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Zircons are the oldest remaining witnesses of Earth's near-surface processes, and conditions in the Hadean and Archaean crust are derived predominantly from their trace element and isotopic compositions. However, quantitative assessment of element and isotope partitioning between zircon and melt remains incomplete. We experimentally determined the effect of phosphorus (P) abundance on zircon-melt partition coefficients of Al (DAl), Li (DLi), and P (DP). Results indicate that P content has opposite effects on DAl and DLi, whereas the partitioning of P itself and other trace elements is independent of P abundance. Parametrization of our results yields new assessments of the aluminum saturation index (ASI) and P and Li contents of Hadean magmas. Magma ASI values are ~0.5 lower than previously thought and consistently remain below 1 during the first ~1 Ga of Earth evolution, suggesting involvement of only igneous protoliths. First peraluminous (ASI > 1) melts do not appear until ca. 3.6 Ga, supporting the hypothesis that a transition from a tectonic style dominated by vertical motion to horizontal tectonics accompanied by partial melting of sediments did not occur before that time. New calculated magma Li concentrations for young zircons are in much better agreement with the continental crust Li abundance. Average calculated Archaean and Hadean magma Li concentrations are unrealistically large (>1000 ppm), suggesting that Li in zircons formed before 2 Ga is not primary. Calculated magma P abundances are uniform (~1900 ± 400 ppm) throughout Earth history, suggesting sufficient crustal P was available throughout the Hadean to support the origin of life. [ABSTRACT FROM AUTHOR]

Although subduction is a continuous process, arc system behavior is non-steady-state, leading to uncertainty surrounding the composite spatial and temporal evolution of transcrustal arc magma plumbing systems. This study integrates field, geochronologic, and geochemical data sets from the central Sierra Nevada arc section to investigate the extent to which spatial inheritance is recorded in arc geochemical compositions, and how these signals may be modified by dynamic arc behaviors through time, from arc-wide flare-ups, migration, and crustal thickening to regional magma focusing. Geochemical patterns across Mesozoic arc rocks characterize persistent spatial signals of inheritance, whereas geochemical trends during Cretaceous arc activity provide the temporal component of simultaneous dynamic processes. Distinct bulk-rock isotopic signals define each of the three Mesozoic magmatic flare-ups, which, during Cretaceous arc magmatism, is coupled with eastward arc migration. Additionally, Cretaceous magmatic and tectonic thickening doubled the thickness of arc crust, and magmatism was focused toward a central zone, culminating in the formation of the ∼1100 km² Tuolumne Intrusive Complex. During magma focusing, temporal signals of magma mixing outweighed the previously pervasive signal of spatial inheritance. Distinct dynamic behaviors effectively primed the arc by the Late Cretaceous, generating transcrustal hot zones of increased magma mixing, recycling, long-term storage, and homogenization. Non-steady-state behavior in the Sierra Nevada resulted in mountain building and voluminous continental crust formation by transforming the physical, thermal, and chemical properties of the lithosphere over tens of millions of years. [ABSTRACT FROM AUTHOR]

The Neoproterozoic granitic rocks of Mount Abu Kibash and Tulayah in the central Eastern Desert of Egypt are of geodynamic interest and provide us with important information about the evolution and growth of the northern part of the Arabian–Nubian Shield (ANS) continental crust. They are primarily composed of granodiorites and syenogranites based on new field, mineralogical, and geochemical analyses. The granodiorites are marked by an enrichment of LILEs such as Sr, K, Rb, Ba compared to HFSEs like Nb, Ta, Ti and show a higher concentration of LREEs relative to HREEs. This composition suggests a subduction-related setting and aligns with the characteristics of subducted I-type granites in the ANS. Chemistry of the analyzed primary amphiboles in the investigated granodiorites support a calc-alkaline nature, mixed source and subduction-related setting. The granodiorites represent an early magmatic phase in this setting, likely formed from a mix of mantle-derived mafic magmas and lower crust material, with subsequent fractional crystallization. On the other hand, syenogranites exhibit high SiO2 (72.02–74.02 wt%), total alkali (7.82–8.01 wt%), and Al2O3 (13.79–14.25 wt%) levels, suggesting their derivation from peraluminous (A/CNK > 1) parental magmas. Their REE-normalized patterns are flat with a pronounced negative Eu anomaly, typical of post-collisional A2-type granites worldwide. These rocks originated from the partial melting of a juvenile lower crustal source (tonalite) in a post-collisional setting, driven by lithospheric delamination that facilitated mantle upwelling and underplating to the lower crust. Interaction between the upwelled mantle and lower crust led to fertilization (enrichment with HFSE and alkalis) of the lithosphere before partial melting. Fractional crystallization coupled with less considerable crustal assimilation are the main magmatic processes during the evolution of these rocks. The transition from subduction to post-collisional setting was accompanied by crustal uplifting, thickening and extensional collapse of ANS continental crust that caused emplacement of large masses of A-type granites in the northern ANS. [ABSTRACT FROM AUTHOR]

Large igneous provinces (LIPs) are often the surface expressions of mantle plume process. Intensive magma could occur in the continental crust when a mantle plume penetrates the Moho. How magmas migrate in the crust, forming LIPs, remains debated. In this study, we employ 2D thermo‐mechanical numerical modelling to study the dynamics of magma intrusion and migration within the continental crust affected by a mantle plume. Our results suggest that (1) lateral magma migration dominates crustal deformation, promoting the possible formation of metamorphic core complexes; (2) two distinct crustal deformation modes are recognized regarding the presence or absence of crustal break‐up, affected by whether a significant vertical magma migration occurs; (3) the crustal thickness, Moho temperature and the length of the preset weak crust–mantle decoupling zone are the three key parameters controlling crustal magma migration. This study highlights the importance of lateral magma migration in the lower crust and provides physical mechanisms for the interpretation of magma migration under LIPs. [ABSTRACT FROM AUTHOR]

The surface gap of tephriphonolite compositions in the Passa Quatro alkaline complex, in SE Brazil, is attributed to non-buoyancy of these high viscosity intermediate compositions during magmatic fractional crystallization at different depths. Thermodynamic and Rayleigh models for three alkaline suites of a strongly silica-undersaturated series were integrated to demonstrate that parental (basanite, nephelinite and alkaline basalt) and residual (phonolites) magmas are cogenetic by fractional crystallization at pressures of 10 kbar and 5 kbar, i.e. at magma chambers located above and below the Conrad discontinuity within the Upper Cretaceous-Palaeogene 40 km-thick continental crust in SE Brazil. The fractional crystallization of the parental magmas produced an ultramafic residual solid (wehrlite, olivine-bearing clinopyroxenite and clinopyroxenite) and residual liquids (evolved basanite and alkaline basalt, and phonotephrite). The latter moved up and built magma chambers at lower depths in the continental crust where those magmas initially crystallized clinopyroxenite extracts and high viscosity residual liquid that was entrapped and prevented to ascent towards the surface. Then, an abrupt change in the extract mineralogy produced a feldspathic-rich extract (leucocratic leucite monzosyenite, mesocratic syenite or leucocratic monzodiorite) and a residual phonolitic liquid with low viscosity. Following the feldspar crystallization, the magma viscosity decreased, acquiring adequate buoyancy that resulted in shallow-crust magma chambers in which phonolite diversification took place. These processes occurred due to the existence of a transcrustal, plumbing architecture where the high viscosity intermediate tephriphonolites were prevented to reach shallower depths, resulting in the Daly gap observed in the Passa Quatro Alkaline Complex. [ABSTRACT FROM AUTHOR]

High‐silica granitoids record the formation and evolution of the continental crust. A new intrusive complex has been recognized among silicic volcanic rocks of the Weixi arc, Southwest China. The intrusions consist of granites, granitic porphyries, and granodiorites. Zircon U‐Pb age data indicate that the Weixi granitoids formed at 248–240 Ma and were coeval with silicic volcanic rocks of the Weixi arc. The Weixi granitoids are enriched in Rb, Th, and U, depleted in Ba, Sr, Nb, Ta, and Ti, and have high light/heavy rare earth element ratios and slightly negative Eu anomalies. The Weixi granitoids have negative εNd(t) values (–9.8 to –7.8) and negative zircon εHf(t) values (–12.02 to –5.11). The geochemical and isotopic features suggest the Weixi granitoids were derived by partial melting of ancient crustal material. The Weixi granitoids and silicic volcanic rocks were derived from the same magma by crystal accumulation and melt extraction, respectively, and they record the formation of a continental arc in the central Sanjiang orogenic belt. [ABSTRACT FROM AUTHOR]

The continental crust is produced by the solidification of aluminosilicate‐rich magmas which are sourced from deep below the surface. Migration of the magma depends on the density (ρ) contrast to source rocks and the melt viscosity (η). At the surface, these silica‐rich melts are typically sluggish due to high η > 1,000 Pa s. Yet at their source regions, the melt properties are complexly influenced by pressure (P), temperature (T), and water contents (XH2O ${X}_{{\mathrm{H}}_{2}\mathrm{O}}$). In this study, we examined the combined P‐T‐XH2O ${X}_{{\mathrm{H}}_{2}\mathrm{O}}$ effects on the behavior of melts with an albite stoichiometry (NaAlSi3O8). We used first‐principles molecular dynamics simulations to examine anhydrous (0 wt % H2O) and hydrous (5 wt % H2O) melts. To constrain the P and T effects, we explored P ≤ 25 GPa across several isotherms between 2500 and 4000 K. The melts show anomalous P‐ρ relationships at low P ∼ 0 GPa and high T ≥ 2500 K, consistent with vaporization. At lithospheric conditions, melt ρ increases with compression and is well described by a finite‐strain formalism. Water lowers the melt density (ρhydrous < ρanhydrous) but increases the compressibility, that is, 1/Khydrous >1/Kanhydrous or Khydrous < Kanhydrous. We also find that the melt η decreases with pressure and then increases with further compression. Water decreases the viscosity (ηhydrous < ηanhydrous) by depolymerizing the melt structure. The ionic self‐diffusivities are increased by the presence of water. The decreased ρ and η by H2O increase the mobility of magma at crustal conditions, which could explain the rapid eruption and migration timescales for rhyolitic magmas as observed in the Chaitén volcano in Chile. Plain Language Summary: The continental crust is produced by solidifying aluminosilicate‐rich magmas. Such magmas are known to be highly viscous at the surface. It is expected that the magmas will become more viscous due to increasing pressure at the deep crustal depths near their sources. However, observations contrast the expectations. Some volcanic eruptions indicate rapid movement of the aluminosilicate‐rich magmas before the eruption. The movement of magma is influenced by its density and viscosity. These properties are influenced by pressure, temperature, and the water contents of the magma. To better understand how these parameters affect magmas in the crust, we performed computer simulations on molten albite with and without water. The albite chemistry mimics the chemistry of aluminosilicate‐rich magmas in the crust. At conditions of the deep crust where magmas originate, the densities of the magmas increase with compression. The magma viscosities also decrease under the same pressure. Our results provide, in part, a plausible explanation for a surprisingly rapid eruption of the Chaitén volcano in Chile. Water lowers both the magma density and viscosity which helps to explain the rapid eruption of the hydrous aluminosilicate‐rich lavas. Key Points: We constrain the combined effects of pressure, temperature, and water contents on aluminosilicate melts with an albitic compositionIn the crust, relatively low temperatures should increase melt viscosity. Yet pressure and H2O lower the viscosity at these conditionsOur results provide a plausible explanation for rapid eruption of lavas which are typically very viscous and should hence be sluggish [ABSTRACT FROM AUTHOR]

Mantle magmas interact with surrounding rocks during their ascent and storage in the continental crust, leading to open system processes as wall rock partial melting. In this study, we have experimentally investigated the reactions between a leucosome depleted migmatite and a primitive K-basaltic of Campi Flegrei (Italy). Experiments were carried out at pressure of 0.8 GPa temperatures from 1250 °C to 1050 °C and constant temperature and thermal gradient conditions. The experimental products consist of biotite-free migmatite, glass and crystals of clinopyroxene, olivine, plagioclase and Cr-spinel with proportions that vary as a function of temperature. Open system isothermal experiments indicate that the chemistry of melts and phase relationships are controlled by the high Al2O3 content of leucosome depleted migmatite with the glass composition shifting from K-trachybasalt towards shoshonite as the temperature decreases from 1200 °C to 1125 °C. At temperatures 1150°C, migmatite assimilation is not exclusively due to the assimilation fractional crystallization process because evidence of mingling and mixing is observed. T-gradient experiment shows melt composition ranging from shoshonite to phono-tephrite moving from the slightly crystalline zone (T = 1250 –1210 °C) at the bottom of the capsule towards the highly crystalline zone (T = 1160 –1140 °C). This SiO2-constant trend indicates that at temperature below the basalt solidus, the assimilation of leucosome depleted crust is represented almost exclusively by the biotite breakdown, leading to the increase in Al, Mg, Fe, Ti, and K activities in the system. The shoshonitic composition obtained in our experiments could represent the parental magma for both Campi Flegrei volcanic district and Vesuvius magmatic systems, indicating modification in a deep storage zone through mixing with the partial melts derived from restitic continental crust. [ABSTRACT FROM AUTHOR]

Complex zoning in crystals including repeated resorption and overgrowth is characteristic for arc magmas and occurs in response to closed-system changes in magmatic P–T– f O2 conditions and open system processes such as magma mixing and degassing or regassing. However, over which time frame do such changes occur? Do zoning patterns record changes occurring during the polybaric ascent of magmas that carry crystals or glomerocrysts sourced from variably mushy magma reservoirs, or alternatively indicate the uptake of antecrysts that experienced long periods of cold storage in plutonic precursors? A priori , these scenarios are endmember models, with the former transcrustal magmatic systems, where the crystals record changing conditions during magma ascent or changing interstitial melt compositions, traditionally preferred over the latter, which we here term transcrustal plutonic systems. In subsolidus plutonic systems, aphyric parental melts would acquire their entirely antecrystic crystal cargo during ascent from plutonic protoliths, and only crystal rims may be related to the host magma. We discuss the evidence for dominantly plutonic antecrystic cargo in some continental arc magmas, identified by considering mineral phase proportions, hydration of crystal rims that indicate hydrothermally altered cargo picked up by fresh melts, and uranium isotope disequilibria between crystals and matrix. We then turn to two-pyroxene thermobarometry and review the evidence for plutonic antecryst dominance revealed by this method in southwest Japan and the southern Taupo Volcanic Zone. We provide additional two-pyroxene data from the Andes, the Cascades, and the Tatun Volcano Group in northern Taiwan, corroborating that the uptake of crystals by aphyric to scarcely phyric melts is prevalent in continental arc magmatic systems. Thus, in many cases transcrustal plutonic systems seem to dominate, implying that a significant proportion of parental melts of continental arc magmas are variably enriched in silica, too hot to carry crystals, and typically too hot and not hydrous enough to be generated by differentiation in frequently postulated lower crustal hot zones, as we will demonstrate here. Our data indicate that in continental subduction zones, the mantle wedge is the source of a diversity of melt compositions (low- to high-silica), irrespective of the age and temperature of the subducting slab. Before discussing some of the implications of the prevalence of non-canonical transcrustal plutonic systems for the thermal structure of the crust, magma ascent processes, volcano monitoring, economic geology, as well as the evolution of continental crustal growth and recycling through deep time, we critically evaluate this novel perspective in terms of published data that might favour more traditional supersolidus transcrustal magmatic systems. This contribution provides the community with the opportunity to consider significantly colder crustal environments than typically accepted, and outlines avenues of future research. [ABSTRACT FROM AUTHOR]

Determining the volume and timing of magmatism during rifting and breakup is challenging due to the similar density and seismic velocity of inherited continental crust, magmatic additions and serpentinized mantle; and the difficulty of dating magmatic additions. Here rules of thumb to estimate these are proposed based on the characteristics of the top basement and Moho on seismically imaged margins. A simple kinematic model is used to generate first‐order crustal shapes of margins as a function of magma volume and timing of emplacement, which are successfully compared to a representative number of rifted margins. It appears that 'magma‐rich margins' require melt emplacement in advance of crustal thinning but not necessarily enhanced melt volume, while margins with exhumed mantle require a delay in melt emplacement but not necessarily a low magmatic volume. An alternative classification for the magma‐poor/magma‐rich dichotomy is proposed to better represent the crustal shape variability of rifted margins. [ABSTRACT FROM AUTHOR]

There are two factors, source composition and magmatic differentiation, potentially controlling W‐Sn mineralization. Which one is more important is widely debated and may need to be determined for each individual deposit. The Xitian granite batholith located in South China is a natural laboratory for investigating the above problem. It consists essentially of two separate components, formed in the Triassic at ca. 226 Ma and Jurassic at ca. 152 Ma, respectively. The Triassic and Jurassic rocks are both composed of porphyritic and fine‐grained phases. The latter resulted from highly‐differentiated porphyritic ones but they have similar textural characteristics and mineral assemblages, indicating that they reached a similar degree of crystal fractionation. Although both fine‐grained phases are highly differentiated with elevated rare metal contents, economic W–Sn mineralization is rare in the Triassic granitoids and this can be attributed to less fertile source materials than their Jurassic counterparts, with a slightly more enriched isotopic signature and whole‐rock εNd(226Ma) of –10.4 to –9.2 (2σ = 0.2) compared with εNd(152Ma) of –9.2 to ‐8.2 (2σ = 0.2) for the Jurassic rocks. The initial W‐Sn enrichment was derived from the metasedimentary rocks and strongly enhanced by reworking of the continental crust, culminating in the Jurassic. [ABSTRACT FROM AUTHOR]

A relation between tectonics and arc magmatism has been proposed in the west Pacific‐type accretionary orogens, but the specific mechanism remains unclear. This study examines the Cretaceous records in NE Asia in order to unravel this link. Two tectono‐magmatic episodes, namely the Early and Late Cretaceous, are recognized. The first episode was under (trans‐)extension, consisting of both mafic and felsic, depleted and enriched, and deep‐ and shallow‐derived arc magmas. The second episode experienced several compressive events with highly evolved and shallow‐derived (mid‐crustal level) arc magmas. We propose that (trans‐)extension thinned the arc crust, facilitating deep mafic magmas to ascend and cool rapidly, maintaining their geochemical diversity. Compression led to magmatic emplacement around the middle crust; and the warm crust allowed highly‐evolved granitoids to form. Therefore, tectonic setting controls arc magmatism in NE Asia, and is likely representative of other west Pacific‐type orogens. Plain Language Summary: Arc magmas are produced where oceanic plates subduct into the mantle. Their chemical composition varies in different tectonic settings, but the specific mechanism is unclear. We explore this question using the NE Asian setting during the Cretaceous. Here, the Early Cretaceous arc magmas reveal diverse compositions when in a setting undergoing extension. However, the Late Cretaceous magmas uniformly contain high silica contents when the continental crust was under compression. This implies that thin arc crust under extension facilitated the ascent of deeply‐derived magmas and these cooled rapidly and kept their chemical diversity. In contrast, crust under compression prohibited the ascent of deep magmas, instead inducing crustal melting and slower cooling in the middle crust, thus increasing the silica content. Therefore, tectonics strongly affected the nature of arc magmatism in NE Asia, and possibly other west Pacific‐type orogens. Key Points: Cretaceous magmatism in the NE Asian arcs was diverse during extension, but highly evolved under compressionExtension induced deep magmas to ascend and cool rapidly; Compression restrained deep magmas and extended coolingArc magmas were controlled by alternating extensional and compressional regimes during subduction retreat in west Pacific‐type orogens [ABSTRACT FROM AUTHOR]

Geochemical, geochronological (U–Pb zircons, ID-TIMS) and isotope-geochemical (Sm–Nd) studies of the rocks of the Bambukoy volcano-plutonic association, which form the Zhanok-Bambukoy volcano-tectonic structure within the Anamakit–Muya terrane on the northern flank of the Barguzin–Vitim superterrane of the East Transbaikalian segment of the Central Asian orogenic belt. The association includes volcanic rocks of the Zhanok Suite (dacites and rhyolites mainly), as well as leucocratic and biotite granites of the Bambukoy Complex that cut through them. The granites of this complex host the Mokhovoe tin deposit, which is attributed to the tin-porphyry formation. Subvolcanic rocks of the Zhanok Suite are considered as ore-bearing. The geochemical features of the volcanic rocks of the Zhanok Suite and the granites of the Bambukoy complex bring them closer to S-type granites, and belonging to a single tin-bearing Bambukoy volcanic-plutonic association. The formation of this association is determined by the age interval 834 ± 23–818 ± 7 Ma. The isotopic data point to a source of parental magmas from the rocks of the Bambukoy volcano-plutonic association, formed as a result of mixing of the material of two crustal sources, the mature Early Precambrian and the juvenile Early Baikal. The geochemical data also point to an exclusively crustal source of the rocks of this association. Thus, the Bambukoy tin-bearing volcano-plutonic association was formed in the Neoproterozoic time (Tonian), most likely under lithospheric extension conditions due to a source with a complex and long crustal prehistory. [ABSTRACT FROM AUTHOR]

Detailed textural and compositional study of calc-alkaline lamprophyres and minettes from Zeneta, SE Spain Neogene Volcanic Province (NVP) are used to unravel the magma sources and differentiation processes involved in their formation. The presence of xenocrysts of various origins indicates a hybrid nature involving mantle-derived alkaline lamproitic and continental crust-derived granitic parental magmas. A new U-Th-Pb zircon age of Zeneta minettes allows contextualizing their generation in time and space during regional lamproite magma intrusion and crustal anatexis in the NVP. Interaction and mixing of these compositionally contrasted magmas resulted in the formation of hybrid calc-alkaline lamprophyre minette. This process is reflected by the phases that crystallized from the hybrid magma, particularly phlogopite, and by the whole-rock composition of the less fractionated rocks. The calculated contribution of lamproitic and crustal-derived magma end-members in minette formation are 30–40% and 60–70%, respectively. Mixing of end-member magmas of contrasting rheological properties was possible only in a calculated thermal-window of 1025–1125°C, after cooling of intruding lamproitic magma and heating of host granitic anatectic region. The calculated thermal window fits with the estimated rheological properties of Zeneta minettes and the crystallization temperature of early minette-derived phlogopite. Furthermore, fractional crystallization was identified for the first time in the Zeneta minettes, based on the observed whole-rock line of descent from the less evolved mixed magmas through intermediate to felsic minettes and associated textural and compositional features of late crystallized phases. Polytope Vector Analysis allowed an integrated quantitative characterization of magma differentiation, including magma mixing and subsequent fractional crystallization. The identification of mixing and fractionation processes in calc-alkaline minettes genesis, which otherwise does not show spatial and temporal association in the field with granitic bodies, opens a new scenario to be considered in understanding the petrogenesis of these rocks. [ABSTRACT FROM AUTHOR]

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma's evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits. [ABSTRACT FROM AUTHOR]

Arc magmatism plays a key-role in the growth and differentiation of continental crust. In particular, the prolonged magmatic flux events control the genesis of deep crustal hot zones where magma accumulation and fractionation favour the continental arc crust evolution and geochemical stratification. In this view long-lived magmatic systems located in arc domains, with their erupted products spanning from basalts to rhyolites are formidable archive for the understanding the evolution of transcrustal magmatic plumbing systems and the construction of a stratified continental crust. This study focuses on the long-lived (ca. 9 Ma) Miocene-Holocene Cordillera de San Buenaventura volcanic system in the Southern Puna Plateau (NW Argentina), a unique natural laboratory where exploring the building up of MASH-zones (or deep crustal 'hot zones') and related sustained volcanism. Synthesis of new and published data, together with new thermobarometry and fractional crystallization modelling, indicates a cyclic scenario with mantle melts undergoing fractional crystallization dominated incipient and waning stages alternate to major mafic magma recharge events during the building up phase of the MASH-zone. This magmatic scenario is also discussed in the light of the coeval geodynamic framework dominated by the subduction of the Nazca plate and the eastward migration of the frontal arc magmatism. [ABSTRACT FROM AUTHOR]

Arc magmas, the building blocks of the Phanerozoic continents, are compositionally diverse. The most prominent compositional diversity is that some arcs show early Fe enrichment while some others show the opposite trend. What causes this Fe differentiation diversity is important for understanding continent formation but remains highly debated. Here, we use pressure-sensitive geochemical proxies, combined with experimental results, to evaluate the petrological mechanism(s) for the different Fe trends in arc magmas that traverse through crusts of various thicknesses. We show that magnetite starts to fractionate only at MgO ≤ 4 wt% for nearly all arc magmas and thus has no bearing on the early Fe depletion in calc-alkaline arc magmas. The Fe enrichment at MgO > 4 wt% for tholeiitic arc magmas is largely caused by clinopyroxene fractionation. The culprits for the Fe depletion at MgO > 4 wt% in calc-alkaline arc magmas change from pyroxene- to garnet-dominated (±amphibole) as the arc crust thickens. The similarity between the upper continental crust and the calc-alkaline arc magmas suggests that calc-alkaline arc magmas are an essential component for the continental crust. The high La/Yb and Dy/Yb estimates for the average upper continental crust imply that garnet fractionation is an intrinsic feature of the upper continental crust. Thus, crustal thickness, that is differentiation pressure, exerts a first-order control on arc magma compositions and high-pressure intracrustal differentiation in thickened crust is necessary for making the Phanerozoic continental crust. [ABSTRACT FROM AUTHOR]

Compositions of arc magmas depend on several factors and are often thought to reflect conditions in the mantle wedge and at the slab-mantle interface. However, in continental arc settings, magmas are also influenced by assimilation of continental crust. Here, we present measurements and modeling of 238U-230Th activity ratios, Sr, Nd, Hf, and Pb isotopic compositions, and major and trace element concentrations in young, historic lavas erupted from Reventador, an active stratovolcano in the Ecuadorian Andes. In arc lavas, 238U-230Th disequilibria are often assumed to reflect processes occurring in the mantle wedge, as U and Th behave differently in this relatively oxidized and fluid-rich environment. Enhanced mobility of hexavalent U in aqueous fluids results in (230Th/238U) < 1 and elevated (238U/232Th), which are common in arc lavas. However, the majority of Reventador lavas have (230Th/238U) = 1.0–1.1 and (238U/232Th) = 0.94–1.12, the latter of which is considerably lower than the depleted mantle ((238U/232Th) ∼ 1.5, Sims and Hart, 2006). While this Th enrichment could be due to melting of subducted oceanic crust, approximately linear trends between (230Th/232Th), wt. % SiO 2 , and radiogenic isotope ratios indicate otherwise. We argue that crustal assimilation lowers long-term, or time-integrated, (238U/232Th) in Reventador magmas. To quantify the effects of assimilation we modeled stepwise assimilation and fractional crystallization. Observed trends between (230Th/232Th), 87Sr/86Sr, ε Nd , ε Hf , and 208Pb/206Pb can be reproduced by up to 10% assimilation, which is consistent with previous regional studies. However, reproducing the full spectrum of isotopic diversity among Reventador lavas requires heterogeneous basalt compositions. In a broader context, this study emphasizes the need to consider crustal processes when examining continental arcs. While 238U-230Th disequilibria develop in the mantle wedge, they can be overwritten by subsequent interaction with continental crust. [ABSTRACT FROM AUTHOR]

Significant volumes of magma can be intruded into the crust during continental break‐up, influencing rift evolution by altering the thermo‐mechanical structure of the crust and its response to extensional stresses. Rift magmas additionally feed surface volcanic activity and can be globally significant sources of tectonic CO2 emissions. Understanding how magmatism may affect rift development requires knowledge on magma intrusion depths in the crust. Here, using data from olivine‐hosted melt inclusions, we investigate magma dynamics for basaltic intrusions in the Main Ethiopian Rift (MER). We find evidence for a spatially focused zone of magma intrusion at the MER upper‐lower crustal boundary (10–15 km depth), consistent with geophysical datasets. We propose that ascending melts in the MER are intruded over this depth range as discrete sills, likely creating a mechanically weak mid‐crustal layer. Our results have important implications for how magma addition can influence crustal rheology in a maturing continental rift. Plain Language Summary: Continental rifting, the break‐up of continents to form new ocean basins, is a key component in the tectonic cycle that affects Earth's surface environment. The rifting process is aided by magmatic activity in its final stages, which weakens the crust by heating it. This is believed to facilitate present‐day rifting in Ethiopia, where we find rift‐related volcanoes. The depth of magma storage in the rifting crust will determine how heat is distributed, and therefore how the physical properties of the crust are altered. Here we study melt inclusions, small pockets of magmas trapped within growing crystals beneath rift volcanoes. Using the concentrations of CO2 and H2O in melt inclusions we infer the pressures (and therefore depths) that they formed. Our results demonstrate that magmas rising through the Ethiopian crust consistently stall at a depth range of 10–15 km beneath the surface. Furthermore, the diverse chemical composition of our melt inclusions show that magmas are stored in multiple small bodies versus a larger mixed magma reservoir. This study therefore provides new insights into how magmas are stored in the Ethiopian crust before volcanic eruptions and suggests that rising magmas may produce a weak layer in the middle of the rifting crust. Key Points: We determine magma storage conditions in the Main Ethiopian Rift through geochemical analysis of olivine‐hosted melt inclusionsVolatile saturation barometry reveals that basaltic melts are focused at 10–15 km depth in the Ethiopian crustGeochemical heterogeneity in melt inclusions suggests that magma storage is likely to occur in semi‐discrete sills [ABSTRACT FROM AUTHOR]

We report the discovery of one of the largest ancient (>3.0 Ga) crustal terranes on Earth. Granitoids with crystallization ages >3.0 Ga and/or Sm-Nd depleted mantle model ages ≥3.2 Ga define a -1000 x 100 km belt on the western margin of the Rae craton, Canada, referred to herein as the Perry River terrane (PRT). Zircon U-Pb-Hf-O isotope and whole-rock geochemical data from granitoids show that the PRT is a predominantly juvenile 3.3--3.2 Ga terrane that was partially reworked by more evolved ca. 3.1 Ga magmatism. These findings call for a reassessment of the timing and extent of ancient continental growth on Earth. A global compilation of zircon Hf isotope data from 3.6 to 3.0 Ga igneous rocks reveals clusters of relatively juvenile (initial εHf -2 to +3) rocks at ca. 3.31 and ca. 3.23 Ga, which include samples from the PRT and 13 other terranes worldwide. Other global zircon data sets also document age peaks between 3.3 and 3.2 Ga, and a cluster of broadly chondritic initial εHf values around 3.2 Ga. The 3.3--3.2 Ga period may therefore have been a time of enhanced net continental growth on Earth, and the PRT is one of the largest terranes preserved from that time. Furthermore, zircon Hf isotope data from 3.3--3.1 Ga PRT granitoids and 3.5--3.0 Ga igneous rocks worldwide yield little evidence for parent magmas that interacted with or derived from pre--3.6 Ga continental material. Contrary to some continental-growth models, this latter observation suggests that the volume of continental crust established by 3.6 Ga was relatively small. [ABSTRACT FROM AUTHOR]

The genesis of intermediate intrusions is highly controversial, and one of the hot topics is whether they represent frozen melts or cumulates in the evolution of magmatic systems. Distinguishing accumulation from crystallization melt differentiated along the liquid line of descent is the key issue. The Paleoproterozoic intermediate intrusions in southern North China Craton provide an excellent case to decipher this issue. Multiple lines of evidence, including mineral textures, geochemistry as well as alphaMELTS modeling, indicate disequilibrium between whole‐rock and minerals, with melt extraction occurring at temperatures of 760°–820°C and with 10–40 wt.% of trapped melts. Effective water storage, revealed by amphibole and clinopyroxene hygrometers, plays a crucial role in promoting crystal‐melt segregation in pluton‐sized reservoirs in the upper crust. This study demonstrates that the accumulation in intermediate magmas can be identified even without evident complementary initial and extracted melts and provides deep insights into the genesis of intermediate continental crust. Plain Language Summary: The genesis of intermediate rocks has long been controversial since they are analogs of the average composition of continental upper crust. The key topic is whether intermediate rocks represent frozen melts of intermediate magmas or crystal residues after melt extraction in the evolution of felsic magmatic systems. Here we carried out a comprehensive study on the Paleoproterozoic intermediate intrusions in the southern North China Craton, which is considered to have recorded the process of crystal accumulation and melt segregation in the shallow crust. Upon mineral texture, geochronologic, whole‐rock and mineral geochemical, and thermodynamic investigation, we propose that crystal accumulation and crystal‐melt segregation processes can be identified in intermediate magmas with the melt extraction temperatures and proportions of trapped melts recorded by zircon trace elements. Amphibole and clinopyroxene hygrometers revealed high water content of the melts, which likely decreased the viscosity of melts and facilitated effective cumulate‐melt segregation. This study provides a powerful reference to see through the accumulation in intermediate magmas, record the processes of crystal‐melt segregation, and definitively resolve the debate concerning the genesis of intermediate intrusions. Key Points: Crystal accumulation in intermediate magmas can be identified by mineral texture and geochemistryThe effective water storage system in the reservoirs is key to promoting crystal‐melt segregationCrystal‐melt segregation and accumulation are fundamental processes to form evolved continental upper crust [ABSTRACT FROM AUTHOR]

Arc magmas, the building blocks of continental crust, are depleted in total iron (Fe), have higher ratios of oxidized Fe to total Fe (Fe3+/∑Fe), and record higher oxygen fugacities (fO2’s) compared with magmas erupted at mid-ocean ridges. Garnet crystallization could explain these observations if garnet removes substantial amounts of Fe2+, but not Fe3+, from magma, yet this model for continental crust generation has never been tested experimentally. Analysis of garnets and melts in laboratory experiments show that the compatibilities of Fe2+ and Fe3+ in garnet are of similar magnitudes. Our results indicate that fractional crystallization of garnet-bearing cumulates will remove 20% of total Fe from primary arc basalts but negligibly alter the Fe3+/∑Fe ratio and fO2 of the melt. Garnet crystallization is unlikely to be responsible for the relatively oxidized nature of basaltic arc magmas or the Fe-depletion trend observed in continental crust. [ABSTRACT FROM AUTHOR]

Charnockites form an important component of the lower continental crust. Quantitative investigation on the properties of magmas that can stabilize orthopyroxene at solidi is crucial to understanding the petrogenesis of igneous charnockites. This study has performed detailed petrologic analyses and thermodynamic constraints on the Paleoproterozoic high-maficity (FeOT + MgO = 5–14 wt%) and peraluminous charnockites from the Jining Complex in the North China Craton. These charnockites occur as intrusions in granulite facies terranes and contain the mineral assemblages including prevalent perthitic/antiperthitic feldspars and garnet with minor biotite (usually less than ~5 vol%) beside orthopyroxene. The Jining charnockitic magmas were ascertained to have ultrahigh temperatures up to 1050–1100°C, poor H2O contents around 0.14–0.42 wt% and limited aluminum saturation indexes (ASIs) of 1.0–1.3. The stabilization of orthopyroxene at the solidus is attributed to low magmatic H2O contents and ASIs, which have maxima of 1.2 wt% and 1.5, respectively, and are positively correlated to bulk-rock maficity. Such charnockitic magmas could not release H2O-rich fluids near solidi, as the H2O is buffered by the orthopyroxene–biotite pair. Moreover, combined geochemical discrimination and progressive melting modelling reveal that the Jining charnockites were generated by partial melting of a greywackic granulite source, with about 15%–40% entrainment of solid phases in mushy magmas. The melting occurs at temperatures as high as 1050–1100°C, obviously beyond biotite stabilities, and involves quartz, feldspars and garnet as melting reactants, which differs from the previous proposition that peraluminous charnockites are related to biotite dehydration melting. The resultant magmas are substantially enriched in maficity and depleted in H2O due to both the melt compositions per se and the high entraining capability. Such peraluminous charnockite plutons massively emplaced in granulite facies terranes indicate post-orogenic ultrahigh-temperature anatexis of metasedimentary rocks in conditions close to the crustal dry solidus. [ABSTRACT FROM AUTHOR]

Trace-element anomalies in the continental crust (e.g., Nb-Ta-Pb) are useful to decipher the formation and evolution of continents. We found that the trace-element patterns of upper, middle, and lower crust are all marked by strongly negative phosphorus anomalies, which were not likely to have been generated directly by mantle melting. In order to address this "crust composition paradox," we compiled major- and trace-element data from global arc magmas, igneous minerals, and deep arc cumulates and found that the phosphorus deficit in continental crust is coupled with an elevated Th/La ratio. This feature can be best explained by the fractional crystallization of apatite during arc magma evolution rather than the influence of a subducted slab. Accumulation of apatite-bearing mafic cumulates in deep arcs followed by foundering into the upper mantle causes the mismatch in the phosphorus systematics between the mantle and the continental crust. This process plays a critical role in shaping the chemical composition of continental crust. [ABSTRACT FROM AUTHOR]

During the differentiation of arc magmas, fractionating liquids follow a series of cotectics, where the co‐crystallization of multiple minerals control the melt compositional trajectories, commonly referred to as liquid lines of descent (LLD). These cotectics are sensitive to intensive properties, including fractionation pressure and melt H2O concentration, and changes in these variables produce systematic differences in the LLDs of arc lavas. Based on a compilation of experimental studies, we develop two major element proxies that exploit differences in LLDs to constrain the fractionation conditions of arc magmas. Near‐primary fractionating magmas evolve along the olivine‐clinopyroxene cotectic, which is pressure‐sensitive. We use this sensitivity to develop a proxy for early fractionation pressure based on the normative mineral compositions of melts with 8 ± 1 wt.% MgO. Fractionation in more evolved magmas is controlled by the clinopyroxene‐plagioclase cotectic, which is strongly sensitive to magmatic H2O contents. We use this relationship to develop an H2O proxy that is calibrated to the normative mineral components of melts with 2–4 wt.% MgO. These two proxies provide new tools for estimating the variations in pressure and temperature between magmatic systems. We applied these proxies to compiled major element data and phenocryst assemblages from modern volcanic arcs and show that in island arcs early fractionation is relatively shallow and magmas are dominantly H2O‐poor, while continental arcs are characterized by more hydrous and deeper early fractionation. These differences likely reflect variations in the relative contributions of decompression and flux melting in combination with distinct upper plate controls on arc melt generation. Plain Language Summary: Within volcanic arcs, magmas evolve from silica‐poor basalts to more silica‐rich compositions. This process is dominantly controlled by the minerals that crystallize from the magmas and generates characteristic changes in magma compositions that can be measured in erupted lavas. The crystallizing minerals and evolution in magma composition are sensitive to changes in the conditions at which magmas crystalize including the amount of water dissolved in the magma and the depth of crystallization within the crust. We develop two new methods that use changes in magma composition to understand how these conditions vary between different volcanic arcs. We find that arcs built on continental crust typically erupt lavas that began to crystallize at greater depths and are more water‐rich, while arcs built on oceanic crust primarily erupt water‐poor lavas that began to crystallize at shallower depths. These differences have important implications for the processes by which new continental crust is created within volcanic arcs. Key Points: The major element evolution of arc magmas is controlled by the fractionation of pressure and H2O sensitive mineral assemblagesWe use these relationships to develop two proxies that calculate early fractionation pressure and H2O contents from magma compositionsContinental arcs are dominantly H2O‐rich and deeper fractionating, while island arcs are more H2O‐poor and shallower fractionating [ABSTRACT FROM AUTHOR]

The Dongxiang tungsten–copper deposit is a large W–Cu deposit located in the northeast of Jiangxi province in south China. Previous studies have mainly considered the geochemical and isotopic attributes of the ore deposit, but information is still lacking on the genesis and setting of Dongxiang W–Cu mineralization-related intrusive rocks. This paper presents systematic elements and Sr–Nd–Hf isotopic data of the Dongxiang granodiorite porphyry. The Dongxiang granodiorite porphyry is intermediate–acidic in composition, with SiO2 contents of 60.00–75.16 wt.%, Al2O3 contents of 10.15–18.53 wt.%, an K2O contents of 2.95–4.28 wt.%. The REEs content ranges from 64.2 to 198.1 ppm, with LREE/HREE ratios of 7.67–17.47. It is characterized by adakitic geochemical affinities with high Sr/Y and (La/Yb)N ratios but low Y and Yb contents. A slight Eu anomaly, extreme depletion in Y and Yb, relatively low MgO content, and relatively high 207Pb/204Pb ratios together indicate that the Dongxiang granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. Based on zircon εHf(t) values (−11.8–−4.5), two-stage Hf model ages (1.33–1.94 Ga), and the regional geological setting, it can be inferred that Dongxiang granodiorite porphyry magma is mainly derived from Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. [ABSTRACT FROM AUTHOR]

The Bushveld Complex of South Africa is underlain by a fine-grained sill complex which most workers interpret to represent the quenched parent magmas to the intrusion. The sills have unusually high Pt contents (up to ~ 25 ppb) and Pt/Pd ratios (average 1.50) exceeding those in most other mantle magmas globally. Unusually high Pt/Pd is also found in many Bushveld cumulates. Understanding the origin of the high Pt/Pd is important for exploration, in view of the contrasting monetary value of the metals, but also for unravelling the petrogenesis of the intrusion. Here, we review existing platinum-group element (PGE) data and present the first radiogenic W isotope data on a Bushveld rock, to evaluate a range of potential models, including PGE fractionation prior to final magma emplacement and within the Bushveld magma chamber, magma derivation from the sub-continental lithospheric mantle (SCLM), contamination of Bushveld magma with Pt-rich continental crust, and a meteoritic component in the mantle source to the magmas or in the crust with which the magmas interacted. We identify three key processes causing fractionation of metals prior to final magma emplacement and within the Bushveld chamber, namely crystallisation of Pt alloys, partial melting of cumulus sulfides triggered by flux of volatiles followed by sulfide melt percolation, and mobilisation of PGE by percolation of volatiles through the cumulate pile. The currently available W and Ru isotope data are inconsistent with derivation of the Bushveld magmas from mantle or crustal sources containing an enhanced meteoritic component relative to normal post-Hadean mantle. [ABSTRACT FROM AUTHOR]

Magma produced by melting of continental crust and mantle at the Archean-Proterozoic boundary are compositionally variable and chemical compositions provide evidence for the mixing of two sources. Understanding the composition of hybrid magma is essential for determining the comparative influence of crust and mantle sources during orogenesis. The hybrid granites are less documented in Indian cratons, especially less in Dharwar Craton. Here we present petrographic and whole-rock geochemical data of Madgulapalli granitic rocks situated in the NE part of the Eastern Dharwar Craton (EDC), to elucidate their petrogenesis and role in crust formation. The Madugulapalli granites (MPG) are composed chiefly of plagioclase, quartz, and alkali feldspar with associated biotite showing alteration and inter-granular textures. Geochemically, they are metaluminous to peraluminous in nature with calc-alkaline hybrid granite. The hybrid granites exhibit both negative and positive europium anomalies; the lower Rb/Sr, Rb, Sr, and higher Sr/Y, (Dy/Yb)N ratios suggest that the interaction of older rocks with residual garnet source melted at high pressures. We hypothesize that hybrid granites are formed by interaction (e.g., metasomatism, mingling, or mixing) between parental magmas and pre-existing rocks with the influence of sanukitoid melts (heat source) in a subduction environment. The genesis of the hybrid granites demonstrates the mixing coupled with differentiation in the petrogeny's residue system in a syn-collision setting followed by continental crust stability in EDC during the Neoarchean period. [ABSTRACT FROM AUTHOR]

Magmatic Ni–Cu–Co–platinum group element deposits are notoriously difficult exploration targets owing to a lack of alteration haloes or other extended distal footprints. Success requires prediction of prospective terranes, followed by identification of suitable host intrusions and deposition sites within those intrusions. At the regional scale, potential ore-hosting magmas tend to have lithophile trace element trends falling on mixing lines between primitive or slightly depleted source mantle and typical upper continental crust, with several significant exceptions. Most known deposits have parent magmas that are in the upper range of FeO content for given MgO compared with baseline data sets for continental large igneous province magmas. At the scale of individual intrusions, the presence of cumulate rocks, both mafic and ultramafic, is key. These can be recognized in regional datasets using combinations of magnesium number (molar MgO/(MgO + FeO), Al2O3, TiO2 and Zr contents. Combinations of alteration-resistant element ratios between Ni, Cr and Ti are also useful and can also be applied to moderately weathered samples. Concentrations and ratios of Cu and Zr are useful in discriminating chalcophile-enriched and depleted magma suites. In combination, these approaches can be combined to discriminate highly prospective cumulate-dominated magmatic suites and individual intrusions from non-cumulate suites with limited potential. Supplementary material: Supplementary Appendix 1, procedure for determination of FeO–MgO contents of magmas from olivine-liquid mixing lines, and Supplementary Appendix 2, procedure and error analysis for correcting major element whole rock analyses volatile and sulfide free, are available at https://doi.org/10.6084/m9.figshare.c.6267664 [ABSTRACT FROM AUTHOR]

The source of massive magma production at volcanic rifted margins remains strongly disputed since the first observations of thick lava piles in the 1980s. However, volumes of extruded and intruded melt products within rifted continental crust are still not accurately resolved using geophysical methods. Here we investigate the magma budget alongside the South Atlantic margins, at the onset of seafloor spreading, using high-quality seismic reflection profiles to accurately estimate the oceanic crustal thickness. We show that, along ~ 75% of the length of the Early-Cretaceous initial spreading centre, the crustal thickness is similar to regular oceanic thickness with an age > 100 Ma away from hot spots. Thus, most of the southernmost Atlantic Ocean opened without anomalously hot mantle, high magma supply being restricted to the Walvis Ridge area. We suggest that alternative explanations other than a hotter mantle should be favoured to explain the thick magmatic layer of seaward dipping reflectors landward of the initial mid-oceanic ridge. [ABSTRACT FROM AUTHOR]

The Palandöken volcanics are made up of a thick volcanic sequence consisting dominantly of tuffs and intercalated lava flows in Erzurum-Tekman basin. According to the data obtained from geochemical analyses, the silica contents of the lavas range from 47.44 % (basalt) to 67.68 % (dacite) and Mg# 11–53%. While alkaline (latite and benmoreite) and subalkaline lavas are generally enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) in conformity with each other, they show significant negative Nb, Ta anomalies and very weak Eu anomaly. There are also examples (N15, N19) in these rocks that differ in their elements behavior. These geochemical characteristics indicate that, starting from the source magma, various differentiation processes like magma mixing and melt effect, occurred. Whereas the Nd (143Nd/144Ndi) isotope values of the volcanic rocks vary in a narrow range of 0.51281 and 0.51267, Sr isotope (87Sr/86Sri) values have a relatively wider range between 0.70362 and 0.70500, and εNd(t) values (+0.71 to +5.14). Isotope and geochemical data; supports that these volcanics were formed by the partial melting of spinel-lherzolite subcontinental lithospheric mantle-derived magma at different rates, but assimilation of continental crust also played an important role, along with magma mixing and fractional crystallization, which constitute the main differentiation process. Palandöken volcanic rocks have similar geochemical characteristics with the nearby Ilica, Kandilli and Yolçatý volcanics in general and their properties are compatible with eastern Anatolian magmatism that was formed in a geodynamic setting of post-collisional extension. [ABSTRACT FROM AUTHOR]

SE China is regarded as one of the most important mineral resource bases in China. The spatio‐temporal distribution of the magmatism and mineralization in the area has a distinct pattern due to the uneven intensity of crust–mantle interactions. We analysed gravity, magnetic and magnetotelluric (MT) data from the study area. The lithosphere in the north‐eastern and coastal parts of South China features intense magnetic, low resistivity anomalies and low density of lithospheric mantle material components. Meanwhile, the crust in the Nanling region features high resistivity and low magnetic granitic pluton. As we view from the north‐east to the south‐west, the crust–mantle interaction in SE China weakens unevenly and the magmatic origins for ore‐forming are progressively shallow. In the continental margin area, the subducted plate partially melted and rose along deep faults, interacting with the lithospheric mantle, which created conditions for the formation of the large porphyry Cu deposits. In the inland Nanling region, the Palaeo‐Pacific Plate has subducted to a considerable depth, the influence of deep disturbances was diminished, and therefore the metallogenic magmas of W–Sn deposits are dominated by continental crust remelting granites. While the tectonic environment of the Pb–Zn–Ag polymetallic deposits is in a transitional zone between porphyry Cu deposits and W–Sn deposits, small amounts of femic magma mixed with large amounts of granitic magma to form the mineralized granites. The geophysical data provide corresponding evidence to support the mineralization dynamics model based on oblique Pacific subduction. [ABSTRACT FROM AUTHOR]

The Birsa and Devgaon leucogranites represent contemporaneous episodes of highly fractionated felsic magmatism associated with the Paleoproterozoic Malanjkhand granitoids in the Bastar craton, Central India. Major element oxides geochemistry reveals that two leucogranites are strictly granite in composition and both show calc-alkaline affinity. Geochemical discrimination diagrams inferred that these leucogranites shows affinity towards I-type magma with metaluminous characters. Geochemical classification inferred that the Birsa leucogranite preferred to be magnesian whereas Devgaon leucogranite designated to be ferroan type. Geothermobarometry estimation suggested that 1.2–4.5 kbar pressure and 750°–830°C temperature conditions at the shallow depth of the continental crust is responsible for the emplacement of leucogranites. Crystallization evolution of feldspar in the leucogranite provided evidences of late stage felsic magmatism in the Malanjkhand pluton. Molybdenum enrichment in the leucogranite possibly due to crystal fractionation under high oxygen fugacity conditions inherited from the magma chamber in the continental crust. Anomalous high concentration of Mo in the Devgaon leucogranite is contributed from episodic hydrothermal system with poor supply of sulphur. Occurrences of molybdenite in the Devgaon leucogranite provides high exploration potential to investigates granite molybdenite system in the Bastar craton. [ABSTRACT FROM AUTHOR]

To study the formation of S-type ultra-potassic granitic melts under the conditions of the continental crust, we conducted experiments on partial melting of plagioclase-free garnet–two-mica metapelite (with accessory apatite and ilmenite) at 6, 10, and 15 kbar and 700–900°C. Rock melting is driven by a series of peritectic melting reactios as a function of pressure and starts at temperatures of 750–800, ~800, and ~850°C at 6, 10, and 15 kbar, respectively, reflecting the positive dP/dT slope of the solidus. These P–T-conditions of melting, compositions of mineral assemblages and granitic melts formed during melting of plagioclase-free metapelites are similar to those formed during melting of plagioclase-bearing two-mica assemblages. The high K2O content (7–8 wt %) at a K2O/Na2O ratio of >8–10 is the main feature of the composition of the melt, which forms upon melting of plagioclase-free metapelite. These features are similar to the compositions of S-type ultra-potassic rhyolites, which form in extension tectonic settings. [ABSTRACT FROM AUTHOR]

The evolution of Earth's atmospheric O 2 levels on long timescales is modulated in part by the composition of magmatic gases, specifically their oxidation state and speciation. Here, we examine how magma differentiation affects the oxygen fugacity and composition of magmatic gases. Variations in temperature, pressure, composition, and redox conditions of evolving magmatic systems result in complexities, which have not been fully treated previously. Taking all these variables into account, we develop a multipronged approach to a comprehensive understanding on the role of magmatic gases on atmospheric oxygenation. This includes a compilation of petrological observations on the redox systematics of mid-ocean ridge basalts, a geochemical model for magma crystallization in oxygen-closed systems with variable initial redox conditions, and a thermodynamic framework for gas–melt systems with multi-component C-H-O-S volatiles. By considering magmatic differentiation at variable depths, we show that magma crystallization progressively changes the redox state of residual melts and coexisting gases due to differences in iron speciation between the melt and cumulate minerals. In thick crusts, high pressures of magma differentiation suppress magnetite saturation but promote garnet crystallization, increasing magmatic oxygen fugacity by ∼4–8 orders of magnitude and thereby resulting in oxidized gases. In thin crusts, the prevalence of magnetite prevents significant oxidation of the magma, yielding reduced gas emission. Hence, magmatic gases from thick crusts are much less effective O 2 sinks, which does not appear to be affected by gas decompressional transport or polybaric degassing from the deep crustal magmatic zone to the atmosphere. Depending on how crustal thickness during active magmatism varies with time, magmatic gases may play an important role in modulating atmospheric O 2 levels on million-year timescales. Rapid growth of continental crust in the late Archean appears to have been associated with the first evidence for significant crustal thickening during magmatism. If so, this would have led to a substantial decrease in O 2 sink, possibly permitting atmospheric O 2 to rise to a new state. [ABSTRACT FROM AUTHOR]

Based on a relevant geochronological U-Pb zircon dataset (n = 47) from a sample (PBL-109) of the Cerro Punta Blanca pluton (CPB), which is part of a calc-alkaline suite, we corroborate the development of protracted magmatic activity with three major crystallization events for this Permian magmatism: 278 ± 1, 283 ± 2, and 289 ± 2 Ma, which outcrop in the Cordón del Portillo, Cordillera Frontal (CF) of Argentina. These ages can be assigned to the lower section of the magmatic record of the Choiyoi magmatism (ca., 290-265 Ma), while the age of 289 Ma represents the oldest known age for the Choiyoi, indicating the start of this magmatism during the Artinskiense. Considering these geochronological data, we postulate the presence of a deep mush reservoir where protracted magmatic activity permitted the prolonged crystallization of antecrysts (ca. 283–289 Ma). Migration of the parental magma from the mush reservoir zone occurred near the time of emplacement and culminated in the formation of an ephemeral magma chamber at shallow levels, where zircon autocrysts crystallized (ca. 278 Ma). Age spectra reported within individual samples support the idea of massive magma migration when conditions were favorable (e.g., thermally matured crust). In this view, the studied "older" Choiyoi magmatism represents a continuous magmatic event lasting 11 Ma and corresponds to a single magmatic episode rather than different periods of magmatic activity and subsequent emplacements. A later alkali-calcic magmatic event is recorded at 265 ± 4 Ma from a sample of the Cerro Bayo pluton (MH-0113), which could represent the end of the lower section of the Choiyoi magmatism. Whole-rock Sm-Nd, Rb-Sr, and Lu-Hf data in zircon, along with ages reported for the studied igneous and inherited zircon from the CPB; together with isotopic data and ages from the detrital zircon found in the Carboniferous accretionary complex of Chile, indicate that the source of the Permian parental magma in this region was a heterogeneous continental crust mainly formed by Devonian and Carboniferous rocks, related probably to a magmatic arc. However, some contribution from the Carboniferous accretionary complex of Chile to the parental magma should be consider. [Display omitted] • Permian Choiyoi arc magmatism in the Andean margin. • Generation and evolution of granitic magmas based on U-Pb zircon. ages. • Sources inferred from isotopic studies. [ABSTRACT FROM AUTHOR]

The controversy over the origin of massive chromitites in layered intrusions has recently become more contentious than ever before. At issue is whether they are produced via gravity settling/in situ crystallization of chromite directly on the chamber floor or by kinetic sieving, metasomatic replacement, or sill-like intrusions beneath the chamber floor, i.e., in deep parts of the cumulate pile. The latter group of models implies that massive chromitites have never been on the chamber floor. In this paper, we show that decisive clues to the 'chamber floor dilemma' come from field relations of massive chromitite with magmatic dropstones in the Bushveld Complex, South Africa - the largest fossilized magma chamber in the Earth's continental crust. The roof sequences in such basaltic magma chambers are known to be inherently unstable; therefore, crustal instability results in their breakdown and collapse as angular blocks (i.e., magmatic dropstones) through the resident melt column onto the upward-growing chamber floor. We have discovered such magmatic dropstones in the sequences that host massive UG1, UG2, and MG2 chromitites in the Critical Zone of the Bushveld Complex. The dropstones are easily recognizable in the field because they are composed of fine-grained melanorite/orthopyroxenite, which are texturally dissimilar from and have sharp contacts with adjacent cumulate rocks (chromitite, anorthosite, norite, etc.). The dropstones range in shape from angular to lenticular fragments a few centimetres in size to large tabular dropstones of ∼0.5–1.0 m across and ∼10 m long. The dropstones indent pre-existing layers of chromitite/anorthosite beneath them and are covered by subsequently deposited layers of the same rocks above them. Some dropstones appeared to have knifed into chromitite/anorthosite layers and cut them off, and a few dropstones appeared to have been driven into the floor cumulates and crumpled the layers outwards and upward. Also, some beheaded dropstones indicate the truncation of the floor cumulates by planar erosional surfaces. The physical relationships of dropstones with their host rocks indicate that: (1) there was almost invariably a sharp interface between the top of the inward-growing cumulate pile and the overlying resident melt; (2) the uppermost part of the cumulate pile was coherent and igneous layering, involving chromitites, was generally fully developed right up to the crystal-liquid interface; (3) by the time of dropstones's landing, the chromitite layers were already formed on the chamber floor, with the resident melt immediately overlying them; (4) the existence of chromitite layers at the crystal-liquid interface implies their formation through the deposition of chromite alone directly onto the chamber floor; and (5) such crystal deposition requires the resident melt in the chamber to be chromite-only saturated (i.e., no other liquidus phases in the chamber). The occurrence of magmatic dropstones thus rules out the formation of massive chromitites by processes that operate at some depth in the cumulate pile (e.g., kinetic sieving, metasomatic replacement, or sill-like intrusions) and rather indicate their deposition via in situ crystallization from a chromite-only-saturated magma directly on the upward-growing floor of a Bushveld magma chamber. A thorough review of this concept demonstrates its high potential in explaining most field, textural and chemical features of massive chromitites in the Bushveld Complex. [ABSTRACT FROM AUTHOR]

The relationship between mafic magmatic enclaves (MMEs) and host granitoids is ongoing debate due to their significant roles in understanding deep magmatisms and geodynamic processes. This paper reports on Early Palaeozoic granitoids and associated MMEs from the Delingha pluton in the South Qilian Accretionary Belt (NW China) to constrain their petrogenesis and draw implications. The MMEs, occurring as ellipsoidal to rounded shapes, are andesitic and have the same crystallization age (~445 Ma) and mineral assemblage as the host granitoids. However, minor isotopic differences between them and compositional and textural disequilibria on minerals (e.g. plagioclase and amphibole) do not support a cumulate origin that the MMEs were formed at earlier stage of the same magmatic system, but forcefully reflect magma hybridization processes between mafic and felsic magmas, during which the hybridized magma was broken up into discrete enclaves by convective motion in the host felsic magma. Accordingly, the primitive compositions of the MMEs likely originated from metasomatized mantle wedge source, while mantle-derived melt underplated and partially melted the lower continental crust to form the host rocks with a certain mantle contribution. Thus, the Delingha pluton is the product of crust-mantle interaction at an active continental margin subduction setting rather than syn-collisional environment, indicating that subduction of the South Qilian Ocean located between the Central Qilian Block and the Oulongbuluke Block may have lasted till to ~445 Ma. [ABSTRACT FROM AUTHOR]

Syn-exhumation magmatism in collisional orogens is an important process for crustal differentiation and crust-mantle interaction at convergent plate boundaries. It is intriguing to elucidate which factors control the geochemical composition of such magmatic products. To answer this question, a combined study of whole-rock major-trace elements and Nd-Fe isotopes, mineral O isotopes, and zircon U–Pb ages and trace elements was carried out for syn -exhumation granites from the Sulu ultrahigh-pressure (UHP) metamorphic belt in east-central China. Several granitic plutons of Triassic age were newly found in this typical collisional orogen, with a total exposure area of ∼10 km2, suggesting large-scale partial melting of the deeply subducted continental crust in the terminal stage of continental collision. Field observations indicate that the massive granites show little deformation. The granites are high-K calc-alkaline and exhibit enrichment in LILE and LREE but depletion in HFSE relative to HREE in trace element distribution patterns. Zircons in these granites contain relict magmatic cores characterized by steep HREE patterns with strong negative Eu anomalies. These cores show middle Neoproterozoic U-Pb ages of 724–779 Ma, consistent with the protolith age of UHP metaigneous rocks in the Dabie-Sulu orogenic belt. Zircon rims exhibit oscillatory zoning, and are characterized by Triassic U-Pb ages of 210–216 Ma, low LREE contents and steep HREE patterns with significant negative Eu anomalies, suggesting their growth from granitic magmas during exhumation of the deeply subducted continental crust. The granites have low δ18O values of 2.0–6.1‰ for quartz, 1.1–5.2‰ for whole-rock, and 0.9–3.2‰ for zircon cores. The low δ18O values and Neoproterozoic U-Pb ages of zircon cores in the granites are characteristic feature of the deeply subducted continental crust in the northern margin of the South China Block. One coesite inclusion was found in the anatectic zircon rim, pointing to the deep origin of anatectic melts at a subarc depth of >80 km. Whole-rock SiO 2 contents are correlated with major and trace elements, which are ascribed to crystal fractionation of mainly biotite and plagioclase during magma evolution. In particular, these granites exhibit highly variable δ56Fe values from 0.05 to 0.30‰, which are correlated with Fe3+/ΣFe, SiO 2 , Al 2 O 3 , Nb/Ta and Eu/Eu*. This suggests that the crystal fractionation of biotite would have controlled the Fe isotope variation in the granites. Therefore, the syn -exhumation granites experienced significant geochemical differentiation mainly through the fractional crystallization during the magma evolution. A compilation of syn -exhumation granites in the typical collisional orogens of the world shows that such granites were mainly formed through dehydration melting of hydrous minerals during decompressional exhumation. They fall into the magnesian group with relatively low REE and HFSE (like Ti, Nb and Zr) contents, distinct from the geochemical compositions of A-type granites. Therefore, syn -exhumation granites record crustal differentiation in the terminal stage of continental collision. [ABSTRACT FROM AUTHOR]

The existing data on the composition, petrogenesis, magma sources and geodynamic settings of Adakite Magmatism and its input in the formation of the Earth's continental crust as well as its association with the onset of plate tectonics are reviewed and summarized. A vast amount of data have been accumulated over 30-year period from the first use of the term "Adakite Magmatism" in 1990, showing the presence of adakites in numerous sites of both Cenozoic magmatism at the Pacific convergent margins and Mesozoic and Paleozoic magmatic complexes formed in various geodynamic settings. Adakites are represented by different subtypes and are found in spatial and temporal association with specific Nb-enriched basalts and Cu-Au mineralization. The adakites are compared with Precambrian tonalite-trondhjemite-granodiorite (TTG) series showing similarities and differences. Various petrogenetic models of Adakite Magmatism and relevant geodynamic settings are reviewed. This review shows that adakites may be found in a very wide range of geodynamic settings and that the presence of such rocks in magmatic series does not always suggest their origin from partial melting of basalts of subducting oceanic crust. [ABSTRACT FROM AUTHOR]

The geochemistry of major Low Tatra granitic types, namely Prašivá porphyritic Bt (biotite)-granodiorite and Ďumbier Bt-tonalite, indicate their derivation from initial hybrid magmas and represent a mixture among several magma pulses formed via melting of the heterogeneous lower crust. The high K calc-alkaline peraluminous character, along with high Ba, Sr + LREE contents correspond to the partial melting of K-rich mafic and the intermediate hydrated lower crustal source in equilibrium with amphibole or possibly garnet with variable involvement of metasedimentary and/or felsic metaigneous sources. The zircon isotopic age of 360.4 ± 2.7 Ma recorded from diatexite reflects the timing of hightemperature metamorphism of subducted continental crust, and thus corresponds in an initial anatectic process within the present Tatric Unit. The magmatic ages are in the largely overlapping sequence of 353 ± 2 Ma for the Ďumbier tonalite and 352 ± 3 Ma and 351.9 ± 2.9 Ma for Prašivá Aln (allanite bearing)-subtype and Mnz (monazite bearing)-subtypes, which indicate successive multiple emplacement of magma batches and natural evolution towards their more crustal character. Magmatism in the Low Tatra Mts. represents a post-collisional plutonic system related to the slab break-off mechanism described in the close Malá Fatra crystalline basement as well. Heat from mantle upwelling and volatiles from previous subduction forced the melting of the lower crust towards K-rich mafic or intermediate lithologies, as well as during the emplacement of long-lasting melting of felsic metasedimentary crustal sources. The crystalline core of the Low Tatra Mts. is another example of composite granite pluton in the Western Carpathians, which represents a product of the multiphase Late-Variscan post-collisional setting. [ABSTRACT FROM AUTHOR]

The variation of crustal thickness of an orogenic belt through time will provide critical insights into the switch of tectonic setting. The geochemistry of subduction and collision-related magmatism is indicative of the crustal thickness. Late Palaeozoic magmatic products are prevalent in central west Junggar orogenic belt (C-WJOB), and can be employed to determine the temporal changes in crustal thickness as well as the tectonic evolution. Here, we constrain the crustal thickness and discuss the tectonic evolution of C-WJOB through by integrating Sr/Y and La/Yb ratios, zircon U-Pb ages and Hf isotopic compositions of the Late Palaeozoic igneous rocks. Our results show that the crust of C-WJOB was much thinner (20–25 km) than normal continental crust (average at 33 km) in the Early Carboniferous, and began to thicken from 350 Ma to 330 Ma at a slow rate. Crustal thickening was caused by the addition of subduction-related magma sourced from depleted-mantle but with contributions of subducted sediments. The crust started to thicken significantly at ~330 Ma and reached to a maximum thickness of ~40 km between 322 Ma and 310 Ma. The timing of maximum thickness corresponded with the emplacement of calc-alkaline to high-K calc-alkaline I-type dioritic magmas as well as adakitic magma. These magmas were generated by melting of both depleted mantle and juvenile lower crust, which was probably triggered by underplated mantle-derived basaltic magma. Lastly, crustal thinning happened between 310 Ma and 295 Ma due to regional post-collisional extension, although voluminous granitic magmatism occurred. The granitic magmas were formed by remelting of the juvenile lower crust, with a few contribution of mantle material. This study on the variation of crustal thickness in the Late Palaeozoic C-WJOB provides insight into how integrated geochemical and isotopic data can elucidate the complex histories of orogenic belts. [ABSTRACT FROM AUTHOR]

Southernmost Tibet exhibits an anomalously twice the normal thickness of average continental crust. There is no available theory to explain and the driving mechanism remains uncertain. Here, we interpret a north-striking, 180 km-long deep seismic reflection profile traversing the southern Lhasa terrane (SLT) to the central Lhasa terrane (CLT). In addition to reflections showing subducting Indian crust, our results reveal lateral heterogeneity between the SLT and CLT, where north-dipping reflections beneath the CLT outline a tilted crystalline basement, while the non-reflective domain beneath the SLT represents homogeneous juvenile crust. Our integrated analysis leads to models calling upon episodic magmatism onto the southern margin of the basement to result in progressive construction of the SLT. We hypothesize that this crustal thickening via crustal-scale magma accretion contributed to surface uplift of the southern margin of the Tibetan plateau and leading to the development of the vast internal drainage system of Tibet. Mechanism driving continental growth on modern Earth has long been debated. By interpreting the long deep seismic reflection data across the ongoing India-Eurasia collision zone, the authors report crustal-scale magma accretion onto the south of central Lhasa terrane produced net continental growth. [ABSTRACT FROM AUTHOR]

The La Quinta Formation is a Triassic-Jurassic volcano-sedimentary unit exposed in Colombia and Venezuela, that crops out along both flanks of the Serranía del Perijá and in western Mérida Andes. It is composed of reddish mudstones and sandstones interbedded with basaltic-to-rhyolitic lava flows and ignimbrites. This succession is locally intruded by dacitic-rhyolitic hypabyssal bodies, felsic dikes and small monzodioritic intrusions. The volcanism recorded in La Quinta comprises the whole subalkaline compositional spectrum from basaltic andesites-alkali basalts (plagioclase-augite), though andesites-trachyandesites-dacites (plagioclase-augite-ß quartz-amphibole) and rhyolites-alkali rhyolites (ß quartz-sanidine-plagioclase-biotite). Magnetite, ilmenite, hematite, zircon and apatite are recurrent accessory phases and suggest dominant oxidized conditions (+1.2 Ni-NiO to hematite-magnetite buffers) in the magmas. Clinopyroxene and ilmenite-magnetite geothermobarometry suggest an early crystallization of the former (ca. 1120 °C and 4.6 kbar) in the middle portion of a normal-to-thickened continental crust (26-49 km), and later fractionation of the Fe oxides (ca. 720 °C). In addition, some samples exhibit calc-silicate alteration formed of hydrated grossular-andradite, epidote and zeolites in association with possible sediment-hosted stratiform copper occurrences. According to mineralogical and geochemical evidence, these rocks belong to a single comagmatic suite in which differentiation processes were driven by low-pressure fractional crystallization and middle-crustal assimilation. Moreover, these rocks exhibit geochemical features indicative of low degrees of partial melting of a spinel lherzolite (or an enriched source) in a hybrid setting between subduction-related arc and intracontinental rifting. Thus, we propose a mixed tectonic scenario in which subduction of the Farallon plate beneath western South America combined with transtensional tectonics resulting from the break-up of Pangea, generated volcanic activity with an inherited arc-signature behind (landward) the arc axis. [ABSTRACT FROM AUTHOR]

Andesites are iconic of subduction zone magmatism. Yet intermediate magmas (57–66 wt % SiO2) are less abundant than generally thought in arc settings. A comparison of experimental hydrous liquid lines of descent, melt inclusions and bulk-rock compositions demonstrates the importance of polybaric crystallization–differentiation in producing the compositional range and dictating the relative abundance of arc melts, but also highlights the preponderant role of mixing (sensu lato) in producing andesitic magmas. Based on their P2O5 contents, at least 74% of the arc magmas with around 64 wt % SiO2 are inferred to be mixing products. In addition to their surprisingly low abundance, andesitic melt inclusions are characterized by relatively low H2O, Al2O3, ± Na2O contents compared to the ranges measured in mafic and silicic melt inclusions. These compositional characteristics suggest that there is a sweet spot for the production of andesitic melts delimited by the low-pressure stability limit of amphibole (<150 MPa) and the adiabatic ascent path of mafic melts, but that this low-pressure differentiation pathway plays a minor role in the production of silicic arc magmas that principally form along high-pressure hydrous liquid line of descents (>700 MPa) before decompression. The compositional bimodality recorded by the melt inclusions and in well-preserved intra-oceanic arc crustal sections is a fundamental characteristic of differentiation in transcrustal arc magmatic systems, with important consequences for the chemical evolution of the continental crust. We propose that the overall bimodality shown by arc melts does not relate to a compositional gap in the differentiation mechanisms but results from a combination of (1) the disparity in volume of differentiated magmas produced by low and high-pressure crystallization–differentiation and (2) the strong nonlinearity of the high-pressure liquid lines of descent in composition–temperature–crystallinity space related to crystallization of amphibole-rich assemblages. In this context, the compositional characteristics shared by andesitic magmas and the continental crust principally depict the central role of mixing and mass balance processes in producing andesitic compositions. The step in differentiation efficiency encountered by hydrous magmas entering the amphibole stability field at high pressure plays an important role in defining the silicic component involved in these scenarios. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of magma emplacement of the intruded zoned pluton, we report high-precision Ca isotopic data of 23 granitoids (including granodiorite and quartz diorite), 5 mafic enclaves, and 7 hornblende and plagioclase mineral pairs from the Early Cretaceous Fangshan pluton, Beijing, China. Δ44/40Ca Hbl-Pl of rocks span from 0.02 ± 0.15‰ to 0.23 ± 0.12‰, which likely reflects equilibrium inter-mineral isotope fractionation. The granodiorites exhibit ∼0.30‰ variation in Ca isotopic compositions, with δ44/40Ca ranging from 0.47 ± 0.08‰ to 0.77 ± 0.09‰. The diorites and the enclaves yield δ44/40Ca of 0.51 ± 0.03‰ to 0.64 ± 0.05‰, and 0.54 ± 0.06‰ to 0.66 ± 0.11‰, respectively, which are lower than that of the upper continental crust (0.72 ± 0.10‰). Ca isotopic variation cannot be ascribed to K decay due to their low ε Ca values (< ±1.0). Theoretical study showed that Hbl fractional crystallization could counteract Ca isotope fractionation effect of their co-existing Pl crystallization. Source heterogeneity cannot account for Ca isotopic variation because δ44/40Ca does not correlate to (87Sr/86Sr) i. Instead, the Ca isotopic variation is likely controlled by partial melting and residual mineralogy. Specifically, δ44/40Ca of the granodiorites are negatively correlated with (Dy/Yb) N , reflecting various magma pools derived from different crustal depths with clinopyroxene and garnet residua. Modeling calculations suggest that the low Ca isotopic signature can be caused by ∼10% partial melting of sources with various proportions of garnet and clinopyroxene (from 5% garnet + 95% clinopyroxene to 40% garnet + 60% clinopyroxene). The diorites intruded earlier than the granodiorites, which can be slightly contaminated by surrounding basement rock. Ca isotopic compositions of enclaves are similar to those of their host rocks. Considering the spatial structure of the Fangshan pluton, it should be assembled by at least four magma pulses derived from various crustal depths through ballooning. Our results show that Ca isotopes can be used as a potential tool to trace magma source depth and decipher the process of magma emplacement of intrusive pluton, which is important to understand the continental crustal growth. [ABSTRACT FROM AUTHOR]

• The Hotaka-Takidani volcano-plutonic complex is a felsic magmatic system. • The complex was long-lived (1.5 Myr) and sourced from a 15 km-thick reservoir. • The reservoir was built by a low long-term average magma flux (6 × 10−6 km3*km−2*yr−1). • A first episode of extraction led to the eruption of the 400 km3 Nyukawa dacite. • A threefold increase of the magma flux led to the emplacement of the pluton. Defining the physico-chemical evolution of felsic magmatic reservoirs in the middle-upper continental crust is crucial for understanding the connection between granitic plutons and silicic volcanic rocks and for research on the trigger mechanisms of volcanic eruptions. In this study, we investigate the formation and evolution of the Hotaka-Takidani volcano-plutonic complex (Japan) using a comprehensive approach that integrates zircon petrochronology with phase-equilibria and thermal modelling. The Takidani pluton is a Pleistocene tilted zoned intrusion of granodiorite-granite composition associated with at least two large caldera-forming eruptions. We have investigated the three uppermost units of the pluton and the oldest and more voluminous Nyukawa eruption, which deposited more than 400 km3 (DRE, dense rock equivalent) of crystal-rich dacitic ignimbrite. Amphibole thermobarometry, U-Pb zircon dates and geochemical data indicate that the Takidani pluton and the Nyukawa dacite were sequentially sourced from a 10–12 km-thick long-lived magmatic reservoir in the middle crust. Thermal evolution of the reservoir led to the extraction of the Nyukawa magma, followed by brief storage in the upper crust and eruption at ca. 1.706 ± 0.091 Ma. For two of the units of the pluton, we combine high-spatial resolution zircon U-Pb geochronology with zircon chemical data. Applying the Ti-in-zircon thermometer, we observe that magma within the reservoir was stored at a relatively constant temperature of ca. 700 °C for 300 kyr and subsequently, starting from 1.4 Ma, the temperature increased progressively reaching 820–850 °C at 1.1 Ma. This temperature shift is inconsistent with a constant magma flux and suggests an increase of the magma injection rate into the reservoir. Using the distribution of zircon ages and thermal simulations, we determined that the reservoir was built by a fairly low average magma flux of ca. 6 × 10−6 km3*km−2*yr−1, shifting to a magma supply rate which is three to four times higher during the last 300 ka of zircon crystallisation. This increase in magma flux caused the final emplacement of the Takidani magma in the upper crust, where it rapidly crystallized. The integration of geochronological data with phase-equilibria and thermo-chemical modelling demonstrates that multiple melt extraction events occurred during the evolution of the Hotaka-Takidani magmatic system. Only the first one triggered a major eruption, while subsequent events resulted in the emplacement of the Takidani pluton in the shallow crust. [ABSTRACT FROM AUTHOR]

The Charcas Intrusive Complex (CIC), comprised of monzogranites and granodiorites is located at the eastern edge of the Mesa Central in México. The CIC was dated by U/Pb on zircon crystals, from Tithonian to Rupelian ages and three distinct magmatic pulses were identified: (1) Tithonian (∼150 Ma), (3) Ypresian to Lutetian (∼55–∼44 Ma), and (3) Rupelian (∼30–∼27 Ma). The Early Cretaceous to Lutetian major and trace element magma compositions, suggest that the arc monzogranites were emplaced in a growing continental crust while the Ypresian granodiorites show typical boron enrichment observed in central Mexico. The Lutetian and Rupelian granodiorites plot inside the field of cordilleran granites or continental arc magmatism where magma mixing is common and are considered as I-type granites presenting high concentration of Ba and Sr, and high Sr/Y and La/Yb ratio values. The most developed and intensely mineralized (Zn–Pb) hydrothermal event is Lutetian in age, corresponding to the peak of magma fertility conditions determined by zircon trace element chemistry and is well correlated to the skarn occurrences at around ∼47 Ma. The Ag mineralization event is related to the Rupelian dike's emplacement. Inherited zircon grains found in the magmas highlight the shallow position of the magma plumbing and the importance of the early Cretaceous magmatic intrusion in the formation of the Rupelian silver mineralization. • The Charcas Intrusive Complex present a long magmatic history from Tithonian to Ruplian • The Charcas Intrusive Complex show the complexity of swarm dyke emplacement and how punctal are the mineralized events. • Zircon crystal magmatic fertility proxy are in good agreement with the mineralization event observed. • Inherited zircon found in the latest magmatic events illustrate the shallow crust growth and the importance of magma recycling. • Ypresian magmatism boron enrichment point out the moment of subduction decoupling and continental extension beginning. [ABSTRACT FROM AUTHOR]

The classical paradigm of the 'big magma tank' chambers in which the melt differentiates, is replenished, and occasionally feeds the overlying volcanos has recently been challenged on various grounds. An alternative school of thought is that such large, long-lived and largely molten magma chambers are transient to non-existent in Earth's history. Our study of stratiform chromitites in the Bushveld Complex—the largest magmatic body in the Earth's continental crust—tells, however, a different story. Several chromitites in this complex occur as layers up to 2 m in thickness and more than 400 kms in lateral extent, implying that chromitite-forming events were chamber-wide phenomena. Field relations and microtextural data, specifically the relationship of 3D coordination number, porosity and grain size, indicate that the chromitites grew as a 3D framework of touching chromite grains directly at the chamber floor from a basaltic melt saturated in chromite only. Mass-balance estimates imply that a few km thick column of this melt is required to form each of these chromitite layers. Therefore, an enormous volume of melt appears to have been involved in the generation of all the Bushveld chromitite layers, with half of this melt being expelled from the magma chamber. We suggest that the existence of thick and laterally extensive chromitite layers in the Bushveld and other layered intrusions supports the classical paradigm of big, albeit rare, 'magma tank' chambers. [ABSTRACT FROM AUTHOR]

A zircon with an age of ~2.9 Ga, much older than all existing dates, has been discovered for the first time in basalts of the Afanasy Nikitin Rise. Such an ancient age is typical of continental crust rocks of Western Hindustan or Antarctica. Analyses have revealed the geochemical similarity of magmas of the Conrad and Afanasy Nikitin rises and their difference from Crozet Rise magmas owing to their different formation conditions. Emplacement of the Conrad and Afanasy Nikitin rises occurred ~80–90 Ma ago under the influence of the same Conrad hotspot near the spreading Indian–Antarctic Ridge. This hotspot is a satellite of the giant Kerguelen Plume, active in the Eastern Indian Ocean from 130 Ma ago to the present. The plume formed the Ninetyeast Ridge in the ancient spreading center, and plume magmas leaked along the spreading zone up to the formation area of the Conrad and Afanasy Nikitin rises. During interaction of the Kerguelen Plume with the spreading zone and transform faults, nonspreading blocks of the ancient continental lithosphere of the Gondwana may have been preserved. [ABSTRACT FROM AUTHOR]