Mass wasting at the base of the South central Chilean continental margin: the Reloca Slide

Offshore south central Chile (35° S–42° S), the morphology of the lowermost continental slope and trench floor witnesses a voluminous submarine mass-wasting event. The blocky slide body deposited in the Chile Trench at 73°46´ W 35°35´ S was targeted for study during RRS JAMES COOK Cruise JC23 and termed Reloca Slide. Its size of about 24 km3, its steep and high headscarp, the spatial distribution of slide deposits and the cohesive nature of major slide blocks make it interesting to address the issue of tsunami generation. We have obtained seismic reflection data that partly reveal the internal structure of the slide body. Gravity core samples were retrieved that will allow the slide to be dated and linked to the history of sedimentation and slope stability along this particular segment of the Chilean convergent margin. At present we assume a Holocene age for the sliding event

Hangrutschungen in den Ozeanen – So what?

Bergstürze und das Abrutschen von Sedimenten auf Kontinentalhängen und den untermeerischen Hängen von Inseln ist ein Phänomen, dessen Bedeutung für die Gestaltung von Unterwasserlandschaften mit den aktuellen Möglichkeiten der Unterwasserkartierung immer deutlicher wird. Obwohl große Rutschungen nicht häufig vorkommen sind ihre direkten und indirekten Folgen für dicht besiedelte Küsten gewaltig, da sie ganze Küstenstreifen zurückverlagern und Tsunamis auslösen können. Hier werden einige historische Beipiele gezeigt

Water input and water release from the subducting Nazca Plate along southern Central Chile (33°S-46°S)

The age of the subducting Nazca Plate off Chile increases northward from 0 Ma at the Chile Triple Junction (46°S) to 37 Ma at the latitude of Valparaíso (32°S). Age-related variations in the thermal state of the subducting plate impact on (a) the water influx to the subduction zone, as well as on (b) the volumes of water that are released under the continental fore arc or, alternatively, carried beyond the arc. Southern Central Chile is an ideal setting to study this effect, because other factors for the subduction zone water budget appear constant. We determine the water influx by calculating the crustal water uptake and by modeling the upper mantle serpentinization at the outer rise of the Chile Trench. The water release under fore arc and arc is determined by coupling FEM thermal models of the subducting plate with stability fields of water-releasing mineral reactions for upper and lower crust and hydrated mantle. Results show that both the influx of water stored in, and the outflux of water released from upper crust, lower crust, and mantle vary drastically over segment boundaries. In particular, the oldest and coldest segments carry roughly twice as much water into the subduction zone as the youngest and hottest segments, but their release flux to the fore arc is only about one fourth of the latter. This high variability over a subduction zone of <1500 km length shows that it is insufficient to consider subduction zones as uniform entities in global estimates of subduction zone fluxes

Thermal control of the seismogenic zone of southern central Chile

We developed thermal models for the Chile subduction zone along two profiles at 38.2°S and 42°S within the rupture area of the 1960 M = 9.5 Valdivia earthquake and south of the 2010 M = 8.8 Maule earthquake. The age difference of the subducting Nazca Plate has a major impact on the thermal regime, being much younger and hotter in the south. Seafloor heat flow observations confirm this difference but also indicate that in the southern area, heat advection at the outer rise cools the incoming plate. Heat flow values derived from the depth of gas hydrate bottom-simulating reflectors are in general agreement with probe and borehole measurements. The positions where the plate interface reaches temperatures of 100–150°C and 350–450°C differ between the two profiles. If these temperatures control the updip and downdip limits of the interplate seismogenic zone, the seismogenic zone widens and shifts landward to greater depths from south to north. Observed microseismicity, however, seems to fade at temperatures much lower than 350–450°C. This discrepancy can be explained in three alternative ways: (1) deformation in a thick subduction channel controls the seismic/aseismic transition; (2) microseismicity recorded over a limited time period does not represent the rupture depth of large interface earthquakes; or (3) the serpentinized mantle wedge controls the downdip limit

Geochemical, Geophysical and Morphological Results from the Chilean Southern Volcanic Zone: The Role of Fluids in Generating the Highest Magmatic Output

In the Collaborative Research Center (SFB574), which studies the role of volatiles and fluids in subduction zones, we have compiled a comprehensive geochemical data set from the Chilean Southern Volcanic Zone. Here we focus on the middle volcanic front (MVF from 34.5-38°S) and the southern volcanic front (SVF from 38-43°S). We also have data from the behind the VF (BVF) volcanism in Argentina. This data set is augmented by calculations of volcano volume, a seismic profile from the forearc through the VF between 39-40°S and geophysical studies offshore the SVF. On the Sr vs Nd isotope diagram, the MVF almost completely overlaps the BVF samples. On Pb isotope diagrams, the MVF falls on the radiogenic end of the positive backarc array. On 206Pb/204Pb vs Sr and Nd isotope diagrams, the unradiogenic end of the BVF array has an EMORB type composition, suggesting an EMORB type of mantle wedge composition. The VF lavas can be explained largely by two component mixing of trench sediments (+/- subducting slab) and an EMORB type of mantle wedge. Combined with higher erupted volumes over shorter time scales for the SVF compared to the MVF (Völker et al., 2011, JVGR), the higher fluid mobile to fluid immobile (e.g. U/Th, Pb/Ce and Ba/Nb) ratios point to a higher fluid flux, whereas the lower more to less immobile incompatible (e.g. La/Yb, La/Sm, Th/Yb, Ta/Yb) element ratios are consistent with higher degrees of melting. On the Sr vs Nd and 206Pb/204Pb vs Sr and Nd isotope ratio diagrams, the SVF is shifted to higher Sr and Nd isotope ratios. We interpret these variations to indicate derivation of the fluids from seawater altered oceanic crust and/or mantle and sediments. The Pb isotopic composition of the SVF is identical to the MVF and is clearly dominated by the composition of the trench sediments. Delta 18O of olivine correlates inversely with U/Th and Nd isotope ratios, extending to lower and higher d18O than found in olivines in mantle peridotites. The low d18O and high U/Th and Nd isotope component present in the SVF (in Llaima and Villarrica) is interpreted to reflect fluids derived from hydrothermally altered oceanic crust and serpentinized upper mantle of the incoming plate, whereas the high d18O endmember primarily in the MVF points to fluids derived from subducted sediments. Beneath the VF between 39-40°S, where Villarrica, one of South America’s most active volcanoes, is located, a low-velocity seismic anomaly, together with high Vp/Vs ratios, is interpreted to reflect greater fluid ascent above the subducting Valdivia Fracture Zone. The combined morphologic (volume), geochemical and geophysical data suggest an enhanced fluid presence beneath much of the SVF (Llaima, Villarrica and Puyehue Volcanoes), probably caused by a stronger hydration of the incoming plate around and between the Valdivia and Chiloe Fracture Zones

Kinetic parameter estimation from TGA: Optimal design of TGA experiments

This work presents a general methodology to determine kinetic models of solid thermal decomposition with thermogravimetric analysis (TGA) instruments. The goal is to determine a simple and robust kinetic model for a given solid with the minimum of TGA experiments. From this last point of view, this work can be seen as an attempt to find the optimal design of TGA experiments for kinetic modelling. Two computation tools were developed. The first is a nonlinear parameter estimation procedure for identifying parameters in nonlinear dynamical models. The second tool computes the thermogravimetric experiment (here, the programmed temperature profile applied to the thermobalance) required in order to identify the best kinetic parameters, i.e. parameters with a higher statistical reliability. The combination of the two tools can be integrated in an iterative approach generally called sequential strategy. The application concerns the thermal degradation of cardboard in a Setaram TGA instrument and the results that are presented demonstrate the improvements in the kinetic parameter estimation process