Petrogenesis of the Monzonite in the Jiashan Area, Northern Jiangsu, China: Constraints from Whole-Rock Geochemistry and Zircon U–Pb Ages and Lu–Hf Isotopes

Abstract

Recent discoveries of fluorite–barite deposits in the Donghai–Linshu area in northern Jiangsu Province, China, underscore the region’s mineral potential, yet detailed geological investigations remain limited. In this study, we examined monzonite and quartz monzonite from drill cores in the Jiashan mining area using petrography, U–Pb zircon dating, zircon trace element geochemistry, whole-rock geochemistry, and zircon Lu–Hf isotopes. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) zircon U–Pb analyses were conducted to constrain the crystallization ages of the monzonite (127.06 ± 0.54 Ma and 126.83 ± 0.75 Ma) and quartz monzonite (127.2 ± 0.5 Ma and 128.59 ± 0.62 Ma) to the Early Cretaceous, marking a significant magmatic event. Many of the zircons contain inherited Neoproterozoic cores (718–760 Ma and 800–860 Ma), indicating the assimilation of deep crustal materials of this age. The monzonite is metaluminous, with moderate SiO₂ (61.61–62.41 wt.%), high alkalis (Na₂O + K₂O = 7.48–7.92 wt.%), and A/CNK = 0.72–0.91. The quartz monzonite has higher SiO₂ (66.26–68.18 wt.%) and alkalis (8.32–9.33 wt.%). Both rock types exhibit similar trace and rare earth element patterns: enrichment in large-ion lithophile and light rare earth elements, depletions in Nb, Ta, and Ti, no significant Zr-Hf depletion, and weak negative Eu anomalies (δEu ≈ 0.84–1.00). Their low Zr + Nb + Ce + Y contents, Ga/Al ratios, and TFeO/MgO ratios indicate that they have an I-type granite affinity. The Early Cretaceous zircons have highly negative ε_Hf(t) values (−33.7 to −23.5) and ancient two-stage model ages (2622–3247 Ma), which are consistent with derivation from Archean crust. The inherited Neoproterozoic zircons have younger Paleo–Mesoproterozoic T_DM2 ages. The evidence suggests that both intrusions were mainly generated by partial melting of ancient Archean basement, with minor mantle input. The magma generation was likely triggered by crustal anatexis induced by the underplating of mantle-derived magmas in an extensional tectonic regime, coeval with Early Cretaceous magmatism in the Sulu orogen.

1. Introduction

Fluorite, distinguished by its characteristic fluorescence under ultraviolet light or cathode ray excitation, holds substantial industrial significance beyond its esthetic value. This mineral and its derivatives are critically important in multiple strategic emerging industries, including advanced materials, information technology, new energy, high-end manufacturing, and energy conservation [1,2]. Its strategic relevance stems from its indispensable applications in areas closely linked to national security, as well as its highly heterogeneous global distribution. High-purity fluorine compounds derived from fluorite are essential in sensitive sectors such as national defense, aerospace, semiconductor technology, and new energy, leading to its designation as a critical strategic non-metallic mineral by major economies, including China, the United States, and the European Union. China hosts abundant fluorite resources, which are mainly distributed in South China, the southern segment of the Greater Khingan Range, the Qinling–Qilian–Kunlun Orogenic Belt, and the Altyn region [3,4,5,6,7]. The eastern China Sulu Orogenic Belt, formed during the Indosinian orogeny through subduction and collision between the North China and South China blocks [8,9], experienced extensive magmatism in the Late Mesozoic, including widespread Early Cretaceous granitic intrusions [10]. Previous research on Mesozoic magmatic rocks in this region has largely centered on the magma sources, petrogenesis, tectonic setting, and their implications for the post-collisional evolution of the orogenic belt [11,12,13,14,15,16].

Recent discoveries of fluorite–barite deposits in the Donghai–Linshu area, located in the southwestern segment of the Sulu Orogenic Belt, have drawn attention to the region’s mineral potential. Early Cretaceous granites are also present within the mining district, providing an opportunity to investigate the relationship between the magmatism and mineralization. A detailed understanding of these granitic rocks is essential for elucidating the evolution of the felsic magmatism and the genesis of the fluorite–barite deposits in this area. In this study, we employed an integrated analytical approach, including field geological surveys, drill core observations, and laboratory analyses of monzonite and quartz monzonite samples from the Jiashan fluorite–barite mining area in Donghai-Linshu area. The analytical methods included laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon dating, in situ zircon trace element analysis, whole-rock major and trace element geochemistry, and zircon Lu–Hf isotope analysis. The objectives of this study were to precisely determine the emplacement age, classify the genetic type, characterize the magma source, and reconstruct the petrogenetic history of these intrusive rocks. The findings provide a better understanding of their origin and provide important data for assessment of the metallogenic prospects of the Donghai–Linshu area.

2. Geologic Background

The Qinling–Dabie–Sulu Orogenic Belt, extending across central China, is a major tectonic feature formed during the Indosinian orogeny through the collision and amalgamation of the North China and South China blocks. Its easternmost segment, the Sulu Orogenic Belt, is bounded to the west and north by the Yishu Fault—the Shandong segment of the Tancheng–Lujiang Fault Zone—and the Wulian–Weihai Fault, respectively, which separate it from the North China Block. To the south, the Jiashan–Xiangshui Fault demarcates its boundary with the Yangtze Block. The belt exhibits a general NNE-SSW structural trend (Figure 1a). Recognized as a world-class high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic terrane, the Dabie–Sulu Orogenic Belt is distinguished by extensive exposures of HP and UHP metamorphic rocks. Investigations of these units indicate that the continental crust of the South China Block was subducted to mantle depths during the Triassic [17,18]. Based on lithological assemblages and metamorphic grade, the Sulu Orogenic Belt can be subdivided into a southern HP metamorphic zone and a northern UHP metamorphic zone (Figure 1a). The region has experienced multiple magmatic episodes, predominantly during the Precambrian, Indosinian, Jurassic, and Cretaceous. The Precambrian magmatic activity in the Sulu Orogenic Belt is represented by Meso- to Neoproterozoic orthogneisses and eclogites [19,20]. The Indosinian magmatism is characterized by alkali-rich intrusions in the eastern part of the orogen, including the Jiazi Mountain, Xingjia, and Cuoshan plutons, which have emplacement ages of 225 to 205 Ma [13,14,21,22,23,24]. The Late Jurassic magmatic rocks are primarily exposed on the Jiaodong Peninsula and are interpreted as products of partial melting of thickened crust. They are aged 160 to 150 Ma [24,25]. Furthermore, leucocratic bands (156–151 Ma [26]) and pegmatites [27] are extensively developed within the gneisses in the high-pressure to ultrahigh-pressure terrane.

Early Cretaceous magmatic rocks (143–111 Ma [11,12,14,15,16,29,30,31,32,33,34,35,36]) are widely distributed throughout the Dabie–Sulu Orogenic Belt and are generally attributed to post-collisional magmatic activity following the orogeny between the North China and South China blocks. The presence of Neoproterozoic inherited zircon cores in some of the Early Cretaceous granites suggests the incorporation of deeply subducted Neoproterozoic orthogneisses in their magma sources [16,31,37,38].

3. Geology and Samples of the Jiashan Fluorite–Barite Deposit

The study area is situated in the Donghai-Linshu region along the southwestern margin of the Sulu ultrahigh-pressure (UHP) metamorphic belt (Figure 1a). The regional structural framework, influenced by the Tan-Lu Fault Zone, is dominated by NNE-NE and nearly E-W trending faults. These structures not only control the spatial distribution of the Mesozoic intrusive rocks but also function as critical ore-controlling features, and they host a series of non-metallic deposits—including the Jiashan fluorite–barite deposit examined in this study—along the E-W and NNE-NE trending fault zones (Figure 1b). Outcrops in the Donghai–Linshu area predominantly consist of pre-Indosinian metamorphic rocks and Mesozoic sequences. The pre-Indosinian metamorphic basement is mainly composed of various orthogneisses, with subordinate paragneiss, marble, kyanite quartzite, and eclogite [39,40]. Granitic gneisses that have undergone retrograde amphibolite-facies metamorphism constitute over 80% of the pre-Indosinian metamorphic rocks [28]. Previous studies indicate that the protoliths of the eclogites and orthogneisses were primarily Neoproterozoic rift-related bimodal volcanic rocks [41,42], which subsequently experienced UHP metamorphism [28,43,44,45]. The Mesozoic strata are dominated by the Lower Cretaceous Qingshan Formation and the Upper Cretaceous Wangshi Formation. The Qingshan Formation consists of sedimentary volcanic breccias, andesite, and andesitic volcanic breccias, while the Wangshi Formation consists of silty mudstone, sandstone, and conglomeratic sandstone, with localized copper mineralization.

Mesozoic magmatic rocks are extensively distributed in the Donghai–Linshu area, and their emplacement ages are concentrated in the Cretaceous (127–118 Ma [12,30,31,32]). These intrusions generally exhibit NE to NNE trends, collectively forming an NE-striking magmatic belt (Figure 1b). In the contact zone between the Taolin and Jiashan plutons, secondary faults and dense joint systems are well developed and frequently contain cataclasites and mineral veins filled with fluorite and barite. Representative fluorite–barite occurrences (or deposits) include those in Chutuan, Jiashan, Shanzuokou, Luozhuang, and Shuanghu.

The Jiashan fluorite–barite deposit, the focus of this investigation, is located on the eastern margin of the Jiashan pluton (Figure 1b). The Jiashan pluton is primarily composed of medium-grained monzogranite, as well as subordinate medium-grained porphyritic granodiorite, fine-grained porphyritic quartz diorite and monzonite. It predominantly intrudes into biotite monzonitic gneiss and K-feldspar gneiss of the regional metamorphic basement. A network of secondary fractures and densely jointed zones, which are mineralized with barite and fluorite, is developed along the periphery of the pluton. The Jiashan fluorite–barite deposit is specifically hosted within a fault zone along the pluton’s margin (Figure 2a).

The surface geology in the Jiashan mining area is dominated by the Donghai Group, comprising biotite monzonitic gneiss, biotite plagioclase gneiss, and biotite K-feldspar gneiss. Mesozoic magmatic rocks are extensively exposed within the area, including monzogranite, lamprophyre, (quartz) monzonite, fine-grained aplite dikes, and granite porphyry. With the exception of the monzogranite, which forms stock-like intrusions in the Donghai Group, the other lithologies typically occur as NE-trending dikes (Figure 2a). In contrast to the predominant NE orientation of these dikes, the main orebody of the Jiashan fluorite–barite deposit strikes approximately N-S (Figure 2a). Drill core logging confirms that the subsurface lithology is generally consistent with the surface exposures (Figure 2b), although amphibolite is additionally encountered in drill holes ZKB001 and ZKB401. The Mesozoic magmatic rocks intersected by the drill cores are predominantly monzonite and quartz monzonite (Figure 2b).

According to the mineral geological survey data from the Jiangsu Geological Exploration Institute, eight fluorite–barite mineralized veins has been identified within the Jiashan mining area, including two principal veins (Brt-1 and Brt-2) with widths of >0.5 m. Trenching data indicate that the main orebody (Brt-1) attains a maximum width of 5.4 m, strikes NNW to approximately NS, dips westward at 64°, extends over 600 m along strike, and exhibits gradual southward thinning. The vein is characterized by the coexistence of fluorite and barite, and the average CaF₂ and BaSO₄ contents are 20.41% and 50.45%, respectively. The immediate host rocks comprise granitic gneiss and biotite-hornblende plagioclase gneiss. The subsidiary Brt-2 vein measures approximately 0.7 m in width, strikes NW at 335°, and dips westward at 70°. This vein also contains associated fluorite and barite mineralization, with CaF₂ and BaSO₄ contents of 16.01% and 71.25%, respectively. Its wall rocks consist of lamprophyre dikes and biotite plagioclase gneiss.

Due to intense surface weathering in the study area, surface samples are not suitable for whole-rock geochemical analysis; therefore, we selected drill core samples for our analyses. The analyzed samples, obtained from drill cores collected within the mining area, comprise monzonite and quartz monzonite. In the drill core, the monzonite and quartz monzonite is usually cut by fluorite–barite veins, demonstrating that the fluorite–barite veins intruded later than the monzonite and quartz monzonite. The monzonite hand specimens exhibit gray-black to light brown coloration and display either fine-grained monzonitic (Figure 3a) or porphyritic textures (Figure 3b). Mineralogically, they predominantly consist of plagioclase (35%–50%) and alkali feldspar (30%–45%), with subordinate amphibole (2%–7%) and biotite (~5%). Quartz is present in trace amounts in some samples. The accessory minerals mainly include zircon (Figure 3b) and apatite. The plagioclase occurs as euhedral to subhedral crystals ranging from 0.2 to 1.5 mm in size, as well as phenocrysts up to 2 mm, and the composition is predominantly andesine to labradorite. Some of the phenocrysts exhibit distinct zoning (Figure 3b), and partial sericitization can be observed in certain grains. The alkali feldspar occurs as subhedral crystals, mostly measuring 0.2–1.2 mm, ns exhibits varying degrees of argillic alteration. Mafic minerals exhibit different extents of chloritization. The quartz monzonite hand specimens display gray-brown coloration and medium- to fine-grained, locally porphyritic textures (Figure 3c). Their mineral assemblage includes plagioclase (20%–35%), alkali feldspar (40%–50%), quartz (10%–15%), and minor biotite (2%–5%) (Figure 3d). The accessory minerals comprise zircon, sphene (Figure 3d), and apatite. The plagioclase crystals (0.5–2.0 mm) exhibit more developed polysynthetic twinning and greater euhedrality than the alkali feldspar, and some of the grains exhibit sericitization. The alkali feldspar is predominantly orthoclase (0.5–2 mm) with partial kaolinization. The quartz occurs as anhedral interstitial grains (0.3–0.8 mm) between feldspar grains. The biotite forms subhedral flakes (0.5–1 mm) with chloritization alteration.

4. Analytical Procedures

Zircon separation was performed using conventional magnetic separation and heavy liquid techniques to obtain preliminary concentrates of non-magnetic heavy minerals. Representative zircon grains were manually selected under a binocular microscope and mounted in epoxy resin. The mounts were subsequently polished to expose approximately one-third to one-half of each zircon grain for analysis. Transmitted and reflected light microscopy, as well as cathodoluminescence (CL) imaging, were employed to characterize the morphology and internal structures of the zircons.

The U–Pb zircon dating was conducted via laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) at the Microanalysis Laboratory of Nanjing Hongchuang Exploration Technology Service Co., Ltd. The analytical system comprised a Resolution SE 193 nm deep-ultraviolet laser (Applied Spectra, West Sacramento, CA, USA) coupled with an S155 dual-volume sample cell and an Agilent 8900 ICP–MS instrument (Agilent, Santa Clara, CA, USA). Each analysis spot was pre-ablated with five laser pulses (3 μm depth) to eliminate surface contamination. The analytical conditions included a spot size of 30 μm, a repetition rate of 5 Hz, and a fluence of 3.5 J/cm². The data reduction was performed using the Iolite software (2010) package [46]. Zircon standard as utilized as the external calibrant, while GJ-1 was analyzed as a quality control reference material. After every 10–12 sample analyses, two analyses of 91500 and one analysis of GJ-1 were conducted. The trace element data were processed using the Iolite program [47].

The whole-rock major and trace element analyses were performed by the ALS Laboratory Group (Guangzhou, China) and Nanjing Hongchuang Exploration Technology Service Co., Ltd., Nanjing, China, respectively. The major element concentrations were determined via X-ray fluorescence (XRF) spectrometry. The sample preparation involved thoroughly mixing 2 g of dried powder with Li₂B₄O₇ flux in a 1:5 ratio and fusing the mixture into glass beads at 1150–1250 °C. The trace element analyses were conducted using ICP–MS. The sample digestion procedure was as follows: 50 mg of dried sample powder were weighed into a Teflon bomb, followed by sequential addition of 1 mL of high-purity HNO₃ and 1 mL of high-purity HF. The sealed bomb was placed in a steel jacket and heated at 190 °C for over 24 h. After cooling, the solution was evaporated to dryness on a hotplate at 140 °C. Subsequently, 1 mL of HNO₃ was added and the solution was evaporated again. Then, 1 mL of high-purity HNO₃, 1 mL of Milli-Q water, and 1 mL of an internal standard solution containing 1 μg/g of In were added. The bomb was resealed and heated at 190 °C for over 12 h. The final solution was transferred to a polyethylene vial and diluted to 100 g with 2% HNO₃ for ICP–MS measurement.

The fluoride (F) concentrations were determined using the ion-selective electrode (ISE) method at Nanjing Hongchuang Exploration Technology Service Co., Ltd. A 0.5 g sample aliquot was thoroughly mixed with 4 g of NaOH in a nickel crucible, followed by coverage with an additional 1 g of NaOH. The crucible was heated gradually to 700 °C in a muffle furnace, held at this temperature for 15 min, and then cooled. The fused material was transferred into a 250 mL plastic beaker containing approximately 60 mL of hot water. After rinsing the crucible with hot water, the solution was cooled, transferred to a 100 mL volumetric flask, shaken thoroughly, and filtered or clarified. A 10 mL aliquot of the supernatant was placed in a 50 mL plastic beaker, mixed with 7.5 mL of sodium citrate solution, and treated with two drops of phenol red indicator. The pH was adjusted to a rose-red hue using sodium hydroxide solution (50 g/L) and then was adjusted to an orange-red hue using hydrochloric acid (1 + 1) to achieve a pH of 6.8–7.1. Subsequently, 2.5 mL of triethanolamine buffer solution was added, and the mixture was transferred to a 50 mL volumetric flask, diluted to volume with water, and gently mixed. The fluoride content was measured using the ion-selective electrode method.

The in situ zircon Lu–Hf isotope analyses were performed at Nanjing FocusMS Technology Co., Ltd. Nanjing, China, using a 193 nm ArF excimer laser ablation system (Resolution LR) coupled to a Nu Plasma II multi-collector inductively coupled plasma mass spectrometer (MC–ICP–MS). The deep-ultraviolet laser beam, which was homogenized and focused onto the zircon surface, was operated at an energy density of 4.5 J/cm². Each analysis consisted of a 20 s gas blank measurement followed by 40 s of ablation using a 44-μm spot size and a repetition rate of 9 Hz. The resulting aerosol was transported by helium from the ablation cell, mixed with argon, and introduced into the MC–ICP–MS for isotope ratio measurement. The data acquisition employed an integration time of 0.3 s per cycle, generating approximately 133 datasets over the 40 s ablation period. The analytical quality was monitored by alternating analyses of three zircon reference materials (including GJ-1, 91500, Plešovice, Mud Tank, and Penglai) after every 15 unknown zircon grains.

5. Results

5.1. Whole-Rock Major and Trace Elements

The whole-rock major and trace element analytical results are presented in

Table 1. Whole-rock major and trace element data for the Jiashan monzonite and quartz monzonite.

Sample No.	ZKB002-1	ZKB002-2	ZKB002-3	ZKB002-5	ZKB002-6	ZKB401-8	ZKB401-10	ZKB401-12-3
Depth (m)	21.7	24.8	27.5	46.6	47.7	39	45	50
Lithologies	Quartz Monzonite
Major element (wt.%)
SiO2	66.26	68.18	67.41	66.96	66.59	68.16	67.54	66.53
TiO2	0.50	0.44	0.49	0.52	0.53	0.46	0.49	0.54
Al2O3	14.39	15.12	15.35	15.38	14.91	15.26	15.13	15.49
Fe2O3 T	3.76	3.16	3.43	4.17	4.03	3.43	3.66	3.91
MnO	0.15	0.06	0.07	0.08	0.09	0.06	0.09	0.09
MgO	1.29	1.32	1.46	1.48	1.68	1.48	1.48	1.62
CaO	5.12	2.58	2.76	1.86	3.15	2.50	2.72	2.91
Na2O	4.00	4.54	4.46	5.74	4.48	4.19	4.16	4.29
K2O	4.32	4.42	4.36	3.59	4.33	4.24	4.53	4.42
P2O5	0.22	0.18	0.20	0.22	0.21	0.21	0.21	0.22
LOI	4.17	1.93	2.11	2.23	3.23	1.42	1.89	2.15
Mg#	44	49	50	45	49	50	49	49
A/CNK	0.70	0.89	0.90	0.92	0.84	0.95	0.91	0.90
Trace element (μg/g)
Li	13.9	6.48	7.65	9.51	11.6	7.24	9.94	9.22
Be	1.98	2.04	2.06	1.79	1.86	2.25	2.08	2.05
Sc	6.95	5.34	6.03	4.71	5.43	6.03	6.41	6.57
V	60.1	46.8	50.8	50.3	50.4	53.9	56.2	55.5
Cr	29.0	27.5	29.3	31.8	43.1	28.3	33.0	33.5
Co	8.21	7.29	7.68	5.96	8.31	8.07	8.66	8.66
Ni	10.8	9.65	11.0	11.6	13.5	10.7	11.4	11.7
Cu	2.68	6.46	3.11	3.50	2.50	9.37	18.8	3.58
Zn	83.7	68.4	69.2	77.8	75.4	59.1	111	82.3
Ga	21.1	21.4	22.2	23.2	21.5	22.4	22.6	21.8
Rb	106	87.4	98.6	71.2	80.9	95.8	96.9	90.7
Sr	402	453	548	262	270	580	514	477
Y	19.9	14.6	13.3	13.4	14.4	13.3	14.9	15.2
Zr	234	271	233	190	176	208	237	225
Nb	10.9	11.3	10.1	9.1	7.9	9.6	10.4	10.5
Mo	0.53	0.16	0.20	0.38	0.42	0.21	0.33	0.20
Sn	1.15	1.10	1.05	1.02	0.96	1.11	1.12	1.19
Cs	0.62	0.41	0.45	0.30	0.35	0.99	0.85	0.52
Ba	1486	1769	1875	1123	1822	1719	2106	2184
La	53.5	56.4	41.9	40.5	34.9	43.8	46.9	48.5
Ce	97.4	102	80.3	74.0	65.5	80.5	88.2	93.5
Pr	10.9	11.1	9.49	8.37	7.57	8.85	9.83	10.4
Nd	40.0	39.3	34.5	31.0	28.4	32.6	34.6	37.9
Sm	6.55	5.99	5.46	4.76	4.79	5.20	5.60	6.08
Eu	1.84	1.84	1.59	1.40	1.40	1.49	1.49	1.76
Gd	5.65	5.25	4.65	4.12	3.95	4.00	4.68	5.09
Tb	0.74	0.64	0.59	0.51	0.56	0.52	0.59	0.61
Dy	3.80	2.94	2.76	2.82	2.69	2.68	2.91	3.14
Ho	0.69	0.53	0.51	0.50	0.55	0.50	0.55	0.60
Er	2.03	1.44	1.38	1.40	1.51	1.44	1.48	1.59
Tm	0.28	0.23	0.22	0.21	0.21	0.21	0.22	0.22
Yb	1.86	1.43	1.34	1.21	1.23	1.30	1.45	1.39
Lu	0.27	0.22	0.21	0.21	0.18	0.21	0.22	0.21
Hf	6.16	7.34	6.03	5.14	4.57	5.49	5.96	5.99
Ta	0.83	0.84	0.71	0.68	0.59	0.70	0.77	0.75
W	1.43	0.95	1.20	1.33	1.58	0.74	0.75	0.95
Tl	0.50	0.43	0.46	0.31	0.37	0.44	0.45	0.44
Pb	22.3	19.7	17.5	13.3	11.0	20.3	28.4	41.5
Bi	0.05	0.02	0.02	0.02	0.05	0.03	0.02	0.03
Th	8.95	9.87	6.83	7.65	6.20	7.88	8.11	7.71
U	2.05	1.76	1.28	1.48	1.39	1.61	2.00	1.76
∑REE	226	229	185	171	153	183	199	211
(La/Yb)N	20.6	28.3	22.4	24.1	20.3	24.3	23.2	25.1
Eu/Eu *	0.90	0.98	0.94	0.95	0.95	0.96	0.86	0.94
Sample No.		ZKB001-3	ZKB401-12-1	ZKB001-1	ZKB001-2	ZKB401-1	ZKB401-2	ZKB001-12
Depth (m)		63.6	50	30	32.7	18.2	19	233.7
Lithologies		Quartz monzonite		Monzonite
Major element (wt.%)
SiO2		66.32	66.56	62.41	62.16	62.28	61.61	62.10
TiO2		0.63	0.52	0.60	0.58	0.70	0.68	0.84
Al2O3		15.21	16.02	14.62	14.36	15.26	14.61	15.54
Fe2O3 T		4.75	3.75	5.53	5.36	6.59	6.04	5.74
MnO		0.09	0.07	0.11	0.10	0.13	0.13	0.11
MgO		1.33	1.61	4.62	4.46	3.76	3.49	2.92
CaO		2.09	2.86	4.39	4.82	3.37	5.34	4.64
Na2O		4.67	4.47	3.65	3.75	4.11	3.83	3.84
K2O		4.64	3.92	3.83	4.17	3.53	4.02	3.90
P2O5		0.27	0.22	0.23	0.23	0.29	0.26	0.37
LOI		2.11	1.55	1.74	2.15	3.63	3.72	2.87
Mg#		40	50	66	66	57	57	54
A/CNK		0.92	0.95	0.81	0.74	0.91	0.72	0.82
Trace element (μg/g)
Li		10.2	9.05	11.9	7.53	23.5	13.0	11.0
Be		1.51	2.07	1.71	1.84	1.70	2.13	2.30
Sc		5.10	6.49	14.6	14.5	16.0	15.3	12.0
V		58.0	55.1	102	100	120	116	99.0
Cr		10.0	29.2	223	227	108	103	88
Co		9.72	8.65	19.4	18.9	20.8	17.9	15.9
Ni		5.1	11.6	66.5	65.3	29.8	27.7	27.6
Cu		3.4	3.75	29.7	33.7	8.8	10.9	6.0
Zn		102	79.8	79.0	124	106	76.9	98.6
Ga		19.9	23.0	20.2	19.4	21.4	18.9	21.9
Rb		101	82.7	89.6	98.8	88.4	98.7	120
Sr		270	619	489	499	381	405	568
Y		16.7	13.1	18.7	19.3	21.2	19.8	18.4
Zr		275	213	211	220	203	183	251
Nb		10.7	9.6	10.5	10.4	11.1	10.0	9.5
Mo		0.26	0.23	0.06	0.20	0.42	0.24	0.07
Sn		1.05	1.01	0.95	0.92	1.20	1.07	1.15
Cs		0.30	0.70	1.50	0.27	0.24	0.27	0.68
Ba		1810	2025	1717	1718	1531	1410	1705
La		52.2	48.3	45.4	47.1	50.4	44.8	51.4
Ce		98.5	90.7	83.9	86.1	92.7	81.8	98.5
Pr		11.6	10.1	9.7	10.0	10.2	9.2	11.2
Nd		43.5	36.6	36.5	37.8	36.4	33.4	41.7
Sm		7.0	5.75	6.0	6.4	6.1	5.2	6.7
Eu		2.1	1.71	1.9	1.9	1.6	1.5	1.9
Gd		6.0	4.70	5.3	5.3	5.5	5.0	5.9
Tb		0.8	0.58	0.7	0.8	0.8	0.6	0.8
Dy		3.8	2.73	4.0	3.7	3.9	4.0	3.8
Ho		0.6	0.51	0.7	0.8	0.8	0.7	0.7
Er		1.8	1.33	2.1	2.2	2.4	2.1	1.9
Tm		0.2	0.19	0.3	0.3	0.4	0.3	0.2
Yb		1.3	1.09	1.8	2.0	2.2	2.0	1.6
Lu		0.2	0.20	0.3	0.3	0.3	0.3	0.3
Hf		7.50	5.43	5.82	5.71	5.23	4.65	6.36
Ta		0.68	0.66	0.77	0.77	0.85	0.76	0.59
W		1.22	0.88	1.18	1.28	1.19	1.00	1.50
Tl		0.47	0.41	0.45	0.49	0.41	0.44	0.47
Pb		29.0	29.2	29.3	26.2	12.8	14.3	22.8
Bi		0.10	0.03	0.08	0.12	0.05	0.04	0.07
Th		5.90	7.42	7.90	8.77	8.56	7.88	6.69
U		0.97	1.55	1.82	1.96	1.74	1.58	1.17
∑REE		230	204	199	205	214	191	226
(La/Yb)N		29.9	31.8	18.1	17.3	16.8	16.1	22.8
Eu/Eu *		0.96	0.98	1.00	0.98	0.84	0.89	0.91

Note: Fe₂O₃ ^T represents total iron expressed as ferric iron (Fe³⁺). Eu/Eu * (2 × Eu_N/(Sm_N + Gd_N)) denotes the europium anomaly.

. Due to samples’ elevated loss on ignition (LOI) values (1.42–4.17 wt.%; Table 1), the major element concentrations were recalculated to 100% on an anhydrous basis for petrogenetic discussion. The five monzonite samples exhibit moderate SiO₂ contents (61.61%–62.41%), classifying them as intermediate rocks. They are characterized by high Na₂O (3.65%–4.11%) and K₂O (3.53%–4.17%) concentrations, with K₂O/Na₂O ratios ranging from 0.86 to 1.11. On the total alkali versus silica (TAS) diagram (Figure 4a), all of the samples plot within the monzonite field, which is consistent with the petrographic observations. On the K₂O versus SiO₂ diagram (Figure 4b), the samples plot in the transition zone between the high-K calc-alkaline and shoshonitic series. The rocks exhibit moderate Al₂O₃ contents (14.36–15.54 wt.%) and belong to the metaluminous series (A/CNK = 0.72–0.91). Additionally, they exhibit high MgO (2.92–4.62 wt.%), Mg# (54–66), TiO₂ (0.58–0.84 wt.%), P₂O₅ (0.23–0.37 wt.%), total Fe₂O₃ (5.36–6.59 wt.%), and CaO (3.37–5.34 wt.%) values. In contrast, the quartz monzonite samples possess higher SiO₂ (66.26–68.18 wt.%), Na₂O (4.00–5.74 wt.%), and K₂O (3.59–4.64 wt.%) contents. On the TAS diagram (Figure 4a), they plot within the quartz monzonite field, while on the K₂O versus SiO₂ diagram (Figure 4b), they primarily plot within the high-K calc-alkaline series. Their Al₂O₃ contents (14.39–16.02 wt.%) are slightly high than those of the monzonites, and they are also classified as metaluminous (A/CNK = 0.70–0.95). The quartz monzonites exhibit lower MgO (1.29–1.68 wt.%), Mg# (40–50), TiO₂ (0.44–0.63 wt.%), P₂O₅ (0.18–0.27 wt.%), total FeO* (3.16–4.75 wt.%), and CaO (1.86–5.12 wt.%) contents compared to the monzonite samples.

The monzonite and quartz monzonite from the Jiashan area display comparable total rare earth element (REE) contents, ranging from 191 to 226 μg/g and 153 to 230 μg/g, respectively. Their Chondrite-normalized (La/Yb)_N ratios are 16.1–22.7 and 20.3–31.8, while their Eu anomalies (Eu/Eu*) are 0.84–1.00 and 0.97–1.02. The Chondrite-normalized REE diagrams (Figure 5a) reveal that the two rock types have consistent REE distribution patterns, but the quartz monzonite exhibits slightly lower light REE concentrations than the monzonite. The primitive mantle-normalized trace element spider diagrams (Figure 5b) indicate enrichment in large-ion lithophile elements (e.g., Rb, Ba, and Th) and light REEs, as well as depletions in high-field-strength elements (e.g., Nb, Ta, and Ti) for both lithologies. Notably, Zr and Hf do not exhibit significant depletion. The pronounced similarity of the trace and rare earth element patterns of the two rock types implies that they have a close genetic relationship. The geochemical characteristics of the quartz monzonite and monzonite include moderately high Sr (381–569 μg/g and 262–619 μg/g) and La (44.8–51.4 μg/g and 34.9–56.4 μg/g) contents, intermediate Y (18.4–21.0 μg/g and 13.1–19.9 μg/g) and Yb (1.62–2.15 μg/g and 1.06–1.86 μg/g) contents, and Sr/Y ratios of 18.0–30.8 and 16.1–47.1, respectively. Their (La/Yb)_N values (16.1–22.7 and 20.3–31.8) are marginally lower than those characteristic of typical adakitic rocks (Figure 6).

5.2. U–Pb Zircon Ages

For this investigation, four samples from drill cores ZKB001 (B001, monzonite), ZKB002 (B002, quartz monzonite), and ZKB401 (B401-1, monzonite; B401-2, quartz monzonite) were selected for zircon U–Pb isotope and trace element analysis. The results are presented in

Table 2. U–Pb zircon dating isotopic data for the Jiashan monzonite and quartz monzonite.

Spot No.	Th	U	Th/U	Isotope Ratios						Isotopic Ages (Ma)
	ppm			207Pb/206Pb	1σ	207Pb/235U	1σ	206Pb/238U	1σ	207Pb/235U	1δ	206Pb/238U	1δ
Monzonite (B001), 127.06 ± 0.54 Ma, MSWD = 0.24, n = 19
B001-1	605	329	1.84	0.0490	0.0027	0.1326	0.0070	0.0198	0.0002	126.4	6.4	126.7	1.6
B001-2	289	261	1.10	0.0492	0.0043	0.1330	0.0112	0.0198	0.0004	126.1	10.0	126.1	2.4
B001-3	138	130	1.06	0.0499	0.0048	0.1361	0.0128	0.0201	0.0004	128.0	11.3	128.0	2.8
B001-4	196	227	0.86	0.0489	0.0029	0.1346	0.0080	0.0200	0.0003	127.6	7.1	127.8	1.9
B001-5	139	134	1.04	0.0482	0.0045	0.1323	0.0120	0.0201	0.0005	125.1	10.8	128.0	3.0
B001-6	344	287	1.20	0.0483	0.0029	0.1296	0.0078	0.0196	0.0003	123.1	7.0	125.3	1.8
B001-7	75	76	0.99	0.0508	0.0075	0.1459	0.0226	0.0201	0.0006	135.3	19.7	128.2	3.5
B001-8	170	211	0.81	0.0469	0.0038	0.1319	0.0105	0.0203	0.0004	124.9	9.3	129.4	2.7
B001-9	116	158	0.73	0.0659	0.0029	1.1784	0.0494	0.1299	0.0017	786.2	23.1	786.9	9.5
B001-10	394	253	1.56	0.0471	0.0050	0.1276	0.0121	0.0202	0.0005	121.1	10.9	129.0	3.0
B001-11	154	168	0.91	0.0481	0.0033	0.1316	0.0086	0.0201	0.0003	124.6	7.7	128.3	2.1
B001-12	356	173	2.06	0.0649	0.0031	0.9565	0.0480	0.1072	0.0018	679.1	25.1	656.4	10.4
B001-13	154	112	1.37	0.0482	0.0043	0.1319	0.0111	0.0202	0.0003	124.3	10.0	128.8	2.1
B001-14	107	63	1.71	0.0703	0.0038	0.9559	0.0490	0.0983	0.0018	674.2	25.2	604.3	10.6
B001-15	176	94	1.87	0.0503	0.0056	0.1372	0.0149	0.0202	0.0004	128.0	13.2	128.9	2.6
B001-16	127	160	0.79	0.0491	0.0037	0.1348	0.0095	0.0201	0.0003	127.4	8.5	128.3	2.0
B001-17	109	147	0.74	0.0494	0.0039	0.1373	0.0108	0.0201	0.0003	129.3	9.6	128.6	2.2
B001-18	54	18	3.05	0.0639	0.0053	1.1537	0.0931	0.1327	0.0029	759.4	44.4	802.3	16.6
B001-19	66	72	0.92	0.0531	0.0086	0.1447	0.0231	0.0197	0.0007	133.6	20.1	125.7	4.2
B001-20	99	309	0.32	0.0664	0.0015	1.3067	0.0291	0.1425	0.0015	847.4	12.8	858.6	8.5
B001-21	112	142	0.79	0.0500	0.0045	0.1376	0.0124	0.0201	0.0004	129.9	11.1	128.2	2.5
B001-22	160	200	0.80	0.0497	0.0054	0.1339	0.0126	0.0200	0.0006	127.1	11.3	127.8	3.7
B001-23	44	336	0.13	0.0665	0.0014	1.2440	0.0259	0.1362	0.0009	821.9	11.0	823.1	5.4
B001-24	262	246	1.07	0.0473	0.0031	0.1306	0.0082	0.0201	0.0004	124.1	7.4	128.4	2.3
B001-25	258	196	1.32	0.0481	0.0078	0.1342	0.0216	0.0200	0.0005	127.0	19.4	127.3	3.1
Quartz monzonite (B002), 127.2 ± 0.5 Ma, MSWD = 0.27, n = 22
B002-1	215	172	1.25	0.0485	0.0039	0.1330	0.0103	0.0200	0.0003	125.6	9.2	127.6	2.2
B002-2	232	205	1.13	0.0491	0.0060	0.1352	0.0164	0.0200	0.0007	128.1	14.7	127.9	4.4
B002-3	243	325	0.75	0.0490	0.0022	0.1773	0.0081	0.0261	0.0003	165.1	7.0	165.9	2.2
B002-4	313	248	1.26	0.0482	0.0026	0.1299	0.0068	0.0198	0.0003	124.4	6.3	126.4	1.7
B002-5	86	83	1.04	0.0513	0.0090	0.1399	0.0244	0.0199	0.0005	130.7	21.8	127.3	3.5
B002-6	230	166	1.38	0.1062	0.0091	0.3195	0.0303	0.0214	0.0004	274.2	22.3	136.6	2.6
B002-7	254	227	1.12	0.0483	0.0033	0.1342	0.0093	0.0200	0.0003	127.2	8.3	127.4	1.8
B002-8	324	253	1.28	0.0492	0.0037	0.1309	0.0087	0.0196	0.0003	126.2	8.6	125.4	2.1
B002-9	136	155	0.87	0.0478	0.0037	0.1311	0.0098	0.0201	0.0004	124.4	8.7	128.1	2.4
B002-10	184	176	1.05	0.0486	0.0046	0.1314	0.0117	0.0200	0.0004	125.8	11.1	127.6	2.7
B002-11	67	81	0.83	0.0452	0.0064	0.1276	0.0171	0.0204	0.0006	119.9	15.2	130.1	4.0
B002-12	171	177	0.96	0.0496	0.0035	0.1319	0.0084	0.0198	0.0003	126.2	7.8	126.6	2.2
B002-13	285	250	1.14	0.0483	0.0028	0.1339	0.0078	0.0200	0.0003	126.9	7.0	127.7	1.9
B002-14	371	243	1.53	0.0465	0.0035	0.1294	0.0096	0.0199	0.0004	123.0	8.7	127.1	2.6
B002-15	137	185	0.74	0.0473	0.0038	0.1325	0.0104	0.0203	0.0004	125.4	9.3	129.6	2.7
B002-16	220	280	0.79	0.0491	0.0030	0.1359	0.0083	0.0202	0.0003	128.7	7.4	128.6	2.0
B002-17	251	170	1.48	0.0497	0.0070	0.1401	0.0179	0.0207	0.0009	132.2	15.7	132.1	5.6
B002-18	87	57	1.52	0.0480	0.0058	0.1344	0.0162	0.0200	0.0005	124.5	14.3	127.8	3.4
B002-19	143	126	1.14	0.0473	0.0050	0.1315	0.0129	0.0205	0.0006	124.4	11.6	130.6	3.7
B002-20	544	366	1.49	0.0474	0.0022	0.1293	0.0060	0.0198	0.0002	123.0	5.3	126.5	1.3
B002-21	136	218	0.63	0.0492	0.0053	0.1371	0.0141	0.0204	0.0005	129.4	12.4	130.1	3.0
B002-22	27	15	1.74	0.0572	0.0165	0.1557	0.0444	0.0204	0.0015	135.3	36.6	130.2	9.3
B002-23	96	122	0.79	0.0485	0.0055	0.1341	0.0145	0.0203	0.0005	126.4	12.8	129.4	3.5
B002-24	123	135	0.92	0.0475	0.0039	0.1305	0.0103	0.0202	0.0004	123.2	9.3	128.9	2.4
B002-25	251	201	1.25	0.0500	0.0036	0.1360	0.0091	0.0201	0.0004	128.7	8.1	128.0	2.3
Monzonite (B401-1), 126.8 ± 0.8 Ma, MSWD = 0.58, n = 8
Cretaceous zircons
B401-1-11	156	180	0.87	0.0486	0.0046	0.1366	0.0135	0.0202	0.0004	128.7	12.0	128.6	2.7
B401-1-13	479	315	1.52	0.0535	0.0057	0.1446	0.0153	0.0196	0.0005	136.2	13.5	125.2	3.0
B401-1-14	1802	618	2.92	0.0503	0.0039	0.1411	0.0103	0.0202	0.0004	133.7	9.1	129.0	2.7
B401-1-17	51	170	0.30	0.0510	0.0064	0.1433	0.0183	0.0200	0.0005	134.7	16.2	127.6	3.5
B401-1-26	133	363	0.37	0.0491	0.0022	0.1357	0.0061	0.0201	0.0002	128.8	5.4	128.4	1.4
B401-1-29	396	320	1.24	0.0509	0.0040	0.1359	0.0095	0.0197	0.0004	128.9	8.5	126.1	2.2
B401-1-31	1345	359	3.74	0.0503	0.0057	0.1418	0.0174	0.0202	0.0006	134.0	15.4	129.2	3.9
B401-1-33	836	1228	0.68	0.0485	0.0021	0.1310	0.0058	0.0196	0.0002	124.8	5.2	125.1	1.3
Triassic zircon
B401-1-16	26	162	0.16	0.0488	0.0031	0.2241	0.0138	0.0337	0.0006	203.4	11.5	213.4	3.4
718.2–771.6 Ma zircons
B401-1-3	49	67	0.74	0.0643	0.0025	1.1323	0.0432	0.1272	0.0013	761.7	20.9	771.6	7.2
B401-1-4	140	161	0.87	0.0661	0.0035	1.1066	0.0560	0.1213	0.0016	753.1	26.9	738.0	8.9
B401-1-5	211	187	1.13	0.0710	0.0018	1.1893	0.0367	0.1215	0.0017	791.5	16.9	740.4	9.2
B401-1-6	392	128	3.07	0.0631	0.0020	1.0745	0.0342	0.1235	0.0013	737.0	16.9	750.8	7.5
B401-1-7	196	104	1.89	0.0652	0.0020	1.0719	0.0301	0.1200	0.0011	741.7	15.9	730.2	6.2
B401-1-15	147	140	1.06	0.0658	0.0033	1.0602	0.0481	0.1179	0.0023	731.4	24.0	718.5	13.5
B401-1-18	213	123	1.73	0.0659	0.0046	1.1271	0.0784	0.1245	0.0022	761.1	37.1	756.4	12.7
B401-1-19	503	270	1.87	0.0647	0.0011	1.1152	0.0199	0.1256	0.0008	761.8	9.5	762.7	4.9
B401-1-20	150	237	0.63	0.0645	0.0013	1.1005	0.0229	0.1241	0.0010	751.8	11.1	754.0	6.0
B401-1-23	210	326	0.64	0.0648	0.0024	1.1004	0.0407	0.1232	0.0014	751.8	19.9	749.0	8.0
B401-1-25	176	203	0.87	0.0640	0.0026	1.1022	0.0467	0.1247	0.0017	752.2	22.6	757.5	9.8
B401-1-27	289	322	0.90	0.0638	0.0013	1.0478	0.0224	0.1197	0.0010	726.4	11.1	728.6	5.9
B401-1-30	102	141	0.72	0.0653	0.0029	1.1299	0.0508	0.1248	0.0018	764.1	24.3	758.1	10.4
B401-1-34	83	138	0.60	0.0642	0.0029	1.0782	0.0441	0.1224	0.0019	740.4	21.9	744.2	11.0
809–845.4 Ma zircons
B401-1-1	111	462	0.24	0.0672	0.0024	1.2443	0.0445	0.1337	0.0015	819.6	20.0	809.0	8.6
B401-1-2	60	329	0.18	0.0674	0.0015	1.2878	0.0337	0.1386	0.0017	841.5	13.9	836.7	9.5
B401-1-8	78	472	0.16	0.0665	0.0016	1.2672	0.0349	0.1360	0.0017	830.4	15.6	821.7	9.7
B401-1-9	87	388	0.23	0.0664	0.0011	1.2293	0.0214	0.1342	0.0008	812.8	9.8	811.6	4.3
B401-1-12	110	258	0.43	0.0664	0.0015	1.2468	0.0289	0.1364	0.0010	819.5	13.1	824.4	5.8
B401-1-22	215	450	0.48	0.0665	0.0012	1.2236	0.0254	0.1341	0.0010	810.7	11.5	811.2	5.8
B401-1-24	75	317	0.24	0.0669	0.0014	1.2615	0.0289	0.1369	0.0014	827.2	13.1	827.3	7.9
B401-1-28	76	307	0.25	0.0670	0.0015	1.2708	0.0288	0.1380	0.0012	831.5	13.0	833.3	6.8
B401-1-32	50	328	0.15	0.0679	0.0020	1.3200	0.0366	0.1401	0.0015	853.2	16.4	845.4	8.6
Other zircons
B401-1-1	120	295	0.41	0.0751	0.0014	1.7938	0.0371	0.1742	0.0020	1041.9	13.5	1034.9	1041.9
B401-1-2	300	816	0.37	0.0716	0.0011	1.5619	0.0246	0.1587	0.0012	954.5	9.8	949.3	954.5
Quartz monzonite (B401-2), Mean age = 128.6 ± 0.6 Ma, MSWD = 0.22, n = 21
B401-2-1	156	188	0.83	0.0492	0.0036	0.1365	0.0096	0.0203	0.0003	128.9	8.6	129.3	1.9
B401-2-2	124	105	1.18	0.0474	0.0041	0.1344	0.0117	0.0205	0.0004	126.1	10.4	130.6	2.5
B401-2-3	157	217	0.72	0.0509	0.0067	0.1428	0.0181	0.0206	0.0006	134.4	15.9	131.7	3.5
B401-2-4	138	173	0.80	0.0510	0.0053	0.1512	0.0148	0.0217	0.0005	142.0	12.8	138.2	2.8
B401-2-5	68	49	1.39	0.0527	0.0074	0.1411	0.0196	0.0203	0.0006	132.3	17.8	129.8	4.1
B401-2-6	138	201	0.69	0.0512	0.0063	0.1413	0.0169	0.0202	0.0007	139.0	18.5	129.2	4.3
B401-2-7	109	117	0.93	0.0499	0.0056	0.1377	0.0159	0.0201	0.0005	129.4	14.1	128.3	3.3
B401-2-8	194	172	1.13	0.0487	0.0038	0.1355	0.0100	0.0203	0.0004	127.9	8.9	129.8	2.3
B401-2-9	213	159	1.34	0.0493	0.0045	0.1370	0.0118	0.0204	0.0004	129.2	10.5	130.0	2.7
B401-2-10	207	183	1.13	0.0466	0.0036	0.1293	0.0099	0.0203	0.0004	122.5	8.8	129.5	2.4
B401-2-11	67	63	1.06	0.0488	0.0059	0.1366	0.0160	0.0204	0.0005	127.1	14.1	129.9	3.2
B401-2-12	80	65	1.24	0.0458	0.0062	0.1283	0.0170	0.0206	0.0006	120.3	15.2	131.2	3.7
B401-2-13	223	262	0.85	0.0477	0.0033	0.1343	0.0103	0.0200	0.0004	127.3	9.2	127.9	2.5
B401-2-14	109	156	0.70	0.0534	0.0078	0.1452	0.0199	0.0201	0.0006	136.3	17.4	128.1	3.9
B401-2-15	144	167	0.86	0.0491	0.0058	0.1350	0.0158	0.0200	0.0005	127.5	14.1	127.9	3.1
B401-2-16	295	253	1.17	0.0482	0.0026	0.1339	0.0070	0.0202	0.0003	127.0	6.3	128.8	1.6
B401-2-17	33	32	1.06	0.0624	0.0039	1.1098	0.0682	0.1299	0.0020	755.4	36.0	786.8	11.4
B401-2-18	204	174	1.17	0.0494	0.0060	0.1434	0.0187	0.0207	0.0006	134.8	16.5	132.2	3.9
B401-2-19	73	55	1.32	0.2528	0.0456	1.6704	0.5430	0.0311	0.0041	734.0	148.7	195.7	25.0
B401-2-20	135	172	0.78	0.0486	0.0047	0.1329	0.0123	0.0200	0.0004	125.5	11.0	127.7	2.7
B401-2-21	234	202	1.16	0.0536	0.0065	0.1541	0.0197	0.0205	0.0007	144.5	17.4	130.6	4.3
B401-2-22	96	110	0.87	0.0499	0.0046	0.1365	0.0122	0.0201	0.0005	128.5	10.8	128.1	3.3
B401-2-23	106	52	2.04	0.0540	0.0087	0.1423	0.0209	0.0204	0.0008	131.2	18.4	130.0	5.1
B401-2-24	63	50	1.27	0.0662	0.0036	1.2012	0.0627	0.1321	0.0018	789.1	29.0	799.4	10.5
B401-2-25	294	262	1.12	0.0471	0.0040	0.1295	0.0108	0.0200	0.0004	123.1	9.7	127.8	2.7
GJ-1
GJ-1-1	21	270	0.08	0.0598	0.0015	0.8137	0.0205	0.0984	0.0007	602.5	11.5	605.0	4.3
GJ-1-2	19	255	0.08	0.0596	0.0015	0.8112	0.0207	0.0987	0.0007	601.0	11.6	607.0	4.1
GJ-1-3	19	254	0.08	0.0599	0.0013	0.8145	0.0181	0.0985	0.0007	603.3	10.1	605.8	4.3
GJ-1-4	19	254	0.08	0.0593	0.0014	0.8035	0.0197	0.0982	0.0007	596.9	11.1	603.6	4.1
GJ-1-5	18	245	0.07	0.0598	0.0018	0.8215	0.0234	0.0994	0.0009	607.1	13.0	611.0	5.1
GJ-1-6	19	251	0.07	0.0598	0.0015	0.8046	0.0203	0.0977	0.0007	597.5	11.4	601.0	4.3
GJ-1-7	19	253	0.07	0.0599	0.0013	0.8153	0.0182	0.0985	0.0008	603.9	10.2	605.6	4.8
GJ-1-8	18	249	0.07	0.0600	0.0013	0.8182	0.0171	0.0990	0.0008	605.7	9.6	608.8	4.4
GJ-1-9	18	242	0.07	0.0602	0.0016	0.8200	0.0215	0.0991	0.0007	606.0	12.0	609.3	4.0
GJ-1-10	19	248	0.07	0.0599	0.0014	0.8258	0.0192	0.0995	0.0008	611.0	10.5	611.6	4.5
GJ-1-11	19	251	0.07	0.0594	0.0015	0.8036	0.0206	0.0979	0.0007	596.9	11.6	602.3	4.0

. The zircon U–Pb concordia diagrams and weighted mean age calculations were generated using IsoplotR (2018) software [48]. The zircons from all samples are characterized as colorless, transparent, and euhedral short-prismatic crystals. For sample B001, the zircon dimensions typically range from 100 to 200 μm in length and from 70 to 150 μm in width, yielding length-to-width ratios of 2:1–3:1. Cathodoluminescence imaging revealed that the zircons have well-developed oscillatory zoning, which is consistent with a magmatic origin [49]. A minor population of zircons exhibits a rounded morphology with homogeneous, bright CL internal structures and oscillatory-zoned overgrowth rims (insets in Figure 7), suggesting that they are inherited or captured zircons.

Twenty-five analytical spots yielded Th contents of 44.4–605 μg/g, U contents of 17.7–336 μg/g, and Th/U ratios of 0.15–3.05, which are consistent with the characteristics of magmatic zircon [49]. Five spots on rounded zircons yielded Neoproterozoic ²⁰⁶Pb/²³⁸U ages ranging from 604.3 ± 10.6 Ma to 858.6 ± 8.5 Ma. One yielded a discordant age and was therefore excluded from the calculation of the weighted mean age. The remaining 19 spots yielded clustered ²⁰⁶Pb/²³⁸U ages, with a weighted mean age of 127.1 ± 0.5 Ma (n = 19, MSWD = 0.24; Figure 7a).

The red circles represent the positions of the spots for the zircon U–Pb ages and trace elements, and the yellow circles are the locations of the zircon in situ Lu–Hf analysis. The scales on the cathodoluminescence images are all 100 μm.

The zircon crystals from monzonite sample B401-1 exhibit dimensions of 80–200 μm in length and 80–100 μm in width, with length-to-width ratios ranging from 3:2 to 3:1. Based on the morphological characteristics, these zircons can be classified into two distinct types: rounded grains, interpreted as inherited or captured zircons, and euhedral short-prismatic crystals displaying well-defined magmatic oscillatory zoning [49]. Analytical results from 34 spots yielded Th contents of 25.6–1802 μg/g, U contents of 66.7–1228 μg/g, and Th/U ratios of 0.15–3.74. Spot B401-1-16, characterized by low Th (26 μg/g) and U (162 μg/g) contents and a low Th/U ratio (0.16), is interpreted to be of metamorphic origin. Its ²⁰⁶Pb/²³⁸U age of 213.4 ± 3.4 Ma corresponds to the Indosinian metamorphic event in the Dabie–Sulu Orogenic Belt [18]. Spot B401-1-10 yielded a ²⁰⁷Pb/²⁰⁶Pb age of 1062.4 ± 38.2 Ma, while spot B401-1-21 yielded a ²⁰⁶Pb/²³⁸U age of 949.3 ± 6.5 Ma. The remaining 31 analytical spots are predominantly concentrated in three distinct age clusters (Figure 7b): 125.1–129.2 Ma, 718.5–771.6 Ma, and 809.0–845.4 Ma. The corresponding weighted mean ages are 126.8 ± 0.8 Ma (n = 8, MSWD = 0.58), 748.8 ± 2.0 Ma (n = 14, MSWD = 3.7), and 821.8 ± 2.3 Ma (n = 9, MSWD = 2.9).

The zircon crystals from quartz monzonite sample B002 predominantly range from 100 to 250 μm in length and from 70 to 130 μm in width, with length-to-width ratios of 2:1 to 3:1. The cathodoluminescence (CL) images display well-developed oscillatory zoning, characteristic of a magmatic origin [49]. The analytical results for 25 spots yielded Th contents of 26.7–544 μg/g, U contents of 15.3–366 μg/g, and Th/U ratios of 0.63–1.74, consistent with magmatic zircon characteristics [49]. After excluding spot B002-6 (33% concordance), spot B002-3 (²⁰⁶Pb/²³⁸U age of 165.9 ± 2.2 Ma), and spot B002-22 (high analytical uncertainty), the remaining 22 spots yielded clustered ²⁰⁶Pb/²³⁸U ages ranging from 125.4 ± 2.1 Ma to 132.1 ± 5.6 Ma, with a weighted mean age of 127.2 ± 0.5 Ma (n = 22, MSWD = 0.27; Figure 7c).

The zircon grains from quartz monzonite sample B401-2 range from 100 to 200 μm in length and from 80 to 120 μm in width, with length-to-width ratios of 2:1 to 3:1. Cathodoluminescence imaging revealed that the majority of the grains exhibit well-developed oscillatory zoning, consistent with a magmatic origin. A subordinate population of rounded zircons displays internal magmatic oscillatory zoning with bright, homogeneous overgrowth rims, suggesting an inherited or captured origin. The analytical results of 25 spots yielded Th contents of 33.3–295 μg/g, U contents of 31.5–262 μg/g, and Th/U ratios of 0.69–2.04, all of which are characteristic of magmatic zircons. After excluding spot B401-2-19 (−16% concordance) and spots B401-2-4 (138.2 ± 2.8 Ma), B401-2-17 (786.8 ± 11.4 Ma), and B401-2-24 (799.4 ± 10.5 Ma) due to their discordant ages, the remaining 21 spots yielded clustered ²⁰⁶Pb/²³⁸U ages ranging from 127.7 ± 2.7 Ma to 132.2 ± 3.9 Ma, with a weighted mean age of 128.6 ± 0.6 Ma (n = 21, MSWD = 0.22; Figure 7d).

In summary, both the monzonite and quartz monzonite from the Jiashan area were emplaced during the Early Cretaceous and have crystallization ages constrained between 126 and 129 Ma. These intrusions also contain abundant Neoproterozoic inherited or captured zircons, with ages predominantly ranging from 720 to 845 Ma.

5.3. Zircon Geochemistry

Zircons in magmatic rocks exhibit diverse origins; however, only those crystallized directly from the melt during magma solidification (i.e., magmatic zircons) can accurately record the source characteristics and physicochemical conditions of their parental magma. In this study, we focused exclusively on Cretaceous-aged zircons for detailed investigation. The in situ trace element analytical results are presented in

Table 3. Zircon in situ trace element data for the Jiashan monzonite and quartz monzonite.

Sample	P	Ti	Y	Nb	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb
Monzonite (B001)
B001-1	218	5.36	1385	9.30	0.07	95.5	0.20	3.82	6.98	2.85	32.7	10.5	125	45.6	219	45.4	419
B001-2	181	5.23	1208	5.93	0.09	61.5	0.12	1.63	3.86	1.86	20.7	7.54	96.7	38.8	193	42.2	403
B001-3	233	8.75	1320	3.12	0.13	46.0	0.18	2.70	5.30	2.60	24.9	8.75	109	42.0	212	45.8	430
B001-4	172	5.33	1382	5.84	0.07	57.6	0.08	1.56	3.18	1.84	19.8	7.45	102	42.1	225	50.2	493
B001-5	312	7.62	1228	3.57	0.73	52.0	0.28	2.47	3.67	2.02	20.5	7.19	96.1	38.6	199	44.0	425
B001-7	273	8.37	735	2.40		28.9	0.10	1.93	3.45	0.97	14.8	5.01	61.2	23.2	117	25.5	241
B001-8	158	4.00	1188	5.35		51.0	0.07	1.16	3.10	1.71	17.9	6.45	87.5	36.0	190	42.6	418
B001-10	233	7.25	1465	4.24		77.8	0.16	3.00	4.84	2.41	25.2	8.93	114	45.7	235	51.3	477
B001-11	211	4.09	1001	3.37	0.06	40.9	0.20	2.89	5.00	2.36	19.8	6.29	75.9	29.8	156	35.2	343
B001-13	361	6.82	996	2.22	0.29	42.8	0.27	3.31	5.38	1.61	23.7	7.66	87.5	31.9	151	30.8	279
B001-15	516	11.36	1278	1.86	1.05	39.8	0.68	6.95	9.52	2.90	36.6	10.8	121	41.9	192	37.9	331
B001-16	167	5.40	1192	4.22	0.01	46.9	0.07	1.57	3.42	1.92	18.5	6.76	89.4	36.1	189	41.4	403
B001-17	228	3.08	968	3.21		34.2	0.07	1.13	2.54	1.35	14.6	5.16	70.7	28.7	152	34.3	341
B001-19	262	15.43	483	2.18	0.02	28.6	0.10	1.60	2.67	0.50	10.2	3.50	41.9	14.8	73.4	15.5	144
B001-21	280	2.38	843	2.05	0.11	31.5	0.06	1.00	2.19	1.20	12.3	4.47	59.6	24.7	135	30.5	309
B001-22	218	15.60	1564	5.31	0.08	47.7	0.09	1.63	4.13	1.96	21.7	8.54	118	48.3	252	56.5	556
B001-24	193	5.73	1019	4.10	0.34	50.1	0.16	1.59	2.88	1.40	14.6	5.37	73.1	30.4	161	36.9	366
B001-25	175	3.57	1994	3.05	0.03	67.7	0.30	7.27	13.1	4.61	54.7	17.3	192	65.4	306	59.4	518
Quartz monzonite (B002)
B002-1	279	4.69	1204	3.89	0.03	57.9	0.19	3.48	6.34	2.25	28.4	9.05	106	37.9	184	37.5	346
B002-2	696	4.51	779	3.73	3.90	57.3	0.97	4.87	3.19	1.26	13.3	4.64	58	23.7	124	27.2	276
B002-4	183	3.33	923	4.27	0.19	56.3	0.14	1.85	2.96	1.63	17.4	5.92	74	28.5	143	30.7	290
B002-5	184	5.27	921	1.59	0.11	25.7	0.21	3.42	4.41	2.11	19.5	5.97	76	28.6	144	31.3	307
B002-7	144	4.04	1022	4.21		53.8	0.08	1.38	2.94	1.57	16.6	5.89	77	30.2	159	35.6	355
B002-8	237	4.48	870	3.63	0.51	53.1	0.22	1.86	3.32	1.59	17.5	5.65	70	26.9	137	29.5	281
B002-9	321	3.10	1138	3.03	0.06	37.9	0.14	1.78	3.71	1.73	17.9	6.43	86	35.0	181	39.4	392
B002-10	258	4.63	1100	4.15	0.06	52.0	0.12	2.23	4.33	1.53	20.7	7.08	88	33.7	170	37.5	353
B002-12	273	3.14	1298	3.04	0.09	45.0	0.16	3.18	5.83	2.73	26.7	8.72	106	39.8	200	42.2	402
B002-13	178	5.81	1577	5.85	0.01	87.2	0.09	1.96	4.59	2.23	25.5	9.23	120	48.7	250	54.6	515
B002-14	261	4.76	1287	4.39	0.05	73.8	0.13	2.35	5.16	2.46	24.6	8.28	104	39.7	195	40.6	381
B002-15	103	2.22	718	2.14	0.06	28.8	0.08	1.12	2.05	1.23	11.4	3.94	49	19.5	108	25.4	271
B002-16	231	5.10	1766	7.33	0.10	49.1	0.08	1.36	3.80	2.10	25.2	9.35	129	53.5	277	59.8	574
B002-17	219	4.97	913	3.71	0.05	62.7	0.13	1.74	2.90	1.36	16.2	5.32	72	28.5	143	31.3	291
B002-18	313	20.3	788	1.52	0.08	25.3	0.23	3.46	5.28	1.12	21.6	6.55	73	25.2	117	23.3	209
B002-19	282	5.90	1089	2.33	0.09	37.7	0.18	3.11	5.41	1.91	23.5	7.50	91	34.3	169	36.0	335
B002-20	220	5.07	1337	6.44	0.11	86.2	0.14	2.17	4.29	1.86	22.1	7.87	101	40.4	210	45.9	446
B002-21	274	3.81	1052	4.23	0.08	31.0	0.03	0.80	1.87	1.06	12.0	4.76	70	30.3	172	40.3	416
B002-23	184	7.38	1218	4.28	0.01	44.5	0.08	1.60	3.55	1.81	18.3	6.73	91	37.0	196	43.5	415
B002-24	257	4.43	1047	2.40	0.02	42.5	0.12	1.96	4.10	1.76	18.4	6.47	82	32.5	167	36.5	350
B002-25	187	5.09	1099	3.55	0.11	59.3	0.16	2.24	3.90	1.85	19.6	6.56	85	33.1	172	37.6	365
Monzonite (B401-1)
B401-1-11	292	4.55	695	2.43	0.16	31.7	0.08	1.00	2.30	0.65	11.0	3.86	52.9	20.9	113	25.5	257
B401-1-13	796	9.96	718	2.06	3.24	45.2	0.81	4.12	3.04	1.14	12.5	4.32	55.0	21.7	113	25.8	260
B401-1-14	474	13.0	5998	12.2	0.11	336	1.47	25.3	41.5	19.2	185	55.3	599	196	840	157	1300
B401-1-17	170	2.93	506	4.23		10.1		0.23	0.92	0.53	7.23	2.84	39.9	15.9	81	17.7	170
B401-1-26	224	3.56	854	6.67		15.8		0.54	1.73	0.90	13.2	5.32	69.3	26.7	133	28.0	261
B401-1-29	216	5.52	1324	3.40	0.02	56.9		4.17	6.91	1.55	28.7	9.53	111	40.6	202	43.9	430
B401-1-32	659	9.27	5579	10.0	0.73	315	6.04	78.3	85.2	33.8	244	63.1	614	187	773	142	1199
B401-1-34	850	3.21	4509	130	0.11	79.5	0.17	2.62	7.33	0.17	48.6	23.1	335	140	752	171	1663
Quartz monzonite (B401-2)
B401-2-1	203	4.94	1363	6.52		58.3	0.06	1.50	3.15	1.52	18.7	6.92	97.6	40.9	222	50.0	489
B401-2-2	302	7.45	898	2.32	0.01	37.9	0.14	2.48	4.33	1.30	20.1	6.45	76.3	28.3	139	29.1	267
B401-2-3	83.1	2.03	991	2.32	0.01	28.3	0.10	1.75	3.34	1.79	18.1	5.90	74.0	29.1	154	34.2	347
B401-2-5	278	17.0	754	1.29		23.0	0.16	2.67	4.67	1.15	19.7	6.23	70.6	24.0	112	22.3	198
B401-2-6	123	2.90	1167	5.07		41.4	0.04	1.03	2.80	1.31	14.5	5.72	80.4	33.9	187	44.1	448
B401-2-7	160	4.75	762	3.44		42.4	0.03	0.93	2.14	0.86	10.9	4.17	56.1	23.0	124	27.7	276
B401-2-8	202	4.87	1051	4.77		61.2	0.09	1.47	3.11	1.36	16.9	5.92	79.9	32.1	169	37.7	365
B401-2-9	741	4.41	827	3.08	3.51	65.3	0.94	4.23	3.58	1.39	14.8	5.09	64.9	25.8	131	28.5	274
B401-2-10	145	3.17	680	2.58	0.12	38.7	0.08	1.12	2.00	1.00	10.6	3.86	50.5	20.2	107	24.2	241
B401-2-11	216	10.4	673	1.62		26.2	0.06	1.31	2.75	0.64	13.2	4.64	58.2	21.6	104	21.7	202
B401-2-12	249	12.5	661	2.09	0.02	30.2	0.07	1.42	3.19	0.67	13.3	4.80	56.2	21.0	102	21.1	193
B401-2-13	103	4.11	1079	4.37		54.9	0.06	1.22	2.96	1.33	14.3	5.36	73.6	31.3	171	40.7	421
B401-2-14	97	2.43	758	3.47		34.5	0.04	0.66	1.94	0.92	9.8	3.68	50.0	21.9	125	28.9	306
B401-2-15	425	3.11	1017	4.29	0.35	50.1	0.11	1.59	3.14	1.11	16.6	6.19	80.5	31.8	165	35.7	339
B401-2-16	137	4.50	1068	4.05		64.3	0.09	1.45	3.00	1.52	17.6	6.28	80.1	32.5	171	37.7	368
B401-2-18	206	4.65	1222	3.20		54.0	0.16	2.93	5.44	1.95	25.6	8.61	102.3	38.3	194	41.1	394
B401-2-20	205	4.53	1167	4.66	0.04	45.7	0.07	1.29	3.22	1.55	17.3	6.57	87.7	35.3	186	41.6	403
B401-2-21	104	2.13	1182	1.83	0.02	41.1	0.22	3.08	5.73	2.64	23.9	7.67	93.3	35.5	181	40.5	398
B401-2-22	159	5.02	898	3.58		42.9	0.06	1.03	2.19	1.05	12.6	4.81	63.4	27.2	149	33.9	332
B401-2-23	332	22.1	1342	1.42	0.02	31.5	0.39	6.97	10.78	1.79	40.2	12.1	132	44.8	197	37.3	318
B401-2-25	178	5.6	1306	5.52		61.2	0.08	1.53	3.55	2.04	21.2	7.55	96.2	39.3	205	44.2	443
GJ-1
GJ-1-1	29.0	3.96	273	1.87	b.d	21.4	0.06	0.94	1.90	1.33	8.87	2.43	24.1	7.69	34.4	6.93	63.7
GJ-1-2	36.0	4.55	270	1.77	b.d	20.5	0.02	0.88	2.12	1.24	8.62	2.32	23.5	7.54	32.9	6.57	60.7
GJ-1-3	37.1	4.58	269	1.74	b.d	20.7	0.06	0.92	2.13	1.25	8.71	2.29	23.1	7.45	32.6	6.51	60.5
GJ-1-4	35.5	5.04	266	1.63	b.d	20.7	0.04	0.87	2.01	1.30	8.24	2.28	22.7	7.30	32.0	6.50	60.7
GJ-1-5	b.d	4.13	256	1.70	b.d	19.8	0.06	0.83	1.92	1.28	7.86	2.16	22.3	7.06	31.6	6.26	58.1
GJ-1-6	38.9	4.76	256	1.67	b.d	19.9	0.05	0.90	1.89	1.28	7.94	2.14	21.9	7.04	31.4	6.38	59.3
GJ-1-7	33.9	4.21	259	1.65	b.d	20.2	0.05	0.88	1.98	1.28	8.20	2.30	23.2	7.16	32.1	6.47	59.8
GJ-1-8	b.d	4.10	258	1.59	b.d	20.3	0.04	0.93	2.05	1.26	7.93	2.21	22.4	7.24	31.8	6.43	58.4
GJ-1-9	38.3	4.11	251	1.55	b.d	19.7	0.04	0.82	1.99	1.23	8.46	2.17	22.0	6.99	30.5	6.16	56.7
GJ-1-10	34.0	4.64	261	1.62	b.d	20.3	0.05	0.95	2.06	1.22	8.43	2.24	22.0	7.26	32.2	6.37	59.4
GJ-1-11	31.4	4.60	262	1.63	b.d	20.0	0.04	0.86	2.10	1.27	8.35	2.27	22.8	7.33	32.0	6.42	58.5

. All of the analyzed zircon spots display Chondrite-normalized rare earth element (REE) patterns characterized by significant heavy rare earth element (HREE) enrichment and light rare earth elements (LREE) depletion. As illustrated on the REE diagrams (Figure 8), all of the zircons exhibit pronounced positive Ce anomalies and weakly negative Eu anomalies, consistent with typical magmatic zircon signatures.

5.4. Zircon In Situ Lu–Hf Isotopes

A total of 95 Lu–Hf isotope analyses were performed on zircons from four samples, including 80 Early Cretaceous-aged grains and 15 Neoproterozoic-aged grains. The initial Hf isotope compositions for the Early Cretaceous zircons were calculated using their respective weighted mean ages, while the Neoproterozoic zircons were uniformly referenced to 800 Ma. The analytical results are provided in

Table 4. Zircon in situ Lu–Hf isotope data for the Jiashan monzonitic rocks.

Spot No.	Age (Ma)	176Lu/177Hf	176Hf/177Hf	±2σ	εHf(t)	±2σ (Ma)	TDM1 (Ma)	TDM2 (Ma)
Monzonite (B001), 127.1 ± 0.5 Ma, MSWD = 0.24, n = 19
B001-001	127.1	0.001407	0.281894	0.000008	−28.8	0.3	1929	2948
B001-002	127.1	0.001276	0.281835	0.000008	−30.9	0.3	2004	3074
B001-003	127.1	0.001762	0.281923	0.000008	−27.8	0.3	1905	2886
B001-004	127.1	0.001396	0.281823	0.000008	−31.3	0.3	2027	3102
B001-005	127.1	0.002325	0.281948	0.000011	−27.0	0.4	1900	2836
B001-006	127.1	0.001274	0.281821	0.000009	−31.4	0.3	2022	3104
B001-007	127.1	0.000560	0.281858	0.000008	−30.0	0.3	1935	3021
B001-008	127.1	0.001238	0.281871	0.000010	−29.6	0.3	1951	2996
B001-009	127.1	0.001591	0.281815	0.000008	−31.6	0.3	2048	3119
B001-010	127.1	0.001323	0.281853	0.000009	−30.2	0.3	1980	3035
B001-011	127.1	0.001289	0.281826	0.000010	−31.2	0.3	2017	3094
B001-012	127.1	0.002306	0.281917	0.000008	−28.1	0.3	1942	2901
B001-013	127.1	0.000840	0.281878	0.000010	−29.3	0.4	1921	2979
B001-014	127.1	0.002188	0.281849	0.000009	−30.5	0.3	2033	3049
B001-015	127.1	0.001360	0.281859	0.000008	−30.1	0.3	1975	3024
B001-016	127.1	0.001473	0.281859	0.000008	−30.1	0.3	1981	3025
B001-017	127.1	0.001479	0.281806	0.000007	−31.9	0.3	2055	3139
B001-018	127.1	0.000848	0.281802	0.000009	−32.0	0.3	2026	3143
B001-019	127.1	0.000656	0.281913	0.000008	−28.1	0.3	1864	2902
B001-020	127.1	0.001415	0.281853	0.000009	−30.3	0.3	1986	3036
B001-021	800	0.001495	0.282295	0.000007	−0.2	0.3	1368	1694
B001-022	800	0.001506	0.282280	0.000007	−0.8	0.2	1390	1727
B001-023	127.1	0.001157	0.281875	0.000007	−29.5	0.2	1941	2987
B001-024	127.1	0.001172	0.281939	0.000009	−27.2	0.3	1853	2848
Quartz monzonite (B002), 127.2 ± 0.5 Ma, MSWD = 0.27, n = 22
B002-001	127.2	0.001246	0.281871	0.000009	−29.6	0.3	1953	2997
B002-002	127.2	0.000978	0.281865	0.000006	−29.8	0.2	1946	3007
B002-003	127.2	0.001261	0.281927	0.000008	−27.6	0.3	1875	2875
B002-004	127.2	0.000877	0.281843	0.000009	−30.6	0.3	1972	3056
B002-005	127.2	0.000954	0.281893	0.000010	−28.8	0.4	1907	2947
B002-006	127.2	0.001534	0.281827	0.000009	−31.2	0.3	2029	3094
B002-007	127.2	0.001183	0.281850	0.000008	−30.3	0.3	1977	3040
B002-008	127.2	0.001206	0.281876	0.000007	−29.4	0.3	1943	2985
B002-009	127.2	0.001164	0.281839	0.000008	−30.7	0.3	1992	3065
B002-010	127.2	0.001123	0.281864	0.000008	−29.9	0.3	1956	3011
B002-011	127.2	0.001954	0.281942	0.000009	−27.2	0.3	1889	2846
B002-012	127.2	0.001250	0.281850	0.000010	−30.4	0.3	1982	3042
B002-013	127.2	0.001482	0.281865	0.000008	−29.9	0.3	1973	3011
B002-014	127.2	0.000867	0.281836	0.000009	−30.8	0.3	1981	3071
B002-015	127.2	0.001144	0.281864	0.000008	−29.8	0.3	1956	3011
B002-016	127.2	0.001650	0.281917	0.000008	−28.0	0.3	1908	2898
B002-017	127.2	0.001483	0.281862	0.000008	−29.9	0.3	1977	3017
B002-018	127.2	0.000806	0.281882	0.000009	−29.2	0.3	1915	2971
B002-019	127.2	0.001095	0.281890	0.000008	−28.9	0.3	1918	2955
B002-020	127.2	0.001160	0.281883	0.000008	−29.2	0.3	1932	2971
B002-021	127.2	0.001144	0.281928	0.000009	−27.6	0.3	1868	2873
B002-022	127.2	0.000530	0.281894	0.000009	−28.7	0.3	1884	2943
B002-023	127.2	0.001200	0.281880	0.000009	−29.3	0.3	1937	2976
B002-024	127.2	0.001200	0.281865	0.000008	−29.8	0.3	1959	3010
B002-025	127.2	0.001149	0.281884	0.000008	−29.1	0.3	1928	2967
Monzonite (B401-1), 126.8 ± 0.8 Ma, MSWD = 0.58, n = 8
B401-1-005	126.8	0.000892	0.281971	0.000009	−26.0	0.3	1796	2777
B401-1-007	126.8	0.003585	0.281871	0.000011	−29.8	0.4	2080	3008
B401-1-008	126.8	0.002794	0.282024	0.000012	−24.3	0.4	1813	2671
B401-1-009	126.8	0.002129	0.281796	0.000007	−32.4	0.3	2106	3164
B401-1-013	126.8	0.001193	0.281788	0.000008	−32.5	0.3	2064	3175
B401-1-014	126.8	0.001020	0.281886	0.000009	−29.1	0.3	1920	2963
B401-1-015	126.8	0.001087	0.282007	0.000010	−24.8	0.4	1755	2701
B401-1-019	126.8	0.002864	0.281759	0.000011	−33.7	0.4	2202	3247
B401-1-021	126.8	0.001597	0.282044	0.000009	−23.5	0.3	1727	2622
B401-1-001	800	0.002570	0.282310	0.000008	−0.3	0.3	1386	1695
B401-1-002	800	0.001205	0.282055	0.000009	−8.6	0.3	1694	2215
B401-1-003	800	0.003034	0.282193	0.000009	−4.7	0.3	1577	1971
B401-1-004	800	0.001690	0.282330	0.000007	0.9	0.3	1325	1622
B401-1-006	800	0.002548	0.282361	0.000008	1.5	0.3	1313	1583
B401-1-010	800	0.000489	0.282101	0.000009	−6.6	0.3	1600	2090
B401-1-011	800	0.001611	0.282399	0.000009	3.4	0.3	1226	1468
B401-1-012	800	0.001198	0.282153	0.000010	−5.1	0.3	1556	1997
B401-1-016	800	0.001960	0.282370	0.000009	2.2	0.3	1278	1542
B401-1-017	800	0.001063	0.282055	0.000010	−8.5	0.4	1688	2210
B401-1-018	800	0.002639	0.282197	0.000008	−4.3	0.3	1554	1948
B401-1-020	800	0.001871	0.282356	0.000008	1.7	0.3	1295	1571
Quartz monzonite (B401-2), 128.6 ± 0.6 Ma, MSWD = 0.22, n = 21
B401-2-001	128.6	0.001094	0.281865	0.000009	−29.8	0.3	1952	3007
B401-2-002	128.6	0.000886	0.281843	0.000009	−30.5	0.3	1972	3054
B401-2-003	128.6	0.001102	0.281849	0.000007	−30.3	0.3	1975	3043
B401-2-004	128.6	0.000377	0.281895	0.000009	−28.7	0.3	1876	2939
B401-2-005	128.6	0.000856	0.281923	0.000011	−27.7	0.4	1861	2882
B401-2-006	128.6	0.001645	0.281926	0.000009	−27.7	0.3	1896	2879
B401-2-007	800	0.001335	0.282151	0.000011	−5.3	0.4	1565	2007
B401-2-008	128.6	0.001486	0.281840	0.000009	−30.7	0.3	2007	3063
B401-2-009	128.6	0.001314	0.281885	0.000009	−29.1	0.3	1936	2965
B401-2-010	128.6	0.001586	0.281882	0.000009	−29.2	0.3	1954	2973
B401-2-011	128.6	0.000640	0.281907	0.000010	−28.3	0.3	1872	2915
B401-2-012	128.6	0.000906	0.281875	0.000010	−29.4	0.4	1929	2985
B401-2-013	128.6	0.002374	0.281907	0.000007	−28.4	0.3	1961	2924
B401-2-014	128.6	0.001606	0.281885	0.000010	−29.1	0.3	1951	2967
B401-2-015	128.6	0.001068	0.281900	0.000009	−28.5	0.3	1902	2931
B401-2-016	128.6	0.000813	0.281893	0.000009	−28.8	0.3	1899	2945
B401-2-017	128.6	0.000935	0.281789	0.000008	−32.5	0.3	2049	3171
B401-2-018	128.6	0.001021	0.281871	0.000009	−29.5	0.3	1940	2993
B401-2-019	128.6	0.000668	0.281880	0.000010	−29.2	0.3	1910	2973
B401-2-020	128.6	0.001330	0.281814	0.000008	−31.6	0.3	2036	3119
B401-2-021	128.6	0.001564	0.281850	0.000009	−30.3	0.3	1997	3042
B401-2-022	128.6	0.001167	0.281851	0.000009	−30.3	0.3	1976	3039
B401-2-023	128.6	0.001058	0.281901	0.000008	−28.5	0.3	1900	2929
B401-2-024	128.6	0.001502	0.281828	0.000008	−31.1	0.3	2026	3091
B401-2-025	128.6	0.001173	0.281835	0.000010	−30.9	0.3	1998	3073
Standard
TANZ		0.000054	0.281821	0.000009
TANZ		0.000055	0.281823	0.000008
TANZ		0.000053	0.281830	0.000008
TANZ		0.000054	0.281820	0.000010
TANZ		0.000054	0.281827	0.000008
TANZ		0.000053	0.281821	0.000010
GJ-1		0.000255	0.282020	0.000010
GJ-1		0.000255	0.282016	0.000012
GJ-1		0.000250	0.282011	0.000012
GJ-1		0.000250	0.282018	0.000012
91500		0.000309	0.282307	0.000011
91500		0.000313	0.282306	0.000014
91500		0.000308	0.282314	0.000010
91500		0.000308	0.282301	0.000013
91500		0.000307	0.282302	0.000011
91500		0.000308	0.282318	0.000011
91500		0.000320	0.282306	0.000014
91500		0.000321	0.282310	0.000014
Plešovice		0.000148	0.282474	0.000008
Plešovice		0.000136	0.282466	0.000008
Plešovice		0.000139	0.282486	0.000009
Plešovice		0.000125	0.282484	0.000011
Plešovice		0.000125	0.282483	0.000009
Plešovice		0.000132	0.282479	0.000010
Plešovice		0.000068	0.282473	0.000010
Plešovice		0.000063	0.282483	0.000009
Plešovice		0.000135	0.282473	0.000009
Plešovice		0.000086	0.282478	0.000009
Plešovice		0.000131	0.282480	0.000009
Plešovice		0.000077	0.282476	0.000011
Plešovice		0.000135	0.282477	0.000009
Plešovice		0.000135	0.282483	0.000009
Plešovice		0.000083	0.282481	0.000010
Mud Tank		0.000082	0.282524	0.000010
Mud Tank		0.000079	0.282511	0.000011
Mud Tank		0.000093	0.282519	0.000010
Mud Tank		0.000091	0.282518	0.000010
Penglai		0.000270	0.282912	0.000013
Penglai		0.000269	0.282909	0.000013
Penglai		0.000268	0.282908	0.000013
Penglai		0.000265	0.282904	0.000013
Penglai		0.000272	0.282921	0.000013
Penglai		0.000269	0.282902	0.000012
Penglai		0.000279	0.282918	0.000013
Penglai		0.000277	0.282900	0.000014

(Supplementary Table S4). The Early Cretaceous zircons exhibit ¹⁷⁶Lu/¹⁷⁷Hf ratios of 0.000530–0.003585 and ¹⁷⁶Hf/¹⁷⁷Hf ratios of 0.281759–0.282399, yielding ε_Hf(t) values of −33.7 to −23.5 (Figure 9a). The corresponding two-stage Hf model ages (T_DM2) range from 2623 to 3247 Ma (Figure 9b). In contrast, the Neoproterozoic zircons exhibit ¹⁷⁶Lu/¹⁷⁷Hf ratios of 0.000489–0.003034 and ¹⁷⁶Hf/¹⁷⁷Hf ratios of 0.282055–0.282399, ε_Hf(t) values of −8.6 to +3.4 (Figure 9a), and T_DM2 ages of 1468–2215 Ma (Figure 9b). These results indicate that the two populations of zircons had distinct crustal residence histories. The consistent Hf isotopic signatures of the zircons from both the monzonite and quartz monzonite further support the inference that there is a genetic relationship between these two rock types.

6. Discussion

6.1. Emplacement Timing of the Monzonite

The Phanerozoic magmatic rocks in the Sulu Orogenic Belt are primarily documented to be within three distinct age intervals: Triassic (225–205 Ma [13,14,21,23,24]), Jurassic (160–150 Ma [24,29]), and Cretaceous (130–118 Ma [12,15,16,30,32]). The Cretaceous magmatism was the most widespread episode and comprised mantle-derived mafic rocks (ca. 120 Ma [12,33]), normal granites (126–118 Ma [12,30,32]), and A-type granites (127–125 Ma [12,34]).

In this study, LA–ICP–MS U–Pb zircon dating of four magmatic rock samples from the Jiashan fluorite–barite mining area yielded Early Cretaceous emplacement ages ranging from 126 to 129 Ma. These results are consistent with previously documented Early Cretaceous magmatic activity in the Sulu Orogenic Belt and are slightly older than the reported crystallization ages of the adjacent Linian pluton (122 ± 5 Ma) and Kangrishan pluton (119 ± 2 Ma, [31]). Consequently, the monzonite and quartz monzonite in the Jiashan mining area represent products of Early Cretaceous magmatism within the Sulu Orogenic Belt.

6.2. Petrogenesis

6.2.1. Petrogenetic Type

Based on their genetic characteristics, granitic rocks are classified into I-type, S-type, and A-type granites [50,51]. The presence of peraluminous minerals such as cordierite is a key mineralogical indicator for S-type granites; however, no such minerals were observed in the Jiashan monzonite and quartz monzonite samples. Furthermore, these rocks exhibit metaluminous geochemical characteristics, contrasting with the strongly peraluminous nature typical of S-type granites (A/CNK > 1.1 [50]). The Ga/Al ratios (2.48–2.85 and 2.45–2.66) and Zr + Nb + Ce + Y values (averages of 338 μg/g and 332 μg/g) of the Jiashan rocks are significantly lower than the lower thresholds for typical A-type granites (≥2.6 and ≥350 μg/g for Ga/Al and Zr + Nb + Ce + Y values, respectively). Additionally, their low TFeO/MgO ratios (2.08–3.02 and 1.08–1.77) contrast markedly with those of A-type granites (TFeO/MgO > 16 [52]). Magmatic zircons, which crystallize directly from parental melts, preserve records of the source characteristics and magmatic evolution [53]. Trace element compositions of the zircons from the Jiashan samples further confirm an I-type affinity (Figure 10). Collectively, these lines of evidence demonstrate that the Jiashan monzonite and quartz monzonite belong to the I-type granite series.

6.2.2. Source Characteristics and Petrogenesis

The Jiashan monzonite and quartz monzonite exhibit elevated fluorine (F) concentrations (801–1199 μg/g and 725–3836 μg/g, respectively), significantly exceeding the average F abundance of the global silicate crust (~557 μg/g [54]), classifying these magmatic rocks as fluorine-rich granitoids. The genesis of such fluorine-enriched granitoids is closely linked to high F concentrations in both the magma source region and during the magmatic evolution. Potential source regions for fluorine-rich granitoids primarily include two origins [55]: (1) partial melting of fluorine-rich crustal materials, such as fluorine-bearing sedimentary rocks or metagranites; and (2) decomposition of fluorine-bearing minerals within the mantle, including apatite, amphibole, and mica, as well as nominally anhydrous minerals such as olivine and pyroxene [56,57,58,59,60]. Partial melting of fluorine-rich metasedimentary or metaigneous source rocks can generate intermediate to felsic magmas enriched in fluorine. Subsequent crystallization differentiation may lead to the formation of lithium- and fluorine-rich rare-metal granites/pegmatites or the exsolution of fluorine-rich hydrothermal fluids [61]. For example, the source of Late Mesozoic granites in the Nanling Range, South China, has been interpreted to be fluorine-enriched Mesoproterozoic crust [62,63,64]. Metasomatism affecting the mantle source in subduction or intraplate settings is a key mechanism for introducing mantle-derived fluorine [65,66]. In subduction zones, slab dehydration releases fluorine-rich fluids that metasomatize the overlying mantle wedge, creating an enriched mantle source. Subsequent mantle melting can then produce fluorine-rich melts [67]. Additionally, the positive correlation between fluorine and K₂O observed in intraplate basalts, such as Deccan tholeiites, Hawaiian tholeiites, alkaline basalts, and Atlantic mid-ocean ridge alkaline rocks, suggests magma derivation from phlogopite-bearing mantle sources [68]. Under later tectonic or thermal perturbations, such metasomatically enriched mantle sources may undergo a low degree of partial melting, generating potassium- and fluorine-rich alkaline magmas [69].

The Jiashan monzonite and quartz monzonite are classified as I-type granites, precluding their origin via a low of degree partial melting of metasedimentary rocks. Their elevated fluorine contents are more plausibly attributed to contributions from mantle-derived melts or fluids. This interpretation is supported by multiple lines of evidence. First, the SiO₂ contents of the Jiashan monzonite (61.61–62.41 wt.%) and quartz monzonite (66.26–68.18 wt.%) are within the intermediate range. Their compatible element concentrations, such as Cr (87.9–227 μg/g and 9.81–43.1 μg/g) and Ni (27.6–66.5 μg/g and 5.10–13.5 μg/g), are relatively low and significantly lower than those typical of primary magmas derived from melting of mantle peridotite (Cr = 500–600 μg/g, Ni = 250–300 μg/g [70]). Primitive mantle-normalized trace element diagrams reveal that the samples are enriched in large-ion lithophile elements (e.g., Rb, Ba, and Th) and light rare earth elements, as well as depleted in high-field-strength elements (e.g., Nb, Ta, and Ti), indicating an affinity with continental crust [71]. Furthermore, the zircon Hf isotope compositions of the Jiashan rocks are highly enriched (ε_Hf(t) = −33.7 to −23.5), collectively suggesting a predominantly crustal source for the magmas. Second, the substantial variation in the zircon ε_Hf(t) values, spanning approximately 10 epsilon units, cannot be explained by melting of a single crustal source. The elevated Mg# values of the monzonite (54–66) and quartz monzonite (40–50), which exceed those of pure crustal melts (<45 [72]), indicate the involvement of deep mantle-derived components in the parental magmas. The presence of Neoproterozoic-aged zircons further supports the occurrence of mantle contributions. Although previous studies have attributed the presence of Neoproterozoic inherited zircons in Early Cretaceous granites in the Dabie–Sulu Orogenic Belt to deeply subducted orthogneisses [31,37,38,42], the significantly different two-stage Hf model ages of the Neoproterozoic zircons analyzed in this study suggest they are more likely captured grains rather than inherited grains. This implies that the parental magma of the Jiashan monzonite assimilated Neoproterozoic felsic igneous rocks prior to its final consolidation. Given that the SiO₂ contents of the monzonite range from 61.61 wt.% to 62.41 wt.%, the primitive magma would have had an even lower SiO₂ content before assimilation, indicating a contribution from mantle-derived components.

The zircon ε_Hf(t) values of the Jiashan monzonite and quartz monzonite exhibit limited variation, ranging from −33.7 to −23.5, with corresponding two-stage Hf model ages predominantly between 2623 and 3247 Ma. This indicates that their source materials were primarily ancient crustal components derived from the primitive mantle during the Archean. The Sulu Orogenic Belt hosts numerous granitoids and minor mafic rocks contemporaneous with the Jiashan intrusions. These Cretaceous intrusions include A-type granites [12,34] and normal granites [30,32]. The Cretaceous A-type granites (−26.1 to −19.8 [12]) and mafic rocks (−23.5 to −21.1 [12]) exhibit consistently enriched zircon ε_Hf(t) values. Although zircon Hf isotope data are unavailable for the Cretaceous normal granites, their whole-rock Nd isotope compositions are similar to those of A-type granites [12,31], suggesting that they have comparable Hf isotope characteristics. These findings imply that the Jiashan monzonite and quartz monzonite were derived from a more ancient crustal source than other contemporaneous granitoids in the Sulu Orogenic Belt.

To the south of the Sulu Orogenic Belt, the Middle-Lower Yangtze River Belt also experienced extensive Early Cretaceous magmatism, which can be divided into three stages. The first stage, associated with porphyry Cu–Au mineralization (e.g., granodiorites in the Tongling area, 148–133 Ma), exhibits zircon ε_Hf(t) values of −38.6 to −6.6 [73]. The second stage comprises shoshonitic volcanic rocks in fault-controlled basins (e.g., volcanic rocks in the Ningwu Basin) and were derived from an enriched lithospheric mantle with ε_Hf(t) values of −13.3 to −3.8 [73]. The third stage is represented by A-type granites (e.g., Binjiang, Fushan, and Banshiling plutons in the Fanchang Basin) with ε_Hf(t) values of −7.9 to 0, indicating reworking of Neoproterozoic crustal materials [73]. The low zircon ε_Hf(t) values of the first-stage magmatic rocks in the Tongling area closely resemble those of the Jiashan intrusions, while the second- and third-stage magmas exhibit significantly different Hf isotope signatures. This suggests that the Jiashan magmas share a similar ancient crustal source with the first-stage magmatic rocks in the Middle-Lower Yangtze River Belt.

To the west of the Tancheng–Lujiang Fault Zone, the Dabie Orogenic Belt also hosts Early Cretaceous magmatic rocks, which are predominantly granitic in composition. These granitoids can be subdivided into two groups: earlier ore-barren and later Mo–Pb–Zn-related granitoids (Figure 11) [21,74,75,76,77,78,79,80,81]. The zircon εHf(t) values of the ore-barren granitoids (peaking around −28; [76,79,80,82]) are similar to those of the Jiashan monzonite and quartz monzonite, suggesting a relatively consistent crustal source for both regions. The North Dabie and Central Dabie tectonic units, exposed within the Dabie Orogenic Belt, are composed primarily of Neoproterozoic orthogneisses and paragneisses, respectively. The zircon ε_Hf(t) values of these gneisses are generally greater than −15 (Figure 11) [43,83,84]. Although the Sr–Nd–Pb isotope compositions of Early Cretaceous magmatic rocks in the central Dabie region resemble those of the North Dabie Neoproterozoic gneisses, leading some researchers to propose a genetic link [85], this interpretation faces a significant contradiction. If the North Dabie Neoproterozoic gneisses evolved to 130 Ma with an average crustal Lu/Hf ratio, their calculated ε_Hf(t) values would exceed −20. This contrasts sharply with the observed ε_Hf(t) values of Early Cretaceous magmatic rocks in the Dabie–Sulu Orogenic Belt, including the Jiashan monzonite, most of which are below −20. This discrepancy indicates that the Mesozoic magmatic rocks in the Dabie Orogenic Belt could not have been derived directly from the melting of North Dabie Neoproterozoic gneisses and instead originated from more ancient crustal materials.

Regarding the nature of this ancient crust, some scholars have proposed that it resembles the oldest exposed basement in the Lower Yangtze region, specifically the Kongling Group [86,87]. The Kongling Group comprises Archean gneisses and migmatites (2.7–3.4 Ga) and Paleoproterozoic deformed granites (1.65–2.20 Ga). When the zircon Hf isotope compositions of these rocks are projected to approximately 130 Ma using an average crustal Lu/Hf ratio, their calculated ε_Hf(t) values fall below −35 (Figure 11) [86,87]). This isotopic signature is significantly more ancient than that inferred for the source of the Jiashan monzonite. Alternatively, recently reported dioritic to granitic gneisses in the Douling Group in the South Qinling Orogenic Belt have yielded zircon ε_Hf(t) values ranging from −10.1 to +4.4. When projected to 130 Ma using an average crustal Lu/Hf ratio, these values align closely with the Hf isotope compositions of Early Cretaceous magmatic rocks in the Dabie–Sulu Orogenic Belt, including the Jiashan monzonite (Figure 11) [88]. Crustal materials with similar isotopic characteristics are also minimally exposed within the Dabie Orogenic Belt (e.g., Huangtuling gneiss [89]). Given that the oldest Hf model ages of the Early Cretaceous magmatic rocks in the Dabie–Sulu Orogenic Belt closely match those of the Douling Group granitic gneisses (and the Huangtuling gneiss) and no samples exhibit model ages older than those of the Douling Group, it is plausible that the Mesozoic magmatic rocks in the Dabie–Sulu Orogenic Belt, including the Jiashan monzonite, were generated directly via partial melting of ancient materials similar to the Douling Group [90].

Despite differences in their major element compositions, the Jiashan monzonite and quartz monzonite display highly consistent Chondrite-normalized rare earth element (REE) patterns, primitive mantle-normalized trace element spider diagrams, and zircon εHf(t) values, indicating that they were derived from cogeneric magmas through magmatic evolution. On Harker diagrams (Figure 12), the Jiashan rocks, together with contemporaneous mafic rocks, normal granites, and A-type granites within the Sulu Orogenic Belt, exhibit broadly linear evolutionary trends. There are negative correlations between the SiO₂ content and the TiO₂, Al₂O₃, FeO*, MgO, CaO, and P₂O₅ contents, while there is a positive correlation between the SiO₂ content and the K₂O content. These trends suggest fractional crystallization of minerals such as Fe-Ti oxides, plagioclase, apatite, and amphibole and/or biotite. However, the absence of pronounced Eu anomalies in the Jiashan samples indicates that the amount of plagioclase fractionation was not significant.

In summary, based on the results of this study, we propose that the Jiashan monzonite and quartz monzonite originated through mixing of felsic magmas derived from partial melting of ancient crustal materials analogous to the Kongling Group and mantle-derived mafic magmas, followed by fractional crystallization of minerals, including ilmenite, apatite, amphibole, and/or biotite.

6.3. Geological Significance

The formation of fluorine-rich granites is closely associated with specific tectonic settings, including (1) subduction zone environments, such as active continental margins or island arcs. For example, the Late Mesozoic W-Sn metallogenic granites in South China are genetically linked to the subduction of the Paleo-Pacific Plate, and their elevated fluorine contents were potentially derived from fluids released by dehydration of the subducted slab. (2) Post-collisional extensional settings: Fluorine-rich granites in such contexts often exhibit A-type affinities, indicative of anorogenic extensional regimes. (3) Intraplate rift or mantle plume environments: These environments are exemplified by fluorine-rich alkaline granites in the East African Rift, which are closely associated with mantle plume activity.

The Dabie–Sulu Orogenic Belt formed through the Indosinian collision between the South China and North China blocks [9]. The extensive Early Cretaceous magmatism in the region postdates the Indosinian collision by approximately 100 Ma, supporting the widely accepted interpretation that its formation was related to post-collisional orogenic collapse. Studies indicate that from the Jurassic to Early Cretaceous, regional tectonic extension and lithospheric thinning occurred in the North China Block and the Lower Yangtze region [91]. This tectonic activity was attributed to the westward subduction of the Paleo-Pacific Plate beneath the Asian continental plate. As part of the Early Cretaceous magmatism within the Dabie–Sulu Orogenic Belt, the Jiashan magmatic rocks are broadly associated with the subduction of the Paleo-Pacific Plate during the Yanshanian. On the Rb–(Y+Nb) tectonic discrimination diagram (Figure 13), all of the Jiashan samples plot within the post-collisional granite field, which is consistent with an extensional tectonic environment.

Fluorine plays a critical role in magmatic evolution by modifying melt physicochemical properties and directly influencing rare metal enrichment and mineralization processes. Fluorine-rich granites are not only potential sources of fluorine but also hold particular significance for rare metal mineralization [92]. As a volatile component, fluorine significantly reduces the viscosity of the melt during magmatic stages, prolonging differentiation and promoting extreme enrichment of rare metals (e.g., W, Sn, Nb, Ta, and REE) in residual melts [93,94,95]. Furthermore, high fluorine concentrations suppress the crystallization of biotite and amphibole, facilitating the preferential precipitation of rare metal minerals such as wolframite and columbite [55,96], thereby directly controlling the mineralization type and scale. During hydrothermal stages, fluorine forms stable complexes with metal cations (e.g., Nb⁵⁺), such as NbF₂(OH)₃ and [Nb(OH)₃F₃]⁻ [97,98], enhancing their mobility and ultimately leading to large-scale ore precipitation under abrupt physicochemical changes (e.g., cooling and boiling). Studies indicate that many large to super-large rare metal deposits are consistently fluorine-rich [61,99,100]. Fluorine-rich granites are often associated with tungsten–tin quartz-vein deposits (e.g., the South China W-Sn metallogenic belt [101]) and Nb-Ta-REE deposits (e.g., the Baerzhe deposit in Inner Mongolia [99,102]). Thus, fluorine-rich granites serve as both carriers of rare metals and chemical engines for mineralization, and the fluorine content and magmatic–hydrothermal evolution paths collectively determine efficiency of the enrichment and the economic value of the deposit. Research has demonstrated that fluorine governs the mineralization of high-field-strength elements (e.g., W, Sn, Nb, Ta, REE, and U) by modifying the physicochemical properties of magmatic–hydrothermal fluids [92] and can be associated with fluorite and cryolite deposits [103]. The Jiashan fluorine-rich quartz monzonite exhibits moderate SiO₂ content but significantly higher fluorine concentrations than average in the global silicate crust. As a highly incompatible element, fluorine tends to become concentrated in residual melts during magmatic evolution. Therefore, the area may hold potential for rare metal mineralization associated with the Early Cretaceous high-silica granites.

7. Conclusions

In this study, based on integrated isotopic geochronology, petrogeochemistry, and isotopic analyses of monzonite and quartz monzonite from drill cores in the Jiashan fluorite–barite mining area in northern Jiangsu, in conjunction with regional geological data, the following conclusions were drawn:

(1)

U–Pb zircon dating constrains the emplacement ages of the Jiashan monzonite (127.1 ± 0.5 Ma and 126.8 ± 0.8 Ma) and quartz monzonite (127.2 ± 0.5 Ma and 128.6 ± 0.6 Ma) to the Early Cretaceous, indicating that they represent products of contemporaneous magmatic activity within the Sulu Orogenic Belt.

(2)

The Jiashan monzonite and quartz monzonite are metaluminous, alkali-rich I-type granites. They exhibit highly consistent trace element and rare earth element characteristics, including enrichment in large-ion lithophile elements (Rb, Th, and U) and light rare earth elements and depletion in high-field-strength elements (Nb, Ta, and Ti). Their uniform zircon Hf isotope compositions (ε_Hf(t) = −33.7 to −23.5) indicate that they were primarily derived from partial melting of Archean crustal sources, with minor contributions from mantle-derived materials.

(3)

The quartz monzonite formed through fractional crystallization of the parental monzonitic magma, which involved minerals such as ilmenite, apatite, amphibole, and/or biotite. The emplacement of the Jiashan intrusions is associated with localized extension triggered by the westward subduction of the Paleo-Pacific Plate during the Yanshanian. The discovery of fluorine-rich magmatic rocks in the Jiashan area suggests that this area has significant potential for rare metal mineralization related to the Early Cretaceous high-silica granites.