Search

Our understanding of the geological history of early Archean crust is limited by poor preservation of igneous features in rocks that have experienced multiple metamorphic and deformation events. Thus, regions with the best preserved Eoarchean rocks, as for example, the northern part of the Itsaq Gneiss Complex (IGC) of Greenland, have been the most intensively studied. The IGC underwent metamorphism at ca 3.6 and 2.7 Ga (Nutman & Bennett 2018). The grade of 2.7 Ga metamorphism varies from granulite facies in the southern part of the IGC (Fӕringehavn terrane) to lower amphibolite facies in the north (Isukasia terrane). This study compares the preservation of zircon in rocks from both terranes of the IGC.Zircon grains from granitic gneisses in the Fӕringehavn terrane have rounded igneous cores with weak oscillatory zoning, surrounded by well-developed light-CL metamorphic rims. The 207Pb/206Pb zircon age obtained by in situ Secondary Ion Mass Spectrometry (SIMS) of these grains is ca 3.64 Ga for the cores, with metamorphic rims recording an age of ca 2.7 Ga. The Isukasia terrane extends either side of the Isua Supracrustal Belt (ISB), rock samples were collected from both the outer (SSE of the ISB) and inner (NNW of the ISB) Isukasia sub-terranes (Nutman & Bennett 2018). Zircon grains from the outer sub-terrane have well preserved igneous morphologies with evidence of metamictisation and fluid alteration but little to no metamorphic rims. The 207Pb/206Pb zircon ages are scattered towards 2.7 Ga, interpreted as the time of metamorphism, with a subgroup at ca 3.79 Ga that is interpreted as a minimum age for magmatic zircon. However, as the samples collected in the vicinity yielded an age of 3.82 Ga (Nutman et al. 1999, Kielman et al. 2018), the age of ca 3.79 Ga may have been disturbed by subsequent events. Zircon grains from the inner sub-terrane of Isukasia have well-preserved igneous cores with oscillatory zoning. Rounding of pyramidal terminations and thin rims are due to metamorphism. The age of crystalization of the protolith as recorded by igneous zircon is ca 3.71 Ga. The difference in the degree of the metamorphism at 2.7 Ga is visible in the structures and preservation of zircon grains. In this example, rounded cores and well-developed metamorphic rims characterize granulite facies, whereas well-preserved cores with oscillatory zoning and thin metamorphic rims represent lower amphibolite facies.This research was funded by NCN grant UMO2019/34/H/ST10/00619 to MAKReferencesKielman, R., Whitehouse, M.,Nemchin, A., & Kemp, A., (2018). A tonalitic analogue to ancient detrical zircon. Chemical Geology, 499, 43-57.Nutman, A.P. & Bennett, V.C., (2018). The 3.9-3.6 Ga Itsaq Gneiss Complex of Greenland. In: Van Kranendonk, M.J., Bennett, V.C. & Hoffmann, J.E., (Eds.). Earth’s Oldest Rocks (2nd ed.), Elsevier, 375-399.Nutman, A.P., Bennett, V.C., Friend, C.R. & Norman, M.D., (1999). Meta-igneous (nongneissic) tonalites and quartz-diorites from an extensive ca. 3800 Ma terrain south of the Isua supracrustal belt, southern West Greenland: constraints on early crust formation. Contrib. Mineral. Petrol. 137, 364–388.

Interpreting Archean geology is often challenging due to the rocks having obscure field relationships and polymetamorphic histories (Kusiak et al. 2019; Dunkley et al. 2020). In such circumstances, U-Pb isotopic analysis of zircon is crucial for revealing the geological history. This study investigates Archean gneisses from the Saglek Block in Canada, which record magmatic and metamorphic history between ca 3.9 Ga and 2.5 Ga. The predominant lithology is the Uivak gneiss which is primarily composed of tonalite-trondhjemite-granodiorite (TTG) with subordinate intermediate to mafic components. Uivak gneiss is traditionally divided into Uivak I and Uivak II, where Uivak I is grey gneiss and Uivak II is characterized by augen texture and Fe-rich geochemistry (Collerson and Bridgwater, 1979). Ages for the magmatic protoliths of Uivak I are >3.6 Ga, whereas Uivak II ages vary between ca 3.6-3.3 Ga (Sałacińska et al. 2019; Wasilewski et al. 2021 and references therein). This study presents geochemical and U-Pb zircon geochronology from Mentzel and Maidmonts Islands. Augen gneiss on Mentzel Island fits the definition of Uivak II augen gneiss and yield a U-Pb zircon age of ca 3.3 Ga. A similar age was reported for Maidmonts gneiss (Sałacińska et al. 2019) and Illuilik gneiss (Wasilewski et al. 2021). On Mentzel Island, granitic bodies intruded the augen gneiss at ca 2.7 Ga and 2.5 Ga during high-T metamorphism. New dating confirms that augen gneiss on Mentzel Island and elsewhere in the Saglek Block belongs to Uivak II gneisses of ca 3.3 Ga. Variations in rare earth element concentration between different ca 3.3 Ga rocks can be attributed to the involvement of different crustal components in the magmatic protolith. On Maidmonts Island, the augen gneiss intrudes grey gneiss with a protolith age of ca 3.7 Ga, which confirms deformation and metamorphism of Uivak I gneiss before ca 3.3 Ga. This research was funded by NCN grants UMO2019/34/H/ST10/00619 to MAK. References:Collerson, K.D. & Bridgwater, D. 1979. Metamorphic development of early Archaean tonalitic and trondhjemitic gneisses: Saglek area, Labrador. In: Barker, F. (Ed.), Trondhjemites, Dacites, and Related Rock. Elsevier, Amsterdam, 205–271.Dunkley et al. 2020. Journal of the Geological Society, 177 (1), 31–49.Kusiak et al. 2018. Chemical Geology, 484, 210–223.Sałacińska et al. 2019. International Journal of Earth Sciences, 108, 753-778.Wasilewski et al. 2021. Precambrian Research, 359, 106092.

The Tethyan oceans are the internal sotry-tellers of the amalgamation, tenure and break up of Pangea. All tethyan oceans have been mostly consumend and only remnants of them occur now along the margins of the Atlantic, Mediterranean, Black and Caspian seas, as well as in the Alpine-Himalayan and adjacent orogens. The Rheic (~500 to ~300 ma, some-times Ran or Proto-Tethys) closed during the amalgamation of Pangea and the Neo-Tethys (~270 to ~20 ma) is the main witness of its break-up. The Paleotethys is the ocean that shared an internal position during most of Pangea’s tenure. There is no consensus about its origin, some suggest that opened during the latest stages of Pangea’s amalgamation (Devonian-Carboniferous) whereas others considert it a remnant of the mostly subducted Rheic ocean after Gondwana-Laurussia collision. We have studied the Shanderman eclogites (NW Iran) and put them into their context within other HP rocks in the area because they a potential candidate to represent the Paleotethys ocean. They are metamorphosed oceanic rocks (protolith oceanic tholeiitic basalt with MORB composition). Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation. In this contribution we will show the new petrological, geochemical and geochronological results from this eclogites to shed light on the evolution of the tethyan oceans during the Paleozoic. The protolithic oceanic crust of Shanderman crystallized ~350 Ma, metamorphic age suggest that this piece of ocean subducted soon after forming, representing, perhaps, a subduction initiation or a ride-subduction event. We also found a metasomatic event at ~280 ma. Considering its relation with other HP rocks in Iran, we interpret that the Shanderman ophiolites are not a fragment of the Paleotethys but a fragment of the Rheic (Ran/Prototethys) ocean.

In the Bhagirathi River Transect of the Garhwal Himalaya, India, the existence of the Jhala Normal Fault (JNF) and its movement sense are disputed. The JNF has been considered either as part of the South Tibetan Detachment System (STDS) or as a distinct, more southerly discontinuity within the Higher Himalayan Crystalline Sequence (HHCS). Field studies reveal that the JNF lies entirely within the HHCS, with both the JNF footwall and hanging-wall preserving thrust-related shear markers within amphibolite facies HHCS rocks. Rare extensional shear markers are, however, observed at the base of the JNF hanging-wall. New U-Pb zircon rim and monazite SHRIMP ages of 33.8 ± 0.8 Ma and 30.7 ± 0.5 Ma obtained in this study represent the timing of metamorphism in the JNF hanging-wall and footwall, respectively. Together, the field and geochronological evidence suggest that during Eocene-Oligocene channel flow in the HHCS, the slow-moving marginal part of the channel representing the JNF hanging-wall was trailing its more rapidly extruding footwall, resulting in apparent normal-sense movement across the JNF. The intrusion of 21.4 ± 2.3 Ma (monazite U-Pb age) tourmaline-bearing leucogranites within the JNF hanging-wall testifies to its ongoing uplift as part of the exhuming Miocene HHCS channel. The absence of any metamorphic break or distinct extensional shear zone at the JNF indicates that it originated as an intra-channel discontinuity rather than a major lithotectonic boundary.

The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a continental arc that is part of the Himalayan-Alpine orogeny. Late Cretaceous magmatism in this belt is dominated by high-K calc-alkaline, shoshonitic, and alkaline rocks that occur over an area of ~600 km (E-W) and ~200 km (N-S). We present new geochemical data (whole rock major and trace element analyses, mineral compositions, U-Pb zircon and titanite ages, zircon trace element data, and Sr-Nd-Pb isotopic analyses) for 153 samples, with compiled data for an additional 265 samples. Magmatism is diachronous across the arc. In the north, Cycle-I (92–84 Ma) commenced with tholeiitic and calc-alkaline basalts and andesites, and continued with felsic extrusive rocks. Cycle-II (84–70 Ma) includes mainly intermediate and felsic extrusive rocks. Over time,the low-K granitoids progressively give way to calc-alkaline granitoids in the north. In the south, Cycle-I (84–78 Ma) includes high-K trachyandesites, trachytes and felsic extrusive rocks. Cycle-II (78–65 Ma) comprises leucitites, trachybasalts, and other K-rich rocks. Shoshonitic granitoids in the south show ages between 80 and 65 Ma. Clinopyroxene compositions in trachyandesites and leucitites indicate initial crystallization at ~38 km depth and 1120 °C. Amphibole joins the phase assemblage at ~8 km depth and T

Since its foundation in 2005, Europlanet has sought to reach out and engage with planetary scientists across the globe. Today, Europlanet has a global role to connect the international planetary community through the common aim of working together to explore and understand our Solar System and exoplanetary systems beyond. It is therefore both timely and necessary to put in place a framework for a community-led roadmap for global collaboration as part of Europlanet’s future development as both a Research Infrastructure and as a Society. The Strategic Plan for Europlanet 2024 Research Infrastructure’s Global Collaboration andIntegration Development that represents the outcome of a dedicated effort to define how to expand and intensify the new relationship between Europlanet and African, but also between Europlanet and North and South American and Asian collaborators, will be presented. Europlanet 2024 RI has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871149.

The Paleoproterozoic thermal evolution of the north-Indian continental margin is debatable as the Lesser Himalaya granites are interpreted either as a subduction-zone volcanic arc or rift-related magmatism during Columbia assembly or disintegration processes, respectively. Integrated mineralogical, geochemical investigations, temperature estimates from Ti solubility in biotite and zircon, and computational phase equilibria modeling from the Wangtu Gneissic complex (WGC), Himachal Himalaya reveal peraluminous nature for most of the WGC rocks that crystallize at ~650 °C and ~ 1.0–1.1 GPa. The U-Pb ages from magmatic zircons from the WGC exhibit two prominent age clusters at 1867 Ma and 2487 Ma. The U-Pb zircon data and modeled phase equilibria for metasedimentary rock reveal the generation of S-type peraluminous magma parental to the WGC, through melting of preexisting supracrustal rocks at ~1800 Ma, within ~850–900 °C and 1.1–1.2 GPa, similar to P-T conditions observed in modern-day subduction zone settings. The results obtained from this study reveal the north Indian continental margin was an active subduction zone during the Paleoproterozoic Columbia supercontinent assembly that extends across the Himalayas.

We constrain the multistage tectonic evolution of the Palaeoproterozoic UHT metamorphic (P ​= ​0.9–1.0 ​GPa, T >1000 ​°C, t ​= ​2088–2031 ​Ma) Bakhuis Granulite Belt (BGB) in Surinam on the Guiana Shield, using large- to small-scale structures, Al-in-hornblende thermobarometry and published fluid inclusion and zircon geochronological data. The BGB forms a narrow, NE–SW striking belt between two formerly connected, ~E–W oriented granite-greenstone belts, formed between converging Amazonian and West African continental masses prior to collision and Transamazonian orogeny. Inherited detrital zircon in BGB metasediments conforms agewise to Birimian zircon of West Africa and suggests derivation from the subsequently subducted African passive margin. Ultrahigh-temperature metamorphism may have followed slab break-off and asthenospheric heat advection. Peak metamorphic structures result from layer-parallel shearing and folding, reflecting initial transtensional exhumation of the subducted African margin after slab break-off. A second HT event involves intrusion, at ca. 0.49 ​GPa, of charnockites and metagabbros at 1993–1984 ​Ma and a layered anorthosite at 1980 ​Ma, after the BGB had already cooled to

This paper reports on an ice-wedge pseudomorph that formed and is preserved in metavolcanic host material that was later transformed to metamorphic solid bedrock. It has been dated to 1,895 ± 5 Ma by U–Pb geochronology of zircon in the bedrock, an Early Proterozoic age. Detailed observation of the deformation structures of the wedge points to an ice-wedge pseudomorph based on typical downbending around the wedge and vertical lamination in the inner part of the wedge due to slumping into the wedge after the ice melted, along with a few remains of lateral pressure structures (such as folds and upturned strata) in the adjacent host sediment. The interpretation of the wedge structure as an ice-wedge pseudomorph confirms previous work on this topic. This ice-wedge pseudomorph demonstrates for the first time the existence of permafrost at c. 1.9 Ga. It indicates that permafrost and associated conditions were present in lowlands at low latitude at discrete time intervals early in Earth’s history. Although some caution should be applied, mean annual air temperature appears to have been slightly below the freezing point at that time.

The early Paleozoic paleogeography of East Gondwanan terranes, including the North China Craton (NCC), is contentious, primarily reflecting the paucity of integrated geochronological, biogeographic, and tectonic data sets. Our new sensitive high-resolution ion microprobe data from 14 sandstones of the Taebaeksan Basin, Korea, indicate that its platform shelf sequences, typified by trilobite faunal assemblages diagnostic of the NCC, record the vestige of coeval arc magmatism. Detrital zircons analyzed from the sandstones yielded Eoarchean to Early Ordovician ages, which define three distinct types of distribution patterns characterized by: (1) double peaks at ca. 1.85 Ga and 2.50 Ga diagnostic of basement rocks in the NCC; (2) minor peaks at ca. 1.75, 1.6, and 1.2–1.1 Ga in addition to double peaks; and finally (3) a scattered array of late Paleoproterozoic to Neoproterozoic zircons lacking double peaks. The marked contrasts among the three types reflect significant changes in provenance, most likely linked to variations in paleo-water depths during the “Sauk” transgression. Longshore- or onshore-directed currents, associated with an increase in water depth, apparently brought outboard oceanic detritus and benthic trilobites into the relatively flat outer shelf of the Taebaeksan Basin. As a result, fine-grained sandstones received a large amount of detritus from distal sources, yielding mixed signatures in zircon age patterns and trilobite assemblages. Excluding the basal sandstone-conglomerate unit, five siliciclastic formations contain syndepositional zircon populations, and their weighted mean 206Pb/238U ages decrease upsection from 512 ± 5 Ma to 483 ± 2 Ma, indicating a sedimentary influx from contemporaneous volcanic activity. In conjunction with arc-related bulk-rock geochemistry and juvenile Nd isotopic signature, early Paleozoic detrital zircons likely represent the first-cycle detritus supplied for ∼30 m.y. from the proto-Japan arc that initially formed at ca. 520 Ma. Together with the occurrence of ca. 700–500 Ma detrital Pacific Gondwana zircons in fine-grained sandstones, Paleozoic arc-sourced detritus suggests that the Korean Peninsula was paleogeographically linked to an ancient convergent margin, perhaps extending from the Terra Australis orogen.

The Napier Complex of Enderby and Kemp Lands forms the north-western part of the East Antarctic Shield and consists predominantly of gneisses and granulites metamorphosed during a ca. 2.8 Ga high-grade and a ca. 2.5 Ga ultra-high temperature event. The western segment of the Napier Complex includes coastal outcrops, islands and nunataks around Amundsen and Casey Bays, and the Tula Mountains. This region records some of the highest metamorphic temperatures measured on Earth, affecting a variety of gneisses as old as ca. 3.8 Ga. Five samples of orthogneiss from the less-studied eastern Tula Mountains, including three granitic, one trondhjemitic and one dioritic gneiss, were dated by zircon U-Pb Secondary Ion Mass Spectrometry (SIMS). The three orthogneisses yield protolith ages of 3750 ± 35 Ma (granitic), 3733 ± 21 (trondhjemitic) Ma and 3560 ± 42 Ma (dioritic), whereas the two other granitic orthogneisses record ages of 2903 ± 14 Ma and 2788 ± 24 Ma. Zircon growth during metamorphism occurred at 2826 ± 10 Ma, and also between 2530 Ma and 2480 Ma. Samples from the Tula Mountains can be geochemically subdivided into Y-HREE-Nb-Ta depleted and undepleted groups. Eoarchean granitoids are included in both geochemical groups, as are Meso- and Neoarchean granitoids. The Y-HREE-Nb-Ta depleted granitoids can be generated by medium- to high-pressure melting of mafic crust, whereas undepleted granitoids can be generated by low-pressure melting. However, relatively high potassium contents in most samples, and the presence of xenocrystic/inherited zircon in some, reflect the likely involvement of felsic crustal sources. This diversity in granitoid composition occurs across the Napier Complex. The lack of a simple correlation between protolith age and geochemical type is an indication that magmatism during the Eoarchean (and later) involved diverse sources and processes, including re-melting and recycling of various crustal components, rather than just the formation of juvenile crust.

The ‘channel flow’ concept is generally associated with the collisional mountain belts (such as the Himalaya) to explain the exhumation of deeper crustal materials. According to the concept, the top part of the subducting plate gets ‘molten’ and tries to return to the surface following the ‘pipe flow’ mechanism via a combination of Poiseuille- and Couette Flows. In this study, we employed these concepts to address a long-standing debate related to the existence and cryptic nature (normal/ reverse) of an orogen parallel discontinuity, named the Jhala Normal Fault (JNF) present in the Bhagirathi River section of the Garhwal Higher Himalaya. More importantly, while a group of researchers consider the JNF to be the northern boundary of the Higher Himalayan channel (i.e., the South Tibetan Detachment System), another group put the JNF well inside the channel. In this scenario, understanding the mechanism of deformation at the JNF will not only solve this local issue but will also provide us with new insights into the geodynamic evolution of an orogeny. Based on fresh field observations and SHRIMP geochronological data (zircon and monazite), a model is being proposed in the current study to explain the origin and evolution of the JNF. The presence of amphibolite-grade rocks across the JNF, along with the lack of well-developed extensional markers, confirm that the fault is located within the Higher Himalayan channel, and not at the channel boundary. The U-Pb zircon rim ages of 33.8 ± 0.8 Ma and 30.7 ± 0.5 Ma obtained from the JNF hanging wall (northern block) and footwall (southern block), respectively, are considered as the ages of peak metamorphism. The hanging wall, which was present at the slow-moving marginal part of the channel during Eocene, eventually lagged behind the relatively faster and warmer central part. As a result, the footwall (southern) block experienced a faster exhumation, resulting in normal-sense movement along the JNF, as documented by sparse extension markers. At 21.4 ± 2.3 Ma (monazite U-Pb age), tourmaline-bearing leucogranite intruded in the JNF hanging wall, rupturing the host. This indicates the passive uplift of the JNF hanging wall (in a brittle domain) as a part of the Higher Himalaya. Hence the JNF originated as an intra-channel discontinuity, and our proposed model predicts the origin of a ‘normal fault’ during crustal channel flow.

The metamorphic pressure–temperature (P–T) conditions across the Main central thrust (MCT) in the Arun area have been investigated. The MCT marks the tectono-metamorphic boundary between the overlying high-grade High Himalaya crystalline sequences (HHCS) and the underlying low-grade Lesser Himalaya sequences (LHS). The metamorphic rocks regionally preserve an inverted Barrovian sequence (i.e., intermediate P/T type metamorphism) devoid of previously reported high-pressure metamorphism. The metamorphic grade increases upwards from 670–740 °C and 6.9–9.4 kbar in the MCT zone and lower HHCS to 760–835 °C and 10.0–11.1 kbar in the middle HHCS. Orthoamphibole gneisses in the middle HHCS yield prograde Barrovian-type metamorphism, such as staurolite inclusions in garnets, showing an intermediate P/T gradient. The differences in the tectonic setting and metamorphic evolution imply that the metamorphic units in the Arun area do not correspond to the other high-pressure units in eastern Himalaya. Zircon and monazite U–Pb ages from kyanite gneiss of the lower HHCS reveal the MCT activity, associated with fluid-present anatexis, at ca. 20–14 Ma. Furthermore, similar K–Ar white mica ages (ca. 13–7 Ma) in the hanging wall and footwall of the MCT could represent the timing of later deformation events in shear zones or cooling, possibly associated with exhumation accompanied by activities on younger, structurally lower thrust faults such as the lower MCT. The similar P–T conditions near the MCT in this area could result from recrystallization during syn-metamorphic thrusting, whereas the middle HHCS away from the MCT preserve the original Barrovian metamorphic sequences related to crustal thickening. This and previous studies imply that different P–T profiles near the MCT according to each transect observed in Nepal could be apparent and the cumulative result of polyphase metamorphism.

Caldera fault zones, identified in many modern and ancient volcanoes, have been the subject of geological and geophysical observations and of analog and numerical modeling. However, the physicochemical processes in fault zones during a caldera collapse are still poorly understood. Here, we present field observations from a caldera fault zone in the Cretaceous Jangsan Caldera, SE Korea. The fault zone is ∼30 m wide and juxtaposes an intracaldera rhyolitic volcanic complex against older dacitic rocks; it consists of a minor fault, a main fault, and a series of fault-related intrusions (rhyolite and tuffisite). The main fault dips 90°–88°NW (vertically to steeply inward) and strikes N30°–40°E. A layer of pseudotachylyte (less than ∼10 cm thick) with some injection veins occurs along the main fault. The pseudotachylyte contains rounded to sub-rounded clasts, commonly displaying fuzzy or embayed boundaries, as well as euhedral feldspar microlites (

The Imjingang belt, which is located between the Nangrim and Gyeonggi Massifs, is divided into the Imjin group in the north and the Samgot unit in the south. The southeastern part of the Imjin group, which is located within South Korea, is called the Jingok unit. The Samgot unit consists of amphibolite, psammitic schist, meta-alkali granite and meta-calc-silicate rock. The amphibolite experienced prograde metamorphism from 648-550 °C/13-11 kbar to 715 °C/11 kbar and was then retrograded to ca. 579-569 °C/6.7-6.3 kbar. The psammitic schist was metamorphosed at ca. 710 °C/11 kbar and then retrograded to ca. 670-660 °C/11-10 kbar. These data indicate that the Samgot unit underwent clockwise prograde metamorphism with peak metamorphism conditions of 715-710 °C/11 kbar, which is confirmed by pseudosection analysis. The results of this and previous studies indicate that the metamorphic grade increases southward from the garnet and staurolite zones (630-500 °C/9-3 kbar) through the kyanite zone (710-665 °C/9 kbar) in the Jingok unit to the Samgot unit (715-710 °C/11 kbar) of the Imjingang belt. This metamorphic pattern indicates that the Imjingang belt underwent regional intermediate-P/T metamorphism. The SHRIMP U-Pb age dating of zircons from the amphibolite and meta-alkali granite yields intrusion ages of ca. 371-361 Ma and 373 Ma, respectively. From the psammitic schist, ages of ca. 401-370 Ma are obtained from the youngest detrital zircons and ages of ca. 251-249 Ma are obtained from the metamorphic zircons. In addition, the SHRIMP U-Pb age dating of titanite from the amphibolite yields a retrograde metamorphic age of ca. 229-214 Ma. The whole-rock chemical composition of the amphibolite plots in the back-arc basin basalt field on the tectonic discrimination diagrams. These data indicate that the Imjingang belt, including the Samgot unit, consists of Devonian sedimentary rocks that were deposited in a back-arc basin and intruded by mafic and felsic igneous rocks at ca. 373-361 Ma. Finally, the Imjingang belt underwent intermediate-P/T metamorphism during the Triassic (251–249 Ma) instead of high-P/T metamorphism, indicating that the Imjingang belt is not the extension of the Dabie-Sulu collision belt but a back-arc basin within the North China Craton that underwent intermediate-P/T metamorphism due to the closure of the back-arc basin (arc-continent collision) during the collision between the North and South China Cratons along the Hongseong-Odesan collision belt within the Gyeonggi Massif.

© the authors.Glacial sedimentary facies are recognised in the Palaeoproterozoic (Orosirian) Bergslagen Group in central Sweden, described previously as post-orogenic conglomerates in the Grythyttan Field. The evidence is provided by the presence of macro boulders in a megaclastic to conglomerate rock formation or diamictite around lake Brunnsjon, south of Grythyttan. Pebble to cobble size conglomerates discordantly overlie a megaclastic rock formation, with facetted clasts resembling flatirons. The sedimentary facies assemblage resembles an ice-front resedimented sequence, previously interpreted as an alluvial fan by the writers. A glacial interpretation is supported by evidence of permafrost and related periglacial structures in coeval, 1895 ± 5 Ma (U–Pb zircon age), metavolcaniclastic rocks in the Bergslagen Group. The association of glacial sedimentary facies, permafrost and banded ironstones in the low-latitudinal Bergslagen Group suggests its similarity to better known ‘Snowball Earth’ deposits from Palaeoproterozoic and particularly Neoproterozoic times.

This article reviews the geology of the Sveconorwegian orogen in south Scandinavia and existing tectonic models for the Mesoproterozoic to Neoproterozoic Sveconorwegian orogeny. It proposes an updated geodynamic scenario of large, hot, long-duration continental collision starting at c. 1065 Ma between proto-Baltica and another plate, presumably Amazonia, in a Rodinia-forming context. An orogenic plateau formed at 1280 Ma as a back-arc Cordillera-style plateau, and then grew further stepwise after 1065 Ma, as a collisional Tibetan-style plateau. Voluminous mantle- and crustal-derived Sveconorwegian magmatism took place in the hinterland in the west of the orogen, mainly: (i) bimodal magmatism at 1280–1145 Ma, overlapping with extensional intramontane basin sedimentation, (ii) the calc-alkaline Sirdal magmatic belt at 1065–1020 Ma, (iii) the hydrous ferroan hornblende-biotite granite (HBG) suite at 985–925 Ma and (iv) the anhydrous ferroan massif-type anorthosite-mangerite-charnockite (AMC) suite at 935–915 Ma. High-alumina orthopyroxene megacrysts in anorthosite imply mafic underplating at 1040 Ma and remelting of the underplates at 930 Ma. Overlapping with magmatism, protracted low-pressure, granulite-facies metamorphism reached twice ultra-high temperature conditions of 0.6 GPa-920 °C at 1030–1005 Ma and 0.4 GPa-920 °C at 930 Ma, respectively. These features imply shallow asthenosphere under the crust. Towards the foreland in the east, metamorphism shows an increasing high-pressure signature eastwards with time, with peak P-T values of 1.15 GPa-850 °C at 1150–1120 Ma in the Bamble-Kongsberg lithotectonic units, 1.5 GPa-740 °C at c. 1050 Ma in the Idefjorden lithotectonic unit, and 1.8 GPa-870 °C at c. 990 Ma in the Eastern Segment under eclogite-facies conditions. These are attributed to retreating delamination of the dense sub-continental lithospheric mantle and growth of the orogenic plateau towards the foreland. After c. 930 Ma, convergence came to a halt, the orogenic plateau collapsed, and 16 km of overburden was removed by extension and erosion.

The granites with I- and S-type affinity in the Variscan segments of the Alpine West-Carpathian edifice belong to the oldest intrusions within the European Variscides. Granites and granodiorites of the West-Carpathian crystalline basement are mostly classified as S-type, whereas tonalities and granodiorites belong to the I-type suite. Both suites probably originated in the volcanic arc setting as product of subduction-related regime in the Galatian superterrane (Broska et al. 2013). The I- and S-type granite bodies were firstly identified in the West-Carpathian Tribeč Core Mountains and the new SHRIMP and CHIME datings recognised their Visean geotectonic overprint. The subduction-related I-type granites show the age span 364-358 Ma followed by the intrusion of the S-type granites dated by SHRIMP on 358 Ma. The bimodal SHRIMP data of a dyke placed within S-type granites show ages 351 Ma and 330 Ma, or primary vs. alteration age. The CHIME age from monazite dating shows 347 Ma because monazite indicate probably early stage of massive granite alteration perhaps during collisional process, younger zircons represents later phase of the event. CHIME dating of newly formed monazite in greisenised S-type granite gives the age 344 Ma. The granite showing strong greisenization (total degradation of feldspars and formation of quartz - white mica assemblages) is dated by SHRIMP on 355 Ma. The greisenised granite contains abundant tourmaline with high dravitic molecule, Sr-rich apatite and common monazite. Abundant tiny stoichiometrically pure apatite grains in this granite indicate their exsolution from feldspars enriched in phosphorus. The S-type granite dyke from the ridge of the Tribeč Mts gives zircon SHRIMP age 355 Ma and CHIME monazite age 342 Ma. The dating results of the Tribeč granites identified: (1) older Upper Devonian/Lower Mississippian subduction-related I-type tonalites (ca. 364-351 Ma), and (2) S-type granites Middle/Upper Mississippian (Visean) intruding in time span 342-330 Ma reflecting probably of the collisional event in the Variscan orogeny. Dual evolution of the Tribeč Mts. Variscan granitic rocks is partly corroborated by Hf isotopes from the dated zircons with εHf(t) = +3.5 ~ –2.4 for the older granites, and εHf(t) = –0.3 ~ –4.9 for the younger ones. The evolution of the I- and S-type granites seems to be rather different from the granite evolution known in the Bohemian Massif and therefore the origin of Variscan hybrid granites from the Western Carpathians we placed on the SW side of Galatian volcanic arc as result of Paleo-Tethys subduction (see Stampfli and Borel, 2002, Stampfli et al. 2013).Acknowledgments: Support from Slovak Research and Development Agency: APVV SK-KR-18-0008, APVV-14-0278/, APVV-18-0107, and VEGA 2/0075/20 are greatly appreciated.

During the amalgamation, tenure and break up of Pangea several oceans played a major tectonic role. Remnants of them now occur mostly along the margins of the Atlantic, Mediterranean, Black and Caspian seas, as well as in the Alpine-Himalayan and adjacent orogens. Of those oceans, three (Iapetus, Tornsquist and Rheic) were closed during the amalgamation of Pangea and another (Neo-Tethys) is the main witness of its break-up.The Paleotethys is the enigmatic ocean that shared an internal position during most of Pangea’s tenure. There is no consensus about its origin, some suggest that opened during the latest stages of Pangea’s amalgamation (Devonian-Carboniferous) whereas others considert it a remnant of the mostly subducted Rheic ocean after Gondwana-Laurussia collision. The Shanderman eclogites, in NW Iran are a potential candidate to represent the Paleotethys ocean. They are metamorphosed oceanic rocks (protolith oceanic tholeiitic basalt with MORB composition). Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation.In this contribution I will show the new petrological, geochemical and geochronological results from this eclogites to shed light on the Paleotethyan problem. The piece of oceanic crust preserved at Shanderman area (Iran) crystallized some time in the mid-Carboniferous (~330 Ma) showing the paleotethys kept expanding during the Gondwana-Laurussia collisions that amalgamated Pangea. Metamorphic ages, suggest that subdution initiated in this segment of the Paleotethys between 310 and 290Ma. We integrate this results into a tectonic reconstruction that shows a major plate reorganization within Pangea during the late Carboniferous and early Permian (320-270 Ma) that questions its role as a supercontinent.

Mylonitic orthogneisses in the Kathmandu area, central Nepal have been investigated using whole-rock and mineral chemistry, Rb-Sr isotopes, and zircon U-Pb age dating. Zircon REE patterns determine...

Background The 238U–230Th disequilibrium dating of the mineral zircon (ZrSiO4) provides an efficient tool for investigating the time scales of Quaternary magmatic processes. In situ mass spectrometric U–Th microanalysis of zircon requires careful calibration and correction of the measured isotope data, particularly for the instrumental fractionation of U and Th isotopes. Findings For the selection of suitable calibration materials for U–Th isotopic analysis using a laser ablation multiple collector inductively coupled plasma mass spectrometer (LA-MCICPMS), we estimated the homogeneity of four reference zircons (91500, TEMORA 2, FC1, and Plešovice) and two zircon working standards (LKZ-1 and BRZ-1) in terms of their 232Th/238U ratios, based on the Pb isotopic compositions measured by a sensitive high-resolution ion microprobe (SHRIMP). The measured LA-MCICPMS 232Th/238U ratios of the zircons were calibrated externally using the SHRIMP 208Pb/206Pb-based average value of the 91500 zircon, 232Th/238U = 0.351 ± 0.035 (error corresponds to 1 standard deviation). The molecular interference-corrected 230Th/232Th ratios of the zircons were calibrated based on the assumption that the Plešovice zircon is in 238U–230Th secular equilibrium. After the calibration and correction, the activity ratios of 230Th/232Th and 238U/232Th for all reference zircons and working standards were plotted on the equiline. Conclusions This study confirms that the 91500 zircon is relatively homogeneous in terms of U/Th ratios (relative standard deviation = ~ 10%) and does not support a recent claim that the Plešovice zircon is not in 238U–230Th radioactive equilibrium. The working standards LKZ-1 and BRZ-1 can be used to check the reliability of U–Th isotopic analyses for Quaternary zircons.

We present data from the Mesozoic Keumkang, Palbong, and Baekhwa granites in Garorim Bay, in the southwestern part of the Gyeonggi massif, South Korea. Using major and trace element concentrations, Sr-Nd-Pb isotopic compositions, and sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages, we aim to constrain the petrogenesis of the granites and explain their origin within a broader regional geological context. SHRIMP U-Pb zircon ages of 232.8 ± 3.2, 175.9 ± 1.2, and 176.8 ± 9.8 Ma were obtained from the Keumkang, Palbong and Baekhwa granites, respectively. The Late Triassic Keumkang granites belong to the shoshonite series and show an overall enrichment in large ion lithophile elements (LILE), a depletion in high field strength elements (HFSE) relative to primitive mantle, compared with neighboring elements in the primitive mantle-normalized incompatible trace element diagram with notable high Ba and Sr contents, and negligible Eu anomalies. The Keumkang granites are typified by highly radiogenic Sr and unradiogenic Nd and Pb isotopic compositions: (87Sr/86Sr)i = 0.70931–0.70959, (143Nd/144Nd)i = 0.511472–0.511484 [(eNd)i =–17.0 to–16.7], and (206Pb/204Pb) = 17.26–17.27. The Middle Jurassic Palbong and Baekhwa granites belong to the medium- to high-K calc-alkaline series, and show LILE enrichment and HFSE depletion similar to the Keumkang granites, but exhibit significant negative anomalies in Ba, Sr, and Eu. Furthermore, they have elevated Y and Yb contents at any given SiO2 content compared with other Jurassic granitoids from the Gyeonggi massif. The Palbong and Baekhwa granites have slightly less radiogenic Sr and more radiogenic Nd and Pb isotopic compositions [(87Sr/86Sr)i = 0.70396–0.70908, (143Nd/144Nd)i = 0.511622–0.511660, (eNd)i =–15.4 to–14.7, (206Pb/204Pb) = 17.56–17.76] relative to the Keumkang granites. The Keumkang granites are considered to have formed in a post-collisional environment following the Permo-Triassic Songrim orogeny that records continent-continent collision between the North and South China blocks, and may have formed by fractional crystallization of metasomatized lithospheric mantle-derived mafic melts. The Palbong and Baekhwa granites may have been produced from a gabbroic assemblage at pressures of less than ~15 kbar, associated with subduction of the paleo-Pacific (Izanagi) plate at the Eurasian continental margin. Elevated eNd(t) values in the granitoids from the southwestern part of the Gyeonggi massif relative to those of the central and northern parts, together with the comparatively shallow depth of origin, imply the presence of an exotic block in the Korean lithosphere.

The depositional and metamorphic ages, and provenances of metasedimentary rocks from the Nam Co Complex in the Son La area, Song Ma Suture Zone, northwestern Vietnam, were investigated in order to reveal the convergent tectonic history between the Indochina and South China cratons. This complex is structurally characterized by an antiformal metamorphic core consisting of two distinct metamorphic zones: inner garnet and outer biotite zones. The U-Pb isotopic dating on detrital zircon from metasandstones of the Nam Co Complex yielded major population (> 50%) around ~850 Ma with minor population scattered between 1.2 to 3.0 Ga. The age spectra as well as the morphologies, internal structures and geochemical features of detrital zircon are accounted for by magmatic activities prevalent at the convergent plate margin during the Neoproterozoic. In contrast, the UTh- Pb isotopic compositions of monazite from a garnet-zone schist defined a common Pb mixing line with the lower intercept age of 234 ± 10 Ma (2σ) reflecting the Indosinian metamorphic event. The U-Pb age distribution pattern of detrital zircon in the Nam Co Complex is compatible with that of the South China craton rather than that of the Indochina craton. In summary, sedimentary protoliths of the Nam Co Complex were deposited in a convergent-related basin along the southwestern margin of the South China craton during the Neoproterozoic, and then was finally amalgamated to the Indochina craton via the southerly subduction of South China craton during the Indosinian orogeny.

The eventual docking of an exotic continental mass over the course of a Wilson cycle is marked by intracontinental sites of prograde metamorphism, contractional deformation, and syn- or post-collisional magmatism. This study shows that inherited premagmatic zircon in subsequently emplaced granitoid rocks provides another line of evidence for the collisional orogeny. Following the continental collision between the North and South China Cratons, Jurassic granitoids intruded widely throughout the central Korean Peninsula in association with the subduction of the Paleo-Pacific plate. The latest Early to Middle Jurassic (177–167 Ma) granitoids occur throughout the cratonic Gyeonggi Massif, whereas Early Jurassic (194–184 Ma) granitoids occur locally along the Okcheon Metamorphic Belt to the southeast of the massif. These two spatiotemporal groups differ profoundly in their age patterns and O-Hf isotopic signatures of inherited zircon. The younger group yields a typically North China-like Archean-Paleoproterozoic (mostly 2.5–1.8 Ga) zircon inheritance. In contrast, inherited zircons from the older group exhibit exclusively Neoproterozoic (ca. 0.9–0.7 Ga) and Paleozoic (ca. 0.4 Ga) cluster along with Archean-Paleoproterozoic populations. The exotic feature of the protolith of the older group is further indicated by significantly lower δ18O (− 0.9 to + 4.9‰) and positive eHf (+ 3 to + 15) values of the Cryogenian zircon cores. The results of zircon analysis demonstrate that South and North China-like terranes were juxtaposed infracrustally along the southeastern margin of the Gyeonggi Massif during the pre-Jurassic collisional orogeny, and then selectively provided major source material to the older and younger Jurassic granitoids, respectively.

We present the SHRIMP U-Pb detrital zircon and K-Ar illite 1M d /1M and 2M 1 ages, suggesting new insight into the Phanerozoic polyphase orogenies preserved in the northeastern Okcheon Belt, Korea since the initial basin formation during Neoproterozoic rifting through several successive contractional orogens. The U-Pb detrital zircon ages from the Early Paleozoic strata of the Taebaeksan Zone suggest a Cambrian maximum deposition age, and are supported by trilobite and conodont biostratigraphy. Although the age spectra from two sedimentary groups, the Yeongwol and Taebaek Groups, show similar continuous distributions from the Late Paleoproterozoic to Early Paleozoic ages, a Grenville-age hiatus (1.3–0.9 Ga) in the continuous stratigraphic sequence from the Taebaek Group suggests the existence of different peripheral clastic sources along rifted continental margin(s). In addition, we present the K-Ar illite 1M d /1M ages of the fault gouges, which confirm fault formation/reactivation during the Late Cretaceous to Early Paleogene (ca. 82–62 Ma) and the Early Miocene (ca. 20–18 Ma). The 2M 1 illite ages, at least those younger than the host rock ages, provide episodes of deformation, metamorphism and hydrothermal effects related to the tectonic events during the Devonian (ca.410 Ma) and Permo-Triassic (ca. 285–240 Ma). These results indicate that the northeastern Okcheon Belt experienced polyphase orogenic events, namely the Okcheon (Middle Paleozoic), Songrim (Late Paleozoic to Early Mesozoic), Daebo (Middle Mesozoic) and Bulguksa (Late Mesozoic to Early Cenozoic) Orogenies, reflecting the Phanerozoic tectonic evolution of the Korean Peninsula along the East Asian continental margin.

This study involves investigations on the Upper Paleoproterozoic iron formation (viz., Seosan iron formation) from the Seosan Group, Gyeonggi Massif of the southwestern Korean Peninsula. It occurs as thin banded layers within meta-arkosic sandstone, formed by alternating processes of chemical (hydrothermal) and detrital depositions under a shallow marine environment. It mainly consists of alternating layers of iron oxides, mostly hematite, and quartz. Minor amounts of magnetite surrounded by muscovite, clinopyroxene and amphibole indicate hydrothermal alteration since its formation. Meta-arkosic sandstone is composed of recrystallized or porphyroclastic quartz and microcline, with small amounts of hematite and pyrite clusters. The Seosan iron formation has high contents of total Fe2O3 and SiO2 with positive Eu anomalies similar to those of other Precambrian banded iron formations, and its formation is clearly related to hydrothermal alteration since its deposition. Detrital zircon SHRIMP U-Pb geochronology data from a meta-arkosic sandstone (SN-1) and an iron formation (SN-2) show mainly two age groups of ca. 2.5 Ga and ca. 1.9–1.75 Ga. This together with intrusion age of the granite gneiss (ca. 1.70–1.65 Ga) clearly indicate that the iron formations were deposited during the Upper Paleoproterozoic. The dominant Paleoproterozoic detrital zircon bimodal age peaks preserved in the Seosan iron formation compare well with those from the South China Craton sedimentary basins, reflecting global tectonic events related to the Columbia supercontinent in East Asia.

The Eastern Pontides Orogenic Belt, one of the best examples of a fossil continental arc in the Alpine-Himalayan system, is characterized by adakitic magmatism during the Early Cenozoic. Popular models correlate the adakitic magmatism to syn- or post-collisional processes occurring after the collision between the Eastern Pontides Orogenic Belt and the Tauride Platform at the end of Late Mesozoic and/or beginning of the Cenozoic. We present new geological, petrological and chronological data from andesites and felsic tuffs exposed in the Bayburt area, in the southern part of the Eastern Pontides Orogenic Belt, and discuss the nature of the transition from adakitic to non-adakitic activities in a continental arc. Major, trace and rare earth element concentrations of both andesites and felsic tuffs clearly suggest that they are related to arc magmatism in a continental arc with adakitic composition. The isotopic compositions are permissive of mixing between a component similar to depleted mantle and a second component that is either mafic lower crust or subducted oceanic crust. 39Ar/40Ar hornblende and U/Pb zircon dating indicate that this adakitic magmatism in the Bayburt area ended by about 47 Ma, and transformed into non-adakitic, granitoid arc magmatism in the area immediately north of Bayburt in the Lutetian (∼46 Ma). Based on our new results in conjunction with available data, we propose that the beginning of northward rollback of a south-directed subducting slab, and simultaneous opening of a slab window related to ridge subduction, triggered both adakitic magmatism for approximately a 10 Myr period between 57.6 and 47 Ma and arc-parallel extension that caused the opening of the Early Cenozoic sedimentary basins. We also suggest that the shallow marine environment, in which Nummulite-bearing sandy limestones accumulated in the Early Cenozoic, was transformed into a saline-lake environment during the pyroclastic activity that produced the studied felsic tuffs at ∼47 Ma.

Elevated heat flow in association with mafic magmatism in an orogenic belt commonly leads to high-temperature, low-pressure (HTLP) metamorphism and the production of granulite-facies assemblages. We studied such a HTLP complex in the vicinity of the Sancheong–Hadong anorthosite-mangerite-charnockite-granite (AMCG) suite, Yeongnam Massif, Korea, in order to constrain the P–T conditions, timing, and duration of metamorphism. This complex primarily consists of massif-type anorthositic-gabbroic bodies emplaced at ∼1.87–1.86 Ga and a series of country rocks comprising orthopyroxene-bearing gneisses as well as anatectic granites and migmatites. Migmatitic gneisses were studied in detail because melt-related features are abundant and well preserved; for example, inclusion-rich peritectic phases such as cordierite or K-feldspar are characteristic for the prograde melt-forming stage, whereas biotite-quartz symplectites mantling garnet or orthopyroxene represent the cooling stage consuming melt. Pseudosection P–T analyses of migmatitic gneisses suggest peak metamorphic conditions of 810–840 °C and 5.9–6.2 kbar, followed by near-isobaric cooling and melt crystallization at ∼780 °C and ∼5.5 kbar. SHRIMP (sensitive high-resolution ion microprobe) U–Th–Pb ages of zircon and monazite from six migmatitic gneisses are in the range of 1870–1854 Ma. The oldest age, recorded only in high Y monazite, suggests that prograde metamorphism commenced at ∼1870 Ma. In contrast, melt crystallization had culminated by 1860–1855 Ma producing widespread leucosomes and anatectic granites. Our results suggest that high thermal gradient (∼40 °C km−1) attending the granulite-facies metamorphism is attributable to coeval, pulse-like emplacement of anorthositic-gabbroic magmas. Moreover, the HTLP metamorphism lasted over a period of ∼15 Ma, indicating a long-lived process corresponding to the late stage of Paleoproterozoic (∼1.95–1.85 Ga) hot orogenesis in the North China Craton.