Fault Kinematic Analysis Research Articles

Structural records of the Late Cretaceous–Cenozoic extension in Eastern China and the kinematics of the Southern Tan-Lu and Qinling Fault Zone (Anhui and Shaanxi provinces, PR China)

Our study of the Late Cretaceous–Cenozoic extension in Eastern China is a kinematic analysis of faults (≈1500 striated fault data, 175 stress solutions at 90 sites) that has permitted us to separate stress fields belonging to six tectonic events. A WNW–ESE extension (1) has affected Eastern China from the Campanian to the Late Palaeocene–Early Ypresian. Under this extension, the Qinling (QLFZ) and Southern Tan-Lu (STLFZ) Fault Zones have been dextral transtensional fault zones. A first transpressional event (2) (NNE–SSW shortening) has occurred during the Late Ypresian–Lower Lutetian; the QLFZ and the STLFZ have been dextral transpressional fault zones. A NE–SW extension (3) has affected the Weihe graben during the Palaeogene; after a second transpressional event (4), the NE–SW extension (5) has been rejuvenated during the Late Miocene and the QLFZ has been a normal fault zone again and the STLFZ a sinistral transtensional fault zone; synrift subsidence has occurred in the Weihe graben. The second transpressional event (4) (WNW–ESE shortening) has occurred during the Late Oligocene–Early Miocene, during a period of uplifting and exhumation. At that time, the STLFZ and the QLFZ have become sinistral transpressional fault zones. A period of extension (6) has taken place during the Late Pliocene–Quaternary; the extensional direction has trended ≈NNW–SSE; during this event, the QLFZ has been a sinistral transtensional fault zone and the STLFZ a dextral transtensional fault zone. These results are compared with those previously published in order to evaluate the regional significance of these tectonic events.

Geodynamic significance of the TRM segment in the East African Rift (W-Tanzania): Active tectonics and paleostress in the Ufipa plateau and Rukwa basin

The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in an NW–SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E–W extension for the entire EARS. The central part of the TRM rift segment is well exposed in the Ufipa plateau and Rukwa basin, within the Paleoproterozoic Ubende belt. It is also one of the most seismically active regions of the EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage is the best expressed in the field and caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting (our third and last stress stage).

The Caribbean–North America–Cocos Triple Junction and the dynamics of the Polochic–Motagua fault systems: Pull‐up and zipper models

The Polochic‐Motagua fault systems (PMFS) are part of the sinistral transform boundary between the North American and Caribbean plates. To the west, these systems interact with the subduction zone of the Cocos plate, forming a subduction‐subduction‐transform triple junction. The North American plate moves westward relative to the Caribbean plate. This movement does not affect the geometry of the subducted Cocos plate, which implies that deformation is accommodated entirely in the two overriding plates. Structural data, fault kinematic analysis, and geomorphic observations provide new elements that help to understand the late Cenozoic evolution of this triple junction. In the Miocene, extension and shortening occurred south and north of the Motagua fault, respectively. This strain regime migrated northward to the Polochic fault after the late Miocene. This shift is interpreted as a “pull‐up” of North American blocks into the Caribbean realm. To the west, the PMFS interact with a trench‐parallel fault zone that links the Tonala fault to the Jalpatagua fault. These faults bound a fore‐arc sliver that is shared by the two overriding plates. We propose that the dextral Jalpatagua fault merges with the sinistral PMFS, leaving behind a suturing structure, the Tonala fault. This tectonic “zipper” allows the migration of the triple junction. As a result, the fore‐arc sliver comes into contact with the North American plate and helps to maintain a linear subduction zone along the trailing edge of the Caribbean plate. All these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates.

Discussions on the character and interpretation model of Kelasu deep structures in the Kuqa area

Abstract The character and interpretation model of deep structures in the Kelasu belt are discussed from growth strata, thrusting sequence, salt accumulation, and imbricate patterns between the shallow and deep structures. Seismic data shows that the fold hinges of growth strata in the south limb migrate toward north from deep to shallow, the growth axial surface connected along these fold hinges dips southward, and strata thickness in its south are thicker than that in the north. These characteristics of growth strata are completely different from that of basement-involved structures and salt structures. By the kinematic analysis of faults on the southern and northern sides of the Kela-2 structure, the northern fault is considered to thrust northward and form Kela-2 structure firstly, and then be cut through by the southern fault. Strong thrusting of the southern fault caused the Kela-2 structure to uplift several kilometers, and made the peripheral plastic rocks passively flow and accumulate in the footwall, this course is very similar to the pump suction. Based on this model, the sub-salt and sub-coal thrusting systems are interpreted in the deep Kelasu belt. In the sub-salt structural layer, the remaining lower part of Kela-2 structure in the footwall of its southern fault is the northern Keshen anticlinal belt. The discovery of the northern Keshen anticlinal belt and the Jurassic sub-coal thrusting structures greatly widens the exploration scope of the Kelasu belt, showing an enormous exploration potential.

Mesoscale folds and faults along a flank of a Syrian Arc monocline, discordant to the monocline trend

Abstract Orientations of folds and small faults were measured in Turonian and Senonian rocks along the western limb of the Ramallah monocline in Israel, one of the structures comprising the Syrian Arc fold belt (SAFB). The minority of the folds, aligned NNE–SSW, are compatible with the WNW–ESE shortening trend of the SAFB, whereas the majority of them, aligned ENE–WSW, are not compatible with this shortening trend. Kinematic analysis of faults’ attitude indicates NNW–SSE shortening and ENE–WSW extension in accordance with the shortening of the majority of folds. Based on the folds trends, scale, and geometry, as well as the associated fault kinematics, we conclude that the folding mechanism is tectonic shortening and not intraformational folding due to landsliding or collapse owing to karst activity as previously postulated. We propose that a minority of the folds, compatible with the major trend of the Ramallah monocline, are parasitic small folds within the SAFB. The majority of the folds, which are not compatible with the SAFB, were formed owing to NNW–SSE shortening that has been associated with Miocene to Recent movement along the Dead Sea Transform.

Neogene–Quaternary tectonic evolution of the Leeward Antilles islands (Aruba, Bonaire, Curaçao) from fault kinematic analysis

Aruba, Bonaire, and Curaçao are islands aligned along the crest of a 200-km-long segment of the east–west-trending Leeward Antilles ridge within the broad Caribbean–South America plate boundary zone presently characterized by east–west, right-lateral strike-slip motion. The crust of the Leeward Antilles ridge represents the western segment of the Cretaceous–early Cenozoic Great Arc of the Caribbean, which obliquely collided, with the continental margin of northern South America in early Cenozoic time. Following the collision, the ridge was affected by folding and was segmented by oblique, northwest-striking normal faults that have produced steep-sided, northwest-trending, elongate islands and narrow shelves separated by deepwater, sediment-filled and fault-controlled basins. In this paper, we present the first fault slip observations on the Neogene carbonate rocks that cover large areas of all three islands. Our main objective is to quantify the timing and nature of Neogene to Quaternary phases of faulting and folding that have affected the structure and topography of this area including offshore sedimentary basins that are being explored for their petroleum potential. These data constrain three fault phases that have affected Aruba, Bonaire, and Curaçao and likely the adjacent offshore areas: 1) NW–SE-directed late Paleogene compression; 2) middle Miocene syndepositional NNW–SSE to NNE–SSW extension that produced deep rift basins transverse to the east–west-trending Leeward Antilles ridge; and 3) Pliocene–Quaternary NNE-trending compression that produced NW–SE-trending anticlines present on Aruba, Curaçao and Bonaire islands. Our new observations – that include detailed relationships between striated fault planes, paleostress tensors, and bedding planes – show that prominent bedding dips of Neogene limestone on Aruba, Bonaire and Curaçao were produced by regional tectonic shortening across the entire Leeward Antilles ridge rather than by localized, syndepositional effects as proposed by previous workers. We interpret Pliocene–Quaternary NNE-directed shortening effects on the Leeward Antilles ridge as the result of northeastward extrusion or “tectonic escape” of continental areas of western Venezuela combined with southeastward shallow subduction of the Caribbean plate beneath the ridge.

Fault-kinematic and geomorphic observations along the North Tehran Thrust and Mosha Fasham Fault, Alborz mountains Iran: implications for fault-system evolution and interaction in a changing tectonic regime

Neighbouring faults can interact, potentially link up and grow, and consequently increase the seismic and related natural hazards in their vicinity. Despite evidence of Quaternary faulting, the kinematic relationships between the neighbouring Mosha Fasham Fault (MFF) and the North Tehran Thrust (NTT) and their temporal evolution in the Alborz mountains are not well understood. The ENE-striking NTT is a frontal thrust that delimits the Alborz mountains to the south with a 2000 m topographic front with respect to the proximal Tehran plain. However, no large instrumentally recorded earthquakes have been attributed to that fault. In contrast, the sigmoidally shaped MFF is a major strike-slip fault, located within the Alborz Mountains. Sinistral motion along the eastern part of the MFF is corroborated by microseismicity and fault kinematic analysis, which documents recent transtensional deformation associated with NNE-SSW oriented shortening. To better understand the activity of these faults on different timescales, we combined fault-kinematic analysis and geomorphic observations, to infer the kinematic history of these structures. Our fault kinematic study reveals an early dextral shear for the NTT and the central MFF, responsible for dextral strike-slip and oblique reverse faulting during NW-oriented shortening. This deformation regime was superseded by NE-oriented shortening, associated with sinistral-oblique thrusting along the NTT and the central-western MFF, sinistral strike-slip motion along subsidiary faults in the central MFF segment, and folding and tilting of Eocene to Miocene units in the MFF footwall. Continued thrusting along the NTT took place during the Quaternary. However, folding in the hanging wall and sinistral stream-offsets indicate a left-oblique component and Quaternary strike-slip reactivation of the eastern NTT-segment, close to its termination. This complex history of faulting under different stress directions has resulted in a composite landscape with inherited topographic signatures. Our study shows that the topography of the hanging wall of the NTT reflects a segmentation into sectors with semi-independent uplift histories. Areas of high topographic residuals and apparent high uplift underscore the fault kinematics. Combined, our data suggest an early mechanical linkage of the NTT and MFF fault systems during a former dextral transpressional stage, caused by NW-compression. During NE-oriented shortening, the NTT and MFF were reactivated and incorporated into a nascent transpressional duplex. The youngest manifestation of motion in this system is sinistral transtension. However, this deformation is not observed everywhere and has not yet resulted in topographic inversion.

Active transpression in the northern Calabria Apennines, southern Italy

An integrated analysis of geomorphologic and structural data, offshore seismic profiles and local network seismicity, is used to shed light on the hitherto poorly known active deformation field that affects the Southern Apennines orogen in northern Calabria region. In the Southern Apennines, Middle Pleistocene waning of Miocene–Early Pleistocene thin-skinned frontal thrust belt motion toward the Apulian foreland to the NE was coeval to onset of regional uplift, which is documented by flights of raised marine terraces. Short-wavelength (∼ 5–10 km) and amplitude (∼ 20–50 m) undulations are superposed to the regional uplift (∼ 100 km length and ∼ 500 m amplitude scale) profile of Middle–Upper Pleistocene marine terraces on the Ionian Sea coast of northern Calabria stretching along the borders of the Sila and Pollino mountain ranges and across the intervening Sibari coastal plain. The secondary undulations spatially coincide with the last generation of ∼ W- to ∼ WNW-striking folds traced in bedrock and locally within Early to Middle Pleistocene continental to transitional deposits. The very recent activity of these structures is highlighted by a range of fluvial geomorphic anomalies and by involvement in folding and locally transpressional faulting of the Middle Pleistocene and younger depositional sequences submerged beneath the continental shelf. We argue that the local-scale, but pervasive undulations in the deformation profile of marine terraces represent shallow-crustal folds grown within a recent and still active transpressional field. A major structural culmination bound by fore- and retro-verging transpressional shear zones is represented by the Pollino mountain range and its offshore extension in the Amendolara ridge, and a further SW-directed transpressional belt is found in northern Sila and adjacent sea bottom. Epicenter distribution and focal solutions of low- to moderate crustal earthquakes illuminate the two NW-SE trending structural belts beneath the Amendolara ridge and northern Sila, where partitioning between thrust and left strike-slip motion occurs in response to ∼ E to ∼ NE directed shortening. A local ∼ NW-SE extension is recorded by fault-kinematic analysis on NE-SW striking fault segments parallel to the coast on the eastern flank of Pollino. These small-length normal faults do not form a through-going lineament, rather they accommodate the seaward collapse of the uppermost crust above the deeper shortening compartment. Conversely, the active transpression testified by geomorphic, structural and seismicity data is accommodated along deep-seated oblique back-thrusts that involve the Apulian foreland plate underlying the now inactive thin-skinned accretionary wedge down to near-Moho depths. In light of the tight interlacing between regional and local components of deformation affecting the marine terraces, we suggest that the large-scale uplift in this sector of Calabria may reflect whole crustal-scale folding. The novel seismotectonic frame reconstructed for this region is consistent with GPS velocities suggesting that large part of geodetic shortening detected between the Apennines and the Apulian block on the eastern side of southern Italy might be accommodated in northern Calabria.

Fault kinematics and tectonic stress in the seismically active Manyara–Dodoma Rift segment in Central Tanzania – Implications for the East African Rift

The Eastern Branch of the East African Rift System is well known in Ethiopia (Main Ethiopian Rift) and Kenya (Kenya or Gregory Rift) and is usually considered to fade away southwards in the North Tanzanian Divergence, where it splits into the Eyasi, Manyara and Pangani segments. Further towards the south, rift structures are more weakly expressed and this area has not attracted much attention since the mapping and exploratory works of the 1950s. In November 4, 2002, an earthquake of magnitude Mb = 5.5 struck Dodoma, the capital city of Tanzania. Analysis of modern digital relief, seismological and geological data reveals that ongoing tectonic deformation is presently affecting a broad N–S trending belt, extending southward from the North Tanzanian Divergence to the region of Dodoma, forming the proposed “Manyara–Dodoma Rift segment”. North of Arusha–Ngorongoro line, the rift is confined to a narrow belt (Natron graben in Tanzania) and south of it, it broadens into a wide deformation zone which includes both the Eyasi and Manyara grabens. The two-stage rifting model proposed for Kenya and North Tanzania also applies to the Manyara–Dodoma Rift segment. In a first stage, large, well-expressed topographic and volcanogenic structures were initiated in the Natron, Eyasi and Manyara grabens during the Late Miocene to Pliocene. From the Middle Pleistocene onwards, deformations related to the second rifting stage propagated southwards to the Dodoma region. These young structures have still limited morphological expressions compared to the structures formed during the first stage. However, they appear to be tectonically active as shown by the high concentration of moderate earthquakes into earthquake swarms, the distribution of He-bearing thermal springs, the morphological freshness of the fault scarps, and the presence of open surface fractures. Fault kinematic and paleostress analysis of geological fault data in basement rocks along the active fault lines show that recent faults often reactivate older fault systems that were formed under E–W to NW–SE horizontal compression, compatible with late Pan-African tectonics. The present-day stress inverted from earthquake focal mechanisms shows that the Manyara–Dodoma Rift segment is presently subjected to an extensional stress field with a N080°E direction of horizontal principal extension. Under this stress field, the rift develops by: (1) reactivation of the pre-existing tectonic planes of weakness, and (2) progressive development of a new fault system in a more N–S trend by the linkage of existing rift faults. This process started about 1.2 Ma ago and is still ongoing.

Kinematic constraints on intra‐arc shear and strain partitioning in the southern Andes between 38°S and 42°S latitude

On the basis of structural field work, fault kinematic analysis, and the analysis of digital imagery, we describe the northern part of the southern Andean intra‐arc Liquiñe‐Ofqui Fault Zone (LOFZ) as an SC‐like fault zone system accommodating part of the Nazca–South American plate convergence obliquity. Kinematic modeling suggests that the LOFZ accommodated 124 (+24/−21) km of dextral displacement between 40°S and 42°S and 67 (+13/−11) km between 38°S and 40°S since the Pliocene. Associated vertical axis rotations are 31 ± 4° clockwise and 9 ± 1° counterclockwise along synthetic and antithetic faults, respectively. Mean Pliocene to recent shear rates along the LOFZ decrease northward from 32 ± 6 mm/yr to 13 ± 3 mm/yr compatible with partitioning of half of the convergence obliquity into the intra‐arc zone north of 40°S and complete partitioning to the south. The displacement gradient along the intra‐arc zone results in margin‐parallel shortening of the fore arc.

Geologic Evolution of the Caylloma Epithermal Vein District, Southern Peru

The silver- and base metal-rich Caylloma epithermal district in the Tertiary volcanic belt of southern Peru has been worked intermittently since the Incaic period and has produced over 100 million ounces (Moz) of Ag. Intermediate-sulfidation mineralization is present in veins hosted by Miocene andesitic volcanic and volcaniclastic rocks, with minor ore in underlying folded Jurassic sedimentary basement. New 40 Ar/ 39 Ar dates give a host rock age of 20.30 ± 0.11 Ma (andesitic volcanic matrix), a hydrothermal alteration age of 18.35 ± 0.17 Ma (adularia in vein wall rock), and postmineralization ages of 11.8 ± 0.8 and 12.25 ± 0.07 Ma (sanidine and biotite from a rhyolite dome). Gangue minerals include quartz, calcite, rhodonite, rhodochrosite, pyrite and minor adularia, illite, barite, and helvite. Ore minerals include sphalerite, galena, chalcopyrite, and tetrahedrite. Hydrothermal alteration is pervasive in lava flows but weak and localized near veins in volcaniclastic rocks. Hydrothermal alteration types include silicification (quartz-adularia and quartz-illite) and propylitization (chlorite + calcite ± illite). Banded veins show four stages of mineral precipitation: (1) early sugary quartz, chalcedony, pyrite; (2) manganese minerals; (3) quartz + sulfides; and (4) late calcite + quartz. Cyclic bands in the manganese stage (early sulfides, coarse- to medium-grained quartz, late rhodonite + calcite + chalcedony) are a few millimeters to 5 cm thick and form ore bands up to 1 m thick. Veins occupy dextral normal faults (020°–050°, 45°–70° SE) and extension fractures (060°–090°, 70°–90° SE) and are 1 to 25 m wide and as much as several kilometers long. The veins display complex and multi-episodic filling with textures characteristic of open-space precipitation such as crustiform banding, symmetric banding, vugs, breccias, and cockade and comb textures. We present a structural model in which the principal veins formed in subparallel northeast-striking dextral-normal faults and related extension fractures within a northwest-striking structural corridor bounded by sinistral regional faults; second- and third-order veins formed by bookshelf sliding related to movement on higher-order, dominantly strike-slip faults. Slickenlines have low rakes (20°–50° SW), and fault-kinematic analysis suggests the extension axis was oriented 4°/330° and the shortening axis 55°/234°, in agreement with the strain field commonly proposed for the early-middle Miocene of southern Peru. Ore grade is discontinuous, with high-grade ore zones having strike lengths of tens to hundreds of meters and extending about 300 m downdip. Ore shoots in fault-hosted veins are narrow subvertical zones a few tens of meters wide (measured in the plane of the vein), separated by lower-grade ore zones. Ore shoots in extension fractures are shorter downdip and horizontally more continuous. Some ore shoots occur as half-cymoids that form along the main vein only in the hanging wall of synmineral transverse faults. Mineral composition and metal content are zoned horizontally and vertically; silver, base metals, and calcite and manganese minerals increase to the northeast and downward, and sulfide content increases gradually with depth. Shallower levels of the hydrothermal system are exposed to the west and southwest in the district. Evidence from sulfur isotopes and high-salinity fluid inclusions is consistent with a model in which magmatic fluids played a role in the hydrothermal system, introduced through channels of enhanced structural permeability. The cyclic nature of mineral precipitation with abrupt changes in mineralogy, textures, and fluid composition leads us to postulate that cyclic injections of magma-derived hydrothermal fluids occurred. Economic mineralization is estimated to have formed at a depth of about 650 m below the paleowater table, with a temperature of formation of ~270°C.

Syn‐extension leucogranite deformation during convergence in the Eastern Central Alps: example of the Novate intrusion

AbstractThe Novate intrusion is a Late Alpine leucogranite that intruded the structures related to dextral back‐thrusting along the Periadriatic Fault System in the Eastern Central Alps. The Novate granite was heterogeneously deformed from amphibolite to greenschist facies conditions during cooling of the intrusion. The deformation inside the granite is characterized by strongly localized and anastomosed ductile shear zones surrounding lenses of weakly deformed granite and by late faults formed at the brittle–ductile transition. The fault kinematic analysis of conjugated shear zones suggests that the Novate leucogranite was emplaced at 25 Ma in an extensional regime along the southern tip of the Forcola Fault. A model of extensional jog opening by vertical shearing along the Forcola Fault provided the space for magma accommodation. The Novate granite is the first evidence for orogen‐parallel syn‐extensional leucogranite emplacement during the Oligocene collision in the Alps.

Fission track and fault kinematics analyses for new insight into the Late Cenozoic tectonic regime changes in West-Central Sulawesi (Indonesia)

The left-lateral strike-slip Central Sulawesi Fault System (CSFS, composed of the NNW Palu–Koro (PKF) and the ESE Matano faults) is located within the eastern Indonesian triple junction between the Pacific, Indo-Australian and Eurasian plates. Fault kinematic and fission-track analyses show that the Late Cenozoic central Sulawesi deformation results from three successive tectonic regimes: (1) A Late Miocene–early Pliocene (5 Ma) WNW-trending shortening characterized by transpressional deformation along the PKF and compressional in the Poso area. This tectonics resulted from the collision between the Banggai–Sula block with Sulawesi. It produced locally a transpressional regime as a consequence of the northward extrusion of the Central Sulawesi block limited by the PKF. (2) A Pliocene collapse tectonic regime associated with W-trending extension. Coeval with these events regional cooling and exhumation took place. (3) A Quaternary transtensional regime resulting from the combined effects of the Central Sulawesi block northward motion, and extension related to back-arc spreading behind the North Sulawesi subduction (Tomini Gulf).

Active extension in Val d'Agri area, Southern Apennines, Italy: implications for the geometry of the seismogenic belt

SUMMARY Integration of geologic, geomorphologic and seismologic data sets is used to reconstruct the recent tectonic evolution and active deformation pattern in the Val d'Agri area, located in the seismically active axial sector of the Southern Apennines (Italy). The western portion of the Apennines thrust belt has been affected by Pliocene–Quaternary extension during easterly roll-back and crustal delamination of the Adriatic slab. The bulk of Quaternary extension has been accommodated by SW-dipping oblique and normal faults, which have attained mature morphologic and structural features and, nowadays, separate mountain ranges from intermontane basins. However, in the present seismogenic belt, coseismic faulting locally occurs on NE-dipping structures, which might cut the inherited Pleistocene landscape. In the Val d'Agri basin, in spite of the large Early–Middle Pleistocene, displacement occurred on SW-dipping faults bordering its eastern flank, our investigations show that the recent basin evolution has been controlled by a NE-dipping fault system (Monti della Maddalena fault system, MMFS). This fault system cuts across the Monti della Maddalena range, west of the Agri valley and has not yet created an evident tectonic landscape. Notwithstanding, fault motion since the Middle Pleistocene might explain geomorphologic and hydrographic anomalies of the Agri river and its valley, where fault-controlled subsidence has captured the river course and produced an aggrading plain within a regional uplift context. Recent and ongoing motion is documented by fault scarplets in loose deposits, 14C ages of palaeosols and the spatial relation with low to moderate instrumental seismicity. Results from fault kinematic analysis are compatible with fault-plane solutions of local and regional seismic events, and indicate ∼NE–SW oriented extension. Recognition of the MMFS as a potential seismogenic fault increases the longitudinal extent of the NE-dipping, morphologically immature seismic sources in the Southern Apennines and argues against the range-bounding fault model for active extension in the region. The regional size of the NE-dipping seismogenic belt may result from impingement of a mantle wedge beneath the Apenninic chain and possibly track the external front of crustal delamination.

Post-Eocene extensional tectonics in Southern New Caledonia (SW Pacific): Insights from onshore fault analysis and offshore seismic data

Ductile to brittle extensional deformation following thrusting of the peridotites nappe during the Upper Eocene has been shown to play a major role in the Tertiary tectonic evolution of the northern part of the main island of New Caledonia and its eastern and western margins. In this study, we provide new tectonic data from southern New Caledonia that allow to better constrain the tectonic evolution of the southern part of the main island. We present a kinematic analysis of faults and striations obtained mainly from exposures of sedimentary rocks in the region of Nouméa with complements from measurements made farther north at Népoui within post-obduction Middle-Miocene deposits. We also present additional results of an interpretation of seismic lines from the lagoon south of the Nouméa Peninsula which provide constraints on the current tectonic regime of southern New Caledonia. Extensional faults in the Nouméa region have been studied within terranes of various ages including pre- and syn-obduction deposits and ophiolites. Hence, we demonstrate that important extensional events have affected the southern part of the New Caledonia block after the obduction of the peridotite nappe. The direction of maximum extension is variable at the scale of the region. Both high angle and low angle normal faults are present and block rotation is observed at some localities. This suggests that detachments accommodating significant displacements are cutting through the sedimentary pile. The average final strain pattern of the region can be regarded as the results of a multidirectional flattening, a hypothesis consistent with vertical uplift associated with regional extension. These results are in good agreement with conclusions of earlier workers showing late extensional evolution of the ophiolites along the chain and generalized extension in northern New Caledonia. The extensional faulting event in southern New Caledonia started after the obduction of the ophiolite, probably during the Oligocene. Extension was still active after the Middle Miocene, as shown by normal faulting in the Népoui conglomerates. Quaternary neotectonic features are observed in the lagoon and correspond to groups of short segments of vertical faults having orientation of N90, N40–50, N0–10 and minor N140, delineating subsiding areas. These faults are reactivated features with orientations corresponding to trends of coastlines and other main morphological features of the island. This study enhances the strong influence of normal-faulting neotectonics and recent tectonics on the current landscape evolution of southern New Caledonia. We infer that these tectonic processes played an important role during the weathering of the peridotites and subsequent development of the lateritic Ni-bearing layers as they increase the penetration of ground waters within the actively expending peridotite basement.

Late Paleozoic faults of the Altai region, Central Asia: tectonic pattern and model of formation

The present kinematic and dynamic analysis of large-scale strike-slip faults, which enabled the formation of a collage of Altai terranes as a result of two collisional events. The Late Devonian–Early Carboniferous collision of the Gondwana-derived Altai-Mongolian terrane and the Siberian continent resulted in the formation of the Charysh–Terekta system of dextral strike-slip faults and later the Kurai and Kuznetsk–Teletsk–Bashkauss sinistral strike-slip faults. The Late Carboniferous–Permian collision of the Siberian and Kazakhstan continents resulted in the formation of the Chara, Irtysh and North-East sinistral strike-slip zones. The age of deformation of both collisional events becomes younger toward the inner areas of the Siberian continent. In the same direction the amount of displacement of strike-slip faulting decreases from several thousand to several hundred kilometers. The width of the Late Paleozoic zone of deformation reaches 1500 km. These events deformed the accretion-collision continental margins and their primary paleogeographic pattern.

A synthesis: Late Cenozoic stress field distribution at northeastern corner of the Eastern Mediterranean, SE Turkey

Abstract Fault kinematic analysis and inversion of focal mechanisms of shallow earthquakes reveal significant evolution of the regional stress regime in the northeastern most corner of the Eastern Mediterranean region since the Mio-Pliocene to the present time. This study was carried out in the interaction area between the Arabian/African plates and the Anatolian block. The evolution of stress regimes consists of a change from older transpression to younger transtension. Both strike-slip stress regimes having a NNW- to northwest-trending σ Hmax ( σ 1 ) and ENE- to northeast-trending σ Hmin ( σ 3 ) axes induce a sinistral component of displacement on the major intra-continental Karatas–Osmaniye and Misis–Ceyhan faults elongated with the northeast-trending Misis Range between Adana and Osmaniye provinces (sub-area i ) and by a NNE-trending plate boundary Amanos fault running along Amanos Range between Antakya and Kahramanmaras provinces (sub-area ii ). The inversion results show that the transtensional stress regime is dominantly strike-slip to extension, with an ENE- to northeast-trending σ Hmin ( σ 3 ) axis for sub-areas ( i ) and ( ii ), respectively. The inversions of earthquake focal mechanisms indicate that the transtensional stress regime is still active in the whole study area since probably recent Quaternary time. To cite this article: S. Over et al., C. R. Geoscience 336 (2004).

Large-scale fault kinematic analysis in Noctis Labyrinthus (Mars)

Noctis Labyrinthus (Mars) is characterized by many tectonic features, which represent brittle deformation of the crust. This tectonic setting was analysed by remote sensing of the Viking Mars Digital Image Model (MDIM) mosaic and Mars Orbiter Camera (MOC) global mosaic, in order to identify deformational events. The main features are normal faults producing horst-graben structures, strike-slip faults, and related en-echelon and pull-apart basins. Using the criterion of cross-cutting relationships and analysis of secondary structures, to infer sense of movement of faults, two deformational phases were identified in the Noctis Labyrinthus area. The first, D1, located mainly in the northern part, is characterized by transtensional faults (Noachian). The second, D2, recorded in the southern part of the Noctis Labyrinthus by an orthorhombic extensional fault pattern along NNE and WNW trends, is related to the Valles Marineris formation (Late Noachian–Early Hesperian). A third tectonic event, D3, represented by the partly known dextral NW strike-slip faults cross-cutting the Valles Marineris Canyon System (Late Hesperian?-Amazonian?), was not found in Noctis Labyrinthus at the scale and resolution considered.

Cenozoic tectonic evolution of the White Mountains, California and Nevada

The White Mountains represent the westernmost range of the central northern Basin and Range province. They are situated to the east of the unextended Sierra Nevada and represent a crustal block that is bounded along its western flank by the high-angle White Mountains fault zone. The fault zone accommodates up to ∼8 km of total dip-slip displacement. Investigation of the structural and thermal history of the White Mountains indicates a two-stage Cenozoic tectonic evolution. Preextensional Miocene volcanic rocks preserved along the eastern side of the range unconformably overlie Mesozoic granitic basement and currently dip up to 25° to the east, recording the total Cenozoic tilt of the crustal block. Apatite fission-track and (U-Th/He) thermochronological data indicate that the White Mountains underwent rapid exhumation and eastward tilting in the middle Miocene, starting at ca. 12 Ma. Geologic mapping (1:10,000), fault kinematic analysis, and dating of younger volcanic sequences show that following middle Miocene east-west extension, the White Mountains have been dominated by right-lateral transtensional deformation related to the Walker Lane belt. The eruption of late Miocene and Pliocene volcanic sequences in the eastern White Mountains postdates the majority of the uplift of the range, as evidenced by infilling of paleodrainages and the presence of east-directed flow fabrics. Fault kinematic indicators from the White Mountains fault zone are characterized by apparent overprinting of dip-slip fault-motion indicators by right-lateral slickenfibers and fault striations, demonstrating that the range-bounding fault system along the western side of the White Mountains was reactivated as a dextral strike-slip fault system. At the northern and southern ends of the range, Pliocene right-lateral transtension along this northwest–southeast-trending fault systems resulted in the formation of northeast-trending pull-apart basins that truncate the mountain range and transfer strike-slip displacement eastward from the Owens Valley fault zone to the Fish Lake Valley fault zone. The inception of strike-slip faulting in Fish Lake Valley occurred at ca. 6 Ma as constrained by late Miocene volcanic units. Right-lateral faulting on the western side of the White Mountains occurred at ca. 3 Ma and is distinctly younger than the faulting in the Fish Lake Valley area, indicating a westward migration of transcurrent deformation through time.

Stress field analysis at the El Teniente Mine: evidence for N–S compression in the modern Andes

There is a large database of triaxial stress measurements at the El Teniente Mine, Central Chile, but the complex geology, severe topography, and proximity of all measurements to extensive mining excavations made interpretation of the stress field difficult. The measurements were analyzed using three-dimensional numerical stress analysis and decomposition of the stress field into gravitational and tectonic components. By removing gravitational stresses plus local effects from the tectonic component of the stress field a calculation of the far-field tectonic stress tensor is made. It is shown that variations in the tectonic component of stress are related to shear zones cutting through the mine. The far-field major principal component of the tectonic stress field was found to be oriented approximately N–S. This is consistent with the most recent direction of local shortening based on kinematic analysis of faults, but is perpendicular to the direction of regional crustal shortening. There appears to be a limiting envelope to the magnitude of the stress field implying that the shear zones are in a state of limiting equilibrium with regional tectonic driving forces.