A teleseismic and petrological study of the crust and upper mantle beneath the geothermal anomaly Urach/SW-Germany

Glahn, A.; Sachs, Peter M.; Achauer, U.

doi:10.1016/0031-9201(92)90133-g

Cited by 30 publications

(12 citation statements)

References 32 publications

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“…For the LJrach arca, a 3-D inversion of the P-phase residuals reveals a low-velocity anomaly of 4 per cent from the Moho to a depth of SO km explained by metasomatism accompanied by increased temperatures (Glahn, Sachs & Achauer 1992). In the Rhine Graben area, the presence of slow materials beneath the graben proper characterizes the 28-53 depth range of the tomographic model.…”

Section: Discussion a N D I N T E R P R E T A T I O N : A M mentioning

confidence: 97%

Massif Central (France): new constraints on the geodynamical evolution from teleseismic tomography

Granet

Stoll²,

Dorel

et al. 1995

Geophysical Journal International

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The Massif Central, the most significant geomorphological unit of the Hercynian belt in France, is characterized by graben structures which are part of the European Cenozoic Rift System (ECRIS) and also by distinct volcanic episodes, the most recent dated at 20 Ma to 4000 years BP. In order to study the lithosphere‐asthenosphere system beneath this volcanic area, we performed a teleseismic field experiment. During a six‐month period, a joint French‐German team operated a network of 79 mobile short‐period seismic stations in addition to the 14 permanent stations. Inversion of P‐wave traveltime residuals of teleseismic events recorded by this dense array yielded a detailed image of the 3‐D velocity structure beneath the Massif Central down to 180 km depth. The upper 60 km of the lithosphere displays strong lateral heterogeneities and shows a remarkable correlation between the volcanic provinces and the negative velocity perturbations. The 3‐D model reveals two channels of low velocities, interpreted as the remaining thermal signature of magma ascent following large lithospheric fractures inherited from Hercynian time and reactivated during Oligocene times. The teleseismic inversion model yields no indication of a low‐velocity zone in the mantle associated with the graben structures proper. The observation of smaller velocity perturbations and a change in the shape of the velocity pattern in the 60–100 km depth range indicates a smooth transition from the lithosphere to the asthenosphere, thus giving an idea of the lithosphere thickness. A broad volume of low velocities having a diameter of about 200 km from 100 km depth to the bottom of the model is present beneath the Massif Central. This body is likely to be the source responsible for the volcanism. It could be interpreted as the top of a plume‐type structure which is now in its cooling phase.

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Section: Discussion a N D I N T E R P R E T A T I O N : A M mentioning

confidence: 97%

Massif Central (France): new constraints on the geodynamical evolution from teleseismic tomography

Granet

Stoll²,

Dorel

et al. 1995

Geophysical Journal International

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“…Volcanism in southern Germany is confined to a few small regions including the Urach and Hegau provinces to the east of the Rhine Graben, the rift flanks of the Rhine Graben and the Kaiserstuhl volcano which is axially located within the graben where it bisects the Vosges-Black Forest dome Glahn et al, 1992; Fig. 2).…”

Section: Southern Germanymentioning

confidence: 99%

Tertiary-Quaternary intra-plate magmatism in Europe and its relationship to mantle dynamics

Wilson

Downes

2006

Memoirs

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Anorogenic intra-plate magmatism was widespread in Europe from early Tertiary to Recent times, extending west to east from Spain to Bulgaria, and south to north from Sicily to northern Germany. Magmatism is spatially and temporally associated with Alpine-Pyrenean collisional tectonics, the development of an extensive lithospheric rift system in the northern foreland of the Alps, and, locally, with uplift of Variscan basement massifs (Massif Central, Rhenish Massif, Bohemian Massif). The volcanic regions vary in volume from large central volcanoes (e.g. Cantal, Massif Central;Vogelsberg, northern Germany), to small isolated plugs (e.g. Urach and Hegau provinces in southern Germany). Within the Mediterranean region, the Dinarides, the Pannonian Basin and Bulgaria, anorogenic volcanism locally postdates an earlier phase of subduction-related magmatism.The major and trace element and Sr-Nd-Pb isotope characteristics of the most primitive mafic magmatic rocks (MgO > 6 wt %) provide important constraints on the nature of the mantle source and the conditions of partial melting.. These are predominantly sodic (melilitites, nephelinites, basanites and alkali olivine basalts); however, locally, potassic magma types (olivine leucitites, leucite nephelinites) also occur. In several localities (e.g., Sicily; Vogelsberg and the Rhine Graben, Germany; Calatrava, central Spain) olivine-and quartz-tholeiites form a significant component of the magmatism. The sodic magmas were derived by variable degrees of partial melting (~ 0.5 -5 %) within a transitional zone between garnet-peridotite and spinel-peridotite mantle facies, close to the base of the lithosphere; the potassic magma types are interpreted as partial melts of enriched domains within the lithospheric mantle. Mantle partial melting was induced by adiabatic decompression of the asthenosphere, locally in small-scale, plume-like, diapirs which appear to upwell from ~ 400 km depth. 2Tertiary and Quaternary volcanic activity within Europe occurs in two principal geotectonic settings: referred to as orogenic and anorogenic by Wilson & Bianchini (1999). Occurrences of calc-alkaline volcanism (orogenic) in the Alpine chain, the Carpathians and the Mediterranean region (Harangi et al., this volume) can be explained geodynamically in terms of contemporaneous subduction, and will not be considered further in this review. Here emphasis is placed on the extensive anorogenic, dominantly alkaline, volcanic province to the north of the Alpine collision zone, including the Massif Central of France, the Rhenish Massif of northern Germany, the Rhine Graben, and the Eger Graben within the northern part of the Bohemian Massif in the Czech Republic (Figs. 1 & 2). Further to the east mafic alkaline volcanism (anorogenic) post-dates a major phase of subduction-related volcanism in the Pannonian Basin, the Dinarides (Serbia, Slovenia, Croatia, N. Bosnia), Bulgaria and western Turkey. Further south,within the Mediterranean region, anorogenic volcanism occurs in Sicily, Sardinia, Monte V...

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“…The sparse data indicate a dominance of olivine-rich (60% to 90% olivine) peridotites (GLAHN et al, 1992). This increase is represented by a compositional variation from primitive to depleted peridotites.…”

Section: Discussionmentioning

confidence: 97%

Seismic, Structural and Petrological Models of the Subcrustal Lithosphere in Southern Germany: A Quantitative Revaluation

Weiss

Siegesmund

Bohlen

1999

Pure appl. geophys.

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Anisotropy in the subcontinental lithosphere becomes increasingly important, because it is observed in many seismic studies especially for P n -waves. Typical rocks of the uppermost mantle are peridotites, which predominantly exhibit a pronounced elastic anisotropy. This anisotropy is mainly caused by the anisotropic elastic properties and the lattice preferred orientation (here referred to as texture) of olivine. To evaluate the elastic anisotropy of peridotites from the subcontinental lithosphere, specimens of the Northern Hessian Depression (Germany) and the Balmuccia Ultramafic Massif (Northern Italy) have been used. They comprise four olivine texture types, which are characteristic for olivine textures observed worldwide. The bulk rock elastic properties have been calculated using olivine and orthopyroxene textures, their single-crystal elastic constants at ambient pressure/temperature conditions and their volume fraction. Clinopyroxene and spinel are assumed to be randomly distributed. The effect of four different orientations of the foliation within the uppermost mantle has been evaluated, since this orientation is usually unknown.Two of the olivine textures have a pronounced azimuthal dependence of compressional waves when a horizontal foliation within the uppermost mantle is presumed. These variations cause significant azimuthal variations of the P-wave reflections coefficients at the Moho. Primarily, we predict a significant azimuthal dependence of the critical points where the reflected amplitude increases from approximately 15% to 95%. Possibly, these azimuthal variations can be detected by seismic reflection measurements carried out at earth surface.The remaining two texture types only manifest a small directional dependence. When anisotropy of compressional waves is observed in seismic studies, these latter types can only be of subordinate importance. However, all of the peridotites investigated are able to explain the seismically observed azimuthal variations of compressional waves when a vertical foliation is proposed. This ambiguity can be substantially reduced when shear waves (S-waves) are considered. The directional distribution of S-wave velocities and of the S-wave splitting exhibits characteristic patterns for the different olivine texture types. This could be used to discriminate between different texture types and orientations of the foliation within the uppermost mantle. A fundamental requirement for a more comprehensive interpretation is the availability of detailed S-wave observations. The maximum S-wave splitting in the peridotites investigated coincides with the maximum of the faster (leading) S-wave. This may be of importance to detect S-wave splitting in future seismic studies.

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A teleseismic and petrological study of the crust and upper mantle beneath the geothermal anomaly Urach/SW-Germany

Cited by 30 publications

References 32 publications

Massif Central (France): new constraints on the geodynamical evolution from teleseismic tomography

Massif Central (France): new constraints on the geodynamical evolution from teleseismic tomography

Tertiary-Quaternary intra-plate magmatism in Europe and its relationship to mantle dynamics

Seismic, Structural and Petrological Models of the Subcrustal Lithosphere in Southern Germany: A Quantitative Revaluation

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