Magmatic Features Research Articles

Record of Late Oligocene silicic volcanism in the Hrvatsko Zagorje Basin, Croatia: Insights from U-Pb zircon geochronology and volcanology

The Hrvatsko Zagorje Basin, represents a part of the Slovenian Strait, an Oligocene-Middle Miocene seaway connection between Central Paratethys and Mediterranean. Volcanic deposits within basin are key geochronological markers for understanding the evolution of this important segment of the Paratethyan realm. The timing, eruption styles, magma characteristics, and depositional environments of these events, however, remain poorly understood. In this study, we investigate volcaniclastic sequences from Donje Jesenje and Varaždinske Toplice using sedimentological, mineralogical, petrographical, geochemical, paleontological, and zircon U-Pb geochronological analyses. Zircon dating yielded 24.09±0.13 Ma for Donje Jesenje and 23.35±0.15 Ma for Varaždinske Toplice, corresponding to Late Oligocene. At both sites, the volcaniclastic deposits show evidence indicative of deposition from large explosive eruptions in a submarine environment. Post-depositional alteration processes have led to zeolitization of the glassy components in Donje Jesenje and alteration into clay minerals and silicification in Varaždinske Toplice, under burial diagenesis. Whole-rock geochemistry indicates rhyolitic, subduction-type volcanism, similar to older Periadriatic and younger Carpathian-Pannonian Region magmatism. The temporal and spatial position of Hrvatsko Zagorje Basin magmatism provides a link between these regional magmatic provinces. And allows us to hypothesise their geodynamic link during the Late Oligocene – Early Miocene tectonic reorganization of wider Alpine-Carpathian-Dinaride area.

Potassium alkaline volcanism of Alaid volcano, Kuril Islands: the role of subduction melange in magmogenesis

New data are presented on the contents of major elements and trace elements, Sr-Nd-Pb isotopes in the Holocene high-potassium basic lavas of the Alaid volcano, located in the north of the Kuril island arc in the junction zone with the Kamchatka volcanic segment. According to petrochemical criteria, two groups of coeval rocks are distinguished: Ne-normative shoshonites and high-potassium subalkaline basalts, which are similar to each other in a number of geochemical characteristics. Chondrite-normalized REE distribution spectra show enrichment in LREE, with flat HREE distribution spectra, and the absence of Eu and Ce anomalies. MORB-normalized incoherent element concentrations show LILE enrichment and a well-defined negative Ta-Nb-Ti anomaly typical of suprasubduction volcanics. High K2O/Rb and Rb/Sr ratios indicate the presence of biotite and amphibole in the magmatic source, while low Sr/Y ratios and flat distribution spectra of medium and heavy lanthanides indicate the absence of garnet in the restite paragenesis. Significant variations in the contents of macro- and microcomponents at similar MgO concentrations indicate a heterogeneous magmatic source, and taking into account linear mixing trends in isotope and discrimination diagrams, experimental data, suggest the involvement in magmogenesis of not only the peridotite mantle, but also amphibole-clinopyroxene mineral paragenesis. An analysis of the literature data shows that in «cold» island arcs, manifestations of potassium alkaline magmatism are often, if not in all cases, associated with local extension zones. Since such zones are associated with the adiabatic rise of a hot and plastic asthenosphere, it can be assumed that subduction melange formed along the boundary of the slab and supra-subduction mantle, consisting of hydrated fragments of ultrabasites and metamorphosed oceanic crust transformed into amphibole-bearing pyroxenites, was involved in the melting. This mechanism makes it possible to logically explain the geochemical and isotopic features of the anomalous alkaline magmatism of the Kuril island arc and the connection with the anomalous tectonics of its northern segment. The results obtained may be important in discussing the genesis of potassium alkaline magmas manifested in subduction geodynamic settings.

Petrogenesis and Metallogenic Significance of the Demingding Mo-Cu Porphyry Deposit in the Gangdese Belt, Xizang: Insights from U-Pb and Re-Os Geochronology and Geochemistry

The 1500 km-long Gangdese magmatic belt is a crucial region for copper polymetallic mineralization, offering valuable insights into collisional porphyry copper systems. This study focuses on the Demingding deposit, a newly identified occurrence of molybdenum–copper (Mo-Cu) mineralization within the eastern segment of the belt. While the mineralization age, magmatic characteristics, and tectonic context are still under investigation, we examine the deposit’s petrology, zircon U-Pb geochronology, whole-rock chemistry, and Re-Os isotopic data. The Demingding deposit exhibits a typical alteration zoning, transitioning from an inner potassic zone to an outer propylitic zone, which is significantly overprinted by phyllic alteration closely associated with Mo and Cu mineralization. Zircon U-Pb dating of the ore-forming monzogranite porphyries reveals crystallization ages ranging from 21 to 19 Ma, which is indistinguishable within error from the mean Re-Os age of 21.3 ± 0.4 Ma for Mo veins and veinlets hosted by these porphyries. This alignment suggests a late Miocene magmatic event characterized by Mo-dominated mineralization, coinciding with the continuous thickening of the continental crust during the collision of the Indian and Asian continents. The ore-forming porphyries range in composition from granodiorite to monzogranite and are classified as high-K calc-alkaline with adakite-like features, primarily resulting from the partial melting of subduction-modified thickened mafic lower crust. Notably, the ore-forming porphyries exhibit higher fO2 and H2O levels than barren porphyries in this area during crustal thickening, highlighting the significant contributions of hydrous and oxidized fluids from their source to the Mo-Cu mineralization process. Regional data indicate that the Gangdese porphyry metallogenic belt experienced concentrated Cu-Mo mineralization between 17 and 13 Ma. The formation of Mo-dominated deposits such as Demingding and Tangbula in the eastern segment of the belt, with slightly older ages around 20 Ma, underscores the presence of a significant porphyry Mo metallogenic event during this critical post-collision mineralization period.

Granites of the Chazangcuo Copper–Lead–Zinc Mining Area in Tibet, China: Magma Source and Tectonic Implications

Intermediate-acidic granites occur extensively in the Chazangcuo copper-lead-zinc mining area (hereinafter referred to as the Chazangcuo mining area) in Tibet, China. Exploring their rock types, sources, and tectonic settings is essential for understanding the genesis of granites in the region. This study investigated the petrology of the Chazangcuo granites, as well as the geochemical characteristics of their major elements, trace elements, and rare earth elements (REEs). Results indicate that the Chazangcuo granites are high-K calc-alkaline metaluminous rocks. These granites are enriched in large-ion lithophile elements (LILEs; e.g., Rb and Ba), depleted in high-field-strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), with a relative enrichment in light rare earth elements (LREEs), and relatively depleted in heavy rare earth elements (HREEs), exhibiting a V-shaped distribution pattern and weak negative Eu anomalies. The granites are classified as typical I-type granites, displaying characteristics of crust-derived magmas with contributions from mantle sources and exhibiting significant fractional crystallization. The Chazangcuo granites were derived from the partial melting of mafic rocks, with protoliths formed in a moderate temperature environment. Influenced by the subduction of the Neotethys Ocean, the Chazangcuo granites were formed in an arc caused by the collision between the Indian and Eurasian plates (also referred to as the Indo–Eurasian collision) during the Late Triassic. Under the effect of geological activities such as upwelling of the asthenosphere and fluid intrusion and differentiation, metal mineralization was prompted to be distributed in the granite fissures, forming the Cu-Pb-Zn polymetallic deposits of Chazangcou in Tibet, suggesting that the granites are closely associated with mineralization.

Petrological relationships between plutonic and volcanic rocks in a continental volcanic arc system: Evidence from plutonic xenoliths in the Sierra de Pachuca, Mexico

Relatively abundant plutonic xenoliths found in some lava domes, lava flows, and scoria cone deposits were employed to study the features and processes between the magmatic plumbing systems and volcanic rocks in the Sierra de Pachuca, central-eastern Mexico. We present petrographic, geochemical, isotopic data and five U-Pb ages for some plutonic xenoliths and the Sierra de Pachuca host rocks to provide evidence of magmatic processes existing under this volcanic range. The phaneritic plutonic xenoliths were grouped into six lithological types based on petrography, chemical data, and isotopic ages. Four types (A to D) are hosted by the El Ventoso lava dome. Their compositions span from calc-alkaline gabbro to granite, with U-Pb zircon ages ranging from 23.1 ± 1.4 to 21.6 ± 0.6 Ma. These ages are contemporaneous with the emplacement of rhyolitic ignimbrites found at the base of the Sierra de Pachuca (22.8 ± 0.5 Ma U-Pb zircon age). The trace element patterns for these Late Oligocene-Early Miocene plutonic xenoliths display enrichment of LILE relative to HFSE and enrichment of LREE respecting to HREE typical of subduction-related rocks. Negative P, Ti, and Eu anomalies in these patterns also suggest fractional crystallization processes in magmas that produced the A to D types. Two more types of plutonic xenoliths (E and F) display gabbro and syenite compositions, respectively, and are hosted by the San Miguel-Santa María Regla columnar jointed basalts (gabbro samples) and by the El Prieto scoria cone (syenite samples). Based on one U-Pb zircon age (2.4 ± 0.2 Ma) and geological correlations, these plutonic xenoliths and their host rocks were emplaced in the Quaternary. They exhibit alkaline compositions, and their trace element patterns indicate an enriched mantle source with positive Ba and Pb anomalies, not typical of subduction-related magmas. The isotopic values (87Sr/86Sr = 0.70390 to 0.70502 and εNd = −2.99 to +0.76) for the Late Oligocene-Early Miocene A to D types and host rocks suggest the interaction of magmas with continental crust components. In contrast, the Quaternary xenoliths of E and F types and their host rocks display isotopic data (87Sr/86Sr = 0.70396 to 0.70602 and εNd = +0.13 to +3.66) that evidence of less interaction with continental crust components. In all studied xenoliths, the Pb isotopic ratios (206Pb/204Pb = 18.60–18.87; 207Pb/204Pb = 15.57–15.63 and 208Pb/204Pb = 38.39–38.68) lie on a mixing line between a mantle-like member and a radiogenic component such as the Paleozoic Acatlán complex that probably underlie the Sierra de Pachuca area. Based on the results obtained, it is proposed that the Late Oligocene-Early Miocene A to D type xenoliths represent the plumbing systems from which the volcanic rocks of the Sierra de Pachuca were extruded. On the other hand, the E and F types also represent the roots or magmatic reservoirs from which the Quaternary lava flows and scoria cones, located in the rear-arc part of the active front of the Trans-Mexican Volcanic Belt, were formed. Additionally, these two types of xenoliths and their Quaternary host rocks have hybrid geochemical characteristics of alkaline magmas influenced by crustal components produced during a slab rollback stage.

Late Cenozoic intraplate volcanism as a trigger for hydrothermal venting in the Arctic southwestern Eurasia Basin

Intraplate volcanism has occurred for the last 35 million years within Northeast Atlantic and Arctic margins, including the western Barents Sea, Svalbard, and northern Greenland. Earlier studies have suggested that some of this volcanism might be sourced from nearby mid-ocean ridges. However, legacy data does not reveal correlations between the sporadic volcanism, despite comparable setting, ages, and compositions of basalts across the area. Here, we utilize a compilation of geophysical data to document late Cenozoic intraplate volcanism affecting the northeastern Yermak Plateau and southwestern Eurasia Basin located north of Svalbard. The identified seabed and subsurface features include volcanic (Mound-A) and hydrothermal vent systems (Tayrona Vent) formed approximately 10 and 2.6 million years ago, respectively. These intraplate volcanic products are coincident in age and origin with observed hydrothermal systems on Svalbard and Northeast Atlantic. We propose that these magmatic features are the result of intraplate volcanism associated with seismic and thermal anomalies in the mantle beneath northern Svalbard.

Tectonic reevaluation of West Cameroon domain: Insights from high-resolution gravity models and advanced edge detection methods

The West Cameroon region, characterized by a diverse geomorphology of highlands and plains resulting from tectonic processes across different geological ages, has been extensively explored for natural resources. Recognizing the significance of its tectonic and magmatic features associated with seismic and volcanic activity, this study focuses on geodynamic investigations of the Cameroon Volcanic Line (CVL). Despite previous efforts, detailed structural geophysical studies of the West Cameroon domain have proven inconclusive, prompting a comprehensive structural reinterpretation. Utilizing the high-resolution SGG-UGM-2 satellite gravity model and innovative processing techniques, including the horizontal gradient of a modified tilt (HGSTDR), the balanced horizontal gradient (BHG), the tilt of the horizontal gradient (TAHG), the improvised horizontal gradient tilt angle (impTAHG), and the Tilt Depth method, our research aims to enhance the interpretational quality of tectonic lineaments. By separating regional and residual anomalies in the Bouguer gravity map and applying a combination of filters to delineate geological units, the BHG filter emerges as a robust tool that highlights subsurface edges without generating false features. This approach unveils previously undetected NNW-SSE-oriented lineaments, confirming the presence of deep fractures and faults in Bafoussam, Nkongsamba, and along the Benue Trough, corroborated by newly discovered NNW-SSW trending lineaments. The study suggests that the region’s topography is overcompensated by deep mountain roots and compressive tectonism. Digitizing the BHG filter produces a structural map, revealing predominant NE trends in identified geological margins, including NNE-SSW, N-S, NW-SE, E-W, and NE-SW directions. Geological contacts between granite and high-grade gneiss are indicated by NNW-SSE and NNE-SSW trending lineaments along the Benue Trough. These results contribute significantly to the understanding of the tectonic setting of the West Cameroon Domain.

Origin and Affinities of the Malmberget Iron Oxide-Apatite Deposit, Northern Sweden: Insights From Magnetite Chemistry and Fe-O Isotopes

European iron ore production is primarily sourced from magnetite dominated iron oxide-apatite ore deposits in the northern Norrbotten ore province of northernmost Sweden. The Malmberget iron oxide-apatite deposit is at present the largest iron ore resource in Europe and is an amphibolite facies grade analogue of the world-famous Kiirunavaara iron oxide-apatite deposit. The Malmberget rock association is characterised by multiple phases of deformation, metamorphism, and alteration that resulted in a geometrically and petrologically complex deposit that is genetically ambiguous. Primary ore textures and emplacement structures of the Malmberget iron oxide-apatite deposit have largely been recrystallised during metamorphic overprinting and now comprise dominantly medium- to coarse-grained granoblastic magnetite. However, isotopic characteristics are preserved and when combined with trace element chemistry, these can be used to understand magmatic vs. hydrothermal origin of the deposit. To unravel the primary origin of the Malmberget magnetite ore, we combined magnetite trace element chemistry and Fe-O stable isotopes to investigate the massive magnetite in the Fabian-Kapten and ViRi ore bodies of the Malmberget iron oxide-apatite deposit. Trace element correlations indicate a high-temperature magmatic to a transitional high-temperature magmatic-hydrothermal origin of the Malmberget iron oxide-apatite ore deposit, with data plotting into fields of clear magmatic affinity in trace element discrimination diagrams. Fe-O data fall into established magmatic fields regardless of subsequent metamorphic modifications, underlining a dominantly (ortho-)magmatic origin of the investigated deposits. Despite an overall magmatic to magmatic-hydrothermal origin for the two ore bodies studied, Fe-O isotope equilibrium calculations of the magnetite suggest a possible temperature discrepancy between the Fabian-Kapten ore body and the ViRi ore body, the latter showing a more pronounced magmatic character. These variations in trace element contents and Fe-O isotopes can be explained by the proximity of the more magmatic signatures to the centre of the ore forming magmatic system.

Unraveling the Magmatic-to-Carbothermal Processes in the Ba–Sr–REE Mineralization of the Sevattur Carbonatites, India

AbstractThe Neoproterozoic Sevattur carbonatite complex (India) consists of calcite carbonatite, silicate-poor- and silicate-rich (banded and blue) dolomite carbonatite. The trace element composition of the calcite and ferroan dolomite shows that most of them have magmatic characteristics. The predominance of dolomite carbonatite over calcite carbonatite and the absence of a genetically related silicate suite at Sevattur suggest a dolomitic parental magma derived by the direct melting of the mantle. Regardless of the prevalent magmatic character of the Sevattur carbonatites they host a plethora of Ba–Sr–REE minerals formed throughout the orthomagmatic-to-carbothermal stages under varying activities of ${\mathrm{F}}^{-}$,${\mathrm{CO}}_3^{2-}$, ${\mathrm{PO}}_4^{3-},\kern0.5em$and ${\mathrm{SO}}_4^{2-}$. The orthomagmatic stage begins with the crystallization of calcite carbonatite containing xenocrystic diopside, antecrystic Y-bearing calcite (Cal-I), and primary benstonite, apatite, and richterite in a Sr–Mg-rich calcite (Cal-II) matrix. Fractionation of apatite, carbocernaite, and cordylite-(Ce) together with the enrichment of Mg, Fe, Na, and F in late-magmatic stages, forms the dolomite carbonatite. The decomposition of benstonite to norsethite, Ba–Ca carbonate, and strontianite occurs within dolomite carbonatite at the same stage with minimal wall-rock assimilation. Interaction between the xenocrystal clinopyroxenite and the primary magma during late-magmatic stages has resulted in the formation of aegirine and phlogopite in calcite carbonatite. Similarly, the prolonged assimilation of clinopyroxenite by the evolving magma leads to the formation of magnesio-riebeckite and magnesio-arfvedsonite within the banded- and blue carbonatites. The increasing activities of ${\mathrm{PO}}_4^{3-},{\mathrm{SO}}_4^{2-}$, and H2O during the carbothermal stage, destabilizes precursor carbocernaite and cordylite-(Ce), resulting in an assemblage consisting of synchysite-(Ce), ancylite-(Ce), daqingshanite, hydroxylbastnäsite-(Ce), ferriallanite-(Ce), monazite-(Ce), and baryte in dolomite carbonatite. In the banded carbonatite, the carbothermal stage is characterized by ferri-winchite, tremolite-actinolite, and phlogopite crystallization. Further contamination and differentiation of the carbothermal fluid have resulted in the crystallization of quartz and albite in blue carbonatite. Phlogopitization within the blue carbonatite and clinopyroxenite results from late K enrichment in the carbothermal fluids.

Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent

A rare porphyritic charnockite that is girdled by and mineralogically grades to biotite granite occurs as a part of the Chotanagpur Granite Gneissic Complex (CGGC) in and around Massanjore, Jharkhand, India. Preservation of certain textural features, including (a) euhedral to subhedral grains of orthopyroxene, (b) low dihedral angle subtended by orthopyroxene and plagioclase grains, and (c) relict intergranular and porphyritic textures, are consistent with the view that orthopyroxene in the studied rocks has a magmatic origin. Preserved magmatic features and other petrological attributes of these rocks do not support any significant mass change beyond a few tens of microns during the overprinting high-grade metamorphism. The geochemical variation of the felsic rock suite (porphyritic charnockite and biotite granite) indicates that they are cogenetic and are derived from a ferroan A-type granitoid magma by crystal fractionation. The observed geochemical trend of the studied felsic rock suites has been simulated by phase equilibria modelling in the open system using the system components Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2. The observed mineralogical and geochemical attributes and the results of the modelling study are consistent with a petrogenetic process in which high magma temperature (> 900 °C), low pressure, and low water activity in the parental melt favoured the separation of an orthopyroxene bearing cumulate assemblage (orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + magnetite) in the initial part of the magmatic differentiation. Removal of this anhydrous cumulitic assemblage raised the bulk H2O content in the residual melt. Orthopyroxene became unstable with respect to biotite in the evolved melt that eventually crystallised minerals that formed the biotite granite. An increase in magma fO2 also restricts the orthopyroxene stability in felsic magma. Taken together all the petrological and geochemical attributes, we demonstrate that fractionation of an orthopyroxene-bearing crystal cumulate from the melt is essential to form the charnockites, and that the biotite granite forms from the evolved melt after the fractionation. The charnockite-biotite granite association of the studied area was formed in an extensional tectonic setting, presumably during the breakdown of the Columbia Supercontinent.

Enclaves as mushy magma strain archives: New perspectives on composite magmatic fabrics in plutons

Mineral fabrics within igneous intrusions can archive both tectonic and magmatic processes. However, whether magmatic state fabrics reflect primary magmatic processes or regional tectonic strain is often ambiguous. To investigate when fabrics are formed, one can compare the mineral fabrics to primary magmatic features, such as the interface between solidified magmas in mingling zones. The monzodioritic Fanad pluton shows a NNE-SSW–aligned petrofabric parallel to the strike of a nearby shear zone, with dioritic enclaves aligned parallel and oblique to this petrofabric. We therefore aimed to test if the enclaves’ internal fabrics are passive and align with enclave morphology or result from progressive overprint by regional tectonic strain. Crystallographic preferred orientation and anisotropy of magnetic susceptibility data from all enclaves and the host monzodiorite revealed a NNE-SSW petrofabric parallel to the regional tectonomagmatic fabric. However, anisotropy of anhysteretic remanent magnetization data within petrofabric-oblique enclaves revealed a primary fabric parallel to the enclave long axis. Therefore, we interpret enclave morphologies to reflect earlier magmatic state deformation, with fabrics being realigned to regional tectonic deformation. These two distinct petrofabrics were interpreted in the context of the magmatic processes and the evolving late Caledonian paleostress field, with earlier magma processes distinguished from subsequent tectonic overprinting occurring in the magmatic state. Our new data show that multiple fabrics are preserved within enclaves even though all fabric development occurred within a magmatic state. Our results also show that enclaves can effectively record successive strain events, providing new insight with which to decipher tectonomagmatic processes.

Apatite and pyroxene as records of magmatic–hydrothermal processes and platinum-group mineral (PGM) formation in the Wengeqi mafic–ultramafic intrusion, Inner Mongolia, China: The role of oxidized, H2O-rich magmas

The Devonian Wengeqi mafic–ultramafic intrusion, situated on the northern margin of the North China Craton (NCC) — an Andean-style convergent margin during the Paleozoic — hosts many platinum-group minerals (PGMs), especially within the S-deficient, magnetite-rich clinopyroxenite zones. These PGMs occur in two distinct associations: Pt-rich PGMs (e.g., sperrylite) closely associated with primary magnetite and Pd-rich PGMs (e.g., sudburyite, kotuskite, arsenopalladinite) associated with secondary minerals (e.g., actinolite, pyrite). The mechanisms underlying the formation of PGMs in S-deficient rocks and the spatial decoupling of various PGM types remain elusive. The relationship of PGM formation and characteristics of magmas at convergent margins is also not well understood. In this contribution, we utilized apatite and clinopyroxene textures and chemistry alongside whole-rock SrNd isotopes to characterize i) the nature of the parental magma from which the Wengeqi intrusion crystallized, and ii) the magmatic–hydrothermal processes that operated to generate the Pt- and Pd-rich PGM. Based on the composition of clinopyroxene and clinopyroxene–melt partition coefficients, the parental magma of the Wengeqi intrusion is estimated to have an arc-like affinity on a primitive mantle-normalized trace-element diagram. This, together with the EMI-like SrNd isotope signature, implies that the Wengeqi magma was sourced from metasomatized SCLM beneath the NCC with an EMI-like composition. Three types of apatite (Ap1, Ap2, and Ap3) were identified within the intrusion. Ap1 and Ap2 are magmatic in origin, and appear as isolated grains, whereas Ap3 occurs as stringers or heterogeneous domains within Ap1 and Ap2, and likely resulted from hydrothermal modification of magmatic apatite. Notably, the abundant Ap2 exhibits higher VS contents and Eu/Eu* ratios than the less common Ap1, and contains S predominantly in the form of S6+, suggesting that the Wengeqi magma was relatively oxidized, with fO2 > FMQ + 1.2. Based on the chemistry of magmatic apatite, the Wengeqi magma had ∼5 wt% H2O, which, together with its high fO2, facilitated crystallization of magnetite, causing reduction of the magma by removal of Fe3+. This reduction process promoted PGM nucleation by decreasing PGE solubility in the magma, leading to the association of PGM with magnetite. Additionally, the oxidized, H2O-rich magma likely released oxidizing fluids, selectively mobilizing Pd rather than Pt, separating Pt-rich PGMs from Pd-rich PGMs. The budget of PGE in the parental magma could have been increased by i) metasomatism of the SCLM source (e.g., by carbonatitic fluids), which would have elevated the concentration of PGE in the mantle source, and ii) the high fO2 and H2O levels of the magma, which would have delayed sulfide saturation. Accordingly, mantle metasomatism and high fO2–H2O are deemed favorable for enrichment of PGE in magmas within convergent margins.

Is plate tectonics a post-Archean phenomenon? A petrological perspective

The petrogenesis of contemporary igneous and metamorphic rocks is commonly explained by plate tectonics, but how far back in time does this relationship hold? Here we investigate whether the distinctive petrological features of recent ocean crust, subduction-related magmatism and regional metamorphism can be unambiguously identified in the Archean geological record. From an igneous perspective based on geological relationships and Th–Nb systematics, it is difficult to claim that any Archean ‘ophiolite’ was part of a global plate system rather than deriving from a plume ascending through attenuating lithosphere. Furthermore, the rarity of subduction-related rocks, particularly their plutonic equivalents, which have good preservation potential, is consistent with the concept of local convergence and short-lived subduction. From a metamorphic perspective, the appearance of orogenic eclogites in the Paleoproterozoic, the widespread occurrence of blueschists and ultrahigh-pressure metamorphic rocks since the late Neoproterozoic, and a change from a unimodal to a bimodal distribution of metamorphic T / P during the Proterozoic, are responses to secular cooling and the evolution of global tectonics since the Archean. Our petrological perspective is that plate tectonics analogous to that on Earth today is probably a post-Archean phenomenon.

Rift to Post‐Rift Tectonostratigraphy of the Sverdrup Basin in Relation to Onset of the High Arctic Large Igneous Province (HALIP) in the Early Cretaceous, Arctic Canada

AbstractA summary of the Jurassic‐Cretaceous rift to breakup tectonostratigraphy of the onshore Sverdrup Basin is correlated to the offshore Amerasia Basin in order to reconstruct a tectonic setting for the High Arctic Large Igneous Province (HALIP). The rift climax from the Canadian rifted margin is correlated with hyper‐extension of the continent‐ocean‐transition zone. Hyper‐extension of the continental lithosphere can accommodate plate motions of Arctic Alaska‐Chukotka away from the Canadian Arctic Islands and Lomonosov Ridge between ∼155 Ma and 135–133 Ma. After lithospheric breakup at ∼135–133 Ma, correlation of the post‐rift stage to the seafloor spreading anomalies M10n to M4n that are associated with oceanic crustal domains can accommodate plate motions from 135–133 Ma to 128 Ma. The uncertainties associated with the earliest magmas of HALIP overlap with the uncertainties on the timing of the latest seafloor spreading. The first main pulse of HALIP in the Aptian at 124–120 Ma post‐dates seafloor spreading and so HALIP was emplaced in a tectonic setting that closely resembles the present state of the south and eastern Amerasia Basin. At the paleogeographic center of the HALIP, the Alpha Ridge complex is consistent with the magmatic character and history of similar Cretaceous oceanic plateau in terms of volume and duration.

Origin of the Kunduleng Granite and Its Associated Uranium Anomaly in the Southern Great Xing’an Range, NE China

The Kunduleng granite hosts one of several significant uranium anomalies within the southern Great Xing’an Range, NE China. Whole-rock geochemistry and mineral chemistry data, along with the zircon U-Pb-Hf isotope have been used to constrain the petrogenesis of this granitic intrusion and the origin of the uranium anomaly. Microscopically, quartz, alkali-feldspar, and plagioclase are the essential mineral constituents of the granite, with minor biotite, while monazite, apatite, xenotime, and zircon are accessory minerals. Geochemically, the silica- and alkali-rich granites show a highly fractionated character with “seagull-shaped” REE patterns and significant negative anomalies of Ba and Sr, along with low Zr/Hf and Nb/Ta ratios. The granite has positive zircon εHf(t) values ranging from +12.7 to +14.5 and crustal model ages (TDM2) of 259–376 Ma, indicating a Paleozoic juvenile crustal source. Uraninite and brannerite are the main radioactive minerals responsible for the uranium anomaly within the Kunduleng granite. Uraninite presents well-developed cubic crystals and occurs as tiny inclusions in quartz and K-feldspar with magmatic characteristics (e.g., elevated ThO2, Y2O3, and REE2O3 contents and low CaO, FeO, and SiO2 concentrations). The calculated U-Th-Pb chemical ages (135.4 Ma) are contemporaneous with the U-Pb zircon age (135.4–135.6 Ma) of the granite, indicating a magmatic genesis for uraninite. The granites are highly differentiated, and extreme magmatic fractionation might be the main mechanism for the initial uranium enrichment. Brannerite is relatively less abundant and typically forms crusts on ilmenite and rutile or it cements them, representing the local redistribution and accumulation of uranium.

Contrasting magma chemistry in the Candelaria IOCG district caused by changing tectonic regimes

Iron oxide-copper-gold (IOCG) deposits are a vital source of copper and critical elements for emerging clean technologies. Andean-type IOCG deposits form in continental arcs undergoing extension, and they have a temporal relationship with magmatism although they do not exhibit a close spatial relation with the causative intrusions. The processes required to form IOCG deposits and their potential connections to iron oxide–apatite (IOA)-type mineralization remain poorly constrained, as well as the characteristics of magmatism linked to both deposit types. Here we combine zircon U–Pb geochronology with zircon trace element geochemistry of intrusive rocks associated with the Candelaria deposit, one of the world’s largest IOCG deposits, to unravel distinctive signatures diagnostic of magmatic fertility. Our results reveal a marked transition in the geochemistry of intrusions in the Candelaria district, characterized by changes in the redox state, water content and temperature of magmas over time. The oldest magmatic stage (~ 128–125 Ma), prior to the formation of the Candelaria deposit, was characterized by zircon Eu/Eu* ratios of 0.20–0.42, and redox conditions of ΔFMQ − 0.4 to + 1.0. The earliest magmatic stage related to the formation of Fe-rich mineralization at Candelaria (118–115 Ma) exhibits low zircon Eu/Eu* ratios (0.09–0.18), low oxygen fugacity values (ΔFMQ ~− 1.8 to + 0.2) and relatively high crystallization temperatures. In contrast, the youngest stage at ~ 111–108 Ma shows higher zircon Eu/Eu* (~ 0.37–0.69), higher oxygen fugacity values (ΔFMQ ~ + 0.4 to + 1.3) and a decrease in crystallization temperatures, conditions that are favorable for the transport and precipitation of sulfur and chalcophile elements. We conclude that Candelaria was formed through two distinct ore-forming stages: the first associated with a reduced, high temperature, water-poor magma developed under a low tectonic stress, followed by a more oxidized, water-rich, and low temperature magmatic event related to a compressional regime. The first event led to Fe-rich and S-poor IOA-type mineralization, while the second event with geochemical signatures similar to those of porphyry copper systems, generated the Cu- and S-rich mineralization. This late stage overprinted preexisting IOA mineralization resulting in the formation of the giant Candelaria IOCG deposit.

Possibility of Lunar Crustal Magmatism Producing Strong Crustal Magnetism

AbstractThe Moon generated a long‐lived core dynamo magnetic field, with intensities at least episodically reaching ∼10–100 μT during the period prior to ∼3.56 Ga. While magnetic anomalies observed within impact basins are likely attributable to the presence of impactor‐added metal, other anomalies such as those associated with lunar swirls are not as conclusively linked to exogenic materials. This has led to the hypothesis that some anomalies may be related to magmatic features such as dikes, sills, and laccoliths. However, basalts returned from the Apollo missions are magnetized too weakly to produce the required magnetization intensities (>0.5 A/m). Here, we test the hypothesis that subsolidus reduction of ilmenite within or adjacent to slowly cooled mafic intrusive bodies could locally enhance metallic FeNi contents within the lunar crust. We find that reduction within hypabyssal dikes with high‐Ti or low‐Ti mare basalt compositions can produce sufficient FeNi grains to carry the minimum >0.5 A/m magnetization intensity inferred for swirls, especially if ambient fields are >10 μT or if fine‐grained Fe‐Ni metals in the pseudo‐single domain grain size range are formed. Therefore, there exists a possibility that certain magnetic anomalies exhibiting various shapes such as linear, swarms, and elliptical patterns may be magmatic in origin. Our study highlights that the domain state of the magnetic carriers is an under‐appreciated factor in controlling a rock's magnetization intensity. The results of this study will help guide interpretations of lunar crustal field data acquired by future rovers that will traverse lunar magnetic anomalies.

Amorphous Core Distribution Transformer with Improved Efficiency and Low Loss for Power Sector Application

The amorphous transformer (AMTD) is an energy-efficient transformer that minimizes both airborne pollutants and the amount of energy required to create power. This research investigates the use of amorphous material in transformer construction rather than the usual silicon steel core. It outperforms silicon steel in terms of magmatic characteristics. Because of its high resistivity and low thickness, adopting amorphous as a transformer core instead of a traditional transformer can eliminate 70% of transformer no load losses. When deciding which transform to install and use in the electrical network, the total prices of silicon steel and amorphous steel are considered. The total owed cost (TOC) of any specific transformer is calculated by discounting future transformer losses (losses from both load and no load) to present value and leveling them across the transformer's lifetime. The characteristics of amorphous and conventional electrical cold-rolled grain-oriented(CRGO) materials were evaluated. Amorphous metal is a special type of alloy with an irregular molecular arrangement rather than a well-organized crystalline structure. Amorphous metal can be utilized for the transformer core to increase transformer efficiency. The material's increased magnetic characteristics and physical dimensions lead to much lower hysteresis and eddy current losses. Using amorphous metal cores can minimize transformer core loss by more than60 percent. High power-density transformers are in high demand in many applications where weight and available space are severely constrained, such as power electronics. While electromagnetic device weights and sizes normally decrease at higher frequencies, core loss may increase considerably.

Neoarchean high-Mg basalt and rhyolite bimodal complex in the Yinshan Block, North China Craton: Petrogenesis and tectonic implications

Plate tectonics plays an important role in Earth’s evolution, but it is a difficult and controversial issue to trace the operation of plate tectonics in the Archean. Calc-alkaline magmas are a diagnostic feature of modern subduction-related magmatism and thus identification of Archean subduction-related calc-alkaline magmas is crucial for understanding when Archean plate tectonics operated. Here we present zircon U-Pb, whole-rock geochemical and Sr-Nd isotopic data for a metamorphosed Neoarchean calc-alkaline bimodal volcanic complex from the Yinshan Block, the North China Craton. Zircon U-Pb dating results indicate that these meta-volcanic rocks were erupted in the late Neoarchean (∼2570 Ma). Its mafic unit is characterized by high contents of K2O (0.68–4.20 wt%), MgO (Mg# = 62.0-73.4), Cr (332-904 ppm), Ni (105-269 ppm), and is enriched in light rare earth elements (REEs), but depleted in heavy REEs and Nb, Ta and Ti. These geochemical features are similar to those of high-Mg basalts in the Phanerozoic arc setting. They have positive εNd(t) values (+1.3 to + 2.4), indicating that they were derived from the depleted mantle wedge. The felsic unit has variable K2O content (1.42–4.95 wt%) and K2O/Na2O ratios of 0.23–1.36 with positive εNd(t) values (+0.7 to + 3.1). They show characteristics of modern adakites with high Sr/Y and LaN/YbN ratios, suggesting that they were generated by partial melting of the thickened juvenile mafic lower crust. We conclude that the studied Neeoarchean bimodal meta-volcanic complex was formed during subduction-zone retreating and root delamination in a Neoarchean arc. Our results further indicate that plate tectonics had already operated in the Neoarchean in the Yinshan Block.

Evolution of Silurian to Devonian magmatism associated with the Acadian orogenic cycle in eastern and southern Newfoundland Appalachians: Evidence for a three-stage evolution characterized by episodic hinterland- and foreland-directed migration of granitoid magmatism

Abstract The migration and character of magmatism over time can provide important insights into the tectonic evolution of an orogen. We present evidence for three separate stages of compositionally distinct granitoid magmatism associated with the Acadian orogenic cycle in the eastern and southern Newfoundland Appalachians. The interpretations are based on new zircon U-Pb ages, geochemical data, and Sr-Nd-Hf-O isotopic data for 18 samples from 15 Silurian and Devonian granitoid plutons, combined with previously published data. The three stages outline hinterland- and foreland-directed migration trends and represent subduction (435–420 Ma), syncollision (415–405 Ma), and postcollision (395–370 Ma) settings in the Acadian orogenic cycle. The Silurian plutons (435–420 Ma) of the first stage consist mainly of quartz diorite, tonalite, granodiorite, monzogranite, and syenogranite, with high-K calc-alkaline and enriched Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = −5 to −2; εHf[t] = −3 to −1; δ18O = +6‰ to +8‰). They are interpreted to record the subduction of oceanic lithosphere of the Acadian seaway that separated the leading edge of composite Laurentia, represented by the Gander margin, and Avalonia. Early Devonian plutons (415–405 Ma) of the second stage contain more voluminous monzogranite and syenogranite; they have calc-alkaline to high-K calc-alkaline features, adakite-like compositions, and more depleted Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = −6 to 0; εHf[t] = +1 to +3; δ18O = +5‰ to +6‰). Plutons of this stage occur mostly to the northwest of the Silurian granitoids, indicating a regional-scale northwestward (hinterland-directed) migration of magmatism with a rate of >9 km/m.y. The migration is interpreted to have been related to the progressive shallow underthrusting of Avalonia beneath the Gander margin (composite Laurentia) at least as far as 90 km inboard. The Middle to Late Devonian plutons of the third stage (395–370 Ma) consist mainly of monzogranite, syenogranite, and alkali-feldspar granite, which are silica- and alkali-rich granites with large negative Eu anomalies. These rocks are concentrated along both sides of the Dover–Hermitage Bay fault zone, which represents the boundary between Avalonia and composite Laurentia, to the southeast of the Silurian and Early Devonian igneous rocks. This stage of magmatism represents a foreland-directed (retreating) migration. The Early Devonian and Middle to Late Devonian episodes of magmatism were separated by a gap between 405 Ma and 395 Ma and recorded an evolution from (high-K) calc-alkaline to alkaline compositions, ascribed to partial delamination of Avalonian lithospheric mantle in a postcollisional setting.