TY - JOUR A1 - Thomas, R. A1 - Förster, Hans-Jürgen A1 - Rickers, Karen A1 - Webster, J. D. T1 - Origin and evolution of extremely F-rich hydrous melt fractions and hydrothermal fluids during differentiation of highly evolved tin-granite magmas Y1 - 2004 SN - 0016-7037 ER - TY - JOUR A1 - Förster, Hans-Jürgen A1 - Rhede, Dieter T1 - Mineralogy of the Niederschlema-Alberoda U-Se-polymetallic deposit, Erzgebirge, Germany : III. First indication of complete miscibility between tennantite and giraudite Y1 - 2004 ER - TY - JOUR A1 - Bergner, Andreas G. N. A1 - Trauth, Martin H. T1 - Comparison of the hydrologic and hydrochemical evolution of Lake Naivasha (Kenya) during three highstands between 175 and 60 kyr BP N2 - Three diatomite beds exposed in the Ol Njorowa Gorge south of Lake Naivasha, Central Kenya Rift, document three major lake-level highstands between 175 and 60 kyr BP. Diatom transfer-function estimates of hydrological and hydrochemical parameters suggest that a deep and large freshwater lake existed during the highstands at 135 and 80 kyr BP. In contrast, a shallower but more expanded freshwater lake existed at 110 kyr BP. The best analog for the most extreme highstand at 135 kyr BP is the highstand during the Early Holocene humid period from 10 to 6 kyr BP. The environmental conditions as reconstructed from diatom assemblages suggest long-lasting episodes of increased humidity during the high lake periods. This contrasts to the modern situation with a relatively shallow Lake Naivasha characterized by rapid water level fluctuations within a few decades. The most likely cause for the variable hydrological conditions since 175 kyr BP is orbitally driven insolation changes on the equator and increased lateral moisture transport from the ocean. Y1 - 2004 UR - http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V6R-4DJBSX8-1- N&_cdi=5821&_user=1584062&_orig=search&_coverDate=12%2F02%2F2004&_sk=997849998&view=c&wchp=dGLbVzz- zSkzS&md5=b3fffa6b95a86827cd25fd74be3 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Schmidt, C. A1 - Farges, Francois T1 - In-situ study of the iron species in silicate melts Y1 - 2004 SN - 0016-7037 ER - TY - JOUR A1 - Botcharnikov, Roman E. A1 - Koepke, J. A1 - Holtz, Francois A1 - McCammon, C. A1 - Wilke, Max T1 - The oxidation and structural state of Fe in hydrous ferrobasaltic melt Y1 - 2004 ER - TY - JOUR A1 - Bartosch, Thorsten A1 - Wassermann, Joachim T1 - Wavelet coherence analysis of broadband array data recorded at Stromboli volcano, Italy N2 - We present a wavelet coherence method that is capable of displaying local coherence information between two seismic stations in the sense of a spectrogram. We have analyzed the vertical components of a 20-min-long time series from four stations that were situated in the seismic near field of Stromboli volcano. Typical volcanic seismic signals recorded in the near field of Stromboli volcano consist of continuous volcanic tremor superimposed on frequent Strombolian explosion signals. The tremor exhibits a banded and frequency-stable structure, whereas the broadband explosion signals span two or three frequency decades. We demonstrate that signals related to explosion earthquakes are strongly correlated within the network over 1.5 frequency decades. Using synthetic data, we show how coherent signal portions can be extracted out of noisy data using a coherence-filtering method. A time delay analysis using coherence information results in a coarse source location estimation that lies within the crater region. With the exception of randomly fluctuating coherence peaks, low correlations have been observed in the characteristic bands that are assumed to be generated by continuous tremor. In the low-frequency band that is related to the ocean microseisms (period approximate to 4-8 sec), we observe mostly high correlation that breaks down during the appearance of explosion earthquake signals. Based on further analysis using the inverse wavelet transformation, we propose a model that describes the breakdown phenomenon as a superposition of two independent events Y1 - 2004 SN - 0037-1106 ER - TY - JOUR A1 - Bowman, Dan A1 - Korjenkov, Andrey A1 - Porat, Naomi A1 - Czassny, Birka T1 - Morphological response to quaternary deformation at an intermontane basin piedmont, the northern Tien Shan, Kyrghyzstan N2 - The Tien Shan is a most active intracontinental mountain-building range with abundant Quaternary fault-related folding. In order to improve our understanding of Quaternary intermontane basin deformation, we investigated the intermontane Issyk-Kul Lake area, an anticline that was up-warped through the piedmont cover, causing partitioning of the alluvial fan veneer. To follow the morphological scenario during the warping process, we relied on surface-exposed and trenched structures and on alluvial fans and bajadas as reference surfaces. We used air photos and satellite images to analyze the spatial -temporal morphological record and determined the age of near surface sediments by luminescence dating. We demonstrate that the up-warped Ak-Teke hills are a thrust-generated subdued anticline with strong morphological asymmetry which results from the coupling of the competing processes of up-warp and erosional feedback. The active creeks across the up-warped anticline indicate that the antecedent drainage system kept pace with the rate of uplift. The rivers which once sourced the piedmont, like the Toru-Aygyr, Kultor and the Dyuresu, became deeply entrenched and gradually transformed the study area into an abandoned morphological surface. The up-warp caused local lateral drainage diversion in front of the northern backlimb and triggered the formation of a dendritic drainage pattern upfan. Luminescence dating suggest that the period of up-warp and antecedent entrenchment started after 157 ka. The morphologically mature study area demonstrates the response of fluvial systems to growing folds on piedmont areas, induced by a propagating frontal fold at a thrust belt edge, following shortening. (C) 2004 Elsevier B.V All rights reserved Y1 - 2004 SN - 0169-555X ER - TY - JOUR A1 - Kohler, A. A1 - Ohrnberger, Matthias A1 - Scherbaum, Frank A1 - Stange, S. A1 - Kind, F. T1 - Ambient vibration measurements in the Southern Rhine Graben close to Basle N2 - This study presents results of ambient noise measurements from temporary single station and small-scale array deployments in the northeast of Basle. H/V spectral ratios were determined along various profiles crossing the eastern masterfault of the Rhine Rift Valley and the adjacent sedimentary rift fills. The fundamental H/V peak frequencies are decreasing along the profile towards the eastern direction being consistent with the dip of the tertiary sediments within the rift. Using existing empirical relationships between H/V frequency peaks and the depth of the dominant seismic contrast, derived on basis of the lambda/4-resonance hypothesis and a power law depth dependence of the S-wave velocity, we obtain thicknesses of the rift fill from about 155 m in the west to 280 in in the east. This is in agreement with previous studies. The array analysis of the ambient noise wavefield yielded a stable dispersion relation consistent with Rayleigh wave propagation velocities. We conclude that a significant amount of surface waves is contained in the observed wavefield. The computed ellipticity for fundamental mode Rayleigh waves for the velocity depth models used for the estimation of the sediment thicknesses is in agreement with the observed H/V spectra over a large frequency band Y1 - 2004 SN - 1593-5213 ER - TY - JOUR A1 - Friedrich, A. M. A1 - Lee, J. A1 - Wernicke, B. P. A1 - Sieh, K. T1 - Geologic context of geodetic data across a Basin and Range normal fault, Crescent Valley, Nevada N2 - [1] Geodetic strain and late Quaternary faulting in the Basin and Range province is distributed over a region much wider than historic seismicity, which is localized near the margins of the province. In the relatively aseismic interior, both the magnitude and direction of geodetic strain may be inconsistent with the Holocene faulting record. We document the best example of such a disagreement across the NE striking, similar to55degrees NW dipping Crescent normal fault, where a NW oriented, 70 km geodetic baseline records contemporary shortening of similar to2 mm/yr orthogonal to the fault trace. In contrast, our geomorphic, paleoseismic, and geochronologic analyses of the Crescent fault suggest that a large extensional rupture occurred during the late Holocene epoch. An excavation across the fault at Fourmile Canyon reveals that the most recent event occurred at 2.8 +/- 0.1 ka, with net vertical tectonic displacement of 4.6 +/- 0.4 m at this location, corresponding to the release of similar to3 m of accumulated NW-SE extension. Measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event, implying a moment magnitude M-w of at least 6.6. No prior event occurred between similar to2.8 ka and similar to6.4 +/- 0.1 ka, the C-14 calender age of strata near the base of the exposed section. Assuming typical slip rates for Basin and Range faults (similar to0.3 mm/yr), these results imply that up to one third, or similar to1 m, of the extensional strain released in the previous earthquake could have reaccumulated across the fault since similar to2.8 ka. However, the contemporary shortening implies that the fault is unloading due to a transient process, whose duration is limited to between 6 years ( geodetic recording time) and 2.8 ka ( the age of the most recent event). These results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements Y1 - 2004 SN - 0278-7407 ER - TY - JOUR A1 - Gottesmann, Bärbel A1 - Förster, Hans-Jürgen T1 - Sekaninaite from the Satzung granite (Erzgebirge, Germany) : magmatic or xenolithic? N2 - In the earliest emplaced granite subintrusion of the multiphase peraluminous Satzung pluton, Erzgebirge, Germany, a mineral aggregate was observed consisting of sekaninaite (X-Fe = 0.74-0.94), Zn-rich hercynite (X-Zn = 0.03- 0.11), tri- and dioctahedral layer silicates of different composition and color, and minor quartz. Geological, textural, and compositional criteria argue that the sekaninaite, hercynite, quartz, and the brown biotite are not primary or secondary granite minerals, but are of metamorphic origin representing a xenolith uptaken from the granite melt near its level of emplacement. The metamorphic origin is supported by the occurrence of this mineral assemblage in metamorphic rocks exposed locally in the Erzgebirge basement. Reaction of the polymineralic metamorphic aggregate with the surrounding melt and subsequent interaction with alkali-, F- and LILE-rich residual fluids account for the widespread decomposition of the sekaninaite and formation of several layer silicates including green biotite, muscovite, berthierine/Fe chlorite, and sericite. The observed enrichment of the relic sekaninaite and its replacement products in elements such as Na, Li, Be, Rb, Cs, and F is result of interaction of the metamorphic fragment with the surrounding melt/fluid, in accordance with the evolved nature of the Satzung magmatic-hydrothermal system Y1 - 2004 SN - 0935-1221 ER -