Neoproterozoic continental arc magmatism in the western Yangtze Block (South China) provides critical insights into early crust-mantle evolution during circum-Rodinia subduction-accretionary orogenesis. However, the specific processes of Neoproterozoic continental crustal growth and stratification remain unclear. Herein, we present a comprehensive synthesis of mineral chemistry, zircon U-Pb-Hf isotopes, whole-rock major and trace elements as well as SrNd isotopes from representative Neoproterozoic Igneous Intrusive Complexes (NIICs) in the western Yangtze Block, including the Tianquan (TIC; ca. 833-825 Ma) and Shimian complexes (SIC; ca. 781-779 Ma) in this study, alongside the previously reported Nanba (NIC; ca. 796-790 Ma) and Luding complexes (LIC; ca. 783-779 Ma). The NIICs comprise mafic gabbros through intermediate diorites to highly fractionated silica-rich granitoids, suggesting a coherent calc-alkaline differentiation trend. They exhibit variable but predominantly depleted whole-rock SrNd (e.g., TIC: epsilon Nd(t) = -0.08 similar to +4.55; NIC: epsilon Nd(t) = -0.60 similar to +1.91; LIC: epsilon Nd(t) = +2.35 similar to +5.10; SIC: epsilon Nd(t) = +0.50 similar to +6.07) and zircon Hf isotopes (TIC: mean epsilon Hf(t) = +7.75 similar to +11.89; NIC: mean epsilon Hf(t) = +4.33 similar to +5.66; LIC: epsilon Hf(t) = +4.03 similar to +7.69; SIC: epsilon Hf(t) = +5.69 similar to +9.81), indicating a heterogeneous mantle source metasomatized by subducted components. Combined with "crust-like" trace element signatures, systematic whole-rock compositional variations, and hornblende P-T estimates, the NIICs represent middle-upper crustal sections, which underscore a three-stage evolution for Neoproterozoic continental arc crustal growth and fractionation: (1) the generation of primary basaltic melts from heterogeneous metasomatized mantle source infiltrated by subducted components; (2) the long-lived supply of metasomatized mantle-derived melts, magma mixing, and polybaric crystallization-driven differentiation within a trans-crustal magmatic system; and (3) extraction of high-silica melts in a shallow mush reservoir. Integrated with previous studies, our findings demonstrate that this complex array of petrogenetic processes-alongside the partial melting of diverse crustal sources-ultimately governed the maturation and vertical stratification of the Neoproterozoic continental arc crust in the western Yangtze Block.

Rapid uplift, denudation and recycling of continental arcs intimately link surface processes and deep crustal magmatism. However, direct petrological records of such rapid surface-crust recycling remain scarce. Here, we investigated Late Permian (256–250 Ma) granitic rocks from Hainan Island, South China, which formed within the eastern Paleo-Tethyan arc system. New elemental and isotopic data reveal a decoupling between whole-rock elemental geochemistry and oxygen isotopes in zircon. The studied rocks are metaluminous in composition (A/CNK < 1.1) and show an affinity with I-type granites. Moreover, their zircon Hf isotopic compositions overlap with those of ∼272–265 Ma mafic to intermediate arc rocks in the region, indicating their derivation from juvenile arc igneous protoliths. In contrast, their zircon δ18O values (7.83–16.06‰; mean 10.55‰ ± 0.32; 2SD) are higher than those of juvenile arc magmatic rocks (generally δ18O < 7‰) and are comparable to those of S-type granites (generally δ18O > 8‰). This implies that the protoliths of these Late Permian granitic rocks had experienced some degree of low-temperature water–rock interaction at Earth's surface. This elemental-isotopic decoupling is interpreted to reflect a rapid denudation and recycling loop within a Paleo-Tethyan continental arc. Tectonic uplift exposed juvenile igneous protoliths to surface conditions, where low-temperature water-rock interaction elevated their δ18O signatures. The weathered materials were then rapidly eroded, transported over short distances, and buried and remelted within a back-arc system. This scenario provides the most plausible explanation for the observed decoupling between whole-rock I-type mineralogical and elemental characteristics and zircon oxygen isotopic compositions in the Late Permian granitic rocks from Hainan Island, South China. Such decoupling may represent an important yet underrecognized aspect of continental arc evolution, reflecting efficient surface-deep coupling. Enhanced exposure and weathering of juvenile arc rocks likely promoted silicate weathering and potentially increased atmospheric CO₂ consumption during the Late Permian, with implications for contemporaneous climate evolution.

Felsic magmatism in Yunkai Massif, South China documents the vital transition from the paleo-Tethyan to paleo-Pacific tectonic regimes. This study integrates detailed zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd-Hf-O isotopic analyses on Phanerozoic felsic igneous rocks from the western Yunkai Massif, South China. Four magmatic episodes were identified with distinct petrogenetic and tectonic implications. The Late Ordovician to Early Silurian (456 similar to 436Ma) felsic igneous rocks are dominated by I-type granitoids sourced primarily from the early Proterozoic basement [whole-rock epsilon(Nd)(t)=-10.4 similar to-5.7, t(DM2)(Nd)=1.64 similar to 2.03Ga; zircon epsilon(Hf)(t)=-11.0 similar to-7.8, t(DM2)(Hf)=1.91 similar to 2.12Ga, delta O-18 > 7.5 parts per thousand] and formed in a post-collisional extensional setting. The Late Permian (254 similar to 253Ma) felsic rocks is characterized by high-temperature S-type granites and rhyolites with whole-rock epsilon(Nd)(t) < -5.0 and zircon epsilon(Hf)(t)=-9.7 to -6.2 and delta O-18=7.9 parts per thousand similar to 9.2 parts per thousand], recording crustal thickening and ultrahigh-temperature anatexis during the final closure of paleo-Tethyan Ocean. Coeval Jurassic (182 similar to 152Ma) low-Si syenite-monzonite and high-Si rhyolite suites (epsilon(Hf)(t)=-5.0 to +0.8) manifest the juvenile arc-ancient crust hybridization under back-arc extension induced by paleo-Pacific plate subduction. The Early Cretaceous (132 similar to 127Ma) magmatism features elevated epsilon(Hf)(t) (from +1.4 to +8.4, t(DM2)(Hf)=0.64 similar to 1.09Ga) and low delta O-18 (6.0 parts per thousand similar to 6.5 parts per thousand), signifying arc crustal melting and accretion tectonically linked to Paleo-Pacific slab rollback. Systematic isotopic evolution trends, i.e., epsilon(Hf)(t) rising from -11.0 to +8.4 and delta O-18 decreasing from >8 parts per thousand to 6.0 parts per thousand, reveal progressive crustal rejuvenation from ancient paleo-Tethyan domains to juvenile paleo-Pacific arc components. The secular trends coincide with (ca.190 similar to 180Ma) basin reorganization (EW -> NE trends) and onset of the paleo-Pacific subduction (ca.200 similar to 180Ma), marking the Mesozoic tectonic transition in South China. Our findings therefore provide robust petrogenetic constraints for decoding the multi-plate interactions and continental reconfiguration mechanisms in East Asia.

To better understand the magma sources of Changbaishan and Longgang volcanoes in northeastern China, we investigated the metasomatism and melting history of the northeastern North China Craton (NCC). Our study includes whole-rock major and trace elements, platinum group element (PGE), and ReOs isotopic analyses of peridotite xenoliths entrained in Cenozoic volcanic rocks from the Changbaishan and Longgang volcanic fields. The peridotites are predominantly lherzolites with a small proportion of harzburgite, showing variable Al2O3 contents (0.41-3.77 wt%). The more depleted samples (Al2O3 < 2 wt% & CaO < 2 wt%) yield a Re-depleted model age (T-RD) of approximately 1.80 Ga, consistent with other parts of the NCC. The peridotites exhibit increasing PGE patterns, with pronounced enrichment of Pd. The Pd enrichment in the peridotites is linked to subduction-derived materials, indicating that Pd was likely enriched through rock-melt reactions during metasomatism. Based on the tectonic setting, we propose that following the cratonization of the northeastern NCC, the lithospheric mantle remained stable and refractory for a long period until metasomatism caused by silicate melts released during ancient subductions. Additionally, these xenoliths show significant depletion in Re, Cu, and S, suggesting that after refertilization, the lithospheric mantle underwent recent low-degree partial melting. Therefore, we suggest that the magma sources for the Changbaishan and Longgang volcanic fields comprise a mixture of EM I (derived from the mantle transition zone), DMM (asthenospheric mantle), and minor EM II (lithospheric mantle).

The Yungang Grottoes located in Datong area, North China, have experienced extensive surface and structural damage. Previous studies have recognized the importance of temperature and water during weathering, but the quantitative evaluation on both the physical and chemical weathering remains absent. Here we conducted geochemical analyses on the sculpture-hosting sedimentary rocks of Shiku Member in Jurassic Yungang Formation. The results reveal that feldspar dissolution is predominant during chemical weathering, while the effects caused by other factors like calcic cement and sulphate are minor. The estimated chemical weathering rate of feldspar is 7.84 × 10−21 - 2.7 × 10−18 mol·cm-2·s−1, with an average cumulative chemical weathering amount of 1.46 × 10−11 mol·cm-2·y−1. The mass loss caused by chemical weathering is about 0.000061% per year and the annual mass loss rate is approximately 0.00015%–0.00018% when the effect of physical weathering is considered. The damage (5% mass loss) of Yungang Grottoes (450–520 AD) began in ca. AD 800 and all grottoes will be destroyed in the upcoming 4,000–5,000 years without protection. As the chemical weathering of feldspar is controlled by local temperature change, the grottoes should be accommodated in relatively constant low-temperature environment through adding eaves and air conditioners.

The coupling between the lithosphere and mantle dynamics is important for Earth's tectonic movement and deformation. Plate driving forces changing from subduction to viscous flow drag can potentially explain the continuous plate convergence where subducting slabs are detached. However, tectonic expressions in different slab detachment scenarios are inconsistent and the role of mantle flow in plate convergence remains enigmatic. Through numerical modeling, we demonstrate that plate convergence can be caused by mantle flow induced by slab detachment and regulated by lithospheric mantle-ridge interaction. Spreading ridge-trench collision has minimal effects on the deformation of overriding plates, whereas continent-trench collision can lead to substantial tectonic uplift at suture zones. Mid-ocean ridges bounding incoming plates accelerate plate motion in ridge-trench collision scenarios and induce considerable tectonic uplift in continent-trench collision scenarios, as evidenced by the acceleration of the Farallon-Pacific ridge spreading and the rapid uplift of the Himalayas after slab detachment episodes.

The origin of Fe-rich intrusion remains debatable regarding the respective role of magmatic evolution and Fe enrichment in the source. Here, we report detailed mineral and bulk-rock geochemistry of Permian-Triassic (251-250 Ma) mafic intrusions from the Tengxian area in Yunkai Massif, South China. These rocks consist of hornblende norites, show Fe-rich affinities with high FeO*(FeO* = FeOt / (FeOt + MgO) in weight ratio, >0.8, based on total iron oxide in the rock), and exhibit significant enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) but depletion in Sr and high field strength elements (HFSEs), resembling subduction-related magmas. In addition, they show remarkable features that include very high delta O-18 values in zircon (delta O-18 = 8.8-10.6 parts per thousand) and apatite (delta O-18 = 8.7-10.8 parts per thousand), and extremely enriched SrPb [e.g. Sr-87/Sr-86(i) = 0.7181-0.7196, Pb-207/Pb-204(i) = 15.77-15.78, Pb-208/Pb-204(i) = 38.95-39.05] and nonradiogenic NdHf isotopic compositions [e.g. epsilon(Nd)(t) = -11.1 similar to - 10.1, epsilon(Hf)(t) = -8.8 similar to -7.3] in bulk rocks. These characteristics distinguish the Tengxian norites from modern arc basalts and subduction-related magmas in the Paleo-Pacific Tectonic Domain. Instead, they are isotopically similar to Cenozoic Tibetan and Mediterranean potassic to ultrapotassic rocks in the Tethys Tectonic Domain. Regardless of variable influence by orthopyroxene and plagioclase accumulation, the intrinsically low SiO2 and high FeOt and Fe/Mn ratios in these rocks were likely attributed to significant contribution of a Fe-rich mantle component such as Si-poor pyroxenite, which might have formed through crystal accumulation of mafic magmas at mantle conditions. The highly evolved Sr-Nd-Pb-Hf isotopic signatures and very high delta O-18 values in zircon and apatite required substantial (10-20 %) involvement of recycled crust in the mantle source. The combined mineral and bulk-rock geochemical data suggest that the parental magmas for the Tengxian norites originated from a metasomatized mantle wedge through addition of terrigenous sediment-derived melt following the subduction of Paleo-Tethys Ocean beneath the Yunkai Massif.

The dissolution behavior of feldspar is fundamental to understand geological processes such as surface mass cycling, chemical weathering, mineral deposition and global climate change. In this study, we select oxalic acid – one of the most popular organic acids in nature as a buffer solution to simulate the chemical weathering process of feldspar under natural environments. A total of 34 fluid–feldspar reaction experiments are performed to investigate the effects of temperature, pH, and specific surface area (SSA) on the dissolution mechanism of feldspar. Based on PHREEQC modelling of saturation index of secondary minerals, we obtain the overall dissolution rate of feldspar, which is predominantly influenced by pH and temperature, with SSA exerting a secondary effect. The dissolution rates of Na, K, Ca and Si show a positive correlation with temperature and SSA, whereas that of Al exhibits a negative correlation with SSA and a weak correlation with temperature. Based on chemical reaction kinetics, the reaction order of feldspar dissolution in oxalic acid is estimated to be approximately 0.47, suggesting that the dissolution rate of feldspar is primarily controlled by a desorption process. Our new experimental results reveal that the anomalous Al dissolution behavior, which are likely due to the formation of aluminum complexes on the feldspar surface, have potentially significant for understanding the Al enrichment mechanism during the chemical weathering of the continental crust.

This paper presents a comprehensive study including petrography, zircon U-Pb dating and in-situ Hf-O isotope compositions, whole-rock major and trace element and Sr-Nd-Pb-Hf isotope compositions on two mafic intrusions from the Gaozhou region in Yunkai Massif, South China, with aims to understand their petrogenesis and tectonic setting. Zircon U-Pb dating reveals an age range of 447~451Ma, confirming their emplacement in the Late Ordovician. Samples from the Chenliukeng Village contain a large amount of amphibole and can be regarded as appinites, whereas those from the Youweiyong Village are Ca-Al-rich and Mg-rich gabbros with the occurrence of calcic plagioclase (An>95). Both types of mineral assemblage indicate that the parental magmas were hydrous subalkaline basalts probably formed at a subduction zone. The two mafic intrusions are characterized by enrichment of large ion lithophile elements (LILEs) and light rare earth elements (LREEs) but depletion in high field strength elements (HFSEs), analogues to modern arc mafic magmas. They show highly variable and enriched zircon Hf-O isotopic compositions and bulk-rock Sr-Nd-Pb-Hf isotopic features, while correlations between the bulk-rock Nb/La and Sr-Nd-Hf isotopes argue against a significant role of crustal assimilation and/or contamination. We thus conclude that the large Sr-Nd-Pb-Hf-O isotopic variations reflect the different proportional addition of recycled crustal components in the mantle sources. Further zircon Hf-O isotope modelling results show that the melting source for the appinites likely contained 20%~50% of the subducted terrigenous sediment, while the proportion of this recycled sediment component in the source of gabbros was 35%~45%. Based on the paleogeographic reconstruction that the Yunkai Massif was ever located between the Proto-Tethys Ocean and the East Gondwana continent during the Late Ordovician, we consider the subduction of Proto-Tethys Ocean as a likely mechanism to interpret the petrogenesis of contemporaneous arc mafic magmatism in the study region. Following the subduction, the terrigenous sediments had been dehydrated and melted to enrich the overlying mantle wedge, which experienced hydrous melting to form the water-rich subalkaline basaltic magmas. The subsequent fractional crystallization and/or accumulation generated the appinites and Ca-Al-rich and Mg-rich gabbros. Our results therefore provide key geochronological and petrological evidence for the subduction of Proto-Tethys Ocean beneath the Yunkai Massif during Early Paleozoic.

Benxi formation, Yanchang gas field in Ordos Basin, is rich in natural gas resources, but the sedimentary environment is complex, the lateral changes of sand bodies are rapid, and the continuity of gas reservoirs is poor. Exploring its sand body types and development models can provide useful reference for oil and gas exploration in this area. Based on core observation and logging data analysis, the characteristics of sedimentary microfacies in Benxi formation are studied. The results show that Benxi formation is a barrier coastal deposit, and three types of deposits can be further identified: barrier bar, lagoon and tidal delta. From west to east, the area shows the change law of lagoon-barrier sand bar-shallow sea shelf. Barrier coast deposits were formed by wave and tidal transformation in the northern and southern deltas of the basin under the control of ancient uplift, and their evolution was mainly influenced by the central ancient uplift and climate. The research results are of theoretical and practical significance for perfecting the sedimentary model of coastal system affected by tides and predicting the distribution law of favorable reservoirs in barrier bar.

A-type granites generally have much lower water, higher temperature, and incompatible element concentrations than I-type granitoids. Yet it remains unclear why I-A-type granitic complexes occur in convergent plate margins. Here we conduct geochemical analyses on apatite and mafic minerals from the late Cretaceous I-A-type granitic complex in Fuzhou area, SE China, aiming to decipher differentiation, fluid metasomatism, and degassing that primarily control the compositional diversity of felsic magmas. Apatites in both rock types are F-rich and show large H2O and delta D variations, i.e., 341-3892 ppm H2O and -325 to +336 parts per thousand delta D in I-type granitoids; 67-1366 ppm H2O and -251 to +1439 parts per thousand delta D in A-type granites. H2O in apatite is negatively correlated with La/Sm and Sr/Y in the I-type granitoids, whereas it is positively correlated with Ce and total rare earth element (REE) concentrations in the A-type granites. Once H2O increases up to hundreds of ppm, both rock types show a rapid decrease of H2O/Ce, an increase of F/Cl, and extensive H isotope fractionation. Arfvedsonite occurs as a late crystallizing mineral in the A-type granite and has much higher contents of Na2O, K2O, F, and high field strength elements (HFSE) than hornblende in the I-type granitoids, indicating the addition of F-HFSE-rich alkaline fluids during its magmatic evolution. The consumption of arfvedsonite and formation of aegirine further indicate the role of fluid metasomatism and H-2 degassing via a reaction of 3Na(3)Fe(5)Si(8)O(22)(OH)(2) + 2H(2)O = 9NaFeSi(2)O(6) + 2Fe(3)O(4) + 6SiO(2)+5H(2). The combined geochemical data demonstrate that the systematic differences in mineral assemblage, whole-rock composition, magma temperature, H2O content, and delta D of apatite between the I- and A-type granites are likely attributed to varying degrees of differentiation, fluid metasomatism and magmatic degassing. The I-type granitoids experienced hornblende, biotite, plagioclase, K-feldspar, and apatite fractionation and close-system degassing. The A-type granite was likely formed from the I-type monzogranitic magma that was metasomatized by the mantle-derived F-HFSE-rich alkaline fluids to produce the peralkaline magma, which further experienced K-feldspar + plagioclase + biotite + apatite fractionation and open-system degassing. Further numerical estimation indicates that the primary magma of Fuzhou granitic complex contained similar to 3.0 wt% H2O, and the lower water content of A-type granite was likely attributed to strong degassing during its emplacement. Our results indicate that some peralkaline A-type granites can be generated from relatively water-poor I-type granitic magmas by fluid metasomatism and degassing.

The early Triassic (~250 Ma) hornblende gabbro from the Tengxian area of Yunkai Massif, South China, contains a mineral assemblage of clinopyroxene, hornblende, biotite, plagioclase, K-feldspar and quartz and accessory apatite, and zircon and ilmenite. Based on mineral association and crystallization sequence, two generations of the mineral assemblage have been identified: clinopyroxene + plagioclase + apatite (zircon) in Generation I and ilmenite + hornblende + biotite + K-feldspar + quartz in Generation II. The high crystallization temperature (T = 999–1069 °C) of clinopyroxene and its coexistence with labradorite (An = 52–58) indicate that Generation I crystallized in a basaltic magma, while the hornblende’s relatively low crystallization temperature (T = 780–820 °C) and coexistence with K-feldspar and quartz suggest that Generation II formed in an evolved alkaline melt. The mineralogical records are likely attributed to pulsed intrusion of the late-stage evolved magma into a crystal mush, like in Generation I. The bulk-rock geochemical data include a sub-alkaline affinity, arc-type trace element features, and highly enriched Sr-Nd-Pb-Hf isotopic compositions, consistent with the isotopic records from the accessory minerals, e.g., the very high δ18O values in both zircon and apatite and significantly negative εHf(t) in zircon. The combined mineral and bulk-rock geochemical data suggest that the primary magma for the Tengxian hornblende gabbro was derived from a mantle wedge that had been metasomatized by voluminous subducted terrigenous sediment-derived melts in response to subduction of the Paleo-Tethys Ocean.

We conduct a comprehensive study including bulk -rock and mineral geochemical analyses, Rhyolite-MELTS and phase equilibrium modeling on Caledonian (422-436 Ma) granitic plutons from the Yangchun region of Yunkai Massif, South China, aiming to estimate the melting P-T-H 2 O conditions and decipher the mechanism for crustal anatexis. These rocks are typical S -type granites with presence of muscovite and garnet, resembling those plutons in the European Variscan Belt. The Rhyolite-MELTS modeling yields a crystallization sequence of quartz, plagioclase, K -feldspar, biotite and muscovite. Apatite shows homogeneous texture and occurs as columnar euhedral to subhedral crystal hosted in plagioclase and mica. Further Nd isotope analyses on apatite yield highly nonradiogenic Nd compositions with an e Nd (t) from -14.3 to -8.2 and a T DM2 Nd range of 1.83-2.33 Ga, which are obviously less radiogenic than the bulk -rock e Nd (t) (-8.4 - -7.1) and T DM2 Nd (1.75-1.85 Ga). The zircon crystals span a wide e Hf (t) range from -13.0 to +0.8 and T DM2 Hf range of 1.36-2.22 Ga. The remarkable Nd isotopic difference between the bulk granite and apatite, systematic bulk -rock e Nd (t) variations against SiO 2 , P 2 O 5 and Sm/Nd, and the large e Hf (t) variation of zircon in these S -type granites are likely attributed to disequilibrium melting of Proterozoic heterogeneous crust, during which residual garnet and apatite had been variably entrained in the anatectic melt. Further phase equilibrium modeling indicates that the melting conditions of Yangchun S -type granites include metasedimentary protoliths, -5.0 wt% water, P = 6-7 kbar, T = 700-800 degrees C, with a geothermal gradient of 35-40 degrees C/km. The estimated residual apatite and garnet are 0.07-0.10 wt% and 3.8-9.0 wt% in the protoliths, respectively. The combined results therefore suggest a relatively hot crust across the Yunkai Massif, probably due to mantle upwelling and crustal extension during early to middle Silurian.

The lunar magma ocean (LMO) hypothesis predicts that the uppermost mantle (-60-100 km) is composed of ilmenite-bearing cumulate (IBC), which may have sunk deeply due to gravitational instability. However, the extent to which this process restructured the lunar mantle and influenced mare volcanism remains unclear. Here, we approach this issue by examining pyroxenes in Chang'E-5 (CE5) basalts and petrological modeling. We show that the low Mg# and negative anomalies in Ti and Ta of CE5 basalts cannot be produced by extensive fractionation of peridotite-derived low-Ti basalts, but were most likely formed through partial melting of a shallow (< 100 km) IBC pyroxenite source. This model is also applicable to the -3.0 Ga lunar basaltic meteorites. The increasing involvement of IBC sources in young lunar magmas, also revealed by the remote-sensing data, implies an inefficient gravitational restructuring process during the late LMO stage and provides new insights into the thermochemical state of the lunar interior.

South China block contains abundant rare metal resources that have widely been considered to be associated with highly evolved granitic magmatism and related fluid metasomatism. Here we perform detailed geochemical analyses on apatite and bulk rock from the ore-bearing granites (equigranular zinnwaldite granite) and ore-barren granites (porphyritic biotite granite and granitic dyke) at Qianlishan pluton, South China, to decipher the respective roles of magmatic and fluid processes and further understand the petrogenesis of rare metal granite (RMG). Apatites from both granite types are F-rich, displaying heterogeneous textures and large compositional variations in Cl, Sr, rare earth elements (REEs), Ga, Th, and U. Relative to the ore-barren granite, the apatites from ore-bearing granite contain lower Sr but higher & sum;REE, Th + U and Ga, reflecting more evolved features. The oscillatory compositional zonation and bimodal O-Nd isotopic compositions in apatite from the ore-barren granite indicate multiple-pulse intrusion instead of other open-system processes such as magma mixing and/or crustal assimilation during magmatic evolution, while the additional occurrence of monazite and lower delta O-18 (< 8 parts per thousand) in half of the apatite crystals from the ore-bearing granite require further influence of hydrothermal metasomatism. In combination with their high W + Sn concentrations and La tetrad effect in chondrite-normalized REE patterns, the ore-bearing granite experienced extensive metasomatism, during which the fluids in equilibrium with the metasomatic apatite were likely magmatic in origin. We therefore suggest that multiple-pulse magmatic intrusion and fluid metasomatism are two predominant factors during the formation of highly evolved RMG, such as the Qianlishan pluton in South China. Our results demonstrates that apatite geochemistry can be a potential approach to monitoring the magmatic evolution and fluid metasomatism during rare metal mineralization.

Detailed sedimentary microfacies research is important to determine favorable target areas for oil and gas exploration. In order to clarify the sedimentary microfacies characteristics of Chang 7 in the Ordos Basin, the types and distribution of Chang 7 sedimentary microfacies were studied using logging, core, analysis and testing data. The results show that delta facies is developed in the Chang 7, mainly in the delta front subfacies, including distributary channel, natural levee, interdistributary bay and mouth bar. The underwater distributary channel sand body, as the skeleton sand body, is relatively well developed and is the main place for oil and gas accumulation. The thick fine sediments in Chang 7 sedimentary period are mainly mudstone and silty mudstone. Multi channel sand bodies and extremely thick fine-grained rocks form a high-quality source reservoir cap rock association.