Ocean Plate Stratigraphy Research Articles

Sanbagawa Subduction: What Went in, How Deep, and How Hot did it Get?

The Sanbagawa belt is a “coherent” oceanic subduction-type metamorphic region representing a rock package predominantly derived from oceanic crust and accreted at depths of 20–80 km (300–700 °C). The thermal structure and lithological layers are complexly deformed but semi-continuous, in contrast to more commonly reported subduction-related domains dominated by mélange. The coeval Shimanto accretionary complex records accretion at depths <15 km and the rocks are primarily terrigenous sediments. The Sanbagawa belt has a greater proportion of mafic rocks than the Shimanto complex, implying progressive peeling-off of oceanic plate stratigraphy with more basaltic oceanic crust slices accreted at deeper levels. Tectonic exhumation can be explained by three separate phases dominated by buoyancy-driven upflow, ductile thinning, and normal faulting.

Beyond the Akiyoshi Orogeny: unravelling overturned structures and tectonic processes in the Permian accretionary complex of the Mine-Akiyoshidai area, Yamaguchi, western Japan

The concept of the Akiyoshi Orogeny emerged from geological studies of the overturned Akiyoshi Limestone. However, our understanding of the stratigraphy and geological structure of the siliceous–clastic rocks surrounding the Akiyoshi Limestone remains incomplete. We therefore conducted a geological survey within the Beppu unit, which is distributed north of the Akiyoshi Limestone. We found substantial overturning of the strata, even within the siliceous–clastic rocks that form the upper section of the ocean plate stratigraphy within the accretionary complex. The Tsunemori Formation, representing sediments of the forearc or trench slope basin, has also undergone overturning. Extensive overturned structures therefore exist throughout the entire accretionary complex of the Mine-Akiyoshidai area. To understand the mechanism behind these overturned structures within the accretionary complex, we focused on the collision and deformation resulting from the interaction between the accretionary wedge and a massive seamount, along with the back-stop. The overturning of the forearc or slope basin sediments suggests that post-accretion deformation along a large lateral fault may have occurred during the collision between the South and North China blocks. These tectonic events during and after accretion may represent the true nature of the Akiyoshi Orogeny. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Evolution of the Neo-Tethys traced by Late Triassic to Early Cretaceous marine remnants in the eastern segment of the Yarlung-Tsangpo suture zone, southern Tibet

Widely distributed siliceous mélanges in the Yarlung-Tsangpo suture zone preserve significant information of the Neo-Tethys and subduction-accretion processes. Similar ophiolites and siliceous mélanges are well exposed in the Xigaze and Zedong areas, however, their relationship including age assignments, depositional environments, and accretionary process remains vague. Based on radiolarian biostratigraphy (56 species belonging to 35 genera), black cherts from the Carnian to the Norian (Late Triassic), red cherts from the Aalenian to Bathonian (Middle Jurassic), and siliceous mudstones of the Berriasian (Early Cretaceous) are distinguished from siliceous mélange in the Zedong area. Values of Al/(Al + Fe + Mn) indicate that the siliceous rocks are biogenic silica derived. The diagrams of Al2O3/(Al2O3 + Fe2O3) vs Fe2O3/TiO2 and Al2O3/(Al2O3 + Fe2O3) vs LaN/CeN indicate siliceous rocks were deposited far from the ridge. Weak positive Ce anomaly and low ratio of LaN/CeN indicate that siliceous rocks were deposited in a deep-sea basin proximal to terrigenous sources. Comprehensive summary of studies on Bainang siliceous mélange, Xigaze ophiolite, Zedong ophiolite, and Zedong siliceous mélange reconstructs the Ocean Plate Stratigraphy (OPS) and the evolution of the Neo-Tethys since the Late Triassic till the Early Cretaceous. Mélanges in Xigaze and Zedong were formed in different intra–oceanic subduction-accretion systems at different times in the Neo-Tethys Ocean during the Cretaceous.

A new tectonic model for the Itmurundy Zone, central Kazakhstan: linking ocean plate stratigraphy, timing of accretion and subduction polarity

The Itmurundy Zone of Central Kazakhstan is a key structure in the core of the Kazakh Orocline representing a typical Pacific-type orogenic belt hosting accretionary complex, ophiolite massifs and serpentinite mélange. The main controversies in the existing tectonic models of the Itmurundy Zone are about the timing of subduction and accretion, the direction and kinematics of subduction and the number of oceanic plates. A new model for the early Paleozoic tectonic story of the Itmurundy Zone is postulated in this paper, based on new detailed geological and U–Pb detrital zircon age data, combined with previously documented geological, U–Pb age, microfossil, geochemical and isotope data from igneous rocks, deep-sea sediments and greywacke sandstones. The present study employs the Ocean Plate Stratigraphy (OPS) model to explain the tectonic processes involved in the evolution of the Itmurundy Zone and to present a holistic story of Ordovician oceanic plate(s), which accretion formed an accretionary complex. The detailed mapping allows distinguishing three types of OPS assemblages: (1) Chert-dominated, (2) OIB-hosting, and (3) MORB-hosting. The U–Pb ages of detrital zircons from sandstones of OIB and Chert types show unimodal distributions with similar main peaks of magmatism at 460–455 Ma in the provenance, and their maximum depositional ages (MDA) span 455–433 Ma. Two samples from OPS Type 3 show the peaks of magmatism both at ca. 460 Ma and the MDA of 452 Ma and 459 Ma, respectively. The MDA of sandstones and microfossils data from chert show the younging of strata to the south and SE in Types 1 and 2 and to NEE for Type 3 (in present coordinates) suggesting double-sided subduction to the NNW and SEE and, accordingly, the co-existence of pieces of two oceanic plates in Ordovician time. The U–Pb zircon data from both igneous and clastic rocks indicate a period of subduction erosion in early Ordovician time. As a whole, the accreted OPS units of the Itmurundy Zone record the timing of subduction and accretion from the early Ordovician to the early Silurian, i.e., 60 Ma at shortest.

Magnetic fabric of Ocean Plate Stratigraphy mélanges: a tool for unravelling protracted histories of oceanic plates from seafloor spreading to tectonic emplacement into accretionary wedges

Multiple magnetic fabrics, referred to as F1–F5, were revealed through the anisotropy of magnetic susceptibility in an Ocean Plate Stratigraphy (OPS) mélange of the Neoproterozoic–Cambrian Blovice accretionary complex, Bohemian Massif. The fabrics post-date the formation of the mélange and the rotation of basalt blocks within the matrix and are interpreted in terms of a complex structural history of the mélange. Excluding local fabrics, the F1 fabric formed earlier along the mélange belt, recording shortening of the accretionary wedge front, whereas the higher grade F4 fabric pervasively overprinted both blocks and matrix in the SW part of the belt, recording shearing and vertical shortening at deeper structural levels closer to a megathrust surface. The preservation of angular relationships between the F1 and F4 fabrics across different parts of the mélange suggests that the blocks were only strained and not rotated during deformation, exemplifying the notion that the OPS mélanges may be a product of deformation at very shallow levels. The F1–F5 fabrics may be viewed as snapshots in a protracted evolution of OPS, where the earlier fabrics in basalt blocks may record the travel path of an oceanic plate from mid-ocean ridge towards the trench, before being overprinted in the accretionary wedge. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: Thin-section photomicrographs, anisotropy of magnetic susceptibility data and summary diagrams for magnetic fabric types are available at https://doi.org/10.6084/m9.figshare.c.7008173

Lithofacies, petrography, and geochemistry of the Lamphun oceanic plate stratigraphy: As a record of the subduction history of Paleo-Tethys in Chiang Mai-Chiang Rai Suture Zone of Thailand

Lithofacies, petrography, and geochemistry of the Lamphun oceanic plate stratigraphy: As a record of the subduction history of Paleo-Tethys in Chiang Mai-Chiang Rai Suture Zone of Thailand

Recognizing different types of ocean plate stratigraphy in the southeastern South Qilian Accretionary Belt, northeastern Tibet Plateau

Dissection of relicts of ocean plate stratigraphy (OPS) in orogens could provide important insights into oceanic evolution, orogenic formation and continental growth. Here we describe a study of petrology, geochronology, geochemistry and Sr–Nd isotopes for OPS in the South Qilian Accretionary Belt with the aim of providing new constraints on the evolution of the Proto-Tethys Ocean (PTO). Three types of OPS units were recognized by their differing petrological, geochemical and isotopic features. Type 1 OPS, representing relicts of ocean islands or seamounts, comprises ocean island basalt and gabbro ( t = 525 ± 4 Ma, ( 87 Sr/ 86 Sr) i = 0.7035–0.7039 and ε Nd ( t ) = +3.63 to +4.16) and (siliceous) carbonate rocks. Type 2 OPS, representing fragments of normal oceanic crust, consists of normal mid-ocean ridge basalt (N-MORB) and basaltic andesite (( 87 Sr/ 86 Sr) i = 0.7059–0.7063 and ε Nd ( t ) = +6.33 to +7.44), chert and siliceous mudstone. Type 3 OPS could be oceanic plateau-derived and comprises enriched (E)-MORB and dolerite (( 87 Sr/ 86 Sr) i = 0.7051–0.7064 and ε Nd ( t ) = +4.81 to +6.24), carbonate–siliceous mudstone and carbonate rock. These OPS units witnessed evolution of the PTO. Using available studies on regional arc-type magmatism and U–Pb geochronological data for detrital zircon in this study, a model of ‘trench jam accompanying subduction flip induced by accretion of the OPS’ is put forward. Supplementary material : Zircon U–Pb data, whole-rock major and trace element data and a supplementary figure are available at https://doi.org/10.6084/m9.figshare.c.6764637 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Preliminary Study of Accretion Complexes of Mangilu Area, Pangkep Ragency South Sulawesi

The exposure of Mesozoic rocks in the Mangilu area, both as a result of tectonic deformation in the form of mélange, low-high degree metamorphism and deep-sea sediments (flysch, radiolarian cherts, and sediment flow in the form of olistostrome), which formed in the subduction zone indicates complex accretionary rocks. The purpose of this study is to identify and study the accretionary complex trace rocks of the Mesozoic era. The method used in this study was field observation, including collection of geological data, tectonic deformation, rock groups and laboratory analysis (petrography). In general, the accretion complex is divided into 2 categories, namely a). oceanic volcanic groups and sediments of the oceanic crust; b). terigenous sediments from continents with sialic beds. The oceanic volcanic group consists of gabbro, diabase, dolerite, pillow and hyaloclastic lava, and oceanic sediments consist of radiolarian chert and mali limestone. The terigen sedimentary group consists of flysch type sandstones and olistostrome flow sediments with components in the form of granite, granodiorite, dacite and diabase. Other components found in autoclastic breccia rocks in the Mangilu area consist of metaperidotite, serpentinite, quartzite and metachert. Based on the Oceanic Plate Stratigraphy (OPS) arrangement, the autoclastic breccia rocks in the Mangilu area consist of bottom up, namely ultramafic/serpentinite, gabbro, diabase, pillow basaltic lava, hyaloclastic, radiolarian chert, mali limestone and flysch sediments. The mixing of rocks originating from oceanic plates with continental plates in autoclastic breccias indicates that the Mesozoic accretion complex in the Mangilu area has experienced strong deformation in the form of thurst in the Tertiary era.

Paleogeographic reconstruction of regional accretionary complex architecture, Franciscan Complex, northwestern San Francisco Bay Area, California, USA

Abstract The Franciscan Complex of western California, USA, the archetypal subduction accretionary complex, cannot serve as a model subduction accretionary complex unless its local-to-regional architecture is clearly understood. Yet, architectural details are not clearly understood in many regions, including the northwestern San Francisco Bay Area. Here, Cenozoicage, dextral strike-slip faulting on faults of the San Andreas System fragmented the original architecture, forming crustal blocks and juxtaposing fragments of accretionary rock of different tectonostratigraphy. One little-known Cenozoicage fault and block boundary, the Tamarancho Shear Zone, separates northeastern crustal blocks that are dominated by Franciscan rocks from southwestern blocks with significantly different Franciscan accretionary tectonostratigraphy. The northeastern blocks have abbreviated accretionary stacks with at least one blueschist-facies accretionary unit, whereas the southwestern blocks lack blueschist-facies accretionary units and have either a westward-and-downward–younging Franciscan tectonostratigraphy or thrustsheet stacks composed of partial sequences of ocean-plate stratigraphy rocks. The northwestern San Francisco Bay Area Franciscan Complex is bounded on the southwest by the San Andreas fault (sensu stricto) and on the northeast by the Petaluma Valley–Point Richmond–Silver Creek fault. Using paleogeographic reconstruction, the original Franciscan Complex accretionary architecture of the northwestern San Francisco Bay Area can be partially reconstructed by removing block separations on San Andreas System faults and enhanced by unfolding Cenozoic folds. Accretionary units of the northwestern San Francisco Bay Area Franciscan Complex were originally assembled ~190 km southeast of their present locations, west of the southern Diablo Range. Reconstruction of the accretionary complex in that location and considerations of tectonostratigraphy require that the Novato Block, located northeast of the Tamarancho Shear Zone, and the Mt. Tamalpais Block, to its southwest, be separated along or across strike in the reconstructed accretionary complex. Either dual subduction zone or faulted plate geometries produced the northwestern San Francisco Bay Area segment of the accretionary complex, and each model highlights the possibilities of along- or across-strike variations in the structure and history of the accretionary complex.

The El Cortijo Formation: Ocean Plate Stratigraphy in the Tandilia Belt Paleoproterozoic basement (Argentina). Insights into subduction-accretion processes in the southern sector of the Río de la Plata Craton

An Ocean Plate Stratigraphy (OPS) sequence is a record of the oceanic crust geological evolution which allows the identification of paleo-oceans preserved in suture zones of orogenic belts. In the Paleoproterozoic basement of the Tandilia Belt (Argentina), Río de la Plata Craton, the El Cortijo Formation (ECF) crops out in a large suture zone with an E-W orientation and vertical to subvertical inclination. It includes a low-grade metavolcano-sedimentary sequence constituted by metacherts, metabasites, metacarbonate, metawacke, and phyllite. In order to provide genetic interpretations of the ECF, based on the OPS model, petrographic, geochemical, and geochronological studies of some of these rocks were performed. Mineral assemblages identified in metabasites, metawacke, and phyllite indicate a transition from prehnite-pumpellyite to greenschist facies conditions. Metabasites, classified as metavolcanite of intermediate to basic composition, chlorite schist and tremolite-actinolite schist, are interbedded between metacherts and metacarbonate bands. Geochemical analyses revealed particular chemical fingerprints which indicate that the protoliths of these metabasites would have been part of a volcanic arc rock association consistent with adakites, Nb-enriched basalts, high-Mg andesites, and “normal” tholeiitic to calc-alkaline basalts and andesites. The metawacke and the phyllite seem to derive from wackes and semi-pelites, respectively, whose main source is consistent with igneous-metamorphic rocks of acidic to intermediate composition linked to a continental arc system. The first LA-ICP-MS U–Pb data obtained for detrital zircons of the phyllite from the ECF yielded a weighted average age of 2138 ± 9 Ma and a youngest individual 207Pb/206Pb spot age of 2047 ± 22 Ma, which locates the maximum sedimentation age in the early Orosirian, during the maximum tectono-magmatic activity of the Tandilia Belt. According to Lu–Hf data, phyllite zircons derived from crustal sources and yielded Archean Hf model ages. Moreover, εHf(t) data of this rock exhibit a more subchondritic signal than the corresponding for some plutons of the Tandilia Belt, which could be indicating that zircons were not derived from plutons but are instead representative of the host rocks of such plutons. In this sense, the information indicates that the top of the sequence, constituted by the metawacke and the phyllite, represents the arrival of the oceanic plate to the trench zone. The study of the ECF has revealed conclusive evidence to postulate that the whole unit corresponds to the upper part of an OPS sequence of convergent type linked to intra-oceanic arc and continental fore-arc trench tectonic environments. The presence of this oceanic sequence, now preserved in a subduction-accretion complex, allows the Tandilia Belt to be classified as a Paleoproterozoic Pacific-type orogenic belt.

The Wulanmoren Accretionary Complex Unravels Early Devonian to Late Triassic Multiple‐Arc Amalgamation in the Tianshan Orogen (NW China)

AbstractReconstructing the tectonic architecture of the southern Altaids is of great importance to piece together the continental growth history of the Central Asian continent. In this paper, we address the subduction‐accretion process of the Paleo‐Tianshan Ocean, one branch of the South Tianshan Ocean, in the southern Altaids, through a detailed geological and geochemical investigation of the Wulanmoren Accretionary Complex (WAC). The WAC is composed of ophiolitic mélanges, ocean plate stratigraphy mélanges, and turbiditic coherent units. In this study, we present key geological, petrological, and geochemical evidence indicating back‐arc and ocean island affinity of the igneous rocks of the WAC. Zircon U‐Pb dates of these rocks ages range between 380.2 ± 1.3 and 302.0 ± 5.3 Ma. The sedimentary matrix units of the mélanges were deposited in the Early Devonian (∼405 Ma) to the Late Triassic (∼222 Ma), rather than Silurian strata as previously thought. However, the ages of some detrital zircons in the sedimentary matrix are Precambrian, pointing to a complex evolution involving multiple ocean island terrains and island arcs of different ages that accreted from the mid‐Paleozoic to the Early Mesozoic.

The significance of cherts as markers of Ocean Plate Stratigraphy and paleoenvironmental conditions: New insights from the Neoproterozoic–Cambrian Blovice accretionary wedge, Bohemian Massif

The Ediacaran to early Cambrian Blovice accretionary complex, Bohemian Massif, hosts abundant chert bodies that formed on an oceanic plate and were involved in subduction beneath the northern margin of Gondwana. Field relationships of cherts to their host, their microstructure and elemental as well as isotopic compositions revealed diverse processes of chert petrogenesis reflecting depositional environment and position on the oceanic plate. The deep-water cherts formed through a hydrothermal precipitation of silica-rich gels on outer trench swell of the subducted slab with none or only minor addition of terrigenous material. On the contrary, the shallow-water cherts formed in lagoons on seamount slopes, and at least some of them represent a product of hydrothermal replacement of former carbonate and/or evaporite precursors. For both chert types, the hydrothermal fluids were of low temperature and continuous pervasive hydrothermal alteration of oceanic crust, together with an elevated Si content in Neoproterozoic seawater, served as the major source of silica. On the other hand, minor carbon enrichment in chert is mostly linked to variable incorporation of organic matter that was deposited on the seafloor. Rare earth element (REE) systematics of the cherts indicate predominantly oxygenated environment for the shallow-water cherts whereas the deep-water cherts were deposited in diverse redox conditions, depending on their distance from hydrothermal vent. Using these data, we demonstrate that the cherts once formed a part of Ocean Plate Stratigraphy (OPS) now dismembered and mixed with terrigenous siliciclastic material to form OPS mélanges. Combining our data with those from the existing literature, we show that cherts can serve as significant markers of OPS since the Archean, recording a complex interplay between seafloor-related volcanic (production of MORB- and OIB-like magmas) and sedimentary processes, hydrothermal activity at mid-ocean ridges and seamount chains as well as at outer slopes of subducting slabs. However, the cherts also exhibit a secular change in composition and petrogenesis most profoundly affected by an overturn in seawater silica cycle across the Precambrian–Phanerozoic boundary.

Heterogeneous Subgreenschist Deformation in an Exhumed Sediment-Poor Mélange.

Many described subduction complexes (or mélanges) exhumed from seismogenic depths comprise thick, turbidite‐dominated sequences with deformed zones containing clasts or boudins of more competent sandstone and/or basalt. In contrast, many active subduction zones have a relatively small thickness of sedimentary inputs (<2 km), turbidite sequences are commonly accreted rather than subducted, and the role of pelagic sediments and basalt (lavas and hyaloclastites) in the deforming zone near the plate interface at <20 km depth is poorly understood. Field investigation of Neoproterozoic oceanic sequences accreted in the Gwna Complex, Anglesey, UK, reveals repeated lenticular slices of variably sampled ocean plate stratigraphy (OPS) bounded by thin mélange‐bearing shear zones. Mélange matrix material is derived from adjacent OPS lithologies and is either dominantly illitic, likely derived from altered siliciclastic sediment, or chloritic, likely derived from altered volcanics. In the illitic mélange, mutually cross‐cutting phyllosilicate foliation and variably deformed chlorite‐quartz‐calcite veins suggest ductile creep was cyclically punctuated by transient, localized fluid pulses. Chlorite thermometry indicates the veins formed at 260 ± 10°C. In the chloritic mélange, recrystallized through‐going calcite veins are deformed to shear strains of 4–5 within a foliated chlorite matrix, suggesting calcite veins in subducting volcanics may localize deformation in the seismogenic zone. Shear stress‐strain rate curves constructed using existing empirical relationships in a simplified shear zone geometry predict that slip velocities varied depending on pore fluid pressure; models predict slow slip velocities preferentially by frictional sliding in chlorite, at pore fluid pressures greater than hydrostatic but less than lithostatic.

Paleozoic ocean plate stratigraphy unraveled by calcite U-Pb dating of basalt and biostratigraphy

Oceanic mafic volcanic rocks preserve unique information regarding the nature and evolution of tectonic plates. However, constraining their age is commonly challenging because of their lack of datable minerals and high degrees of alteration. We present in situ laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of calcite phases in altered basalts in a Paleozoic subduction complex (eastern Australia). Calcite enclosed in amygdules and filled in fractures yielded two distinctive ages with contrasting geochemical signatures. These results, combined with new biostratigraphic and whole-rock geochemical data, suggest that oceanic islands formed in the Panthalassa Ocean at about 365 million years ago, accreted to eastern Gondwana at about 330 million years ago, and underwent brittle deformation at about 305 million years ago. Calcite U-Pb geochronology is valuable to help constrain minimum formation ages of volcanic rocks and their deformation history, ultimately improving ability to unravel the geological record of accretionary complexes, and more generally ancient underwater volcanic systems.

Mélanges and chaotic rock units: Implications for exhumed subduction complexes and orogenic belts

• Most of chaotic units (>64%) form at shallow depth ( T <250 °C) of convergent margins. • Deep ( T >250 °C) mélanges are mostly polygenetic, reworking shallow chaotic units. • Chaotic units have implications for convergent margins evolution and seismicity. • New potential constraints for Precambrian plate tectonics and modern seismicity . Most of mélanges occurring in exhumed subduction complexes and orogenic belts are commonly interpreted as the product of tectonic processes (e.g., underplating and return flow) acting at intermediate to great depths ( T > 250 °C, depth >10–15 km). Conversely, observations on modern and ancient non- to poorly metamorphosed subduction complexes around the world, clearly show that the largest part (c. 64.7%) of mélanges and chaotic rock units are already formed at shallower structural levels ( T < 250 °C, depth <10–15 km). They mainly consist of broken formations (>21.5%), sedimentary (c. 20%), polygenetic (>13.7%), and diapiric (c. 6.7%) mélanges. Tectonic mélanges are limited to about 2.7%, suggesting that tectonics is not an efficient mixing process at shallow structural levels. We document that the subduction of structural inheritances (e.g., ocean-continent transition zones, and ocean plate stratigraphy) plays a significant role in forming and differentiate the different types of chaotic units at shallow depths, also controlling the location of the plate interface and the dynamics of the wedge front (i.e., tectonic accretion vs. erosion). However, not all chaotic units that formed at shallow structural levels can be subducted and, as subducted, their fate could be very different if they become part of the plate interface or if they share the fate of the lower plate. Our findings demonstrate that the evidence that the larger part of mélanges and chaotic units form at shallow depths has significant implications for a better understanding of the tectonic evolution of subduction complexes and orogenic belts, ranging from the mode and time of Precambrian Earth evolution and the onset of plate tectonics to the role of mélanges in controlling the seismic behavior.

Reconstructed ocean plate stratigraphy sequences from the Permian subduction-accretionary complex in the Qinghai-Tibet Plateau

The Permian Tethys subduction-accretionary complex (SAC) in the Qinghai-Tibet Plateau (QTP) is distributed in six geotectonic provinces, which are known as the Zongwulong-Ganjia, the Western Kunlun, the Eastern Kunlun, the Ganzi-Litang, the Xijinwulan-Jinshajiang-Ailaoshan and the Longmucuo-Shuanghu-Nujiang from north to south. The SAC is a set of mélange generated by subduction of oceanic crust at trenches, which consists of relics from mid-ocean ridge, abyssal plains, oceanic island-seamounts, intra-oceanic arcs and trench turbidites. In this paper, we apply the ocean plate stratigraphy (OPS) theory to reconstruct the OPS sequence of the Permian SAC in the QTP. We divided the Permian SAC in the QTP into two types, i.e., convergent zone and accretionary zone according to their tectonic environments. Six relics from mid-ocean ridge, five relics from abyssal plain, five relics from seamount, two relics from intra-oceanic arc, two relics from fore-arc trench, and seven relics from continental fore-arc trench were recognized and then the OPS sequences from different tectonic environments were reconstructed. The spatial-temporal distributions and evolution of ocean basins during the Permian represented by six SACs are discussed.

Late paleozoic–mesozoic subduction and accretion of the paleo-pacific plate: insights from the ocean plate stratigraphy of the wandashan accretionary complex, NE China

ABSTRACT The Wandashan accretionary complex (AC) is located in the easternmost part of Northeast China and consists of the Raohe complex in the east and Yuejinshan complex in the west. It represents an excellent location for insights into Paleo-Pacific subduction and accretion processes. However, the protolith (mainly contains Ocean Plate Stratigraphy ‘OPS’ and ophiolite) nature and tectonic evolution of the Wandashan AC are under debate. This contribution reports three representative geological sections, conducts the OPS reconstruction, compares the reconstructed Wandashan OPS with the adjacent Bikin OPS in Russia and Inuyama–Mino–Neo OPS in Japan, and re-accessed detrital zircon U-Pb age data of the Wandashan area. The results show that the protolith of the Yuejinshan complex is consistent with the OPS formed on a back-arc basin. This back-arc basin formed in the Early Permian and eventually closed after ~216 Ma, and the basin materials emplaced and metamorphosed at ~210–180 Ma to form the metasedimentary rocks and greenschists. The Raohe complex has a relatively complete OPS, which mainly includes Carboniferous–Permian coastal- to shallow-sea- limestones, Middle Triassic–Early Jurassic pelagic cherts, Middle Jurassic hemipelagic siliceous shales/mudstones and slates, and a Middle Jurassic–Early Cretaceous turbidite sequence. The provenances of the trench fill (turbidites) include the widespread Precambrian basement in NE China, the Yuejinshan complex, seamounts and seafloor sediments on the subducted slab, and the adjacent Jiamusi, Khanka, and Songnen massifs. The Raohe OPS experienced decollement, submarine sliding, diapirism, offscraping, underplating, out-of-sequence thrusting, and progressive disruption during the process of accretion, forming the Raohe complex in the Middle Jurassic–Early Cretaceous (~169–133 Ma). Together, the Raohe and Yuejinshan complexes form the Wandashan AC.

A story of Devonian ocean plate stratigraphy hosted by the Ulaanbaatar accretionary complex, northern Mongolia: implications from geological, structural and U–Pb detrital zircon data

A story of Devonian ocean plate stratigraphy hosted by the Ulaanbaatar accretionary complex, northern Mongolia: implications from geological, structural and U–Pb detrital zircon data

Carbon, oxygen, and strontium isotopic fingerprint in Neoproterozoic to early Cambrian limestones in an active margin setting: A record of local environment or global changes?

The Ediacaran to early Cambrian limestones preserved within the Blovice accretionary wedge, Bohemian Massif, are part of Ocean Plate Stratigraphy (OPS) and provide an intriguing example of how paleooceanographic and palaeoenvironmental conditions at active plate margins may be recorded by isotopic composition. Field relations, petrography and geochemical data elucidate the complex interplay of oceanic, diagenetic and volcanic processes. Rare calcite-dominated primary oolitic/pisolitic limestones were deposited on the slopes of seamount volcanoes in shallow-water lagoons and their formation was simultaneous with volcanic activity. In contrast, volumetrically more abundant re-deposited limestones occurring as layers within siliciclastic, graywacke-dominated successions consist of clastic fragments derived from previously formed carbonate ramps, which were disrupted during subduction and subsequently incorporated in deep-water turbidity currents. In both limestone types, the major/trace element as well as C, O and Sr isotope signatures are well preserved and provide a fingerprint of various limestone depositional conditions that can be directly linked with paleooceanic and paleogeographic interpretations. The observed spatial distribution of carbonate-bearing silicate rocks with elemental and isotopic compositions that differ from primary limestones suggest their common origin at active margins and indicate that some of these rocks have been formed by hydrothermal activity. Finally, we demonstrate that the carbonate member of OPS may provide important insights into the polarity and dynamics of subduction zones.

Detrital zircon U-Pb-Hf isotopes and whole-rock geochemistry of Ediacaran - Silurian clastic sediments of the Uzbek Tienshan: sources and tectonic implications

ABSTRACT The paper presents first high-precision data, U-Pb detrital zircon ages, whole-rock geochemistry, Hf-in-zircon and whole-rock Nd isotopes, from pre-Devonian (Ediacaran and Silurian) clastic sediments (sandstones) of the Tamdytau, Bukantau and Nuratau mountainous ranges of the Kyzylkum Desert and Nuratau Range in the western Uzbek Tienshan. The sediments form a turbidite-type complex associated with ocean plate stratigraphy units (oceanic pillow basalt, chert, siliceous mudstone and siltstone) and arc volcanic rocks. Four sandstone samples from the Tamdytau and Northern Nuratau Mts. (Besapan and Kaltadavan formations, respectively) yielded maximum depositional ages in the range of 570–540 Ma. These ages indicate the formation of pre-Devonian sedimentary units during a relatively narrow time interval from the latest Neoproterozoic (Ediacaran) to the earliest Cambrian, i.e. ca. 50–70 Myr. Five samples of turbidites from the Bukantau Mts. (Baimen Fm.) yielded a maximal depositional age of ca. 440 Ma, i.e. early Silurian (Llandovery). The petrographic, major and trace element compositions, as well as εNd(t) values ranging from -16 to -9 of those sandstones suggest their generally mature character and derivation from recycled orogens with a limited contribution of juvenile crust material. All sandstone samples yielded similar detrital zircon U-Pb age patterns characterized by major peaks at 650–570, 870–730, 1050–900 and 2400 Ma and by a smaller peak at ca. 1800 Ma. These patterns are similar to the U-Pb age spectra from the basement of the Tarim Craton. However, the Kyzylkum basement may contain a larger proportion of late Archaean rocks and igneous formations related to Ediacaran – earliest Cambrian orogenic events. All samples showing U-Pb detrital zircon age spectra with peaks at 650–570 Ma carry relatively large amounts of zircon grains with juvenile Hf isotope characteristics, i.e. positive εHf(t) (up to +10) suggesting their derivation from continental or Island arcs. The presence of exotic tectonic blocks composed of Ediacaran arc-type rocks hosted by the accretionary complex of the South Tienshan suggests that an extended arc system once existed at the southern convergent margin of the Turkestan Ocean. That arc system provided clastic material for the Palaeozoic sediments of the South Tienshan, but was probably destroyed by tectonic erosion during early Palaeozoic oceanic subduction.