Zircon Trace Element Research Articles

From Burial to Exhumation: Emplacement and Metamorphism of Mafic Eclogitic Terranes Constrained Through Multimethod Petrochronology, Case Study from the Lévézou Massif (French Massif Central, Variscan Belt)

Abstract Linking mineral growth and time is required to unravel the evolution of metamorphic rocks. However, dating early metamorphic stages is a challenge due to subsequent retrograde overprinting. A fresh eclogite and a former eclogite retrogressed under amphibolite facies from the southern French Massif Central (Lévézou massif, Variscan belt) were investigated with a large panel of geochronometers (U–Pb in zircon, rutile and apatite, Lu–Hf and Sm–Nd in garnet) in a petrological context tightly constrained by petrographic observations, trace element analyses and phase equilibrium modelling. Both samples recorded similar HP conditions at 18–23 kbar and 680–800°C, whereas the retrogressed eclogite later equilibrated at 8–9·5 kbar and c.600°C. In the retrogressed sample, most of the zircon grains are characterized by negative Eu anomalies and HREE enrichment, and yield an Ordovician U–Pb date of 472·3 ± 1·7 Ma, interpreted as the emplacement age of the mafic protolith. In agreement with other data available for the Variscan belt, and based on zircon trace element record and whole-rock geochemistry, this age is considered to represent the magmatism associated with the extreme thinning of the continental margins during the Ordovician. In the same sample, a few zircon rims show a weaker HREE enrichment and yield a date of 378 ± 5·7 Ma, interpreted as a prograde pre-eclogitic age. Lu–Hf garnet dating from both samples yields identical dates of 357 ± 13 Ma and 358·0 ± 1·5 Ma inferred to approximate the age of the high-pressure metamorphic peak. Fresh and retrogressed samples yield respectively 350·4 ± 7·7 Ma and 352 ± 20 Ma dates for Sm–Nd garnet dating, and 367·8 ± 9·1 Ma and 354·9 ± 9·5 Ma for U–Pb rutile dating. Apatite grains from the retrogressed sample give a mean age of 351·8 ± 2·8 Ma. The similarity between all recorded ages from distinct chronometers and radiometric methods (U–Pb, rutile, apatite; Lu–Hf, garnet; Sm–Nd, garnet) combined with P–T estimations from high-pressure metamorphic rocks equilibrated under different conditions testifies to very fast processes that occurred during the Variscan orogeny, highlighting a major decompression of 15–8·5 kbar in less than 7 Myr, and suggesting mean exhumation rates in excess of 6·3 mm/yr.

Metallogeny of the continental collision-related Jiagang W-Mo deposit, Tibet: Evidence from geochronology and petrogenesis

The Jiagang W-Mo deposit is the first greisen-type tungsten deposit recognized in the Lhasa terrane, and thus it has important genetic implications for understanding the regional tungsten mineralization potential. Greisen-type orebodies dominate in the deposit. Ores characterized by veinlets and dissemination are located in intensively altered monzogranite and contact zones between the monzogranites and sedimentary rocks. The minor quartz vein-type orebodies occuring as large quartz veins mainly precipitated in the sedimentary rocks. Intrusions associated with the Jiagang deposit are monzogranites, which can be subdivided into medium-grained monzogranite (MMG), porphyritic monzogranite (PMG), and fine-grained monzogranite (FMG). The zircon U-Pb ages of the PMG and MMG are 18.2 ± 0.2 Ma and 18.6 ± 0.1 Ma, respectively. These ages are consistent with the muscovite 40Ar-39Ar plateau ages (18.7 ± 0.2 Ma, 18.5 ± 0.2 Ma) and the molybdenite Re-Os isochron age (19.0 ± 0.3 Ma) within errors, indicating that the Jiagang W-Mo mineralization took place during the post-collisional stage of the Indo-Asian continental collision. The mineralization is temporally, spatially and genetically associated with the monzogranitic intrusions. The FMGs have the lowest SiO2 contents (70.8–71.5 wt%), lowest differentiation index (DI = 85.7–86.3) and least obviously negative Eu anomalies (Eu/Eu* = 0.22–0.42). The PMGs and MMGs have higher SiO2 contents (72.6–76.3 wt%), higher differentiation index (DI = 89.3–92.7) and more negative Eu anomalies (Eu/Eu* = 0.11–0.24). Almost all of the rocks are strongly peraluminous (A/CNK = 1.02–1.29), enriched in LILEs and depleted in HFSEs. Concentrations of K2O, CaO, FeOT and TiO2 of the three types of monzogranites show negative correlations with SiO2, while P2O5 exhibits the opposite trend. Values of Nb/Ta decrease with SiO2 contents, and those of (La/Yb)N increase with La contents. Whole rock εNd(t) of the FMGs range from −11.3 to −11.1 with two-stage Nd isotopic model ages (TDM2) of 1741–1797 Ma, which are similar to those of the PMGs and MMGs (εNd(t) = −10.9– −10.6; TDM2 = 1709–1816 Ma). Zircon εHf(t) values of the PMG and MMG range from −13.8 to −5.3 with two-stage Hf isotopic model ages of 1439–1979 Ma. These data suggest that the ore-forming monzogranites are strongly peraluminous S-type granites, which should be derived from anatexis of the Proterozoic metagreywackes underneath the central Lhasa subterrane. The PMG and MMG are highly fractionated through various degrees of fractional crystallization of plagioclase, K-feldspar, biotite, monazite and allanite from the parental melts represented by the FMG. Zircon trace elements suggest that oxygen fugacity of the ore-forming magmas is relatively low and decreased as the magmas evolved, which is favorable to remove substantial tungsten from melts into the tungsten-mineralizing hydrothermal fluids. A high degree of fractional crystallization of the crustally-derived magmas with relatively low magmatic oxidation state are the critical factors determining the generation of the tungsten mineralization in the Jiagang deposit. Combined with the existing breakthroughs in prospecting exploration, we propose that the central Lhasa subterrane has great metallogenic potential in W-(Mo) mineralization associated with the Indo-Asian continental collision.

Tracking crystal-melt segregation and magma recharge using zircon trace element data

The Cretaceous Yunshan caldera complex in SE China consists of an unusual coexisting assemblage of peraluminous and peralkaline rhyolites and a resurgent intra-caldera porphyritic quartz monzonite. In this study, we use zircon trace element data to study the compositional differences of zircons from cogenetic magmas and to track the evolution of the entire magmatic system. Our results indicate that the zircons from the peraluminous and peralkaline rhyolites formed from highly evolved compositions with high Hf concentrations and low Ti contents, and low Th/U and Zr/Hf ratios, which are distinct from those of the intrusive porphyritic quartz monzonite. Zircons from the peraluminous and peralkaline rhyolites display overlapping Zr/Hf and Hf, but the zircons from the peralkaline rhyolites have extremely low Eu/Eu* ratios (<0.1) and Ti contents (2.26–13.3 ppm). The lack of overlapping zircon trace element compositions between the volcanic and intrusive caldera units is interpreted to represent crystal–melt segregation processes. In addition, zircon grains from the porphyritic quartz monzonite and a few zircon grains from the peraluminous rhyolite display distinctly bright rims and whole grains in cathodoluminescence imaging, which have high Ti, Zr/Hf, and Eu/Eu*, and are similar to those of zircons from the mafic microgranular enclave within the porphyritic quartz monzonite. We interpret these signatures to reflect crystallization from a relatively hot and less evolved magma indicating a magma chamber recharge event. We further developed a model in which the magmas of the peraluminous and peralkaline rhyolites were successively extracted from a primitive crystal mush by crystal–melt segregation with a rejuvenation of the crystal mush after the extraction of the peraluminous rhyolitic melt, leaving behind residual mushes solidified as porphyritic quartz monzonite. Our study shows that trace element analyses of zircons can effectively be used to pinpoint multiple crystal–melt segregation and melt extraction events as well as magma recharge processes in silicic magmatic systems.

Late Eocene magmatism of the eastern Qiangtang block (eastern Tibetan Plateau) and its geodynamic implications

Post-collisional magmatism offers significant clues to reveal the deep dynamic process and surface uplift of plateaus. New zircon U-Pb ages, biotite Ar-Ar ages, zircon trace elements, and whole-rock geochemistry, integrated with published data of igneous rocks from the eastern Qiangtang block (eastern Tibetan Plateau) were determined to unravel the geodynamics and constrain the uplift history. These igneous rocks consist of few mafic and many intermediate-felsic series. Geochronological studies reveal that the magmatism mainly occurred in ~43–33 Ma. The late Eocene igneous rocks are characterized by high potassium, enrichment in large ion lithophile elements (LILE, e.g., Rb, Ba, Th, U), depleted in high field strength elements (HFSE, e.g., Nb, Ta, Ti), negligible Eu anomalies, with a wide range of highly incompatible element ratios. The parental magmas of these rocks were most probably generated by different degrees of partial melting of the lithospheric mantle, which were heterogeneously metasomatized by subduction related multiphase fluids/melts. Whole-rock geochemistry, zircon trace elements, and thermodynamic modeling results suggest that the parental magmas experienced complicated and different differentiation processes. Mantle metasomatism, fractional crystallization, and magmatic recharge made contributions to the enrichment of incompatible elements and the wide range ratios between highly incompatible elements. In combination with the estimated Eocene crustal thickness, we suggest that the southward continental subduction of the Songpan-Ganzi block triggered the magmatism, thickened the crust, and induced the surface uplift to no more than ~3 km in the late Eocene.

Origin of Paleozoic granitoids in the Yuhai Cu–Mo deposit, Eastern Tianshan, NW China and implications for regional metallogeny

The Yuhai porphyry Cu–Mo deposit is located at the eastern section of the Dananhu–Tousuquan Arc in Eastern Tianshan, NW China. Cu–Mo mineralization generally occurs as disseminations and veins in potassic and phyllic alteration zones, and is predominantly hosted in the Yuhai quartz diorite, granodiorite and minor syenogranite intrusions. New LA–ICP–MS zircon U–Pb dating indicates that the acidic syenogranite was emplaced at 318–320 Ma, younger than the intermediate rocks (i.e., quartz diorite and granodiorite) with Silurian ages. The acidic to intermediate intrusions exhibit geochemical affinities with normal arc rocks (e.g. high Y and Yb contents, and low Sr/Y ratios), in contrast with the subducted slab-derived adakites hosting large porphyry Cu deposits (e.g. Tuwu–Yandong) in the middle section of the Dananhu–Tousuquan Arc. The Yuhai acidic syenogranite rocks have high SiO2 (≥74.90 wt%), and K2O (≥3.48 wt%), relatively low Mg# and compatible element contents (e.g. Cr = 0.65–3.37 ppm; Ni = 0.63–1.02 ppm), and strong depletions in HFSE (e.g. Nb, Ta, and Ti). These geochemical features, coupled with isotopic data such as low initial 87Sr/86Sr (≤0.7033), positive εNd(t) (4.0 to 5.9) and εHf(t) (≥11) values, young Hf model ages, and variable 206Pb/204Pb ratios (18.549 to 19.465) reported in this study, suggest that their parental magmas originated from the partial melting of a juvenile lower crust and mixed with some old crustal components beneath the Dananhu–Tousuquan Arc. In contrast, the Yuhai intermediate intrusions exhibit relatively low SiO2 and K2O contents, high Mg# values (40–56), and a wide range of εHf(t) values, suggesting a source of sub-continental lithospheric mantle metasomatized by slab-derived fluids and melts. Zircon trace element and plagioclase compositions of the Yuhai granitoids further imply that the Silurian intermediate intrusion-related magma was moderately oxidized (mostly EuN/EuN* > 0.6) and water-rich (~9 wt%), favorable for the copper mineralization, whereas the Carboniferous syenogranite-related magma was weakly oxidized (mostly EuN/EuN* = 0.3–0.6) but also hydrous (~6 wt%). Combined with the regional tectono-magmatic activities and metallogenic processes, we suggest that the Yuhai Cu–Mo deposit and associated granitoids were formed in an arc setting, and that the magma nature and its source components are the key factors constraining the distribution, scale and style of the porphyry copper mineralization in Eastern Tianshan.

Using zircon trace element composition to assess porphyry copper potential of the Guichon Creek batholith and Highland Valley Copper deposit, south-central British Columbia

The Late Triassic Guichon Creek batholith is a large (~ 1800 km2), composite, zoned batholith that hosts several large porphyry Cu-Mo deposits of the Highland Valley Copper district. The batholith consists of intrusive rocks that range in composition from gabbro to quartz monzonite. Adjacent to the mafic margin of the batholith is the Gump Lake granodiorite to quartz monzonite stock. A new U-Pb zircon age of 218 ± 0.18 for the Gump Lake stock indicates that magmatism in the region began at least seven million years prior to the emplacement of the main Guichon Creek batholith rocks at 211 Ma. Zircons from fifteen samples from the Guichon Creek batholith were analyzed by laser ablation ICP-MS to characterize the magmatic evolution and ore fertility of the batholith. The trace element composition of zircon record early, lower crustal, fractional crystallization followed by five pulses of magma recharge and mixing in an upper-crustal, oxidized, magma chamber as well as degassing of the magmatic-hydrothermal fluids that formed the porphyry copper deposits. Zircons from the early barren rocks have chondrite-normalized Eu/EuN* values of 0.19 to 0.56 and estimated temperatures of 850 to 750 °C. The middle to late intrusions that host porphyry copper mineralization have zircon Eu/EuN* values of 0.30 to 0.74 and slightly lower estimated temperatures of 800 to 600 °C. Late porphyritic stocks and dikes from the mineralized centers contain zircon crystals elevated in Y, Nb, Ta, and REE concentration relative to zircon from the earlier intrusions. This distinct change in zircon composition coincides with the copper mineralization, suggesting that zircon chemistry can be used as a tool to identify the genetic evolution of a crystallizing magma chamber and potential for mineralization.

Provenance of Jurassic-Cretaceous Tethyan Himalayan sequences in the Thakkhola Section- Nepal, inferring pre-collisional tectonics of the central Himalaya

The Jurassic-Cretaceous (Upper Tethyan) flysch well exposed in the Thakkhola Section, Nepal, was deposited prior to the continent-continent collision between the Indian and Eurasian plates. This Tethyan Himalayan Sequence (THS) has preserved the extreme northern passive margin of the Indian plate with its direct deposition onto the eroded Precambrian rocks in the lowest part of this relatively continuous section. The clastic rocks of the THS, as they are useful to constrain the paleogeography and paleotectonics of the Himalayan Orogen. In this study, we report the petrography, detrital zircon U-Pb isotopic ages, and zircon trace element data for sandstone samples from the Upper part of a Triassic stratigraphic section. The mineral modal composition data indicates that these quartz-rich units were derived from recycled orogen. This is supported that the youngest zircons analyzed can be dated to ~400 Ma that predates the depositional age by hundreds of millions of years. A total of 85% of the zircon ages are <1,500 Ma and the oldest dated zircon is ~3300 Ma. What these sections share in terms of detrital zircon signals are peaks at pre-Rodinian, a Grenvillian, a Gondwanan, and nothing either younger, except for the weak presence or total absence, of a Cretaceous zircon age signal. More importantly, these results drive us to surmise that either sedimentary or crystalline, in the Indian plate that has provided the unusual mix of 475–675 Ma and 825–950 Ma age peaks, with the latter associated with an Eastern African super deltaic fan.

Polyphase Zircon Growth during Slow Cooling from Ultrahigh Temperature: an Example from the Archean Pikwitonei Granulite Domain

AbstractQuantifying the timescales of Archean ultrahigh temperature (UHT) metamorphism is essential for constraining the style of plate tectonics on the early Earth. However, such timescales can be difficult to quantify, due to the antiquity of Archean rocks and the extreme thermal conditions of UHT metamorphism. We constrain the timescales of Archean UHT metamorphic processes recorded by a single rock sample from the Pikwitonei granulite domain (northwestern Superior Province), through the integration of two U–Pb zircon petrochronologic techniques. In this study we combine: (1) high-spatial resolution laser ablation split-stream inductively coupled mass spectrometry (LASS) on in situ zircon (in thin section) and hand-picked zircon; and (2) high-precision isotope dilution thermal ionization mass spectrometry (ID-TIMS) analyses on microsampled fragments from the same hand-picked zircon analysed by LASS. Phase equilibria modelling and Zr-in-rutile thermometry suggest the rock followed a P–T path characterized by decompression at &amp;gt; 960 °C, followed by near-isobaric cooling at ∼0·8 GPa. In situ LASS zircon analyses could be interpreted to record zircon growth at broadly ∼2665 Ma, though the large uncertainties on isotopic dates make potentially distinct growth episodes difficult to distinguish. ID-TIMS U–Pb dates of zircon fragments reveal a polyphase zircon growth history over a 24 Ma duration, from 2673 to 2649 Ma. Zircon trace element compositions, textures, and microstructural relationships, as well as evaluation of zircon-garnet equilibrium, suggest zircon grew during melt crystallization, after UHT decompression and garnet resorption. Variable Ti concentrations within zircon domains indicate: (1) zircon crystallized through the temperature interval of ∼875 °C to ∼730 °C, potentially in isolated rock domains with variable zircon saturation temperature; and/or (2) zircon crystallized over a narrower temperature interval in isolated rock domains with variable aTiO2 and/or aSiO2. Collectively, the data suggest the west-central Pikwitonei granulite domain reached peak UHT conditions prior to 2673 Ma, after which suprasolidus conditions in the lower crust persisted for at least 24 Ma. Such an interpretation would be impossible if based on either the LASS or ID-TIMS zircon data alone, which highlights the utility of applying both techniques in tandem to constrain metamorphic timescales in ancient UHT terranes.

Petrogenesis and tectonic setting of the Cretaceous volcanic-intrusive complex in the Zijinshan ore district, Southeast China: Implications for different stages of mineralization

Volcanic–subvolcanic rocks and associated Cu-Au-Ag-Pb-Zn mineralization within the Zijinshan ore district, located in the southwestern part of Fujian Province, represent a large metallogenic district within the southeastern coastal volcanic belt of China. This study presents new whole-rock geochemical, Sr–Nd–Hf isotopic, and zircon trace element data for igneous rocks within the Zijinshan area. Combining these new data with previously published geochronological results allows to constrain the magmatic and hydrothermal history and to understand the ore-related geological setting. Our results provide evidence of multi-stage metallogenic events within the Zijinshan district that can be roughly divided into early stage Cu-dominant (ca. 105–102 Ma) and late-stage Pb-Zn-enriched Ag-polymetallic (ca. 95–92 Ma) mineralization. Igneous rocks associated with the early stage of mineralization are enriched in the large ion lithophile elements (LILEs), depleted in the high field strength elements (HFSEs) with negative Nb, Ta and Ti anomalies, and have relatively high Mg# (35.9–63.5), low initial 87Sr/86Sr (0.7065–0.7088), relatively depleted εNd(t) and εHf(t) values (-3.6 to −2.3 and −5.04 to 0.85, respectively), and younger two-stage Hf model ages (1.4–1.1 Ga), suggesting that the components from metasomatized mantle were incorporated. The zircons in these early stage rocks are with elevated Ce4+/Ce3+ values (358–1029) indicating the high oxygen fugacity. In comparison, the igneous rocks associated with the late stage of mineralization have high initial 87Sr/86Sr values (0.7071–0.7103), enriched εNd(t) and εHf(t) values (−6.6 to −5.5 and −8.92 to −4.15, respectively), and older two-stage Hf model ages (1.7–1.4 Ga), that are indicative of formation from magmas that incorporated ancient crustal material. The late-stage igneous rocks contain zircons with low Ce4+/Ce3+ values (20–387) that are indicative of low oxygen fugacity conditions. Besides, the late stage ore-related igneous rocks are of high silica contents with highly evolved chemical signatures, indicative of intensive fractionation processes. The diverse metal endowments may be attributed to different sources, oxygen fugacity and magmatic evolution levels of the ore-related magmas. The Cretaceous magmas in Zijinshan were likely generated under an extensional setting. The lithospheric extension triggered partial melting of the fertile metasomatized subcontinental mantle, incorporating a large amount of mantle-derived components and generated the early Cu-Au-Mo mineralization. Later, a local and temporary shift to the more compressional environment would weaken the contribution of mantle. More ancient crustal materials were incorporated in the late stage and the magmas underwent intensive fractional crystallization, leading to the generation of Ag-polymetallic mineralization in the Zijinshan ore district.

North Atlantic Craton architecture revealed by kimberlite-hosted crustal zircons

Archean cratons are composites of terranes formed at different times, juxtaposed during craton assembly. Cratons are underpinned by a deep lithospheric root, and models for the development of this cratonic lithosphere include both vertical and horizontal accretion. How different Archean terranes at the surface are reflected vertically within the lithosphere, which might inform on modes of formation, is poorly constrained. Kimberlites, which originate from significant depths within the upper mantle, sample cratonic interiors. The North Atlantic Craton, West Greenland, comprises Eoarchean and Mesoarchean gneiss terranes – the latter including the Akia Terrane – assembled during the late Archean. We report U–Pb and Hf isotopic, and trace element, data measured in zircon xenocrysts from a Neoproterozoic (557 Ma) kimberlite which intruded the Mesoarchean Akia Terrane. The zircon trace element profiles suggest they crystallized from evolved magmas, and their Eo- to Neoarchean U–Pb ages match the surrounding gneiss terranes, and highlight that magmatism was episodic. Zircon Hf isotope values lie within two crustal evolution trends: a Mesoarchean trend and an Eoarchean trend. The Eoarchean trend is anchored on 3.8 Ga orthogneiss, and includes 3.6–3.5 Ga, 2.7 and 2.5–2.4 Ga aged zircons. The Mesoarchean Akia Terrane may have been built upon mafic crust, in which case all zircons whose Hf isotopes lie within the Eoarchean trend were derived from the surrounding Eoarchean gneiss terranes, emplaced under the Akia Terrane after ca. 2.97 or 2.7 Ga, perhaps during late Archean terrane assembly. Kimberlite-hosted peridotite rhenium depletion model ages suggest a late Archean stabilization for the lithospheric mantle. The zircon data support a model of lithospheric growth via tectonic stacking for the North Atlantic Craton.

Zircon constraints on granite derivation in the northern North China Craton

Zircons with core-rim structure are common in granitoids worldwide. Mostly, the cores have strikingly older ages than the rims. Whether the zircon cores are inherited from the source of the granitoids or just occasionally captured from the wallrocks during magma ascent is highly controversial. In this paper, three Mesozoic granites with diverse ages and geochemical compositions but uniformly ~1.8 Ga zircon cores are reported from the Fengning area of North China Craton. The zircon cores in the Bingshanliang I-type granites have much higher δ18O values (8.3‰ to 10.1‰) than the magmatic zircons, strongly arguing against that these zircon cores are from the source of the granites. Instead, they could come from the wallrock during magma ascent. This conclusion is consistent with the occurrence of ~1.8 Ga S-type granites and meta-sedimentary rocks in the region which are characterized by high δ18O values. Similarly, zircon cores in the Wudaoying and Niuquanziba granites share many similarities in trace elements with the widely outcropped ~1.8 Ga granitoids, suggesting their probably xenocrystic origin from the Paleoproterozoic granitoids. The xenocrystic speculation is further supported by the lack of obviously modified internal textures and trace element imprints in the ~1.8 Ga zircon cores due to the effect of the Mesozoic anatexis if they had been derived from the source region of the granites. Combined with the bulk rock Nd isotopic and magmatic zircon Hf isotopic compositions, the three Mesozoic granites are suggested to be derived from the late Archean lower crust. It is inferred that ~2.5 zircon cores in some Mesozoic granitoids from other parts of the North China Craton are also likely captured grains from the wallrock during magma intrusion into the ~2.5 Ga basement rocks, rather than from the source. The magmatic zircon trace elements from the Wudaoying and Niuquanziba granites fingerprint the adakitic and A-type characters of their respective magma, implying their utility in tracing granites' derivation.

LA-ICP-MS/MSを用いたジルコン中の微量元素測定 における高確度化の検討

LA-ICP-MS/MSを用いたジルコン中の微量元素測定 における高確度化の検討

Genesis of alkaline-peralkaline A-type granite from El Dair complex, SW Arabian-Nubian Shield, Sudan: geochronology, geochemistry and isotopic constraints

The formation time and origin of the Neoproterozoic alkaline-peralkaline rocks from the SW Arabian-Nubian Shield (ANS) are poorly constrained. An assessment of petrography, whole-rock geochemistry, incorporated with zircon U–Pb dating, trace element, and Hf isotope, has been done on the El Dair granitic complex, NE Nuba Mountains, Sudan. LA-ICPMS U–Pb zircon ages from two granite samples yield a weighted mean of 567.3 ± 2.5 Ma and 598.3 ± 21 Ma, respectively, signifying that the El Dair complex was formed at ca. 560–600 Ma. The El Dair granite samples exhibit alkaline-peralkaline affinity (A.I. = 1.04–1.17) and are classified as high-K calc-alkaline series. The samples display similar composition with typical A-type granite: e.g., elevated Na2O + K2O contents, Ga/Al, FeOT/MgO, TiO2/MgO, ratios, and HFSEs (i.e., Zr, Ta, Nb, and Y) with negative Ba, Sr, and Ti anomalies and depleted contents of CaO, MgO, and P2O5. The El Dair granite samples illustrate high Zr (563–1163 ppm) contents, yielding high magma temperatures of 884–966 °C. The zircon trace elements investigations show HREE enrichment and positive Ce but negative Eu anomaly, characteristic of igneous zircons. The initial eHf(t) of + 4.2 − +5.8 and eNd isotopic values of + 1.83 − +1.92 from El Dair A-type granite samples are rather enriched than the values of depleted mantle (eHf ~ + 14 and eNd ~ + 6.5). Whole-rock elemental and isotopic data from the El Dair complex apparently denote that the magmas were produced via low degrees partial melting of juvenile crust through the assemblage of ANS during Neoproterozoic time.

Petrogenesis and oxidation state of granodiorite porphyry in the Jurassic Chuankeng skarn Cu deposit, South China: Implications for the Cu fertility and mineralization potential

Large-scale Jurassic porphyry–skarn Cu mineralization in the Qin-Hang metallogenic belt of South China has attracted much attention, but comparative studies of porphyries in large- and small-scale deposits are lacking. In this paper, we present new zircon U–Pb ages, trace element composition and Hf isotopic composition as well as whole-rock geochemical and Sr–Nd isotopic compositions for the porphyries associated with mineralization in the small-scale Chuankeng Cu deposit. Drawing on our data for the Chuankeng deposit and existing data for the nearby giant Dexing Cu deposit, we aim to identify factors controlling the mineralization potential of both deposits. Granodiorite porphyries of Chuankeng deposit were emplaced at ca. 161–158 Ma. They have moderate SiO2 contents of 61.9–66.1 wt% and high Sr/Y (59–135) and (La/Yb)N (4–14) ratios. Their high MgO contents (0.2–2.9 wt%), lack of negative Eu anomaly, depletion in Y and Yb, relatively high initial 86Sr/87Sr ratios (0.7076–0.7078), and low εNd(t) values (−4.5 to −4.9), indicating that the Chuankeng porphyries were derived from partial melting of delaminated lower crust. The Middle–Late Jurassic Chuankeng porphyries are considered to have been formed in a localized intra-continental extension environment along the Jiangshao Fault in response to far-field stress from Paleo-Pacific Plate subduction. Although no Middle–Late Jurassic magmatic arc rocks have been found in the study area, the Chuankeng porphyries display similar characteristics to arc rocks. On the basis of their zircon εHf(t) values (−2.6 to +0.9), two-stage Hf model ages (1.4–1.1 Ga), and regional geological history, we infer that magma source of Chuankeng porphyries were mainly Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. Thus their arc-like features were inherited from the Neoproterozoic juvenile crust that formed by subduction of oceanic crust during the Jiangnan orogeny. Chuankeng porphyries have lower zircon Ce4+/Ce3+ and higher Ti-in-zircon temperatures and lower whole rock εNd and zircon εHf values than the Dexing porphyries, indicating they are less oxidized and less hydrous and with more involvement of the ancient crustal material in the magma source, which could explain the relatively small-scale Cu mineralization in Chuankeng. This study highlights the values of integrated studies of whole rock Nd and zircon trace element and Hf isotopic compositions in assessing the potential for Cu mineralization.

Zircon U-Pb-Hf isotopes and mineral chemistry of Early Cretaceous granodiorite in the Lunggar iron deposit in central Lhasa, Tibet Y, China

The Lunggar iron deposit belongs to the Bangong-Nujiang metallogenic belt and is located in central Lhasa on the Tibetan Plateau. In the Lunggar deposit, iron mineralization formed in the skarnization contact zone between the Early Cretaceous granodiorite and the late Permian Xiala Formation limestone. In this study, we achieved detailed zircon U-Pb-Hf isotopes and mineral chemistry for the Early Cretaceous granodiorite. Zircon U-Pb dating results indicate that the Early Cretaceous granodiorite emplaced at ca. 119 Ma. Based on the trace elements in zircons and the mineral chemical composition of amphibole and biotite, the Early Cretaceous granodiorite was believed to form under condition of high temperature (>700 °C), low pressure (100–400 MPa), and relatively high oxygen fugacity (lg/O2)(−13.6 to −13.9) and H2O content (4%–8%). Zircon trace elements, Hf isotope and biotite chemistry collectively reveal that significant juvenile mantle-derived magmas contributed to the source of the granodiorite. The relatively high log/O2 and shallow magma chamber are beneficial for skarn iron mineralization, implying remarkable potential for further prospecting in the Lunggar iron deposit.

Geochemistry and zircon trace elements composition of the Miocene ore‐bearing biotite monzogranite porphyry in the Demingding porphyry Cu‐Mo deposit, Tibet: Petrogenesis and implication for magma fertility

Demingding is a poorly studied post‐collisional porphyry Cu‐Mo deposit, located in the eastern part of the Gangdese porphyry copper belt. In this study, we present LA‐ICP‐MS zircon U‐Pb dating, whole‐rock geochemistry, and zircon trace elemental data for the mineralization related biotite monzogranite porphyry in Demingding. Zircon U‐Pb dating shows that the weighted mean 206Pb/238U ages of the Miocene biotite monzogranite porphyry is 20.36 ± 0.46 Ma (MSWD = 2.6, n = 21). The Miocene biotite monzogranite porphyry is characterized by high SiO2, K2O, and Al2O3 contents and shows adakite‐like signatures. These rocks have high Sr/Y ratios, fractionated REE patterns with low HREE abundances, enrichment in LILE compared with HFSE, and have (87Sr/86Sr)i values of 0.7059 to 0.7062, εNd(t) values of −2.35 to −1.67 and (206Pb/204Pb)i ratios of 18.50–18.55. These features are similar to other Miocene adakite‐like intrusions in the Gangdese belt. We propose that the biotite monzogranite porphyry shares the same petrogenesis with other Miocene ore‐bearing adakite‐like intrusions in the Eastern Gangdese belt and was derived from remelting of the subduction‐modified, eclogitized Tibetan lower crust and mixing with hydrous mafic magmas from metasomatized Tibetan mantle. The zircons from biotite monzogranite porphyry have only minimal negative Eu anomalies (EuN/EuN* &gt; 0.3), and exhibit large ratios of Ce4+/Ce3+(average value of 113), 10,000*(EuN/EuN*)/Y (3.94–8.14, &gt;1), Ce/Nd (9–58, Average value of 30), (Ce/Nd)/Y (0.008–0.127, &gt;0.003), and low value of Dy/Yb (0.15–0.24, &lt;0.3), indicating that the biotite monzogranite porphyry is relatively hydrous and oxidized. The biotite monzogranite porphyry, therefore, is believed to be a relatively fertile intrusion with certain exploration potential.

Whole-rock and zircon geochemistry of the Xiaoliugou granites, North Qilian Orogen (NW China): Implications for tectonic setting, magma evolution and W–Mo mineralization

Ordovician W–Mo polymetallic mineralization-related granites are widely developed in the western section of the North Qilian Orogen, NW China. In order to shed light on the tectonic setting, magma evolution and genesis of mineralization in the orogeny, highly evolved granitic rocks (monzogranites) from the Qibao and Qiqing deposits in the Xiaoliugou ore field were studied. Typical of subduction-related A-type granites, the Xiaoliugou granitic rocks are enriched in SiO2, Rb, Th, U, Ta, Nd, Zr and Hf but relatively depleted in Ba, Sr, P and Eu. The variable initial whole rock 87Sr/86Sr ratios (0.62937–0.70543) and wide range of zircon εHf(t) values (−18 to 6) suggesting mantle–crust interaction and mixing of depleted mantle and deep crust in the source area. Whole-rock elemental and Rb–Sr isotopic geochemistry suggest slow cooling, significant fractional crystallization, weak wall-rock assimilation/contamination and intense fluid differentiation/metasomatism during the genesis of the Xiaoliugou granitic rocks. Zircon U–Pb dating yielded three age clusters: Precambrian (>540 Ma) (n = 32), Ordovician (~450 Ma) (n = 40), and Cretaceous (~135 Ma) (n = 18). Zircon internal textures indicate a range of sources including residual/detrital zircons from the magma source region and local sediments, magmatic and fluid-altered zircons, and late stage hydrothermal zircons. Zircon trace element and Lu–Hf isotopic compositions suggest fluid metasomatism during granite emplacement in the Ordovician and overprinting by a more evolved, oxidized fluid in the Cretaceous. Involvement of a late, high-temperature, highly fractionated, F-rich fluid could have enhanced W–Mo mineralization. Consequently, a two-stage genetic model is proposed for the Xiaoliugou granitic-minerogenic system involving primary mineralization in the Ordovician (~450 Ma), followed by a Cretaceous magmatic hydrothermal overprint (~135 Ma).

Petrogenesis and tectonic significance of Neoproterozoic meta-basites and meta-granitoids within the central Dabie UHP zone, China: Geochronological and geochemical constraints

A combined geochemical (whole-rock elements and Sr-Nd-Pb isotopes, zircon trace elements and Hf isotopes) and geochronological (zircon U–Pb ages) study was carried out on the relatively low-grade meta-basites and meta-granitoids from Longjingguan within the central Dabie ultrahigh-pressure (UHP) metamorphic zone, east-central China. Zircon investigations indicate that the meta-basites were formed at ∼772 Ma and subsequently experienced granulite-facies metamorphism at ∼768 Ma and a later thermal overprint at ∼746 Ma, while the meta-granitoids recorded three groups of zircon ages at ca. 819 Ma, 784 Ma and 746 Ma. The meta-granitoids can be subdivided into low-Si and high-Si types, and they were derived from mid-Neoproterozoic partial melting of the Neoarchean and Paleoproterozoic metamorphic basement rocks of the South China Block, respectively. These Neoproterozoic zircon ages are consistent with the protolith ages of the Dabie Triassic UHP meta-igneous rocks. In addition, the low-grade rocks have bulk-rock Pb isotope compositions overlapping with the UHP meta-igneous rocks. Therefore, the low-grade meta-basites and meta-granitoids could be interpreted as counterparts of the UHP meta-igneous rocks in this area, suggesting the same petrogenesis for their protoliths in the Neoproterozoic.Trace element patterns indicate that the low-grade rocks have better preserved their protolith compositions than their equivalent UHP rocks, and thus they are more suitable for elucidating the Neoproterozoic evolution of the northern margin of the South China Block. Zircon ages combined with geochemical features strongly suggest that the protoliths of the meta-granitoids and meta-basites were formed in a magmatic arc and a continental rifting setting, respectively. More specifically, the granitoids derived from partial melting of Neoarchean and Paleoproterozoic basement materials at ∼819 Ma in a magmatic arc setting, whereas the precursors of the meta-basites are products of a continental rifting event at about 784 to 772 Ma. The obtained results provide new geochronological and geochemical constraints for the Neoproterozoic evolution of the northern margin of the South China Block, which can further contribute to the understanding of the breakup of the supercontinent Rodinia.

Zircon Petrochronology of the Meghri-Ordubad Pluton, Lesser Caucasus: Fingerprinting Igneous Processes and Implications for the Exploration of Porphyry Cu-Mo Deposits

AbstractThe trace element composition of zircon, especially in tandem with U-Pb geochronology, has become a powerful tool for tracing magmatic processes associated with the formation of porphyry copper deposits. However, the use of the redox-sensitive Eu and Ce anomalies as a potential mineral exploration proxy is controversial. This study presents a comprehensive, temporally constrained data set of zircon trace element compositions (n = 645) for three compositionally distinct magmatic series identified in the Meghri-Ordubad pluton, southernmost Lesser Caucasus. The 30 million years of Cenozoic magmatism in the Meghri-Ordubad pluton are associated with several ore-forming pulses leading to the formation of porphyry copper deposits and epithermal-style mineralization. Our zircon geochemical data constrain the thermal and chemical evolution of this complex intrusive suite and allow an evaluation of the usefulness of zircon as a mineral exploration proxy for porphyry copper deposits. Our results combined with Rayleigh fractionation modeling indicate that the trace element composition of zircon (Th/U, Hf, Ti, YbN/DyN, Eu anomalies) is influenced by the composition and the water concentration of the parental magma, as well as by co-crystallizing titanite and apatite. In contrast, the variations of Ce anomalies remain difficult to explain by magmatic processes and could rather be ascribed to relative fluctuations of the redox conditions. In the Meghri-Ordubad pluton, we do not observe any systematic patterns between the trace element composition in zircons and the different ore-forming pulses. This questions the reliability of using the trace element composition in zircon as an exploration mineral proxy, and it rather emphasizes that a good knowledge of the entire magmatic evolution of a metallogenic province is required.

High oxidation magmatic evolution in the Naruo porphyry Cu deposit, Tibet, China

The Naruo porphyry Cu deposit is the third largest deposit discovered in the Duolong metallogenic district. Previous research has focused mainly on the geochemistry of the ore-bearing granodiorite porphyry; the metallogenesis remains poorly understood. In the present work, on the basis of outcrops and drilling core geological mapping, phases of early mineralization diorite, two inter-mineralization granodiorite porphyries, and late-mineralization granodiorite porphyry have been distinguished. Furthermore, the alteration zones were outlined, and the vein sequence was identified. The diorite and three porphyry phases were subjected to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (La–ICP–MS) zircon U–Pb dating and in situ Hf isotope analyses as well as bulk major element, trace element, and Sr–Nd isotopic analyses. Molybdenite Re–Os dating was also conducted.The zircon U–Pb dating results show that the diorite and porphyry intrusions were emplaced at about 120 Ma, and the molybdenite Re–Os isochron age is 118.8 ± 1.9 Ma; this indicates that the Naruo porphyry Cu deposit was formed during a continuous magmatic–hydrothermal process. All of the diorite and granodiorite porphyry samples showed arc magmatic characteristics. Moreover, the moderate (87Sr/86Sr)i ratios and low εNd(t) and εHf(t) values of the diorite and porphyry intrusions suggest the source region of the juvenile lower crust. The lower (87Sr/86Sr)i and (143Nd/144Nd)i ratios and higher εNd(t) values and incompatible element concentrations than those in the granodiorite porphyry samples indicate a two-stage magmatic generation process for the intrusions. The early mineralization diorite has a high Cu concentration, implying that the source is enriched in Cu. However, the slightly lower Cu content of the late-mineralization granodiorite porphyry samples might imply Cu release from magmas and deposition within the metallogenic stage. The multiple stages of intrusions and subsequent volcanism within the Duolong metallogenic district, together with high Sr/Y features, indicate persistent magmatism during the metallogenic epoch, which is necessary for maintaining the activity of magmatic–hydrothermal and mineralization processes. Thus, the high Cu content in the source region, mantle-derived melt upwelling, and multiple stages of persistent magmatism were favorable for the formation of the Naruo porphyry Cu deposit.The high Fe2O3/FeO ratios of the diorite and granodiorite porphyry intrusions show very high oxidation features, which is coincident with estimated magmatic oxidation state calculated by the zircon trace element compositions. The high oxidation facilitates sulfur and chalcophile metals to be scavenged into the magmatic–hydrothermal systems, which is crucial for the metallogenesis of the Naruo porphyry Cu deposit.