Active Continental Arc Research Articles

Effect of crustal stress state on magmatic stalling and ascent: case study from Puyehue-Cordón Caulle, Chile

The Southern Volcanic Zone (SVZ) in Chile is an active continental arc with a complex history of volcanism, where a range of magmatic compositions have been erupted in a variety of styles. In the Central SVZ, both monogenetic and polygenetic volcanoes exist, in close proximity to the Liquiñe-Ofqui Fault System (LOFS), but with variable local stress states. Previous studies have inferred varying crustal storage timescales, controlled by the orientation of volcanic centres relative to the N-S striking LOFS and σHMax in this region. To assess the relationship between volcanism and crustal stress states affected by large-scale tectonic structures and edifice controls, we present whole rock geochemical data, to ensure consistency in source dynamics and crustal processing, mineral-specific compositional data, thermobarometry, and Fe–Mg diffusion modelling in olivine crystals from mafic lavas, to assess ascent timescales, from the stratovolcanic edifice of Puyehue-Cordón Caulle and proximal small eruptive centres. Textural observations highlight differences in crystal maturation timescales between centres in inferred compression, transpression, and extension, yet source melting dynamics remain constant. Only samples from the stratovolcanic edifice (in regional compression) preserve extensive zonation in olivine macrocrysts; these textures are generally absent from proximal small eruptive centres in transtension or extension. The zonation in olivines from stratovolcanic lavas yields timescales on the order of a few days to a few weeks, suggesting that even in environments which inhibit ascent, timescales between unrest and eruption of mafic magmas may be short. Significantly, high-resolution compositional profiles from olivine grains in the studied samples record evidence for post-eruptive growth and diffusion, highlighting the importance of careful interpretation of diffusion timescales from zoned minerals in more slowly cooled lavas when compared with tephra samples.

Zirconium stable isotope fractionation during intra-crustal magmatic differentiation in an active continental arc

Zirconium (Zr) stable isotope variations occur among co-existing Zr-rich accessory phases as well as at the bulk-rock scale, but the petrologic mechanism(s) responsible for Zr isotope fractionation during magmatic differentiation remain unclear. Juvenile magma generation and intra-crustal differentiation in convergent continental margins may play a crucial role in developing Zr isotope variations, and the Northern Volcanic Zone of the Andes is an ideal setting to test this hypothesis. To investigate the influence of these processes on Zr stable isotope compositions, we report δ94/90ZrNIST of whole rock samples from: 1) juvenile arc basalts from the Quaternary Granatifera Tuff, Colombia; 2) lower crust-derived garnet pyroxenites (i.e., arclogites), hornblendites, and gabbroic cumulates found in the same unit; and 3) felsic volcanic products from the Doña Juana Volcanic Complex, a dacitic composite volcano in close proximity to and partially covering the Granatifera Tuff. The basalts have δ94/90ZrNIST values ranging from −0.025 ± 0.018 ‰ to +0.003 ± 0.015 ‰ (n = 8), within the range of mid-ocean ridge basalts. The dacites have δ94/90ZrNIST values ranging from +0.008 ± 0.013 ‰ to +0.043 ± 0.015 ‰ (n = 14), slightly positive relative to the Granatifera and mid-ocean ridge basalts. In contrast, the (ultra)mafic cumulates have highly variable, predominantly positive δ94/90ZrNIST values, ranging from −0.134 ± 0.012 ‰ to +0.428 ± 0.012 ‰ (n = 15). Individual grains and mineral fractions of major rock-forming phases, including garnet (n = 21), amphibole (n = 9), and clinopyroxene (n = 18), were analyzed from 8 (ultra)mafic cumulates. The mineral fractions record highly variable Zr isotopic compositions, with inter-mineral fractionation (Δ94/90Zrgarnet-amphibole) up to 2.067 ‰. Recent ab initio calculations of Zr–O bond force constants in rock-forming phases predict limited inter-mineral Zr isotope fractionation in high-temperature environments, suggesting that the large fractionations we observe are not the product of vibrational equilibrium processes. Instead, we propose a scenario in which large Zr isotopic fractionations develop kinetically, induced by sub-solidus Zr diffusion between coexisting phases via changes in Zr distribution coefficients that arise from changes in temperature. Altogether, Zr isotope variability in this calc-alkaline continental arc setting exhibits no correlation with indices of magmatic differentiation (e.g., Mg#, SiO2), and is not a simple function of fractional crystallization. Furthermore, the garnet clinopyroxenite cumulates studied here represent density-unstable lower arc crust material; consequently, material with isotopically variable δ94/90Zr can be recycled into the mantle as a consequence of lower crustal foundering.

Petrogenesis of Neoproterozoic high-K intrusion in the southwestern Yangtze Block, South China: Implication for the recycled subducted-sediment in the mantle source

The study of K-enriched intrusive rocks is essential for deciphering mantle metasomatism beneath active continental arcs. In this contribution, high-precision zircon U–Pb–Hf isotope, whole-rock geochemistry, Sr–Nd isotope, and mineral chemistry analyses were performed to evaluate the petrogenesis and geodynamic system of the Yunnongfeng intrusion on the southwestern margin of the Yangtze Block. The Yunnongfeng intrusion consists of a high-K to shoshonitic rock assemblage with variable lithology from gabbro-diorite to granite. Zircon U–Pb dating gives concordant crystallization ages of ca. 782.5 ± 3.8 Ma for gabbro-diorite, ca. 774 ± 4.1 and 776 ± 4.1 Ma for diorite, ca. 770 ± 4.7 Ma for quartz monzonite, ca. 763 ± 3.4 Ma for quartz syenite, and ca. 764 ± 16 Ma for granite. These samples also show similar Sr–Nd, and Lu–Hf isotopic compositions, implying a common magma source. The similar crystallization age and regular variation of major and trace element contents suggest that these rocks were formed through fractional crystallization of cogenetic primitive mantle magmas. The enriched εNd(t) (−5.7 to − 5.1) and εHf(t) (−6.7 to − 1.2) values, high Rb/Y and Th/La ratios, slight Nd–Hf decoupling, and high-K and Th contents demonstrate that their lithospheric mantle source was enriched by slab-related fluid and sediment-related melt. The samples also exhibit remarkable enrichment in large-ion lithophile elements and depletion in high-field-strength elements, indicative of subduction-related arc magmatism. Taking into account previous studies, we suggest that the western margin of the Yangtze Block experienced a long-term subduction process during the Neoproterozoic, and the Yunnongfeng intrusion formed in an extensional back-arc basin. Based on the K-enriched mafic–intermediate rocks from the western margin of the Yangtze Block commonly show high K2O/Na2O, Rb/Sr, low Ba/Rb ratios, and enriched εNd(t) values, our study, coupled with numerous previous reports, proposes that the K-enrichment resulted from the breakdown of phlogopite, owing to subduction-related sediment melt reacting with peridotite in the mantle source area.

Paleo‐Pacific Plate Subduction and Basement Mobilization Triggered Large‐Scale Formation of Mesozoic Gold Deposits in the Northern Margin of the North China Craton

AbstractThe northern margin of the North China Craton (NNCC) hosts Mesozoic gold deposits of significant economic importance. The metal sources of these gold systems have long been debated with mainly magmatic‐hydrothermal versus metamorphic fluid models. Mercury (Hg) isotopes, which undergo unique mass‐independent fractionation, can provide important insights into the source of metals in gold deposits due to the close association between Hg and Au in such systems. Here, we investigated the Hg isotopic composition of six gold deposits of the Middle Jurassic to Early Cretaceous age and potential source rocks in the NNCC. Variable ∆199Hg values were observed in bulk ore and pyrite samples (−0.28‰ to 0.34‰, n = 51) and coeval granites (−0.21‰ to 0.13‰; n = 25). The negative ∆199Hg values of bulk ore and pyrite samples mostly agree with that observed for metamorphic basement rocks (−0.37‰ to 0.11‰; n = 32). The positive ∆199Hg values of bulk ore and pyrite samples agree with those reported in marine sediments (0‰–0.3‰). So the data suggest binary mixing of ocean‐recycled Hg originated from the subducted oceanic slab, and terrestrial‐recycled Hg from the Precambrian basement in Mesozoic gold deposits. The contribution of Hg (and Au, by analogy) from both reservoirs varies depending on active continental arc versus intracontinental setting and is ultimately controlled by translithospheric heat flow driven by paleo‐Pacific plate subduction.

To sink, or not to sink: The thermal and density structure of the modern northern Andean arc constrained by xenolith petrology

Abstract The thermal and compositional structure of arcs influence magmatic differentiation and lower-crustal foundering, two key processes impacting the evolution of the continental crust. Although many studies have proposed time scales of lithospheric recycling based on convective downwelling calculations, these models depend on the composition, density (ρ), and thermal structure of the lower crust and mantle, which are difficult to quantify in active continental arcs. Here, we constrained these properties for the Andean Northern Volcanic Zone using direct petrologic observations from a unique suite of lower-crust and mantle xenoliths from Mercaderes, Colombia. Chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb dates for zircons within the host tuff indicate the xenoliths erupted no earlier than 238 (±19) ka and thus capture a recent snapshot of the arc and subarc mantle. Equilibrium pressure-temperature (P-T) estimates for 81 xenoliths define three distinct thermal domains, interpreted as (1) a steep conductive geothermal gradient in the lower arc crust; (2) a convecting mantle wedge; and (3) cooled mantle in proximity to the subducting slab. Our results indicate the presence of an ~10–14-km-thick, high-density lithospheric root that is ~0.1 g/cm3 denser than the underlying mantle. Unlike records from exhumed paleoarcs, Rayleigh-Taylor instability calculations using our P-T-ρ constraints are unrealistically short for the northern Andes. We suggest the presence of partial melts in this hot arc root as a potential source of buoyancy preventing or significantly slowing down foundering.

Ordovician carbonate factory turnover tracked by its depositional, diagenetic, and carbon and oxygen isotope record

Throughout Earth's history, carbonate factories have been production systems which appeared, declined and re-appeared (in modified form) in function of biotic evolution and systemic stability. Reconstructing the history of these intricate systems requires a combined assessment of sedimentological, paleoecological, geochemical and diagenetic criteria. Here, the Ordovician of the western Tarim Basin (Darriwilian to Katian, ramp-platform to basin settings) is used as the case example to test a multiproxy approach, including statistical analysis of proxy data. We identify stratigraphic segmentation of these strata in terms of facies/mineralogy, diagenesis and a first comprehensive data set of component-specific carbon and oxygen isotope values. The published bulk carbon and oxygen isotope data are analysed in the second step to extract marine diagenetic versus burial/meteoric signatures (virtual bulk values, Monte-Carlo simulation). Finally, a synoptic chemo-chronostratigraphic plot for the Ordovician of the western Tarim Basin with segments lasting from tens of Myrs down to several 100 kyrs is proposed. A long-term trend of increasing δ13C values culminates in the early Katian at 3.2 ‰ followed by a steady decrease. A baseline shift, arguably due to the initiation of a bahamite-type factory, blurs the globally reported Guttenberg carbon-isotope excursion (GICE). A medium-term (Darriwilian to earliest Sandbian) negative δ13C isotope excursion coincides with the demise of the Darriwilian sponges-pelmatozoa factory (suecicus Event, term proposed in this study) and a positive δ18O excursion. This event might represent the effects of volcanism/SO2 outgassing during the switch from a passive to an active continental arc. The suecicus Event masquerades the middle Darriwilian carbon-isotope excursion (MDICE).

Petrogenesis of mafic‐intermediate dykes from the Central Qilian belt, NW China: Significance of the role of subducted compositions in sub‐arc mantle

Subduction system in the Qilian orogenic belt experienced the variability of an active continental arc in space and time related to the subduction of the Proto‐Tethys Ocean. Zircon U–Pb geochronology and whole‐rock chemical and Sr–Nd isotopic data of mafic to intermediate dykes in the western part of the Central Qilian belt (WCQB) are used to track magma provenance from compositionally variable reservoirs in the sub‐arc mantle and constrain the magmatic evolution of the rear‐arc at 450–445 Ma. Petrological, whole‐rock chemical and zircon U–Pb dating results reveal that the studied dykes mainly comprise calc‐alkaline lamprophyre (CAL), high Mg# andesitic porphyrite (HMA) and high FeO hornblende gabbro (HFG) with crystallization ages of 447, 453 and 448 Ma, respectively. Among them, CAL and HMA have affinities in high‐K calc‐alkaline suites, high REE contents (∑REE = 131.1–202.3 ppm) with high LaN/YbN values (6.77–17.99), enriched in large‐ion lithophile elements (LILE, e.g., Rb and U), and depleted in high‐field‐strength elements (HFSE, e.g., Nb, Ta, and Ti). They also have high Th/La (0.20–0.46), Th/Nb (0.67–1.64) and Th/Yb (3.88–14.11) ratios, and relatively high whole‐rock initial 87Sr/86Sr ratios (0.707469–0.708493) and εNd(t) values (−4.7 to −3.1). Whereas, HFG is affinities in medium to high‐K calc‐alkaline suites, and has moderate rare earth elements (∑REE = 70.1–112.5 ppm) with flat REE patterns (LaN/YbN = 2.12–3.05) and exhibits enriched LILE, and Sr–Nd isotopes ((87Sr/86Sr)i = 0.713496–0.729216, εNd(t) = −2.93 to +2.04). Such typical “continental” geochemical features of the different K‐rich dykes do not result from crustal assimilation but reflect an enriched mantle source resulting from their mantle heterogeneity due to recycling of different subducted sediments. The temporal evolution of the geochemical characteristics of mafic‐intermediate dykes is consistent with an extension setting triggered by removing the thickened arc crust root in the WCQB.

Late Palaeozoic tectonic evolution of the eastern Palaeo-Asian Ocean: new evidence from the early Permian arc magmatic suites in the Kulun region

AbstractLate Palaeozoic igneous rock associations in response to subduction, accretion, and final closure of the eastern Palaeo-Asian Ocean play a significant role in understanding the geodynamic evolution of the southeastern Central Asian Orogenic Belt. Previous studies have identified a Permian arc magmatic belt associated with the southward-dipping subduction of the eastern Palaeo-Asian Ocean along the Solonker–Changchun suture zone. The genetic mechanism and associated geodynamic settings are of great importance in deciphering the evolution of the eastern Palaeo-Asian Ocean. This paper presents zircon U–Pb–Hf isotope and whole-rock geochemical analyses for a suite of magmatic rocks including the early Permian diorite porphyrites (ca. 281.0 Ma), andesites (ca. 276 Ma) and rhyolites (ca. 275 Ma) in the Kulun region. The diorite porphyrites and andesites have high SiO2 and total alkali contents, and low MgO contents and Mg no. values, with enrichments in large ion lithophile elements and depletions in high-field-strength elements. These geochemical characteristics, together with low-Sr and high-Yb contents, a weak concave-upward shape of middle rare earth elements and negative Eu anomalies, suggest that these intermediate igneous rocks were generated by partial melting of amphibolitic lower crust at a crustal depth of 30–40 km. The rhyolites have heterogeneous isotopic compositions, with ϵHf(t) values and TDM2 ages of –20.8 to +0.5 and 3578∼1494 Ma, implying that they were likely derived from partial melting of a mixed source dominated by recycled ancient crust with minor juvenile crustal materials. The rhyolites show potassic affinity with relatively high K2O and very low Na2O, which was attributed to liquid immiscibility of felsic magma and subsequent limited fractional crystallization of plagioclase. The regional igneous associations, metamorphic events, and coeval sedimentary rocks along the Solonker–Changchun suture zone indicate that the early Permian igneous rocks were formed in an active continental arc environment in response to southward subduction of the eastern Palaeo-Asian Ocean.

Reassessing the intrusive tempo and magma genesis of the late Variscan Aar batholith: U–Pb geochronology, trace element and initial Hf isotope composition of zircon

The Variscan orogeny was responsible for the formation of a significant volume of igneous basement throughout present-day Europe. Detailed understanding of these rocks has, however, been obfuscated by significant overprinting during younger geologic events. In order to better understand the formation of this basement, we present U–Pb dates, trace element concentrations and Hf isotope compositions of zircon from 17 intrusions of the Variscan Aar batholith, located in the Aar Massif, Central Alps, Switzerland. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used to generate a large set of U–Pb dates, trace element and Hf isotope compositions on untreated zircon, as well as zircon pretreated by chemical abrasion. Furthermore, a subset of samples was also analyzed for high-precision U–Pb geochronology using chemical abrasion, isotope dilution, thermal ionization mass spectrometry (CA-ID-TIMS). The U–Pb dates of both dating techniques are significantly dispersed, indicating that they are influenced by multiple forms of complexity, including inheritance, domains of secondary alteration likely related to Alpine overprint or growth, decay damage related Pb-loss, and potentially protracted magmatic growth. Decay-damage related Pb-loss is likely a subordinate source of age scatter within the data, therefore chemical abrasion pretreatment is not capable of completely mitigating the observed analytical scatter. After rejection of outliers, the remaining data still exhibit excess scatter of several percent among 206Pb/238U dates in individual samples, however it is possible to interpret reasonable geologic ages from these data. These new U–Pb zircon age interpretations indicate the Aar batholith grew incrementally through four major magmatic pulses, which occurred at approximately 348, 333, 309 and 298 Ma. Based on the trace element and Hf isotope geochemistry, the melt source(s) of the Aar batholith evolved throughout the duration of batholith formation and growth. The transitioning from (i) melting of depleted mantle at 348 Ma during a stage of active continental arc magmatism (εHf = + 12 to + 10), (ii) melting of metasomatically enriched lithospheric mantle, possibly contaminated by crust during the 333 Ma pulse (εHf = − 10 to − 3), followed by (iii) an increasing incorporation of a juvenile mantle components during the 309 and 298 Ma pulses (εHf = − 3 to + 6). Finally, these new U–Pb ages yield a more detailed understanding of the Variscan Aar batholith by integrating the new detailed mapping of Aar Massif for the Geological Atlas of Switzerland, allowing for more accurate characterization and categorization of variably deformed heterogeneous intrusive bodies.

Post-collisional extension of the South Altun subduction-collision belt, northern Tibetan Plateau: Insight from phase equilibria modeling and zircon geochronology of pelitic migmatites

• Continental collision led to the burial of pelitic rocks in the South Altun. • Pelitic migmatites were formed under the conditions of ∼850–870 °C and 0.6–0.7 GPa. • High- T/P type metamorphism and migmatisation lasted for ∼10 Myr (457–447 Ma) • Continental subduction to post-collisional extension took place in ∼50 Myr. The South Altun subduction-collision belt in the northern Tibetan Plateau is one of the rare examples of ultradeep subduction (>350 km). In addition to subduction-related low-temperature/pressure ( T/P ) type metamorphic rocks, the belt also exposes high- T/P metamorphic rocks with well-developed migmatitic structures, which provide insight into the post-collisional process. Phase equilibria modeling of the Tula pelitic migmatites indicates peak conditions of ∼850–870 °C and 0.6–0.7 GPa for the high- T/P type metamorphism and migmatism. Phase equilibria modeling predicts this high temperature could result in the production of 10–20 vol% melt in metapelites, producing stromatic migmatites observed in multiple outcrops. Based on results of zircon U-Pb geochronology of granulite-facies migmatites, we interpret the supra-solidus conditions to last for ∼10 Myr (457–447 Ma), corresponding to short-lived granulite-facies metamorphism in post-collisional extension. The deposition of the protolith is inferred to occur immediately before the metamorphism on active continental arcs based on the youngest detrital and oldest metamorphic ages. Combined with studies on subducted-related metamorphic rocks, these findings suggest that the South Altun belt experienced the continental subduction (early collision) to the post-collisional extension within a period of ∼50 Myr. At the same time, the thermal regime of this orogenic belt evolved from low- T/P to high- T/P whereas the high- T/P regime predominates the orogenic belt towards the end of orogenic evolution, as evidenced by regional high- T/P type metamorphic rocks and overprinting on the ancient low- T/P regime of exhumed subduction-related rocks.

The timeline of prolonged accretionary processes in eastern Central Asian Orogenic Belt: Insights from episodic Paleozoic intrusions in central Inner Mongolia, North China

Abstract Updating magmatic profile in crucial constituent terranes across the Central Asian Orogenic Belt presents a key to chronicling the timeline of prolonged accretionary processes and termination of the Paleo-Asian Ocean in the northern China–southern Mongolia tract. Here we performed a systematic geochronological and geochemical study on a spectrum of Paleozoic intrusions from the Erenhot region in central Inner Mongolia, North China, within the hinterland of the tract, with four distinct magmatic episodes unraveled. Combining these episodes with the previously documented events from contiguous regions defines two major tectono-magmatic cycles. The early Paleozoic cycle (500–450 Ma) evolved from initial fluid-fluxed tholeiitic and calc-alkaline granitoids to melt-fertilized mafic-intermediate magmatism. It appears to experience the initiation and maturation of a Western Pacific-type intra-oceanic arc system that culminated in ridge subduction. The late Paleozoic cycle expanded in magmatic expression from sporadic Late Devonian (373–365 Ma) calc-alkaline intermediate-felsic pulses through Early-Middle Carboniferous (356–320 Ma) medium to high-K calc-alkaline flare-up to a Late Carboniferous–Early Permian (310–277 Ma) province of diverse lithologies. These magmatic episodes seem to encompass a complete active continental arc–back-arc system that spanned from resuming oceanic plate subduction through slab rollback and backarc rifting to ridge-trench collision and backarc basin closure. Featuring a Rodinia-aged terrane affinity and a representative Paleozoic magmatic profile, the Erenhot region provides an optimal site for correlating the evolution of mosaic terranes in southern Mongolia and northern China, and for evaluating the coupled evolution of shifting tectonic regimes and plural crustal generation mechanisms within a retreating accretionary orogen.

A newly discovered Late Cretaceous metamorphic belt along the active continental margin of the Neo-Tethys ocean

Abstract High-grade metamorphic rocks and crustal melts provide crucial evidence for growth and differentiation of the continental crust, and are widespread in collisional orogens. However, their importance in the evolution of continental arcs remains poorly understood. Metamorphism and related anatexis in the preserved continental margin of the Neo-Tethys ocean serves as a key natural laboratory to investigate this process. Along the Neo-Tethyan arc margin, the Gaoligong shear zone, Yunnan region of China, is an important locality for linking Lhasa in the north with Sibumasu and Burma in the south. Here, Late Cretaceous granulite-facies metamorphism and crustal anatexis have been identified for the first time in the Gaoligong area. Zircon and monazite U-Pb dating indicates that S-type granites formed at 87–73 Ma, granites and buried pelitic sediments were simultaneously metamorphosed at 75–70 Ma during Neo-Tethyan subduction, and all lithologies were overprinted by a younger 40–30 Ma magmatic and strike-slip event related to India-Asia collision. Phase equilibria modeling of high-grade anatectic gneiss in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicates peak pressure-temperature (P–T) conditions of 780–800 °C and 6.5–7.5 kbar and defines a cooling and decompressional P–T path for the metapelites. This demonstrates that sediments within the Neo-Tethyan active continental arc were buried to >20 km depth at 75–70 Ma. In combination with the metamorphic record of the Lhasa, Burma, and Sibumasu blocks, an extensive Late Cretaceous metamorphic belt must have formed along the Neo-Tethyan subduction zone. This spatially correlates with coeval gabbro-diorite suites exposed in the Gangdese, Sibumasu and Burma terranes that were triggered by thinning of the lithospheric mantle. This prolonged Late Cretaceous mantle-derived magmatism and lithospheric thinning may have provided a regional-scale heat source for high-grade metamorphism and crustal anatexis along the active continental margin of the Neo-Tethys ocean.

A synthetic geochemical and geochronological dataset of the Mesoproterozoic sediments along the southern margin of North China Craton: Unraveling a prolonged peripheral subduction involved in breakup of Supercontinent Columbia

Controversial issues on the Paleo-Mesoproterozoic tectonic setting of the southern margin of North China Craton (NCC) restricted our understanding of its role in breaking up the Columbia/Nuna Supercontinent. Existing models are still arguing on whether the southern margin was an intra-continental rift or active continental margin. Previous studies mainly focused on the magmatic records in the Paleoproterozoic Xiong’er Group, while the overlain sedimentary series and their depositional nature and the related tectonic environment were not yet well constrained. In this study, we scrutinized the comprehensive geochronological and geochemical dataset for the Mesoproterozoic sedimentary rocks along the southern margin of NCC. Our new results, together with the previous geochemical data show that the interior part of NCC southern margin (e.g. Wufoshan Group of the Song-Ji area) is dominated by the materials from the mature continental crust. Approaching the marginal area of southern NCC (e.g. Gaoshanhe and Guandaokou Groups of the Xiaoqinling-Luanchuan area), sediments are more enriched in magmatic arc fragments and unfractionated materials. Detrital zircon geochronological results revealed a progressive younging tendency from the northern Song-Ji to southern Xiaoqinling-Luanchuan areas. Together with the newly-reported zircon hafnium data, the synthesized dataset in this study favors the hypothesis that the southern NCC during the Paleo-Mesoproterozoic was in an active continental arc setting under a prolonged peripheral subduction regime, which was surrounding the marginal areas of the Columbia/Nuna Supercontinent.

Use of detrital zircon U–Pb ages to assess the timing of deposition of Cretaceous trench-fill deposits in the active continental arc along the East Asian margin

Abstract The Cretaceous Shimanto accretionary complex in southwestern Japan consists mainly of trench-fill deposits and formed in an active continental margin setting along the East Asian margin. Here, we present U–Pb ages of detrital zircons from the complex and compare youngest detrital zircon ages obtained from trench-fill sandstones with true depositional ages inferred from radiolarian fossils to assess the accuracy of zircon ages for estimating the timing of deposition of the trench-fill sediments. Four different methods were used to calculate the youngest detrital zircon ages, giving four different measures: youngest single-grain age (YSG), weighted mean age of the youngest cluster overlapping in age at 1σ (YC1σ) or 2σ (YC2σ), and youngest cluster age estimated using the Mixture Models (auto) of the DensityPlotter program (YCM). The YSG and YC1σ show good agreement with true depositional ages for Albian–Cenomanian strata, which were deposited during weak magmatic activity, and we find no age gap between YC2σ and the true depositional age, but YCM is clearly older. For Turonian–Maastrichtian strata, which were deposited during a period of strong magmatism, YC2σ and YCM correspond to the true depositional ages, and there is no age gap between YC1σ and the true depositional age. However, YSG is clearly younger than the true depositional age for Turonian–Maastrichtian strata. These results indicate that YC1σ and YC2σ show the closest correspondence to the true depositional ages, which suggests that these two measures best represent the true depositional age of trench-fill deposits in an active continental margin.

Middle Paleoproterozoic tectonic evolution of the Trans-North China Orogen, North China Craton: Constraint from the intermediate-acid magmatism in the Lüliang area

The excellent middle-Paleoproterozoic tectono-thermal activities from the Lüliang Complex can provide pivotal constraints on the tectonic evolution of the Trans-North China Orogen between Eastern and Western blocks of North China Craton. LA-ICP-MS zircon dating gives emplacement ages of 2189 ± 16 Ma for gneissic diorite, 2188 ± 11 Ma for gneissic quartz monzonite, 2153 ± 9 Ma for gneissic granite in Chijianling area, respectively. The gneissic diorites have high Al2O3 (15.89–16.69 wt%), MgO (3.35–4.96 wt%), low Sr/Y (11.3–16.6), (La/Yb)N (7.40–8.44), enrichment of LILE and depletion in HFSE, especially Nb, Ta, indicating partial melting of mantle wedge fluxed by the fluids. The gneissic quartz monzonites and gneissic granites belong to high K calc-alkaline and shoshonitic series and show right inclined REE patterns, consisting with I-type granite. Zircon Hf and whole-rock Nd isotopic compositions (εHf(t) = +0.1 to +5.3 and − 7.8 to −1.7; εNd(t) = −0.4 to +0.4 and − 1.8 to −0.6) of the gneissic quartz monzonites and gneissic granites are identical to those of dominant Neoarchean basement materials with addition of Mesoarchean vestiges to a certain extent. The diversity of source material (including continental and volcanic arc materials) resembles to magmatism in normal continental arc margins. The spatial distribution, rock assemblage and decreasing rock formation pressure further hint the tectonic transformation from compression to extension regime in local areas. Taking into account the prevalence magmatic records and contemporaneous deposition of middle-Paleoproterozoic in the Trans-North China Orogen, it suggests an active continental arc setting at ~2.2 Ga and local tectonic extension regime with back-arc basin at ~2.1 Ga for a consequence of the Paleoproterozoic subduction between the Eastern block and Western block of the NCC.

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The excellent middle-Paleoproterozoic tectono-thermal activities from the Lüliang Complex can provide pivotal constraints on the tectonic evolution of the Trans-North China Orogen between Eastern and Western blocks of North China Craton. LA-ICP-MS zircon dating gives emplacement ages of 2189 ± 16 Ma for gneissic diorite, 2188 ± 11 Ma for gneissic quartz monzonite, 2153 ± 9 Ma for gneissic granite in Chijianling area, respectively. The gneissic diorites have high Al2O3 (15.89–16.69 wt%), MgO (3.35–4.96 wt%), low Sr/Y (11.3–16.6), (La/Yb)N (7.40–8.44), enrichment of LILE and depletion in HFSE, especially Nb, Ta, indicating partial melting of mantle wedge fluxed by the fluids. The gneissic quartz monzonites and gneissic granites belong to high K calc-alkaline and shoshonitic series and show right inclined REE patterns, consisting with I-type granite. Zircon Hf and whole-rock Nd isotopic compositions (εHf(t) = +0.1 to +5.3 and − 7.8 to −1.7; εNd(t) = −0.4 to +0.4 and − 1.8 to −0.6) of the gneissic quartz monzonites and gneissic granites are identical to those of dominant Neoarchean basement materials with addition of Mesoarchean vestiges to a certain extent. The diversity of source material (including continental and volcanic arc materials) resembles to magmatism in normal continental arc margins. The spatial distribution, rock assemblage and decreasing rock formation pressure further hint the tectonic transformation from compression to extension regime in local areas. Taking into account the prevalence magmatic records and contemporaneous deposition of middle-Paleoproterozoic in the Trans-North China Orogen, it suggests an active continental arc setting at ~2.2 Ga and local tectonic extension regime with back-arc basin at ~2.1 Ga for a consequence of the Paleoproterozoic subduction between the Eastern block and Western block of the NCC.

Ages and petrogenesis of the late Triassic andesitic rocks at the Luerma porphyry Cu deposit, western Gangdese, and implications for regional metallogeny

The Tibetan Plateau is one of the most significant Cu poly-metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry Cu mineralization. This study investigates a new occurrence of Cu mineralization-related andesitic porphyries in the western domain of the Gangdese magmatic belt and assesses its petrologic, zircon U-Pb geochronology, whole-rock chemistry, and Sr-Nd-Hf-Pb isotope data. Zircon U-Pb dating of three ore-related porphyries yields crystallization ages of 212–211 Ma. These ages are consistent with previous molybdenite Re-Os dating, indicating a late Triassic magmatic and Cu mineralization event in the western Gangdese magmatic belt. Nb, Ta, and Ti depletion, Th and LREE enrichment, and high La/Yb and Th/Yb ratios in addition to high U/Yb ratios from zircons suggest that the magma was generated in an active continental arc setting. The porphyries have radiogenic isotopic compositions with (87Sr/86Sr)i 0.70431–0.70473, εNd(t) +1.1 to +3.8, (207Pb/204Pb)i 15.601–15.622, and (208Pb/204Pb)i 38.450–38.693, as well as high positive zircon εHf(t) values from +6.2 to +10.6 (mean value 8.3), corresponding to model ages (TDM) ranging from 509 Ma to 819 Ma (mean 646 Ma). This suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment-derived melts during the subduction of the Neo-Tethys Ocean. The mineralization-related porphyries contain amphibole and epidote, as well as high whole-rock Fe2O3/FeO and zircon Ce4+/Ce3+ ratios, suggesting hydrous and highly oxidized parent magmas. Considering the existing Cu mineralization and highly oxidized magma of the well-preserved Triassic andesitic igneous rocks in the western Gangdese belt, the subduction-related continental arc magma system is favorable for subduction-related porphyry Cu deposits. The existence of Luerma porphyry mineralization demonstrates that there are at least five generations of porphyry Cu-(Mo-Au) mineralization in the Gangdese magmatic belt, which advances the timeframe of porphyry mineralization to the late Triassic.

Conditioned duality between supercontinental ‘assembly’ and ‘breakup’ LIPs

A compilation of 178 more precise ages on 10 potential Large Igneous Provinces (LIPs) across southern Africa, is compared to Earth’s supercontinental cycles, where 5 more prominent LIP-events all formed during the assembly of supercontinents, rather than during breakup. This temporal bias is confirmed by a focused review of field relationships, where these syn-assembly LIPs formed behind active continental arcs; whereas, the remaining post-assembly – and likely breakup-related – LIPs never share such associations. Exploring the possibility of two radically different LIP-types, only the two younger breakup events (the Karoo LIP and Gannakouriep Suite) produced basalts with more enriched asthenospheric OIB-signatures; whereas, all assembly LIPs produced basalts with stronger lithospheric, as well as more or less primitive asthenospheric, signatures. A counterintuitive observation of Precambrian breakup LIPs outcropping as smaller fragments that are more peripherally located along craton margins, compared to assembly LIPs as well as the Phanerozoic Karoo breakup LIP, is explained by different preservation potentials during subsequent supercontinental cycles. Thus, further accentuating radical differences between (1) breakup LIPs, preferentially intruding along what evolves to become volcanic rifted margins that are more susceptible to deformation within subsequent orogens, and (2) assembly LIPs, typically emplaced along back-arc rifts within more protected cratonic interiors. A conditioned duality is proposed, where assembly LIPs are primarily sustained by thermal blanketing (as well as local arc hydration and rifting) below assembling supercontinents and breakup LIPs more typically form above impinging mantle plumes. Such a duality is further related to an overall dynamic Earth model whereby predominantly supercontinent-orientated ocean lithospheric subduction establishes/revitalizes large low shear velocity provinces (LLSVPs) during assembly LIP-activity, and heating of such LLSVPs by the Earth’s core subsequently leads to a derivation of mantle plumes during supercontinental breakup.

Early Cretaceous sedimentary provenance and structural evolution of the central Sanandaj–Sirjan Zone, Iran: implications for palaeogeographic reconstructions of the northern Neo-Tethyan margin

ABSTRACT The Early Cretaceous was an important epoch in the evolution of the Earth system in which major tectonic episodes occurred, especially along the Alpine–Himalayan belt. The paucity of reliable palaeogeographic data from the central segment of this geological puzzle, however, hampers the reconstruction of a panoramic view of its Early Cretaceous palaeogeography and geodynamic setting. Here we present multidisciplinary provenance data from Lower Cretaceous strata of the overriding plate of the Neo-Tethyan subduction zone (the Sanandaj–Sirjan Zone; SSZ, of central Iran), including structural, basin-fill evolution, petrographic and geochemical analyses. Sandstone provenance analysis of Lower Cretaceous red beds suggests the occurrence of sub-mature litho-quartzose sandstones attributed to an active continental arc margin in convergent setting predominantly derived from plutonic, quartzose sedimentary and metamorphic rocks exposed in the central SSZ. Weathering indices indicate moderate chemical weathering in the source area which may be related to close source-to-sink relationships or arid climate. Our palaeogeographic reconstructions and original geological mapping indicate that the erosion of uplifted basement rocks exposed in horst blocks provided the sediment sources for the syn-extensional deposition of uppermost Jurassic–lowermost Cretaceous conglomerates and Lower Cretaceous siliciclastic red beds within a continental retro-arc basin during initiation of the ‘Neo-Tethys 2ʹ. The polyphase tectonic reactivation along the principal fault of the study area controlled the syn- and post-extensional tectonostratigraphic evolution that reflect the corresponding mechanical decoupling/coupling along the northern Neo-Tethyan plate margin.

Contrasting tectonic settings in Northern Chon Aike Igneous Province of Patagonia: subduction and mantle plume-related volcanism in the Marifil formation

ABSTRACT The northern zone of the Chon Aike Igneous Province, located in the North Patagonian Massif, exhibits extensive outcrops of Jurassic volcanic rocks of the Marifil Formation. In the Arroyo Verde area, the initial volcanic stage of the Marifil Formation, that we denominate V0 (192.6 ± 2.5 Ma), includes coulées, megabreccias and lapilli tuffs assigned to plinian-type volcanism. This magmatism was generated by cold-wet-oxidized magmas that resemble those produced in active continental margins and volcanic arcs. The second stage, located unconformably over the first, includes welded lava-like ignimbrites, massive lapilli tuff and rhyolitic lava flow that resemble the Snake River-type volcanism. The magma that produces this volcanic stage exhibit the characteristics of hot-dry-reduced magmas emplaced in intraplate continental environments associated with continental rifting. This stage coincides with the V1 volcanic episode early recorded in the Marifil Formation.