Subduction zone processes and crustal growth mechanisms at Pacific Rim convergent margins: modern and ancient analogues

2020 ◽  
Vol 158 (1) ◽  
pp. 1-12
Author(s):  
Yildirim Dilek ◽  
Yujiro Ogawa
Keyword(s):  
East Asia ◽  
Subduction Zone ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Pacific Rim ◽  
Convergent Margins ◽  
Lithospheric Extension ◽  
Subduction Zone Processes ◽  
Crustal Exhumation ◽  
Se China

AbstractContinents grow mainly through magmatism, relamination, accretionary prism development, sediment underplating, tectonic accretion of seamounts, oceanic plateaus and oceanic lithosphere, and collisions of island arcs at convergent margins. The modern Pacific–Rim subduction zone environments present a natural laboratory to examine the nature of these processes. The papers in this special issue focus on the: (1) modern and ancient accretionary margins of Japan; (2) arc–continent collision zone in the Taiwan orogenic belt; (3) accreting versus non-accreting convergent margins of the Americas; and (4) several examples of ancient convergent margins of East Asia. Subduction erosion and sediment underplating are important processes, affecting the melt evolution of arc magmas by giving them special crustal isotopic characteristics. Oblique arc–continent collisions cause strong deformation partitioning that results in orogen-parallel extension, crustal exhumation and wrench faulting in the hinterland, and thrust faulting–folding in the foreland. Trench-parallel widths of subducting slabs exert major control on slab geometries, the degree of coupling–decoupling between the lower and upper plates, and subduction velocity partitioning. An initially large width of the subducting Palaeo-Pacific Plate against East Asia caused flat subduction and resistance to slab rollback during the Triassic Period. These conditions resulted in shortening across SE China. Foundering and delamination of the flat slab during the Early Jurassic Epoch led to slab segmentation and reduced slab widths, followed by slab steepening and rollback. This pull-away tectonics induced lithospheric extension and magmatism in SE China during Late Jurassic – Cretaceous time. Melting of subducted carbonaceous sediments commonly produces networks of silicate veins in CLM that may subsequently undergo partial melting, producing ultrapotassic magmas.

Rock and age relationships within the Talkeetna forearc accretionary complex in the Nelchina area, southern Alaska

2020 ◽  
Vol 57 (6) ◽  
pp. 709-724
Author(s):  
John Barefoot ◽  
Elisabeth S. Nadin ◽  
Rainer J. Newberry ◽  
Alfredo Camacho
Keyword(s):  
Subduction Zone ◽  
Elevated Temperatures ◽  
Accretionary Prism ◽  
Fault System ◽  
Petrographic Analysis ◽  
Spreading Ridge ◽  
Current Configuration ◽  
Ridge Subduction ◽  
South Central ◽  
Subduction Zone Processes

Subduction zone processes are challenging to study because of the rarity of good exposures and the complexity of rock relationships within accretionary prisms. We report the results of field mapping and petrographic, geochemical, and geochronological analyses of the McHugh Complex accretionary prism mélange in south-central Alaska that was recently exposed due to retreat of the Nelchina Glacier. Our new mapping and analyses of the mélange, as well as adjacent Talkeetna arc intrusives, suggests that the previously mapped trace of the Border Ranges fault should shift northward in this location. Detailed petrographic analysis places this mélange exposure with the Potter Creek assemblage of the McHugh Complex. Blocks of pillow lavas within the mélange have both mid-ocean ridge basalt and intra-plate geochemical affinities, attesting to the complex relations of subduction-zone inputs in an alternating erosive–accretionary margin. A new zircon U–Pb age and geochemical analyses of a set of felsic dikes that cross-cut the accretionary sequence provide constraints on the regional tectonic evolution, including near-trench plutonism associated with the migration of a subducting spreading ridge along the southern Alaska margin during the Paleocene–Eocene. The McHugh section and cross-cutting dikes in this location are pervasively hydrothermally altered, which we attribute to elevated temperatures related to ridge subduction. Late-stage motion along the Border Ranges fault system, which is also recorded in the area, may also have contributed to the widespread alteration. Our data indicate that the Talkeetna volcanic arc and associated accretionary prism sediments were in their current configuration by 55 Ma.

Origin and emplacement of an inferred late Jurassic subduction-accretion complex, Euboea, eastern Greece

1991 ◽  
Vol 128 (1) ◽  
pp. 27-41 ◽  
Author(s):  
A. H. F. Robertson
Keyword(s):  
Shallow Water ◽  
Subduction Zone ◽  
Late Jurassic ◽  
Carbonate Platform ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Late Triassic ◽  
Accretionary Complex ◽  
Alkali Basalts

AbstractIn northern Euboea, central eastern Greece, an up to 3 km-thick polygenetic melange (Pagondas complex) is structurally interleaved between a Triassic–Jurassic carbonate platform (Pelagonian Zone) and an overriding harzburgitic ophiolite. The melange mainly comprises late Triassic shallow-water limestone and calciturbidites, radiolarites, Triassic–Jurassic tholeiites, alkaline basalts and minor andesites. The units concerned range from kilometre-sized thrust sheets, and detached blocks, to broken formation and structureless, or bedded matrix-supported conglomerates (diamictite). The melange includes remnants of Neotethyan oceanic lithosphere, overlain by radiolarites, hemipelagic carbonates and distal calciturbidites derived from a Mesozoic carbonate platform. Tholeiites were erupted at a Triassic–Jurassic spreading axis, whilst within-plate-type alkali basalts are interpreted mainly as seamounts. Kilometre-scale detached blocks of shallow-water coralline limestone are identified as collapsed atolls, formed within an ocean and/or along the rifted continental margin. Volcaniclastic sediments are locally interbedded with radiolarite, and reflect post-volcanic erosion of the ocean floor. Intra-oceanic convergence began, apparently in late early Jurassic time, giving rise to the Euboea ophiolite above an inferred westwards-dipping subduction zone. The Pagondas Complex then developed as an accretionary prism. The subduction trench later collided with the Pelagonian passive margin, driving the hot Euobea ophiolite over the accretionary complex, to produce amphibolites and greenschists of the metamorphic sole. Trench–margin collision then drove the entire supra-subduction zone complex, apparently eastwards, downflexing the Pelagonian carbonate platform to form a foredeep in which late Jurassic (Kimmeridgian–Tithonian) radiolarian sediments accumulated. During emplacement, the accretionary complex was disrupted and partly resedimented as debris flows, turbiditic volcaniclastic sandstone and shale in a foredeep, or foreland basin setting.

Fate of sediments on the descending plate at convergent margins

1981 ◽  
Vol 301 (1461) ◽  
pp. 233-251 ◽  
Keyword(s):  
Continental Crust ◽  
Sedimentary Cover ◽  
Indirect Evidence ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Silica Content ◽  
Isotopic Ratios ◽  
Convergent Margins ◽  
Arc Magmas ◽  
Sediment Cover

The evolution of the continents and of continental crust is strongly dependent on the trajectory of the sedimentary cover on the descending oceanic lithosphere at arc systems. Although direct calculations of accretion are not reliable, indirect evidence strongly suggests that most of the sediment cover is either accreted or underplated (subcreted) to the upper plate. This evidence includes the increased thickening of accretionary prism beneath parts of the inner trench slope that cannot be explained by deformation within the prism and by protolith composition both in subophiolitic metamorphics and in blueschist terrains. That a small fraction of this sediment cover is transported to depths of at least 100 km is demonstrated in several ways. Flux calculations of mass and selected elements through arc systems require addition of a few tens of metres of sediment to the arc magmas. Global correlations of variations between arc magma characteristics and regional geological parameters show: (1) a strong correlation between silica content of average arc magmas and thickness or maturity of crust in the upper plate, attributed to upper plate contamination; (2) regional variations in 87 Sr/ 86 Sr and Pb isotopic ratios of arc basalts that correlate spatially with isotopic ratios in the non-calcareous components of pelagic sediments. This correlation is argued to reflect the variation of terrigenous material in the basal pelagics that are involved in magma production. Subduction of continental crust to depths of 100 km, either as part of the descending plate or by tectonic erosion of the upper plate is not supported by these correlations. Recycling rates of continental crust by accretion and subcretion and of mantle by subduction of oceanic lithosphere in contemporary arcs are very large compared with the growth rate of continental crust, which appears similar to the magma production rates in arc systems. This present production rate of continental crust is very much smaller than that during early Earth history, and is compatible with Phanerozoic ocean freeboard changes. In addition, average SiO 2 and K 2 O contents of contemporary arc magmas are much lower than those estimated for mean continental crust, leading to the conclusion that the magmas being produced at active arcs cannot be used as a model for the development of most of the Earth’s continental areas.

Across-arc variations in Mo isotopes and implications for subducted oceanic crust in the source of back-arc basin volcanic rocks

Geology ◽  
2021 ◽  
Author(s):  
Xiaohui Li ◽  
Quanshu Yan ◽  
Zhigang Zeng ◽  
Jingjing Fan ◽  
Sanzhong Li ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
Volcanic Rocks ◽  
Isotope Ratios ◽  
Oceanic Lithosphere ◽  
Magma Source ◽  
Benioff Zone ◽  
Subduction Zone Processes ◽  
Subducted Oceanic Crust ◽  
Back Arc

Molybdenum (Mo) isotope ratios provide a potential means of tracing material recycling involved in subduction zone processes. However, the geochemical behavior of Mo in subducted oceanic crust remains enigmatic. We analyzed Mo isotope ratios of arc and back-arc basin lavas from the Mariana subduction zone (western Pacific Ocean), combining newly obtained element and Sr-Nd-Pb-Li isotope data to investigate subduction zone geochemical processes involving Mo. The Mo isotope ratios (δ98/95MoNIST3134; U.S. National Institute of Standards and Technology [NIST] Mo standard) of the volcanic rocks showed clear across-arc variations, decreasing with increasing depth to the Wadati-Benioff zone. The high δ98/95Mo values in the Mariana Islands (–0.18‰ to +0.38‰) correspond to high 87Sr/86Sr, low 143Nd/144Nd, and radiogenic Pb isotope ratios, suggesting that altered upper oceanic crust played an important role in the magma source. The low δ98/95Mo values in the Central Mariana Trough (–0.65‰ to –0.17‰) with mantle-like Sr-Nd-Pb but slightly low δ7Li values provide direct evidence for the contribution of deep recycled oceanic crust to the magma source of the back-arc basin lavas. The isotopically light Mo magmas originated by partial melting of a residual subducted slab (eclogite) after high degrees of dehydration and then penetrated into the back-arc mantle. This interpretation provides a new perspective with which to investigate the deep recycling of subducted oceanic lithosphere and associated magma petrogenesis.

scholarly journals Late Cretaceous–Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey

2009 ◽  
Vol 146 (4) ◽  
pp. 567-590 ◽  
Author(s):  
SAMUEL P. RICE ◽  
ALASTAIR H. F. ROBERTSON ◽  
TIMUR USTAÖMER ◽  
NURDAN İNAN ◽  
KEMAL TASLI
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Suture Zone ◽  
Passive Margin ◽  
Early Eocene ◽  
Volcanic Arc ◽  
Eastern Pontides

AbstractSix individual tectonostratigraphic units are identified within the İzmir–Ankara–Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayıkayası Formation of Campanian–Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayıkayası Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of ~75% (by volume) serpentinized peridotite (mainly harzburgite), ~20% diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Mélange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadağ Formation, of Campanian–Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian–Early Eocene Sütpınar Formation (~1500 m thick) is a coarsening-upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene–Eocene Sipikör Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic arc units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian–Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys.

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