The age of the Kagenfels granite (northern Vosges) and its bearing on the intrusion scheme of late Variscan granitoids

In the Saxothuringian part of the Vosges (France), a first series of Variscan plutonic rocks (diorites to granites) has been intruded by several younger granites. Rocks of both the older generations have been cross-cut by the late orogenic Kagenfels granite. The averages of the hitherto published mineral ages of the earlier rock generations are 331 and 334 Ma, respectively, whereas Rb-Sr and K-Ar dates around 290 Ma have been reported for the Kagenfels granite. Because of the unlikely large age hiatus, a redetermination of the intrusion age of the Kagenfels granite formation appeared to be irrevocable. The newly obtained mineral ages on the Kagenfels granite (K-Ar and ⁴⁰Ar/³⁹Ar biotite ages as well as single zircon radiogenic ²⁰⁷Pb/²⁰⁶Pb data: 331 ± 5 Ma) are about 40 Ma older than the previous results. They are interpreted as giving the time of emplacement of the Kagenfels granite during the latest Visan. The mineral ages of the earlier plutonic rocks in this part of the Variscan Orogeny in all probability are not significantly different from their ages of intrusion. Therefore the age concordance of all three granitoid generations constrains a rather narrow time interval of orogenic magmatism close to the Lower-Upper Carboniferous boundary.     

The Variscan tectonic inheritance of the Upper Rhine Graben: evidence of reactivations in the Lias,Late Eocene–Oligocene up to the recent

Processing of gravity and magnetic maps shows that the basement of the Upper Rhine Graben area is characterized by a series of NE–SW trending discontinuities and elongated structures, identified in outcrops in the Vosges, Black Forest, and the Odenwald Mountains. They form a 40 km wide, N30–40° striking, sinistral wrench-zone that, in the Visean, shifted the Variscan and pre-Variscan structures by at least 43 km to the NE. Wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340–325 Ma. The sub-vertical, NE–SW trending discontinuities in the basement acted as zones of weakness, susceptible to reactivation by subsequent tectonism. The first reactivation, marked by mineralizations and palaeomagnetic overprinting along NE–SW faults of the Vosges Mountains, results from the Liassic NW–SE extension contemporaneous with the break-up of Pangea. The major reactivation occurred during the Late Eocene N–S compression and the Early-Middle Oligocene E–W extension. The NE–SW striking basement discontinuities were successively reactivated as sinistral strike-slip faults, and as oblique normal faults. Elongated depocenters appear to form in association with reactivated Variscan wrench faults. Some of the recent earthquakes are located on NE–SW striking Variscan fault zones, and show sinistral strike-slip focal mechanisms with the same direction, suggesting also present reactivation.     

SOIL CREEP DYNAMICS,SOIL MOISTURE AND TEMPERATURE CONDITIONS ON A FORESTED SLOPE IN THE GRANITIC VOSGES MOUNTAINS,FRANCE

Soil creep, soil water tension and soil temperature were monitored at the Schildmatt experimental site over a 7 month period, in order to study the dynamics of creep movements measured with a specially designed strain gauge probe. The limited displacements and the very low signals which had to be measured were taken into account in estimating the uncertainty in measurements. The results obtained emphasize the very discontinuous and highly reversible character of the creep movements and their seasonal nature. Displacements occurred mainly during two events: their size were 10 mm and 2 mm, but the overall displacements for the whole intensive study period (January–July 1985) was only 3 mm. The relationships with soil moisture and temperature conditions indicated that ice segregation and saturated conditions are major influences, but more needs to be known about the way they act on soil creep.     

Three-dimensional numerical modelling of thermal transfer through the Vittel aquifer (Vosges, France), including approximated topographical effects

Summary. A geothermal and hydrochemical anomaly was observed in the Lower Triassic sandstone aquifer in the Vittel region (Vosges, France). This anomaly was attributed to a hydrothermal spring under sedimentary cover. In order to localize the hot spring and to quantify more precisely its flow rate and temperature, it is necessary to consider the 3-D thermal problem by taking into account the complex geometry of the domain and the flow rate in the aquifer. A 3-D numerical model of thermal conductive and forced convective transfer, developed for hydrological problems including approximate geometrical and topographical effects, is used which (i) can be directly applied to geologic strata (aquifers) with varying thickness and top and base slope; and (ii) allows calculation of heat flux anomalies associated with fluid flow in such geologically realistic aquifers.
The heat transfer equation is formulated in an orthogonal curvilinear coordinate system. As most geometries dealing with geothermal phenomena in sedimentary basins are nearly horizontal, this formulation can be simplified, leading readily to numerical solution with a finite difference method. The application of the 3-D model to the Vittel aquifer gives temperature results in agreement with measurements. These results provide evidence for the importance of associated forced convection and topographical effects for ground temperature distribution, and show clearly that heat flow in many basins is interpretable only if careful hydrological and thermal studies are made.     

Two-sided Variscan thrust tectonics in the Vosges Mountains,northeastern France

Abstract

Variscan convergence produced two-sided (bivergent) crustal-scale thrusting in the Vosges Mountains. In the northern Vosges the central polymetamorphic crystallines were thrust to the NW over Cambrian to Silurian low-grade and very low-grade metamorphic clastics. Synorogenic upper Devonian - lower Carboniferous turbidites and volcanics were folded into NW-vergent structures which display SE-dipping slaty cleavage. The entire sequence shows increasing metamorphism and deformation from NW to SE. Late right-lateral strike-slip faulting along the Lalaye-Lubine fault zone outlasted thrusting. In the southern Vosges a lower Carboniferous turbiditic basin that was fringed on the south by a volcanic arc was tectonically shortened by south-directed tectonic imbrication of slivers of varied rocks including ultramafics, gneissic basement, and synorogenic elastics. The increasing degree of deformation and metamorphism towards the north suggests a thrust contact with the polymetamorphic gneisses of the central Vosges. The final stages of Variscan convergence were accompanied by voluminous granitic plutonism and by faulting along NNE-SSW and E-W-trending strike-slip faults. The tectonic evolution reflects progressive Variscan closure of a previously extended basinal crust in a high-temperature regime.     

Hot contacts of garnet peridotites in middle/upper crustal levels: new constraints on the nature of the late Variscan high-T/low-P event in the Moldanubian (Central Vosges/NE France)

P–T  paths based on parageneses in the immediate vicinity of former high-temperature contact zones between mantle peridotites and granulitic country rocks of the Central Vosges (NE France) were derived by applying several conventional thermometers and thermobarometric calculations with an internally consistent dataset. The results indicate that former garnet peridotites and garnet–spinel peridotites were welded together with crustal rocks at depths corresponding to 1–1.2 GPa. The temperature of the crustal rocks was about 650–700 °C at this stage, whereas values of 1100 °C (garnet peridotites) and 800–900 °C (garnet–spinel peridotites) were calculated for the ultramafic rocks. After emplacement of the mantle rocks, exhumation of the lower crust took place to a depth corresponding to 0.2–0.3 GPa. The temperatures of the incorporated peridotite slices were still high (900–1000 °C) at this stage. This is indicated by the presence of high- T  /low- P parageneses ( c . 800 °C, 0.2–0.3 GPa) in a small (1–10 m) contact aureole around a former garnet peridotite. Crustal rocks distant to the peridotites equilibrated in the same pressure range at lower temperature (650–700 °C). High cooling rates (10²–10³ °C Ma⁻¹) were calculated for a garnet–biotite rock inclusion in the peridotites and for the crustal rocks at the contact by applying garnet–biotite diffusion modelling. Minimum rates of 0.75–7.5 cm a⁻¹ are required for vertical ascent of rock units (30 km vertical distance) derived from the crust–mantle boundary, resulting in a late Variscan (340 Ma) high- T  /low- P event.     

Historical mining and smelting in the Vosges Mountains (France) recorded in two ombrotrophic peat bogs

Two peat sequences were sampled in the vicinity of the main mining districts of the Vosges Mountains: Sainte-Marie-aux-Mines and Plancher-les-Mines. Lead isotopic compositions and excess lead fluxes were calculated for each of these radiocarbon-dated sequences. Geochemical records are in very good agreement with the mining history of the area, well known over the last millennium. Except for an anomaly corresponding to the Middle Bronze Age which has not yet been resolved, there is no clear geochemical evidence of local metal production in the Vosges before the 10th century as excess lead deposition archived between 500 BC and 500 AD is attributed to long-range transport of polluted particulate matter. The approach described here can be applied to other mining districts where archaeological evidence is scarce or even lacking, but where past exploitation is suspected.     

Transfrontier macroseismic observations of the Ml = 5.4 earthquake of February 22, 2003 at Rambervillers,France

The 2003 Ml = 5.4 Rambervillers earthquake, north-east of France, is the largest seismic event recorded north of the Alps since the 1992 Ms = 5.3, I₀ = VII, Roermond earthquake, Netherlands. With a maximum macroseismic intensity of VI-VII EMS-98, the 2003 event was broadly felt to a distance of 300 km from the epicentre. It provides a unique opportunity to test and compare the different procedures used in France, Germany and Switzerland when evaluating macroseismic intensities. The main purpose of this paper is to present a common transfrontier macroseismic map based on the EMS-98 intensity scale. Maximum horizontal accelerations recorded in the area are compared to the intensity values, and we propose to use a differential technique to re-estimate the magnitude of the 1682 Remiremont, I₀ = VIII, earthquake, which occurred 40 km south of Rambervillers.     

Tertiary tectonics of the Dannemarie Basin, upper Rhine graben, and regional implications

Recently released seismic reflection data, together with previous seismic and well data, are used to describe the development of the Dannemarie basin, in the SW end of the Upper Rhine Graben. The Dannemarie Basin was formed during the main rifting phase of the Upper Rhine Graben as an asymmetrical graben trending NE–SW. Post-rift tectonism shifted the depocenter southward and changed the overall shape of the basin. Miocene Jura compression did not result in the formation of folds, as in the adjacent Mulhouse Horst. Strike slip faulting was dominant in the post-rift period and new faults were created, most notably the north trending and transpressional Belfort Fault. The boundary of the Dannemarie Basin with the Vosges Mountains is part of a restraining bend, which may account for the uplift of the southernmost part of the Vosges Mountains.