Transcurrent Faults Research Articles

The Sierra Nevada de Santa Marta (Colombia) and Nevado de Famatina (Argentina): The effects of tectonic syntaxis on the topography of the Andes

The Sierra Nevada de Santa Marta (Santa Marta) in Colombia and Nevado del Famatina (Famatina) in Argentina are two isolated peaks within the Andes of South America, having elevations of about 5,500 and 6,000 m, respectively. Both massifs are bounded by major wrench faults of opposite kinematics but comparable magnitude in their lateral displacement. Despite the volumes of research available, little has been said in the literature about the tectonics surrounding these particular systems. In this context, digital terrain elevation (DEM), regional geology, satellite imagery and geophysical data were analysed to illustrate how a network of transcurrent faults uplifted the peaks. We propose a model to account for topography by the opposed movement of faults operating in two compartments: internal (acute) and external (obtuse). Fault motion caused uplift of the internal compartments: a) the Santa Marta tectonic syntaxis is generated by the sinistral Santa Marta-Bucaramanga Fault on the west and the dextral Oca-Pilar Fault to the north whilst, b) the Famatina tectonic syntaxis is caused by the Valle Fértil sinistral fault on the western side and the dextral Tucumán lineament to the north. Elevation maps documenting the lateral displacement of modern alluvial fans provide evidence of the existence and kinematics of these faults. Active since the Neogene, the transcurrent faults resulted in displacements in the order of 25–60 km, with velocities of approximately 1–2 cm/year. Seismic records suggest that the syntaxis occurred after reactivation of oblique discontinuities in the basement due to the convergence of the Nazca, Caribbean, and South American plates. This tectonic framework led to the formation of a remarkable positive relief and the development of internal positive compartments subject to constrictive forces. Simultaneously, external distensive and negative compartments controlled the syntectonic deposition of thick sedimentary sequences. The significant topographic difference between the internal positive compartments and their external negative counterparts triggered high rates of erosion, transport, and ultimately sedimentation. Regional subsurface surveys indicate strong anomalies of the underlying bedrock influenced by tectonic syntaxis.

Onset of the anorogenic alkaline magmatism in the Nigerian Younger Granite province: Constraints from the Daura and Dutse complexes

The Younger Granite province of Niger and Nigeria exemplifies a classical anorogenic alkaline ring granite belt with southward age migration from ca. 470 Ma to 140 Ma. However, the precise age transition from the older Nigerien Younger Granite (NrYG) to the younger Nigerian Younger Granite (NaYG) is poorly constrained. The Daura and Dutse complexes, located at the northernmost tip of the NaYG province, represent a temporal and spatial link between the NrYG and NaYG provinces. The Daura complex is composed of amphibole syenite and biotite granite, while the Dutse complex consists of fayalite syenite and arfvedsonite aegirine granite. Similar to other alkaline rocks of the NrYG and NaYG provinces, the Daura and Dutse samples all chemically show typical A1-type granite features, such as high alkalis (K2O + N2O = 8.33–11.27 wt%.), Ga/Al ratios, Zr + Nb + Ce + Y contents (527–2345 ppm) and FeOt/(FeOt+MgO) ratios (0.03–0.70) as well as elevated HFSEs. The NdHf and Pb isotopic systematics show that all the syenite-granites yield εNd (t) = −2.9 to +1.5, ɛHf (t) = −3.8 to +16.7, and 206Pb/204Pb = 17.818 to 19.555, suggestive of magmas derived from a slightly depleted mantle source with OIB imprints. A reduced to slightly oxidized redox state is invoked for the parental melt based on estimations from mineral chemistry. The Daura amphibole syenite is composed of >60% alkali feldspar, show high Eu/Eu* (>1), Ba/Zr (>3.5) values and cumulate textures, resembling an alkali feldspar cumulate rock. The other alkaline granitic rocks were likely generated from variable fractional crystallization of the residual melt with distinct crustal contaminations. Zircon UPb dating reveal that the Daura amphibole syenite and biotite granite were emplaced at 324 ± 1 Ma and 321 ± 3 Ma, respectively, whereas the Dutse granitoids showed episodic intrusive periods of ca. 264 Ma and 232 Ma. All these results predate other anorogenic alkaline complexes of the NaYG and update the oldest age (ca. 214 Ma in previous references) recorded in the alkaline granite province. To the north, it connects well with ages from the Zinder complex (~330 Ma) in the southernmost NrYG province, reflecting a significant link between the NrYG and NaYG provinces. From a broad view, a linear age migration from north to south in the Niger-Nigeria Younger Granite province remains well preserved, although temporal and spatial intervals exist in local region. This emplacement pattern can be traced to the periodic and repeated reactivation of lithospheric shear zones and transcurrent faults.

Geodynamic and plate kinematic context of South China Sea subduction during Okinawa trough opening and Taiwan orogeny

The geodynamics and plate tectonics of the South China Sea (SCS)-Taiwan region since Miocene times are uncertain because the former extent and tectonic configuration of the subducted easternmost SCS along the Manila trench is uncertain. Here we unravel the regional kinematic context from main offshore constraints including published unfolding of the Manila slab from seismic tomography, which provides insight on restoring the subducted part of the SCS. We reconstruct a bayonet-shaped, stepped northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment we call ‘S3’, trending N070° that roughly parallels the present SCS shelf; a 350-km long ~N-S trending segment S2 that steps north to Hualien; and, a third segment S1 that extends from east of Hualien beneath the Ryukyu subduction zone trending N085° that ends near Miyako Island in the Ryukyus.The distance between present COB and S1 gives extension through time in the Okinawa trough, with a maximum of ~100 ± 20 km extension since late Miocene (10 Ma). We interpret S1 as a zone of weakness since ~18 Ma that ruptured from Miyako Island to east of Hualien as a tear fault, with the Huatung basin-Philippine Sea plate (HB-PSP) subducting northwestward between the two sides of the tear fault. The Manila transcurrent fault initiated ~18 Ma ago at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc, which began collision ~7 Ma ago along the EU margin. From ~7 to 6.5 Ma Taiwan was uplifted west of the Longitudinal valley. The Luzon arc and forearc basins were shortened within the Coastal range. Plate kinematic reconstructions from ~18 Ma to Present are synthesized in terms of continental or oceanic nature of the main PSP-HB and EU entities before their subduction that provide new understanding on Taiwan, PSP-SCS kinematics, and regional histories.

Glacitectonic rafts and their role in the generation of Quaternary subglacial bedforms and deposits

AbstractLandforms and sediments on the palaeo–ice stream beds of central Alberta record glacitectonic raft production and subsequent progressive disaggregation and moulding, associated substrate ploughing, and grooving. We identify a subglacial temporal or developmental hierarchy that begins with incipient rafts, including en échelon hill-hole complexes, hill-hole pairs, and strike-slip raft complexes, all of which display patterns typical of transcurrent fault activation and pull apart. Many display jigsaw puzzle–style fragmentation, indicative of substrate displacement along shallow décollement zones and potentially related to patchy ice stream freeze-on. Their gradual fragmentation and smoothing produces ice flow-transverse ridges (ribbed moraine), hill-groove pairs, and paraxial ridge and groove associations. Initiator scarp and megafluting associations are indicative of raft dislodgement and groove ploughing, leading to the formation of murdlins, crag-and-tails, stoss-and-lee type flutings and drumlins, and Type 1 hogsback flutings. Downflow modification of rafts creates linear block trains (rubble stripes), stoss-and-lee type megaflutings, horned crag-and-tails, rubble drumlinoids, and murdlins, diagnostic of an immature palaeo–ice stream footprint. Lateral ice stream margin migration ingests disaggregated thrust masses to form ridged spindles, ladder-type morphologies, and narrow zones of ribbed terrain and Type 2 hogsback flutings, an assemblage diagnostic of ice stream shear margin moraine formation.

\u2018Conjugate\u2019 coseismic surface faulting related with the 29 December 2020, Mw 6.4, Petrinja earthquake (Sisak-Moslavina, Croatia)

We provide here a first-hand description of the coseismic surface effects caused by the Mw 6.4 Petrinja earthquake that hit central Croatia on 29 December 2020. This was one of the strongest seismic events that occurred in Croatia in the last two centuries. Field surveys in the epicentral area allowed us to observe and map primary coseismic effects, including geometry and kinematics of surface faulting, as well as secondary effects, such as liquefaction, sinkholes and landslides. The resulting dataset consists of homogeneous georeferenced records identifying 222 observation points, each of which contains a minimum of 5 to a maximum of 14 numeric and string fields of relevant information. The earthquake caused surface faulting defining a typical ‘conjugate’ fault pattern characterized by Y and X shears, tension cracks (T fractures), and compression structures (P shears) within a ca. 10 km wide (across strike), NW–SE striking right-lateral strike-slip shear zone (i.e., the Petrinja Fault Zone, PFZ). We believe that the results of the field survey provide fundamental information to improve the interpretation of seismological, GPS and InSAR data of this earthquake. Moreover, the data related to the surface faulting may impact future studies focused on earthquake processes in active strike-slip settings, integrating the estimates of slip amount and distribution in assessing the hazard associated with capable transcurrent faults.

Uplift Quantification and Erosion Rate Estimation in Northwestern Tunisia from Topographic and Lithologic Data

Digital elevation modeling (DEM) was used to determine key morphological features such as hypsometry, slopes and topographic evolution in correlation with tectonic regimes and erosion mechanisms. This contribution discusses the tectonic model of northern Tunisia, which since 1977 has been described by geologists as an allochthonous unity domain of the Serravallian-Tortonian. This study presents new data from the erosion rate calculation following the establishment of these units and then proposes another view on regional tectonics. Therefore, the example used of Oued Sedjnene gives a rising rate of the order of 0.01 mm/year, almost equivalent to the results found in surrounding medeterranean belt (ex. Italy and Turkey). The structure and geomorphology of northern Tunisia is a result of folding of Cenozoic basin. However located tangential structure are related to transcurrent faults and not overthrust structure.

Paleoseismologic trenching confirms recent Holocene activity of the major Algeciras fault system in southern Colombia

The Algeciras Fault System (AFS) in Colombia, which is characterized by its predominant dextral strike-slip movement, is part of the major transcurrent fault system known in Ecuador, Colombia and Venezuela as the Eastern Frontal Fault System, that disconnects the North Andean Block (NAB) from the South American plate in a process of tectonic escape. It is responsible for some of the most important seismic events in the seismic history of Colombia that occurred in 1827 with Mw 7.1 that destroyed large part of all settlements in the Huila Department and caused considerable damage and loss of life in the capital of Bogota. More recently another event of Mw 7.0 took place in 1967 that also caused damage in the capital, and in December 2019 an event of Mw 6.0 caused minor damage in various settlements in the Eastern foothills of the Eastern Cordillera. So far, mapping studies based on data obtained from satellite imagery, airphotos and structural field data have outlined the complexity of the AFS and have identified the existence of at least six tectonic basins occurring along the main fault of the system. In 2016, within the framework of activities of the Space Geodesy Research Group of the Geohazards Directorate of the Geological Survey of Colombia (SGC) a program of morphotectonic field studies was carried out in and around the Algeciras pull-apart basin in the Huila Department that led to the opening of two exploratory paleoseismologic trenches. This paper presents the results of the first of these two trenches, located in the center of the Algeciras valley at a place named Lagunillas. It is situated at the rim of a shallow fault-dammed lake formed by an uphill facing scarp generated by the dextral strike-slip displacement of a shortcut fault that traverses the alluvial fill of the basin along its longitudinal axis. The results of the paleoseismologic study prove the occurrence of seven seismic events with magnitudes Mw 7.0 during the Holocene with an average recurrence interval of 1300–1400 years. This constitutes a significant contribution to the study of seismic hazard assessment of the AFS that complements, in a quantitative way, the evidence provided by the data of historic seismicity of this major fault and points out the considerable danger that the fault presents to the country as a whole and in particular to the metropolitan area of Bogota.

The Upper Jurassic Garedu Red Bed Formation of the northern Tabas Block: elucidating Late Cimmerian tectonics in east-Central Iran

The Garedu Red Bed Formation (GRBF) of the northern Tabas Block (Central-East Iranian Microcontinent, CEIM) is a lithologically variable, up to 500-m-thick, predominantly continental unit. It rests gradually or unconformably on marine limestones of the Esfandiar Subgroup (Callovian–Oxfordian) and is assigned to the Kimmeridgian–Tithonian. In the lower part, it consists of pebble- to boulder-sized conglomerates/breccias composed of limestone clasts intercalated with calcareous sandstones, litho-/bioclastic rudstones and lacustrine carbonates. Up-section, sharp-based pebbly sandstones and red silt-/fine-grained sandstones of braided river origin predominate. Palaeocurrent data suggest a principal sediment transport from west to east and a lateral interfingering of the GRBF with marine greenish marls of the Korond Formation at the eastern margin of the Tabas Block. Westwards, the GRBF grades into the playa deposits of the Magu Gypsum Formation. Red colours and common calcretes suggest arid to semi-arid climatic conditions. The onset of Garedu Red Bed deposition indicates a major geodynamic change with the onset of compressive tectonics of the Late Cimmerian Tectonic Event (LCTE), being strongest at the eastern margin of the northern Tabas Block. When traced southwards, the same tectonic event is expressed by extension, indicating a shift in tectonic style along the boundary fault between the Tabas and Lut blocks. The complex Upper Jurassic facies distribution as well as the spatio-temporal changes in tectonic regime along the block-bounding faults are explained by the onset of counterclockwise vertical-axis rotation of the CEIM in the Kimmeridgian. The block boundaries accommodated the rotation by right-lateral strike slip, transpressional in today’s northern and transtensional in today’s southern segments of the block-bounding faults. Rotation occurred within bracketing transcurrent faults and continued into the Early Cretaceous, finally resulting in the opening of narrow oceanic basins encircling the CEIM. Palaeogeographically, the GRBF is part of a suite of red bed formations not only present on the CEIM, but also along the Sanandaj-Sirjan Zone (NW Iran), in northeastern Iran and beyond, indicating inter-regional tectonic instability, uplift and erosion under (semi-)arid climatic conditions across the Jurassic–Cretaceous boundary. Thus, even if our geodynamic model successfully explains Late Jurassic tectonic rotations, fault motions and facies distribution for the CEIM, the basic cause of the LCTE still remains enigmatic.

The effect of recent resurfacing in volcanic areas on the distribution of co-seismic ground deformation due to strike-slip earthquakes: New insights from the 12/26/2018 seismic event at Mt. Etna

We analyzed the dispersion of the co-seismic fracturing due to the December 26, 2018 event at Mt. Etna (Italy) along the deformation belt matching the seismogenic source at depth. Our study, based on measurement of 390 ground fractures, reconstructed the variability of the geometry and the changes in the rank (length and displacement) of the ground breaks, through different compound lava fields. The study evidenced that the narrow capable dextral fault zone emerges where ancient lavas crop out or are draped by a thin layer of younger lava flows. Conversely, within recent compound lava fields, consisting of multiple superimposed flow units, the main mechanical anisotropy within the near-surface layers inhibited the along-dip fault propagation. The vertical restriction of the fault propagation produced a spread ground deformation, responding to the motion along the blind main fault. Our results provide a significant example how the laterally changing near-surface stratigraphy of an active volcano edifice can influence the ground effects due to the co-seismic displacement along strike-slip active fault. This evidence could represent new insights to be considered in predicting the susceptibility zone around active transcurrent faults in volcanic settings, prone to instabilities for future seismic events.

Is the Eastern Denali fault still active?

AbstractThe Denali fault, a transcurrent fault system that extends from northwestern Canada across Alaska toward the Bering Sea, is partitioned into segments that exhibit variable levels of historical seismicity. A pair of earthquakes (M 6.2 and 6.3) on 1 May 2017, in proximity to the Eastern Denali fault (EDF), exhibited source mechanisms and stress conditions inconsistent with expectations for strike-slip fault activation. Precise relocation of ∼1500 aftershocks revealed distinct fault strands that are oblique to the EDF. Calculated patterns of Coulomb stress show that the first earthquake likely triggered the second one. The EDF parallels the Fairweather transform, which separates the obliquely colliding Yakutat microplate from North America. In our model, inboard transfer of stress is deforming and shortening the mountainous region between the EDF and the Fairweather transform. This is supported by historical seismicity concentrated southwest of the EDF, suggesting that it now represents a structural boundary that controls regional deformation but is no longer an active fault.

Channel to the Strait : the geological history of the Tamar Valley–Launceston area

The Tamar Valley occupies the Tamar Graben, a geological structure defined by a series of parallel NW-trending faults which have lowered the dolerite basement to below sea level. The resulting narrow trough, some 50 km long and 5 km wide, has been partially infilled with soft sands, clays and gravels, with intercalated basalt flows in places, of mainly Paleogene (lower Tertiary) age. Low hills of hard Jurassic dolerite define the structure on either side. The graben was formed during the break-up of Gondwana, the separation of Australia from Antarctica, and the making of Tasmania, in the Cretaceous-early Cenozoic period, some 70–140 million years ago (Ma). A spreading ridge had propagated eastwards through the Great Australian Bight but was unable to break through the Bass Strait area, and instead a large wedge of crust containing the future Tasmania was pulled away from the corner of Antarctica on a series of transcurrent faults. The associated crustal stretching in the Bass Strait area resulted in the formation of the deep ‘hole’ of Bass Basin, which had offshoots onto what became Tasmania, including the Tamar Graben. For much of its life, the Tamar River was a major feeder stream into the Bass Basin, carrying large volumes of sediment eroded from the Tasmanian highlands. The course of its major tributary, the South Esk River, within the southern part of the graben was completely blocked by basalt flows near the present Evandale about 35 Ma, forcing it into a new course to the west through the dolerite, to form the Cataract Gorge.

TRANSTENSIVE ORIGIN OF THE ENCADENADAS-VALLIMANCA CORRIDOR (BUENOS AIRES, ARGENTINA): A REVISION AND A NEW PROPOSAL FROM SATELLITE IMAGES

The Encadenadas-Vallimanca Corridor (EVC) corresponds to a morphostructural linear feature defining the northern boundary of the Sierra de la Ventana and Tandil hills in the Buenos Aires province. The scarcity of concluding geological studies has resulted in diverse tectonic and hydrographic interpretations regarding the genesis of the corridor. A new analysis of surface morphology, mainly derived from satellite imagery, led to the identification of a series of gentle and elongated en échelon left-stepping relief features or ridges with cross-sectional asymmetric flanks, having an average length of 20 km and oriented sub-latitudinally at 20° to the ENE strike of the corridor. The arrangement of these ridges reminds a tectonic scenario of right-lateral transcurrent faulting, for which, the limiting parallel faults fulfill the function of synthetic Riedel type shear. Besides, the cross-sectional asymmetry of the ridges suggests extensional normal faulting coherent with a transtensional right-lateral flower structure. Shallow seismicity of Mw 4.0 registered by the year 2016 in the proximities of the lineament could suggest recent fault activity. Also, previous gravity potential field mapping in the area seems to highlight basement anomalies underneath the sedimentary cover, coinciding with the main lineament of the Corridor. Based on all this information, the EVC is considered to be the surface expression of dextral transtensional fault activity.

Geomorphological Analysis of the Southwestern Margin of Xanadu, Titan: Insights on Tectonics

AbstractEvidence for tectonic activity on Titan is provided by the presence of eroded mountain ranges. Xanadu is an equatorial region of Titan characterized by a complex topography, even though, overall, it has a lower average elevation compared to its surroundings. We investigated Xanadu's southwestern margin, a part of the region composed of heavily eroded and rugged terrains to the north and east, and of smoother, more uniform terrains to the west and south. The central portions of southwestern Xanadu (SW Xanadu) are characterized by an extensive fluvial network. The presence of such a distinctive feature was the main reason motivating the study of this area, given its potential to provide tectonic indications. Through detailed geomorphological mapping (map scale 1:700,000) on Synthetic Aperture Radar data and analysis of both fluvial drainage patterns and Digital Terrain Models, we identified several putative tectonic structures in this area: normal faulting to the west and east, thrust faulting to the north, and small‐scale strike‐slip faulting in its central parts. Pull‐apart basins are depressions bounded by both dip‐slip faults and by (overlapping and/or bending) segments of a major transcurrent fault, i.e., they are basins generated in transtensional tectonic settings. We propose that central SW Xanadu is a pull‐apart basin, bordered by both normal and thrust faults and formed by transtensional tectonics, which we consider to be the most recent tectonic phase active in this area. This basin is characterized by small‐scale strike‐slip faulting within it, on which a fluvial network has subsequently imposed.

Petrogenesis of the peralkaline Dutsen Wai and Ropp complexes in the Nigerian younger granites: implications for crucial metal enrichments

ABSTRACT The Dutsen Wai and Ropp complexes are parts of the over 50 within-plate alkaline ring complexes in north-central Nigeria. These complexes consist mainly of A-type granites that were emplaced between 175 Ma (in Dutsen Wai) and 149 Ma (in Ropp). They are characterized by moderately negative zircon ԑHf(t) values (–9.8 to – 5.86) with Paleoproterozoic (1597–1884 Ma) crustal model ages (TDMc), suggesting the mantle-derived parental magmas have been substantially modified by assimilation of crustal materials. The granites exhibit elevated HFSEs (e.g., Nb and Zr) and LILE (e.g., Rb and REE) concentrations, with higher values in the peralkaline than in the aluminous granites, but are depleted in compatible elements (e.g., CaO, MgO, Ba and Sr). This is typical of highly differentiated granites associated with rare metal mineralization. The peralkaline plutons show REE patterns with strong negative Eu anomalies, significant M-type lanthanide tetrad effect (TE1,3 = 1.16–1.32), and non-CHarge and Radius Controlled (CHARAC) behaviour of some HFSEs. The positive correlation of Na2O vs. Nb (r2 = 0.92) and Nb vs. TE1,3 (r2 = 0.7), increasing degree of albitization and shift in eutectics of granite minimum towards Ab-Qtz sideline indicate that Na-rich fluid plays an important role in the complexation between F and other incompatible elements in open system processes. Fluorine also favoured the retention of these crucial metals in the peralkaline melt until late magmatic-stage during which the breakdown of the F-HFSEs and F-REE complexes was accompanied by crystallization of pyrochlore and REE-bearing accessory minerals. We proposed that the emplacement of these A-type granites was probably linked to the prevailing transtension regime before the fragmentation of Gondwana during the Mesozoic period which reactivated some deep-seated Pan-African transcurrent faults. This, in turn, caused pressure release and channelled fluid, which triggered partial melting of the lower part of the lithospheric mantle.

Post-rift submarine volcanic complexes and fault activities in the Baiyun Sag, Pearl River Mouth Basin: New insights into the breakup sequence of the northern South China Sea

Post-rift volcanisms and fault activities are significant for understanding the tectonic-sedimentary evolution of rifted continental margins and associated hydrocarbon entrapments. In this study, a series of post-rift fault-associated volcanic activities have been found in the northern continental margin of the South China Sea (SCS). However, their episodes and relationships with the progressive continental breakup are still doubtful. Here, new 2D/3D seismic, borehole, dating, and biostratigraphic data are used to investigate the characteristics of the post-rift volcanism and fault activities in the Baiyun Sag (BYS), Pearl River Mouth Basin. The newly-found fault-associated volcanic complexes include thirteen submarine volcanic mounds and associated lava flows, together with igneous sills that are mainly composed of basalts and tuffs. Seismic stratigraphic analysis combined with KAr dating from cores confirms that post-rift volcanism in the BYS climaxed along with the breakup of the SCS mainly in three episodes: (1) the first episode near Oligocene/Miocene boundary (23.3 Ma); (2) the second at the middle Early Miocene (17.6 Ma); and (3) the new-found third episode at the late Early Miocene (17.1 Ma). Also, fifty-three syn-sedimentary faults are interpreted, which are characterized by a WNW trending normal fault group separated by an ENE trending transcurrent fault group. And there is evidence that these fifty-three faults were long-lived from ca. 32–17.1 Ma and served as important conduits for the upward migration of the magma. The three episodes of volcanism and tectonic fault activities are related to the progressive continental breakup in the northern SCS margin, and they represent the tectonic signature of the early stage of the post-rift subsidence after the lithospheric breakup which extends to the top of a hypothetical breakup sequence (32–17.1 Ma) in the BYS. Furthermore, this study proves that the diachronous continental breakup in the SCS margin can result in corresponding changes in depositional architectures, along with a breakup sequence characterized by the deposition of a ‘sandstone‑carbonate-shale’ regressive-transgressive cycle. The sedimentological changes and associated tectonic features recorded in the Baiyun Sag suggest an exceptionally active tectonic setting in the time of the formation of the breakup sequence (Early Oligocene-Early Miocene) along the northern SCS margin.

Calcite twinning fabrics along the Middle America trench, Costa Rica and the Motagua sinistral fault, Honduras and Jamaica: Tectonic implications for the Caribbean plate

The Cretaceous oceanic crust of the Caribbean plate has a long and complex tectonic history as an indentor plate bounded by transcurrent faults (N and S) and subduction margins (W [east slab dip] and E [west slab dip]) with no strain data. Miocene forearc sediments and accreted ophiolites are exposed along the central Pacific coast of Costa Rica and preserve a variety of folding and faulting styles. These clastic sediments, deposited in the forearc as the Middle America trench evolved, contain calcite cements and are cross cut by calcite veins. Analysis of the mechanical twins in these two calcite groups (8 samples, n = 267 twins) at Punta Dominical and the Nicoya Peninsula ophiolite preserve a consistent sub-horizontal shortening strain that is oriented parallel to the current trench axis, as are most of the accretion-related fold axes. Differential stress magnitudes for the calcite twinning strain average −450 bars, and there is little evidence of a twinning strain overprint (low NEVs). Obduction along the Middle America trench involves, in part, a component of trench-parallel horizontal shortening.The Motagua fault originates in the Middle America trench and strikes east as the northern boundary of the Caribbean plate as a sinistral margin. The Roatan Islands are a series of islands composed of south-dipping rocks along the southern side of the Motagua fault. Recent, deformed clastic sediments are drapped over gneisses, schists (40Ar-39Ar biotite age of 14 Ma), conodont-free marbles and ophiolitic fragments of presumed Cretaceous age. Twinning studies (n = 6 samples, n = 425 twins) of these marbles preserve a N–S, horizontal shortening strain, normal to the sinistral plate boundary. Differential stress magnitudes for the calcite twinning strain average −36 MPa. Only in a combined sample (n = 189 grains) is a strain overprint (high NEVs; n = 47) present, which records horizontal shortening strain at 132°, 5°. Jamaica is also along the eastern Motagua fault (Cayman trough) and twinning strain studies in Eocene limestones and younger calcite veins (n = 4 samples; n = 136 twins) preserve a horizontal shortening strain normal to the sinistral plate boundary.Twinning strain results are compared to regional GPS, focal mechanism and SKS anisotropy results around the Caribbean plate, especially along the Middle America trench on the western margin of Costa Rica with some new insights into subduction dynamics.

Structural evolution and U/Pb zircon age of the Xambioá gneiss dome, contributions to the Araguaia fold belt tectonic history

The Araguaia belt in central Brazil is an important key to re-access ancient geological settings, as it records the Gondwana agglutination and the final stages of an oceanic basin closure. Small basement inliers occur along transversal position in the Araguaia belt and could compose the extension of Amazonian craton. The structural analysis of the Xambioá gneiss dome region shows that three main deformational events were responsible for the actual scenario. The first deformational event was a NW-SE non-coaxial compression event (Dn), which led to the formation of ductile structures, such as open and slightly open folds (Fn), from a previous Sn-1 structures, axial plane foliation and spaced foliation (Sn), in the mantling metasedimentary sequence, and the mylonitic foliation (Sn) in dome rocks. This event was associated with a thrust system developed under regional greenschist to local upper amphibolite facies. The second deformational event Dn+1 was characterized by refolding with Sn transposition, followed by asymmetric Fn+1 folds and transposed foliation (Sn+1), and local stretching patterns forming boudins and Ln+1 lineations. The third deformational event Dn+2 is represented by WNW-ESE sinistral transcurrent faults (Sn+2) which sectioned the Dn structures and formed shear zones of different scales. U–Pb zircon ages in gneiss and in a migmatite of the Xambioá dome indicate Mesoarchean (~2.93 Ga) crystallization ages. U–Pb zircon provenance ages from metasedimentary rocks bordering the Xambioá dome show significant contribution of Archean to Neoproterozoic sources. The consistent loss of Pb in the dome rocks evidences tectono-metamorphic events presumably connected to the lithosphere ocean closure and continental collision responsible for the Araguaia Belt edification during Neoproterozoic-Cambrian period.

Faulting within the San Juan–southern Gulf Islands Archipelagos, upper plate deformation of the Cascadia subduction complex

Abstract The San Juan–southern Gulf Islands Archipelago of Washington State, USA and western Canada is located on the upper plate of the Cascadia subduction zone, in the forearc between the trench and volcanic arc. Onland and island investigations show many faults within the region that primarily represent old, inactive faults associated with transport, subduction and accretion of tectonostratigraphic terranes. However, until recently little geologic investigation and mapping have been done in the offshore. From these narrow straits, channels and sounds we have collected and interpreted high-resolution multibeam echosounder bathymetric data, 3.5 kHz sub-bottom and Huntec seismic-reflection profiles, and piston-cores to identify and date recently active faults. Previous studies by us focused on the earlier recognized active Devils Mountain fault zone that bounds the southern part of the Archipelago and the recently reported newly mapped active Skipjack Island fault zone that bounds the northern part. These transcurrent fault zones appear to be deforming and rotating the Archipelago. We concentrate on the unique deformation occurring within the seaways to determine the relationship and styles of faulting associated with these active bounding fault zones and relate the fault geometry and kinematics to one other subduction complex, the New Hebrides island arc of Vanuatu.

Geological structures controlled the rupture process of the 2011 M9.0 Tohoku-Oki earthquake in the Northeast Japan Arc

By interpreting the 2D/3D seismic survey data acquired in the surrounding ocean areas of the Northeast (NE) Japan Arc, we clarified the detailed geological structure and demonstrated that the basic structure in the hanging-wall plate of the subduction system consists of many structural blocks (segments) separated by NW–SE trending large transcurrent faults (strike-slip faults). This structural configuration showed a close relationship with the distribution of foreshocks, mainshock, and aftershocks, coseismic slip models of the 2011 M9.0 Tohoku-Oki megathrust earthquake, coseismic slip area of M-7 class earthquakes, quasi-static slip rates, back slip rate, and seismic tomography images. In addition, the coseismic slip models revealed that the trenchward forearc of the structural blocks between the Offshore Hidaka tectonic line and the Honjo-Sendai tectonic line fitted well with the coseismic slip area of the 2011 Tohoku-Oki earthquake. These findings suggest that the structural blocks bounded by these two tectonic lines slipped rapidly trenchward when the mainshock occurred. The M7 earthquakes were also concentrated along these two tectonic lines, thereby suggesting a close relationship between seismic activity and the inherited geological structure of the overriding plate in the NE Japan forearc.

Extensional tectonics during the Tyrrhenian back‐arc basin formation and a new morpho‐tectonic map

AbstractWe present a new tectonic map focused upon the extensional style accompanying the formation of the Tyrrhenian back‐arc basin. Our basin‐wide analysis synthetizes the interpretation of vintage multichannel and single‐channel seismic profiles, integrated with modern seismic images, P‐wave velocity models, and high‐resolution morpho‐bathymetric data. Four distinct evolutionary phases of the Tyrrhenian back‐arc basin opening are further constrained, redefining the initial opening to Langhian/Serravallian time. Listric and planar normal faults and their conjugates bound a series of horst and graben, half‐graben and triangular basins. Distribution of extensional faults, active throughout the basin since Middle Miocene, allows us to define an arrangement of faults in the northern/central Tyrrhenian mainly related to a pure shear which evolved to a simple shear opening. At depth, faults accommodate over a Ductile‐Brittle Transitional zone cut by a low‐angle detachment fault. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variation throughout the back‐arc basin combined with wide‐angle seismic velocity models allows to explore the relationships between shallow deformation, faults distribution throughout the basin, and crustal‐scale processes as thinning and exhumation.