Search results for "Cataclastic rock"
showing 9 items of 9 documents
Fluid storage and migration properties of sheared Neptunian dykes
2019
Abstract Neptunian dykes are widely reported along the Tethyan carbonate platforms and are commonly considered as subsurface baffles or barriers to fluid flow. However, the fluid storage and migration properties of sheared Neptunian dykes are poorly known. For this reason, we investigate the inner structure and fluid flow properties of two Neptunian dykes, which can be characterized by different architectures if involved or not in brittle shearing processes. The dykes strike ca. WNW-ESE and crosscutting the tight Jurassic limestones exposed at Maranfusa Mt., NW Sicily, Italy. The unsheared and sheared Neptunian dykes are almost sub-vertical and at high-angle with respect to the horizontal p…
Cataclastic solution creep of very soluble brittle salt as a rock analogue
1998
Until about the late 1960s, macroscopically ductile deformation of quartz was seen as a microscopically cataclastic process by most geologists (cf. the origin of the name ‘mylonite’). Undulatory extinction, subgrains, recrystallised grains and even crystallographic preferred orientations were interpreted as due to water-assisted brittle deformation processes. Nowadays, by contrast, the occurrence of these optical microstructures is considered as conclusive and unequivocal evidence for dislocation creep. The abundance of these microstructures in naturally deformed rocks lead to the conclusion that dislocation creep is the most important ductile deformation mechanism within the Earth’s crust.…
Evolution of mica fish in mylonitic rocks
2003
Abstract Mineral fish are lozenge-shaped porphyroclasts, single crystals in a finer grained matrix, which occur in ductile shear zones and which are commonly used as shear sense indicators. Mineral fish of biotite, tourmaline, K-feldspar, garnet, hypersthene and quartz occur in mylonites but most common are white mica fish. These mica fish can be subdivided into six morphological groups that develop by different mechanisms determined by different initial shapes and orientations. The principal mechanisms of formation are intracrystalline deformation combined with rigid body rotation. Concomitant selective grain size reduction occurs by recrystallisation, cataclastic separation, pressure solu…
Micro- to macro-scale internal structures, diagenesis and petrophysical evolution of injectite networks in the Vocontian Basin (France): implications…
2015
27 pages; International audience; This study discusses the characteristics of two Lower Cretaceous injectite networks in the Vocontian Basin (SE France) using combined structural, sedimentary, diagenetic, and petrophysical analyses. Internal structures, at both the macro- and micro-scale, and diagenetic phases characterising these injectite networks have been described. Simultaneously, precementation porosity values were estimated and parameters controlling the geographical distributions of these values were analysed and statistically tested. All of the data were integrated so as to reconstruct the spatial evolution of the porosity from the time of injection to modern times through five maj…
Stress induced grain boundary migration in very soluble brittle salt
1999
Abstract Grain boundary migration (GBM) was studied in-situ at room temperature, atmospheric pressure and an applied diffmfwerential stress of ∼9.5 MPa under the optical microscope, in a wet aggregate of an elastic-brittle salt (sodium chlorate). The aggregate was previously deformed predominantly by a combination of grain boundary sliding, pressure solution and cataclastic solution creep. After deformation, but when the sample was still under differential stress, undeformed, fracture-free grains were observed to grow at the cost of deformed, intensely fractured grains. GMB rates typically fell in the range 2--10 μm/day. GBM took place only as long as the sample was under stress. Boundaries…
Low-Grade Mylonites
2009
The temperature range for these mylonites is thought to be roughly between 250 and 500 °C. There is a gradual transition between cataclasites and low-grade mylonites. Whereas many feldspar porphyroclasts in low-grade mylonites still show fracturing by cataclasis, the quartz is usually deformed by crystal-plastic processes as shown by its change in shape and by undulose extinction. At increasing temperature bulging recrystallisation starts to manifest itself along the lobate contacts and eventually recrystallisation by subgrain rotation takes over (Chapter 10).
Hydraulic properties of fault zones in porous carbonates, examples from central and southern Italy
2016
We present the results of in situ permeability measurements performed, using a portable field permeameter, on normal and strike-slip fault zones that crosscut high-porosity carbonate grainstones. The measurement sites expose in the Cretaceous Orfento Formation of the Majella Mountain (Abruzzo, Italy), and the Lower Pleistocene deposits of the Favignana Island (Sicily, Italy). Nine small-displacement, compactive shear banding-based fault zones have been tested in the field. The fault offset ranges between 10 and 200 centimeters. The acquired permeability data indicate a two orders of magnitude decrease of porosity and permeability from the host rock to the cataclastic fault cores. A clear de…
Miocene NNE-directed extensional unroofing in the Menderes Massif, southwestern Turkey
1995
Structural investigations in the central part of the Menderes Massif (Odemis-Kiraz submassif) reveal the presence of a large-scale, low-angle extensional shear zone with a top-to-the-N-NE shear sense. Regional ductile deformation was accompanied by the intrusion of two syntectonic granodiorites that have been dated with the Ar-40/Ar-39 method. One hornblende isochron age of 19.5 +/- 1.4 Ma and two biotite plateau ages of 13.1 +/- 0.2 and 12.2 +/- 0.4 Ma, respectively, constrain that extension was already active in the early Miocene. Successive tectonic denudation of the Odemis-Kiraz submassif resulted in the formation of a N-dipping detachment fault, in which ductile fabrics were severely r…
Tectonic and lithological constraints on the evolution of the Karoo graben of northern Malawi (East Africa)
1995
The results of a lithostratigraphic, tectonic and kinematic study of the Karoo deposits of northern Malawi are reported. The objective of the lithostratigraphic study is to correlate the deposits of the Karoo basins of northern Malawi with the well-known deposits of southern Tanzania, thus establishing a stratigraphic framework through which the timing of faulting can be constrained. The kinematic analysis of faulting constrains the opening direction for the Karoo graben in this area and provides basic data to discuss the Karoo graben development within the regional tectonic framework of south-eastern Africa. The studied adults are defined by moderately to steeply dipping cataclastic zones …