Pb Dating Of Zircons Research Articles

The Jurassic through Early Cretaceous Magmatic Belt of the Southern Margin of the Chukotka Terrane, Northeast Russia: New Results of U–Pb Dating of Zircon

The Jurassic through Early Cretaceous Magmatic Belt of the Southern Margin of the Chukotka Terrane, Northeast Russia: New Results of U–Pb Dating of Zircon

Late Ordovician Bentonites From the Southern Ordos Basin: Response to the Subduction of the Proto‐Tethys Ocean

ABSTRACTThe connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO2 (57.94–77.95 wt.%) and Al2O3 (9.21–14.33 wt.%), classifying them within the low‐potassium alkali basalt to medium‐potassium calc‐alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right‐dipping, with a more pronounced negative Eu anomaly (δEu = 0.48–0.67). The zircons in the bentonites yield two‐stage model ages ranging from 546 to 956 Ma, along with εHf(t) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto‐Tethys Ocean along the southern margin of the North China Block.

Permian-Triassic volcanic and plutonic records of the Argentine Frontal Cordillera: A review with new U–Pb and Hf-isotope zircon data

The Permian-Triassic magmatism of western Argentina and Chile represents one of the most outstanding silicic magmatic events of the southwestern Gondwana margin, notably marked by the development of the Choiyoi Magmatic Province (CMP). We provide a comprehensive review of its volcanic and plutonic record in the Argentine Frontal Cordillera. The volcanic rocks form three distinct sequences. The oldest is depicted by the Las Lozas volcanic sequence of the northern Frontal Cordillera for which new U–Pb zircon data (288 ± 2 Ma and εHft values ranging from −3.97 to +0.73) reassigns these outcrops to the early Cisuralian, aligning with volcanic records of northern Chile (ca. 297-288 Ma). The middle sequence, deposited during the late Cisuralian-late Guadalupian interval, is ascribed to the Choiyoi Group, which is characterised by a transition from andesitic (ca. 280-270 Ma) to rhyolitic compositions (ca. 270-262 Ma), including a remarkable mid-Guadalupian ignimbrite flare-up event (ca. 265 Ma). The upper sequence, composed of andesite-dacite-rhyolite, is associated with the Guanaco Sonso basin situated in the westernmost region, deposited from the late Lopingian to the middle Triassic period (ca. 254-240 Ma). The volcanic successions were developed in an extensional/transtensional setting, with facies and thickness variations controlled by normal faults, some of them active during the eruption of caldera-forming ignimbrites. Regarding the plutonic component, it comprises over sixty granitoid bodies forming the Colangüil and El Portillo batholiths and scattered stocks throughout the Frontal Cordillera. The early-stage plutons (ca. 285-272 Ma) exhibit calc-alkaline tonalite-diorite to granodiorite-monzogranite compositions and overlap in age with the lower andesitic section of the Choiyoi Group, while the late-stage plutons (ca. 265-252 Ma) display syenodiorite and alkali granite compositions and are in most cases younger than the Choiyoi Group succession. Compiled U–Pb zircon geochronological data reveal a distinctive Permian-age phase characterized by a rapid expansion of magmatism from the Gondwana margin towards its interior, followed by a slower westward shift of the main magmatic belt, predominantly recorded in the Frontal Cordillera of Argentina.

Petrogenesis and tectonic implication of the Triassic monzogranite from the central segment of the East Kunlun Orogen, NW China

The Triassic granitoids in the East Kunlun Orogenic Belt (EKOB) are crucial for understanding the tectonic evolution of the Paleo-Tethys Ocean. This study presents zircon U–Pb ages, Lu–Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotope compositions from monzogranite plutons in the central segment of EKOB to constrain their petrogenesis and tectonic evolution. These monzogranites are dominant composed of mineral assemblages of K-feldspars, plagioclase, minor biotite and accessory minerals. U–Pb dating of zircons from the Xinle South (XLS), Nanshankou (NSK) and Changgou South (CGS) plutons yield ages of 251 Ma, 232 Ma and 221 Ma, respectively. The studied monzogranites have relatively high SiO2 and Al2O3, but have low contents of TiO2, Fe2O3T, MgO relative to the coeval granodiorites. These monzogranites are classified as fractionated I-type granites, ranging from calc-alkaline to high-K calc-alkaline compositions. Their negative εNd(t) values (−4.2 to −6.3) and zircon εHf(t) values (−6.1 to −9.3) suggest that magma generation occurred through partial melting of ancient lower crust, followed by extensive fractional crystallization. Integrating our new data with regional geological evidence, we propose that the Early Triassic XLS monzogranite emplaced in a localized extensional environment linked to the northward subduction of the Paleo-Tethys oceanic plate. In contrast, during the post-collisional extensional phase of the Late Triassic, the formation of the NSK and CGS monzogranite plutons was directly influenced by asthenospheric upwelling, lower crust delamination, and subsequent continental rifting.

The leaky chronometer: Evidence for systematic cryptic Pb loss in laser ablation U‐Pb dating of zircon relative to CA‐TIMS

AbstractU–Pb dating of zircon via laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) has become a primary method for determining the age of crystalline rocks and the provenance and maximum depositional age of (meta)sedimentary rocks. Although chemical abrasion has become a standard approach for mitigating Pb loss in zircon dated via high‐resolution thermal ionization mass spectrometry (CA‐TIMS), laser ablation dating is rarely accompanied by chemical abrasion. We evaluate the accuracy of U–Pb dates acquired via LA‐ICP‐MS relative to CA‐TIMS through analysis of a large database of paired analyses from the same zircon crystals. We show that laser ablation 206Pb/238U dates are systematically younger than their CA‐TIMS counterparts, with a greater shift in detrital zircon (−2.0%) versus igneous or metamorphic zircon (−0.9%). Although systematic biases related to “matrix effects” may be a contributing factor, our analysis suggests that unmitigated cryptic Pb loss is likely widespread in laser ablation U–Pb datasets.

Southernmost limit of felsic magmatism along North Almora Thrust in the Himalayan domain

We present significant findings of the Kausani Granite Gneiss within the Inner Lesser Himalayan Sedimentary Zone (iLHSZ) just north of the North Almora Thrust (NAT). The Kausani Granite Gneiss body lies within the quartzite of the Someshwar Formation and has a tectonized contact and a discordant relationship on the north side. Detailed seismic profiling across the body also confirms a similar result. Cathodoluminescence images of zircon from the Kausani body show no inheritance of older cores. The U–Pb ages from the zircon populations separated from the Kausani body give a crystallization age of 1866 ± 3 Ma. Along with the Upalda granite gneiss and Toneta granite gneiss near the Alakhnanda Thrust in the Garhwal Himalaya and the Dungeshwari granite gneiss near the Dailekh Thrust in Nepal, the Kausani Granite Gneiss north of NAT Kumaun Himalaya forms a major terrain boundary. These gneissic bodies mark the southernmost extent of felsic magmatism at NAT, rather than the Main Central Thrust. An about 1.8 billion years‐old magmatic event in the LHSZ suggests that it is a currently active continental margin inside the ‘Greater India’ region, now situated in the Himalayan domain. However, the Pb‐loss modelling of the U–Pb zircon data reveals thermal events during the Himalayan Orogeny (~45 Ma).

High-precision U[sbnd]Pb zircon dating of explosive volcanism in an early bi-modal volcano-sedimentary sequence from the Isle of Mull, North Atlantic Igneous Province

The North Atlantic Igneous Province (NAIP) forms one of the best studied Large Igneous Provinces (LIP) on the planet, however, significant uncertainties regarding the age and nature of the early onset of volcanism across the province remain. In order to better understand the onset and timing of volcanism within the NAIP, we present a new study of the mixed volcano-sedimentary deposits exposed at the base of the Isle of Mull lava pile, Inner Hebrides, Scotland. The study area comprises organic rich estuarine sediments, intimately mixed and interdigitated with bi-modal composition volcaniclastic and pyroclastic interlayers, including a prominent stratigraphically constrained c. 30 cm thick water-lain rhyolitic ignimbrite. Pristine magmatic zircons liberated from the ignimbrite reveal a high precision UPb age of 62.035 ± 0.041 Ma (2σ) giving a robust age for early volcanism in this part of the province. Field observations reveal evidence for mafic phreatomagmatic eruptive deposits both above and below the rhyolite documenting the bimodal explosive nature of the initial magmatism in this area and, importantly, that mafic magmatism initiated before the dated unit. The bi-modal explosive eruptions periodically inundated an otherwise quiet and low energy Danian aged estuarine environment prior to its inundation with lava as magmatism took hold in the region.

Devonian plutons in the eastern Meguma terrane, Nova Scotia, Canada: zircon U–Pb, Lu–Hf, and O isotopic compositions, age, and petrogenetic implications

Abundant granitic plutons intruded the eastern Meguma terrane of Nova Scotia in the middle- to late Devonian. Less voluminous diorite–tonalite and gabbro intrusions are associated with the granitic plutons along the northern margin of the terrane adjacent to the Cobequid–Chedabucto fault zone. All plutons contain metasedimentary xenoliths, and the mafic plutons show magma mingling textures with their adjacent granitic plutons. New U–Pb zircon data from autocrystic zircon in 13 samples indicate coeval emplacement of mafic and granitic plutons between ca. 382 and 368 Ma. However, the zircon grains contain numerous inherited domains that range in age from Palaeoproterozoic to Devonian. These inherited ages correspond to detrital zircon U–Pb dates from the Cambrian to Ordovician metasedimentary host rocks. Zircon oxygen isotopic data (δ18O) are between +7.4 ± 0.2‰ and +9.3 ± 0.3‰ indicating significant involvement of the crust as the magma source or contaminant. If the high δ18Ozrn values are a result of contamination, the contaminant was likely the metasedimentary rocks of the Meguma terrane. Hafnium isotopic data from autocrystic zircon have εHf( t) between −6.0 ± 1.5 and +2.1 ± 2.5. The new zircon U–Pb, O, and Hf isotopic data from plutons in the eastern Meguma terrane are indistinguishable from published data from the South Mountain Batholith. The data suggest that Devonian magmatism in the Meguma terrane post-dated the main orogenic event that caused folding and regional metamorphism and involved the same magma source and/or contaminants throughout the terrane.

On the Age-Old Problem of Dating a Granite: Combined Zircon, Apatite, and Titanite Petrochronology in an I-Type Granite from Mt Stirling, Australia

Abstract To address the limitations of current dating methods, it is crucial to not only enhance existing techniques like U–Pb zircon dating but also explore alternative tools. This study focuses on three common mineral phases—zircon, apatite, and titanite—in an I-type granite. The goal is to assess their reliability as dating tools and propose improved methods for dating granitic rocks. In the case study of the Mt Stirling pluton within the Mt Buller igneous suite in Southeastern Australia, significant variability in laser ablation U–Pb zircon ages (around 100 million years) was observed. To improve the reliability of zircon age data and reduce non-magmatic-related variabilities, a data filtering protocol is applied. This protocol involves several steps such as trimming zircons with excessive K and Ca, excluding zircons with unusual core–rim age relationships, removing zircons with excessive non-formula elements (Al, Fe, and Mn), identifying hydrothermally altered zircons, and applying a 10% discordance threshold. The filtered Concordia Age (406 ± 1 Ma; mean square weighted deviation (MSWD) = 0.7, n = 80) of the host rock exhibits improved precision and reduced error compared to the unfiltered data (399 ± 2 Ma; MSWD = 9.3, n = 240). The filtered individual dates show less scatter and a mean that is different (i.e. outside statistical uncertainty), noting that their total still spans a considerable time range of ~50 million years, exceeding the individual zircon analytical reproducibility of 2 standard errors (~15 million years of 2 SE). Caution is advised when using the proposed error for the pooled analyses as a definitive precision. Similarly, trace element filtering approaches were applied to apatite and titanite samples from Mt Stirling, two phases that arguably cannot be inherited. For apatite, monitoring Ca and P as well as Zr/Y and Th/U ratios, along with identifying age groupings based on Sr concentrations, was effective in eliminating outliers and enhancing dating precision. In the case of titanite, monitoring Ca and Ti, Sr/Zr and Sr/Th ratios, and Sr/Ca and Zr/Ti ratios successfully enhanced dating precision. Notably, apatite and titanite grains were grouped in distinct Sr concentrations (high-, mid-, and low-Sr), with these groups corresponding to different date groups: high-Sr apatite and high- and low-Sr titanite returned c. 403 Ma, while low-Sr apatite and mid-Sr titanite returned c. 420 and 393 Ma, respectively. The spuriously younger or older dates may indicate an open system and influences from various common-Pb sources. The 403 Ma date coincides with the filtered zircon data, placing further confidence in the coupled approach, and is interpreted here as the igneous intrusion age. Notable is that this age is 25 Myr older than previously reported K–Ar age data, thus far considered to be the age of the intrusion. This study underscores the potential for erroneous zircon dates due to cryptic chemical influences. To enhance the reliability of age interpretation using laser ablation analyses, employing a petrochronological approach using split-stream combined age and trace element data is recommended in addition to the combination of multiple geochronometers. In the case of Mt Buller, it has proven crucial to carefully verify chemical closure of all applied geochronometers by monitoring concomitant trace element concentrations. Applied to other intrusions, petrochronology can play a critical role in obtaining reliable age information, even for igneous rocks that appear pristine. With this, we emphasise the importance of a careful approach towards individual age data interpretation, which can be produced fast and in abundance with modern analytical approaches.

Postcollisional Molybdenum Porphyry Mineralization in the Middle Tien Shan: First Isotopic U–Pb Zircon Data for Rocks from the Molo-Sarychat Pluton (Eastern Kyrgyzstan)

Postcollisional Molybdenum Porphyry Mineralization in the Middle Tien Shan: First Isotopic U–Pb Zircon Data for Rocks from the Molo-Sarychat Pluton (Eastern Kyrgyzstan)

New paleofloristic and geochronological U–Pb zircon data in late Paleozoic deposits of the Matzitzi formation in southern Mexico

The fossil flora of the Matzitzi Formation, is a fluvial unit of late Paleozoic age exposed in southern Mexico, has been studied since the last century; however, the discovery of new plant elements during the last decade imposes a reevaluation of two aspects that have always been the subject of debate: the depositional age of the unit and the taxonomy of its paleoflora. The objective of the present work is to report new paleofloral records from two areas of the Matzitzi Formation as well as their chronological implications. The study sites are named Carretera and Coatepec. Nineteen genera and 11 species have been identified in beds from the Carretera site, whereas 23 genera and 16 species in beds from the Coatepec site. The analysis of floral assemblages of both sites shows that they share 49% of taxa. Ovopteris, Lesleya, Lobatopteris, and Trigonocarpus are unique to the Carretera site, while Coatepec is characterized by the presence of cf. Bjuvia, Schizoneura, and Velascophyllum. When analyzing the greatest ranges of the paleoflora awareness for the Carretera site indicates that deposition of these beds took place in a time interval that may span between Pennsylvanian and lower Permian. On the other side, the floral assemblage recovered from the Coatepec site indicates that the hosting beds were deposited in upper Permian time. U–Pb detrital zircon geochronology indicates that the maximum depositional age of the fossiliferous beds at the Carretera and Coatepec sites are of 276 ± 15 Ma and 254 ± 11 Ma, respectively. The integration of the paleontological and geochronological data obtained in this work suggests that the analyzed floral assemblage recovered from the Carretera site is of Kungurian age, whereas the one from the Coatepec site is of Lopingian age. Alternatively, we explore the possibility that deposits that are presently grouped within the Matzitzi Formation could be the vestiges of different fluvial cycles associated with different tectonic settings. Finally, the work on this unit has not finished, since there are still localities where its flora and age are still unknown.

Late Paleozoic Potassic Intrusions of the Eastern Part of the Nikolaev Line and Associated W–Mo–Cu–Au Mineralization: First Isotopic U–Pb Zircon Data (LA-ICP-MS Method) for Rocks from the Adyrtor Intrusions (Middle Tien Shan, Eastern Kyrgyzstan)

Late Paleozoic Potassic Intrusions of the Eastern Part of the Nikolaev Line and Associated W–Mo–Cu–Au Mineralization: First Isotopic U–Pb Zircon Data (LA-ICP-MS Method) for Rocks from the Adyrtor Intrusions (Middle Tien Shan, Eastern Kyrgyzstan)

Late Jurassic magmatism in the Ligurian‐Piedmont Ocean constrained by zircon ages of mafic and felsic meta‐intrusives

AbstractPaleogeographic reconstructions show that the Ligurian‐Piedmont Ocean (LPO) was a relatively narrow oceanic basin but the actual amount of oceanic lithosphere generated and the timing of magmatic accretion are still subjects of debate. New U–Pb dating of zircon from two pairs of FeTi‐oxide metagabbro and metaplagiogranite s.l. of the Susa and Lanzo Valleys Ophiolites (Western Alps) yields Late Jurassic magmatic ages (~150 Ma), 10–15 Ma younger than most of the magmatism in the LPO. The potential significance of the geochronological data presented are discussed in relation to the structural architecture of the LPO, emphasizing that the investigated ophiolites represent the youngest oceanic lithosphere accreted in the Western Alps.

Late Neoproterozoic to early Cambrian high-grade metamorphism from Mikir Hills (Assam-Meghalaya gneissic Complex, northeast India): Implications for eastern Gondwana assembly

Mikir Hills region, which represents the eastern segment of the Assam-Meghalaya Gneissic Complex (AMGC) in northeast India, constitutes part of the Eastern Gondwana. The Mikir Hills preserves multiple metamorphic and magmatic events ranging from Early Mesoproterozoic to Early Cambrian. Out of these events, documenting the late Neoproterozoic to early Cambrian tectonothermal events is helpful in correlating the continental blocks of Eastern Gondwana. We present an integrated study involving field relations, petrology, P–T history and zircon-monazite geochronology of hitherto poorly studied pelitic and quartzo-feldspathic gneisses from the Mikir Hills region. These gneisses have experienced at least three deformation events (D1, D2 and D3) with dominant foliation indicated by ENE–WSW striking and shallow-moderately dipping (<40°) S2 gneissic foliation. The peak metamorphism in pelitic and quartzo-feldspathic gneisses is characterized by garnet(core)–K-feldspar–sillimanite–plagioclase–biotite–rutile–quartz–ilmenite–melt and garnet–plagioclase–K-feldspar–biotite–quartz–ilmenite–melt assemblages, respectively. The application of thermobarometric methods constrains the peak P–T conditions of 7.5–8.4 kbar at 674–778 °C and 6.7–7.4 kbar at 601–618 °C for pelitic and quartzo-feldspathic gneisses, respectively. These results are consistent with the values estimated using phase equilibria modelling and melt reintegration approach. The results of pseudosection modelling suggests a clockwiseP–Tpath for pelitic gneisses involving migmatisation during peak metamorphism followed by near isothermal decompression from 8.0 to 8.6 kbar at 768–780 °C to 4.0–5.0 kbar at 720–765 °C. In contrast, quartzo-feldspathic gneisses preserved slightly lower peak P–T conditions at 3.8–4.6 kbar and 590–650 °C. The U–Pb zircon dating of migmatised pelitic and quartzo-feldspathic gneisses yielded concordant ages of1647 ± 11 Ma and 1590 ± 7 Ma, respectively. These dates represent the inherited igneous protolith components, possibly equivalent to the Mesoproterozoic granulite facies metamorphism in the western AMGC. The rarely preserved cores of monazite in pelitic gneisses yielded an older population of1058 ± 35 Ma, most likely representing a weak tectonic imprint associated with the amalgamation of India with Western Australia and East Antarctica in the Rodinia assembly. However, the majority of monazite grains in pelitic and quartzo-feldspathic gneisses show high Th/U ratios with ages between 496 ± 7 Ma and 467 ± 16 Ma, indicating the timing of migmatisation that is contemporary with voluminous ∼ 500 Ma granite magmatism in and around the Mikir Hills. The similarities inP–T–thistoriesestimated in this study (eastern AMGC) and those obtained from the Sonapahar-Umpretha region (central AMGC) confirm that these domains experienced common tectonometamorphic history during Pan-Africanorogeny. The dominance of Late Neoproterozoic migmatisation and magmatism in the Mikir Hills region indicate that the eastern AMGC represent an active convergent margin with Western Australia and East Antarctica and evolved as a hot orogen during the assembly of Western and Eastern Gondwana continental fragments.

Late Paleozoic Stages of Ore Formation in the Middle Tian Shan: Isotopic U–Pb Zircon Dating (LA-ICP-MS Method) of Intrusive Rocks from the Sonkul and Kokturpak Plutons (Eastern Kyrgyzstan)

Late Paleozoic Stages of Ore Formation in the Middle Tian Shan: Isotopic U–Pb Zircon Dating (LA-ICP-MS Method) of Intrusive Rocks from the Sonkul and Kokturpak Plutons (Eastern Kyrgyzstan)

A New Insight into the Genesis of Graphite Deposits in Madagascar Using U–Pb Zircon Dating and Electron Microprobe Analysis

Madagascar is globally recognized as an important producer of high-quality flaky graphite. However, current research on graphite deposits in Madagascar remains insufficient. Previous studies have linked the genesis of Madagascan graphite deposits to the metamorphism of sedimentary organic matter. Here, we provide a case study of graphite deposits in Madagascar, combining new data from the Ambahita graphite deposit (AMG) in southern Madagascar with data from the Antanisoa graphite deposit (ANG) in central Madagascar and the Vohitasara graphite deposit (VOG) on the east coast of Madagascar. We note that the mineral assemblages of graphite-bearing rocks in the AMG, ANG, and VOG are not typical of metamorphic mineral assemblages but rather the results of filling and metasomatism by mantle-derived fluids that occurred after peak metamorphism. Electron microprobe analysis indicates that the graphite of the AMG, VOG, and ANG is usually associated with phlogopite or Mg-biotite; the phlogopite shares a common genesis with other widespread phlogopite deposits across Madagascar. We reveal that the distribution of graphite deposits in Madagascar is primarily controlled by ductile shear zones between blocks. Ductile shear zones that extend deep into the mantle can provide an ideal migration channel and architecture for the emplacement of mantle-derived fluids. The graphite mineralization formed no earlier than the peak metamorphism (490 Ma) and no later than the intrusion of pegmatite veins (389 ± 5 Ma). The distribution of graphite deposits, graphite orebody morphologies, mineral associations, and geochemical data suggest that the genesis of graphite deposits in Madagascar is linked to mantle-derived fluid filling rather than the metamorphism of sediments, as previously suggested. These findings have important implications for similar deposits in Madagascar and potentially globally.

Oligocene–Miocene arc magmatic activities associated with the giant Reko Diq porphyry Cu–Au deposit, western Chagai arc, Balochistan, Pakistan

The Chagai belt to the north of the Afghan block and the east of the Iranian block in the western part of Pakistan is known for occurrence of Oligocene to Miocene calc‐alkaline magmatic belt. The present study discusses the characteristics of episodic magmatic activities that contributed to mineralization for the Reko Diq porphyry complex in the western part of the Chagai belt. U–Pb dating of zircons from volcanic rocks of the Reko Diq porphyry complex yielded ages of 25.8 ± 1.8 and 12.29 ± 0.44 Ma for two phases of magmatic crystallization. Geochemical analyses of whole‐rock rhyolite and dacite indicate that the rock units are peraluminous calc‐alkaline, derived from Andean‐type subduction. The magma was formed due to partial melting of the thickened mafic lower crust in a continental arc setting in relation to the subduction of the Neotethys along the Makran subduction zone. The abundance of zircons, Hf, REE, U/Pb and Th indicates high degrees of magmatic evolution. Moreover, the Sr and Nd isotopic data indicate the fractional contribution of depleted N‐MORB mantle to the Reko Diq magmas through bulk mixing with magmas derived from the lower continental crust. Short‐lived magmatic systems repeated magma injection, and various episodes of hydrothermal fluid flow have led to the formation of porphyry mineralization. Emplacement of the Reko Diq porphyry complex and related Cu–Au mineralization is associated with a series of tectonic–magmatic events at different episodes of the Oligocene–Miocene times.

Geochemical fingerprinting of continental crust trapped in Cadomian volcanic arcs along northern Gondwana

During the Ediacaran to Cambrian periods, the extensive Avalonian–Cadomian accretionary orogen formed along the northern margin of the Gondwana (Pannotia) supercontinent. One of the best-preserved magmatic arcs within this orogenic system is the Davle volcanic complex (DVC) in the Teplá–Barrandian unit of the Bohemian Massif. Using detailed field observations, petrography, major/trace element concentrations, Nd–Hf isotopic compositions as well as U–Pb zircon dating, we interpret a complex evolutionary history of the DVC as comprising three main stages. The first stage (∼610–570 Ma) is represented by a volcano-plutonic association of andesite, dacite, rhyolite and tonalite–trondhjemite–granodiorite (metamorphosed to orthogneiss). A wide range of major/trace element contents together with highly variable εNd values (+3.6 to –5.1) suggest derivation from a juvenile (mantle-derived) source with subsequent assimilation of cratonic crust during magma emplacement, also supported by the modelling of the assimilation–fractional crystallization (AFC) process. The second stage (∼580–560 Ma) is characterized by a gradual termination of the volcanic arc activity, followed by a deposition of marine siliciclastic succession comprising, from the bottom to the top, laminated tuffs, silicified black shales (Lečice Member), and a thick turbidite greywacke–shale–conglomerate sequence (Štěchovice Group). The third stage of poorly constrained age (∼570–500 Ma) is represented by an intra-arc extension and intrusion of juvenile trondhjemite and related rhyolite dykes (εNd +4.8 to +8.4). Finally, we compare these findings with zircon U–Pb ages and whole-rock Nd isotopic data from other Cadomian terranes and propose that the cratonic crust played an important role in recycling along the whole orogenic belt. Thus, we conclude that the Cadomian Orogen formed as a collage of fringing (such as modern Japan, Taiwan, or Philippines) and continental (as modern Andes) arcs of variable evolutionary stages rather than as a belt dominated by intra-oceanic island arcs.

Geochemical and isotopic evidence for early neoproterozoic (ca. 1000 Ma) subduction-related magmatism in the central Borborema Province, Brazil

Early Neoproterozoic (1000-920 Ma) rocks related to the Cariris Velhos event in the central Borborema Province have been linked to either continental rifting or accretionary-collisional orogenesis. The Serra do Jatobá Suite is located in the southwestern part of the Alto Pajeú Terrane along with coeval metasedimentary sequences and Ediacaran granites. This suite is composed of alkali-calcic, meta-to peraluminous granodiorites to monzogranites that share similarities with both ferroan- and magnesian granite series. Chondrite normalized REE (Rare Earth Elements) patterns are moderately fractionated with pronounced negative Eu anomalies. Incompatible element spidergrams show a negative Nb–Ta anomaly, similar to those observed in Cordilleran-type granites. U–Pb zircon data constrain the crystallization ages at around 1000 Ma, whereas calculated εNd(t) values range between −1.74 and −0.94. Obtained TDM model ages range from 1.76 to 1.54 Ga, which corresponds with source ages for the Cariris Velhos magmatic rocks. Our findings suggest that subduction took place in the early Neoproterozoic in the Borborema Province, pointing to an accretionary nature for the Cariris Velhos event.

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

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