Geological and geochemical characteristics of the Miaoya syenite-carbonatite complex, Central China: Implications for the origin of REE-Nb-enriched carbonatite

Journal Pre-proofs Geological and Geochemical Characteristics of the Miaoya Syenite-Carbonatite Complex , Central China:Implications for the Origin of REE-Nb-enriched Carbonatite Jian-Hui Su, Xin-Fu Zhao, Xiao-Chun Li, Wei Hu, Mi Chen, Yi-Lin Xiong PII: DOI: Reference:

S0169-1368(19)30353-1 https://doi.org/10.1016/j.oregeorev.2019.103101 OREGEO 103101

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Ore Geology Reviews

Received Date: Revised Date: Accepted Date:

23 April 2019 27 August 2019 29 August 2019

Please cite this article as: J-H. Su, X-F. Zhao, X-C. Li, W. Hu, M. Chen, Y-L. Xiong, Geological and Geochemical Characteristics of the Miaoya Syenite-Carbonatite Complex , Central China:Implications for the Origin of REENb-enriched Carbonatite, Ore Geology Reviews (2019), doi: https://doi.org/10.1016/j.oregeorev.2019.103101

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Geological and Geochemical Characteristics of the Miaoya Syenite-Carbonatite Complex , Central China：Implications for the Origin of REE-Nb-enriched Carbonatite Jian-Hui Su1, Xin-Fu Zhao1*, Xiao-Chun Li2, Wei Hu1,3, Mi Chen4, Yi-Lin Xiong4 1

State Key Laboratory of Geological Processes and Mineral Resources, and School of

Earth Resources, China University of Geosciences, Wuhan 430074, China 2

Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR,

China 3

No.4 Geology Team of Guangxi Zhuang Autonomic Region, Nanling, 530033, China

4

Geological Survey of Hubei Province, Wuhan 430034, China

* Corresponding author: Xin-Fu Zhao Email: [email protected]

Abstract Carbonatites are well known as economic resources for rare metals, such as rare earth elements (REE) and Nb. However, the origin and evolutionary processes of carbonatites and related silicate rocks as well as the relevant rare metals enrichment mechanism are highly controversial. In this study, we present detailed petrographic observations and geochemical data on the Miaoya syenite-carbonatite complex, which hosts both Nb and REE resources. The Miaoya syenites consist predominantly of K-feldspar, with minor zircon, nioboaeschynite, pyrochlore, and Fe-Ti oxides, and have positive Nb, Ta, Zr and Hf anomalies on primitive mantle-normalized patterns. There are two types of carbonatites at the Miaoya Complex: calciocarbonatites and ferrocarbonatites. Calciocarbonatites consist mainly of calcite, apatite, and biotite, together with allanite, monazite, bastnäsite(-Ce), and parisite-(Ce). Ferrocarbonatites which are the later products of the complex and occur as dykes cutting both calciocarbonatites and syenites, contain ankerite, calcite, apatite, and fluorite, bastnäsite-(Ce), and parisite-(Ce). The carbonatites have lower Nb, Ba, U, Th, and Zr, but higher P, Sr and REE concentrations than the associated syenites. However, both rock types have similar zircon U-Th-Pb ages (430-440Ma), and nearly identical initial 87Sr/86Sr ratios (0.70325 to 0.70413) and εNd(t) values (2.5 to 3.2), implying that they were derived from a common source of carbonated silicate magmas. A genetic model of combined fractionation and immiscibility is proposed for the Miaoya complex. Fractionation of the carbonated silicate magmas lead to Nb

enrichment in syenite and the immiscibility of the parental calcium carbonatite melts when the magmas reached a carbonate saturation level, together with partitioning of P, Sr, and REE into the parental carbonatite melts. During further fractionation of the carbonatite melts, REE components were elevated to economic values in the final ferrocarbonatites. This model can be widely applicable to other alkaline-carbonatite complexes and provides a reasonable explanation for extreme enrichment of rare metals in such rocks. Key words: syenite-carbonatite complex; magmatic evolution; rare earth elements; enrichment mechanism of rare metals

1. Introduction Carbonatites have attracted more and more attentions due to the economic interests of rare metals, such as REE and Nb. Until now, more than 527 carbonatite occurrences have so far been recorded in the world (Woolley and Kjarsgaard, 2008). However, only about 30 mineralized carbonatites host economic resources of REE and Nb (Verplanck et al., 2016; Woolley and Kjarsgaard, 2008). Radiogenic isotope studies have confirmed that carbonatites are derived from the mantle (Bell and Blenkinsop, 1989). But the mechanism that leads to ore-grade enrichments of Nb and REE in carbonatite is still in a matter of debate. Several processes have been proposed to be responsible for rare-element mineralization in carbonatites, including liquid immiscibility, fractional crystallization, and hydrothermal processes (Linnen et al., 2014; Verplanck et al., 2016). Precursory igneous processes in carbonatites are essential for contributing to their

unusual trace-element signatures. Carbonatites are typically associated with alkali silicate igneous rocks, such as melilitite, nephelinite, ijolite, and syenite (Barker, 1989). Experimental results have confirmed that carbonatite can be generated from parental carbonated silicate melts via either fractional crystallization or liquid immiscibility (Freestone and Hamilton, 1980; Gittins, 1988; Hamilton, 1989; Kjarsgaard and Hamilton, 1988; Pirajno et al., 2014). Liquid immiscibility has often been advocated because field and isotopic evidence has revealed intimate relationships between many carbonatite intrusions and their associated silicate rocks (Barker, 1989). However, the behavior of various trace elements, particularly rare

metals, during evolution in natural carbonatites is inconsistent with the experimental data (e.g., Veksker et al., 1998, 2012). Veksker et al. (1998) have experimentally shown that most REE, except for La, partition preferentially into silicate liquids during

the

immiscibility

of

carbonatite

melts.

Recent

experiments

on

carbonate/silicate liquid-liquid D values have also confirmed that Nb, Zr, REE, Th and U are enriched in silicate melts (Veksler et al., 2012). Such experimental data appear to be inconsistent with the enrichment of REE in most carbonatite complexes (Castor, 2008; Mariano, 1989), leading to doubts on the validity of the immiscibility model. But numerous published experimental results and melt inclusion studies on major element compositions have suggested that calciocarbonatite can be produced by liquid immiscibility from silicate liquids (Guzmics et al., 2011, 2012; Lee and Wyllie, 1998; Panina and Motorina, 2008), an interpretation supported by the fact that most carbonatites worldwide are Ca-rich (Jones et al., 2013; Woolley and Kempe, 1989). Therefore, there is a knowledge gap on whether liquid immiscibility process promote concentrations of rare metals in carbonatite melts. Previous studies in Mountain Pass have confirmed that primary REE-bearing mineral phases such as bastnäsite can crystallize from the magma. But hydrothermal processes have been regarded as indispensable for most REE deposits, such as Bayan Obo (Smith et al., 2015), Maoniuping (Xie et al., 2009, 2015), Amba Dongar (Doroshkevich et al., 2009) and Bear Lodge (Moore et al., 2015). The ligands in fluids such as F–, OH–, Cl–, SO42–, CO32–, and PO42– likely play a key role in removing REEs from magmatic systems. In addition, both field evidence and experimental data

confirm that the normal fractionation trend of carbonatites is from Ca-carbonatite to Fe-carbonatite (Gittins, 1989; Le Bas, 1989), and that REE are always enriched in the late stage Fe-carbonatites. These Fe-carbonatites are very enriched in volatiles, representing the residual magma or carbohydrothermal residual (Mitchell, 2005). In brief, carbonatite related REE-Nb deposits likely involve a complicated evolution related to both magmatic to hydrothermal processes. To better understand the origin of carbonatite and enrichment mechanism of rare metals, it requires detailed petrographic and geochemical studies on natural carbonatites and their associated alkaline rocks, and compares how such data can be reconciled with experimental studies. The Miaoya syenite-carbonatite complex is located in South Qinling belt, central China, which hosts both Nb and REE resources just like the Bayan Obo deposit (Li, 1980; Xu et al., 2010). Since its first discovery by Li (1980), the Miaoya Complex has attracted many researchers (Xu et al., 2010; Ying et al., 2017; Zhu et al., 2016; Zhang et al., 2019). Xu et al. (2014, 2015) suggested that the carbonatitic magma in Miaoya was generated directly in the mantle and has no co-genetic origin with syenite. This assumption can ideally account for zircon from the syenites yields an age of 766 ± 25 Ma, while the age of monazite from the carbonatites is 233.6 ± 1.7 Ma (Xu et al. 2014). However, Ying et al. (2017) indicated that zircon with Neoproterozoic age in syenite was inherited from calc-alkaline granitic rocks. New studies from Zhu et al. (2016) and Ying et al. (2017) suggested that the Miaoya complex was firstly emplaced in the Early Silurian (440-430Ma) during the opening of the Mianlue Ocean (Wu et al. 2013). Then, research by Ying et al. (2017) and

Zhang et al. (2019) also recorded a monazite age at ~230Ma, which was interpreted to represent a metasomatic event during the Triassic. Although several geochronology and geochemical studies have been carried on Miaoya complex, the genesis of carbonatite is still unclear, which hinders our understanding how magmatic processes control REE and Nb enrichment in carbonatites and alkaline magmas. Here, we present a comprehensive study of the geology, mineralogy, and geochemistry of the Miaoya syenite-carbonatite complex. Our new dataset allows us to propose a new genetic model for the origin of carbonatite and the enrichment of REE and Nb in these rocks, which can be also widely applied to other REE-Nb mineralized carbonatites worldwide. 2. Geological Background The Miaoya Complex is located in the southern margin of the Qinling Orogen, Central China. The Qinling-Dabie Orogenic Belt extends east-west for nearly 2500 km across Central China and marks a suture zone between the North and South China Blocks (Fig.1a-b). The belt is further divided into the North Qinling belt and the South Qinling belt along the Shangdan suture (Fig.1b). Previous studies proposed that the belt was formed by northward subduction of the Shangdan oceanic crust and subsequent collision between the North China Block and South Qinlin Terrane (Meng and Zhang, 1999). U-Pb isotopic ages obtained from ophiolites and related volcanic rocks indicate formation of the late Paleozoic to Middle Triassic Mianlue Ocean, which separated the South Qinling orogen from the South China block. The closure of the Mianlue Ocean during the early-middle Triassic led to the final collision of the

North China and South China Blocks (Meng and Zhang, 1999). Silurian magmatism has been widely reported in the South Qinling Belt (Fig.1c), including 450-400-Ma ultramafic to mafic dyke swarms, 440-430-Ma trachytes in the Ziyang-Lang’ao area (Zhang et al., 2007), ca. 430-Ma Tianbao trachytes (Chen et al., 2014), the ca. 440-Ma Shaxiongdong (Xu et al., 2008), and the 440-430-Ma Miaoya syenite-carbonatite complex (Ying et al., 2017; Zhu et al., 2016). The origin of the magmatism has been attributed to a Silurian rifting event along the northern margin of the Yangtze Block during opening of the Paleotethyan Ocean (Dong et al., 2011; Wu and Zheng, 2013). 3. Geology of the Miaoya Complex The Miaoya complex forms an elliptical body about 3km long and 0.5-0.8km wide exposed at the surface (Fig.2). The complex intrudes early Silurian sedimentary and volcanic rocks, including carbonaceous slate and weakly metamorphosed tuff in the northern part, and Precambrian sedimentary and volcanic rocks in the southern part (Fig.2). It is well exposed on both sides of the Wenyu River, which splits the complex in the geological map (Fig.2). It consists predominantly of syenite with local outcrops of carbonatite in the southern part (Fig.2). The carbonatites are divided into calciocarbonatites and ferrocarbonatites varieties. The good outcrops reveal a close spatial association between the carbonatites and silicate rocks (Fig.3a-c). Although carbonatites locally intrude the syenites as veins, most of the syenites contain pervasive microscopic aggregations of calcite (Fig.3b), suggesting that they are coeval phases. The ferrocarbonatites occur as dykes (<10cm-0.5m wide) in the northern part

of the complex and cut all other types of rocks (Fig.3f). The complex has a measured reserve of ~1.21Mt TREE (~1.73wt. %) and ~0.93 Mt Nb2O5 (~0.12wt. %). According to a geological survey report (Ma, 1981), Nb and REE have mineralized zones which are associated with specific lithofacies. Syenite and calciocarbonatites host most of Nb ores, whereas REE mineralized zones are coincident with distribution area of carbonatite (Fig.2). Ferrocarbonatites have the highest grade REE, and occur mostly in southern part of the complex. Important Nb minerals are pyrochlore and columbite, and main REE minerals include allanite, monazite, bastnäsite-(Ce), and parisite-(Ce) (Li, 1980; Ma, 1981; Xu et al., 2010). In addition, zirconium and phosphorus are also locally enriched as associated resources in the Miaoya deposit because zircon and apatite are abundant in syenites and calciocarbonatites, respectively. 4. Petrography 4.1 Syenites Fresh syenites in the complex consist mainly of potassium feldspar with zircon, Nb-bearing minerals, and Fe-Ti oxides as accessory minerals. Euhedral K-feldspar crystals constitute over 70 vol. % of the rock, and are classified as orthoclase and microcline based on their microstructures (Fig.4a-b). Many feldspar crystals are partly altered to sericite (Fig.4a-b). Zircon occurs as individual grains or mineral aggregates; individual crystals (0.2-1mm long) are euhedral to subhedral, and are locally fractured (Fig.5b). Trace nioboaeschynite, pyrochlore and columbite are the main Nb-bearing minerals. Iron-titanium oxides include ilmenite, magnetite, and trace amounts of rutile,

and are mostly anhedral in shape. In the northern part of the intrusive complex, syenites locally have porphyritic textures (Fig.2, Fig.4c), in which K-feldspar phenocrysts up to 2mm long are set in a finer-grained K-feldspar groundmass (Fig.4c). 4.2 Calciocarbonatites Calciocarbonatites consist mainly of calcite, accompanied by variable amounts of apatite and biotite, minor REE-bearing minerals and trace amounts of magnetite, ilmenite, and columbite. Euhedral-subhedral calcite is poikilitic with variable sizes. The medium-size grains are 1-3 mm in diameter with obvious core-rim textures under OM-CL imaging, which are characterized by relatively bright orange color cores gradually fading to dark orange rims (Fig.4e). The relatively fine-grained calcites (0.5mm) are homogeneous and have weak core-rim textures (Fig.4e-f). Several carbonatite bodies have coarse to pegmatitic calcite grains (>3mm), which have core-rim textures similar to those of medium-grained calcites described above (Fig.4i). Biotite is unevenly distributed through the rocks and locally shows banded structures (Fig.3d). Most grains are euhedral and >1mm in length. Apatite is also inhomogeneously distributed in the rocks and can constitute up to 20 vol. % of some samples. The apatite occurs as individual, ovate grains up to 0.5mm long and/or in lumpy to banded aggregates. Apatite grains are green to blue under CL imaging (Fig.5e-f), similar to magmatic apatite in carbonatites around the world (Hornig-Kjarsgaard 1998). Rare earth element-bearing minerals, including allanite, monazite, bastnäsite-(Ce), and parisite-(Ce), make up 1-5% vol. of the rocks. Most

allanite grains are euhedral to subhedral (Fig.6b), and are locally associated with biotite (Fig.6c). They can be cracked and locally replaced by REE-bearing carbonate minerals, e.g., bastnäsite-(Ce) (Fig.6b). Allanite-quartz veinlets locally crosscut calcite crystals and interstitial material (Fig.6d). Two texturally distinct types of monazite

are

recognized:

sparse,

relatively

large,

(>100um)

isolated

euhedral-subhedral grains (Fig.6e), and abundant, fine-grained, anhedral crystals that occur in veinlets or as interstitial grains (Fig.6f). In addition, small quantities of bastnäsite-(Ce) and parisite-(Ce) are associated with vein or moniliform monazite assemblages (Fig.6h). Columbite is the main Nb-bearing minerals in carbonatites and are locally associated with apatite (Fig.6a). 4.3 Ferrocarbonatites The ferrocarbonatites are slightly oxidized with dark orange or brown colors in outcrops (Fig.3f). They occur as dykes cutting calciocarbonatites and syenites, and are mainly composed of ankerite and calcite with accessory apatite, fluorite, bastnäsite(-ce), parisite-(Ce), and monazite (Fig.4j, Fig.6i). Bastnäsite(-ce) and parisite-(Ce) are associated with fluorite (Fig.6j). All the minerals are typically fine-grained and anhedral. 4.4 Carbonatite metasomatism Fenitization has not been reported in the Miaoya Complex, but the complex has widespread carbonate alteration. Syenites have been pervasively metasomatized by carbonatitic melts resulting in a slightly grey in color in the field. Altered syenites contain ankerite, calcite, apatite, and rare earth minerals, all of which are interstitial to

K-feldspar (Fig.5c-d). Under OM-CL imaging, the K-feldspars have blue to purple color cores surrounded by irregular dark rims (Fig.5a), which are associated with calcite, ankerite, and apatite. Zircon grains also show metasomatic textures in OM-CL images; pristine magmatic crystals have dull blue colors, whereas the altered grains have bright yellow-green rims (Fig.5b). Some extremely metasomatized zircon grains exhibit only bright yellow-green colors and they contain abundant inclusions of calcite, ankerite, apatite, and REE-bearing minerals, suggesting carbonatitic melt metasomatism. Locally, K-feldspar and zircon grains are present in the calciocarbonatites (Fig.4f, Fig.5e-f). These grains have OM-CL colors and textures similar to those in the altered syenites, and were likely inherited from the earlier carbonated silicate melts. 5. Analytical Methods 5.1 Optical microscopy cathodoluminescence (OM-CL) analysis Polished thin sections of representative samples were examined by OM-CL, using a Leica DM2700P microscope coupled with a CITL MK5-2 system, at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. The system was operated at 13 kV accelerating voltage and a current density of about 350μA. 5.2 Zircon U-Th-Pb dating analysis Two samples including a fresh syenite (16MY-21) and a carbonatite (14MY-37) are prepared for Zircon U-Th-Pb dating analysis. In situ U-Th-Pb isotopic compositions for zircon from syenite are determined on polished thin section, and

zircon grains were separated from the carbonatite samples and mounted using resin. Zircon separation was carried out by conventional magnetic and density techniques for concentration of non-magnetic heavy fractions. Typical zircon grains were then handpicked under a binocular microscope, mounted in epoxy, and polished to half their thickness. The morphologies and internal structures were examined with transmitted and reflected light microscopy and by SEM-CL imaging prior to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). U-Pb dating of the zircon was conducted by LA-ICP-MS at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. An Agilent 7500a ICP-MS instrument was used to acquire ion-signal intensities while laser sampling was performed using a GeoLas 2005. Detailed operating conditions for the laser ablation system and the ICP-MS instrument and for data reduction are described by Liu et al. (2008, 2010) and are briefly summarized here. Helium was applied as a carrier gas and argon was used as the make-up gas. Zircon 91500 (Wiedenbeck et al., 1995) was used as an external standard for U-Pb dating, and was analyzed twice every 5 analyses. The zircon standard GJ-1(Jackson et al., 2004) was analysed as an unknown for data quality control. Each analysis incorporated a background acquisition of approximately 20-30 s (gas blank) followed by 50 s of data acquisition from the sample. Off-line selection and integration of background and analytic signals, and time-drift correction and quantitative calibration for trace element analyses and U-Pb dating were performed by ICPMSDataCal (Liu et al., 2008, 2010). The Concordia diagram and weighted mean U-Pb ages were plotted and

calculated using the ISOPLOT/EX 3.23 software package (Ludwig, 2003). During analysis, standard GJ-1 yielded a weighted

206

Pb/238U age of 602 ± 1.1 Ma (1σ),

which is in good agreement with the recommended age (Jackson et al., 2004). 5.3 Whole-rock major and trace element analysis Major and trace elements of whole-rock samples were determined at ALS Minerals- ALS Chemex, Guangzhou. The samples were crushed and powdered in an agate ring mill to pass a 200 mesh sieve. For major elements, about 1g of calcined sample was mixed with lithium borate flux (Li2B4O7 – LiBO2) and fused in an auto fluxer at about 1000°C to form a flat glass disc for analysis by X-ray fluorescence spectrometry (XRF). For the trace element analyses about 50mg of sample was mixed with the lithium boron flux and fused at 1025°C. The resulting glass was dissolved in an acid mixture containing nitric, hydrochloric and hydrofluoric acids and the solution was analyzed by ICP-MS. Major and trace element determinations were carried out using a Philips PW 2400 XRF and an Agilent 7500a ICP-MS, respectively. Analyses of rock standards indicate a precision and accuracy typically better than 2% and 5%, respectively, for the major and trace elements. 5.4 Electron microprobe analysis (EMPA) Quantitative EMP analyses were performed using a JXA-8230 Superprobe equipped with wavelength-dispersive spectrometers at the Center of Material Research and Analysis, Wuhan University of Technology (WUT). The instrument was set to operate at an accelerating voltage of 15 kV and a beam current of 20 nA. The standards used in this study included: orthoclase for K, albite for Na, almandine for Si

and Al, diopside for Ca, hematite for Fe, celestite for Sr and barite for Ba for feldspars; and calcite for Ca, hematite for Fe, diopside for Mg, rhodonite for Mn, and celestite for Sr for carbonate minerals. Data were corrected using the internal ZAF correction program (Armstrong, 1991). Oxygen was calculated from cation stoichiometry, and the feldspar chemical formula was calculated based on 8 cations, whereas the carbonates were calculated on the basis of 6 cations. 5.5 Carbon and oxygen isotopic analyses Carbon and oxygen isotopic compositions of calcite from the carbonatites and the associated syenites were measured at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, using a MAT251 isotope ratio mass spectrometer. Carbonate minerals were dissolved by phosphoric acid at 25°C for 12 hours (McCrea, 1950). The carbon-oxygen isotopic results are expressed as per mil variation relative to PDB and SMOW, respectively. 5.6 Whole-rock Sr-Nd isotopic analyses Whole-rock Sr-Nd isotopic compositions were conducted at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. Sr isotopic compositions were determined on a Triton Ti TIMS and Nd isotopic compositions were determined by a Neptune plus MC-ICP-MS. Measured 146

87

Sr/86Sr and

143

Nd/144Nd ratios were normalized to

86

Sr/88Sr=0.1194 and

Nd/144Nd=0.7219, respectively. During analysis, the NBS987 and BCR-2 standard

yielded

87

Sr/86Sr=0.71025±0.00008 (2σ) and

143

Nd/144Nd=0.512643±0.000015 (2σ),

respectively. εNd(t) and (87Sr/86Sr)i ratios were calculated using the U-Pb zircon age

from the calciocarbonatites from this study. 6. Results 6.1 Zircon U-Th-Pb ages Zircon grains in syenite are euhedral and most over 200μm long. Zircon grains also show complicated textures in OM-CL images for carbonatitic melt metasomatism. Primary magmatic crystals have dull blue colors, whereas the altered grains have bright yellow-green rims (Fig.5b). Zircon grains in syenites are U-poor (most<70ppm) and Th-rich (most>3000 ppm) (Table1), and hence most of grains yield discordant U –Pb ages. However, they have consistent and reliable Th-Pb ages. Fifteen analyses on the cores and 5 analyses at the rims yielded similar Th-Pb ages within errors (Table 1). All 20 analyses have a weighted mean Th-Pb age of 443 ± 4 Ma (N = 20; Fig. 7a). This age is therefore considered to be the crystallization timing of Miaoya syenite. Sample 14MY-27 of coarse-grained calciocarbonatite was collected for zircon U-Pb dating (Table 2). The zircon grains are large and euhedral, and have complex textures under OM-CL and SEM-CL imaging. Pristine magmatic crystals have dull blue colors under OM-CL imaging and are dark in SEM-CL images with magmatic oscillatory zoning (Fig.7b). Altered grains have rims with bright yellow-green colors in OM-CL images corresponding to brighter domains under SEM-CL imaging. The cores have higher Th and U contents (Th up to1229ppm; U up to124ppm) than rims (Th: 289ppm; U: 47ppm).

Thirteen analyses on the cores and 4 analyses at the rims

yielded undistinguished U-Pb ages (Table 2, Fig.7b). All 17 analyses yielded concordant and consistent ages on the Concordia diagram, with a weighted mean

average age of 428±3Ma (MSWD=0.44, N=17) (Fig.7b). 6.2 Whole-rock chemistry 6.2.1 Major elements A completely fresh syenite sample (16MY-21) contains SiO2 (55.3wt. %), Al2O3 (18.0wt. %), Fe2O3 (2.90wt. %), MgO (1.42wt. %), and low CaO contents of 3.25wt.% (Table3). It is high in K2O (11.8wt. %) with very low Na2O/K2O ratios of 0.05. However, most of the syenites have been metasomatised by carbonatitic melts (Fig.5a-d). These samples (MY-22, MY-26) have much higher CaO and Fe2O3 but lower SiO2 and K2O than the pristine rocks (16MY-21). The higher CaO and Fe2O3 contents are consistent with the presence of more calcite and ankerite in the carbonatised syenites. The carbonatites are low in silica (SiO2<10 wt. %) and exhibit a wide range in CaO (34.7-51.4 wt. %), Fe2O3 (1.93-5.36 wt. %), and MgO (0.20-1.48 wt. %) contents (Table3). The nonvolatile components of calciocarbonatite are mainly CaO and the samples show high CaO/(CaO+MgO+Fe2O3+MnO) ratios of 0.85-0.96. In contrast, the ferrocarbonatites are enriched in Fe2O3 (14.40%), MgO (7.36%), and MnO (3.43%), with much lower CaO/ (CaO+MgO+Fe2O3+MnO) ratios of~0.54. MgO and MnO display weakly positive correlations with FeO (Fig.8b-c). The carbonatites, especially calciocarbonatites, have high P2O5 (3.30 wt. % on average) and SrO contents (0.52 wt. % on average). Some samples contain K-feldspar phenocrysts, and hence have higher SiO2 and lower CaO contents (e.g., MY-13). 6.2.2 Trace elements The fresh syenites are rich in Nb (626ppm), Zr (866ppm) and Ba (3372ppm).

In contrast, most of the carbonatite samples, including both calciocarbonatites and ferrocarbonatites varieties, have lower Nb contents (most <200ppm), Zr contents (<300ppm) and Ba contents (<1000ppm).

The carbonatitised syenites also have Nb

contents (330-955ppm), Zr contents (284-616ppm), and Ba contents (2960-4470ppm) higher than those of the carbonatites (Table4). Sr concentrations in the calciocarbonatites (>3000ppm) are much higher than those in the ferrocarbonatites (~2000ppm) and the syenites (<1000ppm) (Fig.8d). The calciocarbonatites with high apatite and calcite consistently have higher Sr contents. The syenites are characterized by enrichment in Nb, Ta, Ba, U, Th, Zr and Hf, and variable depletion of Sr in the primitive mantle-normalized trace element patterns (Fig.9a). In comparison, the carbonatites have more obvious negative anomalies of Ta, Zr, and Hf than the syenites (Fig.9a). Both carbonatites and syenites have Nb contents positively correlating with TiO2 and Ta (Fig.8e-f). All rocks of the Miaoya complex have elevated REE concentrations. Samples of the calciocarbonatites have REE (mainly LREE) concentrations of 1774-8578ppm, which are much higher than those in the fresh syenites (372ppm) (Table4). However, the metasomatized syenites can have REE concentrations similar to those of the calciocarbonatites (Table4). Ferrocarbonatites have the highest REE contents of 8301-13430ppm (Table4). Thus, there is a clear progressive enrichment trend of REE from syenite to ferrocarbonatites. Both carbonatites and syenites display steep right-sloping, chondrite-normalized REE patterns without significant Eu or Ce anomalies (Table4, Fig.9b). The ferrocarbonatites have (La/Yb)N ratios of 85-152

higher than those in the calciocarbonatites (31-57) and syenites (24-31)(Table 4). 6.2.3 Sr-Nd isotopes Bulk rock samples of calciocarbonatites, ferrocarbonatites, and syenites were analyzed for Rb-Sr and Sm-Nd isotope compositions to constrain the magma source. A zircon age of ~430Ma was applied to all the samples for calculation of initial Sr-Nd isotopic ratios (Table5). The calciocarbonatites have initial 87Sr/86Sr ratios of 0.70374 almost identical to those of the ferrocarbonatites (0.70413), but are slightly higher than those of the syenites (0.70325). Meanwhile, both the calciocarbonatites and ferrocarbonatites also have nearly identical εNd(t) values of 2.56 and 2.49, which are slightly lower than those of the syenites (3.22) (Fig.10). 6.3 Mineral chemistry Electron microprobe analyses (EPMA) were conducted on calcite, ferrodolomite, and K-feldspar from different lithologies of the Miaoya Complex. 6.3.1 Carbonate minerals Calcites from calciocarbonatites with different textures contain 52-53 wt. % CaO with minor amounts of FeO (0.5-2.0 wt. %), MgO (0.1-0.8%), and MnO (0.3%-1.3%). All are very rich in SrO (>1.5%). The medium- and coarse-grained calcites have core-rim textures under OM-CL imaging (Fig.4e). The bright cores contain higher Ca and Sr than the dark rims, but have lower contents of Fe, Mg and Mn (Table6, Fig.11). The fine-grained calcites have homogeneous OM-CL color similar to the dark rims of the coarse calcite grains, and also have similar Ca, Fe, Mg, Mn and Sr contents (Table6, Fig.11). Calcites in the ferrocarbonatites have lower CaO (51.5%) and SrO (0.44%) but

higher FeO (2.05%), MgO (0.32%) and MnO (2.23%) than those in the calciocarbonatites (Table6, Fig.11). On average, ankerites from ferrocarbonatites contain CaO (29.2%), FeO (14.7%), MgO (8.7%) (Fe:Mg=1:1), MnO (3.5%), and SrO (0.17%). Ankerite and calcite in the syenites, which formed during metasomatism by carbonatitic melts, have major element compositions similar to those from the ferrocarbonatites (Fig. 11).

6.3.2 K-feldspar

The K-feldspar grains typically show irregular core-rim textures under OM-CL imaging (Fig.5a). The cores of the K-feldspar grains in the syenites are composed of SiO2 (63.9%-64.7%), Al2O3 (18.2%), K2O (16.8-17.3%), Na2O (0.27-0.40%), and minor BaO (0.19-0.70%), FeO (0.08-0.11%), and SrO (0.23-0.24%). Their rims contain lower SiO2 (62.7%-63.3%), K2O (16.0-16.2%) and FeO (0.03-0.04%), but have higher Na2O (0.48-0.54%), BaO (1.72-1.79%), Al2O3 (18.4-18.5%) and SrO (0.24-0.27%) (Table7, Fig.12). The K-feldspar phenocrysts and matrix grains in the porphyritic syenites have similar major element compositions. They contain SiO2 (63.9%), Al2O3 (18.2%), K2O (16.8%), Na2O (0.40%) and BaO (0.75%) on average. It is notable that K-feldspar from the calciocarbonatites have major element compositions almost identical to those in the syenites (Table7, Fig.12). Similarly, the rims of K-feldspars in the calciocarbonatites are more enriched in Ba, Al, and Na than the cores, but have lower Si, K, and Fe contents. Al and Ba correlate negatively with Si, and K has a slightly negative correlation with Na (Fig. 12).

6.3.3 Carbon and oxygen isotopes

Carbon and oxygen isotopes of calcite and ankerite from the carbonatites and syenites are presented in Table 8. Calcites from the calciocarbonatites have δ13C values of -5.6 to -3.2‰ and δ18O values of 10.4 to 15.7‰. Calcite and ankerite from the ferrocarbonatites have δ13C values of -3.6 to -3.5‰ and δ18O values of 12.1 to 12.2‰. Carbonate minerals from the carbonatitic syenites have δ13C andδ18O values of -3.5‰ to -4.7‰ and 11.7‰ to 13.5‰, respectively, which are similar to those in the carbonatites. 7. Discussion 7.1 Relationship between the carbonatites and syenites in Miaoya Complex As mentioned above, the syenites and carbonatites of the Miaoya complex have been once interpreted to form from different sources according to their different ages (Xu et al., 2014, 2015). This conclusion has been excluded based on recent research from Zhu et al., (2016), Ying et al., (2017) and Zhang et al., (2019). Zhu et al. (2016) recently obtained a LA-ICP-MS age of 445.2 ± 2.6 Ma for the syenite and 434.3 ± 3.2 Ma for the carbonatite, respectively. These ages were confirmed by Ying et al. (2017), who reported LA-ICP-MS zircon U-Th-Pb ages of 442.6 ± 4.0 Ma and 426.5 ± 8.0 Ma for syenite and carbonatite, respectively. These new ages are consistent with our zircon Th-Pb age for syenite and U-Pb age for a calciocarbonatites, hence suggesting that both the syenites and carbonatites of the complex were emplaced round 440-430Ma. It is notable that zircon ages of the carbonatites are about 10Ma years younger than those of the syenites. The isotopic data are consistent with field

observations, showing that the carbonatites locally intruded the syenites. However, this can be also due to the analysis errors which can’t be distinguished by LA-ICP-MS U-Pb technique. It should also be noted that the carbonatites are typically slightly younger than associated silicate rocks using U-Pb dating in most carbonatite complexes throughout the world (Bell et al., 1998; Chen and Simonetti, 2013; Woolley and Kjarsgaard, 2008). Gervasoni et al. (2017) have shown that SiO2-free and low silica carbonate melts crystallize baddeleyite not zircon, which can only crystallize from melts with higher concentration of SiO2. Our studies show that zircons in the carbonatites and syenites have similar textures. Their cores are dark in SEM-CL images with oscillatory zoning, suggesting a magmatic origin. The rims are intergrown with calcite and can contain mineral inclusions of carbonate, apatite and monazite. Therefore, we suggest that zircons from both syenites and carbonatites presumably crystallized from carbonated silicate magmas (Fig.14b), and some zircon grains were subsequently trapped by carbonatite melts during fractionation. Zircon grains subsequently underwent carbonatitic metasomatism at their rims during the evolution of carbonatite melts. The U-Pb ages obtained from cores and rims of zircons are hence considered to be the crystallization timing of syenites and carbonatites, respectively, for the Miaoya complex. Both cores and rims of zircons from the carbonatites yield undistinguishable U-Pb age of 428±3Ma in this study, suggesting a co-genetic origin for the syenites and carbonatites. Ying et al. (2017) reported that zircons in the carbonatites and syenites have similar εHf(t) values ranging from +3.1 to +8.9. The Miaoya syenites

and carbonatites also have similar Sr-Nd isotopes (Fig.10). The consistent initial Hf, Sr and Nd isotopes indicate that both the carbonatites and syenites were derived from a common source of carbonated silicate magma. 7.2 Evolution of the Miaoya Complex 7.2.1 Early evolution of the carbonated silicate magmas Both the carbonatites and syenites are characterized by enrichment in Nb, Zr, and REE (mainly LREE), indicating that the parental magmas were initially enriched in these elements. Field and petrographic observations have shown that the syenites were pervasively altered by carbonatitic melts, producing ankerite, calcite, apatite, and rare earth minerals, all of which are interstitial to K-feldspar crystals (Fig.5c-d). This clearly shows that the syenites formed by the accumulation of K-feldspar slightly earlier than the carbonatite melts during evolution of the parental magmas. Such an interpretation is supported by the petrographic evidence that K-feldspars in the calciocarbonatites have textures and compositions similar to those in the syenites (Fig.4f). We suggest that such K-feldspar “phenocrysts” crystallized from early carbonated syenite magma and were subsequently captured by carbonatite melts (Fig.14b). Similarly, zircons in the carbonatites have colors and CL-textures similar to those in the syenites, reflecting the same magmatic process (Fig.14b). During evolution of the carbonated syenite magmas, they gradually reached a saturation level for nioboaeschynite, pyrochlore and columbite which incorporated most of Nb into the syenites. The positive correlation between Nb and Ta in these rocks implies that Ta was also incorporated into the Nb-enriched minerals. In addition to pyrochlore and

columbite, significant Nb and Ta may also be incorporated into Ti oxides such as ilmenite and rutile, resulting in the observed positive correlation between Nb and TiO2. However, such carbonated syenite melts were not pristine magmas from mantle as shown by their low magnesium content. Previous studies have shown that primitive mantle-derived carbonatite magmas are characterized by high Mg numbers (Eggler 1989). Regionally coeval alkali basalt and lamprophyre have been reported in the Ziyang-Langao area (Fig.1c). We thus suggest that the carbonated syenite melts likely represent fractionated products of a parental alkali mafic magma (Fig.14).

7.2.2 Genesis of carbonatite melts

Carbonatites are typically associated with alkali silicate rocks and have been thought to form from parental carbonated silicate melts via either fractional crystallization or liquid immiscibility (Freestone and Hamilton, 1980; Gittins, 1988; Hamilton, 1989; Kjarsgaard and Hamilton, 1988; Pirajno et al., 2014). In the Miaoya complex, syenites and carbonatites are distinct in their major element compositions, and there is no continuous evolutionary trend from syenites to carbonatites. Such a relationship is difficult to explain by fractional crystallization given the lack of intermediate rock types between the two endmembers. Likewise, fractional crystallization cannot account for the entirely different mineral assemblages in the carbonatites and syenites. Thus, we propose that there was a process of carbonatite-silicate liquid immiscibility in the Miaoya complex. Experimental results

and studies of melt inclusions have confirmed that carbonatitic and silicate magmas can be formed by liquid immiscibility (Guzmics et al., 2011, 2012; Lee and Wyllie, 1998; Panina and Motorina, 2008). It is noted that carbonate minerals, apatite, and rare earth minerals are ubiquitously interstitial to K-feldspar crystals in the Miaoya syenite. These pervasive mineral “matrices” may represent carbonate melt residuals which were trapped interstitial to silicate minerals (Fig 14b). They have been called “carbonate ocelli” and have been considered as evidence in support of immiscibility of carbonate melts (Kjarsgaard and Hamilton, 1988). As discussed above, K-feldspars and zircons crystallized from early carbonated syenite magma were subsequently trapped by carbonatite melts. Thus, we propose that the parental carbonatite droplets were separated from carbonated silicate melts when the latter reached saturation in carbonate phases after extensive crystallization of silicate minerals (Fig.14b). Then, some droplets start coalescing and eventually to form carbonatite veins or intrusive structurally crosscut syenites. However, many droplets were not assembled and were dispersed within syenite intrusion and formed the mineral “matrices”. The partition of elements between silicate and carbonatite melts has been emphasized to explain the initial enrichment of REE concentrations in carbonatites (Bell et al., 1998). In general, syenites have higher Nb, Ta, Zr, and Hf contents and lower REE (mainly LREE) concentrations than those in the carbonatites. However, experimental studies have shown that most of the REE partition preferentially into silicate liquids during carbonatite immiscibility (Veksler et al., 1998, 2012). Studies on melt inclusions in natural samples have argued that parental carbonatite melts

separated from silicate magmas are carbonate-salt liquids enriched in Ca, alkalis, CO2, S, F, Cl, and S, rather than pure carbonate melts (Panina and Motorina, 2008). This observation has been confirmed by recent experimental studies that high concentrations of rare metals can be expected in salt-rich melts (fluoride, chloride, phosphate, and sulfate) (Veksler et al., 2012). Jones et al. (1983) have demonstrated that bastnaesite can precipitate coevally with calcite in a synthetic carbonatite mixture with suitable proportions of CO2, H2O, and F. Apatite, monazite, and fluor-carbonate minerals contains the most rare earth elements in carbonatites. Martin et al. (2013) have also confirmed that REE partition preferentially into carbonate melts relative to silicate melts within creasing bulk water contents of the system. For above reasons, we therefore suggest that volatile components, such as P, F，Cl and H2O, play key roles in the enrichment of REE in carbonatite melts. That is why previous experimental results on silicate and pure/dry carbonate melts system without volatile contents are not consistent with observed geological relationships. However, Zr, Nb, and Hf consistently partition into silicate liquids at most experimental conditions (Hamilton et al., 1989; Martin et al., 2013; Veksker et al., 1998, 2012), which is also seen in the Miaoya Complex. 7.2.3 Fractionation of carbonatite melts Our detailed petrographic observations have shown that the carbonatites within the Miaoya complex have undergone significant fractionation, resulting in diversification of compositions, which have been ignored by previous studies from Xu et al., (2014, 2015), Zhu et al., (2016) and Ying et al., (2017). The mineral

assemblages of early-stage calciocarbonatites, composed of coarse-grained calcite, apatite, and biotite, are compatible with experimental results and field observations that fractional crystallization of carbonatite initially involves precipitation of calcite, apatite, and minor silicate phases (Hornig-Kjarsgaard, 1998; Le Bas, 1989). The cores of coarse-grained calcite in the Miaoya carbonatites contain higher Ca and Sr, but lower Fe, Mg and Mn than the rims and the associated fine-grained calcite grains (Fig.11), indicating that the carbonatite magmas become more enriched in Fe and Mg during the fractionation. The ferrocarbonatites are products of further fractionation, as shown by field relationship crosscutting calciocarbonatites (Fig.3f). Fluorite began to crystallize at the ferrocarbonatites stage, suggesting that more volatile contents were accumulated at this stage. In addition, the carbonatites show a trend of REE enrichment from calciocarbonatites to ferrocarbonatites, and gradually reach a saturation level of monazite and bastnäsite(-Ce) during magma evolution. Such an evolutionary trend from Ca-carbonatite to Fe-carbonatite has been reported in previous studies of both experimental and natural examples (Gittins, 1989; Le Bas, 1989). Fractionation of carbonatite melts (or carbonatitic metasomatism) had an important effect on the major and trace element compositions of the Miaoya syenite-carbonatite complex (Table3, 4). Carbonatitic metasomatism is pervasive within the syenite intrusion and the associated early Silurian sedimentary and volcanic rocks. The metasomatized syenites have high REE concentrations, similar to those of the calciocarbonatites (Fig. 9). K-feldspar and zircon grains in the syenites and

carbonatites have irregular metasomatic rims, which are associated with carbonate minerals and have compositions different from the pristine cores (Fig.12, Table1-2). Such mineral textures and compositional variations are also attributed to carbonatitic metasomatism. 7.3 Mantle source and crustal contamination Carbon, oxygen, and Sr-Nd isotopes have been used to constrain the mantle sources of carbonatites. Carbon and oxygen isotopes of syenites and carbonatites in the Miaoya Complex have a wide range and display a weakly positive correlation (Fig.13). Most of the O isotopic ratios fall outside the range of mantle values, a feature typical of many carbonatite intrusions around the world (Bell and Simonetti, 2010). Several possibilities have been proposed to account for the large variations of O isotopes: Rayleigh fractionation, crustal contamination, and post-magmatic processes. Post-magmatic processes have little effect on the C isotopic compositions but can produce large variations in the O isotope records (Deines, 1989). Rayleigh fractionation and crustal contamination will lead to correlations between C and O isotopes, such as those displayed in the Miaoya carbonatites. The (87Sr/86Sr)i ratios of carbonatites in Miaoya are slightly higher than those of the syenites(Fig.10), whereas εNd(t) become weakly lower from syenites to carbonatites. Because fractional crystallization has no effect on Nd and Sr isotopic compositions (Bell and Blenkinsop, 1989), the weakly gradual enriched trend in initial Sr and Nd isotopes from syenites to carbonatites may imply incremental contamination by crustal materials during evolution of the magma, which may also be responsible for the observed C-O isotope

trend. As discussed above, it is suggested there was a metasomatic event during the Triassic in this region (Ying et al., 2017; Zhang et al., 2019). Isotopes of Miaoya complex may be lightly influenced by the metasomatic fluid, which has been confirmed in contemporary Shaxiongdong complex in this region (Chen et al., 2018). Although there is evidence of weak crustal contamination or metasomatic overprint for the Miaoya magmas, the Sr and Nd isotopes of the melts were not significantly modified due to their very high Sr and REE contents (Table.4). The initial Nd and Sr isotopic ratios of the Miaoya complex are close to those of OIB (Fig.10). Ying et al. (2017) reported zircon εHf(t) values of +3.1 to +8.9 for these rocks, which are consistent with the bulk rock Nd isotopes. Such isotopic ratios demonstrate that the parental magmas were derived from a relatively depleted mantle source. The Miaoya Complex has initial Nd and Sr isotopic ratios similar to those of the Shaxiongdong

syenite-carbonatite

complex

(Xu

et

al.,

2008)

and

other

contemporaneous alkali magmatic rocks in the southern Qinling region, including ultramafic to mafic dyke swarms, lamprophyre, and trachytes (Fig. 10; Xu et al., 2001; Zhang et al., 2007). These magmatic rocks were likely related to a continental rifting event that occurred in the northern part of the South China Block during the opening of Paleotethys in the late Paleozoic (Wu and Zheng, 2013). Therefore, we suggest that the Miaoya Complex and other early Silurian alkali magmatic rocks in the region were derived from a relatively depleted mantle source.

8. Genetic model and Conclusions As discussed above, both the Miaoya carbonatites and syenites were likely fractionated from carbonated syenite magmas. This interpretation is supported by their field relationships and Sr-Nd isotopic compositions. Such carbonated syenite melts likely represent fractionated products of parental magmas derived from mantle source (Fig.14). Generation of the carbonatites in the Miaoya Complex underwent a complex evolution process involving both fractional crystallization and liquid immiscibility (Fig.14). Syenites in the Miaoya Complex consist predominantly of K-feldspar, which represent an early stage accumulates of fractional crystallization. We speculate that the parental calcium carbonatite melts were immiscible from the carbonated silicate magmas when the magmas reach a saturation level of carbonate phases after extensive crystallization of silicate phases (Fig.14). Such a mechanism may be very similar to the formation of immiscible volatile phases in calc-alkaline silicate magmas (Hedenquist and Lowenstern, 1994). The parental calcium carbonatite melts were enriched in Ca, Sr, and REE, and had a major portion of volatile/salt components. Fractionation and evolution of the parental calcium carbonatite melts formed calciocarbonatites and ferrocarbonatites in sequence, causing the REEs to become gradually enriched as crystallization proceeded.

Acknowledgments This study was financially supported by the national key R&D program of China (2017YFC0602401), NSFC Project (41822203), and the Fundamental Research Funds

for the Central Universities, China University of Geosciences (Wuhan) (CUG140618 and CUGCJ1711), and a research fund from Geological Survey of Hubei Province. We are grateful to Zu-Wei Lin, Jia-Qiang Ren and Li-Ping Zeng for their help in the field and lab works. We appreciate the comments from chief editor-Prof. Franco Pirajno and two anonymous reviewers, which improved the manuscript. We thank Prof. Mei-Fu Zhou for his suggestions on an earlier version of the manuscript and Prof. Paul Robinson for polishing English.

References Armstrong, J.T., 1991. Quantitative Elemental Analysis of Individual Microparticles with Electron Beam Instruments. In: K.F.J. Heinrich and D.E. Newbury, Electron Probe Quantitation. Springer US, Boston, MA, pp. 261-315. Barker, D.S., 1989. Feild relations of carbonatites. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 38-69. Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic compositions of East African carbonatites: Implications for mantle heterogeneity. Geology 15, 99. Bell, K., Blenkinsop, J., 1989. Neodymium and Strontium Isotope geochemistry of carbonatites. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 278-297. Bell, K., Simonetti, A., 2010. Source of parental melts to carbonatites-critical isotopic constraints. Mineralogy and Petrology 98, 77-89. Bell, K., Kjarsgaard, B.A., Simonett, A., 1998. Carbonatites-into the 21th century. Journal of Petrology 39, 1839-1845.

Castor, S.B., 2008. The Mountain Pass Rare-earth Carbonatite and Associated Ultrapotassic Rocks, Calfornia. The Canadian Mineralogist 46, 779-806. Chen, H., Tian, M., Wu, G., Hu, J., 2014. The Early Paleozoic Alkaline and Mafic Magmatic Events in Southern Qinling Belt, Central China: Evidences for the Break-up of the Paleo-Tethyan Ocean. Geological Review 60, 1437-1452. Chen, W., Lu, J., Jiang, S., Ying, Y., Liu, Y., 2018. Radiogenic Pb reservoir contributes to the rare earth element (REE) enrichment in South Qinling carbonatites. Chemical Geology, 494: 80-95. Chen, W., Simonetti, A., 2013. In-situ determination of major and trace elements in calcite and apatite, and U–Pb ages of apatite from the Oka carbonatite complex: Insights into a complex crystallization history. Chemical Geology 353, 151-172. Deines, P., 1989. Stable isotope variations in carbonatites. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 301-350. Dong, Y., Zhang, G., Neubauer, F., Liu, X., Genser, J., Hauzenberger, C., 2011. Tectonic evolution of the Qinling orogen, China: Review and synthesis. Journal of Asian Earth Sciences 41, 213-237. Doroshkevich, A.G., Viladkar, S.G., Ripp, G.S., Burtseva, M.V., 2009. Hydrothermal REE Mineralization in the Amba Dongar Carbonatite Complex, Gujarat, India. The Canadian Mineralogist 47, 1105-1116. Eggler, D.H., 1989. Carbonatites, primary melts, and mantle dynamics. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 561-579. Freestone, I.C., Hamilton, D.L., 1980. The Role of Liquid Immiscibility in the

Genesis of Carbonatites - An Experimental Study. Contributions to Mineralogy and Petrology 73, 105-117. Gervasoni, F., Klemme, S., Rohrbach, A., Grützner, T., Berndt, J., 2017. Experimental constraints on the stability of baddeleyite and zircon in carbonate- and silicate-carbonate melts. American Mineralogist 102, 860-866. Gittins, J., 1988. The origin of Carbonatite. Nature 335, 295-296. Gittins, J., 1989. The origin and evolution of carbonatite magmas. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 580-599. Guzmics, T., Mitchell, R. H., Szabó, C., Berkesi, M., Milke, R., Abart, R.,2011. Carbonatite melt inclusions in coexisting magnetite, apatite and monticellite in Kerimasi calciocarbonatite, Tanzania: melt evolution and petrogenesis. Contributions to Mineralogy and Petrology 161, 177-196. Guzmics, T., Mitchell, R. H., Szabó, C., Berkesi, M., Milke, R., Ratter, K., 2012. Liquid immiscibility between silicate, carbonate and sulfide melts in melt inclusions hosted in co-precipitated minerals from Kerimasi volcano (Tanzania): evolution of carbonated nephelinitic magma. Contributions to Mineralogy and Petrology 164, 101-122. Hamilton, D.L., 1989. The genesisi of carbonatites by immiscibility. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 388-403. Hamilton, D.L., Bedson, P., Esson, J., 1989. The behaviour of trace elements in the evolution of carbonatites. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 405-427.

Hart, S.R., 1988. Heterogeneous mantle domains: signatures, genesis and mixing chronologies. Earth and Planetary Science Letters 90, 273-296. Hedenquist, J.W., Lowenstern, J.B., 1994. The role of magmas in the formation of hydrothermal ore deposits. Nature 370, 519. Hornig-Kjarsgaard, I., 1998. Rare Earth Elements in Sövitic Carbonatites and their Mineral Phases. Journal of Petrology 39, 2105-2121. Jackson, S.E., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004. The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology. Chemical Geology 211, 47-69. Jones, A.P., Wyllie, P.J., 1983. Low-temperature glass quenched from a synthetic, rare earth carbonatite: implications for the origin of the Mountain Pass Deposit, California. Economic Geology, 1721-1723. Jones, A.P., Genge, M., Carmody, L., 2013. Carbonate Melts and Carbonatites. Reviews in Mineralogy and Geochemistry 75, 289-322. Kjarsgaard, B.A., Hamilton, D.L., 1988. Liquid immiscibility and the origin of alkali-poor carbonatites. Mineralogical Magazine 52, 43-55. Le Bas, M.J., 1989. Diversification of carbonatite. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 428-445. Lee, W., Wyllie, P.J., 1998. Petrogenesis of Carbonatite Magmas from Mantle to Crust, Constrained by the System CaO-(MgO+FeO∗)-(Na2O+K2O)-(SiO2+Al2O3+TiO2) -CO2. Journal of Petrology 39, 495-517. Li, S., 1980. Geochemical features and petrogenesis of Miaoya corbonatites.

Geochemica, 345-355. Ling, W., Ren, B., Duan, R., Liu, X., Mao, X., Peng, L., Liu, Z., Cheng, J., Yang, H., 2008. Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication. Science Bulletin 53, 2192-2199. Linnen, R.L., Samson, I.M., Williams-Jones, A.E., Chakhmouradian, A.R., 2014. Geochemistry of the Rare-Earth Element, Nb, Ta, Hf, and Zr Deposits, Treatise on Geochemistry, pp. 543-568. Liu, Y., Hu, Z., Gao, S., Günther, D., Xu, J., Gao, C., Chen, H., 2008. In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard. Chemical Geology 257, 34-43. Liu, Y., Hu, Z., Zong, K., Gao, C., Gao, S., Xu, J., Chen, H., 2010. Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS. Chinese Science Bulletin 55, 1535-1546. Ludwing, K. R., 2003, User's manual for Isoplot 3.00: a geochronological toolkit for Microsoft Excel. Ma, Y., 1981. Geological survey report of Miaoya Nb-REE deposit. Wuhan: Geological Survey of Hubei Province Mariano, A., 1989. Nature of economic mineralization in carbonatites and related rocks. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 149-172. Martin, L.H.J., Schmidt, M.W., Mattsson, H.B., Guenther, D., 2013. Element

Partitioning between Immiscible Carbonatite and Silicate Melts for Dry and H2O-bearing Systems at 1–3 GPa. Journal of Petrology 54, 2301-2338. Masuda, A., Nakamura, N., Tanaka, T., 1973. Fine structures of mutually normalized rare-earth patterns of chondrites. Geochimica Et Cosmochimica Acta 37, 239-248. McCrea, J.M., 1950. On the Isotopic Chemistry of Carbonates and a Paleotemperature Scale. The Journal of Chemical Physics 18, 849-857. Meng, Q., Zhang, G., 1999. Timing of collision of the North and South China blocks: Controversy and reconciliation. Geology 27, 123-126. Mitchell, R.H., 2005. Carbonatites and carbonatites and carbonatites. Canadian Mineralogist 43, 2049-2068. Moore, M., Chakhmouradian, A.R., Mariano, A.N. and Sidhu, R., 2015. Evolution of rare-earth mineralization in the Bear Lodge carbonatite, Wyoming: Mineralogical and isotopic evidence. Ore Geology Reviews 64, 499-521. Palme, H., O'Neill, H.S.C., 2003. Cosmochemical estimates of mantle composition. In: R.W. Carlson, The mantle and core, treatise on geochemistry. Elsevier, Amsterdam, pp. 1-38. Panina, L.I. and Motorina, I.V., 2008. Liquid Immiscibility in Deep-Seated Magmas and the Generation of Carbonatite Melts. Geochemistry International 46, 448-464. Pirajno, F., González-Álvarez, I., Chen, W., Kyser, K.T., Simonetti, A., Leduc, E. and LeGras, M., 2014. The Gifford Creek Ferrocarbonatite Complex, Gascoyne

Province, Western Australia: Associated fenitic alteration and a putative link with the ~1075Ma Warakurna LIP. Lithos, 202-203: 100-119. Smith, M.P., Campbell, L.S., Kynicky, J., 2015. A review of the genesis of the world class Bayan Obo Fe–REE–Nb deposits, Inner Mongolia, China: Multistage processes and outstanding questions. Ore Geology Reviews 64, 459-476. Taylor, H.P., Frechen, J., Degens, E.T., 1967. Oxygen and carbon isotope studies of carbonatites from the Laacher See district, West Germany and the Alnö district, Sweden. Geochimica Et Cosmochimica Acta 31, 407-430. Veksker, I.V., Petibon, C., Jenner, G.A., Dorfman, A.M., Dingwell, D.B., 1998. Trace Element Partitioning in Immiscible Silicate – Carbonate Liquid Systems: An Initial Experimental Study Using a Centrifuge Autoclave. Journal of Petrology 39, 2095-2104. Veksler, I. V., Dorfman, A. M., Dulski, P., Kamenetsky, V. S., Danyushevsky, L. V., Jeffries, T., Dingwell, D. B., 2012. Partitioning of elements between silicate melt and immiscible fluoride, chloride, carbonate, phosphate and sulfate melts, with implications to the origin of natrocarbonatite. Geochimica Et Cosmochimica Acta 79, 20-40. Verplanck, P.L., Mariano, A.N., Mariano, A., 2016. Rare Earth Ore Geology of Carbonatites. In: P.L. Verplanck and M.W. Hitzman, Rare Earth and Critical Elements in Ore Deposits. Society of Economic Geologist, Littleton, pp. 5-32. Wang, K., Wang, Z., Zhang, Y., Wang, G., 2015. Geochronology and Geochemistry of Mafic Rocks in the Xuhe, Shaanxi, China： Implications for Petrogenesis and

Mantle Dynamics. Acta Geologica Sinica 89, 187-202. Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W. L., Meier, M., Oberli, F., Quadt, V. A. R. J., 1995. Three natural zircon standards for U–Th–Pb, Lu–Hf, trace element and REE analyses. Geostandards Newsletter. 19, 1-23. Woolley, A.R., Kempe, D.R.C., 1989. Carbonatites: neomenclature, average chemical compositions, and element distributon. In: K. Bell, Carbonatites: Genesis and Evolution. Unwin Hyman, London, pp. 1-13. Woolley, A.R., Kjarsgaard, B.A., 2008. Paragentic types of carbonatite as indicated by the diversity and relative abundances of associated silica rocks: evidence from a global database. The Canadian Mineralogist 46, 741-752. Wu, Y., Zheng, Y., 2013. Tectonic evolution of a composite collision orogen: An overview on the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt in central China. Gondwana Research 23, 1402-1428. Xie, Y., Hou, Z., Yin, S., Dominy, S. C., Xu, J., Tian, S., Xu, W., 2009. Continuous carbonatitic melt–fluid evolution of a REE mineralization system: Evidence from inclusions in the Maoniuping REE Deposit, Western Sichuan, China. Ore Geology Reviews 36, 90-105. Xie, Y., Li, Y., Hou, Z., Cooke, D. R., Danyushevsky, L., Dominy, S. C., Shuping Yin, 2015.

A model

for

carbonatite

hosted

REE

mineralisation

—

the

Mianning–Dechang REE belt, Western Sichuan Province, China. Ore Geology Reviews 70, 595-612. Xu, C., Campbell, I. H., Allen, C. M., Chen, Y., Huang, Z., Qi, L., Zhang, G., Yan,

Z.,2008. U–Pb zircon age, geochemical and isotopic characteristics of carbonatite and syenite complexes from the Shaxiongdong, China. Lithos 105, 118-128. Xu, C., Chakhmouradian, A. R., Taylor, R. N., Kynicky, J., Li, W., Song, W., Fletcher, I. R., 2014. Origin of carbonatites in the South Qinling orogen: Implications for crustal recycling and timing of collision between the South and North China Blocks. Geochimica Et Cosmochimica Acta 143, 189-206. Xu, C., Kynicky, J., Chakhmouradian, A.R., Li, X., Song, W., 2015. A case example of the importance of multi-analytical approach in deciphering carbonatite petrogenesis in South Qinling orogen: Miaoya rare-metal deposit, central China. Lithos, 227: 107-121. Xu, C., Kynicky, J., Chakhmouradian, A.R., Campbell, I.H., Allen, C.M., 2010. Trace-element modeling of the magmatic evolution of rare-earth-rich carbonatite from the Miaoya deposit, Central China. Lithos 118, 145-155. Xu, X., Xia, L., Xia, Z., Huang, Y., 2001. Geochemical characteristics and petrogenesis of the early Paleozoic alkali lamprophyre complex from Langao county. Acta Geoscientia Sinica, 55-60. Yang, C., Liu, C., Liu, W., Wan, J., Duan, X., Zhang, Z., 2017. Geochemical characteristics of trachyte and Nb mineralization process in Tianbao Toownship, Zhuxi County, Southern Qinling. Acta Petrologica Et Mineralogica 36, 605-618. Ying, Y., Chen, W., Lu, J., Jiang, S., Yang, Y., 2017. In situ U–Th–Pb ages of the Miaoya carbonatite complex in the South Qinling orogenic belt, central China.

Lithos 290-291, 159-171. Yue, S., Zhai, Y., Deng, X., Yu, J., Lin, Y., 2013. Fluid inclusion and H-O isotope geochemistry and ore genesis of the Yindonggou deposit， Zhushan County， Hubei， China. Acta Petrologica Sinica, 27-45. Zhang, C. L., Gao, S., Yuan, H., Zhang, G., Yan, Y., Luo, J., Luo, J., 2007. Sr–Nd–Pb isotopes of the Early Paleozoic maficultramafic dykes and basalts from South Qinling belt and their implications for mantle composition. Science in China (Series D: Earth Sciences), 857-865. Zhang, W., Chen, W.T., Gao, J., Chen, H., Li, J., 2019. Two episodes of REE mineralization in the Qinling Orogenic Belt, Central China: in-situ U-Th-Pb dating of bastnäsite and monazite. Mineralium Deposita. Online. Zhu, J., Wang, L., Peng, S., Peng, L., Wu, C., Qiu, X., 2016, U-Pb zircon age, geochemical and isotopic characteristics of the Miaoya syenite and carbonatite complex, central China. Geological Journal 52, 938-954. Zindler, A., Hart, S., 1986. Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493-571.

Figure Captions Figure 1. Simplified geotectonic map showing the location of the southern margin of the Qinling orogen (a-b) (modified from Ling et al. (2008); Yue et al. (2013)) and the distribution of early Silurian alkali magmatic rocks (c) (modified from Yang et al. (2017))

Figure 2. A simplified geological map of the Miaoya syenite-carbonatite complex (modified from Ma (1981)) Figure 3. Photographs of typical rocks and the field relationships. (a)Carbonatites intrude syenites in the northern part of the Miaoya Complex; note that the syenites were also metasomatized by carbonatitic melts; (b) Enlarged part of Figure (a) showing a diffuse boundary between the carbonated syenites and calciocarbonatites; note the coarse calcite aggregations (white color) in the syenites; (c)A field outcrop of syenites (dark gray) and calciocarbonatites (white)without clear boundaries; (d)Fresh calciocarbonatites with banded biotite; (e)Fresh syenites showing dark gray colors; (f) Ferrocarbonatites dyke cutting calciocarbonatites. Figure 4. Photomicrographs (CPL: crossed-polarized light) and OM-CL (Optical microscopy cathodoluminescence) images for representative rock types from the Miaoya Complex. (a)Photomicrograph and (b) OM-CL image for syenites which contain dominantly K-feldspar, with minor zircon; (c) Photomicrograph of porphyritic syenite; (d)Photomicrograph of calciocarbonatites, which consists mainly of calcite, apatite, and biotite; (e)Medium-grained calcite with core-rim textures and relatively fine-grained, homogeneous calcites under CL imaging(scale same as D); (f) OM-CL image of calciocarbonatites containing minor K-feldspar-note that the calcites are relatively fine grained without core-rim textures compared with those in(e); (h)Photomicrograph and (i) OM-CL image of coarse-grained calciocarbonatites - note the calcite grains with core-rim textures;(j) OM-CL image of ferrocarbonatites mainly composed of ankerite and calcite with accessory phases of apatite (green) and fluorite

(blue). Abbreviations: Ap=apatite, Ank=ankerite, Cal=calcite, Bt=biotite, Fl=fluorite, Mc=Microcline, Or=orthoclase, Qz=quartz, Ser=sericite, Zr=zircon Figure 5. Photomicrographs and OM-CL images of representative minerals showing carbonatitic metasomatism. (a) OM-CL image of K-feldspar in carbonatitic syenite note that the feldspar has a dark rim due to carbonatitic alteration; (b) CL image of zircon in syenite showing a dark core and bright rim; (c) and (d) CL image of carbonatitic syenite, where calcite, ankerite and apatite are interstitial to K-feldspar; (e) CL image of zircon grains in calciocarbonatites with complicated textures; (f) CL image of K-feldspar grains in calciocarbonatites. Ap= apatite, Ank= ankerite, Cal=calcite, Or=orthoclase, Qz=quartz, Ser=sericite. Figure 6. BSE images showing typical Nb and REE minerals from the Miaoya Complex.(a) Columbite associated with apatite in calciocarbonatites; (b)Euhedral allanite replaced by bastnäsite-(Ce) in calciocarbonatites;(c) Allanite associated with biotite in calciocarbonatites;(d)Allanite-quartz veinlets infilling interstices between calcite crystals in calciocarbonatites; (e)Euhedral monazite in calciocarbonatites; (f) Monazite veinlet in calciocarbonatites; (h)Bastnäsite-(Ce) and parisite-(Ce) veinlets in calciocarbonatites;

(i)Fine-grained

REE

minerals

in

ferrocarbonatites;

(j)

Bastnäsite(-Ce) isspatially associated with fluorite. Aln=allanite, Ap=apatite, Bas= bastnäsite-(Ce),

Cal=calcite,

Col=columbite,

Fl=fluorite,

Mnz=monazite,

Par=parasite-(Ce), Qz=quartz. Figure 7. (a) Weighted mean Th-Pb age of zircon from syenite; (b) Concordia plot of zircon U-Pb ages for calciocarbonatites

Figure 8. Bivariant diagrams of major and trace elements for the Miaoya syenites and carbonatites. Figure 9. Primitive mantle-normalized trace element (a) and chondrite-normalized REE (b) distributions for the rocks of the Miaoya Complex. Normalization values are from Palme and O'Neill (2003) and Masuda et al. (1973), respectively. Figure 10. εNd(t) vs initial Sr isotope plot of rocks from the Miaoya Complex, plotted data include those from Xu et al. (2014). MORB and OIB field are from Zindler and Hart(1986); The mantle end-member components are from Hart (1988); EACL: East African Carbonatite Line (Bell and Blenkinsop, 1987); SXD: syenite-carbonatite complex in the Shaxiongdong area (Xu et al., 2008); LGB: gabbro-diabase-basalt suite in the Langao-Ziyang area (Wang et al., 2015; Zhang et al., 2007); LGL: lamprophyre in the Langao-Ziyang area (Xu et al., 2001). Figure 11. Compositional variations (in atoms per formula unit) of calcite in carbonatites and syenites of the Miaoya Complex. Figure 12. Compositional variations (in atoms per formula unit) of K-feldspars from syenite, porphyritic syenite, and calciocarbonatites of the Miaoya Complex. Figure 13. Carbon and oxygen isotopic compositions of carbonate minerals from carbonatites and syenites of the Miaoya Complex.

Primary carbonatite regions from

Taylor et al. (1967) and Jones et al. (2013); plotted data include those from Xu et al. (2014) Figure 14. An integrated petrogenetic model for the Miaoya complex involving fractionation and liquid immiscibility. (a) A proposed evolutionary process for the

formation of the Miaoya Complex from carbonated silicate magmas to carbonatite melts; (b) The parental calcium carbonatite melts undergo immiscible separation(Ⅲ) from carbonated syenite melts( ② ) after extensive fractionation of the silicate phases(II). The carbonated syenite melts likely represent the fractionated products(I) of the parental mantle magmas(①); (c) Fractionation and evolution of the parental calcium carbonatite melts that formed the calciocarbonatites and ferrocarbonatites.

Table 1. LA-ICP-MS U-Th-Pb data from zircons in the Miaoya syenite. Th

U

U-Th-Pb isotopic ratios Th

Sample

pp

pp /U

m

m

207

Pb

235

206

1σ

/ U

Pb

238

55

20

1.24

27 21-01

02

09

12

0.87

46 21-02

16MY-

47

36

14

2.

21-03*

59

56

5

18 25

4

21-04

46

0

04

36

14

0.60 26

21-05

98

3

67

3

41

17

1.52

24 21-06

57

6

03

22

39

5.

0.63

21-07*

33

5

7

36

47

1.20 47

21-08*

10

1

99

11

8.

13

8.80

21-09*

08

1

6

05

10

68

1.

0.47

21-10*

48

8

5

71

50

10

1.02

49 21-11

90

5

66

72

9.

74

4.23

21-12

16MY-

56

7

14 07

76

44

9

3

0.0

0.0

9

1681

3

568

7

441

7

0

0.022 03

6 00

1 3

444

1 5

7

67

7

3 00

0.1 26

436 3

2

0.07

9

1 411

4 0.0

05

83

717

0.022

22

1.70 32

21-13

8

429

4

0.0

68

4 00

8

0.09

7

0.0

2

0.6 16MY-

360 6

4

02

9

396

0.021

58

8

1 00

0.0

86

444 8

0.0 4

0.06

5 951

1

0.021 2

0.0 16MY-

1

4

01

9

1 432

0

7 2318

2

75

1 190

1

00

0.0

23

7

0.0

4 0.05

433

5 0.022

89 0.0

16MY-

805

6

10

3

5 00

0.0

85

4

0.0 0.021

0.15

270 2

4

6

0.6 16MY-

498

6

99

7

7

2 00

01

3

451

1 466

7 0.0

0.0

11

939

0.021

0.02

8

4

6

0.1 16MY-

4 00

00

0

450 2

0.0

0.0 29

8

1 310

1

6

0.04 36

481

0.022 8

0.0 16MY-

439

4

02

4

7

0

3 00

0.0 50

433

2 469

0

5

0.07

7

0.0

0

15

343

943

0.022 02

0.1 16MY-

8

4

4

0.0

4

442

1

5 00

0

93

8

0.0

03

48

439

2

0.022

0.04

σ

4

0.0

0.0 16MY-

Th

8

452

515

7

55

1

1 00

1

4

639

0.021 01

24

Pb/

1

5 0.0

0.07

σ

232

492

3 00

3

1.53

/ U

208

0.0

0.0

0.1 44

238

1

4

1

47

Pb

1

7

12

819

0.022

0.05

σ

206

3

0.0

8 16MY-

/ U

00

02

19

235

1

0.0

0.0 27

0.66

Pb

0

0.07

57

1σ

Th

0

63 1

232

207

0.022

94 0.0

55

Pb/

03

6 16MY-

U-Th-Pb isotopic age (Ma)

0.0 0.07

67 1

1σ

/ U 0.0

16MY-

208

1009 9

4

2 476 0

0.1 16MY-

71

18

2.18 38

21-14

5

.6

0.0 0.07

86 72

04 93

7 33

0.67 88

21-15

38

31

70

16

0.88 54

21-16

30

16 10 23 16

1.86

44

21-17

1

49

2

47

58

29

19

0.53

21-18

70

5

.9

92

29

27

21-19

83

0.75 63

44

57

41

0.78 14

7

21-20

17

0

94 3

572

8

454

7

0

0.0

01

1 00

7 0

457

1 462

9

0.022

04

7

4

0.0

33

2 00

9

0.07

7

0.0

01

0.0 16MY-

454 0

0.022

43 0

438

4

0.0

50 65

445

2 00

3

0.07

8

8

0.0

1

0.0 16MY-

458

1 465

5

0.022 01

3

1069

4

0.0

30

4 00

9

0.07

8

3

0.0

1

0.0 16MY-

451

1 437

4

0.022 03

6

644

4

0.0

26

3 00

6

0.07

8

1

0.0

2

0.1

16MY-

448

1 455

8

0.022 02

01

8

4

0.0

1

525

4

0.07

65

2 00

8

63

443 6

0.0

01

0.0 16MY-

0

0.022

31

2 492

4

0.0

9

1177

2

0.07 45

6 00

3

0.0 16MY-

0.0 0.022

591

438 9

3

*Rims of the zircons grains which are yellow-green colures in OM-CL images.

6

Table 2. LA-ICP-MS U-Pb data from zircons in the Miaoya carbonatite. *Rims of the zircons grains which are white colures in SEM-CL images. Th

U-Pb isotopic ratios

U

U-Pb isotopic age(Ma)

Samp (ppm

(ppm

Th/U

207

Pb/

20

207

Pb/

2

1σ

le )

)

2601

53

6

14M

0.00 48.8

14M 95

6.7

0.548

0.03

U

0.069

207

Pb/ P

0.00

9

05

0

12

0.00

0.519

0.02

0.068

0.00

0

37

9

10

0.00

0.549

0.03

0.068

0.00

Pb/238 1σ U

13 444

20

430

7

425

16

429

6

445

23

428

7

3 13 435

26

206

1σ U

554 36

Pb/235

1σ b

0.0556

Y-03

206

1σ 38

U

207

0.0586

Y-01

641

Pb/

2

1σ 35

Pb

206

6

14M Y-04

752

132

5.7

0.0585

14 550

39

4

53

7

12

0.00

0.496

0.01

0.068

0.00

17

8

67

7

08

0.00

0.521

0.02

0.068

0.00

23

3

24

3

09

0.00

0.504

0.03

0.068

0.00

34

7

00

7

13

0.00

0.511

0.02

0.066

0.00

4

* 14M 258

251

1.0

0.0525

Y-05 14M 556

133

4.2

0.0551

Y-06 14M 1881

56

33.6

0.0546

Y-07 14M 1495

120

12.5

79

410

11

428

5

417

93

426

15

426

5

415

20

429

8

419

16

416

5

430

67

430

17

469

57

430

26

12

433

5

445

21

430

8

432

13

430

6

476

23

431

7

437

16

430

6

431

17

432

6

424

20

429

7

458

25

431

9

13 394

0.0554

Y-08

306

9 10 432

25

0

41

7

09

0.01

0.526

0.10

0.068

0.00

2

14M Y-09

320

14

23.5

0.0609

39 635

12

7

12

9

28

0.01

0.586

0.08

0.069

0.00

9

* 14M Y-10

52

8

6.7

0.0713

44 969

50

8

90

0

44

0.00

0.532

0.01

0.069

0.00

20

8

87

4

09

0.00

0.549

0.03

0.068

0.00

1

* 14M 2169

205

10.6

0.0561

Y-12 14M 1807

63

28.6

0.0597

Y-14 14M 628

258

2.4

14M 1125

69

16.3

14M 262

174

1.5

14M 89

20.9

14M 42

16.7

20

9

12

0.00

0.530

0.01

0.069

0.00

21

5

93

0

09

0.00

0.597

0.03

0.069

0.00

13 4 11 8 13 709

38

7

59

2

12

0.00

0.537

0.02

0.068

0.00

24

5

42

9

10

0.00

0.529

0.02

0.069

0.00

28

4

60

3

09

0.00

0.517

0.02

0.068

0.00

0

478

96

11 443

0.0545

Y-22

34

454

0.0557

Y-21

703

5

0.0564

Y-20

1857

38

0.0631

Y-19

80

591

0.0560

Y-15

4 454

3 14 391

36

8

98

7

12

0.00

0.570

0.03

0.069

0.00

8

14M Y-24

33

37

0.9

0.0617 48

*

17 665

0

93

1

14

3

Table 3. Major element compositions (wt.%) of the Miaoya syenites and carbonatites. Sa

MY-4 MY-1

mpl

MY-1

MY-1

MY-2

MY-2

14M

14M

14M

14M

14M

MY-3

MY-3

MY

MY

16M

Y-04

Y-05

Y-22

Y-23

Y-34

1

3

-22

-26

Y-21

1 2

3

5

1

e Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Ferro

Ferro

Typ

o-

o-

o-

o-

o-

o-

o-

o-

o-

o-

o-

-

-

Sye

Sye

Syen

e

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

nite

nite

ite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite 39.

41.

55.3

1.20

8.51

15.70

3.07

9.50

3.92

2.43

0.90

6.14

3.03

0.64

0.78 1

2

1

0.6

0.8

7

6

12.

16.

18.0

7

5

4

6.4

6.1

5

0

0.9

0.5

3

1

1.8

1.8

4

7

12.

9.3

3

4

0.3

0.3

7

2

9.0

9.3

11.8 0

SiO 12.70

2

TiO 0.05

0.06

1.79

0.35

0.10

0.06

0.03

0.04

0.06

0.51

0.03

0.08

0.87

2

Al2 0.26

0.66

7.03

1.21

2.92

O3

1.10

0.65

0.23

0.24

0.82

0.07

0.16

4.73

Fe2 5.40

1.93

4.07

2.80

1.98

O3

2.72

1.93

2.89

1.57

5.36

14.75

14.05

3.24

Mn 0.97

0.61

0.69

0.67

0.67

O

0.63

0.64

0.64

0.38

0.51

3.23

Mg 0.37

1.48

1.06

0.41

O

0.28

0.20

0.43

0.27

1.04

7.29

Ca 48.3

34.7

49.0

44.5

O

48.7

51.2

51.4

49.4

47.1

30.1

Na2 0.24

0.11

0.11

0.10

O

0.10

0.03

0.01

0.02

0.07

0.01

K2 0.13

2.80

0.44

2.01

O

0.85

0.54

0.08

0.07

0.25

0.03

1.72

4.07

0.13

4.80

4.57

0.98

5.52

2.36

1.25

1.40

5.08

0.26

Ba <0.01

0.09

0.01

0.11

O

0.05

0.04

0.02

0.01

0.02

<0.01

SO 0.80

1.72

0.29

0.38

3.05

2.15

0.57

0.23

2.36

0.36

Sr 0.36

0.25

0.28

0.52

0.51

O

0.45

0.60

0.58

1.01

0.85

0.22

LO 38.35

23.73

36.01

35.24

I

37.43

40.66

39.14

32.82

40.73

100.3 99.46

100.1 98.99

4

100.2 99.41

1

98.98 98.81

99.70 3

99.94

99.82

97.72

0.5

0.3

3

6

0.5

0.1

6

7

0.1

0.0

2

9

12.

11.

67

15

99.

98.

99.2

00

58

5

0.09

0.37

0.23

0.02

39.28

30.16

Tot al

31.55

9

0.19

0.83

34.96

9

0.87

0.61

3

2 0.7

<0.01

0.08

2.57

2 1.7 0.27

2.90

0.01

0.61

0.07

P2 O5

3.25

0.02

0.11

0.16

1.42

30.2

39.4

0.05

0.24

7.42

1.02

48.3

2.90

3.63

0.44

1.10

0.21

4.76

97.02

Table 4. Trace element compositions (ppm) of the Miaoya syenites and carbonatites.

Sam

MY-

MY-

MY-

MY-

MY-

MY-

14M

14M

14M

14M

14M

MY-

MY-

MY

MY

16M

ple

2

12

13

15

21

41

Y-04

Y-05

Y-22

Y-23

Y-34

31

33

-22

-26

Y-21

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Calci

Ferro

Ferro

o-

o-

o-

o-

o-

o-

o-

o-

o-

o-

o-

-

-

Sye

Sye

Syen

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

carbo

nite

nite

ite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

natite

3.60

3.30

74.4

11.6

31.3

42.6

11.3

6.90

1.90

1.40

5.30

1.40

2.30

Type

184 Rb

130

167 .5

Ba

Th

U

184.5

8.74

9.74

90.2

12.1

1.45

820

30.1

4.35

168

26.3

3.5

969

71.0

25

716

17.55

3.57

476

94.0

199

407

38.2

38.4

218

33.2

6.82

150.5

7.50

19.2

225

23.6

46

44.8

438

5.95

447

296

0

0

51.

33.

8

8

48.

21.

5

2

330

955

626

43

24.0

21

17

4

1.2

2.1

2

6

96.7

3372

334

54

17.8

Nb

195.5

110

786

289

75.3

290

484

98.8

21.6

40.5

191

28.4

115.5

Ta

0.60

1.80

11.4

3.80

5.30

19.3

52.6

12.3

1.10

6.50

28.2

0.40

1.00

56

12. 4 W

5

1

9

4

6

5

1

1

bdl

1

4

5

9

Cs

0.18

0.15

1.87

0.36

0.31

1.05

0.1

0.05

0.06

0.05

0.28

0.07

0.13

1.35

102 Sr

3390

2480

2640

4660

4520

7730

4160

5170

4870

8290

6640

2030

1790

818

241

5 Cr

20

10

10

bdl

bdl

10

10

10

10

10

10

bdl

bdl

20

20

7.58

V

92

8

240

62

78

113

119

33

46

28

146

224

283

144

179

113

Zr

73

15

364

231

611

162

175

56

18

130

190

227

168

616

284

866

Hf

1

0.2

3.2

2.1

3.9

3.3

0.9

0.4

0.2

0.8

1.4

1.6

1.4

6.6

3.5

7.42

Ga

12.3

4.7

18.1

7.2

9

12.7

21.9

7.3

11.4

4.1

8.2

17.9

24.4

28

33

19. 1 La

1440

451

438

564

575

561

2870

555

1080

317

545

2570

5020

240

390

96

Ce

2810

837

878

1095

1040

1040

4000

999

2020

576

996

3940

6230

427

687

153

43.

69.

15.0

Pr

288

83.9

91.6

118.5

105.5

107

351

98

217

56.5

101.5

343

471 9

6

8

230

54

33

9.34

149 Nd

1045

288

331

421

363

375

997

351

720

207

372

1070

1310 .5 21.

Sm

135

37.3

48.5

60.4

50.3

52.9

116

54.6

100

34.2

58.8

129

134 5

Eu

Gd

Tb

Dy

43

102

20.5

145.5

11.7

27.2

3.3

16.2

15.9

39.4

5.04

26

19.4

48.5

5.93

28.4

16.1

39.7

4.88

25

17.1

41

5.05

24.4

31.9

81.1

11.2

60.2

14.85

42.4

5.67

31.1

25.2

62.2

6.88

33

9.47

26.6

3.45

17.45

16.15

44.7

5.46

27.8

36.9

89.6

10.3

49

7.6

11.

3

7

20.

29.

4

9

2.9

4.3

5

8

16.

23.

42.1

3.07

91.7

7.55

10.9

53.5

1.03

4.98

9

5 115

Y

835

90.1

133.5

143.5

131.5

129.5

276

146.5

151

86

122

319

342

104

21.5 .5

Ho

Er

Tm

30.2

69.2

6.67

2.97

7.26

0.91

4.61

4.94

10.8

11.4

1.22

4.57

11.15

1.4

1.44

4.35

9.92

1.24

10.55

24.8

3.21

5.63

14.45

2.08

5.89

14.35

2.05

3.22

4.72

8.21

9.49

11.45

1.17

25.7

1.57

3.4

3.4

4.3

4

9

8.9

10.

3

85

1.2

1.2

1

8

9.99

0.86

26.3

2.30

3.55

0.32

7.1 Yb

27.2

6.27

7.02

7.69

9.1

6.97

18.2

11.95

12.15

7.2

8.46

21.5

23.7

7.4

2.07

7

Lu

2.74

1.01

1.07

1.14

1.36

1.02

2.46

1.72

1.78

1.07

1.22

3.34

ΣRE 6165

1774

1898

2388

2247

2247

8578

2187

4301

1269

2195

1.0

0.9

4

6

1343

105

161

0

6

9

3.68

0.30

8301

372

E ΣLR

1320 5761

1709

1803

2278

2150

2153

8366

2072

4162

1200

2089

142

8089

890

EE

7

331 1

ΣHR 404

65.1

95.2

109

97.2

94.0

212

115

138

68.4

105

212

223

166

1.08

1.07

1.08

1.06

1.06

1.08

0.95

0.91

0.91

0.93

0.93

0.99

1.1

1.1

198

40.9

EE 1.1 δEu

1.09 1

δCe

δSm

1.01

0.60

0.98

0.60

1.02

0.65

0.99

0.96

0.65

0.63

0.97

0.64

(La/

0.83

0.57

0.97

0.72

0.96

0.67

0.97

0.97

0.75

0.89

0.72

0.58

113.1 37.97

51.6

44.75

52.61

45.32

57.73

Yb)N

33.31

63.76

31.58

46.21

0.9

0.9

5

4

0.6

0.6

3

3

151.9

24.

37.

30.5

3

01

8

1

7.2

7.6

1

3

2.3

3.3

5

4

1.0

1.5

7

9

26.

22.

6

2

93.

81.

3

1

0.78

0.86

0.50

0.73

85.74

1

(La/ Sm)

6.89

7.81

5.83

6.03

7.38

6.85

15.97

6.56

6.97

5.98

5.98

12.86

24.18

6.24

N

(Gd/ 3.10

3.59

4.64

5.22

3.61

4.87

3.69

2.94

4.23

3.06

4.37

3.45

3.20

2.92

Yb)N Th/ 0.90

8.34

6.92

7.51

2.84

4.92

0.47

0.99

4.87

0.39

0.51

73.61

18.76

0.95

U Nb/ 326

61.1

68.9

76.1

14.2

15.0

9.20

8.03

19.6

6.23

6.77

71.0

116

26.0

Ta Zr/H 73.0

75.0

114

110

157

49.1

194

140

90.0

163

136

142

120

117

f

Table 5. Sr-Nd isotopic compositions of Miaoya carbonatites and syenites. Sam

Type

Rb(

Sr(p

87

Rb/

(87Sr

±2σ

t(M

(87Sr

Sm(

Nd(

147

S

143

Nd/

±2σ

(143Nd/

εNd(

TDM

ple

pp

pm)

86

Sr

m)

/86Sr ) 0.70

MY-

Calciocarbo

339

14M

natite

0

Calciocarbo

517

14M

natite

0

Calciocarbo

487

MY-

natite

0

Ferrocarbon

203

MY-

atite

0

Ferrocarbon

179

atite

0

MY-

102 Syenite

5

MY-

m)

Nd

104

0.08

395

000

6

09

7

430

393

0.70

0.0

0.70

000

430

361

9

08

5

0.70

0.0

0.70

185

430

368

1

08

4

0.70

0.0

0.70

54.6

430

424

3

05

1

0.70

0.0

0.70

100

06 0.0 000

0.07 60

0.06

6

0.70

0.0

0.70

06

430

328

25

45

426

0.8 2.50

12

0

0.512

0.5122

393

0.7 2.49

11

7

04 0.0 21.5

0.512

150

0.5122 000

507

0.8 3.27

52

0

05 0.0 33.0

0.512

230

0.5122 000

04 1

4

0.5122

000

0.09

8

0.512

134

06 08

11

0.0

69

000

458

0.8 2.49

03

0.09

3

9

0.5122 000

0.70 322

02

0.512

3

430

0.8 2.30

000

0.36

727

478

129

0

547

0.5122 000

0.0

37

0.70

0.512

720

131

6

9

03

0.00 401

33

0.0

0

430

0.7 2.90

03

20

000

0.5122

462

351

107 000

(Ga

0.0

75

425

t)

03

0.00

818

14

0.08 000

0.512 000

80

369

Nd)i

)

135

0.09 363

144

Nd

0.0

5

403

144

0.70

0.65 Syenite

26

m)

11

130

22

)i

0.00

2.30 33

m/144

39

1.40 31

pp

0.00

1.90 Y-22

pp

31

6.90 Y-05

0.0

/86Sr

0.00

3.60 2

a)

501

46 02

0.8 3.17 0

Table 6. Major elements for carbonate minerals in carbonatites and syenites.

Sample

Type

16MY-49

16MY-37

16MY-42

16MY-21

Coarse-grained

Medium-grained

Fine-grained

calciocarbonatite

calciocarbonatite

calciocarbonatite

Syenite

Core

Rim

Core

Rim/Fine grains

Calcite

Calcite

Ankerite

N=30

N=32

N=21

N=37

N=20

N=6

N=7

53.4

52.5

53.2

52.6

52.3

53.0

29.2

FeO

0.65

1.78

0.46

1.32

2.02

1.17

15.41

MgO

0.17

0.26

0.24

0.40

0.75

0.48

8.45

MnO

0.46

0.71

0.30

0.35

1.29

1.56

3.02

SrO

1.67

1.19

2.60

2.29

1.16

0.35

0.31

*CO2

43.6

43.6

43.6

43.8

44.5

44.1

43.8

Total

100.1

100.1

100.1

100.2

101.0

100.6

100.3

1.93

1.89

1.92

1.89

1.85

1.89

1.05

Fe

0.02

0.05

0.01

0.04

0.06

0.03

0.43

Mg

0.01

0.01

0.01

0.02

0.04

0.02

0.42

Mn

0.01

0.02

0.01

0.01

0.04

0.05

0.09

Sr

0.03

0.02

0.05

0.04

0.02

0.01

0.01

Mean CaO

wt.%

Cations Ca

O=6 apfu

* Calculated by charge balance Table 7. Major elements for K-feldspars in syenites and carbonatites. Sample Type

16MY-21

16MY-9

16MY-7

16MY-38

Syenite

Carbonatitic syenite

Porphyritic syenites

Calciocarbonatite

Core

Rim

Rim

Phenocryst

Matrix

Core

Rim

N=29

N=12

N=12

N=16

N=18

N=15

N=18

N=11

64.7

63.3

63.9

62.7

63.9

63.6

65.5

63.7

Al2O3

18.2

18.5

18.2

18.4

18.2

18.2

18.0

18.7

K2O

17.3

16.2

16.8

16.0

16.8

17.0

16.9

16.2

Na2O

0.27

0.48

0.40

0.54

0.29

0.25

0.29

0.41

CaO

0.01

0.01

0.01

0.01

0.00

0.05

0.01

0.08

BaO

0.19

1.72

0.70

1.79

0.75

0.84

0.10

1.91

FeO

0.11

0.03

0.08

0.04

0.03

0.03

0.34

0.03

SrO

0.23

0.27

0.24

0.24

0.24

0.24

0.23

0.34

Total

101.0

100.5

100.3

99.7

100.2

100.2

101.4

101.4

Cations

O=8 2.96

2.98

2.96

2.98

2.97

3.01

2.96

Mean SiO2

Si

wt.%

apfu

2.99

Core

Al

0.99

1.02

1.00

1.02

1.00

1.00

0.97

1.02

K

1.02

0.97

1.00

0.97

1.00

1.01

0.99

0.96

Na

0.02

0.04

0.04

0.05

0.03

0.02

0.03

0.04

Ca

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Ba

0.00

0.03

0.01

0.03

0.01

0.02

0.00

0.03

Fe

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

Sr

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

Table 8. C-O isotopic compositions of calcites from the Miaoya carbonatites and syenites. Sample

Type

δ13CPDB(‰)

δ18OPDB(‰)

δ18OSMOW(‰)

14MY-22

Calciocarbonatite

-3.20

-18.06

12.24

14MY-05

Calciocarbonatite

-5.16

-19.88

10.37

MY-2

Calciocarbonatite

-4.01

-19.68

10.57

MY-12

Calciocarbonatite

-4.66

-17.51

12.81

MY-21

Calciocarbonatite

-5.06

-18.20

12.10

MY-13

Calciocarbonatite

-4.91

-16.89

13.45

14MY-19

Calciocarbonatite

-5.55

-14.73

15.68

14MY-25

Ferrocarbonatite

-3.56

-18.14

12.16

14MY-08

Ferrocarbonatite

-3.45

-18.20

12.10

14MY-28

Syenite

-3.47

-18.61

11.68

14MY-35

Syenite

-4.67

-16.82

13.52

Formation of Miaoya carbonatites involving both crystal fractionation and fluid immiscibility. Both carbonatites and syenites were fractionated from carbonated syenitic magma. REE enrichment are associated with fractionation processes of parental calcium carbonatite.