M. Schimmel - Academia.edu (original) (raw)

Papers by M. Schimmel

Some of the most voluminous mafic potassic provinces of the world are located in SE and Central B... more Some of the most voluminous mafic potassic provinces of the world are located in SE and Central Brazil emplaced into proterozoic mobile belts and whose magmas date ~85 Ma. Their origins are controversial, some interpreted these magmatisms as an end-stage of Paraná volcanism. On the other hand, reconstructions of plate motion suggest that, at ~ 85 Ma ago, the location

ABSTRACT The lithospheric structure of the mid-plate South American continent has been studied wi... more ABSTRACT The lithospheric structure of the mid-plate South American continent has been studied with surface and body wave tomography, as well as receiver functions, in the last few years, using several temporary seismic station experiments. Joint inversion of group velocities and waveform data are beginning to delimit the Amazon and San Francisco cratons at depth. Despite the low density of stations in northern Brazil, both cratons seem to be less thick than the North American craton. A mid-continent strong low-velocity anomaly at 100-300 km depth beneath the Pantanal basin, also seen at other global-scale tomographic studies, reveals a weak lithosphere (consistent with low Te and higher seismicity); the origin of this major anomaly is not fully understood yet. In the intracratonic Parana basin, joint inversions of receiver function and Rayleigh-wave dispersion, integrated with results from teleseismic body-wave tomography, indicate a fragmented nature of the crust beneath the basin as opposed to previous models of a single cratonic block. Future plans for more detailed lithospheric studies will be discussed in view of the installation of the Brazilian permanent seismic network, as well as the operation of the Brazilian Equipment Pool for temporary deployments.

ABSTRACT New geological mapping in the central Taiwan mountain belt, together with a new collapse... more ABSTRACT New geological mapping in the central Taiwan mountain belt, together with a new collapsed data set of relocated seismicity, indicate that the basal detachment beneath the thin-skinned Western Foothills possibly ramps down in the crystalline basement along their eastern flank. Consequently, the basement appears to be involved in the deformation in the more internal Hsuehshan Range. Furthermore, seismic tomography data indicate a shallowing of higher Vp velocity material beneath the Hsuehshan Range than beneath the Western Foothills. Therefore, we propose that the basement is possibly being uplifted to form a basement-cored culmination beneath the Hsuehshan Range. These basement rocks appear to be located at progressively shallower structural levels than the basement rocks beneath the Western Foothills. This structural architecture is similar to that in other orogens worldwide, where the thin-skinned foreland fold-and-thrust belt ends hinterlandward with a ramp down into the middle to lower crust and, subsequently, the involvement of basement rocks in the deformation. However, we are uncertain if this basement culmination is somehow linked to the outcropping basement rocks of the Tananao Complex in the Central Range or if two different types of basement rocks are juxtaposed across the Lishan fault.

We used the regional seismic tomography to study the upper mantle beneath SE and Central Brazil. ... more We used the regional seismic tomography to study the upper mantle beneath SE and Central Brazil. This method is based on the inversion of P- and S-wave relative travel time residuals (VanDecar, 1991) obtained from more than 80 stations in an area of 20 x 20 degrees. The ~11000 P and PKP residuals and ~8000 S, ScS, SKS, and SKKS residuals have been obtained from waveform cross-correlations for up to 12 simultaneous stations. Our results show correlations of seismic anomalies with the main tectonic structures and reveal new anomalies not yet observed in previous works. High velocity anomalies in the western portion of the Sao Francisco Craton support the hypothesis that this craton was part of a major Neoproterozoic plate. Low velocity anomalies beneath the Tocantins Province (mainly fold belts between the Amazon and Sao Francisco cratons) are interpreted as due to lithospheric thinning. Assumpcao et al. (2004) showed a good correlation between intraplate seismicity and low velocity a...

Pure and Applied Geophysics, 2015

Geophysical Research Letters, 2015

ABSTRACT Surface geological data indicate that the structural architecture and kinematics of the ... more ABSTRACT Surface geological data indicate that the structural architecture and kinematics of the thrust belt in central Taiwan, from the Central Range to the frontal thrust in the west, is not that of a simple west-verging imbricate stack. In particular, the Hsuehshan Range appears to be an oblique thrust system that is inverting an Eocene-age extensional basin, resulting in a complex interaction between faults and folds. Field mapping indicates that there is a major structural break between the Hsuehshan Range and the Western Foothills in the west, and with the Central Range in the east. Because of the complexity caused by oblique thrusting, determining the structure at depth across the thrust belt is difficult from surface data alone. Therefore, we have incorporated seismicity data to see how deep the major faults in the thrust belt penetrate and, where possible, what their kinematics are. Moment magnitudes for each event have been recalculated to energy release, and maps and cross sections cut through the volume to determine where the major energy release has been taking place. In Central Taiwan, these data indicate that a significant portion of the energy release in the thrust belt is within or along the boundaries of the Hsuehshan Range. The Western Foothills show patchy energy release with a local concentration at between 8 and 10 km depth. Focal mechanisms here suggest that roughly west-directed thrusting is dominant. At the transition into the Hsuehshan Range, across the Shanghua and Shuili-Keng faults, there is a sudden deepening of the seismic activity, with major energy release taking place to depths of about 20 km. The majority of focal mechanisms suggest highly oblique to strike-slip faulting, in keeping with field observations. There is a marked drop in seismic activity at the eastern flank of the Hsuehshan Range, along the Lishan Fault. This integration of field geological observations with seismicity data has proven to be an important step in interpreting the crustal structure, kinematics and evolution of the Taiwan thrust belt.