Negative Eu Anomalies Research Articles

Geochemical and isotopic evidence for early neoproterozoic (ca. 1000 Ma) subduction-related magmatism in the central Borborema Province, Brazil

Early Neoproterozoic (1000-920 Ma) rocks related to the Cariris Velhos event in the central Borborema Province have been linked to either continental rifting or accretionary-collisional orogenesis. The Serra do Jatobá Suite is located in the southwestern part of the Alto Pajeú Terrane along with coeval metasedimentary sequences and Ediacaran granites. This suite is composed of alkali-calcic, meta-to peraluminous granodiorites to monzogranites that share similarities with both ferroan- and magnesian granite series. Chondrite normalized REE (Rare Earth Elements) patterns are moderately fractionated with pronounced negative Eu anomalies. Incompatible element spidergrams show a negative Nb–Ta anomaly, similar to those observed in Cordilleran-type granites. U–Pb zircon data constrain the crystallization ages at around 1000 Ma, whereas calculated εNd(t) values range between −1.74 and −0.94. Obtained TDM model ages range from 1.76 to 1.54 Ga, which corresponds with source ages for the Cariris Velhos magmatic rocks. Our findings suggest that subduction took place in the early Neoproterozoic in the Borborema Province, pointing to an accretionary nature for the Cariris Velhos event.

Provenance, chemical weathering, and sedimentary environment of the aquifer sediments: Implication for arsenic enrichment in groundwater

High arsenic (As) groundwater has been widely observed in the world, but the provenance, chemical weathering, and sedimentary environment of aquifer sediments hosting high As groundwater remain poorly understood. The geochemical and isotopic characteristics of high-resolution aquifer sediments were investigated to unravel the roles of provenance, chemical weathering, and sedimentary environment of the aquifer sediments. The average values of rare earth elements (REEs) showed the enrichment of light REEs and flat heavy REEs in the aquifer and the Yellow River sediments. The chemical index of alteration reflected incipient and moderate weathering (41 to 71). The δ13CSOM (−27.4‰ ± 4.3‰) and C/N values (8.1 ± 5.8) indicated aquatic environment of sedimentation. Shallow aquifer sediments mostly had relatively high ΣREEs contents and negative Eu anomalies, demonstrating that the aquifer sediments were mainly derived from the Yellow River (up to 94.3% ± 5%). Deep aquifer sediments had relatively low ΣREEs contents and positive Eu anomalies, which originated from the Yinshan Mountains (up to 72.2% ± 20.4%) principally with igneous and metamorphic rocks. Moreover, recycling of the Yellow River sediments from Northeastern Tibetan Plateau enhanced the silicate weathering and increased contents of Fe/Mn oxides and As. The δ13CSOM and C/N values evidenced that organisms of paleo-lake or paleo-Yellow River were responsible for abundant sedimentary organic matter. Concentrations of Fe, Mn, and As were high in shallow groundwater from the plain. The As enrichment in the shallow groundwater was jointly controlled by the provenance and chemical weathering of the aquifer sediments (14%), sedimentary environment (10%), reductive dissolution (35%) of Fe/Mn oxides, As desorption under elevated pH (20%), and competitive adsorption of HCO3- (21%). This study systematically reveals the roles of provenance, chemical weathering, and sedimentary environment of the aquifer sediments and highlights joint contributions of geochemical processes and geochemical conditions to As enrichment in groundwater.

Zircon U-Pb and Whole-Rock Geochemistry of the Aolunhua Mo-Associated Granitoid Intrusion, Inner Mongolia, NE China

The Aolunhua Mo deposit is a typical porphyry deposit, which is located in the middle southern section of the Da Hinggan Range metallogenic belt. Here, we report LA-ICP-MS zircon U-Pb age data from the Mo-associated granitoid, together with the element geochemistry of the zircons, discussing the source material of the ore-forming rock of the deposit. The zircon data constrain the crystallization age of the granite porphyry as 135.0 ± 1.0 Ma, correlating it with the widespread Yanshanian intermediate–felsic magmatic activity. The Th/U ratio of the zircon is greater than 0.1, with a significant positive Ce anomaly (Ce* = 1.72–188.71) and a negative Eu anomaly (Eu* = 0.05–0.57). The zircons show depleted LREE and enriched HREE patterns, as well as low La and Pr contents, suggesting crystallization from crust-derived magmas. Based on the geology of the ore deposit and the age data, in combination with the regional geodynamic evolution, we infer that the Aolunhua Mo deposit was formed near the peak stage of Sn poly-metallic metallogenesis in the Da Hinggan Range region at around 140 Ma, associated with a tectonic setting, characterized by the transition from compression to extension. Based on a comparison with the newly found Mo deposits along the banks of the Xilamulun River, we propose that the Tianshan–Linxi is an important Mo-metallogenic belt. It also suggests an increased likelihood for the occurrence of Mo along the north bank of the Xilamulun River.

Geochronology, Petrogenesis, and Tectonic Setting of the Late Triassic Banpo Pluton from the Western Part of the North Qinling Orogenic Belt

Precise determination of the tectonothermal events at the Qinling–Qilian junction is significant for understanding the tectonic evolution of the eastern branch of the Paleo-Tethys. The Banpo pluton outcrops in the northern margin of the North Qinling were chosen as the research subject and their formation and tectonic environment were investigated using zircon U-Pb age and geochemical compositions. The weighted average values of 206Pb/238U ages of samples from three sites of the Banpo pluton corresponded to 213.4 ± 2.1 Ma (MSWD = 0.56), 213.0 ± 1.6 Ma (MSWD = 0.92), and 216.3 ± 2.3 Ma (MSWD = 2.0). All the samples are rich in light rare earth elements, exhibiting a seagull-type right-leaning partitioning curve, with obviously negative Eu anomalies. In addition, based on the regional geological data, it can be concluded that the Banpo pluton was formed during the transition period from a post-Orogenic environment to an anorogenic environment. The results indicated the final stage of the Triassic orogeny and the closure phase of the Paleo-Tethys. Also, it shows closure of the Paleo-Tethys-Mianxian-Lueyang Ocean by the Late Triassic period as well as the completion of the collision between the North China and Yangtze Blocks along the Qinling Orogenic Belt.

Early Jurassic and Late Cretaceous plagiogranites in Nain–Baft ophiolitic mélange zone in Iran: remnants of rift–drift and SSZ evolution of a Neotethyan seaway

We have investigated the geology, geochemistry and geochronology of various plagiogranite intrusions that are spatially associated with ophiolitic subunits in a mélange terrain exposed within the Nain–Baft fault zone along the western boundary of the Central–East Iranian Microcontinent (CEIM). One group of plagiogranites is intrusive into foliated amphibolites, whereas the plagiogranites of the other group are intrusive into gabbros, dyke swarms and pillow lavas that are tectonically juxtaposed. U–Pb zircon dating of the first group of plagiogranites has revealed near-concordant crystallization ages of 176.94 ± 0.71, 179.84 ± 0.92 and 190.40 ± 2.1 Ma, indicating the early Jurassic timing of their emplacement. U–Pb zircon dating of the second group of plagiogranites has revealed a weighted average age of 92.34 ± 0.38 Ma, indicating that they were emplaced in the early Late Cretaceous. The Early Jurassic plagiogranites are low-K, sub-alkaline rocks with negative Eu anomalies, low Ti and high La and Ce contents. They display elevated ratios of large ion lithophile elements to high field strength elements. They were part of a magmatic system that facilitated the earliest rift–drift stages of a Neotethyan seaway development, and their magmas were produced by fractional crystallization of a mafic melt associated with asthenospheric upwelling beneath a rift system. The Late Cretaceous plagiogranites are low-K, sub-alkaline rocks with negative Eu anomalies, high Y and low Ta contents. They show light REE depletion relative to flat heavy REE patterns, and high Ba/Th ratios. Magmas of these plagiogranites were the products of partial melting of amphibolites in the subducting oceanic lithosphere in the same Neotethyan seaway. Thus, we posit that plagiogranite rocks in suture zones can be excellent trackers of geochemical, geochronological and magmatic evolution of various types of oceanic crust through rift–drift, seafloor spreading and subduction initiation stages within the same ocean basins in the past. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Geodynamics and nature of the basement of the northern Lhasa Terrane: Insights from Early Cretaceous highly fractionated I-type granites in the Beila and Dongga areas, central Tibetan Plateau

Collisional orogenic belts serve as excellent places for investigating geodynamic process and growth mechanism of the continental crust. As one of the largest collisional orogenic belts worldwide, the Tibetan Plateau is formed by the amalgamation of multiple tectonic terranes. However, the nature and composition of the crustal basement beneath the northern Lhasa Terrane, located in central Tibetan Plateau, is still a matter of debate. Here, we investigated a series of Early Cretaceous granites in the Beila and Dongga areas, northern Lhasa Terrane. Zircon U-Pb dating reveals that the Beila and Dongga granites were emplaced at ca. 118 Ma and 110 Ma, respectively. These granites are characterized by high SiO2 and K2O, low TiO2 and P2O5 contents and low Mg#. They exhibit enrichment in light rare earth elements, significant negative Eu anomalies, and depletion in Ba and Sr. These geochemical features suggest that they belong to highly fractionated I-type granites. Both the Beila and Dongga granites display similar and enriched whole-rock Sr-Nd and zircon Hf isotope compositions, implying a likely common ancient crustal origin. Given the temporal sequences and redox conditions during their formation, it is highly probable that the Beila and Dongga granites formed during the syn-collision stage between the Lhasa and Qiangtang Terranes and the breakoff of the Bangong-Nujiang oceanic slab, respectively. Integrated with coeval magmatism in the central Tibetan Plateau, our new data reveal the presence of a regionally preserved ancient basement beneath the northern Lhasa Terrane, analogous to the equivalent basement beneath the central Lhasa Terrane.

Early Paleozoic metamorphism and anatexis of lower retro−/back-arc crust in the western Central Qilian belt, NE Tibet

The tectonic-thermal mechanism of crustal melting provides vital information on continental differentiation and orogenic evolution. This study aims to understand the evolution and tectonic setting of newly discovered lower crustal leucosome-rich granulites of the Qilian Orogen, NW China. Tonalitic leucosome within garnet amphibolite occurs in net-like arrays or as stringers and has diffuse boundaries with the host, with enriched LILE, and high Sr and Sr/Y ratios, similar to that of adakite, formed by water-fluxed melting. However, granitic leucosome within garnet granitic gneiss shows sharp contacts with the host, and has low Sr, Ba, K and Pb but high Rb, Rb/Sr, with negative Eu anomalies, consistent with dehydration melting. Petrographic observations, geochemical data and pseudosection modelling suggest that garnet amphibolite experienced water-fluxed melting and garnet granitic gneiss underwent dehydration melting, respectively. LA-ICP-MS zircon and titanite dating indicate the anatectic event proceeded at ∼480–470 Ma. Phase equilibrium modelling suggests the garnet amphibolite and garnet granitic gneiss share a similar P-T path involving decompression heating from ∼12.1 kbar/711–746 °C to reach peak temperatures of 798–836 °C at 10.4 kbar, and subsequently decompression cooling to 4.6–7.6 kbar/600–672 °C. The calculated P-T conditions suggest Barrovian-type metamorphism with thermal gradients of 24.2 °C/km for the Central Qilian lower crust. We interpret a retro−/back-arc setting resulting from the southward subduction of the North Qilian oceanic lithosphere.

Late Cryogenian and early Ediacaran rare-metal rich granites in the Eastern Desert of Egypt: constraints from zircon ages and whole-rock Sr- and Nd- and feldspar Pb-isotopic compositions

Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian–Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U–Pb ages and O-isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96‰ and yielded ages of 628–633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7–678.9 Ma with δ 18 O V-SMOW c . 5.95‰. All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics. Supplementary material : Details of analytical details and supplementary tables and figures are available at https://doi.org/10.6084/m9.figshare.c.6949402

Geochemistry of the North Gondwana Paleozoic Araba and Naqus formation siliciclastics, Sinai: implications for provenance, paleoweathering, and tectonic setting

ABSTRACT The Araba and Naqus formations in Ras Milan, Sinai, constitute part of the major continuous Paleozoic clastic belt stretching across northern Gondwana. They are sandstone-dominated successions, resting on Precambrian granitic basement, with lowermost thin basal polymictic conglomerate deposits (1–2 m), marking the unconformity. The Araba Formation section is composed mainly of varicoloured violet to reddish brown, fine to coarse-grained laminated and planner and overturned cross-bedded sandstones, while the overlying Naqus Formation is characterized by chaotically distributed poorly sorted quartz pebbles to cobbles within a moderately-sorted coarse- to medium-grained quartz arenite and by abundance and variety of large-scale tabular and trough cross bedding. Modal QFL classification of Araba and Naqus formation sandstones revealed that they are merely quartzose sandstones (quartz arenites). Geochemistry of the succession shows extremely wide compositional ranges for almost all major elements, but the Araba Formation is relatively enriched in SiO2, TiO2, Fe2O3*, Na2O, P2O5, and depleted in Al2O3, MgO, CaO and K2O relative to Naqus Formation. Only the Araba Formation samples are depleted in the transition elements Ni, Cr and Co and oppositely possess extreme enrichment in the HFSEs (i.e. Zr, Hf, Y, Nb, Ta, Th, U), whereas both formations show variable depletion in the LILE Rb, K and Ba, and excessive REE abundances relative to the PAAS and UCC, and LREE-enriched patterns with marked negative Eu anomalies. The provenance of the Naqus and Araba formations could be an earlier felsic magmatic source, which has undergone extensive sedimentary recycling. They possess high compositional maturity and were subjected to intensive to moderate weathering during humid climatic conditions. Passive margin tectonic setting is implied which denotes the derivation of Araba and Naqus formation siliciclastics from stable continental regions or plate interiors and deposition in intracratonic basins.

Geochronology and Geochemistry of Ore‐related Granitoids in the Giant Gariatong Rb Deposit, Tibet and Implications for Rb Metallogeny in China

AbstractRubidium (Rb) deposits mostly occur in the South China and Central Asia orogenic belts and are often closely associated with highly differentiated granites. This study investigates a newly‐discovered giant Rb deposit at Gariatong in the Central Lhasa terrane in Tibet. Detailed field studies and logging data revealed that the Rb mineralization mainly occurs in monzogranite and is related to greisenization. LA‐ICP‐MS U‐Pb dating of zircon yielded ages of 19.1 ± 0.2 Ma and 19.0 ± 0.2 Ma for greisenized monzogranite and fresh monzogranite, respectively. The monzogranites are characterized as strongly peraluminous, with high contents of SiO2, Al2O3, K2O and Na2O as well as a high differentiation index. They are enriched in light rare earth and large ion lithophile elements with significant negative Eu anomalies and depleted high field‐strength elements. Petrological and geochemical features of these ore‐related monzogranites suggest that they are highly fractionated S‐type granites, derived from remelting of crustal materials in a post‐collisional setting. The geochemistry of zircon and apatite points to a low oxygen fugacity of the ore‐related monzogranite during the magma's evolution. The discovery of the Gariatong Rb deposit suggests that the Central Lhasa terrane may be an important region for rare metal mineralization.

Continental Arc Plutonism in a Juvenile Crust: The Neoproterozoic Metagabbro-Diorite Complexes of Sinai, Northern Arabian-Nubian Shield

Based on new field, petrographic, and whole-rock geochemistry data, we investigated three discrete metagabbro-diorite complexes (MGDC) across the E-W Sinai to contribute to increasing knowledge of the evolution of the juvenile continental crust of the Neoproterozoic Arabian–Nubian Shield. The three MGDCs vary in the dominance of the gabbroic versus dioritic rock types among each of them. Gabbroids are distinguished into pyroxene-hornblende gabbros and hornblende gabbros, whereas dioritic rocks have been subdivided into diorites and quartz diorites. The studied MGDC rocks are almost metaluminous and possess prevalent calc-alkaline characteristics over subsidiary tholeiitic and alkaline affinities. The most distinctive feature in the profiles of the investigated MGDCs on the N-MORB-normalized spider diagrams is the coincidence of stout negative Nb anomalies and projecting positive Pb spikes, which is typical of igneous rocks evolved in subduction zones. The three MGDC samples exhibit variably LREE-enriched patterns [(La/Yb)N = 4.92–18.55; av. = 9.04], either lacking or possessing weak to negligible positive and negative Eu anomalies. The calculated apatite and zircon crystallization temperatures reveal the earlier separation of apatite at higher temperatures, with the obvious possibility of two genetic types of apatite and zircon in the magma (cognate vs. xenocrystic) since both accessories have yielded very wide ranges of crystallization temperatures. The investigated MGDCs were formed in a continental arc setting, particularly a thick-crust arc (>39 km). The parent magmas comprised components derived from the melting of the mantle wedge, subducting oceanic lithosphere, and subducting overlying sediments. The mantle input was from a spinel–garnet transitional mantle source at a depth of ca. 75–90 km. The impact of slab-derived fluids was much greater than that of slab-derived melts, and so subduction-related fluids had a crucial effect on metasomatizing the partially melted mantle source. The parent mantle-derived magma has been subjected to substantial crustal contamination as a dominant mechanism of differentiation.

Genesis of the Early Indosinian Darongshan Granitoid in South China: Response to the Subduction of the Eastern Paleo-Tethys Ocean

The Bangxi–Chenxing suture zone is an essential area from which information about the closure history of the eastern Paleo-Tethys Ocean can be obtained. The Darongshan granitoid, which is adjacent to this suture, lies among the widely distributed granitic rocks and few basic rocks in the southern Guangxi Province. Herein, we report the petrogeochemistry, zircon U–Pb ages, and zircon Hf isotopic data of the Darongshan pluton in this region. The LA-ICP-MS U–Pb zircon analysis indicates that the Darongshan pluton had formed at 249.9±2.6 Ma. The Darongshan granites are silica-rich (SiO2=65.68–72.91 wt%, mean=69.89 wt%) with high Na2O contents (Na2O=0.46–6.58 wt%, mean=3.49), relatively high Mg (Mg#=35.12–73.31, mean=57.73), and an average Fe2O3T+TiO2+MnO+MgO of 4.96. These features are similar to those of the Mg-andesitic/dioritic rock- (MA-) like tonalite–trondhjemite–granodiorites (TTGs). Chemical analyses show that all rocks are enriched in large-ion lithophile elements (Rb, Th, and U) and light rare earth elements, with weak negative Eu anomalies (Eu/Eu∗=0.27–0.67), and Ta, Nb, and Ti depletion, with typical arc-like affinity. The zircon Hf isotopic results show zircon ƐHft values ranging from -18.2 to -7.4 and the TDM2 model ages 1.74–2.41 Ga. The petrogeochemistry and zircon Hf isotopic signatures indicate the magma generation of the Darongshan granitoid with fluid/melt released from the subducted slab and the fluid/melt assimilated and mixed with the mantle peridotite during ascent. Combining previous extant information on Permo–Triassic subduction/collision-related magmatism in the Bangxi–Chenxing with that of the Jinshajiang–Ailaoshan–Song Ma suture zones, the Darongshan granitoid is interpreted as a magmatic formation that was generated in an active continental margin arc environment during the subduction of the Early Indosinian eastern Paleo-Tethys Ocean and the South China Block, further supporting the idea that closure occurred during the Middle–Late Triassic.

Petrogenesis of the late Cenozoic potassium-rich volcanism in the NW Tibetan Plateau: Constraints on the mantle evolution through post-orogenic events

The late Cenozoic Heishi Beihu volcanic rocks represent potassium-rich magmatic events at the northwesternmost margin of the Tibetan Plateau following the Indian–Asian continental collision. The petrogenesis of this juvenile igneous activity plays a crucial role in revealing the geochemical features of the deep mantle and contributes to our understanding of orogenic geodynamic evolution. This study, identified three eruption episodes at Heishi Beihu volcano (7.1–6.2, 4.3–1.4, and 1.3–1.0 Ma) using SHRIMP zircon U-Pb dating. Geochemically, the three episodes are characterized by shoshonitic affinities (K2O = 2.96–4.36 wt%) and crust-like trace-element signatures (negative Ta, Nb, and Ti anomalies), with enrichment in light rare earth (LREE) and large-ion lithophile elements (LILE), depletions in high-field-strength elements (HFSE), and small negative Eu anomalies (0.74–0.86). Their enriched whole-rock Sr ([87Sr/86Sr]i = 0.7072–0.7090), Nd (εNd(t) = −6.91 to −6.24), and zircon Hf (εHf(t) –5.64 to −9.13) isotopic compositions, and high zircon δ18O values (+7.4‰ to +10.6‰), are indicative of an enriched and heterogeneous mantle source (EMII-type) that contained recycled continental crust. The Heishi Beihu volcanic rocks were derived by low-degree (2%) partial melting of a mantle source with dominant pyroxenite and minor peridotite under conditions of the garnet-eclogite-facies. Results obtained from clinopyroxene–liquid geothermobarometry are indicative of diverse magma reservoirs, ranging from deep crustal levels (41–56 km) during Episode I to shallower depths for Episodes II (26–35 km) and III (17–29 km). In combination with the geological development of the area, we infer that magmatism at Heishi Beihu was genetically related to asthenospheric upwelling and induced by underthrusting of the Indian lithosphere beneath Western Kunlun.

Mid-Miocene silicic explosive volcanism of the Tokaj Mts., eastern-central Europe: Eruption chronology, geochemical fingerprints and petrogenesis

The Tokaj Mts. volcanism occurred in a thinning continental lithosphere regime at the final stage of the subduction process. Using high-precision zircon U-Pb dating, four major explosive eruption events were distinguished. Among them the 13.1 Ma Sátoraljaújhely and the 12.0 Ma Szerencs eruptions could have yielded large amount of volcanic material (possibly > 100 km3) and they were associated with caldera collapse as shown by the several hundred-metre-thick pyroclastic deposits and the long (>100 km) runout pyroclastic flow in case of the 13.1 Ma eruption. The 12.3 Ma Hegyköz and the 11.6 Ma Vizsoly eruptions were relatively smaller. The volcanic products can be readily distinguished by zircon and glass trace elements and trace element ratios, which can be used for fingerprinting and to correlate with distal deposits. The Rb, Ba, Sr content and strong negative Eu-anomaly of the glasses reflect extreme crystal fractionation, particularly for the Szerencs rhyolitic magma. The silicic volcanic products of the Tokaj Mts. show compositional similarities with the so-called ‘dry–reduced–hot’ rhyolite type consistent with an origin in an extensional environment, where the primary magmas were formed by near-adiabatic decompression melting in the mantle with subordinate fluid flux. In contrast, some of the older Bükkalja rhyolitic magmas evolved via more hydrous evolutionary paths, where amphibole played a role in the control of the trace element budget. The significant increase of zircon ε Hf values from −8.8 to + 0.2 in the rhyolitic pyroclastic rocks of Tokaj Mts. with time implies that mantle-derived magmas became more dominant. This can be explained by the specific tectonic setting, i.e. the final stage of subduction when the descending subducted slab became almost vertical, which exerted a pull in the upper lithosphere leading to thinning and accelerated subsidence as well as asthenospheric mantle flow just before the slab detachment.

Petrography, geochemistry and detrital zircon U–Pb dating of the Pliocene‐Pleistocene Dupi Tila Formation from the Lalmai Anticline, Bengal Basin: Regional tectonic implications

The Bengal Basin is a well‐known foreland basin that archives the tectonic evolution of the Himalayan and Indo‐Burman Ranges (IBR). The Dupi Tila Formation is the youngest among the stratigraphic successions of the Bengal Basin, which witnessed the last phase of the Himalayan uplift. However, there is still controversy regarding sediment provenances since the Himalayan and IBR are in the late Neogene exhumation stage. In this study, the petrographical and geochemical compositions of the Dupi Tila sandstones from the Lalmai Anticline of the Bengal Basin are examined to infer the source rocks, tectonic settings, palaeoclimate and weathering intensity in provenance areas. The detrital modes and geochemical discriminations, as well as Chondrite‐normalized rare earth elements patterns with enrichment in light rare earth elements and nearly flat heavy rare earth elements and negative Eu anomalies (average Eu/Eu* = 0.77) indicate dominantly felsic source rocks. The geochemical data also suggest that these source rocks in provenance areas were influenced by weak to moderate chemical weathering (chemical index of alteration: 65.64–75.62) and multiple recycling under warm and humid to semi‐humid climatic conditions. The detrital zircon ages show three dominant peaks at ca. 100, 500 and 1000 Ma with minor 1700 Ma. The amount of young zircon grains (<120 Ma) is noticeably higher (~18%) in this Lalmai outcrop compared to the Dupi Tila samples from the Sylhet Trough and Chittagong‐Tripura Fold Belt. Results from integrated zircon geochronology and geochemistry indicate that the detritus are likely derived from a recycled orogen provenance related mainly to active continental margin setting with subordinate influence from passive setting. Therefore, the regionally extensive Himalayan Orogen appears to be the primary sediment source, with additional mixing from the IBR and recycled sediments originating from the Gangdese batholith of the Trans‐Himalaya.

Petrogenesis and Geodynamic Implications of Cretaceous Nb-Enriched Mafic Dykes in the East Kunlun Orogen, Northern Tibet Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd Isotopes

There is a magmatic lull period in the East Kunlun orogen (EKO) during the Jurassic to the Cretaceous. However, due to the lack of records of magmatic activity restricts our understanding of the late Mesozoic magmatic-tectonic evolution of the EKO. Herein, an integrated study of geochronology, whole-rock geochemistry and Sr-Nd isotopes were conducted for the Cretaceous mafic dykes in the EKO, Northern Tibet Plateau, to reveal their petrogenesis and geodynamic implications. LA-ICP-MS Zircon U-Pb dating reveals that the studied mafic dykes comprising diabase and diabase porphyry emplaced at ca. 80.9 ± 0.8 Ma. The Cretaceous mafic dykes have low contents of SiO2 (46.36 wt.%~47.40 wt.%) but high contents of MgO (6.79 wt.%~7.38 wt.%), TiO2 (1.91 wt.%~2.13 wt.%), Nb (12.4~18.3 ppm) and Nb/U ratio (31~39), resembling Nb-enriched mafic dykes. They exhibit chondrite-normalized rare earth element (REE) and primitive mantle-normalized trace element patterns, remarkably similar but not identical to the oceanic island basalts (OIB). The moderate REE fractionation ((La/Yb)N = 3.55~5.37), weak negative Eu anomalies (δEu = 0.87~0.97) and relative enrichment of Rb, Ba, K, as well as high contents of Cr and Ni and slightly depleted Sr-Nd isotopes (εNd(t) = −0.18~1.33), suggest that the studied dykes originate from a partial melting of spinel lherzolite and a little of garnet which was previously modified by subducted sediments. Combined with other evidence, we propose that the studied Cretaceous Nb-enriched mafic dykes in the Northern Tibet Plateau were formed in the intraplate setting, which may be a partial melting of the enriched mantle in the lower lithosphere caused by the activity of the East Kunlun strike-slip fault.

Petrogenesis and Tectonic Evolution of Huashigou Granitoids in the South Qilian Orogen, NW China: Constraints from Geochronology, Geochemistry, and Sr–Nd–Hf–O Isotopes

The origin of granitic rocks from the South Qilian orogenic belt is of great significance for understanding the continental tectonic framework of Western China. Currently, scholars have different opinions on the tectonic evolution of the South Qilian. Huashigou granite, which exhibits multiple intrusive episodes, is a suitable example for studying the tectonic evolution of the South Qilian. New zircon U–Pb ages and the whole-rock elemental and Sr–Nd–Hf–O isotopic compositions of Huashigou granitic rocks are presented here to investigate their petrogenesis and discuss the tectonic implications for the evolution of the South Qilian orogenic belt. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 368.7 ± 3.5 Ma, 261.5 ± 0.63 Ma, and 262.2 ± 1.4 Ma for granodiorites from the Hua1 pluton, quartz diorites from the Hua2 pluton, and porphyritic tonalites from the Hua4 pluton, respectively. Late Devonian granodiorites from the Hua1 pluton belonged to the metaluminous calc-alkaline series and were characterized by an enrichment in LREEs, a depletion in HREEs, negative Eu anomalies, and Sr/Y ratios of 9.17 to 11.67. They showed (87Sr/86Sr)i ratios of 0.712356 to 0.71195, εNd(t) values of −6.56 to −6.14, and an εHf(t) value of −2.06. Middle Permian granitic rocks mainly consisted of quartz diorites and porphyritic tonalites, which are part of the metaluminous tholeiitic series and weakly peraluminous tholeiitic series, respectively. Quartz diorites from the Hua2 pluton were characterized by an enrichment in LREEs, depletions in HREEs and HESEs, weak negative Eu anomalies, and Sr/Y ratios of 13.25 to 14.79. They showed (87Sr/86Sr)i ratios of 0.705905 to 0.705971, εNd(t) values of +0.78 to +0.82, and a δ18OV-SMOW value of 12.4‰. Porphyritic tonalites of the Hua4 pluton were characterized by an enrichment in LREEs, depletions in HREEs and HESEs, weak negative Eu anomalies, and Sr/Y ratios of 9.22 to 12.74. They showed (87Sr/86Sr)i ratios of 0.719528, εNd(t) values of −8.57, and a δ18OV-SMOW value of 11.8‰. We can conclude that Late Devonian granodiorites were derived from the partial melting of enriched and shallow-depth crustal materials, whereas Middle Permian granitic rocks were formed by the delamination of a thickened lower crust after the closure of the Paleo-Tethys Ocean, which caused the underplating of mantle-derived basaltic magma, inducing the partial melting of the lower crust at different depths. Our results show that there were at least two important stages of compressional and extensional tectonic switches in the South Qilian orogenic belt during the Late Paleozoic Era, and the evolution of Altyn Tagh–Qilian–North Qaidam had evident stages.

Origin of the Permian high silica A-type granites in Halajun, South Tienshan, NW China: Implications for crystal-liquid segregation and rare metal fertilization

High silica A-type granites (HSAGs) are important carriers of rare metal elements. Formation of HSAGs by crystal-liquid segregation would facilitate fertilization of rare metals and rare earth elements (REE). In this work, we present detailed petrology, whole-rock geochemistry, and in-situ zircon UPb ages and HfO isotopic compositions of the Halajun HSAGs in the South Tienshan Orogenic Belt (STOB). In combination with the previous study of the Halajun syenite and monzonite, we unravel the genetic connection of these granitoids and further explore the metallogenetic potentiality of HSAGs along the STOB in China. The Halajun granites have geochemical affinities of HSAGs with high SiO2 contents (> 70 wt%), whole-rock zirconium saturation thermometry (680–860 °C), high Ga/Al ratios and high field strength elements (HFSE) contents. The HSAGs (273–279 Ma), monzonite (280 Ma) and syenite (283 Ma) have similar formation ages, identical mineral assemblages, and consistent variations in major elements, implying a common magma reservoir of their parental magma. The Tamu and Huoshibulake HSAGs have high SiO2 (74.5–78.1 wt%) contents, low Sr (5–28 ppm) and Ba (7–60 ppm) contents, high Rb/Sr ratios (11.6–87.5), and strong negative Eu anomalies (0.01–0.08). Combined with the petrographic features, these geochemical variations suggest that they are the extracted melt. Conversely, the geochemical (high Sr and Ba concentrations, and Eu/Eu* near unity) and petrographic features of monzonite and syenite represent the residual silicic cumulate (crystals ± trapped melt). The Kezi'ertuo and Halajun II HSAGs have SiO2 (71.9–76.5 wt%) contents, Sr (35–101 ppm) and Ba (60–541 ppm) contents, Rb/Sr ratios (1.9–8.9), and negative Eu anomalies (0.04–0.43), indicating the intermediate component (extracted melt + fractional crystals) in the consecutive system of crystal-liquid segregation. In-situ zircon HfO isotopes for the Halajun granitoids indicate a complex trans-crustal magmatic process involving crystal-liquid segregation and wall-rock assimilation. The long-time span of Tarim Large Igneous Province (TLIP) sustained injection of mantle-derived magma and/or advective heat to the magma chamber (> 1 Ma). Owing to the prolonged magma evolution, the highly fractionated silicic magma with high incompatible elements and F contents was extracted from the magma mush, and formed the HSAGs.

Material composition of the Mesozoic igneous rocks of the Mikhailovsky massif and small bodies of the Evotinskiy ore district (Southern Yakutia, Aldan-Stanovoi shield)

The petrographic and geochemical characteristics of the Mesozoic igneous rocks of the Mikhailovsky massif, including the sills and dikes of the Evotinsky ore district located in the central part of the Nimnyr terrane of the Aldan-Stanovoy shield, were examined. This study revealed for the first time that the Mikhailovsky Massif is composed of quartz monzonites, while the sills and dikes are composed of quartz syenites. These rocks are geochemically close to the shoshonite-latite series of island arc rocks and are enriched in LREE and depleted in HREE, characterized by aweak negative Eu-anomaly. The sequence of magmatism development in the Mesozoic has been established: the formation of rocks of the Mikhailovsky massif and most small bodies occurred in the post-collision period, followed by the intrusion of quartzsyenite dike bodies in theanorogenicstages of territorial development.The study suggeststhat all the studied igneous rocks of the northeastern part of the Evotinsky region are characterized by a duality of geochemical composition,which indicates either intense mantle-crustal interactionor the existence of two sources of both mantle and crustal originat that time.

Polymetallic tungsten skarn mineralisation related to the Periadriatic intrusion at Lienzer Schlossberg, East Tyrol, Austria

Abstract A regional tungsten anomaly was discovered and explored in the Lienzer Schlossberg area that is part of the crystalline Austroalpine nappe complex of the Eastern Alps in the 1970/80-ties. Tungsten is present as scheelite, which occurs in steeply SSW dipping WNW-ENE oriented quartz veinlets and joints within the porphyritic dioritic to tonalitic/granodioritic host rocks of the Oligocene Lienz/Edenwald intrusion and in the exoskarn, which developed at the contact of the intrusion with Ca-rich lithologies. The skarn system is characterised by two stages: (1) a primary high-temperature calc-silicate stage characterised by grossular, diopside-hedenbergite, vesuvianite, wollastonite and Ca-plagioclase and (2) a retrograde skarn stage including scheelite-bearing massive sulphide ores (pyrrhotite, chalcopyrite, tremolite-actinolite, diopside-hedenbergite) and scheelite-rich fault rocks with calcite, sericite and chlorite. The two ore stages, the mineral paragenesis and composition is like that of a reduced tungsten skarn; i.e., garnet is grossular-rich, clinopyroxene is diopside-hedenbergite. Vesuvianite contains up to 1.8 mass % fluorine. Scheelite has been studied by cathodoluminescence (CL), electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Three types of scheelite (Scheelite 1–3) are distinguished. In short-wave UV light, all types show blue fluorescence but CL revealed internal micro-textures in scheelite grains which are dominated by oscillatory zoning. Prolonged hydrothermal activity is indicated by dissolution-replacement and overgrowth textures affecting the primary zonation and trace element composition of scheelite. The distribution of rare earth elements (REE) in Scheelite 1 in tonalite-hosted quartz veinlets shows a convex (i.e., middle REE-enriched), heavy REE-depleted pattern with negative Eu anomalies (EuA ). The evolution of REE patterns from skarn-hosted Scheelite 2 and 3 illustrates a gradation of convex REE patterns with high ΣREE and distinct negative Eu anomalies to relatively flat REE patterns with small to no EuA . Scheelite at Lienzer Schlossberg has one of the highest ΣREE+Y contents of all scheelite-bearing ore settings in the Eastern Alps but incorporates minor Mo and the least Sr. High Na and Nb contents together with the positive correlation of REE+Y vs. Na+Nb+Ta suggests that the main exchange vectors for REE incorporation in scheelite is via a combined coupled substitution mechanism. Results of this study confirm the genetic similarity with reduced tungsten skarns and highlight the tungsten potential of this area.