The Petrogenesis of Early Permian Granodiorites in the Northern Segment of the Changning-Menglian Suture Zone, Western Yunnan, and Their Tectonic Implications

Abstract

The Changning-Menglian suture zone, as the remnant of the main Paleo-Tethyan oceanic basin in its southern segment, lacks direct magmatic evidence constraining the timing of subduction initiation in its northern segment. The petrogenesis and tectonic setting of the newly discovered Early Permian (~280 Ma) Wayao granodiorite in the northern segment remain unclear, hindering our understanding of the timing of subduction initiation and processes of the Paleo-Tethyan Ocean in the Changning-Menglian suture zone. This study presents systematic petrographic, zircon U-Pb geochronological, whole-rock major and trace element geochemical, and Sr-Nd-Hf isotopic analyses on the newly discovered Early Permian granodiorite in the Wayao area, northern segment of the Changning-Menglian suture zone, western Yunnan. Zircon U-Pb dating yields a crystallization age of ca. 280 Ma, confirming its emplacement during the Early Permian. The petrogeochemical characteristics indicate that it belongs to the metaluminous, calc-alkaline series of I-type granite. It is enriched in large-ion lithophile elements (LILEs; e.g., Rb, Th, U, La, Pb) and depleted in high-field-strength elements (HFSEs; e.g., Ba, Nb, Sr, Ti), exhibiting a pronounced negative Eu anomaly. Whole-rock Sr-Nd isotopes (εNd(t) = −5.6–−6.1) and zircon Hf isotopes (εHf(t) = −1.34–−10.01) suggest that the magma was predominantly derived from the partial melting of ancient crustal material (primarily metamorphosed basic rocks, such as amphibolite), with a minor addition of mantle-derived components (magma mixing). Combined with petrogeochemical discriminant diagrams (e.g., Sr/Y vs. Y, Rb vs. Yb + Ta) and the regional geological context, this granodiorite is interpreted to have formed in an active continental margin tectonic setting associated with the eastward subduction of the Paleo-Tethys Ocean (represented by the Changning-Menglian Ocean). This discovery fills the gap in the record of Early Permian subduction-related magmatic rocks in the northern segment of the Changning-Menglian suture zone. It provides crucial petrological evidence constraining that the eastward subduction and consumption of the northern Paleo-Tethys Ocean had already commenced by the Early Permian.

1. Introduction

The Sanjiang Tethys Orogenic Belt, situated in Southwestern China, constitutes an integral component of the eastern segment within the global Tethyan tectonic domain that traverses the Eurasian continent. The region has undergone the complete evolutionary sequence of the Paleozoic-Mesozoic Proto-Paleo-Neo-Tethys Ocean accretionary orogeny, as well as the Cenozoic Indo-Eurasian collision orogeny. Comprehensive geological records pertaining to the evolutionary history of the Tethys Ocean have been systematically preserved [1,2,3,4]. Among these, the Paleo-Tethys Ocean, which evolved from the Late Paleozoic to the Early Mesozoic, exerted the most significant impact on the tectonic-magmatic-stratigraphic framework in the Sanjiang region, resulting in the formation of three major suture zones: The Changning-Menglian, Jinsha River-Ailao Mountain, and Ganzi-Litang. The Changning-Menglian suture zone, a geological remnant of the Paleo-Tethys Ocean’s southern main oceanic basin evolution, attracts considerable research interest concerning its tectonic development.

Numerous comprehensive studies have been systematically conducted by previous researchers regarding the evolutionary processes of the Changning-Menglian Paleo-Tethys Ocean. The presence of radiolarian chert within the turbidite of the Lower Devonian Hot Spring Formation provides compelling evidence for the expansion of the oceanic basin during the Early Devonian period [5]. The mid-ocean ridge basalt (MORB) from the Nongba-Ganlongtang Ocean in the central segment of the Changning-Menglian Belt, along with the oceanic island basalt (OIB) identified in the Laochang area of the southern segment, provides compelling evidence that the Paleo-Tethys Ocean reached its mature stage during the Carboniferous period [6,7,8]. The Late Carboniferous to Permian, comprising basalt, andesite, granodiorite, and granite within the Yunxian-Jinggu magmatic arc, is interpreted as the product of subduction processes associated with the Paleo-Tethys Ocean [9,10,11,12]. However, the Triassic Lincang granite batholith originated in a continent–continent collision setting, subsequent to the full closure of the oceanic crust [13,14]. Furthermore, the Triassic blueschist formations identified in the Lancang-Huimin region provide compelling evidence that constrains the timing of the post-subduction closure continental collision to the Middle to Late Triassic period [15]. These studies have systematically elucidated the fundamental processes of the opening and expansion, subduction, and closure and collision of the Changning-Menglian Paleo-Tethys Ocean. Nevertheless, research on the rock records pertaining to the initial subduction phase of the Changning-Menglian Paleo-Tethys Ocean remains relatively limited. Exclusively, scholars have undertaken comprehensive chronological and geochemical investigations on granodiorites characterized by an Early Permian arc tectonic setting in the Jinghong region of southern Yunnan. The findings demonstrate that the southern segment of the Changning-Menglian Ocean initiated subduction processes during the Early Permian period [9]. Nevertheless, Early Permian lithological units associated with subduction processes in the northern segment of the Changning-Menglian Belt remain undocumented in the existing literature. Consequently, critical scientific inquiries, including the temporal consistency of subduction between the northern and southern oceanic plates of the Changning-Menglian Ocean, as well as the comparative analysis of subduction processes in these regions, necessitate further comprehensive investigation and elucidation.

This research focuses on the newly identified Early Permian granodiorite located in the Wayao area within the northern segment of the Changning-Menglian suture zone (Figure 1). Comprehensive investigations encompassing petrographic analysis, zircon U-Pb geochronology, major and trace element geochemical characterization, and Sr-Nd-Hf isotopic geochemistry were conducted to elucidate the age of its emplacement, the petrogenesis, the characteristics of the provenance area, and the tectonic setting during its formation. Furthermore, based on the integration of previous research findings, this study systematically examines the lithological assemblage types and spatio-temporal evolutionary characteristics of magmatic rocks associated with the Late Paleozoic Paleo-Tethys Ocean evolution in the Changning-Menglian suture zone. Ultimately, the geodynamic mechanisms and deep-seated processes that characterized the Late Paleozoic epoch within the Changning-Menglian Paleo-Tethys Ocean were clarified.

2. Geological Setting

Situated within the southern Sanjiang Tethyan orogenic belt, the Changning-Menglian suture zone extends approximately north–south for 250 km, with a width ranging from 5 to 30 km, tectonically juxtaposed between the Simao and Baoshan blocks (Figure 1b). Having experienced Proto-Tethyan and Paleo-Tethyan accretionary orogenesis and Cenozoic India-Eurasia continental collision orogenesis, it includes rock assemblages and structural records from three stages: Proto-Tethyan, Paleo-Tethyan, and Cenozoic.

The Nantinghe, Niujingshan, and Manxin areas within the Changning-Menglian belt widely expose Early Paleozoic ophiolitic mélanges, considered remnants of Proto-Tethyan Ocean evolution [19,20,21,22,23,24]. Among these, the zircon U-Pb age of cumulate gabbro in the Nantinghe ophiolitic mélange is 473 Ma [19], consistent with the cumulate anorthosite (471 Ma, Liu et al. [21]) in the Mengku area, Shuangjiang County, adjacent areas. These rocks exhibit N-MORB or E-MORB geochemical characteristics, indicating the existence of a mature oceanic basin in the Changning-Menglian Tethyan Ocean during the Early Ordovician. Concurrently, the Middle Ordovician-Silurian Mengdingjie Group within the Changning-Menglian belt contains abundant turbidite sediments such as mudstones and sandstones interbedded with siliceous rocks, bearing Middle Silurian conodont fossils. Their lithological and sedimentary facies characteristics reflect formation in a passive continental margin environment, suggesting that the Changning-Menglian Proto-Tethyan Ocean had reached a considerable scale by the Ordovician. Middle Ordovician high-Mg adakitic rocks (468 ± 2 Ma, Wang et al. [20]) in the Niujingshan area, Middle-Late Ordovician metamorphic volcanic rocks (459–456 Ma, Nie et al. [25]) in the Huimin area, Silurian-Devonian dacite (428.9 ± 1.5 Ma, Lehmann et al. [26]) and granodiorite porphyry (401.0 ± 1.7 Ma, Ru et al. [27]) in the Dapingzhang area, and Late Silurian-Early Devonian intermediate-acidic volcanic rocks (421.2–417.6 Ma, Mao et al. [28]) in the Dazhonghe area all exhibit geochemical characteristics of arc magmatic rocks and are considered products of Changning-Menglian Proto-Tethyan oceanic subduction consumption.

As the main oceanic basin of the southern segment of the Paleo-Tethyan Ocean, the Changning-Menglian suture zone preserves abundant stratigraphic and rock records related to Paleo-Tethyan Ocean evolution. Relatively typical ophiolites are developed in the Tongchangjie, Ganlongtang-Nongba, and Laochang areas. Among these, the Tongchangjie ophiolite is relatively well-preserved, with rock assemblages mainly consisting of harzburgite, dunite, N-MORB-type cumulate gabbro and basalt, and OIB-type alkaline basalt [29]. Fossil evidence preserved within sedimentary interbeds or siliceous rock caps of the ophiolite indicates that these ophiolites formed during the Early Carboniferous to Late Carboniferous. Carboniferous to Late Permian Ocean island-marine volcanic-sedimentary sequences exhibit extensive exposure throughout the region within the Changning-Menglian suture zone, with lithological assemblages including alkaline basalt, radiolarian siliceous rock, limestone, and tuffaceous mudstone, mainly exposed in the Yiliu, Laochang, and Shuangjiang areas [30,31]. These rock records indicate that the Changning-Menglian Paleo-Tethyan Ocean had opened by the Carboniferous. Throughout the Late Carboniferous to Early Permian interval, seafloor spreading of the Changning-Menglian Ocean basin continued, depositing the Carboniferous-Permian Yutangzhai Formation (CPy), dominated by oolitic-bioclastic limestone, and the Carboniferous-Permian Guangse Formation (CPg), dominated by deep-water siliceous rock, siliceous mudstone, radiolarian siliceous rock, and oceanic basalt, constituting an oceanic basin-ocean island-seamount paleogeographic pattern. Jian et al. [32] discovered SSZ-type ophiolite in the Niujingshan area, with zircon U-Pb ages of 272–264 Ma, possibly representing the timing of the Changning-Menglian Paleo-Tethyan oceanic crust subduction. The Yunxian-Jinggu magmatic arc and its lateral continuation host voluminous Middle Permian to Triassic volcanic and plutonic assemblages related to Paleo-Tethyan oceanic crust subduction and collision [33,34,35,36,37], represented by the Lincang batholith, with the main rock types being diorite-quartz diorite-granodiorite assemblages. Previous studies suggest that the principal section of the Lincang granite batholith formed in two tectonic environments: syn-collisional orogeny (250–237 Ma) and post-collisional extension (235–203 Ma) of the Paleo-Tethyan Ocean, with a small number of magmatic rocks related to oceanic basin subduction (>252 Ma) in the early stage [38]. The Lincang granites are juxtaposed with Carboniferous-Permian ridge-ocean island type volcanic rocks in the western Changning-Menglian belt and Permian-Triassic arc volcanic rocks in the eastern South Lancangjiang belt, forming a symmetrically distributed ridge volcanic rock-ophiolite-arc magmatic rock belt. The eastern part of the Lincang batholith records Late Triassic volcanic rocks contemporaneous with the Lincang granite, including volcanic rocks of the Menghai, Xiaodingxi, and Manghuihe formations, comprising Late Triassic rhyolite, basalt, and andesite. The zircon U-Pb ages of these volcanic rocks range from 231 Ma to 210 Ma [39,40]. These Triassic magmatic rocks formed during the collisional orogenic process between the Baoshan and Simao blocks after the closure of the Paleo-Tethyan Ocean. Cenozoic India-Eurasia plate continental collision is mainly manifested within the Changning-Menglian belt by Eocene intermediate-acidic rocks related to lithospheric mantle delamination and leucogranites related to strike-slip shearing. The former is represented by Eocene granite porphyry and granite in the Laochang and Jinla areas [41], and the latter by Miocene granite in the Wayao area (Figure 2).

3. Sample Collection and Analytical Methods

Samples for this study were all collected from Changli Village, Wayao County, Baoshan City, Yunnan Province (Figure 2), located in the northern segment of the Changning-Menglian suture zone. The rock outcrop area is small, mostly covered by vegetation. Field observation and laboratory petrographic identification show that it is mainly composed of medium-coarse grained granodiorite. Microscopic characteristics show that the Wayao samples are primarily granodiorite (Figure 3a,b). The rock exhibits a granular texture, with the main minerals being quartz, plagioclase, hornblende, and biotite. Quartz is anhedral granular, with grain sizes of 0.3–1.2 mm, clean crystal surfaces, distributed between other mineral grains, exhibiting distinct undulatory extinction, and interference colors up to first-order yellow-white. Locally, it occurs in bands showing oriented arrangement (Figure 3c). Quartz dissolution embayment structures are visible. The plagioclase is subhedral, with grain sizes of 0.3–1.5 mm (Figure 3d). Biotite shows slight sericitization, appearing brownish-yellow.

Whole-rock major elements (except FeO by potassium dichromate titration) and trace elements were analyzed at the Beijing Uranium Geology Institute (Beijing, China) using X-ray fluorescence (XRF) [42,43]. ICP-MS analysis (Finnigan MAT Element I) determined trace element concentrations. The analytical precision for SiO₂ by XRF is estimated to be better than 1%, for other major oxides by XRF better than 2%, and for ICP-MS analysis better than 5%. Internal standards and detection limits are detailed by Wang et al. [44]. During field sampling, weathered surfaces, veins, and inclusions are removed, and ≥5 kg of fresh bedrock is collected. Drill core samples are cleaned to remove drilling mud contaminants. Large samples are manually crushed to <5 cm fragments using a ceramic hammer. In the laboratory, samples are coarsely crushed. After each crushing step, the crusher is meticulously cleaned by brushing, blowing with compressed air, wiping with ethanol, and rinsing with ultrapure water. The coarsely crushed sample is piled into a cone shape (coned) and divided into quarters (quartered). One diagonal pair of quarters is selected. This coning and quartering process is repeated three times until the sample quantity is reduced to approximately 500 g. The sample is then finely ground to a particle size of <74 μm (passing a 200-mesh nylon sieve). Particles failing to pass the sieve are returned for regrinding. If metallic contamination is detected, the sample is treated by soaking in 0.1 mol/L HCl for 10 min, followed by washing with ultrapure water until neutrality is reached. Finally, the prepared samples are stored: major element samples are placed in glass vials, while trace element samples are placed in acid-washed PTFE bottles. Zircon LA-ICP-MS U-Pb dating was completed at Beijing Zhihui Geological Technology (Beijing, China). Instrument conditions and analytical procedures are similar to those detailed by Wang et al. [44]. Individual analyses report 1σ uncertainties, while weighted mean ages carry 95% confidence errors. In the laboratory, samples are crushed to 2–3 mm using a tungsten carbide jaw crusher. The crushed material is then subjected to ultrasonic cleaning in ultrapure water for 10 min and dried at a low temperature (60 °C). Dual-density separation is performed using tribromomethane (ρ = 2.89 g/cm³) to remove light minerals and diiodomethane (ρ = 3.3 g/cm³) to remove heavy fractions. Centrifugation is carried out at 3000 rpm for 20 min, and this process is repeated four times. The separation is optimized using magnetic separation. Hand-picking under a binocular microscope is conducted with strict criteria: priority is given to long-prismatic, euhedral crystals. Crystals must be completely transparent and free of cloudy or metamictized areas. There is zero tolerance for inclusions (especially crystals containing apatite or quartz inclusions). Selected zircon grains undergo intensive cleaning: 1. soaking in 3 mol/L HNO₃ for 30 min, 2. rinsing thoroughly with ultrapure water, and 3. ultrasonic cleaning in absolute ethanol for 5 min. Zircon grains are arranged by size and mounted in low-fluorescence epoxy resin, which is cured at 40 °C for 24 h. The mounts are then polished to expose the maximum cross-section of the zircon grains, ensuring clear visibility of zoning patterns. Cathodoluminescence (CL) imaging is used to identify magmatic oscillatory zoning and metamorphic overgrowths/rims. Backscattered Electron (BSE) imaging is used as an auxiliary method to detect micro-fractures and compositional variations. Finally, analytical spot locations are selected and documented.

Zircon Hf isotopes were analyzed via MC-ICP-MS (Thermo Finnigan Neptune + Geolas UP193 laser, San Jose, CA, USA) at the CAGS Institute of Mineral Resources (Beijing, China). The beam size was 44 μm with a laser pulse frequency of 8–10 Hz. Instrument conditions, analytical procedures, standards, and uncertainties for individual analyses are similar to those detailed by Wang et al. [44]. Rock pretreatment enhancement, multi-stage heavy liquid separation, upgraded electromagnetic separation, and rigorous hand-picking under microscopy are employed. Selected zircon grains undergo final purification: boiling in 6 mol/L HCl at 60 °C for 1 h → rinsing with ultrapure water → ultrasonic cleaning in absolute ethanol. Zircons are mounted in low-fluorescence epoxy resin (curing shrinkage < 0.1%) and arranged in groups by grain size. Mounts are polished to expose central cross-sections, ensuring the preservation of core zoning patterns. Cathodoluminescence (CL) imaging identifies: magmatic oscillatory zoning, metamorphic/metasomatic domains, LA-ICP-MS trace element mapping locates low-Lu domains (Lu < 0.5 ppm). Analytical spots are positioned according to strict criteria: 1. >20 μm away from core-rim boundaries (avoiding mixed-age domains), 2. within low Y/Ho ratio zones (Y/Ho ≈ 28–40), indicating the absence of hydrothermal alteration, and 3. avoiding fractures and dissolution pits (preventing atmospheric Hf contamination).

Sr-Nd isotope analysis was performed using a multi-collector Finnigan MAT 261 mass spectrometer at Beijing Craton Innovation Geology Technology Co., Ltd., (Beijing, China). After spiking with ⁸⁵Rb-⁸⁴Sr/¹⁵⁰Nd-¹⁴⁹Sm, ~100 mg samples underwent HF-HNO₃ dissolution (150 °C) in PTFE vessels and Rb-Sr-Sm-Nd separation by two-column ion exchange [45]. ⁸⁶Sr/⁸⁸Sr ratios were normalized to 0.1194, and ¹⁴⁶Nd/¹⁴⁴Nd ratios to 0.7219. Analytical precision: NBS-987 ⁸⁷Sr/⁸⁶Sr = 0.710215 ± 11 (2σ, n = 22); La Jolla ¹⁴³Nd/¹⁴⁴Nd = 0.511852 ± 4 (2σ, n = 24). Targeting plagioclase for Sr isotopes and monazite for Nd isotopes, the separation process begins with coarse crushing followed by ferromagnetic removal using hand-held magnet adsorption, ultrasonic cleaning in ultrapure water, and drying at 60 °C. Sequential density separation is then performed: light minerals are extracted with tribromomethane (ρ = 2.89 g/cm³) while heavy minerals (plagioclase and monazite) are enriched with diiodomethane (ρ = 3.3 g/cm³). Subsequent electromagnetic separation precedes rigorous binocular microscopy hand-picking with dual-operator cross-verification. For analysis, 200–300 mg of purified plagioclase and 10–20 mg of monazite are weighed, digested via high-pressure bomb dissolution, and processed through chemical separation. Strict procedural blank control is maintained throughout (Sr blanks < 100 pg, Nd blanks < 50 pg) with all operations conducted within a Class-100 laminar flow hood.

4. Results

4.1. Zircon U-Pb Dating

Fifteen zircon grains from the granodiorite sample (WY-18-13-1) yield a concordia age of 276.7 ± 1.2 Ma (Figure 4a; MSWD = 1.9, n = 15). On the U-Pb concordia diagram, they plot on the concordia curve, showing good concordance. Twenty zircon grains from the sample (WY-18-13-2) were analyzed in situ, showing variable Th (184–1173 ppm) and U (451–8011 ppm) contents, with Th/U ratios ranging from 0.12 to 0.61. Sixteen of these zircons yield a concordia age of 280.05 ± 0.49 Ma (Figure 4b; MSWD = 0.21, n = 16). Both granodiorite samples show Early Permian crystallization ages.

4.2. Whole-Rock Element Composition

The major element analysis results for Wayao samples are listed in

Table 1. Whole-rock element.

Sample No.	WY-18-13	WY-18-14	WY-18-15	WY-18-16	WY-18-17	WY-18-18	WY-18-19	WY-18-20	WY-18-21	WY-18-22	WY-18-23	WY-18-24
SiO2	65.84	64.31	65.59	66.47	67.66	65.82	64.28	65.08	66.38	63.72	64.73	66.37
TiO2	0.67	0.88	0.72	0.58	0.52	0.73	0.62	0.47	0.61	0.89	0.65	0.55
Al2O3	15.60	15.02	16.35	14.71	15.39	15.08	16.15	14.83	15.76	15.02	15.36	14.95
TFe2O3	4.53	5.32	4.38	4.27	4.05	4.55	5.13	4.62	4.16	5.45	4.98	4.41
MnO	0.08	0.06	0.05	0.09	0.07	0.08	0.07	0.09	0.06	0.08	0.08	0.09
MgO	2.21	2.65	2.26	2.02	1.85	2.31	2.54	2.3	2.05	3.16	2.73	2.11
CaO	4.61	4.78	4.25	5.12	3.89	4.45	4.69	4.92	4.17	5.16	4.79	4.45
Na2O	3.24	3.55	3.47	2.95	2.9	3.36	3.78	3.62	3.03	4.19	3.18	2.87
K2O	1.93	1.95	2.07	2.28	2.45	1.82	1.92	2.48	2.18	1.55	2.12	2.71
P2O5	0.15	0.27	0.13	0.17	0.15	0.35	0.2	0.1	0.21	0.1	0.15	0.2
LOI	0.60	0.75	0.55	0.76	0.45	0.75	0.39	0.82	0.8	0.56	0.65	0.75
T0TAL	99.46	99.54	99.82	99.42	99.38	99.30	99.77	99.33	99.41	99.88	99.42	99.46
Li	50.82	72.11	58.32	39.48	61.25	80.39	44.57	55.19	63.37	49.23	52.98	59.69
Be	2.27	2.98	3.15	2.79	4.57	3.26	3.81	4.02	3.94	3.12	3.47	4.22
Sc	11.03	11.8	13.12	9.87	12.35	10.58	15.25	13.03	12.17	10.82	11.29	12.51
V	72.81	84.42	76.71	69.73	65.38	77.19	80.62	79.37	72.15	93.25	82.16	73.94
Cr	46.53	42.15	61.36	56.39	35.71	49.94	68.22	52.39	58.52	85.35	62.64	73.64
Co	10.26	12.63	11.58	9.37	13.15	10.29	10.94	9.87	9.55	10.23	11.19	11.42
Ni	9.61	9.78	10.25	12.11	8.92	10.59	12.38	9.14	10.81	13.06	9.66	10.53
Cu	15.75	17.83	8.54	9.61	12.59	14.22	15.35	22.07	14.28	19.25	13.19	15.67
Zn	99.46	75.36	108.27	90.65	95.18	86.42	112.08	103.45	97.81	100.05	95.07	89.28
Ga	18.67	18.42	17.63	20.55	18.17	19.35	21.6	17.26	18.95	19.22	19.84	20.1
Rb	69.82	122.09	108.35	76.79	68.85	110.23	95.77	78.64	92.1	100.38	85.26	98.88
Sr	344.76	289.55	356.14	330.5	328.97	290.02	310.85	325.69	368.65	340.26	338.9	345.13
Y	22.24	31.26	25.13	22.87	18.6	20.95	20.73	21.58	24.02	32.4	27.15	29.3
Zr	110.07	108.2	89.25	97.66	105.34	118.92	120.09	135.17	114.26	102.38	110.55	123.48
Nb	12.94	15.32	14.56	13.2	11.68	12.5	12.8	13.17	12.83	14.21	13.09	12.77
Mo	0.48	0.29	0.36	0.45	0.52	0.63	0.47	0.43	0.56	0.45	0.5	0.68
Cd	0.23	0.18	0.25	0.15	0.18	0.22	0.24	0.19	0.2	0.25	0.23	0.19
In	0.06	0.09	0.07	0.05	0.07	0.1	0.08	0.09	0.05	0.06	0.1	0.08
Ba	340.73	290.5	358.93	472.15	558.62	360.94	320.11	435.1	380.25	402.93	500.86	345.6
La	59.31	47.1	40.65	68.13	55.92	30.9	49.18	58.06	72.35	64.29	60.4	57.2
Ce	113.12	94.62	75.07	104.15	108.6	122.36	115.7	110.23	98.44	138.2	125.17	118.65
Pr	11.96	10.9	8.73	9.05	12.37	11.55	13.06	9.64	10.39	11.38	12.22	11.8
Nd	40.80	34.2	50.62	45.18	39.06	42.5	46.34	45.26	38.45	41.15	40.3	43.48
Sm	7.22	11.38	9.2	8.38	7.55	10.26	8.05	7.39	7.16	6.93	7.8	8.51
Eu	1.24	1.29	1.24	1.53	1.38	1.32	1.57	1.22	1.19	1.45	1.3	1.28
Gd	6.15	5.08	6.76	7.48	5.52	6.04	7.36	8.35	6.23	6.5	6.92	6.31
Tb	0.86	0.94	1.03	0.9	0.78	0.83	1.15	0.87	0.86	0.94	0.95	0.99
Dy	4.45	5.23	3.85	4.08	4.69	4.32	3.93	4.77	5.14	4.15	3.99	4.48
Ho	0.82	0.66	0.95	1.16	0.85	0.88	0.93	0.78	0.74	0.83	0.8	0.97
Er	1.80	3.02	1.56	1.98	2.05	2.4	1.91	1.85	1.79	1.83	1.95	2.56
Tm	0.30	0.41	0.33	0.28	0.35	0.3	0.25	0.35	0.38	0.29	0.3	0.28
Yb	1.98	2.72	2.23	1.85	1.96	2.05	3.19	1.9	2.18	2.5	2.48	2.01
Lu	0.30	0.24	0.38	0.33	0.41	0.28	0.29	0.3	0.35	0.28	0.33	0.37
Hf	3.11	4.16	4.32	3.15	3.36	3.5	2.87	3.35	3.62	3.22	3.9	3.65
Ta	1.06	1.31	1.46	1.19	1.23	1.55	1.2	1.05	1.35	1.15	1.38	1.26
Pb	15.45	21.72	18.36	13.55	22.5	19.18	18.6	16.32	15.58	14.2	17.5	16.82
Bi	0.22	0.31	0.25	0.19	0.22	0.2	0.15	0.25	0.29	0.18	0.19	0.21
Th	23.75	15.7	25.26	31.08	20.13	22.05	28.37	23.55	24.02	18.45	19.36	20.08
U	2.46	2.23	3.84	2.75	3.56	4.12	2.55	2.38	3.04	3.17	2.88	2.5
LREE	233.64	199.49	185.51	236.42	224.88	218.89	233.90	231.80	227.98	263.40	247.19	240.92
HREE	16.65	18.30	17.09	18.06	16.61	17.10	19.01	19.17	17.67	17.32	17.72	17.97
L/R	14.03	10.90	10.85	13.09	13.54	12.80	12.30	12.09	12.90	15.21	13.95	13.41
(La/Yb)N	21.50	12.42	13.08	26.42	20.46	10.81	11.06	21.92	23.81	18.45	17.47	20.41
(Ce/Yb)N	15.88	9.66	9.35	15.64	15.39	16.58	10.07	16.12	12.54	15.36	14.02	16.40
(Sm/Eu)N	2.21	3.34	2.81	2.08	2.07	2.95	1.94	2.30	2.28	1.81	2.27	2.52

. The rock body has SiO₂ content ranging from 63.72 wt% to 67.66 wt%, with an average of 65.52 wt%. K₂O content ranges from 1.55 wt% to 2.48 wt%, with an average of 2.12 wt%. In the K₂O%-SiO₂% diagram (Figure 5b), samples fall in the calc-alkaline series field. Na₂O content ranges from 2.87 wt% to 4.19 wt%, with an average of 3.53 wt%. Total alkali (K₂O + Na₂O) values range from 5.17 wt% to 6.10 wt% (K₂O% + Na₂O% < 8 wt%), with an average of 5.47 wt%. Overall, K₂O% < Na₂O%, with K₂O%/Na₂O% values ranging from 0.37 wt% to 0.94 wt%, with an average of 0.65 wt% < 1. The magnesium number (Mg#) ranges from 47.50 to 53.46, with an average of 49.84, indicating that the rock body is relatively K-poor, alkali-poor, Na-rich, and has a high Mg#. On the TAS (SiO₂ vs. K₂O + Na₂O) diagram (Figure 5a), sample points fall in the granodiorite field, generally consistent with field observations and microscopic identification. Al₂O₃ content ranges from 14.71 wt% to 16.35 wt%, with an average of 15.35 wt%, indicating low aluminum content. The aluminum saturation index A/CNK ratio ranges from 0.84 to 1.06, and A/NK from 1.72 to 2.15, classifying them as metaluminous rocks (Figure 5c). The above characteristics indicate that the Wayao Lincang rock body generally belongs to the metaluminous calc-alkaline series.

4.3. Trace Elements

Trace element analysis results and related parameters for Wayao samples are listed in Table 1. The total rare earth element (ΣREE) content of this rock body ranges from 185.51 × 10⁻⁶ to 240.92 × 10⁻⁶, with an average of 228.67 × 10⁻⁶. LREE/HREE = 10.90–15.21 (average 12.91), (La/Yb) _N = 11.06–26.42 (average 18.15). In the chondrite-normalized diagram (Figure 6), they show a right-sloping pattern, indicating LREE enrichment and HREE depletion. Eu exhibits a distinct negative anomaly, with δEu values ranging from 0.47 to 0.65 (average 0.54). The Wayao Lincang rock body is significantly enriched in large ion lithophile elements (LILEs) such as Rb, Th, U, La, and Pb, while relatively depleted in high field strength elements (HFSEs) such as Ba, Nb, Sr, and Ti (Figure 6).

4.4. Sr-Nd Isotope Data

The Sr-Nd isotope analysis results and related parameters for Wayao samples are listed in

Table 2. Sr-Nd isotope data.

Sample No.	Rb	Sr	87Rb/86Sr	87Sr/86Sr	SE	(87Sr/ 86 Sr) i	Sm	Nd	147Sm/144Nd	143Nd/144Nd	SE	εNd(t)	TDM	TDM2	fcc
WY-18-13	69.82	344.76	0.586376	0.709112	0.000007	0.706890	7.22	40.80	0.1069	0.512325	0.000007	−6.1	1177	1282	−0.4
WY-18-15	108.35	356.14	0.880941	0.709161	0.000005	0.705659	9.20	50.62	0.1099	0.512353	0.000005	−5.6	1169	1245	−0.4
WY-18-16	76.79	330.5	0.672778	0.709143	0.000006	0.706435	8.38	45.18	0.1121	0.512345	0.000004	−5.7	1207	1264	−0.4
WY-18-17	68.85	328.97	0.606019	0.70914	0.000009	0.706742	7.55	39.06	0.1169	0.512346	0.000005	−5.7	1264	1276	−0.4
WY-18-18	110.23	290.02	1.100552	0.709175	0.000007	0.704644	10.26	42.50	0.1459	0.51234	0.000003	−5.8	1817	1371	-0.4
WY-18-19	95.77	310.85	0.892107	0.709127	0.00001	0.705657	8.05	46.34	0.1050	0.512347	0.000004	−5.7	1126	1241	−0.4
WY-18-20	78.64	325.69	0.699162	0.709148	0.000006	0.706385	7.39	45.26	0.0987	0.512352	0.000011	−5.6	1057	1215	−0.4
WY-18-21	92.1	368.65	0.723409	0.709125	0.000008	0.706285	7.16	38.45	0.1126	0.512343	0.000004	−5.8	1215	1269	−0.4
WY-18-22	100.38	340.26	0.854230	0.709172	0.000008	0.705915	6.93	41.15	0.1018	0.512334	0.000002	−5.9	1111	1254	−0.4

and

Table 3. Hf isotope data.

Sample No.	176Hf/177Hf	1σ	176Lu/177Hf	1σ	176Yb/177Hf	1σ	εHf(0)	εHf(t)	TDM1	TDM2
WY18-13_3	0.282564	0.000013	0.000468	0.000003	0.015403	0.000182	−7.34	−7.34	959	1357
WY18-13_5	0.282544	0.000017	0.001161	0.000015	0.038634	0.000411	−8.06	−8.06	1006	1397
WY18-13_25	0.282530	0.000015	0.000770	0.000005	0.025187	0.000050	−8.56	−8.56	1015	1425
WY18-13_6	0.282538	0.000015	0.000568	0.000009	0.017911	0.000383	−8.26	−8.26	998	1408
WY18-13_8	0.282551	0.000014	0.001231	0.000038	0.043103	0.001736	−7.81	−7.81	998	1383
WY18-13_9	0.282534	0.000013	0.000765	0.000009	0.025933	0.000160	−8.41	−8.41	1009	1417
WY18-13_10	0.282580	0.000014	0.000741	0.000011	0.023304	0.000155	−6.78	−6.78	944	1326
WY18-13_31	0.282529	0.000012	0.000566	0.000006	0.019168	0.000345	−8.60	−8.60	1011	1427
WY18-13_14	0.282517	0.000013	0.000735	0.000031	0.024758	0.001214	−9.03	−9.03	1033	1451
WY18-13_15	0.282541	0.000014	0.000630	0.000008	0.021444	0.000330	−8.18	−8.18	997	1404
WY18-13_33	0.282490	0.000017	0.000851	0.000034	0.030098	0.000953	−9.97	−9.97	1073	1503
WY18-13_17	0.282530	0.000014	0.000549	0.000013	0.018791	0.000595	−8.57	−8.57	1010	1426
WY18-13_38	0.282497	0.000013	0.000608	0.000011	0.020639	0.000346	−9.74	−9.74	1057	1490
WY18-13_18	0.282734	0.000015	0.001749	0.000024	0.062018	0.000828	−1.34	−1.34	749	1024
WY18-13_19	0.282489	0.000014	0.001250	0.000009	0.041314	0.000319	−10.01	−10.01	1086	1505
WY18-13_41	0.282520	0.000015	0.000565	0.000005	0.018907	0.000291	−8.91	−8.91	1024	1444

. The Wayao granodiorites have ⁸⁷Rb/⁸⁶Sr ratios of 0.58638–1.10055 and ⁸⁷Sr/⁸⁶Sr ratios of 0.709112–0.709161 (Table 2). Their ¹⁴⁷Sm/¹⁴⁴Nd ratios range from 0.098712 to 0.145948, and ¹⁴³Nd/¹⁴⁴Nd ratios range from 0.512325 to 0.512353 (Table 2). Isotope ratios recalculated based on the sample zircon U-Pb age yield initial (⁸⁷Sr/⁸⁶Sr) _i values of 0.704644–0.79689, εNd(t) values of (−5.55948) to (−6.10567), and corresponding Nd model ages (T_DM2) of 1215–1371 Ma (Table 3).

4.5. Zircon Hf Isotope Characteristics

Based on the age data, Hf isotope compositions of 16 zircon grains were tested (

Table 4. U-Pb isotope data.

Sample No.				Isotopic Ratios						Isotopic Ages (Ma)
	Pb	Th	U	207Pb/206Pb	207Pb/206Pb	207Pb/235U	207Pb/235U	206Pb/238U	206Pb/238U	207Pb/206Pb	207Pb/206Pb	207Pb/235U	207Pb/235U	206Pb/238U	206Pb/238U
	(ppm)	(ppm)	(ppm)	Ratio	1sigma	Ratio	1sigma	Ratio	1sigma	Age (Ma)	1sigma	Age (Ma)	1sigma	Age (Ma)	1sigma
WY-18-13-1	9	62.2	195	0.0529	0.0021	0.3048	0.0121	0.0422	0.0008	324	88.9	270	9.4	266	5.2
WY-18-13-2	9	63.7	176	0.0500	0.0022	0.2938	0.0133	0.0429	0.0009	195	104	262	10.5	271	5.3
WY-18-13-3	19	145	368	0.0534	0.0018	0.3231	0.0110	0.0443	0.0009	346	50	284	8.5	279	5.4
WY-18-13-4	12	77.7	229	0.0554	0.0017	0.3439	0.0127	0.0449	0.0009	432	65.7	300	9.6	283	5.8
WY-18-13-5	22	192	423	0.0510	0.0015	0.3092	0.0096	0.0441	0.0008	239	66.7	274	7.4	278	5.2
WY-18-13-6	27	147	523	0.0517	0.0014	0.3260	0.0098	0.0459	0.0010	272	61.1	287	7.5	289	6.2
WY-18-13-7	10	63.5	200	0.0525	0.0020	0.3112	0.0123	0.0433	0.0009	306	87.0	275	9.5	273	5.8
WY-18-13-8	24	169	473	0.0512	0.0016	0.3116	0.0107	0.0440	0.0009	250	72.2	275	8.3	278	5.4
WY-18-13-9	10	74	188	0.0546	0.0023	0.3285	0.0147	0.0437	0.0009	394	94.4	288	11.2	276	5.3
WY-18-13-10	22	180	446	0.0530	0.0017	0.3090	0.0099	0.0425	0.0008	328	72.2	273	7.6	268	4.7
WY-18-13-11	18	178	360	0.0538	0.0019	0.3023	0.0109	0.0410	0.0008	361	80	268	8.5	259	4.8
WY-18-13-12	21	145	429	0.0524	0.0018	0.3033	0.0107	0.0421	0.0008	306	77.8	269	8.3	266	5.0
WY-18-13-13	12	67.6	242	0.0568	0.0021	0.3309	0.0127	0.0426	0.0009	483	47.2	290	9.7	269	5.8
WY-18-13-14	24	168.7	476	0.0520	0.0016	0.3126	0.0100	0.0437	0.0008	287	69	276	7.7	275	4.8
WY-18-13-15	13	86.9	260	0.0530	0.0020	0.3108	0.0121	0.0427	0.0008	328	88.9	275	9.4	270	4.7
WY-18-13-16	78	329	1568	0.0513	0.0012	0.3256	0.0081	0.0460	0.0008	254	53.7	286	6.2	290	4.8
WY-18-13-17	29	130	617	0.0541	0.0015	0.3206	0.0086	0.0433	0.0007	372	63	282	6.6	273	4.3
WY-18-13-18	50	241	994	0.0512	0.0013	0.3213	0.0096	0.0455	0.0009	256	59.2	283	7.4	287	5.5
WY-18-13-19	26	179	539	0.0540	0.0016	0.3215	0.0103	0.0436	0.0010	372	64.8	283	7.9	275	6.2
WY-18-13-20	14	169	2065	0.0482	0.0016	0.0506	0.0034	0.0074	0.0004	122	81.5	50.1	3.3	47.3	2.5
WY-18-13-21	25	133	469	0.0510	0.0015	0.3444	0.0110	0.0488	0.0008	239	66.7	301	8.3	307	5.2
WY18-13_22	38	279	848	0.0514	0.0003	0.2904	0.0036	0.0410	0.0005	257	39	259	3	259	3
WY18-13_23	66	664	1326	0.0514	0.0002	0.3106	0.0030	0.0439	0.0004	257	39	275	2	277	2
WY18-13_24	26	202	519	0.0515	0.0003	0.3153	0.0032	0.0445	0.0004	261	10	278	2	280	2
WY18-13_25	28	251	552	0.0523	0.0003	0.3179	0.0033	0.0441	0.0004	298	19	280	3	278	2
WY18-13_26	22	200	451	0.0520	0.0004	0.3134	0.0037	0.0437	0.0004	287	-14	277	3	276	2
WY18-13_27	69	818	1348	0.0520	0.0003	0.3094	0.0031	0.0432	0.0004	283	11	274	2	273	2
WY18-13_28	36	250	724	0.0517	0.0003	0.3155	0.0029	0.0443	0.0004	272	15	278	2	279	2
WY18-13_29	32	184	653	0.0524	0.0003	0.3275	0.0039	0.0454	0.0005	302	15	288	3	286	3
WY18-13_30	45	274	930	0.0517	0.0003	0.3141	0.0033	0.0440	0.0004	272	13	277	3	278	2
WY18-13_31	77	498	1549	0.0517	0.0002	0.3193	0.0027	0.0448	0.0003	272	9	281	2	282	2
WY18-13_32	378	934	8011	0.0516	0.0001	0.3205	0.0034	0.0450	0.0005	333	7	282	3	284	3
WY18-13_33	30	218	598	0.0522	0.0003	0.3159	0.0036	0.0439	0.0004	295	15	279	3	277	2
WY18-13_34	26	195	507	0.0521	0.0003	0.3249	0.0035	0.0453	0.0004	287	15	286	3	286	2
WY18-13_35	41	251	822	0.0521	0.0003	0.3231	0.0032	0.0450	0.0004	287	13	284	2	284	2
WY18-13_36	81	1173	1458	0.0517	0.0002	0.3163	0.0032	0.0444	0.0004	272	9	279	2	280	2
WY18-13_37	25	195	493	0.0518	0.0003	0.3199	0.0030	0.0448	0.0003	276	19	282	2	283	2
WY18-13_38	29	216	576	0.0523	0.0003	0.3230	0.0029	0.0448	0.0003	298	18	284	2	282	2
WY18-13_39	37	293	728	0.0523	0.0003	0.3240	0.0029	0.0450	0.0003	298	13	285	2	284	2
WY18-13_40	185	769	3928	0.0519	0.0002	0.3151	0.0028	0.0440	0.0004	283	12	278	2	278	2
WY18-13_41	69	680	1353	0.0513	0.0003	0.3108	0.0032	0.0440	0.0004	254	11	275	3	277	3

). The ten data points tested for WY-18-13 have ¹⁷⁶Lu/¹⁷⁷Hf ratios between 0.00055 and 0.00175, ¹⁷⁶Hf/¹⁷⁷Hf ratios between 0.282489 and 0.282734, εHf(t) values between −10.01 and −1.34, and Hf isotope two-stage depleted mantle model ages (T_DM2) of 1023–1504 Ma, concentrated between 1357 and 1450 Ma. This section may be structured using subheadings and should include a concise and accurate description of the experimental results, their interpretation, as well as the deducible experimental conclusions.

5. Discussion

5.1. Emplacement Age of Paleo-Tethyan Granitic Magma

Previous studies on the Lincang granite indicate that its main emplacement age is Late Triassic. Zircon ages of the Lincang granite range from about 235 Ma to ~203 Ma [52,53,54]. However, within the Lincang batholith, older granitic rocks exist [55], which are intruded by younger Middle-Late Triassic magmas. This study employs LA-ICP-MS dating, obtaining concordia ages of 276.7 ± 1.2 Ma and 280.05 ± 0.49 Ma from two typical magmatic crystallization zircon samples from the Lancangjiang granodiorite. The error ranges for both zircon ages are small. These reliable zircon U-Pb age data indicate that the emplacement age of the Wayao samples is ~280 Ma. Accompanying the Paleo-Tethyan subduction-closure evolution process, a series of granitic magmatic records developed east of the Changning-Menglian suture zone. For example, D. Hennig [9] collected granodiorite samples in Jinghong, Lincang, with an age of 283 Ma. Deng et al. [14] collected two granodiorite samples in the Lincang area with ages of 261 ± 1 Ma and 252 ± 1 Ma. Middle Triassic zircon U-Pb ages within the Lincang granite range from ~245 Ma to ~239 Ma [56]. Contemporaneous with the magmatic rocks, a set of Late Early Triassic-Middle Triassic rhyolite, dacite, andesite, and basalt developed, with zircon U-Pb ages ranging from 250 ± 4 Ma to 237 ± 3 Ma [57]. Previous studies of the Lincang batholith’s igneous rocks define three key magmatic episodes: pre-Early Triassic (~252 Ma), spanning the Late Early to Middle Triassic (250–237 Ma), and Late Triassic (235–203 Ma) [14].

5.2. Petrogenesis

5.2.1. Rock Type

Granites are typically classified into three types: I-type, S-type [58], and A-type [59], primarily based on petrographic and geochemical characteristics and the nature of the magma source region. However, distinguishing between different types of granites requires comprehensive mineralogical, petrological, and geochemical joint discrimination. Research suggests that the (Na₂O + K₂O/CaO)/Zr + Nb + Ce + Y diagram and (FeO*/MgO)/(10,000 Ga/Al) diagram can effectively distinguish highly fractionated granites from unfractionated granites. In Figure 7a,b, Wayao sample points are concentrated in the unfractionated I, S granite region, indicating they belong to unfractionated granites. Furthermore, this granodiorite also possesses petrographic and geochemical characteristics distinct from A-type granites, mainly manifested in the absence of alkaline mafic minerals in the granodiorite samples, low TFeO/MgO ratios (average 1.80) and 10,000 Ga/Al values (average 2.36), differing from the chemical composition of A-type granites (TFeO/MgO > 10, 10,000 Ga/Al > 2.6). The aluminum saturation index A/CNK [molar Al₂O₃/(CaO + Na₂O + K₂O)] of the granodiorite samples is 0.84–1.06, inconsistent with peraluminous S-type granites, and the mineral assemblage contains hornblende, displaying characteristics of I-type granites. Therefore, the Wayao granodiorite is an I-type granite. Figure 5b reveals two distinct evolutionary trends between the 280 Ma samples and younger regional rock units: the former exhibits low K₂O contents (1.55–2.48 wt%) with metaluminous characteristics (A/CNK = 0.84–1.06), indicating derivation from amphibolite partial melting; whereas the latter displays elevated K₂O (>3 wt%) and peraluminous signatures (A/CNK > 1.1), reflecting crustal melting dominance during later magmatic stages.

5.2.2. Magma Source

The Wayao granodiorite samples are characterized by metaluminous and calc-alkaline series, depletion in Ba, Nb, Sr, and Ti, and enrichment in Rb, Th, U, and Pb (Figure 6a,b). These features resemble typical crustal melts [61,62,63]. The Wayao granite has negative zircon εHf(t) values, ranging from −1.34 to −10.01, corresponding to Paleoproterozoic model ages (T_DM^C). Collective analysis reveals the ancient crust as its dominant reservoir (Figure 8; Dong et al. [13]). This result coincides with the ‘steep Hf isotope array’ model proposed by Mulder et al. [64], demonstrating the predominant role of recycled ancient basement in magma generation. In the (Na₂ + K₂O)/(FeO + MgO + TiO₂) vs. (Na₂O + K₂O + FeO + MgO + TiO₂) diagram (Figure 9a), Wayao granite samples are mainly concentrated in the amphibolite melting field, highly overlapping with experimental data from Patiño Douce [65], indicating that their magma source region is dominated by amphibolite melting. The process of amphibolite melting producing granitic melts aligns with the experimentally constrained model of Rapp & Watson [66], where low-temperature melting conditions (<800 °C) show consistency with the zircon Ti-in-zircon thermometry results (average 645 °C) in this study. The CaO/ (FeO + MgO + TiO₂) vs. (CaO + FeO + MgO + TiO₂) diagram (Figure 9b) further verifies that the magma source region is dominated by amphibolite, reflecting the remelting of ancient metamorphic basic rocks (e.g., fragments of subducted oceanic crust).

5.2.3. Magma Evolution Process

The Wayao granodiorite has relatively high SiO₂ content (63.72–67.66 wt.%), low Al₂O₃ content (14.71–16.35 wt.%), and high Na₂O/K₂O ratio (1.06–2.70) (Figure 5b). It is a typical calc-alkaline rock, metaluminous (A/CNK 0.84–1.06), characterized by high Y (18.6–32.4 ppm) and heavy REE (Yb_N = 10.88–16.00 ppm) contents (Figure 6a,b), and a relatively pronounced negative Eu anomaly (Eu/Eu* = 0.45–0.63). Abundant K-feldspar, plagioclase, quartz, and biotite, along with low MgO content (1.85–3.16 wt.%), indicate the fractionation of mafic minerals. These characteristics resemble sodic arc magmas [67], Archean tonalite-trondhjemite-granodiorite (TTG) assemblages alongside Phanerozoic arc-related magmatic rocks [68,69]. The K₂O content of the samples (1.55–2.71 wt%) is higher than typical adakites. Additionally, high Cr (35.71–85.35 ppm) and Ni (8.92–13.06 ppm) contents and Mg# values (47.50–53.46) are similar to slab-derived melts. The Wayao Lincang rock body is significantly enriched in LILEs such as Rb, Th, U, La, and Pb, while relatively depleted in HFSEs such as Ba, Nb, Sr, and Ti, resembling arc magmas (Figure 10a). Basaltic parental melts undergoing AFC acquire TTG-characteristic geochemistry [70]. The absence of xenoliths or zircon xenocrysts in the granodiorite and homogeneous Hf isotope composition is inconsistent with an assimilation model [71]. Geochemical trends of partial melting (Figure 10b,c) indicate that partial melting, rather than AFC, is the primary formation mechanism for the Lincang rock body. Mushkin et al. [72] proposed that extreme fractional crystallization of mantle melts might produce K-rich granites associated with arcs, accompanied by abundant intermediate intrusions. Dehydration melting of sodic granites might form K-rich granites [73,74]. Although sodic TTGs can generate large volumes of granodioritic melts with higher K content than the protolith, the upward extraction of such melts would lead to LILE depletion in the terrane [75]. Ultimately, the partial melting of K-rich mafic rocks [76] or mixing of sodic granitic melts with K-rich mafic magmas [77] are plausible models. Such K-rich magmas might contain enriched mantle components formed by fluid reaction during the subduction of altered oceanic crust. Enrichment in LILEs and light REEs (Figure 6a,b) and depleted radiogenic isotope compositions suggest they originate from an enriched mantle source rich in LILEs and light REEs but depleted in radiogenic isotopes [78]. Titanium-in-zircon temperatures have been widely used to determine the crystallization temperature of igneous rocks [79]. The sample rocks have relatively low zircon Ti temperatures (average = 645 °C). Therefore, the Wayao granodiorite formed from the melting of 1.37–1.21 Ga mafic crust. Metasomatic reactions between fluids derived from dehydration of the overlying mantle wedge and previously subducted oceanic crust might have produced such a source.

The presence of plagioclase rapakivi texture and quartz dissolution embayment structures in granitic rocks is the most direct evidence of magma mixing in the source region. Petrographic observations of the Wayao samples reveal quartz grains displaying embayed dissolution textures (Figure 3c) combined with the presence of acicular apatite crystals (Figure 3d). These textural features collectively suggest that the parental magma underwent magma mixing prior to its emplacement and crystallization [80]. Microphotographs (Figure 3b,c) reveal quartz dissolution embayments and biotite sericitization, indicating hydrothermal alteration and supergene weathering. Quantification using the Chemical Index of Alteration (CIA = [Al₂O₃/(Al₂O₃ + CaO* + Na₂O + K₂O)] × 100, where CaO* represents silicate-bound calcium) yields values of 45–52 [81]. These values fall below the typical weathering threshold (CIA > 60), demonstrating insignificant major element mobilization. Rb/Ba ratios (0.12–0.42) overlap with unaltered I-type granites (0.2–0.5), confirming Rb preservation. Consistently, negative Eu/Eu* anomalies (0.47–0.65) and zircon Ti-in-zircon temperatures (~645 °C) reflect magmatic origins. Consequently, weathering has not significantly modified the original magmatic signatures of high-field-strength elements (HFSE) and rare-earth elements (REE), validating their use in petrogenetic interpretations. The initial ⁸⁷Sr/⁸⁶Sr ratio of Wayao granite rocks is 0.709112–0.709175, εNd(t) values are −6.1 to −5.6, plotting between crust and mantle (Figure 10d), supporting mantle-derived material injection into the crust [82,83,84,85]. As shown in Figure 10d, the Wayao granite plots on the upper left side of the mixing line between magmatic and sedimentary sources based on the Sr-Nd isotopic composition of the Lancang Group basement, supporting a magma source derived from mixed magmatic-sedimentary rocks with different mixing proportions. The crustal residence age indicated by T_DM^C of 1.37–1.21 Ga suggests that the magma may originate from low-temperature partial melting of a Late Paleozoic crustal source. It is undeniable that the Lincang rock body is ore-bearing, implying its source region is not solely a product of crustal remelting but also involves mantle material participation. Nb/La = 0.18–0.36 (average 0.25), significantly lower than the crustal average (Nb/La = 0.4; Rudnick and Gao [86]), indicating that the Wayao Lincang rock body was intruded by mantle-derived magmas. Melting experiments show that melts produced by the partial melting of mafic lower crust generally have Mg# values <40; melts formed by simultaneous participation of mantle and crust components have Mg# values of 40–70; melts formed by 20%–30% partial melting of mantle lherzolite mostly have Mg# > 70. The Wayao Lincang rock body has Mg# values of 47.50–53.46 (mean 49.84). In the w(TFeO) vs. w(MgO) diagram (Figure 11a), samples plot along a mixing trend line, indicating the participation of mantle-derived components in the initial magma. The samples exhibit elevated εHf(t) values (−1.34) and Mg# (53.5), with Nb/La ratios (0.25 ± 0.05) below the continental crust average (0.4), indicating the input of subduction-fluid-modified mantle components [62]. Binary mixing modeling of Sr-Nd isotopes (Figure 10d) reveals 10%–15% mantle contribution, while rapakivi textures (Figure 3b) and quartz dissolution structures provide petrographic evidence for magma mixing. Collectively, the source represents a hybrid of ancient mafic lower crust and enriched mantle material, characteristic of hybridized sources in active continental margin subduction zones [66]. The formation of the Wayao granodiorite involved multi-source magma generation, encompassing the partial melting of ancient crustal material and mantle-derived magma mixing. Its evolution was controlled by multiple processes (e.g., partial melting-dominated with mixing-assisted mechanisms), generating at least two distinct geochemical trends (Figure 5b and Figure 10). The εHf(t) values in Figure 8 bifurcate into two data clusters (−1.34 to −5.6; −8.6 to −10.01), which, combined with the Sr-Nd mixing trend in Figure 10d, demonstrate differential contribution proportions between the mantle end-member (high εNd(t)) and crustal end-member (low εHf(t)) during magma hybridization.

Figure 10. (a) Plots of Sr/Y versus Y diagram (modified after Defant and Drummond [68]; Castillo [70]). (b). La vs. Zr/Sm, (c). Zr vs. Zr/Sm. (d). Diagrams of initial Sr–Nd isotopic composition for the Wayao granitoids. (Small white dots along the mixing curves display each 10% increment of mixing). The Sr–Nd isotopic data for Mandi and Shao La mafic rocks and the granite and metasedimentary rocks of the Greater Himalayan Complex (GHC) are from Parrish and Hodges [82], Imayama and Arita, [84]; Miller et al. [83]; Visonà et al. [85]. Other data cited from Henning et al. [9]; Deng et al. [14]; Dong et al. [49]; Cong et al. [50]. Acronym: ADR = Adakite-Dacite-Rhyolite; PM = partial melting; FC = crystalline fractionation.

Figure 10. (a) Plots of Sr/Y versus Y diagram (modified after Defant and Drummond [68]; Castillo [70]). (b). La vs. Zr/Sm, (c). Zr vs. Zr/Sm. (d). Diagrams of initial Sr–Nd isotopic composition for the Wayao granitoids. (Small white dots along the mixing curves display each 10% increment of mixing). The Sr–Nd isotopic data for Mandi and Shao La mafic rocks and the granite and metasedimentary rocks of the Greater Himalayan Complex (GHC) are from Parrish and Hodges [82], Imayama and Arita, [84]; Miller et al. [83]; Visonà et al. [85]. Other data cited from Henning et al. [9]; Deng et al. [14]; Dong et al. [49]; Cong et al. [50]. Acronym: ADR = Adakite-Dacite-Rhyolite; PM = partial melting; FC = crystalline fractionation.

5.3. Tectonic Setting of Late Paleozoic Granite Formation and Constraints on the Eastward Subduction Process of the Paleo-Tethyan Ocean

Southwestern Yunnan constitutes a key element within the convergent system marking the terminal closure of the Tethyan Ocean [87,88]. As mentioned, the evolution process of the Paleo-Tethys in southwestern Yunnan during the Late Paleozoic is not well constrained; Wang et al. [89] proposed that the Changning-Menglian belt is a continuously evolving ocean from Proto- to Paleo-Tethys, successively forming the eastern Proto-Tethyan and western Paleo-Tethyan oceanic accretionary complexes. Accumulated data in recent years have confirmed the existence of the suture zone [90,91,92,93,94,95] and the different nature of the blocks on both sides. However, most domestic researchers believe that the boundary between the Sukhothai arc and the Indochina terrane, the Lancangjiang, was not a wide ocean but possibly only a back-arc basin formed by the eastward subduction of the Changning-Menglian Ocean. Indeed, in the early literature, some scholars equated it with the Changning-Menglian belt. The Changning-Menglian suture zone preserves signatures of oceanic subduction, continental collision, and post-collisional uplift through multiphase magmatism [96]. Whereas the complex evolution of the Changning-Menglian Paleo-Tethys is generally resolved, Late Carboniferous–Late Triassic magmatic regimes continue to provoke debate [3].

The Late Paleozoic granites of the Baoshan Block studied in this paper are metaluminous calc-alkaline series, belonging to I-type granites, mainly distributed in arc and syn-collisional zones (Figure 10a and Figure 11b). Therefore, the Early Permian (290 Ma–260 Ma) intrusions are considered to have formed in a subduction-collision environment. The Wayao samples have Nb/Ta ratios of 8.1–12.5, lower than MORB (Nb/Ta = 16.7) and Cenozoic adakites formed by the direct partial melting of subducted slabs. On the (Sr/Y)/Y diagram (Figure 10a), the samples plot on island arc rocks, proving the island arc nature of the Wayao Lincang rock body [97]. Therefore, enrichment in LILEs and light REEs like Th and U, and depletion in HFSEs like Nb, Ta, and Ti, are reactions indicating the source region experienced metasomatism by dehydration fluids from subducted oceanic crust slabs [98]. Furthermore, the rock body has a mean Nb/U of 4.66, falling between the range of subduction fluids (Nb/U = 0.22; Ayers [99]) and global subducted sediments (Nb/U = 5; Plank and Langmuir [100]), also indicating the existence of subduction.

Figure 11. (a) w(TFeO)~w(Mgo)diagrams (after Zorpi et al. [101]) for the Wayao samples (b). Rb versus Yb + Ta tectonic discrimination diagram (after Pearce et al. [102]). Data cited from Henning et al. [9]; Deng et al. [14]; Dong et al. [49]; Cong et al. [50]. Acronyms: WPG—Within plate granite; ORG—ocean ridge granite; VAG—volcanic arc granite; syn-COLG—syn-collisional granite.

Figure 11. (a) w(TFeO)~w(Mgo)diagrams (after Zorpi et al. [101]) for the Wayao samples (b). Rb versus Yb + Ta tectonic discrimination diagram (after Pearce et al. [102]). Data cited from Henning et al. [9]; Deng et al. [14]; Dong et al. [49]; Cong et al. [50]. Acronyms: WPG—Within plate granite; ORG—ocean ridge granite; VAG—volcanic arc granite; syn-COLG—syn-collisional granite.

The high-Mg diorite assemblage is one of the important characteristics of oceanic subduction magmatism. In Figure 10a, Wayao samples fall into the volcanic arc granite field, reflecting their formation in an oceanic subduction environment. In summary, the above indicates that the Wayao samples formed in an extensional tectonic background during the oceanic subduction stage. According to ophiolitic complex records, the opening of the Changning-Menglian Paleo-Tethys occurred in the Middle Devonian [103]. The Late Carboniferous–Middle Permian hosted peak subduction magmatism along the Changning-Menglian Paleo-Tethys, where continuous subduction (Late Carboniferous to Permian–Early Triassic) generated the Yunxian-Jinggu arc (Figure 12). Late Carboniferous–Middle Permian granodiorite-mafic-ultramafic suites emplaced along the Simao Terrane’s western margin reflect Changning-Menglian Paleo-Tethyan subduction [104,105]. The appearance of contemporaneous mafic-ultramafic rocks with Late Permian Lincang granitic rocks provides support for a subduction environment [106].

The rock-forming age of the Wayao Lincang rock body is 260–290 Ma, consistent with the magmatic activity period (~252 Ma) during the subduction stage of the southern segment of the Paleo-Tethyan Ocean basin. In summary, it is considered that the rock-forming mechanism process of the Wayao samples occurred at 275 Ma. At that time, with the continuous subduction of the Paleo-Tethyan oceanic crust, the lithospheric mantle stretched and thinned under gravity influence. Reduced pressure led to asthenospheric upwelling, heating and melting the lithospheric mantle to produce mafic magma. The ascending mafic magma underplated the ancient crust, causing partial melting to form granitic magma, which mixed with the mafic magma. Finally, the initial magma with characteristics of crust-mantle mixing ascended and emplaced along tectonic channels (Figure 12).

Figure 12. Tectonic background for the generation of Wayao granodiorite in northern Baoshan, modified from Qiu et al. [107].

Figure 12. Tectonic background for the generation of Wayao granodiorite in northern Baoshan, modified from Qiu et al. [107].

6. Conclusions

(1) The granites of the Lincang rock body within the Baoshan Block in southwestern Yunnan formed at 276.7~280.05 Ma, representing products of Late Paleozoic magmatic activity.

(2) The granodiorite in the Lincang rock body is mainly composed of medium-coarse-grained and fine-grained granodiorite. It has high Si, poor K, poor alkalis, low Na, high Mg#, is enriched in large ion lithophile elements (LILEs) such as Rb, Th, U, La, and Pb, and relatively depleted in high field strength elements (HFSEs) such as Ba, Nb, Sr, and Ti. It belongs to the metaluminous calc-alkaline series. It has a high aluminum saturation index (A/CNK ratio 0.84–1.06) and Zr/Hf ratios of 20.66–41.84 (average 32.18), indicating that the Wayao samples are I-type granites.

(3) The Late Paleozoic I-type granites are products of the partial melting of crustal metamorphic volcanic components. They originated from the mixing of magma derived from the partial melting of ancient crustal material and mantle-derived magma introduced by underplating, with a relatively low proportion of mantle component. They formed in an active continental margin background related to the eastward subduction of the Paleo-Tethyan Ocean.