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We present overview for geological studies of the terranes of the Sikhote-Alin orogenic belt in the Russian Far East. The belt is formed by accretionary prisms with alternating tectonic packets of thrust-like slices which consist of complexly deformed marine (pelagic and hemipelagic deposits, as well as oceanic plateau and paleo-guyot fragments), marginal oceanic turbidites and chaotic (subduction melange) formations. We reconstruct a stepwise history of accretion of paleo-oceanic crustal fragments of different ages, based on detailed lithological-biostratigraphic and structural analysis. We propose geodynamic model for evolution of the eastern margin of the paleo-Asian continent during the Mesozoic time by combining geological observations for the region with geological data for others terranes of the Sikhote-Alin Orogenic Belt. We recognize several principal Mesozoic geological processes that have led to formation of the continental crust at the eastern margin of Asia: (i) accretion of paleo-oceanic fragments to the continent margin during the subduction of the paleo-Pacific plate along the convergent margins, (ii) subsequent intense deformation of rocks of the accretionary prisms of the transform margin including folding and multiple thrusting which led to a multifold increase in thickness of sediments, (iii) formation of granitic–metamorphic complexes due to intrusion of the orogenic granites into the accretionary prisms.

The southern Sierra Nevada foothills, central California (USA), expose a fossil pre–40 Ma bedrock pediment which we call the southern Sierra Nevada pediment. We document this landscape with multiple types of data, and also report new apatite ^4He/^3He, (U-Th)/He, and zircon (U-Th)/He data from the pediment that significantly expand the spatial extent of southern Sierra low-temperature thermochronology data westward into the foothills. Applying recently published thermal modeling software for thermochronologic data, which uses a transdimensional Bayesian Monte Carlo Markov chain statistical approach, we tightly constrain the thermal history of the southern Sierra Nevada pediment. Integrating this thermal history with numerous previously published data sets from across the southern Sierra, we present a chronology of tectonic and landscape evolution of the southern Sierra Nevada. For the first time we cover the entire width of the range, integrate the numerous published data sets into a single coherent geologic story, and link each phase of this story to a potential mechanism. Modeling results are consistent with a three-phase cooling history for the southern Sierra Nevada pediment. Rapid exhumation ca. 95–85 Ma resulted in cooling to between 55 °C and 100 °C. Following this, slow cooling to surface conditions occurred from 85 Ma to 40 Ma at rates consistent with those estimated for the axial southern Sierra during the same time period by previous studies. Little if any additional cooling occurred post–40 Ma. We hypothesize that a thin sedimentary cover protected the 40 Ma bedrock landscape through much of the last 40 m.y., and that this cover eroded away post–10 Ma, re-exhuming the southern Sierra Nevada pediment as a fossil pre–40 Ma landscape. Each of these three phases of cooling links to a distinct tectonic or geomorphic regime, including the profound rapid exhumation of the southern Sierra Nevada–Mojave segment of the Cretaceous arc due to subduction of a large oceanic plateau, the formation of the low-relief landscape of the high-elevation areas of the southern Sierra Nevada with more limited tectonic forcing, and Eocene activity on the Western Sierra Fault System.

Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.% MgO). This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modelling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf = 32–35, Ti/Zr = 107–147), producing flat REE and HFSE profiles ([La/Yb]pm= 0.9–1.3), with abundances of 3 to 10 times primitive mantle and with minor negative anomalies of Nb ([Nb/La]pm= 0.6–0.8) and Th [(Th/La]pm= 0.6–0.9). Initial isotope compositions (eNd) range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping ∼ 50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between ∼2830 and ∼2820 Ma; are compositionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.

There is a Mid–Late Mesozoic (Jurassic–Cretaceous) arc magmatic belt in southern Qiangtang subterrane associated with the north-dipping subduction of the Bangong–Nujiang Tethyan Ocean. Early Mesozoic (Triassic) magmatism, tectonic evolution of the southern Qiangtang subterrane, and the mechanism of its crustal growth, however, remain unclear. This paper reports zircon U–Pb age, whole-rock major, trace elemental, and Sr-Nd-Hf isotopic components for the Mesozoic Tanggula Pass rhyolites in southern Qiangtang subterrane. Our new data reveal a significant, previously unrecognized stage of magmatism in southern Qiangtang subterrane. The Tanggula Pass rhyolites are moderately-strongly peraluminous (A/CNK = 1.09–1.54), highly fractionated (SiO2 > 73%) and ultrapotassic (K2O/Na2O > 44%). Zircon U–Pb dating by LA-ICP-MS yields a concordant age with a weighted mean 206Pb/238U age of 235.9 ± 0.86 Ma (n = 18, MSWD = 0.25). The large variations of major and trace element concentrations are mainly attributed to fractional crystallization of plagioclase, hornblende, Fe-Ti oxides, and accessory minerals such as apatite, allanite, monazite, and zircon in the shallow level. K-feldspar mainly occurs as cumulated mineral, resulting in high K2O contents and K2O/Na2O ratios. The rhyolites were derived by partial melting of mixed source rocks including older sedimentary rocks in the upper crust and juvenile materials, triggered by north-dipping subduction of the Bangong-Nujiang Tethyan oceanic lithosphere. The eruption age of Middle Triassic suggests that the initiation of northward subduction of the Bangong-Nujiang Tethyan ocean took place earlier than is currently assumed. Whole-rock Nd (ca. 1.55 to 2.34 Ga) and zircon Hf (ca. 1.77 to 2.33 Ga) data reflect the presence of the Proterozoic basement in the southern Qiangtang subterrane. Basaltic magma underplating and accretion of intra-oceanic arc complexes and oceanic plateau contributed to vertical crustal growth and lateral crustal growth, respectively.

Crust forming processes on the early Earth have long been debated and relatively few rock and mineral samples exist with which to evaluate many hotly contested themes. The Acasta Gneiss Complex contains rock units with crystallization ages exceeding 4.0 Ga, making them the oldest known evolved rock units in the world. However, the AGC has experienced a long and complex history with multiple periods of igneous intrusion, deformation and metamorphism. Indeed, previous workers have demonstrated that orthogneisses within the AGC have igneous ages ranging from ∼4.03 to ∼3.4 Ga. This large range in crystallization ages gives us the opportunity to investigate the evolution of Earth’s earliest known continental crust through a period of greater than 1 billion years. Here we present an updated geologic map of key areas within the Acasta Gneiss Complex in which we delineate units based upon age as well as composition. Whole-rock geochemistry, zircon LA-ICPMS U–Pb geochronology and SIMS O-isotope analyses from a large suite of samples indicate a significant change in mode of crust formation over 400 million years. These data document a gradual change from shallow crustal processes generating basaltic to andesitic compositions at 4.02 Ga to deep-seated partial melting of hydrated basalt, represented by voluminous Archean TTG-like intrusions at 3.6 Ga. We find no evidence that classic Archean TTG-like rock units are present within the AGC prior to 3.6 Ga, suggesting a significantly different tectonic process at work prior to this time. We invoke an oceanic plateau-like model to describe the evolving nature of crust formation within the AGC, which forms a buoyant, evolved nucleus. This nucleus then initiates deep-seated partial melting of mafic crust forming voluminous TTG-like units at ∼3.6 Ga. This ultimately serves to stabilize the crust and forms a nucleus for later formation of the Slave craton.

Shatsky Rise in the Northwest Pacific is the best example so far of an oceanic plateau with two potential hotspot tracks emanating from it: the linear Papanin volcanic ridge and the seamounts comprising Ojin Rise. Arguably, these hotspot tracks also project toward the direction of Hess Rise, located ∼1200 km away, leading to speculations that the two plateaus are connected. Dredging was conducted on the massifs and seamounts around Shatsky Rise in an effort to understand the relationship between these plateaus and associated seamounts. Here, we present new 40Ar/39Ar ages and trace element and Nd, Pb, and Hf isotopic data for the recovered dredged rocks and new trace elements and isotopic data for a few drill core samples from Hess Rise. Chemically, the samples can be subdivided into plateau basalt-like tholeiites and trachytic to alkalic ocean-island basalt compositions, indicating at least two types of volcanic activity. Tholeiites from the northern Hess Rise (DSDP Site 464) and the trachytes from Toronto Ridge on Shatsky’s TAMU massif have isotopic compositions that overlap with those of the drilled Shatsky Rise plateau basalts, suggesting that both Rises formed from the same mantle source. In contrast, trachytes from the southern Hess Rise (DSDP Site 465A) have more radiogenic Pb isotopic ratios that are shifted toward a high time-integrated U/Pb (HIMU-type mantle) composition. The compositions of the dredged seamount samples show two trends relative to Shatsky Rise data: one toward lower 143Nd/144Nd but similar 206Pb/204Pb ratios, the other toward similar 143Nd/144Nd but more radiogenic 206Pb/204Pb ratios. These trends can be attributed to lower degrees of melting either from lower mantle material during hotspot-related transition to plume tail or from less refractory shallow mantle components tapped during intermittent deformation-related volcanism induced by local tectonic extension between and after the main volcanic-edifice building episodes on Shatsky Rise. The ocean-island-basalt-like chemistry and isotopic composition of the Shatsky and Hess rise seamounts contrast with those formed by purely deformation-related shallow mantle-derived volcanism, favoring the role of a long-lived mantle anomaly in their origin. Finally, new 40Ar/39Ar evidence indicates that Shatsky Rise edifices may have been formed in multiple-stages and over a longer duration than previously believed.

Detrital zircon U-Pb and fission track double-dating and Hf isotopes from the Mesozoic and Cenozoic strata in the southern Alaska forearc basin system reveal the effects of two different modes of flat-slab subduction on the evolution of the overriding plate. The southern margin of Alaska has experienced subduction of a spreading-ridge (ca. 62–50 Ma) and an oceanic plateau (ca. 40–0 Ma). When a subducting spreading-ridge drives slab flattening, our data suggest that after the ridge has moved along strike retro-arc sediment sources to the forearc become more predominant over more proximal arc sources.. Spreading-ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent, thin sedimentary strata in the forearc basin. When a subducting oceanic plateau drives slab flattening, our data suggest that basin catchments get smaller and local sediment sources become more predominant. Crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that, combined, create topography and increase rock exhumation rates. Consequently, the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation. The cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages. This study demonstrates the merit of double-dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large-scale tectonic processes in magmatic regions.

Newly collected, high resolution multi-beam sonar data are combined with previous bathymetry data to produce an improved bathymetric map of Shatsky Rise oceanic plateau. Bathymetry data show that two massifs within Shatsky Rise are immense central volcanoes with gentle flank slopes declining from a central summit. Tamu Massif is a slightly elongated, dome-like volcanic edifice; Ori Massif is square shaped and smaller in area. Several down-to-basin normal faults are observed on the western flank of the massifs but they do not parallel the magnetic lineations, indicating that these faults are probably not related to spreading ridge faulting. Moreover, the faults are observed only on one side of the massifs, which is contrary to expectations from a mechanism of differential subsidence around the massif center. Multi-beam data show many small secondary cones with different shapes and sizes that are widely-distributed on Shatsky Rise massifs, which imply small late-stage magma sources scattered across the surface of the volcanoes in the form of lava flows or explosive volcanism. Erosional channels occur on the flanks of Shatsky Rise volcanoes due to mass wasting and display evidence of down-slope sediment movement. These channels are likely formed by sediments spalling off the edges of summit sediment cap.

In this contribution we use VMS mineral systems in the Bryah rift-basin to constrain the tectonic setting of the widespread mafic and ultramafic magmatism that characterises the rift-basin in question. Two distinct, but temporally closely associated, lithostratigraphic sequences, Narracoota and Karalundi Formations, are discussed. The Karalundi Formation is the main host of VMS mineral systems in the region. The Karalundi Formation consists of turbiditic and immature clastic sediments, which are locally intercalated with basaltic hyaloclastites, dolerites and banded jaspilites. We propose that the basaltic hyaloclastites, dolerites and clastics and jaspilites rocks, form a distinct unit of the Karalundi Formation, named Noonyereena Member. The VMS mineral systems occur near the north-east trending Jenkin Fault and comprise the giant and world-class DeGrussa and the Red Bore deposits. The nature of these deposits and their intimate association with terrigenous clastic rocks and dominantly marine mafic volcanic and subvolcanic rocks, as well as the common development of peperitic margins, are considered indicative of a Besshi-type environment, similar to that of present-day Gulf of California. Our Re-Os age data from a primary pyrite yielded a mean model age of 2012 ± 48 Ma, which coincides (within error) with recent published Re-Os data (Hawke et al., 2015) and confirms the timing of the proposed geodynamic evolution. We propose a geodynamic model that attempts to explain the presence of the Narracoota and Karalundi Formations as the result of mantle plume activity, which began with early uplift of continental crust with intraplate volcanism, followed by early stages of rifting with the deposition of the Karalundi Formation (and Noonyereena Member), which led to the formation of Besshi-type VMS deposits. With on-going mantle plume activity and early stages of continental separation, an oceanic plateau was formed and is now represented by mafic-ultramafic rocks of the Narracoota Formation.

The geological evolution of the Earth during the mid-Cretaceous were shown to be anomalous, e.g., the pause of the geomagnetic field, the global sea level rise, and increased intra-plate volcanic activities, which could be attributed to deep mantle processes. As the anomalous volcanic activities occurred mainly in the Cretaceous Pacific, here we use basalt chemical compositions from the oceanic drilling (DSDP/ODP/IODP) sites to investigate their mantle sources and melting conditions. Based on locations relative to the Pacific plateaus, we classified these sites as oceanic plateau basalts, normal mid-ocean ridge basalts, and near-plateau seafloor basalts. This study shows that those normal mid-ocean ridge basalts formed during mid-Cretaceous are broadly similar in average Na-8, La/Sm and Sm/Yb ratios and Sr-Nd isotopic compositions to modern Pacific spreading ridge (the East Pacific Rise). The Ontong Java plateau (125-90 Ma) basalts have distinctly lower Na-8 and Nd-143/Nd-144, and higher La/Sm and Sr-87/Sr-86 than normal seafloor basalts, whereas those for the near-plateau seafloor basalts are similar to the plateau basalts, indicating influences from the Ontong Java mantle source. The super mantle plume activity that might have formed the Ontong Java plateau influenced the mantle source of the simultaneously formed large areas of seafloor basalts. Based on the chemical data from normal seafloor basalts, I propose that the mantle compositions and melting conditions of the normal mid-ocean ridges during the Cretaceous are similar to the fast spreading East Pacific Rise. Slight variations of mid-Cretaceous normal seafloor basalts in melting conditions could be related to the local mantle source and spreading rate.

New geochemical and petrological results are presented for greenstones from the Erdenetsogt Formation hosted by the Tsetserleg accretionary terrane in the Hangay region, with particular emphasis on newly found picritic and andesitic rocks. These rocks occur mostly in the lower portion of the Erdenetsogt Formation as massive lavas, sills, and dykes closely associated with varicolored bedded ribbon cherts and siltstones. The protoliths of the studied greenstones comprise (1) plume-derived tholeiitic greenstones with oceanic plateau basalt affinity, (2) arc-derived, calc-alkaline andesites. The plume-derived rocks are characterized by chemical signatures such as slight LREE enrichment similar to that of tholeiitic OIB and the existence of ferropicrite with high FeO* (>14 wt%) and MgO (12–22 wt%), which is characteristic of large igneous provinces (LIPs), including oceanic plateaus. Therefore, their tholeiitic composition and high-Fe and -Ti contents require melting of the source mantle peridotite with addition of some recycled Fe- and Ti-rich basaltic material. The andesites are characterized by glassy texture, high MgO content (up to 7 wt%), and significant LREE enrichment with depletion in Nb and resemble sanukite type of high-magnesian andesite (HMAs). We infer that the Hangay tholeiitic greenstones probably represent an accreted upper section of an oceanic plateau that developed in the deep-water region of the Hangay-Henteypaleo-ocean in the Upper Silurian-Lower Devonian. The Hangay HMAs may have been produced by subduction of young oceanic plate after an oceanward back-stepping of the subduction zone that was a result of the collision during the Carboniferous of the oceanic plateau and the active continental margin of the Central Mongolian Massif.

Phanerozoic growth of continental crust has widely been considered as an important geological phenomenon and mainly occurs in an arc setting. However, the crustal growth models (mantle-derived basalt underplating or accretion of island or intra-oceanic arc complexes or oceanic plateau) have been disputed. Here we present new zircon LA–ICPMS U–Pb age, whole-rock major and trace element, Sr–Nd and zircon Hf isotopic data for Late Mesozoic intermediate–felsic intrusive rocks in the Rena Co area in southern Qiangtang, central Tibet. LA–ICP–MS zircon U–Pb dating for two granodiorite and three diorite samples and one granodiorite porphyry sample gives ages of ca. 150 Ma, ca. 112 Ma, respectively, indicating they were generated in the Late Jurassic–Early Cretaceous. All rocks are sub-alkaline in composition and belong to the high-K cal-alkaline series. The ~ 150 Ma diorites (SiO2 = 57.9–61.2 wt.%) exhibit relatively high MgO (3.13–3.88 wt.%) and Cr (52.4–282 ppm) contents and Mg# (47–51) values, similar to magnesian diorites. They are geochemically characterized by uniformly low eNd(t) (− 5.5 to − 5.2), high (87Sr/86Sr)i (0.7071 to 0.7078) and Th/La (0.22–0.32), and variable zircon eHf(t) (− 8.7 to + 4.8) values. They were probably generated by melting of oceanic sediment diapirs, followed by interaction with the surrounding mantle during the northward subduction of Bangong–Nujiang Oceanic lithosphere. The ~ 150 Ma granodiorites and ~ 112 Ma granodiorite porphyries are characterized by low MgO ( 15% wt.%) and Sr (> 400 ppm) and low Y (

Based on the new geological, mineralogical, and geochemical data on the crystalline rocks of the Paleozoic ophiolite associations in the Sikhote-Alin (Russian southern Far East), we have reconstructed the tectonic setting of their formation. Two ophiolite associations have been recognized: peridotite–troctolite and peridotite–gabbronorite, differing mainly in the structure of the cumulative part of their sections. In the peridotite–troctolite association, the base of the cumulative unit is formed mostly by olivine–plagioclase rocks (troctolites and olivine gabbro), and in the peridotite–gabbronorite association, by essentially pyroxene rocks (pyroxenites and wehrlites). We have established that the ophiolite rocks crystallized at different pressures: troctolites—12 kbar. The crystalline rocks form a single geochemical series, with the accumulation of lithophile elements and LREE in more differentiated varieties. The REE patterns of rocks are in good correlation with their mineral composition. We assume that the Sikhote-Alin ophiolites formed at the basement of an oceanic plateau growing as a result of mantle plume intrusion.

The Laramide orogeny (~ 80–50 Ma) was an anomalous period of mountain-building in the western United States that occurred more than 1000 km inboard of the Farallon Plate subduction margin. It is widely believed that this orogeny is coincident with a period of flat (subhorizontal) subduction. However, the factors that caused the Farallon Plate to evolve from a normal (steep) geometry to flat subduction are not well understood. Three proposed factors are: (1) a westward (trenchward) increase in North America motion, (2) an increased slab suction force owing to the presence of thick Colorado Plateau lithosphere, and (3) subduction of a low-density oceanic plateau. This study uses 2D upper mantle scale numerical models to investigate these factors. The models show that trenchward continental motion is the primary control on subduction geometry, with decreasing slab dip as velocity increases. However, this can only create low-angle subduction, as the Farallon Plate was old (> 100 Myr) and denser than the mantle. A transition to flat subduction requires: (1) subduction of a buoyant oceanic plateau that includes an 18-km-thick crust that does not undergo metamorphic densification and an underlying depleted harzburgite layer, and (2) a slab break-off at the landward side of the plateau. The break-off removes the dense frontal slab, and flat subduction develops as the buoyant plateau deflects the slab upward. The slab suction force has only a minor effect on slab flattening, but the thickness of the Colorado Plateau lithosphere controls the depth of the flat slab. With a continental velocity of 4 cm/yr and a 400-km-wide oceanic plateau, flat subduction develops within 15 Ma after plateau subduction. The flat slab underthrusts the continent at ~ 200 km depth, eventually extending > 1500 km inboard of the trench.

We present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy (OPS), and on the petrology and geochemistry of basalts from mid-oceanic ridges (MORB) and oceanic islands (OIB) using examples from four accretionary complexes (AC) in SW Japan: Akiyoshi, Mino–Tamba, Chichibu and Shimanto. The key to the problem is the model of OPS, which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid-oceanic ridge to a subduction zone. We propose the reconstruction of the tectonic settings of basalts according to their relationships with associated OPS sediments, their petrogenesis and their geochemical features. Five types of OPS are recognized in the accretionary complexes of SW Japan: (1) sandstone/shale; (2) sandstone/shale and chert; (3) sandstone/shale, chert and MORB; (4) sandstone/shale, chert, MORB and gabbro (± peridotite); (5) seamount OPS including OIB, cap carbonates, slope clastics and basal shale/chert. The alkaline, tholeiitic or calc-alkaline composition of basaltic melts, which are typical of oceanic islands, mid-oceanic ridges and island-arcs, respectively, can be identified by the sequence in crystallization of their major phenocrysts, i.e. olivine (ol), clinopyroxene (cpx) and plagioclase (pl), and by their compositions. Alkaline and calc-alkaline mafic lavas are characterized by an ol → cpx → pl succession, whereas tholeiitic melts by their ol → pl ± cpx succession. Titanium-rich minerals, e.g., Ti–augite, kaersutite, Ti–biotite, are typical of alkaline lavas. The application of geochemistry-based tectonic discrimination diagrams is also a powerful tool, if not supported by geological and petrological data, may result in confusion due to magma contamination, post-magmatic alteration, and secular change of mantle thermal conditions. We propose that a direct comparison of normalized multi-element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination. Our OPS–petrology–geochemistry method allows us to confirm the above conclusions that the lavas of the Akiyoshi, Mino–Tamba and Southern Chichibu AC formed in oceanic islands, because they are associated with seamount OPS sediments, crystallized from ol to cpx and pl, contain Ti–augite and kaersutite and are enriched in TiO2, LREE and Nb. In this paper we present geochemical data from the Inuyama basalts of the Mino–Tamba AC and from the Toba complex in the huge Mikabu greenstone belt of the Chichibu AC. The Inuyama basalts are in contact with Jurassic pelagic cherts, but their geochemical features are confusing; they contain phenocrysts of ol, Ti–augite and kaersutite and therefore probably formed in seamounts. The Toba volcanic rocks are a part of the huge ophiolite belt; they have flat to slightly LREE-enriched REE patterns, are characterized by an ol → cpx succession of phenocrysts and they plot in the OIB field in binary plots suggesting they formed in an oceanic plateau.

The tectono-magmatic evolution of the Bangong-Nujiang Tethyan Ocean (BNO) plays a crucial role in understanding the Tibetan Plateau accretion before the Cenozoic India-Asia collision. The microcontinents and oceanic plateau recognized recently within the BNO provide important clues for constructing the subduction process between BNO and the Qiangtang terrane. In this contribution, we provide a comprehensive overview of the multidisciplinary information from magmatism, metamorphism, stratigraphy, geochronology, geochemistry, Hf isotopic data, ophiolite suites, and paleomagnetism to gain insights into the spatially and temporally related geodynamic processes of the BNO. A compilation of geochronological data indicates that the emplacement of the diverse igneous suites occurred mainly during three stages: stage 1 (190–150 Ma), stage 2 (130–110 Ma), and stage 3 (110–70 Ma). The igneous suites, including granitoids, mafic intrusions and volcanic rocks, formed two arcuate E–W trending belts that parallel the Bangong-Nujiang suture zone and are correlated to the double sided subduction of the BNO. We infer that the BNO initially opened at ~270Ma between the Lhasa terrane and Qiangtang terrane, although the relationship between the BNO and Longmu Tso-Shuanghu paleo-Tethyan ocean is still unclear. Age data related to metamorphism, arc magmatism, supra-subduction zoneophiolites, and sedimentary strata indicate that the northward subduction of the BNO started at ~190 Ma, followed by the subduction of microcontinents beneath the Qiangtang terrane at 195 Ma. In contrast, the subsequent southward subduction of the BNO started at ~170 Ma, resulting in the opening of the Shiquanhe-Namuco ocean. As indicated by the high Mg volcanic suite, intra-ocean subduction within the BNO also occurred during 170-145Ma, possibly related to the resistance from subduction of ocean plateau and slab retreat. Based on evidence from petrology, isotope geochronology, and isotopic geochemistry, we also infer that the magmatic lull during 145-130Ma is related to the slab subduction of ocean plateau beneath the southern Qiangtang subterrane. The closure of the BNO was most likely diachronous, which started as early as Late Jurassic and continued to the late Early Cretaceous (120-110Ma).

Many groups or chains of seamounts border, or are associated with, oceanic plateaus but their origin and relationship with plateau volcanism are debated. An example is Ojin Rise Seamounts, a group of ~80 seamounts located northeast of the 147–134 Ma Shatsky Rise, an oceanic plateau that was formed along the trace of a triple junction in the northwest Pacific Ocean. A notable topographic feature of Ojin Rise Seamounts is that they are distributed in such a way that they appear to be connected to another oceanic plateau in the east, the ~100 Ma Hess Rise. Many seamounts are arranged in a NW–SE direction (almost in the same absolute plate motion direction) and some are organized into seamount chains consisting of several volcanic cones connected by a common platform, reflecting a complex volcanic history. Here we report petrography as well as major and trace element, Sr, Nd, Pb, and Hf isotope, and 40Ar-39Ar age data for basalts dredged from five seamounts in the western part of Ojin Rise Seamounts. We found that the 40Ar-39Ar ages of the cones (123.7–120.7 Ma) are distinctly younger than the magnetic lineation age (M9-M7; 134–132 Ma) around the chain. The younger age suggests either a protracted development for the seamount chain, previously proposed to have formed near-ridge, or age difference between the platform and cones. The morphological and age differences are supported by petrography and geochemistry: platform basalts are aphyric, whereas cone basalts are slightly to highly plagioclase-phyric (up to 48 vol%); platform basalts are depleted in trace element and isotope composition, but cone basalts are enriched with high Nb/Ti and 87Sr/86Sr, and low 143Nd/144Nd and 176Hf/177Hf ratios. The depleted signature of the platform basalts is similar to that of the abundant normal type basalts of Shatsky Rise with an isotope composition that overlaps with that of normal mid-ocean ridge basalts (N-MORB), whereas trace elements are enriched (e.g., higher Nb/Zr and Nb/Ti than N-MORB). However, slight geochemical differences between the Ojin platform basalts and Shatsky normal type basalts exist and are expressed in higher 208Pb/204Pb isotope ratios of the former. The depleted signature implies shallow mantle dilution of the (enriched) Shatsky plume tail near a ridge. In contrast, the enriched signature of the cone basalts indicates little contribution from N-MORB source mantle as (enriched) plume volcanism moved away from the ridge. The enriched features (Nb/Zr and 176Hf/177Hf) of the Ojin Rise cone basalts increase with increasing distance from Shatsky Rise and conform with a geochemical evolution model that involves increasing contribution from a highly enriched Hess Rise source component with time.

The Yap Arc was considered to have derived from the proto-Yap-Izu Bonin-Mariana arc system. It is a rare example of subduction of an oceanic plateau with short arc–trench distance and consists mainly of metamorphic rocks, which are distinct from the Izu Bonin-Mariana arc system. However, it is not known on the origin and formation time of the basement rocks of the Yap Arc. For the first time, in this study we provide the results of radiometric age-dating and whole-rock major element, trace element and Sr–Nd–Pb–Hf isotope analyses for the metamorphic basement rocks (amphibolites) of the Yap Arc. These rock samples can be classified into three groups based on their major and trace element compositions. Group 1 samples have strong depletion of LREEs and a Dupal-type isotopic signature, and they represent forearc basalts (FABs) of the nascent Yap forearc. Group 2 samples have an alkali basalt-like geochemistry and oceanic island basalts (OIBs) type trace element patterns, and they represent the basalts of the Caroline Plateau. Group 3 samples have island-arc-type negative anomalies of Nb–Ta–Zr–Hf, and they may represent the volcanic rocks of the proto-Yap Arc. These amphibolites were formed at 21 Ma according to 40Ar/39Ar amphibole dating and in situ SIMS U Pb titanite dating, and they record the timing of the collisional event between the Caroline Plateau and the proto-Yap Arc. We propose that the Yap arc has been evolving distinctly from the Izu-Bonin-Mariana Arc since this collision time. These rocks were metamorphosed and brought onto the present Yap Arc as a result of the collision between the proto-Yap Arc and the Caroline Plateau. Based on the new results of age-dating and geochemistry of this study, we propose three stages of tectonic evolution for the Yap Arc as a result of collision from the Caroline plateau: an early stage (proto-Yap Arc) of subduction of the Caroline Plate, collision of the proto-Yap Arc with the in-coming young Caroline Plateau, and rejuvenated plate subduction at the Yap Trench with limited volcanism.

Shi et al. (2020) commented on our recent work (Li et al. 2019), which reconstructed the Wilson cycle of the Bangong-Nujiang Tethyan Ocean. They questioned our preferred latest Jurassic-Early Cretaceous Lhasa-Qiangtang initial collision model, and argued that the Bangong-Nujiang Tethyan Ocean did not close until the Late Cretaceous, based on the existence of Mid-Cretaceous OIB-type mafic rocks, arc-type magmatism and marine sedimentation as well as paleomagnetic data. Here we respond to all these pieces of evidence separately and eventually conclude that the observations and data they provided are not proof supporting the persistence of the Bangong-Nujiang Tethyan Ocean into the Late Cretaceous. Our preferred latest Jurassic-Early Cretaceous Lhasa-Qiangtang initial collision model thereby still holds.

The Western Cordillera of Colombia is interpreted as an igneous province derived from the Colombian-Caribbean Oceanic Plateau (CCOP) and assumed that contained no high-grade metamorphic rocks. The Mistrato Quartz-diorite and Sabanalarga Batholith however, as part of the CCOP, contain some rocks that evidence granulite facies metamorphism. Here we define the Mistrato Granulite as a different unit from the Mistrato Quartz-diorite and correlated with the Pantanillo Granulite, which has been previously defined as a different unit from the Sabanalarga Batholith. We use field relationships, petrography, mineral chemistry and whole rock chemistry analyses to evidence the metamorphism. The Mistrato Granulite, which outcrops into the inner regions of the Colombian Western Cordillera, hosts a Ca-richer recrystallized assemblage, which consists of plagioclase + clinopyroxene + ortopyroxene + quartz + ilmenite, and a Ca-poorer relict assemblage, which consists of plagioclase + clinopyroxene + orthopyroxene + ilmenite + actinolite, this latter mineral interpreted as retrogression of clinopyroxene. The anhydrous nature and polygonal granoblastic texture of the recrystallized assemblage supports the metamorphism of a gabbroic protolith that reached granulitic conditions, determined by thermodynamic calculations to be of 900 ± 50 °C and below 1.1 GPa. Geochemical analyses reveal that these rocks may have formed in an island arc linked to the evolution of the CCOP during the Late Cretaceous. We have found that the geochemistry of the Mistrato and Pantanillo granulites, together with their regional settings, are comparable, suggesting that both units could have derived from similar mafic oceanic rocks and underwent a similar tectonic evolution. This interpretation differs from previous ideas that explain the Pantanillo Granulite as a result of the interaction between the Central and Western Cordilleras.

A model that places development of IOCG (and porphyry-epithermal) mineralization at ca. 1.60–1.575 Ga in eastern Proterozoic Australia into the context of a modern-day suprasubduction zone is presented here. This model depicts a change from a rollback subduction geometry in which extensional basins were developing in the overriding plate from ca. 1.67–1.604 Ga to a flat-slab subduction environment where ca. 1.65–1.604 Ga arc-magmatism was shut off and hot, extensional basins were inverted under high-temperature/low-pressure metamorphic conditions. The change in subduction architecture was induced by the arrival of a buoyant oceanic plateau at the site of subduction at ca. 1.604 Ga. Subduction was associated with the development of F-rich, S-poor metasomatized subcontinental lithospheric mantle (SCLM) as the result of slab melting within the rollback and/or the flat-slab subduction geodynamic setting. Eclogitisation and densification of the frontal oceanic slab resulted in slab steepening, a sudden upwelling of hot asthenosphere under the present-day Olympic Dam area and transient upper crustal uplift. The sudden heat input triggered slab melting and partial melting in the mantle to produce anhydrous, F-rich, S-poor melts that interacted with the metasomatized SCLM. Fractionation of resultant mafic melts with minimal to no crustal input resulted in generation of the dominantly A-type older Hiltaba Suite granites that were emplaced at upper crustal levels and an ignimbrite flare-up that is now recognised as the Gawler Range Volcanics. Highly fractionated magma that stalled in the upper crust exsolved volatile-rich and metalliferous fluids that mixed with meteoric and basinal brines to produce IOCG mineralization through the Olympic Domain including the supergiant Olympic Dam deposit. Further slab steepening and retreat of the posterior buoyant oceanic plateau resulting in additional upwelling of the asthenosphere and progressive development of an asthenospheric wedge in a normal subduction geometry. Slab retreat can be tracked by the progressive younging of Hiltaba Suite granites in a present-day approximately westerly to southwesterly direction. Heat introduced through progressive development of the asthenospheric wedge resulted in dehydration of the buoyant oceanic lithosphere to produce S-rich fluids that interacted with the asthenosphere to produce oxidised, S-rich partial melts. These melts interacted with the metasomatized SCLM resulting in generation of dominantly I-type magmas and porphyry-epithermal systems in the southwestern Gawler Craton (Central Gawler Gold Province). The location of IOCG and porphyry-epithermal deposits is also dictated by the location of lithospheric-scale structures that acted as conduits for fluids and melts associated with mineralization. The suprasubduction zone environment of mineralization is informed by modern analogues of the Late Cretaceous to Early Eocene Laramide Orogeny in the western United States, present-day slab geometries in the Andes of South America, and by the formation of Cretaceous IOCG and Cu-porphyry deposits in the Chilean Coastal Cordillera. Refereed/Peer-reviewed

The North China Craton (NCC) is fundamentally characterized by Mesozoic intraplate deformation controlled by preexisting basement fabrics and far-field stress fields. In this study, a structural analysis of typical outcrops and representative sections was conducted to investigate the Mesozoic deformation in the central NCC. Our analysis indicates that this Mesozoic deformation is a typical example of thick-skinned tectonics and that the central NCC experienced two stages of deformation during this period. The first stage was driven by nearly east-west maximum compressional stress during the Late Jurassic, which led to the development of north-south-trending structures in the central NCC, such as the Luliangshan range and Qinshui Basin. The second stage involved NNW-SSE maximum compressional stress during the Late Cretaceous, which resulted in the development of east-west-trending structures and the activation of large sinistral strike-slip faults, such as the Huoshan-Fushan fault. The key mechanism for the deformation during the Late Jurassic was the low-angle subduction of the Paleo-Pacific Plate beneath the NCC, which also laid the foundation for the later destruction of the craton during the Cretaceous. Moreover, a Late Cretaceous collision between the southeastern Eurasian continent and an unknown block or oceanic plateau may have resulted in the subsequent deformation of the NCC.

The genesis of an oceanic plateau provides important information on the composition and melting dynamics of the deep mantle. The Caroline Rise, consisting of the West and the East Caroline Ridges, has played an important role in the evolution of the subduction system of the western Pacific; however, the nature and origin of the Caroline Rise are poorly known. Here, on the basis of seafloor sampling, we confirm for the first time that the Caroline Rise represents an oceanic plateau (the Caroline Plateau) that formed as a large igneous province. The Caroline Plateau is connected with the Caroline Seamount Chain to the east, and the seamount chain formed above a deep-rooted hotspot. To investigate the nature of the mantle source of the Caroline Plateau and its genetic relationship with the Caroline Seamount/Island Chain, we age-dated basalt samples from the Caroline Plateau and analyzed their major and trace elements and Sr–Nd–Pb–Hf isotopes. The samples can be classified as alkali or tholeiitic basalt. The tholeiitic basalts (15.62 ± 3.16 to 19.26 ± 0.35 Ma) are older than the alkali basalts (8.13 ± 0.81 Ma) and the volcanics of the Caroline Seamounts/Islands to the east. The tholeiitic basalts have trace element patterns similar to those of basalts of the Ontong Java Plateau. We suggest that the tholeiitic basalts represent the main stage of volcanism on the Caroline Plateau and the alkali basalts the late stage. The alkali basalts of the plateau have isotopic compositions similar to those of the basalts of the Caroline Islands, indicating an origin from the same enriched mantle end-member. The tholeiitic basalts with a MORB-like depleted geochemistry indicate the involvement of depleted components in their mantle source, and the Sr–Nd–Pb–Hf isotope compositions of the tholeiitic basalts can be reproduced by mixing alkali basalt with a depleted MORB mantle component. Based on the relatively low Sm/Yb ratios of the two groups of basalts, the Caroline Plateau is inferred to have formed on a young Caroline Plate with a thin lithosphere. We suggest that the geochemistry and ages of formation of volcanic rocks in the Caroline Plateau/Seamount system can be explained by the activities of the Caroline hotspot. The volcanic rocks of the Caroline Plateau and Islands show increasing alkalinity and Sm/Yb ratios with time, which reflect thickening of the lithosphere and decreasing activity of the Caroline mantle plume.

Early Jurassic igneous rocks are abundant in the Nanling Range, southeastern China. They are closely related with economically significant deposits, but the tectonic-magmatic controls on their formation are still controversial. This paper reports zircon U–Pb–Hf–O isotopes for the rhyolites, and whole-rock major–trace element and Sr Nd isotope compositions for the rhyolites and andesites/dacites in the Changpu and Dongkeng basins located in the southern part of Jiangxi Province. The Changpu and Dongkeng rhyolites have high K2O contents (4.1–7.6 wt%) and K2O/Na2O ratios (> 1). Both groups are enriched in HFSE, LREE and show pronounced Nb–Ta–Eu–Sr–P–Ti negative anomalies. Geochemically, they can be classified as A-type and are similar to A2-type granitoids globally. Their highly evolved whole-rock Sr Nd isotopes and elevated zircon δ18O (Changpu rhyolites: (87Sr/86Sr)i = 0.7140 to 0.7156, eNd(t) = −7.2 to −8.7, δ18O = 8.76 to 9.93‰; Dongkeng rhyolites: (87Sr/86Sr)i = 0.7149 to 0.7162, eNd(t) = −6.4 to −7.9, δ18O = 7.04 to 9.78‰) are consistent with their generation dominated by remelting of exisiting crustal materials in an extensional environment. The slightly more radiogenic zircon Hf isotopes of the Dongkeng rhyolites, eHf(t) = −2.1 to −7.1 as compared with −6.1 to −8.3 of Changpu rhyolites, likely signify some mantle contribution. The Changpu high-Mg andesites–dacites are geochemically similar to high-Mg andesites (HMAs) of the Setouchi arc volcanic belt in Japan and the Piip Volcanos in the western Aleutian Arc. They have very low eNd(t) from −7.8 to −11.3 and highly radiogenic (87Sr/86Sr)i values from 0.7143 to 0.7154. Similar to HMAs in Setouchi, we suggest that they may be derived from melting of subducted sediments and followed by melt-mantle interaction. SIMS zircon U Pb dating yielded extrusive ages of ~190 Ma for both Changpu and Dongkeng rhyolites. The new dating results constrain the minimum age of extrusion of rhyolites and andesites-dacites from the same volcanic sequence to be the earliest Jurassic period. Igneous rocks of this age have very limited distribution in south China. While those found in the coastal regions show features similar to arc rocks, these in the hinterland are rift related. We propose that formation of the Early Jurassic A-type rhyolites and high-Mg andesites–dacites may provide evidence for foundering/delamination of a previously subducted oceanic plateau beneath southeastern China.

North America (NA) experienced pronounced changes in continental-scale drainage characterized by a reversal for much of the continental interior from north into the Canadian arctic to south into the Gulf of Mexico (GoM) from the Mid-Cretaceous to the Paleocene. However, the driving mechanism for these profound drainage reorganizations remain unexplained. Here, we investigate the role of mantle flow on landscape evolution, by coupling dynamic topography with surface processes. This approach enables us to simulate catchment dynamics and the rearrangement of sediment transport in response to mantle flow. We show that a west-to-east drainage reversal can be induced by the NA overriding the subducted Farallon plate. Moreover, augmented dynamic subsidence caused by a basalt-to-eclogite transformation of an oceanic plateau within the Farallon slab, depressed the GoM region and expanded the integrated drainage to the GoM since the Early Paleocene. For the first time, we show that dynamic topography can explain the north-to-south continental-scale drainage reorganization in North America.

The mafic–ultramafic Fariman complex in northeastern Iran has been interpreted as a Paleo-Tethyan ophiolitic fragment with subduction- and plume-related characteristics as well as a basin deposit on an active continental margin. Contributing to this issue, we present geochemical, geochronological, and mineralogical data for transitional and tholeiitic basalts. Thermodynamic modeling suggests picritic parental magmas with 16–21 wt% MgO formed at plume-like mantle potential temperatures of ca. 1460–1600 °C. Rare pyroxene spinifex textures and skeletal to feather-like clinopyroxene attest to crystallization from undercooled magma and high cooling rates. Chromium numbers and TiO2 concentrations in spinel are similar to those in intraplate basalts. 40Ar–39Ar dating of magmatic hornblende yielded a plateau age of 276 ± 4 Ma (2σ). Transitional basalt with OIB-like trace element characteristics is the predominant rock-type; less frequent are tholeiitic basalts with mildly LREE depleted patterns and picrites with intermediate trace element characteristics. All samples show MORB-OIB like Pb/Ce, Th/La, and Th/Nb ratios which preclude subduction-modified mantle sources and felsic crustal material. Tholeiitic basalts and related olivine cumulate rocks show MORB-like initial eNd values of + 9.4 to + 6.2 which define a mixing line with the data for the transitional basalts (eNd ca. + 2.6). Initial 187Os/188Os ratios of 0.124–0.293 support mixed sources with a high proportion of recycled mafic crust in the transitional basalts. High concentrations of highly siderophile elements are in agreement with the high mantle potential temperatures and inferred high-melting degrees. It is argued that the Fariman complex originated by melting of a mantle plume component as represented by the OIB-like transitional basalt and entrained asthenosphere predominant in the MORB-like tholeiites. Two lines of evidence such as association of the Fariman complex with pelagic to neritic sedimentary rocks and the tectonic position at the boundary of two continental blocks defined by ophiolites and accretionary complexes of different ages suggest formation in an oceanic domain. Thus, we interpret it as a fragment of an oceanic plateau, which escaped subduction and was accreted as exotic block in the Paleo-Tethyan suture zone.

The subduction of the Farallon Plate has altered the temperature and composition of the mantle transition zone (MTZ) beneath the United States. We investigate MTZ structure by mapping P‐to‐S conversions at mineralogical phase changes using USArray waveform data and theoretical seismic profiles based on experimental constraints of phase transition properties as a function of temperature and composition. The width of the MTZ varies by about 35 km over the study region, corresponding to a temperature variation of more than 300 K. The MTZ is coldest and thickest beneath the eastern United States where high shear velocity anomalies are tomographically resolved. We detect intermittent P‐to‐S conversions at depths of 520 km and 730 km. The conversions at 730‐km depth are coherent beneath the southeastern United States and are consistent with basalt enrichment of about 50%, possibly due to the emplacement of a fragment of an oceanic plateau (i.e., the Hess conjugate).

The detrital zircon population in quartzitic conglomerates from the northern Tanzania Craton yield ages between 2640 Ma and 2790 Ma which includes most of the igneous history from this part of the craton. The igneous evolution is characterised by mafic volcanism with an oceanic plateau‐like geochemical signature at ~2800 Ma followed by diorite and tonalite–trondhjemite–granodiorite dominated magmatism between 2790 and 2700 Ma, which transitioned into more evolved high‐K magmatism between 2700 and 2620 Ma. The eHf values of the detrital zircons range from +2.4 to −1.4 and change with time from radiogenic Hf pre‐2700 Ma (98% positive eHf) to unradiogenic Hf post‐2700 Ma (41% positive eHf). The petrological progression from mafic to felsic crust is reflected in the detrital age distribution and Hf isotopes and is consistent with juvenile mafic crust slowly maturing into more evolved felsic crust through a series of successive partial melting events in an oceanic‐plateau‐like environment.

The Archean Banded Gneissic Complex (BGC) of the Aravalli Craton (NW India) is volumetrically most important basement complex scattered along the northwestern margin of the Indian craton. It is mainly comprised of grey gneisses, undeformed granitoids and volcano-sedimentary sequence. Amongst various lithocomponents, the grey gneisses represent the oldest component of the BGC. Rock association comprising tonalite, trondhjemite and granodiorite (TTG) form a major component of the grey gneisses. Geochemically, the TTG are essentially sodic in nature (avg. K2O/Na2O = 0.31) and characterized by high Al2O3 (avg. 15.5 wt%), Na2O (avg. 5.3 wt%) and Sr (avg. 413 ppm), and low Y (avg. 10 ppm) contents. They are characterized by enrichment of large ion lithophile elements (LILE) and light rare earth element (LREE) contents. On chondrite- and primitive mantle normalized trace element diagrams, the TTG exhibit: (i) highly fractionated rare earth element (REE) patterns; and (ii) negative anomalies of Nb and Ti. These geochemical characteristics of the TTG suggest that they were not produced from partial melting of mid-oceanic ridge basalts/normal oceanic crust. Instead we propose that the TTG rocks of the Aravalli Craton were formed by partial melting of an enriched source (oceanic plateau) in a subduction setting; with melting taking place at variable depths.

The late Archaean Shimoga schist belt in the Western Dharwar Craton, with its huge dimensions and varied lithological associations of different age groups, is an ideal terrane to study Archean crustal evolution. The rock types in this belt are divided into Bababudhan Group and Chitradurga Group. The Bababudhan Group is dominated by mafic volcanic rocks followed by shallow marine sedimentary rocks while the Chitradurga Group is dominated by greywackes, pillowed basalts, and deep marine sedimentary rocks with occasional felsic volcanics. The Nb/Th and Nb/La ratios of the studied metabasalts of the Bababudhan Group indicate crustal contamination. They were extruded onto the vast Peninsular Gneisses through the rifting of the basement gneiss. The Nb/Yb ratios of high-magnesium basalts and tholeiitic basalts of Chitradurga Group suggest the enrichment of their source magma. Based on the flat primitive mantle-normalized multi-element plot with negative Nb anomalies and Th/Ta-La/Yb ratios, the high-magnesium basalts and tholeiitic basalts are considered to have erupted in an oceanic plateau setting with minor crustal contamination. The high-magnesium basalts and tholeiitic basalts formed two different pulses of same magma type, in which the first pulse of magma gave rise to high-magnesium basalts which were derived from deep mantle sources and underwent minor crustal contamination en route to the surface, while the second pulse of magma gave rise to tholeiitic basalts formed at similar depths to that of high-magnesium basalts and escaped crustal contamination. The associated lithological units found with the studied metavolcanic rock types of Bababudan and Chitradurga Groups of Dharwar Supergroup of rocks in Shimoga schist belt of Western Dharwar Craton confirm the mixed-mode basin development with a transition from shallow marine to deep marine settings.

The study of this alkaline plutonic complex was multidisciplinary, mixing field observations and measurements, AMS, petrography, mineralogy, geochemistry (major and traces), isotopic geochemistry Rb / Sr and Sm / Nd and geochronology U-Pb on zircons. The synthesis of the results shows the minor participation of several sources (metasomatised mantle and continental fragments) in addition to the predominant source which is the typical asthenospheric mantle of the Kerguelen plume. In a dynamic and open magmatic system, the contaminated magmas formed the oldest magmatic and calcic series of the complex. The second and younger magmatic series produced (in a closed environment) more and more agpaitic rocks during differentiation. The incremental emplacement of the intrusions occurred between 11.7 (in the south) and 7.9 Ma (in the north). Finally, the type of construction of this pluton makes it a unique known example of laccolith in oceanic within-plate settings.; L'étude de ce complexe plutonique alcalin fut multidisciplinaire mêlant, observations et mesures sur le terrain, ASM, pétrographie, minéralogie, géochimie (majeur et traces), géochimie isotopique Rb/Sr et Sm/Nd et géochronologie U-Pb sur zircons. La synthèse des résultats démontre la participation minoritaire de plusieurs sources (manteau métasomatisé et fragments continental) en plus de la source prédominante qui est le manteau typique du panache de Kerguelen. Dans un environnement magmatique ouvert, les magmas contaminés ont formé la plus ancienne série magmatique calcique du complexe. La seconde et plus jeune série magmatique a produit (dans un environnement clos) des roches de plus en plus agpaïtique au cours de la différenciation. La mise en place progressive mais diachrone des intrusions s'est faite entre 11,7 (au sud) et 7,9 Ma (au nord). Enfin, le mode de construction de ce pluton en fait un exemple unique connu de laccolithe en contexte intraplaque océanique.

The study of this alkaline plutonic complex was multidisciplinary, mixing field observations and measurements, AMS, petrography, mineralogy, geochemistry (major and traces), isotopic geochemistry Rb / Sr and Sm / Nd and geochronology U-Pb on zircons. The synthesis of the results shows the minor participation of several sources (metasomatised mantle and continental fragments) in addition to the predominant source which is the typical asthenospheric mantle of the Kerguelen plume. In a dynamic and open magmatic system, the contaminated magmas formed the oldest magmatic and calcic series of the complex. The second and younger magmatic series produced (in a closed environment) more and more agpaitic rocks during differentiation. The incremental emplacement of the intrusions occurred between 11.7 (in the south) and 7.9 Ma (in the north). Finally, the type of construction of this pluton makes it a unique known example of laccolith in oceanic within-plate settings.; L’étude de ce complexe plutonique alcalin fut multidisciplinaire mêlant, observations et mesures sur le terrain, ASM, pétrographie, minéralogie, géochimie (majeur et traces), géochimie isotopique Rb/Sr et Sm/Nd et géochronologie U-Pb sur zircons. La synthèse des résultats démontre la participation minoritaire de plusieurs sources (manteau métasomatisé et fragments continental) en plus de la source prédominante qui est le manteau typique du panache de Kerguelen. Dans un environnement magmatique ouvert, les magmas contaminés ont formé la plus ancienne série magmatique calcique du complexe. La seconde et plus jeune série magmatique a produit (dans un environnement clos) des roches de plus en plus agpaïtique au cours de la différenciation. La mise en place progressive mais diachrone des intrusions s’est faite entre 11,7 (au sud) et 7,9 Ma (au nord). Enfin, le mode de construction de ce pluton en fait un exemple unique connu de laccolithe en contexte intraplaque océanique.

The Ordos Basin in China has about 10 km of Neoarchean to Quaternary sediments covering an enigmatic basement of uncertain origin. The basement is tectonically stable, has a thick mantle root, low heat flow, few earthquakes, and has been slowly subsiding for billions of years. The basement has geophysical signatures that indicate it is dominantly intermediate to mafic in composition, and is similar to some other cratons world-wide, and also to several major oceanic plateaus. It was accreted to the amalgamated Eastern Block and Central Orogenic belt of the North China Craton (NCC) in the Paleoproterozoic, then involved in several Proterozoic tectonic events including being over-thrust by an accretionary orogen, and intruded by Andean arc-related magmas, and then involved in a continent-continent collision during amalgamation with the Columbia Supercontinent. Thus, the basement rocks are deformed, metamorphosed to granulite facies, and determining their initial origin is difficult. We suggest that the data is consistent with an origin as an oceanic plateau that accreted to the NCC and, later experienced different episodes of differentiation associated with later subduction and collisions. Formation of cratonic lithosphere by accretion of oceanic plateaus may be one mechanism to create stable cratons. Other cratons that apparently formed by partial melting of underplated and imbricated oceanic slabs are stable in some cases, but also re-activated and “de-cratonized” in some cases in Asia, where they have been affected by younger subduction, hydration, slab roll-back, and melt-peridotite reactions. This suggests that the initial mode of craton formation may be a factor in the preservation of stable cratons, and de-cratonization is not only influenced by younger tectonic activity.

Continental crust formed billions of years ago but cannot be explained by a simple evolution of primary mantle magmas. A multi-step process is required that likely includes re-melting of wet metamorphosed basalt at high pressures. Such a process could occur at depth in oceanic crust that has been thickened by a large magmatic event. In Central America, variations in geologically inferred, pre-existing oceanic crustal thickness beneath the arc provides an excellent opportunity to study its effect on magma storage, re-melting of meta-basalts, and the potential for creating continental crust. We use surface waves derived from ambient noise tomography to image 6% radially anisotropic structures in the thickened oceanic plateau crust of Costa Rica that likely represent deep crustal melt sills. In Nicaragua, where the arc is forming on thinner oceanic crust, we do not image these deep crustal melt sills. The presence of these deep sills correlates with more felsic arc outputs from the Costa Rican Arc suggesting pre-existing thickened crust accelerates processing of primary basalts to continental compositions. In the Archean, reprocessing thickened oceanic crust by subsequent hydrated hotspot volcanism or subduction zone volcanism may have similarly enhanced formation of early continental crust. This mechanism may have been particularly important if subduction did not initiate until 3 Ga.

Plateau related rocks accreted to the Caribbean plate margins provide insights into the understanding of the intra-oceanic evolution of the Caribbean plate and its interaction with the continental margins of the Americas. Petrologic, geochemical and isotope (Sr and Nd) data were obtained in rocks from the Santa Fe Gabbro-Tonalite and Buritica Tonalite in the Western Cordillera of Colombia. Field relations and whole rock–mineral geochemistry combined with juvenile isotope signatures of the different rocks present in the area, suggest that initial melts, represented by the Buritica Tonalite, formed due to asthenospheric upwelling at ∼100 Ma, which intrude the Colombian-Caribbean Oceanic Plateau (CCOP) basalts, and subsequent migration of the Caribbean plate towards the northeast resulted in subduction initiation and the formation of the Santa Fe tonalitic units at ∼90 Ma on the CCOP. The relation of the Santa Fe Batholith with other units from the Caribbean, such as Aruba and the Buga Batholiths suggests the existence of an immature arc constructed on the Caribbean Plateau, which partially accreted onto a continental margin of South American in pre-Eocene times, or migrated to the present day position in the Lesser Antilles.

We tested the accuracy of trace element discrimination diagrams for basalts using new datasets from two petrological databases, PetDB and GEOROC. Both binary and ternary diagrams using Zr, Ti, V, Y, Th, Hf, Nb, Ta, Sm, and Sc do a poor job of discriminating between basalts generated in various tectonic environments (continental flood basalt, mid-ocean ridge basalt, ocean island basalt, oceanic plateau basalt, back-arc basin basalt, and various types of arc basalt). The overlaps between the different types of basalt are too large for the confident application of such diagrams when used in the absence of geological and petrological constraints. None of the diagrams we tested can clearly discriminate between back-arc basin basalt and mid-ocean ridge basalt, between continental flood basalt and oceanic plateau basalt, and between different types of arc basalt (intra-oceanic, island and continental arcs). Only ocean island basalt and some mid-ocean ridge basalt are generally distinguishable in the diagrams, and even in this case, mantle-normalized trace element patterns offer a better solution for discriminating between the two types of basalt.

The effect of paleo-Pacific subduction on the geological evolution of the western Pacific and continental China is likely complex. Nevertheless, our analysis of the distribution of Mesozoic granitoids in the eastern continental China in space and time has led us to an interesting conclusion: The basement of the continental shelf beneath East and South China Seas may actually be of exotic origin geologically unrelated to the continental lithosphere of eastern China. By accepting the notion that the Jurassic–Cretaceous granitoids in the region are genetically associated with western Pacific subduction and the concept that subduction may cease to continue only if the trench is being jammed, then the termination of the granitoid magmatism throughout the vast region at ~88 ± 2 Ma manifests the likelihood of “sudden”, or shortly beforehand (~100 Ma), trench jam of the Mesozoic western Pacific subduction. Trench jam happens if the incoming “plate” or portion of the plate contains a sizeable mass that is too buoyant to subduct. The best candidate for such a buoyant and unsubductable mass is either an oceanic plateau or a micro-continent. We hypothesize that the basement of the Chinese continental shelf represents such an exotic, buoyant and unsubductable mass, rather than seaward extension of the continental lithosphere of eastern China. The locus of the jammed trench (i.e., the suture) is predictably located on the shelf in the vicinity of, and parallel to, the arc-curved coastal line of the southeast continental China. It is not straightforward to locate the locus in the northern section of the East China Sea shelf because of the more recent (

Cenozoic strata from forearc basins in southern Alaska record deposition related to two different types of shallow subduction: Paleocene–Eocene spreading-ridge subduction and Oligocene–Recent oceanic plateau subduction. We use detrital zircon geochronology (n = 1368) and clast composition of conglomerate (n = 1068) to reconstruct the upper plate response to these two subduction events as recorded in forearc basin strata and modern river sediment. Following spreading-ridge subduction, the presence of Precambrian and Paleozoic detrital zircon ages in middle Eocene–lower Miocene arc-margin strata and Early Cretaceous ages in lower Miocene accretionary prism–margin strata indicates that sediment was transported to the basin from older terranes in interior Alaska and from the exhumed eastern part of the Cretaceous forearc system, respectively. By middle-late Miocene time, diminished abundances of these populations reflect shallow subduction of an oceanic plateau and associated exhumation that resulted in an overall contraction of the catchment area for the forearc depositional system. In the southern Alaska forearc basin system, upper plate processes associated with subduction of a spreading ridge resulted in an abrupt increase in the diversity of detrital zircon ages that reflect new sediment sources from far inboard regions. The detrital zircon signatures from strata deposited during oceanic plateau subduction record exhumation of the region above the flat slab, with the youngest detrital zircon population reflecting the last period of major arc activity prior to insertion of the flat slab. This study provides a foundation for new tectonic and provenance models of forearc basins that have been modified by shallow subduction processes, and may help to facilitate the use of U-Pb dating of detrital zircons to better understand basins that formed under changing geodynamic plate boundary conditions.

The Ontong Java Plateau (OJP) represents the result of a significant event in the Earth's geologic history. Limited geophysical and geochemical data, as well as the plateau's relative isolation in the Pacific ocean, have made interpretation of the modern day geologic structure and its 120 Ma formation history difficult. Here we present the highest resolution image to date of the wave speed structure of the OJP region. We use a data set that combines Rayleigh waves extracted from both ambient noise and earthquake waveforms and an iterative finite-frequency tomography methodology. The combination of datasets allow us to best exploit the limited station distribution in the Pacific and image wave speed structures between 35 km and 300 km into the Earth. We image a region of fast shear wave speeds, greater than 4.75 km/s, that extends to greater than 100 km beneath the plateau. The wave speeds are similar to as observed in cratonic environments and are consistent with a compositional anomaly that resulted from the residuum of eclogite entrainment during the plateau's formation. The combination of our imaged wave speed structure and previous geochemical work suggest that a surfacing plume head entrained eclogite from the deep mantle and accounts for the anomalous buoyancy characteristics of the plateau and observed fast wave speeds.

Fifteen multi-dimensional diagrams for basic and ultrabasic rocks, based on log-ratio transformations, were used to infer tectonic setting for eight case studies of Borborema Province, NE Brazil. The applications of these diagrams indicated the following results: (1) a mid-ocean ridge setting for Forquilha eclogites (Central Ceara domain) during the Mesoproterozoic; (2) an oceanic plateau setting for Algodoes amphibolites (Central Ceara domain) during the Paleoproterozoic; (3) an island arc setting for Brejo Seco amphibolites (Riacho do Pontal belt) during the Proterozoic; (4) an island arc to mid-ocean ridge setting for greenschists of the Monte Orebe Complex (Riacho do Pontal belt) during the Neoproterozoic; (5) within-plate (continental) setting for Vaza Barris domain mafic rocks (Sergipano belt) during the Neoproterozoic; (6) a less precise arc to continental rift for the Gentileza unit metadiorite/gabbro (Sergipano belt) during the Neoproterozoic; (7) an island arc setting for the Novo Gosto unit metabasalts (Sergipano belt) during Neoproterozoic; (8) continental rift setting for Rio Grande do Norte basic rocks during Miocene.

The Black Sea region comprises Gondwana-derived continental blocks and oceanic subduction complexes accreted to Laurasia. The core of Laurasia is made up of an Archaean-Palaeoproterozoic shield, whereas the Gondwana-derived blocks are characterized by a Neoproterozoic basement. In the early Palaeozoic, a Pontide terrane collided and amalgamated to the core of Laurasia, as part of the Avalonia-Laurasia collision. From the Silurian to Carboniferous, the southern margin of Laurasia was a passive margin. In the late Carboniferous, a magmatic arc, represented by part of the Pontides and the Caucasus, collided with this passive margin with the Carboniferous eclogites marking the zone of collision. This Variscan orogeny was followed by uplift and erosion during the Permian and subsequently by Early Triassic rifting. Northward subduction under Laurussia during the Late Triassic resulted in the accretion of an oceanic plateau, whose remnants are preserved in the Pontides and include Upper Triassic eclogites. The Cimmeride orogeny ended in the Early Jurassic, and in the Middle Jurassic the subduction jumped south of the accreted complexes, and a magmatic arc was established along the southern margin of Laurasia. There is little evidence for subduction during the latest Jurassic-Early Cretaceous in the eastern part of the Black Sea region, which was an area of carbonate sedimentation. In contrast, in the Balkans there was continental collision during this period. Subduction erosion in the Early Cretaceous removed a large crustal slice south of the Jurassic magmatic arc. Subduction in the second half of the Early Cretaceous is evidenced by eclogites and blueschists in the Central Pontides and by a now buried magmatic arc. A continuous extensional arc was established only in the Late Cretaceous, coeval with the opening of the Black Sea as a back-arc basin.

We present three 3D numerical models of deep subduction where buoyant material from an oceanic plateau and a plume interact with the overriding plate to assess the influence on subduction dynamics, trench geometry, and mechanisms for plateau accretion and continental growth. Transient instabilities of the convergent margin are produced, resulting in: contorted trench geometry; trench migration parallel with the plate margin; folding of the subducting slab and orocline development at the convergent margin; and transfer of the plateau to the overriding plate. The presence of plume material beneath the oceanic plateau causes flat subduction above the plume, resulting in a “bowed” shaped subducting slab. In plateau-only models, plateau accretion at the edge of the overriding plate results in trench migration around the edge of the plateau before subduction is re-established directly behind the trailing edge of the plateau. The plateau shortens and some plateau material subducts. The presence of buoyant plume material beneath the oceanic plateau has a profound influence on the behaviour of the convergent margin. In the plateau + plume model, plateau accretion causes rapid trench advance. Plate convergence is accommodated by shearing at the base of the plateau and shortening in the overriding plate. The trench migrates around the edge of the plateau and subduction is re-established well behind the trailing edge of the plateau, effectively embedding the plateau into the overriding plate. A slab window forms beneath the accreted plateau and plume material is transferred from the subducting plate to the overriding plate through the window. In all of the models, the subduction zone maintains a relatively stable configuration away from the buoyancy anomalies within the downgoing plate. The models provide a dynamic context for plateau and plume accretion in Phanerozoic accretionary orogenic systems such as the East China Orogen and the Central Asian Orogen (Altiads), which are characterised by accreted ophiolite complexes with diverse geochemical affinities, and a protracted evolution of accretion of exotic terranes including oceanic plateau and terranes with plume origins.

We present a new numerical trace element mass balance model for adiabatic melting of a pyroxenite-bearing peridotite for estimating mantle potential temperature, depth of melting column, and pyroxenite fraction in the source mantle for a primary ocean basalt/picrite. The Ocean Basalt Simulator version 1 (OBS1) uses a thermodynamic model of adiabatic melting of a pyroxenite-bearing peridotite with experimentally/thermodynamically parameterized liquidus-solidus intervals and source mineralogy. OBS1 can be used to calculate a sequence of adiabatic melting with two melting models, including (1) melting of peridotite and pyroxenite sources with simple mixing of their fractional melts (melt-melt mixing model), and (2) pyroxenite melting, melt metasomatism in the host peridotite, and melting of the metasomatized peridotite (source-metasomatism model). OBS1 can be used to explore (1) the fractions of peridotite and pyroxenite, (2) mantle potential temperature, (3) pressure of termination of melting, (4) degree of melting, and (5) residual mode of the sources. In order to constrain these parameters, the model calculates a mass balance for 26 incompatible trace elements in the sources and in the generated basalt/picrite. OBS1 is coded in an Excel spreadsheet and runs with VBA macros. Using OBS1, we examine the source compositions and conditions of the mid-oceanic ridge basalts, Loihi-Koolau basalts in the Hawaiian hot spot, and Jurassic Shatsky Rise and Mikabu oceanic plateau basalts and picrites. The OBS1 model shows the physical conditions, chemical mass balance, and amount of pyroxenite in the source peridotite, which are keys to global mantle recycling.

Plate tectonics is the governing theory that unifies the Earth Sciences and is unique to Earth. The sinking of lithosphere in subduction zones drives plate tectonics but exactly how and why subduction begins (subduction initiation, SI) remains enigmatic. Most SI models require exploitation of existing lithospheric weaknesses but these are now produced by plate tectonics; so how did the first subduction zones form? One possibility is SI along a plume head-cold lithosphere interface, but no examples have been documented. On the basis of three key observations, we show here that the Late Cretaceous tectonic evolution of Central America, NW South America and the Leeward Antilles is consistent with plume-induced SI (PISI) which nucleated along the southern and western margins of the Caribbean Plate (Caribbean Large Igneous Province, CLIP) at ~ 100 Ma. (1) Trace element chemistry of most 100 Ma and younger units interpreted as CLIP that are exposed along the southern margin of the Caribbean Plate and NW South America, record subduction additions which increased with time beginning at 100 Ma. These ‘plume- and arc-related’ (PAR) units are distinguishable from: (a) global oceanic plateau basalts (OPB); (b) 140–110 Ma OPB along the western edge of the CLIP; and (c) post-100 Ma OPB in the northernmost CLIP. Whereas the older OPB are compositionally identical to global OPB, the younger northerly CLIP units are similar to oceanic island basalts and record lower degrees of partial melting than PAR units exposed along the southern and western peripheries of the CLIP. Both the older and the younger northerly CLIP units lack evidence of subduction modification. (2) There is no known hiatus between CLIP and younger arc units, suggesting continuous tectono-magmatic evolution from plume to arc. (3) Generation of the CLIP and earliest, overlying and crosscutting arc units overlaps in time, space, chemical and isotopic compositions; both units are consistent with derivation from Galapagos Plume-like mantle which became increasingly subduction-modified with time. These observations illustrate that formation of the CLIP and earliest arc volcanism reflects partial melting of the same hybrid plume-subduction-modified source in a single, rapidly evolving tectonic environment. The scale of Late Cretaceous PISI in the SW Caribbean realm is consistent with the expected large scale of lithospheric collapse as seen for other SI examples, extending some 1400 km from southern Costa Rica–Panama to western Colombia and 1700 km from Ecuador to the Leeward Antilles (Aruba and Curacao). This first documented example of PISI may be relevant to the start of plate tectonics which may have started when subduction began around Precambrian plume heads. Establishment of lava chemostratigraphy designed to establish the composition of early SI magmatic successions might provide keys for deciphering whether SI occurred along a collapsed transform (like the IBM arc; early MORB-like lavas) or around a mantle plume (like the Caribbean; early plateau-like lavas). Recognition of this first example of PISI further suggests that interaction of a sufficiently large plume head with sufficiently dense oceanic lithosphere in Precambrian time may have triggered the modern regime of plate tectonics.

We disagree the transitional supra-subduction zone model of Feng et al. (Int J Earth Sci (Geol Rundsch) 105:491–505, 2016) for the tectonic setting of Jifeng ophiolite suite in NE China. Existence of the komatiite in the Jifeng ophiolite indicates an oceanic plateau environment for this ophiolite suite within the so-called Xinlin–Xiguitu ocean.