Geochemistry

The 1960 rhyodacitic fissure eruption in the Cordón Caulle Volcanic Complex (CCVC), located in Southern Andes (40.5°S) was a unique volcanic episode. The remarkable eruption was triggered by the greatest recorded subduction-zone earthquake, starting 38 h after the main shock, 240 km inland. The structural behaviour, two compound fissures opening along a margin-oblique (NW) structure related to the Quaternary evolution

ABSTRACT The recent geomagnetic secular variation is mainly characterized by the large growth of the South Atlantic Magnetic Anomaly during the last three centuries, first documented by the geomagnetic model gufm1 (Jackson et al., 2000). We report new paleomagnetic results (directions and paleointensities) from several sites in two well dated lava flows in Chile, the 1835 AD eruption of the Osorno volcano and the 1751 AD eruption of the Llaima volcano. In addition, paleointensities were obtained on 14 samples from bricks of shelters built along the main road across the Andes from Santiago (Chile) to Mendoza (Argentina) in 1770±5 AD. The results confirm the high reliability of the global geomagnetic model gufm1 for the last three centuries with a large amplitude of the secular variation in inclination (∼20°) and intensity (∼25μT). Results from three 14C dated volcanic units in the time interval 1400-1750 AD indicate that more paleomagnetic results in well dated lava flows are necessary to improve the robustness of existing global geomagnetic models. At this stage, precise paleomagnetic or archeomagnetic dating in South America using global models should be restricted to the last 3 centuries.

The 1960 rhyodacitic fissure eruption in the Cordón Caulle Volcanic Complex (CCVC), located in Southern Andes (40.5°S) was a unique volcanic episode. The remarkable eruption was triggered by the greatest recorded subduction-zone earthquake, starting 38 h after the main shock, 240 km inland. The structural behaviour, two compound fissures opening along a margin-oblique (NW) structure related to the Quaternary evolution

Forty-three 40 Ar/ 39 Ar age determinations of lava flows, domes, ignimbrites, and dikes, plus 14 C dates from seven distal tephra layers, combined with stratigraphy, geochemistry, and Sr and Th isotope data, establish an eruptive chronology for the Puyehue-Cordón Caulle ...

In this study, the influence of lead nitrate as a hazardous environmental pollutant was studied through experimental tests to assess its physicochemical effects in soils. Artificially contaminated soil specimens were prepared using sand and two kinds of clays. Direct shear, consolidation, electrical resistivity and unconfined compression tests were conducted. In addition, the influence of lead cation on atterberg limits, pH and particle size distribution of soils was evaluated. Overall, the presence of lead ion in mixtures including bentonite increased the shear strength due to a flocculated structure and replacement of sodium cations by hydrogen ions which is along with the reduction of double-layer thickness. However, due to the broken bonds and rearranging of kaolinite particles to a weaker form, the strength of sand–kaolinite mixtures decreased with the increase of lead concentration. Based on the obtained results, with the addition of lead concentration, the compression index and electrical resistivity of all specimens decreased. Due to the acidic nature of positively charged lead cations, pH of the specimens directly affected and tended to a more acidic range. These findings indicate that the presence of lead ion improves the strength of some kinds of soils including bentonite and decreases the strength parameters of soils with kaolinite.

... of Geological Sciences AJ-20, University of Washington, Seattle, Washington 98195 ABSTRACT Epidote phenocrysts (Psi9_24) in Lara-mide-age ... Some epidote crystals are bent and cracked where they abut corners of plagioclase or quartz phenocrysts, presumably due to the ...

ABSTRACT The Zhangjiakou-Penglai Fault Zone (ZPFZ), as a large-scale WNW-trending active fault zone with frequent seismic activity, is an area prone to moderate to intense earthquakes across North China. A detailed analysis of the ZPFZ has been carried out based on earthquake activity, deep structural response, dynamic mechanism and physical simulation by conducting an en échelon fault model experiment. The results show that the ZPFZ is a lithospheric active fault zone that has controlled some small en échelon Quaternary pull-apart basins and has triggered many earthquakes as seismogenic structures. The earthquake location and intensity distribution by the experimental simulation fit well with those of actual earthquakes. The earthquake distribution is controlled obviously by the en échelon structural properties. The intensity of seismic activity is strong in the middle and weak at the western and eastern ends of the fault zone, migrating from the southeast to the northwest along the entire fault zone. This WNW-trending fault zone in North China, is closely related to the surrounding plate activities. The ZPFZ is not only dominated by the collision of the Indian Plate to the Eurasian Plate, but is also influenced by the subduction of the Pacific Plate. It depends on the comprehensive reflection of two geodynamic settings from the western collision of the Indian to the Eurasian plates and the eastern subduction of the Pacific Ocean Plate to the Eurasian Plate.

In stick-slip experiments modeling the occurrence of earthquakes, the meta-instability stage (MIS) is the process that occurs between the peak differential stress and the onset of sudden stress drop. The MIS is the final stage before a fault becomes unstable. Thus, identification of the MIS can help to assess the proximity of the fault to the earthquake critical time. A series of stick-slip experiments on a simulated strike-slip fault were conducted using a biaxial servo-controlled press machine. Digital images of the sample surface were obtained via a high speed camera and processed using a digital image correlation method for analysis of the fault displacement field. Two parameters, A and S, are defined based on fault displacement. A, the normalized length of local pre-slip areas identified by the strike-slip component of fault displacement, is the ratio of the total length of the local pre-slip areas to the length of the fault within the observed areas and quantifies the growth o...

The properties of atomic nuclei with closed shells, “magic numbers” of neutrons or protons, have long provided the benchmarks for models of nuclear structure. The single-particle properties of nuclei near closed shells have been established by nuclear reactions in which a proton ...

ABSTRACT The El'gygytgyn impact structure in northeast Russia was drilled in 2008/2009. The 3.5 Ma old structure has a rim-to-rim diameter of 18 km and is the only known impact structure that has been formed on a siliceous volcanic target. The petrophysical, rock- and paleomagnetic properties, including attempted reorientation of samples, along the El'gygytgyn drill core were analyzed. Physical properties, such as bulk density, porosity, seismic velocity, and electrical conductivity, clearly showed the propagation of shock and the associated fracturing. The grain density, however, was probably influenced by the postimpact hydrothermal activity and/or the distribution of impact melt. The highest values of electrical conductivity coincided with higher concentrations of particular metals as indicated by Raschke et al. (2012a). The rock- and paleomagnetic investigations showed iron-titanium oxides with varying oxidation/reduction states as the main magnetic fraction in the core samples and indicated them as carriers for remanent magnetization. With few exceptions, most samples showed normal polarity of characteristic remanent magnetization and confirmed that the impact occurred after the Gauss/Gilbert (approximately 3.596 Ma) reversal. Shallower inclinations than that expected for a 3.5 Ma dipole field were probably due to impact-related block movements and/or compaction.