Subduction Zone

This paper starts with an overview of recent developments pertaining to sediment routing systems that may connect fluvial, estuarine and coastal environments. It discusses sediment runoff analyses on a basin scale and methodologies for developing a budget of littoral sediment. It then focuses the discussion on recent findings obtained through collaborative research in the framework of a Center-of-Excellence program. The topics covered include the following: field observations of offshore-going sediment fluxes in the surf zone; reservoir sedimentation; an interrelationship between the riverbed morphology and habitat of a class of fish as influenced by sediment runoff; modeling of the transport of mixtures of non-cohesive and cohesive sediments with emphasis on wash load; reappraisal of traditional flow-control structures for river stabilization; and the dynamics of sediment gravity flows. Collectively, the coverage emphasizes the importance of addressing highly nonlinear fluid-sediment interactions.

Seabeam data reveal two deep subcircular reentrants in the lower arc slope of the New Hebrides island arc that may illustrate two stages in the development of a novel type of forearc basin. The Malekula reentrant lies just south of the partly subducted Bougainville sea; mount. This proximity, as well as the similarity in morphology between the reentrant and an indentation in the lower arc slope off Japan, suggests that the Malekula reentrant formed by the collision of a seamount with the arc. An arcuate fold-thrust belt has formed across the mouth of the reentrant, forming the toe of a new accretionary wedge. The Efate reentrant may show the next stage in basin development. This reentrant lies landward of a lower-slope ridge that may have begun to form as an arcuate fold-thrust belt across the mouth of a reentrant. This belt may have grown by continued accretion at the toe of the wedge, by underplating beneath the reentrant, and by trapping of sediment shed from the island arc. These processes could result in a roughly circular forearc basin. Basins that may have formed by seamount collision lie within the accretionary wedge adjacent to the Aleutian trenches.

Splay faults within accretionary complexes are commonly associated with the updip limit of the seismogenic zone. Prestack depth migration of a multichannel seismic line across the north Ecuador-south Colombia oceanic margin images a crustal splay fault that correlates with the seaward limit of the rupture zone of the 1958 (Mw 7.7) tsunamogenic subduction earthquake. The splay fault separates 5-6.6 km/s velocity, inner wedge basement rocks, which belong to the accreted Gorgona oceanic terrane, from 4 to 5 km/s velocity outer wedge rocks. The outer wedge is dominated by basal tectonic erosion. Despite a 3-km-thick trench fill, subduction of 2-km-high seamount prevented tectonic accretion and promotes basal tectonic erosion. The low-velocity and poorly reflective subduction channel that underlies the outer wedge is associated with the aseismic, de ´collement thrust. Subduction channel fluids are expected to migrate upward along splay faults and alter outer wedge rocks. Conversely, duplexes are interpreted to form from and above subducting sediment, at $14to 15-km depths between the overlapping seismogenic part of the splay fault and the underlying aseismic de ´collement. Coeval basal erosion of the outer wedge and underplating beneath the apex of inner wedge control the margin mass budget, which comes out negative. Intraoceanic basement fossil listric normal faults and a rift zone inverted in a flower structure reflect the evolution of the Gorgona terrane from Cretaceous extension to likely Eocene oblique compression. The splay faults could have resulted from tectonic inversion of listric normal faults, thus showing how inherited structures may promote fluid flow across margin basement and control seismogenesis.

The north Ecuador-south Colombia (NESC) margin has three transverse morphotectonic segments (the Manglares, Tumaco, and Patia segments), each with different tectonic and structural patterns. Following the 1906 subduction earthquake, the NESC margin has been the site of three megathrust events in 1942, 1958, and 1979 for which the rupture zones abut one another. We first investigated variations in heat flow derived from bottom simulating reflectors (BSR) observed along multichannel seismic lines sampling the three morphotectonic segments. Strong along-strike variations of the BSR-derived heat flow, just landward of the deformation front, suggest that each morphotectonic segment has a specific thermal regime. Finite element thermal models show that these variations are mainly produced by changes in the age and the dip of the oceanic plate and local hydrothermal cooling. We then examined the relationship between seismogenesis and thermal structure along the plate boundary. The updip limits of the 1942 and 1979 seismogenic zones, estimated from the aftershock area and rupture zone, reach the trench, where the temperature at the top of the subducting plate appears to be 50°-60°C. Between these events the seismogenic zone of the 1958 earthquake is restricted to a region landward of a prominent outer basement high where the temperature appears to be 100°-120°C. We propose that on the NESC margin the updip limit of the seismogenic zone is primarily controlled by low-temperature processes except for the 1958 event for which the seismogenic updip limit appears to be related to a structural feature in the upper plate.

Major and trace element and Sr-Nd-Hf-Pb isotopic data for the most primitive Tertiary lavas from the Veneto region (South-Eastern Alps, Italy) show the typical features of HIMU hotspot volcanism, variably diluted by a depleted asthenospheric mantle component ( 87 Sr/ 86 Sr i =0.70306-0.70378; " Ndi =+3.9 to +6.8; " Hfi =+6.4 to +8.1, 206 Pb/ 204 Pb i =18.786-19.574). P-wave seismic tomography of the mantle below the Veneto region shows the presence of low-velocity anomalies at depth, which is consistent with possible upwellings of plume material. Between the depths of 100-250 km the velocity anomalies are approximately 2-2.5% slower than average, implying a temperature excess of about 220-280 K, in agreement with estimates for other mantle plumes in the world. In this context, the Veneto volcanics may represent the shallow expression of a mantle upflow. The presence of a HIMU-DM component in a collision environment has significant geodynamic implications. Slab detachment and ensuing rise of deep mantle material into the lithospheric gap is proposed to be a viable mechanism of hotspot magmatism in a subduction zone setting.

Chemical variations along with changes in microstructure of the principal constituent minerals make it possible to identify at least four equilibrium stages in the evolution of the Yangkou garnet peridotite in the Su-Lu ultrahigh-pressure metamorphic belt, eastern China: Stage I-----a primary garnet lherzolite stage represented by coarse-grained (a few millimeters size) porphyroclastic aluminous pyroxenes þ chromian spinel AE garnet; Stage II-----an ultrahighpressure (UHP) stage defined by fine-grained matrix phases (0Á1---0Á3 mm size) of garnet þ extremely low-Al orthopyroxene þ high-Na clinopyroxene þ chromite; Stage III-----a medium-pressure stage defined by fine-grained mineral aggregates (50Á1---0Á2 mm size) mainly composed of aluminous spinel þ high-Al orthopyroxene in the matrix; Stage IV-----an amphibolite-to greenschist-facies stage defined by poikiloblastic amphibole. Orthopyroxene---clinopyroxene thermometry and an empirical spinel barometer give temperatures of around 800---830 C and pressures of 1Á2---2Á9 GPa for porphyroclasts of Stage I. Garnet---orthopyroxene, garnet---clinopyroxene and empirical spinel geothermobarometers give relatively uniform P---T conditions for the matrix garnet---orthopyroxene---clinopyroxene--chromite assemblage of Stage II ( $730---760 C and 3Á6---4Á1 GPa). Aluminous spinel---olivine pairs in the aggregates give $650---680 C at 1Á0---1Á5 GPa for Stage III. The granulation of the studied rocks may have taken place during subduction (Stages I and II) of the host peridotite. The lack of kelyphitic rims around the matrix garnet and the preservation of incompatible assemblages in the matrix of the studied rocks is due to extremely low H 2 O activity during the early decompression stage. The peak temperature of associated eclogites in the Yangkou UHP unit is 700---800 C at 3Á1---4Á1 GPa. These observations suggest that the mantle fragment (garnet peridotite) and the crustal fragment (eclogite) in the Yangkou UHP unit both experienced a common UHP metamorphic event and that the exhumation path obtained by these reference points supports nearly isothermal decompression of the unit. The Yangkou UHP unit is considered to have been exhumed as part of a larger crustal mass (c. 410 km in size) along with the surrounding orthogneisses. Such isothermal decompression paths have also been reported from other areas of the Su-Lu belt and the Dabie Mountains. As the orthogneisses volumetrically account for 490% of these areas, buoyancy-controlled uplift probably played an important role in the exhumation of the UHP rocks, at least from the upper mantle to the lower crust.

  The Permian ophiolite emplaced in the Yakuno area, Kyoto Prefecture, consists of metavolcanic sequences, metagabbro and a troctolitic intrusion. The metavolcanics are associated with thick mudstone through a contact that shows the flowage of lava over unconsolidated mud layers on the sea floor. The metavolcanics and metagabbro have rare earth element (REE) patterns that are similar to enriched (E)‐ and transitional (T)‐types ([La/Yb]N = 0.77–11.2) of mid‐oceanic ridge basalts (MORB), whereas their Nb/La ratios (0.40–1.20) are as low as those of back‐arc basin basalts (BABB). Cr‐spinels in the metavolcanic rocks have Cr♯ of 40–73 and an Fe3+♯ of 9–24, numbers which are comparable to the values of BABB. These lines of evidence suggest that the Yakuno ophiolite originated more likely from an early stage back‐arc basin rather than from an oceanic plateau, as has been suggested by some researchers. The troctolitic body that intrudes as a 0.5‐km long lens in the metagabbro is composed o...

Granulite facies relics are found in the early Paleozoic kyanite-bearing melanocratic metagabbro from the Fuko Pass metacumulate mass of the Oeyama belt, southwestern Japan. The granulite facies assemblage consists of relict Al-rich clinopyroxene (up to 8.5 wt.% A1,OJ and pseudomorphs of spinel and plagioclase. The spinel pseudomorphs consist mainly of symplectic intergrowth of corundum and magnetite with minor gahnitic spinel. The plagioclase pseudomorphs are composed mainly of clinozoisite with minor kyanite. The symplectite suggests oxidation and Mg-depletion of the original spinel: hercynite (3FeAl,O,) + (0) = corundum (3A1,03) +magnetite (Fe304). This oxidation reaction may have taken place at 700-900°C temperature. The melanocratic metagabbro has later been hydrated to form the epidote amphibolite assemblage represented by clinozoisite+kyanite+paragonite. The clinozoisite+kyanite assemblage has further reacted to form margarite at a lower temperature. The first granulite facies assemblage implies that the metacumulate has originally constituted a basal part of thick oceanic crust, and then has experienced the high-P/T type metamorphism in a subduction zone. This indicates that the thick oceanic crust has been formed and accreted to the Circum-Pacific orogenic belt in the early Paleozoic time.

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The lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring Rayleigh and Love wave phase velocities in the period range 100-250 s. Spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 = m = 10. Slow regions are evident at the East Pacific Rise, northeast Africa, Tibet, Tasman Sea, southwestern North America, and triple junctions in the northern Atlantic and Indian oceans. Fast regions occur in Australia, western Pacific, and the southern Atlantic. These features are also found by a completely different analysis based on the Backus-Gilbert method. The Backus-Gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000-km radius and the errors are about 1 'Yo of the phase velocity in the zeroth-order spherically symmetric earth. Inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors. However, resolution analysis by the Backus-Gilbert method shows that the current data do not have enough resolution for everywhere on the globe. Only a few regions currently have adequate azimuthal coverage. Thus confirmation of the above correlation requires a more complete data set.

In November 2007 we conducted a water column and seafloor mapping study of the submarine volcanoes of the Aeolian Arc in the southern Tyrrhenian Sea aboard the R/V Urania. On 26 conductivity-temperature-depth casts and tows we measured temperature, conductivity, pressure, and light scattering and also collected discrete samples for helium isotopes, methane, and pH. The 3 He/ 4 He isotope ratio, an unambiguous indicator of hydrothermal input, showed a clear excess above background at 6 of the 10 submarine volcanoes surveyed. Marsili seamount had the highest anomaly, where the 3 He/ 4 He ratio reached a d 3 He value of 23% at 610 m depth compared with background values of ∼5%. Smaller but distinct d 3 He anomalies occurred over Palinuro, Enarete, Eolo, Sisifo, and Secca del Capo. Although hydrothermal emissions are known to occur offshore of some Aeolian subaerial volcanoes, and hydrothermal deposits have been sampled throughout the arc, our results are the first to confirm active discharge on Marsili, Enarete, Eolo, Sisifo, and Secca del Capo. Samples collected over Lametini, Filicudi North, Alicudi North, and Alcione had d 3 He near the regional background values, suggesting either absence of, or very weak, hydrothermal activity on these seamounts. Hydrocasts between the volcanoes revealed a consistent d 3 He maximum between 11% and 13% at 2000 m depth throughout the SE Tyrrhenian Sea. The volcanoes of the Aeolian arc and the Marsili back arc, all <1000 m deep, cannot contribute directly to this maximum. This deep 3 He excess may be a remnant of tritium decay or may have been produced by an unknown deep hydrothermal source.

This article examines hydrothermally altered ophiolitic ultramafic rocks (HAOU), specifically Listvenite, which
are thrust over the Meatiq dome in the context of gold mineralization. These rocks represent gneissic complexes
located in Egypt’s eastern desert. The analyses presented herein are essential for understanding the distribution
of sheared serpentinite on and beneath the surface and the underlying domal structure. This study offers critical
insights into the distribution of serpentinite at Meatiq. It combines remote sensing, aerial and ground magnetic
data with petrological, geochemical, and geological analyses to create precise geological maps of potential
subsurface igneous structures commonly linked to gold mineralization. Remote sensing is used to test for rock
differentiation; intensive field geological investigations were conducted along several traverses. Petrographic
and geochemical analysis of selected samples confirmed Au content in some localities. Additionally, tomographic
inversion of the collected magnetic land profiles has unveiled previously unidentified subsurface distributions of
magnetic susceptibilities, which are essential for explaining the observed surface magnetic anomalies and for
understanding the subsurface arrangement of various rock units. Results show that the HAOU rocks have a lower
magnetic susceptibility signature relative to the adjacent serpentinites, the serpentinite from South Meatiq shows
relatively high gold content, and the gold content decreases with carbonation and alteration of the serpentinite
into talc-carbonate, as detected geochemically. The procedure followed in the present study can be regionally
applied to studying HAOU rocks of similar geologic conditions. The novelty of this study, beyond the introduction
of a novel workflow, lies in the revelation that the rocks forming the Meatiq dome are in thrust contact
with steeply dipping suprastructure units.

Crustal architecture in formerly contiguous basement terranes in SE Australia, Tasmania and northern Victoria Land is a legacy of late Neoproterozoic-Cambrian subduction-related processes, culminating in formation of the Delamerian-Ross orogen. Structures of Delamerian-Ross age were subsequently reactivated during late Mesozoic-Cenozoic Gondwana breakup, strongly influencing the geometry of continental rifting and providing clues about the origins and configuration of the pre-existing basement structures. An oceancontinent transform boundary developed off western Tasmania follows the trace of an older Paleozoic strikeslip structure (Avoca-Sorell fault system) optimally oriented for reactivation during the final separation of Australia from Antarctica. This boundary cuts across rocks preserving an earlier record of arc-continent collision during the course of which continental crust was subducted to mantle depths and Cambrian maficultramafic island arc rocks were thrust westwards over late Neoproterozoic-Cambrian passive margin sequences. Collision was accompanied by development of a foreland basin into which 520-600 Ma arcderived detrital zircons were shed. Following a reversal in subduction polarity, and change to transcurrent motion along the Gondwana margin, Tasmania migrated northward along the proto-Avoca fault system before entering a subduction zone located along the Heathcote-Governor fault system, precipitating a second collision, south-vergent thrusting, and tectonic reworking of the already accreted Cambrian arc-forearc assemblages and underlying passive margin sequences.

The Rhodope Metamorphic Province (RMP) straddles the border between Greece and Bulgaria and represents a synmetamorphic nappe-system of Alpine age that was formed during the Cretaceous to Mid-Tertiary collision of Apulia and paleo-Europe. The RMP consists of at least three different units in terms of P-T-t evolution (Mposkos & Krohe, 2000): The structurally lowermost Pangaeon complex, the intermediate Sidironeron and Kechros complexes and the uppermost Kimi complex (Fig. ).

Se recopila una base de datos de 2547 mecanismos focales de terremotos para modelar el campo de esfuerzo tectónico en Costa Rica, sur de Nicaragua y norte de Panamá. Se determinan 86 tensores regionales de esfuerzo. La orientación general del esfuerzo horizontal máximo (SH Max) es subparalela a la dirección de convergencia N 32° E de la placa de Cocos con la placa Caribe a lo largo de la fosa mesoamericana, con una rotación horaria de +-20° por debajo de los 30 km de profundidad. Se identifican tres órdenes de esfuerzos: el primero debido al movimiento absoluto de la placa de Cocos, el segundo generado por la interacción triple de esta con las placas Caribe y Nazca, y el tercero debido a contrastes de densidad impuestos por las cordilleras volcánicas, ígneas y sedimentarias activas y paralelas a la fosa, las cuales en combinación con fallas regionales y sus interacciones, actúan en conjunto como deflectores de los esfuerzos tectónicos locales que rotan hacia el norte y oeste. Los datos GNSS observados y modelados del campo de velocidades horizontales, orientados al NNE, presentan una correlación notable con las direcciones del SH Max interpoladas en la capa superior. Estas características, junto con las permutaciones locales y regionales de los ejes del elipsoide de esfuerzos, explican las interacciones de los regímenes tectónicos y sus complicaciones neotectónicas. Se genera un escenario 2D-3D detallado con límites sismo tectónicos realistas y más objetivos, utilizando categorías de regímenes de esfuerzo junto con la relación tectónica R'. Los resultados tienen aplicación práctica en estudios de amenaza y riesgo sísmico, exploración de recursos naturales.

The upper tectonic unit of the Cabo Ortegal Complex (northwest Spain) comprises an ordered rock sequence of ultramafic and mafic rocks and quartzofeldspathic gneisses. The entire assembly forms part of a transitional mafic crust. In an early Paleozoic subduction episode, most of this crust was metamorphosed at eclogite facies and high-pressure granulite facies conditions. Field and microstructural observations suggest that this metamorphism occurred simultaneously with deformation, producing a pervasive tectonic fabric that developed under a strain regime of bulk coaxial deformation. Downdip extension of the crust in the subduction zone is inferred to have thinned the rock sequence. The relatively high pressures and high temperatures (770-900 ؇C and Ͼ1.2-1.7 GPa) during deformation at peak conditions, in addition to the significant thinning of the units, suggest a tectonic setting of ductile slab breakoff as the cause of the intense and widespread deformation.

This paper summarizes the findings of two field trips to the Aceh Province, which were made by the authors, in early 2006 and late 2007. The purpose of the trips was to assess and provide guidance to the rebuilding process following the 26 December 2004 earthquake and ...

We presents the results of studying the rocks used in the construction of a port berth of the city of Phanagoria. It is shown that in the 5th-3rd centuries BC, Phanagoria received large quantities of building stone of various types from the Black Sea coast of Turkey (the cities of Sinop, Trabzon, and Hopa) and the coasts of the Aegean Sea (Aegina and Rhodes). The expediency of such deliveries was due to an acute shortage of building stone on the Taman Peninsula and the need for Phanagoria's residents to create the necessary port infrastructure.

This paper presents the results of an interpretation of ASTER products and structural data in the investigation of suture zones of cordilleran-type orogenic belts. These results have been interpreted under the light of structural analysis, isotopic and metamorphic geology, to investigate the history of tectonic evolution of the Cuyania Terrane. The capacity of ASTER sensors to acquire visible and thermal infrared data, not supported only field work, but also allowed the distinction between different rock types as well as the reinterpretation of lineaments, something not always possible using conventional cartographic methods. Following a brief description of the main pervasive fabrics recorded by rocks of this area, we present the integration of DTM and colour composite of ASTER images showing a three-dimensional view of some of the main structures of the area, in particular the large-scale F3 folds, and discuss their role in the evolution and structural geometry of the rocks. We shall demonstrate the advantages of using DTM models for structural mapping in areas of difficult access such as NW Sierras

Two distinct episodes of serpentinisation have been identified within the peridotites of the Lizard complex. The first episode (primary serpentinisation) is represented by the complex and pervasive hydration of the Lizard peridotite. The second (later) episode is characterised by a pale to dark green, pseudo-fibrous mixture of lizardite and chrysotile that is restricted to fractures (vein serpentine). Mineralised northnorth-west and east-north-east trending fault zones contain fragments of vein serpentine generated during this second episode. Faults with similar orientations and mineralogy within the gabbro unit contain adularia which have been previously dated by Ar 40 -Ar 39 and K-Ar methods at 210-220 Ma (Triassic). Stable isotope ratios indicate that the mineralisation within the gabbro and peridotite is genetically similar. The primary and secondary serpentinisation episodes are therefore interpreted as pre-Triassic in age. A latest Carboniferous to early Permian age is proposed for the formation of vein serpentine and a late Devonian to Carboniferous age is proposed for the primary serpentinisation episode. This is envisaged to have taken place post-obduction but a pre-obduction initiation of serpentinisation cannot be discounted.

Eleven glasses recovered from Holes 786A and 786B were fresh enough for volatile analysis by infrared spectroscopy. The compositions of these glasses range from boninitic to rhyolitic. The glasses from the boninites contain 1.4 to 1.7 wt% H 2 O, while the rhyolitic glasses contain 2 to 6 wt% H 2 O, and all glasses have less than 30 to 40 ppm CO 2 . The highest H 2 O contents are probably the result of seawater alteration. The unaltered dacitic to rhyolitic glasses were probably quenched at low pressures corresponding to depths of 0-700 m below the seafloor, also corresponding to the depths of collection of these samples, although the water depths may have been different between the Eocene and the present. The lower boninitic H 2 O contents in vesicular glasses suggest shallow quenching on the seafloor.

The age and origin of magmatic complexes along the Pacific Coast of Central America have important implications for the origin and tectonic evolution of this convergent plate margin. Here we present new 40 Ar/ 39 Ar laser age dates, major and trace element data, and initial Sr-Nd-Pb isotope ratios. The 124-109 Ma tholeiitic portions of the Santa Elena complex formed in a primitive island arc setting, believed to be part of the Chortis subduction zone. The geochemical similarities between the Santa Elena and Tortugal alkaline volcanic rocks suggest that Chortis block may extend south of the Hess Escarpment. The Nicoya, Herradura, Golfito, and Burica complexes and the tholeiitic Tortugal unit formed between 95 and 75 Ma and appear to be part of the Caribbean Large Igneous Province, thought to mark the initiation of the Gala ´pagos hotspot. The Quepos and Osa complexes (65-59 Ma) represent accreted sections of an ocean island and an aseismic ridge, respectively, interpreted to reflect part of the Gala ´pagos paleo-hotspot track. An Oligocene unconformity throughout Central America may be related to the mid-Eocene accretion of the Quepos and Osa complexes.

. The Northern Taiwan Volcanic Zone NTVZ is a Late Pliocene-Quaternary volcanic field that occurred as a result of extensional collapse of the northern Taiwan mountain belt. We report here mineral compositions, major and trace element and SrrNd isotope data of high-Mg basaltic andesites from the Mienhuayu, a volcanic islet formed at ; 2.6 Ma in the Ž . central part of the NTVZ. The rocks are hypocrystalline, showing porphyritic texture with Mg-rich olivine Fo f 81-80 , Ž . Ž . bronzite En f 82-79 and plagioclase An f 66-58 as major phenocryst phases. They have uniform whole-rock composi-Ž . tions, marked by high magnesium MgO f 5.9-8.1 wt.%, Mg value f 0.6 relative to accompanying silica contents Ž . Ž . Ž SiO f 52.8-54.5 wt.% . The high-Mg basaltic andesites contain the highest TiO ; 1.5 wt.% and lowest K O ; 0.4 2 2 2 . wt.% among the NTVZ volcanic rocks. In the incompatible element variation diagram, these Mienhuayu magmas exhibit Ž . Ž . mild enrichments in large ion lithophile LILE and light rare earth elements LREE , coupled with an apparent Pb-positive Ž . spike. They do not display depletions in high field strength elements HFSE , a feature observed universally in the other Ž . NTVZ volcanics. The high-Mg basaltic andesites have rather unradiogenic Nd ´Nd fq5.1-7.2 but apparently elevated Ž 87 86 . Sr Srr Sr f 0.70435-0.70543; leached values isotope ratios. Their overall geochemical and isotopic characteristics are Ž . similar to mid-Miocene ; 13 Ma high-Mg andesites from the Iriomote-jima, southern Ryukyus, Japan. Despite these magmas have lower LILE and LREE enrichments and Pb positive spike, their Aintraplate-typeB incompatible element variation patterns are comparable to those of extension-induced Miocene intraplate basalts emplaced in the Taiwan-Fujian region. Therefore, we interpret the Mienhuayu magmas as silica-saturated melts derived from decompression melting of the ascended asthenosphere that had been subtly affected by the adjacent Ryukyu subduction zone processes. This interpretation is consistent with the notion that in the northern Taiwan mountain belt post-orogenic lithospheric extension started in Plio-Pleistocene time.

The offshore Tumbes-Guayaquil forearc basin in the accretionary prism of Northern Peru-Southern Ecuador shows evidence of gravity-driven large-scale deformation systems active during the Late Neogene-Quaternary period. Subsurface data and the construction of eight structural cross-sections show that the ~8 km-thick Oligocene-Quaternary sedimentary infill is detached seaward and completely decoupled from the underlying inner accretionary prism systems. The Corvina décollement in the Tumbes basin and the Posorja décollement in the Guayaquil basin constitute two thin-skinned gravity tectonic systems associated with kilometer-scale, updip "raft" extensional structures paired with downdip fold-thrust systems (Barracuda and Domito thrust systems). Although many previous studies have described the structural and stratigraphic architecture of the Tumbes-Guayaquil forearc basin, no model explicitly accounts for this anomalous large-scale gravity tectonics. We propose that this gravity tectonic style, more commonly observed in passive continental margins, is primarily controlled by the combination of tectonostratigraphic features, including crustal-scale transtensional deformation related to oblique convergence along the Northern Andean margin, basal décollement slope tilting, strong sediment accumulation, and the presence of overpressured shales.

We characterise the aftershock sequence following the 2016 Mw=7.8 Pedernales earthquake. More than 10,000 events were detected and located, with magnitudes up to 6.9. Most of the aftershock seismicity results from interplate thrust faulting, but we also observe a few normal and strike-slip mechanisms. Seismicity extends for more than 300 km along strike, and is constrained between the trench and the maximum depth of the coseismic rupture. The most striking feature is the presence of three seismicity bands, perpendicular to the trench, which are also observed during the interseismic period. Additionally, we observe a linear dependency between the temporal evolution of afterslip and aftershocks. We also find a temporal semi-logarithmic expansion of aftershock seismicity along strike and dip directions, further indicating that their occurrence is modulated by afterslip. Lastly, we observe that the spatial distribution of seismic and aseismic slip processes is correlated to the distribu...

The direction of convergence between the Rivera and North American plates becomes progressively more oblique (in a counter-clockwise sense as measured relative to the trench-normal direction) northwestward along the Jalisco subduction zone. By analogy to other subduction zones, the forces resulting from this distribution of convergence directions are expected to produce a NW moving, fore-arc sliver and a NW-SE stretching of the fore-arc area. Also, a series of roughly arc parallel strikeslip faults may form in the fore-arc area, both onshore and offshore, as is observed in the Aleutian arc. In the Jalisco subduction zone, the Jalisco block has been proposed to represent such a fore-arc sliver. However, this proposal has encountered one major problem. Namely, right-lateral strike-slip faulting within the fore-arc sliver, and between the fore-arc sliver and the North American plate, should be observed. However, evidence for the expected right-lateral strikeslip faulting is sparse. Some evidence for right-lateral strike-slip faulting along the Jalisco block-North American plate boundary (the Tepic-Zacoalco rift system) has been reported, although some disagreement exists. Right-lateral strike-slip

This paper gives evidence of multiple tsunami inundation of the Sound of Lefkada (NW Greece) since the mid-Holocene based on the analysis of sediment cores by means of geomorphological, sedimentological, geochemical, micromorphological and micropalaeontological methods. Layers of sand, gravel and shell debris, mostly unsorted, were found intersecting autochthonous lagoonal muds of the sheltered and quiescent inner-sound environment. They are further characterized by erosional unconformities at their base, rip-up clasts from the underlying sediments, fining upward sequences and an upward increase in sorting. The coarse grained high energy deposits include macro-and microfaunal remains typical of open-marine, partly even deep-water conditions which underlines their allochthonous character. Several distinct event layers indicate multiple tsunami passage across the sound. Earth resistivity measurements and vibracore transects revealed that the entire sound has been affected by catastrophic wave events. Thin sections of tsunami-influenced sediments found in lateral parts of the sound show a mixture of marine, lagoonal and terrigenous material. The inner Sound of Lefkada, well protected against storms, thus represents an excellent trap for tsunamigenic deposits. A preliminary local tsunami geochronology is based on 9 radiocarbon dates and diagnostic ceramic fragments. Several early tsunami impacts hit the sound between the 6th and 3rd millennium BC. Younger events seem to be consistent with tsunami landfalls that hit adjacent areas around 1000 cal BC, 395-247 cal BC as well as in Roman and medieval times. Vibracore data document an isthmuslike shallow-water environment which existed in the central sound and which was repeatedly inundated by tsunami wave action. Multiple tsunami passage eroded a natural channel which, we suggest, is the precursor of the famous waterway excavated by the Corinthians in the 7th century BC. Based on historical data, it is concluded that the navigable channel across the sound was repeatedly choked with sediments by tsunamigenic inundation during the following centuries. This study reveals a high tsunami risk for the Sound of Lefkada with at least one strong event in every 500-1000 years.

The South Portuguese Zone (SPZ) constitutes the southernmost segment of the Variscan Iberian Massif. It is bounded to the north by the Beja‐Acebuches Ophiolitic Complex and related accretionary wedge. To the south lie the Iberian Pyrite Belt (IPB) and flysch deposits forming the southern extent of the zone. Structural analysis within the Spanish side of the SPZ supports continuous south propagating deformation, evolving from early synmetamorphic thrusting in the internal zone to thin‐skinned tectonics in the southern external domain. The accretion of the SPZ to the Ossa Morena Zone is also witnessed by the presence of various mélanges, observed throughout the investigated area. Part of the mélanges observed in the IPB are related to the volcanics and mineralizations setting. A key point to understand the IPB mineralizations genesis is to constrain the volcanogenic model. One underestimated feature is the large amount of submarine calc‐alkaline ignimbritic facies, implying the presen...

Evolution of the Red Sea/Gulf of Suez and the Central Atlantic rift systems shows that an initial, transtensive rifting phase, affecting a broad area around the future zone of crustal separation, was followed by a pre-oceanic rifting phase during which extensional strain was concentrated on the axial rift zone. This caused lateral graben systems to become inactive and they evolved into rift-rim basins. The transtensive phase of diffuse crustal extension is recognized in many intra-continental rifts. If controlling stress systems relax, these rifts abort and develop into palaeorifts. If controlling stress systems persist, transtensive rift systems can enter the pre-oceanic rifting stage, during which the rift zone narrows and becomes asymmetric as a consequence of simple-shear deformation at shallow crustal levels and pure shear deformation at lower crustal and mantle-lithospheric levels. Preceding crustal separation, extensional denudation of the lithospheric mantle is possible. Progressive lithospheric attenuation entails updoming of the asthenosphere and thermal doming of the rift shoulders. Their uplift provides a major elastic source for the rift basins and the lateral rift-rim basins. Their stratigraphic record provides a sensitive tool for dating the rift shoulder uplift. Asymmetric rifting leads to the formation of asymmetric continental margins, corresponding in a simple-shear model to an upper plate and a conjugate lower plate margin, as seen in the Central Atlantic passive margins of the United States and Morocco. This rifting model can be successfully applied to the analysis of the Alpine Tethys palaeo-margins (such as Rif and the Western Alps).

3c. In the Thrace Evros basin, Early Miocene (22-19.5 Ma) calc-alkaline and K-alkaline rocks occur, suggesting an origin from both lithospheric mantle and crust related to postcollisional extensional processes and core complex exhumation. In the Thrace basin, Naalkaline basalts occurred at 8.9-4.5 Ma; decompression melting of an asthenospheric source may be related to a westward mantle flow generated by the block movement along the North Anatolian fault system; 3d. The South Moesian block has an N-S line of Na-alkaline basalts that started in the Oligocene and become younger toward the south at 21.4-19.4 Ma. They have an asthenospheric source that may be connected to local fractures related to Tisia-Dacia block rotation movements around stable Moesia. Thus, the mantle dynamics and melt generation in CPR and surrounding areas are echoes of many subduction, collision, rotation and extension processes of several microplates that acted variably in the convergence between Africa (chiefly...

Two campaigns of Global Positioning System (GPS) measurements were carried out in the Concepcio ´n-Constitucio ´n area of Chile in 1996 and 1999. It is very likely that this area is a mature seismic gap, since no subduction earthquake has occurred there since 1835. In 1996, 32 sites were occupied in the range 35°S-37°S, between the Pacific coast of Chile and the Andes near the Chile-Argentina border. In 1999, the network was extended by the installation of 9 new points in the Arauco region whereas 13 points among the 1996 stations were reoccupied. The analysis of this campaign data set, together with the data recorded at eight continuous GPS sites (mostly IGS stations) in South America and surrounding regions, indicates a velocity of about 40 ± 10 mm/yr in the direction N80 -90°S for the coastal sites with respect to stable cratonic South America. This velocity decreases to about 20 -25 mm/yr towards the Andes. We interpret this result as reflecting interseismic strain accumulation above the Nazca-South America subduction zone, due to a locked thrust zone extending down to about 60 km depth.

The M w 9.0 Tohoku-oki Japan earthquake and many of its subsequent aftershocks and triggered events were very well recorded, providing opportunity for detailed study of source, path, and site effects. In previous work, we utilized mainshock data to demonstrate faster attenuation with distance in backarc than in forearc regions, positive event terms for high frequency intensity measures for multiple ground motion prediction models, and minimal scaling of site amplification with V s30 at high frequencies. In this paper, we consider two subsequent events, one M w 6.7 on the plate interface that ruptured in the mainshock and one M w 6.3 inland from the volcanic front, to examine if similar ground motion features are apparent from these data sets. We continue to find evidence for the divergence in attenuation rate in forearc and backarc regions, despite the fact that the events are located on opposite sides of the volcanic front. The site response for these events does not appear to follow previously observed patterns for Japan, being relatively similar to V s30 -scaling in active crustal regions generally.

This study was funded by the GEM Foundation as part of the Pacific Earthquake Engineering Research Center's (PEER's) Global GMPEs project. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect those of the sponsors. vi vii CONTENTS ABSTRACT .

In this study we test whether principal components of the strain rate and stress tensors align within Switzerland. We find that 1) Helvetic Nappes line (HNL) is the relevant tectonic boundary to define different domains of crustal stress/surface strain rates orientations and 2) orientations of T-axes (of moment tensor solutions) and long-term asthenosphere cumulative finite strain (from SKS shear wave splitting) are consistent at the scale of the Alpine arc in Switzerland. At a more local scale, we find that seismic activity and surface deformation are in agreement but in three regions (Basel, Swiss Jura and Ticino); possibly because of the low levels of deformation and/or seismicity. In the Basel area, deep seismicity exists while surface deformation is absent. In the Ticino and the Swiss Jura, where seismic activity is close to absent, surface deformation is detected at a level of ~2 10 -8 /yr (~6.3 10 -16 /s). Motivation. GPS networks, that measure long-term deformation at the surface, provide a unique opportunity to place seismic activity in context with geological observations resulting of long periods of tectonic activity (i.e. sea-level changes, geology, and erosion rates). Although they highlight various periods of times, the relationship between surface deformation (i.e. GPS), crustal seismicity (i.e. moment tensors principal components), and strain in the asthenosphere (i.e. shear wave splittings) is of genuine interest, both for understanding the origin of the surface deformation observed and quantifying seismic hazard. For instance, the comparison of directions of principal components of both stress and strain tensors helps understanding whether stress accumulates along faults 1-5 or through blocks , whether seismic ruptures are triggered , encouraged or impeded and, finally, how stress is transferred to surrounding fault systems . Also, the comparison between strain rates and asthenosphere strains sheds light on the upper mantle strength and reveals whether the current tectonic period could be responsible and/or parented to the anisotropy detected in the mantle . Across strongly active plate boundaries, linking seismic activity and surface deformation is made easier because strain rates are high (>10 -7 /yr) and permanent GPS networks are dense . There, higher strain rates tend to shorten seismic cycles lengths 27 , enabling us to document larger portions of the seismic cycle and informing us on the preparation of future mainshocks. For slowly deforming intra-plate regions, however, we understand less about the relationship between surface deformation and seismicity: strain rates are smaller, seismic activity may not be sufficient to deform the surface while seismic hazard may still be significant . We take Switzerland for an example of this situation and investigate the link between GPS strain rates and the seismicity observed since 2 decades.