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The evolution and final closure of the Neo-Tethys Ocean are one of the most important geological events that have occurred on Earth since the Mesozoic. However, the evolution of the Neo-Tethys is not well constrained, in particular whether its opening occurred in the Permian or the Triassic and whether a plume was involved with its opening or not. In this study, we present geochronological and geochemical data for mafic igneous rocks in mélanges along the Yarlung Zangbo suture zone (YZSZ) in southern Tibet to constrain the timing and mechanism of opening the Neo-Tethys Ocean. Based on field observations, the YZSZ mélanges can be divided into three segments. The western (west of Zhongba) and eastern (Sangsang-Renbu) segments are composed of ocean plate stratigraphy representing accretionary complexes that formed during subduction of Neo-Tethyan oceanic lithosphere beneath the southern margin of the Asian continent. Mélanges in the central segment (Zhongba-eastern Saga) typically have a siliciclastic matrix, and represent Tethyan Himalayan strata that were structurally mixed with the southern margin of the Asian continent. Based on our and previously published geochemical data, the mafic rocks in the YZSZ mélanges are ocean island basalt (OIB)-like, with ages in the Late Permian-Middle Triassic, the Middle-Late Jurassic, and the Early Cretaceous, respectively. An OIB-like block with an age of ca. 253 Ma is identified from the Zhongba mélanges in the western segment, and it is the oldest OIB lithology yet identified in the YZSZ mélanges related to the evolution of the Neo-Tethys Ocean. Geochemical features indicate that this OIB-like block is distinct from typical OIBs and would be formed during continental rifting to incipient seafloor spreading. In the framework of plate divergent-convergent coupling systems and based on literature data for early Middle Triassic seamounts, radiolarian cherts, and normal mid-ocean ridge basalt-like oceanic crust, we conclude that opening of the Yarlung Zangbo Neo-Tethys Ocean would mainly occur at ~250–243 Ma in the Early Triassic, not later than the early phase of Middle Triassic. In addition, a mantle plume was not involved in opening the Yarlung Zangbo Neo-Tethys Ocean. On the other hand, we have also identified a suite of ca. 160 Ma OIB-like basaltic sills from the Bainang mélanges in the eastern segment, which is the same age as the OIB lithologies previously reported in the Zhongba mélanges. Based on the sill-like occurrence and absence of plume-related rock associations in this region, the Bainang OIB-like rocks might result from Middle-Late Jurassic continental rifting in northern Gondwana. Magmatism related to this tectonic event is preserved in both the YZSZ mélanges and Himalayan strata, but its tectonic significance requires further investigation. Based on this study of the YZSZ mélanges and the previous studies of YZSZ ophiolites, Gangdese belt igneous rocks, and sedimentary rocks, we have reconstructed the entire Wilson Cycle of the Yarlung Zangbo Neo-Tethys Ocean, mainly involving continental rifting and ocean opening, subduction initiation, ultraslow-spreading ridge-trench conversion, subduction re-initiation, and oceanic closure and initial India-Asia collision for the tectonic emplacement of ophiolites. These processes were associated not only with magmatic flare-ups and lulls in the Gangdese belt but also with two stages of ophiolite obduction. Our data therefore provide new insights into the evolution of the Yarlung Zangbo Neo-Tethys Ocean and related Tethyan geodynamics. [ABSTRACT FROM AUTHOR]

Continental rifts can form when and where continents are stretched. If the driving forces can overcome lithospheric strength, a rift valley forms. Rifts are characterised by faults, sedimentary basins, earthquakes and/or volcanism. With the right set of weakening feedbacks, a rift can evolve to break a continent into conjugate rifted margins such as those found along the Atlantic and Indian Oceans. When, however, strengthening processes overtake weakening, rifting can stall and leave a failed rift, such as the North Sea or the West African Rift. A clear definition of continental break-up is still lacking because the transition from continent to ocean can be complex, with tilted continental blocks and regions of exhumed lithospheric mantle. Rifts and rifted margins not only shape the face of our planet, they also have a clear societal impact, through hazards caused by earthquakes, volcanism, landslides and CO2 release, and through their resources, such as fertile land, hydrocarbons, minerals and geothermal potential. This societal relevance makes an understanding of the many unknown aspects of rift processes as critical as ever. [ABSTRACT FROM AUTHOR]

The Lesvos ophiolite, Greece, was recently identified as an analog to the External Liguride Unit formed at an ocean‐continent‐transition (OCT) setting. To further study the evolutionary history of this body, we analyzed highly siderophile element abundances and Re‐Os isotopic compositions of 14 Lesvos peridotites, in combination with petrology, bulk‐rock major, and trace element geochemistry. Almost all the Lesvos peridotites fall within the field of global OCT and mid‐ocean‐ridge (MOR) peridotites, indicating that these rocks have not experienced subduction‐related processes. The near‐horizontal 187Os/188Os versus Al2O3 trend over a wide range of Al2O3 (0.45–3.66 wt. %) may have been caused by recent melt depletion during rifting and thinning of the Lesvos lithosphere. Combining data from available global ophiolitic peridotites, we find that a large proportion of the more Al‐depleted supra‐subduction‐zone (SSZ) peridotites show lower Os/Ir, higher Pd/Ir and remarkably elevated radiogenic Os relative to other tectonic environments (OCT and MOR). By linking this kind of geochemical evolution to the Wilson Cycle, a complete picture emerges: (a) In the OCT to MOR stages, the extensional rifting environment may lead to mild to moderate melt depletion, followed by, or associated with, infiltration of S‐saturated (high fS2) basaltic magmas; (b) when progressing into the SSZ stage, more extreme degrees of mantle melt depletion may be driven by aqueous fluids in the sub‐arc mantle. During this stage, high‐fO2 slab‐derived fluids and/or S‐undersaturated (low fS2) boninitic magmas may infiltrate the sub‐arc mantle, followed by subsequent S‐saturated forearc basaltic magma infiltration. Plain Language Summary: Establishing the relationship between the geochemical evolution and geodynamic mechanism of the Earth's upper mantle is an important objective of the study of ophiolites. There are two major aims of this study: (a) Using highly siderophile elemental (HSE) and Re‐Os isotopic geochemical tools to evaluate the tectonic setting for the Greek Lesvos peridotites; (b) on the basis of geochemical and isotopic comparisons among available global ophiolitic peridotites from various tectonic settings to reconstruct the Earth's upper mantle evolution. First, we find that although the Lesvos peridotites underwent S‐saturated melt overprinting after primary melt extraction that was related to the Mesozoic Pangea breakup, they did not experience subduction‐related processes. Second, we summarize that supra‐subduction‐zone (SSZ) peridotites in other ophiolites have not only recorded extremely high degrees of melt depletion but also show significantly higher Pd/Ir ratios and more radiogenic 187Os/188Os, compared with ocean‐continent‐transition (OCT) and mid‐ocean‐ridge (MOR) peridotites that formed beneath spreading centers. We believe that episodic infiltrations by S‐saturated and/or undersaturated melts/fluids may be an important driving force for these mantle compositional changes during the Wilson Cycle, which can also cause HSE‐bearing sulfides/alloys to be abnormally enriched, and possibly lead to formation of platinum group elements (PGE)‐rich chromite ore deposits. Key Points: The Lesvos peridotites belong to ocean‐continent‐transition (OCT) mantle tectonites with relatively unfractionated highly siderophile elemental (HSE) patternsThe Lesvos peridotites were formed recently, synchronous with Pangea breakup that led to formation of embryonic Neo‐Tethyan oceanic basinEpisodic infiltration by S‐saturated or undersaturated melts/fluids, dominates the evolution of lithosphere during the Wilson Cycle [ABSTRACT FROM AUTHOR]

Despite its global significance, much of the Wilson Cycle, which infers kinematic inversion from plate divergence to convergence, remains conjectural, in particular for what concerns subduction initiation. We present a high-resolution 3D thermomechanical numerical model of the Wilson Cycle, evolving from continental rifting through breakup and oceanic spreading to convergence and self-consistent subduction initiation. In the models, intra-oceanic subduction initiates off-ridge and is an intrinsically three-dimensional process. Its location is controlled by convergence-induced ridge swelling, and the subduction geometry is controlled by three main factors: (1) the inherited compositional and thermal heterogeneity of the ridge and oceanic lithosphere from rifting and seafloor spreading; (2) the curvature/obliquity of the ridge with respect to the convergence direction and (3) the duration of transition from plate divergence to convergence. The modelled mechanisms are consistent with geological records, for example in the Oman subduction-obduction system, and are undervalued elements of the Wilson Cycle. • Ridge swelling allows near-ridge intraoceanic subduction initiation. • Structural inheritance from the divergent stages of the Wilson Cycle is essential to near-ridge subduction initiation. • Obliquity of the ridge with respect to convergence direction is essential for near-ridge subduction initiation. • Ridge swelling induced near-ridge subduction initiation is compatible with the geological records of the Oman ophiolite. [ABSTRACT FROM AUTHOR]

In the Phanerozoic, plate tectonic processes involve the fragmentation of the continental mass, extension and spreading of oceanic domains, subduction of the oceanic lithosphere and lateral shortening that culminate with continental collision ( i . e . Wilson cycle). Unlike modern orogenic settings and despite the collection of evidence in the geological record, we lack information to identify such a sequence of events in the Precambrian. This is why it is particularly difficult to track plate tectonics back to 2.0 Ga and beyond. In this study, we aim to show that a multidisciplinary approach on a selected set of samples from a given orogeny can be used to place constraints on crustal evolution within a P-T-t-d-X space. We combine field geology, petrological observations, thermodynamic modelling (Theriak-Domino) and radiogenic (U-Pb, Lu-Hf) and stable isotopes (δ 18 O) to quantify the duration of the different steps of a Wilson cycle. For the purpose of this study, we focus on the Proterozoic Nagssugtoqidian Orogenic Belt (NOB), in the Tasiilaq area, South-East Greenland. Our study reveals that the Nagssugtoqidian Orogen was the result of a complete three stages juvenile crust production (X juv ) – recycling/reworking sequence: (I) During the 2.60–2.95 Ga period, the Neoarchean Skjoldungen Orogen remobilised basement lithologies formed at T DM 2.91 Ga with progressive increase of the discharge of reworked material (X juv from 75% to 50%; δ 18 O: 4–8.5‰). (II) After a period of crustal stabilization (2.35–2.60 Ga), discrete juvenile material inputs (δ 18 O: 5–6‰) at T DM 2.35 Ga argue for the formation of an oceanic lithosphere and seafloor spreading over a period of ~ 0.2 Ga (X juv from < 25% to 70%). Lateral shortening is set to have started at ca . 2.05 Ga with the accretion of volcanic/magmatic arcs ( i . e . Ammassalik Intrusive Complex) and by subduction of small oceanic domains (M1: 520 ± 60 °C at 6.6 ± 1.4 kbar). (III) Continental collision between the North Atlantic Craton and the Rae Craton occurred at 1.84–1.89 Ga. Crustal thickening of ~ 25 km was accompanied by regional metamorphism M2 (690 ± 20 °C at 6.25 ± 0.25 kbar) and remobilization of pre-existing supracrustal lithologies (X juv ~ 40%; δ 18 O: 5–10.5‰). Rates and durations obtained for seafloor spreading (175 ± 25 Ma), subduction (125 ± 75 Ma) and continental collision ( ca . 60 Ma) are similar to those observed in Phanerozoic Wilson Cycle but differ from what was estimated for Archean terrains. Therefore, timespans of the different steps of a Wilson cycle might have progressively changed over time as a response to the progressive cratonization of the lithosphere. [ABSTRACT FROM AUTHOR]

Worldwide comparison of lithospheric investigation results achieved from projects of COCORP, BIRPS, DEKORP, LITHOPROBE, ICDP, ECORS and SINOPROBE enables us to expand the classical Wilson cycle, which mainly describes evolution of ocean plates, into a complete and detailed cycle that describes generation, development and evolution of both ocean and continent plates. The expanded Wilson cycle presented in this paper introduces the evolution sequences of continental lithospheric processes by adding into the classical Wilson cycle with ocean-continent transition, continental collision and accretion, as well as continental rifting and splitting in details. These mentioned continental lithospheric processes have been presented by the author in a series of recent review papers in detail, and their summary and further deduction is presented in this paper. [ABSTRACT FROM AUTHOR]

Keywords: Atlantic; Iceland; Continental breakup; Plate tectonics; Icelandic-type crust; SDRs; Geochemistry; Geophysics; North Atlantic; Wilson Cycle; Structural inheritance; Reactivation; Rifting; Magmatism; Lithosphere; Slow-spreading ridges; Small-scale mantle convection; Ridge segmentation; Mantle melting anomaly; Mantle gradient EN Atlantic Iceland Continental breakup Plate tectonics Icelandic-type crust SDRs Geochemistry Geophysics North Atlantic Wilson Cycle Structural inheritance Reactivation Rifting Magmatism Lithosphere Slow-spreading ridges Small-scale mantle convection Ridge segmentation Mantle melting anomaly Mantle gradient N.PAG N.PAG 1 07/29/20 20200701 NES 200701 The North Atlantic Realm, defined as the region of Pangaea breakup north of the Charlie-Gibbs Fracture Zone, is the type example locality for the Wilson Cycle. These questions related to the trans-oceanic Greenland-Iceland-Faroe Ridge (GIFR), the composition of the 30-40 km thick Icelandic-type crust under it, the high-velocity lower crust beneath seaward-dipping reflectors (SDRs) at the ocean margins and the contrasting tectonic histories of the oceans north and south of the GIFR. The complex, unstable and evolving tectonics that has characterized both continental and oceanic lithosphere in the North Atlantic Realm in the past, and is ongoing to the present day, manifests itself to a particularly extreme degree on the GIFR. It suggests that Icelandic-type lower crust beneath the GIFR is not gabbroic as often assumed but instead comprises magma-inflated, hyper-extended, ductile mid- and lower continental crust, whereas the upper crust comprises a cap of basaltic lavas and intrusions. [Extracted from the article]

The North Atlantic, extending from the Charlie Gibbs Fracture Zone to the north Norway-Greenland-Svalbard margins, is regarded as both a classic case of structural inheritance and an exemplar for the Wilson-cycle concept. This paper examines different aspects of structural inheritance in the Circum-North Atlantic region: 1) as a function of rejuvenation from lithospheric to crustal scales, and 2) in terms of sequential rifting and opening of the ocean and its margins, including a series of failed rift systems. We summarise and evaluate the role of fundamental lithospheric structures such as mantle fabric and composition, lower crustal inhomogeneities, orogenic belts, and major strike-slip faults during breakup. We relate these to the development and shaping of the NE Atlantic rifted margins, localisation of magmatism, and microcontinent release. We show that, although inheritance is common on multiple scales, the Wilson Cycle is at best an imperfect model for the Circum-North Atlantic region. Observations from the NE Atlantic suggest depth dependency in inheritance (surface, crust, mantle) with selective rejuvenation depending on time-scales, stress field orientations and thermal regime. Specifically, post-Caledonian reactivation to form the North Atlantic rift systems essentially followed pre-existing orogenic crustal structures, while eventual breakup reflected a change in stress field and exploitation of a deeper-seated, lithospheric-scale shear fabrics. We infer that, although collapse of an orogenic belt and eventual transition to a new ocean does occur, it is by no means inevitable. [ABSTRACT FROM AUTHOR]