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Alkaline rocks are widely distributed in various geological environments and are important carriers for exploring the formation and compositional diversity of continental crust. Extensive studies have investigated the processes of mantle melting and crustal differentiation that produced such rocks. However, the potential interaction processes between mantle-derived magma and crust during their formation are poorly constrained. In this study, we focus on a Paleoproterozoic garnet-bearing syenite in the Xiong'er large igneous province (LIP) on the southern margin of the North China Craton through detailed whole-rock and mineral analyses. The high K2O (7.4–8.8 wt %) syenite emplaced at ~1772 Ma with ancient inherited zircon (1800–2800 Ma). The dominant mineral assemblage is composed of clinopyroxene, garnet, and K-feldspar with a small amount of titanite. Complex compositional oscillatory zoning of clinopyroxene and garnet indicates that magma mixing played a significant role in the formation of the syenite. We estimated the major elements composition for melts in equilibrium with clinopyroxene and calculated the clinopyroxene/melt partition coefficients by crystal lattice strain model, thus calculating the trace elements of the equilibrated melts. The equilibrium melts of high Mg# (>85) clinopyroxene have high CaO/Al2O3 (>0.6) and low Hf/Sm (<0.4), which suggests a role for carbonatitic metasomatism of the mantle. The variables La/Yb (24.4–56.1), Dy/Yb (0.8–5.9), and Yb (0.6–10.3 μg/g) indicate that the initial melts were formed by 1% to 2% partial melting of spinel-garnet phlogopite lherzolite. An REE-based model for melts in equilibrium with low Mg# (<85) clinopyroxene indicates that 10% to 30% felsic magma from ancient crust participated in hybridization. In addition to well-documented magma mixing, the oscillatory zoning of garnet is also related to competition with titanite. The initial alkaline magmas have a high water content (~4 wt %), which delays the crystallization of K-feldspar, leading to the enrichment of K2O, until the K-feldspar accumulates in the shallow crust to form the syenite. Magma mixing under an open system further leads to alkalinity enrichment. Magma source and crustal evolution jointly determine the potassium-rich characteristics of syenite. Multiple episodes of magma mixing and fractional crystallization occur in the crust (700–300 MPa), suggesting complex and vertically extensive magma chambers. This study represents the first identification of carbonatitic metasomatism as a mantle source in the Xiong'er LIP. Furthermore, it offers a new perspective on magma mixing between the mantle and crust in transcrustal magmatic systems, contributing to the formation of alkaline rocks. [ABSTRACT FROM AUTHOR]

Subduction erosion at convergent margins is a leading mechanism for the destruction (recycling and reworking) of continental crust. But because of the lack of direct evidence, it is not straightforward to identify erosive events and their intensities in fossil subduction zones. The Heilongjiang accretionary complex in northeastern China was formed during the early Mesozoic subduction of the Paleo-Pacific Ocean. We investigated amphibolites from this accretionary complex, whose protoliths (based on whole-rock trace elements and Sr-Nd-Hf isotopes) were mafic continental arc magmatic rocks (255-249 Ma; zircon core U-Pb ages) from the upper plate. Phase equilibria modeling constrained by mineral geochemistry indicates that the amphibolites and their wall rocks were first heated to low granulite facies (750-800 °C, ~7 kbar) at 251-244 Ma (zircon rim U-Pb ages) and then cooled to ~700 °C with increasing pressure (8-9 kbar) before 213-187 Ma (titanite and apatite U-Pb ages). To explain the occurrence of the lower arc crustal lithologies in the accretionary complex and their metamorphic history, we propose that the subducting plate strongly eroded the forearc crust, allowing the plate interface to advance landward and scrape the amphibolites and wall rocks formed under the old arc, which finally were exhumed along the subduction channel and became components of the complex. The case study exemplifies direct petrological evidence of strong subduction erosion occurring in an ancient orogen, thus implying that consumption of the entire forearc crust could occur within only ~50 m.y. [ABSTRACT FROM AUTHOR]

The four major mining areas in Panxi are the main production areas of strategic resources of iron and titanium in China. Both iron and titanium can be comprehensively utilized. In the ore concentration area, iron is mainly recovered from magnetite, and titanium is mainly recovered from ilmenite. The types of recovery from other minerals are rarely reported. Recently, it was found in the research of strong deformation ore in Panxi that the iron content in the ore is low, mainly occurs in chlorite group, and has no use value; Titanium can be effectively utilized, and its occurrence mechanism differs greatly from the four major ore concentration areas. In order to find out the occurrence state of titanium in the ore, various mineralogy research methods were used to conduct in-depth research on the ore. The research results show that the main carrier minerals of titanium in the ore are anatase and ilmenite, accounting for 51.39% and 21.54% of the total titanium respectively. The two minerals are closely associated or exist independently, and gangue minerals such as irregular interstitial carbonates are widely distributed between grains; The content of anatase and ilmenite with particle size above 0.074 mm is low, accounting for 35.64% and 43.92% respectively, and the degree of mineral liberation after fine grinding is low. In addition, due to heavy alteration of ore, a small amount of titanium is also distributed in minerals such as anatase chlorite group transition phase and sphene, which are poorly crystallized and cannot be effectively used. That is, the ore is a fine vanadium titanium magnetite ore that is difficult to be beneficiated and smelted and has complex titanium occurrence. Based on the embedding characteristics of the ore, a mixed titanium separation process flowsheet was developed, which involves the enrichment of titanium in the shaking table after raw ore rod grinding, and the pre-enrichment product roasting, grinding, acid washing, titanium flotation and acid leaching. A titanium concentrate with a TiO2 grade and recovery of over 50% was obtained. The research results provide new theoretical support for the development of subsequent titanium separation and smelting processes in this area, releasing stagnant titanium resources, and have important reference significance for the comprehensive utilization of similar types of ores. [ABSTRACT FROM AUTHOR]

Giant Nb deposits hosted by alkaline igneous rocks worldwide are characterized by hydrothermal and/or metamorphic modifications after magmatic crystallization. However, the impact of secondary processes on Nb mineralization in alkaline igneous rocks remains controversial. In this study, U–Pb ages, elemental, and Nd isotope compositions of titanite from a series of Nb-rich dyke swarms in the Ziyang region of South Qinling (China) have been investigated to unveil Nb remobilization and enrichment histories during magmatic and hydrothermal processes. Three types of titanite are documented: magmatic, deuteric, and hydrothermal. The magmatic titanite (Ttn I) grains are euhedral wedge-shaped, while the deuteric type (Ttn II) occurs as coronas on magmatic ilmenite. The hydrothermal titanite (Ttn III) occurs as either bead-like clusters within the cleavage planes of chloritized biotite or as anhedral grains (lesser than 200 μm in diameter) coexisting with hydrothermal actinolite, chlorite, fluorite, and/or REE-rich oxides. The magmatic titanite grains from the most primitive igneous rocks have U–Pb ages of 455 ± 25 Ma and are characterized by high levels of Nb2O5 (up to 1.4 wt%) and other high field strength elements (HFSE, up to 1.3 wt% ZrO2), rare earth elements (REE), and V, and high mean crystallization temperatures (880 ± 40 °C), suggesting that they nucleated and crystallized in a high-T and Nb-rich alkaline magma during the Early Paleozoic. The gradual decrease in V, Sr, and Ba in Ttn I from mafic to intermediate dykes exemplifies the role of fractionation on magmatic enrichment of Nb (mean of 170 ppm and 7300 ppm for Ttn I in mafic and intermediate dykes, respectively) and other incompatible elements (e.g., Ta, Zr, Hf, Sn, Y, and REE) in the residual melt. The deuteric and hydrothermal types of titanites in each lithology have lower concentrations of HFSE (e.g., Nb mean of 140 ppm and 860 ppm for Ttn II in mafic and intermediate dykes, respectively), Sn, LREE, and Y but higher Al, F, V, Sr, and HREE contents than their magmatic counterpart. The deuteric and hydrothermal types of titanite have U–Pb ages of 420 ± 25 Ma and 232 ± 49 Ma, respectively, supporting two distinct hydrothermal events at Ziyang. The magmatic and deuteric types of titanite have similar ranges of εNd(t) values (+ 1.4 to + 3.5 and + 2 to + 4.2, respectively), indicative of a common source for these two generations. The hydrothermal titanite also has comparable εNd(t) values (+ 0.8 to + 2.7) to the magmatic and deuteric types, indicating a minimal external contribution to Nd (and by analogy Nb as well) from the late hydrothermal fluids. The deuteric and late hydrothermal F-rich fluids in Ziyang dyke swarms both remobilized the dispersed Nb in magmatic ilmenite, amphibole, and biotite to form secondary titanite (Ttn II, III), which is beneficial to the metallurgical extraction of this critical metal. Therefore, both magmatic fractional crystallization and hydrothermal remobilization contributed to Nb mineralization. [ABSTRACT FROM AUTHOR]

The tremolite nephrite deposit in Dahua county, Hechi City, Guangxi province, China is a new genetic type of nephrite deposit. It is hosed by Mg-poor limestone (~1.30 wt.% MgO) and intruded by diabase (~45 wt.% SiO2). The Mg and Si contents of these rocks are lower than those of the tremolite (58.18 wt.% SiO2, 13.18 wt.% CaO, 24.16 wt.% MgO), indicating an obviously insufficient source for the metallogenic material that generated the deposit. In particular, some tremolite nephrite ore bodies have no clear contact metamorphism between the host and intrusive rocks, which have the characteristics of stratified mineralization (stratified tremolite nephrite). The origin and mineralization of stratified tremolite nephrite remain poorly constrained. To address this shortcoming, the mineralogy, geochemistry and Sr isotopic of host rock, altered marble, stratified tremolite nephrite and intrusive rock in the Dahua stratified tremolite nephrite deposit were studied. The results show: stratified tremolite nephrite mainly consists of aggregates of microcrystalline-cryptocrystalline tremolites with content exceeding 95%. The in situ rare earth elements (REEs) distribution pattern of hydrothermal calcite in the contact position between stratified tremolite nephrite and marble is similar to that of marine carbonate rock, showing obvious enrichment of HREE, which is different from calcite in limestone and marble. 87Sr/86Sr of stratified tremolite nephrite is relatively uniform, with an average value of 0.7070, within the range of Permian seawater. The mean value of Y/Ho in the hydrothermal calcite is 51.24, indicating that the marine fluid has not been impregnated by terrigenous materials. In summary, the hydrothermal fluid rich in Ca and Si is formed after marine carbonate rocks are altered by marine fluids. Hydrothermal fluids alter diabase rocks formed by altered minerals like titanite, chamosite, zoisite, etc. This process leads to the formation of metallogenic hydrothermal fluids abundant in Si, Ca, Fe and Mg. The metallogenic hydrothermal fluids migrate in faults and fractures of marble and crystallize to form tremolite nephrite under suitable ore-forming conditions. [ABSTRACT FROM AUTHOR]

An early Paleozoic eclogite belt extends discontinuously for ~500 km in the East Kunlun Orogen, northwestern China, which provides insight into the evolution of the Proto-Tethys Ocean. However, the nature and age of the eclogite protoliths and subsequent metamorphism are unclear. Here, we report mineral chemical, zircon, and titanite geochronological; whole-rock major and trace elemental; and Sr-Nd isotopic data for eclogites from the Xiarihamu area in the western East Kunlun Orogen. At a minimum, these eclogites underwent peak eclogite-facies metamorphism at 27-28 kbar and 630-650 °C, post-peak decompression, and retrograde amphibolite-facies overprinting. Geochemically, eclogites have characteristics typical of enriched mid-oceanic-ridge basalts and oceanic-island basalts. Inherited magmatic zircon cores yielded a protolith age of 828 Ma, and metamorphic zircons yielded peak and post-peak decompression ages of 443 Ma and 422 Ma, respectively. A titanite U-Pb age of 413 Ma constrains the timing of later amphibolite-facies overprinting. The protoliths of the Xiarihamu eclogites were the products of continental rift-related basaltic magmatism, which was generated during the initial breakup of Rodinia. The protoliths experienced eclogite-facies metamorphism in a continental subduction/collisional setting during the early Paleozoic. The formation of the Xiarihamu eclogites suggests that the Proto-Tethys Ocean had closed by 443 Ma. Given the spatio-temporal relationship between the Xiarihamu magmatic Cu-Ni sulfide deposit and the eclogites studied, the former may have formed in a post-collisional extensional setting. The eclogites and magmatic Cu-Ni sulfide deposit from the Xiarihamu area jointly reveal the evolution of the East Kunlun Orogen from Neoproterozoic supercontinent breakup to early Paleozoic tectonic transitions from collisional convergence to post-collisional extension. [ABSTRACT FROM AUTHOR]

Although carbonatite-alkaline complexes are the primary source of the world's niobium (Nb) supply, the mineralization style is largely variable in these complexes and the processes behind their formation are still poorly understood. Exemplifying with our new observations on the ~430 Ma Miaoya and Shaxiongdong carbonatite-syenite complexes in the southern Qinling orogenic belt, central China, show that disseminated Nb mineralization in these two deposits is pervasive throughout the entire complexes in both syenite and carbonatite. Both magmatic and hydrothermal processes have contributed to Nb mineralization in both deposits, despite differences in the mineralization style. The Nb-bearing minerals in the mineralized Miaoya syenites include magmatic U-poor pyrochlore, rutile, and ilmenite with minor amounts of columbite, and hydrothermal columbite and rutile, whereas those in the mineralized carbonatites are mainly magmatic U-poor pyrochlore, uranpyrochlore, U-rich betafite, and rutile with minor amounts of columbite, and hydrothermal columbite and rutile. On the other hand, the Nb-bearing minerals in the mineralized Shaxiongdong syenites include magmatic U-poor pyrochlore, titanite, rutile, and ilmenite, and hydrothermal fersmite, rutile, and ilmenite, whereas those in the mineralized carbonatites are mainly magmatic U-poor pyrochlore without any hydrothermal Nb-bearing minerals. Field observations, whole-rock chemical and Sr-Nd isotopic compositions strongly constrained that assimilation of U-rich rocks (e.g., the hosting Yaolinghe and Meiziya Groups) and magma differentiation are responsible for diverse magmatic Nb mineralization in the two deposits. On the other hand, the diverse assemblages of hydrothermal Nb minerals in Miaoya and Shaxiongdong are mainly controlled by variations in the nature of the fluids, which is constrained to be genetically related to ~220 and ~420 Ma hydrothermal events, respectively. In summary, both magma evolution (e.g., differentiation, assimilation) and late hydrothermal overprinting are responsible for the diverse Nb mineralogy in carbonatite-alkaline complexes, a situation that is commonly observed worldwide. [ABSTRACT FROM AUTHOR]

In order to decipher element mobility in UHP meta-sedimentary rocks in the continental subduction zone, major and trace element compositions are investigated for a continuous profile from a representative UHP region in the Dabie Mountains. Among the lithologic contact zone, contents of K, Ca, LREE, and LILE exhibit varying degrees of downward trends in both marble and eclogite toward the contact zone, indicating that marble and their associated eclogite can release a large amount of K, Ca, and a small number of LILEs and LREEs. Titanite is the main Ti phase in both marble and eclogite. Titanite rims around rutile can occasionally be seen in eclogite. Contents of Ti and HFSE exhibit a well-coupled relation among marble and eclogite, indicating that substantial Ti and HFSEs were migrated from eclogite to marble, in accord with the capacity of a melt medium. Rutiles and titanites in marble exhibit a relatively limited variation in Nb/Ta ratios (12.9–16.2), similar to those of titanites in eclogite (14.2–16.7), which demonstrates that rutiles and titanites in marble were sourced from eclogite because of short-distance migrations of Ti and HFSEs. According to the P-T path and the temperature and pressure conditions of the peak metamorphism reported by previous studies, the eclogite associated with marble may not form supercritical fluids in the subduction zone because of the addition of carbonate minerals. [ABSTRACT FROM AUTHOR]

Volcaniclastic rocks are important unconventional oil and gas reservoirs from which it is difficult to determine the protolith due to strong metasomatic alteration. Intensive alteration has occurred in much of western China, but few robustly documented examples are known from which to assess the alteration processes. Further recognition from the petrological and mineralogical record is essential to quantify the diagenetic environment, the degree of alteration, and its impacts. Permian volcanic rocks are widely developed in the western Sichuan Basin (southwestern China), with a thickness of more than 200 m. The thickness of volcaniclastic rocks in the Permian Emeishan Basalt Formation is up to 140 m, with a 5600~6000 m burial depth. In this study, we demonstrate an approach to recognizing hydrothermal alteration by the occurrence of scapolite megacryst mineral pseudomorphs (SMMPs) in Permian volcaniclastic rocks in the Sichuan Basin (southwestern China). The results show that SMMPs in the Permian volcaniclastic rocks in the western Sichuan Basin mainly occur in the lower part of the Permian basalts as intragranular minerals and rock inclusions. Scapolite is transformed into quartz and albite, and only the pseudomorph is preserved, indicating secondary hydrothermal fluid metasomatic alteration. Scapolite is formed after microcrystalline titanite and is the product of the high-temperature pneumatolytic metasomatism of plagioclase from the mafic protolith during the post-magmatic stage. The mixing of meteoric water and barium-rich hydrothermal fluid leads to the precipitation of barite; additionally, the pores are filled with barite and halite after the alteration of scapolite. The silicification and hydrothermal dissolution of scapolite and the albitization of sodium-rich matrix minerals increase the pore volume, which is conducive to the later recharge by hydrothermal fluids. The discovery of SMMPs can serve as an indicator of the high-temperature pneumatolytic metasomatism and mixing of meteoric water and deep hydrothermal fluid. [ABSTRACT FROM AUTHOR]

Black shale-hosted vanadium (V) deposits account for about 80% vanadium resources in the world, but only <2% vanadium in the black shale can be extracted mainly due to insufficient recognition on the occurrence mode of vanadium. It is commonly agreed that most vanadium in the black shale is hosted in clay minerals and organic matters, but it is not clear how the other parts of vanadium exist and whether there exists a vanadium mineral, which has limited our understanding of metallogenic mechanism of black shale-hosted vanadium deposits. The Jiujiang Basin at the Lower Yangtze Block is a significant black shale-hosted vanadium metallogenic district. In this work, we conducted systematic studies of mineralogy, lithology and geochemistry on the occurrence of vanadium hosted in the black shales. Electron probe microanalysis (EPMA), Raman spectroscopy, and X-ray diffraction (XRD) show that the main vanadium-hosting mineral in the black shale is mannardite, with a structural formula of B a 0.96 ⋅ H 2 O T i 5.87 V 1.87 3 + V 0.11 4 + S i 0.07 C r 0.07 F e 0.02 3 + O 16.00 , space group I41/a, unit-cell parameters a = b = 14.346(7) Å, c = 5.899(1) Å, α = β = γ = 90°, Z = 4. Data from EPMA, TESCAN integrated mineral analyzer (TIMA), and whole-rock geochemistry indicate that 12.32–44.06% (average 24.95%) vanadium exists in mannardite. Most vanadium atoms in mannardite occupy its structural sites as trivalent vanadium (V3+), forming chemical bonds with O atoms as V O 2 − , whereas a minor amount of vanadium atoms replace titanite atoms (Ti4+) as quadrivalent vanadium (V4+) by isomorphism. Mannardite precipitates under a strong reductive condition with sufficient trivalent vanadium species, titanium and biogenic barium (bio-barite). Our first identification of mannardite in black shale-hosted vanadium deposits thus sheds light on the occurrence mode of vanadium and the metallogenic mechanism of black shale-hosted vanadium deposits. [ABSTRACT FROM AUTHOR]

Gold deposits in Precambrian cratons were mostly generated during the formation and stabilization of the cratons, but the North China craton is unusual in that its gold deposits were mainly formed ~1.7 b.y. after its stabilization. A magmatic-hydrothermal origin or mantle-derived fluid source has been proposed for the giant gold deposits of the Jiaodong District in the eastern North China craton, but direct evidence is sparse, and the mineralization processes remain controversial. Here, we present the results of a comprehensive geological, geochronological, and geochemical study of the gold mineralized Xiejia diorite beneath the Linglong ore field at Jiaodong to link the gold mineralization to underlying magmatism. Magmatic zircon and titanite grains from the Xiejia diorite have laser ablation--inductively coupled plasma--mass spectrometry (LA-ICP-MS) U-Pb ages of 121.3 ± 0.9 Ma to 120.8 ± 1.1 Ma and 121.7 ± 3.9 Ma, respectively, which are indistinguishable from the time of gold deposition throughout the Jiaodong District as constrained by previous studies. The diorite has a shoshonitic composition and is characterized by strong enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) along with significant depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs). Samples of the diorite have high initial 87Sr/86Sr ratios, but low εNd(t) and εHf(t) values and low Pb isotope ratios. These geochemical characteristics are akin to those of contemporaneous mafic dikes in most gold mines at Jiaodong, indicating that the Xiejia diorite was most likely derived from an enriched lithospheric mantle source. The upper part of the diorite intrusion is pervasively altered and mineralized, containing an average of 0.32 g/t Au, but locally up to 7.59 g/t. Hydrothermal titanite from the mineralized diorite has a LA-ICPMS U-Pb age of 122.3 ± 4.3 Ma, which is consistent with the gold-bearing pyrite Re- Os isochron age of 122.5 ± 6.7 Ma. Ore-related sericite aggregates from the Dongfeng gold deposit above the Xiejia diorite have a 40Ar/39Ar plateau age of 122.6 ± 1.3 Ma. Pyrite from the mineralized diorite yielded δ34SCDT values of 2.1‰-9.7‰, which are comparable with those of pyrite (δ34SCDT = 5.8‰-8.1‰, where CDT indicates the Canyon Diablo troilite standard) from gold ores of Dongfeng. Pyrite grains from both groups also have similar Pb isotope compositions. The S and Pb isotope data are consistent with values of mafic dikes that are spatially and temporally associated with gold veins in the Linglong ore field. The results presented here thus indicate a possible genetic link between gold mineralization in the Xiejia diorite and underlying magma presumably represented by the Xiejia diorite. The auriferous fluids exsolved from that magma and migrated upward along the Potouqing fault to form the Dongfeng gold deposit above the Xiejia diorite. The mineralized diorite thus links shallow gold mineralization to deep-seated mantle-derived magmatism generated during the extensive destruction of the North China craton induced by the rollback of the subducted paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

The Mangling intrusive complex has different dioritic to granitic phases and is spatially and temporally related to molybdenum deposits in the Qinling Orogen. Zircon U-Pb dating of the Mangling intrusive complex indicates that dioritic rocks (biotite diorite and biotite diorite enclave; ca. 150-147 Ma) formed earlier than granitic rocks (medium- to fine-grained and fine-grained monzogranite and K-feldspar granite; ca. 145-141 Ma). The Mangling dioritic rocks exhibit large ion lithosphere element (e.g., Rb) and light rare earth element enrichment and high field strength element (e.g., Nb, Ta, and Ti) depletion. They have low to moderate SiO2 (51.33-58.16 wt%), high MgO (3.10-4.75 wt%) and Mg# (48-60), and negative zircon εHf(t) values (-11.6 to -6.8), suggesting origination from the continental lithospheric mantle that may have been metasomatized by previous sedimentderived melts and slab-derived fluids constrained by high Nb/Y, Th/Yb, and Rb/Y ratios. The Mangling granitic rocks are I-type granites and have high SiO2 (67.90-81.88 wt%) and low MgO (0.16-0.74 wt%). They have low and negative zircon εHf(t) values (-18.7 to -1.9) and old zircon Hf twostage model ages (2334-1287 Ma), as well as similar mineral fractionation (e.g., hornblende, biotite, sphene, and apatite) with the Mangling dioritic rocks, indicating that they were derived from the remelting of old crustal rocks (e.g., Xiong'er and Kuanping groups) by the evolved underplated mafic magma. Compared with the Taoguanping mineralized monzogranite in the Northern Qinling Belt, zircon geochemistry (e.g., Ce4+/Ce3+, Eu/Eu*, and ΔFMQ [relative fayalite-magnetite-quartz buffer]) indicates that magma of the Mangling intrusive complex (except the biotite diorite) has high oxygen fugacity and small fractionated granitic intrusions, which are coeval with the biotite diorite enclave or younger than the Mangling granitic rocks, may have potential for generating porphyry molybdenum mineralization. The combination of this study and previous studies corroborates that the Qinling Orogen underwent an intracontinental orogenic evolution in a post-collisional compression to extension transitional setting during the Late Jurassic to Early Cretaceous, affected by far-field Paleo-Pacific slab subduction. [ABSTRACT FROM AUTHOR]

Ion-adsorption rare earth element (REE) deposits in South China are currently the main source of heavy rare earth elements (HREE). The Gucheng deposit in western Guangdong Province is one example of HREE mineralization hosted in weathered coarse-grained biotite granites (CGBG). Titanite is a common accessory mineral in the CGBG and contains significant amounts of total REE (31 621 to 38 431 ppm), especially HREE (18 906 to 22 249 ppm). Titanite with a U-Pb age of 102.6 ± 1.9 Ma in the CGBG crystallized under relatively high temperatures (722–798 °C), high f H 2 O , and high f O 2 conditions in the late magmatic stage, and has similar Nd isotopic compositions similar to the host CGBG: 143Nd/144Nd = 0.512062 to 0.512125 and εNd(t) = –7.4 to –8.6. Backscattered electron (BSE) imaging and TESCAN integrated mineral analyzer (TIMA) measurements show that titanite in the CGBG has been altered partly to fergusonite-(Y), rutile, calcite, quartz, and fluorite. The hydrothermal fluid responsible for titanite alteration was enriched in C O 3 2 − and F, and was probably exsolved from the granitic magma. HREE released from the alteration of titanite were mostly scavenged by fergusonite-(Y) and rutile, which have been further replaced by gadolinite-(Y) and synchysite-(Ce). In addition, gadolinite-(Y) in the alteration assemblages exhibits further alteration and is characterized by elevated P O 4 3 − a n d S O 4 2 − contents in the altered parts. These results demonstrate that magmatic titanite in the CGBG underwent complex hydrothermal alteration, with a preferential accumulation of HREE in fergosnite-(Y) and gadolinite-(Y) in the alteration assemblages. Preferential HREE enrichments in magmatic titanite, and its alteration assemblages, are shown to play significant roles in the formation of the Gucheng HREE deposit. [ABSTRACT FROM AUTHOR]

The regolith-hosted rare earth element (REE) deposits in the Nanling Mountain Range, South China, are the most important source of heavy REE (HREE) in the world. A perplexing thing is that only a few of these deposits are relatively enriched in HREE and most of them are actually light REE (LREE)-enriched, although they are all originated from the granitic bedrocks with similar HREE concentrations. This is supposed to be related to the redistribution of REE in the weathered bedrocks due to groundwater-rock interaction, however, it remains enigmatic how REEs are mobilized and fractionated in the interaction. Titanite is an important REE contributor to the regolith-hosted REE deposit. Here, we investigate textural and compositional variations of the titanite from the granitic bedrocks to weathered profiles in the Zuokeng regolith-hosted REE deposit, the largest one that is newly discovered in this region. Together with thermodynamic modelling, we deduce the nature of the fluids, temperature range for titanite alteration, and the mechanism of REE fractionation. Primary titanite is of magmatic in origin and shows relatively high REE contents and negative Eu anomaly on the chondrite-normalized REE pattern. Secondary titanite is commonly associated with chloritized biotite and is characterized by extremely low REE, high Al2O3, F and significant positive Eu anomaly, typical of authigenic origin due to chloritization of biotite under oxidized conditions in supergene environment. From the bedrocks upward to the surface, primary titanite is gradually replaced by calcite, synchysite-(Ce) and TiO2 in the weathered bedrocks. This is interpreted as the result of infiltration of the F, carbonate-rich, alkaline fluids derived from local groundwater through the bedrocks. The irregular dark patches in primary titanite display typical alteration texture and may have formed through fluid leaching of primary titanite. The patches in primary titanite have lower REE concentrations and higher LREE/HREE ratios than magmatic domains, indicating that the groundwater preferentially scavenges HREE from primary titanite, leaving behind LREE in weatherable secondary minerals, such as synchysite-(Ce) and allanite. Mass balance calculation results also confirm that more HREE are lost from weathered bedrocks than LREE. Therefore, the interaction of groundwater and granitic bedrocks may be favorable to enrich LREE rather than HREE in the regolith. This may explain why most regolith-hosted REE deposits like Zuokeng in South China are of predominant in LREE. This study highlights the role of groundwater in mobilizing, fractionating and enriching REE from the granitic bedrocks to resultant regolith-hosted REE deposits. [ABSTRACT FROM AUTHOR]

The Baishuizhai, Shituling and Zhushanxia deposits from the Xiazhuang district represent to date the only known occurrences of early Yanshanian (Middle to Upper Jurassic) granite-related high-temperature hydrothermal uranium deposits (175–145 Ma) in the Nanling Metallogenic Belt, South China. Whole-rock geochemistry of ore samples combined with chemical and mineralogical signatures of the hydrothermal phases associated with the U mineralisation characterised a coeval potassic and propylitic alteration fingerprint: (i) the potassic alteration is defined by Na and Ca depletion of the granitic host rock and precipitation of adularia, dioctahedral Fe-muscovite, biotite and secondary quartz; and (ii) the propylitic alteration is marked by whole-rock enrichment in Ca, Fe, Mg, Mn and Ti mainly associated with the precipitation of (Mn)-epidote, Fe-chlorite, fluorapatite, titanite, calcite, APS and Fe-Cu-Pb-Cd-Bi-Mo-sulfide minerals. The high-temperature conditions of the hydrothermal system was demonstrated by the typologies of alteration such as greisen, chlorite geothermometry giving temperature estimates of the ore fluid ranging from 316 to 455°C, minor W mineralisation and the high Zr contents in titanite. Besides, high Rb, Ba, Be, Y, Nb, W, Ta and Mo contents in ore samples, mineral assemblages and chemical signatures of the hydrothermal phases showed evidence for the alteration of fractionated felsic granitic host rocks and the contribution of enriched magmatic-derived fluids. Therefore, these characteristics define a magmatic-hydrothermal genetic model directly related to the intrusion of early Yanshanian granites in the Nanling belt. In this new metallogenic model, highly fractionated high-K calc-alkaline A2-type granitic plutons have provided magmatic fluids, heat and metal sources to the early Yanshanian high-temperature hydrothermal U system. Uranium (±W-Sn-Nb-Ta-Li)-rich fluids were derived from fractionated peraluminous residual silicate melts. Uranium was enriched in a high-temperature, highly saline, F-rich, acid and reducing fluid, and dominantly carried as fluoride complexes. This mineralising fluid percolated in the Indosinian U-rich host granites within the cupolas of early Yanshanian granites and produced characteristic propylitic and potassic (including greisen) hydrothermal alteration. During the hydrothermal alteration, the pH and T variations of the mineralising fluid and the subsequent precipitation of F- and P-bearing hydrothermal phases induced the destabilisation of U complexes, winch eventually triggered the deposition of the U mineralisation. [ABSTRACT FROM AUTHOR]

The rates and mechanisms by which deeply subducted continental crust was exhumed back to the surface are not well understood, but can be better characterized using multimineral petrochronology. Here, we combine zircon, titanite, and apatite U-Pb ages from leucogranite and phengite gneiss with a pressure-temperature (P-T) path from eclogite to provide robust quantitative constraints on cooling and exhumation of the Sulu belt, a large ultrahigh-pressure metamorphic terrane in eastern China. The leucogranite, which formed during exhumation, is enriched in light rare earth elements (REE) relative to heavy REE and in large ion lithophile elements relative to high field strength elements, similar to hydrous crustal melts. Whole-rock Sr-Nd isotope compositions indicate that the leucogranite was not directly derived from the host phengite gneiss, but was more likely sourced from deeper in the exhuming crust. For the gneiss, mantles on inherited zircon yield an age of 230 ± 2 Ma and a temperature of 802 ± 36 °C based on a minimum pressure of 2.9 GPa, which records the minimum timing and P-T of initial decompression. Overgrowths on inherited zircon from the leucogranite constrain crystallization to 224 ± 1 Ma, coeval with the growth of zircon rims in the gneiss, at a temperature of 764 ± 42 °C and a pressure within the quartzeclogite facies. Titanite and apatite define single populations with lower concordia intercept ages of 222 ± 3 Ma and 198 ± 7 Ma, at temperatures of 720 ± 30 °C and ~450 ± 100 °C, respectively, recording the timing of passage through the quartz-eclogite to the amphibolite facies and then the transition to the upper greenschist facies. Although the data yield a nearly constant cooling rate of 10.9-3.6+4.5 °C/m.y., exhumation was completed in two stages. The first stage from coesiteeclogite facies to ~1.2 GPa, corresponding to the depth of the Moho, occurred at a rate of 7.5-2.6+5.8 km/m.y. Thereafter, exhumation into the mid-crust occurred at a much slower rate of 0.87-0.71+0.86 km/m.y. The first stage of faster exhumation was accompanied by migration of leucogranite melt along foliation in the gneiss, which would have decreased the average density and weakened the crust, enhancing the rate of return flow. [ABSTRACT FROM AUTHOR]

A second occurrence of bobtraillite is described from the Gejiu nepheline syenite, southwestern China. The extremely rare and complex boron-bearing zirconium silicate is associated with albite, orthoclase, jadeite, fluorite, andradite, titanite, as well as other REE and zirconium-bearing minerals, catapleiite, moxuanxueite, låvenite, eudialyte, britholite-(Ce), and calcioancylite-(La). The EMP and LA-ICP-MS analyses of the studied material give an empirical formula: (Na 9.70 Li 0.42 K 0.08□1.80) Σ12.00 (Sr 10.61 Ca 1.14 Fe 0.07□0.18) Σ12.00 (Zr 12.87 Ti 0.53 Nb 0.31 REE 0.08 Y 0.06 U 0.02 Th 0.01□0.12) Σ14.00 (Si 42.41 B 5.59 Al 0.02) Σ48.02 O 132 (OH) 12 ⚫ 12H 2 O. Bobtraillite is trigonal, with space group P3¯c 1, a=19.6977(6) , c=9.9770(3) Å, V=3352.4(2) Å 3 , Z=1. Single-crystal structure refinement revealed that all sodium occupies the Na(1) and Na(2) sites; the site occupancy of these two positions is 0.835(18) and 0.15(2), respectively, suggesting that Na(1) site is Na dominant, while Na(2) is a vacancy-dominant site. The [8]-coordinated site has been assigned to Sr and Ca, with free occupancy factors, 0.874(10) and 0.126(10), respectively. These new data indicate that the ideal formula of bobtraillite could be written as (Na, □) 12 (□ ,Na) 12 Sr 12 Zr 14 (Si 3 O 9) 10 [Si 2 BO 7 (OH) 2 ] 6 ⚫ 12H 2 O. [ABSTRACT FROM AUTHOR]

Accurately defining the peak ages and timescales of high‐temperature metamorphism is fundamental to unravelling tectonic dynamics. However, metamorphic constraints are frequently hampered by a large spread of zircon U–Pb ages without explicit textural relationships. Integrated garnet and zircon petrochronology may clarify ambiguous ages retrieved from ancient high‐temperature metamorphic rocks. There is a long‐standing debate on the interpretation of the spread of zircon ages from c. 2.5–1.8 Ga for the granulites of the North China Craton. In order to clarify the timing and duration of (ultra)high‐temperature metamorphism in the North China Craton, we investigated a mafic granulite and the adjoining gneiss from the Yinshan Block of the North China Craton using zircon and titanite U–Pb geochronology combined with garnet Lu–Hf and Sm–Nd geochronology. Pseudosection modelling and conventional thermobarometric calculations constrain the peak metamorphic conditions to be ~1.0 GPa and ~850°C. The near‐complete lack of major‐element zoning in garnet, aside from ~2 μm diffusion profiles at crystal rims, suggests complete re‐equilibration at peak temperatures followed by fast cooling from high temperatures. The Lu–Hf garnet age of 1870 ± 4 Ma and Sm–Nd age of 1870 ± 7 Ma, determined on the same garnet fractions, are indistinguishable from the zircon U–Pb age of 1866 ± 11 Ma obtained from zircon that grew contemporaneously with garnet, evidenced by the chemical equilibrium of coexisting garnet and zircon, and are additionally consistent with a titanite U–Pb age of 1876 ± 7 Ma. We interpret this close agreement of ages, within uncertainty, coupled to the existence of flat Sm–Nd–Hf profiles in garnet that also has well‐preserved Lu zoning, to reflect a short‐lived high‐temperature metamorphic event that was terminated by rapid exhumation and cooling. The short‐lived (<4 Myr) high‐temperature metamorphism may be generated in the lowermost parts of the crust through magmatic underplating/intraplating during extension that follows collision of the Ordos and the Yinshan Blocks. [ABSTRACT FROM AUTHOR]

The alkaline complex in the southwest region of Luxi Terrane of the North China Craton is spatially correlated with the newly discovered Longbaoshan REE deposit. Its petrogenesis, however, remains ambiguous. In this study, we present an integrated petrology, whole-rock geochemistry, sphene U-Pb and rare earth element data from the Longbaoshan alkaline complex to investigate the petrogenesis, magma source and tectonic evolution. The Longbaoshan alkaline complex consists of mafic to intermediate rocks of hornblende diorite and alkaline hornblende syenite porphyry, biotite monzonite porphyry and aegirine diorite porphyrite. The hornblende diorites show a composition of low SiO2, high MgO, Fe2O3 and moderate Na2O, CaO and are metaluminous and medium-to-high-K calc-alkaline. The hornblende syenite porphyries, biotite monzonites and argirine diorite porphyrites display a relatively higher content of SiO2, Na2O, K2O and Al2O3 and lower contents of MgO, Fe2O3 and CaO and are metaluminous, peralkaline, high-K calcic-alkaline and shoshonite. The sphene U-Pb data shows that the parent magma of the hornblende diorite was emplaced at ca. 120 Ma. All these samples show a common depletion in Th, Nb-Ta and Zr-Hf and enrichment in large ion lithophile elements (e.g., Pb, Ba, Sr) and Light Rare Earth Elements. The magma may have experienced fractionation of pyroxene, amphibole, sphene, apatite and zircon during its evolution. The variable La content, La/Sm, Rb/Sr and (Ta/Th) N ratios indicate that the parent magma may produce by partial melting of a mantle source that was interacted with sediment-derived melts in a subduction setting. Therefore, we propose that the parent magma of the Longbaoshan alkaline complex was derived from a lithospheric mantle which was metasomatized by sediment-derived melt in a prior subduction process. The enriched magma was emplaced through an extension process and experienced subsequent fractionation and assimilation with the continental crust during the rollback of the Paleo Pacific Ocean plate. [ABSTRACT FROM AUTHOR]

Magmatic zircon tends to present characteristic trends in trace element compositions in response to magma petrogenesis and metallogenesis, such that zircon may provide a window into melt evolution not accessible by whole rock chemistry. The Yangla large Cu deposit is located in the central part of the Jinshajiang Suture Zone, southwest China, constrained between the Jinshajiang and Yangla Faults. In this study, the trace elements and hafnium isotopic compositions of zircons from quartz diorite were studied. Previous published relevant data of Yangla granitoid plutons (i.e., dioritic enclave, granodiorite, and quartz monzonite porphyry) also have been systematically cited and discussed. The result shows that the crystallization temperature and two-stage Hf mode ages (tCDM; the age of the source rocks for the magmas) gradually increased while the oxygen fugacity (fO2) and εHf(t) values gradually decreased, corresponding to the diorite enclave (~232 Ma), through granodiorite (~208 Ma) and quartz monzonite porphyry (~202 Ma), and to quartz diorite (~195 Ma). It is suggested that four plutons were from the same three-component mixing of upper crust + lower crust + mantle magmas, while the upper crustal metasediments ratios were gradually increased from the early to late stage. The increasing upper crust inputs resulted in higher melting temperatures and compositions of the initial magma. All melts experienced distinct fractional crystallization of apatite, titanite, and amphibole, and the later granite melts experienced higher assimilation and fractional crystallization degrees than the early ones in the evolution processes four stages of intrusive rocks. These Yangla granitoids are the products of large-scale acid magmatic emplacement activities in the Triassic-early Jurassic and have a good metallogenic potential of the Cu-W polymetallic deposit. [ABSTRACT FROM AUTHOR]

Research on the mineralogical and geochemical characteristics of altered end-Guadalupian basaltic volcanoclastic rocks can increase the understanding of the alteration history of the overlying stratabound Nb(Ta)-Zr(Hf)-REY-Ga mineralization in the Late Permian coal-bearing sequences. In this paper, based on petrographic observations in addition to XRD, XRF, and ICP-MS analyses, we present and discuss in detail the relationships between primary and secondary minerals and outline the distribution of major and trace element chemistry in the middle/Late Permian basaltic volcaniclastics from the ELIP's zone, western Guizhou, southwest China. The primary clastic suite consists of plagioclase-group minerals, clinopyroxenes, feldspathoids, spinels, and basaltic glasses. Fragments of mafic and, less commonly, felsic and alkaline volcanic rocks are minor components of the studied samples. The alteration products are represented by various chlorite-group minerals (including abundant chamosite), quartz, calcite, albite, analcime, barite, and pyrite, along with relatively minor amounts of titanite, sanidine, magnetite, rutile, and copiapite. The mineralogical and geochemical characteristics of the studied volcaniclastics provide strong evidence correlating them with the high-Ti basalt group, widely distributed within the inner Emeishan large igneous province (ELIP) and coeval rift zone of the middle and outer ELIP. After deposition, the volcaniclastics reacted with complex solutions including heated meteoric waters and were periodically infiltrated by seawater and ascending hydrothermal fluids. As a result, the primary volcanic rocks partly lost alkalis, titanium, silica, and most of the trace elements. These elements, especially the incompatible elements, were probably enriched in the overlying tuffaceous and coal-bearing sequences in the middle and outer ELIP. • Primary and secondary minerals of Emeishan basaltic volcaniclastics were presented. • The volcaniclastics reacted with complex solutions from various sources. • The primary volcanic partly lost alkalis, Ti, Si, and most of the trace elements. • The lost elements were probably enriched in the overlying sediments. [ABSTRACT FROM AUTHOR]

The occurrence of the polymetallic Nb layer in the upper Permian Xuanwei Formation in southwest China has been documented extensively. The origin of Nb, as well as other metals like Zr and rare earth elements (REEs), has received much research attention; however, the source of these elements remains enigmatic. In recent studies, an uncommon Nb-rich titanite (CaTiSiO 5) has been discovered in the Emeishan basalts beneath the Xuanwei Formation in the eastern Yunnan–western Guizhou region. However, its origins and genetic relationship to the polymetallic Nb layer remain unclear. In this study, we used in situ microanalytical and U Pb dating techniques to investigate the titanite in these Emeishan basalts. Our objectives were to determine the origins of the titanite and its relationship to the polymetallic Nb layer in the lowermost Xuanwei Formation. The basalts consist of approximately 70%–90% phenocrysts and 10%–30% matrix. The phenocrysts are mainly coarse-grained (>30 μm) plagioclase, clinopyroxene, and Fe-Ti oxides (ilmenite and magnetite), whereas the matrix comprises mainly fine-grained (<30 μm) titanite and glass. The titanite is hypautomorphic or xenomorphic and occurs as small, disseminated grains within the matrix. The titanite U-Pb dating of basalt sample reveals a Tera–Wasserburg lower intercept age of ca. 259.6 ± 4.3 Ma, which corresponds to the age of the eruption timing of Emeishan large igneous province (ELIP; 260.9–257.4 Ma). This implies that the formation of titanite within the matrix can be attributed to rapid cooling of residual melt subsequent to fractional crystallization of a substantial quantity of phenocrysts. The LA-ICP-MS analysis reveals that the trace element composition of titanites in the Emeishan basalts exhibits similarities to weathering-type titanite, as evidenced by elevated La N /Yb N ratios and low concentrations of Y, ΣREE, Th, and U, as well as reduced Lu/Hf and Th/U ratios. Thus we propose that these titanites crystallised during the late-stage magmatic evolution, resulting from magmatic fractional crystallization and subsequent weathering alteration. The materials required for titanite crystallization in the basalt matrix primarily sourced from the residual melt, while weathering dissolution of plagioclase and clinopyroxene in the phenocrysts may have provided additional Ca and Eu for titanite formation. As weathering progressed, the Nb-rich titanite underwent a transformation into Nb-rich anatase and gradually became enriched in the regolith. This material was subsequently transported to nearby basins and deposited in terrestrial environments, resulting in formation of the polymetallic Nb layer in the lowermost Xuanwei Formation. Our findings provide insights into the origins and evolution of titanite in the Emeishan basalts, as well as formation of the polymetallic Nb layer in the lowermost Xuanwei Formation in the eastern Yunnan–western Guizhou region, southwest China. [Display omitted] • Nb-rich titanite is widely present in the Emeishan basalts in the southwest China. • The titanite originated from fractional crystallization and weathering alteration. • The Nb-rich anatase in the Xuanwei Formation was derived from ELIP basalts. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) mobilize, fractionate, and are re-distributed during supergene processes, and thus provide a powerful tool with which to quantitatively reconstruct the effects of chemical weathering. Moreover, under certain conditions, the REEs can concentrate to levels in the regolith sufficient to form giant regolith-hosted REE deposits, that are now responsible for much of the World's production of heavy REEs (HREEs). Understanding the supergene behavior of the REEs is an important first step towards applying the REEs as a geochemical tool and meeting the growing global demand of the REEs. Thermodynamic calculations predict that dissolution of the main REE minerals in REE-rich protoliths, namely synchysite-(Y), gadolinite-(Y), hingganite-(Y), yttrialite-(Y), allanite-(Ce), eudialyte, chevkinite-(Ce), britholite, euxenite and loparite-(Ce), should occur spontaneously during weathering. It therefore follows that a high abundance of these minerals in the protolith implies high mobility of the REEs during weathering and consequently a high potential for the discovery of economic REE resources. Dissolution of apatite is promoted by metamictization or structural distortion and could be also important at low pH. In contrast, some LREE-fluorocarbonate minerals, notably bastnäsite-(Ce) and parisite-(Ce), and monazite-(Ce) are likely thermodynamically stable in acidic environments. Thus, they would be preserved in the regolith. Zircon, titanite, aeschynite, fergusonite, and xenotime-(Y) are resistant to acidic dissolution, consistent with their common occurrence as residual minerals. In the cases of the world-class regolith-hosted REE deposits in South China, the groundwater is mildly acidic to circumneutral and carbonate-rich. The REEs are consequently transported dominantly as hydrated cations and carbonate complexes, depending on the pH. The general inheritance of the REE pattern of the regolith groundwater in the clay-sorbed fraction in the regolith indicates that the REEs in regolith are scavenged from the regolith groundwater. Elemental anomalies of specific REEs in the clay-sorbed fraction are very likely caused by an anomalously high REECO 3 + fraction in the corresponding regolith groundwater, suggesting a preferential uptake of the REECO 3 + complexes by the clay minerals, feasibly by halloysite through intercalation as interlayer complexes. This reaction is expected to be particularly important for the sorption and enrichment of the HREEs in the regolith. Depending on the pH and carbonate concentration of the water, surface complexation on clay minerals or interlayer intercalation particularly in halloysite control the pattern of REE enrichment. Mixing of the regolith groundwater with the alkaline and carbonate-rich aquifer groundwater increases the pH and carbonate concentration and, in turn, affects the ability of the mixed water to transport the HREEs. Interplay of aqueous complexation with the regolith mineralogy significantly affects the REE fractionation and re-distribution during groundwater-regolith interaction. [ABSTRACT FROM AUTHOR]

As a common Ca‐ and Ti‐ bearing silicate mineral in many types of hydrothermal deposits, titanite usually contains high concentrations of trace elements. Its mineral chemistry and U–Pb isotope can reveal the physicochemical conditions and geochronology of the ore‐forming systems. In this contribution, we present a detailed study on titanite which precipitated during the Fe mineralization in the Duotoushan deposit. Due to coexistence with hydrothermal minerals, low Th/U ratios (0.02–0.3), and depletion in rare earth elements (REE), all the studied titanites are classified into a hydrothermal group. The negative correlation between [REE3+ + (Al, Fe)3+] and [Ca2+ + Ti4+] indicates that REE mainly entered the lattice of titanite via the mechanism of substitution. In addition, titanite grains are characterized by HREE, Zr, and Nb enrichments with LREE depletion, suggesting that the complexation of F− at neutral to alkaline pH conditions may have caused the fractionation of REE. At Duotoushan, the titanite grains coexist with quartz, epidote, amphibole, and magnetite, and exhibit positive Eu anomalies (δEu = 1.04–1.31) but lack Ce anomalies, indicating that ore‐forming fluids may have been derived from a relatively low oxygen fugacity and high fH2O environment. Titanite yielded an in‐situ U–Pb lower‐intercept age of 307.2 ± 4.8 Ma (MSWD = 0.97), consistent with the syn‐ore amphibole 40Ar‐39Ar plateau age (305 ± 6 Ma). Since the mineralization ages are obviously younger than country rocks, the previous syn‐sedimentary ore‐forming model for Duotoushan Fe–Cu mineralization can be excluded. Integrating the characteristics from ore deposit geology, periods of mineralization events, and spatial–temporal distribution of magmatism, we proposed that the Duotoushan Fe–Cu mineralization event may be linked with a hidden granite in its orefield. [ABSTRACT FROM AUTHOR]

The Luxi Terrane (eastern China) exposes widespread Early Cretaceous alkaline rocks, whereas their petrogenesis remains controversial, including fractional crystallization, partial melting and crustal contamination regime. Here, we present petrology, geochemistry, sphene U-Pb geochronology and trace element data from the syenogranite, quartz syenite and quartz monzonite of the Guandimiao alkaline complex rocks to investigate their petrogenesis. Geochemical data suggest that these alkaline rocks show alkalic and peralkaline characters, and high Ga/Al ratios, SiO2, light rare-earth element (LREE), Zr and Nb, and low MgO, CaO, Eu contents, corresponding to A-type granites. Sphene trace elements in syenogranite and quartz monzonite show obvious fractionation between LREE and heavy rare-earth element (HREE) and high Th/U ratios, indicating a magmatic origin. They yield U-Pb lower intercept ages of 128 ± 2.3 Ma and 127 ± 1.3 Ma, representing the crystallization ages of these alkaline rocks. The negative correlations between CaO, Fe2O3 (Total), MgO, P2O5, TiO2, MnO and the pronounced depletion in Nb, Ta and Ti suggest that the alkaline rocks were formed by fractional crystallization. Additionally, the positive correlation between La/Hf and La, Th and Th/V, Ce/Yb and K2O, and Tb/Yb and Yb suggest that the alkaline melts are generated by partial melting. Such high Rb/Nb, (Th/Nb)N and Nb/Th ratios indicate crustal contamination during the magma emplacement. We, therefore, propose the magma source of the alkaline rocks in the Guandimiao complex originated by partial melting of lithospheric mantle, which experienced fractional crystallization and crustal contamination processes during its emplacement. Such complex alkaline rocks were probably formed in an extensional back-arc setting induced by the retreat of the subducting Izanagi plate. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Water-fluxed melting of hornblende and dehydration melting of biotite in the crust root. • An anatectic event proceeded at ca. 480–470 Ma in the Central Qilian belt. • A hot retro−/back-arc setting is proposed to provide enough heat for anatexis and metamorphism. [ABSTRACT FROM AUTHOR]

• The first in-situ LA–ICP–MS dating of titanite in the A vein of porphyry deposits has been analyzed in polished thin section. • The titanite dating data (44.4 ± 1.5 Ma) in the A1 vein of the Lancang Laochang polymetallic deposit further delineates the evolutionary timeline from magma to ore-forming fluid in 45–43 Ma. • From magma to the initial ore-forming fluid in the Laochang deposit, a slightly pressure increase (from 93 MPa to 98 MPa) and a minor decrease of temperature (from 697 °C to 680 °C) and log f O 2 (from −16.78 to −17.29) have been revealed. The Laochang polymetallic deposit is the only large deposit in the Changning–Menglian Junction Zone. The deposit features by deep porphyry-skarn Mo–(Cu) and shallow vein Pb–Zn–(Ag) mineralization. Researches on the deposit have yielded extensive data, however, details about the initial evolution from magma to ore-forming fluid remain unclear. This study centers on the in-situ analysis of biotite from the porphyry, as well as phlogopite and titanite from the A vein, leading to the following insights: (1) The biotite geothermobarometer suggests the porphyry intruded in a moderate depth (2.57–4.27 km), with average parameters as P = 93 MPa, T = 697 °C, and log f O 2 = -16.78. (2) The A vein in the deposit can be further subdivided into A1 K-feldspar vein and A2 quartz vein. The phlogopite in the A1 vein formed at P = 98 MPa, T = 681 °C, and log f O 2 = -17.29. The pressure of the A1 vein is slightly higher than the static pressure of wall rock, attributed to pressure increment from the initial exsolved fluid. Conversely, the temperature and oxygen fugacity experience a slight decrease, due to buffering of the adjacent tuff. (3) The in-situ LA–ICP–MS U–Pb dating of the titanite in the A1 vein yields 44.4 ± 1.5 Ma (MSWD = 1.8, n = 48), comparable to the emplacement age of the porphyry (44.6–44.4 Ma). It is slightly older than the main mineralization age (43.78 Ma), further delineated the initial evolution sequence from magma to ore-forming fluid. Our research suggests that the in-situ analysis of titanite is crucial for preciously tracking the magma–fluid system, as titanite records both time and temperature information. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water-rich magma fractionation contributes to the formation of high Sr/Y rocks. • Quantifying crustal thickness by Sr/Y ratios should consider water-rich magma fractionation. • A Late Devonian-early Carboniferous continental arc setting developed in central Beishan. The petrogenesis of intermediate-silicic rocks with high Sr/Y ratios that are closely associated with porphyry Cu-Au mineralization and TTGs remains uncertain. This study presents new geochronological and geochemical data for high Sr/Y granodiorites and associated mafic microgranular enclaves (MMEs) from the Late Devonian–early Carboniferous Suanjingzi batholith in the Beishan orogen, NW China. The MMEs, dioritic and fine-grained, share mineral assemblages with their hosts but contain more amphibole. Similarities in ages and Sr-Nd-O isotopes between the MMEs and their hosts indicate that they share a common magma source. Our geochemical studies and quantitative modeling imply that upper crustal fractional crystallization of water-rich magma, represented by the associated MMEs, played a crucial role in forming the Late Devonian–early Carboniferous high Sr/Y rocks in central Beishan. High H 2 O contents promote amphibole crystallization and delay plagioclase appearance, giving rise to higher Sr and lower Y contents in evolved magma. Additionally, titanite fractionation can contribute to high Sr/Y ratios by decreasing Y contents. The MMEs, the best available proxy for the parental magma, originated from the partial melting of a mantle wedge metasomatized by subduction fluids. This study emphasizes the significance of upper crustal fractional crystallization of water-rich magma in forming high Sr/Y rocks. The possible increment caused by amphibole-dominated fractionation within the upper crustal level should be considered when employing Sr/Y ratios to quantify crustal thickness. Moreover, we argue that Late Devonian–early Carboniferous magmatism in central Beishan occurred in a continental arc setting, providing a stronger basis for understanding the Paleozoic tectonic evolution of the Beishan orogen. [ABSTRACT FROM AUTHOR]

Migmatite, generated from anatexis or partial melting, links metamorphism with magmatism and can be used to investigate the source of magmas. Zircon and titanite, as refractory minerals in migmatite, can illuminate both the conditions of partial melting and the sources of associated granites. Mesozoic granitoids in the Jiaodong Peninsula, eastern China, have been studied extensively for their origins as partial melts of the lower continental crust. However, Jurassic metamorphism and partial melting of their hypothesized parent rocks have rarely been reported and discussed. In this study, we investigated the morphology, interior structure, U-Pb geochronology, and trace element compositions of zircon and titanite from diverse migmatites in the Yantai-Rushan area of the Jiaodong Peninsula. For leucosomes, inherited metamorphic and magmatic (or anatectic) zircon cores yield Paleoproterozoic ages, indicating a North China affinity; in contrast, anatectic zircon domains with high rare earth element concentrations show Jurassic ages of 160–154 Ma. For mafic melanosomes, metamorphic zircon and titanite yield ages of 154–149 Ma and c. 150 Ma, respectively; in contrast, two inherited metamorphic zircons record Triassic ages, suggesting an affinity with the ultrahigh-pressure rocks in the Sulu orogen. For granites, the oldest age of anatectic zircons is 175 Ma. Altogether, these data demonstrate a long-lived (c. 25 Myr), Jurassic, metamorphic-anatectic event in the Jiaodong Peninsula. These new findings prove that three lithotectonic units—the Jiaobei terrane, Sulu orogen, and preexisting granites in the Jiaodong Peninsula—were all sources for protracted Jurassic partial melting. This study deepens our understanding of the links between metamorphism and magmatism in demonstrating the diverse rock types that simultaneously source granites. • A Jurassic metamorphic-anatectic event was identified in the Jiaodong Peninsula of eastern China. • Rocks of North and South China block affinity were co-involved in the Jurassic partial melting. • This provides robust evidence for multiple origins of Jurassic and later granitoids. [ABSTRACT FROM AUTHOR]

The deeply subducted continental crust commonly undergoes partial melting during its exhumation from mantle to crustal depths. Peritectic minerals are commonly produced during decompressional melting, providing an important record of the timing, P–T conditions, and mechanisms of crustal anatexis in continental subduction zones. A combined study of petrography, mineral inclusions, mineral major and trace element compositions, phase equilibrium modelling, zircon and titanite U–Pb dating, and zircon Hf–O isotopes was carried out to characterize peritectic minerals in ultrahigh‐pressure (UHP) metamorphic gneisses from the Sulu orogen, China. Field and petrographic observations reveal that the crustal anatexis was extensive and is recorded by folded leucosomes, corroded phengite relicts, cuspate K‐feldspar and quartz, pseudomorphs of melt films along grain boundaries, and multiphase crystal inclusions in zircon, garnet, and phengite. The multiphase crystal inclusions represent the crystallized product of anatectic melt droplets trapped in the peritectic zircon and garnet as well as the residual UHP phengite. The peritectic origin of both zircon and garnet is identified by their compositional characteristics, and the peritectic origin of garnet is further supported by phase equilibrium modelling which shows an increase in garnet contents as partial melting proceeds. The modelled phase diagrams also indicate that the two peritectic minerals were produced through two episodes of phengite dehydration melting. The first occurred at 237 ± 3 Ma under P–T conditions of ≥2.6 GPa and 810–880°C, corresponding to thermobaric ratios of ~312–338℃/GPa. The second took place at 222 ± 2 Ma under P–T conditions of 1.5–2.1 GPa and 730–760℃, corresponding to thermobaric ratios of 362–487℃/GPa. In comparison to peak UHP metamorphic P–T conditions of 2.8–4.0 GPa and 720–870℃ for thermobaric ratios of 218–257℃/GPa, it appears that the decompressional melting is associated with an increase in thermal gradients during the exhumation in the different stages. Whereas the first is caused by decompression during initial exhumation of the deeply subducted continental crust, the second is caused by decompression during relamination of the UHP slices into the collision‐thickened orogenic lower crust. Peritectic amphibole and titanite were also recognized by comparing their petrographic textures with natural samples and experimental products. They were produced through water‐fluxed melting at 217 ± 3 Ma under lower P–T conditions, suggesting the liberation of aqueous fluids from the underlying exhuming UHP rocks. All of the peritectic minerals generally show compositional inheritance from their precursor minerals. Nevertheless, they commonly underwent dissolution when anatectic P–T conditions deviate significantly from those of peritectic reactions. This is indicated by the dissolution of peritectic zircon and garnet and by the occurrence of anhedral and embayed peritectic amphibole. As a consequence, the behaviour of peritectic minerals provides a snapshot of crustal anatexis for geochemical differentiation in collisional orogens. [ABSTRACT FROM AUTHOR]

A new member of the non-stoichiometric perovskite group mineral species, liguowuite, ideally WO3 , has been found in the Neoproterozoic Sinian biotite-quartz monzonite in the southern part of the Panzhihua–Xichang region (Nanyang village: 26 ∘ 46′8.21′′ N, 101 ∘ 27′13.86′′ E), China. It is associated with hornblende, pargasite, ferro-hornblende, annite, hydrobiotite, phlogopite, orthoclase, microcline, albite, quartz, kaolinite, ilmenite, goethite, hematite, magnetite, pyrite, zircon, zoisite, titanite, epidote, diopside, tourmaline, almandine, fluorapatite, monazite-(Ce), allanite-(Ce), bastnäsite-(Ce), xenotime-(Y), scheelite, moissanite, tellurite, wumuite, and tewite. Liguowuite occurs as greenish yellow prisms, ranging from 0.05 to 0.1 mm in diameter, and it is transparent with a greasy luster and a white streak. Liguowuite exhibits a triclinic pseudomorphism composed of nanoparticles with many cracks and nanovoids. This mineral is brittle and has a Mohs hardness value of approximately 3–4. The calculated density is 7.22 g cm -3. Electron microprobe analyses gave (average weight percent, wt %, of 15 spot analyses of 4 samples) K2O = 0.01, WO3 = 99.23, TeO2 = 0.03, CaO = 0.06, Na2O = 0.04, and total 99.37, yielding the empirical formula W1.00O3 , based on O apfu=3 and ideally WO3. The strongest five diffraction lines (d Å (I)(hkl)) are 3.8552 (88)(002), 3.7685 (88)(020), 3.6590 (100)(–200), 2.6928 (43)(022), and 2.6258 (60)(202). Liguowuite is monoclinic and is in space group P 2 1/n , with a= 7.32582(18) Å, b= 7.54767(18) Å, c= 7.71128(18) Å, β= 90.678(3) ∘ , V= 426.348(19) Å 3 , and Z= 8. The crystal structure data were refined using the Rietveld refinement method and X-ray powder diffraction data. The reliability factors (R factors) were Rwp= 0.0604 and Rp= 0.0454, with χ2 = 1.707. Liguowuite consists of corner-sharing distorted and tilted [ WO6 ] octahedra, in which the W atoms are off-center and form six W–O bonds ranging from 1.7 to 2.2 Å with the surrounding oxygen atoms. According to the hierarchical scheme for perovskite supergroup minerals, liguowuite is the first reported example of A -site vacant single oxide, i.e., a new perovskite subgroup. [ABSTRACT FROM AUTHOR]

The South Altyn ultrahigh-pressure (UHP) metamorphic belt is claimed to host the deepest subducted continental crust based on the discovery of former stishovite, and thus can provide unique insights into the tectonic evolution from deep continental subduction and exhumation to arc–backarc extension. In this article, we present detailed studies of petrography, mineral chemistry, phase equilibria modelling and zircon U–Pb dating for three representative samples involving garnet amphibolite (A1531 & A1533) and associated garnet-biotite gneiss (A1534) from the UHP belt. Three phases of metamorphism are inferred for the rocks. The first phase high-pressure (HP)–UHP-type eclogite facies is represented by the mineral assemblages of garnet and phengite inclusions in zircon and garnet cores with the high grossular (XGrs = 0.33–0.34). The Si contents of 3.40–3.53 and 3.24–3.25 p.f.u. in phengite inclusions yield pressure conditions of >1.7–2.3 GPa for A1533 and 2.5–2.55 GPa for A1534 at a fixed temperature of 770°C. The second phase medium-pressure (MP)-type overprinting of garnet amphibolite facies shows P–T conditions of 0.8–1.2 GPa/750–785°C based on the stability fields of corresponding mineral assemblages, the measured isopleths of Ti contents in biotite and amphibole cores, and XGrs in garnet. The third phase low-pressure (LP) type overprinting includes early-stage heating to peak granulite facies followed by cooling towards a late-stage amphibolite facies. The peak granulite facies is represented by the high Ti amphibole mantle, high Zr titanite and the intergrowths of clinopyroxene + ilmenite in A1533 & A1531, with P–T conditions of 800–875°C/0.80–0.95 GPa. The late-stage is defined by the solidus assemblages, giving P–T conditions of 0.5–0.7 GPa/720–805°C. U–Pb geochronology on metamorphic zircons from A1533 and A1534 gives three ages of c. 500 Ma, c. 482 Ma and c. 460 Ma. They are interpreted to represent the HP-UHP, MP and LP types of metamorphism respectively, based on cathodoluminescence (CL) images, mineral inclusions and trace element patterns. Combining the regional geology and metamorphic evolution from the Altyn Orogen, a tectonic model is inferred, including the following tectonic scenarios. The small Altyn Microcontinent (AM) was subducted to great mantle depths with dragging of the surrounding vast oceanic lithosphere to undergo the HP-UHP eclogite facies metamorphism during the early subduction stage (c. 500 Ma) of the Proto-Tethys Ocean. Then, the subducted slabs were exhumed to a thickened crust region to be overprinted by the MP-type assemblages at c. 482 Ma. Finally, an arc–backarc extension was operated within the thickened crust region due to the retreat of subduction zones. It caused evident heating and the LP-type metamorphic overprinting at c. 460 Ma, with a fairly long interval of 30–40 Myr after the HP-UHP metamorphism, distinct from the short interval of <5–10 Myr in the Bohemian Massif. [ABSTRACT FROM AUTHOR]

Mixing of cogenetic magmas represents an important process in granite petrogenesis but is difficult to identify and is consequently often overlooked due to the absence of obvious isotopic distinctions between the mixed melts. We have conducted in situ elemental and O isotope analyses on apatite from Cretaceous Zhangzhou calc-alkaline granite in southeast China. We integrated these data with microanalyses on other minerals (plagioclase, zircon, and titanite) as well as whole-rock geochemistry to decipher the mixing history of this granitic complex. The apatite occurs as an early crystallizing phase forming inclusions in biotite, plagioclase, and titanite, and is characterized by core-rim zonation textures with a dark core and bright rims in backscattered images. The core domains have remarkably higher SO3 and Li concentrations but much lower SiO2, REE, and Y concentrations than the rim domains. However, both the cores and rims show geochemical compositions similar to that from typical I-type granite and also have mantle-like O isotope compositions (the core has δ18O = 5.3-6.8‰ and the rim has δ18O = 5.2-6.4‰, respectively), indicating crystallization from granitic melts derived from newly accreted crust. The combined major and trace element and O isotope compositions of apatite and whole-rock geochemistry suggest that compositional evolution of the Zhangzhou granite involved mixing between two cogenetic magma batches, with variable degrees of subsequent differentiation. Batch I magma was a low-SiO2 and high-SO3 melt, whereas Batch II magma was a high-SiO2 and low-SO3 melt that experienced devolatilization. The high-S content in apatite cores further suggests the parental magma of the Zhangzhou granite likely originated from a sulfur-rich source comprising mainly newly accreted arc crust in response to subduction of the paleo-Pacific Ocean. The geochemical records of these magmatic processes are rarely observed in coeval zircon, titanite, and plagioclase. Our study, therefore, demonstrates that apatite geochemistry is potentially a more suitable monitor of complex magmatic evolution, including devolatilization and mixing of isotopically indistinguishable magmas. [ABSTRACT FROM AUTHOR]

There are more than 80 porphyry (or skarn) Mo deposits in northeastern China with Jurassic or Cretaceous ages. These are thought to have formed mainly in a continental arc setting related to the subduction of the Paleo-Pacific oceanic plate in the Jurassic and subsequent slab rollback in the early Cretaceous. The Jurassic Daheishan porphyry Mo deposit is one of the largest Mo deposits in NE China, which contains 1·09 Mt Mo with an average Mo grade of 0·07 %. To better understand the factors that could have controlled Mo mineralization at Daheishan, and potentially in other similar porphyry Mo deposits in NE China, the geochemical and isotopic compositions of the ore-related granite porphyry and biotite granodiorite, and the magmatic accessory minerals apatite, titanite and zircon from the Daheishan intrusions, were investigated so as to evaluate the potential roles that magma oxidation states, water contents, sulfur and metal concentrations could have played in the formation of the deposit. Magmatic apatite and titanite from the causative intrusions show similar εNd(t) values from –1·1 to 1·4, corresponding to TDM2 ages ranging from 1040 to 840 Ma, which could be accounted for by a mixing model through the interaction of mantle-derived basaltic melts with the Precambrian lower crust. The Ce and Eu anomalies of the magmatic accessory minerals have been used as proxies for magma redox state, and the results suggest that the ore-forming magmas are highly oxidized, with an estimated ΔFMQ range of +1·8 to +4·1 (+2·7 on average). This is also consistent with the high whole-rock Fe2O3/FeO ratios (1·3–26·4). The Daheishan intrusions display negligible Eu anomalies (Eu/Eu* = 0·7–1·1) and have relatively high Sr/Y ratios (40–94) with adakitic signatures; they also have relatively high Sr/Y ratios in apatite and titanite. These suggest that the fractionation of amphibole rather than plagioclase is dominant during the crystallization of the ore-related magmas, which further indicates a high magmatic water content (e.g. >5 wt%). The magmatic sulfur concentrations were calculated using available partitioning models for apatite from granitoids, and the results (9–125 ppm) are indistinguishable from those for other mineralized, subeconomic and barren intrusions. Furthermore, Monte Carlo modelling has been conducted to simulate the magmatic processes associated with the formation of the Daheishan Mo deposit, and the result reveals that a magma volume of ∼280 km3 with ∼10 ppm Mo was required to form the Mo ores containing 1·09 Mt Mo in Daheishan. The present study suggests that a relatively large volume of parental magmas with high oxygen fugacities and high water contents is essential for the generation of a giant porphyry Mo deposit such as Daheishan, whereas a specific magma composition (e.g. with unusually high Mo and/or S concentrations) might be less critical. [ABSTRACT FROM AUTHOR]

• This study provides new insights into the P–T – t history of deeply-subducted continental crust with the utilization of zircon petrochronology. • Identification of omphacite, phengite and garnet inclusions in zircons indicate that the felsic crust probably has transformed during the eclogite-facies metamorphism. • P–T – t path of the orthogneisses demonstrates two-stages of exhumation for the UHP terrane. The early-stage faster exhumation is likely related to melt activity. Reconstruction of pressure–temperature–time (P – T – t) path of volumetrically-dominant orthogneisses in deeply subducted continental crusts is challenging due to their simple amphibolite-facies mineral assemblages. To provide new insights into this issue, a detailed study of mineral inclusions, trace elements and U-Pb ages within robust zircon containers, together with titanite U-Pb dating and petrology were conducted on ultrahigh-pressure (UHP) orthogneisses from the northern Sulu belt. The following P–T–t conditions of three metamorphic stages were constrained: (i) cathodoluminescence (CL)-grey zircon cores (ca. 238–237 Ma) with flat heavy rare earth element (HREE) patterns include garnet, phengite and omphacite that yield estimated P–T conditions of 2.3–2.8 GPa/730–800 °C, corresponding to prograde high-pressure (HP) metamorphism before the UHP peak. (ii) CL-dark zircon mantles (ca. 224 Ma) contain multiphase solid inclusions of plagioclase + K-feldspar + quartz and show extremely low Th/U ratios (≤0.08) and negative Eu anomalies, demonstrating their crystallization from hydrous melt at 2.0–1.8 GPa/890–820 °C during HP eclogite-facies exhumation. In addition, titanite grains are characterized by high LREE contents (1939–5239 ppm), Th/U ratios (0.37–0.81) and crystallization temperatures (830–801 °C), suggesting their peritectic origin. The lower intercept age (220 ± 4 Ma) of titanite is broadly consistent with the ages of the zircon mantles, indicating that they both crystallized from the melt at the same stage. (iii) CL-bright zircon rims (ca. 212–211 Ma) preserve low-pressure mineral inclusions of plagioclase, K-feldspar and quartz, and they show low Th/U ratios (0.03–0.12) and steep HREE patterns with negative Eu anomalies, witnessing amphibolite-facies overprinting at 1.0–0.8 GPa/610–550 °C. Combined with the metamorphic peak conditions of 3.2 GPa/840 °C at ca. 232 Ma constrained by previous studies from the same area, the P – T – t path of the northern Sulu UHP belt is reconstructed. The data reflects two-stage exhumation of this terrane, including an early-stage (5.8 km/m.y.) and a later-stage slower (3.1 km/m.y.) exhumation processes. The faster exhumation during early decompression was probably enhanced by extensive melting activity recorded by the CL-dark zircon mantles from the orthogneisses. [ABSTRACT FROM AUTHOR]

A suite of Jurassic–Cretaceous migmatites was newly identified in the Liaodong Peninsula of the eastern North China Craton (NCC). Anatexis is commonly associated with crustal thickening. However, the newly identified migmatites were formed during strong lithospheric thinning accompanied by voluminous magmatism and intense deformation. Field investigations show that the migmatites are spatially associated with low-angle detachment faults. Numerous leucosomes occur either as isolated lenses or thin layers (dykes), parallel to or cross-cutting the foliation. Peritectic minerals such as titanite and sillimanite are distributed mainly along the boundaries of reactant minerals or are accumulated along the foliation. Most zircons show distinct core–rim structures, and the rims have low Th/U ratios (0.01–0.24). Zircon U–Pb dating results indicate that the protoliths of the migmatites were either the Late Triassic (224–221 Ma) diorites or metasedimentary rocks deposited sometime after c. 1857 Ma. The zircon overgrowth rims record crystallization ages of 173–161 Ma and 125 Ma, which represent the formation time of leucosomes. These ages are consistent with those reported magmatic events in the Liaodong Peninsula and surrounding areas. The leucosomes indicate a strong anatectic event during the Jurassic–Cretaceous period. Partial melting occurred through the breakdown of muscovite and biotite with the presence of water-rich fluid under a thermal anomaly regime. The possible mechanism that caused the 173–161 Ma and 125 Ma anatectic events was intimately related to the regional crustal extension during the lithospheric thinning of the NCC. Meanwhile, the newly generated melts further weakened the rigidity of the crust and enhanced the extension. [ABSTRACT FROM AUTHOR]

Late Cretaceous–Eocene granites are widespread in the Tengchong terrane and related to subduction and closure of the Neo–Tethyan Ocean. However, the reason of their compositional and spatial variations is still under explored. This study reports zircon U–Pb geochronological, whole–rock and Nd isotopic data for Guyong, Houqiao and Menglong granites in the Tengchong terrane. Our data show that the three plutons crystallized at 70.4 ± 0.3Ma, 64.4 ± 0.3Ma and 47.6 ± 0.2Ma. Guyong monzogranites show an I–type affinity and may have experienced fractional crystallization of plagioclase, biotite and sphene. Negative εNd(t) values (−9.19 to −11.01) with two-stage model ages (T2DM = 1.59–1.78 Ga) indicate that Guyong monzogranites are derived from a predominantly Paleoproterozoic crustal source with little involvement of mantle–derived materials in an extensional setting. Lower εNd(t) (−9.33 to −11.63) and negative correlations of HREE, LREE, Th, and Y vs. SiO2 indicate that Houqiao plutons are S–type granites derived from a pure crustal source during crustal thickening. Low Zr/Hf and Nb/Ta ratios, zircon saturation temperature (TZr = 750°C–786°C) and negative δEu (0.11–0.40) of Menglong biotite granites indicate that they have experienced fractional crystallization of plagioclase, biotite and sphene. Relatively high εNd(t) (−6.81 to −7.07) values indicate that they are products of felsic magma mixed with mafic magma, which is also supported by numerous coeval mafic–intermediate rocks (Eocene) such as metagabbros, diorites and MMEs (mafic microgranular enclaves) in the western Tengchong terrane. A process of slab rollback and slab breakoff may have triggered the late Cretaceous–Eocene magmatism and the compositional variation of associated granitoids in the Tengchong terrane. [ABSTRACT FROM AUTHOR]

Dongguashan is one of the largest porphyry-skarn Cu-Au deposits in eastern China and titanite is found in the ore system. Five types of both magmatic and hydrothermal titanites are distinguished, based on their textural and chemical characteristics. Types 1 and 2 titanites are magmatic in origin whereas types 3, 4, and 5 are hydrothermal. Magmatic titanites are wedge-shaped and display concentric and sector zoning, whereas hydrothermal titanites show a wide range of textures that vary with different alteration stages. REE, Sn, Mo, and Cu are enriched in magmatic titanites (types 1 and 2). In contrast, vanadium and HFSE are enriched in hydrothermal titanites, especially in type 4 titanite from the propylitic alteration zone. Magmatic titanite (type 1) coexists with magnetite and K-feldspar and crystallized in oxidized and H2O-rich magma at 730–760 °C. Type 2 titanite contains ilmenite inclusions reflecting changes in the fO2 of the magma chamber, possibly caused by input of mafic magma. The mobility and enrichment of HFSE and association with fluorapatite reflect the F-rich composition of the magmatic-hydrothermal fluid at Dongguashan. The relationship between titanite textures and chemistry indicates that titanite can serve as a recorder of magmatic-hydrothermal processes in porphyry copper systems. U-Pb dating of type 4 titanite from the propylitic alteration zone and type 5 titanite from skarn yielded ages of 139.0 ± 2.6 Ma and 137.0 ± 2.0 Ma, respectively, indicating that it formed synchronously with the associated quartz monzodiorite. [ABSTRACT FROM AUTHOR]

We report new U–Pb zircon age data, zircon in situ oxygen isotope, mineral chemistry, whole-rock geochemistry and Sr–Nd isotopic compositions from the Early Devonian ultrapotassic Gucheng pluton in the North China Craton, and discuss its petrogenesis. The Gucheng pluton is exposed in the northern part of the North China Craton and forms a composite intrusion, consisting of K-feldspar-bearing clinopyroxenite, clinopyroxene-bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene (Wo43–48En19–35Fs18–38), sanidine (An0Ab3–11Or89–97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in situ oxygen isotopes (δ18O = 5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the North China Craton. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the North China Craton facing the Palaeo-Asian Ocean. [ABSTRACT FROM AUTHOR]

Robust quantification of pressure (P)–temperature (T) paths for subduction‐related HP/UHP metamorphic rocks is fundamental in recognizing spatial changes in both the depth of detachment from the down‐going plate and the thermal evolution of convergent margin sutures in orogenic belts. Although the Chinese southwestern (SW) Tianshan is a well‐known example of an accretionary metamorphic belt in which HP/UHP metabasites occur in voluminous host metasedimentary schists, information about the P–T evolution of these rocks in the eastern segment is limited, precluding a full understanding of the development of the belt as a whole. In this study at Kekesu in the eastern segment of the SW Tianshan, we use microstructural evidence and phase equilibrium modelling to quantify the peak and retrograde P–T conditions from two lawsonite‐bearing micaschists and an enclosed garnet–epidote blueschist; for two of the samples we also constrain the late prograde P–T path. In the two micaschist samples, relics of prograde lawsonite are preserved in quartz inclusions in garnet, whereas in the metabasite, polymineralic aggregates included in garnet are interpreted as pseudomorphs after lawsonite. For garnet micaschist TK21, which is mainly composed of garnet, phengite/paragonite, albite, chlorite, quartz and relict lawsonite, with accessary rutile, titanite and ilmenite, the maximum P–T conditions for the peak stage are 18.0–19.0 kbar at 480–485°C. During initial exhumation, the retrograde P–T path passed through metamorphic conditions of 15.0–17.0 kbar at 460–500°C. For garnet–glaucophane micaschist TK33, which is mainly composed of garnet, glaucophane, phengite/paragonite, albite, chlorite, quartz, relict lawsonite and minor epidote, with accessary titanite, apatite, ilmenite and zircon, the maximum P conditions for the peak stage are >24.0 kbar at 400–500°C. During exhumation, the P–T path passed through metamorphic conditions of 17.5–18.5 kbar at 485–495°C and 14.0–17.5 kbar at 460–500°C. For garnet–epidote blueschist TK37, which is mainly composed of garnet, glaucophane, epidote, phengite, chlorite, albite and quartz, with accessary titanite, apatite, ilmenite, zircon and calcite, the prograde evolution passed through metamorphic conditions of ~20.0 kbar at ~445°C to Pmax conditions of ~21.5 kbar at 450–460°C and Tmax conditions of 19.5–21.0 kbar at 490–520°C. During exhumation, the rock passed through metamorphic conditions of 17.5–19.0 kbar at 475–500°C, before recording P–T conditions of <17.5 kbar at <500°C. These results demonstrate that maximum recorded pressures for individual samples vary by as much as 6 kbar in the eastern segment of the SW Tianshan, which may suggest exhumation from different depths in the subduction channel. Furthermore, the three samples record similar P–T paths from ~17.0 to 15.0 kbar, which suggests they were juxtaposed at a similar depth along the subduction interface. We compare our new results with published information from eclogites in the same area before considering the wider implications of these data for the orogenic development of the belt as a whole. [ABSTRACT FROM AUTHOR]

Much of the global picture of crustal evolution has been constructed using zircon. While this has revealed a rich and complex history, this view is necessarily incomplete because of the lithology-specific affinity of zircon and the high temperatures needed to reset the U-Pb and Lu-Hf systems inherent within it. Here we use a five mineral, multi-isotope system approach to compare the record of crustal evolution recorded by zircon versus the picture provided by monazite, titanite, apatite, and rutile from the Yong-Ding and Luan rivers, northern China. These other minerals sample more diverse lithologies and temperature-pressure conditions that reflect additional tectonothermal events to those recorded solely by zircon. Zircon from both studied rivers predominantly reflects magmatic features, yielding age peaks at 2.6-2.3, 2.0-1.8, and 0.38-0.13 Ga, corresponding to the major magmatic events in their catchments. However, the detrital zircon record from both catchments fails to record and detail several important tectonothermal events. Specifically, the detrital monazite U-Pb ages cluster into two Paleoproterozoic peaks of ca. 1.95 and 1.85 Ga, while detrital apatite and rutile ages document unimodal and protracted U-Pb age peaks at 1.9-1.6 Ga. The different U-Pb closure temperatures of monazite, apatite, and rutile likely record two metamorphic events and the subsequent cooling history--key details that are absent from or obscured in the zircon record. The Phanerozoic mineral U-Th-Pb ages correspond to multiple magmatic events between 0.40 and 0.24 Ga and subsequent 0.24- 0.20 Ga metamorphism. The 0.60-0.25 Ga rutile U-Pb ages along with 0.33-0.24 Ga U-Pb ages in some zircon grains with radiogenic Hf isotope compositions from the Luan River do not match the geological records in the North China Craton, but instead reflect the protracted subduction-accretionary history of the Central Asian Orogenic Belt. In addition to their U-Th-Pb ages, Nd model ages of monazite, titanite, and apatite, plus zircon Hf model ages provide additional constraints on regional crustal evolution. The Nd model age information is blurred by the fact that the relationship between the Sm/Nd of these minerals and their former host rocks is not precisely known. Taken at face value, the monazite Nd model ages have two Neoarchean peaks at 2.9-2.7 and ca. 2.5 Ga, that may correspond to two crustal growth episodes, while the titanite Nd model ages with predominant peaks at 2.2-1.8 and 1.5-1.3 Ga broadly correspond with those derived from the whole-rock analyses of the wide spread Phanerozoic granitoids, and hence record extensive crustal reworking. In contrast, the zircon Hf model ages are strongly skewed to a 2.9-2.7 Ga period and fail to record the post-Archean evolution of this region. These data highlight the power of integrating the U-Th-Pb age and Lu-Hf/Sm-Nd isotope compositions of multiple detrital minerals, with a broad range in geochemical behavior and closure temperatures, to gain a more complete understanding of tectonothermal history and crustal evolution than zircon alone. [ABSTRACT FROM AUTHOR]

The Sanshilipu monzogranites is located in the northern margin of the South Qinling Block, with an outcrop of about 10 km2, and as an intrusion into Palaeozoic Danfeng ophiolitic mélange. The samples consist mainly of plagioclase, K‐feldspar, quartz, biotite, and minor titanite, apatite, magnetite, with contents of SiO2 (61.73–68.49%), Al2O3 (14.58–16.61%), K2O + Na2O (5.79–8.87%), MgO (1.07–2.91%), and low TiO2 (0.55–0.83%), similar to those of I‐type granite. They also show high concentrations of LREE, Pb, and Sr, slightly negative Eu, but low HREE, Nb, Ta, and Y. High Sr and Sr/Y, low Y characteristics are similar to those of adakite. High precision LA‐ICP‐MS U–Pb dating and trace element analysis of zircon in the Sanshilipu granite yielded a concordant age of 205 ± 1 Ma. This age is apparently younger than the closure age of the Mian‐Lue Ocean (242–221 Ma). We propose that the Sanshilipu monzogranites formed by magma mixing of thickened lower crust and limited mantle‐derived mafic magma during post‐collision of the South China and North China blocks. [ABSTRACT FROM AUTHOR]

Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwest China. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure-temperature (P-T) paths were retrieved, indicative of metamorphism of a possible subduction environment. Peak metamorphic P-T conditions (790~920 °C/28~41 kbar) of garnet clinopyroxenite suggest that they experienced high pressure to UHP metamorphism, and the UHP metamorphism occurred in the coesite- or diamond-stability field. The UHP metamorphic event is further confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from within the garnet. SIMS U-Pb dating of metamorphic titanite indicates that the post peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian (~ 389~370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this orogen in the Paleozoic. It can be further inferred that most of the UHP rocks of this orogen are now buried in the depth. [ABSTRACT FROM AUTHOR]

Various styles of ore deposits may form from a single magmatic-hydrothermal system. Identification of a possible genetic link between different ore types in a region is not only of critical importance for a better understanding of the magmatic-hydrothermal processes, but can also help in successful mineral exploration. Both iron oxide-apatite (IOA) and iron skarn deposits are closely associated with intrusive rocks of intermediate to felsic in composition, but whether these two ore types can form from the same magmatic intrusion remains poorly understood. In this study, we present a comparative study between a newly identified subsurface IOA ore body located at the apex of a diorite porphyry and the iron skarn ore bodies located immediately above it in the Jinniu volcanic basin of the Daye district, Middle-Lower Yangtze River metallogenetic belt (MLYRMB), eastern China in order to highlight a genetic link between these two styles of mineralization. The IOA ores are dominated by Ti-rich magnetite with variable amounts of fluorapatite, diopside, and actinolite. This mineralogical assemblage is distinctly different from the iron skarn ores, which consist mainly of Ti-depleted magnetite and subordinate pre-ore garnet and diopside, and post-ore quartz, chlorite, calcite, and pyrite. In addition, magnetite from the IOA ores is characterized by well-developed ilmenite lamellae and has high concentrations of Ni, V, Co, and Ga, consistent with high temperature crystallization, whereas magnetite grains from the iron skarn ores usually exhibit oscillatory growth zones and contain much lower Ni, V, Co, and Ga, indicating their formation under relatively low temperatures. Titanite and fluorapatite from the IOA ores have U-Pb ages of 132.5 ± 2.4 Ma to 128.4 ± 3.0 Ma, which match a titanite U-Pb age for the associated iron skarn ores (132.3 ± 2.0 Ma), and are consistent with zircon U-Pb ages for the ore-hosting diorite porphyry (130.4 ± 0.7 Ma to 130.3 ± 0.5 Ma). This age consistency supports a possible genetic link among the diorite porphyry, IOA ores, and iron skarn ores. We propose that the IOA and skarn ores are the products of two consecutive mineralization stages of the same magmatic-hydrothermal system, involving a high-temperature, hypersaline fluid coexisting with the diorite porphyry magma during emplacement and a subsequent low temperature, diluted hydrothermal fluid. Other IOA and iron skarn deposits of similar ages (130 Ma) are found in a series of volcanic basins in the MLYRMB, which forms one of the world's largest IOA metallogenic belts. The close association of the two ore styles identified at Daye provides a useful exploration guide for IOA and iron skarn deposits both on a local and regional scale. [ABSTRACT FROM AUTHOR]

Retrograde eclogite and garnet amphibolite of the Lüliangshan unit of the Shenglikou area, North Qaidam, were studied with emphasis on rutile and titanite. A special focus is on the formation of rutile and its corona of titanite (Ttn1) in retrograde eclogite and on coarse-grained titanite (Ttn2) from the garnet amphibolite. Using zirconium (Zr)-in-rutile and Zr-in-titanite thermometers, the temperatures estimated for the formation of an early generation of rutile are 823–884 °C at 2.5–2.8 GPa, while 812–894 °C at 1.3–1.5 GPa are derived for the formation of coronitic Ttn1 in the retrograde eclogite. Therefore, isothermal decompression must have occurred during exhumation, which also has triggered the partial melting of the retrograde eclogite. Ttn2 of the garnet amphibolite has high REE contents and high Th/U ratios, indicating that it is newly grown from a Ti, Ca, and LREE enriched anatectic melt derived from the partial melting of retrograde eclogite. LA-ICP MS U-Pb dating yields a lower intercept age of 423±4 Ma for Ttn2, which is consistent with the granulite-facies metamorphic age of the retrograde eclogite. Moreover, a temperature of 781–823 °C at 1.0–1.2 GPa is obtained for Ttn2, which fits the P-T conditions of the HP granulite-facies metamorphic stage (P=1.07–1.24 GPa and T=774–814 °C), and documents that the crystallization of the melt occurred at the granulite-facies stage at 423 Ma. The high amount of REE of the garnet amphibolite is a consequence of the formation of Ttn2 from the melt. The contents and ratios of Zr and Hf in rutile and Ttn2 differ from those in the garnet amphibolite, and the whole rock Zr/Hf ratios of retrograde eclogite and garnet amphibolite are both higher than the respective ratios in rutile and Ttn2, suggesting that rutile and titanite cannot be the major carriers of Zr and Hf accounting for the high whole rock Zr/Hf ratios. [ABSTRACT FROM AUTHOR]

[Display omitted] • New U-Pb geochronology and trace element data of hydrothermal rutile and titanite were obtained. • The Chaihulanzi deposit is a subduction-related orogenic gold deposit. • The northern NCC has exploration potentials for Early Permian lode gold deposits. The Chifeng-Chaoyang region, located along the northern margin of the North China Craton, is an important gold producer in China, with a proven gold reserve of about 500 tons. Most gold deposits are fault-controlled and formed in the Mesozoic, but the absolute ages of gold mineralization in this region have not been well constrained due to the lack of suitable dating minerals. This study presents in situ U-Pb ages of hydrothermal rutile and titanite for the Chaihulanzi gold deposit and obtains a distinctive age. The Chaihulanzi deposit (∼27 t Au) is located in the western portion of the Chifeng-Chaoyang region and mainly hosted in the carbonaceous mica schist of the Neoarchean-Paleoproterozoic Jianping Group along NW to NWW striking faults. It contains auriferous quartz veins and disseminated ores in hydrothermal alteration zones, with pyrite and pyrrhotite as the predominant ore minerals. Based on field and petrographic observations, four stages of mineralization process can be identified, involving stage I quartz-pyrite, stage II quartz-pyrite-pyrrhotite-chalcopyrite, stage III quartz-polymetallic sulfides, and stage IV quartz-calcite. Stage II represents the main gold stage and contains abundant hydrothermal rutile and titanite, which are intergrown with pyrite, pyrrhotite and native gold. Rutile grains have high contents of V, Nb, Fe, Cr, W and low contents of Zr and yield a Tera-Wasserburg lower intercept age of 285.4 ± 8.5 Ma (n = 37, MSWD = 3.9). Titanite grains show low Th/U and La/Yb ratios (0.03 to 0.66 and 0.26 to 3.98, respectively) and flat chondrite-normalized REE patterns (LREE/HREE = 0.88–5.72, Eu/Eu* = 0.71–1.71), with a Tera-Wasserburg lower intercept age of 282.3 ± 3.4 Ma (n = 20, MSWD = 2.1). Combined with the emplacement age of a post-ore mafic dyke (ca. 275.5 Ma), the timing of the Chaihulanzi deposit can be constrained to Early Permian, representing a new gold mineralization epoch in the Chifeng-Chaoyang region. On the basis of available geological and geochronological evidence, the Chaihulanzi deposit can be classified as an orogenic gold deposit formed during the southward subduction of the paleo-Asian Ocean. These new findings likely have important implications for future regional gold exploration. [ABSTRACT FROM AUTHOR]

Mineralogical, geochemical and geochronological results of the Huayangchuan uranium (U)-polymetallic deposit. (a)-(d) Backscattered electron (BSE) images of titanite grains collected from Huayangchuan REE-U-Nb-Pb deposit; (e)-(h) backscattered electron (BSE) images of the betafite (main U-Nb-bearing mineral phase in Huayangchuan deposit) and its alteration; (i) and (j) LA-ICP-MS U-Th-Pb ages of the titanite from the Huayangchuan deposit; (k) primitive-mantle-normalized trace element spider diagram of Taihua Group gneiss (gray lines), pegmatite (orange lines) and carbonatite dykes (red lines); (l) chondrite-normalized rare earth element (REE) pattern of Triassic titanite (red lines) and Cretaceous titanite (green lines). [Display omitted] • C and O isotopic compositions and zircon U-Pb ages identified the Triassic carbonatite magmatism in the Huayangchuan deposit. • Titanite U-Pb isotopic dating revealed two sets of ages for mineralization: during the Late Triassic and the Early Cretaceous. • Late Triassic carbonatite magmatism (∼220 Ma) was responsible for the U-Nb-REE mineralization. • Early Cretaceous hydrothermal fluid (∼140 Ma) contributed to the Nb, Ti and U remobilization. The supergiant Huayangchuan uranium (U)-polymetallic deposit is situated in the west part of Lesser Qinling Orogen, Central China, which is renowned for its unique metallogenic type and complex mineralization processes. This newly-discovered deposit contains economic endowments of U, Nb, Pb, Se, Sr, Ba and REEs. The genesis of this deposit remains hugely controversial and the related magmatic and metallogenic framework have not been well established. In our study, we present newly obtained zircon U-Pb age data, whole-rock trace elements, detailed SEM observation, carbon and oxygen isotope determination and titanite U-Pb age result to provide geochemical and geochronological constraints on the magmatic and hydrothermal metallogenic processes in Huayangchuan ore district and give insight into the REE, Nb and U mineralization and remobilization mechanism. Carbonatite in Huayangchuan deposit is rich in Ba, Sr, Nb, U and REE and the δ18O SMOW and δ13C PDB (‰) values of carbonatite vary between + 7.30 ‰ to + 9.80 ‰ and − 6.00 ‰ to − 7.20 ‰, respectively, which is the unique characteristic of igneous carbonatite. The total REE contents of carbonatite range from 1319.5 to 2535.8 ppm, significantly higher than that of the granite pegmatite dykes and Taihua Group granitic gneiss. Two zircon grains from the Huayangchuan carbonatite yield the 206 Pb / 238 U age of 223 ± 5.6 Ma and 217 ± 8.6 Ma. Uranium and niobium are mainly hosted in the primary mineral of betafite, minorly in uraninite and fergusonite. REE are remained in various REE carbonates, phosphates and silicates, e.g. allanite, parite, monazite, apatite, yttrialite and xenotime. Betafite contains numerous mineral inclusions of calcite, allanite and apatite, which displays as vermicular relicts with metasomatic corrosion texture. The intimate relationship between betafite, calcite, apatite, allanite and REE carbonates implies that U and Nb mineralization occurred during carbonatite-related magmatic stage. Late Triassic carbonatite magmatism (∼220 Ma) was responsible for the world-class U-Nb-Mo-REE mineralization in the Qinling Orogen. Whereas, LA-ICP-MS U-Pb data of titanite collected from Huayangchuan carbonatite reveal two sets of ages in the Huayangchuan deposit: during the Late Triassic and the Early Cretaceous. LA-ICP-MS data of the Triassic titanite and Cretaceous titanite in Huayangchuan deposit yield the lower intercept age of 223.1 ± 9.4 Ma and 141.9 ± 4.7 Ma respectively in the Tera-Wasserburg (238U/206Pb - 207Pb/206Pb) diagram. Cretaceous hydrothermal titanites show enrichment in Y, HREEs and depletion in TiO 2 and LREEs relative to the Triassic magmatic titanites. Primary betafite and titanite were subjected to later hydrothermal alteration. The close genetic relation between altered titanite and Ti-Fe-Nb-Pb-U mineral inclusions demonstrates that Early Cretaceous hydrothermal fluids contributed to the Nb, U and Ti remobilization. Early Cretaceous regional granitic magmatic activity brought hydrothermal fluids to alter the early carbonatite magmatic pyrochlore and titanite. U, Nb, Ti, Y, Pb and HREEs were transferred and subsequently re-precipitated into uraninite, and hydrothermal titanite. [ABSTRACT FROM AUTHOR]

Coeval shoshonitic and calc-alkaline to high-K calc-alkaline rock series were discovered in the eastern North China Craton (NCC). Here, we report zircon and titanite U Pb dating, zircon oxygen isotopic, whole-rock major and trace element and Sm Nd isotopic data for these rocks. Zircon and titanite U Pb geochronology suggests that the coeval shoshonitic to calc-alkaline mantle-derived magmas from the Jinan terrane were emplaced at ∼2.5 Ga and recorded multi-phases of metamorphic imprints. The shoshonitic series in Group I show higher K 2 O, but in contrast, the calc-alkaline to high-K calc-alkaline series (Group II) are characterized by higher Na 2 O. The two groups have enriched light rare earth elements (LREE) and depleted/nearly flat heavy rare earth elements (HREE). They also show negative anomalies in some HFSE and positive anomalies in LILE. Therefore, the geochemical data, Sm Nd and O isotopes included, show that the Jinan shoshonitic to calc-alkaline magmas were generated by melting of the metasomatized mantle at an ancient continental arc. Distinct geochemical features possibly suggest different mantle source features (metasomatic agents). The elevated zircon δ18O values imply that the weathering was significant during the end of Archean. In addition, the crustal reworking or intra-crustal recycling process played an important role in the continental crust evolution. The low-δ18O magmas documented here possibly indicate high-temperature water-rock interaction that occurs between continental crust and meteoric water. This study represents an example of co-existed shoshonitic and calc-alkaline mantle-derived magma derived from the melting of metasomatized mantle above an ancient subduction zone. Similar coeval associations of shoshonitic to calc-alkaline mantle-derived rocks, in combination with high-P granulites and crust-derived granites, may be used to constrain the ancient subduction-collisional belts. • Coeval shoshonitic to calc-alkaline intrusions from Jinan formed at ∼2.5 Ga. • They were formed by melting of metasomatized mantle at an ancient continental arc. • O isotopes imply significant weathering during the end of Archean. • The low zircon δ18O result from hydrothermal alteration by meteoric water. [ABSTRACT FROM AUTHOR]

The stratiform ferromanganese bodies in the Mesozoic chert formations of central Sikhote-Alin (Katen R., J3) and Nadanhada-Alin (Khuntseling settlement, J2–3), and the vein manganese deposit (Ktab) at the Glubinny settlement area (central Sikhote-Alin) are characterized for the first time. Jurassic primary ores occur as interlayers in clayey–siliceous units. They consist of grains and globules of Mn and Fe oxides of the psilomelane–pyrolusite group and goethite. The interlayers also contain the allogenic products of eroded sialic rocks (quartz, potassium feldspar, albite, kaolinite, muscovite, paragonite, illite, and zircon) and accessory ore minerals (monazite, sphalerite, galena, apatite, cassiterite, barite, pyrite, titanite, rutile, native silver, auricupride, cerianite, tetrahedrite, and intermetallic Cu5Zn3 and Ni7Cu4). In the vein ores, spessartine and rhodonite fill veinlets and form a matrix of tectonic breccia. Manganese oxides form crusts (up to 4 cm) on the Triassic chert lumps and blocks. They likely represent the products of oxidation and breakdown of former hydrothermal–metasomatic manganese carbonates and silicates in a supergene environment. In contrast to the manganese minerals from the stratiform ores, those of the vein ores do not contain Co, Ni, Zn, and Pb, which are involved in the sulfides and sulfoarsenides (Co-gersdorffite and Ni-cobaltite, smaltite, pentlandite, and other minerals). Magnetite; titanomagnetite; barite; chalcopyrite; pyrrhotite; galena; argentite; zircon; titanite; wollastonite; anhydrite; REE phosphates, silicates, and oxides; bismuthine; native Ag, W, Cu, Zn, and Ni; and intermetallic compounds (Cu5Zn3, (Pd, Pt)5Cu and Pd4Cu) are also recognized in the vein manganese ores. [ABSTRACT FROM AUTHOR]

[Display omitted] • •Mafic granulites in the Wuhe Complex formed in the Paleoproterozoic and were overprinted by a Mesozoic metamorphic event. • •Mesozoic metamorphic event reached amphibolite-facies (T = 677–723 ℃, P = 3.8 kbar). The Wuhe Complex in the southern section of the Jiao-Liao mobile belt (JLMB) consists of an Archean–Paleoproterozoic crystalline basement and is essential for understanding the intricate tectonic evolution history of the southeastern North China Craton (NCC). Owing to the lack of Mesozoic metamorphic ages reported from the southern section of the JLMB, it is unclear whether the Wuhe Complex experienced Mesozoic tectonothermal overprint events. Titanites are common uranium-bearing minerals for U–Pb dating and are prone to metamorphic, tectonothermal, or hydrothermal processes. Thus, titanites were used in this study to unravel late metamorphic overprint events. Mesozoic titanites from the mafic granulites of the Wuhe Complex are believed to be of metamorphic origin and have experienced amphibolite-facies metamorphism, with a temperature range T = 677–723 ℃ and a pressure of P = 3.8 kbar. Laser ablation-inductively coupled plasma-mass spectroscopy U–Pb dating and in situ U–Pb dating of titanites yielded ages of 163–112 Ma and 123 Ma, respectively. This implies that the Wuhe Complex may have experienced a Mesozoic metamorphic overprint event during the tectonic transition period (from a subduction-related compressive setting to a tectonic stretch setting). Given the large number of Mesozoic intrusive rocks distributed across the NCC, it is important to rule out the effect of late tectonothermal events when studying Neoarchean or Paleoproterozoic metamorphism in the NCC. [ABSTRACT FROM AUTHOR]