UPb Ages Research Articles

Provenance of multi-stage volcanic ash recorded in the Late Carboniferous coal in the Jungar Coalfield, North China, and their contribution to the enrichment of critical metals in the coal

The origins of partings within the Late Carboniferous No. 6 coal in the Jungar Coalfield, North China, and their relationship to the enrichment of critical metals in the coal, is poorly understood. This study combines UPb ages and LuHf isotope data of zircon, whole-rock geochemistry, LA–ICP–MS elemental mapping, and selective chemical extraction experiments to investigate the provenance of the partings and the occurrence mode of critical metals in the partings collected from the exploration area in the northwest of the Jungar Coalfield. It was found that the zircons in the kaolinite-dominant partings yielded a single age group of ca. 300 Ma at the latest Carboniferous (Gzhelian), indicating that the partings are alteration products of air-fall volcanic ash (tonsteins). The zircons are characterized by negative εHf(t) values and a continental arc tectonic setting, suggesting a genetic connection between the volcanic ash and the Late Paleozoic continental arc that existed in the Inner Mongolia Paleo-Uplift, related to the southward subduction of the Paleo-Asian oceanic plate beneath the northern margin of the North China Block. During the devitrification of volcanic glasses to kaolinite in the mires, the incompatible elements, such as Nb, Ta, Zr, Hf, and rare earth elements (REEs and Y, REY), preserved in the volcanic glasses were leached out as they are incompatible with the crystal lattice of kaolinite. Niobium and Ta, similar to Ti in ionic radii, were preferentially incorporated into fine-grained Ti oxides as reprecipitated products in the alteration process of volcanic ash. The enrichment of Nb, Ta, and Ti in organic matter in the tonsteins suggests that they have some mobility during alteration of volcanic ash and could be, to some extent, transported into the enclosing peats. Zirconium, Hf, and REY were fixed by organic matter admixed with the volcanic ash after their deposition in the mires. Meanwhile, they could also be transported into the enclosing peats, as no secondary minerals formed could substantially retain them. Although Li and Ga were able to be incorporated into the crystal lattice of kaolinite during their crystallization, they could also be transported into the enclosing peats due to their fluid-mobile nature. Both the leaching of a voluminous amount of volcanic ash contacting with the peats and the input of the volcanic ash as an admixture into the peats contributed to the enrichment of critical metals in the Late Carboniferous coal in the Jungar Coalfield.

Tectonic and climate forcing of exhumation in the SE Tibetan Plateau over the past 7 Ma: Insights from the deltaic-submarine fan system in the Andaman Sea, northeastern Indian Ocean

The Tibetan Plateau and its adjacent areas are a typical example for studying the relationship between plateau uplift, climate change, and surface erosion. It has been argued that the South Asian monsoon (SAM) strengthened significantly at 10–8 Ma, whereas others suggested that the SAM weakened at that time. Here we report a large deltaic-submarine fan system in the Andaman Sea with a high sediment accumulation rate during the Pliocene. We propose that the formation of the deltaic-submarine fan was a result of climate and tectonics over the past 7 Myr. Our findings are based on multi-method provenance analyses (heavy minerals, bulk-rock geochemistry, detrital zircon UPb ages, and seismic data) of the Late Miocene-Pleistocene deltaic-submarine fan system. The analyses, in combination with those of the modern river sediments and potential source regions, suggest that the Upper Miocene sediments were mainly derived from the eastern Lhasa Terrane and northern West Burma Terrane (Upper Salween and Upper Irrawaddy, respectively), whereas the Pliocene-Pleistocene deposits were primarily derived from the eastern Lhasa Terrane, northern West Burma Terrane, and Tengchong Terrane (Lower Salween River), with small inputs from the Sibumasu and Baoshan terranes. We propose a modified scenario in which the Salween initiated in the early Late Miocene (10 Ma) and the Irrawaddy developed a modern geometrical morphology after the Pliocene. These two large rivers transported eroded materials from the SE Tibetan Plateau into the Andaman Sea and formed the deltaic-submarine fan. The high sediment accumulation rate (>530 m/Myr) in the Pliocene is consistent with the strengthened SAM and heterogeneous crustal deformation of the SE Tibetan Plateau during the same interval. We conclude that both the climate and tectonics have direct effects on exhumation of the SE Tibetan Plateau over the past Late Miocene-Quaternary.

The Gharuchah-Sofla intrusion (northwestern Sanandaj-Sirjan zone, Iran): Age, petrology, geochemistry and tectonomagmatic implications

The Cretaceous Gharuchah-Sofla intrusion is a composite batholith consisting of a variety of mafic to felsic rocks in the northwestern Sanandaj-Sirjan zone, Iran. Both its age and the relationship between various rock types in the intrusion are unknown. To address these issues, we conducted a detailed age, petrologic, and geochemical study of the intrusion, their country rocks, and mafic microgranular enclaves (MMEs) hosted therein. Plutonic rocks from the main mass of the intrusion, dated at ~110 Ma by in-situ zircon UPb method, are dominated by gabbroic, dioritic, and quartz dioritic with subordinate granodioritic rocks. Magmatic rocks occurring mostly along margins of the intrusion have Late Ediacaran zircon UPb ages (~560 Ma). Both the Early Cretaceous and the Ediacaran magmatic rocks are sub-alkaline; the former has I-type affinity whereas the latter has S-type affinity with a tendency towards I-type. Both sets of rocks are characterized by continental crust-like trace element patterns showing negative anomalies in Nb, Ta, Sr, P, Eu, and Ti of variable intensity. Early Cretaceous gabbroic rocks exhibit unfractionated rare-earth element patterns (La/Yb = 1.9–3.0) and negative ZrHf anomalies. In contrast, other rocks of the Early Cretaceous and Ediacaran magmatic rocks show fractionated rare-earth element patterns (La/Yb = 11.0–16.8) along with the lack of such anomalies. MMEs, which occur within Early Cretaceous plutonic rocks, have major and trace element compositions similar to the gabbroic rocks. Contrasting Nd isotopic ranges are present between the Early Cretaceous plutonic rocks and the MMEs (ɛNd = +2.0 to +4.1) and the Ediacaran magmatic rocks (ɛNd = −5.8 to −0.4). Based on the geochemical and isotopic data obtained, we suggest that (i) the Ediacaran magmatic rocks formed by melting of Cadomian basement rocks below the blocking temperature of UPb exchange between zircon and melt, (ii) the MMEs represent frozen melts (i.e., calc-alkaline basalts) that formed the gabbroic rocks in the Early Cretaceous instruction, and (iii) fractional crystallization with slightly concomitant assimilation of Cadomian basement rocks was a key process forming intermediate and silicic rocks of the intrusion. The ~110 Ma Gharuchah-Sofla intrusion was likely associated with a continental margin arc related to the subduction of the Neotethys, providing solid evidence that this segment of the arc was built directly on the Cadomian basement.

Consecutive underplating of cognate magmas: Contributions to the enclaves and large-volume plagiogranites in the North Qaidam orogen (NW China)

Magma mingling between mafic and felsic magmas is a plausible mechanism for the formation of mafic microgranular enclaves (MMEs) which are common worldwide. Through dissecting the MMEs with parentage of magma mingling, it can be ascertained how two types of magmas with contrasting physicochemical properties interplay and what implicit information magma mingling records in crust-mantle interaction. Here we present petrography, geochronology, major and trace elements, Sr-Nd-Hf isotopes, and mineral geochemistry for rock associations from the North Qaidam orogen, which provides new insights into the processes of magma mingling, petrogenesis of large-volume host plagiogranites and crust-mantle magmatic interaction. MORB (mid-ocean ridge basalt)-like and arc-like magmas can be distinguished from mantle-derived mafic samples with zircon UPb ages ranging from 480 to 465 Ma. MORB-like magmas originated from a MORB-type asthenospheric mantle, whereas arc-like magmas were derived from an ultra-depleted asthenospheric mantle as a result of consecutive extraction of MORB-like magmas and late-stage metasomatism by subduction-related aqueous fluids. Given the content discrepancies for major oxides, gabbro-dioritic MMEs are formed by incipient mechanical mingling between gabbro-diorite magmas and felsic plagiogranite magmas. MMEs and host plagiogranites yield coincident crystallization ages of 478 Ma and overlapped whole-rock SrNd ((87Sr/86Sr)i = 0.7044–0.7052; εNd(t) = +4.6 ∼ +5.6) and zircon Hf isotopes (εHf(t) = +13 ∼ +16). The host plagiogranite magmas are most likely derived by partial melting of pre-existing analogues of gabbro-diorite intrusions under the condition of consecutive underplating of different batches of cognate magmas over short time scales, which in turn determine the consistent isotope compositions between MMEs and host plagiogranites. As for mineral geochemistry, the plagioclases with the highest An% value and the hornblendes implying the highest melt water content, appear within the MME-bearing plagiogranites next to the chilled margin of MMEs, illustrating that aqueous fluid and heat transfer play a pioneering but finite role in incipient magma mingling. The consecutive underplating of cognate mantle-derived magmas as an ultimate engine leads to the partial melting of newly emplaced basites to form massive plagiogranite magmas and geochemically stratified crust. With magma ascent into a shallow level of crust, magma mingling between underplated mafic magmas and resultant plagiogranite magmas is finally realized.

Origin of transitional I-A-type syenite and its relationship to A-type intrusions in the Luzong Basin, the Lower Yangtze River Belt: Insights from geochemistry

There are potential genetic relationships between I- and A-type granitoids, which remain obscure. The origin of transitional I-A-type intrusions could provide new clues for this issue and are important in deciphering the origin of A-type intrusions. Here we report geochemical and isotopic compositions of transitional I-A-type syenites (Makou pluton) from the Luzong Basin in the Lower Yangtze River Belt (LYRB). The Makou pluton is composed of gabbros and syenites. Zircon UPb ages reveal that it was formed at ∼130 Ma, which was slightly earlier than typical A-type intrusions in the LYRB. Geochemical features indicate that the Makou syenites belong to transitional I-A-type igneous rocks. The Sr-Nd-O isotopic compositions and the correlation between major and trace elements of Makou gabbros and syenites suggest that they are cogenetic, whereas the syenites experienced further magma evolution. Geochemical characteristics, especially the high Nb content of gabbros, suggest that the mantle source of the Makou pluton was metasomatized by melts from subducted sediments and slabs, which is similar to Huangmeijian A-type intrusion in the Luzong Basin. Makou syenites have different evolution conditions, e.g., the temperature and oxygen fugacity, compared with the Huangmeijian A-type intrusion. The ferroan character of the Makou syenites was weakened by crystal fractionation at relatively high oxygen conditions to produce the transitional I-A-type intrusions, due to more addition of fluids derived from subducted slabs to the source. This is consistent with the partial melting of the metasomatized lithosphere mantle due to asthenosphere upwelling as a result of ridge subduction beneath the LYRB.

Early Cretaceous Ningguo-Guangde weakly fractionated I-type granitoids, Jiangnan tungsten belt, China: Implications for petrogenesis and W[sbnd]Mo mineralization

Most W mineralization in the world is genetically related with highly fractionated granitoids, but little is known about petrogenesis of weakly fractionated granitoids and its relationship with W mineralization. To reveal the petrogenesis of the weakly fractionated granitic rocks and related mineralization, a combined study of zircon UPb ages, whole-rock major-trace elements and Sr-Nd-Pb isotopes as well as apatite in-situ geochemistry was carried out for the Ningguo-Guangde granitoids in the world-class Jiangnan W belt (total resource of approximately 6.06 Mt WO3), China. Zircon UPb ages indicate that the Ningguo-Guangde granitoids were emplaced in the Early Cretaceous (ca. 138–125 Ma). These samples with moderate silicon (SiO2 = 65.5–68.4 wt%) mainly consist of high-K calc-alkaline granodiorites and monzogranites, which exhibit an affinity for the weakly fractionated I-type granite, with enrichment in light rare earth elements (LREEs), Rb, Th and U, and negative Eu (δEu = 0.64–0.91), Nb, P and Ti anomalies. All samples have Mg# values of 40.3–51.2, Sr contents of 266–411 ppm and Sr/Y ratios of 9.11–29.6, negative whole-rock εNd(t) values (−6.6 to −5.1), high radiogenic Pb isotopic compositions, and high logfO2 values (−21.7 to −12.0). The integrated interpretation of geochemical data show that the Ningguo-Guangde granitoids were likely originated from Neoproterozoic crustal components mixing with metasomatized mantle-derived magmas. A comprehensive discriminant analysis indicates that metal-rich magma source, shallow fractional crystallization and high oxygen fugacity were favorable factors for the weakly fractionated I-type granite-related WMo mineralization in southern region of Anhui Province, eastern China. Furthermore, porphyry or skarn WMo deposits can be regarded as important exploration targets in the Ningguo-Guangde region.

Detrital zircon U[sbnd]Pb geochronology of modern river sediment in the Eastern Pamir Syntaxis and its implications for the formation of the Pamir and growth of the Tibetan Plateau

The Eastern Pamir Syntaxis links the western Tibetan Plateau with the western syntaxis of the Himalayan-Tibetan orogen. Quantifying temporal and spatial variations in uplift rates for the Eastern Pamir Syntaxis is critical for understanding the growth of the Himalayan-Tibetan orogen. To better understand these variations, we report n = 285 new detrital zircon UPb ages from sediments in modern rivers of the Eastern Pamir Syntaxis. When compared with previous work, our data, with a major age mode around ∼107 Ma, indicate that siliciclastic sediments in the Taxkorgan River were primarily derived from Cretaceous rocks. Whereas a less prominent age mode around ∼13 Ma suggests that Miocene rocks made an important sediment contribution to the Taxkorgan River. The other notable age modes are in the range of 200–300 Ma and 600–800 Ma. Our data suggest that detrital zircon UPb signatures for rivers draining the Eastern Pamir Syntaxis change significantly from south to north, and the influence of Cretaceous proto-sources gradually diminishes northward. Because Tibetan sutures are traceable into the Pamir, these data help define the distribution of late Early Cretaceous rocks associated with the closure of the Meso-Tethys within the Pamir. These data support the establishment of the modern-like river pattern in the Eastern Pamir Syntaxis contemporaneous with activity on the Kongur Extensional System in the northeast Pamir.

Sedimentary provenance and age of the Shengshan Island loess on the continental shelf of the East China Sea: Implications for windblown dust transport during the Last Glaciation

Knowledge of the sedimentary provenance and age of loess deposits can help reconstruct windblown dust activity in the source regions. However, we lack firm evidence to unravel the loess provenance on the offshore islands of China. In this study, we used geochemistry, micropaleontology, and optically stimulated luminescence dating to constrain the sedimentary provenance and age of the Shengshan Island loess on the continental shelf of the East China Sea (ECS). The sedimentary age of the Shengshan Island loess ranges from 75.9 ± 7.5 ka to 39.6 ± 3.4 ka, corresponding to low sea-level stands during the Last Glaciation. The zircon UPb age spectrum of the Shengshan Island loess reveals a 96 Ma age peak, attributed to a source from the nearby granites, while the remaining age components are contributed by the Yangtze River sediments. The element characteristics of size-fractioned samples indicate that the Shengshan Island loess originates from the Yangtze River sediments, the surrounding granites, and dust from the Asian interior. The presence of the spores of the freshwater alga Concentricystes supports the conclusion that the Yangtze River sediments are the major source of the Shengshan Island loess. Thus, the Shengshan Island loess is dominantly derived from proximal dust activity with a minor proportion of the fine fraction derived long-distance dust transport. The local dust emissions from the Yangtze River sediments are directly driven by low sea levels and an arid environment on the continental shelf of the ECS during the Last Glaciation. However, this dust activity was terminated during the transition from the Last Glacial to the Holocene when the sea level rose.

Provenances of the Oldest Xiashu loess and Xuancheng loess in southern China: Implications for dust transport and dust proxies of the East Asian winter monsoon

The loess-paleosol sequences of southern China are valuable paleoclimatic archives since the Middle Pleistocene, on the regional and global scales. Knowledge of loess provenance can shed light on dust transport and the development of paleoclimatic proxies for loess deposits. However, there is a research gap regarding the provenance of the Oldest (∼0.9 Ma) Xiashu loess near the Yangtze River valley. The precise source area of the Xuancheng loess in southern China remains to be unidentified. In this study, we used elemental geochemistry and detrital zircon UPb ages to identify the sources of the Oldest Xiashu loess and Xuancheng loess in southern China. The Oldest Xiashu loess is dominantly derived from Yangtze River sediments, and part of its fine-grained dust component originates from the arid regions of Central Asia or northern China. The elemental compositions of the size-fractionated silicates and detrital zircon UPb ages of the Xuancheng loess are like those of the Shuiyang River sediments in the Xuancheng region. These results demonstrate that the Xuancheng loess is mainly the product of local dust activity in the Xuancheng regions, and thus that the Xiashu and Xuancheng loess are the products of independent dust transport processes. This spatial differentiation of loess provenance may be a widespread phenomenon in southern China, and consequently, the grain size compositions of the various loess sections in southern China cannot be used to recover paleo-wind directions on a regional scale. Overall, our study shows that when the grain size compositions from the southern China loess are used to reconstruct East Asian winter monsoon intensity, the signals from local wind fields should first be removed.

Migration of the Palaeozoic magmatic front from Zagros to Alborz mountains with progressive closure of the Palaeo-Tethys Ocean; Insights from Zagros detrital zircon U[sbnd]Pb age and Hf isotopic composition

The northwest-southeast-trending Zagros Fold-and Thrust Belt in south Iran resulted from the late Oligocene to the early Miocene collision of the Arabian and Central Iran blocks. The Zagros Palaeozoic basin holds the key to reveal the tectonic setting of the earlier stages in the development of the Tethyan realm. We aim to document the Palaeozoic tectonic environment of the Zagros Basin and provide critical constraints on the progressive closure of the Palaeo-Tethys. This work presents a combined detrital zircon UPb age and Hf isotopic composition from the Zagros and Alborz basins in an attempt to identify and date major geologic events along the southern margin of the Palaeo-Tethys and reconstruct the regional tectonic history of the northern margin of Gondwana-Land during the Ediacaran-early Palaeozoic interval. Detrital zircons UPb age and Hf-isotope ratio from Zagros second-cycle Devonian and third-cycle Permian sandstones and Alborz Palaeozoic strata indicate main magmatic flare-ups in the Arabian-Nubian Shield including the Tonian island arc magmatism, the Ediacaran post-orocline-tightening magmatism, the late Ediacaran-early Cambrian Protogonos continental arc magmatism. In addition, detrital zircons recorded the Ordovician continuation of the arc activity in the Protogonos during the early Palaeozoic. Therefore, repetitive recycling of the Neoproterozoic crystalline basement and related sedimentary cover of the Arabian-Nubian Shield, i.e., the Saharides, is a plausible source of the Devonian and Permian strata in Zagros. Our results show a close geological tie between Alborz and other Gondwana-Land-derived units in terms of Palaeozoic detritus sources which is in concordance with the location of the suture along the northern margin of the Alborz Mountains. Separation of the Alborz from the Sanandaj-Sirjan zone is accomplished by inserting from the east, the Central Iranian Blocks (Yazd, Posht-e Badam, Tabas, Lut) by strike-slip stacking and anti-clockwise rotation. This created the extensional zone of Northwest Iran.

The Chicxulub impact structure reveals the first in-situ Jurassic magmatic intrusions of the Yucatán Peninsula, Mexico

Impact events that create complex craters excavate mid- to lower-crustal rocks, offering a unique perspective on the interior composition and internal dynamics of planetary bodies. On the Yucatán Peninsula, Mexico, the surface geology mainly consists of ∼3 km thick sedimentary rocks, with a lack of exposure of crystalline basement in many areas. Consequently, current understanding of the Yucatán subsurface is largely based on impact ejecta and drill cores recovered from the 180–200-km-diameter Chicxulub impact structure. In this study, we present the first apatite and titanite UPb ages for pre-impact dacitic, doleritic, and felsitic magmatic dikes preserved in Chicxulub's peak ring sampled during the 2016 IODP-ICDP Expedition 364. Dating yielded two age groups, with Carboniferous dacites (328–318 Ma) and a felsite (330± 9 Ma) overlapping in age with most of the granitoid basement sampled in the Expedition 364 drill core, as well as Jurassic dolerites (169–159 Ma) and a felsite (158 ± 19 Ma) that represent the first in situ sampling of Jurassic-age magmatic intrusions for the Yucatán Peninsula. Further investigation of the Nd, Sr, and Hf isotopic compositions of these pre-impact lithologies and impact melt rocks from the peak ring structure suggest that dolerites generally contributed up to ∼10 vol% of the Chicxulub impact melt rock sampled in the peak ring. This percentage implies that the dolerites comprised a large part of the Yucatán subsurface by volume, representing a hitherto unsampled pervasive Jurassic magmatic phase. We interpret this magmatic phase to be related to the opening of the Gulf of Mexico, representing the first physical sampling of lithologies associated with the southern extension of the opening of the Gulf of Mexico and likely constraining its onset to the Late Middle Jurassic.

Petrogenesis of Early Mesozoic volcanic rocks in southeastern NE China: Geochemical and Sr–Nd–Pb–O isotopic evidences

This paper reports a study of whole-rock geochemical, Sr–Nd–Pb isotopic compositions and zircon UPb ages and O isotopic compositions of Late Triassic to Early Jurassic volcanic rocks of the Yanbian–Dongning area, northeastern China. The obtained data are used to constrain the petrogenesis of these rocks and to provide new insights into the timing of transition from the Paleo-Asian to the Paleo-Pacific tectonic regime. The studied Late Triassic to Early Jurassic volcanic rocks can be divided into two periods: Late Triassic–early Early Jurassic (212–198 Ma) and late Early Jurassic (ca. 181 Ma). The former rocks display high SiO2 and total alkalis contents, high Ga/Al ratios, depleted SrNd and highly radiogenic Pb isotopic signatures, and low zircon δ18O values. The former rocks have a genetic relationship with coeval intrusions, and their primitive melt was derived from juvenile crustal materials and underwent subsequent differentiation and assimilation of low-δ18O rocks. In contrast, the latter rocks have SiO2 contents of 49.00–63.30 wt%, are classified as calc-alkaline, and display arc-type trace-element features. Their geochemical and Sr–Nd–Pb–O isotopic compositions imply derivation from the partial melting of depleted mantle wedge metasomatized by oceanic slab-derived fluid and sediment melt. Combining these new results with published data, the Late Triassic–early Early Jurassic volcanic rocks are inferred to have formed in a rift-like extensional setting, whereas the late Early Jurassic volcanic rocks were generated in a subduction-related setting. The transition from the Paleo-Asian to the Paleo-Pacific tectonic regime occurred during the Early Jurassic.

Genetic pattern of the Albian volcanic rocks in the Ziruco area, Northern Tibet: Implications for A-type granites

Genetic pattern of a continuous volcanic series of andesites, dacites, and rhyolites from the Ziruco area, northern Tibet was debated in this paper to evaluate the later evolution of A-type granites. We present new zircon UPb ages, whole-rock geochemical, zircon Hf isotopic, and whole-rock SrNd isotopic data for these magmatic rocks. Our analysis shows that the zircon UPb ages of the andesites, dacites, and rhyolites are ca. 105.4 Ma, ca.105.3 Ma, and ca.106.8 Ma, respectively. The andesites have high Nb contents (16.3–24.9 ppm) and Nb/U ratios (22.7–32.4), and chondrite normalized REE and primitive-mantle normalized trace element patterns similar to Nb-rich basalts. They were most likely derived from the mantle that had been metasomatized by melts derived from subducted slab and sediment, and then underwent fractional crystallization. The dacites and rhyolites have high Ga/Al ratios (3.05–3.70 and 2.93–3.43, respectively), REE (226–256 and 195–285 ppm, respectively), Nb (30.0–34.4 and 20.3–24.4 ppm, respectively) and Zr contents (443–513 and 147–163 ppm, respectively), and zircon saturation temperatures (856–886 °C and 823–837 °C, respectively), which are similar to A-type granites. The dacites were most likely formed by partial melting of underplated basaltic lower crust with ilmenite and zircon, followed by slight fractional crystallization. The rhyolites were most likely formed by fractional crystallization of the dacite magmas. The minerals of fractional crystallization probably include feldspar, apatite, zircon, and titanite. This continuous volcanic series in Ziruco area may be related to break-off of the Meso-Tethyan slab in northern Tibet during the late Early Cretaceous. Our studies indicate that fractional crystallization is important later evolutionary process for A-type granites from the crustal source area, and it mainly controls the geochemical characteristics of significant negative Ba, Sr, P, Ti, and Eu anomalies of A-type granites from the crustal source area.

Mantle contribution to the generation of the giant Jinduicheng porphyry Mo deposit, Central China: New insights from combined in-situ element and isotope compositions of zircon and apatite

Identifying crust–mantle interaction is important for understanding the genesis of granite-hosted mineral deposits in post-collisional or intracontinental settings. We have used combined zircon-apatite trace element compositions, zircon HfO isotopes and apatite SrNd isotopes, which were all acquired by in-situ techniques, to evaluate the mantle contribution to the formation of a giant porphyry Mo deposit, the Jinduicheng deposit in the East Qinling–Dabie orogenic belt, Central China. Zircons from the host granites yielded a UPb age of ∼139 Ma, suggesting a post-collisional setting for the ore-related intrusion. Most magmatic zircons from the granites have Ti-in-zircon temperatures lower than 830 °C, moderate Zr/Hf ratios (25–55), and mantle-like δ18O values (peaking at ∼5.6‰), similar to typical I-type granites worldwide. The magmatic zircons have variable εHf(t) values (−26.7 to −7.2) and Ti-in-zircon temperatures (646–894 °C, peaking at ∼740 °C). The coexisting igneous apatites have initial 87Sr/86Sr ratios of 0.70694–0.71027, and variable εNd(t) values (−16.0 to −9.3), Sr contents (132–663 ppm), and Eu/Eu* values (0.12–0.47). The Sr–Nd–Hf isotopes of the apatites and zircons, along with the positive correlations between apatite Sr contents, Eu/Eu* values, and εNd(t) values, a positive correlation between Ti-in-zircon temperatures and zircon εHf(t) values, as well as mixing modeling using SrNd isotopes, suggest that at least two end-member melts were involved in the formation of the host granites: one is the ancient lower crust-derived melt, and the other is the metasomatized lithospheric mantle-derived melt, which have relatively enriched and depleted Sr–Nd–Hf isotopic compositions, respectively. We suggest that the post-collisional lithospheric thinning, asthenospheric upwelling and underplating of the mantle-derived mafic magmas may have triggered the crustal melting, magma mixing, and generation of the host granites of the Jinduicheng deposit. We postulate that, besides the heat, the metasomatized lithospheric mantle-derived magmas likely supplied additional volatiles (e.g., Cl, S), facilitating the porphyry Mo formation. Our study highlights that, combined in-situ element and isotope compositions of accessory minerals can provide multidimensional insights into petrogenetic tracing, and enhance the genetic interpretations of granites and related mineral deposits.

Dating fluid infiltration and deformation in the subducted ultramafic oceanic lithosphere by perovskite geochronology

Carbonated ultramafic rocks (i.e., ophicarbonates) form by peridotite serpentinization and carbonation at the seafloor. Their metamorphic evolution is linked to that of serpentinites, hence dating deformation and metamorphism in ophicarbonates will add constraints to the P-T-t history of the subducted ultramafic lithosphere. A potential, yet underexplored, suitable mineral for geochronology in ophicarbonates is perovskite (CaTiO3). We present trace element and geochronological data (LA-ICPMS and ID-TIMS) from perovskite in ophicarbonate rocks and calcite veins from two metamorphic terranes, Lanzo Massif and Val Malenco (Alps). Metamorphic perovskite in ophicarbonates is characterized by enrichment in heavy REE, and strong negative anomalies in Zr and Hf, as well as Sr and Pb, which are attributed to coexistence of a Zr-rich phase and mobilization of these elements by fluids, respectively. Other trace elements broadly reflect the composition of the protolith and allow the distinction of perovskite from mafic and ultramafic rocks.In the Lanzo Massif, the 49.6 ± 1.0 Ma age of perovskite in shear bands constrains H2-mediated carbonate reduction and abiotic methane and graphite formation at near peak metamorphic conditions during deformation. Perovskite from Val Malenco is found in calcite veins cutting across serpentinite shear foliation and its age of 48.9 ± 0.5 Ma coincides with a major thrusting and extension event that is distinct in age from the initial nappe stacking. The Val Malenco perovskite age can be reproduced by LA-ICPMS and ID-TIMS and is proposed as a suitable secondary reference material for metamorphic, low U perovskite. These results show that metamorphic perovskite geochronology yields geologically meaningful UPb ages and is a viable tool to date deformation and fluid flow in the subducted oceanic lithosphere.

Early Cambrian S-type granites in the Sakarya Zone, NE Turkey: A record for transition from subduction to post-collisional extension deduced from U Pb zircon age and Nd Hf isotopes

Cadomian realms have recently received much attention in the Alpine–Mediterranean orogenic belts, with discontinuous outcrops extending from the Alps to the İstanbul Zone, Menderes Massif, Taurides in Turkey and Iran as well. However, they have not been identified in the Sakarya Zone, northern Turkey to date. Here, we present, for the first time, zircon UPb geochronology, zircon Hf-isotopes and trace elements as well as whole-rock geochemistry and Nd-isotopes from the Karameşe metagranitoid in the Yusufeli (Artvin) area, NE Turkey. The zircon UPb age data demonstrate that the Karameşe metagranitoid intruded into the Precambrian basement units in the Early Cambrian (ca. 534–530 Ma). Zircon overgrowths in the Karameşe metagranitoid interpreted as a result of metamorphic overprint yielded ages of 328 Ma. This age indicates that the Sakarya Zone experienced the Variscan metamorphic events at 328 Ma. The Early Cambrian metagranitoid shows that some rocks in the basement of the Sakarya Zone date back to Precambrian in age. The Karameşe metagranitoid is an S-type granite, with high modal content of muscovite (~10%). The samples show highly peraluminous [A/CNK = molar Al2O3/(CaO + K2O + Na2O) = 1.34–1.58] and medium-K calc-alkaline geochemical affinities. The Karameşe metagranitoid displays low REE concentrations and a slight positive Eu anomaly and show slightly light REEs and LILEs enrichments, and HFSEs depletions. The samples have negative εNd(t) of −4.76 to −2.90 and εHf (t) of −4.75 to −1.08 values. These geochemical-isotopic characteristics reveal that the Karamaşe metagranitoid originated through fluid-absent muscovite dehydration melting of heterogeneous metasedimentary source rocks (mostly greywacke), with a minor input of juvenile mafic melt. We argue that the Early Paleozoic metagranitoids along the eastern Sakarya Zone is an expression of crustal thinning in the Cadomian orogenic belt in northern Gondwana, with the tectonic turnover from convergent margin to crustal extension possibly induced by break-off of Tornquist oceanic lithosphere which is a branch of Iapetus Ocean during Early Cambrian.

A new astronomical time scale for the early Jehol Biota in the Luanping Basin, northeastern China

The Early Cretaceous Jehol Biota in northeastern China significantly increased our understanding of the Mesozoic terrestrial ecosystem and the origin and evolution of a number of biological groups. The early evolutional phase of the Jehol Biota is best recorded in the Members 2 and 3 of the Dabeigou Formation (D-M2–3) in the Luanping Basin and their equivalent Huajiying Formation in the Senjitu-Sichakou Basin in northern Hebei Province. To date, however, no complete, high-resolution time scale has been established for these early Jehol Biota-bearing strata, hindering our understanding of the origin of the Jehol Biota. Here we carried out a cyclostratigraphic analysis using a high-resolution relative lake level variation record, called “depth ranks” (i.e., a series of numerically ranked sedimentary facies) in the ∼185-m-thick, continuously lacustrine D-M2–3 in the Yushuxia section, Luanping Basin. Our results suggest that the climate/lake level fluctuations in the Luanping Basin during the development of the early Jehol Biota were strongly paced by orbital cycles, including the 405 kyr and ∼ 100 kyr eccentricity and ∼ 34 kyr obliquity and ∼ 21 kyr precession. By anchoring the 405 kyr-tuned depth ranks to a relatively high-precise zircon UPb age of one tuff layer at the base of Member 3 (131.5 ± 0.4 Ma), we built a high-resolution astronomical time scale, spanning from 132.4 to 130.7 Ma, for the D-M2–3, indicating a ∼ 1.7 Myr duration of the early Jehol Biota and an average sedimentation rate of ∼11 cm/kyr of the D-M2–3 in the Luanping Basin. In addition, we suggest that the periods characterized by warm summer, enhanced hydrological cycle and expanded lake at high obliquity and low precession at eccentricity maximum were most conducive for both development and preservation of the early Jehol Biota.

Late Carboniferous closure of the Junggar-Balkhash Ocean: Insights from the early Permian post-accretionary magmatism in the Barleik Mountains of West Junggar, NW China

Early Permian magmatic rocks in the West Junggar Terrane (WJT, NW China) contain crucial information about the final closure of the Junggar-Balkhash Ocean (JBO) in the southwestern Altaids, whereas their tectonic settings are inconclusive. In this study, we conduct an integrated study incorporating the geochronology, geochemistry and zircon Hf isotopes of a set of volcanic and intrusive rocks from the northwestern Barleik Mountains in the central WJT. Zircon UPb ages of eight volcanic and felsic–intermediate intrusive samples are ∼292–281Ma, corresponding to a regional magmatic flare-up in the central WJT. The volcanic samples include rhyolitic tuff, andesitic tuff, and rhyolitic andesite, characterized by high-K calc-alkaline to shoshonitic I-type granite features. They yield positive εHf(t) values with a narrow range of 9.40–13.52 and two-stage model ages from 421 Ma to 672 Ma. Above isotopic features, in combination with their relatively low Mg# values of 25–35, demonstrate that they were generated by partial melting of the juvenile lower crust. Felsic intrusive rocks include peraluminous I-type granitic porphyry and A2-type K-feldspar granite, and their low Mg# values (21–35) and trace element ratios suggest the partial melting from lower crustal rocks. By contrast, intermediate intrusive rocks include monzonite, diorite and a dioritic dyke, which represent fractionated partial melts sourced from the underplated depleted mantle-derived magma. Based on the occurrence of I-type and A2-type rocks, together with the coeval extensional strike-slip fault systems and a late Carboniferous angular unconformity, we infer that the early Permian magmatism in the central WJT resulted from an extensional post-accretionary setting. Taken together with similar geological evidence from the WJT and East Kazakhstan, the final closure of the JBO is suggested to occur in the late Carboniferous.

Forearc and back-arc mantle characteristics of the mafic-ultramafic rocks of Simlipal complex, Singhbhum Craton, India

The Simlipal complex of Singhbhum Craton is enigmatic in terms of its shape, stratigraphy, age and geodynamic setting. The circular-shaped Simlipal complex has predominant mafic volcanic rocks and quartzites associated with komatiites, komatiitic basalts, picrites, boninites, andesites and other ultramafic rocks. The mafic rocks are subalkaline tholeiitic basalts to basaltic andesites with moderate SiO2 (45.94–54.26 wt%), MgO (6.09–12.21 wt%), Fe2O3 (10.02–16.44 wt%), CaO (8.33–12.12 wt%), Mg # (32–58), low TiO2 (0.4–1.02 wt%), P2O5 (0.08–0.34 wt%), Ni (112–241 ppm) and Cr (104–506 ppm). The chondrite normalized rare earth element (REE) patterns are slightly fractionated [(La/Yb)N = 2.97–5.44] with slight negative to positive Eu anomalies (Eu/Eu* = 0.84–1.46). Their primitive mantle normalized multielement patterns exhibit negative Th, Nb, Ta and positive to negative Ti anomalies. The ultramafic rocks characterized as harzburgites, have high MgO (34.77–38.11 wt%), Ni (1974–2453 ppm), Cr (3875–4610 ppm) and Mg# (80–85), low SiO2 (40.61–44.18 wt%), TiO2 (0.08–0.14 wt%), Al2O3 (2.24–3.79 wt%), Fe2O3 (7.24–9.77 wt%) and P2O5 (∼0.05 wt%). Their chondrite normalized REE patterns exhibit fractionated LREE [(La/Sm)N = 2.07–2.37], depleted MREE, almost flat HREE [(Gd/Yb)N = 0.99–1.14] and a pronounced trough at Nb-Ta; ZrHf and Ti on the primitive mantle normalized multielement patterns. The basalt gave a zircon UPb age of 2843 ± 16 Ma (MSWD = 0.72) which is the crystallization age. HFSE relationship of the basalts indicates back-arc nature and their melting in the spinel-lherzolite field. The peridotites are arc cumulates, exhibiting boninitic characteristics and forearc affinity. Their PGE systematics indicate retention of sulphides in the residue during the partial melting and fractionation of the mantle. These peridotites and basalts were generated in forearc and back-arc environments during the Neoarchean time, subsequently juxtaposed with plume-derived volcanic sequences and the passive margin sediments as the arc progressed towards the continent. The plume-arc accretion model (PAA) is a viable tectonic setting with the presence of komatiites, komatitic basalts, picrites, tholeiitic basalts and peridotites. Further, the metasediments from the passive continental margin accreted with PAA products in the Simlipal complex. The above findings also support the existence of Archean smaller plate configuration and the proximity of the arc to the continental margin. After the formation of the volcano-sedimentary sequences, the meteoritic impact appears to have obliterated the accretionary imprints in the Simlipal complex.

Differentiation of continent crust by cumulate remelting during continental slab tearing: Evidence from Miocene high-silica potassic rocks in southern Tibet

The role played by felsic igneous magmatism in crustal differentiation is of importance for the evolution and habitability of Earth system. However, the petrogenesis of felsic rocks and their genetic links to mafic magmas remain controversial, hindering our understanding of crustal differentiation processes. Cenozoic post-collisional felsic potassic rocks occur widely in the well-known Himalaya-Tibet orogen and are intimately associated, in space and time, with mantle-derived ultrapotassic rocks, which thus provide a clear case study to investigate the genesis of felsic rocks and their genetic relationship with mafic rocks. Here we report zircon UPb ages and HfO isotopes, mineral major elements, and whole-rock elemental and Sr-Nd-Pb isotopic compositions for the TangraYumco high-silica potassic rocks (trachytes) in central Lhasa block of southern Tibet. The results, combined with literature data of the TangraYumco ultrapotassic rocks, can help better illuminate their genesis and the role of ultrapotassic rocks in their generation. The trachytes erupted in the Miocene (~13 Ma), coeval with ultrapotassic lavas in this area. They have very enriched Sr-Nd-Pb-Hf-O isotope compositions similar to those of ultrapotassic rocks. However, they display more fractionated LREEs (light rare earth elements) than ultrapotassic rocks. The trachytes also show nearly constant Y and Yb contents with increasing SiO2. This indicates that they were not derived by fractional crystallization from ultrapotassic magmas or by mixing between ultrapotassic and ancient crust-derived felsic magmas. Instead, given their lower LREE contents than ultrapotassic rocks and occurrence of clinopyroxene antecrysts, we suggest that the TangraYumco trachytes were likely produced by remelting of newly-formed, Sr-Nd-Pb isotopically enriched, and K-rich cumulates that crystallized from ultrapotassic magmas. Moreover, taking into account regional magmatism and tectonics, we propose that the TangraYumco-Xuruco post-collisional coeval magmatism and rift system represent a response to tearing of subducted Indian continental slab. Finally, in combination with the nature of post-collisional magmatism in the Lhasa block, we suggest that in addition to reworking of juvenile and ancient crust, underplating of post-collisional mafic magmas and remelting of their cumulates could be an important way to differentiate continental crust in collisional orogeny zones.