Subduction History Research Articles

A Tale of Evolution of the Central Indian Tectonic Zone (CITZ) With Glimpses on Pre‐Suture Plate Margin Depositional History

ABSTRACTComprehending pre‐suture geological setting and post‐suture intricate tectono‐thermal chronicle in a crustal‐scale orogeny and discerning the temporal connections among different tectonic domains within an orogen yields valuable insights into worldwide tectonic phenomena leading to the reconstruction of paleogeographic configurations of fragmented crustal components within erstwhile supercontinents. Since the tectonic evolution of the Indian subcontinent during the Proterozoic remains a topic of discussion due to multiple controversial views, the Central Indian Tectonic Zone (CITZ) offers a great archive for the protracted geological history of subduction, collision, and suturing of northern Indian cratonic blocks (NIC; composed of Bundelkhand and Aravalli cratons) and southern Indian cratonic blocks (SIC; composed of Bastar, Singhbhum, and Dharwar cratons). Events belonging to two Supercontinents namely, Columbia (ca. 2100 to 1800 Ma) and Rodinia (ca. 1200 to 900 Ma) are embedded within the geological history of CITZ, as it records multiple events that occurred between the Paleoproterozoic and Neoproterozoic. In this backdrop, the present contribution attempts (i) the deconvolution of pre‐suture (pre‐CITZ formation) plate margin basin depositional history including tracking of detrital provenance, and (ii) a review of different stages of collision and suturing as the plate margin evolved in the form of an orogen subsequent to the closure of the basin. A back‐arc basin setup in a subduction margin is recommended for the Mahakoshal Basin which witnessed several tectonic pulses resulting in the formation of alluvial fans/fan deltas along the basin shoreline. It is suggested that the basin was open, at places, even after ca. 1700 Ma, and received sediments.

Linking deep-time subduction history to modern day expressions of dynamic topography

Dynamic topography refers to vertical deflections of Earth’s surface from viscous flow within the mantle. Here we investigate how past subduction history affects present dynamic topography. We assimilate two plate reconstructions into TERRA forward mantle convection models to calculate past mantle states and predict Earth’s present dynamic topography; a comparison is made with a database of observed oceanic residual topography. The two assimilated plate reconstructions ‘Earthbyte’ and ‘Tomopac’ show divergent subduction histories across an extensive deep-time interval within Pacific-Panthalassa. We find that introducing an alternative subduction history perturbs our modelled present-day dynamic topography on the same order as the choice of radial viscosity. Additional circum-Pacific intra-oceanic subduction in Tomopac consistently produces higher correlations to the geoid (more than 20% improvement). At spherical harmonic degrees 1–40, dynamic topography models with intra-oceanic subduction produce universally higher correlations with observations and improve fit by up to 37%. In northeast Asia, Tomopac models show higher correlations (0.46 versus 0.18) to observed residual topography and more accurately predict approximately 1 km of dynamic subsidence within the Philippine Sea plate. We demonstrate that regional deep-time changes in subduction history have widespread impacts on the spatial distribution and magnitude of present-day dynamic topography. Specifically, we find that local changes to plate motion histories can induce dynamic topography changes in faraway regions located thousands of kilometres away. Our results affirm that present-day residual topography observations provide a powerful, additional constraint for reconstructing ancient subduction histories.

Complicated thermo-chemical heterogeneity of the mantle transition zone beneath the Philippine Sea Plate revealed by SS precursors investigation

The Philippine Sea Plate (PSP), a region renowned for its intricate history of multi-stage subduction and back-arc extension, encounters difficulties in elucidating its deep seismic structure, primarily due to the sparse distribution of seismic stations. This study uses over 44,086 traces of SS precursors collected from >1,000 seismic stations over 10–20 years period, to image the mantle transition zone (MTZ) beneath the PSP. With the curvelet denoising technique, we provide high-resolution maps of the depths of the 410 km (D410) and 660 km (D660) discontinuities and the thickness of the MTZ. Notably, we demonstrate a 10–35 km MTZ thickening extending from the West Philippine Basin to the Shikoku Basin, which may be associated with the thermal effect and dehydration of stagnated slabs in the MTZ. Furthermore, the reflection gap and multiple reflectors were both observed in D410 and D660 beneath the Mariana Trench, which suggests that the vertically subducted Pacific plate transports substantial water and non-olivine components into the MTZ in this area. Additionally, a ∼10–25 km MTZ thinning with an abnormally shallow D660 has been observed beneath the Parece Vela Basin and Caroline Plate in the southern PSP, suggesting the potential existence of thermal upwelling from a secondary plume, which may be possibly the tree branch of the Caroline mantle plume in MTZ. Our results provide new seismological constraints on present and past mantle dynamics in and around the PSP.

Provenance and tectonic evolution of the forearc basin along the northwestern Central Qilian belt, northeastern Tibet

The age and properties of detrital zircon grains in a forearc basin provide crucial information on the history of convergent plate margins. These data can be used to constrain provenance dispersal patterns, establish source-to-sink relationships, and reveal the tectonic framework and subduction history. The Qilian orogen in the northeastern margin of the Tibetan Plateau records the tectonic history of the Proto-Tethys Ocean from its initial spreading and subduction to final closure. However, the timing of subduction initiation and the subduction polarity of the Proto-Tethys Ocean remain controversial. The Qilian orogen includes the North Qilian, Central Qilian, and South Qilian belts. A succession of sedimentary rocks along the northwestern margin of the Central Qilian belt, previously considered to be Precambrian in age, has been redefined based on detailed field investigation and geochronology. U-Pb analysis of detrital zircon grains from metasedimentary rocks of the Gongcha Group of the northwestern Central Qilian belt yielded Paleozoic ages between 530 and 470 Ma, with prominent Mesoproterozoic and Paleoproterozoic ages between 1800 and 1000 Ma. In contrast, the overlying Duoruonuoer Group yielded predominantly early Paleozoic ages between 465 and 434 Ma, with a few older age populations. This change in source is reflected in a substantial increase in volcanic detritus within the Duoruonuoer Group as compared to the Gongcha Group. The detrital zircon age spectra and lithologic characteristics indicate the Gongcha and Duoruonuoer Groups constitute the lower and upper volcanic-sedimentary strata in the forearc basin. Based on resemblances of statistical ages and εHf(t) values of zircon, we interpret that the early Paleozoic intrusive and volcanic units and Precambrian basement rocks of the Central Qilian belt were the main source of the Gongcha and Duoruonuoer Groups, verifying the southward subduction of the North Qilian Ocean, a portion of the larger Proto-Tethys Ocean, beneath the Central Qilian belt. The detrital zircon ages reveal that the initial subduction of the Proto-Tethys Ocean in the Qilian orogen occurred ca. 530 Ma and closed ca. 435 Ma. These forearc sedimentary units constitute the tectonic boundaries between the Central Qilian belt and North Qilian belt.

Late Eocene tectonic-geomorphic transition and its dynamic mechanism: Case study of the Beibuwan Basin, northern South China Sea

The continuous sedimentary records of the Beibuwan Basin preserve vital information on the interaction between Tethys and Pacific tectonic domains. The elusive interaction between the lithosphere and mantle significantly impacts the differential evolution of basins. However, the understanding of surface-mantle dynamic coupling beneath the Beibuwan Basin remains unclear. In this study, we analyze Cenozoic tectonic deformation, sedimentation, and mantle dynamic processes in the Beibuwan Basin in the northern South China Sea to clarify the nature of the tectonic-geomorphic transition during the late Eocene. Results show that the basin underwent late Eocene stratigraphic flexural folding, syn-rift transition from NE to EW orientated, and depocenter migration. The orientation of the primary controlling fault system during this period changed from NE-SW to NEE-SWW, the number of syn-depositional faults decreased from 368 to 172. The thickness of depocenters decreased from 5000 m to 1800 m, and the lacustrine Beibuwan Basin became shallower and wider. A comparison of the tectonic-structural history of the Beibuwan Basin with the history of plate subduction reconstructed from global geodynamic models shows that the late Eocene tectonic transition was closely related to changes in the stress field and the mantle wind related to oceanic plate subduction. We conclude that this enduring surface-mantle interaction associated with subduction of the Izanagi-Pacific mid-ocean ridge resulted in the late Eocene tectonic transition and geomorphic changes in the Beibuwan Basin.

Paleozoic subduction of the Palaeo-Asian Ocean plate: constraints from Ordovician–Carboniferous volcano-sedimentary rocks in the northern Beishan orogenic collage, NW China

The subduction history of the Hongshishan Ocean within the Beishan orogenic collage is crucial to our understanding of the evolutionary mechanisms of the Palaeo-Asian Ocean. We describe the petrography, age and geochemistry of an Ordovician–Carboniferous volcano-sedimentary succession that provides a record of the subduction history of the Hongshishan Ocean. We obtained early Ordovician zircon U–Pb ages (482 ± 6 and 472 ± 2 Ma) from the Xianshuihu Formation. The youngest weighted mean detrital zircon age from the Yuanbaoshan Formation is 421.0 ± 8.8 Ma. Most detrital zircons have prominent age peaks at 900–840 and 543–462 Ma, suggesting a main source from the southern Mongolian microcontinent. Volcanic rocks from the Baishan Formation yielded weighted mean ages of 300.3–299.3 Ma. During the Ordovician–Devonian, some volcanic arcs formed on the northern side of the Hongshishan–Baiheshan–Erlegen Ula ophiolitic belt, indicating that the Hongshishan Ocean had a northward subduction polarity. During the Carboniferous, continental arcs were well developed on both sides of the Hongshishan–Baiheshan–Erlegen Ula belt, suggesting bidirectional subduction. An archipelago of multiple arcs of the Hongshishan Ocean resembles that of the West Pacific Ocean. The change in subduction polarity can be attributed to the characteristics of multi-oceanic accretion.

Late Paleozoic–Early Mesozoic subduction history of Mudanjiang Ocean: New insights from greenschist in the Heilongjiang Complex, NE China

This paper presents zircon U-Pb ages, whole-rock major and trace element data, and Sr-Nd-Hf isotopic compositions for the greenschists from the Heilongjiang Complex in NE China. Based on the geochronological and geochemical characteristics, the greenschists from the Heilongjiang Complex can be categorized into three series: Early Permian tholeiitic series (275 ± 1 Ma and 273 ± 1 Ma), Middle Permian alkaline series (261 ± 1 Ma), and Early Jurassic alkaline series (179 ± 1 Ma). The Early Permian tholeiitic greenschist samples are characterized by remarkable negative Nb and Ta anomalies, and they exhibit relatively low whole-rock (87Sr/86Sr)i values (0.703896–0.704252), along with positive εNd(t) values (+7.66 to +8.65) and positive εHf(t) values (+0.92 to +11.51), implying that their protoliths originated from the partial melting of a depleted mantle wedge that has been metasomatized by subducted slab fluids. The Middle Permian alkaline greenschist samples have high Nb (17.3–19.0 ppm), TiO2 (1.40–1.64 wt%), and P2O5 (0.60–0.68 wt%) concentrations, and they are enriched in large ion lithophile elements and light rare earth elements, and depleted in high field strength elements and heavy rare earth elements, with high whole-rock (87Sr/86Sr)i values (0.709434–0.709949), negative εNd(t) values (−4.73 to −4.72) and varied εHf(t) values (−10.11 to +4.86), which compositionally align with those of Nb-enriched basalts. Based on the geochronological and geochemical characteristics, we propose that the protolith generation of Middle Permian alkaline greenschists was associated with the partial melting of a mantle wedge that had been metasomatized by subduction slab-derived melts. The Early Jurassic alkaline greenschist samples display OIB affinities, characterized by whole-rock (87Sr/86Sr)i values ranging from 0.705161 to 0.705926, εNd(t) values between +6.16 and +6.19, and εHf(t) values from +3.44 to +9.32, indicating the formation of the protolith for the Early Jurassic alkaline greenschist was related to the upwelling of the asthenosphere resulting from slab break-off. By integrating regional geological data, we can trace the subduction evolution of the Mudanjiang Ocean back to the Early Permian, and the slab break-off during the Early Jurassic likely corresponded to the early stage of the closure of the Mudanjiang Ocean.

Two-stage Mesozoic oceanic subduction and related mantle metasomatism beneath the South Qiangtang terrane with implications for post-collisional magmatism

Subduction-related metasomatism at convergent margins is a crucial process for the lithosphere evolution of the overriding plate. In the central Tibetan Plateau, tectonic transitions and related mantle metasomatism history of the oceanic subduction beneath the South Qiangtang terrane (SQT) remain ambiguous, which impeded understanding the geological evolution of the SQT during the Mesozoic and interpreting the geodynamic process responsible for the Cenozoic post-collisional magmatism. This paper integrated the new and published geochronological and geochemical data from the Jurassic-Cretaceous magmatic rocks in the western part of the SQT to explore the variations of magmatism and processes of mantle modifications. The Jurassic arc magmatism is characterized by the southward younging migration with increasing zircon εHf (t) values and the east–west linear distribution of ca. 155–150 Ma slab-derived adakites. After a magmatic gap at ca. 145–130 Ma, the Early Cretaceous magmatism (130–100 Ma) with distinct juvenile isotopic compositions reinitiated firstly in the south of the Jurassic magmatic belt. In comparison, a younger phase of felsic rocks (120–100 Ma) spatially and geochemically overlaps the northern Jurassic granitoids with ancient crustal sources. These spatial–temporal-geochemical covariations of magmatism could be best explained by the southward transference of oceanic subduction at the earliest Cretaceous that was induced by the Jurassic accretion of an oceanic plateau onto the SQT. Under such subduction regimes, several high-Nb mafic rocks in the northern and southern magmatic belts which were formed by partial melting of the slab-melts-metasomatized lithospheric mantle respectively recorded the Jurassic and Cretaceous mantle metasomatism beneath the SQT, based on their spatial and geochemical relationships with two phases of the adakites. Combined with other geological evidence, these results contribute to elucidating the Mesozoic geodynamic evolution of the oceanic subduction beneath the SQT, which further has implications on the deep dynamic processes responsible for post-collisional magmatism.

Propagating Neotethys slab break-off beneath Iran following Arabia-Eurasia collision

The closure of the Paleo- and Neotethys resulted in a long history of subduction of oceanic crust and production of a large variety of Phanerozoic magmatic rocks in the region occupied by present day Iran. Adakitic rocks of varying ages are common in this area and have distinctive geochemical signatures that have been variably linked to slab break-off or melting of the lower continental crust. The geographic distribution and age of the adakitic rocks indicates a potential younging trend from northwest to southeast Iran, but this trend was interrupted by an older outlier in the area of Tafresh, in the central part of the Neotethys arc. We obtained new geochemical and U-Pb geochronological data for Eocene volcanic and Miocene intrusive rocks from this anomalous locality. Our results show that adakitic signatures are only present in younger Miocene intrusive porphyritic bodies and not in the main calc-alkaline Eocene volcanic succession as previously thought. The Tafresh adakitic porphyritic bodies have an age of 15.7 ± 0.1 Ma (n = 183, 2σ SE), which fits well with a regional younging of the adakites towards the southeast of Iran. The Tafresh adakitic rocks are classified as the high-silica variety, and show trace element signatures and isotopic values that are consistent with melting of the lower continental crust. We hypothesise that progressive slab break-off provided a mechanism for the formation of high-silica adakitic rocks along the former Neotethys arc.

Spatial−temporal variations in Mesozoic crustal thickness along the northeast Asian continental margin: Response to the subduction history of the Paleo-Pacific Plate

The initial timing and history of subduction of the Paleo-Pacific Plate beneath Eurasia are controversial. The crustal thickness variations at a convergent margin typically reflect the convergent process between the two plates. This study used a recently proposed machine-learning model to estimate the crustal thickness variations along the northeast Asian continental margin during the Mesozoic. The northeast Asian continental margin, particularly the eastern North China Craton, had its thickest crust during the Early Triassic and underwent crustal thinning during the Middle−Late Triassic. The former reflects the subduction and collision between the South China Block and North China Craton, and the latter occurred in a post-orogenic extensional setting. From the Early to Middle Jurassic, sustained crustal thickening occurred along the northeast Asian continental margin, which coincided with initial subduction of the Paleo-Pacific Plate beneath Eurasia. From the Early to Late Cretaceous, the northeast Asian continental margin generally underwent crustal thinning, but crustal thickening events occurred at 130 Ma, 110 Ma, and 90 Ma, which is consistent with rollback of the subducted Paleo-Pacific Plate beneath Eurasia. The relationship between crustal thickness and mineralization suggests that thicker crust favored the formation of porphyry-type Cu-Mo deposits, whereas thinner crust in an extensional setting favored the formation of epithermal Au deposits related to magmatism.

Using compositions of zircon to reveal fertile magmas for the formation of porphyry deposits in the Loei and Truong Son fold belts, northern Laos

The Loei and Truong Son fold belts are well known as being the most geologically important and highly mineralized magmatic arc-related terranes in mainland southeast Asia. Numerous studies have examined the geology, geochemistry, and geochronology but only a few metallogenic and detailed deposit characterizations have been undertaken. This study of zircon geochemical analyses uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to provide U-Pb ages and magmatic fertility of felsic to intermediate volcanic and plutonic rocks from ten prospects in the Loei and Truong Son fold belts, in the northwest Laos region. The geochemical and geochronological analyses suggest at least three episodes of magmatism occurred: Silurian-Devonian (434–411 Ma), Early to Middle Permian (299–277 Ma), and Late Permian to Middle Triassic (253–243 Ma). The variable ranges of ɛHf values (−12 to + 12) suggest that mantle-derived and crustal contamination signatures are related to the history of subduction and arc magmatism in this region. Key trace elements and ratios associated with oxygen fugacity of magmas (e.g., Eu/Eu*, Dy/Yb, Ce/Nd, ΔFMQ) imply that the Phu Kham and the west of Vientiane along the Mekong River are likely to be fertile for porphyry copper deposits. In contrast, the Pha Gnai and other suites are less fertile. Using zircon as a fertility indication can be a valuable tool to distinguish between fertile and barren magmatic suites in this area.

Factors Contributing to Slab Locations and Geometries in Reconstructions of Past Mantle Flow

AbstractIndividual sinking slabs present markedly different geometries between 410 and 660 km depths, from vertical slabs penetrating the lower mantle to slabs stagnating above the lower mantle. The proposed factors determining these contrasted geometries include mantle viscosity and the magnitude and evolution of trench retreat. Here, we assess the success of paleo‐geographically driven global mantle flow models in matching slabs in tomographic models between 400 km and 1,000 km depth. We quantify the spatial match between predicted present‐day mantle temperature anomalies and vote maps of tomographic models. We investigate the sensitivity of the spatial match to input parameters of the mantle flow model: imposed tectonic reconstruction, model start age, and viscosity contrast between the upper and lower mantle. We evaluate the visual match between model slabs and tomographic vote maps for three circum‐Pacific regions with contrasted slab dip angles between 400 km and 1,000 km depth. Predicted model slabs better match slabs inferred from tomography when there is an increase in viscosity at 660 km depth. The temporal evolution of the models and the global match at present day suggest that the subduction history could be refined in the global tectonic reconstructions that we considered. For example, we suggest that the subduction to the east of Japan should be offset by approximately 100 km to the west at ∼80 Ma to match the anchoring of a continuous slab into the lower mantle suggested by tomography.

Driving subsidence mechanisms during the formation of the intracratonic General Levalle basin, central Argentina

The Cretaceous-Cenozoic General Levalle rift basin (GLB) in Central Argentina, near 900 km east from the modern Chile-Peru trench, is an exploratory hydrocarbon frontier located within an intracratonic setting. The basin is 4.5 km deep and can be divided into three major evolutionary stages, synrift, intermediate and postrift. To date, the basin subsidence has not been yet addressed. We particularly made emphasis on the postrift sequence given that records of thousands of metres of Cretaceous and Cenozoic Strata and tectonic and thermal events are not known to account for these large accumulations. In this work we performed a backstripping analysis, in combination with a stretching-thermal model, which were then compared to different dynamic topography studies. From our backstripping models we found a typical rift basin curve, with the largest subsidence at the synrift stage followed by a decrease in values during the postrift. Assuming the synrift stage was driven by tectonic extension, we correlated the tectonic subsidence curve, obtained from backstripping studies, with a stretching-thermal subsidence model. The best fit among subsidence curves was obtained with a stretching factor β = 1.285. However, we observed a mismatch along the postrift part of both curves, resulting in a residual subsidence of ∼323 m. When this anomalous tectonic subsidence was compared to the latest six dynamic topography models, we found a good correlation with one of them. For the models that did not match and using simple isostatic computations, we estimated a lithospheric mantle thickening of 35.4 km to account for the residual subsidence and dynamic topography models. From our analysis it turns out that, in addition to stretching and thermal subsidence, mantle thickening in the lithosphere and in the asthenosphere, controlled the total subsidence in the General Levalle basin. The subduction history of Nazca Plate could have affected the postrift stage in this basin.

Subduction history of the Paleo-Asian oceanic slab along the northern margin of the North China Craton: A case study of zircons and cherts from central Jilin Province, NE China

Abstract This paper presents U-Pb ages and Hf isotope data for detrital zircons and whole-rock geochemical data for siliceous-clastic sedimentary rocks of the Shitoukoumen Formation, central Jilin Province, NE China. The new data combined with published data for the northern North China Craton enable us to constrain the temporal changes in crustal thickness along the Solonker–Xar Moron–Changchun–Yanji suture belt (SXCYB). The Shitoukoumen Formation contains ophiolitic lenses, radiolarian-bearing cherts, and volcanic-sedimentary units of various ages. A radiolarian-bearing volcanic-sedimentary unit exhibits a Bouma sequence, in which detrital zircons from a rhyolitic tuff and siliceous-clastic sedimentary rocks yielded youngest ages of 278–273 Ma, which constrain the depositional age of the unit. The geochemical compositions of the cherts suggest the pelagic deposits contain some continent-derived clastic material and may be near-trench gravity flow deposits. The dominantly depleted zircon εHf(t) values of the sedimentary rocks in the Shitoukoumen Formation record extensive crustal growth during the Paleozoic. The variations in the crustal thicknesses during the Paleozoic to early Mesozoic record a tectonic transition from subduction initiation, mature continental arc, and finally to Paleo-Asian ocean closure. The thickest crust (~58 km) at ca. 245 Ma might have been related to an orogenic peak during the final closure of the Paleo-Asian Ocean along the SXCYB.

Evidence for Ultra-Low Velocity Zone Genesis in Downwelling Subducted Slabs at the Core–Mantle Boundary

Abstract We investigate broadband SPdKS waveforms from earthquakes occurring beneath Myanmar. These paths sample the core–mantle boundary beneath northwestern China. Waveform modeling shows that two ∼250 × 250 km wide ultra-low velocity zones (ULVZs) with a thickness of roughly 10 km exist in the region. The ULVZ models fitting these data have large S-wave velocity drops of 55% but relatively small 14% P-wave velocity reductions. This is almost a 4:1 S- to P-wave velocity ratio and is suggestive of a partial melt origin. These ULVZs exist in a region of the Circum-Pacific with a long history of subduction and far from large low-velocity province (LLVP) boundaries where ULVZs are more commonly observed. It is possible that these ULVZs are generated by partial melting of mid-ocean ridge basalt.

Linking Pacific Plate Motions to Metamorphism and Magmatism in Japan During Cretaceous to Paleogene Times

Plate reconstructions of oceanic domains are generally based on paleo-magnetic and seafloor spreading records. However, uncertainties associated with such reconstructions grow rapidly with increasing geological age because the original oceanic plates have been subducted. Here we synthesize advances in seismic tomographic mapping of subducted plates now lying within the mantle that assist plate reconstructions. Our proposed Japan–NW Pacific subduction histories incorporate tomography results and show three distinct stages comparable to those revealed by geochronology, petrology, and geochemistry. We propose major revisions to previously accepted ideas about the age, kinematics, and identity of the plates outboard of Japan during the Cretaceous–Paleogene Sanbagawa-Ryoke paired metamorphism. These revisions require updates to relevant plate convergence boundary conditions and thermo-dynamic models.

New Insights on the Early Proto-Tethys Subduction History: Evidence from Ages and Petrogenesis of Volcanic Rocks in the Bulunkuole Complex, West Kunlun Orogen

Abstract The Proto-Tethys Ocean has played a significant role in the geological history of Earth. However, ongoing debates persist regarding the timing and polarity of its early subduction. Volcanic rocks associated with iron deposits in the Bulunkuole Complex, West Kunlun Orogen, offer insights into both the complex’s formation age and Proto-Tethys evolution. This study presents newly obtained zircon U–Pb age data (~536 Ma) along with comprehensive whole-rock major and trace element and Sr–Nd–Hf isotope analyses of these volcanic rocks. Our dataset implies that the Bulunkuole Complex partly formed in the early Paleozoic rather than entirely in the Paleoproterozoic, as previously suggested. Geochemically, the volcanic rocks exhibit enrichments in large ion lithophile elements and light rare earth elements, along with depletions in high-field strength elements. They also display elevated initial 87Sr/86Sr values (0.71093, 0.72025) and negative εNd(t) values (−5.13, −6.18), classifying them as continental arc volcanic rocks. These geochemical fingerprints, complemented by zircon εHf(t) values (−12.7 to −1.6), indicate that the parental magmas of the volcanic rocks were produced by partial melting of the lithospheric mantle wedge, which had been metasomatized by subducted sediment-derived melts. The available data, in conjunction with previously published findings, strongly suggest that the Proto-Tethys Ocean subducted southward prior to approximately 536 Ma due to the assembly of Gondwana. Subsequent slab rollback may have resulted in a crustal thinning of 9–25 km during 536–514 Ma. Further shifts in subduction dynamics led to the transition from high-angle subduction to either normal or low-angle subduction, facilitating the formation of a thicker crust ranging from 39 to 70 km between 514 and 448 Ma. This study, therefore, provides valuable insights into the early evolution of the Proto-Tethys Ocean and contributes significantly to our understanding of the tectonic history of the West Kunlun Orogen.

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

Geochronology and geochemistry of granitoids from northern Alxa, northwest China: Petrogenesis and tectonic implications

AbstractMultiple branch oceans existed in the Paleo‐Asian Ocean (PAO), but their closure times are in dispute and unclear, which constrains our understanding of the final closure time of the PAO and the tectonic evolution of the Central Asian Orogenic Belt (CAOB). This study focuses on the Permian plutons of the northern Alxa, which is located in the middle segment of the southern CAOB that recorded the final subduction history of the PAO. We performed the 1:50000 mapping, whole‐rock geochemistry, geochronology, and Sr‐Nd‐Hf isotopic analysis and compiled the Sr‐Nd‐Hf isotopic compositions and whole‐rock geochemical data of igneous rocks from the northern Alxa. LA‐ICP‐MS zircon U–Pb dating reveals the study plutons emplaced in the Early Permian (285–296 Ma). Whole‐rock geochemical data show the intrusion belongs to medium‐K calc‐alkaline peraluminous highly fractionated I‐type granite, enriched in Rb, K, Th, Pb, and depleted in Nb, Ta, Ti, Sr, and P elements, which suggest a subduction arc‐related setting and metaluminous to weak peraluminous parental magma. The weak negative εNd(t) (from −2.3 to −1.2), relatively high ISr (0.704772–0.708037) and depleted mantle model ages TDM (1.14–1.49 Ga), combining with weak negative to slightly positive εHf(t) (from −2.0 to +4.1) and crustal model ages TDMC (1.18–1.43 Ga), indicate that the parental magma might originate from remelting of the Mesoproterozoic lower crust and mixing with mantle‐derived materials. The field occurrence, deformation, and geochemical features, integrating with the compiled data and regional geology, show that the igneous rocks formed before or after the late Early Permian show different features in terms of deformation, zircon saturation temperatures, crustal thickness, potassium contents, and εHf(t) values. This might relate to the closure of the Yagan branch ocean of the PAO in northern Alxa.

Recycled crustal components in the depleted mantle source: Evidence from Early Cretaceous mafic rocks in the southern margin of the North China Craton

Abundant subducted materials are recycled into the deep mantle during the plate subduction process and are further reflected in the postcollision mafic rocks. The Early Cretaceous Mid-Oceanic-Ridge-Basalt (MORB)-like mafic rocks in the southern margin of the North China Craton (SNCC) preserve significant information on recycled materials. These rocks provide a window for discussing the crust-mantle interaction and tracing the history of subduction. The studied rocks comprise the Jingwan metadiabase, Putaozhuang, Nianpanzhuang, and Niujiaowan metahornblende gabbro, with Early Cretaceous ages (140–129 Ma). They show large ion lithophile element enrichment in both the Enriched-MORB and Normal-MORB rare earth element patterns. They are characterized by slightly depleted isotopic compositions, high MgO, Cr, Ni and Mg# values as well as the low SiO2, suggesting a depleted mantle source affinity. The enriched NdHf (εNd(t) = −14.50 to −13.47; εHf(t) = −9.27 to −8.82) and unradiogenic Pb isotopes imply that Jingwan samples originated from a depleted mantle source metasomatized by lower continental crustal materials. Their relatively enriched zircon εHf(t) values (−15.8 to −1.6) and δ18O values (4.82‰–8.77‰) along with their Paleoproterozoic to Neoproterozoic inherited zircons also argue for the contribution of low continental crustal materials from the North China Craton. In contrast, Putaozhuang, Nianpanzhuang, and Niujiaowan samples have positive whole-rock εNd(t) values (4.08–5.20) and εHf(t) values (3.23–5.62). Combined with the existence of Paleozoic zircons, high zircon εHf(t) values, and high Nb/U ratios, these materials suggest that they originated from a depleted mantle source metasomatized by juvenile crust and terrigenous sediments. This is corroborated by variable zircon δ18O values (5.57‰–9.63‰) and mantle-like δ18O values (5.08‰–5.60‰) of Paleozoic inherited zircons from Niujiaowan samples. The distinct geochemical characteristics of Early Cretaceous mafic rocks are induced by the incorporation of different components from subducted crust and sediments into the depleted mantle source. Paleo-Pacific Plate far-field effects controlled the intense lithospheric extension and thinning of the Early Cretaceous MORB-like rocks in the SNCC, which were placed in an immature back-arc basin setting.