Magnetotelluric image of the Chilean subduction zone in the Salar de Atacama region (23°-24°S): Insights into factors controlling the distribution of volcanic arc magmatism.

Abstract The Azuero Peninsula, located in SW Panama, is a region characterized by a long-lived intra-oceanic subduction zone. Volcanism began in Late Cretaceous time, as the result of subduction of the Farallon plate beneath the Caribbean plate. Usually, ancient volcanic arcs related to intra-oceanic subduction zones are not preserved, because they are in areas with difficult access or covered by modern volcanic arc material. However, on the Azuero peninsula, a complete section of the volcanic arc together with arc basement rocks provides the opportunity to study the sedimentation and volcanism in the initial stages of volcanic arc development. The lithostratigraphic unit which records fore-arc evolution is the “Río Quema” Formation (RQF), a volcanic apron composed of volcanic and volcaniclastic sedimentary rocks interbedded with hemipelagic limestones, submarine dacite lava domes, and intruded by basaltic-andesitic dikes. The “Río Quema” Formation, interpreted as a fore-arc basin infilling sequence, lies discordantly on top of arc basement rocks. The exceptionally well exposed arc basement, fore-arc basin, volcanic arc rocks and arc-related intrusive rocks provide an unusual opportunity to study the relationship between volcanism, sedimentation and magmatism during the arc development, with the objective to reconstruct its evolution. The “Río Quema” Formation can be divided into three groups: 1) proximal apron, a sequence dominated by lava flows, interbedded with breccias, mass flows and channel fill, all intruded by basaltic dikes. The rocks represent the nearest materials to the volcanic source, reflecting a coarse sediment supply. This depositional environment is similar to gravel-rich fan deltas and submarine ramps; 2) medial apron, characterized by a volcanosedimentary succession dominated by andesitic lava flows, polymictic volcanic conglomerates and crystal-rich sandstones with minor pelagic sediments and turbidites. These rocks were deposited from high-density turbidity currents and debris flows, directly derived from erupted material and gravitational collapse of an unstable volcanic edifice or volcaniclastic apron; 3) distal apron, a thick succession of sandy to muddy volcaniclastic rocks, interbedded with pelagic limestones and minor andesitic lavas, intruded by dacite domes and by basaltic to andesitic dikes. Bedforms and fossils suggest a quiet, relatively deep-water environment characterized by settling of clay and silt (claystone, siltstone) and by dilute turbidity currents of reworked volcaniclastic detritus. The timing of the initial stages of the volcanic arc has been constrained through a biostratigraphic study, using planktonic foraminifera and radiolarian species. The fossil assemblage indicates that the age of the “Río Quema” Formation ranges from Late Campanian to Maastrichtian, providing a good constraint for the development of the volcanic arc and volcaniclastic apron, during the initial stages of an intra-oceanic subduction zone.

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GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua

Geophysical Journal International ◽

10.1111/j.1365-246x.2009.04371.x ◽

2009 ◽

Vol 179 (3) ◽

pp. 1279-1291 ◽

Cited By ~ 43

Author(s):

F. Correa-Mora ◽

C. DeMets ◽

D. Alvarado ◽

H. L. Turner ◽

G. Mattioli ◽

...

Keyword(s):

El Salvador ◽

Subduction Zone ◽

Central America ◽

Volcanic Arc

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Identification of Jurassic mafic arc magmatism in the eastern North China Craton: Geochemical evidence for westward subduction of the Paleo-Pacific slab

Geological Society of America Bulletin ◽

10.1130/b35787.1 ◽

2020 ◽

Author(s):

Wei Fang ◽

Li-Qun Dai ◽

Yong-Fei Zheng ◽

Zi-Fu Zhao ◽

Li-Tao Ma ◽

...

Keyword(s):

Subduction Zone ◽

North China Craton ◽

North China ◽

The Other ◽

Arc Magmatism ◽

Early Mesozoic ◽

Mantle Sources ◽

Pacific Slab ◽

Cratonic Mantle ◽

T Values

Subduction of the Paleo-Pacific slab beneath the North China Craton (NCC) has exerted a strong influence on the Mesozoic destruction of the craton. However, no Andean-type arc magmatism has been reliably identified in the eastern NCC. Here we report the occurrence of Jurassic arc-like lamprophyres in the Liaodong Peninsula, providing a snapshot of the Paleo-Pacific slab subduction beneath the NCC in the early Mesozoic. Zircon U-Pb dating of the lamprophyres yields consistent ages of 158−155 Ma for magma crystallization. These lamprophyres all exhibit typical arc-like trace element distribution patterns, but show a series differences in their radiogenic isotope compositions and the other geochemical variables. Type 1 lamprophyres exhibit weakly enriched Sr-Nd-Hf isotopes with (87Sr/86Sr)i ratios of 0.7075−0.7085, εNd(t) values of −3.9 to −1.3 and εHf(t) values of −5.4 to −0.3, whereas Type 2 lamprophyres exhibit moderately enriched radiogenic isotopes with (87Sr/86Sr)i ratios of 0.7096−0.7117, εNd(t) values of −12.2 to −7.6 and εHf(t) values of −12.8 to −4.7. There are also systematic differences in zircon Hf isotopes and whole-rock Ba/Th, Ba/La, Sr/Nd, Th/Nd, Th/Yb, and La/Sm ratios for the two types of lamprophyre. Taken together, these similarities and differences can be accounted for by metasomatic reaction of the cratonic mantle wedge with two properties of liquid phase derived from subducting Paleo-Pacific slab. One is aqueous solutions from the subducting basaltic oceanic crust, and the other is hydrous melts from the subducting terrigenous. The two properties of subduction zone fluids were incorporated in different proportions into the mantle sources of these lamprophyres. Accordingly, the lamprophyres were derived from the metasomatic mantle sources. This qualitative interpretation is verified by quantitative modeling of the geochemical transfer at the slab-mantle interface in a paleo-oceanic subduction zone. Therefore, the Jurassic lamprophyres in the eastern NCC provide the geochemical evidence for the crust-mantle interaction during the Paleo-Pacific slab subduction beneath eastern Asia in the early Mesozoic, when the chemical metasomatism by the slab-derived fluids would have weakened the cratonic mantle for its thinning and destruction in the Early Cretaceous.

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Life cycle of an Archean subduction zone from initiation to arc–polarity reversal: Insights from the Zunhua ophiolitic mélange, North China Craton

10.5194/egusphere-egu21-3833 ◽

2021 ◽

Author(s):

Wenbin Ning ◽

Timothy Kusky ◽

Junpeng Wang ◽

Lu Wang ◽

Hao Deng ◽

...

Keyword(s):

Life Cycle ◽

Subduction Zone ◽

North China Craton ◽

Plate Tectonics ◽

North China ◽

Polarity Reversal ◽

Iron Formation ◽

Arc Magmatism ◽

Subduction Initiation ◽

Depleted Mantle

Subduction initiation and arc&#8211;polarity reversal have rarely been recognized in the Archean rock record. We document Neoarchean subduction initiation, fore-arc magmatism, and an arc&#8211;polarity reversal event from the Zunhua structural belt along the eastern margin of the Central Orogenic Belt (COB) of the North China Craton (NCC). The Zunhua ophiolitic m&#233;lange within the Zunhua structural belt is a mappable unit characterized by blocks of metamorphosed harzburgite/lherzolite, podiform chromite &#8211;bearing dunite, pyroxenite, amphibolite, metabasites (basalt and diabase) with rare intermediate volcanics, chert, and tectonic lenses of banded iron formation in a strongly sheared metapelitic matrix. New geochronological and geochemical analyses of magmatic blocks within the ophiolitic m&#233;lange show that the crustal magmatic rocks were produced in a fore-arc region at 2.55&#8211;2.52 Ga from depletion of the harzburgitic&#8211;lherzolitic mantle tectonites. Chemical, petrological, and temporal links between the depleted mantle blocks, and the suite of magmatic blocks derived from partial melting and metasomatism of these depleted mantle blocks, unequivocally shows that they represent part of the same original Neoarchean fore-arc ophiolite suite. After formation and accretion in the oceanic realm, the m&#233;lange was emplaced on the continental margin of the Eastern Block between 2.52&#8211;2.50 Ga, and underwent two stages of metamorphism at ca. 2.48&#8211;2.46 Ga and 1.81 Ga. Metamorphosed intermediate&#8211;mafic volcanic blocks exhibit systematic successive geochemical variations, from MORB-like to volcanic arc-like, and the N-MORB-like meta-basalts show remarkable similarity with the subduction initiation-related Izu&#8211;Bonin&#8211;Mariana (IBM) fore-arc basalts. We suggest that the Zunhua fore-arc complex records continuous geodynamic processes from subduction initiation to arc magmatism. The Zunhua ophiolitic m&#233;lange is part of a ca. 2.5 Ga suture between an oceanic arc of the COB and Eastern Block of the NCC. After the arc&#8211;continent collision, an arc&#8211;polarity reversal event has been proposed to initiate a new eastward&#8211;dipping subduction zone on the western side of the COB. This arc&#8211;polarity reversal can be traced for more than 1,600 km along the length of the orogen, similar in scale, geometry, and duration between collision and polarity flip to the present-day arc&#8211;polarity reversal of the Sunda&#8211;Banda arc during its ongoing collision with the Australia continent. This indicates that a life cycle of an Archean subduction zone, including birth (subduction initiation), maturity (arc magmatism), death (arc-continent collision) and re-birth (arc&#8211;polarity reversal), is recorded in the Zunhua ophiolitic m&#233;lange, and the geodynamics of plate tectonics at the end of the Archean was similar to that of today.&#160;

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Seismic Imaging, Arc Magamtism and Megathrust Earthquake under the Western Pacific Subduction Zone

10.5194/egusphere-egu2020-1600 ◽

2020 ◽

Author(s):

Zhi Wang ◽

Jian Wang

Keyword(s):

Partial Melting ◽

Subduction Zone ◽

Oceanic Crust ◽

Mantle Wedge ◽

Western Pacific ◽

Arc Magmatism ◽

S Wave ◽

Slab Melting ◽

Megathrust Earthquake ◽

The Western Pacific

Arc magmatism and megathrust earthquake occurrence in a subduction zone are deemed to attribute to many factors, including structural heterogeneities, fluid contents, temperature, depth of subducting oceanic crust, and etc. However, how these factors affect them is unclear. The extensive arc magmatism observed on the island arcs is considered to be an indicator on chemical exchange between the wedge mantle and the surface in a subduction zone. Megathrust earthquake frequently occurrence is also considered to be attributed to the slab melting and associated interplate coupling of the subducting plate. The Western Pacific subduction zone is regarded as one of the best Laboratory for seismologists to examine these processes due to the densest seismic networks recording numerous earthquakes. Some of the previous studies suggest that the island-arc magmatism is mainly contributed to the melting of peridotite in the mantle wedge due to fluids intrusion from the dehydration process associated with the subducting oceanic crust. They further argued that the oceanic plate could only provide water to the overlying mantle wedge for arc magmatism, but not melt itself due to that it is too cold to melt at a depth between 100 and 200km. However, some of other studies revealed that the hydrated basalt derived from the mid-ocean ridge will be melted with high T and water saturated on the upper interface of the sbuducting plate in the mantle wedge. We consider that the three-dimensional (3-D) P- and S- wave velocity (Vp, Vs) and Poisson&#8217;s ratio (&#963;) structures of the subduction zone, synthesized from a large-quantity of high-quality direct P-, and S-wave arrival times of source-recive pairs from the well located suboceanic events with sP depth phase data could provide a compelling evidence for structural heterogeneity, highly hydrated and serpentinized forearc mantle and dehydrated fluids in the subduction zones. In this study, we combined seismic velocities and Poisson&#8217;s ratio images under the entire-arc region of the Western Pacific subduction zone to reveal their effects on megathrust earthquake generation and arc magmatism. We find that a ~10 km-thick low-velocity layer with high-V and high-Poisson&#8217;s ratio anomalies is clearly imaged along the upper interface of the subducting Pacific slab. This distinct layer implies partial melting of the oceanic crust due to the deep-seated metamorophic reactions depending on the source of fluids and temperature regime. Such a process could refertilize the overlying mantle wedge and enrich the peridotite sources of basalts under the island arc. Significant low-V and high-Poisson&#8217;s ratio anomalies were observed in the mantle wedge along the volcanic front, indicating melting or partial melting of peridotite-rich mantle and then yield tholeiitic magma there. The present study demonstrates that the combined factors of fluid content, mineral composition and thermal regime play a crucial role in both slab melting and arc-magmatism under the Western Pacific subduction zone.

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Subducting serpentinites release reduced, not oxidized, aqueous fluids

Scientific Reports ◽

10.1038/s41598-019-55944-8 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 12

Author(s):

F. Piccoli ◽

J. Hermann ◽

T. Pettke ◽

J. A. D. Connolly ◽

E. D. Kempf ◽

...

Keyword(s):

Subduction Zone ◽

Oxygen Fugacity ◽

Mantle Wedge ◽

Thermodynamic Modelling ◽

Arc Magmatism ◽

Redox Processes ◽

Arc Magmas ◽

Reducing Conditions ◽

Mid Ocean Ridge ◽

Ocean Ridge

AbstractThe observation that primitive arc magmas are more oxidized than mid-ocean-ridge basalts has led to the paradigm that slab-derived fluids carry SO2 and CO2 that metasomatize and oxidize the sub-arc mantle wedge. We combine petrography and thermodynamic modelling to quantify the oxygen fugacity (fO2) and speciation of the fluids generated by serpentinite dehydration during subduction. Silicate-magnetite assemblages maintain fO2 conditions similar to the quartz-fayalite-magnetite (QFM) buffer at fore-arc conditions. Sulphides are stable under such conditions and aqueous fluids contain minor S. At sub-arc depth, dehydration occurs under more reducing conditions producing aqueous fluids carrying H2S. This finding brings into question current models in which serpentinite-derived fluids are the cause of oxidized arc magmatism and has major implications for the global volatile cycle, as well as for redox processes controlling subduction zone geodynamics.

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Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data

Solid Earth ◽

10.5194/se-6-1169-2015 ◽

2015 ◽

Vol 6 (4) ◽

pp. 1169-1183 ◽

Cited By ~ 14

Author(s):

O. H. Lücke ◽

I. G. Arroyo

Keyword(s):

Costa Rica ◽

Subduction Zone ◽

Gravity Modeling ◽

Northwestern Part ◽

Intraplate Seismicity ◽

Gradual Change ◽

Slab Geometry ◽

Local Networks ◽

Volcanic Arc ◽

Dehydration Reactions

Abstract. The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry in Costa Rica is presented based on 3-D density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. Contrary to commonly assumed, to the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a maximum depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth (> 75 km) intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.

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Evolution of the Pacific Margin, Vancouver Island, and adjacent regions

Canadian Journal of Earth Sciences ◽

10.1139/e77-176 ◽

1977 ◽

Vol 14 (9) ◽

pp. 2062-2085 ◽

Cited By ~ 54

Author(s):

J. E. Muller

Keyword(s):

Subduction Zone ◽

Continental Margin ◽

Upper Jurassic ◽

Vancouver Island ◽

Late Eocene ◽

Volcanic Arc ◽

Late Mesozoic ◽

Clastic Sediments ◽

The Pacific ◽

Uplift And Erosion

The tectonic–stratigraphic evolution of Vancouver Island, a part of the Insular Belt, is reviewed as it relates to the other major tectonic belts recognized in the western Cordillera of Canada and the adjacent United States. The Pacific Belt, recognized south of the international border, is also identified in the west and south of the island. Oldest rocks of the Insular Belt are a late Paleozoic volcanic arc terrane and a crystalline 'basement' that is probably pre-Devonian. A thick Upper Triassic succession of tholeiitic pillow lavas and flows, overlain by carbonate–clastic sediments, rests in part on the Paleozoic. Elsewhere the tholeiite may represent oceanic floor, perhaps formed when the Insular Belt was fragmented and rifted off the continental margin far to the south. Above it the Early Jurassic volcanic arc with related batholiths may have been aligned with a similar terrane in the Intermontane Belt before the two belts assumed parallel positions in late Mesozoic time. An Upper Jurassic – Lower Cretaceous westward thickening clastic wedge indicates uplift and erosion of the volcanic arc in late Mesozoic time. Further west the 'inner Pacific Belt' of Jura-Cretaceous elastics and chert represent slope and trench deposits that have been deformed to mélange or converted to schist. They are coeval and homologous to Franciscan and Chugach Terranes and probably mark the late Mesozoic trench and subduction zone along the continental margin. The Coast Plutonic Belt represents the related volcanic arc, and pre-Cretaceous Insular Belt rocks, unconformably overlain by Cretaceous clastic sediments, represent the arc–trench gap and fore-arc basin. Until Late Cretaceous time convergence of the Insular and Pacific Belts occurred along San Juan Fault. In early Tertiary time Eocene oceanic basalt (Outer Pacific Belt) and Jura-Cretaceous metasediments (Inner Pacific Belt) converged by under-thrusting and (or) strike–slip faulting along Leech River Fault. In Late Eocene time the trench and subduction zone shifted westward to the present core zone of the Olympic Mountains and shifted again in Miocene time to its present position.

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