Search

We used data from 333 continuous Global Positioning System stations, including 26 stations installed in 2006–2007 as part of a collaborative EarthScope experiment, to investigate how deformation is distributed near the Rio Grande Rift. Our previous analysis, using data from 2006 to 2010, was consistent with a nearly uniform east‐west distributed extensional strain rate of ~1.2 nε/year (nanostrain/year) along five profiles spanning a ~1,000‐km region. We built upon this analysis with additional Global Positioning System networks and longer time series of data spanning varying time ranges between 1993 and 2018. In all five east‐west profiles, extensional strain rates are higher within and west of the fault‐defined rift zone than to the east. There is an east‐to‐west increase in Central New Mexico from 0.7 ± 0.1 to 1.8 ± 0.8 nε/year that is significant at the 95% confidence level. We found elevated extensional and shear strain rates of over 10 nε/year along parts of the central Rio Grande Rift, particularly along the southeast edge of the Colorado Plateau along part of the Jemez lineament, as well as elevated dilatational strain rates and uplift above the Socorro magma body. Results from Euler pole analysis of Global Positioning System velocities for sites within the Colorado Plateau show nonrigid behavior with considerable deformation near the plateau margins and internal east‐west extension. Our results suggest the Rio Grande Rift is actively deforming in an evolving tectonic environment. Key Points: Geodetic measurements illuminate active deformation near the Rio Grande Rift and Colorado PlateauDeformation is greater within and directly west of the fault‐defined RGR than to the east in the Great PlainsThe Colorado Plateau behaves as a nonrigid block with elevated strain rate accumulations at its margins [ABSTRACT FROM AUTHOR]

The crustal structure in the interior of Greenland is largely unknown because of its remote location below the up to 3.4‐km‐thick ice sheet. We present a model of the crustal velocity structure in central‐eastern Greenland based on simultaneous inversion of P and S receiver functions for data acquired at 23 broadband stations between the coast and the center of the ice sheet. The area is believed to mainly include Precambrian basement and includes a part covered by Tertiary volcanic rocks and some sedimentary basins. Our results show a westward deepening Moho from less than 20 km at the coast to 50 km below central Greenland. Crustal S wave velocities are generally 3.75 km/s through the whole crust which may be relatively small for Precambrian areas, and Vp/Vs is generally around 1.73, although slightly higher in central Greenland. In the coastal area we observe anomalously low velocities at the top of the crust. In the volcanic area south of Scoresbysund Fjord this layer has very high Vp/Vs (>2), which indicates a high mafic content and the presence of water‐filled cracks in the basaltic material. In the north, outside the volcanic area, Vp/Vs is normal and the low‐velocity layer probably is instead related to the presence of sedimentary basins. At stations in the center of our study area we find low Vs and high Vp/Vs in the lower crust. Based on the Moho topography, our results do not support Airy type isostasy as explanation of the high topography in eastern Greenland. Plain Language Summary: Crustal structure in interior Greenland is largely unknown due to its inaccessibility. The origin of the mountains at the rim of Greenland is enigmatic, and cannot be explained by standard plate tectonic processes. We present the first crustal structure profile across the mountains and to the centre of Greenland which is needed for constraining the possible mechanisms that formed the mountains. We conclude that crustal isostasy cannot explain their presence. Key Points: Crustal structure of interior central‐eastern Greenland shows strong variation in Moho depth from 15 to 50 kmSeismic velocity of the crust is highly variable based on Seismic Receiver Function inversionCrustal Airy isostasy cannot explain the high topography in eastern Greenland [ABSTRACT FROM AUTHOR]

Shortening tectonic structures within Mercury's two largest geological units display a clear contrast in relief, length, and spatial density. The volcanic smooth plains units are deformed by smaller‐scale structures yet host more features per area than the older intercrater plains. Although faulting in the intercrater plains is dominantly attributed to global contraction, it has been unclear whether the smooth plains faults result from volcanic loading, global contraction, or both. We use estimates of fault length and displacement to calculate spatial variations of areal strain for each unit. We find that high strain concentrations within the smooth plains suggest that global contraction has contributed to deformation in these units. The observed contrast in morphology and spatial density of structures between units may primarily reflect differences in mechanical and/or structural characteristics of the lithosphere when faulting was initiated. Plain Language Summary: Slow cooling of Mercury's mantle and core has decreased the radius of the planet by as much as 7 km. This radial contraction put the crust in a state of horizontal compression resulting in widespread thrust faulting. Extensive flood volcanism resurfaced portions of the crust, the most recent deposits of which are termed producing the smooth plains. Thrust faults are also observed within these plains, but it is not clear whether these features formed from global contraction or from bending of the crust due to the weight of the emplaced lavas. In this study, we measure the length of the faults and their relief (height) to calculate the spatial distribution of strain (horizontal shortening) in both the smooth plains and intercrater plains of Mercury. We find that the amount of strain recorded in the smooth plains is best explained by at least some contribution from stresses due to global contraction. Therefore, we suggest that all geological units on Mercury have been deformed by global contraction, indicating that substantial radius decrease occurred after the bulk of volcanic activity had ended. Key Points: We measure the relief of 672 and 584 shortening structures in Mercury's smooth plains and intercrater plains units, respectivelyAreal strain estimates for the smooth plains and intercrater plains are similar, suggesting both units record similar amounts of shortening strain from global contractionDifferences in morphology and fault density of shortening structures may reflect differences in lithospheric structure at fault initiation [ABSTRACT FROM AUTHOR]

Incremental slip rates of the Clarence fault, a dextral fault in the Marlborough fault system of South Island, New Zealand, varied by a factor of 4–5 during Holocene–latest Pleistocene time, as revealed by geomorphic mapping and luminescence dating of faulted fluvial landforms at the Tophouse Road site. We used high‐resolution lidar microtopographic data and field surveys to map the fine‐scale geomorphology and precisely restore the offset features. We dated the offsets using a stratigraphically informed protocol for infrared stimulated luminescence dating. These data show that incremental slip rates varied from ~2.0 to 9.6 mm/year, averaged over multiple earthquakes and millennial timescales. Comparison to incremental slip rates of the nearby Awatere fault suggests that these faults may behave in coordinated (and anticorrelated) fashion. This study adds to a growing body of evidence suggesting that incremental slip rate variation spanning multiple earthquake cycles may be more common than previously recognized. Plain Language Summary: Faults are commonly assumed to accommodate relative tectonic motions (slip) at constant rates when averaged over several large earthquakes. Testing this assumption requires documenting how far a fault has slipped at several different points in time over the past several millennia. In this study, we examine a rare instance in which four independent markers of fault slip over time are recorded in the landscape along the Clarence fault ‐ a major fault in the Marlborough fault system of South Island, New Zealand. We use high‐resolution digital topographic laser scans (lidar) to document the fine‐scale topography of the site, and luminescence dating to determine the ages at which the sediments constituting the landforms were last exposed to sunlight. Together, these markers show that, far from being constant over time, the Clarence fault at Tophouse Road has sped up and slowed by by a factor of four or five over the past eleven thousand years or so. This type of study needs to be conducted on other faults to examine whether they have exhibited similar behavior. Such phenomena can provide insights into the processes controlling tectonic plate behavior over timescales of hundreds to thousands of years. Key Points: Geomorphic analysis of lidar data and a luminescence dating protocol accurately constrain the offset history of a faulted terrace flightClarence fault incremental slip rates, spanning millennia and multiple earthquakes, varied by a factor of 4–5 since latest Pleistocene timeComparison of incremental slip rate variability for the Clarence fault and Awatere fault may suggest coordinated system‐level slip behavior [ABSTRACT FROM AUTHOR]

Abstract The 2016 Kumamoto earthquake, which occurred in the central Kyushu region of Southwest Japan, caused numerous landslides. Mass movements from the events damaged many structures in the Minami-aso village residential areas. We conducted geological and geophysical surveys and monitoring of landslides in one of these residential areas. It was found that the landslide occurred directly adjacent to the earthquake's main surface fault-ruptures. While the landslide slip surface formed within a layer of hydrothermally altered rhyolite at about 15 m depth for the downslope side, the slip surface for the upslope side formed within intact tephra layers due to the shallow dip of the rhyolite layer. Geophysical survey results show that fault ruptures in the tephra layers along with the tectonic faulting induce a decrease in soil strength. It was inferred that the landslide head scarp and upper slip surface formed inside this weak soil. Long-term monitoring of the landslide demonstrated that deformation continued for at least four months after the main slide. Although the initial and the major slide was activated by the earthquake, the landslide did not immediately stabilize and continued to pose risks after the main event. Toward the mitigation for earthquake-induced landslides, post seismic monitoring as well as the relationship between surface fault traces and landslide blocks should be taken into consideration. Highlights • An earthquake-induced landslide was surveyed using geological and geophysical methods. • The landslide occurred adjacent to surface rupture with tectonic displacements. • Part of the slip surface formed in hydrothermally altered rhyolite. • The landslide remained in an unstable state for several months after the main slide. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The ∼2.0 Ga Kongling mafic dikes are the oldest mafic intrusions in South China. • These dikes were formed in a back-arc basin during the assembly of Columbia supercontinent. • The linkage between South China and Northwest Laurentia, Northwest Australia and Siberia needs to be re-examined. Abstract Paleoproterozoic mafic dikes from the Kongling Complex in South China provide an ideal opportunity to examine mantle properties and tectonic evolution of the Yangtze Block and thus to understand the paleo-position of South China in the Columbia supercontinent. The 2.0 Ga dikes are the oldest mafic intrusions identified in the Yangtze Block by far. Samples from the dikes consist of fine to medium-grained dolerite and have variable SiO 2 (43.48–52.61 wt%) and MgO contents (3.17–7.35 wt%). They are enriched in LREE and show slightly negative to positive Eu anomalies (Eu/Eu∗ = 0.85–1.06). Their primitive mantle-normalized trace element patterns are characterized by enrichment of large-ion lithophile elements (Rb, Ba, Pb) and depletion of high-field-strength elements (U, Nb, Ta, Ti). Rocks from the dikes have variable initial 87Sr/86Sr ratios (0.698874–0.710753), εNd values (−3.0 to +4.1) and zircon εHf values (−2.7 to +3.4). These geochemical features indicate that their parental magmas were formed by <10% partial melting of a spinel-bearing lherzolite mantle in a back-arc basin setting. Paleoproterozoic mafic rocks from South China, Northwest Laurentia, Northwest Australia and Siberia had different trace element ratios and crystallization ages, their mantles had different thermal states. Thus, we argue against the previous model that the four continents were assembled together in the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 1D crustal model is gained from the joint inversion of receiver functions surface wave dispersion. • The inversion at the suture zone and eastern belt shows a clear separation between crust and mantle. • All stations within these belts have the Moho depths ranging from 28 km to 34 km. • The different crustal thicknesses obtained reflect the tectonic evolution of the region. Abstract The Malay Peninsula is located within the Sunda shelf that is subdivided geologically into three distinctive tectonic belts; western, central and eastern belts. The north-south orientation of these belts was formed during the Paleo-Tethys subduction process in the Late Paleozoic. Bentong-Raub suture zone separates the central and western belts. While extensive studies have been conducted at the surface and near surface scale, the subsurface model of the Earth's crust and upper mantle layers within this region are relatively few. Crustal structure model is crucial in investigating the cause of local earthquakes, which shocked Peninsular Malaysia between 2007 and 2009. The present study is conducted adopting the joint inversion of the P-wave receiver functions and surface wave dispersions techniques using the data collected from eight Seismological stations in the Malay Peninsula. The receiver function for each station was computed using over a thousand tele-seismic earthquake waveforms, recorded by the three-component broadband seismometers. For each station, the H-k was used to determine the Vp/Vs ratio and the depth to the Moho. This step was conducted to have an initial constraint for the crustal thickness. For the surface wave dispersion calculations, on the other hand, two hundred local and regional earthquakes with focal depth less than 30 km and with magnitudes mb 6.0 and above that occurred along South-East Asia's ring of fire were analyzed. The analyses obtained from these two techniques were jointly inverted through a two-phases of velocity inversion to determine the 1-D velocity profile for each station. The results of inversion indicate that the Moho boundary is getting shallower towards the north of Malay Peninsula, as a 26 km depth of crust-mantle boundary were determined in station SKLT south Thailand. Furthermore, the subsurface profile of the western belt of Malay Peninsula was also found to be highly complicated, with complex receiver function responses being computed beneath the IPM and KUM stations where slow velocity zones are identified within the 10–20 km crustal depth. The region in southern Thailand might also have originated from Indochina/East Malaya block, due to similar crustal velocity characteristics found beneath the region compared to the area beneath KOM, JRM and BTDF stations in the southern part of Malay Peninsula and Singapore. The Vp/Vs ratios for the crust indicate that the crust is generally undisturbed except for station SKLT south Thailand. This may indicate that the occurrence of a large earthquake in the region is not likely. [ABSTRACT FROM AUTHOR]

Highlights • Ongoing and active subduction in the western Makran. • Fracture zones divide Makran into two different subductions of two different dipp of sinking plates. • A mature Aleutian type for the eastern and a Kuril type of subduction for the western Makran. • Size of the plate boundary earthquakes are geometrically limited by different size of coupling areas in eastern and western Makran. • Makran plays important role in seismotectonic of triple junction between Eurasian, Indian and Arabian plates. Abstract The present study combined spatial distribution and mechanism of seismicity, seismicity parameters, geomorphology in satellite imagery and tectonic features in Makran inland to show that the Makran low angle thrust fault is divided into two separate segments. Depth dispersal of earthquakes, especially relocated events, shows that the sinking plate is steeper in the west than in the east of Makran. Significant facts were identified from the variation of Moho depth between west and east, slip rates of the inland faults and crustal shortenings in the north of Makran. The Sistan suture zone plays a significant role in dividing the overriding plate into a non-deforming Helmand block and a less deforming Lut block. These blocks have different resistances against the northward subduction. Large and great events, such as the 1989 Chabahar (M W 5.5) and 1945 Gwadur (M W 8.1), occurred in the south of subduction fronts of the western and eastern Makran, respectively. They occurred in shallow depth and were the pieces of evidence of weak and strong coupling between the oceanic and continental crusts on a low angle and a very low angle reverse faults, respectively. Spectral analysis and depth determination of the instrumental and pre instrumental earthquakes, respectively, helped to separate some plate boundary and intraplate events. This separation, geometry and non-characteristic behavior of the subduction zone, revealed from spatial and temporal distribution of the earthquakes, probably dedicate a mature Aleutian type for the subduction zone in the east. Missing great (M > 6.1) earthquakes, less slip rate of the continental faults and steeper dipping of the sinking plate in the west probably indicate a Kurile type for the Iranian part of subduction. Makran is a bimodal subduction, because geomorphological and seismic pieces of evidence indicate a NNW surficial and right lateral fracture zone in the continental crust and a NW deep and left lateral fracture zone in the oceanic crust, respectively. The fractures and geometry of subductions showed that the eastern Makran has seismotectonically a wider area for potential coupling of a larger earthquake than the western Makran. [ABSTRACT FROM AUTHOR]

Highlights • Key parameters are calibrated in the shear-stress bedrock-incision model. • Differential rock uplift rates are inferred from bedrock channel longitudinal profiles. • Tectonic deformation pattern and controlling factors are explored in active orogen. Abstract Bedrock channel profile analysis is a robust reconnaissance tool for examining the rates and patterns of deformation in active orogens. Here, steepness and concavity indices were extracted from bedrock channels draining the northern Qilian Mountains based on the universal shear stress incision model. The profile analysis reveals a systematic spatial distribution of steepness and concavity indices. The average steepness index for channels draining the western part is approximately 1.6 times higher than that for the eastern part. Through empirical calibration of erosion coefficient K , the influence of channel width, rock strength, discharge and sediment flux are identified, and an approximately 1.1–1.2 times difference in K values is found between the west and east under the hypothesis that lithologic resistance and sediment flux have no contribution. Correlating profile analyses with parameter calibration, an approximate 2–3 times increase in the rock uplift rate is found from the eastern part to the western part of the orogen. The integration of this study with previous work in the eastern part of the mountains indicates that cross-strike (2–4 times) and along-strike (2–3 times) differential rock uplift both exist in the northeastern margin of the Tibetan Plateau. In addition, the abnormal values of concavity are apparently associated with the channels transecting large thrust fault zones. Thus, the shortening deformation may play a dominant role in controlling the differential rock uplift through folding and thrusting of the northeast-directed thrust faults across the northeastern margin of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Highlights • The contemporary stress of Greece was resolved in a grid of 0.25°x025° cells. • Transtensional stress was found in the Aegean, the Corinth Rift and W. Greece. • Transpressional stress dominates NW Greece, Hellenic Arc and Crete. • The S.Aegean Active Volcanic Arc marks a transition zone where stress rotates by 90°. • Relations between stress and faults with implications on seismic hazard are examined. Abstract A massive dataset of over 1900 focal mechanisms of crustal earthquakes with M ≥ 3.5 in the Greek region was employed to resolve the contemporary stress-field using a damped least-squares inversion. The results are in good agreement with the strain-rate field of the Global Strain Rate Model, which was used as reference, both in terms of their principal axes orientations and expected faulting styles. Dual stress-states were identified using the Multiple Inverse Method in regions delineated by joining neighboring Area Sources of the European Seismic Hazard Model 2013 (ESHM13). North-western Greece is mostly affected by transpressional tectonics characterized by NE-SW contraction. Northern/central Greece and the Corinth Rift are dominated by E-W normal faulting, with secondary oblique-normal to strike-slip faulting at the western margin of the latter. North and central Aegean are mainly governed by transtensional regime, characterized by stable N-S extension. The stress-tensor was found to be compatible with the Fault Sources (FS) of ESHM13, in terms of orientation and expected faulting type. Differences were observed in regions of low strain-rate, such as the Southern Aegean, where left-lateral, E-W strike-slip instead of normal faulting was inferred. Discrepancies in areas with strong local heterogeneities were highlighted by anomalies in the stress-ratio, Φ , indicating transtensional regime in the pull-apart basins of Western Greece and transpressional tectonics in north-western Greece and south of Crete. The latter is characterized by stable N-S contraction, SW-NE sinistral strike-slip and E-W reverse faulting in the vicinity of the subduction zone. A low Φ , E-W oriented zone was identified along the active volcanic arc, where a remarkable 90° rotation occurs in the stress field. This rotation is related to the transition from E-W (in the north) to N-S (in the south) normal faulting in Peloponnese and Dodecanese Islands, as well as rearrangement from dextral to sinistral SW-NE strike-slip faulting in North and South Aegean, respectively. [ABSTRACT FROM AUTHOR]

Cretaceous strata are widely distributed across China and record a variety of depositional settings. The sedimentary facies consist primarily of terrestrial, marine and interbedded marine-terrestrial deposits, of which marine and interbedded facies are relatively limited. Based a thorough review of the subdivisions and correlations of Cretaceous strata in China, we provide an up-to-date integrated chronostratigraphy and geochronologic framework of the Cretaceous system and its deposits in China. Cretaceous marine and interbedded marine-terrestrial sediments occur in southern Tibet, Karakorum, the western Tarim Basin, eastern Heilongjiang and Taiwan. Among these, the Himalayan area has the most complete marine deposits, the foraminiferal and ammonite biozonation of which can be correlated directly to the international standard biozones. Terrestrial deposits in central and western China consist predominantly of red, lacustrine-fluvial, clastic deposits, whereas eastern China, a volcanically active zone, contains clastic rocks in association with intermediate to acidic igneous rocks and features the most complete stratigraphic successions in northern Hebei, western Liaoning and the Songliao Basin. Here, we synthesise multiple stratigraphic concepts and charts from southern Tibet, northern Hebei to western Liaoning and the Songliao Basin to produce a comprehensive chronostratigraphic chart. Marine and terrestrial deposits are integrated, and this aids in the establishment of a comprehensive Cretaceous chronostratigraphy and temporal framework of China. Further research into the Cretaceous of China will likely focus on terrestrial deposits and mutual authentication techniques (e.g., biostratigraphy, chronostratigraphy, magnetostratigraphy and cyclostratigraphy). This study provides a more reliable temporal framework both for studying Cretaceous geological events and exploring mineral resources in China. [ABSTRACT FROM AUTHOR]

The Galati-Izvoarele region, located in eastern Romania, came into the public attention relatively recent, when hosted an unusual intense earthquake sequence. During September-November 2013, several hundred shallow crust earthquakes were recorded in the area. There were several attempts to explain the phenomenon, and hypotheses more or less documented have been formed. Some speculations occurred on the potential connection between the seismic swarm and oil industry activities. The paper summarizes the results of local geophysical surveys conducted in the area, jointly analysed with the observed seismicity. The main results of the study reveal the Galati-Izvoarele region as a seismic-active area belonging to the northwest prolongation of North Dobrogea mobile zone. The earthquakes were generated mainly in a highly fragmented local graben-like structure, transversally superposed on the descending slope of the North Dobrogea Promontory. The graben fault system was and might be (re)activated each time when tectonic forces acting in the Carpathians foreland intensify. Changes in the intensity of tectonic forces may reflect in the slip acceleration along Peceneaga-Camena Fault, as observed at the Baspunar Geodynamic Observatory. For example, the paroxysmal phase of the Galati-Izvoarele swarm was shortly preceded by a significant increase of the Peceneaga-Camena Fault slip rate recorded at Baspunar Geodynamic Observatory. To conclude, the Galati-Izvoarele region must be seen as a seismic-prone area and any significant increase of the tectonic stress in the Carpathians foreland may generate another seismic sequence in an unpredictable future. [ABSTRACT FROM AUTHOR]

Conventional well logs serve as effective tools for estimation of pore pressure (PP), tectonic strain and stress magnitudes in normal and thrust faulted parts of the Upper Assam basin. Several models have been developed for prediction of PP and stress magnitudes over the years. Acquiring tectonic strain in active area enhances the accuracy of in situ stress estimate in the Upper Assam. This paper discusses Eaton's sonic model for PP estimation and assesses stress magnitudes incorporating tectonic strain in poroelastic models. Eaton's exponent is varied from 0 to 3 to get best-fit results for PP prediction validated with available modular dynamic tester and mud weight data. PP is estimated for geological formations: Dhekiajuli, Girujan, Tipam, Barail, Kopili, Sylhet, Langpur to the granitic basement in normal and thrust faulted areas of the Upper Assam basin using Eaton's exponent of 1.0. The predicted tectonic strain using uniaxial model varies from −0.0044 to 0.0061. The computed tectonic strain using biaxial poroelastic model ranges from 0.000099 to 0.00077 along NE–SW and from −0.001 to −0.0019 along NW–SE directions for normal faulting regime, respectively. In thrust faulting regime, the tectonic strains are obtained as 0.00092 and 0.00053 along NE–SW and NW–SE directions, respectively. The vertical (S V), maximum (S H) and minimum (S h) horizontal stress gradients range 21.7–23.8, 14.9–23.1 and 12.0–21.4 MPa km−1, respectively. Moreover, we have proposed a multiple linear regression model for evaluation of S h from independent parameters, namely, PP, Poisson's ratio and S V from three wells and dependent parameter as leak-off test (LOT) data. This is further tested with other three wells in the study area. The predicted S h is found to have satisfactory correlation with observed LOT for these wells. [ABSTRACT FROM AUTHOR]

Major faults release tectonic stress not only during large earthquakes, but also through slow aseismic slip associated with microseismic activity. Microearthquakes could be interpreted as the failure of fault asperities. If the slip accumulated during microearthquakes could be estimated with seismological data, the aseismic component of fault slip is more difficult to evaluate. In this study, we are interested in quantifying the aseismic fault slip from the seismic moment released by the simultaneous on fault seismic activity. For that, we study systematically the relationship between total slip and microseismic moment released on a fault modelled as a heterogeneous planar Dieterich–Ruina frictional interface producing earthquakes and aseismic slip. It is shown that for a long enough earthquake sequence, typically involving several occurrences of the largest asperity failure, the seismic moment released is directly proportional to the total (seismic plus aseismic) slip on the fault accumulated during the sequence. In particular, the total seismic moment divided by the fault area represents a fraction of the total slip that is of the order of the apparent density of asperities. The apparent density of asperities is defined as the fraction of the fault area that experienced a dynamic rupture during the sequence. This result provides a strong mechanical support to extend the use of microseismic activity as creepmeters along major active faults, beyond the common analysis of repeating earthquakes. [ABSTRACT FROM AUTHOR]

We have performed a tomographic study of the upper mantle under the Borborema Province by inverting relative P -wave traveltime residuals (including the PKPdf phase). The events were recorded by more than 50 broad-band and short-period stations deployed across the region, resulting in a total data set of 1912 relative residuals. A multichannel phase cross-correlation technique was utilized to develop the measurements, which were then inverted through an iterative, non-linear inversion scheme based on the subspace inversion method. The Fast Marching Method, a grid-based numerical algorithm that traces an interface evolving over a narrow band of nodes that are updated solving the eikonal equation by finite differences using upwind entropy, was considered to solve the forward problem. Traveltimes from outside of the 3-D model were calculated using a global reference model. The resulting tomographic images reveal structure down to depths of ∼600 km, under an area extending approximately 800 km in the EW direction and 900 km in the NS direction. The most important features revealed by the tomographic images include: (i) a relatively fast lithospheric mantle under the southern Borborema Plateau, when compared to the lithospheric mantle north of the Patos Lineament; (ii) a marked, shallow (< 150 km) low-velocity anomaly under the northeastern most corner of the Borborema Province; and (iii) a low-velocity channel bordering the Borborema Plateau at asthenospheric (250–400 km) depths. The lithospheric velocity contrast is interpreted as arising from a colder, stronger lithosphere south of the lineament, while the asthenospheric low-velocity channel is interpreted as resulting from lateral flow from a distant mantle plume (located in SE Brazil). We argue that the rheological contrast validates a stretching model recently proposed to explain the Plateau's elevated topography, and that the postulated lateral flow represents the source of magmas feeding intraplate volcanism in NE Brazil for the past ∼80 Ma. [ABSTRACT FROM AUTHOR]

Abstract—: Deep seismic sounding, continuous seismic profiling, and bathymetric data are used to discuss the structure of the Iceland Plateau and adjacent areas of the Norway-Greenland region. We tentatively suggest the existence of regional nearly NS-trending tectonic discontinuities; these are normal faults that make up the stepwise character of the Iceland Plateau. The steps are successively descending westward. The fault zones contain magmatic features in the form of dikes that penetrate the sediment in several cases, thus providing evidence of their young age. A rift feature confined to magnetic anomaly C5b is tentatively identified in the central Iceland Plateau based on some crustal peculiarities. The central Iceland Plateau and the southern Jan Mayen Basin show an increased heat flow (92-217 mW/m2) whose lateral distribution suggests a boundary between the regions of increased and normal values. The boundary passes through the center of the Jan Mayen Basin and trends nearly NS. It seems to bound the zone of influence due to the Iceland mantle plume from the northeast at present. [ABSTRACT FROM AUTHOR]

Abstract With a little more than 100 years since the publication of seminal and field-defining investigations, active tectonics is still a relatively young sub-discipline of structural geology. This research field addresses the accumulation of strain due to plate tectonic motion and more importantly release thereof through the occurrence of earthquakes (or other strain-releasing events). In that regard, active tectonics aims to characterize the incremental steps of plate tectonics. Determining earthquake chronologies, fault slip rates, and other common objectives importantly feed into our understanding of, for example, fault mechanics and crustal rheology. Characterizing the recurrence of large and potentially devastating earthquakes, is further motivated by seismic hazard assessment and risk mitigation. The primary data source in active tectonics is surface and shallow subsurface evidence of faulting –presenting itself in topographic and stratigraphic data sets respectively. Field observations and air photo interpretation of displaced stratigraphic and geomorphic markers were used almost 40 years ago to formulate end-member models of earthquake recurrence. Technological developments since then –especially within the last two decades– have dramatically increased the abundance and resolution of topographic data sets and the ability to date stratigraphic units and geomorphic surfaces, enabling the formulation of better-informed conceptual models of earthquake recurrence. Here, we provide an overview of the high-resolution topographic data sets and dating methods that enabled the recent advances of active tectonics. Graphical abstract Image 1 Highlights • Advances in active tectonics in 4D, spatially 3D plus temporal dimension. • Overview of global and local topographic data sets and obtaining methods. • Advances in Quaternary dating methods. [ABSTRACT FROM AUTHOR]

The intersection of the Eurasian and Arabian plates and the smaller Anatolian Scholle created the Karlıova Triple Junction (KTJ) in eastern Turkey. In this study, we present analogue model experiments for this region and compare the results with our field observations and data from remote sensing imagery. Our comparison suggests that the sense of slip along curvilinear faults at the west of the KTJ changes along strike moving away from the principal displacement zones, from strike-slip to oblique normal and then to pure normal slip. Although, the active Prandtl cell model has been proposed to explain the overall regional fault pattern at eastern part of the Anatolian Scholle, the map view orientation of the secondary faults within the Karlıova wedge and performed analogue modelling results suggest that the passive wedge-shaped Prandtl cell model with a normal dip-slip component along slip lines is more appropriate in order to explain not only deformation pattern around the KTJ but also internal deformation of eastern part of the Anatolia. Moreover, these faults accumulate the significant amount of deformation that causes to the irregular earthquake behavior and the relatively lower geologic slip-rates along the main fault branch of boundary faults around the KTJ. Abbreviations: Strike-slip; Karlıova Triple Junction (KTJ); continental deformation; North Anatolian Fault Zone (NAFZ); East Anatolian Fault Zone (EAFZ);Varto Fault Zone (VFZ) [ABSTRACT FROM AUTHOR]

Cenozoic convergence, collision and subsequent subduction between African and Eurasian plates are accommodating in overriding Eurasian plate both forming the Aegean extension and the North & East Anatolian fault zones. To understand the kinematic evolution of upper crust, here we provide new paleostress data from the Havran-Balıkesir Fault Zone located at the interaction area between the North Anatolian Fault Zone (NAFZ) and west Anatolian extensional structures. Paleostress reconstructions of fault-slip data reveal that three distinct deformation phases have been experienced in the region. Phase 1 is represented by left-lateral strike-slip faulting with reverse component in the pre-Pliocene period. The Phase 2 is characterized by approximately N-S trending contraction and associated E-W trending extension in Plio-Quaternary, which is spatiotemporally linked to the initiation of NAFZ through the area. The youngest deformation, Phase 3 is attributed to NE-SW trending extension and NW-SE-trending contraction commenced by the Quaternary transpressional tectonics in Southern Marmara Region. These results show that the main contraction axes have been experienced a spectacular anticlockwise rotation (from NW-SE to E-W), which is associated with; (i)the propagation geometry of the NAFZ into the region (ii)slab roll-back and retreat and tearing process on the Aegean subduction system, and (iii)the existence of inherited structures of the İzmir-Balıkesir Transfer Zone. [ABSTRACT FROM AUTHOR]

Plate tectonics describes the horizontal motion of rigid lithospheric plates away from midoceanic ridges and parallel to transforms, towards deep-sea trenches, where the oceanic lithosphere is subducted into the mantle. This process is the surface expression of modern-day heat loss from Earth. One of the biggest questions in Geosciences today is "when did plate tectonics begin on Earth" with a wide range of theories based on an equally diverse set of constraints from geology, geochemistry, numerical modeling, or pure speculation. In this contribution, we turn the coin over and ask "when was the last appearance in the geological record for which there is proof that plate tectonics did not operate on the planet as it does today". We apply the laws of uniformitarianism to the rock record to ask how far back in time is the geologic record consistent with presently-operating kinematics of plate motion, before which some other mechanisms of planetary heat loss may have been in operation. Some have suggested that evidence shows that there was no plate tectonics before 800 Ma ago, others sometime before 1.8-2.7 Ga, or before 2.7 Ga. Still others recognize evidence for plate tectonics as early as 3.0 Ga, 3.3-3.5 Ga, the age of the oldest rocks, or in the Hadean before 4.3 Ga. A key undiscussed question is: why is there such a diversity of opinion about the age at which plate tectonics can be shown to not have operated, and what criteria are the different research groups using to define plate tectonics, and to recognize evidence of plate tectonics in very old rocks? Here, we present and evaluate data from the rock record, constrained by relevant geochemical-isotopic data, and conclude that the evidence shows indubitably that plate tectonics has been operating at least since the formation of the oldest rocks, albeit with some differences in processes, compositions, and products in earlier times of higher heat generation and mantle temperature, weaker oceanic lithosphere, hotter subduction zones caused by more slab-melt generation, and under different biological and atmospheric conditions. [ABSTRACT FROM AUTHOR]

Yunnan Province is located on the southeastern margin of Tibet and represents an important marker in understanding the tectonic evolution of Tibetan Plateau. In this study, we calculated teleseismic P-wave receiver functions at 49 permanent broadband seismic stations in Yunnan Province and estimated crustal thickness and the bulk crust ratios of P-wave to S-wave velocities using the H-κ method together with more detailed crustal structural profiles from the common conversion point stacking method. There is a significant transition of Moho interface and lower crustal composition along latitude 26°N in northwestern Yunnan. Decrease of crustal thickness with a concomitant increase of Poisson's ratio occurs at station CUX. An interesting phenomenon is that a step-like Moho fashion is observed at several stations, which might correspond to local thermal activities, such as partial melt/lower crust delamination. Our results show changes in crustal properties appear to be associated with varieties in upper mantle structure and compositions, combined with other previous studies. We propose the controlling factor of the dynamic processes below 26°N is the result of eastern forward subduction of the Indian Plate; the northern part is controlled by the redirected material flow from the SE Tibet. [ABSTRACT FROM AUTHOR]

The seawater column is typically taken as a homogeneous velocity layer in wide-angle crustal seismic surveys in marine environments. However, heterogeneities in salinity and temperature throughout the seawater layer result insignificant lateral variations in its seismic velocity, especially in deep marine environments. Failure to compensate for these velocity inhomogeneities will introduce significant artifacts in constructing crustal velocity models using seismic tomography. In this study, we conduct numerical experiments to investigate the impact of heterogeneous seismic velocities in seawater on tomographic inversion for crustal velocity models. Experiments that include lateral variation in seawater velocity demonstrated that the modeled crustal velocities were contaminated by artifacts from tomographic inversions when assuming a homogeneous water layer. To suppress such artifacts, we propose two strategies: 1) simultaneous inversion of water velocities and the crustal velocities; 2) layer-stripping inversion during which to first invert for seawater velocity and then correct the travel times before inverting for crustal velocities. The layer-stripping inversion significantly improves the modeling of variation in seawater velocity when preformed with seismic sensors deployed on the ocean bottom and in the water column. Such strategies improve crustal modeling via wide-angle seismic surveys in deep-marine environment. [ABSTRACT FROM AUTHOR]

Previous studies have reached consensus that low velocity zones are widespread in the crust beneath Yunnan region. However, the relationships between the low velocity zones and large faults, earthquake distribution are less investigated by available studies. By analyzing the seismic ambient noise recorded by Yunnan Seismic Networks and Tengchong volcano array, we construct a 3D crustal shear wave velocity model for the Yunnan region, which provides more details of the distribution of intra-crustal low velocity zones in all of Yunnan. The distribution of low velocity zones shows different features at different depths. At shallow depths, the results are well correlated with near surface geological features. With increasing depth, the low velocity zones are gradually concentrated to the northern part of our study area, most likely reflecting variations in crustal thickness beneath the Yunnan region. The low velocity zones are truncated at depth by several large faults in Yunnan. It is interesting that most strong earthquakes (Ms≥5.0) occurred in Yunnan are distributed in low velocity zones or the transition zones between low and high velocity anomalies within the upper-to-middle crust. The crustal structure is composed of a brittle, seismically active upper-to-middle crust and a warm, aseismic lower crust. [ABSTRACT FROM AUTHOR]

In this study, we select 18 SG (superconducting gravimeter) records from 15 GGP stations and 99 vertical, 69 horizontal components of IRIS broad-band seismograms during 2004 Sumatra Earthquake to detect the splitting of higher-degree Earth's free oscillations modes (0S4, 0S7~0S10, 2S4, 1S5, 2S5, 1S6) and 12 inner-core sensitive modes (25S2, 27S2, 6S3, 9S3, 13S3, 15S3, 11S4, 18S4, 8S5, 11S5, 23S5, 16S6) by using OSE (optimal sequence estimation) method which only considers self-coupling. Results indicate that OSE can completely isolate singlets of high-degree modes in time-domain, effectively resolve the coupled multiplets independently, and reduce the possibility of mode mixing and end effect, showing that OSE could improve some signals' signal-to-noise ratio. Comparing the results of SG records with seismic data sets suggests that the number of SG records is inadequate to detect all singlets of higher modes. Hence we mainly select plentiful seismograms of IRIS to observe the multiplets of higher modes. We estimate frequencies of the singlets using AR method and evaluate the measurement error using bootstrap method. Besides, we compared the observations with the predictions of PREM-tidal model. This study demonstrates that OSE is effective in isolating singlets of Earth's free oscillations with higher modes. The experimental results may provide constraints to the construction of 3D Earth model. [ABSTRACT FROM AUTHOR]

Urban faults in Shenzhen are potential threat to city security and sustainable development. To improve the knowledge of the Shenzhen fault zone, interpretation and inversion of gravity data were carried out. Bouguer gravity covering the whole Shenzhen City was calculated with a 1-km resolution. Wavelet multi-scale analysis (MSA) was applied to the Bouguer gravity data to obtain the multilayer residual anomalies corresponding to different depths. In addition, 2D gravity models were constructed along three profiles. The Bouguer gravity anomaly shows an NE-striking high-low-high pattern from northwest to southeast, strongly related to the main faults. According to the results of MSA, the correlation between gravity anomaly and faults is particularly significant from 4 to 12 km depth. The residual gravity with small amplitude in each layer indicates weak tectonic activity in the crust. In the upper layers, positive anomalies along most of faults reveal the upwelling of high-density materials during the past tectonic movements. The multilayer residual anomalies also yield important information about the faults, such as the vertical extension and the dip direction. The maximum depth of the faults is about 20 km. In general, NE-striking faults extend deeper than NW-striking faults and have a larger dip angle. [ABSTRACT FROM AUTHOR]

The Cao Bang Basin is the northernmost of the basins related to the Cao Bang-Tien Yen Fault Zone in northern Vietnam. The basin is filled with a thick series of continental deposits. However, the exact age of the sedimentary basin infill has been under discussion for a long time. Because of new published data, the authors have decided to revisit this basin. Palynological data has allowed us to assign the Cao Bang Basin infill to the Lower Oligocene PC1 complex of the Shangcun Fm. (southern China). Among the saccate grains of gymnosperms, the domination of Cathaya and Pinus was observed, whereas angiosperms are represented by Carya, Celtis, Hammamelidaceae, Ulmus and also Pterocarya, Quercus, the Castanea-Castanopsis-Lithocarpus group, and the Loranthaceae. Among pteridophytes occur Laevigatosporites, Osmundaceae, and Pteris. The sedimentological features of the Cao Bang Basin are distinct from those of other basins from the Cao Bang-Tien Yen Fault Zone. The basin is filled with a wide variety of clastic deposits, from some of coarse-grained, alluvial-fan origin, through sandy beds of fluvial origin up to fine, organic-rich lacustrine deposits. The coarse-grained lithofacies are built of clasts derived mainly from local sources. The sandstones from the basin equally are submature or immature. They contain a lot of lithoclasts, the composition of which depends on the sample location within the basin. The potential source area is composed of older sedimentary units and of granitic rocks. The geochemical samples studied reflect the geochemical composition of silicic source rocks with only a minor contribution of basic components. The succession that fills the basin is interpreted as a typical fill for relatively long-lasting evolving half-graben or strike-slip basins. Moreover, the basin is partly occupied by a subsequent present-day sedimentary basin of Quaternary age. [ABSTRACT FROM AUTHOR]

Abstract: This work is devoted to studying the structure of the northwestern part of the Indian Ocean. Primary materials of the area geological and geophysical survey performed in the southern part of the midoceanic Carlsberg Ridge (research vessel Issledovatel', PGO Yuzhmorgeologiya, 1987) and results of unique studies of the Equator Ridge (the Somali Basin) from a manned underwater vehicle are used. The Rodrigues block is isolated at the southern extremity of the Carlsberg Ridge, which is anomalous in its morphological characteristics. The conclusion is made that this block is a connecting link of the existed continental bridge between the Seychelles Islands and the Maldive Ridge. It is conjectured that the Carlsberg Ridge was formed on a transitional crust. A complex analysis of all data on the structure of the northwestern Indian Ocean convincingly demonstrates that differentiated tectonic movements were the leading geodynamic factor in its evolution. [ABSTRACT FROM AUTHOR]

Abstract: The concept of the role of the biosphere in the evolution of the Earth is proposed and confirmed by calculations. According to this concept, in the prebiosphere period, a shell structure was formed, the global convection occurred in the form of tectonics of small plates, and the absence of continents excluded the involvement of water in the oxidation of igneous rocks. In the biosphere period, photosynthetic organisms began to supply free oxygen and organic matter (OM) to the environment. Oxygen began to take part in the geochemical processes of ore conversion, the formation of the nitrogen-oxygen composition of the atmosphere, and the generation of granitoids from volcanic rock. Global systems for the generation of granitoids of the continental crust and hydrocarbons (HCs), which are formed during subduction-collision absorption of the oceanic crust, have been identified for the first time. On the transit route to the Benioff zone, granites are melted out from oxygen-enriched halmyrolysis products and the thermal metamorphism of OM yields solid allotropic carbon compounds, oil, and combustible and other gases and is accompanied by the release of OM decomposition energy. This is one of the ways to convert biosphere solar energy into the endodynamic processes of the evolution of the Earth. The average annual precipitation of the primary OM in the ocean is 785.5 Mt, and 1.7 km3 of the continental crust are generated. Over the biosphere period, the World Ocean became shallower by 904.5 million km2. Geodynamic and geophysical processes, primarily global convection, in conjunction with biosphere factors, have resulted in the current state of the Earth's shells and the existence of HCs and continental-crust generation systems in them. [ABSTRACT FROM AUTHOR]

This study presents an analysis of the single-channel high-resolution shallow seismic reflection data from Lake Erçek, eastern Anatolia, to provide key information on the deformational elements, on the fault patterns and on the overall tectonic structure of the Lake Erçek Basin. High-resolution seismic data reveal major structural and deformational features, including N-S trending normal faults and W-E trending reverse faults bounding the Lake Erçek Basin, basement highs and folded structures along the marginal sections of the lake. The N-S trending normal faults asymmetrically control the steep western margin and the gentle eastern deltaic section, while the W-E trending reverse faults appear at the northern and southern margins. The N-S trending normal faults, half-graben structure, and the gradual thickening of sediments in the Erçek Basin toward the fault scarps strongly suggest an extensional tectonic regime resulting from an N-S compression. The Erçek Basin is an extension-controlled depocenter; it is a relatively undeformed and flat-lying deep Basin, forming a typical example of the half-graben structure. The N-S trending normal faults appear to be currently active and control the lake center and the E-delta section, resulting in subsidence in the lake floor. In the N- and S-margins of the lake, there is evidence of folding, faulting and accompanying block uplifting, suggesting a significant N-S compressional regime that results in the reverse faulting and basement highs along the marginal sections. The folding and faulting caused strong uplift of the basement blocks in the N- and S- margins, subsequently exposing the shelf and slope areas. The exposed areas are evident in the erosional unconformity of the surface of the basement highs and thinned sediments. The tilted basement strata and subsequent erosion over the basement block highs suggest prominent structural inversion, probably long before the formation of the lake. New high-resolution seismic data reveal the fault patterns and structural lineaments of the Lake Erçek and provide strong evidence for an ongoing extension and subsidence. The present study provides new structural insights that will support future tectonic and sedimentary studies and the development of strategies related to active earthquake faults and major seismic events in the region of Lake Erçek. [ABSTRACT FROM AUTHOR]

Models of orogens identify subduction of oceanic crust as the key mechanism leading to continental collision. Such models, based inter alia on thermobarometric and geochronological evidence preserved in high-pressure metamorphic rocks and subduction-related magmatism, have been used to explain the convergence of Europe and Adria in the Cretaceous-Cenozoic and the subsequent Alpine orogen. Here, we review the metamorphic, igneous, and sedimentary record of the past 300 Ma of the Alpine orogen to show that there is no evidence of igneous activity during subduction initiation and prograde high-pressure metamorphism, leading to an ~50 Ma hiatus in magmatism, or "arc gap." The closure of rift basins forming the Piemont-Liguria ocean did not follow a classical Wadati-Benioff-type subduction. Instead, subduction initiation at passive margins allowed for the accretion of the hydrated portion of the subducting plate within an orogenic wedge as subduction of dry subcontinental lithosphere inhibited magmatism during subduction initiation and ocean closure. [ABSTRACT FROM AUTHOR]

Thrust zones in a deep-water fold-thrust belt, offshore northwestern Borneo, display prominent reflections that can be mapped through a three-dimensional seismic volume. Unlike faultplane reflections obtained from thrusts in other systems, these have positive polarity. Well data show that the reflections in the Borneo data set originate from fault-bound sandstone slices, with porosity-occluding calcite cement, entrained along the thrust zone. The thrust zone can support elevated fluid pressures beneath the fault with the cemented sandstones. Multiple sandstone slices indicate complex patterns of thrust zone localization, perhaps a common feature for deformation in sedimentary multilayers typical of many deep-water depositional successions. [ABSTRACT FROM AUTHOR]

Submarine channel‐systems are globally prevalent on continental margins and their deposits record the transfer of significant volumes of sediment from continental catchments to deep‐water environments. These deposits contain signals of past events that can provide critical insight into the geological history of an area, including the long‐term (>1 Ma) controls on sedimentation. Well‐exposed outcrops of the Late Cretaceous Nanaimo Group, British Columbia, Canada, provide an opportunity to investigate long‐term sediment‐routing in a tectonically active setting. This study combines detrital zircon geochronology with stratigraphic analysis to establish a robust, basin‐wide palaeogeographic framework that constrains the timing and distribution of coarse‐grained sediment transport and deposition in the Nanaimo forearc basin. Three south‐west trending submarine conduits are documented along a 135 km long strike‐oriented transect, parallel to the north‐west/south‐east trending basin. Composite conduit deposits are 350 to 700 m thick, 4 to 16 km wide, and record substantial delivery of coarse‐grained detritus (up to boulder‐sized clasts) within submarine channel‐levée systems. Maximum depositional ages derived from detrital zircon datasets constrain contemporaneous sediment transfer and deposition at each conduit location, which spanned between 73·5 ± 1·3 Ma to 69·1 ± 1·1 Ma around the Campanian–Maastrichtian boundary. Submarine conduits are spaced at 40 km and 70 km, and were likely connected to fluvial drainage systems sourced in uplifted catchments. Widespread, coarse‐grained deposits suggest that surface uplift associated with concurrent regional events (such as deformation and/or magma emplacement) along the North American margin may have promoted sediment delivery to the deep‐water basin. Comparisons to modern and ancient analogues support palaeogeographic interpretations, as well as the interpretation that pervasive coarse‐grained deep‐water sediment delivery was linked to tectonic activity. The integrated stratigraphic–geochronological approach used provides unique insight into the influence of regional tectonics on continental margin physiography and the nature of deep‐water sediment dispersal. [ABSTRACT FROM AUTHOR]

The Sdom Formation (Fm.) comprises an approximately 2 km thick sequence of evaporite sediments that Zak (The geology of Mount Sdom, Ph.D. Thesis, Hebrew University, Jerusalem, p. 208, 1967) postulated as being of early Pliocene age and marine origin. A major core drilling program of Mt. Sdom was undertaken that investigated the upper 1000 m. Integration of the data has thrown into question many of the concepts regarding the Sdom Fm. and Mt. Sdom in particular. The Sdom Fm. is now considered to represent a major non-marine evaporite sequence equivalent in time to the Upper Evaporite Messinian Fm. of the Mediterranean, (5.60-5.50 Ma), which was deposited from the Sea of Galilee to the Dead Sea basin. Mt. Sdom comprises approximately 44 cycles, ranging from sapropelic shales to carnallitites. The beds are subvertical and gave a consistent younging direction to the west, contrary to previous models. The sediments from the upper section of Mt. Sdom represent a shoreline facies; probably the eastern margin of the basin with the center of the basin at depth. Only minor deformation of the sediments was observed along the margins of the salt wall of Mt. Sdom. It is now suggested that the sediments crept with overburden pressure, down the Sdom intergraben fault from a horizontal to vertical position with increased tectonic subsidence. In more recent years, with tensional movement of the Dead Sea Transform, the salt wall became diapiric. The Sdom formation has been correlated throughout Israel and an attempt has been made to correlate the formation with the Messinian evaporites in the Eastern Mediterranean. It is considered here that the Levant Basin and the separate Dead Sea Basin were both tectonically active over the same time period when the climate was predominantly arid. The evidence of multiple evaporite cycles suggests rapid changes in climate from pluviatile to arid, with syndepositional sedimentation and not a deep basin filled with brine. It is postulated that the Messinian Salinity Crisis was an event that extended from the Mediterranean Sea and Dead Sea basins to the Gulf’s of Eilat and Suez, the Red Sea, Gulf of Aden and Danakil Basin in separate tectonically active basins, with shallow brines for the deposition of potassium minerals and even bischofite. This would imply a period of intense aridity for the region. If it is possible to relate all these Middle to Upper Miocene deposits, then this would be one of the largest salinas in the world. [ABSTRACT FROM AUTHOR]

Plate tectonics is a particular mode of tectonic activity that characterizes the present-day Earth. It is directly linked to not only tectonic deformation but also magmatic/volcanic activity and all aspects of the rock cycle. Other terrestrial planets in our Solar System do not operate in a plate tectonic mode but do have volcanic constructs and signs of tectonic deformation. This indicates the existence of tectonic modes different from plate tectonics. This article discusses the defining features of plate tectonics and reviews the range of tectonic modes that have been proposed for terrestrial planets to date. A categorization of tectonic modes relates to the issue of when plate tectonics initiated on Earth as it provides insights into possible pre-plate tectonic behaviour. The final focus of this contribution relates to transitions between tectonic modes. Different transition scenarios are discussed. One follows classic ideas of regime transitions in which boundaries between tectonic modes are determined by the physical and chemical properties of a planet. The other considers the potential that variations in temporal evolution can introduce contingencies that have a significant effect on tectonic transitions. The latter scenario allows for the existence of multiple stable tectonic modes under the same physical/chemical conditions. The different transition potentials imply different interpretations regarding the type of variable that the tectonic mode of a planet represents. Under the classic regime transition view, the tectonic mode of a planet is a state variable (akin to temperature). Under the multiple stable modes view, the tectonic mode of a planet is a process variable. That is, something that flows through the system (akin to heat). The different implications that follow are discussed as they relate to the questions of when did plate tectonics initiate on Earth and why does Earth have plate tectonics. [ABSTRACT FROM AUTHOR]

Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of seafloor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780-2710Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700-2440Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics. [ABSTRACT FROM AUTHOR]

Abstract The Chuan-Dian Fragment (CDF), in the southeastern Tibetan Plateau, is crucially important for understanding the intra–continental deformation behavior of the blocks between the stable Yangtze craton and the Indian Plate after the Indian-Asian collision. The Beiya porphyry-skarn gold–polymetallic deposit at the northwestern part of the fragment may provide an important paleomagnetic result for understanding the deformation behavior of the CDF. The paleomagnetic study of mineralized and intrusive rocks from the ~35 Ma Beiya deposit reveals a high temperature component with site–mean direction of D = 337.6°, I = 32.6°, k = 74.8, with α 95 = 4.4°. Our results show that the Beiya deposit experienced 21.5° ± 3.1° of anticlockwise rotation relative to the stable part of the South China Block since ~35 Ma. The stable part of the Dali faulted-block is deduced to have experienced ~20° clockwise rotation based on a comparison of the fold-axis strike of Triassic strata between the Beiya deposit and surrounding stable area. A best-fit linear regression of the fold-axis strike direction and the tectonic rotation at each sampling site reveals that differential tectonic rotation occurred, accompanied by the horizontal deflection of strata within the CDF. Highlights • The CRM and TRM carried by rocks of the Beiya deposit were isolated. • The Beiya deposit has experienced anticlockwise rotation since ~35 Ma. • Tectonic rotation is closely related to the change of the fold-axis strike within the CDF. [ABSTRACT FROM AUTHOR]

Abstract Active source near-vertical reflection (NVR) data from the interdisciplinary project TIPTEQ were used to image and identify structural and petrophysical properties within the Chilean subduction zone at 38.25°S, where in 1960 the largest earthquake ever recorded (M w 9.5) occurred. Reflection seismic images of the subduction zone were obtained using the post-stack depth migration technique to process the three components of the NVR data, allowing to present P- and S-stacked time sections and depth-migrated seismic reflection images. Next, the reflectivity method allowed to model traveltimes and amplitude ratios of pairs of reflections for two 1D profiles along the studied transect. The 1D seismic velocities that produced the synthetic seismograms with amplitudes and traveltimes that fit the observed ones were used to infer the rock composition of the different layers in each 1D profile. Finally, an image of the subduction zone is given. The Chilean subduction zone at 38.25°S underlies a continental crust with highly reflective horizontal, as well as dipping events. Among them, the Lanalhue Fault Zone (LFZ), interpreted to be east-dipping, is imaged to very shallow depths for the first time. In terms of seismic velocities, the inferred composition of the continental crust is in agreement with field geology observations at the surface along the profile. Furthermore, no measurable amounts of fluids above the plate interface in the continental crust in this part of the Chilean subduction zone are necessary to explain the results. A large-scale anisotropy in the continental crust and upper mantle is qualitatively proposed. However, quantitative studies on this topic in the continental crust of the Chilean subduction zone at 38.25°S do not exist to date. Highlights • Interpretation of P- and S-wave seismic reflection data from the south Chile margin • Reflectivity images show several horizontal as well as dipping crustal reflectors. • Inferred crustal rock compositions are in agreement with geological observations. • Presence of fluids in the continental crust is not necessary to explain the results. • Large-scale crustal and upper mantle anisotropy is qualitatively suggested. [ABSTRACT FROM AUTHOR]

Abstract The Yarlung Zangbo Suture (YZS) is the collisional front between the Indian and Eurasian plates. The deep structure beneath the YZS has long been a focus of research. Its particular tectonic location and formation time provide a natural laboratory for the study of ongoing continental collisional processes. Lateral variations in the Moho discontinuity provide evidence of basic processes governing plate tectonic evolution. The depth and geometry of the Moho provides first-order information for restoration of complex geodynamic systems. This paper presents a studying result of the Moho, both adjacent to and beneath the YZS, obtained using five large dynamite shots along two profiles. These five large shots were combined to construct two single-fold profiles (YZS-A and YZS-B) and obtain high-resolution images of the Moho beneath the YZS. Both profiles show that continental crust thickness beneath the YZS is twice the global average of continental crust, and the depth of the Moho along profile YZS-B is deeper than YZS-A. YZS-A (81°E) indicates a relatively flat Moho without offset related to continent-continent convergence beneath the collision zone. Conversely, a Moho structure with offset and overlapping reflections was imaged beneath profile YZS-B (88°E). Significant lateral variations in the geometry of the Moho discontinuity along the YZS may indicate that the Indian lithosphere is thrusting beneath Tibet at a different angle from west to east. Highlights • We investigate the Moho discontinuity beneath the Yarlung Zangbo Suture (YZS). • Continental crust thickness beneath the YZS is twice the global average. • Depth of the Moho varies across two profiles taken. • The Indian lithosphere may be thrusting beneath Tibet at different angles. [ABSTRACT FROM AUTHOR]

Eastern margin of the Bohemian Massif is a geologically remarkable area, where three different orogenic cycles are meeting—the oldest, Cadomian, building a basement for younger cycles; a younger, Variscan; and the youngest, Alpine, covering the older units. In the past, this area was investigated by gravimetry and seismic methods. Recently, we have supplemented broadband magnetotelluric measurements within the period range of 0.001-1000 s, carried out on 29 stations distributed along a 140-km-long west-east regional profile. The profile direction was based on local geology and then confirmed by a dimensionality and directionality analysis. Data showed moderate effects of cultural noise in the signals and could be successfully processed by robust methods. We carried out a 2D inversion of the data using the REBOCC approach. The inversion results confirm the known near-surface geology and reveal deeper structures. On the west and in the central part of the profile, units of the Bohemian massif (the Moldanubian Zone, the Brunovistulicum) are interpreted. In the east, the Western Carpathians units are encountered. Short-period data agree well with the known near-surface geology of all inner smaller units and bring new knowledge in particular on their thickness. In the shallow structure, several conductive anomalies have been identified which are hypothesized to be related to graphitized layers in the Moldanubian Zone. From long-period data, a new image of the Moldanubian/Brunovistulicum contact and about the structure of the Brunovistulicum, especially the Brunovistulian Massifs, was obtained. [ABSTRACT FROM AUTHOR]

Abstract The structural evolution of the Oligocene Rieserferner pluton (Eastern Alps), developed during pluton cooling and exhumation, includes localized deformation structures consisting of: (i) steeply dipping joints, leucocratic dykes and quartz-feldspar veins, and related ductile shear zones (formed at ∼ 600 °C); (ii) shallowly dipping joints with associated epidote and quartz veins, and related ductile shear zones ( ∼ 450 °C); (iii) steeply dipping mafic dykes and calcite + white mica-bearing brittle-ductile faults ( ∼ 300 °C); (iv) steeply dipping pseudotachylyte-bearing faults (<250 °C); and (v) zeolite-bearing faults (<200 °C). The structures (i-iii) and (iv-v) can be dated to the Oligocene and Early Miocene, respectively. The kinematic analysis suggests a change in local shortening direction from N290° to N350°, interpreted to reflect a change from transtension in the Early Oligocene, associated with a N060°-directed plate divergence, to transpression in the Miocene, associated with a (N)NW-directed plate convergence. This evolution reflects the sequence of transient and long-term geodynamic processes occurring in the Eastern Alps during the Tertiary, including slab break-off of the subducted European slab, the indentation of the Dolomites promontory against the Alpine stack of nappes, and the exhumation and lateral escape tectonics of the Alpine belt. Highlights • A sequence of solid-state ductile and brittle structures occurs in the Rieserferner. • The local shortening direction switched from E-W to N-S during Oligocene. • The switch reflects transition from transtension to transpression during Oligocene. • Transient transtension occurred during pluton intrusion and early stages of cooling. • E-dipping normal shear zones suggest incipient Early-Oligocene extension. [ABSTRACT FROM AUTHOR]

Abstract The present work focuses on the comprehension of the growth mechanisms and dimensional properties of the pre-Pliocene Monte Alpi fault network by mean of integrated field and laboratory analyses. After this multidisciplinary approach, detailed throw profiles are computed for each fault belonging to the Monte Alpi network. Subsequently, the dimensional properties of the individual faults are calculated. Data obtained from this work are discussed in terms of fault growth mechanisms and timing of deformation, and reported in a conceptual tectonic evolution model of the Messinian foreland basin system. Data suggest that originally isolated fault segments developed during the earliest stages of foreland basin formation by re-activation of a pre-existing, Early Cretaceous fault set, and formation of an orthogonal one. These two fault sets formed a scale-independent network. Differently, the same fault sets were also active during its subsequent development forming a scale-dependent fault network characterized by T- and Y-shaped fault intersections. This deformation controlled the half-graben depocenters evolution filled by up to ca. 600 meters of terrigenous deposits during the Late Messinian time. Highlights • Both timing and growth processes are deciphered for the pre-Pliocene fault network. • Main dimensional attributes computed for all analyzed faults. • Inferences on the fault-control evolution of the Messinian foreland basin system. [ABSTRACT FROM AUTHOR]

This work criticizes the entrenched views according to which the orientation of the principal tectonic stress axes can be determined from local (in time and space) observations of the kinematic indicators which jointly allow estimating the strain rate of a crustal block under study. The criticized approach ignores or replaces by subjective assumptions the following factors: (1) The block’s interaction with a hosting medium expressed in terms of the equilibrium conditions of the block; (2) The stress rate which (in addition to stresses) can affect the strain rate; (3)The specific macroscopic mechanical properties of the block’s material under the unknown sought stresses, including the ratio of the stress relaxation time to the period of observations. This approach, which is developed in some Solid Earth sciences and mainly in tectonophysics, is referred to in our paper as the method of local kinematic reconstruction (MLKR) of stresses. After briefly surveying the concept of forces and stresses and discussing the importance of studying the tectonic stresses, this paper refutes the MLKR notions based on general arguments and by the example of certain thought experiments. It is shown that the use of the MLKR for the conditions of the Earth’s interior does not guarantee against obtaining the results that fundamentally and drastically differ from the true tectonic stresses. In the studied rock block, depending on the factors ignored in the MLKR, the principal axes of the strain rate tensor, on one hand, and the principal stress axes, on the other hand, can be oriented discordantly in any arbitrary given fashion. In particular, in the processes accompanied by the release of elastic energy, the maximal rate of elongation can be oriented along the axis of maximal compression, whereas the maximal rate of shortening can be aligned with the axis of the maximal tension. In this paper, the deformation processes that are most detrimental to the results of stress reconstruction by the MLKR are revealed. We introduce the notion of the inherited stress-state regime in which the orientation of the axes of principal stresses during the observation period does not depend on the deformation process and, hence, cannot be in principle determined by the MLKR. An attempt to directly locally recover the stress axes from the kinematic data is a false objective because neither the physical meaning of the stress tensor nor the way it is introduced has anything to do with strains. It is concluded that the MLKR is physically inadequate and that the tectonophysical concept of locality should be abandoned in favor of returning to the notions of classical physics, namely, to using the conservation laws. By the example of several guides on tectonophysics, this paper exposes typical errors in understanding the stress reconstruction problem. [ABSTRACT FROM AUTHOR]

Based on the recent observations about the movement and rheological structure of the lithosphere and deformation pattern of the crust, we developed a three-dimensional finite element model for the northeastern margin of the Tibetan Plateau. The model considered the impacts of both external and internal conditions, including mantle convection, gravitational potential energy and block interactions. We compared the simulated surface movement rates to the observed GPS velocities, and the results revealed that crustal movement gradually decreased toward the edge of the plateau. The factors controlling this pattern are the interactions of adjacent blocks, gravitational potential energy of the plateau, and also mantle convection as well. Additionally, according to the observation that there was an apparent difference between the horizontal movement rate of the lithosphere and convective velocity of the underlying mantle, and also based on the results of seismic anisotropy studies that suggest different strengths and deformation regimes of the lithosphere in different tectonic blocks, we proposed that the impact of mantle convection on the lithosphere may have varied in space, and introduced a parameter named mantle convection intensity factor in numerical simulations. Our simulation results show consistent surface movement rates with GPS observations, which further supports the viewpoint of seismic anisotropy studies, i.e., the degree of coupling between the crust and mantle varies significantly among different blocks. [ABSTRACT FROM AUTHOR]

Over the past 20 years, analyzing the abundance of the isotope chlorine-36 (36Cl) has emerged as a popular tool for geologic dating. In particular, it has been observed that 36Cl measurements along a fault plane can be used to study the timings of past ground displacements during earthquakes, which in turn can be used to improve existing seismic hazard assessment. This approach requires accurate simulations of 36Cl accumulation for a set of fault-scarp rock samples, which are progressively exhumed during earthquakes, in order to infer displacement histories from 36Cl measurements. While the physical models underlying such simulations have continuously been improved, the inverse problem of recovering displacement histories from 36Cl measurements is still mostly solved on an ad hoc basis. The current work resolves this situation by providing a MATLAB implementation of a fast, automatic, and flexible Bayesian Markov-chain Monte Carlo algorithm for the inverse problem, and provides a validation of the 36Cl approach to inference of earthquakes from the demise of the Last Glacial Maximum until present. To demonstrate its performance, we apply our algorithm to a synthetic case to verify identifiability, and to the Fiamignano and Frattura faults in the Italian Apennines in order to infer their earthquake displacement histories and to provide seismic hazard assessments. The results suggest high variability in slip rates for both faults, and large displacements on the Fiamignano fault at times when the Colosseum and other ancient buildings in Rome were damaged. [ABSTRACT FROM AUTHOR]

Abstract The El Hamma-Gabes Region in southeastern Tunisia belongs to the crustal shear zone of the South Atlasic Fault Corridor, which corresponds to the Meso-Cenozoic North African margin. So far, most geological works on this region are on the stratigraphic order. However, there are few tectonic and structural studies carried on the style and mechanism of structural deformation. The present work analyzes the subsurface structure of the El Hamma grabens area based on gravity and seismic data, calibrated by stratigraphic and tectonic elements. The El Hamma-Gabes Zone is characterized by a horst and graben system associated with N130˚-150° trending parallel extensive/transtensive faults. Two main grabens are recognized: the El Hamma graben in the west and the Chenchou graben in the east. They are separated by the Jebel Hallouga horst. These structures relate to two N100˚-120° trending principal shear corridors (PSC) arranged in right echelon, being the Oum Ali-Fejej Shear corridor towards the northwest and the Matmata-Medenine Shear corridor towards the southeast. Stratigraphic and structural data collected from several outcrops were correlated with the tectonic events and paleostress reconstruction. New data shows that the PSCs marked a dextral transtensive kinematic framework during the N80° directed Upper Cretaceous extension. The extensional movements are the N150˚-180° Paleogene extension and associated transpression during the N130° Neogene shortening. The dextral sliding generated and maintained the opening of the El Hamma-Gabes graben system, creating a “pull-apart” basin that opened in an extensive ramp between the two PSCs. The overall extension of this ramp is estimated to 15% of the initial width. Highlights • The El Hamma-Gabes zone corresponds to a relay ramp between two main shear corridors: Bir Oum Ali-Fejej at the North and the Matmata-Medenine at the South. • The distension of this ramp was initiated in the upper Aptian-Albian by a dextral transtensional sliding along the shear corridors under the effect of extensive regional stresses N80. • Its opening was maintained by extension NNW-SSE to N-S during Paleogene and then by dextral transpressive sliding along the two shear corridors during Neogene compressions. • The geophysical data used to detect the subsurface lineaments that insured the structuring of this zone. • This extensive relay ramp represents a pull-apart basins along the crustal shear zone of the South Atlasic Fault Corridor. [ABSTRACT FROM AUTHOR]

Abstract New high-resolution geophysical data over Central Iran defines >30 continental fragments or blocks and lithotectonic domains, which are bounded by large-scale, kinematically-coherent structures that may be traced under significant cover. Normal, inverted normal and basin-bounding faults, and thrusts were transposed to steeper dips with subsequent strike-slip movement. Assembly required three triangular “keystone blocks”, with edges defined by entrained ophiolites, which are required by rotational tectonics and the assembly of at least three adjacent blocks, in this instance combined with anticlockwise rotation of the Lut Block and Central Iranian Microcontinent. Late-kinematic, brittle-ductile to brittle, NNE-to NE-trending structures are superimposed on the macrostructural pattern. From c. 12 Ma onwards, NW-directed compressional tectonics resulted in the development of NNW-trending, dextral, strike-slip structures, notably the Dehshir Fault, which overlapped temporally with the main Cu-bearing, porphyry-forming event and Urumieh-Dokhtar Magmatic Arc development. The Shir-Kuh Block and fragments immediately to the north of it originated approximately 200 km to the north, at the SW edge of the Anarak Metamorphic Complex. Southward movement of the Shir-Kuh Block was due to a combination of dextral movement along the Dehshir Fault and anticlockwise rotation of the Lut and Tabas Blocks. Major faults are delineated in four separate basins: the Shotori Basin, the Kharanaq Basin, the Farrokhi Basin and the Gonabad Basin. Graphical abstract Image Highlights • Structural interpretation of new high-resolution airborne geophysical data over central Iran. • Delineation of over 30 blocks and terranes bounded by large-scale, kinematically-coherent structures. • Confirms anticlockwise rotation of Central Iranian Microcontinent. • Highlights the role of triangular or cuspate “keystone” blocks in terrane assembly. • Shir-Kuh Block displaced 200 km south of the southern edge of the Anarak Metamorphic Complex. [ABSTRACT FROM AUTHOR]

Abstract A new approach is developed to depict the fault lineaments and pertinent tectonic evidence of the Sinai Peninsula, Egypt from gravity and magnetic data. The approach is capable of identifying not only the main basements trends, but also the main trends of the sedimentary structures. The main lineaments trends in the Peninsula were derived from the geologic information as well as the regional and residual gravity and magnetic maps. Joint interpretation has revealed that the deep-seated structures have NW-SE, NE-SW, E-W, and N-S trends, whereas the shallow-seated structures have NE-SW, E-W, NW-SE, and WNW-ESE. Highlights • Lineament investigations utilizing gravity and magnetic data of the Sinai Peninsula, Egypt. • Tectonic evident that controls the study area. • Residual gravity and magnetic maps used to evaluate shallow structures. • Regional gravity and magnetic maps utilized to estimate deep structures. [ABSTRACT FROM AUTHOR]

Abstract Gravity data were analyzed in conjunction with earthquake, seismic reflection, and geological data to investigate the upper crustal structure of the Utica-Mateur region of northeastern Tunisia and relate this structure to the current tectonic environment of northern Tunisia. To accomplish this goal, gravity anomaly maps were constructed using isostatic gravity residual methods, match-filtering to create residual anomalies, and horizontal gravity gradients. Additionally, the depths to the major density contrasts were determined using a 2D power spectrum analysis and Euler deconvolution and 2D forward modeling. The residual gravity anomalies interpreted in conjunction with gradient determined lineaments indicate that there are several gravity maxima related to uplifted regions bounded by lineaments that trend mainly to northeast- and northwest. Based on the Euler deconvolution analysis, the majority of these lineaments are located at shallow depths (<6 km) and can be related to the seismic activity of the region. Correlating these newly imaged lineaments, uplifts and subsiding areas with seismicity and focal mechanism studies, a new structural map is proposed for the Utica-Mateur region. The majority of the region can be interpreted by uplifts and subsiding (pull apart basins) areas bounded by strike-slip faults that contain compressional and extensional stress components. This stress regime is thought to be caused by the reactivation of older structures by the current compressional stress regime due to the convergent of Africa and Eurasia and active rifting of the Sicily basin. However, the proposed recent segmentation of a northeast-retreating subducting slab under Africa that caused a major lithospheric discontinuity to the south of the Utica-Mateur region added second and third order tectonic variations. These variations modified the stress regime which caused the formation of strike-slip faults and the gravity analysis indicates that the entire Utica-Mateur region is still affected by this stress field change. Highlights • Gravity analysis of Northeast Tunisia included an isostatic residual gravity study. • Derivative analysis identified lineaments to be faults that are aligned with seismicity. • Northeast Tunisia is tectonically active due a compression stress regime. • Compressional stress is related to slab rollback and rifting in the Sicilian Rift Zone. [ABSTRACT FROM AUTHOR]

Abstract The magma-poor Newfoundland margin formed following lithospheric stretching, rifting and breakup resulting in the separation of the Grand Banks from Iberia, and northern Newfoundland from Ireland. Mesozoic igneous rocks contemporaneous with rifting have been documented on- and offshore Newfoundland, with later offshore magmatism occurring post-breakup. The Notre Dame Bay Magmatic Province (NDBMP) is a Jurassic-Cretaceous, potentially rift-related occurrence of igneous rocks onshore Newfoundland that includes the gabbroic Budgell Harbour Stock (BHS) and marginal lamprophyre dykes, in addition to the nearby, potentially related, Dildo Pond Intrusion (DPI) and Leading Tickles Stock (LTS). Although the BHS is penetrated by wells, it is poorly exposed at surface, and the deeper structure remained unknown. Here, results of field-based mapping combined with inversion of Full Tensor Gradiometry (FTG) and aeromagnetic data covering the BHS are presented. Although the FTG data are of a higher resolution than the magnetic data, comparable results were obtained from these independent datasets. We found that the dykes form clusters at the ends of density and susceptibility anomalies, interpreted to be lobe-like magmatic conduits. Furthermore, potential-field analysis has revealed the irregular geometry and southward-dipping nature of the BHS, in addition to the presence of multiple, near surface anomalies that may correspond to dyke clusters or other igneous bodies. Structural analysis indicates that emplacement of the dykes was controlled by pre-existing geological structures and that they have probably been deformed post-intrusion, potentially via the reactivation of pre-rift faults. The potential-field investigations and observations of dyke margin lineations from field-based structural analysis indicate that multiple dyke sources and bodies similar to the BHS may also exist. Finally, this study demonstrates that magma-poor margins, such as the Newfoundland margin, may host significant volumes of extension-related magmatic rocks, challenging the concept of a distinction between magma-rich and magma-poor rifting. Graphical abstract Unlabelled Image Highlights • Structure of the Budgell Harbour Stock and related dykes was revealed from field mapping and potential-field data inversion. • The dykes form clusters at the ends of lobe-like magmatic conduits. • Dyke emplacement was likely controlled by pre-existing structures. • The dykes were probably deformed post-intrusion, potentially via the reactivation of pre-rift faults. • Multiple dyke sources and bodies similar to the Budgell Harbour Stock may also exist in the area. • This work demonstrates that magma-poor margins may host significant volumes of extension-related magmatic rocks. • This challenges the concept of simple a distinction between magma-rich and magma-poor rifting. [ABSTRACT FROM AUTHOR]

In this paper we present the results of an investigation on the electric crustal structures depicted by a magnetotelluric (MT) transect cutting through the easternmost sector of the Alta Floresta Gold Province, in the SW Amazon Craton, Brazil. The MT dataset was acquired along a 200 km NNE-SSW transect encompassing 35 broadband and 12 long-period stations, covering a period range of approximately 10 −4 to 10 4  s. We adopted a data processing scheme based on robust estimators over the electromagnetic cross-spectra for combined single and remote reference stations in order to estimate horizontal and vertical transfer functions. The dataset was inverted using a 3-D MT based minimum structure algorithm, considering the data dimensionality, directionality analysis and the irregular station distribution. A set of inversions considering different model parameters have been performed to achieve a model with robust main features and to test the stability of the obtained solutions. A resolution study was also proposed in order to evaluate the average depth of model sensitivity. The electrical structures depicted can improve the understanding of the ancient tectonic features encrypted at the cratonic stable crust, contributing to elucidate the mechanisms that might have controlled its ore genesis. Conductors in the mid-crust correlate with shallow mafic enclave-rich granitic and foliated volcanic facies outcrops, linking the geoelectric anomalies to a possible mid-crustal source correlated to the Statherian magmatism, which is believed to be the main pulse related to gold metallogenesis at this province. [ABSTRACT FROM AUTHOR]