The influence ofdiabase intrusion on the pore structure is crucialwhen attempting to understand petroleum accumulation for unconventionalreservoirs. This study aims to characterize the pore structure ofshale affected by diabase intrusion. A total of 15 core samples wereemployed to analyze the pore structure characteristics through X-raydiffraction, thin section analysis, scanning electron microscopy,total organic carbon content, nitrogen adsorption, and high-pressuremercury intrusion experiments. The contact metamorphic zone is dividedinto high-grade metamorphic, low-grade metamorphic, and normal shalezones according to lithology differences. The porosity and permeabilityof the low-grade metamorphic zone are much better than the other twozones. In addition, the mesopores and macropores in the low-grademetamorphic zone have a more specific surface area, total pore volume,and a lower pore radius than the others. The diabase intrusion increasesthe mesoporous structure’s complexity but reduces the macropores’pore structure heterogeneity. Overall, the diabase intrusion improvesthe low-grade metamorphic zone and has a negative impact on the high-grademetamorphic zone. Diabase intrusion impacts the pore structure byinteracting with fluids, pressure, temperature, and mechanical–thermal–chemicalprocesses. This study provides a quantitative foundation for assessingand predicting shale oil resources in diabase intrusion areas withinterrestrial basins.

Zircon inclusions in garnet (ZiG) can be used as an elastic thermobarometer to estimate the pressure-temperature (P-T) conditions of geologic processes. Although this method is being increasingly applied as a thermometer to natural samples, experimental evaluation of ZiG is limited and has not been investigated at geologically relevant pressures. We present the first high-pressure assessment of the reliability of ZiG thermobarometry by crystallizing almandine with zircon inclusions in piston-cylinder experiments between 700−900 °C and 2.0−3.0 GPa. Zircons entrapped in experiments at >2.0 GPa yield residual inclusion pressures within 1σ of predicted values and yield entrapment temperatures within 17−30 °C of experimental T. Zircon inclusions in experiments performed at 2.0 GPa yield average inclusion pressures that are ∼0.09 GPa higher than predicted values and therefore yield entrapment temperatures 65−73 °C higher than the experimental T. Evaluation of inclusion pressure trends shows that ZiG host-inclusion systems did not undergo non-elastic deformation during experimental exhumation, confirming that ZiG elastic thermobarometry can accurately record P-T conditions of garnet crystallization so long as zircon inclusions do not go into tension post-entrapment. Our high-pressure experiments suggest that the ZiG host-inclusion system may be applicable to a variety of geologic settings and processes, such as subduction zone metamorphism, partial melting, and contact metamorphism.

Research subject. The Svetlinskoye gold–telluride deposit, the largest operating deposit in the Southern Urals, localized within the Svetlinskoye thrust zone of the Kochkar Anticlinorium. Aim. To develop a new geological-genetic model of the deposit based on the results of long-term research at the Svetlinskoye open pit. Materials and methods. The results of geological and structural observations in the open pit, geochemical and mineralogical research, 40 Ar/ 39 Ar isotopic dating of potassium-bearing minerals were analyzed. A review of literature sources was conducted. Results. The formation of the deposit was preceded by the emergence of a deep thrust (D 3 ) related to the onset of the Uralian collision, which destabilized the geological environment. The tectonic couple “thrust–buckling” was in operation, leading to the formation of the Anticlinorium, heating of rocks in its core, plastic and quasi-plastic deformations, growth of dome structures, zonal highgradient metamorphism, and deep metasomatic alterations of rocks. At early stages, a shallow marine basin emerged in the footwall of the thrust, accumulating terrigenous-carbonate sediments with numerous submarine landslide phenomena. The marine basin closed in the С 1v due to the formation of the Anticlinorium and uplift of the territory. The Svetlinsky dome, on whose western slope the deposit is located, played a key role in the localization and transformation of the ore cluster. The growth of the dome led to the deformation and partial destruction of the thrust zone, forming systems of tectonic detachments (thrusts), which became the main fluid-conducting and ore-hosting structures. Dome formation, zonal metamorphism, and granitization were associated with the mobilization and redistribution of ore components (Au, Te). The main ore-forming processes occurred at the early post-collisional stage, in the interval of 289–277 Ma. Conclusions. The structural preparation and ore-mobilizing processes during the formation of the Svetlinskoye deposit took place at the collisional stage (380–290 Ma), while ore deposition and deposit formation occurred in the interval of 289–277 Ma. The Svetlinsky dome played the main role in the formation and localization of the deposit; its formation was likely related to the emergence of deep thrusts under the conditions of the Late Paleozoic collision. This model provides a satisfactory explanation for the gold mineralization of periand inter-dome structures in the Kochkar Anticlinorium, thus indicating their priority for prospecting.

Understanding strain rates in naturally deformed rocks is crucial for reconstructing the tectonic history of orogenic belts. This study focuses on the Chahzar Thrust Zone, located within the Sanandaj-Sirjan metamorphic zone of southwestern Iran, an ideal setting for investigating deformation dynamics through microstructural analysis. We employ fractal analysis of quartz grain boundaries to estimate strain rates and assess deformation conditions. Although quartz microstructures such as bulging (250-400°C), subgrain rotation (400-500°C), and grain boundary migration (500-750°C) have been historically linked to specific temperature ranges, recent studies emphasize that these features are also strongly influenced by strain rate, fluid content, and other variables (Law, 2014). In this context, we apply the box-counting method to quantify the fractal dimension (D) of recrystallized quartz grains, using it as a semi-quantitative proxy for combined deformation conditions. Our results yield estimated strain rates ranging from 10⁻1⁰.⁹ s⁻1 to 10⁻⁶.⁸ s⁻1, which are notably higher than previously reported typical natural strain rates (10⁻12-10⁻15s⁻1). These findings suggest a deformation regime with episodic or localized strain intensification, contributing to a better understanding of strain accommodation in mid-crustal rocks and offering insights into tectonic processes in similar orogenic systems worldwide.

Geological field observations, coupled with laboratory methods including X-ray diffraction, scanning electron microscopy with energy-dispersive spectrometry, electron microprobe, Raman spectroscopy, and cathodoluminescence, were used to solve the complex problem of the origin of automorphic feldspars and coexisting silicates and aluminosilicates dispersed in the Late Cretaceous Ashua limestones and their metamorphosed crystalline varieties in southern Peru. Petrographic and geochemical data reveal at least three distinct generations of feldspar. The earliest generations of consistent crystallographic orientation (albite A cores and B rims), commonly associated with sericite and adularia, are interpreted as magmatic to postmagmatic in origin. They derived from pyroclastic material of the Early Cretaceous Matalaque Formation within the West Peruvian Trough. Albite grains, introduced as volcaniclastic detritus, are found both in the siliciclastic deposits of the Ashua and/or Chilcane formations and sporadically in restricted, evaporitic marine carbonate environments where celestite, barite, and opal A also precipitated. The outermost regeneration rim (albite-oligoclase composition; generation C), exhibiting distinct crystallographic orientations, conferred the automorphic habit to the feldspars within the contact aureole of the Paleogene Chejol hypabyssal dacite intrusion. It crystallized within metasomatic assemblages representative of skarns, alkali-amphibole, and aceite-type metasomatites, as well as propylitic facies, which formed under conditions ranging from ∼500 °C to 150 °C at near-neutral pH (∼8). As the main cations involved in the three-phased processes are Na, K, Mg, and Ca, this feldspar-C generation was associated with cogenetic minerals in crystalline limestone hosts. Al-rich titanite, Mg-chlorite, talc, and authigenic quartz characterize the earliest hydrothermal pulse. The subsequent hydrothermal episode led to the zeolitization and albitization, followed by the formation of quartz pseudomorphs after stilbite and albite.

Groundwater, a critical resource for regional water security and public health, faces escalating threats from heavy metal contamination—a pressing environmental challenge worldwide. This study focuses on the central-south Hunan region of China, a mineral-rich, densely populated area characterized predominantly by non-point-source pollution, aiming to systematically unravel the spatial patterns, source contributions, and associated health risks of heavy metals in local groundwater. Based on 717 spring and well water samples collected in 2024, we determined pH and seven heavy metals (As, Cd, Pb, Zn, Fe, Mn, and Tl). By integrating hydrogeological zoning, lithology, topography, and river networks, the study area was divided into 11 assessment units, clearly revealing the spatial heterogeneity of heavy metals. The results demonstrate that exceedances of Cd, Pb, and Zn were sporadic and point-source-influenced, whereas As, Fe, Mn, and Tl showed regional exceedance patterns (e.g., Mn exceeded the standard in 9.76% of samples), identifying them as priority control elements. The spatial distribution of heavy metals was governed the synergistic effects of lithology, water–rock interactions, and hydrological structure, showing a distinct “acidic in the northeast, alkaline in the southwest” pH gradient. Combined application of the APCS-MLR and PMF models resolved five principal pollution sources: an acid-reducing-environment-driven release source (contributing 76.1% of Fe and 58.3% of Pb); a geogenic–anthropogenic composite source (contributing 81.0% of Tl and 62.4% of Cd); a human-perturbation-triggered natural Mn release source (contributing 94.8% of Mn); an agricultural-activity-related input source (contributing 60.1% of Zn); and a primary geological source (contributing 89.9% of As). Monte Carlo simulation-based health risk assessment indicated that the average hazard index (HI) and total carcinogenic risk (TCR) for all heavy metals were below acceptable thresholds, suggesting generally manageable risk. However, As was the dominant contributor to both non-carcinogenic and carcinogenic risks, with its carcinogenic risk exceeding the threshold in up to 3.84% of the simulated adult exposures under extreme scenarios. Sensitivity analysis identified exposure duration (ED) as the most influential parameter governing risk outcomes. In conclusion, we recommend implementing spatially differentiated management strategies: prioritizing As control in red-bed and granite–metamorphic zones; enhancing Tl monitoring in the northern and northeastern granite-rich areas, particularly downstream of the Mishui River; and regulating land use in brick-factory-dense riparian zones to mitigate disturbance-induced Mn release—for instance, through the enforcement of setback requirements and targeted groundwater monitoring programs. This study provides a scientific foundation for the sustainable management and safety assurance of groundwater resources in regions with similar geological and anthropogenic settings.

This special issue of the journal, dedicated to the memory of Academician Nikolai Leontievich Dobretsov, features papers reflecting the development of his research and ideas in the fields of his scientific interests. The diversity of Dobretsov’s scientific interests determined the broad range of topics covered in the presented papers: tectonics, deep geodynamics, the interaction of plate tectonics and mantle plumes, metamorphism, including ultrahigh-pressure metamorphism in subduction zones, structural patterns of geomagnetic and gravitational fields and their relationship with plume magmatism, and unique mineral deposits.

Abstract The metamorphic architecture of the Variscan basement in the Tatra Mountains provides evidence for nappe tectonics during Variscan continental collision in the Late Palaeozoic. We reconstruct the metamorphic history of the lower unit using phase equilibrium modelling, zirconium-in-rutile geothermometry and in situ LA-ICP-MS Th–U–Pb monazite geochronology of metapelites. We also present new U–Pb zircon ages from upper unit granitoids. In the lower unit, the peak assemblage in staurolite-kyanite schists is garnet + muscovite + biotite + staurolite + kyanite + plagioclase + rutile + quartz. Structurally higher, a kyanite-fibrolite zone is marked by loss of staurolite and abundant kyanite, commonly replaced by fibrolitic sillimanite. P–T conditions increase from 600–640°C and 6–8 kbar in the staurolite–kyanite zone to 640–655°C and 6.5–8.5 kbar in the kyanite–fibrolite zone. Monazite ages show downward younging from 342–332 Ma in the kyanite–fibrolite zone to 338–315 Ma in the underlying staurolite–kyanite zone, revealing a temporally and structurally inverted metamorphic sequence. These ages are younger than zircon ages in upper unit granitoids (353–346 Ma), indicating prograde metamorphism in the lower unit overlapped with late granitoid intrusion above. The inverted metamorphic sequence and spatially decoupled thermal histories of the upper and lower units suggest that nappe stacking played a dual role: accommodating crustal shortening and driving crustal re-equilibration through partial melting and melt migration. These processes are critical for the long-term rheological evolution of orogenic belts and for understanding the coupling between deformation, metamorphism and plutonism in thickened continental crust.

Research subject. The material composition, formation conditions, and age of amphibolites of the Central zone of metamorphism (CZM) of the Rai-Iz massif. Materials and methods. Microprobe studies of minerals were conducted using a Cameca-SX100 microanalyzer; the content of petrogenic elements was determined by an X-ray multichannel spectrometer CPM-35; the REE content was determined by a mass spectrometer with inductively coupled plasma NexION 300S in the Collective Use Center “Geoanalitik”, Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences. 40 Ar/ 39 Ar dating was carried out at the Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences according to A.V. Travin’s method. Results. The petrography and geochemistry of the amphibolites of the CZM Rai-Iz massif were studied; the parameters of their metamorphism were established, and the age of 40 Ar/ 39 Ar was determined. Two types of amphibolites were identified: garnet amphibolites, epidote-garnet amphibolites, and clinopyroxene-amphibole and amphibole-phlogopite-garnet rocks. The main minerals were found to be amphibole and garnet. Amphibole corresponds to edenite, pargasite, and ferropargasite. In some amphibole samples, chemical zonation was established, manifested in the depletion of the marginal parts of Al 2 O 3 and FeO grains relative to the central ones, while the MgO content increased from the center to the edge. Garnets from garnet and epidote-garnet amphibolites exhibited an almandine-grossular composition with pyrope (3–16 %) and spessartine (3–13 %) components; in amphibole-phlogopite-garnet rocks, garnet demonstrated an almandine–pyrope composition. In the pomegranate, the following chemical zonation was established: the FeO content increases from the center to the edge of the grains, while the MnO content decreases. The age of amphibolites determined by the 40 Ar/ 39 Ar method (405.2 ± 5.4 Ma) corresponds to the Lower Devonian. The averaged formation parameters of amphibole-bearing rocks correspond to P = 6–13 kbar, T = 430–860° C, and to the boundary of amphibolite and greenschist facies and the boundary of amphibolite and granulite facies. REE spectra in the studied rocks, normalized relative to chondrite, showed the predominance of heavy lanthanides over light ones. The character of REE distribution is close to N-MORB basalts. Conclusion. The studied rocks formed at the boundary of the early and middle Devonian. Their formation was associated with regional metamorphism in the conditions of the onset of collision.

Abstract The Neoproterozoic carbonaceous metapelites of the Mandhali Formation in the inner Lesser Himalaya contain diagenetic pyrite with above-background levels of Au (>200 ppb) when analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). These metapelites exhibit progressively metamorphosed zones (from south to north), ranging from the chlorite-muscovite zone (~372°C), to the muscovite ± biotite (~520°C) zone, to the greenschist-amphibolite transition (~570°C, >5 kbar). Within this regional framework, we document a hitherto unknown paragenesis of pyrite growth from diagenesis to peak metamorphism along with a localized phase of contact metamorphism, which predates regional metamorphism. A comparative assessment of pyrite trace element concentrations from the progressive metamorphic zones reveals that >80% of Au and ~65% of As is released from diagenetic pyrite during early chlorite dehydration at ~372°C, that is, in the chlorite-muscovite zone. Further into the muscovite ± biotite zone, at the terminal chlorite breakdown stage (480°–520°C), pyrite still occurs as the major sulfide with subordinate pyrrhotite. However, by this stage, ~93% of Au; ~75% of As; and ≥90% of Mo, Cd, Pb, Sb, W, Cu, Bi, Te, and Tl are released from pyrite. With the transition of pyrite to pyrrhotite (500°–550°C), almost all trace elements are released from pyrite into metamorphic fluids, except Co that is incorporated into the metamorphic pyrrhotite. This documented grain-scale elemental mobility is also reflected in bulk-rock Au assays; that is, mean Au of 9.8 ppb in the chlorite-muscovite zone and 1.1 ppb in the muscovite ± biotite zone. Our results suggest that pyrite recrystallization during chlorite dehydration is relatively more significant than pyrite-pyrrhotite transition in terms of Au and As release, and by extension, orogenic gold formation.

A three-dimensional geomagnetic model of the Myutenbay deposit has, been created in the Geosoft Oasis Montaj program, based on digital modelling of magnetic exploration data previously carried out at the site, and using the petrophysical characteristics of the ore-bearing rocks. A three-dimensional model of the ore bodies was created in Micromine software using information from boreholes obtained during the exploration stage of the deposit. The shape of the ore bodies and that of the three-dimensional magnetically disturbing objects in the geomagnetic model were established as identical. A two-dimensional geomagnetic model clearly shows the fault zone, the folded rocks of the Murun suite and the orientation of the ore bodies within the Kosmanachi ore-bearing strata. The mapped magnetic anomalies reflect zones of progressive regional metamorphism, which collectively determined the location of gold ore mineralization. Zones of correlatable magnetic maxima reflect the development of pyrite-pyrrhotite vein-disseminated mineralization, related to areas of gold-producing ore body.

Release of oxygen (oxidized fluids) by growth of ferromanganese garnets and oxygen circulation in subduction zone.

The article considers stratigraphic and structural features of the formation of iron ore deposits confined to the siliceous-carbonate formation of Central Kazakhstan, using the Kentobe-Togai group as an example. A comprehensive analysis of lithological and stratigraphic conditions, morphology of ore bodies, fault systems and metasomatic transformation zones is carried out. Key patterns are revealed: confinement of ore bodies to reactive carbonate-siliceous deposits of the Upper Devonian and Lower Carboniferous; formation of ores in zones of contact metamorphism during the intrusion of granitoids; the active role of faults in the localization and segmentation of deposits; pronounced vertical zoning of the mineral composition of ores; as well as parametric heterogeneity of bodies. These features taken together form unique geological systems, where mineralization is regularly controlled by stratigraphy and structure. Geological maps, sections and three-dimensional wireframe models of the Kentobe-Togay group deposits with visualization of ore bodies, faults and intrusions are presented, demonstrating a close spatial relationship between tectonics, magmatism and iron enrichment. The results emphasize the need to apply modern methods of 3D modeling, geostatistical interpolation and structural analysis in assessing the resources of such deposits, and also show that the established patterns are universal and can be applied to predict and model similar objects.

The Early Mesoproterozoic (1370 Ma BP) age of picrite-picrobasalt volcanism and the associated metamorphism in the riftogenic Ishimbinsko-Tatarskaya suture zone (paleorift) in the southwest of the Siberian Craton is substantiated. Petrogeochemical typification of metavolcanogenic-sedimentary complexes is carried out to establish their protoliths and correlation. First data on Rb-Sr and Rb-Sr и 147 Sm- 143 Nd ID-TIMS systematics of late Precambrian metavolcanogenic rocks in the northern part of the Rybinsk-Panimba volcanic belt in the central part of the North Yenisei Range are presented. According to the petrogeochemical composition, the protoliths of the metavolcanites correspond to picrobasalts and basalts, less often to picrites. As the volcanogenic sedimentary strata in different areas occur on a single marker horizon of carbonaceous shales, we can correlate the age of the volcanogenic Panimba sequence with the Korda suite, considering these formations at the stratolevel of the Early Mesoproterozoic. Geothermobarometry and analysis of the features of regional metamorphism of volcanogenic-sedimentary rocks in the reference areas show a heterogeneous nature of the PT conditions of transformation of the original rocks: 4.8–4.9 kbar/527–549 °C – metatuffites of picrobasalts; 5.0–5.8 kbar/543–612 °C – metabasites; 3.5–4.6 kbar/522–636 °C – metapelites. According to the metamorphic zoning pattern, the progressive metamorphism of the studied rocks belongs to the relatively shallow LP/HT andalusite-sillimanite Idaho type (Buchan type of zoning). Its PT conditions correspond to a transition from the greenschist facies to the boundary between the epidoteamphibolite and amphibolite facies. In terms of the time of manifestation (1056–996 Ma), the metamorphism is close to the Grenville tectonic epoch. The established Precambrian age of picrite-picrobasalt volcanism in the Yenisei Range correlates with the time of manifestation of trondhjemites of the Nemtikhinsky complex and with the reference Mashak plume magmatism in the Southern Urals, which were manifested in a geodynamic setting of continental crust stretching during the breakup of the Nuna supercontinent.

Late Paleozoic architecture, deformation, and geodynamics of the Xing’an–Mongolia intracontinental orogenic belt

The A Vuong Formation, located within the southern Truong Son Belt in central Vietnam, comprises low- to high-grade metamorphic rocks that record crucial insights into the region’s tectonic evolution. Our field investigations reveal that it mainly consists of the psammitic and pelitic schists, intercalated with some mafic or siliceous layers, and locally cut by leucocratic veins. The indicative mineral assemblages in the pelitic to psammitic schists define two metamorphic zones: a greenschist-facies biotite-chlorite zone and an amphibolite-facies staurolite zone. Based on conventional geothermobarometry, the peak metamorphic condition in the staurolite zone was estimated at ca. 5.5–8.7 kbar and 590–640℃, followed by a retrograde stage at 4.4–7.4 kbar and 530–570℃. Notably, a porphyroblastic andalusite observed in a pelitic schist from this zone is rimmed by kyanite with a preferred orientation. In addition, it includes kyanite, sillimanite, and an intergrowth of staurolite + quartz as inclusions. These features suggest their equilibrium during the prograde stage, reflecting a pressure-temperature transition from andalusite to kyanite stability. The prograde metamorphic condition is thus constrained at the triple point of andalusite-kyanite-sillimanite. The petrological evidence and estimated metamorphic conditions for the current pelitic schists support a unique anti-clockwise pressure-temperature trajectory, rather than a clockwise one. Its thermobaric feature is well aligned with the amphibolite-facies metamorphism of the neighboring Dai Loc Complex, and contrasts with that of the Kham Duc Complex (Kontum Massif).

Abstract As a highly coupled aggregate of tectonism, magmatism, and metamorphism, a gneiss dome is usually taken as a vital window for understanding the crustal internal structure and the exchange of material and energy during orogenic exhumation. The Qinghe gneiss dome located in the eastern Chinese Altai orogen, lies in Qinghe County, Xinjiang, records important information of late accretionary orogeny associated with continental uplift and crustal growth. According to the field investigation, the dome shows core–mantle–margin domains, in which the core is composed of migmatized granite and gneiss, the mantle consists of banded gneiss, schist, and leptynite, and the margin has rock assemblages of phyllite, schist, and meta‐sandstone. From the margin to the core, the dome can be divided into chlorite–sericite, andalusite–staurolite, sillimanite–biotite, and sillimanite–garnet metamorphic zones, recording progressive metamorphism. Detailed structural analyses in the Qinghe gneiss dome indicate progressive deformation from the margin to the core. Internal and external detachment faults are clarified, with the former characterized by inflow and outward migration of crustal material and the latter marked by brittle‐ductile deformation with a lineation indicating lateral slip of the upper wall when the dome uplifted. Based on these faults, upper, middle, lower structural layers are observed from the outer to inner domains of the dome. Considering the general geological background and new data, the Qinghe gneiss dome probably predominantly underwent early ductile shear deformation and late heat‐flow diapirism in the early Permian, closely related to upwelling of asthenosphere mantle that resulted from slab break‐off in the extensional tectonic setting.

Abstract Post‐collisional mafic rocks not only record geodynamic processes at the end of the orogenic cycle but also retain various clues regarding preceding interactions between subducted slabs and mantle wedges. However, the latter and related indicators have often been overlooked; in particular, how the continental crust interacts with the mantle in subduction zones and modifies its nature remains ambiguous. This study of post‐collisional mafic rocks in the North Qaidam orogen provides new insights into sophisticated crust–mantle interactions via variable continental subduction. These post‐collisional mafic rocks are consistent with the geochemical nature of arc lava and originated from partial melting of the antecedent metasomatic mantle. Although they possess relatively uniform whole‐rock Sr–Nd isotopes, the mafic rocks from the ultrahigh‐pressure metamorphic terranes present more enriched zircon Hf isotopes and remarkable signals of melt‐driven mantle metasomatism than the other rocks within the non‐ultrahigh‐pressure metamorphic zone. This is attributed to spatially variable continental subduction and the consequent differentiated crust–mantle interactions. Trace element modeling also reveals that a greater proportion of continental component‐derived metasomatic melts are needed to form mafic rocks in ultrahigh‐pressure metamorphic terranes. The whole‐rock magnesium isotopes are between −0.15‰ and −0.38‰, which are negatively correlated with (87Sr/86Sr)i and positively correlated with ɛNd(t) and ɛHf(t). These findings indicate that these mafic rocks exhibit lighter magnesium isotopes when their mantle source is metasomatized by more continental component‐derived melts enriched with radiogenic isotopes. The geochemical distinctions of the post‐collisional mafic rocks verify the contributions from continental subduction to heterogeneous mantle metasomatism and magmatic diversity.

Abstract Epidote‐amphibolites form along the plate interface during subduction infancy and are stable in warm, mature subduction zones that generate slow earthquakes. Epidote‐amphibolite rheology therefore likely influences plate‐scale processes during plate boundary formation and grain‐scale processes that give rise to slip transients. We present optical and electron microscopy of naturally deformed epidote‐amphibolites from beneath the Oman ophiolite (∼7–10 kbar, 400–550°C) to characterize their deformation behavior. Epidote‐amphibolites are fine‐grained, strongly foliated and lineated, and exhibit polyphase fabrics in which amphiboles (grain size ∼10–50 μm) and epidotes (grain size ∼5–20 μm) are strain‐accommodating phases. Two‐point correlation connectivity analysis demonstrates that amphiboles are well‐connected regardless of phase proportions/distributions. Chemical analysis and electron backscatter diffraction reveals amphibole syn‐kinematic metamorphic zonations, strong crystallographic and shape ‐ preferred orientations (CPOs and SPOs), subgrain geometries indicating (hk0)[001] slip, and high average Grain Orientation Spreads (GOS; ∼6°), interpreted as coupled dissolution‐precipitation creep (DPC) and dislocation glide. Epidotes record weak CPOs, low intragranular misorientations, moderate SPOs, and low GOS (∼0–2°), interpreted as deformation by DPC. Depending on phase distributions, epidote‐amphibolite rheology can be approximated as interconnected weak layers of amphibole dissolution creep or a composite rheology of plasticity and fluid‐assisted/diffusion‐accommodated creep. We estimate stress from quartz piezometry (∼30–45 MPa) and strain rates from flow laws and geologic data (6 · 10−11 to 10−13 s−1), and calculate equivalent viscosities of <1018 Pa‐s. On tectonic timescales, such low viscosities are consistent with epidote‐amphibolites serving as strain localizing agents during subduction infancy. On seismic timescales, coupled dislocation glide and diffusion creep exemplify a strain‐hardening deformation state that could culminate in creep transients.

Abstract 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 (~470 Ma) during obduction of oceanic crust, which initiated nucleation of garnet at 500°C to 550°C, 6.2 to 9.3 kbar. (II) Maximum, probably Taconic, burial at 520°C to 610°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°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–Pbtot 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–Pbtot 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 40Ar/39Ar 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.