Stress-state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types (High-Ardenne slate belt, Germany)

Abstract

In the frontal part of the Rhenohercynian fold-and-thrust belt (High-Ardenne slate belt, Germany), two successive types of quartz veins, oriented normal and parallel to bedding respectively, are interpreted to reflect the early Variscan compressional tectonic inversion of the Ardenne-Eifel sedimentary basin. Fracturing and sealing occurred in Lower Devonian siliciclastic multilayers under very low-grade metamorphic conditions in a brittle upper crust. A geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure-temperature conditions of both vein types, allowing the reconstruction of the stress-state evolution in a basin during tectonic inversion. It is demonstrated that bedding-normal extension veins, which developed under low differential stresses and repeatedly opened and sealed (crack-seal) under near-lithostatic fluid pressures, reflect the latest stage of an extensional stress regime. Bedding-parallel veins, which developed at differential stresses that were still low enough to allow the formation of extension veins, cross-cut the bedding-normal veins and preceded the regional fold and cleavage development. These veins show a pronounced bedding-parallel fabric, reflecting bedding-normal uplift and bedding-parallel shearing under lithostatic to supra-lithostatic fluid pressures during the early stages of a compressional stress regime. This kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny.

Fluid overpressures and strength of the sedimentary upper crust

“…It is widely argued that pore-fluid pressures are close to lithostatic, based on the existence of some types of crack-seal and open-void veins (e.g. Etheridge, 1983;Etheridge et al, 1984;Fisher and Brantley, 1992;Hilgers et al, 2006;Van Noten et al, 2011), and based on studies of fault-related mesothermal gold-quartz vein systems, which are suggestive of fault-valve phenomena near the base of the seismogenic zone (e.g. Sibson et al, 1988).…”

“…Studies by Van Noten et al (2011) of the stress-state and fluidpressure evolution in the High-Ardenne slate belt of Germany, based on analysis of quartz veins and fluid inclusions, indicate near lithostatic pore-fluid pressures under very low grade metamorphic conditions of~250 C, and an assumed depth of~7 km based on stratigraphy. They estimated a limiting compressive crustal strength s 1 À s 3 during vein formation of~35e45 MPa, which is consistent with a nominal fluid-retention depth of 1e3 km, near the top of the Lower Devonian siliciclastic section.…”

From Early Contraction to Post-Folding Fluid Evolution in the Frontal Part of the Bóixols Thrust Sheet (Southern Pyrenees) as Revealed by the Texture and Geochemistry of Calcite Cements

“…Fluids play an important role on the Earth's crust as, on one hand, they transport solutes and distribute heat, controlling mineral reactions including precipitation and dissolution [1][2][3][4][5][6][7][8], and on the other hand, they can change the effective stress, favoring the reactivation of existing fractures and the formation of new ones [9][10][11][12].…”

Bedding-parallel calcite veins in the Holy Cross Mountains Fold Belt, central Poland

“…The main detach ment ho ri zons de vel oped along thin shale or marl lay ers favouring flex ural slip and for ma tion of bed ding-par al lel veins (cf. Tan ner, 1989;Noten and Sintubin, 2011). Rare con ti nu ity of veins across fold hinges sug gests that the for ma tion of the veins started in the ini tial stage of subhorizontal short en ing (stage I/II, Fig.…”