Description: The combined passive and active seismic TRANSALP experiment produced an unprecedented high-resolution crustal image of the Eastern Alps between Munich and Venice. The European and Adriatic Mohos (EM and AM, respectively) are clearly imaged with different seismic techniques: near-vertical incidence reflections and receiver functions (RFs). The European Moho dips gently southward from 35 km beneath the northern foreland to a maximum depth of 55 km beneath the central part of the Eastern Alps, whereas the Adriatic Moho is imaged primarily by receiver functions at a constant depth of about 40 km. In both data sets, we have also detected first-order Alpine shear zones, such as the Helvetic detachment, Inntal fault and Sub-Tauern ramp in the north. apart from the Valsugana thrust, receiver functions in the southern part of the Eastern Alps have also observed a north dipping interface, which may penetrate the entire Adriatic crust [Adriatic Crust Interface (ACI)]. Deep crustal seismicity may be related to the ACI. We interpret the ACI as the currently active retroshear zone in the doubly vergent Alpine collisional belt.

Description: This 1D/2D petroleum system modelling study intended to reconstruct the temperature, maturation, migration and accumulation history within the „Tight Gas Area“ on the southern edge of the Pompeckj Block in northern Germany. To better understand hydrocarbon migration and to generate a more reliable predictive model of reservoir characteristics, we integrated detailed information from (i) sedimentological analysis of core and log data, and (ii) a structural reconstruction of the Rotliegend reservoir horizons. One cross section and 12 wells were examined using the 1D/2D simulation software PetroMod® 7.1 of IES GmbH, Jülich; subsequently the results of the 1D modelling were incorporated in the 2D model. The W-E section connects well-known gas fields of the Nordhannover concession and runs perpendicular to the prevalent N-S striking horst-and-graben structures within the Paleozoic rocks. The depth to the major source rocks within the area, the coal-bearing Westphalian strata, varies between 5800 m and around 4700 m in some areas (e.g. Top Westphalian B). Along the section, a pre-Permian erosion of between 400 to 1200 m of Upper Carboniferous sediments was assumed, the actual amount depending on the position relative to horst and grabens. During the Upper Carboniferous and the Rotliegend the temperatures within Westphalian B and Lower Westphalian C sediments remained below 100°C and 75°C, respectively. The temperatures within these sediments increased by about 50°C, before they decreased again to 125°C and 100°C, respectively, due to the Late Jurassic inversion. During on-going burial in the Upper Cretaceous, temperatures rose until they reached their present-day values of about 175°C in Lower Westfalian C, 210°C in Westfalian B, and more than 250°C in Namurian C sediments. According to the temperature history, the maturation of organic matter within these rocks occurred in two important stages. During the Triassic, vitrinite reflectance reached values of 1.5% and 1.0% in Westphalian B and Lower Westphalian C sediments, respectively. The second period of intense maturation was coeval with enhanced subsidence during the Upper Cretaceous, when vitrinite reflectance within Westfalian B and C sediments increased from to 3.0% and about 2.2%, respectively. Maturity within the horst block sediments remained lower by about 1.0%. Within Westphalian B sediments gas generation started during the Middle Triassic and lasted until the Late Tertiary. These rocks became overmature whilst Lower Westfalian C rocks generated gas until the present time and transformed 60-90% of their convertible kerogen into hydrocarbons, the actual amount depending on the structural position. During the Jurassic and the Triassic, when the regional stress field allowed N-S striking faults to be dilatant and to act as migration pathways, high gas columns along the fault zones led to a breakthrough and loss of gas, where thinned Zechstein salt exists.

Description: Obliquely convergent subduction margins commonly exhibit strain partitioning leading to trench-parallel material transport in the forearc. If deformation is localised, large margin-parallel strike-slip faults may form (e.g. in Peru, North-Chile or Sumatra). These faults are typically located far arcward from the deformation front (100-300km) in the internal part of the forearc. To date sandbox experiments, however, show strain partitioning in the deforming accretionary prism only. We therefore designed a series of scaled 3D sandbox experiments to monitor the deformation of the rearward region of the forming wedge. We further test how deformation is dependent on modes of shear force transmission at the base of the wedge. The latter is modelled by shifting the S-line relative to the deformation front. The S-line is the location on the plate interface landward of which basal shear forces are not further transmitted into the overlying wedge. Such a singularity is inescapable in analogue or numerical modelling and may have its natural analogy in the line of intersection (transition zone) of the subducting slab with some brittle-ductile boundary in the continental wedge. Analysis of the 3D surface displacement using an image correlation technique (PIV: particle imaging velocimetry) is used to evaluate material transport and to differentiate kinematic domains on the forming sand wedge. First results for a setting with shear force being transmitted along the entire backstop base show that most of the oblique convergence is accommodated in the fore- and back-thrust system. With proceeding convergence, a fault system evolves on the arcward side of the accretionary wedge, formed by the surface traces of back-thrusts. The main back-thrust is reactivated with a noticeable strike-slip component at the end of each fore-thrust forming cycle. Finally, the back-thrust becomes inactive and a new, more favorably oriented fault is formed in the backstop. This shows that the seemingly decoupled rearward region of the forearc system accommodates a trench parallel displacement component.------------------------

Description: A 400-km-long seismic reflection profile (Andean Continental Research Project 1996 (ANCORP'96)) and integrated geophysical experiments (wide-angle seismology, passive seismology, gravity, and magnetotelluric depth sounding) across the central Andes (21°S) observed subduction of the Nazca plate under the South American continent. An east dipping reflector (Nazca Reflector) is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km. We interpret parts of the Nazca Reflector as a fluid trap located at the front of recent hydration and shearing of the mantle, the fluids being supplied by dehydration of the oceanic plate. Patches of bright (Quebrada Blanca Bright Spot) to more diffuse reflectivity underlie the plateau domain at 15–30 km depth. This reflectivity is associated with a low-velocity zone, P to S wave conversions, the upper limits of high conductivity and high Vp/Vs ratios, and to the occurrence of Neogene volcanic rocks at surface. We interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during Neogene shortening and plateau growth. The imaging properties of the continental Moho beneath the Andes indicate a broad transitional character of the crust-mantle boundary owing to active processes like hydration of mantle rocks (in the cooler parts of the plate margin system), magmatic underplating and intraplating under and into the lowermost crust, mechanical instability at Moho, etc. Hence all first-order features appear to be related to fluid-assisted processes in a subduction setting