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Abstract: The Mesoarchean Tartoq greenstone belt, southern West Greenland, consists of tectonically imbricated slices of metamorphosed basalt, gabbro, peridotite, and sedimentary rocks and is intruded by felsic rocks (now mylonites) [...]

Abstract: Throughout the greater Red Sea rift system the initial late Cenozoic syn-rift strata and extensional faulting are closely associated with alkali basaltic volcanism. Older stratigraphic units are either pre-rift [...]

Author(s): Dan Bassett (corresponding author) [1]; David T. Sandwell [1]; Yuri Fialko [1]; Anthony B. Watts [2] The March 2011 Tohoku-oki earthquake was only the second giant (moment magnitude M [...]

Geophysicists are ramping up their efforts to monitor major undersea faults for movement, and search for signs of the next catastrophic quake., Author(s): Alexandra Witze [sup.1] Author Affiliations: (1) writes for Nature from landlocked Boulder, Inventor Jerry Paros has developed quartz sensors that are helping researchers to detect movements of the sea [...]

The Dog Bay Line was defined in 1992-1993 by H. Williams, K. Currie, and M. Piasecki following mapping of the Carmanville-Comfort Cove Map sheets in northeastern Newfoundland. The strongly deformed [...]

Marathon Gold Corporation's Valentine Gold Property is in west central Newfoundland. The property has four known gold deposits in early exploration stages along 20 kilometers of north-east to south-west trend. [...]

The Kern Canyon fault, the longest fault in the southern Sierra Nevada, is an active structure and has been reactivated at discrete times over the past ~100 m.y. in response to changing lithospheric stresses. After initiation as a Cretaceous transpressional structure, the Kern Canyon fault transitioned into a dextral strike-slip shear zone that remained active as it was exhumed into the brittle regime during regional Late Cretaceous uplift of the Sierra Nevada batholith. The Kern Canyon fault was reactivated during Miocene regional extension as part of a transfer zone between two differentially extending domains in the southern Sierra Nevada. Subsequent normal displacement along the fault began in Pliocene time. New evidence for fault activity, which continued into late Quaternary time, includes its current geomorphic expression as a series of meters-high, west-side-up scarps that crop out discontinuously along the fault's 130-km length. Relocated focal mechanisms of modern earthquakes confirm ongoing normal faulting, and geodetic measurements suggest that the Sierra Nevada is uplifting relative to the adjacent valleys. This evidence for recent activity overturns a long-held view that the Kern Canyon fault has been inactive for more than 3.5 m.y. Its reactivation indicates that deformation repeatedly localized along a preexisting crustal weakness, a Cretaceous shear zone. We propose that a system of interrelated normal faults, including the Kern Canyon fault, is responding to mantle lithosphere removal beneath the southern Sierra Nevada region. The location of the active Kern Canyon fault within the Sierra Nevada--Great Valley microplate indicates that deformation is occurring within the microplate. doi: 10.1130/B30009.1

We present new results on the long-term throw rates of active normal faults in the North Baikal Rift (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Fault-bounded ridges in the NBR display typical morphologies with several contiguous facets separated by fault-perpendicular catchments. Over a range of 20 fault segments analyzed, triangular facet heights vary from ~200 to >900 m. As fault scarps have been developing under similar long-term climatic conditions, we infer that the scatter in mean facet height arises from long-term differences in fault throw rate. We compare the morphology of NBR facets with results obtained in a previously published numerical model of facet growth. Using facet height as an input, model results provide estimates of the long-term fault throw rate. NBR throw rates vary between 0.2 and 1.2 mm [yr.sup.-1]. The throw rates are then compared with the cumulated throw, which has been constrained by geophysical and stratigraphic data in the basins. This provides an estimate of the age of fault and basin initiation. We show that the modern stage of basin development started circa 3 Myr ago, except for the North Baikal basin (~8 Ma). Our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage. Citation: Petit, C., B. Meyer, Y. Gunnell, M. Jolivet, V. San'kov, V. Strak, and N. Gonga-Saholiariliva (2009), Height of faceted spurs, a proxy for determining long-term throw rates on normal faults: Evidence from the North Baikal Rift System, Siberia, Tectonics, 28, TC6010, doi: 10.1029/2009TC002555.

The southern Wairarapa region of the North Island of New Zealand preserves a variably deformed late Quaternary stratigraphic sequence that provides insight into the temporal variability in the partitioning of contraction onto faults in the upper plate of an obliquely convergent margin. Detailed mapping, stratigraphic data, and new radiocarbon and optically stimulated luminescence ages from Quaternary units reveal the interaction between tectonics and sedimentation from ~125 ka to Citation: Schermer, E. R., T. A. Little, and U. Rieser (2009), Quaternary deformation along the Wharekauhau fault system, North Island, New Zealand: Implications for an unstable linkage between active strike-slip and thrust faults, Tectonics, 28, TC6008, doi: 10.1029/2008TC002426.

[1] Fault segmentation models have been developed by using various types of information about faults, including both geological and geophysical data, in order to predict the size of future cascade earthquakes. In these models, however, stress conditions within the fault systems have not been considered in sufficient detail. Major fault systems generally exhibit heterogeneous stress conditions. The Median Tectonic Line active fault system (MTLAFS) is the longest and most active arc-parallel, right-lateral, strike-slip fault system in Japan. The stress conditions along the MTLAFS change from transpression on eastern Shikoku Island to transtension on Kyushu Island. The change of stress conditions along the fault system is caused by the counterclockwise rotation of the Nankai fore-arc sliver in response to the relative motion of the Philippine Sea and Eurasian tectonic plates and back-arc spreading in the Okinawa trough. Here, we propose 'stress condition segmentation' as a concept that deals with the diversity of stress conditions and can be applied in seismic hazard assessment. According to this concept, the MTLAFS is divided into three segments: the East Shikoku, West Shikoku, and Kyushu segments. The East Shikoku and Kyushu segments are under compressional and tensional stress conditions, respectively. Stress in the West Shikoku segment, which is between the other two segments, is transitional from compressional to tensional conditions. In particular, change in the magnitude of fault-normal stresses along strike is one of the key factors that govern the geometry of fault discontinuities, rupture propagation and termination, and, consequently, fault segmentation. Application of our stress condition segmentation concept to the MTLAFS suggests that future earthquakes in the West Shikoku and Kyushu segments will be of lower energy than those in the East Shikoku segment. Citation: Ikeda, M., S. Toda, S. Kobayashi, Y. Ohno, N. Nishizaka, and I. Ohno (2009), Tectonic model and fault segmentation of the Median Tectonic Line active fault system on Shikoku, Japan, Tectonics, 28, TC5006, doi: 10.1029/2008TC002349.

[1] Though orogen-parallel shortening and vertical extension have dominated the tectonic evolution of the central Andes, a significant kinematic shift from horizontal contraction to extension appears to have occurred within the high Puna-Altiplano Plateau, with the establishment of extension oblique to the orogen since late Miocene time. We present data from the southern margin of the Puna Plateau, NW Argentina, where new normal faults have been documented in the Fiambala, Punta Negra, and La Quebrada areas. The unifying characteristics of these areas are that young normal faults reactivate or crosscut older thrust and reverse faults. The relationship between the faults and the late Miocene-Pliocene Punaschotter conglomerate suggests that the extensional faulting must be younger than 3.5 to 7 Ma. Existing data are incomplete but indicate that similar horizontal extension has occurred in many regions throughout the Puna-Altiplano Plateau, while shortening continues along the plateau margins. Given the spatial and temporal distribution of this late Miocene to Pliocene kinematic shift, both lithospheric loss in the Puna Plateau and plateau-wide gravitational extensional spreading enhanced by slowing of plate convergence rate could be responsible. The young, disorganized, horizontal extension in the Andes today may be the precursor to more pronounced extension such as observed on the Tibetan Plateau since mid-Miocene time. Citation: Schoenbohm, L. M., and M. R. Strecker (2009), Normal faulting along the southern margin of the Puna Plateau, northwest Argentina, Tectonics, 28, TC5008, doi: 10.1029/2008TC002341.

[1] We analyzed geologic structures adjacent to the Dead Sea Fault (DSF) along the margins of the Sinai and Arabian plates in northern Israel in order to investigate the style and sequence of deformation associated with a transform plate boundary. The field area, located between the Hula basin in northern Israel and the Lebanese restraining bend in southern Lebanon, is divided into distinct structural blocks by a series of distributed faults that comprise this approximately N-S trending section of the DSF. Cretaceous and Tertiary rocks within and adjacent to the structural blocks are folded into broad anticlines and synclines, with more intense localized shortening manifested by tight folds and thrust duplexes. Kinematic analyses of folds, faults, and veins provide evidence for two directions of regional shortening: (1) NW-SE shortening responsible for the formation of NE-SW trending fold axes and left-lateral strike-slip motion along N-S trending faults and (2) E-W shortening as indicated by N-S trending fold axes, N-S striking thrust faults, and extensional calcite-filled veins that strike E-W. Crosscutting relations and U-Th ages of the vein material suggest that the E-W phase of transform-normal shortening represents the most recent and presently active phase of deformation. The structural analysis provides evidence for the transition from an early (Miocene-lower Pliocene) phase of pure strike-slip motion to a late (Pleistocene to Recent) phase of convergent strike slip. The latter phase is characterized by strain partitioning, which is manifested by discrete left-lateral strike-slip motion across weak N-S faults and the development of a fold-thrust belt in response to transform-normal shortening. Analogous to the strain partitioning observed in southern California, we suggest that blind thrust faults adjacent to the DSF in the study area may pose a seismic risk to populations in northern Israel and southern Lebanon. Citation: Weinberger, R., M. R. Gross, and A. Sneh (2009), Evolving deformation along a transform plate boundary: Example from the Dead Sea Fault in northern Israel, Tectonics, 28, TC5005, doi: 10.1029/2008TC002316.

[1] In offshore regions, studies based on densely spaced reflection seismic data tied to stratigraphic logs demonstrate that active faults can have variable displacement rates over relatively short distances and short time intervals. Here, we demonstrate how high-resolution 3-D ground-penetrating (GPR) data tied to trench-derived stratigraphic logs provide similar information for active faults in onshore regions. To investigate recent ([less than or equal to]24.4 ka) fault activity within the Taupo Rift of New Zealand, we analyze 3-D GPR data acquired over 10 fault strands within the Maleme fault zone. After correlating three prominent GPR reflection horizons with three faulted chronostratigraphic units observed within a trench, we extrapolate the geometries of the horizons over a ~150 x 250 m area of the fault zone and determine slip accumulation patterns and rates. Profiles of cumulative fault displacement measured for horizons older than 12.5 ka exhibit characteristic displacement distributions. By calculating average cumulative displacements with time for five practically complete fault strands, we obtain robust slip rate estimates. Slip rates are variable for time intervals [less than or equal to] 12.5 ka long, suggesting that at least four earthquakes are required for these faults to exhibit uniform slip rates characteristic of their long-term behavior. Citation: McClymont, A. F., P. Villamor, and A. G. Green (2009), Fault displacement accumulation and slip rate variability within the Taupo Rift (New Zealand) based on trench and 3-D ground-penetrating radar data, Tectonics, 28, TC4005, doi: 10.1029/2008TC002334.

Fault zones that slip when oriented at large angles to the maximum compressive stress, i.e., weak faults, represent a significant mechanical problem. Here we document fault weakening induced by dissolution of dolomite and subsequent precipitation of calcite + abundant talc along a low-angle normal fault. Within the fault core, talc forms an interconnected foliated network that deforms by frictional sliding along 50-200-nm-thick talc lamellae. The low frictional strength of talc, combined with dissolution-precipitation creep, can explain slip on low-angle normal faults. In addition, the stable sliding behavior of talc is consistent with the absence of strong earthquakes along such structures. The development of phyllosilicates such as talc by fluid-assisted processes within fault zones cutting Mg-rich carbonate sequences may be widespread, leading to profound and long-term fault weakness.

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses of igneous zircons from the Lake George assemblage in the eastern Yukon-Tanana Upland (Tanacross quadrangle) indicate both Late Devonian (~370 Ma) and Early Mississippian (~350 Ma) magmatic pulses. The zircons occur in four textural variants of granitic orthogneiss from a large area of muscovite-biotite augen gneiss. Granitic orthogneiss from the nearby Fiftymile batholith, which straddles the Alaska-Yukon border, yielded a similar range in zircon U-Pb ages, suggesting that both the Fiftymile batholith and the Tanacross orthogneiss body consist of multiple intrusions. We interpret the overall tectonic setting for the Late Devonian and Early Mississippian magmatism as an extending continental margin (broad back-arc region) inboard of a northeast-dipping (present coordinates) subduction zone. New SHRIMP U-Pb ages of inherited zircon cores in the Tanacross orthogneisses and of detrital zircons from quartzite from the Jarvis belt in the Alaska Range (Mount Hayes quadrangle) include major 2.0-1.7 Ga clusters and lesser 2.7-2.3 Ga clusters, with subordinate 3.2, 1.4, and 1.1 Ga clusters in some orthogneiss samples. For the most part, these inherited and core U-Pb ages match those of basement provinces of the western Canadian Shield and indicate widespread potential sources within western Laurentia for most grain populations; these ages also match the detrital zircon reference for the northern North American miogeocline and support a correlation between the two areas. Resume: Des analyses U-Pb a la microsonde ionique a haute resolution et a haut niveau de sensibilite <> de zircons ignes provenant de l'assemblage de Lake George des hautes terres du Yukon-Tanana (quadrilatere Tanacross) indiquent des impulsions magmatiques au Devonien tardif (~370 Ma) et au Mississippien precoce (~350 Ma). Les zircons se trouvent dans quatre variantes texturales d'orthogneiss granitique d'un vaste secteur de gneiss ceille a muscovite et a biotite. L'orthogneiss granitique du batholite avoisinant de Fiftymile, lequel chevauche la frontiere entre l'Alaska et le Yukon, a donne une plage similaire d'ages U-Pb sur des zircons, suggerant que le batholite de Fiftymile et l'amas d'orthogneiss de Tanacross aient subi de multiples intrusions. Selon nous, tout l'environnement tectonique pour le magmatisme au Devonien tardif et au Mississippien precoce consisterait en une enclave etendue de bordure continentale (vaste region arriere-arc) d'une zone de subduction a pendage nord-est (coordonnees actuelles). De nouveaux ages U-Pb a la microsonde ionique a haute resolution et a haut niveau de sensibilite <> de noyaux de zircons herites, preleves dans l'orthogneiss de Tanacross, et de zircons detritiques, provenant de quartzites de la ceinture Jarvis de la chaine de l'Alaska (quadrilatere Mount Hayes), presentent de grands regroupements autour de 2,0-1,7 Ga et des regroupements moindres autour de 2,7-2,3 Ga ainsi que quelques regroupements subordonnes a 3,2, 1,4 et 1,1 Ga dans certains echantillons d'orthogneiss. De maniere generale, ces ages U-Pb, herites et de noyau, concordent avec ceux des provinces du socle du Bouclier canadien occidental et ils indiquent des sources potentielles etendues dans le bouclier laurentien occidental pour la plupart des populations de grains; ces ages concordent aussi avec la reference pour le zircon detritique pour le miogeocline de l'Amerique du Nord septentrional et supporte une correlation entre les deux secteurs. [Traduit par la Redaction], Introduction Regionally metamorphosed and deformed greenschistand amphibolite-facies metasedimentary and metaigneous rocks crop out over a vast area (~300 km x 500 km) in east-central Alaska and adjacent Yukon (Fig. 1). [...]

The early Neoproterozoic Mackenzie Mountains supergroup (MMSG; ~4 km thick, 779 Ma) was deposited in a large but poorly understood basin. Analysis of new and existing stratigraphic data reveals unexpected, abrupt changes in thickness and lithofacies patterns in formation scale and smaller units over short distances parallel and perpendicular to depositional strike. These isopach and lithofacies patterns depict irregularly subsiding syndepositional sub-basins. These basins may have developed during basin extension in a lower-plate segment of an evolving passive margin, as the result of episodic, excessive subsidence along growth faults parallel to the basin margin, and crustal-scale (transfer) faults at a high angle to the margin. The extent of the lower-plate area is inferred to correspond to the distribution of the MMSG (~500 km strike length); upper-plate segments are inferred to flank the MMSG embayment to the northwest and southeast. A lower-plate model for the arcuate MMSG embayment has important implications for the Mackenzie Mountains zinc district. The present-day regional distribution of known carbonate-hosted base-metal showings suggests that the configuration of the thinned, faulted Neoproterozoic lower-plate segment, together with later reactivation of basement-rooted transfer faults during Neoproterozoic-Paleozoic rifting or Laramide compression, may have been important in focussing metalliferous fluids into overlying units. Le Supergroupe de Mackenzie Mountains, datant du Neoproterozoique (epaisseur ~4 km, 779 Ma) a ete depose dans un bassin vaste mais mal defini. L'analyse de donnees stratigraphiques, nouvelles et existantes, reve le des changements inattendus et brusques dans l'epaisseur et les patrons des lithofacies a l'echelle de la formation et de plus petites unites sur de courtes distances paralleles et perpendiculaires a la direction de la deposition. Ces patrons d'isopaches et de lithofacies decrivent des sous-bassins synsedimentaires a subsidence irreguliere. Ces bassins se sont possiblement developpes durant une extension d'un bassin dans un segment de plaque inferieure d'une bordure passive en evolution et ils auraient ete causes par une subsidence episodique et excessive le long de failles de croissance paralleles a la bordure du bassin et le long de failles (de transfert) a l'echelle de la croute a un angle eleve par rapport a la bordure. L'etendue du secteur de la plaque inferieure correspondrait a la distribution du Supergroupe de Mackenzie Mountains (sur une longueur ~500 km selon la direction) et les segments de la plaque superieure longeraient l'enfoncement du Supergroupe de Mackenzie Mountains au nord-ouest et au sud-est. Un modele de plaque infe rieure pour l'enfoncement arque du Supergroupe de Mackenzie Mountains a des implications importantes pour le district du zinc des monts Mackenzie. La distribution actuelle regionale connue d'indices de metaux de base dans des carbonates suggere que la configuration du segment inferieur neoproterozoique, aminci et faille, et une reactivation posterieure des failles de transfert dans le socle au cours du Neoproterozoique--distension au Paleozoique ou compression durant la compression laramienne, puissent avoir joue un role significatif dans la concentration des fluides metalliferes dans les unites sus-jacentes. [Traduit par la Redaction], Introduction The nature of the early Neoproterozoic epicratonic basin that contains the ~4 km thick Mackenzie Mountains super-group (MMSG) has never been clear. Poorly constrained formation- to group-scale thickness patterns [...]

On the basis of faulting mapped on seismic reflection and bathymetric data, seismicity, current plate motions, and evidence that the Yakutat block may be anomalously thick, we propose a tectonic model for Yakutat-Pacific interactions, including the often-debated Transition fault. To the east, deformation associated with the Queen Charlotte-Fairweather fault system is extending offshore, facilitating westward propagation of strike-slip motion along the eastern segment of the Transition fault. To the west, the oblique-slip Pamplona zone and Transition faults merge at an embayment in the continental margin, where a north-south dextral strike slip fault within the Pacific plate, illuminated by the 1987-1992 earthquake swarm, intersects the Pacific-Yakutat tectonic boundary. These fault patterns are consistent with modern plate motions and reflect a plate boundary reorganization that may be caused by resistance to subduction by the Yakutat block, a possible moderate-sized oceanic plateau. Keywords: collision, Alaska, Yakutat, oceanic plateau, Transition fault, subduction.

Extensional basins often evolve both with the generation of normal faults at all scales, and with tilting in the hanging walls and footwalls of major structures. This paper examines the effect of regional tilting on the development of normal fault arrays in an anisotropic sequence, using the asymmetric Lodeve Basin, France, as a case study. The orientation range of normal faults is found not to match that expected by continued symmetric generation of conjugate normal faults during tilting. Instead, continued generation of new faults preferentially occurred for faults dipping opposite to the direction of tilt, with propagation perpendicular to bedding. The presence of early bedding-perpendicular joints in the competent sandstone units aided propagation of these faults during tilting and this preferential asymmetric development. Bedding-parallel slip surfaces were activated as normal faults during the later stages of bedding tilting, showing complex interaction patterns with later faults downthrowing in the direction opposite to bedding tilting. Hence knowledge of the timing between tilting of the strata and deformation helps in evaluating the likely complexity of fault arrays at subseismic scales in extensional basins, and may also help in understanding the evolution of fault systems in tilted normal fault blocks at the reservoir scale.

We present an analysis of fault hydraulic architecture, based on >700 spatially distributed ground and geothermal spring temperature measurements taken in an active fault zone. Geostatistical simulations were used to extrapolate the measured data over an 800 x 100 m area and develop a high-resolution image of temperatures in the fault. On the basis of the modeled temperatures, a simple analytical model of convective heat transport was used to infer a probability distribution function for hydraulic conductivities in a two-dimensional plane parallel to the land surface, and the partitioning of flow between flow paths of different conductivities was calculated as a fraction of the total flux. The analysis demonstrates the existence of spatially discrete, high-permeability flow paths within the predominantly lower-permeability fault materials. Although the existence of fast-flow paths in faults has been hypothesized for >10 yr, their prevalence and contribution to the total flow of fluid in a fault zone are debated. On the basis of our findings, we conclude that the flux transmitted by an individual fast-flow path is significantly greater than that of an average flow path, but the total flux transported in fast-flow paths is a negligible fraction of the total flux transmitted by the fault. Keywords: fault hydrology, geothermal, heterogeneity, geostatistics, groundwater.

[1] The late Variscan Anti-Atlas of Morocco shows some conspicuous deviations from the standard anatomy of foreland fold-and-thrust belts. Large basement inliers crop out at a very short distance of less than 50 km behind the southeastern front of the fold belt, reminiscent of Windriver-style basement uplifts. In contrast to the Rocky Mountain foreland, however, the Anti-Atlas basement uplifts punctuate tightly folded Paleozoic cover series similar in tectonic style to the Appalachian Valley and Ridge province. Cover shortening is exclusively accommodated by Buckle folding, and the Anti-Atlas fold belt lacks any evidence for duplexing or thrust faults other than the occasional steep reverse fault found near basement inliers. Basement domes have classically been considered as the result of vertical tectonics in a horst and graben fashion, or, alternatively, as large 'plis de fond' [Argand, 1924], basement folds. Unfolding of a large portion of an Ordovician quartzite marker bed reveals a minimum shortening of 17% (30 km). Balancing this section at the crustal scale indicates a lower crustal detachment level at 18 to 25 km depth. Basement shortening is inferred to be accommodated through massive inversion of former extensional faults, inherited from a Late Proterozoic-Lower Cambrian rifling phase. INDEX TERMS: 8005 Structural Geology: Folds and folding: 8015 Structural Geology: Local crustal structure: 8102 Tectonophysics: Continental contractional orogenic belts; 8159 Tectonophysics: Rheology--crust and lithosphere: 9305 Information Related to Geographic Region: Africa; KEYWORD: Anti-Atlas, tectonics, balanced cross Section, folding, foreland fold and thrust belt. Citation: Helg, U., M. Burkhard, S. Caritg, and C. Robert-Charrue (2004), Folding and inversion tectonics in the Anti-Atlas of Morocco, Tectonics, 23, TC4006, doi: 10.1029/2003TC001576.

[1] The South Falkland basin is a partially filled Cenozoic foreland basin located south of the Falkland Plateau. It was formed by flexure of this southern edge of the South American plate when the load represented by Burdwood Bank collided. This continental fragment belongs to the predominantly oceanic Scotia plate. Flexure probably started in early Cenozoic times and has continued to the present day. The whole region is submarine and so the detailed stratigraphy and structure of the basin has been well imaged by seismic reflection profiling. The clarity of this imagery has made analysis of structures within the collision zone possible. The plate boundary itself is an active oblique thrust fault which has controlled the growth of a frontal fold. There is evidence for older phases of thrusting and folding further south. Within and beneath the sediments which blanket the flexed South American plate, normal faulting occurs on a variety of scales. Episodes of stratigraphic growth associated with the largest of these faults demonstrates that they were active during flexural bending. We have modeled the development of the South Falkland basin using two different approaches, both of which are based upon the simplest elastic model. Inverse modeling of free-air gravity and bathymetric profiles suggest that the elastic thickness of the loaded crust is 5-20 km. A complementary approach based upon the spectral analysis of free-air gravity and bathymetry shows that the elastic thickness is 15 [+ or -] 5 km. Both techniques indicate that the flexed continental lithosphere is weak, a conclusion supported by the presence of normal faults within the flexed plate. A small increase in elastic thickness from west to east appears consistent with a change in the density and penetration of normal faulting. INDEX TERMS: 8149 Tectonophysics: Planetary tectonics (5475); 8110 Tectonophysics: Continental tectonics--general (0905); 3025 Marine Geology and Geophysics: Marine seismics (0935): 1236 Geodesy and Gravity: Rheology of the lithosphere and mantle (8160); 1219 Geodesy and Gravity: Local gravity anomalies and crustal structure: KEYWORDS: foreland basin, elastic thickness, continental collision, normal faults, Falkland Islands, flexure. Citation: Bry, M., N. White, S. Singh, R. England, and C. Trowell (2004), Anatomy and formation of oblique continental collision: South Falkland basin. Tectonics, 23, TC4011, doi:10.1029/ 2002TC001482.

[1] The Nordfjord-Sogn Detachment (NSD) zone of western Norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits, suggesting that the zone experienced substantial displacement during Devonian extensional denudation of the Caledonides. Renewed activation occurred in Permian and Jurassic-Cretaceous times. The detachment zone consists of a succession of fault-related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing. In more detail, the lower 1-2 km thick section of the NSD zone consists of mylonites with various protoliths, showing a general upward decrease in metamorphic grade. The mylonitic section is truncated by the NSD fault, defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins. In an attempt to provide precise descriptions of the observed fault rocks, we classify these rocks into (1) noncohesive breccias, (2) cemented and indurated breccias of secondary cohesion, and (3) cataclasites, phyllonites, and mylonites formed with primary cohesion. Along and across-strike sections of the fault reveal the spatial and temporal relationships of the NSD fault. The fault zone consists of a lower section of phyllonites and cataclasites, reaching a total thickness of 50-70 m. Significant volumes of pseudotachylyte were injected into these fault rocks, and were later reworked. Reactivation of the fault is suggested by overprinting carbonate-cemented breccias that are cut by a discrete fault itself associated with breccias and gouge. By comparing the various fault rocks and their formation mechanisms, some constraints can be applied to the unroofing history. The NSD fault developed in the ductile-brittle transition zone of the crust, where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening, before hardening caused a return to frictional flow. At the same time, repeated pulses of pseudotachylyte were generated, possibly lubricating the fault zone and contributing to strain localization. These pseudotachylyte pulses also show that the fault was affected by seismic slip events, before returning to a creep regime within a wider section than that ruptured by earthquakes. Younger cemented breccias and noncohesive breccias and gouge reflect earthquake-rupturing and frictional flow within the seismogenic Crust. INDEX TERMS: 5112 Physical Properties of Rocks: Microstructure; 5114 Physical Properties of Rocks: Permeability and porosity; 5120 Physical Properties of Rocks: Plasticity, diffusion, and creep; 8010 Structural Geology: Fractures and faults; 8159 Tectonophysics: Rheology--crust and lithosphere: KEYWORDS: fault rocks, detachment, Norway, extension, brittle-ductile transition. Citation: Braathen. A., P. T. Osmundsen, and R. H. Gabrielsen (2004), Dynamic development of fault rocks in a crustal-scale detachment: An example from western Norway, Tectonics, 23, TC4010, doi: 10.1029/2003TC001558.

[1] At Iranian longitude, the Arabian plate is moving northward relative to Eurasia (~20 mm [yr.sup.-1] according to GPS). To the east, this relative motion is accommodated by northward subduction under the E-W Makran emerged accretionary prism. To the west, it is accommodated partly by the Zagros fold-and-thrust belt and partly by the Alborz/Kopet Dagh deforming zones further north. This work investigates the NNW striking transition zone that connects Zagros and Makran: the Minab-Zendan fault system. Satellite images, and structural and geomorphic field observations show a distributed deformation pattern covering a wide domain. Five north to NW trending major faults were identified. They exhibit evidence for late Quaternary reverse right-lateral slip, and correspond to two distinct fault systems: the western one transferring the Zagros deformation to the Makran prism, and the eastern one northward transferring the deformation to the Alborz/Kopet Dagh. Tectonic study and fault slip vector analyses indicate that two distinct tectonic regimes have occurred successively since the Miocene within a consistent regional NE trending compression: (1) an upper Miocene to Pliocene tectonic regime characterized by partitioned deformation, between reverse faulting and en echelon folding; (2) a NE trending [[sigma].sub.1] axis transpressional regime homogeneously affecting the region since upper Pliocene. The change is contemporaneous with major tectonic reorganization regionally recorded. Therefore this study provides evidence for active deformation that is not localized, but distributed across a wide zone. It accommodates the convergence and transfers it from collision to subduction by transpressional tectonics without any partitioning process in the present-day period. INDEX TERMS: 8122 Tectonophysics: Dynamics. gravity and tectonics: 8102 Tectonophysics: Continental contractional orogenic belts: 8105 Tectonophysics: Continental margins and sedimentary basins (1212); 8010 Structural Geology: Fractures and faults: 9320 Information Related to Geographic Region: Asia: KEYWORDS: Zagros, Makran, Arabia, Collision, Subduction, transpressional, partitioning, active tectonics. Citation: Regard, V., O. Bellier, J.-C. Thomas, M. R. Abbassi, J. Mercier, E. Shabanian, K. Feghhi, and S. Soleymani (2004), Accommodation of Arabia-Eurasia convergence in the Zagros-Makran transfer zone, SE Iran: A transition between collision and subduction through a young deforming system, Tectonics, 23, TC4007, doi: 10.1029/ 2003TC001599.

[1] Thermochronological investigations of samples collected west of the Alpine Fault zone provide new insight into the early development of the Australian-Pacific (AUS-PAC) plate boundary through New Zealand that is not preserved elsewhere in the modern orogenic system of the South Island. The [sup.40] Ar/[sup.39] Ar, fission track, and (U-Th)/He ages for these samples span the Cenozoic and provide direct constraints on the timing and character of two discrete episodes in the evolution of this tectonic boundary. The initial propagation of the AUS-PAC boundary through the South Island in the early Miocene is expressed as short-lived, geographically localized cooling, which we infer to be due to exhumation, beginning at 23-25 Ma. This is consistent with development of this boundary as an initially distributed zone of deformation, progressively localizing onto discrete fault structures developing primacy of strain accommodation over time. Regionally synchronous development of rapid cooling at 8 Ma corroborates the association of the present obliquely convergent character of the AUS-PAC boundary through the South Island with a marked change in Pacific plate motion at that time. Subsequent increases in cooling rate and a regionally prominent 5 Ma thermochronologic signal illuminate the progressive adaptation of the plate boundary to this new tectonic system over a period of ~3 Myr, culminating in development of the extant tectonic regime. INDEX TERMS: 1035 Geochemistry: Geochronology: 8102 Tectonophysics: Continental contractional orogenic belts: , 8107 Tectonophysics: Continental neotectonics; 8150 Tectonophysics: Plate boundary--general (3040); 8158 Tectonophysics: Plate motions--present and recent (3040); KEYWORDS: Southern Alps, Alpine Fault, tectonic evolution, argon, thermochronology, Australian-Pacific plate. Citation: Batt, G. E., S. L. Baldwin, M. Cottam, P. G. Fitzgerald, M. T. Brandon, and T. L. Spell (2004), Cenozoic plate boundary evolution in the Sooth Island of New Zealand: New thermochronological constraints. Tectonics. 23, TC4001. doi:10.1029/2003TC001527.

[1] It is shown, by numerical modeling, that the recent deformation pattern observed in the northern Apennines, mainly characterized by progressive eastward migration and bowing of the belt, thrusting activity along its external front, and tensional tectonics in the internal area, can be reproduced, at a first approximation, by applying a belt-parallel (SE-NW) compression to the chain, which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones. The above compressional regime, obtained by imposing kinematic boundary conditions to the model, causes the outward escape of crustal wedges from the chain, in particular the northeastward displacement of the Romagna-Marche-Umbria Units and the counterclockwise rotation and northwestward displacement of the Ligurian Units. This kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area, in line with the observed features that concern both strain style and orientation of principal strains. Evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed. Numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central Apennines on tectonic and seismic activity in the northern Apennines. INDEX TERMS: 8110 Tectonophysics: Continental tectonics--general (0905); 8102 Tectonophysics: Continental contractional orogenic belts; 8107 Tectonophysics: Continental neotectonics: 8123 Techonophysics: Dynamics, seismotectonics: 8164 Tectonophysics: Stresses--crust and lithosphere: KEYWORDS: northern Apennines, numerical modeling, extrusion tectonics, Mediterranean, Citation: Viti, M., J. De Luca, D. Babbucci, E. Mantovani, D. Albarello, and F. D'Onza (2004), Driving mechanism of tectonic activity in the northern Apennines: Quantitative insights from numerical modeling, Tectonics, 23, TC4003, doi:10.1029/2004TC001623.

Field data from the Oligocene--Miocene Gulf of Suez rift demonstrate that coeval growth faults, folds, and transfer zones exerted a major control on synrift stratigraphic sequence development. Growth folds in the Suez rift are related to steeply dipping normal faults that propagated upward, resulting in broad, upward-widening monoclines in overlying strata. Folding during fault propagation was accommodated by layer-parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault. The eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall. This evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments. Synrift sediments display onlap and intra-formational unconformities toward the growth monoclines and buried faults, whereas they diverge into broadly synclinal expanded sections away from the growth monocline. Continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments, each successively younger sequence dipping basinward at a shallower angle than the previous one. The resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults. Along-strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low-relief transfer zones. Data from other rift basins indicate that fault-propagation folds are not unique to the Gulf of Suez. Keywords: extension, folding, propagation, sedimentation, Sinai, syntectonic.

The link between back arc extensional tectonics and the emergence history of eclogite bearing units in the Cycladic islands in the Aegean Sea, in the island of Corsica and in the internal Betic Cordillera of the Alboran Sea, is examined. The tectonic style associated with the denudation of Mediterranean eclogites fits an active accretionary-wedge setting.

The hinterland of Spitsbergen's Tertiary fold-thrust belt on the Svalbard archipelago contains a major orogen-parallel lineament from Svartfjella to Eidembukta to Daudmannsodden (SEDL). Structural analyses suggest three stages of evolution of SEDL. A sinistral motion with a backthrust component followed ENE-directed overthrusting and was followed by dextral strike-slip motion. Thus a change from orogen-perpendicular to orogen-parallel motion is suggested. In the foreland, however, the movements were possibly coeval. A model explains this difference between the hinterland and foreland.

Olistoliths of interbedded sandstone and mudstone, and bedded chert compose the Kalvag Melange on Froya, western Norway. These deformational structures likely occurred due to gravitational block gliding in Early Paleozoic olistotromal activity. Large listric extensional, bedding-parallel and synthetic faults with ramp-flat geometries are the major features of the structures. The process of sedimentary melange formation can be better understood by the sequential formation and movement of structures within the olistoliths.

Field and U-Pb geochronological surveys of the Modi Khola area, central Nepal reveal a close temporal/spatial link between contractional and extensional deformation on the bounding fault systems represented by the central Annapurna Range. A gravitational collapse appears to have resulted in alternations between shortening and extension over a few million years that represent the Early-Middle Miocene structural history of the Himalayan orogen. The survey shows a high strain zone concentrated along the Chromrong thrust with the most recent displacement occurring as early as Pliocene.

The sampling of radionuclides along natural fractures and faults is an effective method for the detection of underground nuclear explosions that do not fracture the surface. The 133Xe and 37Ar radionuclides produced by a simulated 1-kilotonne nuclear explosion at the Rainier Mesa, Nevada Test Site, can be detected almost 50 and 80 days after the explosion. The trace gases move along the faults and fractures due to barometeric pressure differences. The short-lived highly dilute radionuclides are transported to the surface within a few weeks to an year.

The seismic reflection method, assisted by geological maps and cross-sections, borehole data and stratigraphic studies, provides the tectonic history of the southern Rocky Mountain trench. Rifting during Proterozoic created the basement ramp upon which sedimentation and culmination occurred throughout Mesozoic. The gravitational instability in uplifted terrain during Tertiary resulted in normal faulting, thus creating the trench. The hinge of the basal detachment controls the trench location. Relationship with the northern Rocky Mountain trench is studied.

A strike-slip model is more suitable than the extension and strike-slip model given by James E. Evans, to explain the Chumstick and other correlative basins of the central Washington Cascades. An initial isostatic footwall uplift due to extensional deformation in the Leavenworth and Entiat-Eagle Creek fault systems, as suggested by Evans, is impossible. The geology of Leavenworth fault area conflicts with the proposed features of footwall upliftment. There are differences between the vertical and the stratigraphic thickness in the Chumstick Formation.

Seismic reflection data from the Trans-Hudson Orogen, Canada, show high-angle faults in the upper crust and low-angle ductile shearing in the rest of the crust. The folding and southwestern fault wedges extrusion are present only in the upper crust. The series of orogen-parallel faults and folds are linked to postcollisional intracontinental deformation. There is a kinematic relation between the high-angle fault/fold structures and low-angle detachment shear zones. The faults in the upper crust produced southwest extrusion of the inner part of the orogen.

The along-axis segmentation of the Afar Rift system, Africa, changes from border fault dominated segmentation to magmatic oceanic-style segmentation. The length and the width of the basins in the active rift zones decrease from south to north, and the volume of the Quaternary basaltic magmatism increases. This indicates that the older and longer faults have been replaced by shorter faults. The new border faults generate escarpments that are topographically smaller than those generated by the older border faults.

The Caledonides of the west of Ireland provide a well-exposed and well-mapped example of an oblique collision zone. The east-northeast trending Deer Park and Achill Beg Fault system is a crustal scale ductile sinistral strike-slip duplex of late Ordovician age, imbricating late Precambrian granulite facies lower crustal rocks, near eclogite facies supracrustal rocks, up to amphibolite facies Dalradian metasedimentary rocks and greenschist facies Cambro-Ordovician rocks. This fault system is correlated with a pre-Devonian component of the Highland Boundary Fault system in southern Scotland. In the Clew Bay area, the high pressure-low temperature facies metamorphic rocks, in tectonic contact with greenschist facies Cambro-Ordovician rocks, are together interpreted as an accretionary prism complex related to northwestward directed subduction. Both of these are allocthonous terrains with respect to the Dalradian terrane to the north (North West Mayo). To the south, the Cambro-Ordovician rocks docked with a probable Dalradian block containing ultramafic intrusives (Deer Park Complex) during the late Ordovician. The Deer Park Complex and South Mayo Trough linked earlier, during the Arenig. Silurian and Lower-Middle Devonian redbed successions sit unconformably on the metamorphic rocks. Deposition and deformation of these cover rocks was controlled by oblique strike-slip movements on the Leck Fault whose strike swings from west-northwest to north-northeast, following earlier basement trends, as it is traced eastwards from Clew Bay. The Leck Fault System may be correlated with the Leannan Fault of northwest Donegal, a splay of the Great Glen Fault system of central Scotland. East of Clew Bay, this sinistral shear generated local dilation on the more northerly trending bend of the Leck Fault. Lower and Middle Old Red Sandstone redbeds were developed here. The west-northwest trend of the Leck Fault in Clew Bay acted as a compressional bend during these sinistral movements and transpressional southwest directed thrusting developed in Silurian rocks. Post-Middle Old Red Sandstone pre-late Tournaisian dextral displacement on the Leck Fault reversed this pattern with transtension in Clew Bay allowing intrusion of small carbonated peridotite bodies into Silurian rocks and easterly directed thrusting of Middle Old Red Sandstone rocks east of the Bay on the transpressional north-south bend. A tectonic model for the region is presented here. This model involves a northwestward directed subduction system, 150 to 750 km of Arenig sinistral strike slip movement, and eastwards insertion of the Connemara block with formation of the Ordovician South Mayo Trough as a pull-apart basin. Subsequently, a further 130 to 650 km eastward displacement of rocks took place south of the Deer Park Fault in later Ordovician times. The magnitudes of these estimates are directly proportional to an assumed maximum wavelength of 1500 km for promontories on the original Laurentian margin, and using the current juxtaposition of terranes, a minimum wavelength of 300 km is inferred.

The Orlock Bridge Fault separates the Ordovician and Silurian turbidite sequences within the Southern Uplands thrust belt. A large biostratigraphical break and the 1 km wide sinistral Slieve Glah Shear Zone associated with the fault in northern Ireland led to previous interpretation as a major regional structure, possibly a terrane boundary. In Scotland, however, the stratigraphical break is much less and an association with inliers of the Moffat Shale Group suggests that the fault is essentially similar to the other tract-bounding faults which originated as syn-[D.sub.1] thrusts within the imbricate stack. Localized sinistral deformation apparent along the trace of the Orlock Bridge Fault in southwestern Scotland, associated with post-[D.sub.1] reactivation, is comparable to that seen at Slieve Glah. Further east, a broad zone (up to 8 km) of sinistral ductile deformation, the Moniaive Shear Zone, is recognized adjacent to the Orlock Bridge Fault over a strike length of about 100 km. However, this zone differs from the Slieve Glah Shear Zone in its width and its location relative to the fault, suggesting that it is not simply related to the fault but represents a more regional deformation. Sinistral reactivation of the Orlock Bridge Fault was possibly initiated in the Wenlock during the peak of sinistral shear at the thrust front, although it may have developed over a long time contemporaneously with, but locally post-dating, the Moniaive Shear Zone. The latter deforms porphyroblasts with the thermal aureole of the c. 392 Ma Caimsmore of Fleet granite pluton, which was emplaced into and largely post-dates the shear zone, but is deformed by the Orlock Bridge Fault. Major dip-slip reactivation of the fault post-dates the Moniaive Shear Zone and regional metamorphism and probably occurred in the Carboniferous or Permian. There is some evidence for a deep crustal feature coincident with the Orlock Bridge Fault, possibly the boundary between different crustal blocks in the collage of terrane fragments accreted during the final closure of Iapetus, which may explain the unusual extent of the reactivation of the Orlock Bridge Fault within the allochthonous Southern Uplands thrust stack. However, the situation of the fault within the Southern Uplands terrane and, in Scotland, the biostratigraphical evidence of no major stratigraphical break across the fault and the lack of any clear relationship between the Orlock Bridge Fault and the Moniaive Shear Zone indicate that the fault should not be regarded as a terrane boundary.

Examination of Themed Fault, a 200-km-long, E-W-oriented, high-angle right-lateral strike-slip fault, extending through central Sinai, helps analyze its slip sense, deformation type, relation to Tih Plateau and timing. Kinematic studies explain the relation of slip on this fault with Suez rift and the Dead Sea transform. Themed Fault exhibits a correlation with reactivation of Early Mesozoic Passive continental margin of north Sinai. Four different phases of central wrenching reactivate the E-W to ENE-WSW-oriented faults in northern Egypt.

The Grand Valley-Star Valley fault between Snake River and Salt River has uniformly tilted fault-bounded blocks. Tilting of the hanging wall decreases with increasing distance from the fault, similar to the tilts northeast of Beaverhead fault. Tilt data flexural calculations show that internal block formation induces rigid behavior of the tilts. Tilting patterns in this Basin and Range province are consistent with a flexural length scale of approximately 8-12 km and deflections of 2-4 km.

Seismic reflection data shows a wide zone of trench-parallel normal faults in the upper trench slope off the Nicoya Peninsula, Costa Rica. This fault extends to accretionary prism through the sedimentary apron, exhibiting a deep-seated deformation process. Underplating changes in basal shear stress and subduction erosion influence the Costa Rica forearc extension. Structural anisotropy in the prism influences the normal fault deep and accretion process is related to the extensional reactivation of previous thrust faults.

Geodetic and geologic studies in California reveal a right-lateral shear zone that exhibits Holocene and Pleistocene fault activity. A tectonic model for the fault activity indicates that the shear zone causes the relative motion between North American and Juan de Fuca plates and Pacific-North American transform motion. Zonal activity continues throughout eastern California and northwestern Nevada and links the seismically active regions.