Wilson Cycle Research Articles

Ocean-continent subduction cannot be initiated without preceding intra-oceanic subduction!

The formation of new subduction zones is a key element of plate tectonics and the Wilson cycle, and many different controlling mechanisms have been proposed to initiate subduction. Here, we provide a brief overview of the known scenarios of subduction initiation in intra-oceanic and ocean-continent tectonic settings. Intra-oceanic subduction is most commonly associated with mechanical heterogeneities within the oceanic lithosphere, such as pre-existing fracture zones, spreading ridges, and transform faults. Numerous and well-recognized examples of new active subduction zones formed in intra-oceanic environments during the Cenozoic, suggesting that the initiation of ocean-ocean subduction must be a routine process that occurs “easily and frequently” in the mode of plate tectonics currently operating on Earth. On the contrary, the most traditional mechanisms for the establishment of classic self-sustaining ocean-continent subduction—passive margin collapse and subduction transference—are surprisingly rare in observations and difficult to reproduce in numerical models. Two alternative scenarios—polarity reversal and lateral propagation-induced subduction initiation—are in contrast much better documented in nature and experimentally. However, switching of subduction polarity due to arc-continent collision and lateral transmission of subducting plate boundaries are both inextricably linked to pre-existing intra-oceanic convergence. We, therefore, conclude that the onset of classic ocean-continent subduction zones is possible only through the transition from a former intra-oceanic subduction system. This transition is likely facilitated by the ductile damage accumulation and stress concentration across the aging continental margin. From this perspective, the future closure of the Atlantic Ocean can be viewed as an archetypal example of the role of transitional process between intra-oceanic subduction (Lesser Antilles) and the development of a new subduction zone at a passive continental margin (eastern North America).

Protolith and metamorphic age of the Sieggraben Eclogites: Implications for the Permian to Cretaceous Wilson cycle in the Austroalpine unit

The Austroalpine eclogite-bearing Sieggraben Complex, exposed at the eastern margin of the Eastern Alps, is considered to represent a subducted and then exhumed fragment of the continental rift, which led to the formation of the Meliata oceanic basin. Combined zircon U-Pb dating, whole rock geochemistry and Hf isotope analysis of the Sieggraben Complex revealed that the eclogite sample shows a protolith age of 242.3 ± 2.6 Ma (Middle Triassic) and displays tholeiitic basalt/N-MORB geochemical characteristics. Associated ultramafic rocks as part of oceanic or subcontinental mantle lithosphere suggest a depleted mantle source and a deep subduction environment. Two zircon grains of eclogites with low Th/U ratios yield ages of 113 ± 2 Ma and 86 ± 4 Ma and represent the approximate age of eclogite metamorphism during Cretaceous. A trondhjemite dike cutting through eclogite gives a crystallization age of 82.19 ± 0.4 Ma and formed by partial melting during decompression. The host metasedimentary rocks are interpreted as old continental crust close to the margin of the Meliata basin were affected by Permian migmatitic metamorphism. The results of this study combined with previous results from the Sieggraben Complex are used to present an updated model for the tectonic evolution of the distal Austroalpine unit associated with the oceanic Meliata relics The Austroalpine Sieggraben Complex represents a location on the distal continental margin during Permian rifting. This piece of continental crust of an inferred paleotectonic position adjacent to the Meliata oceanic lithosphere subducted during Early Cretaceous times to mantle depth. The subducted continental crust was then exhumed incorporating even ultramafic mantle rocks. During exhumation and decompression of mafic rocks, partial melting took place forming the trondhjemite dike in Late Cretaceous times. • A Middle Triassic ptotolith age was found for eclogites of the Sieggraben Complex. • A Cretaceous-aged trondhjemite dike report formed by decompressional melting after eclogite metamorphism. • Paragneiss hosts a Panafrican detrital zircon memory and was affected by Permian migmatization. • A new tectonic model for the distal Austroalpine unit relates with the Meliata Ocean in a Wilson cycle.

Paleozoic to Mesozoic magmatism in North Qaidam, Qinghai Province, NW China: Implications for tectonic evolution

The North Qaidam (NQ) has records Paleozoic–Mesozoic magmatism and metamorphism preseving evidence for the tectonic evolution of this orogen, However, the precise timing and mechanism of subduction, and the collisional and post-collision history of the NQ and neighboring orogens during the Paleozoic–Mesozoic are not well understood. We conducted an integrated investigation involving detailed field observations, petrology, zircon U–Pb geochronology, Lu–Hf isotopes, and whole-rock geochemical data from volcanic rocks from the Maoniushan Formation and intermediate-acid intrusive rocks in the Dadakenwulashan, Habuqige, and Kongquegou areas of NW China to determine their ages and petrogenesis. We also employed a compilation of recently published high-quality data in our assessment, and provide a better understanding of the regional tectonic evolution. Devonian volcanic rock and Triassic intrusive rock samples yielded zircon U–Pb ages of 407 Ma, 378 Ma, 377 Ma, 241 Ma, 232 Ma, and 230 Ma. Using the existing regional data and spatiotemporal distribution of magmatism, possible models to explain the tectonic evolution of the NQ from the Paleozoic to the Mesozoic, which records two Wilson cycles within a branch of the Tethyan orogenic system, were proposed. (1) The transition from compressional to extensional tectonic regimes may have occurred at ∼ 410 Ma in the NQ. (2) Twice rapid crust uplift and erosion formation of the Maoniushan Formation molasse with a volcanic interlayer have been recognized, which is a response to the tectonic regime of slab break-off (410 Ma–390 Ma) and lithosphere delamination (380 Ma–360 Ma), respectively. (3) The tectonic evolution of the NQ was a remote response to subduction of the Paleo-Tethys Ocean during the Mesozoic.

Tectonic evolution of the Qinling Orogenic Belt, Central China – new evidence from geochemical, zircon (U-pb) geochronology and HF isotopes

The paper deals with a review of tectonic evolution in different regions of China with the help of different techniques and models. Tectonic evolution shows that in the shallow layers of China the structural impact is not solid, and huge structural zones are deficient within the list and incline zones where the principal wretchedness and delicate slant zones framed. The Qinling Orogenic Belt (QOB) situated between the North China Craton (NCC) and the Yangtze Craton (YZC) is made from the Northern Qinling Belt (NQB) and the Southern Qinling Belt (SQB). The Hf isotopic creations of zircons from the different rocks recommend that the NQB most likely created on the cellar of the southern NCC. The stones in the SQB show zircon age spectra and Hf-isotope structures like those in the northern YZC, recommending a nearby proclivity. We thusly decipher the SQB to have created on the cellar of the northern YZC. Incorporating the new information in this investigation with those from past works, we propose another structural model for the development and advancement of the QOB during late Mesoproterozoic to early Paleozoic including the accompanying significant occasions: (1) Late Mesoproterozoic to early Neoproterozoic (Grenvillian) toward the north subduction of the Songshugou Ocean; Early-center Neoproterozoic (870-800 Ma) bidirectional subduction and impact; Middle Neoproterozoic (∼800-710 Ma) post-crash expansion; Middle-late Neoproterozoic (710-600 Ma) inside plate augmentation; Late Neoproterozoic-early Paleozoic (600-520 Ma) opening of the Shangdan Ocean; and Early Paleozoic (520-420 Ma) subduction-crash. We accordingly follow in any event two unmistakable Wilson cycles in the QOB.

On the Role of Rheological Memory for Convection‐Driven Plate Reorganizations

AbstractUnderstanding the temporal variability of plate tectonics is key to unraveling how mantle convection transports heat, and one critical factor for the formation and evolution of plate boundaries is rheological “memory,” that is, the persistence of weak zones. Here, we analyze the impact of such damage memory in global, oceanic‐lithosphere‐only models of visco‐plastic mantle convection. Self‐consistently‐formed weak zones are found to be reactivated in distinct ways, and convection preferentially selects such damaged zones for new plate boundaries. Reactivation of damage zones increases the frequency of plate reorganizations, and hence reduces the dominant periods of surface heat loss. The inheritance of distributed lithospheric damage thus dominates global surface dynamics over any local boundary stabilizing effects of weakening. In nature, progressive generation of weak zones may thus counteract and perhaps overcome any effects of reduced convective vigor throughout planetary cooling, with implications for the frequency of orogeny and convective transport throughout Wilson cycles.

Longitudinal expansion fitness of brachiopod genera controlled by the Wilson cycle

The brachiopods constitute one of the major components of the marine metazoan fossil record. On the other hand their apparent decline in importance in forming benthic communities through the Phanerozoic is one of the most striking macroevolutionary and macroecological patterns. Here we analyzed changes in average latitudinal and longitudinal ranges – indices for success of spatial expansion of brachiopod genera – during post-Cambrian Phanerozoic, and compared their fluctuation and scaling behaviour to the changes in continental fragmentation. The results revealed that latitudinal ranges on the longest time scales were highly constrained, while longitudinal ranges shown persistent decrease. The scale-by-scale correlation analysis of Haar fluctuations revealed that there is positive functional dependence of longitudinal ranges at the longest time scales with continental fragmentation. Moreover the ratio of average longitudinal to latitudinal ranges was positively correlated to the continental fragmentation at all time scales. The long term minima in longitudinal ranges and the least elongated shapes in E-W direction of geographic ranges were found during the maximal amalgamation of the Pangaea during Triassic and Jurassic. The failure for brachiopods to regain the dominance in marine biosphere after P-Tr extinction should be related to the tectonic restrictions on their longitudinal ranges during the maximally supercontinental conditions of the planet. Therefore, the pattern exemplified by brachiopods shows that the spatial expansion success (fitness) of a major clade at an eon time scale could be a direct consequence of the multi-scale tectonic reconfigurations.

An Ordovician ophiolitic complex in West Junggar, NW China: Implications for subduction initiation and oceanic arc evolution of the Paleo-Asian Ocean

As a key step of the Wilson cycle, subduction initiation is regarded as a start hallmark of the ocean-continent transformation. However, the crust-mantle interaction and crustal growth processes related to subduction initiation remain enigmatic. Here we report a newly recognized complete magmatic sequence containing three rock assemblages in the Hongguleleng ophiolitic complex (HOC) in West Junggar, NW China. Group I contains typical Mid-Oceanic Ridge (MOR)-derived rocks including abyssal peridotite, gabbro, plagiogranite, and basalt. Group II consists of forearc basalt (FAB) and boninitic gabbro and has a high continentality index (CI > 130), similar to the rock assemblages in the Mariana proto-arc. Group III composed of calc-alkaline andesite and arc tholeiite basaltic andesite exhibits middle CI values (50 < CI < 100), suggesting that they form in a transitional oceanic arc. Zircon U-Pb ages show that the N-MORB gabbro and plagiogranite samples are emplaced at 483–481 Ma, and the boninitic rocks, calc-alkaline andesites, and arc tholeiite basaltic andesites have the crystalline ages of 472–467 Ma, 456 Ma, and 452 Ma, respectively. An increasing trend of Ba/Th and V/Ti ratios from Group I to Group II suggests the addition of aqueous fluid and elevated oxidation in the mantle source during subduction initiation. However, it exhibits an uptrend in Th/Nb and (La/Sm)cn ratios but a downtrend in Ba/Th ratios from Group II to Group III, indicating a significant contribution of slab-derived sediments to the mantle during oceanic arc evolution. Combined with regional data, we consider that there developed an E-W–trending sub-ocean basin of the Paleo-Asian Ocean spanning northern West Junggar and East Kazakhstan during the Middle Cambrian–Ordovician. The MOR-type and forearc ophiolites in northern West Junggar as well as our results suggest that the ocean happened mid-ocean ridge spreading at ca. 512–478 Ma and subduction initiation at ca. 476–467 Ma, and developed a transitional oceanic arc at ca. 456–452 Ma.

Metamorphic diamond from the northeastern margin of Gondwana: Paradigm shifting implications for one of Earth's largest orogens.

We describe the first occurrence of diamond-facies ultrahigh pressure metamorphism along the Gondwana-Pacific margin of the Terra Australis Orogen. Metamorphic garnet grains from Ordovician metasediments along the Clarke River Fault in northeastern Queensland contain inclusions of diamond and quartz after coesite, as well as exsolution lamellae of rutile, apatite, amphibole, and silica. These features constrain minimum pressure-temperature conditions to >3.5 gigapascals and ~860°C, although peak pressure conditions may have exceeded 5 gigapascals. On the basis of these data, we interpret the Clarke River Fault to represent a Paleozoic suture zone and at least parts of the Terra Australis Orogen to have formed through classic Wilson cycle processes. The growth of the Terra Australis Orogen during the Paleozoic is largely attributed to accretionary style tectonics. These previously unknown findings indicate that the Terra Australis Orogen was not just a simple accretionary style orogen but rather a complex system with multiple tectonic styles operating in tandem including collisional tectonics.

Ocean–continent transition of the northeastern Paleotethys during the Triassic: Constraints from Triassic sedimentary successions across the Qinling Orogen, central China

To decode the northeastern Paleotethys ocean–continent transition process, a geological profile is constructed across the southern Ordos Basin, central Qinling Orogen, and northern Sichuan Basin. Along the transect, abundant detrital zircon age data, sandstone petrological compositions, and paleocurrent directions taken from the Triassic sedimentary successions across the Qinling Orogen reveal systematic tectonic variations in ocean–continent transition processes. The Early Triassic sedimentary succession was deposited in a foreland basin which was part of the northeastern Paleotethys Ocean and received recycled North Qinling Orogen detritus in a collisional tectonic setting. This evidence implies that the North Qinling region was undergoing intense erosion during the subduction of the Paleotethys oceanic crust. In the Middle Triassic, continued subduction brought the foreland basin in the Huicheng region to an end, and the depocenter migrated westward to the West Qinling and Songpan-Ganzi regions under a convergent collisional tectonic setting. In the Late Triassic, the West Qinling and Songpan-Ganzi regions were still receiving sediment, while the North and South China Blocks entered the continental collision process. The detrital material in the southern Ordos Upper Triassic Yanchang Formation continued to be eroded from the North China Block in a collisional tectonic setting. The sediments in the northern Sichuan Basin were mainly sourced from the South China Block and South Qinling area in a collisional setting, and the Songpan-Ganzi region continued to converge and eventually evolved into a collisional tectonic setting. The Paleotethys ocean–continent transition represents a complete second half of the Wilson cycle, and mountain building preconditioned the paleotopography and influenced the basin formation.

Geochronological record of Cadomian exterior orogen reworking in bi-modal igneous protoliths of the Cabo Ortegal Allochthon (NW Iberia): the Cambrian onset of the Palaeozoic plate-tectonic cycle

ABSTRACT New geochemical data and radiometric ages of the protoliths of variably reworked metamafic (granulites and gabbros) and felsic rocks (orthogneisses) from the Cabo Ortegal allochthonous Complex are presented. Their igneous precursors were emplaced in ensialic environments and exhibit geochemical signatures transitional to tholeiitic character, probably originating in arc settings (with continental and oceanic components and minor crustal recycling). The new geochronological results (encompassing the Miaolingian and Furongian epochs of the Cambrian) link the aforementioned scenarios to a Cadomian magmatic arc. The 505Ma protoliths of calc-alkaline orthogneisses and mafic granulites would be the oldest in the sequence of intrusion events. The latter and the 498–486Ma protoliths of gabbros (emplaced in sedimentary host sequences later transformed into Variscan high-pressure and intermediate-pressure gneisses) can be considered as snapshots of the ongoing continental arc evolution. The 498–486Ma gabbro intrusives of these gneisses, together with the 505–503Ma orthogneisses, are ascribable to palaeo-geographically separate scenarios before the Variscan amalgamation of their country rocks. They would expand the initiation of rifting of the Gondwana continental margin to the Miaolingian Cambrian epoch. It is inferred that the Cadomian continental-arc (active at least since 750Ma) experienced in the 510–460Ma interval the consequences of a vanishing active subduction. Certain domains flanking the arc underwent forearc sedimentation and deformation, whereas others were affected by an increasing extension (rifting) and/or back-arc basin formation. The latter marked the initiation of the beginning of a Wilson Cycle, which ended in the late Palaeozoicwith the formation of the Variscan interior orogenic belt.

Evolution of the Sumdo Paleo-Tethyan Ocean: Constraints from Permian Luobadui Formation in Lhasa terrane, South Tibet

Reconstructing the evolution of the Sumdo Paleo-Tethyan Ocean (SPTO) is important for understanding the transition from the Paleo-Tethyan system to the Neo-Tethyan system. The existence of the SPTO is inferred from the presence of an (ultra-)high pressure metamorphic belt and dismembered ophiolite bodies that separate the southern Lhasa and northern Lhasa terrane. This paper presents new geochronological and geochemical data for the Luobadui Formation in the Lhasa terrane. The geochemical difference between the Lower Luobadui volcanics and the Upper Luobadui volcanics suggests a source transition from a depleted mantle source to an enriched mantle source, which indicates continental-arc subduction. The integrated geological evidence suggests that the SPTO initially opened during the late Carboniferous (ca. 304 Ma), as verified by the earliest record of oceanic crust. Our new data for the Luobadui volcanic rocks, together with the metamorphic and sedimentary records, support northward subduction of the SPTO lithosphere beneath North Lhasa, most likely starting during the Early Permian (ca. 275 Ma) and lasting until the Middle Permian (ca. 260 Ma). The main closure of the SPTO occurred during Middle–Late Triassic (ca. 240–220 Ma), as recorded by medium-pressure metamorphism and syn-collisional magmatism. The Wilson cycle of the SPTO is hereby reconstructed, providing significant insights into the amalgamation of the Tibetan Plateau.

The generation and evolution of the Archean continental crust: The granitoid story in southeastern Brazil

The Archean Eon was a time of geodynamic changes. Direct evidence of these transitions come from igneous/metaigneous rocks, which dominate cratonic segments worldwide. New data for granitoids from an Archean basement inlier related to the Southern São Francisco Craton (SSFC), are integrated with geochronological, isotopic and geochemical data on Archean granitoids from the SSFC. The rocks are divided into three main geochemical groups with different ages: (1) TTG (3.02–2.77 Ga); (2) medium- to high-K granitoids (2.85–2.72 Ga); and (3) A-type granites (2.7–2.6 Ga). The juvenile to chondritic (Hf-Nd isotopes) TTG were divided into two sub-groups, TTG 1 (low-HREE) and 2 (high-HREE), derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts. The compositional diversity within the TTG is attributed to different pressures during partial melting, supported by a positive correlation of Dy/Yb and Sr/Zr, and batch melting calculations. The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs, indicating the presence of subduction processes concomitant with TTG emplacement. From ∼2.85 Ga to 2.70 Ga, the dominant rocks were K-rich granitoids. These are modeled as crustal melts of TTG, during regional metamorphism indicative of crustal thickening. Their compositional diversity is linked to: (i) differences in source composition; (ii) distinct melt fractions during partial melting; and (iii) different residual mineralogies reflecting varying P–T conditions. Post-collisional (∼2.7–2.6 Ga) A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms, and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle. The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening, regional metamorphism and crustal melting, and post-collisional extension, similar to that seen in younger Wilson Cycles. It is compelling evidence that plate tectonics was active in this segment of Brazil from ∼3 Ga.

The Proto- and Palaeo-Tethys tectonic evolution in Southeastern Tibetan Plateau: Constraints from detrital zircon dating of metasedimentary rocks from the Diancang Shan complex

ABSTRACT Metamorphic rocks from the Diancang Shan (DCS) complex along the Ailao Shan-Red River belt between the South China plate and Simao-Indochina block are studied in this contribution to constrain the Proto- to Palaeo-Tethys tectonic evolution of the eastern Tethys domain. LA-ICP-MS zircon U-Pb geochronological dating is conducted in this study on the metasedimentary rocks (garnet-biotite-plagioclase gneisses, biotite-quartz schists and phyllonites) from different stratigraphical horizons (Proterozoic and Triassic) of the DCS complex. The analyses yielded three major age peaks at ca. 248 Ma, ca. 441 Ma, ca. 1000–900 Ma and one subordinate age peak at ca. 828 Ma. The youngest ages for the samples help to constrain the maximum ages of deposition of the complex at Early Carboniferous and Late Triassic, respectively. The existence of the diagnostic age peak at ca. 440 Ma and the euhedral-subhedral morphology of the detrital zircons in the Palaeozoic and Mesozoic strata may indicate that there were early Palaeozoic magmatic activities along the eastern margin of the Simao-Indochina block. At the meantime, the age peak at ca. 440 Ma was never reported in the early Palaeozoic strata from the western margin of the South China plate, which supports the existence of an early Palaeozoic rift zone, i.e., the Proto-Tethys Jinsha Jiang-Ailao Shan-Song Ma rift zone, being consistent with geochemical discriminations. Furthermore, we conclude, from the significant difference between detrital zircon age data of Silurian to Devonian sedimentary rocks from the Simao-Indochina block and South China plate, the opening of the Palaeo-Tethys ocean since Early Carboniferous, the absence of evidence for the Palaeozoic orogeny, and the successive sedimentation from the Cambrian to Triassic along the western margin of the South China plate, that the Proto-Tethys rifting and subsequent Palaeo-Tethys ocean evolution along the Jinsha Jiang-Ailao Shan-Song Ma zone formed actually a complete ‘Wilson Cycle’ from early Palaeozoic to the Late Triassic.

Multi-proxy evidence for subduction of the Neoproterozoic Adamastor Ocean and Wilson cycle tectonics in the South Atlantic Brasiliano Orogenic System of Western Gondwana

Field, petrographic, geophysical, geochronological, elemental and isotopic data support the identification of distinct components of a Wilson cycle (rift-drift-subduction-collision-collapse) in the South Atlantic Brasiliano Orogenic System (Mantiqueira Province). The main lines of evidence are: 1) Tonian-Cryogenian ophiolite complexes; 2) Hundreds of Hf-Nd-Sr isotope determinations indicating a temporal trend of juvenile to mixed Tonian-Cryogenian-Ediacaran igneous rocks comprising expanded calc-alkaline, magnesian, metaluminous gabbro-tonalite-granodiorite-granite/basalt-dacite-andesite-rhyolite series, developed in island arcs and in continental-margin (Andean-type) arcs; 3) Cratonic-sourced conglomerate-diamictite-sandstone-pelite-carbonate successions deposited in Tonian-Cryogenian rift-passive margins fringing the paleocontinental borders, covered by orogenic basins with contrasting provenance from the arc systems; 4) Paired negative-positive Bouguer anomalies typical of suture zones with ophiolite-bearing accretionary prisms in the lower plate and arc systems in the upper plate; 5) Paired HP/HTmetamorphic belts associated with Ediacaran suture zones and retro-eclogites associated with Tonian subduction. Proposed intracontinental models for this region, both original and revisited, are based on the visual interpretation of restricted space for an oceanic realm and rely on calculations using presumed spreading and subduction rates. However, those do not account for a number of pre-, syn- and post-collisional modifications of the original paleogeography and for plate configurations over a curved planetary surface, with asynchroneity of extensional, accretionary and collisional events over thousands-of-km long orogenic fronts. Scissor-shaped oceanic basins are the rule rather than the exception, with connection of (i) an aulacogen to (ii) a partially enclosed gulf that is, in turn, connected to (iii) an open ocean with complex subduction systems. This configuration leads, after closure of the oceanic realm, to the gradation found in the South Atlantic Brasiliano Orogenic System, with (i) an inverted rift (Paramirim) connected to (ii) a confined orogen with a pre-collisional continental-margin Andean-type arc (Araçuaí), connected, in turn, to (iii) complex accretionary-collisional orogens (Ribeira and Dom Feliciano) with accreted juvenile pre-collisional island arc terranes. This arrangement characterizes, thus, a prime example of a typical subduction-collision orogenic system. The various lines of evidence from distinct fields coherently indicate a full Wilson Cycle with generation and consumption of the Adamastor oceanic lithosphere, followed by continental collisions, ultimately giving birth to the Gondwana paleocontinent.

A hyperextension assemblage, imbricated in Archean–Paleoproterozoic crust, at the base of the Kalak Nappe Complex in the northern Scandinavian Caledonides

The break-up of continents generates dyke swarms, basins and hyperextension assemblages. Once incorporated into new orogens, the latter can provide crucial information about origins and tectonic processes. The Nålfjell Complex in the Caledonian Skillefjord Nappe of northern Norway has many of the characteristics of a hyperextension assemblage, notably the presence of solitary serpentinite bodies exposed by the exhumation of serpentinized mantle and now embedded in schists, amphibolites, mylonites, marbles and felsic gneisses. The Skillefjord Nappe is a lithologically diverse, imbricated and discontinuous allochthon. It consists of felsic gneisses and dykes dated by zircon U–Pb to c. 3100, 2940, 2830, 2510 and 1800–1750 Ma. These rocks yield titanite ages of 2810–2700, 1750, 1660–1590 and 430–420 Ma. Metagabbro intruded at 1995 Ma. The ages and evolution of the Skillefjord Nappe are distinct from those of the structurally higher Svaertholt Terrane (&gt;1030 Ma sediments deformed and intruded by granite at 980–950 Ma) and the Sørøy Terrane (characterized by a multi-stage 900–500 Ma evolution). The assembly of these disparate elements was completed at 420 Ma. The timing of hyperextension is uncertain. The serpentinites have a primitive Pb isotopic composition indicating old depleted mantle lithosphere. Extensional processes from the Paleoproterozoic to Ediacaran are considered. Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/cc/caledonian-wilson-cycle

Oceanic isostasy as a trigger for the rift-to-drift transition

AbstractA long-standing missing link in our understanding of the Wilson cycle is how a continental rift transitions to seafloor spreading. The variety of rift structures and transition timings at rift margins do not easily lend themselves to some specific degree of strain and/or magmatism as the tipping point. Invariably ignored in the process, but a potential key to the conundrum, is the isostatic response that comes with ocean loading during and after inundation. Ocean mass redistribution on variably subsiding crust drives flow in the asthenosphere in much the same way a growing icecap drives a corresponding outward mantle flow. This flow alters mantle tractions of the rift system, with disappearance of basal resistance, and even adds a push to the rifting process. Evidence for ocean inundation facilitating self-sustained seafloor spreading is observed in the Atlantic, around the Afar triple junction, and elsewhere, indicating that the ocean should not be considered simply incidental to the creation of oceanic basins.

Archean versus Phanerozoic oceanic crust formation and tectonics: Ophiolites through time

• Global compilation of the salient features of ophiolites. • Lithological differences between Archean and Proterozoic/Phanerozoic ophiolites. • Subduction-dominant Archean oceanic crust with accretionary cycle plate tectonics. • For Proterozoic and Phanerozoic a combination of both accretionary cycle and Wilson cycles. A global compilation of structural, lithological, and geochemical data on a selection of Archean, Proterozoic and Phanerozoic magmatic complexes, interpreted as ophiolites, is presented. Ophiolites, based on Phanerozoic examples, can be classified into subduction-related and subduction unrelated categories. These categories can be further subdivided into several subtypes depending on the proximity to subduction zones, and on sequential development from rifting – drifting to seafloor spreading for the subduction-unrelated category. From bottom to top ophiolites exhibit a magmatic sequence of ultramafic rocks (upper mantle units), gabbros (layered and isotropic), basaltic dikes and lavas, as well as boninites and felsic dikes and lavas in the subduction-related types. Archean greenstone belts show large variations in their construction, but Eoarchean examples display identical structure and lithology to the Phanerozoic ophiolites, attesting to the operation of seafloor spreading and subduction zone processes in the early Earth's history. Lithological differences between the Archean and Proterozoic/Phanerozoic ophiolites are demonstrated in the common occurrence of komatiites and felsic rocks, and scarcity of sheeted dike complexes in the former, compared to the opposite situation in those ophiolites that are younger than ca. 2 Ga. Geochemically there is a concomitant decrease in the content of incompatible elements (e.g., Sr, Zr, Y, Nb) and an increase in the content of compatible elements (e.g., Mg, Cr, Ni). In terms of tectonic environment analyzes, the Archean ophiolites are more abundantly subduction-related than those of Proterozoic and Phanerozoic ages. The subduction-dominant Archean oceanic crust (ophiolites) was characterized by accretionary cycle plate tectonics, whereas for those of Proterozoic and Phanerozoic ages, a combination of both accretionary cycle and Wilson cycles plate tectonic processes was operative.

Feedback between surface and deep processes: Insight from time series analysis of sedimentary record

Sediment accumulation and subduction at continental margins are hypothesized to be crucial in the operation of Wilson cycle style plate tectonics on Earth. To test this hypothesis, we explore the interaction between continental sedimentation and plate tectonics by utilizing a 3.5 Gyr continent-scale sediment abundance record from the Macrostrat database. Wavelet analysis of a time series of sedimentary rock volume identified a supercontinent-like cycle of ∼500 Myr across the past 3.0 Gyr. Intriguingly, this long-term fluctuation in net sedimentation record that indicates continent-derived sediment flux into oceanic crust is in phase with the vigor of subduction activity (as characterized by zircon εHf and δ18O isotopes) through time. These agreements provide independent evidence for the hypothesis that the operation of Wilson cycle style plate tectonics was facilitated by sediment accumulation and subduction (lubrication) at continental margins. Moreover, wavelet cross-correlation analysis of sediment abundance and subduction flux suggests an increasingly efficient sediment cycling via subduction since ∼3.0 Ga, notably coinciding with transition periods of atmospheric oxygen levels at the beginning and end of the Proterozoic. The results suggest that the co-evolving surface process and plate tectonics that increased long-term net sequestration of organic carbon could have contributed to the initial rise of atmospheric oxygen at the beginning of the Proterozoic and the climb to sustained modern levels in the early Phanerozoic.

Late Carboniferous gabbro-granite suite from West Ujimqin of central Inner Mongolia: Petrogenesis and geodynamic implication

辉长岩和花岗岩组成的双峰式火成岩系列通常产出于威尔逊板块构造旋回的诸多伸展周期。基于其岩石地球化学特征示踪伸展地球动力学过程与相关壳幔相互作用的独特视角，本文报道了中亚造山带东段内蒙古中部西乌旗地区新近识别的晚石炭世猴头庙辉长岩-花岗岩系列。SIMS锆石U-Pb定年揭示辉长岩和花岗岩的侵位年龄分别为~307Ma和~305Ma。辉长岩主要由斜长石、辉石和角闪石组成；SiO₂含量介于50.4%~53.4%之间，呈现镁质、准铝质和钙碱性特征；富集大离子亲石元素，亏损高场强元素；并具有OIB型全岩Sr-Nd （I_Sr（t）=0.704249~0.704330，ε_Nd（t）=+1.73~+3.81）和锆石Hf （ε_Hf（t）=+4.58~+15.16）同位素组成，其锆石δ¹⁸O介于5.75‰~6.61‰之间。这些特征指示辉长岩可能源于俯冲板片流体交代的亏损地幔楔部分熔融。同期花岗岩主要由斜长石、钾长石、石英和黑云母组成；其SiO₂含量变化于76.3%~77.6%，高硅碱、贫铁镁、弱过铝、富钍铀、亏锶钡、Eu负异常，契合典型高分异I型花岗岩的元素地球化学特征；花岗岩具有中等放射性成因的全岩I_Sr（t）（0.704923~0.704981）、ε_Nd（t）值（-0.15~+0.57）和锆石ε_Hf（t）值（-2.63~+7.40），以及高的锆石δ¹⁸O （6.44‰~8.06‰）。鉴于元素和同位素特征指示的高分异特征和高演化源区，猴头庙高硅花岗岩可能衍生自中元古代和古生代多期增生物质所组成的复合中基性地壳的部分熔融及其后的结晶分异作用。综合区域石炭纪-早二叠世蛇绿混杂岩和岛弧岩浆岩时空展布格局，晚石炭世猴头庙辉长岩-花岗岩系列记录了内蒙古中部其时因洋脊俯冲引发的弥散性区域伸展事件。一方面，该事件既有别于建造西乌旗早-中石炭世弧-盆体系的板片回退阶段，又迥异于早二叠世大规模后碰撞伸展过程；另一方面，这些周期性伸展事件共同见证了中亚造山带东段晚古生代威尔逊造山旋回的完整历程。;Coeval bimodal igneous suites of gabbro and granite commonly typify frequent extensional episodes in the Wilson cycle of plate tectonics. With a unique view to tracing extensional geodynamic processes and related crust-mantle interactions through the petro-geochemical characteristics of such suites, this paper reports the newly identified Late Carboniferous Houtoumiao gabbro-granite suite from West Ujimqin of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB). SIMS zircon U-Pb dating unravels the emplacement age of gabbro at ca. 307Ma and that of granite at ca. 305Ma. The gabbros mainly consist of plagioclase, pyroxene and amphibole. They range in SiO₂ from 50.4% to 53.4%, exhibiting magnesian, metaluminous and calc-alkalic affinities, with enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs). They possess OIB-type whole-rock Sr-Nd (I_Sr(t)=0.704249~0.704330, ε_Nd(t)=+1.73~+3.81) and zircon Hf (ε_Hf(t)=+4.58~+15.16) isotope compositions, and zircon δ¹⁸O values from 5.75‰ to 6.61‰. These features suggest that the gabbros might be derived from the partial melting of a depleted metasomatised mantle wedge from subduction-derived fluids. The coeval granites mainly comprise plagioclase, K- feldspar, quartz and biotite. They span in SiO₂ from 76.3% to 77.6%, with high alkalis, thorium and uranium but low iron, magnesium, strontium and barium. They are weakly peraluminous with negative Eu anomalies. These features are typical of highly fractionated I-type felsic magmas. With respect to isotopic compositions, the granites are characterized with medium radiogenic whole-rock I_Sr(t) (0.704923~0.704981), ε_Nd(t) (-0.15~+0.57) and zircon ε_Hf(t) (-2.63~+7.40), and high zircon δ¹⁸O (6.44‰~8.06‰). Given their highly fractionated character and highly evolved sources, the Houtoumiao granites tend to have been derived from the partial melts of the composite mafic to intermediate lower crust composed of multi-stage accretionary materials in the Mesoproterozoic and Paleozoic times, with subsequent fractional crystallization yielding the high-silica granites. Combined with the spatial and temporal distribution patterns of regional Carboniferous-Early Permian ophiolitic mélange and island arc magmatic complexes, the Late Carboniferous Houtoumiao gabbro-granite suite seems to record diffuse regional extension event due to ridge subduction in central Inner Mongolia. On one hand, this event is not only distinct from slab rollback episode of the Early-Middle Carboniferous arc-basin system in West Ujimqin, but also in contrast with large-scale post-collisional extension during Early Permian time. On the other hand, when taken together, these episodic extensional events tend to witness the complete course of the Late Paleozoic Wilson cycle in the eastern CAOB.

The Geochemical and Isotopic Record of Wilson Cycles in Northwestern South America: From the Iapetus to the Caribbean

Isotopic and geochemical data delineate passive margin, rift and active margin cycles in northwestern South America since ~623 Ma, spanning from the Iapetus Wilson Cycle. Ultramafic and mafic rocks record rifting associated with the formation of the Iapetus Ocean during 623–531 Ma, while the initiation of subduction of the Iapetus and Rheic oceans is recorded by continental arc plutons that formed during 499–414 Ma, with alternating compressive and extensional stages. Muscovite 40Ar/39Ar dates suggest there may have been a phase of Carboniferous metamorphism, although this remains tentative. A Passive margin was modified by active margin magmatism that started at ~294 Ma and culminated with collisional tectonics that signaled the final stages of the amalgamation of western Pangaea. Early Pangaea fragmentation included back-arc rifting during 245–216 Ma, leading to a Pacific active margin that spanned from 213–115 Ma. Trench retreat accelerated during 144–115 Ma, forming a highly attenuated continental margin prior to the collision of the Caribbean Large Igneous Province at ~75 Ma.