A large database of structural, geochronological and petrological data combined with a Bouguer anomaly map is used to develop a two‐stage exhumation model of deep‐seated rocks in the eastern sector ...of the Variscan belt. An early sub‐vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks. These events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18−20 kbar to depths equivalent to 8−10 kbar, and for coeval burial of upper crustal rocks to depths equivalent to 8–9 kbar. Following the folding and vertical extrusion event, sub‐horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening. Fabrics that record the early vertical extrusion originated between 350 and 340 Ma, during building of an orogenic root in response to SE‐directed Saxothuringian continental subduction. Fabrics that record the later sub‐horizontal exhumation event relate to an eastern promontory of the Brunia continent indenting into the rheologically weaker rocks of the orogenic root. Indentation initiated thrusting or flow of the orogenic crust over the Brunia continent in a north‐directed sub‐horizontal channel. This sub‐horizontal flow operated between 330 and 325 Ma, and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re‐equilibration. The erosion depth as well as the degree of reworking decreases from south to north, pointing to an outflow of lower crustal material to the surface, which was subsequently eroded and deposited in a foreland basin. Indentation by the Brunia continental promontory was highly noncoaxial with respect to the SE‐oriented Saxothuringian continental subduction in the Early Visean, suggesting a major switch of plate configuration during the Middle to Late Visean.
Reflection seismic section, field structural analysis and gravimetric modelling of orogenic lower crust in the core of a Carboniferous orogenic root reveal details of the polyphase process of ...exhumation. Subvertical amphibolite facies fabrics strike parallel to former plate margins that collided in the NW. The fabrics are developed in both mid‐crustal and lower crustal high‐pressure granulite units as a result of intensive NW–SE intraroot horizontal shortening driven probably by the west‐directed collision. In granulites, the steep fabrics originated as a result of extrusion of orogenic lower crust in a ∼20 km wide vertical ascent channel from lower crustal depths at 350–340 Ma. The large granulite bodies preserve older granulite facies fabrics documenting a two‐stage evolution during the exhumation process. Surface exposures of granulites coincide with the absence of subhorizontal seismic reflectors at depth, suggesting preservation of the ∼20 km wide subvertical tabular structure reaching Moho depths. Horizontal seismic reflectors surrounding the vertical channel structure corroborate a dominant flat migmatitic fabric developed in all tectonic units. This structural pattern is interpreted in terms of subhorizontal spreading of partially molten orogenic lower crust in mid‐crustal levels (765 °C and 0.76 GPa) at 342–337 Ma. Large massifs of extruded and progressively dismembered felsic granulites disturbed mid‐crustal fabrics in the surrounding horizontally flowing partially molten crust. The horizontal mid‐crustal flow resulted in collapse of the supra‐crustal Teplá‐Barrandian Unit (interpreted as the orogenic lid) along a large‐scale crustal detachment above the extruded lower crustal dome. The presence of felsic granulites at the bottom of the orogenic root is considered to be a key factor controlling the exhumation of orogenic lower crust in large hot orogens.
Geochronology, structural and anisotropy of magnetic susceptibility data from the northern Vosges batholith, which belongs to the Northern Vosges-Mid-German Crystalline Rise arc, show contrasting ...emplacement modes of southern granodiorites and northern granites. The ENE-WSW-trending fabrics of granodiorites (346-334 Ma) are parallel to the metamorphic cleavage affecting the host rocks developed during regional compression. The NNW-SSE-trending fabrics of younger granitoids (c. 330 Ma) reveal an extensional emplacement mode, associated with a normal shear zone separating the two magmatic suites. Palaeomagnetism shows that the switch from a compressive to an extensional regime coincides with a regional counterclockwise rotation. The 330-325 Ma extension is further supported by palaeomagnetic and seismic data indicating southeastward tilt of the whole batholith. Finally the system is rotated clockwise without any structural overprint. Data from the Early Carboniferous northern Vosges magmatic arc and remote Bohemian Massif suggest that this evolution is valid for the whole eastern branch of the European Variscan belt, for which the following model is proposed: (1) Late Devonian-Early Carboniferous east-west shortening of the Variscides above the Rhenohercynian subduction zone; (2) axial NNW-SSE shortening of the assembled Variscan orogen associated with (3) "internal" sinistral rotation of inherited Rhenohercynian transform faults and shortening of intervening blocks; (4) east-west extension and dextral "external" rotation of blocks between dextrally reactivated transforms.
We demonstrate that single cells can be controllably compartmentalized within aqueous microdroplets; using such an approach we perform high-throughput screening by detecting the expression of a ...fluorescent protein in individual cells with simultaneous measurement of droplet size and cell occupancy.
In the latter stages of exhumation processes, rocks undergo weathering. Weathering halos have been described in the vicinity of structures such as faults, veins or dykes, with a lateral size ...gradually narrowing with depth, symmetrically around the structures.
In this paper, we describe the geophysical characterisation of such alteration patterns on two granitoid outcrops of the Catalan Coastal Ranges (Spain), each of which is affected by one major fault, as well as minor faults and fractures. Seismic, electric and ground penetrating radar surveys were carried out to map the spatial distribution of P-wave velocity, electrical resistivity and to identify reflectors of electromagnetic waves. The analysis of this multi-method and complementary dataset revealed that, at shallow depth, geophysical properties of the materials are compartmentalised and asymmetric with respect to major and subsidiary faults affecting the rock mass. This compartmentalisation and asymmetry both tend to attenuate with depth, whereas the effect of weathering is more symmetric with respect to the major structure of the outcrops. We interpret such compartmentalisation as resulting from the role of hydraulic and mechanical boundaries played by subsidiary faults, which tend to govern both the chemical and physical alterations involved in weathering. Thus, the smoothly narrowing halo model is not always accurate, as weathering halos can be strongly asymmetrical and present highly irregular contours delimiting sharp contrasts of geophysical properties.
These results should be considered when investigating and modelling fluid storage and transfer in top crystalline rock settings for groundwater applications, hydrocarbon or geothermal reservoirs, as well as mineral deposits.
•We used geophysical methods to characterising weathered formations in granite.•Weathered halos are not symmetric about fault zones.•The weathering is controlled by the presence of faults and fractures.•A new model is proposed to update the alteration halo model.
The present work examines the lithological, structural, geochemical and geochronological records from the Klippen Belt located in the southern Vosges Mountains (NE France). The Klippen Belt is ...represented by discontinuous exposures of serpentinized harzburgite, ophicalcite, gabbro, gneiss and polymictic conglomerate overlain by deep marine pelitic sediments. Structural data and Bouguer anomalies reveal that the Klippen Belt coincides with a significant discontinuity now occupied by a granitic ridge. Gabbro geochemistry indicates a MOR-type affinity similar to recent slow-spreading ridges, but positive Ba, Sr, Th or U anomalies do not exclude the influence of fluids expelled from a subduction zone. A Sm–Nd isochron age of 372 ± 18 Ma is thought to reflect gabbro emplacement from a highly depleted mantle source (ε
Nd
= +11.3), and U–Pb zircon ages from a gneiss sample indicate that the basement found in the Klippen has a Neoproterozoic origin. Combined data indicate the formation of a deep basin during Late Devonian rifting. The Klippen lithologies could testify for the presence of an ocean–continent transition environment subsequently inverted during the Early Carboniferous. Basin inversion during the Middle Visean was probably controlled by rift-related structures, and resulted in folding of the sedimentary successions as well as exhumation along thrust zones of deep parts of the basin represented by the Klippen Belt. Based on correlations with the neighbouring Variscan massifs, it is proposed that the southern Vosges sequences represent a back-arc basin related to the North-directed subduction of the southern Palaeotethys Ocean. This geodynamic reconstruction is tentatively correlated with similar ophiolitic remnants in the northern part of the French Massif Central (Brévenne) and with the evolution of the southern Black Forest. The Late Devonian ophiolites are interpreted as relicts of small back-arc marginal basins developed during general closure of the Palaeozoic subduction systems.
New and old magnetic and gravimetric data acquired in the frame of a geothermal project have been processed in N. Vosges and the adjacent Rhinegraben in order to identify the nature and tectonic ...framework of the graben basement and to select areas with a geothermal potential. In maps, the ENE–WSW striking units of N. Vosges can be followed beneath the sedimentary cover as far as the N35°-striking Upper Rhenish Shear Zone, which shifts these units towards NE. The magnetic basement S and SW of Strasbourg is interpreted as akin to the southern Champ du Feu Massif, consisting of I-type granitoids. Combined with new and old reflection seismic sections, the data show that the petrologic and tectonic contexts in the Illkirch-Grafenstaden area, where a geothermal project is planned, which is similar to the deep geothermal wells of Soultz and Rittershoffen 70 km to the north. The target zone is a N–S fault, partly normal and partly transpressive, which offsets the magnetic, I-type granitoids with high contents of uranium and thorium by about 800 m. Further exploitation of oil along the N–S footwall block attests to the geothermal potential of the area. The NW–SE transpressional regime favours the formation of cracks and increases the porosity and consequently fluid convection. The close borehole ESC-7 and modelling of the temperature distribution lead to expectations of a temperature of at least 150 °C on top of the granite and show that the temperature anomaly results from the heat-productive granitoids and from the blanket effect of the low thermal conductivity tertiary sediments.
Microdroplets: a sea of applications? Huebner, Ansgar; Sharma, Sanjiv; Srisa-Art, Monpichar ...
Lab on a chip,
2008, Letnik:
8, Številka:
8
Journal Article
Recenzirano
The exploitation of microdroplets produced within microfluidic environments has recently emerged as a new and exciting technological platform for applications within the chemical and biological ...sciences. Interest in microfluidic systems has been stimulated by a range of fundamental features that accompany system miniaturization. Such features include the ability to process and handle small volumes of fluid, improved analytical performance when compared to macroscale analogues, reduced instrumental footprints, low unit cost, facile integration of functional components and the exploitation of atypical fluid dynamics to control molecules in both time and space. Moreover, microfluidic systems that generate and utilize a stream of sub-nanolitre droplets dispersed within an immiscible continuous phase have the added advantage of allowing ultra-high throughput experimentation and being able to mimic conditions similar to that of a single cell (in terms of volume, pH, and salt concentration) thereby compartmentalizing biological and chemical reactions. This review provides an overview of methods for generating, controlling and manipulating droplets. Furthermore, we discuss key fields of use in which such systems may make a significant impact, with particular emphasis on novel applications in the biological and physical sciences.
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.PUBLICATION ABSTRACT
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