Using large dynamite shots to image the structure of the Moho from deep seismic reflection experiment between the Sichuan basin and Qinling orogen

The Qinling orogen was formed as a result of the collision between the North and South China blocks. The Qinling orogen represents the location at which the southern and northern parts of the Chinese mainland col- lided, and it＇s also the intersection of the Central China orogen and the north-south tectonic belt. There is evidence of strong deformation in this orogen, and it has had a long and complex geological history. We investigated the structure of the Moho in the southern Qinling orogen using large dynamite shot imaging techniques. By integrating the analysis of the single-shot and the move-out corrections profile, we determined the structure of the Moho beneath the northern Dabashan thrust belt and the southern Qinling orogen, including the mantle suture beneath Fenghuang mountain. The Moho is divided into two parts by the mantle suture zone beneath Fenghuang mountain： （1） from Ziyang to Hanyin, the north-dipping Moho is at about 45-55 km depth and the depth increases rapidly; and （2） from Hanyin to Ningshan, the south-dipping Moho is at about 40-45 km depth and shallows slowly. The mantle suture is located beneath Fenghuang mountain, and the Moho overlaps at this location： the shallower Moho is connected to the northern part of China, and the deeper Moho is connected to the southern part. This may indicate that the lithosphere in the Sichuan basin subducts to the Qinling block and that the subduction frontier reaches at least as far as Fenghuang mountain.

Crustal wide-angle reflection imaging along Lianxian-Gangkou profile in Guangdong province,China

A 400 km-long wide-angle seismic experiment along Lianxian-Gangkou profile in South China was carried out to study contact relationship between southeast continental margin of Yangtze block and northwest continental margin of Cathaysia block. We reconstructed crustal wide-angle reflection structure by the depth-domain pre-stack migration and the crustal velocity model constructed from the traveltime fitting. The wide-angle reflection section shows different reflection （from crystalline basement and Moho） pattern beneath the Yangtze and Cathaysia blocks, and suggests the Wuchuan-Sihui fault is the boundary between them. A cluster of well-developed reflections on Moho and in its underlying topmost mantle probably comes from alternative thin layers, which may be seismic signature of strong interaction between crust and mantle in the tectonic environment of lithosphere extension.

The Variscan Deformation Front (VDF) in Northwest Germany and Its Relation to a Network of Geological Features Including the Ore-Rich Harz Mountains and the European Alpine Belt

The crustal basement of Northwest Germany can be interpreted as an “Avalonian Terrane Assemblage” subdivided by a roughly NW-SE (Hercynian) and SW-NE (Rhenish) running horst and graben system. In Late Devonian and Early Carboniferous times, this assemblage was flooded by the sea and mainly marine carbonates were deposited on the horsts and Stillwater shales in the grabens, as interpretable through magnetotelluric measurements. During the Late Carboniferous Variscan Orogeny, this terrain became the coal-rich foreland of the colliding Rhenohercynian belt. The shale-filled grabens reacted through folding and thrusting with different anticlinal patterns, the main carbonate covered horst in a still unknown way. This horst was the location of the Late Carboniferous basin center and of the inverted oil-rich Mesozoic Lower Saxony Basin (southwestern sector), respectively, with the so-called Bramsche Massif therein. It probably acted as an indenter for the evolution of the Variscan ore-rich Harz Mountains and forced the approaching Rhenohercynian orogen to stack the appropriate tectonic nappes by horizontal shortening to very high altitudes and the root into large depths. Based on seismic evidence this root is still an uncompleted crust/mantle transition zone with a deep reflection seismic and petrological Moho and a shallower hardly reflecting refraction seismic velocity Moho. The alternative, partly unsolved location of the Variscan Deformation Front in Northwest Germany may represent the new findings. The results may be supported by a comparison with features of the northern Alpine deformation belt.