Pseudosection modelling of a relict garnet-core in Palaeoproterozoic rocks from the Gridino area in the southern Belomorian belt of Karelia reveals peak-pressure eclogite-facies conditions of 610-650 degrees C, 18-20 kbar for two retro-eclogite samples and 610-665 degrees C, 23-26 kbar for a rare Mg-rich biotite-orthopyroxene eclogite, suggesting low initial metamorphic field gradients of 6.6-10 degrees C/km. This confirms an earlier finding in Karelia and, considering other Palaeoproterozoic eclogite occurrences worldwide, that 'cold' subduction conditions, characteristic of modern-style subduction, occurred during the Palaeoproterozoic, similar to 2 Ga ago, for the first time in Earth history. However, compositions of most other phases in the retro-eclogite were reset by diffusion, deformation and recrystallisation during subsequent pressure release and heating to variable degrees, a reason for earlier overestimations of temperatures. By contrast, peak-pressure conditions for a biotite paragneiss (640-740 degrees C, 15-18 kbar) that occurs close to the biotite-orthopyroxene eclogite locality already show an early resetting of its initial assemblage. High-pressure granulite-facies peak-temperature conditions of the retro-eclogite at 712 +/- 5 degrees C, 9-12 kbar (along a field gradient of 20 degrees C/km) were determined by Zr-in-rutile thermometry and quartz-in-garnet elastic barometry. These conditions were dated by a Rb/Sr mineral isochron for the biotite-orthopyroxene eclogite at 1830 +/- 20 Ma for the first time. Using existing ages for the peak-pressure conditions, possible slow overall exhumation rates of <0.9 mm/y between eclogite and the granulite-facies stages could be determined that are compatible with erosion as the main exhumation mechanism. The peak-temperature conditions were possibly established by thermal relaxation during early exhumation. However, a younger Rb/Sr mineral isochron for the biotite paragneiss indicates a characteristic Sr-isotopic disequilibrium distribution caused by diffusion during slow cooling between similar to 1800 and 1750 Ma during later exhumation.

The East Pond Metamorphic Suite (EPMS) in the Baie Verte Peninsula, Newfoundland, Canada, provides a unique record of tectono-metamorphic processes during the Middle Ordovician Taconic orogeny. This study utilizes petrochronology to investigate the complex evolution of the EPMS eclogites, revealing new insights into the subduction and exhumation history of parts of the early Paleozoic Laurentian margin. U-Pb geochronology of zircon, rutile, titanite, and apatite—integrated with trace element data—as well as Rb-Sr mineral isochrons constrain the timing and conditions of metamorphism. We also document late Taconic magmatism on the Laurentian margin, indicated by zircon U-Pb dates from pegmatite intrusions crosscutting the eclogite boudins at ca. 444 Ma. These metamorphic rocks exhibit a multistage metamorphic history with eclogite-facies conditions at ca. 483 Ma, followed by retrograde amphibolite-facies overprint during protracted deformation. Subsequent stages of exhumation and cooling are recorded by Rb-Sr mineral isochrons at ca. 460 Ma as well as titanite and apatite at ca. 459 Ma and ca. 452 Ma, respectively. New constraints on exhumation rates indicate that a protracted phase of residence at ultrahigh-pressure conditions was followed by a short-lived pulse of rapid ascent and late Taconic magmatism, suggesting that exhumation of the EPMS was buoyancy driven and modulated by transient thermal perturbations linked to changes in deep subduction dynamics. We establish a new chronological framework providing insights into the tectono-metamorphic evolution of the Laurentian margin and the Notre Dame arc during the Middle Ordovician Taconic orogeny. Additionally, we link tectonic and magmatic events during subduction and collision, highlighting the complex interplay between these processes at different crustal levels.

Subduction transports oxidized material into Earth's interior. The Mariana subduction zone is a representative example of modern plate tectonic regimes and provides a comprehensive set of geological, geochemical and geodynamical data. Here we use thermomechanical-thermodynamic numerical methods to simulate redox dynamics and fluid-melt release along a Mariana-type subduction setting in two dimensions, allowing comparison between our model and long-term oxidation events in the Mariana arc. Our findings demonstrate two main mechanisms of subduction-related mantle oxidation. First, sulfide oxidation during subduction enables fluids to carry substantial redox budgets into the sub-arc mantle. Partially hydrated mantle emerges as the primary fluid contributor, followed by altered oceanic crust. Secondly, oxidized iron-rich (Fe3+) partial melts extracted from slab-top sediments and altered oceanic crust exert a dominant influence on back-arc mantle oxidation. The majority of oxidized material is carried into the deeper mantle with subducted slabs. Our work demonstrates that with the advent of modern plate tectonics and efficient lithospheric recycling, oxidized material carried by Mariana-type subduction zones has had a global impact on Earth's mantle redox evolution and our planet's oxygenation.

The Corner Brook Collisional Complex in western Newfoundland represents an exhumed part of the partially subducted Humber margin of Laurentia metamorphosed at medium grade and intermediate to high-pressure conditions during collision with outboard arcs. It is interpreted as part of an extruded collisional wedge and consists mainly of metapelitic rocks and minor basement orthogneiss. Its subdivision into different metamorphic zones is supported by calculated PT pseudosections that display a continuous increase in metamorphic grade at intermediate-pressure conditions. The PT paths indicate an evolution at five stages: (I) Burial of peri-Laurentian continental crust after initiation of subduction at the end of the early Ordovician (similar to 470 Ma) during obduction of oceanic crust, which initiated nucleation of garnet at 500 degrees C to 550 degrees C, 6.2 to 9.3 kbar. (II) Maximum, probably Taconic, burial at 520 degrees C to 610 degrees C, 8.2 to 11.7 kbar of one group of samples was followed (III) by extrusion and exhumation with simultaneous thermal relaxation. (IV) Subsequent imbrication within the complex during the Salinic orogeny was accompanied by extensive fluid flow due to prograde dehydration of a second group of rocks at mid-crustal levels during burial. A final stage of thermal relaxation (560-650 degrees C, 6.9-9.2 kbar) created a Barrovian zonation. The ensuing observed peak temperature mineral assemblages are pervasive and only relicts of a former high-pressure stage are preserved locally. Interrelated PT paths of opposing direction can be related to mid-crustal stacking. (V) Finally, post-peak metamorphic folding and faulting of the Barrovian zones created an elongated metamorphic dome transected by brittle thrusts. U-Th-Pb-tot dating of monazite inclusions in garnet of one sample yields an age of 438 +/- 14 Ma interpreted as the time of garnet growth near peak temperature conditions at intermediate pressures. Also, two white-mica-bearing assemblages were dated by Rb/Sr mineral isochrones at 429 +/- 6 Ma and 440 +/- 6 Ma, respectively. The U-Th-Pb-tot monazite and older Rb/Sr age combined with existing U/Pb ages of rutile suggest the presence of an older age population around 438 +/- 4 Ma. Published Ar-40/Ar-39 ages of white mica and amphibole combined with the younger Rb/Sr age represent a younger age population around 427 +/- 4 Ma. Both groups are related to successive separate phases of deformation and recrystallization near and/or after the thermal peak. Extensive fluid influx notably influenced the evolution of various segments of the complex but varied strongly between metamorphic zones.

The Samail Ophiolite in the Oman Mountains formed at a Cretaceous subduction zone that was part of a wider Neo-Tethys plate-boundary system. The original configuration and evolution of this plate-boundary system is hidden in a structurally and metamorphically complex nappe stack below the Samail Ophiolite. Previous work provided evidence for high-temperature metamorphism high in the nappe pile (in the metamorphic sole of the Samail Ophiolite), and high-pressure metamorphism in the deepest part of the nappe pile (Saih Hatat window), possibly reflecting a downward younging, progressive accretion history at the Samail subduction zone. However, there is evidence that the two subduction-related metamorphic events are disparate, but temporally overlapping during the mid-Cretaceous.We present the first geochronologic dataset across the entire high-pressure nappe stack below the Samail Ophiolite, and the shear zones between the high-pressure nappes. Our 22 new RbSr multimineral isochron ages from the Saih Hatat window, along with independent new field mapping and kinematic reconstructions, constrain the timing and geometry of tectonometamorphic events. Our work indicates the existence of a high-pressure metamorphic event in the nappes below the ophiolite that was synchronous with the high-temperature conditions in the metamorphic sole. We argue that the thermal conditions of these synchronous metamorphic events can only be explained through the existence of two Cretaceous subduction zones/segments that underwent distinctly different thermal histories during subduction infancy. We infer that these two subduction zones initially formed at two perpendicular subduction segments at the Arabian margin and subsequently rotated relative to each other and, as a consequence, their records became juxtaposed: (1) The high-temperature metamorphic sole and the Samail Ophiolite both formed above the structurally higher, outboard, ‘hot’ and rotating Samail subduction zone and, (2) the high-pressure nappes developed within the structurally lower, inboard, ‘cold’ Ruwi subduction zone. We conclude that the formation and evolution of both subduction zones were likely controlled by the density structure of the mafic-rock-rich Arabian rifted margin and outermost Arabian Platform, and the subsequent arrival of the buoyant, largely mafic-rock-free, full-thickness Arabian lithosphere, which eventually halted subduction at the southern margin of Neo-Tethys.

Subduction transports oxidized material into Earth’s interior. Here, we simulate redox dynamics and fluid-melt release along a complete Mariana-type subduction setting in two dimensions. The Mariana-type subduction was chosen as a representative example of modern plate-tectonic regimes: It provides a very comprehensive set of geological, geochemical and geodynamical data ensuring precise results of long-term oxidation events. Our findings demonstrate two key mechanisms of subduction-related mantle oxidation. Firstly, the sulfide oxidation during subduction enables fluids to carry substantial redox budget into the sub-arc mantle. Partially hydrated mantle emerge as the primary fluid contributor followed by altered oceanic crusts. Secondly, Fe3+-rich partial melts extracted from slab-top sediments and altered oceanic crusts, exert a dominant influence on the back-arc mantle oxidation. The majority of oxidized material is carried into the deeper mantle with subducted slab. Our work demonstrates that with the advent of modern plate tectonics and thus efficient lithospheric recycling, the oxidized material carried by Mariana-type subduction zones has had a profound global impact on Earth's mantle redox evolution and our planet oxygenation.

The Sierra Pie de Palo (W-Argentina) is part of an Ordovician collisional wedge between the Cuyania microcontinent and the Ordovician Famatinian arc along the west Gondwana protomargin. The flatly E-dipping collisional wedge formed by polyphase shearing. The lower plate consists of Neoproterozoic-Cambrian metasedimentary rocks and Mesoproterozoic mafic-ultramafic basement of eastern Cuyania. The Famatinian forearc represents the upper plate composed of Mesoproterozoic metasedimentary rocks intruded by Mesoproterozoic and Ordovician plutons and overlying Neoproterozoic metasedimentary rocks. Pseudosection modeling on 20 samples distributed over the entire wedge yields a range of recorded maximum PT conditions of 7-14 kbar/ 480-590 degrees C along metamorphic gradients of 10-20 degrees C/km. Clockwise PT-paths are common starting from a midcrustal level with gradients of 20-30 degrees C to maximum depth followed by thermal relaxation. Local anticlockwise PT-paths are observed (1) in high-grade basement klippen of the overriding Famatinian arc (8-10 kbar/700-765 degrees C) caused by late emplacement onto the nappe stack and (2) within late upper crustal ductile zones with normal shear sense. Isotopic ages of (re)crystallisation of metamorphic minerals and assemblages comprise: 429 +/- 2 to 434 +/- 7 Ma (Lu-Hf; garnet), 460 +/- 6 Ma (U-Pb monazite in garnet), 404 +/- 7 to 422 +/- 8 Ma (Rb-Sr; white mica) and 403 +/- 4 to 440 +/- 8 Ma (40Ar/39Ar white mica). Including previous data, ages cluster around major peaks at 464 +/- 1 Ma, 436 +/- 3 Ma, 427 +/- 3 Ma, 415 +/- 2 Ma and 405 +/- 1 Ma related to deformation during three orogenic stages: (1) subduction of the lower plate (eastern Cuyania) to the basis of the wedge at 470-455 Ma and later burial of the upper plate (Famatinian forearc) to similar depths at 440-415 Ma, a characteristic of a "hard" collision; (2) exhumation mainly by erosion and (3) late dissection of the wedge by upper crustal thrusts and some normal faulting at the top of the wedge during arrival of the colliding microcontinent Chilenia (405-360 Ma) at the new Devonian leading margin.

Metamorphic soles within ophiolite mélanges record key information on subduction initiation and evolution of paleo-oceans. Mafic granulite and amphibolite occur in metamorphic soles within the Saga and Bairang ophiolitic mélanges of the Yarlung Tsangbo suture zone, southern Tibet. In fresh mafic granulite, the early prograde assemblage (M1) is preserved as inclusions in the core of garnet. Minerals in matrix and garnet mantle define the peak metamorphic assemblage (M2). Near-isothermal decompression (M3) is recorded by the garnet rim and a symplectic corona. The mineral assemblage of the fresh amphibolite only records one major stage. Many samples were overprinted by strong metasomatism at sub-greenschist-facies conditions (M4). According to geochemical fingerprints, the soles originate from a mid-ocean-ridge environment with strong affinities to the non-metamorphic oceanic crust of the Yarlung Tsangbo ophiolites. P-T calculations of the granulites by pseudosection techniques, Zr-in-rutile and REE-based thermobarometry show ∼690-760°C/9.5-12.5 kbar for the prograde (M1) stage, 900-970°C/14-16 kbar for the peak (M2) stage followed by 902-983°C/9.5-12.6 kbar for the retrograde (M3) stage. From the amphibolite P-T conditions of <700-880°C/7-12.5 kbar were derived. This results in a clockwise trajectory with peak-high pressure to ultrahigh-temperature conditions characterizing a “hot” subduction environment. U-Pb dating of magmatic zircon yields ∼133-127 Ma as protolith ages of the soles, almost coeval with the igneous ages of the unmetamorphosed oceanic crust. U/Pb ages of metamorphic zircon show a similar range within uncertainties (∼131-119 Ma) indicating that initiation of subduction subsequently followed the protolith crystallisation. The metamorphic soles were subducted to a depth of 50 km triggering partial melting in the mantle wedge by dehydration reactions and formation of supra-subduction-zone magma. The mantle wedge became cooler and more buoyant when the subduction zone matured, which caused exhumation of the metamorphic soles and surrounding mantle rocks as well as cooling. A new model for a “hot” subduction initiation close to a mid-ocean ridge near the Asian margin is proposed based on the data from this study and previous studies. The relict mid-ocean-ridge basalts after subduction initiation and the subsequent supra-subduction-zone basalts formed the YTSZ ophiolites during ∼130-120 Ma.

ABSTRACT The Baie Verte Line in western Newfoundland marks a suture zone between (1) an upper plate represented by suprasubduction zone oceanic crust (Baie Verte oceanic tract) and the trailing continental Notre Dame arc, with related upper-plate rocks built upon the Dashwoods terrane; and (2) a lower plate of Laurentian margin metasedimentary rocks with an adjoining ocean-continent transition zone (Birchy Complex). The Baie Verte oceanic tract formed during closure of the Taconic seaway in a forearc position and started to be obducted onto the Laurentian margin between ca. 485 and 476 Ma (early Taconic event), whereas the Birchy Complex, at the leading edge of the Laurentian margin, was subducted to maximum depths as calculated by pseudosection techniques (6.7–11.2 kbar, 315–560 °C) by ca. 467–460 Ma, during the culmination of the Taconic collision between the trailing Notre Dame arc and Laurentia, and it cooled isobarically to 9.2–10.0 kbar and 360–450 °C by 454–449 Ma (M1). This collisional wedge progressively incorporated upper-plate Baie Verte oceanic tract rocks, with remnants preserved in M1 high-pressure, low-temperature greenschist-facies rocks (4.8–8.0 kbar, 270–340 °C) recording typical low metamorphic gradients (10–14 °C/km). Subsequently, the early Taconic collisional wedge was redeformed and metamorphosed during the final stages of the Taconic cycle. We relate existing and new 40Ar/39Ar ages between 454 and 439 Ma to a late Taconic reactivation of the structurally weak suture zone. The Taconic wedge on both sides of the Baie Verte suture zone was subsequently strongly shortened (D2), metamorphosed (M2), and intruded by a voluminous suite of plutons during the Salinic orogenic cycle. Calculated low- to medium-pressure, low-temperature M2 conditions in the Baie Verte oceanic tract varied at 3.0–5.0 kbar and 275–340 °C, with increased metamorphic gradients of ~17–25 °C/km during activity of the Notre Dame arc, and correlate with M2 assemblages in the Birchy Complex. These conditions are associated with existing Salinic S2 white mica 40Ar/39Ar ages of ca. 432 Ma in a D2 transpressional shear zone and synkinematic intrusions of comparable age. A third metamorphic event (M3) was recorded during the Devonian with calculated low-pressure, low-temperature conditions of 3.2–3.8 kbar and 315–330 °C under the highest metamorphic gradients (23–30 °C/km) and associated with Devonian–early Carboniferous isotopic ages as young as 356 ± 5 Ma. The youngest ages are related to localized extension associated with a large-scale transtensional zone, which reused parts of the Baie Verte Line suture zone. Extension culminated in the formation of a Middle to Late Devonian Neoacadian metamorphic core complex in upper- and lower-plate rocks by reactivation of Baie Verte Line tectonites formed during the Taconic and Salinic cycles. The Baie Verte Line suture zone is a collisional complex subjected to repeated, episodic structural reactivation during the Late Ordovician Taconic 3, Silurian Salinic, and Early–Late Devonian Acadian/Neoacadian orogenic cycles. Deformation appears to have been progressively localized in major fault zones associated with earlier suturing. This emphasizes the importance of existing zones of structural weakness, where reactivation took place in the hinterland during successive collision events.

Table S1: Mineral analyses; Figure S1: Normal and inverse isochrons for the 40Ar/39Ar dating presented in Figure 10 and Table 3

Subducted oceanic serpentinite carries H2O, ferric iron, carbon and sulfur into the subduction zone, where they are stepwise released during dehydration. These C-O-H-S fluids are intimately linked to magma oxidation and ore formation within magmatic arcs. However, the mechanism of transfer of carbon, sulfur and ferric iron into fluids is poorly known. It is also controversial whether the C-O-H-S fluids can oxidize arc magmas. We present new thermodynamic models for serpentinite to predict the species produced in C-O-H-S fluids during subduction. Closed system modeling provides molar concentrations of species at different P-T conditions, and shows that reducing species generally have high solubilities at low P-T conditions. Oxidizing species mainly partition into the fluid at higher P-T conditions. The concentration of iron in fluids is much lower than that of other major elements. Open-system fluid fractionation shows that only 5-14% of the carbon is lost to the mantle wedge, while the loss of sulfur is as high as 55-100% at sub-arc depths. Almost all carbon and sulfur lost are released as oxidizing species. The redox properties of the fluids are controlled by sulfur, resulting in an oxygen fugacity of the fluids that is 0.6-0.95 log units higher than the HM buffer. Sulfur loss is a function of the whole-rock composition (e.g., Mg/Si, Al, Ca, and especially Fe3+/Fetot ratio) and the geothermal gradient of the subduction zone, with elevated sulfur fluxes predicted for serpentinite in cold subduction zones. The maximum amount of sulfur released in a cold subduction regime is 5.5 times higher than in a warm subduction regime. Our modeling results are consistent with petrological observations and global-arc-basalt oxygen fugacity calculations and highlight that the C-O-H-S fluids released from the subducted slab may contribute considerably to the composition of arc magmas.

Abundant rodingite was found within serpentinized peridotite and spatially close to gabbro and diabase dykes in the Xigaze ophiolite of the Yarlung Zangbo suture zone. Two types of rodingite are identified based on field-and textural relationships as well as on mineral-and bulk-rock compositions. Type I rodingite with porphyroblastic texture occurs along extensional fractures within massive serpentinized peridotite and contains two subtypes representing the early stage of rodingitization. Type II rodingite is associated with a foliated serpentinized host rock and contains three subtypes, characterized by prehnite-absent mineral assemblages with fine-grained porphyritic to aphanitic texture. All rodingite II subtypes experienced a higher degree of rodingitization than Type I. Type I rodingite was formed by metasomatism of CaO-rich fluids from serpentinized peridotite during ocean floor metamorphism at ~ 120-130 Ma. Thermodynamic modeling shows that Type I rodingite originated at low P-T conditions of <-4 kbar and ~ 200-300 degrees C during limited desilication and calcium enrichment. within a highly reduc-ing environment (logfO2 <-35.3). Type II rodingite originated during subduction starting at-120 Ma with most intense desilication and calcium increase under peak P-T conditions up to ~ 13.5-21.5 kbar and ~ 450-550 degrees C. Modeled values of logfO(2 )for the formation of rodingite II subtypes vary from highly oxidized conditions of logfO(2) =-19.7 to-18.6 to relatively reducing conditions of logfO(2) <-~ 26. P-XCO2 pseudosection modelling predicted Type II rodingite to have formed under CO2-poor conditions at X-CO2 <~ 1 x 10(-4 )during subduction to the maximum depth. Hence the rodingite of the Xigaze ophiolite provides important fingerprints recording events during ocean floor spreading and different stages of subduction as well as late exhumation. (C)2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

• Coesite-bearing garnet found in tributaries have led to overestimation of UHP rocks. • Geodynamic models exist alternative to exhumation of a whole UHP unit. • UHP terrane in the Erzgebirge in Saxony consists of UHP rocks embedded in HP rocks.

Very-low-grade metamorphic rocks are difficult to study due to their very low grain size. Nevertheless, mineral phases nucleate from a hydrous phase that is in contact with all precursor phases providing transient equilibrium. This is a prerequisite for ample application of various thermodynamic techniques to quantify peak metamorphic conditions. High resolution geochronology also enables dating of various metamorphic processes at this low temperature. White mica plays a central role for PT estimates as well as for dating.

New structural data from a mid-crustal segment in the Eastern Sierras Pampeanas, coupled with geochronological methods and P–T estimates, reveal polyphase contractional deformation and metamorphism during the Famatinian Orogeny over a long period of time. Peaks of metamorphic monazite and zircon ages are recorded at c. 500 Ma, between 484 and 465 Ma and at c. 440 Ma. Between 484 and 465 Ma the region attained high-temperature (HT) low-pressure (LP) conditions that resulted in widespread partial melting (peak at c. 470 Ma). A contractional phase occurred during this event, as suggested by syn-anatectic structures, as well as folding at subsolidus conditions. Renewed contraction under subsolidus conditions is evidenced by reverse ductile shearing and folding at c. 440 Ma. Thrusting along the La Chilca Shear Zone caused metamorphic inversion. The consistent orientation of folds in the Quebrada del Molle Metamorphic Complex, El Portezuelo Metamorphic–Igneous Complex and the La Chilca Shear Zone as well as WSW-directed thrusting at the later shear zone indicate uniform WSW–ENE-directed shortening. This late deformation records the Ocloyic tectonic phase and brought the Famatinian Orogeny to an end in the Late Ordovician to Early Silurian. Supplementary material: Analytical methods, methods and description of the calculated P–T pseudosection diagrams, bulk compositions, and electron microprobe, U–Pb and 40Ar–39Ar data are available at https://doi.org/10.6084/m9.figshare.c.4697189

通过岩相学与矿物化学分析和视剖面图模拟计算对雅鲁藏布江缝合带中段地区沉积混杂岩带中多硅白云母石英片岩和黑硬绿泥石片岩的变质特征进行研究.多硅白云母石英片岩峰期矿物组合为多硅白云母+绿泥石+钠长石+石英+榍石,峰期条件为366℃/6.4 kbar;黑硬绿泥石片岩峰期矿物组合为阳起石+绿泥石+绿帘石+钠长石+石英+榍石+钛铁矿,峰期条件为363℃/6.1 kbar,黑硬绿泥石为峰后降温减压阶段的产物.雅鲁藏布江缝合带中段地区的沉积混杂岩变质温压条件达到了高压绿片岩相,指示俯冲深度21～23 km,地温梯度15～18℃/km,其变质特征与俯冲洋壳被上部地幔楔刮削进入增生楔系统经历变质作用形成的低级变质岩十分相似.结合前人年代学数据,研究认为雅鲁藏布江缝合带中段地区的沉积混杂岩在增生楔深部经历高压绿片岩相变质作用,形成于单一的特提斯洋洋壳向欧亚大陆南缘俯冲的构造体制之下印度-亚洲大陆初始碰撞时期.

Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma.

The Beloretsk Metamorphic Complex in the SW Urals formed at a convergent eastern margin of Baltica during the Neoproterozoic-Early Cambrian Timanide orogeny. It comprises three major units with lenses of facies-critical metabasites within metasedimentary rocks: A lowermost eclogite unit, an intermediate garnet amphibolite unit and an upper amphibolite-greenschist unit. Pressure (P)-temperature (T)-paths of four rocks from the two lowermost units were determined mainly by PT pseudosection techniques showing similar clockwise loops at different peak metamorphic, water-saturated conditions: A phengite-bearing eclogite shows peak PT conditions of 16.5–18.5 kbar/525–550 °C (stage I) followed by stage II at 11.5–13.0 kbar/585–615 °C. A garnet amphibolite from the intermediate unit yields lower peak conditions of 11.7–14.5 kbar/480–510 °C (stage I) followed by stage II at 9.5–11.0 kbar/535–560 °C. However, a granite gneiss in the eclogite unit shows similar maximum pressures as the eclogite, but higher temperatures at 15.6–16.2 kbar/660–675 °C, whereas a garnet micaschist contains comparable high pressure relicts, but underwent an advanced midcrustal reequilibration at 7.5–9.0 kbar/555–610 °C. We dated the eclogite by a 7-point Rb/Sr mineral isochron (phengite, omphacite, apatite) at 532.2±9.1 Ma interpreted as age of crystallisation of the eclogitic peak PT assemblage. This age is the youngest compared to the known Timanide metamorphic and magmatic ages.