Summary The Melibocus Massif forms a tonalite pluton in the W’ Bergstr?sser Odenwald, which is interpreted as part of a magmatic
arc of Devonian to Carboniferous age. Dikes of various compositions intrude frequently this tonalite.
Different dike-lithologies are associated with different strike directions. Most dikes show evidence of high-temperature shearing.
A probable maximum paleostress direction of ca. 060° can be estimated, i.e. nearly parallel to the known Variscan subduction
zone in the Northwest. Due to their ductile deformation under conditions around the Ar-closing temperature of amphibole, intrusion
likely occurred during the Carboniferous (Mississippian).
The gabbroic to dioritic dikes (malchites) have calc-alkaline composition. Comparison with modern analogues suggests subduction-related
arc magmatism. Rare earth element distributions indicate more than 5% partial melting of the mantle source with limited amounts
of residual garnet.
In contrast to the tonalite pluton the granitoid dikes (alsbachites) are of S-type origin, as indicated by primary muscovite
and chemical composition. This requires involvement of continental material in the dike’s source rather than in the tonalite
host rock’s source. The trace element chemistry of these dikes indicates magma formation in a convergent plate tectonic situation,
i.e. a magmatic arc regime. Therefore, the dikes are probably the late part of the same subduction-related magmatism, which
produced the tonalitic and other plutons of the Bergstr?sser Odenwald. In contrast to the large pluton-forming magmas, formation
of the dikes during late or post-collisional extension or transtension followed by a phase of compression or transpression
is probable.
Zusammenfassung
Geochemie, tektonische Stellung und geodynamische Signifikanz sp?torogener G?nge im Melibocus Massiv, Bergstr?sser Odenwald
Der Melibokus Tonalit-Pluton geh?rt zum Bergstr?sser Odenwald, der als Teil eines devonisch-karbonischen magmatischen Bogens
interpretiert wird. In diesem Pluton treten sehr h?ufig magmatische G?nge unterschiedlicher Zusammensetzung auf.
Die Arbeit zeigt, dass die G?nge unterschiedlicher Zusammensetzung unterschiedliche Streichrichtungen haben. Die meisten der
untersuchten G?nge zeigen Hochtemperatur-Schergefüge. Aus der Lage der zerscherten G?nge l?sst sich eine Pal?ostressrichtung
mit 060° für Sigma 1 ableiten. Diese Richtung weicht nur unwesentlich von der bekannten variskischen Subduktionszone im Nordwesten
ab. Aufgrund ihrer Hochtemperatur-Gefüge, die im Bereich der Schlie?ungstemperatur von Ar in Hornblenden gebildet wurden,
ist das Alter der G?nge wahrscheinlich ebenfalls als Karbon (Mississippian) einzustufen.
Die gabbroiden bis dioritischen G?nge (Malchite) haben eine kalkalkaline Zusammensetzung. Der Vergleich mit rezenten Magmatiten
deutet auf eine Entstehung in einem magmatischen Bogen (Kontinentalrand) hin. Die Seltenerdelementverteilung der G?nge zeigt
einen wahrscheinlichen Aufschmelzungsgrad der Mantelquellregion von über 5% bei einem geringen Anteil von residualem Granat
an.
Im Gegensatz zu den tonalitischen Nebengesteinen zeigen die granitoiden G?nge anhand ihrer modalen (Muskovit) als auch chemischen
Zusammensetzung S-Typ-Charakter. Dies bedeutet eine h?here Beteiligung krustaler Komponente in der Magmenquelle als dies für
den Tonalit angenommen werden darf. Die Spurenelementchemie der granitoiden G?nge zeigt ebenfalls eine Bildung in einem konvergenten
plattentektonischen Regime, d.h. innerhalb eines magmatischen Bogens. Die G?nge stellen somit vermutlich das Produkt eines
sp?ten Abschnittes des subduktionsbezogenen Magmatismus, der auch die Tonalite und andere Plutone im zentralen Bergstr?sser
Odenwald geschaffen hat, dar. Im Gegensatz zu dem Magmatismus der die Plutone erzeugt hat, sind die G?nge wahrscheinlich gegen
Ende der Kollision oder nachfolgend auf diese in eine sich dehnende Kruste intrudiert und in einem nachfolgenden kompressiven
Regime deformiert worden.
Received August 31, 1999; revised version accepted October 9, 2000 相似文献
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While much of the research on neighborhood crime considers the neighborhood as a whole, this study utilizes spatial analysis techniques to examine how the presence of disorder and collective efficacy create unique pockets of opportunities for criminal behavior within neighborhoods. This spatial perspective reveals how the effect of disorder and efficacy upon crime patterns itself varies across a neighborhood. Physical disorder is measured through systematic social observations and the level of collective efficacy is evaluated through survey responses of neighborhood residents. The indices of disorder and efficacy are compared to crime data from police call logs using geographically weighted regression. Our findings demonstrate a complex spatial relationship between disorder and efficacy. The effects of disorder and efficacy are not consistent across an entire neighborhood, but rather display local variations in small geographical areas within neighborhoods, including some pockets of the neighborhood where the relationships between disorder, efficacy, and crime were contrary to the expected relationships. Based upon these findings, we conclude opportunity is central to understanding crime, and emphasize the role of informal social control in neighborhoods. 相似文献
The isotopic composition and mass balances of sources and sinks of sulfur are used to constrain the limnological–hydrological evolution of the last glacial Lake Lisan (70–14 ka BP) and the Holocene Dead Sea. Lake Lisan deposited large amounts of primary gypsum during discrete episodes of lake level decline. This gypsum, which appears in massive or laminated forms, displays δ34S values in the range of 14–28‰. In addition, Lake Lisan’s deposits (the Lisan Formation) contain thinly laminated and disseminated gypsum as well as native sulfur which display significantly lower δ34S values (−26 to 1‰ and −20 to −10‰, respectively). The calculated bulk isotopic compositions of sulfur in the sources and sinks of Lake Lisan lacustrine system are similar (δ34S ≈ 10‰), indicating that freshwater sulfate was the main source of sulfur to the lake. The large range in δ34S found within the Lisan Formation (−26 to +28‰) is the result of bacterial sulfate reduction (BSR) within the anoxic lower water body (the monimolimnion) and bottom sediments of the lake.
Precipitation of primary gypsum from the Ca-chloride solution of Lake Lisan is limited by sulfate concentration, which could not exceed 3000 mg/l. The Upper Gypsum Unit, deposited before ca. 17–15 ka, is the thickest gypsum unit in the section and displays the highest δ34S values (25–28‰). Yet, our calculations indicate that no more than a third of this Unit could have precipitated directly from the water column. This implies that during the lake level decline that instigated the precipitation of the Upper Gypsum Unit, significant amounts of dissolved sulfate had to reach the lake from external sources. We propose a mechanism that operated during cycles of high-low stands of the lakes that occupied the Dead Sea basin during the late Pleistocene. During high-stand intervals (i.e., Marine Isotopic Stages 2 and 4), lake brine underwent BSR and infiltrated the lake’s margins and adjacent strata. As lake level dropped, these brines, carrying 34S-enriched sulfate, were flushed back to the shrinking lake and replenished the water column with sulfate, thereby promoting massive gypsum precipitation.
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The Apuseni–Banat–Timok–Srednogorie magmatic–metallogenic belt (ABTS belt), forms a substantial metallogenic province in the
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respectively, and clearly document increasing age from the northwestern districts to the southeastern districts. Further,
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in ~1 m.y., districts in ~10 m.y., and the entire 1,500 km belt in ~20 m.y. Ages in both Timok and Panagyurishte show systematic
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and mineral dehydration fluids, which facilitate partial melting and metal leaching of SCML and asthenosphere. Cu–Au–Mo–(PGE)
porphyry deposits may develop where melts are trapped at shallow crustal levels, often with associated volcanism and epithermal-style
deposits (South Banat, Timok, and Panagyurishte). Mo–Fe–Pb–Zn skarn deposits may develop where felsic melts are trapped adjacent
to Mesozoic limestones at moderate crustal levels (North Banat and Apuseni). Systematic spatial variations in deposit style,
commodity enrichment, Re–Os ages, and Re concentrations support specific tectonic processes that led to ore formation. In
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