Intraplate Magmatism Research Articles

Magnetotelluric image of the Patagonian slab window: Constraints on upper mantle physical properties and sources of intraplate magmatism

The Patagonian slab window (PSW) is a region of the Southamerican subduction zone where the absence of subducted slabs is interpreted, due to the subduction of the Chile Mid-Ocean Ridge at the Chile Triple Junction. Here we report the results of a long-period magnetotelluric (MT) study conducted in two 300 km-long trench-parallel transects crossing the northern boundary of the PSW in the proximal backarc. We modeled the MT data using 3-D inversion, obtaining an electrical resistivity model of the continental crust and upper mantle up to a depth of ∼150 km. Our model shows a heterogeneous resistivity structure in the uppermost mantle, dominated by resistivities >300 Ωm below the array of sites even within the PSW, and some low-resistivity zones (LRZs, <10 Ωm) mainly at the edge of the array. Using petrophysical models, we estimated the mantle temperature, water content, melt fraction, and viscosity based on obtained resistivity values and a preexistent model of P-wave velocity (Vp) at 50 km and 100 km depth. These estimates suggest that the uppermost mantle within the PSW region is heterogeneous and dominated by high-viscosity blocks, compatible with the continental mantle lithosphere or even subducted slabs. Based on relatively hot and low-viscosity zones estimated in the periphery of LRZs, we interpret the presence of asthenospheric mantle in areas where LRZs coincide with relatively low Vp. According to this interpretation, asthenospheric upwelling in the study area at depths ≤150 km would be localized rather than ubiquitous over the interpreted extent for the PSW. Such localized asthenosphere upwelling processes in the past could explain the scattered distribution of Neogene basaltic lavas in the southern Patagonia backarc. The continental crust exhibits LRZs in the upper and lower crust. Remarkably, ensembles of LRZs at different crustal depths within the presumable area of the PSW were found below the General Carrera Lake, and towards the North Patagonian Icefield, likely indicating the presence of hidden intraplate magmatic and/or hydrothermal systems.

Global mantle perturbations following the onset of modern plate tectonics.

Plate tectonics drives the compositional diversity of Earth's convecting mantle through subduction of lithosphere. In this context, the role of evolving global geodynamics and plate (re)organization on the spatial and temporal distribution of compositional heterogeneities in the convecting mantle is poorly understood. Here, using the geochemical compositions of intracontinental basalts formed over the past billion years, we show that intracontinental basalts with subchondritic initial neodymium-144/neodymium-143 values become common only after 300 million years, broadly coeval with the global appearance of kimberlites with geochemically enriched isotopic signatures. These step changes in the sources of intraplate magmatism stem from a rapid increase in the supply of deeply subducted lithosphere during the protracted formation of Pangea following the widespread onset of "modern" (cold and deep) subduction in the late Neoproterozoic. We argue that the delay (~300 million years) in the appearance of enriched intraplate magmas reflects the time required for the sinking and (re)incorporation of slabs into the sources of mantle-derived magmas.

Upper mantle scale enrichment of Cenozoic intraplate magmatism in Northeast Asia: He-Sr-Nd-Pb-O isotope geochemistry of the basalts around the Korean peninsula

The Earth’s mantle is considered to be geochemically heterogeneous, which is reflected by the diverse composition of oceanic island basalts (OIB). The mantle enrichment resulting in this is attributed primarily to the influx of recycled crustal materials into the mantle through subduction. Additionally, the sub-continental lithospheric mantle (SCLM) complicates the elucidation of mantle heterogeneity. From this perspective, Northeast Asia, where the Pacific stagnant slab in the mantle transition zone and the SCLM distribution are presented, is the suitable site for examining the upper mantle scale enrichment. Here we report He-Sr-Nd-Pb-O isotope values of basalts that erupted around the Korean Peninsula to illustrate the source lithology and components that led to mantle heterogeneity. Our measured helium isotope ratios ranging from 5.7 to 7.3 Ra (3He/4He ratio of air, Ra = 1.39 x 10-6) are mostly within the SCLM range (6.1 ± 0.9 Ra) but lower than the mid-ocean ridge basalt range (MORB; 8 ± 1 Ra). The Sr-Nd-Pb isotope compositions of the basalts generally display a mixture of depleted MORB mantle (DMM), enriched mantle 1 (EM1), and enriched mantle 2 (EM2) components. In addition, the basalts have δ18Oolivine (vs. V-SMOW) values ranging from 4.7 to 5.7 ‰ that deviate from the DMM range (δ18Oolivine = 5.1 ± 0.2 ‰). Our isotopic analysis results highlight the role of the pyroxenite source in the metasomatized SCLM in the genesis of basalts. The low 3He/4He range of the basalts indicates a significant role in the SCLM. Moreover, the delaminated cratonic SCLM and asthenosphere-lithosphere interaction are candidate scenarios for the low 3He/4He ratios. Therefore, we propose that mixing of DMM (high 3He/4He ratio; 7 to 9 Ra) and the metasomatized SCLM (low 3He/4He ratio; 5 to 7 Ra) allowed enrichment within the upper mantle scale for the Cenozoic intraplate magmatism in Northeast Asia.

A subduction-dismembered Neoproterozoic large igneous province in the Qinling Orogenic Belt, China: Implications for 850 Ma–initiated mantle plume activity in the greater Yangtze Block

Large igneous provinces (LIP) provide invaluable clues for recognizing the growth, breakup, and cycles of supercontinents and constraining the activity of ancient mantle plumes (or superplumes). The widespread intraplate magmatism is considered as a possible fingerprint of ancient plume activities and LIPs. Here, we present the results of an integrated study on protoliths of eclogites and amphibolite-facies bimodal volcanic rocks from North Qinling Ultrahigh-pressure Metamorphic (UHPM) Terrane, Qinling Orogen, and identify a dismembered Neoproterozoic LIP. These rocks share similar protolith ages of ca. 850–800 Ma and experienced high- to ultrahigh-pressure metamorphism at ca. 500–480 Ma. The mafic rocks are mainly tholeiitic and display enrichment of LILEs and HFSEs, similar to the E-MORB/OIB characters. They also have typical features of continental flood basalts (CFBs) with low CaO/Al2O3 (0.68–0.87), Lu/Yb (0.14–0.15), Zr/Nb (8–13), high Nb/La (0.87–1.24, mean 1.07), La/Nb (0.80–1.15), La/Ta (11–20), Nb/Yb (3.0–6.2) ratios, and positive εNd(t) (+4.3 to + 5.4). Their occurrence, geochemical features, age data, and high mantle potential temperature (1500–1550 °C) suggest that they are remnants of Neoproterozoic CFBs with mantle plume origin. Based on the lateral distribution length (ca. 300 km) of meta-basaltic rocks and the maximum subduction depths (ca. 100–200 km) recorded by UHP eclogites, the identified ca. 850 Ma-initiated CFBs in the North Qinling terrane should represent an LIP, covering more than 100,000 km2. This Neoproterozoic LIP, together with the coeval volcanic sequences in the South Qinling terrane and the northern Yangtze, would have occupied a maximum landmass of 300,000 km2, which lends support for the onset of a mantle plume at ca. 850 Ma within the Rodinia supercontinent. We conclude that the Qinling Block is one of the fragments of the Rodinia supercontinent with a passive margin covered by CFBs, which was subducted to mantle depths in the Early Paleozoic.

Garnet Pyroxenite Cumulates from Cretaceous Alkaline Intraplate Magmas Underplate the Zealandia Mantle Lithosphere

Abstract The elemental and isotopic properties of garnet pyroxenites can yield information on lithospheric mantle composition, thermal state, and evolution. The 34Ma Kakanui Mineral Breccia in New Zealand contains spectacular but little-studied mantle peridotite and pyroxenite xenoliths that yield new insights into the evolution of a portion of the underlying mantle lithosphere of a former Gondwana margin. The moderately depleted and metasomatized spinel peridotites, as judged from spinel and olivine compositions and bulk rock major and platinum group element abundances, give mineral equilibration temperatures &amp;lt;1020°C and are derived from the middle to shallow (~35 to 50 km) lithospheric mantle when projected onto a 70 mW∙m−2 geotherm. These residues have low Re/Os and Re-depletion 187Os/188Os model ages that range from Eocene (0.05 Ga) to Paleoproterozoic (1.9 Ga), consistent with extraction from a lithospheric mantle comprising fragments with complex depletion histories. Although the peridotites have restricted δ18O (olivine +5.2 to 6.2), evidence for an isotopically heterogeneous mantle column in addition to the 187Os/188Os is seen in clinopyroxene 87Sr/86Sr (0.70244 to 0.70292), εNd (+4.1 to 18.8), 206Pb/204Pb (17.8 to 20.3), and εHf (+10 to +101). Higher metamorphic equilibrium temperatures of the garnet pyroxenites (Fe–Mg exchange of &amp;gt;1150°C) compared to the peridotites indicate their Eocene extraction was from towards the base of this isotopically heterogeneous mantle lithosphere. Pyroxenite bulk compositions point to cumulate origins, and the mineral isotope ratios of 87Sr/86Sr (0.70282 to 0.70294), εNd (+5.5 to 8.0) and 206Pb/204Pb (18.1 to 19.3) match many of the Zealandia metasomatized mantle peridotite xenoliths as well as the primitive intraplate basalts but not the garnet pyroxenite host magmas. In contrast to many global pyroxenite studies, the garnet pyroxenite 87Sr/86Sr and δ18O (+5.2 to 5.8) data provide no evidence for subducted crustal material in the primary magma source region, and Sm–Nd and Lu–Hf isotope data yield mid-Cenozoic ages that are probably related to isotope closure during eruption. An exception is one sample that yields a Lu–Hf isochron age of 111.9 ± 9.1 Ma, which corresponds to the convergence of the Lu–Hf isotope evolution curves of three other samples. Liquids calculated to have been in equilibrium with these cumulates have trace element compositions comparable to primitive alkaline intraplate basalts like those found at the surface of Zealandia. The new data, therefore, indicate that a pulse of intraplate magmatism occurred during or directly after the cessation of long-lived subduction on the former Zealandia Early Cretaceous forearc Gondwana margin, despite any volcanic surface exposure having been long eroded away. The lower lithospheric mantle emplacement of the garnet pyroxenites suggests that the source of the alkaline parent magmas was probably the convecting mantle, which supports conclusions that intraplate magmas in Zealandia have asthenospheric and lithospheric mantle sources.

First identification of late Mesozoic intraplate magmatism in the Chinese north Tianshan: implications for the orogenic architecture and crustal evolution

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical and Sr–Nd–Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced at c . 145–132 Ma. They have positive ε Nd ( t ) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk-rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are probably inherited from Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were probably triggered by thermal relaxation owing to crustal shortening and thickening. These data further imply that the Tianshan changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Supplementary material: LA-ICP-MS zircon U–Pb dating results, whole-rock major and trace element compositions, whole-rock Sr–Nd isotopic data and zircon Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.7167890 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Evidence for long-lived (>100 Myr) continental intraplate volcanism: Mongolia since the last ocean closure

Since the closure of the Mongol-Okhotsk Ocean in the Mesozoic, Mongolia has been in an intraplate tectonic setting; the nearest plate boundary being ∼3,000 km to the east, at the active Pacific subduction front. Throughout this time, Mongolia has experienced magmatism in the form of distinctive, small-volume volcanic fields dispersed along the central and eastern parts of the country. On the basis of geochemical, isotopic, palaeomagnetic and zircon data, the magmatism can be discriminated from preceding post-collisional magmatism. Gradual change from a lithospheric to an asthenospheric mantle source suggests lithospheric delamination occurred beneath Mongolia, starting at ∼140 Ma and terminating at ∼107 Ma. Accordingly, the onset of intraplate magmatism is set at 107 Ma. Regardless of the spatial and temporal occurrence and evolution of the intraplate magmatism in Mongolia, the geochemistry of the resultant volcanic rocks throughout time remains remarkably similar, although the cause of magmatism has been much debated.Through evaluation of available K-Ar and Ar-Ar data from the literature, along with newly-obtained data from three different volcanic fields, we have identified that the intraplate volcanism in Mongolia has been near-continuous since its onset, with hiatuses of only <6 Myr. Since 35 Ma, hiatuses have reduced to <1 My. In light of these findings, we re-evaluate the various models that have been proposed for the origins of this long-lived volcanism and suggest the cause of magmatism results from asthenospheric upwellings initiated by a delamination event in the Mesozoic, but have been prolonged by enhanced mantle flow relating to northward progression of India, the closure of Neo-Tethys, and ultimately the Indo-Asian collision. This example of intraplate magmatism is one of the longest-lived volcanic intraplate regimes on Earth that does not appear to relate to a geophysically-recognisable high heat-flux mantle plume.

Recycled lower oceanic crust signal in early Jurassic A1-type granites, South China: Implications for flat-slab subduction and mantle heterogeneity in the continental back-arc region

Flat-slab subduction is a distinctive phenomenon that leads to the development of a wide orogenic zone (≥ 800 km) along former continental margins, triggering extensive intraplate magmatism and deformation. However, occurrences of flat-slab subduction on ancient convergent margins are exceptionally rare, possibly owing to multiple episodes of structural destruction and/or poor preservation. Furthermore, the impact of flat-slab subduction on mantle heterogeneity remains ambiguous. In this study, we present comprehensive whole-rock geochemical analyses as well as in-situ zircon UPb dating and HfO isotopic data for Early Jurassic A-type granites from the Pitou and Shibixia plutons in the interior of the South China Block to investigate the potential influence of flat-slab subduction on intraplate magmatism. The Pitou granites exhibit characteristics consistent with those of A2-type granite, displaying zircon εHf(t) values ranging from −4.9 to +0.3 and elevated δ18O values of 6.2–7.6‰. These features suggest that the granites formed through the differentiation of a basaltic parental magma, which underwent varying degrees of crustal contamination. In contrast, the Shibixia granites show A1-type geochemical features and were derived from basaltic parental magma without significant crustal contamination. The zircons in these granites exhibit positive εHf(t) values ranging from +6.6 to +10.6 and anomalously low δ18O values of 3.3–4.0‰, suggesting the involvement of recycled altered lower oceanic crust components in their mantle source. This provides strong evidence for the occurrence of flat-slab subduction beneath the interior of the South China Block during the early Mesozoic, which was located at least 800 km away from the trench. Combined with the presence of post-delamination ocean island-like intraplate magmatic rocks in the South China interior, it is suggested that the flat-slab delamination at approximately 190 Ma facilitated late Mesozoic intraplate OIB-like magmatism. This process, associated with flat-slab subduction, is expected to exert a significant impact on mantle isotopic heterogeneity within continental back-arc regions.

Hydrous veined mantle lithosphere and implications for the source of Zealandia intraplate magmas

Although amphibole has long been predicted to be a major component in the mantle source of intraplate volcanic rocks in New Zealand, the physical evidence for this phase, despite inspection of hundreds of peridotite mantle xenoliths from across the country, is limited to a handful of samples in which it is mostly a sparse component. Here, we present a suite of ultra-refractory peridotite xenoliths in an ultramafic lamprophyre from the intraplate Alpine Dike Swarm, New Zealand, that contain abundant MARID-like veins of mica (phlogopite), amphibole (pargasite) and clinopyroxene, with minor to trace rutile, ilmenite, carbonate and apatite. A key feature of inspecting these formerly refractory peridotites (olivine Mg# commonly >92) is that the chemistry of the precipitated metasomatic agent is less diluted than in cases where an invading melt reacts with fertile lithosphere. The bulk compositions of the precipitated veins vary between sub-alkaline basalt and alkaline basanite, with the peridotite wallrock hosting the basanite veins commonly enriched in Fe ± K, Ti and Al. Amphibole in all veins has high Nb, and the 24 Ma age-corrected 87Sr/86Sr values for diopside and amphibole (0.7027 to 0.7031) are indicative of derivation from a depleted mantle free of crustal material, and thus not related to subduction and arc magmatism. The Sr isotope ratios also overlap with the composition of many primitive intraplate magmas across Zealandia. Melt modelling indicates that partial melting of the veins could generate magmas with geochemical aspects of the known intraplate rocks. These rare veined peridotite occurrences therefore confirm that the Zealandia mantle lithosphere contains fusible zones that, if melted, could have played an important role in the source of intraplate basaltic magma.

Continental Residual Topography Extracted From Global Analysis of Crustal Structure

AbstractContinental topography is dominantly controlled by a combination of crustal thickness and density variations. Nevertheless, it is clear that some additional topographic component is supported by the buoyancy structure of the underlying lithospheric and convecting mantle. Isolating these secondary sources is not straightforward, but provides valuable information about mantle dynamics. Here, we estimate and correct for the component of topographic elevation that is crustally supported to obtain residual topographic anomalies for the major continents, excluding Antarctica. Crustal thickness variations are identified by assembling a global inventory of 26,725 continental crustal thickness estimates from local seismological data sets (e.g., wide‐angle/refraction surveys, calibrated reflection profiles, receiver functions). In order to convert crustal seismic velocity into density, we develop a parametrization that is based upon a database of 1,136 laboratory measurements of seismic velocity as a function of density and pressure. In this way, 4,120 new measurements of continental residual topography are obtained. Observed residual topography mostly varies between ±1 and 2 km on wavelengths of 1,000–5,000 km. Our results are generally consistent with the pattern of residual depth anomalies observed throughout the oceanic realm, with long‐wavelength free‐air gravity anomalies, and with the distribution of upper mantle seismic velocity anomalies. They are also corroborated by spot measurements of emergent marine strata and by the global distribution of intraplate magmatism that is younger than 10 Ma. We infer that a significant component of residual topography is generated and maintained by a combination of lithospheric thickness variation and sub‐plate mantle convection. Lithospheric composition could play an important secondary role, especially within cratonic regions.

Recognizing big mantle wedges in deep time: Constraints from the Western Mongolia Collage in Central Asia

Abstract A big mantle wedge (BMW) is defined as the broad region of upper mantle above a stagnant slab in the mantle transition zone (MTZ). It is a common and significant structure within Earth's interior at modern convergent plate margins as revealed by seismic data yet rarely identified in fossil convergent systems. We propose the existence of a BMW beneath the Western Mongolia Collage during the early to middle Paleozoic based on a comprehensive chronology of geological events that characterized the accretionary orogen in this region. The trench-arc system initially developed above a NE-dipping subduction zone, with subduction-related arc magmatism clustered at ca. 530–490 Ma and accumulations of flysch-like sequences from the Cambrian to early Silurian constituting the accretionary wedge of the Altai Zone. The westward migration of the arc was likely driven by slab rollback and trench retreat, leading to gradual formation of a BMW as the slab stagnated at the MTZ. The BMW influenced the tectonic evolution of the entire Western Mongolia Collage, inducing Ordovician–Silurian intraplate magmatism in regions inboard of the migrating magmatic arc and the potential opening of the Mongol-Okhotsk Ocean. Westward movement of the trench-arc continued until the Devonian, resulting in back-arc basin formation in the Chinese Altai and intraplate magmatism in the Hovd and Lake Zones of the Western Mongolia Collage, forming a trench–arc–back-arc and intraplate tectonic system. Mantle flow within the BMW is inferred to have impacted magmatism, basin migration, and the stress and thermal state of the overriding plate.

Ba-Mg isotopic evidence from an OIB-type diabase for a big mantle wedge beneath East Asia in the Early Cretaceous

Beneath Eastern Asia, the world's spatially most extensive, and possibly extremely long-lived big mantle wedge (BMW) occurs, formed by the Izanagi-Pacific slab residing in the mantle transition zone (MTZ). It provides a fascinating model accounting for the intraplate magmatism and earthquake >1800 km distal from the trench which are incompletely considered by classic plate tectonics. Since when the BMW exists is crucial for global and regional geodynamic reconstructions and modeling of material transfer. However, temporal constraints from the geophysical, geodynamic model, tectonic, and magmatic studies yield conflicting results. To contribute to this endeavor, we have characterized BaMg isotopic features of the ∼123 Ma-old, OIB-type Daixi diabase in Eastern China, which is located ∼300 km west of the inferred Izanagi subduction zone. Results show that the diabase has δ138/134Ba (−0.08‰ to 0.04‰) slightly lower than the terrestrial mantle (∼0.03 to 0.05‰). The δ138/134Ba values are negatively correlated with (87Sr/86Sr)i, K/Ti, K/La, and K/Na of the diabase, pointing to the incorporation of subducted sediments into the mantle source. In addition, the diabase also has lower δ26Mg (−0.67‰ to −0.35‰) than the terrestrial mantle (−0.25 ± 0.04‰) and low (87Sr/86Sr)i (0.704254–0.706300), reflecting source contributions of marine Mg‑carbonates. Thus, BaMg isotopes record the source contribution of carbonate-bearing sediments which must have melted in the MTZ (20–22 GPa) according to experimental investigations. High K/U (∼30,500) and Hf/Hf* (∼1.68) ratios of the melts derived from the enriched source moreover require partial melting in the presence of peritectic liebermannite and majorite. These two peritectic phases are formed in the MTZ (410–660 km) after early incipient melting of carbonate-bearing sediments during which the loss of Na-rich, Ca‑carbonate melts has resulted in the removal of Th, U, and some LREE and retention of K, Ba, Zr, and Hf. These findings provide robust evidence that the Daixi diabase originated from an enriched mantle source metasomatized by melts/fluids derived from the stagnant slab at the MTZ. They also place important constraints on the existence of the Izanagi BMW beneath eastern Asia in the Early Cretaceous (∼123 Ma). It reconciles magmatic with previous tectonic and metallogenetic models that showed lithospheric thinning (peak at ∼125 Ma) and gold mineralization flare-up (peak at ∼120 Ma) at the Eastern China continental margin. Thus, our study is important to understand not only the materials cycling and geodynamic processes within a BMW system but also the tectonic-magmatic effects and interactions between the subducted slab and the overlying continental plate.

Contemporaneous alkaline and subalkaline intraplate magmatism in the Dunedin Volcanic Group, NZ, caused by mantle heterogeneity

ABSTRACT Monogenetic volcanism in the Maniototo Basin in the Dunedin Volcanic Group was unusual because the eroded lavas, plugs and dikes comprise spatially and temporally restricted silica-saturated and silica-undersaturated magmas. 40Ar/39Ar dating coupled with existing data and field relationships indicate that volcanism was focused at ∼11 Ma. Major and trace element data show the volcanic rocks to have mafic compositions and little evidence for fractionation and/or crustal contamination, but to have been variably altered. The volcanic rocks comprise an alkaline group and an alkaline to subalkaline transitional group, with one intermediate unit. With the exception of one flow, the transitional group has more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd, 206Pb/204Pb and 208Pb/204Pb than the alkaline group, as well as smaller Ti and K primitive mantle-normalised anomalies. Overall, the different magma compositions cannot be related to varying degrees of melting of equivalent mantle sources. Trace element ratios indicate that residual Ti and K-bearing mantle phases (amphibole, phlogopite) probably played a major role in the source of alkaline group but a smaller role in the transitional group. Therefore, the varying compositions of the Maniototo volcanic rocks relates to melting of a heterogeneous lithospheric mantle, or/and varying degrees of interaction with mantle hydrous metasomes as the magmas ascended.

Zircon U–Pb ages and O–Hf isotopes of Quaternary trachytes from the East Sea: Implications for the genesis of low-δ18O magmas

Quaternary intraplate magmatism formed several volcanic islands and seamounts, including Dokdo (DD), Ulleungdo (UD), Simheungtack (ST), Anyongbok, and Isabu in the southwest of the East Sea back-arc basin. In this study, we present whole-rock geochemical, zircon U–Pb age, and in situ O–Hf isotope data for the submerged volcanic rocks from DD, UD, and ST to provide new insights into the eruption timing of these volcanoes and constrain the magma evolution processes. All samples used in this study were trachytes and exhibited ferroan, alkalic, and metaluminous to weakly peraluminous characteristics. They showed light rare earth element (REE)-enriched patterns with (La/Yb)N ratios of 25.3–31.7 and mostly negative Eu anomalies in a chondrite-normalized REE plot. In addition, they were enriched in large-ion lithophile elements and high field strength elements; they exhibited positive Pb anomalies and strongly negative Ba, Sr, P, and Ti anomalies. The zircons yielded a weighted-mean 206Pb/238U age of 2.61, 0.348–0.704, and 2.76–2.94 Ma for the DD, UD, and ST trachytes, respectively. All zircons exhibited lower δ18O values than normal depleted mantle values, regardless of the crystallization age and spatial distribution of volcanoes. The δ18O values showed no correlation with U contents or Th/U ratios, indicating that the low δ18O signatures were of primary magmatic origin. The Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive εHf values. Binary O–Hf mixing modeling revealed that low-δ18O rocks with positive εHf values from the UD and ST volcanoes were derived from a hybrid source of recycled juvenile crustal materials with low-δ18O and positive εHf signatures and an enriched mantle source with normal δ18O and negative εHf values. The juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to melting. In contrast, the felsic magma that formed the DD volcanoes may have assimilated with regional basement rocks (Triassic–Jurassic granitoids), resulting in increased δ18O values and decreased εHf values relative to those of the UD and ST volcanoes. Our study highlights the significant contribution of recycled oceanic crust materials to the generation of the Quaternary magmas.

Magmatic Native Gold: Composition, Texture, Genesis, and Evolution in the Earth’s Crust

Abstract —Here we report results of microforms’ studies of native gold and its alloys in igneous rocks, modified to varying degrees by secondary processes. We discuss the composition and occurrence of both the deep-seated magmatic gold-bearing alloys and the products of their transformation under conditions of the upper Earth’s crust. Gold-bearing Kamchatka adakites and ankaramites, Ildeus massif mafic-ultramafic intrusions and adakites from the Stanovoy fold system as well as dacites from the Bolivian Andes were formed during melting of either the suprasubduction mantle wedge or the subducted oceanic crust. In depleted peridotites from the Avachinsky Volcano in Kamchatka as well as suprasubduction ophiolites from Polar Urals, Eastern Sayan and the Western Mediterranean Betic–Rifean belt, the gold-bearing mantle was hybridized by subduction-related melts and high-temperature fluids. Volcanic rocks associated with the Lesser Khingan Fe–Mn deposits and Zolotaya Gora Au deposit in Southern Urals as well as Taragai ultramafic rocks in the South Khingan Range display subduction-related geochemical characteristics. Gold-bearing trachytes in the Virginian Appalachians (USA) represent felsic differentiates of mafic intraplate magmas. We propose that one of the principal forms of gold transport into the upper crustal environments is represented by Cu–Ag–Au alloys, which precipitated from mantle-derived silicate melt enriched in chalcophile and siderophile elements. Such Cu–Ag–Au alloy-rich magmatic rocks can either constitute primary sources of precious metals in the mantle-crust system or serve as geochemical precursors to the formation of native gold assemblages in epithermal and mesothermal ore deposits. Presence of magmatic gold particles in subduction-related igneous rocks and mantle restites hybridized by subduction-derived melts and high-temperature fluids suggest the existence of gold-rich horizons in the Earth’s mantle at depths comparable to typical depths of generation of primary convergent zone and some within-plate magmas.

Correction to: Volatiles and Intraplate Magmatism: a Variable Role for Carbonated and Altered Oceanic Lithosphere in Ocean Island Basalt Formation

Correction to: Volatiles and Intraplate Magmatism: a Variable Role for Carbonated and Altered Oceanic Lithosphere in Ocean Island Basalt Formation

Evolved Late Mesozoic continental arc: Constraints of detrital zircons from the western East China Sea

ABSTRACT The Late Mesozoic subduction of Izanagi slab beneath East Asia formed large-scale intraplate magmatism in SE South China and subduction mélanges outcropped in SW Japan to eastern Taiwan Island, but the accompanying arc remains uncertain. We conducted LA-ICP-MS U–Pb zircon dating and trace element analyses of proximal sandstones from the SW East China Sea to trace a Jurassic to Cretaceous magmatic arc. Newly acquired data reveal that arc magmatism mostly developed in episodes of 150–124 and 124–102 Ma, exhibiting characteristics of low-T, high Th/U, U/Yb, Sc/Yb, Th/Nb, and low Nb/Yb, Nb/Hf ratios. This magmatic arc, combined with the SE South China intraplate and residual subduction mélanges, spatially forms a Late Mesozoic trench–arc–intraplate architecture responding to the Izanagi subduction. Its identified tectonic scenarios mainly include slab strike-slip subduction (200–170 Ma), slab stagnation and intraplate foundering (170–150 Ma), slab rollback and arc-root removal (150–102 Ma), and arc migration (102–86 Ma). Both the western East China Sea and Cathaysia block share a unified Paleoproterozoic basement that formed at ca. 1.85 Ga, and the Cathaysia-based magmatic arc occurred then.

Age and origin of a Guadalupian tuff in the E'Xi rift basin in South China: Evidence for the Emeishan continental hotspot track?

AbstractUnlike oceanic hotspot tracks, continental hotspot tracks are difficult to recognise, although they can provide unique insights into crustal deformation and intraplate magmatism. Here, we present whole‐rock geochemical and Sr–Nd isotope, and zircon U–Pb age and Hf isotope data for a tuff from the E'Xi rift basin in the South China Block. The zircons yielded a 206Pb/238U age of 267.0 ± 2.0 Ma, which coincides with the Roadian–Wordian boundary. The whole‐rock geochemical and Sr–Nd isotope data for the tuff indicate it had a mixed mantle–crust source. The zircon trace element and εHf(t) (−6.32 to +7.06) data are also consistent with such a source. Based on the sedimentological and tectonic history, and the geochronology and geochemistry of the tuff, we propose the tuff erupted in a rift and records the hidden hotspot track of the Emeishan mantle plume beneath the northern SCB.

Early Paleozoic mafic intraplate magmatism in the Binaloud zone, NE Iran: Implications for the long-lived mantle plume activity in the northern margin of Gondwana

Early Paleozoic mafic intraplate magmatism in the Binaloud zone, NE Iran: Implications for the long-lived mantle plume activity in the northern margin of Gondwana

Paleozoic Tensional Intraplate Magmatism and Mantle Evolution in Central Iran Zone: Geochemistry, Nd-Sr Isotope Data of Lamprophyres

Paleozoic Tensional Intraplate Magmatism and Mantle Evolution in Central Iran Zone: Geochemistry, Nd-Sr Isotope Data of Lamprophyres