scholarly journals Pulverized quartz clasts in gouge of the Alhama de Murcia fault (Spain): Evidence for coseismic clast pulverization in a matrix deformed by frictional sliding

Geology ◽  
2020 ◽  
Vol 48 (3) ◽  
pp. 283-287
Author(s):  
Emilio Rodríguez-Escudero ◽  
José J. Martínez-Díaz ◽  
Jorge L. Giner-Robles ◽  
Meaza Tsige ◽  
Jaime Cuevas-Rodríguez

Abstract The fault gouge of the Alhama de Murcia fault (southeast Spain) shows a texture that resembles a mylonite, including a prominent foliation, S-C fabric, and isoclinal folds. It also embeds a large number of isolated pulverized quartz clasts (PQCs). Structural analysis indicates that the gouge fabric was mainly developed by slow frictional sliding along phyllosilicate-lined Riedel shear bands during continued shearing. In contrast, the PQCs show tensile fracture network features that are typically reported in seismically pulverized rocks found along seismogenic faults. This suggests that quartz-clast pulverization was due to a transient dilatational mechanism rather than shearing. We propose that the PQCs are the result of a rapid confined stress drop related to transient tensile stresses during coseismic ruptures that interrupt creep faulting along the gouge zone. The present study suggests that there is probably a large amount of evidence for paleoseismicity in fault rocks that is currently overlooked.

1993 ◽  
Vol 30 (7) ◽  
pp. 1363-1373 ◽  
Author(s):  
Donna Kirkwood ◽  
Michel Malo

The principal faults of southeastern Gaspé Peninsula in Quebec consist of a central high-strain zone that is characterized by mainly ductile deformation structures and bordered by low-strain zones each dominated by brittle deformation structures. The overall geometry of shear fractures within the low-strain zones is quite similar to the expected geometry of Riedel shear fractures. The brittle structures overprint the dominant C–S-type fabric of the high-strain zone, which implies that brittle deformation outlasted ductile deformation. The asymmetry of local micro- to meso-scale deformation features along the fault zones reflects the non-coaxiality of the shear. Other features described within the fault zone (stylolitic cleavage, shear bands, and reverse faults) are evidence for a component of shortening perpendicular or oblique to the fault zone. The geometry of the Grand Pabos fault zone (GPFZ), a major fault of southern Gaspé, indicates that deeper seated fault rocks (high-strain zone) have been brought up to higher crustal levels and are presently in contact with brittlely deformed fault rocks (low-strain zone). The proposed model for the evolution of the GPFZ involves Early to Late Devonian, dextral, transcurrent movement accompanied by relatively minor amounts of vertical slip within a dextral transpressive regime. The main pulse of the Acadian orogeny in Gaspé is restricted to the Devonian and therefore occurred later than elsewhere in the Canadian Appalachians.


2021 ◽  
Vol 249 ◽  
pp. 11006
Author(s):  
Nathalie Casas ◽  
Guilhem Mollon ◽  
Ali Daouadji

Earthquakes happen with frictional sliding, by releasing all the stresses accumulated in the prestressed surrounding medium. The geological fault gouge, coming from the wear of previous slips, acts on friction stability and plays a key role in this sudden energy release. A large part of slip mechanisms are influenced, if not controlled, by the characteristics and environment of this tribological “third body”. A 2D granular fault (mm scale) is implemented with Discrete Element Modelling (DEM). A displacement-driven model with dry contact is studied to observe kinematics and properties of the slipping zone. Increasing the length of the granular media increases the slip needed to weaken the friction from friction peak to steadystate. Low-angle Riedel shear bands are mostly observed. Their number increases with the inter-particle friction coefficient, which also influences shear bands formation in their orientation angle (higher friction leads to higher angle with the main slip direction).


2017 ◽  
Vol 24 (1-2) ◽  
Author(s):  
Michal Uhlíř ◽  
Rostislav Melichar

Quarzite as a metasedimentary rock is usually figured in prolongated bands in geological maps. But muscovite quartzite from Krkonoše-Jizera Crystalline Unit in SE surrounding of Příchovice village forms irregular shapes in detailed geological maps (e.g., Mrázová – Štěpánek 2007, see Fig. 1), which do not allow simple interpretation of the geometry of quartzite bodies. To find correct 3D geometry of the bodies, we used standard methods of detailed mapping and documentation of outcrops as well as detailed structural analysis. Locations of terrain edges with quartzite outcrops have been indicated in the map (Fig. 3 –A, B, C). Generaly sub-horizontal to moderately dipping metamorphic foliation has been found. Foliation poles make wide girdle in the plot (Fig. 2) which indicates sub-cylindrical fold structure with horizontal axis in the NW–SE direction.Studied area can be geomorphologically divided into two different parts. The northeastern part of the territory is sub-horizontal plateau, while the southwestern part is generally inclined to the southwest. In the second part, the metamorphic foliation dips to the southwest under such angle, that it seems to be parallel to the inclination of the slope, see the old quarry (Fig. 3B) and SW part of Velká bílá skála (Fig. 3A). The last one show us bent outcrop respecting the change in slope inclination. Large shear bands were directly observed as a part of S-C structure. It indicates that SW limb of the fold was strained under simple shear condition with the drop SW kinematics (Fig. 4). Change in orientation of SW-dipping fold limb was produced by a ductile shear zone.Based on a combination of metamorphic foliation orientation of quartzite and field edges, we can interpret quartzite rocks as a part of one platy body, which forms the overall morphology of the landscape south of Příchovice. In the plateau, erosion stopped at subhorizontally oriented part of the quartzite layer, while denudation of the SW limb of the large fold predeterminates the inclined slope surface to the SW (Fig. 3D). Relics of thin overlying rocks remaining on quartzite in some places and erosion of the small creeks produce bizarre forms in geological map, which seems to be difficult to understand. This study has shown that such complex structure can be decrypted using the detailed structural analysis. In this case it was shown that quartzite forms a relatively simple body which was only slightly bent due to simple shear deformation. 


Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 119 ◽  
Author(s):  
Zhonghang Fang ◽  
Changgen Shi ◽  
Hesheng Shi ◽  
Zerui Sun

The current work focuses on the effect of explosive ratio R on the comprehensive properties of Ti/Al clads manufactured via explosive welding. The lower and upper limits of explosive ratio, namely R1 and R2, were determined according to the R–δf (flyer plate thickness) welding window. Two TA2/1060 explosive cladding plates were successfully manufactured at the different explosive ratios. Microstructure investigation was conducted by optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The small wave bonding interface was observed at R1, where the vortex structure containing the ingot structure appeared periodically. The bonding interface presented a big wave bonding morphology and a locally continuous melting layer at R2. Many prolonged grains and adiabatic shear bands (ASBs) were found near the interface for a greater explosive load. Intermetallic compounds were formed in the bonding zones of the two plates. The thickness of element diffusion area increased with an increasing explosive ratio. Comparative tests of mechanical properties indicated that the tensile shear strength at R1 was higher. The microhardness, tensile strength, and bending performance of the two plates are similar and acceptable. Tensile fracture analysis indicated the fracture mode at R1 was ductile fracture, while the explosive cladding plate at R2 had mainly ductile fracture with quasi-cleavage fracture as the supplement.


Clay Minerals ◽  
2019 ◽  
Vol 54 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Isabel Abad ◽  
Juan Jiménez-Millán ◽  
Catalina Sánchez-Roa ◽  
Fernando Nieto ◽  
Nicolás Velilla

AbstractTwo preferred textures were observed in the Alhama de Murcia Fault rocks: (a) foliated bands (>100 µm thick) rich in well-crystallized dioctahedral micas, quartz, hematite and dolomite; and (b) ultrafine-grained bands (<100 µm thick) made of patches composed of small mica crystals (<15 µm) and dispersed Fe-oxides. In both textures, kaolinite forms intergrowths or patches of randomly oriented crystals filling gaps or opening layers of presumably inherited detrital mica crystals, which is interpreted as an epitaxial growth from fluids. The Na/K ratio of mica crystals in the thin ultrafine-grained bands shows a wider range than the micas from the foliated bands including muscovitic, intermediate Na/K and paragonitic compositions. The absence of the 0.98 nm intermediate peak in the diffractograms indicates that the small micas are submicroscopically paragonite and phengite intergrowths. The d001 values of the K-dioctahedral micas in the <2 µm and whole fractions are clearly different from each other. The d001 values of micas of the <2 µm fraction are larger, indicating a higher K and lower Na content in the small micas. Their composition corresponds to lower temperatures, suggesting their growth during a genetic episode in the fault. The textural relationships indicate a late growth of kaolinite, probably due to the fluid–rock interaction along fault planes and fractures. The neoformed clay minerals might alter the stability of the fault plane. The absence of expandable clay minerals and the relatively high frictional strength of kaolinite under wet conditions might explain the observed velocity-neutral behaviour of this gouge and earthquake propagation towards the surface.


Sign in / Sign up

Export Citation Format

Share Document