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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 40Ar/39Ar 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. [ABSTRACT FROM AUTHOR]

The physical and mechanical processes rooted in the hydrated, serpentinized mantle above subduction zones remain insufficiently explored despite fundamental implications for our understanding of rheology and fluid recycling along subduction interfaces. Through a field‐based investigation, serpentinized peridotites and jadeitite samples from a fossil forearc mantle in the Polar Urals (Russia) are studied here to document fluid–rock interaction processes in the high‐P field, as well as the long‐term evolution of the base of the mantle wedge. Petrographic, geochemical and microstructural observations reveal a complex, protracted evolution of the jadeitite‐forming fluid pathway throughout the gradual cooling of the forearc mantle and increasing serpentinization of the host. It is shown that the jadeitite lenses in the studied locality (a) derive for a large part from a trondhjemitic dyke earlier emplaced in a warm subduction environment, and (b) record the cooling of the subduction hangingwall under high‐P conditions associated with increasing host serpentinization. In the studied locality, the majority of the jadeitites formed at relatively high temperatures (>600°C) by the influx of Na–Al‐rich, slab‐derived metamorphic fluids that were drained along the base of the mantle wedge, parallel to the subduction interface. Changes in bulk‐rock geochemical signatures and in paragenetic sequences also constrain the compositional evolution of the fluid channelized along this drainage, with an increasing sedimentary component. The phlogopite‐bearing walls of the dyke exhibit Rb–Sr and Ar–Ar ages ranging between c. 405 and c. 390 Ma, a range partly overlapping within uncertainty with the previously dated zircons from the jadeitite core (410–⁠400 Ma; U–Pb). This study opens a unique window on the pristine structures formed above the plate interface by melting and fluid–rock interaction in the early subduction stages, as well as their evolution during secular cooling of the base of the mantle wedge. [ABSTRACT FROM AUTHOR]

The La Tinta mélange is a small but singular ultramafic mélange sheet that crops out in eastern Cuba. It is composed of dolerite-derived amphibolite blocks embedded in a serpentinite matrix. The amphibolite blocks have mid-ocean ridge basalt (MORB)-like composition showing little if any imprint of subduction zone component, similar to most forearc and MOR basalts worldwide. Relict Cr-spinel and olivine mineral chemistry of the serpentinized ultramafic matrix suggest a forearc position for these rocks. These characteristics, together with a hornblende40Ar/39Ar age of 123.2 ± 2.2 Ma from one of the amphibolite blocks, suggest that the protoliths of the amphibolite blocks correspond to forearc basalt (FAB)-related rocks that formed during the earlier stage of subduction initiation of the Early Cretaceous Caribbean arc. We propose that the La Tinta amphibolites correspond to fragments of sills and dikes of hypoabyssal rocks formed in the earlier stages of a subduction initiation scenario in the Pacific realm (ca. 136 Ma). The forearc dolerite-derived amphibolites formed by partial melting of upwelling fertile asthenosphere at the beginning of subduction of the Proto-Caribbean (Atlantic) slab, with no interaction with slab-derived fluids/melts. This magmatic episode probably correlates with Early Cretaceous basic rocks described in Hispaniola (Gaspar Hernandez serpentinized peridotite-tectonite). The dikes and sills cooled and metamorphosed due to hydration at low pressure (ca. 3.8 kbar) and medium to high temperature (up to 720ºC) and reached ca. 500ºC at ca. 123 Ma. At this cooling stage, serpentinite formed after hydration of the ultramafic upper mantle. This process might have been favoured by faulting during extension of the forearc, indicating an early stage of dike and sill fragmentation and serpentinite mélanges formation; however, full development of the mélange likely took place during tectonic emplacement (obduction) onto the thrust belt of eastern Cuba during the latest Cretaceous. [ABSTRACT FROM AUTHOR]

Estimates of global growth rates of continental crust critically depend upon knowledge of the rate at which crustal material is delivered back into the mantle at subduction zones and is then returned to the crust as a component of mantle-derived magma. Quantification of crustal recycling by subduction-related magmatism relies on indirect chemical and isotopic tracers and is hindered by the large range of potential melt sources (e.g., subducted oceanic crust and overlying chemical and clastic sediment, sub-arc lithospheric mantle, arc crust), whose composition may not be accurately known. There is also uncertainty about how crustal material is transferred from subducted lithosphere and mixed into the mantle source of arc magmas. We use the resilient mineral zircon to track crustal recycling in mantle-derived rocks of the Caribbean (Greater Antilles) intra-oceanic arc of Cuba, whose inception was triggered after the break-up of Pangea. Despite juvenile Sr and Nd isotope compositions, the supra-subduction zone ophiolitic and volcanic arc rocks of this Cretaceous (∼135–70 Ma) arc contain old zircons (∼200–2525 Ma) attesting to diverse crustal inputs. The Hf–O isotope systematics of these zircons suggest derivation from exposed crustal terranes in northern Central America (e.g. Mexico) and South America. Modeling of the sedimentary component in the most mafic lavas suggests a contribution of no more than 2% for the case of source contamination or less than 4% for sediment assimilation by the magma. We discuss several possibilities for the presence of inherited zircons and conclude that they were transported as detrital grains into the mantle beneath the Caribbean Plate via subduction of oceanic crust. The detrital zircons were subsequently entrained by mafic melts that were rapidly emplaced into the Caribbean volcanic arc crust and supra-subduction mantle. These findings suggest transport of continental detritus, through the mantle wedge above subduction zones, in magmas that otherwise do not show strong evidence for crustal input and imply that crustal recycling rates in some arcs may be higher than hitherto realized. [ABSTRACT FROM AUTHOR]

• Blueschist-facies fault rocks are reported for the first time in the Zagros suture. • The studied Seghin complex resembles a Mariana-type margin serpentinite channel. • The studied fault rocks were produced by seismic faulting at 20 to 35 km depth. • Structural evidence show that fluids are intimately associated with the seismic cycle. • Seismic instabilities can form or propagate in a fully-serpentinized environment. The architecture and pressure-temperature conditions reached by a Cretaceous block-in-matrix serpentinite mélange exposed in the Zagros suture resemble those imaged in the active Mariana subduction zone. There, large magnitude-earthquakes (M > w 9) have never been recorded but smaller events – of poorly-constrained physical origin – in the range M ∼ w 3-6 are widespread. Field and petro-structural constraints led to a first report of blueschist-facies seismic fault-related rocks in the Zagros serpentinite melange, including breccias, foliated cataclasites and ultracataclasites; all observed within a foliated mafic metatuffaceous block embedded in serpentinite schists. Fine-scale petrological characterization of ultrafine-grained, fluidized cataclastic material reveals the presence of newly-formed glaucophane, lawsonite, phengite, albite and pumpellyite, an assemblage inferred (based on thermodynamic modelling) to have crystallized in the lower lawsonite-blueschist facies at ∼0.6-1.0 GPa and 230-300 °C. Extensional veins containing similar mineral assemblages are observed crosscutting the aforementioned rocks but are also identified as comminuted fragments in all fault-related lithologies. Crosscutting relationships among the multiple generations of fluidized ultracataclasites and brecciated blueschists suggest that episodic faulting and hydrofracturing were contemporaneous processes at ∼20-35 km depth, i.e., at similar conditions as reported for metabasalts expelled by Mariana serpentinite mud volcanoes. Mechanical modelling confirms that the studied fault-related features can only have formed under nearly lithostatic pore fluid pressure conditions, maintaining the system in a critically unstable regime that promoted recurrent seismic faulting, as monitored in the Mariana seismogenic zone. These fluids are likely associated with externally and deeply-generated fluid pulses that may have reached the seismogenic window, imprinting a Ta-Th-Nb-HREEs-enriched trace element signature. This new faulted blueschist occurrence highlights the physical nature and the mechanical processes operating within fluid-saturated fault zones in the serpentinized subduction channel. [ABSTRACT FROM AUTHOR]

We investigate the late Cretaceous blueschist-facies (480 °C-1.8 GPa) segment of the Zagros suture zone, a well-preserved block-in-matrix paleo-subduction channel. We aim to determine the relative chronology, conditions of deformation, and potential fluid sources and processes associated with the widespread occurrence of lawsonite + clinopyroxene + glaucophane veins and aragonite-bearing hydraulic breccias. We use a multi-scale approach methodology to provide new insights into deep fluid flow mechanisms as well as to constrain possible sinks of CO 2 -bearing fluids in the subducting slab. Petrological analyses suggest that silicate-rich vein systems began precipitating during early burial and evolved with ongoing burial and shearing-related deformation in the blueschist-facies, while most carbonate-rich veins and hydrofractures formed at near-peak P-T conditions. In situ LA-ICP-MS trace element analyses reveal that: (i) individual silicate host-vein pairs have similar REE signatures, reflecting local-scale fluid-mediated element redistribution, (ii) carbonate-bearing veins and metasediments also have similar trace element signatures and (iii) lawsonite in blueschist-hosted veins exhibit REE enrichments along their rims, suggesting an increasing contribution of metasedimentary-derived fluids upon approaching peak P-T. Carbonate O C isotope compositions of the veins and metasedimentary rocks range from +13.6 to +17.9‰ (δ18O VSMOW) and − 1.0 to +3.1‰ (δ13C VPDB), demonstrating metasedimentary-derived fluid sources related to large-scale H 2 O homogenization with far-traveled mafic- ultramafic-derived fluids. Sr Nd isotopic ratios in carbonate veins and the adjacent host resemble their host composition indicating that host rock-buffered isotopic homogenization occurred between the infiltrating fluids and the rock matrix, possibly during episodic porous flow. Thermodynamic modeling predicts that decarbonation via fluid-assisted reactions is inefficient at blueschist-facies and that carbon release likely occurs deeper along the subduction interface (i.e., at eclogite-facies). We propose that deeply produced H 2 O-rich fluids interacted with the carbonate-bearing lithologies along the subduction interface facilitating fluid-mediated decarbonation and further fluid transport as hydraulic pulses (e.g., porosity waves) that traveled at the kilometer-scale parallel to the subduction interface, (i) contributing to the isotopic homogenization herein observed and (ii) triggering episodic hydrofracturing in the lawsonite-blueschist-facies (≈50-60 km depth). Veinsets in exhumed subducted rocks hence provide a unique opportunity to understand fluid-rock interaction processes in the region at which episodic tremor and slow slip events phenomena occur. [ABSTRACT FROM AUTHOR]

An increasing number of seismological studies report transient seismicity clusters in the mantle wedge several kilometers above the subduction interface. Their physical significance with respect to subduction zone seismo-tectonics remains poorly understood. Jadeitites are known to form and/or be associated with mantle wedge serpentinites in the c. 30–70 km depth range, and thus may yield information on deformation mechanisms in this region of deep subduction environments. We herein document and compare brittle-viscous features recorded in jadeitites from Polar Urals (Russia), Kashin state (Myanmar) and Motagua fault region (Guatemala) – some of the most important jadeitite occurrences worldwide. In the Polar Urals we identified ultramafic-hosted pristine jadeitite-bearing veins c. 1 km above a Devonian paleo-subduction interface, interpreted as metasomatized former felsic dyke networks crosscutting the mantle wedge peridotites. Here, both jadeitites and associated amphibole-rich dark granofels display widespread brittle-ductile deformation fabrics such as shear bands, foliated cataclasites and breccias, cemented through dissolution-precipitation processes by omphacite and sodic amphiboles, a mineral assemblage typical of high-pressure–low-temperature subduction zone conditions. Electron probe and laser ablation ICP-MS mapping indicate that these brittle-viscous networks display a substantial metasomatic imprint highlighted in the dark granofels by variations in major and trace elements. Switches between viscous and brittle deformation patterns are attested by crystallographic-preferred orientations of jadeite in some of the shear zones that crosscut the host jadeitites. Strikingly similar mineral assemblages and deformation patterns were observed in the Kashin and Motagua samples. Observed deformation features in these localities can be classified into three categories (tectonic breccias, foliated cataclasites and hydraulic breccias), which may occasionally form in sequence and exhibit mutually overprinting textures. Some of the foliated cataclasites contain fine-grained and foliated "shard-like" features forming a radial omphacite-jadeite spherulitic texture, interpreted as former pseudotachylyte that evokes a paleo-seismic origin. We interpret these healed fault networks as recording external fluid influx within fracture zones that repeatedly ruptured along former "dyke" networks. These high permeability drains likely (i) contribute to the transfer of highly pressurized plate-interface metamorphic fluids into the mantle wedge; and (ii) trigger seismic instabilities recorded in the basal part of active mantle wedge sections. These findings provide new insights into the current understanding of the rheology (e.g., serpentinization ratio) and stress state in the mantle wedge, with implications for subduction interface seismogenesis. [Display omitted] • Common evidence for brittle features in exhumed jadeitites • Breccias and foliated cataclasites formed at high pressure in the mantle wedge • Evidence for tightly coupled brittle events and multiple fluid infiltration events • Brittle features in jadeitites form in a serpentinite-poor environment. • They are interpreted as markers of paleo-seismicity along mantle wedge base. [ABSTRACT FROM AUTHOR]

The Cubito-Moura Unit is a high-P metamorphic succession that occurs in the southern part of the Ossa-Morena Complex (SW Iberian Massif). It includes a series of metasedimentary, metafelsic and metamafic rocks affected by a high-P, low to intermediate-T metamorphic event during Late Devonian times. Geochemistry of the metabasic rocks reveals that the generation of the protoliths occurred in a supra-subduction zone setting during Late Ediacaran to Early Ordovician times, either in a back-arc or fore-arc context. The eclogites contain atoll-like garnets, omphacite, amphibole, phengite (up to Si = 3.38 apfu), paragonite, rutile and quartz. Thermodynamic modelling in the MnNCKFMASTH system indicates a high-P metamorphic event at ~24 kbar and ~ 585 °C followed by a thermal peak at ~19 kbar and ~ 630 °C, and a subsequent exhumation to ~15 kbar. This P-T path indicates deep subduction at c. 370 Ma of this arc-related section. The lithostratigraphy and tectonothermal evolution of the Cubito-Moura Unit are equivalent to that of a number of units along the Iberian, Armorican and Bohemian massifs that can be correlated as a part of the same Basal Allochthonous Terrane. These units define a single Late Devonian high-P, low- to intermediate-T metamorphic belt developed during the first stages of the Variscan Orogeny. [Display omitted] • Glaucophane-bearing eclogites occur in the Cubito-Moura Unit (SW Iberian Massif). • Peak-P conditions calculated for the Safira eclogite are 24 kbar – 585 °C. • Safira eclogite is part of the Late Devonian high-P belt of the Variscan Orogen. [ABSTRACT FROM AUTHOR]