Zircon Trace Element Research Articles

Machine Learning Could Revolutionize Mineral Exploration

Using a global data set of zircon trace elements, new research demonstrates the power of machine learning algorithms to accurately identify and locate porphyry copper deposits.

Formation of Late Paleoproterozoic Gaositai Hornblendite in Northern North China Craton: Evidence from Zircon U-Pb Isotopes and Amphibole Trace Elements

Paleoproterozoic tectonic evolution of the northern North China Craton has been a hot research topic. We firstly identified a 1.85 Ga hornblendite from the Gaositai mafic–ultramafic complex, in northern Hebei. Systematic studies of petrology, zircon U-Pb geochronology, and in situ mineral major and trace elements of hornblendite are the key to revealing the petrogenesis of the Paleoproterozoic ultramafic rock and the tectonic evolution of northern North China Craton. LA-ICP-MS zircon U-Pb dating suggests the Gaositai hornblendite formed at 1851 ± 44 Ma. The late Paleoproterozoic ultramafic rocks, together with coeval post-collisional granites, formed a bimodal igneous assemblage. Both hornblende and its equilibrium melt compositions show strongly fractionated HREE patterns, relative enrichments in LREEs and LILEs, and depletions in HREEs and HFSEs. The phlogopite-bearing hornblendite magma could have originated from a hydrous garnet-facies mantle source metasomatized by slab-derived silicate melt. Furthermore, the variations of major and trace elements in hornblende from core to rim also reveal the mineral fractional crystallization and magma recharge. Zircon trace elements, melt composition equilibrium with hornblendes, and the bimodal igneous assemblage suggest that the generation of the Gaositai Paleoproterozoic hornblendite was likely the product of post-collisional extension related to the collision between eastern and western North China blocks.

Volcano-pluton connections at the Lake City magmatic center (Colorado, USA)

Abstract Exposed at the Lake City caldera (Colorado, USA) is the ca. 23 Ma reversely stratified (rhyolite to trachyte) Sunshine Peak Tuff and post-collapse syenite and monzonite resurgent intrusions. Existing models for this system suggest that the rhyolites are related to the trachyte and resurgent syenite through fractional crystallization, separation, and remobilization (crystal mush model), and that multiple magma batches were involved in the system (Hon, 1987; Kennedy et al., 2016; Lubbers et al., 2020). We use U-Pb zircon CA-ID-TIMS-TEA and zircon trace-element modeling to further probe age and geochemical relationships between the extrusive and intrusive units. Zircon ages and compositions from the erupted units and the syenite overlap, suggesting these magmas were related and may have mixed prior to eruption. Results from the monzonite suggest it was a contemporaneous but distinct magma batch that mixed with parts of the larger system. Trends in zircon geochemistry are decoupled from time, reflecting a complex history of accessory mineral saturation and mixing of magma batches, and a distinct high-Hf population of zircon grains hints at the existence of an additional, independent batch of rhyolitic magma in the system. The new ages we present shorten the lifetime of the Lake City magmatic system from 80 to 300 k.y. (Bove et al., 2001) to 60 to 220 k.y. and suggest the high-silica rhyolite magma crystallized over a minimum of ~160 k.y. This latter timescale likely reflects a protracted history that includes differentiation of a parent melt prior to extraction of eruptible high-silica rhyolite magma.

Extensional Setting of Hainan Island in Mesoproterozoic: Evidence from Granitic Intrusions in the Baoban Group

AbstractThe Mesoproterozoic Baoban Group is the oldest basement in Hainan Island and has played an important role in Columbia (Nuna) supercontinent reconstructions. The Mesoproterozoic granitic intrusions in the Baoban Group are the most widely‐exposed Precambrian magmatic rocks and are the key to understanding the tectonic settings of Hainan Island and its relationship with the South China Block and the Columbia supercontinent. New LA‐ICP‐MS zircon U‐Pb dating on three mylonitic granite samples from the Tuwaishan and Baoban areas yield ages ranging from 1447 Ma to 1437 Ma, representing the absolute timing of the emplacement of the granitic intrusions. Combined with previously published geochronological data for rocks from the Baoban Group and regional mafic intrusions, it is concluded that the Baoban Group formed at 1460–1430 Ma, coeval with the emplacement of the granitic and mafic intrusions. New in‐situ zircon Lu‐Hf isotope analyses for the three mylonitic granite samples yielded positive ∊Hf(t) values, ranging from +0.49 to +8.27, with model ages () ranging from 2181 Ma to 1687 Ma, suggesting that the granitic intrusions originated from a mixed source of Paleoproterozoic crust with juvenile crust. New zircon trace element data show characteristics of high Th/U values of 0.24–1.50, steep slopes from LREE to HREE and negative Pr, Eu anomalies with positive Ce, Sm anomalies, representing typical magmatic zircons formed in continental crust. Compared with available magmatic and detrital zircon ages from Precambrian rocks in the Cathaysia Block, Yangtze Block and western Laurentia, it is inferred that Hainan Island was separated from both the Cathaysia Block and the Yangtze Block, instead being connected with western Laurentia in the Columbia supercontinent. Considering the decreasing tendency of basin deposition time along the western margin of Laurentia, it is proposed that Hainan Island was located to the north or northwest of the Belt‐Purcell Supergroup, along the western margin of Laurentia, during the breakup of the Columbia supercontinent.

Multi‐episodic formation of baddeleyite and zircon in polymetamorphic anorthosite and rutile‐bearing ilmenitite from the Chiapas Massif Complex, Mexico

AbstractMassif‐type anorthosite and comagmatic associations of rutile‐bearing ilmenitite (RBI) and oxide‐apatite‐rich amphibolite (OARA) from the Chiapas Massif Complex (CMC) in southeastern Mexico display a protracted billion‐year accessory mineral record encompassing magmatic crystallization at c. 1.0 Ga to recent ductile shear deformation at c. 3.0 Ma. Multiple discrete zircon populations between these age end‐members resulted from neoformation/recrystallization during local to regional metamorphism that affected the southeastern portion of the CMC. The ubiquitous presence of relict baddeleyite (ZrO2), along with various zircon generations spatially associated with pristine to partly retrogressed Zr‐bearing igneous and metamorphic minerals (e.g., ilmenite, rutile, högbomite and garnet), suggests significant Zr diffusive re‐equilibration (exsolution) during slow cooling and mineral breakdown followed by crystallization of baddeleyite. The subsequent transformation of baddeleyite into zircon was likely driven by reaction with Si‐bearing fluids in several geochronologically identified metamorphic stages. Strikingly contrasting compositional signatures in coeval zircon from anorthosite (silicate‐dominated) and comagmatic RBI (Ti‐Fe‐oxide‐dominated) indicate a major role of fluids locally equilibrating with the rock matrix, as indicated by distinct zircon trace element and oxygen isotopic compositions. A high‐grade metamorphic event at c. 950 Ma is likely responsible for the formation of coarse‐grained rutile (~0.1–10 mm in diameter), srilankite, zircon and garnet with rutile inclusions as well as metamorphic högbomite surrounding Fe‐Mg spinel. Zr‐in‐rutile minimum temperatures suggest >730°C for this event, which may correlate to rutile‐forming granulite facies metamorphism in other Grenvillian‐aged basement rocks in Mexico and northern South America. A younger generation of baddeleyite exsolution occurred during post‐peak cooling of coarse‐grained rutile, reflected in rimward Zr depletion and formation of discontinuous baddeleyite coronas. Baddeleyite around rutile was then transformed into zircon possibly during subsequent metamorphism at c. 920 or 620 Ma, resulting from syn‐kinematic and contact metamorphism, respectively. Regional metamorphism at c. 450 and 250 Ma extensively overprinted the existing zircon population, especially during the Triassic event, as suggested by a significant presence of zircon with this age. Nearly pristine baddeleyite occurring interstitial to ilmenite yielded an isochron age of c. 232 Ma according to in situ U–Pb secondary ion mass spectrometry (SIMS), suggesting either formation during metamorphic peak conditions or post‐peak cooling. Zircon with ages of c. 80–100 Ma in anorthosite is identified for the first time within the CMC and coincides with cooling ages of c. 100 Ma for coarse‐grained rutile. This age is similar to those of rocks occurring ~200 km further to the east in Guatemala, which are also bounded to the Polochic fault system but overprinted by eclogite facies metamorphism. A high‐pressure event in the southern CMC after 200 Ma, however, is presently unsupported. Although the abundance of rutile and ilmenite is unusually high in the CMC anorthosite assemblage compared with common igneous rocks, the reactions documented here nonetheless stress the importance of these phases for generating Zr‐bearing accessory minerals over a wide range of metamorphic conditions.

Pluton incremental growth by multi-stage magma pulsations: Evidence from the Fangshan pluton, North China Craton

The Fangshan intrusive suite is a composite pluton in the North China Craton that resulted from incremental assembly of small magma batches. The pluton consists of four intrusive units with abundant mafic enclaves. Here we clarify its crystallisation history through zircon UPb dating, which indicates prolonged crystallisation of each intrusive unit at upper-crustal levels between 132.5 and 128.7 Ma. The magmas were episodically extracted from a deep storage area and ascended to the final intrusion level at a palaeo-depth of 10–16 km. Zircon trace element and Hf isotopic compositions and Ti-in-zircon temperature of the four intrusive units and mafic enclaves show significant differences and suggest that their crystallisation occurred in isotopically and chemically diverse magma batches. These magma batches formed in the lower crust from the mingling and mixing of various proportions of residual melts, derived from the fractional crystallisation of mafic magmas, with crustal partial melts at high temperatures. Four type of zircons were observed in mafic enclaves based on a simple textural classification, including antecrysts (type 1), xenocrysts (type 2 and type 3), and recrystallised zircon (type 4). Type 1 zircons were not formed at the emplacement level and are “antecrystic”, having formed at a deeper, hotter level and been entrained into the ascending melts. Most type 2 zircons were captured from coarse-grained monzonite, and a very small number of grains were sourced from porphyritic granodiorite. Type 3 zircons display a core-rim texture, illustrating that xenocrysts may successively grow in mafic melts. Type 4 zircons display patchy zoning that represents a disequilibrium texture, manifested by the replacement of U–Th–REE-rich zircon by U–Th–REE-poor zircon, which occurred in response to magma mixing between mafic and felsic melts. This study shows that zircon chemistry coupled with detailed textural analyses can provide a powerful tool to elucidate the complex evolution of a magmatic system.

Zircon geochronological and geochemical insights into pluton building and volcanic-hypabyssal-plutonic connections: Oki-Dōzen, Sea of Japan—A complex intraplate alkaline volcano

Abstract The relationship between plutonic and volcanic components of magmatic plumbing systems continues to be a question of intense debate. The Oki-Dōzen Islands, Sea of Japan, preserve outcrops of temporally associated plutonic, hypabyssal, and volcanic rocks. Post-intrusion uplift juxtaposed Miocene syenites in inferred faulted contact with volcanic trachytes that are cut by rhyolite hypabyssal dikes. This provides a window deep into the timing and origins of magma storage architecture and dynamics. Zircon is ubiquitous in all samples; our aim is to determine what its age and composition can reveal about the plutonic-volcanic connection. Here we show magma source characteristics are recorded in zircon Hf isotopes; source composition and assimilation of heterogeneous hydrothermally altered crust in zircon O isotopes; and extensive fractional crystallization in zircon trace elements. Combined with new UTh-Pb SHRIMP zircon ages, 6.4–5.7 Ma, compositional data show pluton formation was by protracted amalgamation of discrete magma pulses. The rhyolite dike preserves an evolved fraction segregated from these discrete magmas. Synchronous with plutonism was a volcanic eruption of trachyte magma derived from the same source, which may have stalled at a relatively shallow depth prior to eruption. Stalling occurred at least above the amphibole stability zone because amphibole-compatible Sc and Ti were not depleted in the trachyte melt resulting in elevated values of these in volcanic compared to plutonic zircon. Identifying smaller episodic magma pulses in a larger magmatic complex places constraints on potential magma fluxes and eruptible volumes. High-flux, large volume, plume-related ocean island magmatic systems may have extensive vertically distributed multi-stage magmatic reservoirs and subduction-related systems transcrustal magma reservoirs. By contrast, Oki-Dōzen was a low-flux system with incremental pluton growth and small- to moderate-scale eruptions.

Mesoproterozoic accretionary orogenesis: Evidence from ∼ 1.4 Ga metamorphism on the southeastern margin of the North China Craton

The Mesoproterozoic period has always been thought of as an orogenic quiescence stage. However, contemporaneous magmatism and metamorphism indicate that this period was relatively restless. A Mesoproterozoic metamorphic event (~1.4 Ga) was first discovered in the southeastern part of the North China Craton. Samples, including garnet amphibolite and its countryrock biotite plagiogneiss, were collected from Rushan city on the Jiaodong Peninsula. The major elements of the rock are characterized by high Ti, where the trace elements show slight depletions in Th, U and Sr contents, and the REEs show E-MORB like patterns. The mineral assemblage of the garnet amphibolite includes garnet, hornblende and plagioclase. These metamorphic minerals are also found in zircons as inclusions. Cloudy and homogeneous CL images and flat HREE patterns of zircon trace elements in garnet amphibolite indicate a metamorphic origin, and zircon U-Pb age dating obtained an ∼ 1.4 Ga metamorphic age, which is consistent with the second age group age of the countryrock. Our dating results suggest that the Meoproterozoic metamorphic event in the North China Craton is comparable to metamorphic events reported in the Laurentian and Australian Cratons. Similar magmatism and comparable stratigraphy of these ancient cratons also support the Mesoproterozoic era was not an orogenic quiescence stage. Therefore, we infer a giant orogenic belt that existed along the outer margin of the supercontinent of the Columbia in the Earth’s middle age. Long-lived Mesoproterozoic accretionary orogenesis probably affected the edges of supercontinents in a transition stage from the breakup of Columbia to the assembly of Rodinia.

Crustal growth/reworking and stabilization of the western Superior Province: Insights from a Neoarchean gneiss complex of the Winnipeg River terrane

AbstractLong-term stability of the continental lithosphere is attained through a cumulative increase in net buoyancy and rigidity due to progressive compositional differentiation (i.e., cratonization). As stable cratons provided the nucleus for the subsequent accretionary growth and tectono-magmatic reworking that produced modern continental crust, the geodynamic processes that facilitated the stabilization of cratons are critical for understanding the evolution of Earth’s lithosphere. This study uses a portion of the Winnipeg River terrane, one of the oldest terranes of the western Superior Province, as a natural laboratory to investigate Archean crustal growth (partial melting of mantle) and reworking (partial melting of crust) and provides insights into the geodynamic processes driving mantle depletion and crustal remelting. Zircon U-Pb data obtained by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) from an extensive Winnipeg River terrane gneiss complex reveal six major magmatic events at ca. 3060 Ma, 2930–2920 Ma, ca. 2910 Ma, 2830–2800 Ma, 2735–2730 Ma, and ca. 2700 Ma and regional metamorphism at ca. 2900 Ma. Whole-rock geochemistry and zircon Lu-Hf and trace element data indicate that (1) the magmatism at ca. 3060 Ma and ca. 2930–2920 Ma represents reworking of the isotopically evolved components of the incipient Winnipeg River terrane at shallow depths, (2) the ca. 2910 Ma magmatism features a step-change of Hf isotopic compositions from subchondritic to suprachondritic and records the formation of new juvenile magmas and the first reworking of existing juvenile crust, and (3) the magmatism after ca. 2830 Ma largely reflects reworking of the juvenile components of the incipient Winnipeg River terrane at medium to shallow depths prior to the ca. 2700 Ma trans-crustal magmatism associated with the convergence of the Winnipeg River terrane and western Wabigoon terrane. Juvenile magmatism and crustal growth in the Winnipeg River terrane at ca. 2910 Ma are inferred to correspond with significant mantle depletion below the Winnipeg River terrane, which led to a more stable lithospheric mantle in this part of the western Superior Province. Zircon trace element data support a mantle upwelling model rather than lithosphere recycling models for the depletion of mantle at ca. 2910 Ma. This study suggests that crustal growth and mantle depletion bracketed by prolonged, episodic crustal reworking may be a fundamental characteristic of the cratonization process.

Connected volcanic and plutonic association by crystal-melt segregation in the Daiyunshan volcanic field, SE China

The Daiyunshan volcanic field is one of the largest volcanic fields in the volcanic-plutonic complex belt along the coast of SE China, which records a long volcanic activity history from the Late Jurassic to the Late Cretaceous. In this paper, we conduct comprehensive petrological, geochemical, isotopic and zircon trace element analyses for two representative calderas (Shiniushan and Yunshan) to reveal the crystal-melt segregation and magma recharge processes of the Daiyunshan volcanic field. Systematic LA-ICP-MS zircon U-Pb dating and isotope analyses reveal that the porphyritic quartz monzonite, porphyritic granite and rhyolite of the Shiniushan caldera have identical crystallization ages (97–94 Ma) and consistent Nd-Hf isotope compositions [εNd(t) = −3.6 to −2.8; zircon εHf(t) = −2.7 to 1.8], which are consistent with those of the porphyritic quartz monzonite and rhyolites in the nearby Yunshan caldera, indicating that the magmas of the two calderas were derived from a common magma source region. Volcanic-plutonic rocks from two calderas display metaluminous to peraluminous features and have low MgO, FeOT, Ni and Cr contents. We thus suggest that their parental magmas were derived by remelting of pre-existing crust with contributions of juvenile components. The Shiniushan porphyritic granite and rhyolite and the Yunshan rhyolites are characterized by distinctly negative Eu anomalies and depletions of Ba, Sr, P and Ti, while the porphyritic quartz monzonites from both calderas show complementary geochemical signatures, such as positive Ba anomalies and neglectable Eu anomalies. The back-scattered electron (BSE) images and energy-dispersive X-ray spectrometry (EDS) phase mapping of the Shiniushan porphyritic quartz monzonite reveal textural indicators of crystal accumulation, such as imbrication and synneusis of plagioclase phenocrysts. Their interstitial assemblages of K-feldspar, quartz and plagioclase commonly resemble the phenocryst assemblages of porphyritic granite. We believe that the Shiniushan porphyritic granite and rhyolite and Yunshan rhyolites represent extracted melts from the mush reservoir, while porphyritic quartz monzonites in both calderas are inherent cumulates that have lost interstitial melts. Therefore, our study shows that the Late Cretaceous volcanic-plutonic rocks in the Daiyunshan volcanic field should be connected by crystal-melt segregation processes. Furthermore, a typical zigzag variation in zircon εHf(t) values is shown by the Late Jurassic to Late Cretaceous volcanic-plutonic rocks from the Daiyunshan volcanic field, indicating variable contributions of asthenospheric mantle-derived melts and the multistage slab rollback of the subducting paleo-Pacific plate beneath SE China.

A juvenile Paleozoic ocean floor origin for eastern Stikinia, Canadian Cordillera

Abstract The Cordillera of Canada and Alaska is a type example of an accretionary orogen, but the origin of some terranes remains contentious (e.g., Stikinia of British Columbia and Yukon, Canada). Presented herein are igneous and detrital zircon U/Pb-Hf and trace-element data, as well as the first radio larian ages from the Asitka Group, the basement to eastern Stikinia. The data are used to evaluate the role of juvenile and ancient crust in the evolution of Stikinia and the tectonic environment of magmatism. Two rhyolites are dated by U-Pb zircon at 288.64 ± 0.21 Ma and 293.89 ± 0.31 Ma, with εHf(t) = +10. Red chert contains radiolarians that are correlated with P. scalprata m. rhombothoracata + Ruzhencevispongus uralicus assemblages (Artinskian–Kungurian). Detrital zircon U/Pb-Hf from a rare Asitka Group sandstone have a mode at ca. 320 Ma and εHf(t) +10 to +16; the detrital zircon suite includes five Paleoproterozoic zircons (~5% of the population). Detrital zircons from a stratigraphically over lying Hazelton Group (Telkwa Formation) volcanic sandstone indicate deposition at ca. 196 Ma with zircon εHf(t) that are on a crustal evolution line anchored from the Asitka Group. Zircon trace-element data indicate that the Carboniferous detrital zircons formed in an ocean arc environment. The Proterozoic detrital zircons were derived from a peripheral landmass, but there is no zircon εHf(t) evidence that such a land-mass played any role in the magmatic evolution of eastern Stikinia. The data support that eastern Stikinia formed on Paleozoic ocean floor during the Carboniferous to early Permian. Consistent with previous fossil modeling, zircon statistical comparisons demonstrate that Stikinia and Wrangellia were related terranes during the Carboniferous to Permian, and they evolved separately from Yukon-Tanana terrane and cratonic North America.

Tourmaline and zircon trace the nature and timing of magmatic-hydrothermal episodes in granite-related Sn mineralization: Insights from the Libata Sn ore field

AbstractThe Bin Yauri-Libata polymetallic ore district is a Sn and Au ore-bearing district in the Zuru schist belt, Northwestern Nigeria. The Libata Sn ore field is characterized by a set of cassiterite-bearing hydrothermal veins associated with Neoproterozoic Pan-African granites affected by deformation and low-grade metamorphism. The hydrothermal alteration associated with cassiterite-bearing quartz veins in the Libata deposit includes silicification, albitization, chloritization, and potassic alteration. In this study, geochemical and geochronological data from tourmalines and zircons from Sn-bearing lodes, unmineralized and altered granites is applied to reveal the timing, fluid composition, and source of ore-forming materials for tin mineralization in the Libata ore field. Zircon trace element and Hf isotopes [εHf(t) = +4.37 to +10.85] reveal a mantle-derived source with some crustal contribution for the melts forming the Libata Sn-bearing granites. LA-ICP-MS zircon U-Pb dating constrains the magmatic and hydrothermal ages to 650–646 and 649–646 Ma for the Libata granites. Overlapping zircon εHf(t) and 176Hf/177Hf but distinct 176Lu/177Hf and 176Yb/177Hf ratios from magmatic and hydrothermally altered zircons reveal a magmatic source for the hydrothermal fluids which triggered cassiterite deposition in the Libata ore field. Major element chemistry constrain tourmalines from the Libata ore field as schorls that show high alkalis, low-Ca contents, and moderate ☐ values (where ☐ is x-site vacancy). High Li, Zn, and Sn concentrations in tourmaline as well as Li/Sr and Ca-Fe-Mg ratios demonstrate that the tourmaline formed from granite-sourced fluid likely derived from the host Libata granites. Measured δ11B values from the Libata tourmaline range from –15.7‰ to –14.1‰. The δ11B of the mineralizing fluid is estimated to be –13.1 to –11.9‰ for the Libata tourmalines at 400–500 °C and overlaps with averages from fractionated granites worldwide. Therefore, our data show that tourmaline and zircon are useful tracers of magmatic-hydrothermal evolution in rare-metal-bearing granite systems.

Oceanic Zircon Records Extreme Fractional Crystallization of MORB to Rhyolite on the Alarcon Rise Mid-Ocean Ridge

Abstract The first known occurrence of rhyolite along the submarine segments of the mid-ocean ridge (MOR) system was discovered on Alarcon Rise, the northernmost segment of the East Pacific Rise (EPR), by the Monterey Bay Aquarium Research Institute in 2012. Zircon trace element and Hf and O isotope patterns indicate that the rhyolite formed by extreme crystal fractionation of primary mid-ocean ridge basalt (MORB) sourced from normal to enriched MOR mantle with little to no addition of continental lithosphere or hydrated oceanic crust. A large range in zircon ɛHf spanning 11 ɛ units is comparable to the range of whole rock ɛHf from the entire EPR. This variability is comparable to continental granitoids that develop over long periods of time from multiple sources. Zircon geochronology from Alarcon Rise suggests that at least 20 kyr was needed for rhyolite petrogenesis. Grain-scale textural discontinuities and trace element trends from zircon cores and rims are consistent with crystal fractionation from a MORB magma with possible perturbations associated with mixing or replenishment events. Comparison of whole rock and zircon oxygen isotopes with modeled fractionation and zircon-melt patterns suggests that, after they formed, rhyolite magmas entrained hydrated mafic crust from conduit walls during ascent and/or were hydrated by seawater in the vent during eruption. These data do not support a model where rhyolites formed directly from partial melts of hydrated oceanic crust or do they require assimilation of such crust during fractional crystallization, both models being commonly invoked for the formation of oceanic plagiogranites and dacites. A spatial association of highly evolved lavas (rhyolites) with an increased number of fault scarps on the northern Alarcon Rise might suggest that low magma flux for ~20 kyr facilitated extended magma residence necessary to generate rhyolite from MORB.

Direct dating of podiform Chromitite: U-Pb (Zircon, Rutile) and 40Ar/39Ar (Pargasite) evidence from Tiébaghi Cr deposit (New Caledonia)

Dominantly Mesozoic to Proterozoic xenocrystic zircons extracted from Tiébaghi chromitite coexist with a well-defined population (30%) of Eocene magmatic grains (U-Pb: 48.2 ± 1.1 Ma). Since Eocene zircons are absent in the peridotite host rock and are accompanied by rare rutiles with the same age range, it is suggested that both are derived from the circulating melt from which the chromite ore was generated. This hypothesis is strengthened by a similar 40Ar/39Ar age of 46 ± 2 Ma on amphibole that is closely associated with chromitite. These data confirm the Eocene age and supra-subduction setting of the Tiébaghi podiform chromitite, which thus was formed by interaction of peridotite and mafic melt in the final stage of the forearc magmatic event that occurred between 55 Ma and 47 Ma. Modelling the melt associated with chromite formation using zircon trace-elements and REE-zircon partitioning coefficients suggests forearc basalt as a likely candidate and the felsic by-product of peridotite-melt interaction a source for early Eocene magmatic zircons.

Correction to: Zircon Trace Element and O-Hf Isotope Analyses of Mineralized Intrusions from El Teniente Ore Deposit, Chilean Andes: Constraints on the Source and Magmatic Evolution of Porphyry Cu-Mo Related Magmas

Correction to: Zircon Trace Element and O-Hf Isotope Analyses of Mineralized Intrusions from El Teniente Ore Deposit, Chilean Andes: Constraints on the Source and Magmatic Evolution of Porphyry Cu-Mo Related Magmas

Destabilization of Long‐Lived Hadean Protocrust and the Onset of Pervasive Hydrous Melting at 3.8 Ga

AbstractThe nature of Earth's earliest crust and crustal processes remain unresolved questions in Precambrian geology. While some hypotheses suggest that plate tectonics began in the Hadean, others suggest that the Hadean was characterized by long‐lived protocrust and an absence of significant plate tectonic processes. Recently proposed trace‐element proxies for the tectono‐magmatic settings in which zircons formed are a relatively novel tool to understand crustal processes in the past. Here, we present high‐spatial resolution zircon trace and rare earth element geochemical data along with Hf and O isotope data of a new location with Hadean materials, 4.1–3.3 Ga detrital zircons from the 3.31 Ga Green Sandstone Bed, Barberton Greenstone Belt. Together, the hafnium isotope and trace element geochemistry of the detrital zircons record a major transition in crustal processes. Zircons older than 3.8 Ga show evidence for isolated, long‐lived protocrust derived by reworking of relatively undepleted mantle sources with limited remelting of surface‐altered material. After 3.8 Ga, Hf isotopic evidence for this protocrust is muted while relatively juvenile source components for the zircon's parental magmas and flux‐like melting signatures become more prominent. This shift mirrors changes in Hf isotopes and trace element geochemistry in other Archean terranes between ∼3.8 and 3.6 Ga and supports the notion that the global onset of pervasive crustal instability and recycling—A possible sign for mobile‐lid tectonics—Occurred in that time period.

Pleistocene volcanism along the margins of the Canal de Ballenas transform fault, Gulf of California

Pleistocene subaerial volcanism along the margins of the Ballenas Channel, northern Gulf of California, is represented by two morphologically young dacite dome complexes exposed at the opposite edges of sheared continental crust: Isla Coronado in coastal Baja California, and the Lobera volcanic complex in west-central Isla Ángel de la Guarda. Single crystal zircon U-Pb crystallization ages of Coronado and Lobera volcanoes range between ca. 250 and 1000 ka, indicating maximum ages for the eruptions. Eruption ages are directly constrained by an 40Ar/39Ar whole-rock age of 692 ± 164 ka for one of the lava units in the Lobera volcanic complex. Trace elements in Pleistocene zircon indicate continental affinity, which supports radiogenic (Nd, Sr) isotopic data that were modeled using different mixing and AFC scenarios indicating a MORB-type primary magma with significant (~10–20 %) crustal assimilation involving tonalitic basement of the eastern Peninsular Ranges Batholith.

Constraints on the timescales and processes that led to high-SiO2 rhyolite production in the Searchlight pluton, Nevada, USA

Abstract Plutons offer an opportunity to study the extended history of magmas at depth. Fully exploiting this record requires the ability to track changes in magmatic plumbing systems as magma intrudes, crystallizes, and/or mixes through time. This task has been difficult in granitoid plutons because of low sampling density, poorly preserved or cryptic intrusive relationships, and the difficulty of identifying plutonic volumes that record the contemporaneous presence of melt. In particular, the difficulty in delineating fossil magma reservoirs has limited our ability to directly test whether or not high-SiO2 rhyolite is the result of crystal-melt segregation. We present new high-precision U-Pb zircon geochronologic and geochemical data that characterize the Miocene Searchlight pluton in southern Nevada, USA. The data indicate that the pluton was built incrementally over ~1.5 m.y. with some volumes of magma completely crystallizing before subsequent volumes arrived. The largest increment is an ~2.7-km-thick granitic sill that records contemporaneous zircon crystallization, which we interpret to represent a fossil silicic magma reservoir within the greater Searchlight pluton. Whole-rock geochemical data demonstrate that this unit is stratified relative to paleo-vertical, consistent with gravitationally driven separation of high-SiO2 melt from early-formed crystals at moderate crystallinity. Zircon trace-element compositions suggest that our geochronologic data from this unit record most of the relevant crystallization interval for differentiation and that this process occurred in <150 k.y.

Genesis and magma fertility of gold associated high-K granites: LA-ICP-MS zircon trace element and REEs constraint from Bakoshi–Gadanya granites in NW Nigeria

Genesis and magma fertility of gold associated high-K granites: LA-ICP-MS zircon trace element and REEs constraint from Bakoshi–Gadanya granites in NW Nigeria

New high-precision U-Pb zircon age of the Irati Formation (Paraná Basin) and implications for the timing of the Kungurian anoxic events recorded in southern Gondwana

The early Permian Irati Formation is well known for its black shale oil and gas reserves and its widespread lateral correlation throughout the entire Paraná Basin. This unit records an effective water circulation restriction between the Whitehill-Irati Sea and the Panthalassa Ocean, which along with other factors, controlled the organic-rich shale deposition in several southern basins of Gondwana. The Permian was also a period of intense magmatism in this region due to the Terra Australis Orogen (Gondwanides Orogeny). Several volcanoclastic horizons are preserved within the sedimentary record, and in this study, a high-precision chemical abrasion isotope dilution U-Pb zircon age of 275.75 ± 0.29 Ma for a volcanic tuff in the Irati Formation of the southern Paraná Basin is presented. The Kungurian age agrees with previous published radioisitopic and relative ages for the Assistência Member (upper Irati Formation) and Mangrullo Formation, a stratigraphical correlated unit in Uruguay. In addition, zircon trace elements and whole-rock geochemistry allow the constraining of the magmatic characteristics of the volcanic source and its similarity with the lower Choiyoi magmatism (Argentina). Therefore, this study contributes to the understanding of the timing of black shale-bearing rocks of the Irati Formation and the anoxic events recorded in the southern Paraná Basin.