Syn-Eruptive Lateral Collapse of Monogenetic Volcanoes: The Case of Mazo Volcano from the Timanfaya Eruption (Lanzarote, Canary Islands)

The evolution of complex volcanic structures usually includes the occurrence of flank collapse events. Monogenetic cones, however, are more stable edifices with minor rafting processes that remove part of the cone slopes. We present the eruptive history of Mazo volcano (Lanzarote, Canary Islands), including the first detailed description of a syn-eruptive debris avalanche affecting a volcanic monogenetic edifice. The study and characterization, through new geological and morphological data and the analysis of a great number of documentary data, have made it possible to reinterpret this volcano and assign it to the Timanfaya eruption (1730–1736). The eruptive style evolved from Hawaiian to Strombolian until a flank collapse occurred, destroying a great part of the edifice, and forming a debris avalanche exhibiting all the features that define collapsing volcanic structures. The existence of blocks from the substrate suggests a volcano-tectonic process associated with a fracture acting simultaneously with the eruption. The sudden decompression caused a blast that produced pyroclasts that covered most of the island. This study forces to change the current low-hazard perception usually linked to monogenetic eruptions and provides a new eruptive scenario to be considered in volcanic hazards analysis and mitigation strategies development.

From Mesozoic subduction to Cenozoic extension: what controlled the tectonic process of South China Sea?

<p>The South China Sea (SCS) is one of the largest marginal seas in the western Pacific. Widespread onshore outcrops of the late Mesozoic granitic and volcanic rocks suggest that the SCS was once an active margin associated with Paleo-Pacific or proto South China Sea subducted toward South China in the late Mesozoic. It transitioned into rifting after late Cretaceous and then spreading in Oligocene. IODP drilling indicates that SCS transitioned from subduction into sea spreading in a short time (no more than 30 Myrs) and show diachronous breakup both temporally and spatially. What controlled this tectonic process? In order to answer these questions, we used a combination of data sources, including reprocessed magnetic data, drilling/dredging samples, depositional environment and deformation style on multi-channel seismic profiles to constrain the possible spatial distribution of the Mesozoic volcanic arc first and found that the southwest part of the Mesozoic volcanic arc distributes on both sides of the southwest SCS sub-basin, while the northeast part remains nearly in its original location. The results suggest that the initial breakup sites for the SCS margin might be arc area in the southwest and fore-arc area in the northeast during the opening of SCS basin. Mathematical modeling experiments suggest that several circumstances may cause fore-arc breakup, including: steepening of the subducting plate, a pre-existing rheologically/tectonically weak zone in the arc-front/fore-arc in the subduction plate, seamount or plateau subduction and damaging of the fore-arc area. Also if the subducting slab is young or the subduction time is short, fore-arc breakup will occur. Further analysis suggested that along with the rifting, two sources of magma may have contributed to the rifting. One is supposed to be decompressive melting, the other one is deep sourced and constitute the high velocity lower crustal magmatic underplating, which is supposed to be related with the subduction slab break off.</p>

Modeling of stringer deformation and displacement in Ara salt after the end of salt tectonics

The present work considers numerical models of large rock inclusions (stringers) are embedded in many salt bodies. The study has been made to investigate the influence of salt tectonic process, such as downbuilding, on the deformation and displacement of stringers. In this research, the focus has been on establishing numerical models of the deformation and displacement of stringer embedded in salt (at rest) after occurrences of salt tectonics. The problem of influence of eventual tectonic processes at larger stage is addressed on the development of stringers. The numerical model is based on finite element method in combination with adaptive remeshing. The results show that the stringers experience minor sinking and the differential stress in salt and the differential stress in the stringer decrease during the period after salt tectonics. The change of stress of reservoir will influence drilling process and oil or gas production.