Zircon Trace Element Research Articles

Crustal thickening and multipoint delamination for the ca. 90 Ma high-Sr/Y intrusions and the associated porphyry-skarn Cu-Au-Mo mineralization in the western central Lhasa terrane, Tibetan Plateau

The ca. 90 Ma (92−84 Ma) high-Sr/Y intrusions in the western central Lhasa terrane (WCLT) of the Tibetan Plateau record critical information about the late Mesozoic crustal architecture of the Lhasa terrane and may have provided favorable conditions for porphyry mineralization. However, conflicting geodynamic processes have been proposed, and their mineralization potential is unclear. Here, we report the newly discovered Banongzuosi porphyry-skarn Mo-Cu deposit and Qielong skarn Cu-Au and Rongqing porphyry-quartz vein-type Mo mineral prospects. They provide important constraints on the generation of the ca. 90 Ma high-Sr/Y magmas and their associated mineralization potential. Then, integrated studies of the ca. 90 Ma intrusions are performed to address the above issues. Dating shows that intrusions and mineralization in the three areas occurred at 92.4−84.1 Ma. Based on whole-rock geochemistry, the high-Sr/Y intrusions can be divided into low- and high-Mg#-Cr ones. Zircon Hf isotopic data indicate that both ancient and juvenile lower crust existed in the WCLT, with significant juvenile components in the high-Mg# and Cr-rich intrusions. The crustal thickness calculated from the zircon trace element data suggests that the WCLT had thickened crust (>64 km) with local areas thinned by lower crustal delamination at ca. 90 Ma. Regional thickening and local lower crustal delamination formed the low- and high-Mg#-Cr intrusions, respectively. Whole-rock and zircon trace element data reveal that most of the ca. 90 Ma high-Sr/Y intrusions are hydrous and oxidized. The thickened crust resulted in high H2O contents and fO2 of intrusions and promoted porphyry-skarn mineralization. However, crustal thinning and contamination by reduced Precambrian basement decreased the magma fO2 and hindered mineralization. The advantageous tectonic setting and high H2O and fO2 led to the ca. 90 Ma high-Sr/Y intrusions having the potential to form collisional porphyry-skarn Cu-Au-Mo deposits.

Genesis of the Wuchiapingian Formation Tuffs and Their Relationship with the Tectonic Background of the Kaijiang–Liangping Trough in the Northern Sichuan Basin

Controversy surrounds the forming time and tectonic background of the Kaijiang–Liangping Trough in the northern Sichuan Basin. The Wuchiapingian Formation, surrounding this Late Permian trough, contains tuffs, and industrial gas reservoirs have been discovered. However, the genesis of these tuffs, revealed by the drilling wells, remains unclear. In the present work, we analyzed the samples of sedimentary tuff from the core of the study area by macroscopic and microscopic analysis, combined with whole-rock major and trace element analysis, zircon U-Pb dating, and zircon trace element analysis, defining the genesis of the Wuchiapingian Formation tuffs around the Kaijiang–Liangping Trough, in an attempt to describe the initial tectonic context of the trough. The U-Pb ages of the tuffs measured in this study range from 255 to 259 Ma. They are slightly later than the activity of the Emeishan Large Igneous Province. Considering the trough’s distance from the center of the Emeishan Large Igneous Province and its location in the outer zone, it is more likely associated with acidic volcanic eruptions of the island arc. The arc was formed by the subduction activity of the Mianlue Ocean beneath the northern Yangtze Plate. In terms of the timing of activity and the tectonic position of the subduction zone, the Kaijiang–Liangping trough in the northern Sichuan Basin is more closely related to the closing of the Mianlue Ocean.

A Review of the Mineral Chemistry and Crystallization Conditions of Ediacaran–Cambrian A-Type Granites in the Central Subprovince of the Borborema Province, Northeastern Brazil

Ediacaran–Cambrian magmatism in the Central Subprovince (Borborema Province, NE Brazil) generated abundant A-type granites. This study reviews published whole-rock and mineral chemistry data from thirteen Ediacaran–Cambrian A-type intrusions and a related dike swarm. It also presents new mineral chemistry and whole-rock data for one of these intrusions, along with zircon trace element data for five of the intrusions. Geochronological data from the literature indicate the formation of these A-type intrusions during a 55 Myr interval (580–525 Ma), succeeding the post-collisional high-K magmatism in the region at c. 590–580 Ma. The studied plutons intruded Paleoproterozoic basement gneisses or Neoproterozoic supracrustal rocks. They are ferroan, metaluminous to peraluminous and mostly alkalic–calcic. The crystallization parameters show pressure estimates mainly from 4 to 7 kbar, corresponding to crustal depths of 12 to 21 km, and temperatures ranging from 1160 to 650 °C in granitoids containing mafic enclaves, and from 990 to 680 °C in those lacking or containing only rare mafic enclaves. The presence of Fe-rich mineral assemblages including ilmenite indicates that the A-type granites crystallized under low ƒO2 conditions. Zircon trace element analyses suggest post-magmatic hydrothermal processes, interpreted to be associated with shear zone reactivation. Whole-rock geochemical characteristics, the chemistry of the Fe-rich mafic mineral assemblages, and zircon trace elements in the studied granitoids share important similarities with A2-type granites worldwide.

From birth to death: The role of upper-crustal thermal maturation and volcanism in porphyry ore formation revealed in the Yerington district

The current race towards greener energy and its intertwined increase in Cu demand imposes the need to find mineralized centers that are economic despite greater depths. To this end, a better understanding of the processes controlling the metal tonnage of porphyry Cu deposits, the main source of Cu, is needed and the focus of current research and debate. This study provides a comprehensive view of the duration of upper-crustal magmatism and its significance in the degree of metal endowment in porphyry Cu deposits using the Yerington batholith, Nevada, USA, as a case study. The Yerington district constitutes an exceptional example of an exposed porphyry Cu system where the plutonic environment that fed the porphyritic dikes is accessible. Combining trace element geochemistry and high-precision geochronology of zircon from all exposed units, we propose that the thermal maturation of the upper crust by a continuum in magmatic activity without significant hiatuses is a key factor in enabling the formation of large porphyry Cu style mineralization. The Yerington magmatic system transitioned from a volcanically active environment with coeval plutonism to a growing upper-crustal magmatic reservoir that fed the porphyritic dikes and associated mineralized centers to then resume its volcanic activity terminating the ore-forming episode. A relatively high volcanic/plutonic ratio characterized the first expressions of Jurassic magmatism in the district from ∼170 Ma with the coeval eruption of the Artesia Lake volcanics and the protracted emplacement of the McLeod Hill pluton. Geochemically, this period recorded distinctive negative Eu anomalies and a gentle increase in Yb/Dy ratios in zircon with decreasing Ti contents over a large range of zircon crystallization temperatures. This persistent magmatism over ∼2 Myr thermally matured the upper crust, enabling the growth of magmatic reservoirs that formed the Bear and Luhr Hill plutons without known volcanic activity for ∼1.3 Myr. Zircon trace element compositions indicate that this transition occurred as a continuum in decreasing negative Eu anomalies and increasing Yb/Dy with decreasing Ti contents and age across the plutonic units, reaching the more evolved signatures and lowest crystallization temperatures in the zircon from porphyry dikes. An increase in the volcanic/plutonic ratio with the eruption of the Fulstone Spring sequence likely terminated the ore-forming potential of the district. Although many other studies have provided important views on the timing and duration of porphyry Cu deposit formation, the link to their plutonic roots has been limited due to their inaccessibility. Therefore, this study offers the first complete picture into the temporal and chemical evolution of an upper-crustal magmatic system and the roles that factors like prolonged magmatism and volcanism play before and after ore formation. We argue that without the thermal maturation of the upper crust, the construction of a long-lived magmatic reservoir would not have been possible, precluding the formation of porphyry Cu deposits. Under this premise, not only the duration of ore-related magmatic activity, but the occurrence of long-lived precursor magmatism might exercise crucial control on the final tonnage of the deposit and should be considered during exploration for new porphyry deposits.

Classifying zircon: A machine-learning approach using zircon geochemistry

This study presented a novel, rapid, and accurate method for determining zircon origin via a comprehensive analysis of a dataset containing 27,818 zircon trace element sets. This method integrated back propagation neural networks with the AdaBoost algorithm. The optimal classifier characterized as a linear combination of a two-layer neural network model, comprised 100 base classifiers and 400 hidden neurons. It was rigorously trained over 1000 iterations, which resulted in an unbiased error rate of 8.31%. To facilitate practical application, the classifier was integrated into a macro-enabled Excel spreadsheet.

Two phases of granulite-facies metamorphism superimposied on retrograde eclogite: Constraints on the early Paleozoic tectonic evolution of the Qinling Orogenic Belt, central China

Existing studies provide adequate petrological evidences on ca. 500 Ma ultra-high pressure (UHP) metamorphism in the North Qinling Orogenic Belt (NQOB) in central China, but the genesis of 470–420 Ma multi-phase granulite-facies metamorphism in the NQOB and their relationship with the ca. 500 Ma UHP metamorphism remain controversial, resulting in the early Paleozoic evolution of the Qinling Orogenic Belt (QOB) highly debatable. In this study, we present mafic granulites and host felsic gneisses with a “red-eye socket” texture from the Shuanglong area, eastern NQOB, which recorded two phases of granulite-facies metamorphism superimposing on former eclogite-facies metamorphism. The former eclogite-facies metamorphism is indicated by eclogite-facies zircon trace element patterns and 496–495 Ma zircon ages, which are the same with those of the HP–UHP eclogite-facies metamorphic rocks in NQOB. The first granulite-facies metamorphism occurred at 460–448 Ma is characterized by coarse-grained minerals in matrix. Compositions and zonings of these minerals define an anticlockwise P–T path involving a prograde stage (751–763 °C), a high-temperature peak stage (9.2 kbar and 864 °C), and a near-isobaric cooling retrograde stage (8.3 kbar and 818 °C). The second granulite-facies metamorphism occurred at 422–421 Ma is represented by coronal garnet and coexisting fine-grained mineral aggregates. Coronal garnet compositional zonings suggest a clockwise P–T path consisting of a high-pressure peak stage (9.5–11.2 kbar and 748–783 °C) and a decompressing and heating retrograde stage (9.2–9.5 kbar and 789–800 °C). Combining dating results of leucosomes in these rocks and existing data, we proposed a new model for early Paleozoic tectonic evolution of the NQOB. The North Qinling Terrane (NQT), probably separated from the South China Block (SCB) during the breakup of Rodinia, drifted northwards and underwent UHP metamorphism at 500 Ma and then rapidly exhumed to crust level. Later, the Shangdan Ocean subducted northwards beneath the exhumed NQT at 470–440 Ma, resulting in the first granulite-facies metamorphism and contemporaneous migmatization and magmatism. Finally, the closure of the Shangdan Ocean led to collision between the NQT and South Qinling Terrane/SCB and the second granulite-facies metamorphism and anatexis at 422–418 Ma.

The onset of Paleo-Pacific subduction: Key evidence from the Kaishantun Accretionary Complex, northeastern Eurasia

Subduction of the Paleo-Pacific oceanic lithosphere has dominated the tectonic evolution of northeastern Eurasia since the Mesozoic. We document the time of subduction initiation based on the age, character, and paleogeographic record of the Jilin-Yanji Suture that separates the Jiamusi-Khanka Block (of Northeast China) from the northeastern North China Craton. The suture contains a series of accretionary complexes that provide abundant information for elucidating the evolution of the oceanic plates. Zircon U-Pb and Lu-Hf isotope, as well as zircon trace element data, from nine sedimentary rock samples from the Kaishantun Accretionary Complex in the easternmost segment of the Jilin-Yanji Suture document a volcanic arc setting in the end-Permian to Middle Triassic (255−244 Ma) involving the addition of juvenile crust. Based on our new data and previous studies, we propose that southwestern-directed subduction of the Jilin-Heilongjiang Ocean dominated the evolution of regional tectonics between 260 Ma and 230 Ma, which resulted in the formation of arc-related volcano-sedimentary rocks and the generation of accretionary complexes within the Jilin-Yanji Suture. The Paleo-Pacific Ocean started to subduct beneath northeastern Eurasia at ca. 235 Ma, which accelerated the closure of the Jilin-Heilongjiang Ocean and provided the major driving force for the final amalgamation of the northeastern North China Craton and the Jiamusi-Khanka Block.

Petrogenesis of episodic volcanic-intrusive rocks in SE China: Crystal-melt segregation and magma mixing

Crystal-melt segregation and magma mixing are key magmatic processes that generate compositional variabilities in igneous rocks. Distinguishing these processes can provide insight into the evolution of volcanic calderas and the driving force of plate subduction. Intensive episodic magmatism occurred in Southeast China during the Cretaceous, producing a series of volcanic-intrusive rocks during different magmatic stages in chain-like calderas. We conducted comprehensive petrological, geochemical, isotopic, and zircon trace element analyses on two representative calderas (Xiaoxiong and Shiniushan).The results show that the magmatism produced multistage volcanic and coexisting intrusive rocks regarding their crystallization ages (102–88 Ma) and NdHf isotopic compositions (zircon ɛHf(t) = −11.7 to −1.8, whole-rock εNd(t) = −8.3 to −2.4). The volcanic and intrusive rocks are related by fractional crystallization.In general, the erupted silicic rhyolitic rocks are characterized by distinctly negative Eu anomalies (δEu = 0.10–0.71) and depletions of Ba, Sr, P, and Ti, while the coexisting intrusive rocks show distinct or complementary geochemical signatures, such as neglectable Eu anomalies (δEu = 0.92–1.09) and positive Ba anomalies. Furthermore, the whole-rock samples from the calderas have variable δ41K values (from −0.14 ‰ to −0.59 ‰) that show strong correlations with indices of fractional crystallization such as Eu anomaly, Sr content, and K2O/Na2O ratios, indicating a key role of plagioclase during crystal-melt segregation. This is also supported by petrographic evidence for crystal accumulation such as the synneusis of plagioclase phenocrysts. Mafic microgranular enclaves in the volcanic-intrusive rocks indicate that magma recharge events occurred in the magma reservoir. Synthesizing these lines of evidence, we argue the multiple magmatism in plate subduction zone can be sustained by recharge events in the magma reservoir along with crystal-melt segregation processes. Particularly, the volcanic rocks tend to have isotopically lighter K than intrusive rocks, and strongly support that the volcanic rocks represent the extracted melt that is complementary to the cumulative intrusive rocks.

Ages, petrogenesis and metallogenesis implications of the Miocene adakite-like igneous rocks in the Beimulang porphyry Cu Deposit, southern Tibet

Understanding the petrogenesis of Miocene adakite-like igneous rocks is crucial for unraveling the formation processes of post-collision porphyry copper deposits within the Gangdese orogenic belt. This study focuses on the mineralogical, geochronological, and geochemical characteristics of the Beimulang Miocene adakite-like igneous rock series, with particular emphasis on two types of diorite porphyry (DP1 and DP2), to constrain their petrogenesis. Zircon U-Pb dating indicates that the monzogranite (MG), monzogranite porphyry (MGP), DP1, DP2 and granite porphyry (GP) were emplaced at 14.8 ± 0.1 Ma, 14.6 ± 0.1 Ma, 14.6 ± 0.1 Ma, 13.2 ± 0.1 Ma and 12.5 ± 0.1 Ma, respectively. The major element compositions of the Beimulang Miocene intrusions exhibit a differentiation trend. The Sr-Nd isotopic compositions of the MG, MGP, and DP1 align with the mixing line between the juvenile lower crust and the potassic lamprophyres. Conversely, the Sr-Nd isotopic compositions of DP2 and GP fall precisely on the Sr-Nd mixing line between DP1 and the ultrapotassic lamprophyres. Considering the reverse zoning of plagioclase in the DP1 and presence of high-Mg phlogopite in the DP2, we suggest that the Miocene magmatic series at Beimulang likely derived from the mixing of partial melts of Gangdese juvenile lower crust and mantle-derived potassic-ultrapotassic magmas. The increase in Th/Yb ratios from DP1, MG, MGP to DP2 and GP suggests that the mantle metasomatism material may have evolved from slab-derived fluids to melts derived from Indian crustal sediments. The magmatic water content and oxidation calculated from zircon trace elements, are nearly identical among the ore-causative MG and MGP, and the barren GP. However, the decrease in V/Sc ratios from the MG and MGP to GP indicates that magnetite-driven magma sulfide saturation leads to the depletion of chalcophile elements, significantly reducing the Cu mineralization potential of the GP. We suggest that the higher degree of magmatic evolution leads to the barren nature of Beimulang granite porphyry.

Zircon geochemistry from early evolved terranes records coeval stagnant- and mobile-lid tectonic regimes

Determining the mechanisms by which the earliest continental crust was generated and reworked is important for constraining the evolution of Earth's geodynamic, surface, and atmospheric conditions. However, the details of early plate tectonic settings often remain obscured by the intervening ~4 Ga of crustal recycling. Covariations of U, Nb, Sc, and Yb in zircon have been shown to faithfully reflect Phanerozoic whole-rock-based plate-tectonic discriminators and are therefore useful in distinguishing zircons crystallized in ridge, plume, and arc-like environments, both in the present and in deep time. However, application of these proxies to deciphering tectonic settings on the early Earth has thus far been limited to select portions of the detrital zircon record. Here, we present in situ trace-element and oxygen isotope compositions for magmatic zircons from crystalline crustal rocks of the Acasta Gneiss Complex and the Saglek-Hebron Complex, Canada. Integrated with information from whole-rock geochemistry and zircon U-Pb, Hf, and O isotopes, our zircon U-Nb-Sc-Yb results reveal that melting of hydrated basalt was not restricted to a single tectonomagmatic process during the Archean but was operative during the reworking of Hadean protocrust and the generation of juvenile crust within two cratons, as early as 3.9 Ga. We observe zircon trace-element compositions indicative of hydrous melting in settings that otherwise host seemingly differing whole-rock geochemistry, zircon Hf, and zircon O isotopes, suggesting contemporaneous operation of stagnant-lid (oceanic plateau) and mobile-lid (arc-like) regimes in the early Archean.

Prolonged arc accretion during growth of juvenile crust in the Arabian Nubian Shield: Insights from the granitoids of northern Ethiopia

The Arabian Nubian Shield (ANS) is one of the largest juvenile continental crust formed after the Archean. To determine the timing and understand the mechanism of its early crustal growth, we conducted geochronological and geochemical studies on granitoids from northern Ethiopia. A plagiogranite, dated at 929.7 ± 2.2 Ma, represents one of the early granitoids from the ANS. It shows low K2O, TiO2, and REE contents, flat REE pattern and absence of Eu anomaly. Moreover, it exhibits (87Sr/86Sr)i, ƐNd(t) and ƐHf(t) values of 0.70341, +5.0 and +8.4, respectively. Its zircon δ18O value is 4.8‰, lower than the mantle value. These characteristics suggest that it was derived from partial melting of altered oceanic crust. The oxygen fugacity obtained from zircon trace elements is ΔFMQ+1.3, consistent with a subduction setting.Other plutons have much younger ages ranging from 860 to 840 Ma and are mainly medium K, I-type granitoids. These granitoids show low MgO, Ni and Cr contents, low Sr/Y, (La/Yb)N, Nb/Ta and Zr/Sm ratios. They exhibit whole-rock (87Sr/86Sr)i values of 0.70236–0.70304, ƐNd(t) values of 4.2–5.2, ƐHf(t) values of 5.8–7.6 and zircon ƐHf(t) values of 5.5–10.4, slightly lower than coeval depleted mantle. Furthermore, they exhibit fractionated REE patterns, enrichments in LILE and depletion in HFSE. These geochemical features suggest that these granitoids were generated by remelting of arc crust. Compiled data show that the associated basaltic rocks are of arc affinity, which confirms the coeval development of arc magmatism in the southern ANS. Our results suggest that the growth of juvenile crust in the southern ANS started from the early Neoproterozoic and peaked at ca. 880 to 800 Ma, much earlier than those in the northern ANS. The prolonged history accounts for the growth of the vast juvenile crust in the ANS.

The Cambrian collision of the Yangtze Block with Gondwana: Evidence from provenance analyses

The Neoproterozoic to Paleozoic Proto-Tethys Ocean has preserved critical records of Earth’s evolutionary history. The Lower Cambrian detrital strata along the northern margin of the Yangtze Block provide valuable information for gaining insight into the evolution of the Proto-Tethys Ocean, which is important in understanding the collision between the Yangtze Block and the Gondwana assembly. Here, we present comprehensive U-Pb ages and trace elements of zircons from Lower Cambrian detrital strata in the Yangtze Block. Our results revealed prominent age peaks at 600−500 Ma and 1100−800 Ma for detrital zircons in the Cambrian strata. The trace element characteristics of the detrital zircon indicate that the source rocks were mainly intermediate-felsic magmatic suites with minor input from mafic sources. These results suggest that the detrital materials were not only supplied from the interior of the Yangtze Block but also from magmatic sources in the internal orogenic belt of Gondwana. Furthermore, the kernel density estimate plots of detrital zircon U-Pb ages indicate a stable source-sink system in the Yangtze Block during the Early Cambrian. However, our data indicate that the crustal thickness of the Yangtze Block increased significantly since ca. 526 Ma, and the cumulative characteristics of the detrital zircons indicate that the rocks were deposited in a compressional tectonic environment after ca. 526 Ma, in contrast to those during the late Neoproterozoic, which were generally deposited in an extensional tectonic environment. This transition indicates that the initial collision between the Yangtze Block and the Gondwana supercontinent might have occurred at ca. 526 Ma, marking the rapid aggregation of the northern domain of the Gondwana assembly and potentially serving as an important indicator of the closure of the Yangtze-associated Proto-Tethys Ocean. Our findings provide key insights into late Neoproterozoic−early Paleozoic ocean-land evolution.

Carboniferous rifting of the Lhasa Terrane (Tibet, China) and the break-up of East Gondwana based on detrital zircon analyses

The break-up processes of the northern margin of East Gondwana remain uncertain, especially regarding the Lhasa Terrane. In this paper, we conduct a systematic field geological survey, detrital zircon UPb dating, and zircon trace element and Hf isotope analyses in the Carboniferous rift basin in the eastern part of the Lhasa Terrane, including the Nuocuo and Laigu Formations, to reconstruct the break-up history of East Gondwana. The overall Carboniferous depositional environment in the eastern part of the Lhasa Terrane changed from near-shore and shallow marine to slope and moderately deep sea facies, reflecting a transgression. The weighted average age of several of the youngest detrital zircons from the Nuocuo Formation is 346.8 ± 6.4 Ma (4 grains), whereas that of the Laigu Formation is 328.7 ± 6.1 Ma (6 grains). The detrital zircon ages in the Carboniferous strata show similar distributions, dominated by zircons from the Indian continent (∼950 Ma), Australian continent (∼1170 Ma), and Lhasa Terrane (∼340 Ma). The paleogeographic position of the Lhasa Terrane was near the Indian and Australian continents during the Carboniferous. The increase of the ∼340 Ma detrital zircon age peak from the Mississippian to the Pennsylvanian demonstrated that the rift basin recorded a Mississippian magmatic event. The εHf(t) and oxygen fugacity values of partial zircons of ∼340 Ma are similar to those of zircons from intraplate magmatic rocks, further implying the intracontinental rifting in the Lhasa Terrane. Combined with the previous research on magmatic rocks in East Gondwana, including the Lhasa, South Qiangtang, and Himalayan Terranes, our study on sedimentation found that the Lhasa Terrane was in a passive continental margin rifting context during the Mississippian and the rift gradually expanded to become the Sumdo Paleo-Tethys Ocean basin.

Identifying tectonic settings of porphyry copper deposits using zircon trace elements – A semi-supervised machine learning method

Porphyry copper deposits (PCDs), as main sources of Cu resources worldwide, have attracted great attention for both scientific research and mining purposes in the past decades. The formation of PCDs is closely related to magmatic-hydrothermal system formed in both (continental/oceanic) arc and non-arc environments. Many low-dimensional geochemistry discriminants were developed for identifying the tectonic environments where ore-related magmas formed. However, long-term geological processes may obscure the geochemistry information recorded in rocks and minerals, which inevitably introduces uncertainties for identifying tectonic environments when using the low-dimensional discriminant diagrams. Here, we proposed a semi-supervised machine learning (ML) approach based on zircon chemistry data (spanning 16 elements) to identify the tectonic environments of PCDs. The results show that the semi-supervised models perform better in identifying the tectonic environments compared to the conventional low-dimensional discriminants. Moreover, as another benefit of big data analysis, ML model can clarify the systematic geochemistry differences of igneous zircons formed in different tectonic environments. The results suggest that (U+Th)/Yb and LREE/HREE are the top two important zircon chemical features for distinguishing PCDs formed in arc or non-arc environments. Specifically, zircons from non-arc show higher (U+Th)/Yb compared to that of continental arc, while zircons from island arc show lowest (U+Th)/Yb and LREE/HREE. Finally, the semi-supervised learning model was applied to the Dexing porphyry copper deposit to approach the longstanding debate regarding the underlying metallogenic setting. The results support the viewpoint that the Dexing porphyry copper deposit was formed in an intracontinental (non-arc) environment related to asthenosphere upwelling.

Paleo-to-Mesoarchean crustal evolution in the Uauá Block, Northeastern São Francisco Craton, Brazil: New insights from petrography, U–Pb geochronology, Lu–Hf isotopes and trace elements in zircon

The timing of Earth's initial crustal growth and reworking through collisional settings remains an issue of extensive debate. Here, we report a Paleo-to Mesoarchean migmatite-gneiss, temporally- and spatially-associated with a convergent plate boundary in the Uauá Block, Brazil. This rock records an amphibolite-bearing tonalitic residue and pyroxene-bearing granitic leucosome. Orthopyroxene indicates high-temperature metamorphism during leucosome generation, while the widespread retrogressed hornblende in the residue indicates conditions corresponding to amphibolite facies. Zircon grains display LREE-depleted magmatic cores characterized by distinct zoning, crystallized at 3325 ± 70 and 3245 ± 8 Ma. They are enclosed by LREE-enriched metamorphic overgrowth zones and rims formed at 3120 ± 7 and 3069 ± 9 Ma, accompanied by an increase in Ti content. The εHf(t) values decrease with time from +1.55 to −7.06 and Lu/Hf ratios (0.001–0.011) are consistent with the evolution of the Paleo-to Eoarchean crustal sources with TDM Hf model ages between 3.56 and 3.73 Ga. Our findings provide direct evidence of crustal reworking, implicating a Paleoarchean protolith submitted, during early Mesoarchean, to a high-temperature metamorphism spatially-associated with a regional collisional setting in the São Francisco Craton. Further, we surmise that convergent tectonic processes may have played an important role in crustal reworking during the Paleo-to Mesoarchean transition. These observations allowed a comparison between the crustal evolution of the Uauá and Gavião Blocks in the northern São Francisco Craton, as well as with other Archean cratons.

Machine-learning oxybarometer developed using zircon trace-element chemistry and its applications

Abstract Magmatic oxygen fugacity (fO2) is a fundamental property to understanding the long-term evolution of the Earth’s atmosphere and the formation of magmatic-hydrothermal mineral deposits. Classically, the magmatic fO2 is estimated using mineral chemistry, such as Fe-Ti oxides, zircon, and hornblende. These methods, however, are only valid within certain limits and/or require a significant amount of a priori knowledge. In this contribution, a new oxybarometer, constructed by data-driven machine learning algorithms using trace elements in zircon and their corresponding independent fO2 constraints, is provided. Seven different algorithms are initially trained and then validated on a data set that was never utilized in the training processes. Results suggest that the oxybarometer constructed by the extremely randomized trees model has the best performance, with the largest R2 value (0.91 ± 0.01), smallest RMSE (0.45 ± 0.03), and low propagated analytical error (~0.10 log units). Feature importance analysis demonstrates that U, Ti, Th, Ce, and Eu in zircon are the key trace elements that preserve fO2 information. This newly developed oxybarometer has been applied in diverse systems, including arc magmas and mid-ocean ridge basalts, fertile and barren porphyry systems, and global S-type detrital zircon, which provide fO2 constraints that are consistent with other independent methods, suggesting that it has wide applicability. To improve accessibility, the oxybarometer was developed into a software application aimed at enabling more consistent and reliable fO2 determinations in magmatic systems, promoting further research.

Amphibole fractionation as a key driver for oxidation of magmas in convergent margins

During the process of differentiation, the magmas in convergent margins undergo an increase of oxidized nature, accompanied by a decreased Fe content and concentration of heavy Fe isotopes. Garnet and amphibole are both Fe-rich minerals, which can be responsible for this phenomenon through fractional crystallization. One prevailing hypothesis suggests that Fe2+-rich garnet cumulates in the arc root as a "crustal redox filter." However, the stability of garnets is highly dependent on pressure conditions. In contrast, amphibole can crystallize under a broader range of temperature and pressure conditions and is a more common mineral phase in magmas. As such, the contribution of amphibole might have been underappreciated. Here, we conducted elemental composition, zircon trace element, and high-precision Fe isotope analyses on Miocene magmatic rocks from the Gangdese arc to trace the evolution of magmatic oxidation. The results indicate that the enrichment of heavy Fe isotopes in these magmas is primarily controlled by amphibole-dominated fractional crystallization rather than garnet. This also implies that amphibole fractional crystallization may play a role in enhancing the oxygen fugacity of the magmas. Taking a global perspective, we found a pervasive correlation between amphibole fractional crystallization and Fe isotope fractionation in magmatism at convergent plate margins, indicating its widely applicable influence on oxidation. The influence of garnet cannot be entirely neglected in some specific scenarios, such as within thickened continental arcs, but its impact is generally limited. Continuous amphibole fractional crystallization increases oxidation, facilitating the mobilization and concentration of Cu within the magma, thereby enhancing the potential for porphyry deposit formation. This impact is especially notable in spatiotemporally related magmatic events and could be decisive in determining the magmatic mineralization potential.

Implications of Late Triassic–Middle Jurassic detrital zircons from the southeastern margin of the South China Block for the Paleo-Pacific Plate subduction

There existed an early Mesozoic tectonic regime transformation in the South China Block (SCB). Although it was believed that this transformation was closely related to the subduction of Paleo-Pacific Plate, the process and initial time of the subduction of the Paleo-Pacific Plate have been controversial for a long time. Based on the published Upper Triassic and Middle Jurassic succession detrital zircons geochronology from the southeastern margin of the SCB, the newly obtained Late Triassic to Middle Jurassic detrital zircons Hf isotope data, and the available magmatic age data and Hf isotope data, this study discussed the subduction of the Paleo-Pacific Plate. The Hf isotope composition of zircon grains selected from the Early Mesozoic strata of the SCB, spanning from the Late Triassic to the Middle Jurassic, exhibits a consistent temporal trend with that of the Triassic–Middle Jurassic magmatic rocks. Both display a transition from negative to positive εHf(t) values, indicative of a gradually increasing contribution of mantle-derived materials from the Triassic to the Middle Jurassic. Zircon trace elements indicate that a magmatic arc appeared outside the southeastern margin of the SCB at 200–190 Ma and continued to develop into the Middle Jurassic, which may have been generated by the Paleo-Pacific Plate subduction. This study proposed that the Paleo-Pacific Plate subduction was confined to the southeastern coast of the SCB in the Late Triassic, and the subduction of the flat slab was halted by obstruction at the end of the Late Triassic. In the Early Jurassic, the Paleo-Pacific Plate began to subduction again, and arc-related magmatic rocks were formed along the coast of SCB. At the same time, due to the remote effect of the subduction of the Paleo-Pacific Plate, the weak tectonic belt existing in the Nanling area was reactivated, resulting in the Nanling area in the intraplate extensional setting. Subsequently, the continuous subduction of the Paleo-Pacific Plate led to the thickening of the crust along the SCB in the Middle Jurassic, and the Nanling area was still under in the extensional setting.

Geochronology and petrogenesis of multiple magmatic events in the Tianbaoshan orefield, NE China: Implications for tectonic evolution

Recent studies have shown that multistage magmatic and metallogenic events in NE China were dominated by the Paleo-Asian Ocean tectonic regime and the Paleo-Pacific Ocean tectonic regime. However, outstanding questions remain on the petrogenesis and fertility of ore-causative magma in each metallogenic event. In this study, we report new geochronologic and geochemical data on ore-causative intrusions from the Tianbaoshan orefield in the east Jilin-Heilongjiang belt (EJHB), aiming to identify their petrogenesis, magma fertility, and their implications for the geodynamic evolution of the EJHB. Middle Permian Lishan ore-causative quartz monzodiorites with abundant mafic microgranular enclaves (MMEs) were emplaced at ca. 264.9 ± 2.6 Ma. Petrographic and geochemical characteristics (87Sr/86Sr(i) = 0.7049–0.7053, εNd(t) = 2.9–3.7, and εHf(t) = 4.7–11.7) indicate a juvenile crust source injected by a slab-metasomatized mantle component. The Early Jurassic Beishan monzogranites (ca. 192.5 ± 1.8 Ma) were generated by the partial melting of the juvenile underplating basaltic lower crust with subsequent fractional crystallization in response to their highly evolved geochemical features, combined with their depleted Sr-Nd-Hf isotopic signature (ISr = 0.7032–0.7037, εNd(t) = 2.8–3.3, and εHf(t) = 7.2–12.2). Based on the zircon trace element geochemistry, we infer that the Middle Permian quartz monzodiorites had a high oxygen fugacity (Ce4+/Ce3+ = 40–216), potentially generating the Pb-Zn-Cu mineralization. Early Jurassic Beishan monzogranites had a lower magmatic oxygen fugacity (Ce4+/Ce3+ = 14–106), which may account for the Mo-dominated mineralization. A combination of this study and previous results corroborates that the Tianbaoshan orefield records the superposition of different tectonic regimes during metallogenesis.

Recently Identified Mesoproterozoic Strata in South‐Central Idaho Document Late‐Stage Rifting of the Nuna Supercontinent in Western Laurentia

AbstractSedimentary basins are valuable archives of tectonic processes involved in continental rifting. The northern Rocky Mountains preserve the Belt Supergroup, one of the most complete records of Mesoproterozoic strata on Earth; however, debate remains about its tectonic origin. We investigated a recently identified package of Mesoproterozoic strata at Leaton Gulch near Challis, Idaho, using a combination of traditional and newer sedimentological tools. Results suggest that the Leaton Gulch stratigraphic section was deposited in a fluvial setting ca. 1,380–1,317 Ma, spanning the poorly documented interval between late Belt Supergroup deposition at ∼1,370 Ma and recently characterized Deer Trail Group strata that are less than 1,300 Ma. Detrital zircon age distributions from Leaton Gulch demonstrate a similar provenance signature to Missoula Group rocks of the upper Belt Supergroup; however, Leaton Gulch strata are up to ∼70 Ma younger than most prior age constraints on Belt Supergroup rocks. Regional metabentonites (interpreted as metamorphosed reworked tuffs) found within Leaton Gulch and Missoula Group strata show dominantly radiogenic εHf(t), with a range of −8 to +15, interpreted as a mix of primary mantle and remelted metasedimentary sources. Zircon trace element data of the metabentonite from Leaton Gulch suggest a 1,450–1,300 Ma geochemically consistent and moderate–high silica melt source. Collectively, the strata of Leaton Gulch record basin sedimentation during a critical window of Mesoproterozoic time. We speculate that sedimentation during late‐stage Belt Supergroup deposition thickened and stepped westward, abandoning the main Belt basin, culminating with breakup of the Nuna Supercontinent.