Analysis Of Fault-slip Data Research Articles

Oblique rifting triggered by slab tearing: the case of the Alboran rifted margin in the eastern Betics

Abstract. The tectonic evolution of highly oblique continental margins that result from extension above lithospheric subduction–transform edge propagator (STEP) faults is poorly understood. Here, we investigate the case of the Alboran margin in the eastern Betics characterized by crustal thinning of 15–10 km, oblique to the direction of slab retreat. The current deformation patterns indicate that oblique rifting is underway. However, it is unclear whether these conditions are those that prevailed during the formation of the metamorphic domes and intramontane basins. We review the temporal and spatial evolution of Neogene sedimentary basins and brittle deformation in the eastern Betics and exploit offshore seismic reflection lines to propose a crustal-scale section across the oblique margin. The history of sediment infill and rates of subsidence combined with the analyses of fault slip data confirm that brittle extension oriented from north 20∘ E to E–W occurred during an interval spanning from the Serravallian–early Tortonian to the late Tortonian (14–8 Ma). This extension is associated with both normal and strike-slip regimes and the evolution of the strike-slip fault zones flanking the metamorphic domes. The transtensional model forms a coherent scheme linking the ductile deformation associated with metamorphic domes and the formation of E–W- and NW–SE- or NNW–SSE-directed sedimentary basins in the brittle upper crust during the Tortonian. The oblique extension, which is closely associated with STEP faulting, occurred during the regional convergence between Africa and Iberia since the Miocene. Only recently, around 8 Ma, has slab detachment started to migrate westward, leading to tectonic inversion in the eastern Betics. Such a type of narrow oblique-rifted margin associated with transform-like plate boundaries is not unique but is expected to be hardly preserved in the geological record due to the transient nature of retreating subduction systems.

Structural controls on formation of the Xiayu vein-hosted Ag–Pb–Zn–Au orefield during intracontinental extension along the southern margin of the North China Craton

The Xiayu Ag–Pb–Zn–Au deposit, situated in the Early Cretaceous Xiong’er shan area on the southern edge of the North China Craton, comprises the Haopinggou, Shagou, Tieluping, and Houzhanggou deposits, making it the largest Ag producer in the southern North China Craton. Despite significant research efforts, the connection between extensional faults and vein–hosted Ag–Pb–Zn–Au deposits in this area is still not well understood. To address this issue, we introduce new structural data, fault–slip data analysis, and information on epithermal Ag–Pb–Zn–Au mineralization. Two separate paleo–stress inversion methods were applied to determine that the region was affected by two discrete stress fields: E–W transtension and NW–SE transtension. Our palaeostress reconstruction indicates that transtensional tectonics would have affected the emplacement of fault–fill veins (stage I) and extensional veins (stage II). Both types of geometric veins show two distinct stages of formation. The first stage (I) involves the development of quartz–pyrite within hydraulic breccia, transitioning into crack–seal laminated shear veins. These likely formed during a period of regional extension in an east–west direction. The second stage (II) features the deposition of undeformed quartz–sphalerite–galena within pre–existing dilational sites near newly formed normal faults or stage I veins. This second stage likely occurred during a regional extension in a northwest–southeast direction.

Kinematic analysis of the mesozoic - Early Cenozoic deformation in the paipote basin (27°10′S)

An integrated structural and kinematic study focused on the characterization of an Andean Mesozoic basin was carried out in the upper stream of the Paipote Creek, in the western limit of the Southern Puna, Fault slip data analysis (n = 80) and structural observations at different scales were collected from Triassic to Upper Cretaceous volcanic and sedimentary units to constrain the structural architecture and the kinematic evolution of the area. Regional observations provide evidence for syntectonic extensional deposition during the Triassic - Jurassic and positive tectonic inversion from at least the Late Jurassic. Extensional features such as growth strata, harpoon structures and roll-over anticlines, helped to infer two main depocenters controlled by west dipping listric faults. E-W extension directions have been recognized in Triassic - Jurassic units, linked to an extensional basin architecture, and mixed contraction directions were related to compressional and strike-slip deformation in the area. A forward model is proposed based on the interpreted architecture in depth of the basin, defining two major depocenters that, together, define the Paipote basin. A shortening estimate of 21% (5,44 km) was calculated for the basin, wich corresponds to the lowest shortening values reported for the Triassic-Jurassic basins in the Atacama region. The strike-slip deformation can be associated previously with recognized NW-SE strike-slip faults, and aids in proposing the Paipote basin as a transitional zone between the Lautaro basin to the south and the Potrerillos basin to the north.

Current Stress Pattern and Geodynamics of the Baikal Rift System

Abstract—The crustal stress field of the Baikal Rift System has been reconstructed by tectonophysical inversion of focal mechanisms from the catalog of earthquakes recorded by the regional seismological network. Cataclastic analysis of fault slip data developed at the Shmidt Institute of the Physics of the Earth (Moscow) revealed previously unknown features in the behavior of principal stresses. Namely, the maximum deviatoric stresses diverge off the rift axis while the normalized spherical and deviatoric stress tensor components reach high magnitudes in the crust of the Baikal Basin. The obtained stress pattern of the Baikal Rift System is consistent with the rift origin by a joint action of a vertical mantle flow (upwelling branch of convection) and a horizontal flow in the asthenosphere which drives the NW–SE motion of the Amur plate off Eurasia.

KINEMATIC ANALYSIS OF BALANTAK FAULT USING FAULT-SLIP DATA IN BALANTAK AREA, BANGGAI REGENCY, CENTRAL SULAWESI

Balantak is one of the sub-districts in Banggai Regency, Central Sulawesi Province. The research area is along the Balantak Strike-Slip Fault. This study presents geological mapping with focus on the deformation style that occurred within the area. The study provides an analogue of strike-slip structural trap types in convergent setting to support oil and gas field development. This research method was conducted using field observation and kinematic analysis of fault-slip data. Lithology in the study area that is part of the Banggai-Sula microplate has the characteristics of sedimentary rocks that are grainstone intercalating calcareous sandstone and rudstone consisting of limestone fragments. While part of the Sulawesi East Arm has crystalline rocks in the form of ultramafic-mafic rocks such as Peridotite, Serpentinite, Gabbro and Basalt. Structural analysis along the strike-slip fault indicates the collision of Banggai-Sula with Sulawesi East Arm on the side part of the micro-plate generates thrust fold belt along with well-developed uniform tearing faults present. The orientation and shape of the strain ellipsoid is pure shear transpression with the Balantak Fault as its plane of movement. The characteristic of the structure pattern complying with the model shows that the type of structures is en echelon thrusts and folds while the tearing faults are Riedel synthetics of the Balantak dextral Strike-Slip Fault that developed offset on the fold structures.

Kinematic analysis of fault-slip data in the Nanling Tectonic Belt and Cretaceous to Paleogene tectonic evolution of the Central South China Block

• Six tectonic events were inversed from fault-slip analysis in the Nanling Tectonic Belt. • Four Cretaceous tectonic events resulted from the Paleo-Pacific subduction . • Two Paleogene tectonic events were due to the far field effect of the India-Asia collision. Cretaceous tectonic events and Cenozoic geodynamics of the central South China Block are still under debate. A long-term extensional regime or two extension-contraction tectonic cycles were proposed for the Cretaceous tectonic evolution. While Cenozoic geodynamics of the central South China Block were ascribed to the Pacific subduction or the far field effect of the India-Asia collision. Kinematic analysis of fault-slip data were carried out for the Cretaceous to Paleogene Chaling-Yongxing Basin and the Lianshan-Yangshan Domain in the Nanling Tectonic Belt. Kinematic analysis of fault-slip data (409 groups of faults and striations) reveal four Cretaceous tectonic events and two Paleogene tectonic events. i) The early Early Cretaceous extensional regime is represented by a NW-SE horizontal minimum principal stress and a vertical maximum principal stress, which generated NE-striking boundary normal faults of Early Cretaceous basins. ii) The late Early Cretaceous strike-slip regime is characterized by a N-S horizontal maximum principal stress and a E-W horizontal minimum principal stress, which led to tectonic inversion of Early Cretaceous extensional basins and nearly N-S-striking folding of the Lower Cretaceous. iii) The early Late Cretaceous extensional regime is represented by a NW-SE horizontal minimum principal stress and a vertical maximum principal stress, which activated the NE-striking boundary normal faults of Late Cretaceous basins. And iv) the latest Late Cretaceous strike-slip regime is characterized by NW-SE horizontal maximum principal stress and a NE-SW horizontal minimum principal stress, which led to tectonic inversion of Late Cretaceous extensional basins and NNE-striking folding of the Upper Cretaceous. Orientations of maximum or minimum principal stresses imply that two extension-contraction tectonic cycles during the Cretaceous resulted from the Paleo-Pacific subduction. Two Paleogene tectonic events are v) the strike-slip regime characterized by NE-SW horizontal maximum principal stress and a NW-SE horizontal minimum principal stress, and vi) the subsequent extensional regime represented by a NE-SW minimum principal stress and a vertical maximum principal stress. The former generated NW-striking reverse faults and reactivated strike-slipping of NE- and NW-striking conjugate faults whereas the latter formed NW-striking normal faults in the Lower Paleogene clastic rocks. Orientations of maximum or minimum principal stresses indicate that two Paleogene tectonic events in the central South China Block were attributed to the far field effect of the India-Asia collision and subsequent stress relief.

Paleostress reconstruction of faults recorded in the Nied\u017awiedzia Cave (Sudetes): insights into Alpine intraplate tectonic of NE Bohemian Massif

Brittle structures identified within the largest karstic cave of the Sudetes (the Niedźwiedzia Cave) were studied to reconstruct the paleostress driving post-Variscan tectonic activity in the NE Bohemian Massif. Individual fault population datasets, including local strike and dip of fault planes, striations, and Riedel shear, enabled us to discuss the orientation of the principal stresses tensor. The (meso) fault-slip data analysis performed both with Dihedra and an inverse method revealed two possible main opposing compressional regimes: (1) NE–SW compression with the formation of strike-slip (transpressional) faults and (2) WNW–ESE horizontal compression related to fault-block tectonics. The (older) NE-SW compression was most probably associated with the Late Cretaceous–Paleogene pan-regional basin inversion throughout Central Europe, as a reaction to ongoing African-Iberian-European convergence. Second WNW–ESE compression was active as of the Middle Miocene, at the latest, and might represent the Neogene–Quaternary tectonic regime of the NE Bohemian Massif. Exposed fault plane surfaces in a dissolution-collapse marble cave system provided insights into the Meso-Cenozoic tectonic history of the Earth’s uppermost crust in Central Europe, and were also identified as important guiding structures controlling the origin of the Niedźwiedzia Cave and the evolution of subsequent karstic conduits during the Late Cenozoic.

Structural styles of the Aras fault zone with implications for a transpressive fault system in NW Iran

• NE-striking Aras Fault Zone (AFZ) bounds the Talesh and Lesser Caucasus blocks. • The AFZ is characterized by well-developed geological and geomorphological features. • Paleostress results along the AFZ indicate a similar tectonic regime since Pliocene. • The transpressive tectonic regime controls the structural evolution of the AFZ. • Transpressive tectonic regime leads to strain partitioning along the AFZ. Aras Fault Zone (AFZ) is one of the most important intra-plate fault zones within the Turkish-Iranian Plateau. The AFZ is divided into five fault branches based on geometrical and structural properties called the Aras Main, Horadiz, Khodafarin, Asadkandi, and Aslanduz fault branches. Our geometric and kinematic analysis indicates that these faults exhibit compressional left-lateral strike-slip fault characteristics with general directions of NE-SW and dipping to SE. Structural mapping has revealed that the NE section of the AFZ shows typical horsetail fault geometry. Few meters to approximately 17 km of left-lateral displacements were observed along the AFZ, indicating the occurrence of numerous historical earthquake events. Paleostress analysis of fault slip data reveals that the AFZ has developed in the dominant NNE-SSW and NE-SW oriented compressional stress regime. Evaluating the Ratio of Principal Stress Differences (R), Stress Regime Index (R'), and principal stress directions show that the zone is under the transpressional tectonic regime. Paleostress orientations are consistent with orientations of the GPS velocity vectors, which indicates that the region, including the AFZ, is under the effect of the same tectonic regime, at least since Pliocene. The amounts of strike-slip partitioning on discrete strike-slip faults are determined as 33–41%, which means at least 41% of total wrench components in the region have been accommodated by discrete strike-slip faulting along the AFZ. Results indicate that the simple shear component of total stress applied to the area is consistent with the GPS slip velocities.

Spatio-temporal variation of the strain field in the southern Central Andes broken-foreland (27°30′S) during the Late Cenozoic

We present an integrated structural and Anisotropy of Magnetic Susceptibility (AMS) study focused on the characterization of the spatio-temporal variation of the strain field during the main Neogene deformation, of the Argentine Precordillera and the northern Sierras Pampeanas, immediately to the south of the Puna plateau (27°30′S). The AMS from 43 sites and fault-slip data analysis from mesoscale faults (n = 540) were carried out in Lower Miocene to Middle Pliocene sedimentary and volcaniclastic rocks. The AMS results show moderate values of anisotropy degree near to deformation zones, and low and high values of bulk susceptibility. The most predominant magnetic fabric is sedimentary type I and II, with a weak magnetic lineation. In areas where the rocks are deformed, the incipient magnetic lineation are subparallel to the regional structural trend and present a main N–S orientation in the Precordillera and Fiambalá basin, while in the Sierras Pampeanas they are mostly NE-oriented. Combining these results with kinematic analysis from fault-slip data, we identify, in the Precordillera and Fiambalá basin areas, a contractional event with E-W main direction, from ~23 Ma to 5 Ma, mostly active from the onset of deposition of Neogene sequences. During this period, in the NW Sierras Pampeanas, the contraction directions follow a NW orientation. The onset of N–S to NNW contraction, mostly recognized in rocks younger than 5 Ma, exposed in the northern areas of Precordillera and Sierra Pampeanas, documents a change of the strain field during the Early-to-Middle Pliocene, associated with a shift in the contractional direction from E-W to N–S. We relate the change to the rapid uplift of the southern Puna, generating a juxtaposition of an area under N–S extension, affecting the topographically-higher Puna, with the other area under N–S contraction in the adjacent Precordillera and Sierras Pampeanas. We associate these two events as part of the evolution of this segment of the Andes, where the broken foreland setting is active during this time. By combining the AMS and kinematic analysis results, we obtain a timing for the spatio-temporal change of contraction directions, which allows us to compare both the broken-foreland and foreland basins to understand spatio-temporal strain variations.

Structural analysis of the Planchón-Peteroa Volcanic Complex: Insights for the geothermal system

The Planchón-Peteroa Volcanic Complex (PPVC) is located in the Transitional Southern Volcanic Zone of the Andean Ridge. Structural control of the main NNE-striking El Fierro fault system (EFFS) over the volcanic activity has been commonly assumed, although a paucity of evidence remains. The aim of this paper is to explore the relationship between the local stress field, the superficial structural setting and the geothermal fluid flow paths related to the volcanic complex. To conduct the structural analysis, this work combines remote sensing determination of lineaments, recognition of fracture patterns, with the inversion of kinematic indicators on outcrop scale faults, to finally evaluate the role of the local stress field over the 2D slip and dilation tendencies of the recognized structures. Mesoscale morphostructural lineaments present three main directions: ~E-W, ~NE-SW, and ~NW-SE. Major lineaments develop inflections, giving rise to left bends between the NW-SE to E-W along the strike, compartmentalized by ~ NNE trending lineaments. Strike-slip fault solutions with an ENE-WSW to NE-SW oriented shortening axis were obtained from fault-slip data analysis. The inversion of fault kinematic indicators constrains a Quaternary to recent strike-slip regime, with a ~ENE-WSW trending σ1, and a subvertical σ2. Under the defined local stress field, ~NE-SW and ~WNW-ESE oriented structures have high slip tendency, while those spanning from NE-SW to E-W are prone to dilate. Our analysis suggests that these transverse structures exert first-order controls on the location of Vergara Pass Hill, and Peñón River and Azufre River Valleys hydrothermal manifestations. It seems that intersection zones with submeridian structures, as EFFS, increase structural damage and facilitate hot fluid migration. Circulation would profit the most from ~ENE-WSW and ~NW-SE striking outcrop-scale faults and fractures associated with the damage zones.

Superposed deformation in the Península Mitre recess (Fuegian thrust-fold belt, Southern Argentina), and implications for orogenic curve kinematics

A detailed study of the structure of the Península Mitre recess in the Fuegian thrust-fold belt of southern Argentina reveals superposed deformation related to contrasting shortening directions. One group of structures trend parallel to the recess and verge either towards the foreland or towards the hinterland. A second group of structures accommodate contraction superposed on the previous group. Analysis of fault-slip data reveals that the first group is related to σ1 perpendicular to the surface traces of thrusts and/or fold axes, and are therefore compressive structures. In contrast, the paleostress tensors of the second group of structures show σ1 orientations parallel or at a low angle with respect to local structural trends. The style of the superposed structures of the second group, which mostly indicate contraction subparallel to the trend of the recess, is consistent with structures resulting from tangential longitudinal shortening associated with oroclinal bending. This scenario implies that the Peninsula Mitre recess formed as a progressive curve involving rotation due to slip trajectories convergent toward the recess, causing the observed tangential contraction. This kinematic model supports previous interpretations of buttressing of the thrust-fold belt against a basement promontory.

Plio-Quaternary stress states along the Kütahya Fault and surroundings, NW Turkey

The Kutahya Fault, which is one of the major neotectonic structures in western Anatolia, Turkey, is an active fault constraining the southern margin of the approximately E-W trending Kutahya Basin between the Eskisehir Fault to the north and the Simav Fault to the south. In the present study, inversion of both fault kinematic analysis of fault-slip data and focal mechanism solutions from the Kutahya Fault and surroundings is used to understand the Late Cenozoic stress states. The fault kinematic analysis result yielded three different stress regimes from Mio-Pliocene to Quaternary. Firstly, strike-slip faulting developed under a NE-SW trending local compressional regime with 51° ± 24° (σ1) and 140° ± 7° (σ3) trends and Rm ratio was calculated as 0.61, consistent with this faulting. NW-SE trending consistent extensional direction produced local normal faulting with 144° ± 3° (σ3) trend. Secondly, strike-slip faulting developed under a NW-SE trending local compressional regime showing 143° ± 17° (σ1) and 51° ± 10° (σ3) trends and Rm ratio was calculated as 0.51. Finally actual normal faulting developed under a NNE-SSW trend with a regional extensional direction showing 42° ± 14° (σ3) and Rm ratio of 0.56 at the present time. Inversion of the earthquakes gives a NNE-SSW extension direction with 21° ± 19° (σ3) trend and Rm ratio calculated as 0.68 at the triaxial. The Kutahya Fault and surroundings are under an extensional regime at the present time. The reason for the regionally effective NNE-SSW trending extensional regime in western and southwestern Anatolian is complex subduction processes (roll-back, retreat, delamination, slab-tear, slab-break-off and/or slab-pull) of the African Plate and the Anatolian Platelet in the Mediterranean region.

New active faults on Eurasian-Arabian collision zone: Tectonic activity of Özyurt and Gülsünler faults (Eastern Anatolian Plateau, Van-Turkey).

The Eastern Anatolian Plateau emerges from the continental collision between Arabian and Eurasian plates where intense seismicity related to the ongoing convergence characterizes the southern part of the plateau. Active deformation in this zone is shared by mainly thrust and strike-slip faults. The Ozyurt thrust fault and the Gulsunler sinistral strike-slip fault are newly determined fault zones, located to the north of Van city centre. Different types of faults such as thrust, normal and strike-slip faults are observed on the quarry wall excavated in Quaternary lacustrine deposits at the intersection zone of these two faults. Kinematic analysis of fault-slip data has revealed coeval activities of transtensional and compressional structures for the Lake Van Basin. Seismological and geomorphological characteristics of these faults demonstrate the capability of devastating earthquakes for the area.

Synextensional Emplacement of Porphyry Cu-Mo and Epithermal Mineralization: The Zijinshan District, Southeastern China

The Zijinshan district, Fujian Province, southeastern China, is a major mineral field that contains high- and intermediate-sulfidation epithermal Cu-Au-Ag and porphyry Cu-Mo deposits. This contribution discusses the structural geology and the tectonic regime prevalent during mineralization at Zijinshan. Statistically, the district is dominated by NW-striking fault systems that dip at moderate angles (40°–50°) to the northeast and southwest. They played a first-order role in controlling the emplacement of hydrothermal veins and breccias. Most NW-striking faults were active as oblique normal/strike-slip faults during mineralization, as evidenced by the geometry of syntectonic hydrothermal mineral fibers. NE-striking, steeply dipping faults also controlled the emplacement of hydrothermal veins and breccias, and these faults contain syntectonic mineral fibers indicating predominantly dextral strike-slip movements. The kinematic and dynamic analysis of fault-slip data shows that the predominant tectonic regime during mineralization was extensional, with subvertical σ 1 and NNE-to NNW-trending σ 3 . Secondary clusters of subhorizontal σ 1 suggest that short periods of fault reactivation under a strike-slip regime occurred locally. Although the formation of porphyry Cu-Mo systems is commonly thought to be favored by compressive to transpressive tectonic regimes, which lead to a diminution in the rate of volcanic output and to the entrapment of magmas and volatiles in the upper crust, these results show that at least medium-sized porphyry Cu-Mo systems can form under extensional conditions in previously thickened continental crust. This has important exploration implications globally. Based on current geologic knowledge, the district appears to have a high exploration potential at depth, mainly for intermediate-sulfidation epithermal and porphyry-style mineralization.

Stress field reconstruction in an active mudslide

Meso-scale structures from gravitational slope deformation observed in landslides and deep-seated gravitational slope failures are very similar to those of endogenous ones. Therefore we applied palaeostress analysis of fault-slip data for reconstructing the stress field of an active mudslide in Pechgraben, Austria. This complex compound landslide has developed in clayey colluvium and shale and was activated after a certain period of dormancy in June 2013. During the active motion on June 12, 2013, 73 fault-slip traces at 9 locations were measured within the landslide body. The heterogeneous fault-slip data were processed in term of palaeostresses, the reconstructed palaeostress tensor being characterized by the orientations of the three principal stress axes and the stress ratio (which provides the shape of the stress ellipsoid). The results of the palaeostress analysis were compared to airborne laser scan digital terrain models that revealed dynamics and superficial displacements of the moving mass prior and after our survey. The results were generally in good agreement with the observed landslide displacement pattern and with the anticipated stress regime according to Mohr-Coulomb failure criteria and Anderson's theory. The compressional regime was mostly registered at the toe in areas, where a compressional stress field is expected during previous mass-movement stages, or at margins loaded by subsequent landslide bodies from above. On the other hand, extension regimes were identified at the head scarps of secondary slides, subsequently on bulged ridges at the toe and in the zone of horst-and-graben structures in the lower central part of the main landslide body, where the basal slip surface probably had locally convex character. Strike-slip regimes, as well as oblique normal or oblique reverse regimes were observed at the lateral margins of the landslide bodies. The directions of principal stresses could be used as markers of landslide movement directions. Although the multiphase strain indicators were, in general, relatively poorly preserved, the palaeostress analysis revealed several different deformation phases at some landslide parts related to different evolution episodes of the complex landslide. Palaeostress analysis based on the multiple inversion method is an affordable approach for reconstructing stress fields within landslides in soft material. This method is an inexpensive and objective tool for stress field reconstruction even in heterogeneous stress field conditions where the distinction of different faults generations may be impossible.

Stepwise clockwise rotation of the Cenozoic stress field in the Western Carpathians as revealed by kinematic analysis of minor faults in the Manín Unit (western Slovakia)

This study aims at quantitative kinematic analysis of fault-slip data and palaeostress reconstruction of polyphase brittle structures developed in the Manin Unit cropping out in the Middle Vah River Valley of western Slovakia. The Manin Unit neighbours the Pieniny Klippen Belt that follows the boundary between the Paleogene accretionary wedge of the Outer Carpathians and the Cretaceous nappe system of the Central Western Carpathians. After the nappe emplacement during mid-Cretaceous times, the Manin Unit was incorporated into the Pieniny Klippen Belt and attained its complex tectonic style. Based on kinematic analysis of meso-scale faults with slickensides, six (D 1 –D 6 ) brittle deformation stages have been discerned. The relative succession of individual palaeostress states was derived from field structural relationships; their stratigraphic age was estimated primarily by comparison with other published data. Palaeostress analysis in the Manin Unit revealed the existence of six different palaeostress fields acting from the Middle Eocene to the Quaternary. The first three generations of meso-scale brittle structures were formed under a transpressional tectonic regime during the pre-Late Eocene–Early Miocene D 1 –D 3 deformation. Generally, the maximum horizontal stress axis rotated clockwise from a W–E to an approximately N–S direction. Thereafter, a transtensional tectonic regime was characterized by a WNW–ESE to NNW–SSE oriented minimum horizontal stress axis during Middle and Late Miocene D 4 –D 5 deformation. A general extensional tectonic regime influenced the structural evolution of the area in the Pliocene to Quaternary, when a gradual reorientation of the palaeostress field resulted in the development of variable, often reactivated, fault structures.

3D geometry and kinematic evolution of extensional fault-related folds, NW Red Sea, Egypt

Abstract Fault-related folds are common structural features found at a variety of scales in extensional settings, and have been recognized in both outcrop and subsurface studies. However, the detailed geometry and origin of complex 3D folds adjacent to normal faults are poorly known, and, in some cases, are interpreted to be due to strike-slip tectonics and post-rift contraction. Here we examine the 3D geometry of seismic-scale folds in a rift margin – the Red Sea – and discuss the interrelationship between the growth of normal faults and the development of their related folds. Detailed field mapping of the NW Red Sea rift system has shown that the rift margin is dominated by two large extensional fault systems formed by a series of linked NNW-, north–south- and NNE-striking fault segments. These linked segments exhibit distinct zigzag fault patterns and combine to form a number of NNW-trending faults that dip NE with dominant hanging-wall stratal dips to the SW. Hanging-wall stratal dips define 3D extensional fault-related synclinal folds in pre- and early synrift strata. The hanging-wall synclines are kilometre-scale, gently doubly plunging, with curved axial surface traces orientated sub-parallel to the bounding faults. Field data demonstrated that these folds are formed by along-strike variations in fault displacements, and they form transverse synclines combined with hanging-wall extensional fault-propagation folds. The complex 3D geometry of the hanging-wall synclines is the result of the along-strike segment linkage. Adjacent to the bounding faults, the stratal dips are sub-parallel to the faults as a result of extensional fault-propagation folding controlled by highly anisotropic pre-rift strata. Palaeo-strain analyses of fault-slip data, together with analysis of the fold geometry, clearly indicate that the faulting and folding in the NW Red Sea are formed by pure NE–SW extension during the Late Oligocene–Miocene rifting, and that contraction or strike-slip tectonics need not be invoked.

Kinematic Analysis of Fault-Slip Data in the Central Range of Papua, Indonesia

DOI:10.17014/ijog.3.1.1-16Most of the Cenozoic tectonic evolution in New Guinea is a result of obliquely convergent motion that ledto an arc-continent collision between the Australian and Pacific Plates. The Gunung Bijih (Ertsberg) Mining District(GBMD) is located in the Central Range of Papua, in the western half of the island of New Guinea. This study presentsthe results of detailed structural mapping concentrated on analyzing fault-slip data along a 15-km traverse of theHeavy Equipment Access Trail (HEAT) and the Grasberg mine access road, providing new information concerning thedeformation in the GBMD and the Cenozoic structural evolution of the Central Range. Structural analysis indicatesthat two distinct stages of deformation have occurred since ~12 Ma. The first stage generated a series of en-echelonNW-trending (π-fold axis = 300°) folds and a few reverse faults. The second stage resulted in a significant left-lateralstrike-slip faulting sub-parallel to the regional strike of upturned bedding. Kinematic analysis reveals that the areasbetween the major strike-slip faults form structural domains that are remarkably uniform in character. The changein deformation styles from contractional to a strike-slip offset is explained as a result from a change in the relativeplate motion between the Pacific and Australian Plates at ~4 Ma. From ~4 - 2 Ma, transform motion along an ~ 270°trend caused a left-lateral strike-slip offset, and reactivated portions of pre-existing reverse faults. This action had aprofound effect on magma emplacement and hydrothermal activity.

Kinematic Evolution of the Eastern Chalk Draw Fault during Basin and Range Extension: Evaluating the Role Played by Preexisting Structural Fabrics in Along-Strike Displacement Patterns

Basin and Range extensional structures in Trans-Pecos Texas have been interpreted to be strongly influenced by preexisting structures, including igneous centers in the Big Bend region. These igneous centers are interpreted to have deflected propagating faults, as they are rheologically strong relative to the surrounding rocks. We conducted detailed field mapping and analysis of fracture and fault data along the eastern segment of the Chalk Draw Fault in Big Bend National Park to evaluate its kinematic evolution and interaction with Paleogene plutons. Our primary results document the following key relationships: (1) the Rosillos Laccolith and other Paleogene plutons in the study area are pervasively fractured, dominantly by northwest-striking mode I fractures, which generally do not extend into adjacent sedimentary rock sequences; (2) throw on the eastern Chalk Draw Fault is strongly asymmetric, decreasing rapidly as it enters the Rosillos Laccolith; and (3) analysis of fault-slip data in the region documents dominantly N 52° E–directed regional extension along the northwest-striking segment of the Chalk Draw Fault and secondary structures. We interpret these relationships to indicate that the Rosillos Laccolith developed pervasive mode I fractures with a dominant northwest-southeast orientation during cooling under Basin and Range extensional stresses but that this occurred prior to extensional faulting within the region. We suggest that the highly fractured nature of the Rosillos Laccolith resulted in it being rheologically weaker than the surrounding Cretaceous sedimentary rocks, which resulted in (1) hindering southward propagation of the Chalk Draw Fault by dissipating stress at the fault tip within the highly fractured laccolith and (2) the strongly asymmetric distribution of slip due to a strong rheological contrast during fault propagation.

Pre-break-up palaeostress state along the East Greenland margin

This paper describes intraplate deformation and the palaeostress state along the East Greenland margin during the Paleocene between 65 and 55 myr ago, prior to the onset of the NE Atlantic spreading. It is shown that the pre-break-up deformation is the result of dip-oblique/strike-slip tectonics in the SE and compressive tectonics in the north. The reduced palaeostress tensors derived from inversion of the fault-slip data show that the maximum horizontal stress σ 1 is compressive and the orientations of σ 1 change from ENE–WSW in the south to NNE–SSW in the north. The reconstructed palaeostress trajectory map demonstrates that the σ 1 orientations reflect the plate motion path and define small circles whereas the trends of the minimum horizontal stress σ 3 converge and cluster around an area in the Arctic that is interpreted as the rotation pole of Greenland. The intraplate deformation, folding and uplift that affected the Greenland and European margins, the Barents Sea and the North Sea during the Paleocene can be explained by the counter-clockwise rotation of Greenland. The present paper calculates the pole of rotation of Greenland using the kinematics of brittle faults along the plate margin and the palaeostress derived from inversion of fault-slip data analysis as an indicator of motion path.