shoreline migrated a maximum distance of $44 km in an ESE direction. Localised collapse of the delta front followed the end of progradation, as a decrease in volcanic activity left the delta unstable. Comparison with modern lavafed delta systems on Hawaii suggests that syn-volcanic subsidence is a potential mechanism for apparent relative sea level rise and creation of new accommodation space during lava-fed delta deposition. After the main phase of progradation, retrogradation of the delta occurred during a basinwide syn-volcanic relative sea level rise where the shoreline migrated a maximum distance of $75 km in a NNW direction. This rise in relative sea level was of the order of 175^200 m, and was followed by the progradation of smaller, perched lava-fed deltas into the newly created accommodation space. Active delta deposition and the emplacement of lava £ows feeding the delta front lasted $2600 years, although the total duration of the lava-fed delta system, including pauses between eruptions, may have been much longer.

The occurrence of failed breakup basins and deepwater blocks of thinned continental crust is commonplace in the rifting and breakup of continents, as part of passive margin development. This paper examines the rifting of Pangaea-Gondwanaland and subsequent breakup to form the South Atlantic Ocean, with development of a failed breakup basin and seafloor spreading axis (the deepwater Santos Basin) and an adjacent deepwater block of thinned continental crust (the Sao Paulo Plateau) using a combination of 2D flexural backstripping and gravity inversion modelling. The effects of the varying amounts of continental crustal thinning on the contrasting depositional and petroleum systems in the Santos Basin and on the São Paulo Plateau are discussed, the former having a predominant post-breakup petroleum system compared with a pre-breakup system in the latter. An analogy is also made to a potentially similar failed breakup basin/thinned continental crustal block pairing in the Faroes region in the NE Atlantic Ocean.

Ultra-large rift basins, which may represent palaeo-propagating rift tips ahead of continental rupture, provide an opportunity to study the processes that cause continental lithosphere thinning and rupture at an intermediate stage. One such rift basin is the Faroe-Shetland Basin (FSB) on the north-east Atlantic margin. To determine the mode and timing of thinning of the FSB, we have quantified apparent upper crustal b-factors (stretching factors) from fault heaves and apparent whole-lithosphere b-factors by flexural backstripping and decompaction. These observations are compared with models of rift basin formation to determine the mode and timing of thinning of the FSB. We find that the Late Jurassic to Late Palaeocene (pre-Atlantic) history of the FSB can be explained by a Jurassic to Cretaceous depth-uniform lithosphere thinning event with a b-factor of 1.3 followed by a Late Palaeocene transient regional uplift of 450-550 m. However, post-Palaeocene subsidence in the FSB of more than 1.9 km indicates that a Palaeocene rift with a b-factor of more than 1.4 occurred, but there is only minor Palaeocene or post-Palaeocene faulting (upper crustal b-factors of less than 1.1). The subsidence is too localized within the FSB to be caused by a regional mantle anomaly. To resolve the b-factor discrepancy, we propose that the lithospheric mantle and lower crust experienced a greater degree of thinning than the upper crust. Syn-breakup volcanism within the FSB suggests that depth-dependent thinning was synchronous with continental breakup at the adjacent Faroes and Møre margins. We suggest that depth-dependent continental lithospheric thinning can result from small-scale convection that thins the lithosphere along multiple offset axes prior to continental rupture, leaving a failed breakup basin once seafloor spreading begins. This study provides insight into the structure and formation of a generic global class of ultra-large rift basins formed by failed continental breakup.

Observations of a wide (up to 170 km) zone of exhumed continental mantle on the Iberian non-volcanic rifted margin have questioned our understanding of the processes involved in continental breakup and seafloor spreading initiation. Models of continental lithosphere thinning by pure-shear predict melt generation before continental breakup, and thus do not predict the exhumation of mantle. Whilst the paucity of volcanism during breakup on the Iberian margin may be explained by invoking a cooler or depleted mantle, or by poor melt extraction, other lithosphere scale processes may play an important role during continental breakup. We compare melt production predicted by pure-shear models of continental lithosphere thinning to that predicted by an upwelling-divergent flow model, using kinematic constraints appropriate to the Iberian margin. The upwelling-divergent flow model predicts exhumation of a more than 50 km-wide zone of continental mantle prior to melt initiation, and we suggest that this mode of lithosphere deformation may play an important role in the formation of rifted margins.

Active volcanic centers in East Asia have huge potential to pose major volcanic hazards on modern human society. The area around the East Sea (Japan Sea) is one critical element of this, with a population of ca. 200 million along the Korean Peninsula and the Japanese Islands at risk from volcanic hazards. The Ulleungdo in the East Sea (Figure 1) is one of such hazardous volcanoes, which is responsible for one of the largest Holocene eruptions in East Asia (Machida et al., 1984). Ash from the eruption (U-Oki) blanketed large areas of the East Sea and reached