Continental transforms: A view from the Alpine Fault
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Transform fault
Décollement
Continental Margin
The Dead Sea Transform Fault (DSTF) constitutes the transform plate boundary between Africa and Arabia plates and it is one of the biggest strike-slip faults in the world (ca. 1000 km long). This fault formed by mid-Cenozoic breakup of a region that had been stable until that moment; and, therefore this breakup has not been complicated by a previous history. There are still some open questions regarding this strike-slip fault. The links between its two southern segments (Wadi Araba Fault and Jordan Valley Fault), the deformation along the Lebanon and Syrian in its northern part, or the differences in offset between its southern and northern parts remain poorly known. Moreover, active tectonic studies are scarce in some areas as in the Jordanian part of the Dead Sea Transform, which has been considered tectonically inactive in Pleistocene Times. The southern part of this fault is divided in two main segments, the Wadi Araba Fault (WAF) and the Jordan Valley Fault (JVF) connected through the Dead Sea continental pull-apart basin. Active tectonic studies in NW Jordan have traditionally focused on these DSTF structures and have discarded other prominent structures in the region like the Amman Hallabat (AHS) and the Shueib (SHS) faults system, as they have been considered inactive from the Cretaceous. However some recent studies have suggested a possible local reactivation of the northern parts of these structures. In this Thesis I carried out a detailed geological study in the NW Jordan in order to analyze the Quaternary activity of the AHS and SHS based on landscape anlysis trhought geomorphic indexes, field observations, structural analyses and archaeological evidences of recent earthquakes. From a methodological point of view I present in this Thesis two ArcGIS Add-Ins to automatically delineate swath and normalized river profiles. Both tools are programmed in Visual Basic .NET and use ArcObjects library-architecture to access directly to vector and raster data. The SwathProfiler Add-In allows analyzing the topography within a swath or band by representing maximum-minimum-mean elevations, first and iv third quartile, local relief and hypsometry. I have defined a new transverse hypsometric integral index (THi) that analyzes hypsometry along the swath and works better in this kind of representation. The NProfiler Add-In allows representing longitudinal normalized river profiles and their related morphometric indexes as normalized concavity (CT), maximum concavity (Cmax) and length of maximum concavity (Lmax). Both tools facilitate the spatial analysis of topography and drainage networks directly in a GIS environment as ArcMap and provide graphical outputs in image (jpg) and vectorial (wmf) formats. The landscape analysis presented in this Thesis focused in the eastern margin of the Dead Sea, with the intention of analyzing the effects that the Quaternary activity of the Dead Sea Transform Fault (DSTF) produces in the landscape and in the drainage network. This landscape analysis has two well-differentiated parts. First I analyzed the general landscape pattern through the application of spatial-based geomorphic indices as the slope, surface roughness, hypsometry and topographic swath profiles. With this analysis I aimed to describe and evaluate the general stage of landscape evolution in the study area, and examine the links between the tectonic structures and the general topographic patterns. These results of these geomorphic parameters show a good correlation with the active structures of the study area that act as boundaries for erosion processes. They also highlight a clear erosion wave advancing eastwards from the Dead Sea into the TransJordanian Plateau (TJP). Moreover, these analysis lacks clear evidences of a northern structure closing the Dead Sea apart of the NW-SE normal faults related to the AHS and SHS. Secondly, I analyzed several geomorphic indexes in order detect different pattern and highlight differences that could be due to dissimilar tectonic activity along the study area. The geomorphic indexes suggest that the study area is very young and it is in a transient state of landscape development. Normalized profiles have characteristics convex or linear-convex shapes, as well as the hypsometric curves. Area-slope plots have high Ksn values and lacks clear linear correlation, especially in their middles and lower parts (near mouths), due to the transient state of the analyzed rivers. v The field campaigns made in this Thesis have revealed that AHS and SHS structures present clear Quaternary activity and accommodate a small part of the deformation of the southern DSTF. The southwestern part of the AHS acts in the Quaternary as the northernmost continuation of the WAF, whereas the SHS works as a transfer of NW-SE normal faults with low to moderate throws that connects this structure with the JVF. The stress analysis based on fault-slip data for two of the Amman Hallabat (AHF) and Shueib (SHF) structures suggests that most of the structures are coherent with the present-day stress pattern associated to the Dead Sea fault system. In most of the field stations there is a clear overprint of new striations over the older ones. Present-day stress in the region has horizontal to sub-horizontal maximum and minimum compressive axes (?1 and ?3), striking NNW-SSE and ENE-SWS respectively, and a vertical intermediate stress axis (?2). These new findings suggest a rejuvenation of the AHF and the SHF in the Quaternary in the context of the Dead Sea Transform Fault (DSTF) tectonic activity. A seismogenic character of the AHS can be claimed from the damage found in the archaeological site of Tall el-Hamman, which has been recently interpreted as the ancient city of Sodom. The destruction of this city is attributed to bid earthquake, that may be also related with this structure. The NW-SE normal faults bounding the AHS and SHS could merge into a single fault plane that will act as the northern closure of the Dead Sea. Future geophysical research in the area should pay attention to these active structures as research in southern areas has prove fruitless.
Transform fault
Dead sea
North Anatolian Fault
Wadi
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The crustal block of Borgarfjörður in western Iceland was caught between the propagating Reykjanes‐Langjökull Rift Zone (RLRZ) and the receding Snæfellsnes Rift Zone (SRZ) during a Tertiary rift jump at ∼7 Ma. This Tertiary rift jump configuration presents an analogy with the presently unstable plate boundary in south and southwest Iceland. Field examination of the Gljúfurá fault in the Tertiary lavas of Borgarfjörður reveals a complicated history of movements and magmatic activity. During its evolution since Tertiary time, this N‐S fault acted as follows: (1) The fault acted as a possible dextral strike‐slip fault, as judged from Riedel fractures in the oldest associated fault breccia. (2) Then the fault acted as a normal fault, resulting in vertical displacement, new brecciation of part of the oldest breccia, hydrothermal activity, and mineralization dominantly in N‐S mode I veins. (3) The fault acted again as a dextral strike‐slip fault, when the fault was injected laterally by dikes. Magma was injected mainly into the N‐S strike‐slip fault and secondarily into adjacent NNE normal faults. Evidence of this stage are the en échelon geometry of the northerly dikes, cooling cracks oblique to dike edges, flow lineation, elongated vesicles, and soft striations on dike edges, as well as bending and displacement of preexisting dikes. (4) After the emplacement and partial erosion of the northerly dikes, the fault acted dominantly as a strike‐slip fault, with possible reactivation as an open fissure. The Gljúfurá fault strikes obliquely to the NNE trending rifting structures active during crustal formation in this area. Its activity was initially related to a transform zone or an oblique rift connected to the SRZ. Then a shift in the plate boundary occurred around 7–6 Ma when the RLRZ became active. During this shift the Gljúfurá fault probably played a role similar to the N‐S strike‐slip faults of the presently active plate boundary within the South Iceland Seismic Zone and the oblique rift of the Reykjanes Peninsula. These faults may, similar to the Gljúfurá fault, change mode and be injected by dikes if they are sufficiently close to a magma source.
Dike
Transform fault
Echelon formation
Breccia
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Transform fault
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Transform fault
Echelon formation
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Abstract The Santa Clara trough, part of the Ventura basin, California, originated during late Miocene time and then deepened rapidly, probably as the result of crustal extension. Inasmuch as the crustal stretching amounted to about 50 per cent it is inferred that the floor of the trough was greatly attenuated. This stretching was associated with irregular transform movements between the North American and Pacific lithospheric plates. In Pleistocene time, the Transverse Ranges were compressed, and the Santa Clara trough was much constricted. Concomitantly, the modern Gulf of California opened and several major faults originated or were reactivated. During late Cenozoic time, beginning about 30 m.y. ago, coastal California and its Borderland have been part of a broad transform zone with a pliant and yieldable crust. Sedimentary basins within this yieldable belt have been formed by at least five processes: 1) Crustal megarifting, in which a major transform fault meets a spreading center as in the Gulf of California today, 2) Fault-zone rifting, where smaller basins originate within a braided strike-slip fault zone, 3) Fault divergence, where strike-slip faults in map view form long lenses between them with down-tipped triangular basins, 4) Fault-margin sagging, where restraining curvature of a strike-slip fault carries one wall up upon the other to depress the lower wall under its weight. Fault-margin basins may also form where a wall sags as it is stretched in moving around a gentle curve, and 5) Fault-margin folding, where large synclines and depressions oblique to major strike-slip faults originate along fault margins in response to regional simple shear between lithospheric plates. Each of these basin types can be recognized in the region that includes central and southern California and the Borderland. The structure of the region before about 30 m.y. ago, and back in time to well within the Mesozoic Era, was primarily the result of complex plate convergence with only short intervals of divergence and transform movements. Plate-convergence tectonic models need to be reconstructed and depicted for pre-Miocene rocks as new data from coastal and Borderland exploration become available.
Trough (economics)
Transform fault
Echelon formation
Pull apart basin
Neotectonics
Extensional fault
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The hypothesized presence of a detachment underlying the Lake Mead region has created a dichotomy in the interpretations of the roles of strike-slip faults of the Lake Mead fault system in accommodating regional deformation. Our detailed field mapping reveals a previously unnamed left-lateral strike-slip segment of the Lake Mead fault system and a dense cluster of dominantly west-dipping and related normal faults located near Pinto Ridge. We suggest that the strike-slip fault that we refer to as the Pinto Ridge fault: (1) was kinematically related to the Bitter Spring Valley fault; (2) was responsible for the creation of the normal fault cluster at Pinto Ridge; and (3) utilized these normal faults as linking structures between separate strike-slip fault segments to create a longer, through-going fault. Results from numerical models demonstrate that the observed location and curving strike patterns of the normal fault cluster are consistent with the faults having formed as secondary structures as the result of the perturbed stress field around the slipping Pinto Ridge fault, regardless of whether or not the Pinto Ridge fault merges into a regional detachment at depth. Calculations of mechanical efficiency of various normal fault geometries within extending terranes suggest that a preferred west dip of normal faults likely reflects a west-dipping anisotropy at depth, such as a detachment. The apparent terminations of numerous strike-slip faults of the Lake Mead fault system into west-dipping normal faults suggest that a west-dipping detachment may be regionally coherent.
Normal fault
Transform fault
Detachment fault
Stress field
Elastic-rebound theory
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Transform fault
Echelon formation
Fracture zone
Lineament
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Summary The interaction between thrust and strike slip fault systems is well detailed in Pakistan where the Chaman transform zone connects the Makran and Himalayan convergence zones and contains an internal convergence zone in the Zhob district. The transform zone contains numerous strike slip faults of which the Chaman fault proper is the westernmost. We can demonstrate at least 200 km of left lateral displacement along the Chaman fault alone. In the Zhob belt N-S shortening by folds and a major thrust fault amounts to several dozen kilometres. The 400 km wide Makran convergence zone is now being shortened by E-W oriented folds, thrust faults, and reverse faults. As these faults in the Makran zone approach the transform zone, their traces bend to the N and motion on each of them becomes oblique, combining reverse and left lateral slip. They merge continuously with the strike slip faults of the Chaman transform zone. The Makran thrust system and the Chaman transform zone first became active in the late Oligocene or early Miocene. Later (Pliocene?), a component of left lateral shear occurred across the entire Makran Zone in association with the opening of the newly identified Haman-i-Mashkel fault trough S of the Chagai Hills and W of the Ras Koh. The total displacement and displacement rate across the Chaman transform zone varies in response to the rates of convergence in the plates E and W of the zone.
Thrust fault
Transform fault
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An E W trending gigantic ductile shear zone was found during regional geological survey of the 1∶200 000 Quxu Sheet. According to its geometric form and microfabrics, this shear zone has the nature of a normal shear zone. It is the product of collision of the Indian plate and Eurasian continent during the late Eocene (40～42 Ma B.P.). The tectono magmatism in the study area resulted in the decollement in different levels of the earth's crust and formation of a ductile shear zone. This gives relatively reasonable explanations of crustal thickening, tectonic deformation and geophysically indistinct multi layered structure.
Décollement
Collision zone
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Transform fault
Thrust fault
Elastic-rebound theory
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