Reactivated strike–slip faults: examples from north Cornwall, UK

Several strike–slip faults at Crackington Haven, UK show evidence of right-lateral movement with tip cracks and dilatational jogs, which have been reactivated by left-lateral strike–slip movement. Evidence for reactivation includes two slickenside striae on a single fault surface, two groups of tip cracks with different orientations and very low displacement gradients or negative (left-lateral) displacements at fault tips.

Evidence for the relative age of the two strike–slip movements is (1) the first formed tip cracks associated with right-lateral slip are deformed, whereas the tip cracks formed during left-lateral slip show no deformation; (2) some of the tip cracks associated with right-lateral movement show left-lateral reactivation; and (3) left-lateral displacement is commonly recorded at the tips of dominantly right-lateral faults.

The orientation of the tip cracks to the main fault is 30–70° clockwise for right-lateral slip, and 20–40° counter-clockwise for left-lateral slip. The structure formed by this process of strike–slip reactivation is termed a “tree structure” because it is similar to a tree with branches. The angular difference between these two groups of tip cracks could be interpreted as due to different stress distribution (e.g., transtensional/transpressional, near-field or far-field stress), different fracture modes or fractures utilizing pre-existing planes of weakness.

Most of the d–x profiles have similar patterns, which show low or negative displacement at the segment fault tips. Although the d–x profiles are complicated by fault segments and reactivation, they provide clear evidence for reactivation. Profiles that experienced two opposite slip movements show various shapes depending on the amount of displacement and the slip sequence. For a larger slip followed by a smaller slip with opposite sense, the profile would be expected to record very low or reverse displacement at fault tips due to late-stage tip propagation. Whereas for a smaller slip followed by larger slip with opposite sense, the d–x profile would be flatter with no reverse displacement at the tips. Reactivation also decreases the ratio of d_max/L since for an original right-lateral fault, left lateral reactivation will reduce the net displacement (d_max) along a fault and increase the fault length (L).

Finally we compare Crackington Haven faults with these in the Atacama system of northern Chile. The Salar Grande Fault (SGF) formed as a left-lateral fault with large displacement in its central region. Later right-lateral reactivation is preserved at the fault tips and at the smaller sub-parallel Cerro Chuculay Fault. These faults resemble those seen at Crackington Haven.     

A tectonic model for the Tertiary evolution of strike–slip faults and rift basins in SE Asia

Models for the Tertiary evolution of SE Asia fall into two main types: a pure escape tectonics model with no proto-South China Sea, and subduction of proto-South China Sea oceanic crust beneath Borneo. A related problem is which, if any, of the main strike–slip faults (Mae Ping, Three Pagodas and Aliao Shan–Red River (ASRR)) cross Sundaland to the NW Borneo margin to facilitate continental extrusion? Recent results investigating strike–slip faults, rift basins, and metamorphic core complexes are reviewed and a revised tectonic model for SE Asia proposed. Key points of the new model include: (1) The ASRR shear zone was mainly active in the Eocene–Oligocene in order to link with extension in the South China Sea. The ASRR was less active during the Miocene (tens of kilometres of sinistral displacement), with minor amounts of South China Sea spreading centre extension transferred to the ASRR shear zone. (2) At least three important regions of metamorphic core complex development affected Indochina from the Oligocene–Miocene (Mogok gneiss belt; Doi Inthanon and Doi Suthep; around the ASRR shear zone). Hence, Paleogene crustal thickening, buoyancy-driven crustal collapse, and lower crustal flow are important elements of the Tertiary evolution of Indochina. (3) Subduction of a proto-South China Sea oceanic crust during the Eocene–Early Miocene is necessary to explain the geological evolution of NW Borneo and must be built into any model for the region. (4) The Eocene–Oligocene collision of NE India with Burma activated extrusion tectonics along the Three Pagodas, Mae Ping, Ranong and Klong Marui faults and right lateral motion along the Sumatran subduction zone. (5) The only strike–slip fault link to the NW Borneo margin occurred along the trend of the ASRR fault system, which passes along strike into a right lateral transform system including the Baram line.     

Formation of sequential basins along a strike–slip fault–Geophysical observations from the Dead Sea basin

The Dead Sea basin is often cited as one of the classic examples for the evolution of pull-apart basins along strike–slip faults. Despite its significance, the internal structure of the northern Dead Sea basin has never been addressed conclusively. In order to produce the first comprehensive, high-resolution analysis of this area, all available seismic data from the northern Dead Sea (lake)–lower Jordan valley (land) were combined. Results show that the northern Dead Sea basin is comprised of a system of tectonically controlled sub-basins delimited by the converging Western and Eastern boundary faults of the Dead Sea fault valley. These sub-basins grow shallower and smaller to the north and are separated by structural saddles marking the location of active transverse faults. The sedimentary fill within the sub-basins was found to be relatively thicker than previously interpreted. As a result of the findings of this study, the “classic” model for the development of pull-aparts, based on the Dead Sea, is revised. The new comprehensive compilation of data produced here for the first time was used to improve upon existing conceptual models and may advance the understanding of similar basinal systems elsewhere.     

Temporal variation in the geometry of a strike–slip fault zone: Examples from the Dead Sea Transform

The location of the active fault strands along the Dead Sea Transform fault zone (DST) changed through time. In the western margins of Dead Sea basin, the early activity began a few kilometers west of the preset shores and moved toward the center of the basin in four stages. Similar centerward migration of faulting is apparent in the Hula Valley north of the Sea of Galilee as well as in the Negev and the Sinai Peninsula. In the Arava Valley, seismic surveys reveal a series of buried inactive basins whereas the current active strand is on their eastern margins. In the central Arava the centerward migration of activity was followed by outward migration with Pleistocene faulting along NNE-trending faults nearly 50 km west of the center. Largely the faulting along the DST, which began in the early–middle Miocene over a wide zone of up to 50 km, became localized by the end of the Miocene. The subsidence of fault-controlled basins, which were active in the early stage, stopped at the end of the Miocene. Later during the Plio-Pleistocene new faults were formed in the Negev west of the main transform. They indicate that another cycle has begun with the widening of the fault zone. It is suggested that the localization of faulting goes on as long as there is no change in the stress field. The stresses change because the geometry of the plates must change as they move, and consequently the localization stage ends. The fault zone is rearranged, becomes wide, and a new localization stage begins as slip accumulates. It is hypothesized that alternating periods of widening and narrowing correlate to changes of the plate boundaries, manifest in different Euler poles.     

Fault–valve action and vein development during strike–slip faulting: An example from the Ribeira Shear Zone, Southeastern Brazil

Fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of Neoproterozoic–Cambrian age in the Ribeira River Valley area, southeastern Brazil. Geometric and microstructural constraints indicate that foliation–parallel and extensional veins were formed during dextral strike–slip faulting. Both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates, and were crystallized in the presence of CO₂–CH₄ and H₂O–CO₂–CH₄–NaCl immiscible fluids following unmixing from a homogeneous parental fluid. Contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels. Foliation–parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values (319–397 °C and 47–215 MPa), which is compatible with predicted fluid pressure cycle curves derived from fault–valve action. Growth of extensional veins occurred in shallower structural levels, under pressure fluctuating from near hydrostatic to moderately subhydrostatic values (207–218 °C and 18–74 MPa), which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone. Fluid immiscibility and precipitation of quartz in foliation–parallel veins resulted from fluid pressure drop immediately after earthquake rupture. Fluid immiscibility following a local pressure drop during extensional veining occurred in pre-seismic stages in response to the development of fracture porosity in the dilatant zone. Late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity (0.2 to 44 wt.% equivalent NaCl) H₂O–NaCl–CaCl₂ fluid inclusions trapped in healed fractures mainly in foliation–parallel veins, which also exhibit subordinate H₂O–NaCl–CaCl₂, CO₂–(CH₄) and H₂O–CO₂–(CH₄)–NaCl fluid inclusions trapped under subsolvus conditions in single healed microcracks. Recurrent circulation of aqueous–carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post-veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes. A fluid evolution trending toward CH₄ depletion for CO₂–CH₄–bearing fluids and salinity depletion and dilution (approximation of the system H₂O–NaCl) for aqueous–saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history.     

Active strike–slip faulting and macroscopically nonrigid deformation of volcanic rocks in central Japan inferred from a paleomagnetic study

Detailed paleomagnetic investigation of a pyroclastic flow deposit has clarified the deformation mode around an active fault. In central Japan, the early Quaternary Nyukawa Pyroclastic Flow Deposit is cut by the active dextral Enako fault. Activity level of the fault is evaluated on the basis of geological and geomorphological surveys. Then, paleomagnetic samples are collected from 22 sites at exposures located on a lineament that is adjoining and parallel to the Enako fault. Stable thermoremanent magnetization (TRM) of the pyroclastic deposit is isolated through progressive thermal and/or alternating field demagnetization tests. Untilted site-mean directions of the TRMs simultaneously acquired during initial cooling indicate significant clockwise vertical-axis rotation. The lineament was then activated with right-lateral motions through the early Quaternary. Together with the late Quaternary activities along the adjoining Enako fault evaluated by our study, the present result exemplifies a migration of active segments within a fault system during the Quaternary. Paleomagnetic directions on the strike–slip fault are not concordant with uniform deformation predicted by the model of rotation of rigid blocks aligned on a master fault, but suggestive of a periodic deformation as a result of intense fracturing and differential rotation of blocks bounded by nested parallel faults.     

Geochronological constraints on Caledonian strike–slip displacement in Svalbard,with implications for the evolution of the Arctic

The timing of Svalbard's assembly in relation to the mid‐Paleozoic Caledonian collision between Baltica and Laurentia remains contentious. The Svalbard archipelago consists of three basement provinces bounded by N–S‐trending strike–slip faults whose displacement histories are poorly understood. Here, we report microstructural and mineral chemistry data integrated with ⁴⁰Ar/³⁹Ar muscovite geochronology from the sinistral Vimsodden‐Kosibapasset Shear Zone (VKSZ, southwest Svalbard) and explore its relationship to adjacent structures and regional deformation within the circum‐Arctic. Our results indicate that strike–slip displacement along the VKSZ occurred in late Silurian–Early Devonian and was contemporaneous with the beginning of the main phase of continental collision in Greenland and Scandinavia and the onset of syn‐orogenic sedimentation in Silurian–Devonian fault‐controlled basins in northern Svalbard. These new‐age constraints highlight possible links between escape tectonics in the Caledonian orogen and mid‐Paleozoic terrane transfer across the northern margin of Laurentia.     

Pan-African strike–slip tectonics in eastern Cameroon—Magnetic fabrics (AMS) and structure in the Lom basin and its gneissic basement

Field, microstructural, and anisotropy of magnetic susceptibility (AMS) or magnetic fabric studies were applied to identify the sequence and character of the Pan-African structures in the basement of Eastern Cameroon at both sides of the regional scale Bétaré-Oya Shear Zone (BOSZ). The NE-SW trending BOSZ separates older gneisses and migmatites towards SE (domain I) from the younger rocks of the Lom meta-volcano-sedimentary basin towards NW (domain II). In domain I, early, ductile compressional deformation occurred in two events, D1 and D2, under relatively high T conditions. During subsequent cooling, strain partitioned between the competent basement gneisses with only mild compression and the bordering shear zone (BOSZ) with intense simple shear-wrenching (D3). Strain in the less competent rocks of domain II is dominated by simple shear, strike-slip wrenching (D3), with an earlier stage of compressional deformation preserved only in some low strain pods.Magnetic fabrics (AMS) document a progressive change from oblate ellipsoids towards prolate ellipsoids in domain I, when proceeding from the south towards the BOSZ. Foliations are mostly steep but define a girdle with a pole plunging gently towards WSW. The magnetic lineations also plunge mostly towards WSW at shallow angles. These fabrics indicate a compression approximately normal to the BOSZ, which is also the SE margin of the Lom Basin. In the Lom metasediments (domain II), AMS ellipsoids are typically oblate. Foliations trend NE-SW with mostly steep dips. Magnetic lineations plunge gently NE or SW. This fabric with foliations mostly steep and subparallel with the major BOSZ, combined with generally subhorizontal lineations implies the BOSZ as a Pan-African strike–slip shear zone with a subordinate component of compression.At a larger scale, the area is part of a continent-scale shear zone, separating external Pan-African domains of compression along the northern margin of the Congo craton from internal domains dominated by high-angle strike–slip and transpressional deformation. Together with published data, the present study thus demonstrates that transpression is a regional phenomenon in the Pan-African orogen of central and eastern Cameroon.     

Buried oblique‐slip faults in the Irish Caledonides

Despite over a century of geological investigation, the Ordovician evolution of South Mayo, western Ireland, is still imperfectly understood. An example of this is the supposed lateral equivalence of two formations within the succession, the Rosroe and Derrylea Formations of Arenig age, exposed on opposite limbs of a major east–west syncline. These formations exhibit characteristics which suggest that they were not deposited in the same basin. Both formations contain tuff horizons. Geochemical analysis of these tuffs shows that each formation contains chemically distinct volcanic signatures suggesting deposition in separate sub‐basins. Previously the Rosroe Formation on the south limb of the syncline was considered the coarse‐grained proximal equivalent of the finer‐grained Derrylea Formation, both being deposited in a deep‐water fan environment. Previously published palaeocurrent data together with new data show the Rosroe Formation to have been derived from the northeast and therefore it cannot be the proximal equivalent of the Derrylea Formation. Additionally, the two formations show different and distinct associations of heavy mineral assemblages. It is suggested that one explanation for these data is that both formations were deposited in separate sub‐basins controlled by oblique slip sinistral faults, similar in some respects to the Cenozoic basins of the Gulf of California. In the Irish case these faults would have been largely buried by later Ordovician sedimentation. Some models for the Ordovician evolution of this area postulate the presence of an initial oceanic arc situated above a southward directed subduction zone. The presence of thick proximal submarine tuffs derived from an arc environment in the Rosroe Formation suggest that at least by this time the subduction zone was in fact northward directed and outboard of the arc. Copyright © 2002 John Wiley & Sons, Ltd.     

Active faults in Africa: a review

The active fault database and Map of active faults in Africa, in scale of 1:5,000,000, were compiled according to the ILP Project II-2 “World Map of Major Active Faults”. The data were collected in the Royal Museum of Central Africa, Tervuren, Belgium, and in the Geological Institute, Moscow, where the final edition was carried out. Active faults of Africa form three groups. The first group is represented by thrusts and reverse faults associated with compressed folds in the northwest Africa. They belong to the western part of the Alpine–Central Asian collision belt. The faults disturb only the Earth's crust and some of them do not penetrate deeper than the sedimentary cover. The second group comprises the faults of the Great African rift system. The faults form the known Western and Eastern branches, which are rifts with abnormal mantle below. The deep-seated mantle “hot” anomaly probably relates to the eastern volcanic branch. In the north, it joins with the Aden–Red Sea rift zone. Active faults in Egypt, Libya and Tunis may represent a link between the East African rift system and Pantellerian rift zone in the Mediterranean. The third group included rare faults in the west of Equatorial Africa. The data were scarce, so that most of the faults of this group were identified solely by interpretation of space imageries and seismicity. Some longer faults of the group may continue the transverse faults of the Atlantic and thus can penetrate into the mantle. This seems evident for the Cameron fault line.     

Do faults preserve a record of seismic slip: A second opinion

Exhumed fault zones offer insights into deformation processes associated with earthquakes in unparalleled spatial resolution; however it can be difficult to differentiate seismic slip from slow or aseismic slip based on evidence in the rock record. Fifteen years ago, Cowan (1999) defined the attributes of earthquake slip that might be preserved in the rock record, and he identified pseudotachylyte as the only reliable indicator of past earthquakes found in ancient faults. This assertion was based on models of frictional heat production (Sibson, 1975, 1986) providing evidence for fast slip. Significant progress in fault rock studies has revealed a range of reaction products which can be used to detect frictional heating at peak temperatures less than the melt temperature of the rock. In addition, features formed under extreme transient stress conditions associated with the propagating tip of an earthquake rupture can now be recognized in the rock record, and are also uniquely seismic. Thus, pseudotachylyte is no longer the only indicator of fossilized earthquake ruptures.We review the criteria for seismic slip defined by Cowan (1999), and we determine that they are too narrow. Fault slip at rates in the range 10⁻⁴−10¹ m/s is almost certainly dynamic. This implies that features reproduced in experiments at rates as low as 10⁻⁴ m/s may be indicators of seismic slip. We conclude with a summary of the rock record of seismic slip, and lay out the current challenges in the field of earthquake geology.     

Seismotectonics of strike–slip earthquakes within the deep crust of southern Italy: Geometry, kinematics, stress field and crustal rheology of the Potenza 1990–1991 seismic sequences (Mmax 5.7)

We present a revision and a seismotectonic interpretation of deep crust strike–slip earthquake sequences that occurred in 1990–1991 in the Southern Apennines (Potenza area). The revision is motivated by: i) the striking similarity to a seismic sequence that occurred in 2002  140 km NNW, in an analogous tectonic context (Molise area), suggesting a common seismotectonic environment of regional importance; ii) the close proximity of such deep strike–slip seismicity with shallow extensional seismicity (Apennine area); and iii) the lack of knowledge about the mechanical properties of the crust that might justify the observed crustal seismicity. A comparison between the revised 1990–1991 earthquakes and the 2002 earthquakes, as well as the integration of seismological data with a rheological analysis offer new constraints on the regional seismotectonic context of crustal seismicity in the Southern Apennines. The seismological revision consists of a relocation of the aftershock sequences based on newly constrained velocity models. New focal mechanisms of the aftershocks are computed and the active state of stress is constrained via the use of a stress inversion technique. The relationships among the observed seismicity, the crustal structure of the Southern Apennines, and the rheological layering are analysed along a crustal section crossing southern Italy, by computing geotherms and two-mechanism (brittle frictional vs. ductile plastic strength) rheological profiles. The 1990–1991 seismicity is concentrated in a well-defined depth range (mostly between 15 and 23 km depths). This depth range corresponds to the upper pat of the middle crust underlying the Apulian sedimentary cover, in the footwall of the easternmost Apennine thrust system. The 3D distribution of the aftershocks, the fault kinematics, and the stress inversion indicate the activation of a right-lateral strike–slip fault striking N100°E under a stress field characterized by a sub-horizontal N142°-trending σ1 and a sub-horizontal N232°-trending σ3, very similar to the known stress field of the Gargano seismic zone in the Apulian foreland. The apparent anomalous depths of the earthquakes (> 15 km) and the confinement within a relatively narrow depth range are explained by the crustal rheology, which consists of a strong brittle layer at mid crustal depths sandwiched between two plastic horizons. This articulated rheological stratification is typical of the central part of the Southern Apennine crust, where the Apulian crust is overthrusted by Apennine units. Both the Potenza 1990–1991 and the Molise 2002 seismic sequences can be interpreted to be due to crustal E–W fault zones within the Apulian crust inherited from previous tectonic phases and overthrusted by Apennine units during the Late Pliocene–Middle Pleistocene. The present strike–slip tectonic regime reactivated these fault zones and caused them to move with an uneven mechanical behaviour; brittle seismogenic faulting is confined to the strong brittle part of the middle crust. This strong brittle layer might also act as a stress guide able to laterally transmit the deviatoric stresses responsible for the strike–slip regime in the Apulian crust and may explain the close proximity (nearly overlapping) of the strike–slip and normal faulting regimes in the Southern Apennines. From a methodological point of view, it seems that rather simple two-mechanism rheological profiles, though affected by uncertainties, are still a useful tool for estimating the rheological properties and likely seismogenic behaviour of the crust.     

Transfer of stress from the 2004 Mw9.2 Sumatra subduction earthquake promoted widespread seismicity and large strike‐slip events in the Wharton Basin

The 2004 Mw9.2 Sumatra and 2012 Mw8.6 Wharton Basin (WB) earthquakes provide the unprecedented opportunity to investigate stress transfer from a megathrust earthquake to the subducting plate. Comprehensive analyses of this study revealed that the 2004 earthquake excited widespread seismicity in the WB, especially in regions of calculated stress increase greater than 0.3 bars. The 2004 earthquake stressed all three rupture planes of the 2012 Mw8.6 strike‐slip mainshock and the largest Mw8.2 aftershock with mean values of Coulomb stress between 0.3 and 2.1 bars. For the 77 Mw ≥ 4 regional events since 2012, at least one nodal plane for 95% of the events, and both nodal planes for 72% of the events experienced stress increase due to the 2004 earthquake. Results of the analyses also revealed that the regional stress directions in the WB may have controlled the sub‐fault orientations of the 2012 Mw8.6 strike‐slip earthquake.     

Factors controlling the vegetation distribution and coal‐forming environments in a strike‐slip basin. The Pennsylvanian Peñarroya‐Belmez‐Espiel Basin,southern Spain

Coal‐forming environments require humid to perhumid conditions. Tectonics governs the size, location and availability of coal seams developed in such environments. While large Pennsylvanian paralic basins generated thick and continuous coal seams, many other small coeval basins, which were tectonically active, developed a puzzling succession, with carbonaceous deposits that varied in size, thickness and the nature of the coal‐forming flora. This study, conducted in the Peñarroya‐Belmez‐Espiel coalfield, a Variscan strike‐slip basin in the south of Spain, provides insights into this subject. The coal seams analysed, generated in different depositional environments, have quantitatively different palynological assemblages. Lacustrine coals are dominated by lycopsids; distal alluvial plain/marginal lacustrine coals are dominated by sphenophytes and tree ferns, and middle alluvial fan coals are dominated by sphenophytes, tree ferns and lycopsids. This means that when conditions were favourable for peat accumulation, peat accumulated regardless of the nature of the available flora.     

Thermodynamic description of aqueous nonelectrolytes at infinite dilution over a wide range of state parameters

A new, virial-like equation of state (EoS) for describing the thermodynamic properties of aqueous nonelectrolytes at infinite dilution is proposed. It is based on the accurate EoS for a solvent (H₂O) given by Hill (1990) and requires only three empirical parameters to be fitted to experimental data, and these are independent of temperature and pressure. Knowledge of the thermodynamic properties of a pure gas, together with these three parameters, enables prediction of the whole set thermodynamic properties of the solute at infinite dilution (chemical potential, entropy, molar volume, and apparent molar heat capacity) over a wide range of temperatures (0 to 500°C) and pressures (1 to 2000 bars), including the near-critical region. In the cases in which experimental thermodynamic data are lacking, the empirical parameters can be estimated solely from the known standard-state properties of the solute. The new EoS is compatible with the Helgeson-Kirkham-Flowers model for aqueous electrolytes, and thus it can be applied to reactions involving minerals, gases, and aqueous ions, in addition to uncharged species.     

Post-collisional Tertiary–Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review

Mafic alkalic volcanism was widespread in the Carpathian–Pannonian region (CPR) between 11 and 0.2 Ma. It followed the Miocene continental collision of the Alcapa and Tisia blocks with the European plate, as subduction-related calc-alkaline magmatism was waning. Several groups of mafic alkalic rocks from different regions within the CPR have been distinguished on the basis of ages and/or trace-element compositions. Their trace element and Sr–Nd–Pb isotope systematics are consistent with derivation from complex mantle-source regions, which included both depleted asthenosphere and metasomatized lithosphere. The mixing of DMM-HIMU-EMII mantle components within asthenosphere-derived magmas indicates variable contamination of the shallow asthenosphere and/or thermal boundary layer of the lithosphere by a HIMU-like component prior to and following the introduction of subduction components.Various mantle sources have been identified: Lower lithospheric mantle modified by several ancient asthenospheric enrichments (source A); Young asthenospheric plumes with OIB-like trace element signatures that are either isotopically enriched (source B) or variably depleted (source C); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII-EMI components and slightly influenced by Miocene subduction-related enrichment (source D); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII components and significantly influenced by Miocene subduction-related enrichment (source E). Melt generation was initiated either by: (i) finger-like young asthenospheric plumes rising to and heating up the base of the lithosphere (below the Alcapa block), or (ii) decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs (the Tisia block).     

Catalytic oxidation of arsenite and reaction pathways on the surface of CuO nanoparticles at a wide range of pHs

Recently, the wide application of CuO nanoparticles (NPs) in engineering field inevitably leads to its release into various geologic settings, which has aroused great concern about the geochemical behaviors of CuO NPs due to its high surface reactivity and impact on the fate of co-existing contaminants. However, the redox transformation of pollutants mediated by CuO NPs and the underlying mechanism still remain poorly understood. Here, we studied the interaction of CuO NPs with As(III), and explored the reaction pathways using batch experiments and multiple spectroscopic techniques. The results of in situ quick scanning X-ray absorption spectroscopy (Q-XAS) analysis verified that CuO NPs is capable of catalytically oxidize As(III) under dark conditions efficiently at a wide range of pHs. As(III) was firstly adsorbed on CuO NPs surface and then gradually oxidized to As(V) with dissolved O₂ as the terminal electron acceptor. As(III) adsorption increased to the maximum at a pH close to PZC of CuO NPs (~?pH 9.2), and then sharply decreased with increasing pH, while the oxidation capacity monotonically increased with pH. X-ray photoelectron spectroscopy and electron paramagnetic resonance characterization of samples from batch experiments indicated that two pathways may be involved in As(III) catalytic oxidation: (1) direct electron transfer from As(III) to Cu(II), followed by concomitant re-oxidation of the produced Cu(I) by dissolved O₂ back to Cu(II) on CuO NPs surface, and (2) As(III) oxidation by reactive oxygen species (ROS) produced from the above Cu(I) oxygenation process. These observations facilitate a better understanding of the surface catalytic property of CuO NPs and its interaction with As(III) and other elements with variable valence in geochemical environments.     

Uniform slip rates of the Altyn Tagh and the Kunlun faults likely reflect lateral variation of frictional strength of the faults

The slip rate predicted from geodetic and geomorphological measurements is quite uniform on ~800–1,000 km length of the Altyn Tagh and the Kunlun faults. GPS velocity field documents that tectonic loading on the two active faults changes greatly along their strikes. To explore the mechanical relationship between far‐field tectonic loading and fault slip‐rate accumulation, we built a 3D viscoelastic finite‐element model with fault motion governed by frictional strength of contact interfaces. Based on numerical experiments, it is found that the observed uniform slip rate could reflect lateral variation of frictional strength along fault strike. Variation of predicted frictional coefficient ranges from ~0.13 to ~0.02, verifying that the two active faults must be weak for their mechanical strength. In addition, the good fitness between the relatively weak segment of faults and the location of strong earthquakes suggests that seismic activity along the two faults could be related to their frictional strength.