Extensive Sills in the Continental Basement from Deep Seismic Reflection Profiling

Crustal seismic reflection profiling has revealed the presence of extensive, coherent reflections with anomalously high amplitudes in the crystalline crust at a number of locations around the world. In areas of active tectonic activity, these seismic “bright spots” have often been interpreted as fluid magma at depth. The focus in this report is high-amplitude reflections that have been identified or inferred to mark interfaces between solid mafic intrusions and felsic to intermediate country rock. These “frozen sills” most commonly appear as thin, subhorizontal sheets at middle to upper crustal depths, several of which can be traced for tens to hundreds of kilometers. Their frequency among seismic profiles suggest that they may be more common than widely realized. These intrusions constrain crustal rheology at the time of their emplacement, represent a significant mode of transfer of mantle material and heat into the crust, and some may constitute fingerprints of distant mantle plumes. These sills may have played important roles in overlying basin evolution and ore deposition.

High-resolution seismic reflection profiling of the active fold-and-thrust systems in the Shonai backarc basin, northern Honshu, Japan

<p>Northern Honshu, Japan, forms a classical example of the trench-arc-backarc basin system. Along the coast of the Sea of Japan, Miocene aborted rifts were developed filled with thick Neogene sediments and form an active fold-and-thrust belt. Devastative crustal earthquakes, such as the Shonai earthquake 1894 (M7), occurs historically. To reveal the relationship between active fault and fold structure with seismogenic source faults is significant for the evaluation of seismic hazards and possible risk. In the Shonai plain, northern Honshu, we performed 2D high-resolution seismic reflection profiling across the active faults. Seismic data was collected by 10 m shot and receiver interval using Enviro vib and Minivib (IVI) to obtain high-resolution image. Along some of the seismic lines, seismic reflection survey was recorded by fixed 800-1000 channels, producing high number of folds. The resultant seismic profiles provide the image of a fold-and-thrust belt developed in the Miocene volcanic rift basin. Former syn-rift faults reactivated as reverse faults and thin-skinned deformation prevails in the post rift sediments forming detachment in the Miocene over pressured mudstone units. Fault-related folds and wedge thrusting is common feature of the shortening deformation. There are two active thrust systems in the Shonai basin. One is known active fault system along the eastern margin of the Shonai plain and the other is an active-blind - thrust located in the central part of the basin. The late Quaternary tectonic movements along this fault was confirmed by the high-resolution seismic profiling. </p>

Geological studies in the Eastern Indian Ocean: cruise SO258/1 of the R/V Sonne (Germany) with the participation of Russian researchers

New geological-geophysical data were obtained during Cruise SO258 leg 1 of the R/V SONNE carried out in the eastern part of the Indian Ocean in 2017. This expedition was part of the research project INGON, which is a collaboration between the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) and the GEOMAR Helmholtz Centre for Ocean Research Kiel. Multibeam echo-sounder bathymetry, seismic reflection profiling and rock sampling were done on 3 areas on 85° E Ridge and close to the Ninetyeast Ridge. The paper describes the first results.