Arc Belt Research Articles

Detrital Zircons From Lower Palaeozoic Metamorphic Complexes and Silurian–Devonian Strata in the South Kitakami Belt, Northeast Japan: Implications for the Northern Extension of the Terra Australis Orogen in Northeast Gondwana

ABSTRACTTo reconstruct the detailed location of proto‐Japan around northeastern Gondwana during the early Palaeozoic, this article presents detrital zircon U–Pb age spectra for lower Palaeozoic metamorphic complexes and Silurian–Devonian strata from the western margin of the South Kitakami belt in northeast Japan. Psammitic and siliceous schists have youngest age peaks ranging from the Ordovician (479–458 Ma) to early Silurian (ca. 439 Ma). Sandstones have youngest age peaks varying from the early Silurian (ca. 435 Ma) to Late Devonian (370–360 Ma). The U–Pb age spectra exhibit major peaks at 510–500, 480–470, and 450–440 Ma. Excluding the Upper Devonian sandstones, significant age peaks occur at 650–550 and 1300–900 Ma. These data can be interpreted as a Pacific Gondwana signature, indicating a tectonic association with the Terra Australis Orogen that developed along the northeastern Gondwanan margin and Paleo‐Pacific Ocean, extending from eastern Australia (i.e., the Thomson, Lachlan, and Delamerian orogens) to Antarctica (i.e., the Ross Orogen). In northeast Asia, the Pacific Gondwana detrital zircons and 480–470 Ma zircons occur in the Bainaimiao arc belt along the northern margin of the North China Craton and in the Jiangyu continental arc in the Jilin area. The magmatic arcs of proto‐Japan and these regions were part of the Terra Australis Orogen during the Ordovician–early Silurian. A decrease in the proportion of Pacific Gondwana detrital zircons in Upper Devonian strata may be due to multistage trench retreat, such as that recognized in the Tasmanides in eastern Australia, which corresponds to the northern Terra Australis Orogen.

Constraints on the subduction and closure of the Hegenshan Ocean: Magmatic and sedimentary records from central Inner Mongolia, China

Petrological, geochronological, and geochemical data from the volcano-sedimentary sequences, granitoids, and ophiolite relics of central Inner Mongolia, China, were used to reconstruct the subduction and final closure of the Hegenshan Ocean. Geochronological dating and compilation reveal four phases (ca. 360−355 Ma, 348−320 Ma, 320−310 Ma, and 310−275 Ma) of magmatism in the Uliastai continental margin. The ca. 356 Ma I-type Halatumiao granodiorite and Amanwusu ophiolite relics are subduction-related, and the Halatumiao granodiorite provides solid evidence of the northward subduction of the Hegenshan Ocean beneath the Uliastai continental margin at ca. 360−355 Ma. The ca. 348−320 Ma and 320−310 Ma volcanic rocks and granitoids constitute two linear magmatic belts roughly parallel to the Erenhot-Hegenshan ophiolite belt, which record two phases of continental arc magmatism in the Uliastai continental margin. Overall, the ca. 360−310 Ma arc magmatism shows landward migration and then oceanward migration in the Uliastai continental margin, which indicates advancing subduction and subsequent slab steepening of the Hegenshan Ocean. By contrast, the ca. 310−275 Ma magmatic rocks are dominated by I- and A-type felsic volcanic rocks, granites, and dikes, which are post-accretionary, extension-related, and pervasive in the Uliastai continental margin and Erenhot-Hegenshan ophiolite belt. A provenance shift was identified between the Benbatu and Amushan formations of the Amanwusu area of the Erenhot-Hegenshan ophiolite belt. The early detritus was derived from the early Paleozoic rocks in the Sonid Zuoqi arc belt, whereas the late detritus originated from the Early Carboniferous ophiolite relics in the Erenhot-Hegenshan ophiolite belt. The provenance shift and emplacement of pervasive extension-related magmatic rocks imply a Late Carboniferous closure of the Hegenshan Ocean. The Late Carboniferous oceanic closure event in the north of the southeast Central Asian Orogenic Belt is also evidenced by the transition of Hf isotopic composition of zircons dated between ca. 360−310 Ma and 310−275 Ma.

Neoarchean granitoid magmatism and geodynamic process in the northeastern North China craton

Abstract The composition of Archean granitoid rocks changed from predominantly tonalite-trondhjemite-granodiorite (TTG) gneisses in the early Archean (4–3 Ga) to diversified granitoid rock assemblages in the late Archean (3.0–2.5 Ga), marking a crucial transformation in the geodynamic processes of early Earth. However, the reason for this major transition remains enigmatic because the petrogenetic features of different granitoid assemblages and their crust-mantle interactions during different periods are poorly understood. We use variations in the spatial-temporal distribution, lithological association, chemical composition, and petrogenesis of Neoarchean (2.7–2.5 Ga) granitoids and inferred correlative crust-mantle interactions in the Eastern Liaoning Range (ELR) of the northeastern North China craton to explore this geodynamic transition. The early Neoarchean (ca. 2.7 Ga) ELR granitoids were dominated by TTG gneisses, and the late Neoarchean (2.6–2.5 Ga) ELR granitoid typology and compositions became more complex, changing into TTGs and more K2O-rich granitoid rocks. The TTGs can be subdivided into a high-Ca group and a low-Ca group: The 2.71–2.68 Ga high-Ca group TTG magma originated from partial melting of subducted juvenile oceanic crust, and the low-Ca group TTG magma was derived from fractionation crystallization of the high-Ca group TTG magma. The chemical composition of the magmatic sources played a dominant role on the 2.60–2.50 Ga TTG magmatism: the high-Ca and low-Ca group TTG magmas came from low-K mafic rocks and tonalites, respectively. The 2.58–2.49 Ga K2O-rich granitoids can be divided into three petrogenetic series: (1) The high-Ca-Mg group K2O-rich granitoid magma originated from partial melting of high-K mafic rocks, (2) the low-Ca-Mg group K2O-rich granitoid magma was derived from partial melting of sedimentary rocks, and (3) the transition group K2O-rich granitoid magma was sourced from metagreywackes. The 2.71–2.68 Ga TTGs were generated in an island arc belt, and subducted slab melting and subsequent magmatic differentiation were the dominant mechanisms of the TTG magmatism. The 2.60–2.50 Ga diversified granitoids were formed in the oceanic-continental subduction process under the active continental margin; the complicated oceanic slab subduction and arc-arc and arc-continent collisions contributed to the diversity of late Neoarchean granitoid magmatism.

Initial oceanic subduction triggered by arc–continent collision: An example from the convergence between the Paleo-Asian Ocean and the North China Craton

The driving mechanisms for initial oceanic subduction beneath a passive continental margin remain unclear. The Paleozoic convergence history between the North China Craton (NCC) and the Paleo-Asian Ocean provides an ideal opportunity to investigate the driving mechanisms of the onset of oceanic subduction. Our detrital zircon U–Pb dating results yield Middle Devonian to Permian ages (391–273 Ma) in Paleozoic strata within China's Aoji region, specifically in the Bainaimiao arc belt situated between the NCC and Central Asian Orogenic Belt (CAOB). Detrital zircon age spectra, εHf(t) values, and two-stage model ages of the Devonian to Permian sediments suggest zircon contributions from both the NCC and CAOB. Combined with data from various regions along the Bainaimiao arc belt, findings suggest that the Bainaimiao island arc was accreted to the northern margin of the NCC through arc–continent collision during the late Silurian, rendering the NCC margin passive until the end-Devonian. At this point, southward subduction in the Paleo-Asian Ocean beneath the NCC commenced and continued into the Permian, transforming the northern margin of the NCC from passive to active. This initial subduction (ca. 359 Ma) in the Paleo-Asian Ocean resulted from collision-induced magmatism and deformation due to the protracted convergence and also led to a reversal in subduction polarity. Subsequently, in response to Paleo-Asian Ocean subduction, the northern margin of the NCC underwent rapid uplift during the Carboniferous, which led to widespread exposure of the NCC basement rocks in the late Carboniferous.

Provenance and depositional age of metasedimentary rocks in the Frontenac terrane (Grenville Province, Ontario)

The Mesoproterozoic Frontenac terrane in the southern Grenville Province of Ontario is separated by shear zones from the Composite Arc Belt to the west and the Adirondack Lowlands to the east. The majority of the terrane is made up of granulite-facies metasedimentary rocks that are the oldest lithologies recognized in the terrane. Five samples were selected for U–Pb geochronology to constrain (1) metamorphic age, (2) depositional age of sedimentary protoliths, and (3) source regions of detrital zircon. Two pelitic gneisses and a marble are dominated by metamorphic zircon, whereas two quartzites contain a diverse population of detrital zircon that are surrounded by metamorphic overgrowths. Metamorphic zircon have 206Pb/207Pb ages of 1.19–1.16 Ga, and a small population is 1.22 Ga. These ages correspond to the Shawinigan and Elzevirian orogenies and provide minimum ages for deposition. The youngest detrital grains with ages of 1.25–1.24 Ga provide maximum depositional ages. Quartzites (and pelitic gneisses) have a wide range of detrital zircon ages that reflect local Mesoproterozoic Grenville sources and Paleoproterzoic and Archean sources in the northern Grenville Province and elsewhere in Laurentia. Most notable is a large population of 1.9–1.8 Ga zircon, which points towards derivation from the Penokean orogen in the midcontinent or Makkovikian–Ketilidian orogen of Labrador and Greenland, indicating long sedimentary transport distances. The similarities in depositional ages and detrital zircon ages between Frontenac terrane and Adirondack metasedimentary rocks suggest a shared sedimentary history, which we interpret as deposition in the same Trans-Adirondack backarc basin at ca. 1.25 Ga.

Origin of mafic microgranular enclaves from the Late Triassic Cuojiaoma granitic pluton: Implications for the tectonic evolution of the Yidun arc belt, eastern Tibetan Plateau

In-situ U-Pb ages and Hf-O isotopes of zircon are frequently used to study the petrogenesis of mafic microgranular enclaves (MMEs) in granitoids. However, whether zircons in MMEs have recorded the primary isotopes of their host MMEs is still questionable. In this study, MMEs and host granites from the Cuojiaoma granitic pluton in the Triassic Yidun arc belt, eastern Tibetan Plateau, are studied. LA-ICP-MS zircon U-Pb dating of studied MMEs yields an age of 213 ± 2 Ma. Model calculations indicate that the whole-rock composition of the MMEs was different from the melt composition from which the zircon grains grew. The MMEs crystallized during magma mixing based on analyses of zircon trace element and Zr-Hf isotopes. None of zircons in this study have recorded the primary isotope signature of the mafic endmember of MMEs because they are different from the host granite in terms of zircon morphology, ɛHf values and ΔQFM. The Zr isotopic data demonstrate open-system magmatic crystallization for the host granite and that magma mixing for MMEs play key role in controlling Zr isotopic variations. Initial 87Sr/86Sr ratios of An-rich plagioclase crystals in groundmass from MMEs range from 0.7027 to 0.7058, which are significantly lower than host granites (0.7080 – 0.7089). The lowest initial 87Sr/86Sr ratios (0.7027 – 0.7028) are also lower than arc volcanic rocks and similar to a depleted mantle. Combined with previous studies, we propose that MMEs were generated during post-collision extension by mixing of mafic magma of Xiaxiaoliu basalt and felsic magma from host granite.

The role of intra-oceanic arc in the growth of continental crust: Evidence from the Early Paleozoic Bainaimiao arc

The Early Palaeozoic arc-related formations in the northern margin of the North China Craton (NCC) belonging to the Bainaimiao arc belt is an important part of the eastern Central Asian Orogenic Belt (CAOB). The tectonic evolution of this belt remains controversial. Here we present detailed data on the geochronology and geochemistry on a newly identified Early Palaeozoic igneous suite from the Faku area in northern Liaoning. Zircon U–Pb dating of the Faku volcanic and intrusive rocks yielded weighted mean 206Pb/238U ages of ca. 458 Ma and 433–405 Ma, respectively, which represent their crystallization (eruption) times. Zircon Hf isotopic analyses show a low negative to positive εHf (t) values of − 0.33 to + 12.4, implying depleted characteristics of the source. The geochemical features of Laolingshan basaltic andesites display higher TiO2 and lower P2O5 contents, similar to that of mid-ocean ridge basalts, and relatively high Zr/Y and low Ta/Yb ratios, suggesting oceanic island arc basalt affinity. Therefore, we suggest that the Laolingshan basaltic andesites were formed in an intra-oceanic environment. The Bachagou granodiorites, with adakitic geochemical signatures, belong to the calc-alkaline and high-K calc-alkaline series, implying formation in an active continental margin tectonic setting. The Baerhushan granodiorites, which geochemically belong to S-type granites, were probably formed in a syn-collisional environment influenced by arc–continent collision. The Donggou granitoids, which have higher SiO2 and alkali and lower MgO and P2O5, show A-type granite features. Geochemical characteristics of the Donggou A-type granite suggest formation in an extensional setting caused by orogenic intermittent extension. The Baerhushan gabbro diorites, which display properties of both mid-ocean ridge and continental rift basalts, were produced under post-orogenic extensional tectonic setting after the arc–continent collision. Our study traces the Early Palaeozoic tectonic evolution of the south-eastern segment of the CAOB and the related accretionary tectonics.

Final suture of the Palaeo-Asian Ocean domain: Insights from the geochemistry and geochronology of the early to Middle Permian Elitu Formation volcanics

The consumption of the Palaeo-Asian Ocean domain triggered substantial resources and environmental effects, but the final suture timing remains debated. This study presents the zircon U-Pb age and Hf-O isotope, whole–rock element and Sr–Nd–Pb isotope data from the Elitu Formation trachyandesite and rhyolitic tuff in the Bainaimiao arc belt. The zircon U-Pb ages (260–280 Ma) indicate that the Elitu Formation volcanism erupted at the Kungurian to Capitanian. Trachyandesites exhibit an arc-like whole–rock trace element composition and have enriched Sr–Nd–Pb isotopic composition (ISr(t) = 0.7062–0.7065; εNd(t) = −8.8 to −9.4; (206Pb/204Pb)t = 17.14–17.31) and high zircon δ18O (6.08‰–7.59‰) values, which are derived from the partial melting of the lithosphere mantle metasomatised by ancient sediment-derived melts. Rhyolitic tuffs have variable εHf(t) (−7.15 to +10.47) and low δ18O (4.99‰–6.21‰) values and exhibit affinities with I-type felsic rocks. They mainly originate from the partial melting of the basement of the Bainaimiao arc belt. Our compiled geochemical and geochronological data indicate that there were significant differences between the Early to Middle Permian Elitu Formation volcanic rocks and intrusive counterparts and the Early to Middle Triassic magmatic rocks from the Bainaimiao arc belt, and the Late Permian was the key tectonic transition period. The Late Permian transition was compatible with the regional crustal-shortening deformation, greenschist facies metamorphism and shift of deposition environment. This study argues that the Elitu Formation volcanism should be subduction-related and predate the final suture of the Palaeo-Asian Ocean domain at the Changhsingian. The suture of the Palaeo-Asian Ocean domain was not the original trigger of the Kungurian climate change in the North China Craton.

Petrogenesis and geodynamic implications of the Late Devonian dioritic and granitic intrusive rocks in the Dananhu Belt, Eastern Tianshan Orogenic Belt

The Late Devonian magmatism of the Dananhu arc belt in the Central Asian Orogenic Belt provides a critical geological record. This study provides new comprehensive geochronological, geochemical, and Sr–Nd isotopic data of granodioritic and dioritic intrusions in the Dananhu belt. These findings contribute to unraveling the regional tectonic history and constraining the geodynamic processes involved. Zircon U–Pb dating indicates that the granodiorites and diorites were formed at 382.7 ± 3.8Ma and 363.1 ± 4.3Ma, respectively. The granodiorites show characteristics similar to I-type granites with high SiO2, low MgO and Mg# and aluminium saturation index (<1.1), negligible Eu anomalies, low (K2O + Na2O)/CaO ratios and zircon saturation temperatures (average = 696 °C). Granodiorites also show depleted isotope signatures (εNd(t) = +5.85 to +6.27 and low (87Sr/86Sr)i = 0.704082–0.704583) and juvenile TDM ages (741–793Ma), indicating their origin from a juvenile crust. The diorites are characterized by enrichments in large ion lithophile elements, U and Pb, but depleted in Nb and Ta displaying typical geochemical features of a subduction-related origin, together with high εNd(t) (+6.10 to +6.84) and low initial Sr isotopes (0.703745–0.704601), suggesting that they originated from a subduction fluid modified depleted mantle. The petrogenesis of both granodiorites and diorites in the Dananhu arc provides evidence that they formed through magmatic processes in a subduction tectonic setting. Considering the adakites associated with slab melting from previous studies in the Dananhu arc, it is plausible that the north-dipping subduction of the North Tianshan oceanic lithosphere have contributed to the Dananhu arc magmatism during the Late Devonian.

Compositionally variable basement and tectonic affinity of the Bainaimiao arc belt: Implications for crustal growth of the Central Asian Orogenic Belt

As an important part of the southeastern boundary of the Central Asian Orogenic Belt (CAOB), the Bainaimiao arc belt, particularly its tectonic affinity and Precambrian basement composition, is an important element to provide new insights about the crustal growth of the CAOB. However, these remain poorly understood. This paper presents new geochronological, whole-rock geochemical and zircon Hf isotope data on early Paleozoic intrusive rocks from the Bainaimiao arc belt in the southeastern CAOB. The Ordovician gabbroic diorites in the Zhengxiangbaiqi area of the western Bainaimiao arc belt have low SiO2 contents (51.73–54.82 wt%), high TiO2 (0.99–1.07 wt%) and TFe2O3 contents (9.68–9.89 wt%), depletions in Nb, Ta and Ti, and positive εHf(t) values (6.8–11.3). These rocks generated from partial melting of a mantle wedge that has been metasomatized by subducted-derived fluids. The Silurian monzogranites in the Zhengxiangbaiqi area have high contents of SiO2 (72.61–75.12 wt%) and K2O (2.75–4.12 wt%), positive εHf(t) values (0.7–9.3) and abundant Precambrian inherited zircons. These monzogranites originated from partial melting of the thickened juvenile crustal components with significant ancient crustal contamination. The Silurian granites and granodiorites in the Faku area of the eastern Bainaimiao arc belt are characterized by high Na2O contents (4.00–4.52 wt%), high Sr/Y ratios, low MgO (1.15–1.74 wt%) and K2O contents (0.52–1.42 wt%), low K2O/Na2O ratios, and positive εHf(t) values ranging from 0.6 to 8.1. These rocks were derived from partial melting of a subducted slab interacted with mantle peridotite. New zircon U-Pb-Hf isotope data from these early Paleozoic intrusive rocks combined with previous results indicate that the Precambrian basement of the Bainaimiao arc belt is laterally heterogeneous, with Neoarchean-Paleoproterozoic basement beneath the western Bainaimiao arc belt and Paleo-Mesoproterozoic basement beneath the central Jilin area in the eastern Bainaimiao arc belt. The Bainaimiao arc belt has a tectonic affinity different from the North China Craton (NCC) and represents a composite arc system consisting of an ensialic island arc with a basement composition similar to that of the Precambrian microcontinents in the CAOB in the Bayan Obo-Damaoqi-Bainaimiao-Zhengxiangbaiqi and central Jilin areas and an oceanic island arc in the Ongniud-Faku and southern Jilin areas. The involvement of composite arc systems in the amalgamation of the accretionary orogenic belt could be an important mechanism for crustal growth in the CAOB.

Detrital zircon U–Pb and Hf analyses of Silurian–Devonian sediments in the Sukhothai Terrane, northern Thailand: implications for the Mid-Paleozoic arc belt

The Sukhothai Terrane in northern Thailand consists of continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Palaeo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. We present new detrital zircon U–Pb geochronology, Lu–Hf isotope data and geochemical data for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group accumulated between 433 and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China probably extends to the Chiang Rai region to the west of the Sukhothai Terrane, northern Thailand, revealing the northwards subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the mid-Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys Ocean in northern Thailand is comparable with that recently established in Yunnan, SW China. Supplementary material: Detrital zircon U–Pb ages and trace element analyses, zircon in-situ Lu–Hf isotopic compositions and whole-rock geochemical data are available at https://doi.org/10.6084/m9.figshare.c.6858373

Diverse Late Triassic arc magmatism and porphyry Cu deposits in the southeastern Tibetan Plateau: Related to slab tear along a subducting passive margin?

The subduction of the ocean–continent transition (OCT) zone on a passive margin has received limited attention, despite its significant impact on tectono-magmatic processes. This study focuses on the Late Triassic basalts and andesites in the southeastern Tibetan Plateau, where the Yushu-Yidun Arc belt intersects the Longmen Shan Fault system. The goal is to understand the interplay between these linear systems. The basalts exhibit trace element and isotopic signatures resembling those of within-plate enriched mid-ocean ridge basalts or ocean island basalts (EOBs), such as positive NbTa anomalies, high Nb/Th (7.72 to 10.3) and εNd(t) (+2.23 to +6.34) values, and low La/Sm values (2.69 to 4.05), suggesting an asthenospheric mantle source. The contemporaneous andesites display typical arc-like geochemical characteristics (e.g., enrichment in Ba, Th, and U but depletion in Nb, Ta, and Ti), with negative εNd(t) values (−2.41 to −1.08), indicating a mantle wedge source affected by subducted components. Geological evidence indicates that the Longmen Shan Fault zone, previously defined by its magmatic rocks, was an active OCT belt during the Late Triassic, separating the South China Continent from the Garze–Litang Ocean. Consequently, we propose a model suggesting the tearing of a subducted oceanic slab from the continental lithosphere within the OCT belt under the southernmost segment of the Yushu–Yidun Arc belt, driven by strong slab pull in the Garze–Litang Ocean subduction zone. This model effectively explains the intriguing geology of the Songpan–Garze–Hoh Xil Terrane, in which Late Triassic EOBs and normal arc-related igneous rocks coexist and are accompanied by abundant slab-derived mineralized porphyries. Our findings have global implications for investigating geochemically diverse magmatism and associated mineralization on passive continental margins.

Ore Genesis and the Magmatism of the Yuhaixi Mo(Cu) Deposit in Eastern Tianshan, NW China: Constraints from Geology, Geochemistry, Zircon U-Pb and Molybdenite Re-Os Dating

The Yuhaixi Mo(Cu) deposit is a new discovery in the eastern section of the Dananhu-Tousuquan island arc, Eastern Tianshan. However, the genesis of the Yuhaixi Mo(Cu) deposit is still not fully understood. The Yuhaixi intrusion is composed of monzonitic granites, diorites, granites, and gabbro dikes, among which disseminated or veinlet Mo and Cu mineralization is mainly hosted by the monzonitic granites. The LA-ICP-MS zircon U-Pb dating yields emplacement ages of 359.4 ± 1.6 Ma for the monzonitic granite, 298.8 ± 1.8 Ma for the diorite, and 307.0 ± 2.3 Ma for the granite. The Re-Os dating of molybdenite hosted by monzonitic granite yields a well-constrained 187Re-187Os isochron age of 354.1 ± 6.8 Ma (MSWD = 1.7) with a weighted average age of 344.5 ± 3.1 Ma. The Mo mineralization is closely associated with the Yuhaixi monzonitic granite. The Yuhaixi monzonitic granite rocks are characterized by high silica (SiO2 &gt; 70 wt.%), low MgO (0.23–0.36), Ni, Cr contents, and they are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: e.g., K, Ba, Pb and Sr), and depleted in heavy rare earth elements (HREEs) and high field-strength elements (HFSEs: e.g., Nb, Ta and Ti). They are weak peraluminous and have high εHf(t) (11.37–17.59) and εNd(t) (1.36–7.75) values, and varied initial 87Sr/86Sr (0.7037–0.7128) values. The Yuhaixi post-ore granites exhibit similar geochemical and isotopic signatures to the Yuhaixi monzonitic granite. These characteristics suggest that the Yuhaixi felsic rocks are likely sourced from the partial melting of the juvenile lower crust. The Yuhaixi diorite has low SiO2, and K2O contents, relatively high Na2O, MgO (Mg# = 45–53) contents, and depletions in HFSE (e.g., Nb, Ta, and Ti). These geochemical features, coupled with isotopic data such as low initial 87Sr/86Sr (≤0.7043), high εNd(t) (2.5 to 3.0) and εHf(t) (≥11.6) values, and young Hf model ages, suggest that their parental magmas possibly originated from the partial melting of the depleted lithospheric mantle that was metasomatized by hydrous melts or fluids from the subducting oceanic plate. Integrating our new results with previous works on the Dananhu-Tousuquan island arc belt, we suggest that the Yuhaixi Mo(Cu)deposit is likely sourced from the juvenile lower crust, which was formed in an arc setting, where the bipolar subduction of the North Tianshan oceanic slab forms the Dananhu Tousuquan belt to the north and the Aqishan-Yamansu belt to the south. The eastern section of the Dananhu-Tousuquan island arc is a promising target for late Paleozoic porphyry Mo(Cu) deposits.

Multiple mineralization events at Paleozoic Sanchakou porphyry Cu deposit, Xinjiang: New insights from geology, geochronology, fluid inclusions, and H-O-C isotopes

The Sanchakou Cu deposit is located in the eastern section of the Dananhu arc belt in Eastern Tianshan, Xinjiang, and recorded multiple magmatic-mineralization events. The porphyry-style mineralization period produced disseminated, sulfide-dominant veined, and patchy sulfides containing chalcopyrite ± bornite ± carrolite ± molybdenite (Mol-1), which was associated with magnetite ± biotite ± chlorite ± sericite alteration in a suite of quartz diorite intrusions. The overprinting mineralization period contributed to minor Cu and Mo mineralization, featured by later disseminated molybdenite (Mol-2), chalcopyrite, and widespread low-temperature (<280 °C) vein-type stellerite assemblages. Two distinct geological ages of molybdenite (including Mol-1 and Mol-2) from Sanchakou have been determined in this study. The old 187Re/187Os isochron age for euhedral Mol-1 represents the timing of original porphyry-style mineralization (386 ± 16 Ma), in agreement with LA-ICP-MS zircon U-Pb age of dark diorite dykes (390 ± 11 Ma). The young 187Re/187Os age for fine-grained Mol-2 is interpreted to be a maximum age of sulfide formation or remobilization (364 ± 15 Ma), most likely associated with the emplacement of Late Devonian gneissic granite intrusions. Fluid inclusion microthermometry, mineralogy, and physicochemical calculations for the porphyry-type mineralization period (including four stages) at Sanchakou suggest that earlier magmatic fluids have evolved from high T (310–460 °C), high logfO2 (−22 to − 26), and alkaline condition during stage I to low T, low logfO2 (−34), and acidic condition during stage II. The decrease of oxygen fugacity caused by abundant deposition of magnetite in stage I produced large-scale Cu and Mo precipitation. Stage II to IV fluids have gradually decreasing temperatures and salinities, due to involvement of meteoric water that also facilitates the ore deposition. This result is consistent with the evolution of O isotope compositions of the fluids (δ18Ofluids = − 9.3 to 4.3), further implying the significance of fluid mixing instead of fluid boiling that caused ore deposition. Locally high-grade copper concentrations at Sanchakou are likely attributed to the overprinting modification event on the original ore bodies. All of these observations indicate that the Paleozoic Sanchakou ore-forming system is similar to other deformed porphyry Cu systems in the Central Asian orogenic belt (CAOB) and worldwide. The Cu mineralization and modification event at Sanchakou is coincident with the second peak productivity in CAOB. We further suggest that the Paleozoic diorite complex and stellerite alteration can be as a significant exploration target for porphyry-style Cu mineralization in the Eastern Tianshan.

Neoproterozoic slab window in the western Yangtze Block, South China: Evidence from adakitic granodiorites, gabbro-diorites and high-K granites in the Panxi arc belt

Neoproterozoic igneous rocks are widespread along the margins of the Yangtze Block and record key information on the tectonic evolution of the South China Craton. In this paper, we present a comprehensive study of zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Hf isotopes on the Neoproterozoic granodiorites, gabbro-diorites, and high-K granites in the western Yangtze Block. The granodiorites, gabbro-diorites and high-K granites were dated at 848 ± 5.3 Ma, 824 ± 5.1 Ma and 819 ± 1.5 Ma, respectively. The granodiorites have high Sr (567 ∼ 607 ppm) contents and Sr/Y (84.4 ∼ 88.0) ratios and low alkalis (Na2O + K2O = 4.3 ∼ 4.9 wt%) and Y (6.6 ∼ 7.1 ppm) and Yb (0.7 ∼ 0.9 ppm) contents, similar to typical adakitic rocks. They show low MgO (0.9 ∼ 1.3 wt%), Cr (15.2 ∼ 26.7 ppm) and Ni (3.6 ∼ 4.4 ppm) contents and positive εNd(t) (+1.7 to + 4.2) and εHf(t) (+3.0 to + 8.2) values. The parental magmas for granodiorites were generated by partial melting of thickened juvenile mafic lower crust. The gabbro-diorites are characterized by the enrichment in LREEs, significantly negative Nb, Ta and Ti anomalies, and positive εNd(t) (+2.2 to + 4.2) and εHf(t) (+5.8 to + 10.4) values. They are inferred to be derived from partial melting of lithospheric mantle modified by subduction-related fluids. The high-K granites display high Zr + Nb + Ce + Y (208 ∼ 366 ppm) and alkali (Na2O + K2O = 7.6 ∼ 8.4 wt%) contents, high 10000*Ga/Al (2.31 ∼ 2.64) ratios and zircon saturation temperatures, similar to A-type granites. We suggest that these granites were formed by the partial melting of felsic crustal materials under low pressure and high temperature conditions. The association of granodiorites, gabbro-diorites and high-K granites indicates Neoproterozoic oceanic slab subduction in the western Yangtze Block. We suggest that a subducting oceanic slab window can account for Neoproterozoic magmatism in the western Yangtze Block.

The significance of Nd isotope mapping in Precambrian orogenic belts: A case study from the Saguenay region of the Quebec Grenville Province

Fifty new Nd isotope analyses are presented for the Saguenay region of the Quebec Grenville Province. Most samples yield juvenile Pinwarian model ages, with an average depleted mantle model age (TDM) of 1.55 Ga, typical of the Quebecia accreted arc terrane. However, ten samples yield older model ages, averaging 1.78 Ga. These samples have an approximately linear geographical distribution, and are interpreted as melts of old basement panels trapped between juvenile Pinwarian crustal blocks during the accretion of the Quebecia terrane as a composite arc belt. These panels are the most tangible remnants of pre-Pinwarian crust in the Saguenay region, and their mapping is an important step in understanding the geometry of Mesoproterozoic crustal accretion on the SE margin of Laurentia. This study illustrates the usefulness of Nd isotope mapping for interpolating crustal formation ages between U-Pb dated samples in deeply exhumed orogenic belts. The data confirm that the Quebecia composite arc belt consists almost entirely of accreted juvenile Pinwarian arc crust, with less than 5% of older Paleoproterozoic crustal slivers. A comparison with the modern analogue of the Japan Arc suggests that normal plate tectonic processes can insert juvenile arc terranes behind rifted slivers of old crust to create the observed geometrical pattern of crustal formation ages.

Tectonic division of the pre-cenozoic basement of the South China Sea in earth monitoring

The past five decades have witnessed satellite remote sensing become one of most efficient tools for surveying the Earth at local, regional, and global spatial scales. The nature of the basement tectonic unit is closely related to the origin and evolution of the basin. However, such research carried out in the South China Sea (SCS) is relatively limited. In this research, by analyzing the fault structure, gravity and magnetic anomaly characteristics of the SCS, the ophiolite belts, spreading edge zones and the regional deep faults are considered as the boundaries of the tectonic units, and the SCS area can be divided into seven basement tectonic units: Cathaysia massif, Indochina massif, the SCS basin, Philippine island arc belt, Nansha massif, Sunda massif and Sibu accretionary prism. These tectonic units have different tectonic sequences, sedimentary formations and metamorphic types, in addition, they affect the Cenozoic basins overlying them to form different structural types. The research results will help to further understand the pre-Cenozoic basement structure and the tectonic evolution history of the SCS.

Application of data-driven multi-index overlay and BWM-MOORA MCDM methods in mineral prospectivity mapping of porphyry Cu mineralization

The present study applies proposed hybrid mathematical frameworks, namely Data-driven Multi-Index Overlay Method (DMIO) and Best Worst Method-multi objective optimization by ratio analysis (BWM-MOORA) techniques, for generating robust predictive models enhancing mineral prospectivity analysis is demonstrated. These are used for (i) weighting multiple groups of evidence maps acquired from geological databases, such as remote sensing, geological, geochemical, and geophysical, and then (ii) integrating these weighted layers into robust predictive models to assess porphyry copper prospectivity. This case study of the Chahargonbad area is a district of the volcano-plutonic Urumieh–Dokhtar magmatic arc belt. Porphyry copper deposit (exploration and development) models were used for distilling geoscientific datasets that are available into a group of evidence-based layers. The BWM-MOORA method combines two separate processes in which BWM is applied to weight each criterion and sub-criteria, whereas the MOORA approach helps rank these attributes. Each layer is first converted to another space of [0,1] by the sigmoidal logistic function to perform the critical process of integrating each of the evidence layers. Then, a concentration-area fractal model was used to classify evidences into some geospatial populations. In addition, a prospectivity / mineral potential mapping (MPM) analysis is performed using the DMIO, a well-proven, and accurate data-based methodology, to verify the satisfactoriness and validation of the applied methodology. Prediction-area (P-A) and normalized density (Nd) analysis (plots) were performed as validation methods to estimate the reliability and evaluate the relative efficiency of the MPM models. Therefore, these detailed outcomes confirm the validity of the BWM-MOORA model (Nd = 3.17), which is slightly higher than the valid and proper model DMIO (Nd = 3) in determining the specific potential mineralization regions.

Detailed 40Ar/39Ar Geochronology of the Loyalty and Three Kings Ridges Clarifies the Extent and Sequential Development of Eocene to Miocene Southwest Pacific Remnant Volcanic Arcs

AbstractThe 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings Ridges and South Fiji Basin. In this paper we present 33 40Ar/39Ar, 22 micropaleontological, and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites in this little‐studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites, and a granite. Successful Ar/Ar dating of altered and/or low‐K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The 40Ar/39Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25–22 Ma); two are Eocene (39–36 Ma). The granite has a U/Pb zircon age of 23.6 ± 0.3 Ma. 40Ar/39Ar lava ages are corroborated by microfossil ages from associated sedimentary rocks. The VESPA lavas are part of a &gt;3,000 km long disrupted belt of Eocene to Miocene subduction‐related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, speculatively, D’Entrecasteaux Ridge. This belt is the product of superimposed Eocene and Oligocene‐Miocene remnant volcanic arcs that were stranded along and near the edge of Zealandia while still‐active arc belts migrated east with the Pacific trench.

The geochronology, geochemistry and petrogenesis of ca. 2.65 Ga tonalites and ca. 2.61 Ga amphibolites in the Jiefangyingzi area: Implications for the northern boundary of the North China craton

The Bayan Obo–Duolun–Chifeng–Kaiyuan (BDCK) Fault is considered the boundary between the North China Craton (NCC) and Central Asian Orogenic Belt (CAOB). However, the site of this boundary from Duolun to Chifeng and Kaiyuan remains highly controversial. Here, we present an integrated study of petrology, whole‐rock geochemistry, and zircon U–Pb and Sr–Nd–Hf isotope compositions for tonalites and amphibolites in the Bainaimiao arc belt (BAB) to better constrain the northern NCC margin. The tonalites are similar to NCC tonalite–trondhjemite–granodiorites (TTGs), characterized by relatively high Na2O/K2O and Sr/Y ratios and fractionated rare earth element (REE) patterns, with high light REE (LREE) but low heavy REE (HREE) concentrations. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U–Pb dating yields formation ages of 2599–2674 Ma, with a weighted average of 2649.6 ± 3.7 Ma. The εHf(t) values (3.5–7.5), two‐stage model ages (2673–2793 Ma), whole‐rock positive εNd(t) values (1.3–1.9), and two‐stage model ages (2841–2880 Ma) suggest that the Neoarchean tonalites likely originated from remelting of thickened Meso‐Neoarchean mafic crust. LA–ICP–MS U–Pb isotope data reveal that the amphibolites formed at ~2610 Ma. They have high‐Fe tholeiitic compositions and are close to normal mid‐ocean ridge basalt (N‐MORB)‐like rocks, indicating that they were generated from partial melting of the depleted mantle. The existence of Neoarchean basement rocks, combined with seismic and isotope data, suggests that the Jiefangyingzi area is part of the Trans‐North China Orogen (TNCO) in the NCC rather than part of the CAOB and that the northern boundary of the NCC in Chifeng is located north to the Jiefangyingzi area.