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Deformation in the Earth’s crust and the occurrence of earthquakes, volcanism and georesources are caused by processes occurring in the Earth’s interior. Geodynamical models are the only way to study the interplay between the Earth’s (deep) interior and its surface as many of these processes occur on timescales from millions to billions of years. Therefore, novel geological or geophysical observations provide a constant means to improve these models and thereby our understanding of the dynamic solid Earth. This thesis focusses on the interaction between the Earth’s mantle and the tectonic plate motion on top by using novel kinematic observations obtained through plate-tectonic reconstructions based on geological data. One of these observations is the inferred average slab sinking rates, which are obtained by the correlation of the geological record with tomographically imaged slabs in the mantle. These illustrate the deceleration of slabs from plate motion speeds in the upper mantle to an average sinking rate in the lower mantle. Our models with slab sinking rates of 10-15 mm/a have a very limited bulk mantle motion, of only a few mm/a. In these models the preservation of large unmixed zones in the mid-mantle occurs even after 1000 Ma of simulated subduction evolution and mantle convection. We use configurational entropy to quantify and map the mixing of different compositions in our mantle convection models. This entropy may be used to analyse, with a single global measure, the mixed state of the mantle and compare various geodynamic models with each other. Furthermore, the local entropy may be useful to validate geodynamic models against local anomalies in the mantle from seismological or geochemical observations. The deceleration of slabs from subducting plate velocities to the lower mantle average slab sinking rates occurs by thickening or buckling of the subducting plate. High-resolution kinematic reconstructions of the Indian Plate revealed rapid oscillations

Due to the scarcity of rock samples, the Hadean Era predating 4 billion years ago (Ga) poses challenges in understanding geological processes like subaerial weathering and plate tectonics that are critical for the evolution of life. The Jack Hills zircon from Western Australia, the primary Hadean samples available, offer valuable insights into magma sources and tectonic genesis through trace element signatures. However, a consensus on these signatures has not been reached. To address this, we developed a machine learning classifier capable of deciphering the geochemical fingerprints of zircon. This allowed us to identify the oldest detrital zircon originating from sedimentary-derived S-type granites. Our results indicate the presence of S-type granites as early as 4.24 Ga, persisting throughout the Hadean into the Archean. Examining global detrital zircon across Earths history reveals consistent supercontinent-like cycles from the present back to the Hadean. These findings suggest that a significant amount of Hadean continental crust was exposed, weathered into sediments, and incorporated into the magma sources of Jack Hills zircon. Only the early operation of both subaerial weathering and plate subduction can account for the prevalence of S-type granites we observe. Additionally, the periodic evolution of S-type granite proportions implies that subduction-driven tectonic cycles were active during the Hadean, at least around 4.2 Ga. The evidence thus points toward an early Earth resembling the modern Earth in terms of active tectonics and habitable surface conditions. This suggests the potential for life to originate in environments like warm ponds rather than extreme hydrothermal settings.

Uplift and unroofing of Jurassic-Cretaceous, mantle and crust, arc- and plume-related rock units in the Median Belt of the Dominican Republic exposed basement rocks with a protracted record of tectono-thermal events delineating the evolution of the northern edge of the Caribbean plate. In this article we focus on crustal rock units in the north-eastern half of the Median Belt. First Ar/Ar dating of metamorphic ferri-winchite (86.4 ± 2.5 Ma; crystallization date) and albite (82.3 ± 5.8 and 79.8 ± 1.6 Ma; cooling dates) in metabasites of boninitic photolith from the Aptian-Albian Maimón Formation in the Ozama shear zone points to a tectono-metamorphic event in the Upper Cretaceous. Beltwide, this event caused syn-metamorphic N- to NNE-directed, simple-shear dominated, mylonitic and phyllonitic deformation of the Maimón Formation at peak metamorphic conditions of 8.2 kbar and 380°C. Such conditions are consistent with subduction of a coherent portion of forearc (represented by the Maimón Formation) to depths of ~25-29 km. The tectono-metamorphic event dated here overlaps with the inception of Turonian-Coniacian SW-dipping subduction and metamorphic sole formation in a back-arc position recorded in the Moa-Baracoa ophiolite complex in neighboring Eastern Cuba. Contemporaneity between the subduction inception of forearc and back-arc portions of the Caribbean arc and the main pulse of plume activity recorded in the Caribbean Large Igneous Province (CLIP) suggests that plume activity promoted general plate instability leading to a regional-scale plate reorganization. This mantle-plume-induced plate margin reorganization was coeval with the inception of the NE-dipping subduction of the Farallón plate beneath Central America leading to the definition of the Caribbean Plate by double-verging subduction zones along its northern and southwestern margins.

The ophiolitic Villa Clara serpentinite-matrix mélange, central Cuba, forms part of the large ophiolitic belt of the Greater Antilles. The composition of ultramafic and mafic rocks allows classifying them into two main groups, revealing a complex multi-stage formation of oceanic lithosphere in varied tectonic settings: i) group 1 matches fertile MORB-like mantle typical of abyssal/transform fault peridotites, while ii) group 2 shows characteristics of refractory mantle-wedge forearc peridotites. These features are consistent with moderate extent of partial melting (4–8%) of depleted mantle at a mid-ocean ridge setting that created residual abyssal peridotite (group 1) and intense remelting (14–18%) of the latter in a forearc setting that created highly refractory peridotite (group 2). The elemental and isotopic characteristics of groups 1 and 2 serpentinites denote the influx of fluids evolved from the subducting slab. Mafic rocks appear as variably sized tectonic blocks within serpentinite that underwent variable alteration at low pressure. Immobile element concentrations allow identifying two main groups: i) group 1 is consistent with forearc basalts formed during the second stage of melting of (abyssal) peridotite, while ii) group 2 has a compositional pattern like island-arc tholeiitic basalts. A geodynamic evolution from abyssal to forearc settings is presented to explain the nature of the oceanic lithosphere of the Villa Clara ophiolitic bodies and ensuing serpentinization and mélange formation. This model may explain other ophiolitic bodies of the Caribbean arc in Cuba, Dominican Republic and Puerto Rico and elsewhere formed in abyssal/transform fault or forearc settings.

Pore fluid pressure on subduction zone megathrusts is lowered by fluid drainage into the overlying plate, affecting subduction zone seismicity. However, the spatial and temporal scales of fluid flow through suprasubduction zones are poorly understood. We constrain the duration and velocity of fluid flow through a shallow mantle wedge based on the analyses of vein networks consisting of high-temperature serpentine in hydrated ultramafic rocks from the Oman ophiolite. On the basis of a diffusion model and the time-integrated fluid flux, we show that the channelized fluid flow was short-lived (2.1 × 10−1 to 1.1 × 101 years) and had a high fluid velocity (2.7 × 10−3 to 4.9 × 10−2 meters second−1), which is close to the propagation velocities of seismic events in present-day subduction zones. Our results suggest that the drainage of fluid into the overlying plate occurs as episodic pulses, which may influence the recurrence of megathrust earthquakes.

The seismic wavefield, as recorded at the surface, carries information about the seismic source and Earth's structure along the seismic path, essential for the understanding of the interior of our planet. For 40 years seismic tomography studies have resolved the 3D seismic velocity structure in growing detail using seismic traveltimes and waveforms. These studies have been driving our understanding of the dynamics and evolution of the planet, but are limited in their spatial resolution to imaging scales of a few 100 s to 1000 km due to the constraints of the tomographic inversion. Detailed studies of seismic waveforms can resolve finer scale structure but are often reliant on serendipitous source-receiver combinations and provide very uneven coverage of the planet. Therefore, we often lack an understanding of the fine scale structure of the Earth that is important to understand structures and processes such as mantle plumes or details of slab recycling. Here we show evidence that we can exploit slowness vector deviations of the seismic wavefield to extend our knowledge of Earth structure to smaller scales using large datasets. Analysing seismic array data, we show strong and measurable focussing and defocussing effects of the teleseismic P and Pdiff wavefield sampling the deep Earth. We compare the P-wave results to additional S and Sdiff data and find good agreement between both wavetypes. We can link the wavefield deviations to strong velocity variations assuming sharp boundaries are sampled along the path in the deep mantle. The dataset samples the Pacific and Gulf of Mexico well and shows strong horizontal incidence (backazimuth) deviations in the Pacific (up to 14° westwards) and beneath the Gulf of Mexico (up to 5 to 8° east- and west-ward). The backazimuth deviations are also reflected in slowness deviations in the range of ± 0.8 s/° relating to velocity variations in the range of ± 9 km/s. Using 3D raytracing we are able to forward m

Subduction zones are locations on Earth where the oceanic material of one tectonic plate dives below the material (oceanic or continental) of another tectonic plate into the mantle. They are the most complex and dramatic tectonic features on our home planet and have been the subject of intense investigations, some of which pre-date the advent of the theory of plate tectonics. This contribution provides a short review of the science of subduction zones, discusses and reviews the geometry, kinematics and dynamics of subduction zones, and provides an overview and data compilation for the 28 subduction zones that are currently active on Earth. Most of these subduction zones are characterized by four common, and most conspicuous features, namely a deep-sea trench (21 out of 28), a magmatic arc (23), a Wadati–Benioff zone (22), and a slab geometry in seismic tomography (25). Apart from these four general commonalities and several other characteristics that are less ubiquitous, subduction zones show major variability in appearance and behavior. Earlier investigations have proposed that, among others, subduction zone width or subducting plate age exerts a primary control on this variability. The current contribution presents a global set of observational constraints to investigate the role of width and age on six subduction zone parameters (subducting plate velocity, trench velocity, subduction partitioning, overriding plate deformation rate, slab dip angle, and maximum earthquake magnitude). The results show that correlations for slab width are systematically stronger than for plate age, implying a more significant control of slab width on subduction dynamics, which is consistent with earlier geodynamic modeling efforts and scaling formulations. Considering the more dominant role of slab width, and the subordinate role of subducting plate age, it is here proposed to step away from the age-based subduction zone classification of Mariana-type and Chilean-type subduction z

\textit{What is the fate of the lower crust during continental collision?} Chapter 2 incorporates geologic constraints of lower crustal dynamics. Specifically, crustal xenoliths from the Pamir are used to constrain the geodynamic style of the loss of a lithospheric root. Delamination—the peeling back of a dense layer—is favored based on xenolith pressure-temperature-time paths. Moreover, delamination is caused by feedbacks between the lateral escape of the lower crust and cooling at the margins of the orogen. This contrasts with the assumption that delamination and channel flow are decoupled mechanisms. Instead, laterally flowing buoyant lower crust can founder after cooling. \textit{How do sediment diapirs differentiate?} Recent models of sediment diapirs in subduction zones assume diapirs are perfectly round with no internal transport of solid-state material. Chapter 3 tests these assumptions by applying porous and solid-state flow to diapiric differentiation. Not only can diapirs split into a buoyant portion and a dense residue but mushy material flows upward along the diapir margins, driving convection \textit{within} the diapir. Such churning could promote reactions between different lithologies in diapirs, meaning that hybridized material need not only be created in a subduction channel but inside the diapir itself. More broadly, however, geodynamic models of diapirism, delamination, and tectonic processes in general often require many more input parameters than can be tested individually, limiting the robustness of results. \textit{How then can the sensitivity of many input parameters in geodynamic models be tested?} This work streamlines the calculation of linearized sensitivities. Specifically, the technique of \textit{reverse automatic differentiation} is applied to models with many (154) inputs to obtain sensitivities of \textit{all} inputs for a reasonable computational cost ($<$6x forward pass). This technique is applied to models of sediment diapirs

The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings Ridges and South Fiji Basin. In this paper we present 33 40Ar/39Ar, 22 micropaleontological, and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites in this little-studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites, and a granite. Successful Ar/Ar dating of altered and/or low-K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The 40Ar/39Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25–22 Ma); two are Eocene (39–36 Ma). The granite has a U/Pb zircon age of 23.6 ± 0.3 Ma. 40Ar/39Ar lava ages are corroborated by microfossil ages from associated sedimentary rocks. The VESPA lavas are part of a >3000 km long disrupted belt of Eocene to Miocene subduction-related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, speculatively, D’Entrecasteaux Ridge. This belt is the product of superimposed Eocene and Oligocene-Miocene remnant volcanic arcs that were stranded along and near the edge of Zealandia while still-active arc belts migrated east with the Pacific trench. Key Points A major pulse of 25–22 Ma volcanism is documented on the Loyalty and Three Kings Ridges, southwest Pacific Ocean The ridges are part of a more than 3000 km long belt of Eocene to Miocene remnant volcanic arcs, stranded along the edge of Zealandia With care in sample selection, and petrological work, meaningful Ar/Ar ages can be obtained from altered and/or very low-K submarine basalts Plain Language Sum

At convergent plate margin, part of the continental crust can be subducted and exhumed. During continental subduction a pre-existing crust is reworked. Remnants of an older orogen are recycled and subjected to (ultra)-high-pressure metamorphism. During subduction, polycyclic rocks undertake a second metamorphic cycle, whereas monocyclic rocks are metamorphosed for the first time. In reworked rocks the pre-subduction record is overprinted and partially or completely lost. Despite this difficulty, reconstructing the pre-subduction history of the recycled crust is crucial, because pre-subduction characters (such as H2O content) can strongly influence how rocks respond to reworking during subduction. The Dora-Maira Massif is worldwide renowned as a (ultra)-high-pressure continental terrane. However, its northern part remained essentially unexplored in recent times. In this thesis work the northern Dora-Maira Massif is used as a case study to investigate recycling of continental crust. The aim is to constrain what type of crust is subducted and exhumed and to unravel the role of fluids during subduction of polycyclic material. Field work, petrology, thermodynamic modelling and geochronology are integrated. New field and geochronological evidence indicate that the northern Dora-Maira Massif displays an internal architecture more complex than what previously thought. It is subdivided in several tectonic units likewise the southern Dora-Maira Massif. Chemical and isotopic records of the reworked rocks reveal a pre-Alpine history spanning from the Lower Palaeozoic to the Mesozoic. A polycyclic basement preserves relicts of a pre-Alpine Barrovian metamorphism connected with the Variscan orogenesis. The absence of granulite-facies partially molten pre-Alpine rocks indicates that only the upper crust was reworked in the Dora-Maira Massif. Thermodynamic modelling indicates that polycyclic micaschists were rehydrated between the Variscan and the Alpine peak metamorphism. Polycycl

Rocks exhumed from ancient subduction zone interfaces often contain both coherent terranes and block-in-matrix mélanges, but the relationship between these two endmembers and its implications for underplating have not been closely examined. The Catalina Schist is a Cretaceous paleosubduction complex on Santa Catalina Island (California) that contains an amphibolite facies mélange with an underlying unit of coherent amphibolite. In this thesis, I present a metamorphic history of the coherent amphibolite that is based on field and petrographic evidence and pressure-temperature estimates from Raman elastic barometry and trace element thermometry. Rocks from the coherent amphibolite record peak metamorphic conditions of 1.20 to 1.29 GPa and 665 to 691 °C. This is consistent with several amphibolite mélange blocks, but the range of block conditions suggests that some upwards movement of the coherent amphibolite may have occurred at the subduction interface prior to the current juxtaposition of the two units.

Earthquakes occur in a variety of geologic settings throughout the Earth: from volcanic summits all the way down to depths of 660 km at the bottom of the mantle transition zone. Though they pose significant hazard in some regions, earthquakes are also scientific opportunities to gain insight about different processes within the Earth system. Earthquakes all share the common behavior of suddenly releasing energy that had been stored within rock, but the driving forces and physical conditions of individual systems where they occur varies greatly. Earthquake observations that characterize rupture source properties reveal both the similarities and differences between shallow and deep earthquakes. These are key to differentiating the types of processes that could be leading to earthquake failure in different systems under varying physical conditions. Our general understanding of earthquake proprieties are used in the studies presented here to help guide investigations of both volcanic systems and subducting slabs. Here we present two types of earthquake analyses: statistical modeling of shallow volcanic earthquakes and geodynamic modeling for deep earthquake investigation. In a volcanic setting, the driving forces behind the stress changes in the system leading to seismicity can be associated with magma migration and pressure changes within the plumbing of a volcano. Improving our understanding of this relationship could help us to utilize future earthquake occurrences in interpreting changes in a volcano's behavior. Here we use earthquake statistics and statistical hazard modeling to investigate earthquakes occurring during the active 2018 Kīlauea Volcano eruption and find changes in earthquake behavior that temporally align with physical changes in the behavior of the larger volcanic system. Much deeper below Earth's surface, in subducting lithosphere, the driving forces leading to deep (>70 km) earthquakes are associated with the long-term deformation of the subduc

Due to limited exposure and the challenges of field access, the magmatic record of the Ross Orogeny along the Transantarctic Mountains, Antarctica remains ill-constrained. This results in a lack of clarity for Gondwanan tectonics and geodynamics along the paleo-Pacific margin. To better understand spatiotemporal trends in the timing, duration, and source(s) of magmatism, whole-rock geochemistry, U-Pb ages, and Lu-Hf isotopes were measured on zircon in 132 granitoids and 40 gneisses from northern Victoria Land (nVL), the Miller Range (MR), and the Ohio Range (OHR) mountains, spanning ~4,000 km of the Antarctic segment of the paleo-Pacific margin of Gondwana. U-Pb data reveal magmatism in the northern Transantarctic Mountains at nVL initiated by at least ca. 552 Ma, lasting until ca. 467 Ma, magmatism in the central Transantarctic Mountains (cTAM) at the MR spans ca. 573 Ma to ca. 487 Ma, and, the OHR in the southern Transantarctic Mountains (sTAM) records magmatism from ca. 540 Ma to ca. 423 Ma. These age ranges suggest that the duration of magmatism was near-synchronous along the entire margin, but that magmatism first initiated in the cTAM through sVL (ca. 595-590 Ma), before migrating northward and southward into nVL (ca. 552 Ma) and sTAM (i.e., OHR, ca. 540 Ma), respectively. Termination of magmatism followed a similar trend, ending in the cTAM through sVL ca. 485 Ma, then in nVL ca. 467 Ma, and finally in OHR ca. 423 Ma. Thus, our data do not support the long-held suggestion of arc magmatism decreasing in age northward along the margin.Zircon Hf isotope data indicate different magma sources contributed to magmatism as it migrated along the margin. Granitoids from nVL contain minimal mantle input, and were instead dominantly sourced from melting of (meta-)sedimentary source(s). Granitoids from the Ohio Range contain some juvenile input from a relatively young mantle source and contain almost no inherited zircon xenocrysts. Magmatic and metamorphic rocks from the

The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings Ridges and South Fiji Basin. In this paper we present 33 40Ar/39Ar, 22 micropaleontological, and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites in this little-studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites, and a granite. Successful Ar/Ar dating of altered and/or low-K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The 40Ar/39Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25–22 Ma); two are Eocene (39–36 Ma). The granite has a U/Pb zircon age of 23.6 ± 0.3 Ma. 40Ar/39Ar lava ages are corroborated by microfossil ages from associated sedimentary rocks. The VESPA lavas are part of a >3000 km long disrupted belt of Eocene to Miocene subduction-related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, speculatively, D’Entrecasteaux Ridge. This belt is the product of superimposed Eocene and Oligocene-Miocene remnant volcanic arcs that were stranded along and near the edge of Zealandia while still-active arc belts migrated east with the Pacific trench. Key Points A major pulse of 25–22 Ma volcanism is documented on the Loyalty and Three Kings Ridges, southwest Pacific Ocean The ridges are part of a more than 3000 km long belt of Eocene to Miocene remnant volcanic arcs, stranded along the edge of Zealandia With care in sample selection, and petrological work, meaningful Ar/Ar ages can be obtained from altered and/or very low-K submarine basalts Plain Language Sum

The Himalaya and the Tibetan plateau, the highest mountain range on Earth, have been growing continuously for the last 55 Myr since India collided with Eurasia. The forces driving this protracted mountain building process are still not fully understood. Although subduction zones are considered the main driving force for plate tectonics, mantle flow and plate boundary migration, their role in driving the Indian indentation and the northward movement of the collisional plate boundary is yet to be tested with geodynamic models. Here, we use four-dimensional geodynamic physical models to show that active subduction of the Indo-Australian plate along the Sunda subduction zone is probably the main driver of the India-Asia convergence, Indian indentation, and the consequent growth of the Himalaya-Tibet mountains, and also the present-day eastward crustal displacement of southeast Asia. Our experiments show that at least 880 km of northward indentation of India would not have ensued in the absence of the lateral subduction zones. Our experiments with lateral subduction zones show that subduction of the Indian continental lithosphere is maximum close to the eastern and western syntaxes, which ranges between 450 and 500 km. Based on our model results we propose that the protracted growth of collisional mountains on Earth, like the Himalaya, is highly dependent on nearby active subduction zones.

Since the Cretaceous the evolution of the Aegean subduction zone has been controlled by convergence and northward subduction of the African plate beneath the Eurasian plate. Additionally, the realm is dominated by the westward extrusion of Anatolia and north-south extension in the Aegean. Satellite based velocity field measurements show that Anatolia is extruding to the west along the North Anatolian Fault zone, while the southern part of the Aegean domain is moving southward. The southward movement is facilitated by subduction transform edge propagator (STEP) faults in the east and west of the Aegean subduction zone, which mark the transition between the Aegean slab and the Cyprus slab. The southern Aegean domain moves faster to the south than Anatolia is moving to the west and a southward directed sub-lithospheric mantle flow is coupled with slab rollback. This is in agreement with the extensional tectonic processes in the Aegean back-arc. Furthermore, subduction-related processes, including collision and subduction of micro-continents, magma generation at different depth, addition of slab-derived fluids, assimilation, fractionation and magma mixing, add to the diversification of magmatic products. In addition, intra-plate magmatic processes, such as asthenospheric mantle upwelling, are facilitated by slab rollback, slab edge and an approximately vertical gap between the neighbouring Aegean and Cyprus slabs. The seismic anomaly of the gap is situated underneath western Anatolia and reaches in shallower levels into the eastern Aegean. Back-arc tectonic processes, subduction-related processes and intra-plate magmatic processes result diverse Cenozoic magmatic activities. The central aim of this study is the chemical characterization of the magmatic evolution and the timing of Miocene to Quaternary volcanism in the Eastern Aegean. Questions which follow from this aim are: Which magma fluxes from which mantle source are documented in the (isotope) geochemistry of

At convergent plate margin, part of the continental crust can be subducted and exhumed. During continental subduction a pre-existing crust is reworked. Remnants of an older orogen are recycled and subjected to (ultra)-high-pressure metamorphism. During subduction, polycyclic rocks undertake a second metamorphic cycle, whereas monocyclic rocks are metamorphosed for the first time. In reworked rocks the pre-subduction record is overprinted and partially or completely lost. Despite this difficulty, reconstructing the pre-subduction history of the recycled crust is crucial, because pre-subduction characters (such as H2O content) can strongly influence how rocks respond to reworking during subduction. The Dora-Maira Massif is worldwide renowned as a (ultra)-high-pressure continental terrane. However, its northern part remained essentially unexplored in recent times. In this thesis work the northern Dora-Maira Massif is used as a case study to investigate recycling of continental crust. The aim is to constrain what type of crust is subducted and exhumed and to unravel the role of fluids during subduction of polycyclic material. Field work, petrology, thermodynamic modelling and geochronology are integrated. New field and geochronological evidence indicate that the northern Dora-Maira Massif displays an internal architecture more complex than what previously thought. It is subdivided in several tectonic units likewise the southern Dora-Maira Massif. Chemical and isotopic records of the reworked rocks reveal a pre-Alpine history spanning from the Lower Palaeozoic to the Mesozoic. A polycyclic basement preserves relicts of a pre-Alpine Barrovian metamorphism connected with the Variscan orogenesis. The absence of granulite-facies partially molten pre-Alpine rocks indicates that only the upper crust was reworked in the Dora-Maira Massif. Thermodynamic modelling indicates that polycyclic micaschists were rehydrated between the Variscan and the Alpine peak metamorphism. Polycycl

At convergent plate margin, part of the continental crust can be subducted and exhumed. During continental subduction a pre-existing crust is reworked. Remnants of an older orogen are recycled and subjected to (ultra)-high-pressure metamorphism. During subduction, polycyclic rocks undertake a second metamorphic cycle, whereas monocyclic rocks are metamorphosed for the first time. In reworked rocks the pre-subduction record is overprinted and partially or completely lost. Despite this difficulty, reconstructing the pre-subduction history of the recycled crust is crucial, because pre-subduction characters (such as H2O content) can strongly influence how rocks respond to reworking during subduction. The Dora-Maira Massif is worldwide renowned as a (ultra)-high-pressure continental terrane. However, its northern part remained essentially unexplored in recent times. In this thesis work the northern Dora-Maira Massif is used as a case study to investigate recycling of continental crust. The aim is to constrain what type of crust is subducted and exhumed and to unravel the role of fluids during subduction of polycyclic material. Field work, petrology, thermodynamic modelling and geochronology are integrated. New field and geochronological evidence indicate that the northern Dora-Maira Massif displays an internal architecture more complex than what previously thought. It is subdivided in several tectonic units likewise the southern Dora-Maira Massif. Chemical and isotopic records of the reworked rocks reveal a pre-Alpine history spanning from the Lower Palaeozoic to the Mesozoic. A polycyclic basement preserves relicts of a pre-Alpine Barrovian metamorphism connected with the Variscan orogenesis. The absence of granulite-facies partially molten pre-Alpine rocks indicates that only the upper crust was reworked in the Dora-Maira Massif. Thermodynamic modelling indicates that polycyclic micaschists were rehydrated between the Variscan and the Alpine peak metamorphism. Polycycl

Antigorite dehydration is a process able to release, in comparison with other minerals, the highest amount of H2O from a subducting slab. The released fluid delivers critical elements (e.g., S, Cu, and REE) to the overlying subarc mantle, modifying the mantle source of arc magmas and related ore deposits. Whether antigorite breakdown produces oxidising or reducing fluids is debated. Whereas previous studies have investigated antigorite dehydration in serpentinites (i.e., in a (C)AMFS-H2O system), this contribution is devoted to the CMFS-COHS carbonate system, which is representative of the metacarbonate sediments (or carbonate-dominated ophicarbonate rocks) that sit atop the slab. Thermodynamic modelling is used to investigate the redox effect of the carbonate-buffered antigorite dehydration reactions (i.e., brucite breakdown and antigorite breakdown) on electrolytic fluid geochemistry as a function of P-T-fO2. The influence of P-T-fO2 conditions on the solubility of C and S, solute-bound H2 and O2, fluid pH, the average valence states of dissolved C and S, and the fluid redox budget indicates that, in metacarbonate sediments, the CaCO3+antigorite reaction tends to produce reducing fluids. However, the redox state of such fluids is buffered not only by the redox state of the system but also, most importantly, by concomitantly dissolving redox-sensitive minerals (i.e., carbonates, graphite, pyrite, and anhydrite). A qualitative correlation between the redox state of the system and the possible depth of fluid release into the mantle wedge is also derived.

The Nazca-South America subduction zone spans >7,000 km of the South America margin. It is characterized by the subduction of the oceanic Nazca plate beneath continental South America and is responsible for the largest ongoing tectonics recorded in the overriding plate of a convergent margin, including the Andean Mountain belt. The subduction zone is often described as a natural laboratory to study the fundamentals of subduction and as a modern analog to other Cordilleran-style tectonics (e.g., the North American Cordillera). Models which compare the two often focus on the down-going plate and its role in driving processes in the overriding plate and its effects on the mantle. This dissertation explores the relationship between the morphology of the downgoing Nazca slab, the surrounding mantle, and its influence on the overriding plate using seismic tomography. The first two chapters focus on the large-scale morphology of the subducting slab from 90 to 1450 km depth with increasing detail in the second chapter. The final chapter focuses on the crust and connection between subducted bathymetric features of the slab and the development of the forearc and volcanic arc architecture.

At convergent plate margin, part of the continental crust can be subducted and exhumed. During continental subduction a pre-existing crust is reworked. Remnants of an older orogen are recycled and subjected to (ultra)-high-pressure metamorphism. During subduction, polycyclic rocks undertake a second metamorphic cycle, whereas monocyclic rocks are metamorphosed for the first time. In reworked rocks the pre-subduction record is overprinted and partially or completely lost. Despite this difficulty, reconstructing the pre-subduction history of the recycled crust is crucial, because pre-subduction characters (such as H2O content) can strongly influence how rocks respond to reworking during subduction. The Dora-Maira Massif is worldwide renowned as a (ultra)-high-pressure continental terrane. However, its northern part remained essentially unexplored in recent times. In this thesis work the northern Dora-Maira Massif is used as a case study to investigate recycling of continental crust. The aim is to constrain what type of crust is subducted and exhumed and to unravel the role of fluids during subduction of polycyclic material. Field work, petrology, thermodynamic modelling and geochronology are integrated. New field and geochronological evidence indicate that the northern Dora-Maira Massif displays an internal architecture more complex than what previously thought. It is subdivided in several tectonic units likewise the southern Dora-Maira Massif. Chemical and isotopic records of the reworked rocks reveal a pre-Alpine history spanning from the Lower Palaeozoic to the Mesozoic. A polycyclic basement preserves relicts of a pre-Alpine Barrovian metamorphism connected with the Variscan orogenesis. The absence of granulite-facies partially molten pre-Alpine rocks indicates that only the upper crust was reworked in the Dora-Maira Massif. Thermodynamic modelling indicates that polycyclic micaschists were rehydrated between the Variscan and the Alpine peak metamorphism. Polycycl

Lithospheric slab tearing, the process by which a subducted lithospheric plate is torn apart and sinks into the Earth’s mantle, has been proposed as a cause for surface vertical motions in excess of 100 s of meters. However, little is known about the mechanisms that help initiate and control the propagation of slab tearing and the associated uplift. This study aims to explore these processes by means of 3D thermo-mechanical geodynamic modelling of a slab retreat oblique to a continental margin, using the Gibraltar Arc region (Betic Cordillera) as a scenario for inspiration. Our results suggest that the obliquity of the continental passive margin relative to the subduction trench leads to an asymmetric distribution of subduction forces and strength, facilitating the initiation of slab tearing. The model results predict a lateral migration of the tearing point at a velocity ranging between 38 and 68 cm/yr for a sublithospheric-mantle viscosity of up to 1e+22 Pa s. This fast slab tearing propagation yields uplift rates of 0.23–2.16 mm/yr above the areas where the subducted slab is torn apart, depending on mantle viscosity. Although a more detailed parametric exploration is needed, this range of uplift rates is compatible with the uplift rates required to overcome seaway erosion along the Atlantic-Mediterranean marine corridors during the Late Miocene, as proposed for the onset of the Messinian Salinity Crisis.

Deep Slow Slip and Tremors (SSTs) are a combination of transient clusters of tectonic tremors and slow slip associated with extremely elevated fluid pressures. SSTs are thought to reflect a transition from viscous to brittle plate interface rheology and likely exert a first-order control on megathrust seismicity. Nevertheless, the deformation mechanisms governing the source of SSTs remain elusive. We herein document the occurrence of vein networks precipitated and brecciated within the deep SST region under blueschist-facies conditions. These lawsonite-rich vein sets exhibit extensive evidence of brittle deformation and are spatially related to localized, finely milled (cataclastic) shear bands. Petro-geochemical data reveal that brittle deformation was accompanied by the injection of several ultramafic-, mafic- and metasedimentary-derived fluid pulses, imprinting characteristic Cr, high field strength elements, and light over heavy rare earth elements positive anomalies in the vein breccias while leaching light rare earth elements from the cataclastic blueschist host. Our results suggest that metamorphic veins represent zones of mechanical anisotropy within the rock volume prone to localized shearing, brittle deformation and episodic injection of externally derived fluids. These networks demonstrate the importance of former vein sets as structural heterogeneities in triggering fluid-controlled brittle creep events. The combined effects of high pore fluid pressures and rheological heterogeneities in the form of metamorphic veins could trigger the nucleation and propagation of SSTs at the margins of this mechanically anisotropic environment, and thus determine where slip will take place along deep subduction interfaces.

High-pressure dehydration of serpentinite during subduction generates fluids that flux and melt the overlying mantle wedge, forming primary arc basalts. These basalts are substantially more oxidized than their mid-ocean ridge counterparts. At the slab surface of current subduction zones, these deserpentinization fluids are intrinsically oxidized, but, owing to the low sulfur content of subducted serpentinite, they only result in a low mantle wedge oxidation rate, which cannot account for the oxidized source of arc basalts. Here we show that infiltration of sediment-derived fluids modulates and can drastically change the oxidation capacity of deserpentinization slab fluids. The modulation of the deserpentinization oxidation capacity mostly depends on the stability and abundance of dissolved oxidized aqueous species of redox-sensitive elements—notably sulfate—and not solely on the oxidation state of the sediment. Infiltration of CH-bearing fluids derived from graphite-bearing sediment reduces the intrinsically high oxidant capacity of deserpentinization fluids, explaining the relatively low fO observed in natural metaperidotite. Infiltration of sulfate-CO-bearing, sediment-derived fluids—prevalent in modern subduction zones—generates deserpentinization fluids with a high oxidation capacity in cold and hot subduction zones, resulting in a global mantle wedge oxidation rate of 3.5 km yr. Such slab fluids will oxidize the mantle wedge at a rate similar to that of arc-basalt generation and thus account for the oxidized nature of arc volcanism.

Exotic blocks of massive antigorite-serpentinite (antigoritite) document a deep-seated subduction channel in the Villa Clara serpentinite-matrix mélange, central Cuba. The petrological and geochemical characteristics of antigoritite allow distinguishing two types of rock: i) antigoritite and ii) dolomite-bearing antigoritite. Both types are intimately related in field exposures and represent deep peridotite infiltrated by HO-CO fluid mixtures that triggered antigoritization and local carbonation. Fluid infiltration continued after antigoritization forming a vein network as a potential response to hydrofracturing that precipitated tremolitite in the veins and triggered fluid-antigoritite reaction forming blackwalls. The mineralogical and chemical zoning in the blackwalls (Atg + Chl + Tr adjacent to antigoritite and Chl + Tr adjacent to the tremolitite vein) attest for multi-step metasomatic processes during fluid-rock interaction characterized by advection of infiltrating fluid towards the blackwall and, possibly, by diffusion out of the blackwall towards the fluid-filled vein. Tentative thermodynamic modeling of the blackwall domain Atg + Chl + Tr points vein network formation at 400–500 °C and 5–10 kbar during exhumation in the subduction channel, suggesting the infiltration of deep-seated pressurized fluid that triggered hydrofracturing. The chemical compositions of antigoritites, veins and blackwalls indicate a LILE- and LREE-enriched fluid evolved from the subducting plate, while Sr[sbnd]Nd isotope systematics are compatible with an external fluid composed of a mixture of fluids evolved from sediments and, probably to a lesser extent, altered oceanic crust.

The drift history of the Lhasa terrane from Gondwana to Asia plays a crucial role in understanding the Tethys evolution and true polar wander (TPW). However, few reliable paleomagnetic results from Jurassic strata are currently available for reconstructing its northward journey. We performed a combined paleomagnetic and geochronological study on Bima Formation strata in the Xigaze area. Combined with previous results from the Sangri area, our results reveal a paleolatitude of 8 ± 4°S at ∼180 Ma for the reference point (29.3°N, 90.3°E). Along with other paleomagnetic results from the Triassic to Cretaceous, our new results suggest that the Lhasa terrane motion accelerated from ∼2 cm/yr during ∼220–180 Ma to ∼17 cm/yr during ∼180–170 Ma. Paleolatitude information of the North Qiangtang terrane and Tethyan Himalaya is calculated from paleopoles that meet five criteria, which include (a) structural control, (b) well-determined rock age, (c) stepwise demagnetizations, (d) a minimum of 25 specimens or 8 sites are contained, and (e) robust field or reversal tests are provided. Both terranes also show significant acceleration during their northward motion, which may be related to oceanic slab subduction. Thus, all Gondwana-derived microcontinents seem to share a significant acceleration during their northward motion. In addition, recent paleomagnetic results from volcanic rocks dated at ∼155 Ma subdivide the overall northward motion during ∼170–130 Ma into two stages, which include a southward drift during ∼170–155 Ma followed by northward motion during ∼155–130 Ma. These results support the fast Late Jurassic TPW during a ∼10 Myr time span.

Many described subduction complexes (or mélanges) exhumed from seismogenic depths comprise thick, turbidite-dominated sequences with deformed zones containing clasts or boudins of more competent sandstone and/or basalt. In contrast, many active subduction zones have a relatively small thickness of sedimentary inputs (<2 km), turbidite sequences are commonly accreted rather than subducted, and the role of pelagic sediments and basalt (lavas and hyaloclastites) in the deforming zone near the plate interface at <20 km depth is poorly understood. Field investigation of Neoproterozoic oceanic sequences accreted in the Gwna Complex, Anglesey, UK, reveals repeated lenticular slices of variably sampled ocean plate stratigraphy (OPS) bounded by thin mélange-bearing shear zones. Mélange matrix material is derived from adjacent OPS lithologies and is either dominantly illitic, likely derived from altered siliciclastic sediment, or chloritic, likely derived from altered volcanics. In the illitic mélange, mutually cross-cutting phyllosilicate foliation and variably deformed chlorite-quartz-calcite veins suggest ductile creep was cyclically punctuated by transient, localized fluid pulses. Chlorite thermometry indicates the veins formed at 260 ± 10°C. In the chloritic mélange, recrystallized through-going calcite veins are deformed to shear strains of 4–5 within a foliated chlorite matrix, suggesting calcite veins in subducting volcanics may localize deformation in the seismogenic zone. Shear stress-strain rate curves constructed using existing empirical relationships in a simplified shear zone geometry predict that slip velocities varied depending on pore fluid pressure; models predict slow slip velocities preferentially by frictional sliding in chlorite, at pore fluid pressures greater than hydrostatic but less than lithostatic.

The India-Asia collision zone is the archetype to calibrate geological responses to continent-continent collision, but hosts a paradox: There is no orogen-wide geological record of oceanic subduction after initial collision around 60-55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya-Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography.

When continents collide, the arrival of positively buoyant continental crust slows down subduction. This collision often leads to the detachment of earlier subducted oceanic lithosphere, which changes the subsequent dynamics of the orogenic system. Recent studies of continental collision infer that the remaining slab may drive convergence through slab roll-back even after detachment. Here we use two-dimensional visco-elasto-plastic thermo-mechanical models to explore the conditions for post-collisional slab steepening versus shallowing by quantifying the dynamics of continental collision for a wide range of parameters. We monitor the evolution of horizontal mantle drag beneath the overriding plate and vertical slab pull to show that these forces have similar magnitudes and interact continuously with each other. We do not observe slab rollback or steepening after slab detachment within our investigated parameter space. Instead, we observe a two-stage elastic and viscous slab rebound process lasting tens of millions of years, which is associated with slab unbending and eduction that together generate orogenic widening and trench shift towards the foreland. Our parametric studies show that the initial length of the oceanic plate and the stratified lithospheric rheology exert a key control on the orogenic evolution. When correlated with previous studies our results suggest that post-detachment slab rollback may only be possible when minor amounts of continental crust subduct. Among the wide variety of natural scenarios, our modelling applies best to the evolution of the Central European Alps. Furthermore, the mantle drag force may play a more important role in continental dynamics than previously thought. Finally, our study illustrates that dynamic analysis is a useful quantitative framework that also intuitively explains observed model kinematics.

For engineering design and seismic risk assessments, earthquake ground motions are characterized using intensity measures such as peak acceleration or spectral accelerations. Ground motion models (GMMs) estimate statistical distribution of intensity measures given information about the source, source-site path (distance), and site condition. This research pertains to data resources used to develop GMMs for subduction zone regions and adapts a global GMMs to a target region. My initial research developed portions of the NGA-Subduction (NGA-Sub) project database. I worked with other experts to characterize seismic sources and source-to-site paths. The database contains data from 1,880 earthquakes in Alaska, Cascadia, Central America and Mexico, Japan, New Zealand, South America, and Taiwan. Source parameters are related to the earthquake focus and finite fault representations. An important issue was the assignment of event types (intraslab and interface). I developed event type classification procedures that consider hypocenter locations relative to the interface, focal mechanisms, and other factors. The second phase of research involved collaborating with researchers in Mexico to enhance data resources for that region (relative to NGA-Sub) and to use the information to develop a regionally customized GMM. I selected Mexico because it has high seismic hazard, its available GMMs have deficiencies, and it has substantial data from recent events that were not considered in NGA-Sub. The database for Mexico is extended by considering small magnitude (M < 6) events and three large events (M 7.2-8.3) in 2017 and 2018. The latter are particularly important, because they are well recorded over a broad distance range and apply for hazard-critical conditions. These changes increase the size of the database from 593 recordings from 66 events (NGA-Sub) to 1882 recordings from 121 events. These data are examined relative to a global NGA-Sub model, which reveals a number of inter

Listwaenite, a distinctive rock formed by carbonation of peridotite, is important for understanding carbon fluxes and storage in the deep Earth. In northern Oman, this lithology occurs near/at the base of the Semail Ophiolite and has been proposed to have formed in the mantle wedge during Late Cretaceous obduction and ophiolite emplacement. Listwaenite occurs as tabular sheets associated with post-obductional extensional faults. Specifically, listwaenite formed in (1) extensional duplexes bound by shallowly-dipping normal faults, (2) moderately- to steeply-dipping extensional faults, and (3) layers that overlie rocks of the metamorphic sole and unmetamorphosed platform carbonates. Two dolomite veins cutting listwaenite yield near-identical LA-ICP-MS U-Pb ages of 60.3 ± 15.4 and 55.1 ± 4.7 Ma (2 standard error). Thus, listwaenite formed prior to or is coeval with the ∼60-55 Ma veins. One carbonate listwaenite sample yields a LA-ICP-MS U-Pb age of 64.31 ± 6.28 Ma. Further six listwaenite samples yield imprecise ages of ∼33-3 Ma. Thus, listwaenite is interpreted to have formed during at least two post-obductional deformational events in the Oman Mountains. Hydrothermal circulation of carbon-rich fluids along upper crustal extensional faults facilitated listwaenite formation. Our results indicate that listwaenite formed during post-obductional extension, challenging models of listwaenite genesis in the mantle wedge during obduction.

For engineering design and seismic risk assessments, earthquake ground motions are characterized using intensity measures such as peak acceleration or spectral accelerations. Ground motion models (GMMs) estimate statistical distribution of intensity measures given information about the source, source-site path (distance), and site condition. This research pertains to data resources used to develop GMMs for subduction zone regions and adapts a global GMMs to a target region. My initial research developed portions of the NGA-Subduction (NGA-Sub) project database. I worked with other experts to characterize seismic sources and source-to-site paths. The database contains data from 1,880 earthquakes in Alaska, Cascadia, Central America and Mexico, Japan, New Zealand, South America, and Taiwan. Source parameters are related to the earthquake focus and finite fault representations. An important issue was the assignment of event types (intraslab and interface). I developed event type classification procedures that consider hypocenter locations relative to the interface, focal mechanisms, and other factors. The second phase of research involved collaborating with researchers in Mexico to enhance data resources for that region (relative to NGA-Sub) and to use the information to develop a regionally customized GMM. I selected Mexico because it has high seismic hazard, its available GMMs have deficiencies, and it has substantial data from recent events that were not considered in NGA-Sub. The database for Mexico is extended by considering small magnitude (M < 6) events and three large events (M 7.2-8.3) in 2017 and 2018. The latter are particularly important, because they are well recorded over a broad distance range and apply for hazard-critical conditions. These changes increase the size of the database from 593 recordings from 66 events (NGA-Sub) to 1882 recordings from 121 events. These data are examined relative to a global NGA-Sub model, which reveals a number of inter

The NGA-Subduction Project is a multi-year, multidisciplinary project with the goal of developing a ground motion database and ground motion models for global subduction zone earthquakes including those in Japan, Taiwan, Cascadia, Alaska, New Zealand, South America, and Central America. Our ground motion model development is currently at the stage of identifying regional trends in path terms. We use a combination of data inspection and regression techniques to distinguish path effects in the data, including differences between interface and inslab events, forearc/back-arc effects, regional effects, and azimuthal effects. Our approach to model development is to first develop a path model capturing these effects, then to investigate source and site effects. The parameterization of functional form is guided in part by the scaling expected by a generic equivalent point-source stochastic model. We expect regionalization in path and will investigate further regionalization in site response and in overall model bias.

No megathrust earthquake similar to the Magnitude class 9 events in Sumatra in 2004 or in Japan in 2011 was firmly reported at the Lesser Antilles subduction zone. The largest known tsunamis followed either a strong intraplate earthquake (1867, Virgin Islands) or were transoceanic due to the 1755 Lisbon earthquake. In this region, where the convergence rate between the American and Caribbean plate is low, the recurrence time of large earthquakes may be long (several centuries or millennia) and the historical record of such events is short. It is thus difficult to estimate their impact and becomes crucial to gain information from longer-term geological records and tsunami modeling. An increasing number of old prehistoric tsunami deposits have been identified in recent years on several islands in the northern segment of the Lesser Antilles arc, between Antigua and Puerto-Rico, in Anegada, St-Thomas (Virgin Islands), Anguilla and Scrub islands. Here, we carefully review all those studies and evidenced that most tsunami deposits are about 500 to 800 years old (1200 to 1500 cal yrs. CE) likely suggesting a large event or a cluster of events at that time. We combined information provided by the sedimentological records (distribution and altitude of the sediment deposits) and tsunami models to discuss the origin of the middle age Pre-Colombian event(s). We listed all faults as possible sources of tsunamis in this complex tectonic region. We performed 35 run-up models by using high-resolution/topographic grids to compare the simulated wave heights and run-up distance to the sediment record. We showed that few models are able to generate tsunami waves which heights and run-up distances match the characteristic of the observed tsunami deposits. These models are Magnitude class 9 M-thrust earthquakes rupturing the subduction interface between 30 km in depth to the trench facing Anegada Island. Magnitude class 8 outer-rise earthquakes, modeled along the trench, are other candid

The transition along the strike of the Sunda subduction zone, from oceanic subduction in the west to subduction of continental Australian lithosphere in the east is envisioned as one of the canonical examples of the structural changes that take place within an overriding plate when a continental lithosphere wedge enters a subduction zone. Yet, the along-strike offset of the trench toward the Australian margin represents a structural response opposite to the predictions of numerical models. To understand this paradox, we analyse the morphotectonic evolution of Sumba island located at the transition from oceanic to continental Indo-Australian lithosphere subduction. Drainage evolution allows us to constrain the topographic evolution of the island since the Pliocene. Flights of uplifted coral reef terraces document Quaternary deformation. Focal mechanisms of shallow crustal earthquakes constrain the current stress field. Together, these data reveal that the island is affected by dextral en-échelon folding. Offshore, west of the island, reverse and strike-slip focal mechanisms evidence an active dextral transpressional zone. The emergence of the island and dextral shearing of the accretionary prism were triggered by subduction of the western lateral boundary of the Australian continental margin. We contend that the Plio-Quaternary tectonic evolution of the region, with transpression and migration of the trench toward the Australian margin is primarily dictated by shear stress transfer from the lower plate to the overriding plate, favored by strong interplate coupling, and by southwestward escape of the Savu-Sumba block following the impingement of the Australian continental margin against Timor island.

The transition along the strike of the Sunda subduction zone, from oceanic subduction in the west to subduction of continental Australian lithosphere in the east is envisioned as one of the canonical examples of the structural changes that take place within an overriding plate when a continental lithosphere wedge enters a subduction zone. Yet, the along-strike offset of the trench toward the Australian margin represents a structural response opposite to the predictions of numerical models. To understand this paradox, we analyse the morphotectonic evolution of Sumba island located at the transition from oceanic to continental Indo-Australian lithosphere subduction. Drainage evolution allows us to constrain the topographic evolution of the island since the Pliocene. Flights of uplifted coral reef terraces document Quaternary deformation. Focal mechanisms of shallow crustal earthquakes constrain the current stress field. Together, these data reveal that the island is affected by dextral en-échelon folding. Offshore, west of the island, reverse and strike-slip focal mechanisms evidence an active dextral transpressional zone. The emergence of the island and dextral shearing of the accretionary prism were triggered by subduction of the western lateral boundary of the Australian continental margin. We contend that the Plio-Quaternary tectonic evolution of the region, with transpression and migration of the trench toward the Australian margin is primarily dictated by shear stress transfer from the lower plate to the overriding plate, favored by strong interplate coupling, and by southwestward escape of the Savu-Sumba block following the impingement of the Australian continental margin against Timor island.

No megathrust earthquake similar to the Magnitude class 9 events in Sumatra in 2004 or in Japan in 2011 was firmly reported at the Lesser Antilles subduction zone. The largest known tsunamis followed either a strong intraplate earthquake (1867, Virgin Islands) or were transoceanic due to the 1755 Lisbon earthquake. In this region, where the convergence rate between the American and Caribbean plate is low, the recurrence time of large earthquakes may be long (several centuries or millennia) and the historical record of such events is short. It is thus difficult to estimate their impact and becomes crucial to gain information from longer-term geological records and tsunami modeling. An increasing number of old prehistoric tsunami deposits have been identified in recent years on several islands in the northern segment of the Lesser Antilles arc, between Antigua and Puerto-Rico, in Anegada, St-Thomas (Virgin Islands), Anguilla and Scrub islands. Here, we carefully review all those studies and evidenced that most tsunami deposits are about 500 to 800 years old (1200 to 1500 cal yrs. CE) likely suggesting a large event or a cluster of events at that time. We combined information provided by the sedimentological records (distribution and altitude of the sediment deposits) and tsunami models to discuss the origin of the middle age Pre-Colombian event(s). We listed all faults as possible sources of tsunamis in this complex tectonic region. We performed 35 run-up models by using high-resolution/topographic grids to compare the simulated wave heights and run-up distance to the sediment record. We showed that few models are able to generate tsunami waves which heights and run-up distances match the characteristic of the observed tsunami deposits. These models are Magnitude class 9 M-thrust earthquakes rupturing the subduction interface between 30 km in depth to the trench facing Anegada Island. Magnitude class 8 outer-rise earthquakes, modeled along the trench, are other candid

Since the Jurassic, there has been a clear spatiotemporal correlation between different types of metamorphism and active convergent plate margins. However, the extent to which this relationship extends into the past is poorly understood. We compared paleogeographic reconstructions and inferred plate kinematics with the age and thermobaric ratio (temperature/ pressure [T/P]) of metamorphism over the past 2 b.y. The null hypothesis—that there is no spatiotemporal link between inferred plate margins and metamorphism—can be rejected. Low-T/P metamorphism is almost exclusively located near plate margins, whereas intermediate and high-T/P metamorphism skews toward increasingly greater distances from these margins, consistent with three different tectonic settings: the subduction zone, the mountain belt, and the orogenic hinterland, respectively. However, paleogeographic reconstructions suggest that so-called “paired metamorphic belts” are rare and that high and low-T/P localities more commonly occur along strike from each other. The observation that bimodal metamorphism is largely a function of distance from the trench and that end-member T/P types rarely occur in the same place can be explained if the style of orogenesis has evolved from hotter to colder, consistent with the abrupt emergence of low-T/P metamorphism in the Cryogenian. The widespread development of high-T/P rocks in orogenic hinterlands in the Proterozoic was followed by the production and efficient exhumation of low-T/P rocks in subduction channels in the Phanerozoic.

Water is an essential ingredient in transforming primitive mantle-derived (mafic) rocks into buoyant (felsic) continental crust, thereby driving the irreversible differentiation of Earth's lithosphere. The occurrence in Archaean cratons of sodic granites of the tonalite–trondhjemite–granodiorite (TTG) series, high-MgO variolitic basalts, high-Mg diorites (sanukitoids) and diamonds with harzburgitic inclusion assemblages, all require the presence of hydrous fluids in Earth's deep crust and upper (lithospheric) mantle since at least the Paleoarchaean (3.6–3.2 billion years ago). However, despite its importance, where and how water was stored in Archaean crust, and how some water was transported into the upper mantle, are poorly understood. Here, we investigate Archaean crustal fluid budgets through calculated phase equilibria for three protolith compositions — a low-MgO mafic (basaltic) composition, a high-MgO (picritic) composition and an ultrahigh-MgO ultramafic (komatiitic) composition — that are representative of mafic to ultramafic magmatic rocks in Archaean greenstone belts. We show that the mode and stability of hydrous minerals, in particular chlorite, is positively correlated with protolith MgO content, such that high-MgO basalts can store up to twice the amount of crystal-bound H2O than low-MgO basalts. Importantly, ultrahigh-MgO rocks such as komatiite can store four times as much H2O, most of which is retained until temperatures exceeding 700 °C. Warmer geotherms in the early Archaean favoured dehydration of hydrated high-MgO and ultramafic rocks in the deep crust, leading to hydration and/or fluid-fluxed melting of overlying basaltic rocks to produce ‘high-pressure’ TTG magmas. Burial of Archaean mafic–ultramafic crust along cooler geotherms resulted in dehydration of ultramafic material within the lithospheric mantle, providing the source of enriched Archaean basalt that was parental to large volumes of ancient TTG-dominated continental crust.

This work presents applications of the Backward Seismic Analysis (BSA) method for steel storage tanks using a data base of more than 382 steel storage tanks in operation during large subductive earthquakes: Valdivia 1960, Central Chile 1985, Tocopilla 2007, El Maule 2010, Alaska 1964, and others in the United States between 1933 and 1995 (subductive and cortical). It has been recorded that most of the steel storage tanks without anchor systems have failed during large earthquakes. These have been designed with the standards API 650-E, AWWA-D100, and NZSEE, which propose similar procedures for estimating seismic forces, but with different design methods. During different conferences, the causes of the failures were evaluated, concluding that the tanks were designed mainly with the API 650-E code and were unanchored. Moreover, the design codes employed do not consider relevant aspects that condition the seismic response of steel storage tanks. This work develops a prediction model based on the historical information already described, which is capable of efficiently predicting if a steel storage tank will suffer any failures during an earthquake. Various algorithms were evaluated, finding that the Random Forest method exhibits the best results. The results obtained in the prediction of steel storage tank failures reach more than 90% efficiency in most of the evaluated scenarios., Este trabajo presenta aplicaciones del método Backward Seismic Analysis (BSA) para estanques de acero de acuerdo con una base de datos que recopila más de 382 estanques de acero en operación durante terremotos de subducción: el ocurrido en Valdivia en 1960, en Chile Central en 1985, en Tocopilla en 2007, el último de gran magnitud registrado en el Maule en 2010, en Alaska en 1964 y otros de Estados Unidos entre 1933 y 1995 (subductivos y corticales). Se ha registrado que gran parte de los estanques sin sistemas de anclajes han fallado durante grandes terremotos. Estos han sido diseñados principalmente con los códigos API 650-E, AWWA-D100 y NZSEE, los cuales proponen procedimientos equivalentes para estimar las demandas sísmicas, pero con métodos de diseño distintos. Durante diferentes conferencias se evaluaron las causas que originaron las fallas, concluyendo que los estanques estaban diseñados principalmente con el estándar API 650-E y no disponían de sistemas de anclajes. Además, los códigos de diseño más utilizados no consideran en la actualidad los aspectos relevantes que condicionan la respuesta sísmica de los estanques de acero. Este trabajo desarrolla un modelo de predicción basado en la información histórica ya descrita, capaz de predecir de manera eficiente si un estanque presentará fallas durante algún terremoto. Se evaluaron diversos algoritmos, encontrando que el método Random Forest exhibe los mejores resultados. Los resultados obtenidos en la predicción de fallas de estanques alcanzan más del 90 % de eficiencia en la mayoría de los escenarios evaluados.

This work presents applications of the Backward Seismic Analysis (BSA) method for steel storage tanks using a data base of more than 382 steel storage tanks in operation during large subductive earthquakes: Valdivia 1960, Central Chile 1985, Tocopilla 2007, El Maule 2010, Alaska 1964, and others in the United States between 1933 and 1995 (subductive and cortical). It has been recorded that most of the steel storage tanks without anchor systems have failed during large earthquakes. These have been designed with the standards API 650-E, AWWA-D100, and NZSEE, which propose similar procedures for estimating seismic forces, but with different design methods. During different conferences, the causes of the failures were evaluated, concluding that the tanks were designed mainly with the API 650-E code and were unanchored. Moreover, the design codes employed do not consider relevant aspects that condition the seismic response of steel storage tanks. This work develops a prediction model based on the historical information already described, which is capable of efficiently predicting if a steel storage tank will suffer any failures during an earthquake. Various algorithms were evaluated, finding that the Random Forest method exhibits the best results. The results obtained in the prediction of steel storage tank failures reach more than 90% efficiency in most of the evaluated scenarios., Este trabajo presenta aplicaciones del método Backward Seismic Analysis (BSA) para estanques de acero de acuerdo con una base de datos que recopila más de 382 estanques de acero en operación durante terremotos de subducción: el ocurrido en Valdivia en 1960, en Chile Central en 1985, en Tocopilla en 2007, el último de gran magnitud registrado en el Maule en 2010, en Alaska en 1964 y otros de Estados Unidos entre 1933 y 1995 (subductivos y corticales). Se ha registrado que gran parte de los estanques sin sistemas de anclajes han fallado durante grandes terremotos. Estos han sido diseñados principalmente con los códigos API 650-E, AWWA-D100 y NZSEE, los cuales proponen procedimientos equivalentes para estimar las demandas sísmicas, pero con métodos de diseño distintos. Durante diferentes conferencias se evaluaron las causas que originaron las fallas, concluyendo que los estanques estaban diseñados principalmente con el estándar API 650-E y no disponían de sistemas de anclajes. Además, los códigos de diseño más utilizados no consideran en la actualidad los aspectos relevantes que condicionan la respuesta sísmica de los estanques de acero. Este trabajo desarrolla un modelo de predicción basado en la información histórica ya descrita, capaz de predecir de manera eficiente si un estanque presentará fallas durante algún terremoto. Se evaluaron diversos algoritmos, encontrando que el método Random Forest exhibe los mejores resultados. Los resultados obtenidos en la predicción de fallas de estanques alcanzan más del 90 % de eficiencia en la mayoría de los escenarios evaluados.

Exotic blocks of massive antigorite-serpentinite (antigoritite) document a deep-seated subduction channel in the Villa Clara serpentinite-matrix mélange, central Cuba. The petrological and geochemical characteristics of antigoritite allow distinguishing two types of rock: i) antigoritite and ii) dolomite-bearing antigoritite. Both types are intimately related in field exposures and represent deep peridotite infiltrated by H2O-CO2 fluid mixtures that triggered antigoritization and local carbonation. Fluid infiltration continued after antigoritization forming a vein network as a potential response to hydrofracturing that precipitated tremolitite in the veins and triggered fluid-antigoritite reaction forming blackwalls. The mineralogical and chemical zoning in the blackwalls (Atg + Chl + Tr adjacent to antigoritite and Chl + Tr adjacent to the tremolitite vein) attest for multi-step metasomatic processes during fluid-rock interaction characterized by advection of infiltrating fluid towards the blackwall and, possibly, by diffusion out of the blackwall towards the fluid-filled vein. Tentative thermodynamic modeling of the blackwall domain Atg + Chl + Tr points vein network formation at 400–500 °C and 5–10 kbar during exhumation in the subduction channel, suggesting the infiltration of deep-seated pressurized fluid that triggered hydrofracturing. The chemical compositions of antigoritites, veins and blackwalls indicate a LILE- and LREE-enriched fluid evolved from the subducting plate, while Srsingle bondNd isotope systematics are compatible with an external fluid composed of a mixture of fluids evolved from sediments and, probably to a lesser extent, altered oceanic crust.

A recent model of continental arc magmatism states that subducted sediments mix physically with the oceanic slab basalts in the subduction channel and produce diapirs that ascend through the mantle wedge, undergo melting and relaminate to the base of the continental crust. From here, melt or magma batches ascend through the crust, producing the Cordilleran batholiths and associated volcanism ranging in composition from 0 to 25 wt% maficity (FeOt + MgO) and 44–79 wt% SiO2, with a gap around 11.5 wt% maficity and 57–60 wt% SiO2. This model has been predicted by thermomechanical numerical studies and later supported by phase equilibrium experiments; however, thermodynamic modelling to verify whether the composition of the Cordilleran batholiths is reproduced by this model has not yet been carried out to complement the experimental approach. In this article, the evolution of the mélange along the subduction path and during the ascent of the diapirs is investigated, with focus on the conditions of generation of the diapirs, the composition and proportion of melt at the P-T conditions of relamination of the diapirs, the relationship between the basalt:sediment proportion (the composition) of the diapir to this melt composition and proportion and whether the composition of the melts match the Cordilleran batholiths. The key point to test is the process or processes that produce the compositional variability observed in these granitoids. Our findings indicate that (1) parental melts and/or magmas range in maficity from ∼1 to ∼11.5 wt%, with the compositional gap of the Cordilleran trend representing the most mafic composition possible of the parent, (2) the diapirs are restricted to having 50–60% of sediment component: diapirs with lower sediment contents may be too dense to detach from the slab and mélanges with higher sediment contents may be too less dense to be subducted to the depth of formation of diapirs, (3) melts at 1100 °C and 1.5 GPa from these diapirs have the b

[EN] Spherules are documented in ophiolitic mantle rocks such as peridotites and associated chromitites. They consist of: (1) native iron having variable amounts of Ni with/without inclusions of silicate glass or oxides (wüstite), (2) dendritic intergrowth of oxides (magnetite, wüstite and hematite) with/without silicate glass and, (3) silicate glass. Consensually, they are interpreted as indigenous to chromitites and related with high-temperature processes operating in the Earth’s upper mantle. However, their similarity with terrestrial and extraterrestrial spherules found in other settings of the geological record is remarkable. We raise the question on such indigenous origin, relating them to volcanic and cosmic material recycled back to the mantle wedge where chromitites form during subduction., [ES] Rocas del manto superior ofiolitico tales como peridotitas y cromititas contienen esferas. Estas consisten de: (1) hierro native con cantidades variables de Ni con y sin inclusiones de vidrio silicatdo y óxidos (wüstite), (2) intercrecimientos dendríticos de óxidos (magnetita, wüstita y hematites) con o sin vidrio silicatado y, (2) vidrio silicatado. Unísonamente, estas esferulas se interpretan como indígenas a las cromititas y relacionadas con procesos de alta temperatura que tienen lugar en el manto superior terrestre. Sin embargo, su parecido con aquellas esferas de origen terrestre y extraterrestre descritas en otros contextos geológicos es reseñable. En este trabajo cuestionamos el origen autóctono de las esferas en las rocas mantélicas, interpretándolas como material de origen volcánico y cósmico que ha sido reciclado atraves de la cuña de manto superior donde ser forman las cromititas durante los procesos de subducción.

Analyses of olivine-, pyroxene- and plagioclase-hosted melt (now preserved as glass) inclusions (MI) in submarine glasses and subaerial scoria from seven volcanoes along the volcanic front of the Tonga arc provide the first comprehensive dataset including volatile contents (H2O, CO2, S, Cl and F) for this arc. Maximum water contents at each volcano are typical (3-5 wt %) of other arc volcanoes worldwide, and within each volcano, water generally correlates with sulfur, consistent with degassing but not diffusive re-equilibration. The Tonga arc is notable for the eruption of magmas sourced from strongly depleted upper mantle, including boninites in the northern half of the active arc. A key question has been whether such boninites are derived from high degrees of melting actively occurring under the arc, driven by high mantle temperatures and water contents, or from high integrated degrees of melting including melting of depleted mantle in the backarc. This study supports the latter view, based on sub-arc mantle melt fractions of 17-23%, calculated from primary melt water contents and mantle-melt thermobarometry. Such fractions are not high enough to generate boninites from a typical, fertile mantle source in a single melting stage, and melt fractions do not increase north of 22°S, where the boninitic magmas appear. Instead, the northern Tonga arc boninites reflect high cumulative degrees of melting (>30%, with respect to fertile mantle) and occur along the volcanic front where adjacent backarc spreading is fast, proximal and mature. Slab tracers such as the Ba/La ratio peak at around 20-21°S, in the central part of the Tonga arc. A Ba/La peak also appears at about the same latitude in the Lau backarc basin. This peak is consistent with the coolest slab temperatures beneath the arc and backarc at this latitude, as the slab warms to the north due to an increase in mantle potential temperature, and to the south due to less heat extraction from melting. A new concept dev

The Panthalassa Ocean, which surrounded the late Paleozoic-early Mesozoic Pangea supercontinent, was underlain by multiple tectonic plates that have since been lost to subduction. In this study, we develop an approach to reconstruct plate motions of this subducted lithosphere utilizing paleomagnetic data from accreted Ocean Plate Stratigraphy (OPS). We first establish the boundaries of the Panthalassa domain by using available Indo-Atlantic plate reconstructions and restorations of complex plate boundary deformation at circum-Panthalassa trenches. We reconstruct the Pacific Plate and its conjugates, the Farallon, Phoenix, and Izanagi plates, back to 190 Ma using marine magnetic anomaly records of the modern Pacific. Then, we present new and review published paleomagnetic data from OPS exposed in the accretionary complexes of Cedros Island (Mexico), the Santa Elena Peninsula (Costa Rica), the North Island of New Zealand, and Japan. These data provide paleolatitudinal plate motion components of the Farallon, Phoenix and Izanagi plates, and constrain the trajectories of these plates from their spreading ridges towards the trenches in which they subducted. For 83 to 150 Ma, we use two independent mantle frames to connect the Panthalassa plate system to the Indo-Atlantic plate system and test the feasibility of this approach with the paleomagnetic data. For times prior to 150 Ma, and as far back as Permian time, we reconstruct relative and absolute Panthalassa plate motions such that divergence is maintained between the Izanagi, Farallon and Phoenix plates, convergence is maintained with Pangean continental margins in Japan, Mexico and New Zealand, and paleomagnetic constraints are met. The reconstruction approach developed here enables data-based reconstruction of oceanic plates and plate boundaries in the absence of marine magnetic anomaly data or mantle reference frames, using Ocean Plate Stratigraphy, paleo-magnetism, and constraints on the nature of circum-oceanic p

The northern Oman margin is a key area for understanding the emplacement of the Semail Ophiolite and obduction processes in general. This study uses a grid of 2D-multichannel seismic lines tied to well data to characterize the offshore domain of the Semail Ophiolite and reappraises the obduction and post-obduction history of the Oman margin. West of Muscat, in the Sohar basin, the late Cretaceous to Paleogene tectonic mega-sequence records syn- to late-obduction stages and the deposition of erosional products of the autochthonous Arabian sediments, including a major mass transport complex. Syn-obduction thrusting is documented in this sector only, as a major fault emplacing a distal basement high (likely volcanic) onto Campanian sediments over >10 km. To the east, the Hatat and Tiwi basins are characterized by a less-copious Maastrichtian-Paleogene sequence. These basins developed above a domain characterized by the northern equivalent of the Saih Hatat dome and later extensional faults. This sector distinctively records the extensional phase associated with the exhumation and erosion of the subducted continental margin. The dichotomy between the two sectors is linked due to a structural high located offshore, in the continuation of the Semail Gap transfer fault. We propose that this transfer fault, coincident with a major Pan-African structure, affected the architecture of the passive margin during both rifting of the Neotethys and later ophiolite emplacement, that is, during (continental) subduction and obduction.

The NGA-Subduction Project is a multi-year, multidisciplinary project with the goal of developing a ground motion database and ground motion models for global subduction zone earthquakes including those in Japan, Taiwan, Cascadia, Alaska, New Zealand, South America, and Central America. Our ground motion model development is currently at the stage of identifying regional trends in path terms. We use a combination of data inspection and regression techniques to distinguish path effects in the data, including differences between interface and inslab events, forearc/back-arc effects, regional effects, and azimuthal effects. Our approach to model development is to first develop a path model capturing these effects, then to investigate source and site effects. The parameterization of functional form is guided in part by the scaling expected by a generic equivalent point-source stochastic model. We expect regionalization in path and will investigate further regionalization in site response and in overall model bias.

Subduction zones are key loci of geochemical cycling and natural hazards on Earth including large earthquakes and explosive volcanic eruptions. Fluids produced during subduction are thought to play a role in all these processes, however, many aspects of fluid transport in subduction zones remain enigmatic. In this dissertation, three types of fluid-related features are examined: 1) an eclogite-facies vein and 2) an eclogite- facies shear zone block and metasomatic rind, both from the Monviso Ophiolite (Western Alps), and 3) two amphibolite-facies mélange blocks and rinds from the Catalina Schist (CA). The mechanisms, episodicity and duration of fluid transport associated with these fluid pathways are investigated with bulk and in situ Li isotope geochemistry, in situ Sr isotope and trace element geochemistry, and quantitative transport modeling. In the eclogite-facies vein, evidence for five distinct locally-derived fluid compositions suggests a complex process of fluid-rock interaction. The unusual geometry of alteration features in the host rock suggests that initial host rock heterogeneity led to the development of reactive porosity channels. A method for in situ measurement of Li isotopes in garnet by secondary ion mass spectrometry is developed to explore the relative chronology of fluid rock interaction preserved in mineral zoning. The equivalence of natural garnet and garnet-like glass reference materials is demonstrated and a correction procedure for instrumental mass fractionation due to MnO and FeO is proposed. The resulting method is highly adaptable and attains 2-4‰ precision at the 20-μm-scale. Application of this method to garnet from the eclogite-facies shear zone block and rind reveals negative ?7Li excursions to values as low as -9‰ that record fluid-driven Li diffusion and rapid garnet growth. Multiple negative excursions within a single garnet require at least four episodes of fluid infiltration in the shear zone. Lastly, the first fluid transpor