We have analysed >1800 records of very weak microearthquakes (-1.9 12 years) and time distributions of the events. The magnitude-distribution of events from individual re-activated foci obeys Gutenberg-Richter law at least in the magnitude range -1.3<=ML&<=1.3. The typical b-values are close to b=1, which also applies for the whole catalogue of events located in the region. In this respect, the investigated region is similar to other presently deformed regions where seismicity is controlled by far-field stresses. Based on the fault geometry, the evolution of sedimentary basin in the most active part of the region, and the spatial co-incidence of the earthquake epicentres with carbonated mineral springs in a rhomb-shaped domain, we suggest a preliminary model explaining the studied region as a transfer zone with releasing geometry (pull-apart mechanism), operating within the system of dextral wrench faults.
This paper is focused on the progress in the determination of water in glasses and melt inclusions with Raman spectroscopy. Using the presented "Comparator Technique" the water content of a sample is determined by simple comparison with a known standard. A calibration curve is not necessary. Furthermore, with this technique the water concentration in silicate melt inclusions can be determined without exposing the inclusions for measurements. This is very important for extremely water-rich melt inclusions, which would loose H2O on exposure.
Magnetic volume susceptibility of two mica and biotite granodiorites in two quarries (Oberottendorf, Demitz-Thumitz) was determined in the field and in the laboratory. The anisotropy of magnetic susceptibility (AMS) was measured on oriented samples. These AMS investigations are intended as a first test as to whether internal structure and structural evolution of the Cadomian granodiorite plutons from the Lusatian region are reflected by the magnetic fabric. In old quarries and natural outcrops it is very difficult or even impossible to distinguish different granitoid types because of weathering and related features. However, magnetic volume susceptibility determinations now allow such a distinction in the field. IGCP-373
Twenty seven clay-sized (<2 μm) separates from drill core samples of the Upper Oligocene maar near Baruth, Saxony, were mineralogically and chemically characterized using X-ray diffraction analysis coupled with the Rietveld method, X-ray fluorescence analysis, scanning and transmission electron microscopy, and stable isotope analysis. The predominant minerals in the clay fractions are kaolin minerals (kaolinite and halloysite) and opal-A. Abundant Fe- and smectite-rich illite-smectite mixed-layer minerals occur exclusively in the lower turbidites and debris flows. Illite and beidellites are minor components. Accessory phases are anatase, siderite, sanidine, quartz, albite-rich plagioclase, and pyrite. Four main detrital components were detected in the Upper Oligocene maar sediments: 1) biogenic opal-A as diatom fragments, 2) disordered kaolinite (and halloysite) + illite + beidellite + Zr-rich anatase from soils on granodioritic material, 3) Fe- and smectite-rich I-S from weathered basaltic volcanic material and 4) sporadic eolian input of sanidine-bearing, probably phonolithic, ashes. The Mid-Miocene kaolinite-rich clays that cover the maar sediments were derived from eroded saprolites on the Lausitz granodiorite. The δD and δ18O values of the kaolinite-rich clay fractions from various lithologies indicate kaolinization at temperatures of ~15 ± 5 °C from meteoric waters that were isotopically heavier than present-day meteoric waters. There is no evidence for hydrothermal clay formation in the maar.
