Oceanic Plateau Research Articles

Successive accretions of future allochthonous terranes and multiple subduction zone jumps: Implications for Tethyan evolution

Abstract The accretion of future allochthonous terranes (e.g., microcontinents or oceanic plateaus) onto the southern margin of Asia occurred repeatedly during the evolution and closure of the Tethyan oceanic realm, but the specific geodynamic processes of this protracted convergence, successive accretion, and subduction zone initiation remain largely unknown. Here, we use numerical models to better understand the dynamics that govern multiple terrane accretions and the polarity of new subduction zone initiation. Our results show that the sediments surrounding the future terranes and the structural complexity of the overriding plate are important factors that affect accretion of multiple plates and guide subduction polarity. Wide (≥400 km) and buoyant terranes with sediments behind them and fast continental plate motions are favorable for multiple unidirectional subduction zone jumps, which are also referred to as subduction zone transference, and successive terrane-accretion events. The jumping times (~3–20 + m.y.) are mainly determined by the convergence rates and rheology of the overriding complex plate with preceding terrane collisions, which increase with slower convergence rates and/or a greater number of preceding terrane collisions. Our work provides new insights into the key geodynamic conditions governing multiple subduction zone jumps induced by successive accretion and discusses Tethyan evolution at a macro level. More than 50 m.y. after India-Asia collision, subduction has yet to initiate along the southern Indian plate, which may be the joint result of slower plate convergence and partitioned deformation across southern Asia.

Late Mesozoic subduction-accretion in the southern Qiangtang: Insights from the Sumxi igneous complex of west-central Tibet

Knowledge of the evolution of the Bangong-Nujiang Tethyan Ocean is crucial for reconstructing the paleography of the Tethyan Realm, given its significance as a key component of the eastern Tethys. Nonetheless, there has been uncertainty regarding both the timing and the processes involved in the closure of this ocean. This study focused on a 110−106 Ma igneous complex comprising basalts−basaltic andesites, trachyandesites, and granodiorites from the Sumxi area in the western part of the Qiangtang terrane of west-central Tibet. The basalts−basaltic andesites have SiO2 contents of 52.5−58.7 wt% and MgO contents of 2.89−4.63 wt%, and exhibit some arc-like geochemical signatures. However, these rocks also have elevated Nb contents (>10 ppm) and Nb/La ratios (>0.5), as well as enriched Sr-Nd isotopic composition [εNd(t) = −7.40 to −6.00], implying that they are products of a mantle source metasomatized by adakitic melts. The trachyandesites are characterized by intermediate compositions (SiO2 = 63.6−65.2 wt%), high Mg number (40−60), and more enriched εNd(t) values (−8.37 to −7.49). Comparing their geochemical composition to that of mélange rocks, it is postulated that these trachyandesites were formed through the partial melting of a mantle source including mélange matrix rocks within a subduction zone. The granodiorites exhibit adakitic geochemical features (Sr = 830.14−1032.70 ppm, Y = 14.86−15.37 ppm, Sr/Y = 54−68), indicating that they originated from the partial melting of a thickened lower crust in a continental arc setting. Our results, in combination with a synthesis of tectonomagmatism along the Bangong-Nujiang suture zone, provide convincing evidence for subduction of an oceanic plateau and subsequent slab roll-back. The Sumxi igneous complex, with its clear arc affinity, suggests that the Bangong-Nujiang Tethyan Ocean, or at least its western part, remained open until the late Early Cretaceous (ca. 106 Ma).

Oceanic Plateau and Spreading Ridge Subduction Accompanying Arc Reversal in the Solomon Islands

AbstractWe study the collision of the Ontong Java Plateau, reversal of the Solomon Islands arc, and subduction of the Woodlark Basin spreading ridge in the southwest Pacific. Double‐sided subduction and intra‐arc deformation, not just polarity reversal, characterize the rapid Australia‐Pacific plate convergence. The rifted margins of the 0–6.2‐Ma Woodlark Basin separate its unflexed young lithosphere without a trench from the older flexed lithosphere with >8‐km‐deep trenches subducting to either side. A gap evident in the seismicity and tomography between the NE‐subducted slabs of the Solomon Sea and Australia plates indicates that the Woodlark lithosphere likely melts and/or is quickly (<1 m.y.) resorbed into the mantle. A section of the Pacific Plate remains attached within the gap and provides the slab pull to form the Malaita accretionary prism. Quaternary arc‐composition volcanoes that occur on both sides of the Woodlark Basin subduction front are not sourced from a mantle wedge overlying a Wadati‐Benioff zone, but come from and through breaks in the young incoming and subducting lithosphere and the overturning mantle beneath. Though the basin is too weak to sustain plate flexure, arc volcanoes on the subducting crust result in locally strong coupling to the forearc, manifest by tsunamigenic earthquakes. At 150–400‐km depth, the subducted slabs under the Solomon Islands are near vertical. They are near‐horizontal between the 410 and 660‐km mantle discontinuities beneath the Woodlark Basin and further south, whereas beneath the Solomon Sea Basin they dip southwest and penetrate the 660‐km discontinuity, having been detached by the north‐dipping Solomon Sea slab.

Evolution of the Manabí forearc basin in Ecuador: From the collision of Caribbean oceanic plateau to the build up of the Andes and Coastal Cordilleras

We investigate the evolution of the onshore Manabí forearc basin in Ecuador, which has developed on accreted oceanic terranes. We use 2D seismic profiles to identify 10 seismic units, separated by 9 unconformities. These units were dated by correlation with Ricaurte-1 well and regional stratigraphy. Unit S1 represents the first depocenter developed on the oceanic plateau before accretion. The emplacement of NE-dipping oceanic plateau slices evidencing the accretionary process dated to ∼75 Ma (Unconformity U1), was followed by folds and east-dipping thrusts at the Andes foothills that were eroded by unconformity U2 (56–41.3 Ma hiatus). The large distribution of unit S3 (late Eocene-Oligocene) over the topography inherited from the collision, points to the configuration of the post-collision forearc basin. The geometry of slope front fill and the thickening of unit S4 at the foot of the Andes reveals the building of Andean reliefs during the early Miocene. Unit S5 (17.8–15.9 Ma) is fan-shaped and abuts against the Jama fault, evidencing local extensional. After unconformity U5 (∼16 Ma), differential subsidence causes the installation of a westward-prograding sedimentary platform during the middle to late Miocene (S6 to S8). Since the Pliocene, the uplift of the Coastal Cordillera is related to localized shortening across the Jama and Canandé faults. Enhanced tectonic erosion at the tip of the margin,likely related to the Carnegie ridge subduction, could have led to underplating of offscraped material beneath the Coastal Cordillera, contributing to the uplift and enlargement of the Coastal Cordillera. The Pleistocene eastward tilt of the Santo Domingo fan (unit S10) relates to the Coastal Cordillera uplift. The fan is then deformed along the Andean thrust. This study provides a remarkable example of a forearc basin-fill developed on accreted oceanic terranes and controlled by erosional and underplating subduction processes, reactivation of inherited crustal structures, and the rise of peripheral reliefs.

Causes of Cretaceous subduction termination below South China and Borneo: Was the Proto-South China Sea underlain by an oceanic plateau?

The South China, Indochina, and Borneo margins surrounding the South China Sea contain long-lived arcs that became inactive at approximately 85 Ma, even though an embayment of oceanic crust (the ‘Proto-South China Sea’) remained in the intervening region. This oceanic crust eventually subducted in the Cenozoic below Borneo and the Cagayan arc, while the modern South China Sea opened in its wake. To investigate the enigmatic cessation of Mesozoic subduction below South China and Borneo, we studied a fragment of oceanic crust and overlying trench-fill sediments that accreted to NW Borneo during the final stages of Paleo-Pacific subduction. Based on radiolarian biostratigraphy of cherts overlying the pillow basalts and detrital zircon geochronology of the trench-fill, we constrained the minimum age of the oceanic crust during accretion to 40 Ma. This shows that subduction cessation was not related to ridge subduction. Geochemical analysis of pillow basalts revealed an enriched mid-ocean ridge basalt signature comparable to oceanic plateaus. Using paleomagnetism, we show that this fragment of oceanic crust was not part of the Izanagi Plate but was part of a plate (the ‘Pontus’ Plate) separated from the Izanagi Plate by a subduction zone. Based on the minimum 40 Ma age of the oceanic crust and its geochemistry, we suggest that Mesozoic subduction below South China and Borneo stopped when an oceanic plateau entered the trench, while the eastern plate margin with the Izanagi Plate remained active. We show how our findings offer opportunities to restore plate configurations of the Panthalassa-Tethys junction region.

Numerical modeling of induced subduction initiation: Insights from the oceanic plateau accretion

Subduction initiation is a crucial process for plate tectonics. Two scenarios of induced subduction initiation–subduction polarity reversal and subduction transference–are primarily attributed to the accretion of oceanic plateaus. However, the factors governing these two distinct types of subduction initiation remain elusive. Here, we employ 2D thermomechanical numerical models to investigate the dynamics of induced subduction initiation during oceanic plateau accretion. Specifically, we explore the impact of the thickness, density, and rheological strength of the oceanic plateau on subduction initiation. Our results reveal three geodynamic regimes: continuous subduction, subduction transference, and subduction polarity reversal. Thin oceanic plateaus tend to subduct along with slabs into the deep mantle, while thick oceanic plateaus often accrete to the margin, triggering subduction initiation. The rheological strength and density of an oceanic plateau play a significant role in determining whether subduction transference or polarity reversal occurs. Increasing the viscosity and decreasing the density of the oceanic plateau promotes strain concentration in front of the oceanic plateau, resulting in subduction polarity reversal. Our model results provide insights into the dynamics of subduction transference in the Caroline Sea and polarity reversal in Solomon in the western Pacific Ocean.

Petrogenesis and geochemistry of WNW-ESE to NW-SE trending doleritic dykes of the Paleoproterozoic Liptako basement (West African Craton, West Niger)

Doleritic dykes with regional orientations WNW-ESE to NW-SE, cut the Paleoproterozoic Birimian formations of the Liptako basement (Ouest-Niger). Mineralogical compositions studied from these doleritic dykes consist of augite (Wo21-40-En24-45-Fs13-54), pigeonite (Wo8-12-En45-59-Fs31-41), plagioclase, alkali feldspars, titano-magnetite, ilmenite, edenite, apatite, biotite and chlorite. The geochemical affinity of the doleritic dykes in the two trends is similar to oceanic plateau basalts (OPB), with high iron content relative to Mg. Negative Nb, Ti and Ta anomalies and the Y/Nb ratio (1.59–3.15) indicate a continental tholeiitic character for while light rare earth element enrichment, low to moderate Ti contents and the Th/Yb (0.28–0.59) and Nb/Yb (3.25–7.46) ratios suggest sources similar to E-MORB. Their Th/Nb (0.06–0.10), Th/Yb (0.28–0.59), TiO2/Yb (0.54–0.82) ratios suggest that the magma was generated by partial melting (5–17%) of a residual spinel-garnet lherzolite, that could have been part of a mantle plume. Relatively low Mg# (36–51) reflect some degrees of fractional crystallization, with some of this differentiation recorded between the margins and interiors of dykes. This differentiation was accompanied by unusually low degrees of crustal contamination, as indicated by relatively low Th/Ta ratios (1.18–2.03). This petrological and geochemical information provides new constraints on the origin of these WNW to NE trending mafic dykes of the West African Craton.

The Shatsky Rise oceanic plateau formed through plume–ridge interaction

The Shatsky Rise oceanic plateau formed through plume–ridge interaction

Review and tectonic interpretation of Precambrian Avalonia

Abstract Avalonia, defined by its distinctive uppermost Ediacaran–Ordovician overstep sequence, extends from New England through Atlantic Canada to Wales. It unconformably overlies: (1) parts of one cratonic Neoproterozoic arc that which records several pulses at: 760–730 Ma, 680–600 Ma and 580–540 Ma; (2) an 800–760 Ma passive margin sequence; and (3) c. 976 Ma isolated plutons, possibly basement. Comparisons with modern arc dimensions suggest the dip of the Benioff Zone ranged from c. 22° W in Newfoundland to c. 52–67° elsewhere. A 600–580 Ma hiatus in arc magmatism in Cape Breton Island is attributed to overriding an oceanic plateau, leading to a 15° decrease in the dip of the Benioff Zone. The Collector magnetic anomaly along the Grand Banks and the Minas Fault is inferred to mark the Neoproterozoic southern margin of the Avalon Plate consisting of leaky transform faults and trench segments characterized by magnetite serpentinite mantle wedge beneath forearcs. The Minas Fault/Collector Anomaly connects similar arc units in Cape Breton Island and southern New Brunswick, suggesting that they were already offset by the Minas transform fault in the late Neoproterozoic. Similar tectonic, palaeomagnetic and isotopic data in the Timan Orogen of Baltica suggest that Avalonia may correlate with the Kipchak arc.

Deep formation of Earth’s earliest continental crust consistent with subduction

About four billion years ago, Earth’s outer layer is thought to have been composed mostly of a 25- to 50-km-thick basaltic crust that differentiated to form the oldest stable continental crust. However, the tectonic processes responsible for the formation of this continental material remain controversial. Suggested explanations include convergent plate boundary processes akin to subduction operating today and a variety of relatively shallow (<50 km) non-plate-tectonic intracrustal mechanisms. Here we perform high-pressure–temperature melting experiments on an oceanic plateau analogue for the early basaltic crust and show that magmas with the composition of the early continental crust cannot form at pressures <1.4 GPa (~50 km depth). This suggests that Eoarchaean continental magmas are formed in deep (>50 km) subduction-like environments. Our results support previous Eoarchaean field evidence and analyses of igneous rocks that date to 4.0–3.6 billion years ago, which are consistent with subduction-like processes and suggest a primitive type of plate tectonics operated as long as 4 billion years ago on early Earth.

Evidence for a Paleogene boninitic arc following oceanic plateau-continent collision in the Western Cordillera of Colombia

The Caicedo Tuffs is a recently mapped Paleogene volcanic arc unit in the northern Andes, which provides insight into the magmatism of northwestern South America following its collision with the Caribbean-Colombian Oceanic Plateau (CCOP) in the latest Cretaceous. New regional geological mapping, igneous petrography, whole-rock and pyroxene geochemistry, and zircon U-Pb dating are provided for the northern sector of the eastern flank of the Western Cordillera of Colombia (Antioquia). These data reveal that the Caicedo Tuffs unit is predominantly composed of primary volcaniclastic deposits (tuff to breccia) that record mafic subaqueous volcanism and limited orogenic building shortly after collision of the CCOP. The geochemistry of these deposits includes major element characteristics and immobile trace element patterns that are typical of boninites. Zircons from these igneous rocks constrain a crystallization age of ca. 57 Ma, with meso-Proterozoic to Jurassic inherited zircons most likely reflecting continental recycling by turbidites in the subduction zone. The boninitic affinity of the Caicedo Tuffs and existing regional igneous and tectonic constraints can be explained by resuming of subduction and/or sinking of an older oceanic slab along northern South America following collision of the CCOP with South America. The boninitic, primary volcaniclastic deposits of the Caicedo Tuffs are crosscut by basaltic-gabbroic sills and dykes with oceanic plateau-like geochemical affinities, which lack evidence for hydrous melting and are compositionally similar to igneous rocks of the CCOP. These intrusions are interpreted to reflect decompression melting of plume-related mantle inherited during the collision of the CCOP with South America or slab detachment. The occurrence of oceanic plateau-like intrusions in a Paleocene volcanic arc casts doubt on the origin of other oceanic plateau sequences of the Western Cordillera, which are generally attributed to the Cretaceous CCOP. The Caicedo Tuffs is a unique boninite unit of which the detailed spatiotemporal extent and petrogenesis remain to be constrained, but that can provide valuable insight into tectono-magmatic processes during oceanic plateau-continent collision.

Constraints on the structure of the oceanic crust of the Tamu Massif by teleseismic P-wave coda autocorrelation

The Tamu Massif, considered the biggest single volcano on Earth, was formed by the accumulation of enormous amounts of magma erupting to the surface. It is the largest and oldest seamount in Shatsky Rise, which is the third largest oceanic plateau on Earth. However, the formation mechanism of Tamu Massif is still controversial because evidence point to different formation hypotheses. In this paper, we applied the P-wave coda autocorrelation method and used the hydrophone waveform data acquired by the ocean bottom seismometer (OBS) deployed on Tamu Massif to constrain the oceanic crust, and these results provide new finding on the structure of the oceanic crust for Tamu Massif. We hope it can provide some implications to research the formation mechanism of Tamu Massif. These results show that some stations in Tamu Massif received reflection signals from shallower depths that are nearly parallel to the seafloor. We infer that in the shallow oceanic crust, there is a layer composed of alternating eruptions of dense, higher velocity massive lava and sparse, lower velocity pillow lava flows, which have less density and lower velocity compared to the lower oceanic crust, with a strong acoustic impedance contrasts between them and thus able to generate a reflection signal, which is observed in our autocorrelation results.

Early Cretaceous subduction of an oceanic plateau at the Northern Andes; geochemical, metamorphic, and cooling age constraints of the Raspas Metamorphic Complex

The Raspas Metamorphic Complex is a high-pressure unit that includes eclogites, blueschists, and metapelites, with minor garnet amphibolites and greenschists. Although its geochemistry and ages are relatively well known, metamorphic constraints and the origin of its protolith remain unclear. In this study, we present new geochemical, metamorphic, and cooling age data to understand the protolith, metamorphic conditions, and the tectonic implications of this feature for the Northern Andes.Geochemical analyses reveals rocks with N- to E-MORB signatures and trace element ratios typical of a heterogeneous mantle source, like oceanic plateau lavas. Blueschists originated from a deep enriched source, similar to primitive mantle, while eclogites are similar to MORB. Iterative thermodynamic modeling of an eclogite indicates a low T/P gradient of ∼406 °C/GPa during the formation of the assemblage garnet (core), quartz, katophorite, and omphacite cores at ∼598 °C and 1.43 GPa, followed by the formation of atoll garnets and zoisite at 661 °C and 1.63 GPa, around 133 Ma. Peak metamorphic conditions were attained after isobaric heating at 709 °C and 1.61 GPa, resulting in the assemblage of garnet (rim), zoisite (rim), omphacite (rim), and katophorite. 40Ar/39Ar ages around 129 Ma indicate fast exhumation rates of 1.25 to 0.5 cm/yr.We propose that the Raspas Metamorphic Complex represents the interaction of the South American plate with an oceanic plateau during the Early Cretaceous. During the early stages of subduction, it created a flat slab geometry around 130 Ma. As the plateau transformed to eclogite, the decrease in buoyancy caused an increase in subduction dip during a regional roll-back at 129–123 Ma, which triggered the exhumation along the high-pressure belt.

Seismic stratigraphy and structural evolution of the South Korea Plateau, East Sea (Sea of Japan)

AbstractThe South Korea Plateau (SKP), a typical submarine plateau, preserves an important tectono‐sedimentary evolutionary record and represents a major frontier area for petroleum exploration in the East Sea (Sea of Japan). However, its tectonic mechanisms and their controls on sedimentary fill are underexplored. Here, we present the first integrated tectonostratigraphic framework of the SKP using reprocessed, two‐dimensional, seismic‐reflection profiles and borehole data. Four regional megasequence boundaries are interpreted, delineating four tectonostratigraphic packages: the syn‐rift (MS1), post‐rift phase 1 (MS2), post‐rift phase 2 (MS3) and syn‐compression (MS4) megasequences. We propose a four‐stage structural and sedimentary evolution model for the SKP based on the megasequences and structural development. Stage‐1 (latest Late Oligocene−Early Miocene): the SKP was rifted and extended through block faulting, resulting in the formation of rift basins dominated by fan‐delta and shallow‐lacustrine depositional systems. Stage‐2 (late Early Miocene−Middle Miocene): hemipelagic sedimentation prevailed with gravity‐controlled slope failures under a tectonically stable environment associated with slow thermal subsidence. Stage‐3 (late Middle Miocene−Late Miocene): continued thermal subsidence allowed the predominance of hemipelagic biogenic deposits accompanied by intermittent mass‐wasting‐induced turbidites and resulted in the development of a polygonal fault system. Stage‐4 (Early Pliocene−present): the SKP was influenced by E−W compression caused by an eastward movement of the Eurasian plate. Turbiditic and hemipelagic sedimentation was predominant with turbidity‐flow‐leveed channels derived from direct riverine input or through slope failures. Based on this tectonostratigraphic analysis, we reveal the variation in depositional systems and sand‐dispersal patterns for the SKP, highlighting potential targets for sandstone reservoirs: MS1, fan‐deltas and lacustrine‐fan turbidites; MS3, deepwater fan turbidites; and MS4, deepwater fan turbidites, channel‐levee complexes and turbidite frontal‐splay deposits. This study proposes a structural and sedimentary evolution model for the SKP that could enhance our understanding of reservoir potential for petroleum‐exploration in the future.

Nature and Origin of Magnetic Lineations Within Valdivia Bank: Ocean Plateau Formation by Complex Seafloor Spreading

AbstractValdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan‐Gough hotspot at the Mid‐Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi‐linear polarity zones crossing the plateau and following expected MAR paleo‐locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n‐C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading‐type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano.

Upper-plate response to ridge subduction and oceanic plateau accretion, Washington Cascades and surrounding region: Implications for plate tectonic evolution of the Pacific Northwest (USA and southwestern Canada) in the Paleogene

Abstract The interaction between subduction zones and oceanic spreading centers is a common tectonic process, and yet our understanding of how it is manifested in the geologic record is limited to a few well-constrained modern and ancient examples. In the Paleogene, at least one oceanic spreading center interacted with the northwestern margin of North America. Several lines of evidence place this triple junction near Washington (USA) and southern British Columbia (Canada) in the early to middle Eocene, and we summarize a variety of new data sets that permit us to track the plate tectonic setting and geologic evolution of this region from 65 to 40 Ma. The North Cascades segment of the voluminous Coast Mountains continental magmatic arc experienced a magmatic lull between ca. 60 and 50 Ma interpreted to reflect low-angle subduction. During this period of time, the Swauk Basin began to subside inboard of the paleo-trench in Washington, and the Siletzia oceanic plateau began to develop along the Farallon plate–Kula plate or Farallon plate–Resurrection plate spreading center. Farther east, peraluminous magmatism occurred in the Omineca belt and Idaho batholith. Accretion of Siletzia and ridge-trench interaction occurred between ca. 53 and 49 Ma, as indicated by: (1) near-trench magmatism from central Vancouver Island to northwestern Washington, (2) disruption and inversion of the Swauk Basin during a short-lived contractional event, (3) voluminous magmatism in the Kamloops-Challis belt accompanied by major E-W extension east of the North Cascades in metamorphic core complexes and supra-detachment basins and grabens, and (4) southwestward migration of magmatism across northeastern Washington. These events suggest that flat-slab subduction from ca. 60 to 52 Ma was followed by slab rollback and breakoff during accretion of Siletzia. A dramatic magmatic flare-up was associated with rollback and breakoff between ca. 49.4 and 45 Ma and included bimodal volcanism near the eastern edge of Siletzia, intrusion of granodioritic to granitic plutons in the crystalline core of the North Cascades, and extensive dike swarms in the North Cascades. Transtension during and shortly before the flare-up led to &amp;gt;300 km of total offset on dextral strike-slip faults, formation of the Chumstick strike-slip basin, and subhorizontal ductile stretching and rapid exhumation of rocks metamorphosed to 8–10 kbar in the North Cascades crystalline core. By ca. 45 Ma, the Farallon–Kula (or Resurrection)–North American triple junction was likely located in Oregon (USA), subduction of the Kula or Resurrection plate was established outboard of Siletzia, and strike-slip faulting was localized on the north-striking Straight Creek–Fraser River fault. Motion of this structure terminated by 35 Ma. These events culminated in the establishment of the modern Cascadia convergent margin.

Magmatic surge requires two-stage model for the Laramide orogeny

The Laramide orogeny is a pivotal time in the geological development of western North America, but its driving mechanism is controversial. Most prominent models suggest this event was caused by the collision of an oceanic plateau with the Southern California Batholith (SCB) which caused the angle of subduction beneath the continent to shallow and led to shut-down of the arc. Here, we use over 280 zircon and titanite Pb/U ages from the SCB to establish the timing and duration of magmatism, metamorphism and deformation. We show that magmatism was surging in the SCB from 90 to 70 Ma, the lower crust was hot, and cooling occurred after 75 Ma. These data contradict plateau underthrusting and flat-slab subduction as the driving mechanism for early Laramide deformation. We propose that the Laramide orogeny is a two-stage event consisting of: 1) an arc ‘flare-up’ phase in the SCB from 90-75 Ma; and 2) a widespread mountain building phase in the Laramide foreland belt from 75-50 Ma that is linked to subduction of an oceanic plateau.

Possible partial melting and production of felsic melt in a Jurassic oceanic plateau of the Izanagi Plate: Insights from 159 Ma plagiogranites from northern Japan

ABSTRACT A small tonalite – dacite body has been discovered in the Nakanogawa Group, Hidaka Belt, northern Japan, which is a Palaeogene subduction complex formed in the palaeo-Japan trench along the northeastern margin of Eurasia. The tonalites are characterized by extremely low K2O (0.2–0.3 wt.%) and relatively flat chondrite-normalized rare earth element patterns (La/Yb[N] ~2.3), similar to plagiogranites in ophiolites. The major-and trace-element characteristics are consistent with low-pressure partial melting of oceanic crust outside the garnet stability field. Zircon U – Pb dating of the tonalite yielded a weighted-mean 206Pb/238U age of 159.1 ± 1.6 Ma. Late Jurassic oceanic plateau-type basaltic rocks with a small amount of plagiogranitic rocks are distributed sporadically in subduction complexes along the palaeo-Japan arc – trench system. A similar zircon U – Pb age (151.6 ± 1.8 Ma) has been reported for greenstone in the Cretaceous subduction complex along the palaeo-Kuril arc – trench system. The tonalite – dacite block was probably derived from the subduction complex at the junction of the palaeo-Japan and -Kuril arc – trench systems. Thus, the greenstones and the tonalite body were likely part of a large oceanic plateau, which formed at the Izanagi – Pacific–Farallon ridge triple junction during the Late Jurassic – Early Cretaceous.

Tectonic evolution of the Meso-Tethys Ocean in the Jurassic: Birth, growth, and demise of a missing intra-oceanic arc

Reconstructing ophiolite ages and tectonic attributes can elucidate ancient ocean tectonic evolution. We present petrological, chronological, geochemical, and isotopic data for Ritu and Dongco ophiolites (Bangong–Nujiang suture zone, Tibetan Plateau). The ∼171 Ma Ritu and ∼169 Ma Dongco diabase are derived from high-temperature, highly depleted mantle metasomatized by subduction fluids; they are similar to fore-arc basalts. The ∼165 Ma Ritu andesites, from enriched mantle metasomatized by subduction fluids and a small proportion of subduction sediment melts, have affinity with the oceanic plateau. The ∼161 Ma Ritu dacites and Dongco granodiorites arose via interaction between subduction sediment melts and the mantle wedge, and ∼158 Ma Dongco granites were derived from subduction oceanic plate metasomatized by subduction sediment melts; they are all similar to arc magmatic rocks. Their high Na2O and low K2O and Th contents, and depleted zircon εHf(t) values, differ from those of southern Qiangtang terrane continental arc magmatic rocks, indicating intra-oceanic origin. The Middle Jurassic diabase and regional contemporaneous fore-arc basalts and boninites likely formed during intra-oceanic subduction initiation. The Middle–Late Jurassic dacites, granodiorites, granites, and regional contemporaneous high-Mg andesites likely formed in a mature intra-oceanic arc. Therefore, the Meso-Tethys Ocean may contain a ∼1000 km intra-oceanic subduction zone with Middle–Late Jurassic mature intra-oceanic arc. Subduction initiation of the intra-oceanic subduction zone likely arose via subduction transference caused by collage of the oceanic plateau and southern Qiangtang terrane at ∼182–177 Ma. At ∼171–155 Ma, the intra-oceanic arc gradually formed fore-arc basalts, boninites, high-Mg andesites, and tholeiitic/calc-alkaline arc rocks, indicating final maturity. The intra-oceanic arc west section potentially collided with the southern Qiangtang terrane ∼155–145 Ma, while the middle section potentially lasted until Early Cretaceous. Our study constrains Meso-Tethys Ocean evolution, providing an important basis for the study of intra-oceanic arcs in orogenic belts.

New evidence for the Ontong Java Nui hypothesis

The formation of the Ontong Java Nui super oceanic plateau (OJN), which is based on the model that the submarine Ontong Java Plateau (OJP), Manihiki Plateau (MP), and Hikurangi Plateau (HP) were once its contiguous fragments, could have been the largest globally consequential volcanic event in Earth’s history. This OJN hypothesis has been debated given the paucity of evidence, for example, the differences in crustal thickness, the compositional gap between MP and OJP basalts and the apparent older age of both plateaus relative to HP remain unresolved. Here we investigate the geochemical and 40Ar-39Ar ages of dredged rocks recovered from the OJP’s eastern margin. Volcanic rocks having compositions that match the low-Ti MP basalts are reported for the first time on the OJP and new ~ 96–116 Ma and 67–68 Ma 40Ar-39Ar age data bridge the temporal gap between OJP and HP. These results provide new evidence for the Ontong Java Nui hypothesis and a framework for an integrated tectonomagmatic evolution of the OJP, MP, and HP. The isotopic data imply four mantle components in the source of OJN that are also expressed in present-day Pacific hotspots sources, indicating origin from (and longevity of) the Pacific Large Low Shear-wave Velocity Province.