Transpressive Motion Research Articles

Ages and structural relationships in the Ganderian central Cape Breton Highlands, Nova Scotia, Canada

Structural complexity of the Cape Breton Highlands is a key problem in reconstructing tectonic events in the northern Appalachian orogen. A new U–Pb thermal ionization mass spectrometry age of 428.53 ± 0.16 Ma for metarhyolite in the Calumruadh Brook Formation shows that volcanic and sedimentary rocks were deposited before collision of the Aspy and Bras d'Or terranes along the Eastern Highlands shear zone. A new U–Pb laser ablation zircon age of 394 +6/−4 Ma confirms that peak metamorphism in the Middle River complex continued during convergence linked to late stages of the Acadian orogeny. The compressive tectonic environment evolved into a transpressional system after initial collision in the late Silurian and caused a repeated pattern of imbrication of units in the Aspy terrane in the hanging wall in the collision. The shear zones bounding the geological units are curvilinear and have south-directed kinematics, imbricating units and transporting higher grade rocks over lower grade rocks, and moving plutons upward relative to their host rocks during and shortly after intrusion. The vergence of imbrication is parallel to the direction of transpressional movement on the main Eastern Highlands shear zone. This geometry is present in Ordovician–Silurian rocks and repeated in Devonian plutonic rocks, indicating that the overall transpressional tectonic setting was a long-lived feature of the orogen. The shear zones localized late syn- to post-deformational plutons that intruded at ca. 375–370 Ma. By the latest Devonian, emplacement of the ca. 363 Ma Margaree and related plutons marked the beginning of extension in the central Cape Breton Highlands.

Kinematic Analysis of the Nain and Darrech Deh Faults and Their Structural Position in the Western Side of the Central Iranian Range

The western margin of Central Iran – the Nain area – is composed of the Mesozoic ophiolitic mélanges deposited during the Late Cretaceous. The Nain and Darrech Deh faults whose trace indicators can be seen in the study area are among the largest faults therein. These faults have a north-northwest strike and are the right-lateral transpressional active lineaments. The main aim of this research is to perform structural mapping and geometric analysis of structural features along the Nain and Darrech Deh fault system. The research was conducted using satellite imagery and field data. The structural analysis showed that the faults comprise a complex network which formed during two stages: 1) thrust faulting in the Late Cretaceous and 2) reactivation of thrust faults in the form of the right-lateral reverse-slip structures as a result of transpressional movements in the Upper Miocene. The Nain and Darrech Deh faults are presently active and exhibit the right-lateral strike slip displacement with a reverse component.

The seismicity in the middle section of the Altyn Tagh Fault system revealed by a dense nodal seismic array

The left-lateral Altyn Tagh Fault (ATF) system is the northern boundary of the Qinghai-Xizang Plateau, separating the Tarim Basin and the Qaidam Basin. The middle section of ATF has not recorded any large earthquakes since 1598 AD, so the potential seismic hazard is unclear. We develope an earthquake catalog using continuous waveform data recorded by the Tarim-Altyn-Qaidam dense nodal seismic array from September 17 to November 23, 2021 in the middle section of ATF. With the machine learning-based picker, phase association, location, match and locate workflow, we detecte 233 earthquakes with ML -1-3, far more than 6 earthquakes in the routine catalog. Combining with focal mechanism solutions and the local fault structure, we find that seismic events are clustered along the ATF with strike-slip focal mechanisms and on the southern secondary faults with thrusting focal mechanisms. This overall seismic activity in the middle section of the ATF might be due to the northeastward transpressional motion of the Qinghai-Xizang Plateau block at the western margin of the Qaidam Basin.

Sedimentology, geochronology and provenance of the late Permian and Triassic Mitu Group in Peru—The evolution of continental facies along a transform margin

AbstractIn the late Permian and Triassic, the continental Mitu Group formed in extensional basins along the length of the Cordillera Oriental and Altiplano of present‐day Peru. Given the presence of coeval arc systems only in northern Chile and southern Ecuador but not in Peru the tectonic setting of the Mitu basin has been interpreted variably as orthogonal continental rift, sinistral transtensional rift, aulacogen and back‐arc basin. The Mitu Group comprises continental mass flow and alluvial fan, fluvial, aeolian and minor lacustrian facies and hosts thick piles of subalkaline and alkaline intermediate and felsic ignimbrites and mafic lavas. The age of the Mitu Group had originally been established as ranging from the Late Permian to the late Triassic on the basis of structural considerations and scarce biostratigraphic data. Recently, U–Pb zircon ages from ignimbrites and sedimentary rocks have been taken to constrain the Mitu Group to the Middle and Late Triassic. We performed a sedimentological, heavy mineral, and zircon geochronological and Lu‐Hf isotope study of the Mitu Group in 14 sections mainly in southern and central Peru, and one section in northern Peru. Ten new U–Pb concordia ages on ignimbrites intercalated in the Mitu Group successions offer a new robust stratigraphic framework and constrain the stratigraphy of the Mitu Group between 260 and 205 Ma. In combination with maximum likelihood ages of deposition derived from detrital zircon, U–Pb geochronology places the deposition of the Mitu Group between ca. 270 and 194 Ma (lower Guadalupian into the Sinemurian). Detrital zircon U–Pb age distributions and heavy mineral assemblages reflect a strongly recycled Precambrian Amazonian and Palaeozoic proto‐Andean provenance. The Palaeozoic detrital age patterns are highly variable, and temporally and spatially random. A local provenance can generally not be identified. εHf(t) values in zircon obtained from ignimbrites and sedimentary rocks indicate variable degrees of crustal recycling. In the course of the Palaeozoic, εHf(t) values become on average progressively less negative, with a large proportion particularly of Mitu age zircons' εHf(t) values encompassing less evolved and moderately juvenile compositions. Along strike of the basin stratigraphic thicknesses, and rates and times of accumulation vary strongly with larger thicknesses and rates being registered in southern Peru. This suggests that the Mitu basin had been divided into a number of subbasins with individual histories of subsidence, accumulation, and volcanism. Absent a magmatic arc, late Permian–Triassic Peru evolved in a sinistral plate tectonic and regional framework expressed particularly in the sinistral Late Gondwanide orogeny predating the Mitu Group. We interpret that a sinistral transform fault linked the subduction zones in southern Ecuador and northern Chile and that the Mitu Group basin has formed by sinistral transtensional and transpressional movements along a related transcurrent fault inboard of the transform margin. In the broader framework of the accretionary Terra Australis orogen along the western Gondwana margin, this interpretation fits its evolution in the Andean segment in an internally consistent way.

InSAR coseismic deformation field and seismogenic structure of the 2020 Mw6.0 Jiashi earthquake and the implication for the moderate-magnitude seismicity in the southwestern Tian Shan, western China

The Kepingtage fold-and-thrust belt in the southwestern Tian Shan in western China hosted the 2020 Mw 6.0 Jiashi earthquake with no apparent surface ruptures. The thrust nappe structure in this region is characterized by moderate-magnitude (Mw5.5-6.5) seismicity, but the seismogenic mechanisms and controlling factors remain under investigation. In this study, we utilized Sentinel-1A synthetic aperture radar satellite data to reconstruct the InSAR coseismic deformation field of the 2020 Jiashi earthquake. To address the limitation imposed by residual orbital phases during the interferometric measurement, we proposed a novel automatic method that combines ascending and descending track data with terrain features for orbit refinement. Eight comparative tests were conducted to prove the effectiveness of the proposed method. Subsequently, we inverted the jointly constrained deformation field after orbit correction to obtain the fault geometric parameters and slip distribution. Our results show that the 2020 Jiashi earthquake is characterized by right-lateral transpressive motion. The smooth interference fringes demonstrate spatially continuous surface uplift and subsidence without detectable coseismic surface ruptures, with a maximum uplift of ∼0.08 m and a maximum subsidence of ∼0.03 m, caused by the subsurface folding due to deep seismic rupture. This event is best fitted by a north-dipping fault plane with a depth of 4.2 km, a dip angle of 11.6°, and a strike of 276° beneath the Keping thrust fault. In terms of various geometric parameters of the fault, the inversion results of this study are generally similar to the focal mechanism solution provided by USGS (MWb), but are different from the focal mechanism solutions of other institutions and previous research results. Combined with the published geological investigations and seismic reflection surveys, we suggest that the seismogenic structure of the 2020 Jiashi earthquake is the lower ramp of the Keping thrust fault and the abrupt fault bend between the lower and upper ramp may limit the propagation of the coseismic rupture to the surface. The limited rupture of this event is dominated by the irregularities in fault geometry along strike and dip, as well as the lower rock strength of the cover above the detachment, which contribute to a deeper understanding of the seismic behavior in fold-and-thrust belts and the moderate-magnitude seismicity in the southwestern Tian Shan region.

Assessment of the probability of success and risking in hydrocarbon exploration: A case study from Zindapir Anticline, Sulaiman Foldbelt, Indus Basin, Pakistan

Role of the statistical calculation is very important in petroleum exploration business. It is used to calculate the associated risk and determines the chances of geological success prior to drilling of an exploratory well in mapped prospect area. This manuscript is focusing on the geological modelling of Zindapir Anticline, Sulaiman Fold Belt, Indus basin, Pakistan using mainly based on the concept of probability developed by Coordinating Committee for Coastal and Offshore Geoscience Program (CCOP) in East and Southeast Asia in 2000. Study area comprises of Zindapir Anticline with two abandoned wells Well X-1 and Zindapir-1 which were drilled and declared as dry holes. Detailed geological modelling indicates that Zindapir structure is still virgin to flow hydrocarbons, and there are ample chances of compartments, which were developed as result of transpressional movement at the periphery of the structure. Interpreted seismic line also supports the presence of different compartments in structure. These compartments may host hydrocarbon, generated and migrated either from Bharti Syncline and Sulaiman Foredeep or generated by indigenous source rocks possibly deposited in the south of Zindapir-1 and Well X-1. Presence of trap, hydrocarbon charge and reservoir in Zindapir structure indicates there is better probability of success for hydrocarbons, and good chances for the development of traps because of transpressional movement. Traps may contain the hydrocarbon, possibly generated from Bharti Syncline in west and Sulaiman Foredeep in east whereas southern part of Zindapir Anticline was not considered, and northern part of Zindapir Anticline was mapped with very open grid size. Present seismic data is limited which is the major reason that due to poor probability of effective trap it is recommended to acquire additional seismic data for further detailed picture structure of Zindapir Anticline. An equation for the calculation of geological chances success for new development well is also proposed in this manuscript.

Carbonate rocks in northern of West Jiwo Hills Bayat: The indication of thrust belt development in southern Central Java

Bayat, Klaten, Central Java, is one of three locations in Java with complete types of rocks exposed at the earth’s surface. All those rocks are scattered over a short distance in Bayat, revealing past processes of rock deformation (folding, fracturing, and faulting) and present-day processes of rock weathering and erosion. In this study, we present how clastic carbonate rock of the Oyo Formation at northern Jiwo Hills could be separated about ±15 km northern from its platforms as an indication of thrust fault growth. This study uses aerial photography for photogrammetry (drones) combined with structural geology and microfossil analyses (to know the exact formation) from the outcrop observation. Recent studies have certified that drones are one reliable observation tool in various aspects with better resolution, especially in structural geology studies. Aerial photogrammetry is very well done to see the exact condition of a wide area combined with high resolution on an outcrop scale. The result shows that the carbonate rocks are from Oyo Formation (N9–N11) with the Middle Neritic bathymetric zone. The structural geology phenomenon kinematically indicates the impact of the transpressional movement called flower structure. Based on subsurface interpretation, the authors hypothesize this area was the product of an imbrication thrust stack uplifted basement as the result of the thrust fault rather than horst or paleo-basement high.

Frontal expansion of an accretionary wedge under highly oblique plate convergence: Southern Indo-Burman Ranges, Myanmar

The formation of accretionary wedges with oversteepened slopes and uplifted axial zones has been demonstrated to be potentially associated with highly oblique plate convergence by numerical and analog studies. The direct role of this mechanism, or other factor(s) in producing the described structural and morphological features in nature, however, has yet to be confirmed. We used seismic reflection sections, detrital zircon U-Pb ages, and detrital apatite fission-track thermochronological data to examine the effects of highly oblique convergence and sediment reworking on accretionary wedge growth in the Indo-Burma Subduction Zone. A detailed subsurface structural analysis of a two-dimensional seismic survey from the outer wedge of the southern Indo-Burman Ranges, Myanmar, yielded three primary characteristics. These are (1) a narrow, steep deformation front (average width 15.6 km) and a vast, low-relief shelf terrace (average width 49 km); (2) a comparatively long-lived growth thrust fault (FT1) with a convex-up geometry at the rear of the deformation front that controlled the vertical stack of the progradational sequences in the shelf terrace; and (3) a group of NE-striking transtensional faults that cut through entire outer-wedge successions and displays as a series of negative flower-like structures. These characteristic features are roughly consistent with the results of laboratory analog modeling of highly oblique plate convergence but significantly differ from those of natural accretionary wedges that formed under highly oblique convergence conditions, such as those in the Sumatra, Hikurangi, Chile, and Cascadia. We further analyzed the sediment provenance of the southern Indo-Burman Ranges and discovered that the outer-wedge rocks are a product of sediment reworking of the hinterland wedge that began to be uplifted and exhumed in the early Miocene (22−12 Ma) due to transpressional motion between the Indian plate and West Burma Terrane. Our analyses indicate that active sedimentation behind the major growth thrust fault (FT1) provided additional basal shear stress that strengthened the coupling of the interface between the wedge base and décollement and promoted the vertical expansion of the outer wedge of the southern Indo-Burman Ranges from the Neogene to the present day. In contrast, the outer wedge of the central Indo-Burman Ranges has experienced stronger forward accretion since the late Miocene, which could be explained by a smaller degree of obliquity and weaker sediment reworking. Our findings demonstrate that both highly oblique plate convergence and sediment reworking were the primary driving forces that triggered vertical development of accretionary wedges. The results of this research have significant implications for understanding the structures and kinematic evolution of wedge systems at other convergent plate margins, in which seamount passage or subduction erosion is often interpreted as the cause of the steeply tapered wedges.

Crustal Seismic Anisotropy Along the Continental Margin in Western Canada From Receiver Function Analysis

AbstractCoastal British Columbia (BC), Canada, has the highest seismic hazard in the country due to convergent and transpressive deformation at offshore plate boundaries between the Pacific, Juan de Fuca (JdF) and North American (NA) plates. Further landward, the crust of the NA plate is made up of several geologically unique exotic terranes and is unusually thin. Investigating the geophysical features in this area can help us better constrain its tectonic history and the geophysical processes that are currently underway. Here, we conduct an analysis of teleseismic body‐wave scattering data (i.e., receiver functions [RFs]) recorded at stations across western coastal BC including northern Vancouver Island and southeastern Alaska. Using these RFs, we perform a harmonic decomposition with respect to earthquake back‐azimuths to determine the orientation of seismic anisotropy over a series of depth ranges, attributable to either mineral alignment or dipping structures. We find a coherent pattern of margin‐parallel orientations at upper crustal depths that persist onto the mainland at distances 420 km from the margin. Furthermore, dominant receiver function orientations at depth are attributed to dipping faults and interfaces, and fabrics due to lower crustal shearing or inherited from tectonic assembly along the margin. This work supports models for the tectonic assembly of this region that involve a combination of plate subduction and transpressive motion along crustal scale faults that pervade a wide portion of the margin. This work also helps to constrain the current geometries of the subducting Pacific and JdF slabs.

STRUCTURAL-GEODYNAMIC CONTROL OF KIMBERLITE PIPES OF THE YAKUT DIAMOND PROVINCE ACCORDING TO THE DATA OF GRAVISTRUCTURAL ANALYSIS

The article deals with the fundamental concepts of a new method of interpretation of regional gravimetry (scale 1:1000000) based on the idea of the deformational nature of low-frequency gravity anomalies. The method provided an opportunity to identify the direction of tectonic compression in the Yakut diamond-bearing province, to localize segments and axes of inter-shear compression and extension of different kinematics and on that basis to distinguish the shear interaction zones spatially correlating with the location of kimberlite pipes. Particularly, the whole area is characterized by four transpressive compression directions: a pair of orthogonal (dextral with azimuth 8° and sinistral with azimuth 98°) and a pair of diagonal (dextral with azimuth 38° and sinistral with azimuth 128°). These data correlate to those from the regional tectonophysical studies not only within the compression direction azimuths but also within kinematics of transpressive motions for two main phases in geodynamical evolution of the Yakutsk diamond-bearing province (YDP) - predominantly dextral for the first phase of the northeastern compression and sinistral for second phase of the northwestern compression. The article also shows that the Alakit-Olenek mineragenic zone is an extensive (~500 km) area of plastic deformation of rocks ~90 km in width with the right-lateral kinematics of apparent motions of the rocks along its northern and southern boundaries. The southern boundary of the mineragenic zone exhibits the northeaststriking continuity whereas its northern boundary is discontinuous. The boundaries of the Alakit-Olenek mineragenic zone are controlled by the zones of shear interaction of different dynamics and kinematics, which are spatially related to kimberlite pipes and diamond placer deposits. The results of this study imply that the method proposed for interpretation of gravity field can predict the occurrence of structures of geodynamic control of kimberlite magmatism of the Yakut diamond-bearing province.

Offshore bedrock geology of Eclipse Sound and Pond Inlet: connecting the structure and stratigraphy of Bylot and northern Baffin islands

Understanding the Mesoproterozoic and younger structural history of the Eclipse Sound/Pond Inlet area is essential for the interpretation of its Archean to Paleoproterozoic geological history and could have important implications for mineral and petroleum exploration models in the northern Baffin Bay area. The identification of potentially active faults is critical for understanding possible earthquake-related hazards in the area. The integrated interpretation of 1970s-vintage marine seismic data with hill-shaded bathymetry, aeromagnetic data, and onshore geology maps has facilitated the identification of probable Mesoproterozoic (Bylot Supergroup) to Holocene strata on and below the sea floor and a suite of episodically reactivated northwest-striking horst- and graben-bounding normal faults and fault zones. Fault displacement likely occurred during the development of the Mesoproterozoic Borden basin and the Cretaceous–Paleogene opening of Baffin Bay, and in some cases may continue today. Some faults become more west-trending toward the south, which requires parts of these faults to have intermittently accommodated transtensional and (or) transpressional motion, possibly explaining local folds and out-of-graben thrusting. Numerous previously unrecognised faults have been documented, with faults beneath Eclipse Sound (Eclipse Trough) spaced at 5 to 7 km intervals, and at least one fault zone (Cape Hay Fault Zone) that appears to be at least 250 km in length, suggesting faults of similar spacing and scale may be present under Baffin Bay. This study uses a multi-thematic office-based methodology that inexpensively, and with little environmental impact, facilitates the mapping of structures that intersect the sea floor in areas where glaciers have exposed bedrock.

Evidence for Mesoproterozoic collision, deep burial and rapid exhumation of garbenschiefer in the Namaqua Front, South Africa

Metamorphic provinces such as the ∼1 ​Ga Grenvillian, ∼400 ​Ma Caledonide and Triassic Qinling Provinces often contain rocks with high-pressure assemblages such as eclogites, which formed at mantle depths in subduction zones. These are evidence of the accretion of terranes by subduction of oceans and collision to form large tectonostratigraphic provinces. The Mesoproterozoic Namaqua-Natal Province comprises a number of terranes thought to have been assembled by plate-tectonic processes, but they have generally yielded metamorphic pressures below 5 ​kbar, corresponding to <20 ​km, crustal depths, lacking evidence for subduction processes. The Kaaien Terrane in the Namaqua Front contains two large garbenschiefer units with the unusual paragenesis garnet-hornblende-epidote-white mica-plagioclase-ilmenite-quartz. Their protoliths are graywackes influenced by andesitic volcanism during their deposition at ∼1870 ​Ma, in a passive margin of the Rehoboth Province or Kaapvaal Craton. Prograde garnet growth dated at 1165 ​± ​5 ​Ma culminated in peak metamorphic conditions of 645 ​± ​30 ​°C and 10.4 ​± ​0.7 ​kbar, corresponding to 40 ​km depth. This is attributed to subduction of these rocks before collision between the overriding arc-related Areachap Terrane, the Kaaien Terrane and the Kaapvaal-Rehoboth cratonic block during the Namaqua orogeny. Exhumation of the garbenschiefer slabs was followed by rapid cooling, as the 1143 ​± ​5 ​Ma argon dates of hornblende and white mica, with closure temperatures ∼540 ​°C and ∼440 ​°C respectively, are the same within error. This was probably due to tectonic juxtaposition of the garbenschiefer slab with much cooler rock units. The exhumation was accommodated along the Trooilapspan-Brakbosch Shear Zone due to ongoing transpression. Other components of the Namaqua Front have distinctly different P-T-t paths, exemplified by greenschist metamorphism in the 1300 ​Ma Wilgenhoutsdrift Group, and medium-pressure metamorphism in the Areachap Terrane. They were juxtaposed by late-tectonic uplift and transpressional movements. The ∼40 ​km depth of garbenschiefer peak metamorphism is the deepest yet found in the Namaqua-Natal Province and strengthens the plate tectonic model of accretion by collision of terranes at the end of a Wilson cycle. The high pressure paragenesis of the garbenschiefer was preserved due to its location in the Namaqua Front, whereas most other parts of the Namaqua-Natal Province were overprinted by 1100–1020 ​Ma thermal events after the collision events.

The interaction between strike-slip dominated fault zones and thrust belt structures: Insights from 4D analogue models

Strike-slip motion is a fundamental tectonic process around the globe often resulting in prominent surface expressions. The full reconstruction and comprehension of strike-slip dominated structures can be a major challenge due to the complexity of the associated fault patterns. Further complexities occur when strike-slip dominated structures in the foreland interact with thrust belt fronts. Starting from a well-studied natural example (the Sciacca Fault Zone in the Sicilian Channel, Italy) we ran a set of analogue models simulating the interaction between strike-slip dominated fault zones and thrust structures using quartz sand as the analogue material and X-Ray Computed Tomography as a technique to carry out a 4D analysis of model internal structures. During a first phase, a thrust belt was created in our models, which was subsequently affected by a perpendicular fault system that underwent either pure strike-slip, 10°-, 20°-, 30°-transtensional, or 10°-, 20°-, 30°-transpressional motion. In general, transpressional models form pop-up structures, while the pure strike-slip model develops one sub-vertical fault bounded by two converging reverse faults. The 10˚-transtensional model generates a set of Riedel shear faults, which merge during the later stages of deformation. This model also shows a positive elevation change along the strike-slip dominated structures near the intersection with the thrust belt. The 20˚-transtensional model contains some Riedel shear faulting as well, but is dominated by two normal faults with steep dip angles and some minor sub-vertical strike-slip faults in between. This fault architecture is also observed in our 30˚-transtensional model. Three different tectonic regimes interacting with pre-existing and newly formed thrust front led to very different structural settings. These results were of help in better defining the tectonic regime that controlled the strike-slip dominated part of the Sciacca Fault Zone, but they show a fair match with other natural examples as well.

Are segmented fracture zones weak? Analytical and numerical models constrain anomalous bathymetry at the Clarion and Murray fracture zones

Between 150°W and 135°W, the Clarion Fracture Zone (FZ) coalesces from six discrete FZ traces to a single FZ over a period of ∼30 million years, coinciding with a change in plate motion that placed the associated transform fault (TF) in compression. Between 160° and 157°, the Murray FZ is also comprised of several closely-spaced (<50 km) discrete FZs and the associated TF experienced similar transpressional motion. Analysis of newly collected bathymetry data along the Clarion and Murray FZs reveals FZ structures that are inconsistent with predictions from a simple locked fault thermal subsidence model. These structures include FZ-bounded lithosphere that dips towards the old side of the FZ, whereas locked fault models predict it should dip towards the young side, and reversed fault scarp relationships where younger lithosphere lies deeper than older lithosphere. We investigate these anomalous observations using a combination of analytical and numerical models of two closely-spaced fracture zones to test how FZ strength and tectonic motions (compression or extension) affect the evolution of the intra-transform lithosphere. Our models predict that interior blocks within a segmented FZ, initially in isostatic equilibrium, can develop anomalous tilts and scarp depth relationships if the intervening FZs are relatively weak. Model results suggest that unusually low apparent coefficients of friction (<0.01) and tectonic compression are required to reproduce the magnitude of reverse tilt and scarp reversals observed in the Clarion and Murray FZs. We suggest that these low apparent friction coefficients might be the result of near lithostatic pore-fluid pressures associated with compression and alteration processes. Our results provide a tool to constrain histories of tectonic compression across FZs in places where rotation poles or other measures of plate motion may not be well constrained. Our results also imply that FZs are tectonically weak regions of hydrothermal alteration that may carry large volumes of volatiles into the mantle when subducted.

Strain indicators and magnetic fabric in intraplate fault zones: Case study of Daroca thrust, Iberian Chain, Spain

Anisotropy of magnetic susceptibility (AMS) has been applied to the study of shallow fault zones, although interpretation of the results requires establishing clear relationships between petrofabric and magnetic features, magnetic behaviour of fault rocks, and an extensive knowledge of P-T conditions. In this work, we demonstrate that magnetic methods can be applied to the study of heterogeneous fault zones, provided that a series of requisites are met. A major fault zone within the Iberian plate (Daroca thrust), showing transpressional movements during Cenozoic time was chosen for this purpose, because of the exceptional outcrops of fault gouge and microbreccia and its relevance within the context of the northeastern Iberian Plate. Magnetic fabrics were analysed and the results were compared with foliation and S-C structures measured within the fault zone. Clay mineral assemblages suggest maximum burial depths shallower than 2 km (<60–70 °C) for fault rocks in the footwall of the Daroca thrust. The orientation of the AMS axes is consistent with mesostructural strain indicators: kmin parallels the mean pole to S, or it is intermediate between S and C poles; kmax is oriented at a high angle (nearly orthogonal in overall) to the transport direction, which can be explained from both deformational and mineralogical controls. Both magnetic fabrics and kinematic indicators are consistent with a reverse movement for most of the fault zone.

A New Southern North Atlantic Isochron Map: Insights Into the Drift of the Iberian Plate Since the Late Cretaceous

AbstractThis paper presents a new southern North Atlantic plate model from Late Cretaceous to present, with the aim of constraining the kinematics of the Iberian plate during the last 83.5 Myr. This model is presented along with a detailed isochron map generated through the analysis of 3 aeromagnetic tracks and ~400 ship tracks from the National Centers for Environmental Information database. We present a new technique to obtain well‐constrained estimates of the Iberia‐North America plate motions from magnetic anomalies, overcoming the scarcity of large‐offset fracture zones and transform faults. We build an integrated kinematic model for NW Africa, Morocco, Iberia, Europe, and North America, which shows that the deformation is partitioned between Pyrenees and Betic‐Rif orogenic domain during the Late Cretaceous‐Oligocene time interval. In the Eastern Betics domain, the calculated amount of NW Africa‐Iberia convergence is ~80 km between 83.5 and 34 Ma, followed by ~150 km since the Oligocene. The motion of Iberia relative to Europe in the Central Pyrenees is characterized by overall NE directed transpressional motion during the Campanian and the Paleocene, followed by NW directed transpressional movement until the Lutetian and overall NNW directed convergence from Bartonian to Chattian. This motion occurs along the axis of the Bay of Biscay from the Santonian–Campanian boundary to the middle Priabonian, subsequently jumping to King's Trough at Anomaly 17 (36.62 Ma).

Petrographic contribution on the larimar host rock (Dominican Republic) and some notes about its origen

Larimar is an ornamental and semiprecious stone known worldwide as being iconic of the Dominican Republic. This rock is composed mainly of pectolite, usually seen associated with natrolite and calcite, as well as carbonaceous material, chalcocite and hematites. Sometimes, disseminations such as native copper, also occur amongst several other minerals. The rock crops out in a very small area (&lt; 0.3 km2 , Los Checheses-Los Chupaderos mine or simply the Larimar mine) as a result of the transpressional movement of the Arroyo Seco fault which exposed the basement. The host rock is composed mainly of olivine basaltic lava flows (15 - 18% olivine, 6 - 8% pyroxene, 5 - 10% plagioclase and &lt; 1% opaque minerals in a 64 to 72% groundmass), as well as related basaltic breccias. These volcanic rocks are strongly altered (by hydrothermal, tectonic and weathering processes) at different scales. Olivine phenocrysts were highly serpentinized and altered to iddingsite; pyroxene phenocrysts have some degrees of argillization and sericite; and carbonate has formed minerals from plagioclase crystals. Clays and quartz veinlets are also present as secondary minerals. Pectolite and natrolite minerals fill open spaces in the volcanic rock (vesicules, fractures, cavities, crustification and comb structure vugs) and substitute organic pieces (wood) by an epygenic process as a result of temperatures of 200°- 340°C, during a phyllic epithermal transition to mesothermal (quarz-sericitic) alteration. Larimar is not just a unique gemstone but it is also a very rare petrification process. Therefore we propose the term xilolarimar. The formation environment is suggested to be an oceanic island construction prior to the Eocene time, probably Late Cretaceous. Further studies are necessary to understand the blue pectolite (a colour mainly linked to Mn, V and Cu), its formation mode and its petrogenic environment.

Long-term ground deformation patterns of Bucharest using multi-temporal InSAR and multivariate dynamic analyses: a possible transpressional system?

The aim of this exploratory research is to capture spatial evolution patterns in the Bucharest metropolitan area using sets of single polarised synthetic aperture radar (SAR) satellite data and multi-temporal radar interferometry. Three sets of SAR data acquired during the years 1992–2010 from ERS-1/-2 and ENVISAT, and 2011–2014 from TerraSAR-X satellites were used in conjunction with the Small Baseline Subset (SBAS) and persistent scatterers (PS) high-resolution multi-temporal interferometry (InSAR) techniques to provide maps of line-of-sight displacements. The satellite-based remote sensing results were combined with results derived from classical methodologies (i.e., diachronic cartography) and field research to study possible trends in developments over former clay pits, landfill excavation sites, and industrial parks. The ground displacement trend patterns were analysed using several linear and nonlinear models, and techniques. Trends based on the estimated ground displacement are characterised by long-term memory, indicated by low noise Hurst exponents, which in the long-term form interesting attractors. We hypothesize these attractors to be tectonic stress fields generated by transpressional movements.

The pull apart-type Tardets-Mauléon Basin, a key to understand the formation of the Pyrenees

Contrary to recent conceptual models, we evidence that the Mauléon Basin does not only result from the Pyrenean tectonic inversion of an aborted Albian rift involving a N-S extreme crust thinning, with related detachment and mantle exhumation. It actually corresponds to an element of this rift system where E-W dominant regional sinistral strike slip faulting between its European and Iberian margins generated as early as the Latest Aptian (Clansayesian) an oblique pull apart-type basin: the Tardets-Sorholus Trough. Then, towards the Late to Latest Albian period, the active transverse, SW-NE oriented, Barlanès and Saison listric faults provided the main crustal thinning leading locally (Urdach) to mantle exhumation. Finally, at the beginning of the Late Cretaceous, the trough widened through transtension motion (N-S distension associated with E-W sinistral strike slip) leading to the creation of the Mauléon Basin. This geodynamic evolution gives to the Mauléon Basin its logical place between the western Bilbao Basin where oceanic crust developed through dominant N-S extension process and the central and eastern north Pyrenean basins where dominant E-W left lateral strike slip then transpressive motion preclude mantle denudation. From the Late to Latest Cretaceous, the inverted motion turning to generalized regional transpression led to the closure of the trough, then, by gradual uplift from east to west, to the formation of the Pyrenean range.

The Role of Surface Processes in Partitioning of Strain and Uplift, St. Elias Orogen, Southern Alaska

&lt;span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US"&gt;Three-dimensional thermo-mechanical numerical simulations of the ongoing Yakutat–North America collision are used to identify the role of surface processes in triggering localized rapid uplift, exhumation, and strain observed within the St. Elias orogen of southern Alaska. Thermochronological data reveal localized rapid exhumation associated with the Seward-Malaspina and Hubbard Glaciers within a tectonic corner structure where transpressional motion to the south along the Fairweather Fault system transitions to shortening to the north and west within the active fold-and-thrust belt of the St. Elias orogen. The modeled deformation patterns are characteristic of oblique convergence within a tectonic corner, recording the transition from simple shear to contractional strain within a zone spatially consistent with the highest exhumation rates suggesting the corner geometry is the primary control of strain partitioning.&lt;/span&gt;&lt;span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US"&gt;The relative roles of surface-related processes versus tectonics-related processes in the development of this pattern of deformation were tested with the inclusion of an erosional surface model. The presence of surface processes enhanced the uplift and development of a localized rapid exhumation. When spatially and temporally erosion models are employed, the location of maxima is shifted in response. This indicates that efficient erosion, and resultant deposition and material advection can influence the localization of strain and uplift.&lt;/span&gt;