Negative Eu Anomalies Research Articles

The earliest Neoproterozoic Nb-enriched mafic magmatism indicates subduction tectonics in the southwestern Yangtze Block, South China

To better reveal the early Neoproterozoic tectonic process of South China with respect to the assembly of the Rodinia supercontinent, an integrated dataset of geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotopic compositions for diabases that intruded the Kunyang Group in the southwestern Yangtze Block is herein presented. Zircon U-Pb dating gives four weighted mean 206Pb/238U ages of 946 ± 4 Ma, 948 ± 6 Ma, 939 ± 4 Ma, and 918 ± 7 Ma, suggesting mafic magmatism in the earliest Neoproterozoic. The diabases possess Nb = 12.3–30.5 ppm, Nb/U = 19.99–37.06, Nb/La = 0.78–1.05, (Nb/Th)PM = 0.44–0.80, and (Nb/La)PM = 0.75–1.02, geochemically resembling those of typical Nb-enriched basalts. They are tholeiitic in composition with low SiO2 (49.49–51.95 wt%), high TiO2 (2.03–4.65 wt%), MgO (2.50–6.14 wt%), and Fe2O3T (15.38–18.84 wt%) contents. They are enriched in light rare earth elements (LREEs) with weak negative Eu anomalies (Eu/Eu* = 0.75–0.96) and show E-MORB-like characteristics with slight to moderate Nb-Ta depletion. The samples show zircon εHf(t) values ranging from + 5.8 to + 10.3 and whole-rock εNd(t) values from + 0.5 to + 0.9. These elemental and isotopic characteristics suggest that the 0.95–0.92 Ga diabases may have derived from an E-MORB-like magma source with the injection of metasomatized slab melts. Integrating previous studies with our results, we propose that the southwestern Yangtze Block evolved from an intracontinental rift to a passive continental margin in the late Mesoproterozoic, followed by the development of an earliest Neoproterozoic continental arc-back-arc basin system analogous to the Northern Okinawa Trough. The distinct tectonic processes between the southern and northern parts of the Yangtze Block at ca. 1.0–0.9 Ga favour the hypothesis that the final cratonization of the present-day Yangtze Block occurred slightly later than ∼ 0.9 Ga in response to the Rodinia supercontinent assembly.

Subduction-related Late Triassic Luerma porphyry copper deposit, western Gangdese, Tibet, China: Evidence from geology, geochemistry, and geochronology

Due to the difference of lithospheric structure between the eastern and western segment of Gangdese metallogenic belt, it is generally believed that porphyry copper deposits are mainly developed in the east. However, the newly discovered of Luerma porphyry copper deposit in the western segment of Gangdese provides an excellent research object for us to supplement this understanding. The molybdenite re-Os isotope dating of two samples from quartz veinlet ores (ca. 213.1 ± 5.2 Ma and ca. 212.0 ± 3.7 Ma), combined with the LA-ICP-MS zircon U-Pb dating of three ore-bearing quartz monzonite porphyry samples (ca. 212.7 ± 0.9 Ma, 213.1 ± 1.1 Ma, and ca. 211.8 ± 1.8 Ma), indicates a new generation of Late Triassic Luerma copper porphyry-type mineralization events in the western Gangdese magmatic belt. The Luerma porphyry is a strongly peraluminous shoshonite series rock, is rich in silicon total alkalis, potassium and aluminum, has low contents of calcium, magnesium, and iron. It is enriched in light rare earth elements and large ion lithophile elements, relatively depleted in heavy rare earth elements and high field strength elements, and has negative Eu anomalies and no Ce anomalies. The porphyry exhibits relatively low (87Sr/86Sr)i values (0.705617 on average), high εNd(t) values (0.63 on average), high εHf(t) values (11.98 on average), and young two-stage Hf model ages. The Luerma ore-related porphyries are most likely generated dominantly from partial melting of juvenile crust that formed by metasomatized mantle during the subduction of the NeoTethys Ocean to the Lhasa terrane and underwent crystal fractionation during the process. The deposit is currently the oldest and westernmost porphyry deposit in the Gangdese porphyry copper belt, providing evidence that porphyry copper mineralization in this belt began in at least the Late Triassic.

Insights from the Alabama Hills into Mesozoic Magmatism and Tectonics in Eastern California

Abstract New zircon U-Pb ages for the Alabama Hills Granite in Owens Valley, eastern California, range from 103 to 102 Ma, nearly 20 Ma older than previously published zircon ages. The data preclude previously implied links between the pluton and the adjacent Late Cretaceous Mount Whitney Intrusive Suite. Geochronologic and isotopic data indicate a connection between the Alabama Hills Granite and leucogranites to the northwest on the Sierra Nevada crest, as well as a pluton to the southeast in the Coso Range. We refer to these units as the Kearsarge plutons. The suite was intruded from 103 to 100.5 Ma with S87r/S86ri=0.7045 to 0.7060 and εNdi=−2.4 to -4.5 and has distinctive enrichments in high field strength, middle, and heavy rare earth elements, as well as negative Eu anomalies and high Y/Sr. We suggest the Alabama Hills block could not have moved more than 10 km dextrally relative to the Sierra Nevada batholith since the Middle Jurassic and is thus a suitable piercing point for offsets across Owens Valley. The Kearsarge plutons, like other markers on either side of Owens Valley, support approximately 65–75 km of dextral offset across the valley. The suite’s location east of other middle Cretaceous suites, coupled with its mantle-like isotope geochemistry, suggests it could represent backarc magmatism, perhaps controlled by preexisting shear zones or fractures.

Late Carboniferous bimodal volcanic rocks of the West Junggar Terrane, NW China: Implications for the postcollisional tectonic setting of the southwestern CAOB

ABSTRACT The West Junggar terrain (WJT), as a crucial part of the Central Asian Orogenic Belt (CAOB), is distributed with numerous igneous rocks, which provide critical information for crustal growth. However, the closure of the Junggar Ocean (JO) and the beginning of the postcollisional tectonic stage of the WJT have been controversial. This study delimited the regional lithologic units based on remote sensing geological mapping and recognized a series of bimodal volcanic rocks (BVR) in Hala’alate Mountain of the WJT. LA-ICP‒MS zircon U‒Pb geochronology and geochemistry were used to discuss the petrogenesis of the BVR and determine the stage of regional tectonic evolution. Geochronological results yield crystallization ages of 302 ± 4 Ma, 298 ± 2 Ma, 304 ± 1 Ma, and 303 Ma± 2 Ma for the basaltic andesite, basalt, and two rhyolitic samples, respectively. Basalts and basaltic andesites are calc-alkaline, and display enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs). Notably, basaltic andesites in this area were once misjudged as sanukitoids owing to their low contents of Mg#, Ni, Cr, and other characteristics that are inconsistent with the typical definition of sanukitoids. The rhyolites are A2-type granitoids with high SiO2 contents and are depleted in Nb, Ta, P, Ti, and Sr, showing enriched LREE patterns with negative Eu anomalies. These features indicate that the magma of the mafic end-member of the BVR is derived from the partial melting of the depleted lithospheric mantle, whereas the felsic end-member magma can be associated with the remelting of the lower crust due to the upwelling and underplating of mafic magma. In combination with previous studies of simultaneous basic dikes and felsic rocks, a postcollisional tectonic stage was proposed for the WTJ during the late Carboniferous, suggesting that the JO was closed.

Early Yanshanian metallogenesis of the Banjing tungsten deposit in Ganxian, Jiangxi province, China: Constraints from geochemistry, Sr–Nd isotopes, zircon U–Pb, molybdenite Re–Os, and mica 40Ar–39Ar dating

The Banjing tungsten deposit, which has been discovered recently, is located in the northernmost part of the Dabu pluton, southern Jiangxi Province, China. In this study, zircon LA‐ICP‐MS U–Pb dating of the fine‐grained porphyritic biotite granite indicate that it was formed in the early Yanshanian (159.4 ± 2.5 Ma–161.6 ± 0.8 Ma). Whole‐rock geochemical studies have shown the fine‐grained porphyritic biotite granite has SiO2 of 75.82%–76.84%, Al2O3 12.50%–12.87%, MgO 0.07%–0.20%, and CaO 0.64%–1.09%, with A/CNK of 1.017–1.038. It has a total rare earth elements content of 93.9–118.9 ppm with strong negative Eu anomalies (δEu = 0.021–0.081). The biotite granite is enriched in Rb, Th, U, Nd and depleted in Ba, Sr, Nb, Ti. These data suggest the Dabu pluton belongs to S‐type granite. This pluton has ISr of 0.71212–0.72929 and εNd(t) from −9.60 to −10.62 with Nd model ages concentrated in 1732–1838 Ma. These isotopic data in combination with zircon Hf isotopes suggest the biotite granite originated from partial melting of the Middle Proterozoic metamorphic supracrustal rocks in South China, with a minor contribution from juvenile crust. Meanwhile, this study has obtained Re–Os isochron ages of the intrusion‐related and quartz vein‐type molybdenum mineralization are 156.3 ± 2.7 Ma and 157.0 ± 1.1 Ma in the Banjing tungsten deposit, respectively. Sericite from the greisen‐type tungsten‐molybdenum ore has an 40Ar–39Ar plateau age of 156.4 ± 1.0 Ma, interpreted as the formation age of this deposit. Collectively, the Banjing tungsten deposit is considered as a product of the early Yanshanian large‐scale peak mineralization in South China, which was formed in an extensional intracontinental environment caused by the subduction of the Palaeo‐Pacific Plate.

Early Paleozoic intermediate igneous rocks in the Dunhuang Block, southern Central Asian Orogenic Belt: geochronology, petrogenesis, and implications for tectonic evolution

Late Ordovician–Early Silurian intermediate igneous rocks have been detected in the Dunhuang Block, NW China. These igneous rocks help to constrain the tectonic evolution of the Dunhuang Block and the southern Central Asian Orogenic Belt in the early Paleozoic. We carried out zircon U–Pb dating, whole-rock geochemistry and zircon Hf isotope analyses for the early Paleozoic gneissic diorites from the Sanweishan and northern Huangshuihou areas in the Dunhuang Block. The zircon U–Pb geochronology shows that the emplacement ages of the gneissic dioritic rocks were c. 443–440 Ma. The dioritic rocks show varying SiO 2 (48.1–63.1 wt%) and MgO (1.87–3.52 wt%) contents, with high Mg# (46–52) values and negative Eu anomalies (Eu/Eu* = 0.62–0.94). Zircons in the gneissic diorites from the northern Huangshuigou and Sanweishan areas yield variable ε Hf ( t ) values of −4.4 to +10.4 and −8.6 to −6.2, respectively, coupled with low Rb/Sr (0.04–0.34), Rb/Ba (0.06–0.31) and Al 2 O 3 /(MgO + FeO T ) (0.72–1.47) ratios, indicating that they were predominately generated by disequilibrium melting of the juvenile crust and mixed with ancient crustal and minor mantle melts. In conjunction with previously published data, we propose that the early Paleozoic gneissic dioritic rocks were formed in a continental margin arc setting related to the southward subduction of the Palaeo-Asian Ocean. Our findings suggest that the Dunhuang Block was modified and reactivated by the Paleozoic orogenic events related to the evolution of the Palaeo-Asian Ocean, resulting in extensive Paleozoic magmatism–metamorphism over the whole Dunhuang area. Supplementary material: Analytical methods, U-Pb geochronological data, zircon trace element data, zircon Lu-Hf isotopic compositions, and geochemical data for analysed samples, and additional figures are available at https://doi.org/10.6084/m9.figshare.c.6174601

Enrichment of critical elements (Li-Ga-Nb-Ta-REE-Y) in the coals and host rocks from the Daping Mine, Yudongnan Coalfield, SW China

Critical elements in coals and host rocks have attracted much attention due to their growing demand and rising economic significance. This research reports new data of elevated critical elements and mineralogical characteristics of the coals and host rocks from the Daping Mine, Yudongnan Coalfield, neighboring to the previously reported coal-hosted Li and rare earth elements plus yittrium (REY) ore deposit of the Donggou Mine in the same coalfield. The coal in the Daping Mine is mainly a medium-volatile bituminous coal and characterized by a low-ash yield (Ad = 13.08–30.32 %, 19.65 % on average) and a high-sulfur content (1.75–9.25 %, 3.43 % on average). Critical elements including Li, Ga, Nb, Ta, REY are enriched in the coal. Minerals in the Daping coal are mainly clay minerals (including illite, mixed layer of illite/smectite (I/S), kaolinite, and chamosite) and pyrite, and to a lesser extent, calcite, anatase, and marcasite, with traces of zircon, celestite, and baddeleyite. Lithium is mainly associated with illite, and Ga, Nb, Ta, and REY also have an inorganic affinity. The terrigenous materials of the Daping coal were from the intermediate-felsic rocks at the top of the Kangdian Upland rather than the basalts. Hydrothermal solutions also make a great contribution to the enrichment of critical elements and minerals. High-temperature solutions (>200 °C) may be responsible for the weakly negative Eu anomalies. The coal ashes in the Daping Mine have significant concentrations of Li2O (2583 ppm on average), Ga (83.5 ppm on average), (Nb, Ta)2O5 (143 ppm on average), and REO (oxides of REY, 1125 ppm on average), all of which are higher than their respective cut-off grades. Moreover, the floor strata are enriched in these critical elements. Thus, the coal ashes and floor strata are potential resources for extraction of these critical elements.

Geochemical characteristics of apatite and amphibole within the granitic intrusions from the Suyunhe Mo deposit, Xinjiang province, NW China: Insights into petrogenesis and mineralization potential

Textural and compositional variations in apatite and amphibole from mineralized granite (G), granite porphyry (GP), granodiorite porphyry (GDP), and barren tonalite porphyry (TDP) in the Suyunhe ore district, Xinjiang province, NW China revealed differences in their petrogenesis, magmatic properties and mineralization potentials. The higher Cl contents (0.09–0.18 wt%) and Cl/F ratios of apatite, and the higher Mg/(Mg + Fe2+) ratios (0.54–0.62) of amphibole in the barren TDP indicate that the parental magma was mainly generated via melting of the lithospheric mantle. In contrast, the parental magmas of the GDP, G, and GP were mainly derived from melting of the juvenile lower crust. The enrichment of Mn, Y, and heavy rare earth elements (HREEs), depletion of Sr, and strong negative Eu anomalies of the apatite from the GP indicate that it underwent a high degree of fractional crystallization. Moreover, the reverse core-to-rim compositional variations in REE and Sr contents and the La/Y ratios observed in some of the apatite grains, as well as the distinct differences in the major-element compositions (e.g., CaO, MnO, SiO2, and Ce2O3) of the individual zones within single apatite grains, indicate magmatic mixing. The calculated magmatic viscosities (Logη = 4.8–5.0 Pas) at Suyunhe remained below the average value for granitic melts (mostly Logη > 5 Pas) at the same temperature. These results support the hypothesis that low-viscosity magma (e.g., Logη < 5 Pas) may be essential for the formation of porphyry Mo deposits. The physicochemical conditions (including temperature, pressure, and H2O content) estimated based on the amphibole in the mineralized intrusions indicate the existence of a deep magma chamber with a large volume, which continuously released volatiles (e.g., fluorine and water) and effectively reduced the viscosity of the magma.

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

The Palaeozoic granites forming the Dalhousie pluton occur as an elongated body intruded into the core of an antiform in Salkhala metasedimentary rocks and are referred to herein as Dalhousie granites (DG). The studied mesoscopic structures, for example, well‐developed and randomly distributed megacrysts of K‐feldspar at the core part of massif, show undeformed porphyritic nature, whereas augen along with the mylonitic foliation and parallelly aligned feldspar megacrysts are dipping towards north‐north‐east (NNE) in the marginal part. The presence of aplite veins is evidence of final stage crystallization, where these rocks rapidly crystallized from siliceous residual fluids/solutions that escaped along fractures in the granites. Moreover, the granites show intrusive as well as thrusted contact with the Chamba metamorphics. The microscopic study from the marginal parts shows the dynamic recrystallization of quartz along with the fractures filled with secondary material oriented opposite to the top‐to‐the‐SW. Whereas euhedral quartz grains with undeformed grain boundaries, compositional zoning in plagioclase, and magmatic (perthite) texture of K‐feldspar are present in the core of Dalhousie pluton. In addition, a new whole‐rock geochemical dataset of DG is presented and investigated to elucidate the petrogenesis and tectonic environment. The geochemical data shows that DG (dominantly monzogranites) are formed from a pelitic source‐derived, (molar Al2O3/CaO + Na2O + K2O &gt; 1.1) strongly peraluminous (S‐type) calc‐alkaline magma. This magma was generated by muscovite vapour absent dehydration melting. Harker bivariate plots indicate that fractional crystallization was a dominant process during the evolution of these granites. The tectonic discrimination diagrams suggest that DG were generated in syn‐collisional setting. Exceptionally high Pb in DG occurred due to primary melt generation at low‐temperature during partial melting (low‐degree melting) of the pelitic source rock. Trace and rare earth elements characteristics, such as positive anomaly of Zr show a notable amount of zircon as one of the accumulating phases. A pronounced negative Eu anomaly (EuN/Eu* = 0.04–0.66), along with high silica content and highly varied trace element ratios in these rocks, show that these are fairly evolved granites.

Triassic Paleo-Tethyan slab break-off constrained by a newly discovered 211 Ma dacite–rhyolite suite in the Qiangtang terrane, central Tibet

• A newly discovered Late Triassic volcanic suite in the eastern Qiangtang subterrane includes dacites and A-type rhyolite. • This suite was emplaced at 211 Ma and was generated via partial melting of the Qiangtang continental crust. • The formation of this volcanic suite reflects the slab break-off of the Paleo-Tethyan in the Late Triassic. Triassic igneous rocks are widely exposed in the central Qiangtang terrane, Tibet. However, Triassic tectonic–thermal evolution in the central Qiangtang terrane and the evolution of the Paleo-Tethyan Ocean are still unclear. In this study, we report zircon U–Pb ages, and whole-rock major- and trace- element compositions, and Sr–Nd isotope data for the newly discovered Late Triassic Tumen volcanic rocks. The volcanic rocks consist of interlayered dacite and rhyolite (SiO 2 = 63.8–69.7 wt%) with a thickness of approximately 150 m. New zircon U–Pb dating reveals the eruption of this volcanic suite at 211 Ma. Geochemical data show that the volcanic suite has a wide range of K 2 O (1.36–5.46) values and high-molar Al 2 O 3 /(CaO+K 2 O+Na 2 O) values (0.97–1.36). All samples clearly show the enrichment of light rare earth element, with (La/Yb) N = 6.79–11.03 and (La/Sm) N = 3.23–4.44, and distinct negative Eu anomalies (Eu/Eu* = 0.44–0.70). All samples exhibit the depletion of high field strength elements (e.g., Ti, Nb, and Ta), and enrichment in large-ion lithophile elements (e.g., Rb and K). The dacite–rhyolite suite has a narrow range of ( 87 Sr/ 86 Sr) i ratios (0.7102–0.7132) and ε Nd (t) values (−10.2 to −10.0), with Nd isotope model ages of 1.76–1.82 Ga. Zircon saturation temperatures (860℃–921℃) and geochemical characteristics show that the samples are A-type granitoids and were likely generated by partial melting of the Qiangtang continental crust. The rise of the asthenospheric mantle caused by the slab break-off provides a large amount of heat and materials for the igneous rocks in the Shuanghu–Longmucuo suture zone during the Late Triassic.

A zircon trace element and Hf isotope geochemical study of syenites and carbonatite, exemplified by the Epembe alkaline carbonatite complex, Namibia

Abstract The Epembe Complex is one of the Mesoproterozoic (~1200 Ma) carbonatite alkaline complexes situated along the southern margin of the Congo Craton in northwestern Namibia. Nepheline syenites and minor syenites constitute the main lithologies, cross-cut by a calcite-carbonatite dyke. In order to constrain zircon forming-processes and magma sources, cathodoluminescence (CL) imaging combined with trace elements (including REE) as well as Hf isotope compositions of zircon grains extracted from one syenite, five nepheline syenite samples and one carbonatite sample are presented. Syenite zircons are generally unaltered and are characterised by positively sloping REE patterns in a chondrite-normalised diagram, with positive Ce anomalies. Syenite zircon further displays significant negative Eu anomalies attributed to earlier plagioclase formation and fractionation. These features are consistent with zircon formation in a magmatic environment. In the nepheline syenite samples, two zircon types are recognised. Type 1 zircon is magmatic, with homogeneous-grey, unzoned and oscillatory-zoned domains in CL, while type 2 zircon underwent low temperature fluid alteration and displays a cloudy appearance. Type 2 zircon is characterised by enrichment in LREE, Nb and Ti when compared to magmatic type 1 zircon. Carbonatite zircon displays a variety of textures and variable chemical compositions suggestive of the presence of both xenocrystal, altered and magmatic zircon. The Hf concentration and Hf isotope composition of type 1 and type 2 zircon are similar suggesting that zircon alteration did not affect the Hf isotope systematics. The similarity of ƐHf(t) values in zircon from syenite (+0.5 ± 0.4 to +1.5 ± 0.4), nepheline syenite (+1.6 ± 0.3 to +2.7 ± 0.5) and carbonatite (+1.5 ± 0.2 to +1.9 ± 0.1) is consistent with the melts having been derived from a moderately Depleted Mantle.

Petrogenesis of the Early Jurassic Longtang and Menglong Peraluminous Granites in Tengchong Terrane, and their Tectonic Implication

AbstractA comprehensive study of zircon U‐Pb geochronology, in situ Hf isotopes, whole‐rock major and trace element geochemistry, and Nd isotopes was carried out for two Early Jurassic two‐mica granites (Longtang and Menglong) in the southern part of the Tengchong terrane, which is in the northern part of the larger Sibumasu terrane. We assess the origin of the granites and explore their possible genetic relationship to the Paleo‐Tethyan regime. LA‐ICP‐MS zircon U‐Pb dating shows that they were simultaneously emplaced in the Early Jurassic (ca. 199 Ma). They have SiO2 contents of 69.7–75.1 wt% and are mainly strongly peraluminous with alumina saturation index (ASI) values ranging from 1.06 to 1.46. They show similar Mg# (0.29–0.42) to experimental partial melts of metasedimentary rocks under continental pressure‐temperature (P‐T) conditions. They are enriched in light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs), with moderately negative Eu anomalies and flat HREEs patterns. They show negative εNd(t) values (–9.0 to –12.4) and εHf(t) values (–8.0 to –9.1). Elemental and isotopic data suggest that they most likely to formed by muscovite‐dehydration melting of a metapelitic source at lower temperatures in the range of 700°C to 750°C. The granites might represent a post‐collisional tectonic setting response to Paleo‐Tethyan regime.

Geochemistry of Accessory Apatite from the Cu–Ni–Sulfide-Bearing Ultramafic–Mafic Rocks of the Khudolaz Complex (South Urals) as a Monitor of Magmatic and Metasomatic Processes

Abstract —We present results of mineralogical and geochemical studies (optical and electron microscopy, probe microanalysis, and LA-ICP-MS) of accessory apatite from the rocks of four ore-bearing massifs of the Khudolaz Complex: Vostochnyi Buskun, Severnyi Buskun, Malyutka, and Tashly-Tau. Two groups of apatite are recognized by morphology and chemical composition: (1) “magmatic” unaltered apatite (Ap-1) in unaltered and slightly altered rocks and (2) “metasomatized” apatite (Ap-2) surrounded by secondary silicates that replaced primary minerals. Ap-1 is represented by euhedral and subhedral hexagonal crystals with a high content of chlorine (0.7–1.2 wt.% Cl) and an extremely low content of sulfur (&amp;lt;0.05 wt.% SO3). It is enriched in REE (ΣREE = 2.2–3.0 wt.%), shows a pronounced negative Eu anomaly (Eu/Eu* = 0.36–0.58), and is depleted in Co, Ni, and chalcophile trace elements (Zn, Pb, and Bi). The distribution of major and trace elements in Ap-1 made it possible to identify its two generations, early and late, in the Khudolaz Complex. The early generation, characterized by a low content of Ca (Т ≥ 1000 °C, CaO &amp;lt; 54 wt.%), crystallized almost simultaneously with Ca-plagioclase (An81–61). The late generation, characterized by a high content of Ca (Т ≥ 700 °C, CaO &amp;gt; 55 wt.%), is associated with Na-plagioclase (An28–8), amphibole, and phlogopite. Ap-2 is represented by highly cracked grains and is characterized by a low content of chlorine (0.0n–0.5 wt.% Cl) and a high content of sulfur (0.06–0.93 wt.% SO3). The content of fluorine in both groups of apatite varies in the same range (0.6–1.7 wt.% F), which determines its relative inertness during metasomatic processes. Ap-2 is less enriched in REE (ΣREE = 1.1–2.1 wt.%) and shows a less pronounced Eu anomaly (Eu/Eu* = 0.61–0.77) but has high contents of Co, Ni, and chalcophile trace elements. The Ap-1 and Ap-2 show different variations in contents of major elements (Fe, Mg, Na, etc.), which is due to the impact of hydrothermal fluid on the mineral at the postmagmatic stage. It is shown that the low content of sulfur in apatite from unaltered rocks does not indicate a low sulfide ore potential of the Khudolaz Complex. The Cu–Ni sulfide signature of the complex is more clearly evidenced by the composition of metasomatized apatite enriched in S, Co, Ni, and chalcophile elements as a result of their hydrothermal removal from primary sulfide minerals. The high Eu/Eu* value indicates an increase in oxygen fugacity at the postmagmatic stage.

Mohammadabad Manganese deposit, southwest Sabzevar basin, Iran: Evidence of sea-floor exhalation and geochemical studies in the late Cretaceous volcano-sedimentary sequence

The southwest Sabzevar basin in northeast Iran is one of the most important areas for volcanogenic stratiform manganese deposits. The Mohammadabad Mn deposit, found in this basin, is hosted by the upper late Cretaceous marly tuffs in a region that has an active history of tectonism. Their geology, mineralogy and geochemistry, including major, trace and rare earth elements (REE), are described in this work. The main ore minerals include pyrolusite, psilomelane, cryptomelane, with minor braunite and manganite. Four styles of manganese mineralization are recognized: (1) layered; (2) nodular; (3) disseminated; and (4) replacement to massive. Regardless of style, pyrolusite, psilomelane, and cryptomelane usually tend to parallel the stratification of sediments, while braunite veins occur in high angle fractures. The replacement of radiolarian and foraminiferal fossils by manganese minerals during diagenesis near the seawater-sediment interface suggests that mineralization occurred in oxygen-rich conditions under the influence of low-temperature hydrothermal fluids. The geochemistry of trace elements of manganese oxides and rare earth elements gives clear evidence of hydrothermal-exhalative origin for Mohammadabad deposit. In general, ore minerals have Co/Ni ratios above 0.12, and U/Th ratios vary from 0.13 to 11.29. The presence of negative Eu anomalies in manganese minerals shows that the ore-forming fluids were generally low-temperature and oxic during mineral formation. In-situ mineralogy studies based on SEM-EDS have distinguished syngeneic and diagenetic Mn systems during the formation of manganese mineralization. The Mohammadabad deposit is considered a typical case of volcanic hydrothermal exhalative-diagenetic Mn mineralization, in which minerals deposited when hydrothermal fluid was released from oxic to dysoxic water columns.

Reconstruction of provenance and tectonic setting of the Middle Jurrasic Yan'an Formation (Ordos Basin, North China) by analysis of major, trace and rare earth elements in the coals

The Middle Jurassic Yan'an Formation in the Ordos Basin (North China) is an important coal-bearing succession. Twenty coal samples and four samples of silty mudstones were collected from Coal Seam 2 of the Yan'an Formation in order to determine major, trace and rare earth elements; moreover, the geochemistry of the rare earth elements, and in particular yttrium, was investigated. The major elements investigation reveals that Si, Al, Na, K, and Ti are primarily found in clay minerals. Calcium is primarily found in calcite and iron is largely controlled by sulfur. The average REE (rare earth element) contents in the coals and silty mudstones are 15.17 μg/g and 210.57 μg/g, respectively. The Upper Continental Crust-normalized distribution patterns of the REE in the coals and silty mudstones show no obvious fractionation; however, they show negative Eu anomalies and negligible Ce anomalies. Correlations between the REE and the major elements indicate that the REE in the coals and silty mudstones are both derived from eroded rocks in the hinterland and mainly controlled by the presence of detrital minerals. We investigated some diagrams of major element, trace element, and REE from the coal seam to comprehend its provenance and tectonic setting. The findings indicate that they are mainly derived from felsic and intermediate rocks in a continental island arc setting. The REE analysis shows that various provenance areas supplied clastics when coal developed in the Yan'an Formation. The findings imply that provenance analysis should be taken into account when studying the sedimentary environments of coal-bearing successions.

Metallogenesis of Porphyry Copper Deposit Indicated by In Situ Zircon U-Pb-Hf-O and Apatite Sr Isotopes

The origin of the Dexing porphyry Cu deposit is hotly debated. Zircon and apatite are important accessory minerals that record key information of mineralization processes. SHRIMP zircon U-Pb analyses of granodiorite porphyries yield ages of 168.9 ± 1.2 Ma, 168.0 ± 1.0 Ma, and 172.8 ± 1.3 Ma, whereas zircons in the volcanic rocks of the Shuangqiaoshan Group have Neoproterozoic ages of 830 ± 7 Ma, 829 ± 8 Ma, and 899 ± 12 Ma. The porphyry displays zircon in situ δ18O of mantle values (5.5 ± 0.2‰), low apatite 87Sr/86Sr ratios (0.7058 ± 0.0005), and high εHf values (5.1 ± 1.5), which are consistent with mantle-derived magmatic rocks. Apatite from the porphyries has relatively high total rare earth elements (REEs) and negative Eu anomalies, with relatively high Cl and As contents. These features are distinctly different from apatite in the Shuangqiaoshan Group, which shows lower total REE, Cl, and As contents but higher F content and positive Eu anomalies. Zircon in porphyries yields a relative high oxygen fugacity of ∆FMQ + 1.5 based on zircon Ce4+/Ce3+. Apatite in porphyries also shows high oxygen fugacity based on its SO3 and Mn compositions, reaching ∆FMQ + 2, which is different from that of the lower continental crust in general, but similar to subduction-related magmas. In contrast, the oxygen fugacity of the Shuangqiaoshan Group is much lower, suggesting a different origin for its wall rock. Therefore, the Dexing porphyries were not derived from the lower crust but derived from partial melting of the subducting Paleo-Pacific plate.

Magma Evolution and Constraints on the Graphite Mineralization Hosted by the Huangyangshan Alkaline Granite Suite in the East Junggar of Xinjiang Province: Evidence from In Situ Analyses of Silicate Minerals

The Huangyangshan super-large graphite deposit, located in the East Junggar area of the Xinjiang Province, is hosted in and has closely temporal, spatial, and genetic relationships with the Huangyangshan alkaline granites. There are such silicate minerals as amphibole, biotite, pyroxene, and plagioclase occurring in the graphite-bearing granites. The integration of the electron microprobe analysis (EMPA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) enabled us to reveal the physicochemical conditions and evolution process, as well as the relationship of alkaline magmatism with graphite mineralization. The results show that the amphiboles generally have low Al and high Ti, K, Si, and Fe contents, as well as similar rare-earth elements (REEs) patterns and trace element distribution patterns to granites with significantly negative Eu anomalies. In the analyzed samples, primary biotite belongs to Fe-biotite and has characteristics of high Si and Fe and low Al and Mg contents. In the graphite orbicules, the pyroxene phenocrysts develop multiple zonal structures and are characterized by high Si and low Ca and Fe contents. The dominant plagioclase phenocrysts in the graphite orbicules are oligoclase and andesine, with normal and occasionally oscillatory zoning. The calculated crystallization temperature of the pyroxene, amphibole, and primary biotite in graphite orbicules are 840–1012 °C, 681–761 °C, and 658–720 °C, respectively, corresponding with their crystallization order. The pressure and depth calculation results of the amphibole, representing those of the magmatism, are 157–220 Mpa and 5.95–8.32 km, respectively. Both amphibole and biotite crystallized in a reducing environment with extremely low oxygen fugacity. The elemental compositions of these silicates indicate that the Huangyangshan pluton experienced significant mixing of mafic mantle-derived magma and felsic crust-derived magma. The cores of graphite orbicules were formed in a relatively earlier magmatic stage, while the granites and their dioritic enclaves were formed in a later magmatic stage. During magmatism, the mixing of mantle-derived basic magma had an important influence on the evolution and differentiation of the melts. According to the coexisting sulfides with graphite and compositional difference of amphibole and biotite in the granites and graphite ores, the graphite mineralization might be triggered by a magma mixing process.

Origin and distribution of rare earth elements (REEs) in the soils of Meizhou City, southern China with high abundance of regolith-hosted REEs

Currently, regolith-hosted rare earth element (REE) deposits in South China are the major source of global REEs, particularly heavy REEs (HREEs). This type of REE resource contains abundant movable, bioavailable, and ion-exchangeable REEs and may act as an environmental hazard; however, little is known regarding REEs in soils from areas with abundant deposits. Here, we investigated the REEs in the soil, surface water and crops, collected from Meizhou City, Guangdong Province, South China, as a representative region with abundant regolith-hosted REEs. Mean REE concentration (ΣREE) in the soil (318 μg g−1) exceeded the local soil background (169 μg g−1). The LREE/HREE ratio ranged from 2.04 to 69.4 in soil samples, suggesting the enrichment of light REEs (LREEs) compared with HREEs. Most soil samples exhibited positive Ce anomalies and negative Eu anomalies. The highest ΣREE (1162 μg g−1) was detected in forest land, followed by garden land (793 μg g−1) and paddy field (519 μg g−1). According to the correlation analysis, pH as well as soil organic matter (SOM), Fe, and Mn content contributed to REE enrichment, while SOM and Mn content affected REE fractionation. REE enrichment in soil may be related to natural sources (e.g., parent materials) and anthropogenic activities (e.g., fertilizer application and coal combustion). The REE contamination of surface water was not serious. However, ΣREE in crops (7.08 μg g−1·dw) indicated that these elements migrate from soils to plants, producing potential adverse effects on crops and humans. These findings shed new light on the geochemical behavior of REEs in the environments with abundant regolith-hosted REEs and can serve as a reference to prevent and control REE contamination.

Geochronology and geochemistry of the granitoids in the Diancangshan-Ailaoshan fold belt: Implications on the Neoproterozoic subduction and crustal melting along the southwestern Yangtze Block, South China

The Neoproterozoic magmatic and tectonic history of the South China Craton (SCC) is critical for the reconstruction of Rodinia break-up and subsequent Gondwana assembly. Nonetheless, the tectonic attribution of the Neoproterozoic igneous rocks in the southwestern Yangtze is contentious, and the mechanism for crustal anatexis remains unclear. Here, we report mineralogical, whole-rock geochemical and Sr-Nd isotope data, and zircon U-Pb-Hf-O isotope data from the newly found Neoproterozoic trondhjemites and granites in the Diancangshan-Ailaoshan (DCS-ALS) fold belt along the southwestern Yangtze. Both the trondhjemites (ca. 771–762 Ma) and granites (ca. 767 Ma) have high SiO2 and low MgO contents. The trondhjemites have relatively high CaO, Na2O and Sr contents, but low K2O contents and Rb/Sr ratios, and show positive to slightly negative Eu anomalies and heavy rare earth elements (HREEs) depletions, resulting in high Sr/Y and La/Yb ratios. In contrast, the granites have lower CaO, Na2O, and Sr contents, but higher K2O and Rb/Sr, and display negative Eu anomalies and flat HREEs patterns. The trondhjemites have negative εNd(t) (-4.12 to −3.85), positive to negative εHf(t) (-2.50 to + 5.28) and low δ18O (4.37 ‰–7.27 ‰) values. In comparison, the granites have positive εNd(t) (0.09 to 0.26), εHf(t) (+1.24 to + 9.86) and higher δ18O (6.50 ‰–7.24 ‰) values. The distinct elemental and isotopic compositions between the trondhjemite and granite samples reflect two different types of crustal anataxis within different crustal levels. The trondhjemites were formed by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). The granites were derived from dehydration melting of juvenile felsic middle crust. Our results imply that the trondhjemites and granites were formed in a continental arc setting. The melting processes revealed here should be applicable to decipher the widespread Neoproterozoic crustal melting along the southwestern Yangtze, which was most likely fluid-controlled via subduction-induced asthenosphere upwelling. Combined with available regional geological data, we suggest that a long-lived Neoproterozoic (∼880–730 Ma) subduction zone may have extended from the Panxi-Hanna region in the northern/western Yangtze Block to the DCS-ALS fold belt in the southwestern Yangtze. Thus, the SCC may have located on the northwestern margin of Rodinia.

Formation of the Nephrite Deposit With Five Mineral Assemblage Zones in the Central Western Kunlun Mountains, China

Abstract The Saidikulam nephrite deposit, which is famous for its high-quality white nephrite no matter in history and nowadays, is located in the eastern part of the Western Kunlun Orogen, in the northwestern margin of the Tibetan Plateau, Yutian County, Xinjiang, China. Field investigations and petrographic observations revealed the presence of five mineral assemblage zones from granodiorite to dolomitic marble in the Saidikulam nephrite deposit: slightly epidote-altered granodiorite → epidote-altered diopsidite → nephrite → calcite tremolitite → calcite-bearing dolomitic marble. However, little is known about the relationships among these five zones or the formation age of the deposit. The slightly epidote-altered granodiorite consists of plagioclase, orthoclase, quartz, biotite, and epidote, with accessory apatite, zircon, and allanite. They exhibit slightly negative Eu anomalies (0.69–0.72), with declined light rare earth element (LREE) and flat heavy rare earth element (HREE) patterns. They are also strongly enriched in Rb, Zr, U, and Sm and depleted in Hf, Ti, P, and Nb. The epidote-altered diopsidite close to the granodiorite intrusions is a relatively high-temperature metasomatic rock composed of Fe-rich diopside and actinolite, while the calcite tremolitite adjacent to the dolomitic marble is a relatively low-temperature rock composed of prismatic tremolite and calcite. The main mineral component of the nephrite is tremolite, with minor epidote, chlorite, apatite, calcite, graphite, and allanite. The nephrites have low ∑REE contents (4.38–18.53 ppm), with declined LREE and flat HREE patterns. All of the analyzed nephrite exhibits pronounced negative Eu anomalies (δEu = 0.20–0.82), and they are strongly enriched in Rb, U, and Ti and relatively depleted in Ba and HFSEs. SHRIMP U–Pb dating of zircons from the granodiorite yielded a Concordia age of 453.8 ± 3.7 Ma, which is interpreted as the upper limit of the Saidikulam nephrite formation age. The zircons in the epidotized syenite in the deposit yielded a SHRIMP Concordia U–Pb age of 489.2 ± 4.2 Ma. These two ages indicate that the dolomitic marble experienced at least two thermal events. The approximate ages of the nephrite deposits along the giant Kunlun-Altyn Tagh belt indicate that the closure of the Proto-Tethys may have been the predominant driving force for the formation of the whole nephrite deposits. The multistage metasomatism and the Fe absorption of epidote-altered diopsidite had a positive impact on the formation of high-quality nephrite.