Depletion In Nb Research Articles

Zircon U-Pb-Hf Isotopes, Biotite 40Ar/39Ar Geochronology, and Whole-Rock Geochemistry of the Baogeqi Gabbro in the Northern Alxa, Southernmost Central Asian Orogenic Belt

The final closure time of the Paleo-Asian Ocean and the Permo-Carboniferous tectonic settings in the northern Alxa are very important but controversial tectonic issues. The geochronology and petrogenesis of mafic igneous rocks are superior in clarifying regional tectonic settings. Here, we report on zircon U-Pb-Hf isotopes, biotite 40Ar/39Ar geochronology and whole-rock geochemical data of the hornblende gabbro from the Baogeqi gabbro pluton in the northern Alxa. The LA-ICP MS U-Pb analysis of zircon grains from the hornblende gabbro yield a weighted mean age of 262.7 ± 2.3 Ma (2σ, MSWD = 0.74), manifesting that the Baogeqi gabbro pluton emplacement was during the late Middle Permian (Capitanian). The 40Ar/39Ar dating of biotite grains from the hornblende gabbro yields a plateau age of 231.3 ± 1.6 Ma (2σ, MSWD = 0.55), indicating that the Baogeqi gabbro pluton cooled to below 300 ℃ in the Triassic. The hornblende gabbro samples are calc-alkaline with metaluminous character, and show enrichment in large ion lithophile elements (e.g., Rb, Ba, Sr, and K) but depletion in Nb, Ta, P, Th, and Ti relative to primitive mantle. Combined with the positive zircon εHf(t) values (+4.9–+9.4), we suggest that the magmas formed from the partial melting of depleted mantle were metasomatized by slab-derived fluids. Together with regional geology, these geochemical data suggest that the Baogeqi gabbro pluton was formed in an intracontinental extension setting, further indicating that the Paleo-Asian Ocean in the northern Alxa was closed prior to the late Middle Permian (Capitanian), and this region was in a post-collision extensional setting during the Capitanian-Late Permian. In addition, the Triassic cooling of the gabbro pluton may be a record of the decline of the Capitanian-Late Permian post-collisional extension basin due to the far-field effect of subduction-collision during the closure of the Paleo-Tethys Ocean.

Geochronology and petrogenesis of granitoids and associated mafic enclaves from Ghohroud in the Urumieh–Dokhtar Magmatic Arc (Iran): Evidence for magma mixing during the closure of the Neotethyan Ocean

The Ghohroud granitoids (GG), containing mafic microgranular enclaves (MMEs) are located in the central part of the Urumieh‐Dokhtar Magmatic Arc (UDMA) in central Iran. They are associated with the subduction‐related magmatism in the Alpine‐Himalayan orogenic belt. The GG are comprised of a variety of intermediate and felsic rocks, including tonalite, granodiorite, granite, diorite porphyry and monzodiorite. The MMEs are gabbroic diorite and tonalite in composition and characterized by a fine‐grained hypidiomorphic microgranular texture with occasional chilled margins. They show rounded, sharp or irregular contact with the host granitoids. The occurrences of quartz, K‐feldspar and corroded plagioclase indicate that MMEs are the products of mixing between mantle and crust‐derived magmas. New ages of zircon U–Pb dating reveal that the GG in the Kashan area emplaced at ca. 19–17 Ma (Burdigalian). All the samples of MMEs and granitoid host rocks in this study are metaluminous and calc‐alkaline with I‐type affinities. They are enriched in light rare earth elements (LREEs) and show slight negative Eu anomalies (Eu/Eu* = 0.36–0.95). These features in a combination with the relative depletion in Nb, Ta, Ti and P, indicate the granitoids and MMEs are closely associated with subduction‐related magmas at an active continental margin. The host rocks yield relatively homogeneous isotopic compositions of initial 87Sr/86Sr ratios ranging from 0.706036 to 0.707055, εNd(t) values varying from −2.25 to 0.8, and the Nd model ages (TDM) vary in a limited range of 0.70–0.96 Ga. The MMEs show similar initial 87Sr/86Sr ratios (0.706420–0.707366), εNd(t) values (−1.32 to −0.27), TDM (0.68–1.09 Ga) and Pb isotopic compositions with host granitoids, which imply they attained isotopic equilibration during magma mingling and mixing. In combination with the petrographic, chemical and isotopic results, we suggest that the origin of MMEs and their host rocks were related to the interaction between crust‐derived melts and mantle‐derived mafic magmas. The magma‐mixing event possibly occurred during the transition from subduction to collision in the UDMA along with the closure of the Neotethyan ocean.

Genesis and Metallogenic Characteristics of the Zhunsujihua Granitic Intrusions in Sonid Left Banner, Inner Mongolia, China

The Zhunsujihua porphyry Mo-Cu deposit is located in the Erenhot–East Ujimqin metallogenic belt in northeastern China. Granodioritic intrusions in the mining area are dominated by granodiorite and granodiorite porphyry, but the Mo mineralization is limited within the granodiorite. Zircon LA-ICP-MS U-Pb dating yields crystallization ages of 301.5 ± 3.0 Ma for granodiorite and 296.0 ± 3.0 Ma for granodiorite porphyry. These ages constrain the magmatic activity at the Zhunsujihua deposit that took place during the subduction of the Paleo-Asian oceanic plate. Whole-rock geochemical data suggest that the granodioritic intrusions belong to calc-alkaline and high-K calc-alkaline series, and are characterized by enrichment in K, Rb, U, Th, and Pb, and depletion in Nb, Ta, Ti, and P. The negative Eu, Ba, and Sr anomalies suggest that they have experienced extensive fractionation of plagioclase. Trace element compositions of zircons from the Zhunsujihua deposit provide constraints on the oxygen fugacity (ƒO2) of the magma, which is shown to high values with ∆FMQ = +0.5 to +5.6. The wide range of zircon εHf (t) (+1.3~+9.4) values, positive whole-rock εNd (t) (+2.5~+3.9) values, and relatively low initial (87Sr/86Sr)i (0.70367~0.70561) ratios indicate that the magmas mainly originated from a juvenile lower crust source derived from depleted mantle, but mixed with pre-existing crustal components. Moreover, the juvenile lower crust represents the main source of Mo for the Zhunsujihua deposit. A high magmatic oxygen fugacity and fractional crystallization played key roles in forming the Zhunsujihua deposit.

Transition of plastic deformation mechanisms governed by spacing of nano-precipitates in a high entropy alloy

Optimization of the plastic deformation mechanism by reducing the stacking fault energy (SFE) of alloys through precipitation is a promising method to improve the strength–plasticity synergy of high-entropy alloys (HEAs). In this study, two HEAs with the same composition but different deformation mechanisms were developed by controlling precipitation. The dislocation plane slip and stacking fault (SF)-dominated deformation were tuned to be the main deformation mechanisms in the two HEAs. The transition of the deformation mechanism was induced by a change in the spacing (λ) of nano-precipitates. Only at sufficiently small λ (< 6 nm), the regions with reduced SFE around nano-precipitates connected and overlapped owing to the depletion of Ni and Nb, reducing the SFE of the whole matrix. This promoted the formation of SFs during deformation, thereby simultaneously improving strength and plasticity.

Geological, Mineralogical and Geochemical Study of the Aquamarine-Bearing Yamrang Pegmatite, Eastern Nepal with Implications for Exploration Targeting

The Yamrang Pegmatite in the Ikhabu Pegmatite Field, Eastern Nepal is Nepal’s primary source of aquamarine. This paper reports detailed mineralogy and whole rock granite and pegmatite geochemistry, and major and trace element data for alkali feldspar and muscovite in order to classify the aquamarine-bearing Yamrang Pegmatite, elucidate beryl-saturation processes and evaluate potential geochemical exploration tools for beryl-pegmatites. Five internal mineralogical/textural zones were identified in the Yamrang Pegmatite; zone 1 (saccharoidal albite); zone 2 (blocky perthitic microcline); zone 3 (muscovite–microcline–quartz); zone 4 (beryl-quartz), and zone 5 (miarolitic cavities). Zones 1–4 represent the magmatic stage, while zone 5 formed during the hydrothermal stage of pegmatite genesis. Spectacular aquamarines are recovered from miarolitic zone 5, while beryl saturation is found in zones 3, 4, and 5. Based on beryllium (Be) content, Be partition among co-existing minerals at the magmatic stage is beryl &gt; muscovite &gt; tourmaline &gt; alkali feldspar &gt; quartz. In contrast, the sequence at the hydrothermal stage is beryl &gt; muscovite &gt; albite &gt; tourmaline &gt; quartz. The Be content in rock-forming minerals decreases from pegmatite margin to core, and tourmaline could have played a significant role in Be enrichment processes in the marginal pegmatite zone. High temperature, a low degree of fractionation, and the dominance of Be-compatible mineral phases such as muscovite, calcium-rich alkali feldspar and tourmaline resulted in beryl undersaturation in marginal zones. However, low temperature, high fractional crystallization, and low abundance of Be-compatible mineral phases resulted in beryl saturation in inner zones. The strongly peraluminous nature, low total REE content (&lt;500 ppm), mineral assemblage of beryl, tourmaline, spessartine, columbite-tantalite, depletion of Ba, Nb, and enrichment of Pb, Rb, Cs in the primitive mantle normalized multi-element plots suggest that the beryl-bearing Yamrang Pegmatite corresponds to the LCT pegmatite family. Alkali feldspar with K/Rb values of 30–150, Rb ~3000 ppm, Cs &gt;100 ppm, and muscovite, with K/Rb ranging 18–50, Rb ~6000 ppm, Cs &gt; 500 ppm, and Ta &gt; 65 ppm in inner zones (3–5), indicate that the Yamrang Pegmatite is an intermediate-fractionated, beryl-type rare-element (REL) pegmatite. It is probable that whole rock Be content of &gt;10 ppm could be considered an exploration guide to beryl mineralization in the region.

Neoproterozoic tectonic shift from collisional orogenesis to intraplate extension in the Yili Block, southern Central Asian Orogenic Belt

Understanding the tectonic evolution of the many micro-continents in the Central Asian Orogenic Belt is a complex and controversial issue. One such micro-continent, the Yili Block is characterized by Neoproterozoic magmatic rocks, which can provide important constraints on the tectono-magmatic history of the region. Herein, we present a systematic investigation of the petrology, whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes on newly identified leucogranite intrusions and gabbroic dikes in the Wenquan district of the northern Yili Block. Two leucogranite samples yielded zircon U-Pb ages of 983 ± 9 Ma and 905 ± 9 Ma, respectively. Both of muscovite-bearing leucogranites have S-type affinities and show distinctive geochemical compositions similar to peraluminous granites. Furthermore, the leucogranites exhibit low Rb/Sr ratios (0.10–0.49) and elevated zircon εHf(t) values (+3.04 - +13.59), indicating that they were derived from partial melting of supracrustal pelitic and mafic rocks. In contrast, one gabbroic dike sample yielded a zircon U-Pb age of 779 ± 5 Ma. The gabbroic samples have distinctly high Th/Yb (1.10–1.68) and low Nb/La (0.37–0.46) ratios, with enrichment in large ion lithophile elements and depletion in Nb, Ta and Ti, implying that they were sourced from a metasomatic subcontinental lithospheric mantle. Integrated with other available data, we propose that the Yili Block underwent continuously collisional orogenesis during the early Neoproterozoic (ca. 983–780 Ma), with a subsequent tectonic shift from collisional to an intraplate extensional setting at ca. 779–776 Ma. A comparable magmatic evolution also occurred in adjacent micro-continents of the Kazakhstan region and northern Tarim Craton, indicating that these micro-continents may have shared a common Neoproterozoic geodynamic evolution.

Petrogenesis of Miocene igneous rocks in the Tafresh area (central Urumieh‐Dokhtar magmatic arc, Iran): Insights into mantle sources and geodynamic processes

Cenozoic tectono‐magmatism in Iran is widely considered to be related to subduction of the Neo‐Tethys Ocean. We employed whole‐rock and mineral geochemistry and isotopic data of intrusive rocks from Tafresh, central Urumieh‐Dokhtar magmatic arc, to evaluate the role of the mantle in magmatism, to assess the timing of emplacement, and to interpret the tectonic setting. Rock compositions range from gabbro or gabbro‐diorite (plagioclase + pyroxene ± olivine), to diorite (plagioclase + amphibole ± pyroxene), to granodiorite (quartz + plagioclase + K‐feldspar + amphibole + biotite), exhibiting high‐alumina calc‐alkaline affinity. Major oxide and trace element variations vary systematically from less to more evolved rocks suggesting a major role for fractional crystallization processes. Zircon LA‐ICP‐MS U–Pb ages of major rock types are in the range of 24–19 Ma, whereas those of gabbroic dikes are ~17.5 Ma. ԐNd values range between −1.8 and 3.7, and (87Sr/86Sr)i is narrowly restricted to 0.705–0.706, suggesting a common mantle source. The enrichment in light rare earth element (REE) enrichment and flat heavy REE patterns couple depletion of Nb–Ta–Ti indicate that subducting oceanic crust had interacted with the overlying mantle wedge. High‐alumina, mid‐Mg# Tafresh plutonic rocks formed from hydrous melts from which Ca‐pyroxene and magnetite crystallized earlier than plagioclase, whereas late‐crystallizing zircon nucleated while magma traversed through lithospheric mantle and Cadomian crust. Modelling of isotope and incompatible‐element patterns suggests the contribution of no more than ~5% molten sediment or other crustal components in Tafresh magma, at a developmental stage before most plagioclase and amphibole had crystallized. The Miocene Tafresh plutons originated during the final stages of subduction, before the collision between the Arabian and Eurasian plates.

Genesis of the Xiarihamu Magmatic Ni-Co Sulfide Deposit in the East Kunlun Orogen, Northern Tibetan Plateau: In Situ Oxygen Isotope and Geochemical Perspectives

Abstract Convergent margins are commonly deemed to have poor potential to form giant magmatic Ni-Cu-(platinum group element) sulfide deposits, due to the possibly low lithospheric geothermal gradient and the small basaltic magma fluxes. This view, however, is challenged by the recent discovery of the Xiarihamu Ni-Co deposit in the East Kunlun orogen (northern Tibetan Plateau), which contains ~157 million metric tons (Mt) of sulfide ores at 0.65% Ni, 0.013% Co, and 0.14% Cu, making it the world’s 20th largest magmatic sulfide deposit. To investigate the mantle source nature, magmatic processes, and their genetic linkage to Ni-Co mineralization in orogenic belts, we presented new in situ orthopyroxene oxygen isotope and pyroxene trace element data from the mafic-ultramafic cumulate rocks at Xiarihamu. Our results show that orthopyroxene crystals have much higher δ18O (6.40–8.58‰) than those in unmodified mantle peridotite (5.72 ± 0.14‰). Orthopyroxene grains in the primitive harzburgite cumulates have the lowest δ18O values (6.40–7.71‰) and the highest Mg# contents (88.7–83.9). From the harzburgite to the evolved lithologies (e.g., websterite and gabbronorite), the δ18O values of orthopyroxene increase, whereas the Mg# values, Ni contents, and heavy/light rare earth element (HREE/LREE) ratios of orthopyroxene decrease, implying crustal contamination during magma fractionation. The δ18O variations and sharp increases in V/Sc and LREE/HREE ratios from the primitive orthopyroxene crystals (with the highest Ni and Mg#) to the evolved ones (with low Ni and Mg#) indicate that crustal contamination played a critical role in sulfide saturation. The absences of any trend in orthopyroxene δ18O values versus Mg# contents, Ni concentrations, and La/Yb ratios toward unmodified mantle values suggest an enriched mantle source. On the mid-ocean ridge basalt (pyroxene)-normalized multielement plots, both orthopyroxene, clinopyroxene, and calculated parental magma show LREE and large ion lithophile element (LILE) enrichments and depletions in Nb-(Ta), Sr, and Zr-(Hf). The predicted primitive magma trace element compositions and the high-δ18O characteristics of the high-Mg# orthopyroxene grains suggest that the Xiarihamu primitive magma was partly originated from the pyroxenite mantle metasomatized by subducted slab-derived melts and fluids. Given the lower solidus temperature of clinopyroxene relative to olivine, pyroxenites in the mantle wedge may generate voluminous high-Ni magmas during partial melting. The high-Ni magmas are likely conducive to magmatic Ni-Cu sulfide mineralization in orogenic belts.

Geochronology and geochemistry of 2.3 Ga mafic intrusions in the Dengfeng area: Evidence for early Paleoproterozoic subduction in the southern North China Craton

The time of 2.45–2.2 Ga in the early Paleoproterozoic era is called as ‘Quiet Interval’ because of the decreased magmatic activity worldwide. However, tectonic evolution of old continents during this time interval is still in dispute due to the rare geological records, especially for magmatism. In the southern North China Craton (NCC), the Jingwan mafic intrusions intruded into the Songshan Group and its zircon U-Pb dating yielded a weighted mean 207Pb/206Pb age of 2301 ± 16 Ma, and thus they are the only ca. 2.3 Ga mafic magmatic records founded in this region. These diabases belong to low-K tholeiitic series with relatively low K2O (0.1–0.7 wt%) and total alkalis (Na2O + K2O) (2.4–4.7 wt%). They have low SiO2 (44.8–54.1 wt%), slightly variable Fe2O3T (10.1–14.4 wt%), Al2O3 (14.8–17.0 wt%), CaO (5.5–10.6 wt%), and medium to high MgO (6.1–10.8 wt%) and Mg# values (58–65). The rocks display LREE enrichment ((La/Yb)N = 3.02–3.58) without obvious Eu anomaly (Eu/Eu* = 0.87–1.18). They are characterized by obvious depletion in Nb, Zr and Ti, and enrichment of Sr, Ba and Pb, indicative of geochemical features of island arc magmas. The rocks have experienced crystallization from clinopyroxene to orthopyroxene, then plagioclase, suggesting the hydrous fractionation order. They also exhibit variable εNd(t) values ranging from − 0.2 to + 0.8 and zircon εHf(t) values from − 3.0 to + 6.6. These features suggest that the mafic intrusions are formed by partial melting of a garnet-spinel lherzolite and derived from an enriched mantle source metasomatized by slab-derived fluids at a shallow depth. Combined with the previous reported magmatic records, the ca. 2.3 Ga magmatic activity may be a result of the oceanic slab subduction beneath the Eastern Block of the NCC, and the subduction probably continue throughout the early Paleoproterozoic from ca. 2.5 Ga to ca. 2.3 Ga, at least 200 Ma. Therefore, the prevalence of early Paleoproterozoic magmatic activities in the southern NCC indicate that the tectonic activity did not shutdown globally during the interval of the ‘tectono-magmatic lull’.

Zircon U–Pb geochronology and Sr–Nd–Hf–O isotopic constraints on the relationship between Mo and Pb–Zn mineralization in the Haisugou pluton in the southern Great Xing’an Range, northeast China

The Haisugou pluton and its contact zones with Middle Permian strata contain Cu–Mo and Pb–Zn ore deposits, providing an excellent example to study the relationship between Pb–Zn–Ag and Mo mineralization in the southern Great Xing’an Range (SGXR). Here we present U–Pb zircon ages and Sr–Nd–Hf–O isotope data for biotite monzogranite in the Xiaojingzi Pb–Zn deposit and Mo-bearing biotite monzogranite in the Xiaojingzi Cu–Mo deposit. These rocks yield zircon U–Pb ages of 136.2 ± 1.1 and 135.5 ± 1.3 Ma, respectively. The biotite monzogranites are enriched in SiO2 (average = 68.9 wt%) and Na2O + K2O (average = 7.7 wt%), contain 14.3–15.1 wt% Al2O3 (average = 14.7 wt%), and have A/CNK values of 0.97–1.05, indicating the biotite monzogranites are high-K calc-alkaline granites, and peraluminous. The biotite monzogranites are also characterized by negative Eu anomalies (Eu/Eu* = 0.78–0.45), enrichments in Rb, Th, U, Nd, and Hf, and depletions in Ba, Sr, P, Ti, and Nb. The biotite monzogranites have (87Sr/86Sr)i ratios of 0.70519–0.70457, εNd(t) values of + 0.37 to –0.39, and TDM2 ages of 978–915 Ma. They also have zircon εHf(t) values of 3.6–9.1, TDM2 model ages of 959–608 Ma, and δ18O values of 6.68‰–7.42‰. The Mo and Pb–Zn mineralization around the Haisugou pluton were genetically related to the granitic pluton and occurred simultaneously, forming a porphyry system. Geochemical and Sr–Nd–Hf–O isotope data indicate the Haisugou pluton was probably formed by partial melting of juvenile crust and mixing with mantle-derived components. In the Early Cretaceous, the SGXR was in an extensional setting, which was related to asthenospheric upwelling after the closure of the Mongol–Okhotsk Ocean.

Geology, geochronology and geochemistry of the Saishitang Cu deposit in the East Kunlun Orogenic Belt,NWChina

The Saishitang deposit, located in the eastern part of the Eastern Kunlun Orogenic Belt, NW China, hosts important Cu mineralization. The ore occurs as stratiform bodies in Lower–Middle Triassic siltstone and siliceous rock and as lenticular bodies at the contacts between quartz diorite and marble. The whole‐rock geochemistry and Si–O isotopic compositions of the siliceous rocks suggest a sedimentary origin. The quartz diorite has a weighted mean zircon U–Pb age of 215.5 ± 0.9 Ma. The quartz diorite exhibits high SiO2(63.91–69.48 wt%), Al2O3(14.98–17.11 wt%) and Na2O (2.17–4.58 wt%) contents, with A/CNK values of 0.79–1.10, similar to those of calc‐alkaline I‐type granites. The quartz diorite exhibits weak negative Eu anomalies (δEu = 0.80–0.99), enrichment in light rare earth elements, Rb, Ba, K and Pb and depletion in heavy rare earth elements, Nb, Ta, P and Ti. The Pb isotopic compositions suggest that the skarn ore, quartz diorite and host rocks are closely correlated, reflecting a common source. By contrast, the Pb isotopic compositions of sulphide ores hosted within siltstone are heterogeneous, suggesting multiple lower‐crustal and upper‐mantle sources. By integrating our geological and geochemical data, we propose that the Saishitang deposit was formed by exhalative sedimentary mineralization in a back‐arc basin and overprinted by Indosinian skarn mineralization in a post‐collision extensional environment.

Early Permian magmatism above a slab window in Inner Mongolia, North China: Implications for the Paleo-Asian Ocean subduction processes and accretionary crustal growth

Identifying magmatic rock associations in a subduction zone is substantial for understanding the related geodynamic evolution. The final closure time of the Paleo-Asian Ocean and the exact subduction processes have continuously been controversial, hindering our recognition of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). Here we investigated the Early Permian gabbros-granodiorites from Xi Ujimqin in the northern Inner Mongolian region. The gabbros have slightly depleted light rare-earth elements [(La/Yb)N = 0.8] and flat heavy rare earth elements (HREE) [(Gd/Yb)N = 1.1] that are comparable to those of N-MORB. They show depletion in Nb and Ta, positive whole-rock εNd(t) values of +7.7 to +8.7 and zircon εHf(t) values of +8.7 to +10.6. These mafic rocks are interpreted to be products of partial melting of depleted mantle that had been metasomatized by slab-derived fluids, with subsequent fractional crystallization and minor crustal contamination. These granodiorites chemically resemble typical adakites and have MORB-like whole-rock SrNd isotopic compositions (87Sr/86Sri = 0.7028–0.7029; εNd(t) = +8.2–+8.5) and positive zircon εHf(t) (+13.4–+15.9) values, suggesting that they originated from the subducted slab-melts and reacted with mantle wedge peridotite. UPb zircon dating shows emplacement of N-MORB-type gabbros and adakitic granodiorites at ∼297 Ma and ∼290 Ma, respectively. Our new data indicate the presence coeval slab-derived adakites and slab fluid-metasomatized asthenosphere-derived N-MORB-type rocks, indicating that subduction lasted until at least the Early Permian. Such an association along with the extension-related magmatism in northern Mongolia recorded the northward ridge subduction of the Paleo-Asian Ocean during the Late Carboniferous–Early Permian. This model is consistent with the spatial distribution and the ages of magmatic activity with positive εNd(t)–εHf(t) values from this region. Ridge subduction and induced slab windows probably played a key role in Paleozoic crustal growth of CAOB, and by inference in the other accretionary orogens throughout Earth history.

Geochemistry and Zircon U–Pb Geochronology of the Zhuxi Granites in the Jingdezhen Area, Jiangxi Province, China: Implications for the Mesozoic Tectonic Development of South China

Mesozoic granitic magmatism in Northeastern Jiangxi, China is of tectonic significance for the evolution of the South China Block. Whole-rock geochemical and zircon U–Pb geochronological and Lu–Hf isotopic data for Mesozoic Zhuxi granites in the Jingdezhen area of Northeastern Jiangxi were presented. The Zhuxi granites are composed of granodiorite, biotite granite, and two-mica granite. Zircon LA–ICP–MS U–Pb isotopic analyses indicated emplacement at 159–147 Ma. The granites are characterized by a strongly peraluminous nature with high A/CNK values (&gt;1.1), high SiO2 (66.09–74.46 wt.%) and K2O (3.50–5.52 wt.%) contents, depletion in Ba, Nb, Ce, Sr, and Ti, moderately negative Eu anomalies (Eu/Eu* = 0.40–0.63), enrichment in LREE, and depletion in HREE ((La/Yb)N &gt; 7.43). The A/CNK &gt; 1.1, widespread aluminum-rich minerals (e.g., muscovite and tourmaline), indicating they are S–type granites and belong to muscovite–bearing peraluminous granites (MPG). The Zhuxi granites exhibited negative εHf(t) values (−9.9 to −3.7) and the TDM2 model ages of 1840–1442 Ma indicated derivation from ancient crustal sources. The magma is possibly caused by the subsequent process of intracontinental subduction. It is inferred that the Mesozoic magmatism in Northeastern Jiangxi was associated with oceanic–continental convergence of the Paleo–Pacific and Eurasian plates as well as the intracontinental subduction of the Yangtze and Cathaysia blocks. The Zhuxi granites highlight the primary role of oceanic–continental convergence and intracontinental subduction in early Yanshanian granitoid magmatism in South China.

Petrogenesis of post-collisional Middle Eocene volcanism in the Eastern Pontides (NE, Turkey): Insights from geochemistry, whole-rock Sr-Nd-Pb isotopes, zircon U-Pb and 40Ar-39Ar geochronology

The debate about whether Eocene magmatism is considered to be post-collisional or subduction-related or not still continues. Here we offer new 40Ar-39Ar ad U-Pb zircon geochronology, mineral chemistry, bulk rock and Sr-Nd-Pb isotope geochemistry data obtained from the southern dike (SD) suite, in comparison with the northern dike (ND) suite, from the Eastern Pontides. The geochronological data indicate that the SD suite erupted between 45.89 and 45.10 Ma corresponding to the Lutetian (Middle Eocene). The magmas of the ND suite are characterised by slightly more alkaline affinity compared to the SD suite. The trace and rare earth element (REEs) content of the SD suite is characterised by large ion lithophile element (LILEs; Sr, K2O, Ba, Rb) enrichment and depletion of Nb, Ta, and TiO2 elements to different degree with high Th/Yb ratios, which indicate that the magmas forming the SD and ND suites were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. The Sr, Nd and Pb radiogenic isotope ratios of the dikes support the view that the magma for the hydrous group (H-SD) was derived from a relatively more enriched mantle source than the other SD and ND suites. The ND suite and the anhydrous group (A-SD) display similar geochemical features characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios, while the H-SD group has respectively lower LREE/HREE ratios indicating higher melting degree. Detailed considerations of the alkalinity, enrichment and partial melting degree for the source of the studied volcanic rocks indicate that the magmas of the northern dike suite are characterised by slightly more alkaline affinity, whereas the magmas throughout the southern dike suite show increments in the enrichment rate and melting degree. In light of the obtained data and comparative interpretations, the geodynamic evolution and differences in petrogenetic character of the Lutetian magmas from both the northern and southern parts of the Eastern Pontides may be explained by different degrees of melting of a net veined mantle source initially metasomatized by mostly subduction fluids during asthenospheric upwelling due to fragmented asymmetric delamination in a post-collisional extensional tectonic environment.

Petrography, chemical composition, and age constraints of mafic intrusions from the Mesoproterozoic Soisson Intrusive Suite in the southeastern Churchill Province (Canada)

Several kilometre-scale gabbroic intrusions with well-preserved cumulate textures occur over a ∼180 km northwest–southeast strike length area in the Core Zone, within the southeastern Churchill Province. These intrusions (1312–1311 Ma) are devoid of structural and metamorphic overprint and are mainly composed of olivine gabbro. Their overlapping petrographic, geochemical, and mineralogical characteristics suggest that all of these gabbroic intrusions are co-genetic and form the Soisson Intrusive Suite. The Soisson intrusions formed from basaltic parental magmas with low MgO (∼6–7 wt.%) and high Fe–Ti contents. Overall, they are similarly fractionated at the regional scale and incorporated various amounts of upper crustal material, as indicated by field (e.g., xenoliths, hybrid zones) and geochemical (e.g., high HILE/MILE, depletion in Nb±Ta) evidences. The Soisson Intrusive Suite has petrological, geochemical, and mineral chemistry similarities with the troctolite and olivine gabbro cumulates of the Voisey’s Bay and Mushuau intrusions from the ca. 1363 to 1289 Ma Nain Plutonic Suite (NPS), and appears to be contemporaneous with its younger gabbroic–troctolitic intrusion phase, suggesting that the Soisson Intrusive Suite and the gabbroic–troctolitic intrusions of the NPS were formed by similar petrological processes. Furthermore, like many gabbroic–troctolitic intrusions of the NPS (e.g., Voisey’s Bay intrusion), the Soisson intrusions contain Ni–Cu–Co magmatic sulfide mineralization. Among the Soisson intrusions, the Papavoine intrusion located in the southern part of this intrusive suite may be the most prospective intrusion as a Ni, Cu, and Co exploration target. Overall, the Soisson Intrusive Suite’s similarity with the NPS raises questions about their potential genetic link and magmatic connectivity at depth.

Mapping Co–Cr–Cu and Fe Occurrence in a Legacy Mining Waste Using Geochemistry and Satellite Imagery Analyses

Abandoned mining wastes are both an environmental challenge and a possible secondary raw material source. The characterization and monitoring of these sites are often expensive and cumbersome because of the need of repeated field surveys. Remote sensing data are a cost-effective alternative that helps in producing multiscale maps of mining wastes. These maps can be used to investigate and monitor the spatial patterns of different elements within the mining wastes. In this work, Sentinel-2 images are combined with the geochemical samples in order to map the distribution of iron, copper, chromium, and cobalt. The target area was the Vigonzano mining wastes in Northern Apennines (Italy) where there are a small number of geochemical analyses but a large amount of satellite image data. We used the multivariate geostatistical estimation method (Co-Kriging) that exploit the meaningful spatial correlation between the elements of interest and band ratios (obtained from Sentinel-2 images). The concentration maps highlighted subareas for Cu and Cr with an estimated grade of about 0.3% and 0.2%, respectively. In addition, the critical element Co showed an enrichment in the south-east part of the mining wastes, in a similar pattern as Cr. Instead, the obtained maps show Ce, La, Rb, and Nb depletion compared to the surrounding agricultural areas. The concentration maps were intended as a prefeasibility study to determine enriched areas for further detailed investigation.

Late carboniferous continental arc magmatism in the southeastern Central Asian Orogenic Belt: insights from the Erenhot granitic pluton, Inner Mongolia

The closure time of the Hegenshan Ocean and its suturing scenario is debated, which hinders our understanding of the architecture and tectonic evolution of the southeastern Central Asian Orogenic Belt. We present an integrated study of in-situ zircon U-Pb isotopic ages and Hf isotope compositions, whole-rock geochemistry and Sr-Nd isotopes on the less-studied Erenhot granitic pluton in central Inner Mongolia. The <i>ca.</i> 303 to 300 Ma Erenhot pluton is composed of monzogranites, which are high-K calc-alkaline rocks and show I-type affinities. Moreover, positive correlation between Ba and Sr, along with the notably positive Rb and Pb anomalies, negative δEu and depletion in Ba, Eu, Nb and Ti, imply crystal fractionation played an important role in the magma evolution. The pluton also shows relative enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements, typical features of subduction-related magma. Isotopically, predominantly positive whole-rock ε_Nd(t) (0.9–3.8) and zircon ε_Hf(t) (4.50–13.66) values indicate a dominant juvenile crustal source with minor older crustal contamination. Given the mostly Proterozoic model ages (1318–543 Ma) and the presence of xenocrystic zircons, we infer that the Erenhot pluton probably was formed in a continental arc setting. Combined with the available published data, it is proposed that an east-west trending continental arc developed and was accreted onto the Uliastai Continental Margin in the Carboniferous, resulting from the northward subduction of the Hegenshan Ocean. The late Carboniferous continental arc-related magmatism (<i>ca.</i> 303–300 Ma) at Erenhot probably witnessed the waning stage of Hegenshan oceanic lithosphere subduction beneath the Uliastai Continental Margin.

Middle–Late Triassic southward-younging granitoids: Tectonic transition from subduction to collision in the Eastern Tianshan–Beishan Orogen, NW China

Abstract To constrain the closure mechanism and time of the Paleo-Asian Ocean, we report new geochronological and geochemical data for Triassic granites along a NW–SE corridor from Eastern Tianshan to Beishan, NW China. Seven granites have U-Pb ages that young southwards from 245 Ma to 234 Ma in the Kanguer accretionary complex, to 237 Ma to 234 Ma in the eastern Central Tianshan block, to 229 Ma to 223 Ma in the Liuyuan accretionary complex. Granites in the Kanguer accretionary complex formed by fractional crystallization and are peraluminous, high-K, calc-alkaline, and crust-derived. They have very low MgO (Mg# = 6–9), Cr, and Ni contents, and their high εNd(t) (+3.40) and εHf(t) (+4.49 to +11.91) isotopes indicate that the Dananhu arc crust was juvenile. The Huaniushan pluton in the Liuyuan accretionary complex displays the geochemical signatures of both A1- and A2-type granites (Y/Nb = 0.32–3.39). All other granites in the Central Tianshan block and Liuyuan accretionary complex are aluminous A2-types with high K2O + Na2O, Al, rare earth elements (REE), Zr + Nb + Y, Ga, Fe/Mg, and Y/Nb and remarkable depletions of Eu, Ba, Nb, Ta, Sr, P, and Ti. They have a broad range of MgO (Mg# = 9–59), Cr, and Ni contents, Isr (0.70741–0.70945) values, negative εNd (t) (−2.98 to −1.14), and low to moderate εHf(t) (−1.22 to +7.78), which suggests a mixture of mantle and crustal components. These 245–223 Ma granitoids show marked Nb-Ta depletions that point to a subduction origin. Notable enrichments in Nd-Hf isotopes of Late Triassic granites are likely an indication of collision. Integration with previous data enables us to conclude that the delamination of an oceanic slab and mantle upwelling induced partial melting of thickened arc crust during a tectonic transition from a multiple supra-subduction margin to a collisional setting in the Late Triassic.

Zircon trace‐element compositions in Miocene granitoids in Japan: Discrimination diagrams for zircons in M‐, I‐, S‐, and A‐type granites

AbstractDetrital zircons demonstrate high resistance to alteration and, as such retain information about their formation ages and parental magmas for a long period of time. Geochemical researchers have proposed a wide variety of discrimination diagrams applicable to detrital zircons. In our research, we focused on the conventional classification scheme for granites (Mantle, M; Igneous, I; Sedimentary, S; and Alkaline, A types) and sought to characterize zircon trace‐element compositions that are sensitive to differences among these granite types. To accomplish this, we examined trace‐element compositions of zircons extracted from granitoids in the Ohmine granitic rocks and the Ashizuri plutonic complex in southwestern Japan. The zircons showed systematic differences in Nb/P, Ta/P, Ce/P, Ce/Nd, Y/P, Th/U, and Sc/Yb ratios and the Eu anomaly. Zircons in A‐type granite are rich in Nb, Ta, Ce, and Y, and their signatures clearly reflect those elements in their parental bodies. Sc/Yb ratios of zircons in A‐type granites are &lt;0.1, which is similar to those of ocean‐island‐type zircons. Despite their high abundance at the whole‐rock level, zircons in S‐type granite are characterized by low Nb/P, Ta/P, and Th/U ratios. This is attributable to the depletion of Nb, Ta, and Th in the magma by ilmenite and monazite prior to zircon crystallization. In general, S‐type granitic magmas exhibit reducing environments, which decrease the proportions of Ce4+ and Eu3+. These effects lead to a low Ce/Nd ratio and a large negative Eu anomaly in S‐type zircons. On the basis of these findings, we recommend the combined use of Nb/P–Ce/P or Ta/P–Ce/P crossplots and of Sc/Yb ratios to discriminate zircons in M‐, I‐, S‐, and A‐type granites. Although the crossplots are created using data from Miocene granitoids in Japan, the discrimination diagrams are based on the general features of each type of granite.

Origin and tectonic implication of mafic dykes: The Permian diabases in Santanghu Basin, NW China

The Permian mafic dykes of Santanghu Basin offer an opportunity to study the nature of mantle source and tectonic setting of the basin, as well as to provide the theoretical basis for structural transformation of East Junggar region. In this study, zircon U–Pb geochronology, mineral composition analysis, whole‐rock elemental, and Sr‐Nd isotopic geochemistry were conducted to explore the origin and evolution of the primitive magma. LA‐ICPMS zircon U–Pb dating yields ages at 269 Ma. The elemental geochemistry results suggest enrichments in Ba, Pb, and Sr but depletions in Nb, Ta, Zr, and Hf, which indicate that the magma source was influenced by fluid metasomatism. All samples show moderate initial Sr‐Nd isotope results ((87Sr/86Sr)I = 0.704299 to 0.704490 and εNd(t) = +6.16 to +6.83) and have high Sm/Yb ratios, which suggest that the diabases were derived from partial melting of 5%–7% spinel‐garnet Iherzolite lithospheric mantle. Combined with petrological, geochronological data, and the regional tectonic background, it is interpreted that the diabases from Santanghu Basin originated from lithospheric mantle metasomatized by subduction fluids under the background of intracontinental extension.