Minor Strike-slip Faults Research Articles

Assessing the accuracy of combined DEM-based lineament mapping and the normalised SL-index as a tool for active fault mapping

Satellite image-based lineament mapping in combination with the normalised Stream Length Gradient Index (SL/K-index) is one of the most widely used methods to identify active faults in areas where other verification methods, such as faulted strata, geophysical subsurface data, or seismic activity in the upper crust, are unavailable, and to classify their degree of activity. The accuracy of this approach, however, has not yet been assessed rigorously. We assess its accuracy by comparing the results against 27 thrust fault segments that were identified from six seismic reflection profiles with a total length of 340 km. Over 106,000 SL/K points were calculated from 815 river profiles on basis of the SRTM v.3.0 DEM. Standard deviations (SD) of < -2SD (class 1) to > +2SD (class 5) were calculated from the lognormalised SL/K data and five SL/K classes were made and assigned to the nearby lineaments. A comparison with the fault segments from the seismic profiles showed a good coincidence between the presence of knickpoints, SL/K classes 4 and 5 and to a lesser extent class 3. Lineaments with SL/K classes 1 and 2 never corresponded to actual faults. We identified seven master thrusts of which three are very active to highly active, likely older, structures with important amounts of accumulated slip. The other thrusts are probably younger faults with relatively little accumulated slip, yet they are also active to highly active faults. Minor strike-slip faults were identified as very active to highly active structures. Published slip rates shows that at least some of the SL/K class 4 faults experience slip rates of ~1 to ~4 mm a−1 and the SL/K class 5 strike-slip faults may experience slip rates as high as one metre over the course of several months. Most active faults occur where the basal evaporite layer is abnormally thick.

Late Quaternary tectono-geomorphic forcing vis-a-vis topographic evolution of Indus catchment, Ladakh, India

The Indus River valley has frequently reorganized itself to attain geomorphic equilibrium during the Late Quaternary. In this regard, significant advances have been made towards the understanding of the response of landform/ landscape to climate (exogenic) forcings. However, advancements in geomorphic studies on the upper Indus basin focusing on recent tectonics (endogenic) are lacking, thus implementing a partial picture of landscape evolution. This article attempts to synthesize geomorphic indices of active tectonics to understand the prevalence of neotectonic activity in the Ladakh area. A combination of geomorphic field data, morphometric analysis and previously published incision rates, denudation rates, the chronology of landform features and soft-sediment deformation structures are used to suggest the region is undergoing differential tectonic activity. Based on morphometric parameters and landform characteristics, the region is divided into three differentially uplifted morphotectonic segments. The neotectonic activity is inferred to be the response to the thrusting of Indus Molasse over the rigid Ladakh Batholith along with oblique convergence of the Indian plate in the study area. This led to the development of a system of back thrust (Stok Thrust) and cross-cutting minor strike-slip faults. Recurrent tectonic activity largely responding to the differential movement along this system of thrust fault is recorded at 50 ka, 35 ka and 21 ka (Last Glacial Maxima) through lower Greenlandian (~11 ka) to middle Northgrippian (~6 ka), while the climatically induced topographic changes are marked between ~13 and 12 ka.

Active strike-slip faulting in the Zagros Mountains: Geological and geomorphological evidence of the pull-apart Zaribar Lake basin, Zagros, NW Iran

The Zaribar Lake is situated along the Main Recent Fault, a dextral major strike-slip active fault system in the Zagros collision zone. The formation of the Zaribar Lake in Late Pleistocene is associated with the activities of the Main Zagros Reverse Fault, initiated in Late Oligocene, and with the Main Recent Fault, whose inception occurred about 5 Ma ago. Metamorphic, intrusive and ophiolitic rocks in the Zagros suture zone are affected by a normal fault system in the Zaribar area. Geometry and kinematics of these normal faults indicate that the Zaribar Lake is generated in a releasing zone. The strike of the Main Recent Fault varies from 300° to 330° along the Marivan fault segment. The releasing bend of the Marivan Fault around the Zaribar Lake has resulted in the extensional deformation by which the lake has been downdropped between two strike-slip faults. Besides the extensional mechanism of the main right-lateral strike-slip faults that has resulted in the formation of the Zaribar as a large-scale pull-apart basin, minor strike-slip faults have also produced specific landforms around the lake. Small-scale normal faults and large scale grabens developed around the lake are geological indicators of extensional areas. Geomorphological evidence also support the pull-apart origin for the Zaribar Lake. Beheaded rivers, numerous offsets in drainage system, half-broom shaped drainage pattern, sag ponds with different scales, linear and strike-parallel valleys and alluvial fan with high sweep angle and width/length ratio confirm the movements along right-lateral, strike slip faults around the Zaribar.

Retracted: Pierced Salt Domes in the Persian Gulf and in the Zagros Mountain Ranges in Southern Iran and their Relationship to Hydrocarbon and Basement Tectonics

The most enigmatic problems with the nearly 200 salt domes pierced in the Persian Gulf and in the Zagros Mountain Ranges (ZMR) in southern Iran, a unique morphology in the world, have been the matter of this study, which is based on a combination of field work, enhancement of satellite and aerial photographs etc. In the ZMR, structural anomalies are frequently associated with similar facies distribution patterns. In the eastern portion of the region, emergent salt plugs of Infra-Cambrian age exhibit the same alignment patterns. Such trends bear no apparent genetic relationship to the Tertiary folding responsible for the present Zagros fold belt, but rather indicate their affinity with linear basement features which are readily observable on Land sat imagery and aerial photographs. Bending of anticlines in the competent cover rock, combined with minor strike-slip faults and horizontal displacements of parts of folded structures, strongly point to the presence of these basement faults. The salt plugs, which have pierced cover rocks of up to 10000 m thick, are distributed on the Arabian Platform along regional basement faults. The area of diapir outcrops is bounded by the Oman Line to the east and by the Kazerun fault to the west. Pieces of the basement have been brought up to the surface on some of the salt domes. The fragments were transported by rotational ascent of the Hormuz Salt Formation to the present and former land surfaces. The recognition of features related to basement tectonics and realization of their implication in the control and modification of geological processes are important adjuncts to the search for hydrocarbon accumulations in this region. To our best knowledge, data of basement faults in the study area are scarce. Therefore, this study was carried out to determine basement faults and their relation to salt dome distribution. Considering the fold axes bending, the trend of the salt plugs and also the distribution of epicenters of the last century, n umerous new basement faults are introduced in this paper.

The Cerro Aguas Calientes caldera, NW Argentina: An example of a tectonically controlled, polygenetic collapse caldera, and its regional significance

Polygenetic, silicic collapse calderas are common in the central Andes. Here we describe in detail the Cerro Aguas Calientes caldera in NW Argentina, which comprises two caldera-forming episodes that occurred at 17.15 Ma and 10.3 Ma. We analyse the significance of its structural setting, composition, size and the subsidence style of both caldera episodes. We find that the caldera eruptions had a tectonic trigger. In both cases, an homogeneous dacitic crystal-rich (>60 vol.% of crystals) reservoir of batholithic size became unstable due to the effect of increasing regional transpression, which favoured local dilation through minor strike–slip faults from which ring faults nucleated and permitted caldera collapse. Both calderas are similar in shape, location and products. The 17.15 Ma caldera has an elliptical shape (17 × 14 km) elongated in a N30° trend; both intracaldera and extracaldera ignimbrites covered an area of around 620 km 2 with a minimum volume estimate of 140 km 3 (DRE). The 10.3 Ma episode generated another elliptical caldera (19 × 14 km), with the same orientation as the previous one, from which intracaldera and outflow ignimbrites covered a total area of about 1700 km 2, representing a minimum eruption volume of 350 km 3(DRE). In this paper we discuss the significance of the Cerro Aguas Calientes caldera in comparison with other well known examples from the central Andes in terms of tectonic setting, eruption mechanisms, and volumes of related ignimbrites. We suggest that our kinematic model is a common volcano-tectonic scenario during the Cenozoic in the Puna and Altiplano, which may be applied to explain the origin of other large calderas in the same region.

Erosional control on the structural evolution of a transpressional thrust complex on the Alpine fault, New Zealand

The Waikukupa thrust is a 4-km long oblique thrust segment of the New Zealand Alpine Fault that has developed over the last 65,000 years, emplacing mylonite and cataclasite over fluvioglacial gravel. During the last 20,000 years or so, a 2-km long ‘out-of-sequence’ imbricate, the Hare Mare thrust, has formed on the east side of the Waikukupa River valley. The average rate of slip on the two thrusts is estimated at 22–30 mm/year. Analysis of the fault structure in terms of critical wedge theory is consistent with imbrication resulting from a reduction in wedge taper below the critical value due to rapid river erosion. The internal structure of the Waikukupa thrust sheet consists of reverse faults and angular folds forming duplex-like systems, associated with minor strike-slip faults. Within the limits of uncertainty, the structures are consistent with strain accumulating during internal transpressional shear of the thrust sheet while the taper of the latter was subcritical prior to the transfer of fault displacement to the Hare Mare imbricate. The thrust complex forms part of a serrated range front fault system consisting of oblique thrust sections linked by strike-slip faults. We introduce the term ‘serial partitioning’ for this type of partitioned transpressional fault system. Its development is linked to the erosional processes at the range front. An alternative system consisting of parallel thrust and strike-slip faults we here term ‘parallel partitioning’. While angle of obliquity is an important parameter in determining which partitioning model develops, we suggest that erosion rate is also an influential factor.

Palaeostress superimposition deduced from mesoscale structures in limestone: the Matelles exposure, Languedoc, France

This study investigates the reasons for the superimposition of several maximum principal stress directions ( σ 1) in the same area, and examines the contrast between unperturbed areas (stable direction of σ 1) and perturbed areas (changing σ 1 direction). We studied mesoscale structures on a 1000 m 2 continuous limestone exposure near a regional scale strike-slip fault. Local σ 1 directions were deduced from a high concentration of minor strike-slip faults, extension fractures and stylolites formed during the Pyrenean shortening in Languedoc, France. Most of the stylolites were formed in a stress field which was homogeneous on the exposure scale. This was followed by the reactivation of pre-existing extension fractures as strike-slip faults whose activity determined stress perturbations. A very heterogeneous stress field was produced leading to the formation of new localized stylolites and extension fractures, especially at fault terminations and at oversteps. Thus the final pattern shows the superimposition of all these structures. Reactivation of structures was caused by slight temporal changes in the orientation and intensity of the stress field produced by the nearby regional strike-slip faults. Our study suggests that the origin of stress deviations or superimpositions cannot be explained by random measurements of σ 1. It is essential to be able to synthesize the fault pattern and the stress trajectories which it determines, and to do this, a very high density or a selection of data from mesoscale structures is needed.

Structural geology of the Vangorda PbZnAg orebody, Yukon, Canada

The Vangorda PbZnAg orebody is a 7.1 M tonne, polydeformed, polymetamorphosed stratiform massive sulphide orebody in the Anvil mining district, Yukon, Canada. The orebody consists of fine- to medium-grained semi-massive and massive sulphides with a dominant sulphide mineralogy of pyrite, pyrrhotite, sphalerite, galena and minor chalcopyrite. Five sulphide lithofacies have been identified within the orebody; ribbon-banded, carbonaceous, pyritic quartzite; pyritic quartzite; massive pyritic sulphides; baritic, massive pyritic sulphides; and pyrrhotite-sphalerite massive sulphides. The orebody is elongate in a northwest-southeast orientation and plunges shallowly towards the northwest. The host rocks and the various sulphide lithofacies have been complexly deformed during two penetrative phases of deformation (D 1 and D 2, respectively) and associated metamorphism (M 1 and M 2). M 2 metamorphism resulted in extensive recrystallisation and subsequent grain growth of sulphide minerals. M 2 metamorphic grade recorded by arsenopyrite and chlorite thermometry and sphalerite+hexagonal pyrrhotite barometry is of mid-greenschist facies with temperatures of 336° to 363°C, respectively, and a pressure of 4 kb. The earliest structure that can be recognised in the orebody is a penetrative S 1 spaced cleavage that is well-developed in the host phyllites and a differentiated layering in the semi-massive and massive sulphides. However, F 1 folds have not been identified in the orebody, although they do occur within the Anvil District. The S 1 cleavage has been deformed into downward-facing, southwest-verging, recumbent F 2 folds that plunge shallowly northwest-southeast. A penetrative axial planar S 2 crenulation cleavage is developed in the phyllites and ribbon-banded, carbonaceous, pyritic quartzite, but is found only locally in the massive sulphide lithofacies. In the baritic lithofacies, F 2 folds have thickened hinges suggesting remobilisation of the ore. Along the overturned limbs of the F 2 folds and at lithofacies contacts centimetric to metric-scale zones enriched in pyrrhotite, sphalerite and galena are developed. These areas commonly have a significantly reduced grain size, a well-developed sulphide foliation and numerous shear indicators such as winged and rotated clasts. F 2 folds and the S 2 form surfaces are cut by syn- to post-D 2 NW-SE-dipping extensional faults. Minor strike-slip faults cut D 1 and D 2 structures.

Subhorizontal Drilling, L13 Block Central Offshore Netherlands: Remedial Action for Underperforming Rotliegende Gas Fields

The first development well in the L13-FE gas field showed a rapid production decline resulting from a marked pressure depletion. Material balance data indicated less than 10% of the expected volumetric reserves to be connected. This poor connectivity is thought to be due to compartmentalization by minor strike-slip faults, as confirmed by lineations on seismic attribute maps. Fault-related diagenesis and a limited number of scattered, stratigraphically isolated prolific layers, diminishing the vertical permeability, can also contribute to the disappointing well performance. The well was sidetracked subhorizontally with the aim to connect a larger number of the scattered prolific sands, different fault compartments and possible open fracture systems. The reservoir section was drilled with graded rock salt mud in order to minimize formation impairment. During drilling of the 500 m long, 5 7/8 in. subhorizontal section, numerous problems were encountered due to mechanical failures and the heterogeneous nature of the reservoir. Slim-hole equipment failures also necessitate a second sidetrack. A significant amount of prolific sand was encountered and the presence of subseismic faults was recognized from log correlations. The well is producing 1.3 x 10[sup 6]m[sup 3]/d, which is above expectation considering that only 60% of the well could be completed.more » Nederlandse Aardolie Maatschappij's first attempt to challenge such geologically complex, labyrinth-type reservoirs by subhorizontal drilling therefore can be considered successful.« less

Late to post-Variscan deformation phases and palaeostresses in the KTB pilot research well (Bohemian Massif, Germany)

Brittle faults and veins are very widespread in the crystalline rocks of the northern Oberpfalz, particularly in the 4000 m deep Kontinentale Tiefbohrung (KTB) pilot well. In the late Variscan (Late Carboniferous), subvertical tension gashes were formed under NE-SW extension. A genetic relationship between the vein development and late-phase magmatic activity of the late Variscan granites is obvious. Subsequently, but still during the Late Carboniferous, graphite-enriched reverse faults developed under E-W and NE-SW compression. In the deeper part of the KTB pilot hole these faults were formed within the brittle-ductile transition regime of the paragneisses. Since, during the late Variscan, the geothermal gradient was remarkably elevated, the brittle-ductile regime was situated at a relatively high crustal level where cataclasis, crystal plasticity and diffusion-controlled deformation mechanisms were active simultaneously. In post-Variscan time, probably during the Cretaceous, a further generation of reverse faults developed in addition to subhorizontal tension gashes and minor strike-slip faults. During these events the temperature was much lower compared with the conditions during the late Variscan deformations. The reverse faults evolved primarily under N-S compression, which is probably related to the Cretaceous subduction and collision events of the Alpine orogeny further to the south. The youngest, normal, faults are probably connected to the subsidence of the nearby Eger Graben which evolved during the Neogene uplift of the investigated area. The stress data, derived by using faults and striations from surface outcrops and from several oriented core intervals from the KTB pilot well, display weak depth-dependent variations. Although the deformation was polyphase, the “inversion method” has proved to be a suitable mode for determining reliable palaeostress data. However, if the brittle-ductile transition regime or broad shear zones are reached, the data become more and more invalid.

Structural geology of the Blake River Group at the Bousquet mine, Abitibi, Quebec

In the Bousquet mining district, metamorphosed volcanic rocks of the Blake River Group (BRG) exhibit discrete strain features resulting from three generations of structures—D1, D2, and D3. Deformation D1 formed an east–west-trending, subvertical, penetrative schistosity that is coplanar with the axial plane of associated folds. This foliation contains a linear fabric plunging steeply westward, and mineral lineations are subparallel to fold axes and to intersection lineations.Defomations D2 and D3 formed a crenulation cleavage and a set of conjugate kink bands, respectively. The cleavage is oriented east–northeast, and the kink bands are oriented northeast–southwest and northwest–southeast. Both deformations distorted earlier-formed structures to a minor extent. A conjugate set of minor strike-slip faults with orientations similar to the kinks are the youngest structures found in BRG rocks.The volcanic sequence is composed of two lithotectonic domains juxtaposed along fault-related contacts. Each domain exhibits distinctive strain features attributed mainly to a broad network of anastomosing faults. This network of faults disrupted strata and destroyed many internal stratigraphic features, especially in domain 2; it relates to late stages of D1.Domain 1, occupying the northern half of the BRG in the mine area, represents a zone of weakly sheared tholeiitic basalts 750 m thick and is overlain by 150 m of felsic volcaniclastic rocks. Primary textures and structures indicate that this domain forms a south-facing homoclinal succession.Domain 2 is characterized by a strongly strained, 500 m wide belt of anastomosing faults adjacent to the southern margin of domain 1. Narrow bands of schist, mylonite, and phyllonite straddle fault zones and surround less-deformed, lozenge-shaped blocks of metamorphosed volcanic and (or) volcaniclastic rocks.The lack of syngenetic structures and textures, together with intense faulting and transposition, restricts stratigraphic correlations throughout the BRG as well as correlations between this volcanic succession and the adjacent sedimentary units. Structural evidence presented here complicates the original stratigraphic scheme commonly applied to volcano-sedimentary assemblages in the Rouyn–Val D'Or area. It is proposed that faulting is responsible for the spatial distribution of lithologies previously interpreted as resulting from folding phenomena in the Bousquet mining district. Gold mineralization is concentrated in bands of deformed rocks in the fault zones of domain 2 at the Bousquet mine.