Pb Dating Research Articles

Dating hydrothermal processes related to the formation of the Lagoa Real uranium deposits using in situ U–Pb dating of andradite and titanite

To understand the mechanisms and origin of ore deposits, it is essential to know their age. However, the processes responsible for ore formation do not always leave a geochronological record, with hydrothermal processes often either not affecting zircon or causing only partial resetting. The Lagoa Real uranium province hosts the most important U resource in Brazil. The U mineralization is hosted by Na-rich rocks known as albitite, which also contain variable amounts of garnet, clinopyroxene, biotite, amphibole, magnetite and titanite. These rocks are presumed to be the result of hydrothermal alteration of the Lagoa Real intrusive suite, a group of A-type granitic rocks emplaced between 1740 and 1720 Ma. Despite the economic importance of these rocks, determining the age of metasomatism and U mineralization has been extremely difficult, with previous attempts using a variety of methods and targeting the whole rock, titanite, uraninite, heavy-mineral concentrates and zircon, yielding a wide variety of ages in the range of 1.5 to 0.9 Ga. This study is the first to directly date metasomatic minerals (garnet and titanite) with the in situ U–Pb dating method. Garnet and titanite from an unmineralized sample gave U–Pb ages of ca. 545 Ma and ca. 520 Ma, respectively. U–Pb dating of zircon from two other unmineralized samples yielded ages of 1740–1720 Ma, interpreted as igneous ages. Electron-microprobe dating of uraninite from mineralized samples produced ages of 530–520 Ma. Altogether, these results suggest that both metasomatism and U mineralization occurred as a result of fluids associated with the gravitational collapse phase (ca. 530–480 Ma) of the Araçuaí–West Congo orogen. This study illustrates the utility of U–Pb dating of andradite garnet for determining the age of mineralization related to metasomatism.

Ecological risk threshold for Pb in Chinese soils

Derivation of ecological risk threshold (the threshold concentration value that protect a certain proportion of species within the acceptable hazard level) of lead (Pb) is a yardstick and plays a key role in formulating soil protection policies, while the research about deducing soil Pb ecological risk threshold is still limited. In this study, toxicological data of Pb based on 30 different test endpoints was collected from our experiment and literature, and applied into interspecific extrapolation by species sensitivity distribution (SSD) method to derive the hazard concentration for 5% of species (HC5, that can protect 95% of species), the prediction models according to different soil properties were established. The results showed that EC10 (the effective concentrations of Pb that inhibit 10% of endpoint bioactivity) ranged from 205.6 to 1596.3mgkg1, and hormesis induced by Pb were up to 118%. Toxicity data were corrected by leaching and aging process before SSD curves fitting. HC5 was then derived and prediction model was developed, as LogHC5 =0.134pH +0.315 LogOC +0.324 LogCEC +1.077. The prediction model was well verified in the field test, indicating that can correctly estimate Pb ecotoxicity thresholds in different soils. This study provides a scientific frame for deriving the ecological risk threshold of Pb and is of great significance for ecological species protection.

Carbonate U[sbnd]Pb and illite Rb[sbnd]Sr geochronology of sediment-hosted gold: A case study of Yata gold deposit

In situ U–Pb dating of carbonate minerals and Rb–Sr dating of illite was carried out on the Yata sediment-hosted disseminated-type gold deposit in the Youjiang basin, South China. The new study determines the timing of gold mineralization and clarifies the geological conditions required for the successful application of in situ U–Pb dating of alteration-related carbonate minerals. The results suggest that the Yata gold deposit likely formed during two metallogenic episodes. Illite Rb–Sr ages of 178.6 ± 5.8 Ma (MSWD = 1.2) for the 2–0.5 μm fraction and 171.3 ± 3.4 Ma (MSWD = 0.62) for the 0.5–0.2 μm fraction constrain an earlier episode of gold mineralization to >178.6 Ma. Hydrothermal carbonate minerals within the Yata gold deposit are associated with organic matter. In situ U–Pb dating of paragenetically early ankerite and later calcite veins yields ages of 149.0 ± 10.4 Ma (MSWD = 2.0) and 147.3 ± 32.6 Ma (MSWD = 1.8), respectively. These mineral ages and their petrographic relationships provide unequivocal evidence that another episode of gold mineralization occurred in the Early Cretaceous. Importantly, this study demonstrates in situ U–Pb dating is applicable to low-temperature deposits consisting of organic-rich hydrothermal carbonates characteristic of relatively high common Pb. Such deposits potentially include hydrothermal antimony, Carlin-type gold deposits, gold‐uranium, and carbonate-hosted uranium deposits.

The El Cortijo Formation: Ocean Plate Stratigraphy in the Tandilia Belt Paleoproterozoic basement (Argentina). Insights into subduction-accretion processes in the southern sector of the Río de la Plata Craton

An Ocean Plate Stratigraphy (OPS) sequence is a record of the oceanic crust geological evolution which allows the identification of paleo-oceans preserved in suture zones of orogenic belts. In the Paleoproterozoic basement of the Tandilia Belt (Argentina), Río de la Plata Craton, the El Cortijo Formation (ECF) crops out in a large suture zone with an E-W orientation and vertical to subvertical inclination. It includes a low-grade metavolcano-sedimentary sequence constituted by metacherts, metabasites, metacarbonate, metawacke, and phyllite. In order to provide genetic interpretations of the ECF, based on the OPS model, petrographic, geochemical, and geochronological studies of some of these rocks were performed. Mineral assemblages identified in metabasites, metawacke, and phyllite indicate a transition from prehnite-pumpellyite to greenschist facies conditions. Metabasites, classified as metavolcanite of intermediate to basic composition, chlorite schist and tremolite-actinolite schist, are interbedded between metacherts and metacarbonate bands. Geochemical analyses revealed particular chemical fingerprints which indicate that the protoliths of these metabasites would have been part of a volcanic arc rock association consistent with adakites, Nb-enriched basalts, high-Mg andesites, and “normal” tholeiitic to calc-alkaline basalts and andesites. The metawacke and the phyllite seem to derive from wackes and semi-pelites, respectively, whose main source is consistent with igneous-metamorphic rocks of acidic to intermediate composition linked to a continental arc system. The first LA-ICP-MS U–Pb data obtained for detrital zircons of the phyllite from the ECF yielded a weighted average age of 2138 ± 9 Ma and a youngest individual 207Pb/206Pb spot age of 2047 ± 22 Ma, which locates the maximum sedimentation age in the early Orosirian, during the maximum tectono-magmatic activity of the Tandilia Belt. According to Lu–Hf data, phyllite zircons derived from crustal sources and yielded Archean Hf model ages. Moreover, εHf(t) data of this rock exhibit a more subchondritic signal than the corresponding for some plutons of the Tandilia Belt, which could be indicating that zircons were not derived from plutons but are instead representative of the host rocks of such plutons. In this sense, the information indicates that the top of the sequence, constituted by the metawacke and the phyllite, represents the arrival of the oceanic plate to the trench zone. The study of the ECF has revealed conclusive evidence to postulate that the whole unit corresponds to the upper part of an OPS sequence of convergent type linked to intra-oceanic arc and continental fore-arc trench tectonic environments. The presence of this oceanic sequence, now preserved in a subduction-accretion complex, allows the Tandilia Belt to be classified as a Paleoproterozoic Pacific-type orogenic belt.

Tracing the cryptic Sardic (Ordovician) metamorphism across Alpine Europe: the Krndija region in the Slavonian Mountains, Croatia

Results of a combined petrological, geochemical and geochronological study suggest that metasedimentary rock units in the Krndija region of the Slavonian Mountains, Croatia, were affected by at least three major tectonometamorphic imprints: during the Middle Ordovician (Sardic event), the early Carboniferous (Variscan event), and the Cretaceous (Alpine event). All three metamorphic phases are established by electron microprobe-based in-situ U–Th–Pb dating of monazite grains. The Sardic metamorphic event is additionally confirmed by a precise Lu–Hf garnet-whole-rock isochron age of 466.0 ± 2.3 Ma. Taken together, the data unveil a relatively large and well-preserved piece of the cryptic Sardic orogen in central Krndija, that we name the Kutjevo Zone. A Sardic subduction-related metamorphic event (ca. 540-580 ℃, 8–11 kbar) at ca. 466 Ma is manifested in the mineral paragenesis Ca-rich garnet plus rutile. A low degree of retrograde reequilibration suggests a subsequent fast exhumation. Low-Ca cores in some garnets and staurolite relics record a pre-HP metamorphic event that involves isobaric heating from 570 to 610 ℃ at ~ 7 kbar. We attribute this (so far undated) event to mid-crustal contact metamorphism caused by early Sardic magmatism. Southern parts of Krndija (the Gradište Zone) experienced an (additional?) clockwise PT evolution in Variscan times at ca. 350 Ma. Garnet formed with ilmenite during a PT increase from 580 ℃/5 kbar to 600 ℃/6 kbar and underwent later strong retrograde resorption. Slow Variscan exhumation resulted in andalusite formation at < 550 ℃/ < 3.8 kbar. Penetrative Alpine metamorphism was observed in low-grade phyllites in the north. The lithology and metamorphic history of the Kutjevo Zone is similar to what has been reported from the Sardic Strona-Ceneri Zone in the western Alps. Both areas expose metapelitic (metagreywacke) rocks with a pre-middle Ordovician formation age. These metasedimentary rocks are inter-layered with numerous small amphibolitic units as well as metagranitoids and were likely deposited along the active Gondwana margin, perhaps in a fore-arc position, prior to their subduction during the middle Ordovician. According to recent palaeogeographic reconstructions, both the Kutjevo Zone and the Strona-Ceneri Zone have once resided in an eastern sector of the northern Gondwana margin (i.e., in E-Armorica). We conclude that in the Middle Ordovician, important subduction activities took place in this E-Armorican segment of north Gondwana, which is today exposed in the Alps. The W-Armorican segment of north Gondwana (now exposed in the French, German, and Czech Variscides) had probably already mutated from a (Cadomian) subduction setting to an extensional (transtensional–transpressional) setting by the late Cambrian.

Geochemistry and origin of hydrothermal apatite in Carlin-type Au deposits, southwestern China (Gaolong deposit)

Apatite can record the evolution of magmatic–hydrothermal ore systems, but it is unclear whether it is suitable for investigating low-temperature, sediment-hosted hydrothermal ore systems. To fill the knowledge gap. we investigated the Gaolong Carlin-type Au deposit in the Guangxi Zhuang Autonomous Region, southwestern China (Youjiang Basin). Results show that the hydrothermal apatite occurs in quartz–sulfide ores, has an intact crystal form and homogeneous texture, and is F-rich (2.77–3.67 wt%) and Cl-poor (<0.01 wt%). The apatite is enriched in rare earth elements (REEs; ΣREE = 739–2481 ppm) and has middle-REE-enriched chondrite-normalized REE patterns with positive Eu anomalies (δEu = 1.35–2.00). These REE features were inherited from a reducing hydrothermal system in which anion complexation was dominant. The apatite has high Sr contents (up to 0. 9 wt%) and relatively uniform initial 87Sr/86Sr ratios (0.709055–0.709208), suggesting that Sr was leached or derived from the deep continental crust. In situ U–Pb dating of 156.8 ± 8.3 Ma for apatite shows that the Late Jurassic–Early Cretaceous was an important time for the formation of Carlin-type Au deposits in the Youjiang Basin. The Au mineralization was associated with far-field tectonism and deeply sourced hydrothermal ore-forming fluids. Hydrothermal apatite can be used to fingerprint low-temperature, sediment-hosted hydrothermal ore systems.

Crustal evolution of the Laurentian continental margin from the Paleo- through Mesoproterozic: A zircon U–Pb and Hf transect through the western Grenville Province, Ontario, Canada

The Great Proterozoic Accretionary Orogeny along the southern and southeastern margin of Laurentia is arguably the first long-lived, modern-style active plate margin on Earth, representing significant crustal growth and reworking. Here, we present new detrital zircon U–Pb and Hf data, along with zircon and monazite metamorphic ages, from tectonic domains in the southwestern Grenville Province that represent depositional basins formed and reworked during a series of events between 2.2 and 1.2 Ga. As such, the data allow a glimpse into the evolution and assembly of this extensive margin. The Nepewassi domain contains Archean basement overlain by mature sandstone characterized by near-unimodal, ca. 2.7–2.6 Ga detrital zircon peaks and likely correlative with Superior Province basement and its Huronian cover. The Nepewassi domain underwent both Archean (ca. 2.65 Ga) and Killarnean (ca. 1.76 Ga) metamorphism. In addition, all units preserve evidence of Grenvillian high-grade metamorphism between ca. 1.05 and 0.99 Ga. The structurally highest parts of the Nepewassi domain also contain younger sedimentary rocks that received detritus from Killarnean sources, with evolved Hf isotopic compositions indicative of reworked Archean crust. Sedimentary rocks in the Tomiko domain preserve detrital zircon of Penokean and Killarnean age (1.9–1.7 Ga) with evolved Hf compositions, along with Labradorian (1.7–1.6 Ga) grains of more juvenile composition. Detrital zircon from the Kiosk domain yield Penokean through Labradorian ages, with Hf compositions ranging from evolved to juvenile. In contrast to the sedimentary rocks found in these Laurentia-derived parautochthonous domains, similar rocks from younger, more allochthonous units, including the Shawanaga and basal Parry Sound domain, dominantly contain zircon ranging from Pinwarian (ca. 1.45 Ga) through ca. 1.20 Ga that show exclusively juvenile isotopic compositions. The data show that sedimentary basins received detritus from nearby active sources as well as from the nearby Superior continent, and that successively younger sources and basins became increasingly less influenced by continental input as the margin grew wider. The data add to a growing database of similar data from other parts of this several thousand-kilometer-long margin that seemingly displayed little along-strike variation in overall evolution, implying the existence of a vast, Pacific-scale ocean.

Geochronology and geochemistry of the Shanagen hydrothermal vein-type Mo deposit in Derbugan metallogenic belt of the NE China and their geological significance

The Shanagen hydrothermal vein-type Mo deposit belongs to the Derbugan metallogenic belt, which is located in the Ergun block, NE China. The Mo mineralization is mainly developed in sericitized quartz siltstone around alkali-feldspar granite. In this paper, we present Molybdenite Re–Os dating, zircon U–Pb dating and geochemical data with the aim of determining metallogenic epoch and tectonic setting. Molybdenite Re–Os and zircon U–Pb dating of the alkali-feldspar granite indicate that the ore-formation and alkali-feldspar granite emplacement occurred at 143.1 ± 3.8 Ma, and 144.7 ± 0.7 Ma. Both were formed in the early Cretaceous. Chemically, the alkali-feldspar granites are enriched in L rare earth element and LILEs, depleted in H rare earth element and HFSEs, and pronounced negative Eu anomalies, are metaluminous and belong to the high-K calc-alkaline series and highly differentiated I-type granite. Geochemical features and concave upwards rare earth element pattern imply that alkali-feldspar granites were formed from magma generated by partial melting of lower crust. Combining the geochemistry, chronology, and the regional tectonic evolution, we infer that Shanagen hydrothermal vein-type Mo deposit was formed the extensional environment after the closure of the Mongol-Okhotsk Ocean.

Multiproxy sediment provenance analysis of two megafans in the Owambo Basin, northern Namibia

The sediments in two stacked megafans in the Owambo Basin of northern Namibia and southern Angola were made accessible by a c. 400 m long, continuously cored borehole. Previous studies have indicated that the lower buried Paleocene–Eocene Olukonda Megafan was deposited by a palaeo-Kunene River transporting material from the NW (i.e. from the Kunene Intrusive Complex and the adjacent Angola Shield). The morphology of the overlying Eocene–Pliocene Cubango Megafan suggests the input of sediments from the north via the Cubango River. Mineralogical and geochemical data from the upper fan indicate felsic metamorphic and granitoid sources. Previous studies, however, did not provide a unique provenance identifier. Combining detrital zircon U–Pb data from both megafans with previously published and newly obtained mineralogical and geochemical data confirms two distinct provenances. The Olukonda Megafan can now be uniquely attributed by means of its detrital zircon ages to the Kunene Intrusive Complex and the surrounding Epupa Metamorphic Complex. In good agreement with the geochronologically more varied geology of the source region in the north, the Cubango Megafan detrital zircon record shows a wide distribution of Paleoproterozoic to Archean ages, but also a younger age range, probably related to a later Damaran/Pan-African source, which is absent in the Olukonda detrital zircon record. Supplementary material: Data obtained for this study, e.g. geochemical data, heavy mineral composition, heavy mineral morphology, zircon morphology, U-Th-Pb isotopes and ages on zircon, instrument settings, and U-Th-Pb isotope data of analysed reference zircon are available at https://doi.org/10.6084/m9.figshare.c.6280517

Paleoproterozoic Shoshonite Mafic Associations of the Irkut Block (Sharyzhalgai Uplift, Southwest Siberian Craton): U–Pb Age and Conditions of Zircon Crystallization

Abstract —The paper presents data on the composition and age of mafic rocks of the shoshonitic series in the Irkut block of the Sharyzhalgai uplift (southwest of the Siberian Сraton). According to the U–Pb dating of magmatic zircon, the formation of monzodiorites of the Poludennyi massif and gabbro-dolerites in the endo- and exocontact zones of the Toisuk pluton occurred at 1.87 and 1.86–1.85 Ga, respectively. The intrusion of mafic magmas and their underplating into the basement of the crust under postcollisional extension resulted in the near-coeval mafic and granitoid magmatism in the Irkut block between 1.87 and 1.84 Ga. The Paleoproterozoic mafic associations belong to the shoshonitic series and are characterized by enrichment in incompatible elements, including Zr, and low negative εNd(T) values. These geochemical and isotopic characteristics point to the derivation of magma from a long-lived enriched-mantle source, such as the subcontinental lithospheric mantle. The crystallization of zircon from the last portions of the evolved mafic melt is evidenced by low zirconium saturation temperatures (710–965 °C) and zircon enrichment in U and Th with increasing Th/U, reflecting the growth of concentrations of highly incompatible elements in the residual melt.

Alkaline Modification of Arabica-Coffee and Theobroma-Cocoa Agroindustrial Waste for Effective Removal of Pb(II) from Aqueous Solutions.

Arabica-coffee and Theobroma-cocoa agroindustrial wastes were treated with NaOH and characterized to efficiently remove Pb(II) from the aqueous media. The maximum Pb(II) adsorption capacities, qmax, of Arabica-coffee (WCAM) and Theobroma-cocoa (WCTM) biosorbents (qmax = 303.0 and 223.1 mg·g−1, respectively) were almost twice that of the corresponding untreated wastes and were higher than those of other similar agro-industrial biosorbents reported in the literature. Structural, chemical, and morphological characterization were performed by FT-IR, SEM/EDX, and point of zero charge (pHPZC) measurements. Both the WCAM and WCTM biosorbents showed typical uneven and rough cracked surfaces including the OH, C=O, COH, and C-O-C functional adsorbing groups. The optimal Pb(II) adsorption, reaching a high removal efficiency %R (>90%), occurred at a pH between 4 and 5 with a biosorbent dose of 2 g·L−1. The experimental data for Pb(II) adsorption on WACM and WCTM were well fitted with the Langmuir-isotherm and pseudo-second order kinetic models. These indicated that Pb(II) adsorption is a chemisorption process with the presence of a monolayer mechanism. In addition, the deduced thermodynamic parameters showed the endothermic (ΔH0 > 0), feasible, and spontaneous (ΔG0 < 0) nature of the adsorption processes studied.

Origin of Late Cretaceous, enclave-bearing granitoids in southern Tibet: Implications for magma recharge and crustal thickening

Exposures of enclave-bearing granitoids can provide rare opportunities to directly evaluate the connection between compositional variability and the depth of origin of arc magmatic rocks. The ∼1000 km long Gangdese batholith is a composite batholith with composition from mafic to felsic; SiO2 ranges from 51 wt% to 70 wt%. New zircon U−Pb dating of the Nyemo plutons, Renbu plutons, and Xigaze plutons in the Gangdese batholith is consistent with their emplacement and crystallization in the Late Cretaceous (ca. 90−85 Ma). Mafic magmatic enclaves (MMEs) in the plutons are characterized by low SiO2 (50.9−56.0 wt%) and Nb/U, Ce/Pb, and Nb/La ratios coupled with enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements. These geochemical features, combined with depleted whole-rock εNd(t) (+4.2 to +4.7) and zircon εHf(t) (+9.0 to +13.8), suggest that they were derived by partial melting of a depleted mantle source associated with subduction-related fluids. The granitoids with high SiO2 (55.6−66.9 wt%) display adakitic geochemical characteristics, such as low Y and Yb contents, and high Sr/Y and La/Yb ratios. Their positive whole-rock εNd(t) (+4.0 to +5.5) and zircon εHf(t) (+6.9 to +14.3) values, as well as enrichment of incompatible elements, indicate that the granitoids were derived from partial melting of the juvenile lower crust. Geochemical modeling suggests that the compositional diversities of MMEs and adakitic granitoids were inherited from heterogeneous sources. This genetic relationship indicates that the underplated basaltic magmas could have supplied sufficient heat to trigger the melting of the thickened crust and thus formation of the enclave-bearing granitoid. In this regard, the origin of arc rocks can mirror the evolution of crustal thickness. Our results reveal that the crust was thickened to ∼50 km during the Late Cretaceous (90−85 Ma) and provide a magmatic record of crustal thickening prior to the Cenozoic Indo-Asia collision.

Early cretaceous ridge subduction in the Shandong Peninsula, Eastern China, indicated by Laoshan A-type granite

Early Cretaceous A-type granites are widespread in the Shandong Peninsula, which can be used to elucidate the tectonic evolution of the eastern China and the destruction of the North China Craton. However, their genesis is still controversial. Several competing models, ranging from slab break-off, postorogenic extension, foundering of the lower crust and ridge subduction, were proposed. Here, we report zircon U–Pb ages, whole-rock and apatite geochemical compositions of the Laoshan granite and discuss its tectonic implications. The Laoshan granite has typical characteristics of A-type granite with high FeOT/(FeOT + MgO) ratios (0.90–0.97) and 10000*Ga/Al ratios (2.70–3.36) and high total alkali (Na2O + K2O: 7.95–8.70 wt%) contents and Zr+Nb+Ce+Y (most &amp;gt;350 ppm) concentrations. The Laoshan granite is further classified as A1-type based on the Yb/Ta-Y/Nb and Ce/Nb-Y/Nb diagrams and the Nb-Y-3Ga and Nb-Y-Ce triangular discriminant diagrams. Zircon U–Pb dating of two Laoshan granite samples yielded emplacement ages of 117.8 ± 1.0 Ma and 120.1 ± 1.3 Ma, respectively. The oxygen fugacity of the Laoshan granite magma is low, as indicated by zircon Ce4+/Ce3+ ratios (most &amp;lt;300). The crystallization temperature of zircon varies significantly, ranging from 652 to 830°C. The apatite compositions show that the Laoshan granite has high F (2.09–2.72 wt%) and low Cl (0.01–0.09 wt%) contents, consistent with influence by fluid released from the decomposition of phengite. Apatite rare earth elements show that mantle sources are also involved in Laoshan A-type granite. Combined previous studies of A-type granitic plutons in the Shandong Province and the Lower Yangtze River belt with the drifting history of the Pacific plate, we propose that the flat subduction of the spreading ridge between the Pacific and the Izanagi plates was responsible for the formation of Laoshan A-type granite.

Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China

The Kaimuqi area in the Eastern Kunlun Orogen (EKO) contains many lherzolite, olivine websterite, gabbro and diorite intrusions, and new zircon U–Pb dating, Lu–Hf isotope and whole-rock geochemical data are presented herein to further confirm the Late Triassic mafic–ultramafic magmatism with Cu–Ni mineralization and to discuss the petrogenesis and geodynamic setting. Zircon U–Pb dating shows that the Late Triassic ages, corresponding to 220 Ma and 222 Ma, reveal the mafic–ultramafic and dioritic magmatism in Kaimuqi, respectively. Zircon from gabbro has εHf(t) values of −3.4 to −0.2, with corresponding TDM1 ages of 994–863 Ma. The mafic–ultramafic rocks generally have low SiO2, (Na2O+K2O) and TiO2 contents and high MgO contents and Mg# values. They are relatively enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy REEs (HREEs) and high-field-strength elements (HFSEs), indicating that the primary magma was derived from the metasomatized lithospheric mantle. The diorites show sanukitic high-Mg andesite properties (e.g., MgO = 2.78%–3.54%, Mg# = 50–55, Cr = 49.6–60.0 ppm, Sr = 488–512 ppm, Y = 19.6–21.8 ppm, Ba = 583–722 ppm, Sr/Y = 23.5–25.4, K/Rb = 190–202 and Eu/Eu* = 0.73–0.79), with LREEs and LILEs enrichments and HREEs and HFSEs depletions. We suggest that the primary Kaimuqi diorite magma originated from enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments. The Kaimuqi mafic–ultramafic and dioritic intrusions, with many other mafic–ultramafic and K-rich granitic/rhyolitic rocks in the EKO, formed in a dynamic extensional setting after the Palaeo-Tethys Ocean closure.

Early Paleozoic oceanic slab subduction in South China: Evidence from adakite‐like granodiorite and high‐Mg diorite from Puyang pluton in the Wuyi orogenic belt

AbstractThe mechanism of Caledonian orogeny in South China is still controversial. The main argument focuses on the issue that whether there existed oceanic subduction. To answer this question, the complex Puyang pluton in the central part of Wuyi orogenic belt was selected for zircon U–Pb dating, in‐situ Lu–Hf isotopic analysis and geochemical testing. The Puyang pluton is mainly composed of granodiorite and diorite. The results of geochronology indicate that the granodiorite and diorite emplaced at 450 ± 3.9 Ma and 443 ± 4.0 Ma. Their emplacement time were well corresponding to the subduction stage of the Yunkai orogeny in the southwestern part of Cathaysia block during the Early Paleozoic (460–440 Ma). The Puyang adakite‐like granodiorite shows enrichments in Sr, but depletions in Y and Yb contents, high in Na2O, K2O and Al2O3, with εHf(t) values range from −10.5 to −7.4 (mean of −9.0) and two‐stage Hf model ages range from 1.91 to 2.10 Ga. These characteristics indicate that the magmas were generated by partial melting of subducted oceanic crust mixed with melts from the above wedgy mantle peridotite. The Puyang high‐Mg diorite shows enrichments in Sr and Ba, depletions in Rb, Y and Yb contents, and strongly high in MgO and Al2O3 contents, with εHf(t) values of −2.9 to 0 (mean of −1.4) and two‐stage Hf model ages of 1.43 to 1.61 Ga. These indicate that the magmas were mainly generated by partial melting of the wedgy mantle peridotite, mixed by adakitic melts from subducted oceanic slab. Comprehensive analysis shows that Puyang adakite‐like granodiorite and high‐Mg diorite were formed in fore‐arc setting, where the mantle and crustal magmas mixed during the oceanic subduction initiation period. By extension, this study offered important evidences to support the point that the Caledonian orogeny in South China was related to oceanic subduction which initiated prior to ~450 Ma.

Protolith age and metamorphic temperature of the Yokokawagawa metamorphic rocks in Nagano Prefecture, central Japan, and comparison with the Sanbagawa metamorphic rocks

We estimated the protolith age and peak metamorphic temperature of the Yokokawagawa metamorphic rocks (YMR) east of the Itoigawa–Shizuoka Tectonic Line using detrital zircon U–Pb dating and Raman carbonaceous material geothermometry, respectively. U–Pb dating of a psammitic rock yielded a youngest age of ∼100 Ma, which corresponds to the protolith age. Raman carbonaceous material geothermometry results for five pelitic rock samples give metamorphic temperatures of ∼350–380 °C. The protolith age is consistent with those of the Sanbagawa metamorphic rocks (SMR), strongly indicating that the YMR are an extension of the SMR. The increase in peak temperature toward intrusive rocks along the eastern margin of the YMR may indicate that the relatively young ages yielded by previous K–Ar dating of the YMR reflect thermal resetting due to contact metamorphism.

Isoclock: a free and novel routine for common Pb correction in U–Th–Pb data reduction of LA-ICP-MS analysis

New software, Isoclock, focuses on deducing common Pb from reference materials or samples. A novel common Pb correction method has been introduced into the program to process data from hydrothermal/accessory mineral LA-ICP-MS U–Th–Pb dating.

Apatite MAP-3: a new homogeneous and low common lead natural reference for laser in situ U–Pb dating and Nd isotope analysis

MAP-3 apatite has very low common Pb contents and homogeneous U–Pb age, which is particularly rare in apatite and appealing for apatite U–Pb dating analyses.

Modeling GPDA and Its Application in Deep Mineral Prediction in the Jiguanzui Cu‐Au Mining Area in Hubei, China

Geochemical anomalies are the basis of mineral deposit prediction. Through the study of the characteristics of geochemical anomalies, we found that their distribution was consistent with a generalized Pareto distribution (GPD). In the present study, we designed a model for geochemical anomaly extraction via a GPD. In the designed GPD model, we used the kurtosis method to estimate the threshold value of the GPD. Furthermore, a principal component analysis (PCA) was used to extract comprehensive information of different geochemical elements in which minerals are enriched. On this basis, a new algorithm named the GPDA model was designed for deep mineral prediction by using the GPD and PCA, and the methods of the GPDA for selecting parameters were studied. The study data for Ba, Pb, As, Cu, Au, Mo, Co, and Zn originated from 26 exploration lines of the Jiguanzui Cu‐Au mining area in Hubei, China. The proposed GPDA model was applied to deep mineral prediction in the study area. We estimated the parameters of the GPDA model, and the thresholds of Ba, Pb, As, Cu, Au, Mo, Co, and Zn were 457.8612, 56.1823, 28.8454, 910.1272, 89.4283, 34.5267, 84.9445, and 121.4863, respectively. The comprehensive information threshold value was 0.4551. The comprehensive abnormal distribution area of geochemical element contents was obtained from thresholds. The results showed that the method used to identify abnormal areas was consistent with the range of ore bodies identified by actual engineering exploration, demonstrating that the GPDA model was effective. Finally, we predicted that there was a new blind ore body located at a depth of about 1100 m below ground between drill holes KZK10 and KZK11. The results have important theoretical and practical significance for deep ore prospecting.

Late Cretaceous–Paleogene terrestrial sequence in the northern Kitakami Mountains, Northeast Japan: Depositional ages, clay mineral contents, and vitrinite reflectance

AbstractForearc basin deposits on continental margins contain important information that can be used to reconstruct the tectonic setting, volcanism, and climate at the time of their deposition. Coal‐bearing terrestrial to shallow marine strata in Northeast Japan were deposited in a forearc basin along the Eurasian continental margin during the Cretaceous–Paleogene. The rocks exposed in the Kado district, Iwate Prefecture, in the northern Kitakami Mountains include the Upper Cretaceous Yokomichi Formation and the Paleogene Kogawa Group; the latter is known for high‐quality refractory clay (kaolin clay). However, their stratigraphy and sedimentological characteristics are not yet fully understood. To reconstruct the formation and filling of the basin, we investigated field observations, U–Pb dating of tuff samples, XRD analysis of tuff and mudstone samples, and vitrinite reflectance of coal samples in this sequence. The U–Pb ages of the Yokomichi Formation and the Kogawa Group are ∼86 Ma and 58–52 Ma, respectively. The U–Pb age of the kaolin‐dominated tuffaceous rock (“red rocks”) is 56.1 ± 0.2 Ma. The mean random vitrinite reflectance (VRr) ranges from 0.37% to 0.53% through the sequence. We propose the following sequence for the formation and filling of the basin. (1) The basin initially formed during the Coniacian–Santonian (Late Cretaceous) and was filled by fluvial–lacustrine sediment. (2) These sediments kept the shallow burial depths during a ∼28 Myr and made a hiatus (86–58 Ma). (3) The basin was reactivated and covered by tuffs during the Thanetian, and the tuffs were altered to kaolin clay during the Paleocene–Eocene Thermal Maximum. (4) The basin was filled rapidly by alluvial fan deposits and subsided &lt;2300 m (assuming a geothermal gradient of &gt;30 K/km). (5) The basin was uplifted and exhumed at a rate of &gt;50 m/Myr faster than the mean exhumation rate of the Kitakami Mountains since the Paleogene.