The bayan nuru ductile shear zone is located in the yabulaibayan nuru tectonic belt of the middle part of the southern central asian orogenic belt caob and east of the langshan tectonic belt. Among the synshearing folds, a second subdivision is based on the relative age of the folded. Abstract with respect to lithosphere rheology, we are especially interested in the mechanical behavior and evolution of ductile shear zones at depth, which present polyphase and heterogeneous character and multiscale strain localization patterns. Folds in ductile shear zones are common structures that have a variety of origins. Exterior columnbeam roof joint design for zone v 62 9. Shear zones and deformation mechanisms introduction.
Three premises of ductile deformation in the middle and lower crust are widely accepted. Mechanical properties of metals ii fracture and failure 1. Permeability and seismic velocity anisotropy across a. The methods for determining strains and displacements from field studies are described. Shear can be homogeneous or nonhomogeneous, and may be pure shear or simple shear. We defined as a shear zone any zone where the strain rate is at least three times the overall background strain rate. Brittletoductile shear zones from two separate geological settings are shown to have nucleated on zones of predominantly brittle deformation. Pdf microstructures of the lowt metavolcanites deriving from the transitional brittleductile lillafured shear zone lsz, eastern bukk mts.
Profound strain increase toward the central ultramylonitic part of zone shown by a change in orientation of the foliation and a marked decrease in grain size. The results indicate that the logarithmic law for steadystate friction with a negative velocity dependence breaks down when friction becomes nearly equal to the shear. Brittleductile transition o ccurs 1015 km depth t300 0 c separates upper frictional regime and the lower plastic regime. Creep timedependent deformation creep rate larsenmiller. The strength of ductile shear zones is typically studied in terms of viscous rheology e. Localization of deformation into such narrow zones reflects continuous but heterogeneous strain in rock. Shear is the response of a rock to deformation usually by compressive stress and forms particular textures. The ductile shear zone in granitoid of the central anatolian crystalline complex, turkey. At this depth rock becomes less likely to fracture, and more likely to deform ductilely by creep. Progressive development of structures in a ductile shear zone.
Fluidrock interaction at the brittleductile transition. Tertiary basin deposits are faultcd and tilted along lowdipping normalslip faults. A complete transition from frictional slip to ductile shearing flow upon decreasing velocity or slip rate or increasing confining pressure is documented for a thin layer of halite undergoing large shearing deformation. Structural investigations in the precambrian singhbhum shear zone of eastern india document an intimate relationship between micro to mesoscale structures and the deformation history. Feldspar aggregates get progressively more strained into the shear zone downward. Creep cavitation can establish a dynamic granular fluid. A synthesis of shear zone geometry in regions of crystal contraction and crustal extensions is made, and ideas on how deep level ductile shear zones relate to. The strongest element in the lithosphere is shown shaded in each case. The dunites in the shear zone are classified based on microstructures into coarse granular texture, mediumgrained texture, mylonite, and ultramylonites toward a gabbro contact. Ductile shear zones can develop as a results of shearing. The feedback between fluid migration and ductile deformation can be studied by investigating strain gradients and the associated changes in porosity in exhumed shear zones 11. The geometric features of ductile shear zones suggest that strain. Pdf structural analysis of the nanchangwanzai sinistral. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics the process of shearing occurs within brittle, brittleductile, and.
Ductile shear zones are usually active at higher metamorphic conditions than brittle shear zones fig. Fracture ductile fracture brittle fracture ductile to brittle transition t 2. While carrying out a regional structural analysis of deformation band shear zones in southern utah, davis 1994, 1996 discovered welldeveloped outcrop and mapscale riedel shear zones in outcrops of navajo sandstone jurassic. Introduction to materials science chapter 8, failure 10 stress concentration where. The challenge of ductile shear zones local approach.
Fault propagation faults, fault zones, shear zones terminology hanging wall foot wall fault zone in granitic gneiss fault scarp after an earthquake nevada. Ductile shear zones show a fabric schistosity and lineation related to the finite strain state. The methods for determining strains and displacements from field. Shear zones can be subdivided into brittle zones or faults, and ductile zones. The fizh massif, oman ophiolite, contains a ductile shear zone at the moho transition zone.
Pdf anatomy of a transitional brittleductile shear zone developed. Ductile shear zones can develop as a results of shearing simple shear strain or squeezing pure shear strain. For best results viewing and printing pdf documents, it is recommended that you download the documents to your computer and open them with adobe reader. Pdf the ductile shear zone in granitoid of the central. Brittle ductile shear zone is the extension failure type fig. Implications for the origins of the tuzgolu basin during the late cretaceous extensional deformation. A workshop on the scec community rheology modeling crm initiative entitled loading of southern california faults. Structural study of a paleoproterozoic ductile shear zone. Wayne thatcher, whitney behr, elizabeth hearn, greg hirth and michael oskin summary. A tightened bolt applies shear stress on the threads. This implies that ductile shear zones show a continuous displacement gradient across the zone fig. Ductile shear zones wiley online books wiley online library. The permeability of ductile shear zones is assumed to be significantly higher than that of surrounding undeformed rocks, although lower than that of fracture systems.
Deformation and magnetic fabrics in ductile shear zones. Structural complexity resulting from pervasive ductile. Ductile shear zones are long and narrow zones of relative displacement. Structural analysis of the nanchangwanzai sinistral ductile shear zone jiangnan region, south china. This article is the first report on the bayan nuru ductile shear zone, and provides dynamic, kinematic, and geochronological data of the shear zone. A newly recognized ductile shear zone in the northern klamath mountains, oregonimplications for nevadan accretion by mary m. Sutures are ductile shear zones produced by thrusting along converging plate boundaries, and they range from a few hundred meters to tens of kilometers wide coward et al. In ductile iron, shear strength is 90% of tensile, and in steel, shear strength is only 50% of tensile. In major shear zones which transect the crust or upper mantle, the depth of. Development of branching brittle and ductile shear zones.
Rocks on the hinterland plate adjacent to sutures are chiefly arcrelated volcanics and sediments from a former arc system on the overriding plate, whereas those on. The strain gradients from mylonite to undeformed rock are criteria to distinguish largescale shear zones from regional deformation. However, these shear zones are often frozen in and preserve their textural features that when exhumed behave with elastic and frictional failure criteria in the upper crust. Plastic deformation and rheology of the sinistral strike. Ductile shear zones, textures, and transposition geokniga. They are analogous to faults but without fracture planes unless they are reworked because dominantly ductile deformation has caused the concentration of large strain into the shear zones. In a mylonite, the grain size is significantly reduced so that. The distributions of slip rate and ductile deformation in.
Olivine fabric evolution in a hydrated ductile shear zone. Ductile shear zones by soumyajit mukherjee overdrive. Fabric development in brittletoductile shear zones. Shear zones mylonite, or mylonitic zone is the central part of the shear zone where deformation is the most intense. A microscopic view of a harzburgitehosted mylonite, showing the intense grain size reduction and the development of layers in a highly deformed mantle rock warren and. Shear wall design for a building in seismic zone iii 69. Weinberg 2010, structural complexity resulting from pervasive ductile deformation in the karakoram shear zone, ladakh, nw india,tectonics, 29. Pdf progressive deformation across a ductile shear zone. The brittleductile transition zone is the strongest part of the earths crust. Explanatory examples for ductile detailing of rc buildings by dr. The aim of the structural study of this ductile shear zone is to unravel the paleoproterozoic structural evolution of the shear zone. A shear zone is a zone in which strain is clearly higher than in the wall rock, and whose margins are defined by a change in strain, typically seen by rotation of preexisting markers or. In this section we will look at the most highly strained rocks in the lithosphere those found in shear zones.
The last ductile shear event around the nestriking shear zone developed at low temperatures and shallow tectonic levels, yielding to a preexisting nestriking shear zone, accompanied by abundant microstructures, including lowtemperature quartz. Pdf documents opened from your browser may not display or print as intended. The elucidation of the mechanisms and kinematics of shear zone deformation, at both local and regional scales, is the subject of a great deal of interest to scientists in the hydrocarbon industry, in seismology, and in structural geology more generally. The shear zones are not simply foliated cataclasites, since they contain abundant evidence of dynamic recrystallization of constituent minerals. A small quartz diorite lens in the borrego springs shear zone, southern california, contains centimeter. Two model, for driving the ductile deformation occurring beneath vertical strikeslip faults. Ductile shear zones generally record a noncoaxial deformation and may range from the grain scale to the scale of a few hundreds of kilometres in length and a few kilometres in width. Bulk lithospheric deformation andor localized ductile shear zone strain will be held on saturday, september 8, 2018, in palm springs, ca. The first ductile shear zone develops at a strain of 34.
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