Geochemistry, Geochronology, and Prospecting Potential of the Dahongliutan Pluton, Western Kunlun Orogen

Abstract

Triassic granitoids are abundant on the northwestern margin of the Tibetan Plateau. The Dahongliutan pluton, located in the eastern Western Kunlun orogen, formed in the Late Triassic.Previous field studies have identified potential mixing of crustal and mantle magmas. In this study, we used zircon U–Pb ages and major and trace elemental analyses to investigate the tectonic evolution of the pluton, and to determine whether any exchange of mantle-derived material occurred between the pluton and the source area. We found that the pluton has relatively high SiO₂ contents, and the aluminum saturation index is consistent with peraluminous high-K calc-alkaline granite. The pluton is enriched in light rare earth elements; both light and heavy rare earth elements are highly fractionated. The magma that formed the pluton was predominantly derived from the crust; however, a small amount of upper mantle material was involved in the early stages of magma formation. The pluton underwent composite emplacement as a result of tectonic extension and magmatic emplacement, which may have occurred in the late Triassic post-collisional orogenic stage. Late Triassic magmatism provided heat and ore-forming material for Pb–Zn, Cu, Fe, and rare metal mineralization, which is of considerable importance for geological prospecting.

1. Introduction

The Western Kunlun orogenic belt is located in the northwestern Qinghai–Tibet Plateau at the junction of the Paleo-Asian and Tethys tectonic domains. Magmatic activity has occurred frequently throughout this region, producing granitoid rocks. The Western Kunlun orogen was accompanied by evolution of the Paleo-Tethys Ocean during the Indosinian period. As collisional compressive conditions changed to a collisional extension setting, strong intermediate-acid magmatism occurred along the Mazha–Kangxiwa suture zone [1]. Determining the characteristics, genesis, and evolution of the emplaced granitoids is crucial for investigating the evolution of continental orogenic belts.

The Dahongliutan pluton is one of the main plutons of the Sanshiliyingfang Qitaidaban granite belt [2]; it is located in the northern Tianshuihai–Karakoram terrane, on the southern side of the Mazha–Kangxiwa suture zone, and is bounded by the Dahongliutan Fault to the north. Based on geochronological data, the Bureau of Geology and Mineral Resources of Xinjiang suggested that the Dahongliutan pluton formed during the late Cretaceous. Based on petrography, petrochemistry, and chronology, Qiao, et al. [3] suggested that the Dahongliutan monzogranite is a Late Triassic, highly differentiated S-type granite that experienced crustal source contamination in a collisional setting. Wei, et al. [4] suggested that the Dahongliutan pluton is a compound pluton produced during a single period of tectonomagmatic activity that included partial melting of crustal material in a collisional setting after the closure of the Paleo-Tethys Ocean. Zhang, et al. [5] measured an emplacement age of ~217.5 Ma for the Dahongliutan pluton and determined that the pluton was the product of partial melting of crustal material in a post-collisional setting. Ding, et al. [6] measured the emplacement age of the Dahongliutan biotite monzogranite to be 214 ± 1.8 Ma, which indicates that the pluton was produced by late Indosinian magmatism; they postulated that the magma that formed the Dahongliutan pluton contained mantle and Mesoproterozoic crustal components [6,7]. The Dahongliutan rare metal pegmatite deposit is located south of the Mazha-Kangxiwa Fault in the eastern part of the Western Kunlun orogen and is a large Li-Be-Nb-Ta deposit [8]. More than 400,000 tons of Li₂O resources have been explored, and many of the pegmatite veins have not yet been evaluated; thus, this deposit has great metal prospecting potential [9].

Exploration data indicate that the Dahongliutan belt has large- and super large-scale rare metal prospecting potential. The Dahongliutan rare metal pegmatite deposit, a large Li–Be–Nb–Ta deposit, is located south of the Mazha–Kangxiwa Fault in the eastern Western Kunlun orogen [8]. More than 400,000 t of Li₂O resources have been explored; however, many of the pegmatite veins have not yet been evaluated and this deposit has great metal prospecting potential [9]. The pegmatite dikes that surround Triassic rocks in this area suggest ideal conditions for rare metal mineralization [10]. However, it remains unclear whether the emplacement ages of the different lithofacies in the Dahongliutan pluton are consistent. Moreover, it is unclear whether the pluton formed over multiple magmatic stages. Previous research has suggested that the magmatic source of the Dahongliutan pluton was crustal; however, this does not account for dioritic enclaves developed in the samples. The Muztagata pluton (located to the north), Shangqimugan pluton, and Dahongliutan pluton all formed under similar regional geologic settings and exhibit similar emplacement ages. They contain dark inclusions, which previous field studies attributed to mixing of crustal and mantle magmas. Thus, it is important to determine whether any exchange of mantle-derived material occurred between the Dahongliutan pluton and the source area.

In this study, we used data obtained by a 1:50,000 mineral prospective survey and 1:50,000 regional geological survey, along with previous research results, to investigate the petrology, geochemistry, genesis, and tectonic setting of the Dahongliutan pluton and its geodynamic setting in the Late Triassic. The findings of this study provide important data for systematic studies on tectonomagmatic events related to the Western Kunlun orogeny.

2. Geologic Setting

The Western Kunlun orogen, which is located at the junction of the northwestern margin of the Qinghai–Tibet Plateau and the Tarim Block, comprises a composite orogenic belt formed by multiple arc-continent collisions (Figure 1a). The evolution of the Western Kunlun orogen is complex and includes three tectonic units: the northwestern Kunlun, southwestern Kunlun, and Tianshuihai–Karakoram terranes [7,11].

The Dahongliutan pluton is located ~150 km southwest of Hotan County, Xinjiang Uygur Autonomous Region; the Xinjiang–Tibet highway passes through the north bank of the Karakash River on the northern side of the study area. The tectonic setting is the northern Tianshuihai–Karakoram of the Western Kunlun orogen, which lies to the south of the Mazha–Kangxiwa suture zone. To the north, it is adjacent to the Dahongliutan Fault. The rocks surrounding the Dahongliutan granite are from the Triassic Bayanhar and Paleoproterozoic Kangxiwa groups. The pluton, which forms a linear/oval feature (Figure 1) with its long axis trending NW–SE, was emplaced parallel to the Dahongliutan fault zone [3]. According to the intrusive relationships, rock types, intrusion sequence, and genetic types, the intrusive rocks can be divided into seven different types: muscovite monzogranites (first intrusion, Figure 2a), mica monzogranites (second intrusion, Figure 2b), biotite granodiorites (third intrusion, Figure 2c), biotite monzogranites (fourth intrusion), biotite quartz diorites (fifth intrusion, Figure 2d), tonalites (sixth intrusion), and mica granites (seventh intrusion). These intrusions underwent homologous magmatic and spatial evolutions and belong to a relatively complete magmatic evolution sequence. All the rock types contain gray-black deep-sourced diorite inclusions that are predominantly elliptical; however, the long axes of inclusions near the edges of the pluton are roughly parallel to the contact boundary with the surrounding rock. The pluton has experienced regional or dynamic metamorphism to different degrees, and local sections exhibit flaky and gneissic structures. The rocks generally contain feldspar phenocrysts, which have evolved from neutral to acidic (early to late) and form a relatively complete homologous magmatic sequence. There is a pulsating contact with rocks adjacent to each intrusion in the sequence, with the presence of condensation edges.

3. Analytical Methods

3.1. Major and Trace Elemental Analyses

We analyzed the major and trace elemental contents of 23 rock samples from the study area. Sample analyses were performed at the Urumqi Supervision and Inspection Center of Mineral Resources, Ministry of Land and Resources. Major elements were analyzed using X-ray fluorescence (model # Axios, manufacturer:Panaco Netherlands, country of origin: The Netherlands); the analytical accuracy was better than 1–5%. Trace elements and rare earth elements (REEs) were analyzed using inductively coupled plasma mass spectrometry (ICP–MS; model # NexION 300x ICP-MS iCAP6300 Simultaneous spectrometer, manufacturer: PerkinElmer, country of origin: the United States). Detailed descriptions of the analytical methods and analyses can be found in Liu, et al. [12].

3.2. Zircon U–Pb Dating

Zircon U–Pb dating was performed using laser ablation ICP–MS (LA–ICP–MS) on six samples (P22-39TW01, P20-25TW01, P25-08TW01, P25-12, P21-32TW01, and P7-65TW01). Zircon sorting and analyses were performed at the Shared Collaboration (Beijing) Analysis and Testing Center. The rock samples were first mechanically crushed, then washed and sorted using conventional flotation and electromagnetic separation methods. Zircon grains were carefully chosen using a binocular microscope to ensure grains with good crystal form and transparency, and without inclusions or cracks. The number of zircon grains sorted from each sample ranged from 500 to >1000; these grains were then fixed in a colorless and transparent epoxy resin. Transmitted light, reflected light, and cathodoluminescence (CL) photography were performed to select analytical spots on zircon grains. The selected analytical points avoided the locations of internal cracks and inclusions in order to obtain accurate age values.

Zircon age dating was performed using LA–ICP–MS (Neptune, Finnigan) and a Newwave UP 213 laser ablation system. The spot beam diameter used for laser ablation was 25 μm, the frequency was 10 Hz, and the energy density was ~2.5 J/cm²; He was used as the carrier gas. The ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁴Pb (⁺²⁰⁴Hg), and ²⁰²Hg signals were received by ion counters, while ²⁰⁸Pb, ²³²Th, and ²³⁸U signals were received by the Faraday cup, allowing for the simultaneous reception of all target isotopic signals. The analytical accuracy of ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁶Pb/²³⁸U, and ²⁰⁷Pb/²³⁵U was ~2%. Denudation of the sample was measured using the point denudation method, and GJ-1 was used to debug the instrument before analysis. Zircons CJ-1 and M12 were used as external standards. Zircon GJ-1 was analyzed twice before and after every 10 samples for calibration, and one plesovice zircon standard was measured simultaneously.

Data processing of isotope ratios and elemental contents were performed using ICPMSDataCal 8.0. The age calculations and harmonic maps were completed using lsoplot ver. 3.0. Samples with ²⁰⁶Pb/²⁰⁴Pb ages of ≥1000 Ma were excluded from the calculation because they contained a large amount of radiogenic Pb. For samples with ages of <1000 Ma, the more reliable ²⁰⁶Pb/²³⁸U surface age was used. Detailed descriptions of the experimental procedures can be found in Hou, et al. [13].

4. Results

4.1. Petrographic Characteristics

We collected 23 samples from the northern, central, southern, southwestern, and southeastern parts of the pluton. The muscovite monzogranites (samples P22-55 GS, P22-71 GS, P20-15 GS, and D3801GS01) are gray-white with fine-grained hypidiomorphic-granular and massive structures. Euhedral plagioclase (30–35%) crystals have dimensions of 0.1 × 0.25–1 × 2.3 mm; some are replaced by sericite. Interstitial microcline (30%; 0.1–2 × 4.5 mm) is associated with biotite, plagioclase, and quartz. Fine albite stripes are distributed within coarse microcline grains. Quartz grains (25–30%; 0.05–1 × 0.5 mm) are xenomorphic-granular and exhibit strong wavy extinction. Muscovite (5%; 0.05 × 0.2–0.4 × 1.1 mm) is flaky. Flaky biotite (1–5%) is sometimes replaced by chlorite. Small amounts of apatite and white titanium were also observed.

The mica monzogranites (samples P22-39XT01, P26-88 GS, P20-19 GS, P20-03 GS, and P11-15GS01) are gray-white, with fine-grained hypidiomorphic-granular and massive structures. Mineral grain sizes are 0.05–1.7 × 3.5 mm; however, samples are predominantly composed of fine-grained minerals. Plagioclase (30–35%) is euhedral and ranges in size; potassium feldspar (20–25%) exhibits irregular shapes; inclusions of microcline and striped feldspar often replaced interstitial plagioclase. Quartz (25%) is allotriomorphic-granular and exhibits strong wavy extinction. Muscovite (10–15%) is flaky, variable in size, and has an uneven distribution. Biotite (5%) is flaky and commonly replaced by chlorite, with residual visible crystals. A small amount of apatite is also present, along with sericite exhibiting strong wavy extinction. Reticular cracks are filled a small amount of calcite.

The biotite granodiorite (samples P25-08XT01, P25-1-05 GS, and D259GS) is gray-white, with medium to fine-grained hypidiomorphic and massive structures. The main mineral components are plagioclase (45%), microcline (20–25%), quartz (25–30%), biotite (5%), and amphibole (1%). Mineral grains are 0.1–4.5 × 5 mm in size; medium-grained minerals (>2 mm) account for ~45% of the total. Some euhedral plagioclase are replaced by sericite, which has a random distribution. Microcline is irregular and interstitial, and is associated with plagioclase and biotite. Quartz is irregular, exhibits strong wavy extinction, and is associated with plagioclase and biotite. Biotite is flaky, and some grains are replaced by chlorite. Other minerals include small amounts of euhedral amphibole, epidote, sphene, and apatite. Samples are jointed and the surface is locally affected by spherical weathering.

The biotite monzogranite (sample P25-12GS) is gray-white with medium–fine-grained hypidiomorphic-granular and massive structures. The main mineral components are plagioclase (30–35%), microcline (25%), quartz (30–35%), biotite (10–15%), and amphibole (1%). Plagioclase crystals are elongate and exhibit ring structures; some grains are replaced by sericite and zoisite. Microcline is interstitial to plagioclase and biotite. Quartz is irregular and exhibits strong wavy extinction. Biotite is flaky, and some grains are replaced by chlorite. Some amphibole grains are associated with biotite. Epidote, apatite, sphene, and a small number of other minerals are also present. Samples are jointed and the surface is locally affected by alteration.

The biotite quartz diorite (samples P21-20GS and P23-01GS01) is gray with medium–fine-grained hypidiomorphic-granular and massive structures. The mineral grains are 0.1–2.1 × 3.1 mm in size; medium-grained minerals (>2 mm) account for 20–25% of the total. Plagioclase (50%) is tabular with variable grain sizes; some grains are replaced by sericite (1–5%). Hornblende (15%) ranges from euhedral to irregular in shape, and is associated with biotite. Biotite (15–20%) is flaky and randomly distributed. Quartz (15–20%) is interstitial, exhibits strong wavy extinction, and has an uneven distribution. Epidote, sphene, apatite, tourmaline, and small amounts of other minerals are also present.

The tonalite (samples P21-32XT01 and P21-08GS) is light gray-white with fine-grained hypidiomorphic-granular and massive structures. The main mineral components are quartz (25%), plagioclase (40–45%), biotite (20–25%), and amphibole (10%). The mineral grains are predominantly 0.1–2.6 mm in size. Plagioclase exhibits a hypidiomorphic plate strip shape, and some sericite replacement is observed. Biotite is flaky and exhibits weak alteration.

The mica granite (samples P7-65XT03, P9-32GS, and P10-01GS) is gray-white, medium grained, and exhibits hypidiomorphic-granular and massive structures. The main mineral components are plagioclase, potassium feldspar, biotite, muscovite, and quartz. Plagioclase is semi-idiomorphic and columnar; crystals are cloudy and some are extremely undeveloped bicrystals. Potassium feldspar is xenomorphic-granular, and the crystals are clean. Quartz is allomorphic-granular, and the crystals are smaller than those of feldspar. Biotite and muscovite are hypidiomorphic shaped wafers with low degrees of hypidiomorphism. Alteration is less pronounced than in other rock types, with only plagioclase kaolinization and sericitization; however, samples are weathered and the surfaces are broken.

4.2. Major Element Contents

Major elemental analyses (

Table 1. Major element (wt.%) and CIPW norm (wt.%) contents of Dahongliutan granite samples.

Sample	P19-01XT01	P20-25XT01	P6-06XT01	P22-55 GS	P22-71 GS	P20-15 GS	D3801GS01	P22-39XT01	P26-88 GS	P20-19 GS	P20-03 GS	P11-15GS01
Component	1	2	3	4	5	6	7	8	9	10	11	12
SiO2	73.22	64.68	73.4	73.05	70.74	72.39	72.47	72.16	71.92	73.82	57.01	73.95
TiO2	0.18	0.58	0.16	0.24	0.63	0.18	0.19	0.24	0.17	0.19	0.83	0.13
Al2O3	15.02	15.43	14.41	14.22	12.81	15.02	15.11	15.07	15.01	13.93	16.45	14.55
Fe2O3	0.86	2.96	1.06	1.31	2.62	1.1	1.07	1.21	1.64	1.17	4.77	0.77
FeO	1.04	5.2	1.26	1.65	4.31	1.35	1.24	1.46	2.22	1.47	7.15	0.95
MnO	0.03	0.12	0.03	0.05	0.07	0.04	0.03	0.11	0.05	0.04	0.16	0.04
MgO	0.36	1.78	0.21	0.5	1.51	0.45	0.33	0.31	0.46	0.46	3.32	0.33
CaO	0.84	4.05	0.83	0.98	1.86	1.2	0.82	0.96	1.4	1.02	3.31	1.23
Na2O	2.71	2.17	2.67	3.1	3.39	3.05	3.25	3.18	2.6	3.14	2.06	3.35
K2O	5.42	2.73	5.48	4.49	1.78	4.92	5.19	4.9	4.4	4.41	4.63	4.44
P2O5	0.28	0.12	0.44	0.36	0.14	0.28	0.26	0.35	0.06	0.32	0.15	0.23
LOI	0.82	0.93	0.9	0.9	0.77	1.13	0.71	0.88	1.3	0.6	2.1	0.98
Total	100.78	100.75	100.85	100.85	100.63	101.11	100.67	100.83	101.23	100.57	101.94	100.95
Qz	34.74	27.70	35.50	35.27	36.17	32.76	31.68	32.72	35.31	36.27	11.90	34.56
An	2.34	19.35	1.25	2.51	8.33	4.13	2.37	2.48	6.56	2.24	15.47	4.60
Ab	22.94	18.40	22.60	26.24	28.73	25.81	27.51	26.92	22.02	26.52	17.46	28.36
C	3.84	1.83	3.63	3.34	2.26	3.17	3.28	3.63	3.57	3.16	2.39	2.55
Hy	1.86	10.97	1.75	2.90	8.71	2.47	1.96	2.26	3.69	2.64	16.67	1.79
Mt	1.25	4.21	1.54	1.90	3.75	1.60	1.55	1.76	2.37	1.69	6.78	1.12
Ap	0.65	0.28	1.02	0.83	0.32	0.65	0.60	0.81	0.14	0.74	0.35	0.53
DI	89.73	62.26	90.51	88.06	75.43	87.65	89.88	88.61	83.34	88.81	56.77	89.16
SI	3.46	12.00	1.97	4.52	11.10	4.14	2.98	2.80	4.06	4.32	15.15	3.35
Mg#	0.55	0.47	0.36	0.50	0.50	0.52	0.49	0.41	0.37	0.50	0.56	0.53
A/NK	1.45	2.36	1.40	1.43	1.71	1.45	1.38	1.43	1.66	1.40	1.96	1.41
A/CNK	1.34	1.13	1.34	1.31	1.21	1.27	1.28	1.32	1.31	1.29	1.17	1.21
AI	0.54	0.32	0.57	0.53	0.40	0.53	0.56	0.54	0.47	0.54	0.41	0.54
K2O + Na2O	8.13	4.90	8.15	7.59	5.17	7.97	8.44	8.08	7.00	7.55	6.69	7.79
K2O/Na2O	2.00	1.26	2.05	1.45	0.53	1.61	1.60	1.54	1.69	1.40	2.25	1.33
CaO/Na2O	0.31	1.87	0.31	0.32	0.55	0.39	0.25	0.30	0.54	0.32	1.61	0.37
TFeO/MgO	3.92	3.43	8.19	4.40	3.43	4.04	5.19	6.39	6.24	4.26	2.68	3.87
σ	2.19	1.11	2.18	1.92	0.96	2.16	2.42	2.24	1.69	1.85	3.18	1.96
R1	2622.00	2816.00	2630.00	2677.00	3014.00	2556.00	2428.00	2496.00	2794.00	2731.00	1848.00	2675.00
R2	403.00	826.00	382.00	409.00	526.00	445.00	401.00	414.00	467.00	404.00	843.00	434.00
Sample	P25-08XT01	P25-1-05 GS	D259 GS	P25-12 GS	P21-20 GS	P23-01GS01	P21-32XT01	P21-08 GS	P7-65XT03	P9-32 GS	P10-01 GS
Component	13	14	15	16	17	18	19	20	21	22	23
SiO2	65	69.09	66.88	65.35	60.91	57.78	53.91	64.69	72.32	73.93	72.96
TiO2	0.43	0.33	0.36	0.46	0.67	0.75	0.87	0.5	0.2	0.24	0.17
Al2O3	15.97	13.87	15.35	15.32	15.26	16.23	17.41	16.91	14.33	13.93	15.12
Fe2O3	2.86	2.31	2.45	2.91	3.78	3.97	4.16	2.36	1.12	1.2	1.02
FeO	4.32	3.53	3.7	4.35	7.11	7.58	8.46	4.04	1.22	1.53	1.34
MnO	0.1	0.08	0.08	0.1	0.12	0.13	0.16	0.07	0.05	0.04	0.04
MgO	1.5	1.25	1.42	1.64	2.66	3.05	3.75	1.5	0.32	0.48	0.47
CaO	3.3	3.36	3.33	3.32	4.64	5.61	6.47	4.42	1.06	0.9	1.23
Na2O	2.53	2.37	2.61	2.61	2.37	2.34	2.48	3.27	2.42	2.6	2.37
K2O	3.7	3.61	3.56	3.67	2.09	2.13	1.76	1.9	6.6	4.83	4.87
P2O5	0.16	0.11	0.14	0.15	0.15	0.17	0.21	0.22	0.33	0.28	0.36
LOI	1.04	1.09	0.76	0.71	0.57	0.85	0.99	0.82	1.24	0.74	1.18
Total	100.91	101	100.64	100.59	100.33	100.59	100.63	100.7	101.21	100.7	101.13
Qz	24.95	30.84	27.25	24.68	21.45	15.44	8.80	25.13	30.68	37.80	37.59
An	15.35	15.97	15.63	15.51	22.10	26.80	30.84	20.52	3.11	2.64	3.75
Ab	21.44	20.07	22.11	22.11	20.10	19.85	21.06	27.70	20.48	22.01	20.06
C	2.19	0.22	1.48	1.38	1.02	0.28	0.16	1.97	2.07	3.46	4.58
Hy	8.91	7.35	7.95	9.23	15.97	17.60	20.66	8.61	1.88	2.70	2.58
Mt	4.09	3.32	3.51	4.15	5.34	5.59	5.89	3.37	1.62	1.74	1.48
Ap	0.37	0.25	0.32	0.35	0.35	0.39	0.49	0.51	0.76	0.65	0.83
DI	68.28	72.26	70.42	68.51	53.94	47.91	40.30	64.07	90.18	88.36	86.45
SI	10.06	9.57	10.34	10.81	14.78	16.00	18.21	11.48	2.74	4.51	4.67
Mg#	0.49	0.49	0.51	0.51	0.48	0.50	0.52	0.50	0.49	0.51	0.52
A/NK	1.96	1.78	1.88	1.85	2.48	2.64	2.91	2.27	1.29	1.47	1.65
A/CNK	1.16	1.02	1.11	1.10	1.07	1.02	1.01	1.13	1.17	1.33	1.43
AI	0.39	0.43	0.40	0.41	0.29	0.28	0.24	0.31	0.63	0.53	0.48
K2O + Na2O	6.23	5.98	6.17	6.28	4.46	4.47	4.24	5.17	9.02	7.43	7.24
K2O/Na2O	1.46	1.52	1.36	1.41	0.88	0.91	0.71	0.58	2.73	1.86	2.05
CaO/Na2O	1.30	1.42	1.28	1.27	1.96	2.40	2.61	1.35	0.44	0.35	0.52
TFeO/MgO	3.57	3.49	3.23	3.30	3.07	2.84	2.53	3.19	5.41	4.23	3.73
σ	1.76	1.37	1.59	1.76	1.11	1.34	1.63	1.23	2.77	1.78	1.75
R1	2487	2852	2628	2487	2623	2410	2183	2635	2382	2836	2850
R2	742	694	729	738	930	1073	1224	880	411	394	452

Note: 1–7, Damourite Adamellite; 8–12, Two-mica Adamellite; 13–15, Biotite Granodiorite; 16, Biotite adamellite; 17–18, Biotite Quartz Diorite; 19–20, Tonalite; 21–23, Two-Mica Granite; Qz, quartz; An, anorthite; Ab, albite; Or, orthoclase; C, corundum; Hy, hypersthene; Ilm, ilmenite; Mt, magnetite; Ap, apatite; Zr, zircon; Chr, chromite. (1) Mg^# = 100 × Mg²⁺/(Mg²⁺ + Fe²⁺), in which Mg²⁺ and Fe²⁺ are molar fractions; (2) A/NK = Al₂O₃/(Na₂O + K₂O) (mol); (3) A/CNK = Al₂O₃/(CaO + Na₂O + K₂O) (mol); (4) AI = (Na₂O + K₂O)/Al₂O₃ (mol); (5)σ = (Na₂O + K₂O)²/(SiO₂ − 43) (wt.%); (6) DI = Qz + Or + Ab + Ne + Le + Kp.

) indicate that the Dahongliutan pluton is silica-rich (SiO₂ =53.91–73.95 wt.%; average = 68.33 wt.%). The Al₂O₃ content is 12.81–17.41 wt.% (average = 15.08 wt.%), and the aluminum saturation index (A/CNK) ranges from 1.01 to 1.43, indicating peraluminous rocks (Figure 3a). The Na₂O content is 2.06–3.39 wt.% (average = 2.72). The K₂O content is 1.76–6.60 wt.% (average = 3.98 wt.%) and the K₂O/Na₂O ratio is 0.53–2.73 (average = 1.49). The total alkali content (K₂O + Na₂O) ranges from 4.24 wt.% to 9.02 wt.% (average = 6.7). The alkali aluminum index (AI) is 0.24–0.63 (average = 0.45) and the Rittman Portfolio Index (σ) ranges from 0.96 to 3.18, with all values < 3.3 (average = 1.82), thereby exhibiting typical calc-alkaline characteristics. On an SiO₂-K₂O diagram (Figure 3b), the samples fall in the high-potassium calc-alkaline series region. The CaO and TiO₂ contents are low (0.82–6.47 wt.% and 0.13–0.87 wt.%, respectively). The MgO content is 0.21–3.75 wt.% (average = 1.22 wt.%). The total iron (TFeO) content is 1.28–9.49 wt.% (average = 4.07 wt.%), and the TfeO/MgO ratio ranges from 2.53 to 8.19 (average = 4.12), indicating the pluton is Fe-rich and Mg-poor. According to the calculated CIPW norms, corundum (0.16–4.58 wt.%) is present, indicating peraluminous characteristics. The differentiation index (DI) ranges from 40.3 to 90.51 (average = 75.69), indicating a high degree of magmatic differentiation. The consolidation index (SI) ranges from 1.97 to18.21 (average = 7.96), indicating that the magma underwent a high degree of fractional crystallization and was highly acidic. On a total alkali vs. silica (TAS) diagram (Figure 4), 17 samples plot in the granite region. In summary, the Dahongliutan pluton is therefore characterized by high silica, alkali, and potassium contents, but low MgO, TiO₂, MnO, and P₂O₅ contents. These characteristics indicate that the pluton underwent strong fractional crystallization and is a peraluminous granite of the potassium-rich calc-alkaline series.

4.3. Trace Element Contents

Table 2. Trace (×10⁻⁶) and rare earth element (×10⁻⁶) contents of Dahongliutan granite samples.

Sample	P19-01XT01	P20-25XT01	P6-06XT01	P22-55 GS	P22-71 GS	P20-15 GS	D3801GS01	P22-39XT01	P26-88 GS	P20-19 GS	P20-03 GS	P11-15GS01
Component	1	2	3	4	5	6	7	8	9	10	11	12
Rb	194	76.3	179	267	98.99	218	229	331	142	263	173	196
Ta	1.66	1.34	1.2	4.62	1.89	1.89	1	2.07	2.83	3.28	3.23	1.05
Th	9.07	11.32	12.74	17.48	14.63	8.68	9.84	12.9	11.86	11.83	28.84	6.62
Nb	13.96	15.67	12.74	14.89	14.89	14.52	11.2	15.47	12.8	13.59	22.71	12.9
Sr	101	166	69.19	60.98	250	104	118	79.02	152	87.99	143	78.21
Zr	72.3	140	133	106	354	98.42	85.32	110	73.15	86.74	180	65.51
Hf	2.19	7.16	2.62	3.18	9.51	2.47	2.13	2.23	3.3	2.43	6.6	1.93
V	10	118	7.04	16.49	79.22	9.03	8.21	13.02	10.48	9.3	147	4.86
Cr	2.59	27.27	11.54	8.45	63.05	4.44	9.84	15.07	7.5	6.4	86.43	3.66
La	17.8	28.4	20.3	21.5	46.1	17	21.6	25.4	16	27.6	54.8	15.1
Ce	34.5	55.1	42.9	43.4	78.9	32	48.1	54.2	27	54	142	34
Pr	4.11	6.6	5.1	5.57	10.1	3.83	5.16	6.4	3.39	6.47	12.6	3.68
Nd	14.6	24.9	19.1	21	37.2	13.9	18.5	23.7	12.4	23.6	46.8	13.2
Sm	3.46	5.1	4.7	4.76	6.45	3.17	4.1	5.4	2.3	5.16	8.53	3.08
Eu	0.66	1.2	0.57	0.53	1.33	0.7	0.76	0.62	0.73	0.82	1.79	0.39
Gd	3.01	4.5	3.7	3.79	5.66	2.68	3.1	4.2	1.82	4.18	7.97	2.37
Tb	0.46	0.74	0.56	0.56	0.88	0.4	0.41	0.57	0.22	0.56	1.28	0.36
Dy	1.99	3.8	2.3	2.16	4.6	1.61	1.53	2.2	0.87	2.07	6.92	1.57
Ho	0.28	0.75	0.34	0.31	0.91	0.22	0.19	0.3	0.13	0.28	1.39	0.21
Er	0.66	2	0.72	0.72	2.49	0.51	0.44	0.7	0.33	0.66	3.95	0.46
Tm	0.09	0.32	0.1	0.09	0.37	0.07	0.06	0.08	0.04	0.08	0.63	0.06
Yb	0.51	2.2	0.59	0.53	2.23	0.38	0.32	0.55	0.23	0.46	3.83	0.36
Lu	0.07	0.32	0.07	0.07	0.34	0.06	0.05	0.07	0.04	0.07	0.6	0.05
Y	8.20	19.60	12.00	8.60	23.50	6.60	5.40	8.40	3.90	8.00	34.40	6.00
TZr (℃)	738	770	786	765	872	757	747	768	740	748	780	724
Sr/Y	12.32	8.47	5.77	7.09	10.64	15.76	21.85	9.41	38.97	11.00	4.16	13.04
Rb/Sr	1.92	0.46	2.59	4.38	0.40	2.10	1.94	4.19	0.93	2.99	1.21	2.51
Nd/Th	1.61	2.20	1.50	1.20	2.54	1.60	1.88	1.84	1.05	1.99	1.62	1.99
Nb/Ta	8.41	11.69	10.62	3.22	7.88	7.68	11.20	7.47	4.52	4.14	7.03	12.29
Zr/Hf	33.01	19.55	50.76	33.33	37.22	39.85	40.06	49.33	22.17	35.70	27.27	33.94
La/Nb	1.28	1.81	1.59	1.44	3.10	1.17	1.93	1.64	1.25	2.03	2.41	1.17
∑REE	82.20	135.93	101.05	104.99	197.56	76.53	104.32	124.39	65.50	126.01	293.09	74.89
LREE	75.13	121.30	92.67	96.76	180.08	70.60	98.22	115.72	61.82	117.65	266.52	69.45
HREE	7.07	14.63	8.38	8.23	17.48	5.93	6.10	8.67	3.68	8.36	26.57	5.44
LREE/HREE	10.63	8.29	11.06	11.76	10.30	11.91	16.10	13.35	16.80	14.07	10.03	12.77
LaN/YbN	25.04	9.26	24.68	29.10	14.83	32.09	48.42	33.13	49.90	43.04	10.26	30.09
δEu	0.63	0.77	0.42	0.38	0.67	0.73	0.65	0.40	1.09	0.54	0.66	0.44
δCe	0.99	0.99	1.03	0.97	0.90	0.97	1.12	1.04	0.90	0.99	1.32	1.12
Sample	P25-08XT01	P25-1-05 GS	D259 GS	P25-12 GS	P21-20 GS	P23-01GS01	P21-32XT01	P21-08 GS	P7-65XT03	P9-32 GS	P10-01 GS
Component	13	14	15	16	17	18	19	20	21	22	23
Rb	123	132	136	160	119	95.6	53.8	105	164	264	138
Ta	1.81	2.81	2.32	2.99	1.6	1.4	1.12	1.97	0.99	5.47	1.21
Th	23.66	27.7	20.74	18.31	8.74	12.64	7.65	7.27	11.26	19.39	13.48
Nb	13.75	10.62	11.5	13.96	15.27	15.85	15.27	16.38	14.26	15.82	9.5
Sr	161	188	219	216	264	294	262	316	95.72	76.55	118
Zr	133	110	137	144	156	156	163	258	79.43	104	113
Hf	5.31	5.36	6.06	6.45	8.74	5.4	4.38	7.29	1.77	3.11	3.42
V	83.38	58.11	67.25	85.96	120	120	169	53.36	5.81	12.63	14.62
Cr	7.82	15.15	11.54	18.55	30.86	55.25	37.19	18.66	0.076	4.54	7.53
La	30.5	25.3	38	30.2	23.9	45.3	34.1	31.2	23.4	33.3	23.7
Ce	57.9	45.4	67.8	55.5	44	89.6	64.7	38.8	48.4	65.5	44.7
Pr	6.9	6.12	8.52	6.76	5.83	9.82	7.4	6.02	6	8.2	5.4
Nd	25.8	23.3	31.4	25.4	23.4	36.6	28.4	22.8	22.8	30.4	19.5
Sm	5.4	4.94	6.18	5.4	4.88	6.48	5.1	4.01	5.9	6.48	4.4
Eu	1.2	0.9	1.13	1.14	1.44	1.53	1.8	1.46	0.77	0.63	0.89
Gd	4.6	4.41	5.3	4.94	4.49	5.62	4.5	3.6	5.1	5.05	3.99
Tb	0.81	0.76	0.83	0.86	0.77	0.91	0.71	0.54	0.87	0.65	0.72
Dy	4.3	4.13	4.46	4.9	4.4	5.08	3.7	2.73	3.7	2.48	3.76
Ho	0.86	0.81	0.85	0.94	0.88	0.96	0.75	0.52	0.54	0.33	0.63
Er	2.3	2.33	2.35	2.71	2.43	2.59	2.1	1.38	1.3	0.75	1.48
Tm	0.39	0.38	0.37	0.44	0.39	0.41	0.34	0.2	0.2	0.1	0.2
Yb	2.5	2.42	2.3	2.75	2.43	2.69	2.2	1.18	1.2	0.51	1.01
Lu	0.38	0.38	0.36	0.44	0.39	0.45	0.33	0.18	0.17	0.07	0.14
Y	24.5	26.7	23.1	26.4	23.5	23.8	18.9	13.9	15.7	9.5	17.4
TZr (℃)	767	746	768	769	766	753	746	821	733	768	778
Sr/Y	6.57	7.04	9.48	8.18	11.23	12.35	13.86	22.73	6.10	8.06	6.78
Rb/Sr	0.76	0.70	0.62	0.74	0.45	0.33	0.21	0.33	1.71	3.45	1.17
Nd/Th	1.09	0.84	1.51	1.39	2.68	2.90	3.71	3.14	2.02	1.57	1.45
Nb/Ta	7.60	3.78	4.96	4.67	9.54	11.32	13.63	8.31	14.40	2.89	7.85
Zr/Hf	25.05	20.52	22.61	22.33	17.85	28.89	37.21	35.39	44.88	33.44	33.04
La/Nb	2.22	2.38	3.30	2.16	1.57	2.86	2.23	1.90	1.64	2.10	2.49
∑REE	143.84	121.58	169.85	142.38	119.63	208.04	156.13	114.62	120.35	154.45	110.52
LREE	127.70	105.96	153.03	124.40	103.45	189.33	141.50	104.29	107.27	144.51	98.59
HREE	16.14	15.62	16.82	17.98	16.18	18.71	14.63	10.33	13.08	9.94	11.93
LREE/HREE	7.91	6.78	9.10	6.92	6.39	10.12	9.67	10.10	8.20	14.54	8.26
LaN/YbN	8.75	7.50	11.85	7.88	7.05	12.08	11.12	18.97	13.99	46.84	16.83
δEu	0.74	0.59	0.60	0.67	0.94	0.78	1.15	1.17	0.43	0.34	0.65
δCe	0.98	0.89	0.92	0.95	0.91	1.04	1.00	0.69	1.00	0.97	0.97

Note: 1–7, Damourite Adamellite; 8–12, Two-mica Adamellite; 13–15, Biotite Granodiorite; 16, Biotite adamellite; 17–18, Biotite Quartz Diorite; 19–20, Tonalite; 21–23, Two-Mica Granite. The calculation method for zircon saturation temperature (TZr) was based on [17,18]. Zircon LA-ICP-MS U-Pb dating (Table 3) was performed on six samples: P22-39TW01, P20-25TW01, P25-08TW01, P25-12, P21-32TW01, and P7-65TW01.

lists the trace element compositions of the samples. Among the large ion lithophile elements (LILEs), Rb is enriched and Sr is depleted (Figure 5a). Among the high field strength elements (HFSEs) Th is enriched, while Ta and Nb are depleted. The observed Sr depletion may be related to the fractional crystallization of plagioclase. HFSE depletion indicates that the magma source was predominantly crustal material.

4.4. REE Contents

The total REE contents (Table 2) range from 65.5 × 10⁻⁶ to 293.09 × 10⁻⁶ and the pluton is enriched in light REEs (LREEs) and depleted in heavy REEs (HREEs), indicating pronounced fractionation between the two groups. There is no pronounced Ce anomaly. The δEu is >1 for three samples (P26-88 GS, P21-32XT01, and P21-08 GS), and from 0.34 to 0.94 for the other 20 samples, with relatively pronounced negative Eu anomalies. This indicates that the fractional crystallization of plagioclase occurred during magmatic differentiation. The chondrite standardized REE distribution patterns are all right-inclined (Figure 5b). Eu is depleted, and the distribution curves all exhibit pronounced Eu depletion, indicating that all samples shared the same source material and formation mechanism.

4.5. Zircon U–Pb Ages

Table 3. Zircon LA–ICP–MS U– Pb isotope analysis results of the Dahongliutan pluton.

Spot No.	Concentration (×10−6)			Th/U	Isotopic Ratio						Age (Ma)						Concordant
	Pb	Th	U		207Pb/206Pb	1σ	207Pb/235U	1σ	206Pb/238U	1σ	207Pb/206Pb	1σ	207Pb/235U	1σ	206Pb/238U	1σ
P22-39TW01 Muscovite monzogranite
−1	302.12	852.83	1976.09	0.4316	0.0698	0.0013	1.4002	0.0258	0.1446	0.0013	924.07	39.66	889.02	10.90	870.68	7.32	97%
−2	23.03	14.53	621.58	0.0234	0.0697	0.0047	0.3490	0.0226	0.0365	0.0009	920.37	138.89	304.01	17.05	231.16	5.54	72%
−3	140.30	68.74	1522.85	0.0451	0.0903	0.0018	1.1781	0.0280	0.0942	0.0016	1431.79	39.97	790.43	13.04	580.41	9.30	69%
−4	180.20	132.04	576.03	0.2292	0.1590	0.0026	6.3589	0.1086	0.2885	0.0029	2455.55	27.47	2026.62	14.98	1634.21	14.45	78%
−5	50.44	57.90	1580.11	0.0366	0.0501	0.0014	0.2314	0.0066	0.0335	0.0003	211.19	66.66	211.33	5.44	212.27	1.93	99%
−6	127.94	132.19	1494.01	0.0885	0.1225	0.0024	1.5223	0.0467	0.0878	0.0019	1992.28	30.55	939.42	18.79	542.81	11.05	46%
−7	84.97	92.33	2564.62	0.0360	0.0529	0.0055	0.2451	0.0268	0.0332	0.0007	324.13	232.38	222.58	21.84	210.28	4.54	94%
−8	137.01	31.23	4078.24	0.0077	0.0513	0.0016	0.2435	0.0074	0.0343	0.0004	253.77	70.36	221.31	6.07	217.42	2.41	98%
−9	41.04	258.88	1208.14	0.2143	0.0499	0.0023	0.2274	0.0102	0.0332	0.0004	190.82	109.24	208.09	8.40	210.83	2.61	98%
−10	38.51	138.15	837.89	0.1649	0.0561	0.0019	0.3353	0.0113	0.0434	0.0005	457.45	69.44	293.61	8.61	274.10	2.84	93%
−11	25.15	83.18	736.78	0.1129	0.0513	0.0032	0.2376	0.0152	0.0338	0.0008	253.77	142.57	216.48	12.45	214.57	4.82	99%
−12	135.18	73.41	4142.90	0.0177	0.0513	0.0016	0.2382	0.0076	0.0335	0.0004	253.77	65.73	216.93	6.21	212.39	2.57	97%
−13	79.88	27.76	2443.36	0.0114	0.0486	0.0013	0.2315	0.0065	0.0343	0.0003	127.87	61.11	211.40	5.33	217.48	2.13	97%
−14	96.17	21.68	2981.31	0.0073	0.0493	0.0014	0.2306	0.0067	0.0339	0.0004	164.90	66.66	210.66	5.49	215.06	2.51	97%
−15	60.47	21.46	1866.72	0.0115	0.0495	0.0035	0.2306	0.0154	0.0337	0.0005	172.31	155.53	210.72	12.73	213.36	3.28	98%
−16	118.40	25.53	3671.23	0.0070	0.0503	0.0012	0.2351	0.0054	0.0339	0.0003	205.63	51.84	214.43	4.41	214.86	1.72	99%
−17	87.58	21.67	2738.73	0.0079	0.0490	0.0012	0.2282	0.0056	0.0338	0.0003	150.09	54.62	208.74	4.66	214.10	1.72	97%
−18	139.54	31.90	4376.51	0.0073	0.0512	0.0013	0.2385	0.0064	0.0337	0.0004	255.62	59.25	217.17	5.21	213.41	2.21	98%
−19	82.24	34.41	2584.66	0.0133	0.0485	0.0014	0.2262	0.0065	0.0339	0.0003	124.16	70.36	207.07	5.41	214.65	2.10	96%
−20	96.28	26.93	3096.95	0.0087	0.0531	0.0014	0.2436	0.0065	0.0333	0.0004	344.50	59.25	221.38	5.31	210.90	2.42	95%
P20-25TW01 Mica monzogranite
−1	45.30	52.33	1317.43	0.0397	0.0501	0.0015	0.2338	0.0069	0.0338	0.0003	198.23	66.66	213.32	5.72	214.16	1.95	99%
−2	15.76	269.95	388.84	0.6942	0.0528	0.0024	0.2425	0.0109	0.0341	0.0004	316.73	105.55	220.50	8.90	215.96	2.78	97%
−3	46.52	488.85	1294.04	0.3778	0.0510	0.0019	0.2416	0.0095	0.0345	0.0005	238.96	87.02	219.75	7.79	218.64	3.23	99%
−4	45.13	784.04	1156.44	0.6780	0.0523	0.0018	0.2460	0.0086	0.0341	0.0004	298.21	79.62	223.35	7.05	216.09	2.23	96%
−5	72.95	9.06	2155.72	0.0042	0.0515	0.0020	0.2426	0.0095	0.0341	0.0004	261.18	88.88	220.58	7.79	216.07	2.35	97%
−6	74.21	472.44	2100.50	0.2249	0.0512	0.0014	0.2429	0.0066	0.0342	0.0003	250.07	61.10	220.76	5.37	216.76	2.05	98%
−7	17.97	372.01	455.73	0.8163	0.0610	0.0058	0.2743	0.0239	0.0332	0.0009	638.91	203.68	246.14	19.06	210.49	5.53	84%
−8	98.08	940.34	2656.71	0.3540	0.0521	0.0014	0.2474	0.0067	0.0343	0.0004	287.10	59.25	224.42	5.42	217.67	2.58	96%
−9	68.00	795.69	1836.14	0.4334	0.0495	0.0016	0.2368	0.0075	0.0346	0.0004	172.31	78.69	215.81	6.19	219.41	2.39	98%
−10	111.50	754.07	3143.51	0.2399	0.0515	0.0018	0.2432	0.0079	0.0343	0.0005	264.88	78.69	221.05	6.46	217.44	3.28	98%
P25-08TW01 Biotite granodiorite
−1	67.66	524.81	1851.05	0.2835	0.0514	0.0014	0.2360	0.0063	0.0332	0.0003	261.18	62.95	215.13	5.21	210.69	1.84	97%
−2	66.19	475.55	1834.40	0.2592	0.0517	0.0013	0.2377	0.0060	0.0333	0.0003	333.39	59.25	216.52	4.91	211.35	1.85	97%
−3	80.01	531.24	2201.39	0.2413	0.0497	0.0012	0.2326	0.0056	0.0338	0.0003	188.97	55.55	212.37	4.63	214.09	1.68	99%
−4	69.20	587.07	1879.92	0.3123	0.0507	0.0013	0.2380	0.0062	0.0339	0.0003	233.40	59.25	216.74	5.11	215.20	1.87	99%
−5	69.56	618.05	1897.15	0.3258	0.0492	0.0013	0.2301	0.0061	0.0339	0.0003	166.75	62.95	210.29	5.00	214.61	1.82	97%
−6	71.80	612.23	1991.11	0.3075	0.0526	0.0017	0.2417	0.0076	0.0332	0.0003	309.32	76.85	219.85	6.18	210.72	2.02	95%
−7	91.41	625.58	2570.97	0.2433	0.0500	0.0014	0.2345	0.0063	0.0339	0.0003	194.53	62.95	213.91	5.16	214.83	1.96	99%
−8	65.00	464.68	1831.99	0.2536	0.0497	0.0014	0.2310	0.0065	0.0336	0.0003	188.97	66.66	211.01	5.34	213.27	1.63	98%
−9	41.02	291.35	1174.06	0.2482	0.0499	0.0018	0.2281	0.0078	0.0335	0.0004	190.82	85.17	208.64	6.43	212.52	2.50	98%
−10	45.50	314.71	1299.59	0.2422	0.0503	0.0015	0.2348	0.0071	0.0338	0.0003	209.33	39.81	214.17	5.87	214.13	2.05	99%
−11	25.77	188.60	748.27	0.2520	0.0526	0.0036	0.2376	0.0154	0.0337	0.0006	322.28	157.39	216.48	12.64	213.93	3.45	98%
−12	102.61	896.42	2892.67	0.3099	0.0482	0.0014	0.2259	0.0065	0.0339	0.0003	109.35	68.51	206.83	5.39	214.82	1.93	96%
−13	56.53	462.55	1630.22	0.2837	0.0516	0.0016	0.2395	0.0073	0.0336	0.0003	333.39	73.14	218.04	5.97	213.27	1.94	97%
−14	56.95	479.68	1662.06	0.2886	0.0521	0.0017	0.2395	0.0079	0.0333	0.0003	300.06	75.92	217.98	6.44	211.02	1.99	96%
−15	44.84	421.17	1280.93	0.3288	0.0520	0.0018	0.2399	0.0078	0.0336	0.0003	287.10	77.77	218.35	6.39	212.86	2.08	97%
−16	62.86	492.51	1852.86	0.2658	0.0498	0.0014	0.2286	0.0065	0.0332	0.0003	187.12	66.66	209.06	5.36	210.84	1.84	99%
−17	82.07	649.69	2436.01	0.2667	0.0510	0.0015	0.2316	0.0067	0.0330	0.0003	238.96	68.51	211.50	5.51	209.19	1.85	98%
−18	50.79	452.43	1455.21	0.3109	0.0509	0.0020	0.2372	0.0090	0.0339	0.0004	235.25	90.73	216.09	7.35	214.65	2.41	99%
−19	64.26	542.27	1910.07	0.2839	0.0506	0.0016	0.2313	0.0071	0.0332	0.0003	233.40	72.21	211.23	5.82	210.30	2.14	99%
−20	80.62	819.07	1581.40	0.5179	0.0546	0.0019	0.3415	0.0125	0.0453	0.0007	398.20	76.85	298.34	9.48	285.36	4.16	95%
P25-12TW Biotite monzogranite
−1	13.42	175.20	288.28	0.6078	0.0535	0.0019	0.2920	0.0100	0.0396	0.0004	350.06	47.22	260.12	7.90	250.22	2.45	96%
−2	10.04	129.48	255.23	0.5073	0.0509	0.0021	0.2372	0.0104	0.0340	0.0004	235.25	63.88	216.15	8.54	215.26	2.77	99%
−3	59.45	408.14	1627.03	0.2508	0.0506	0.0009	0.2390	0.0043	0.0343	0.0003	233.40	37.96	217.62	3.55	217.36	2.05	99%
−4	31.76	388.16	819.08	0.4739	0.0503	0.0013	0.2342	0.0056	0.0341	0.0004	209.33	93.51	213.69	4.63	216.28	2.73	98%
−5	25.93	223.03	686.87	0.3247	0.0498	0.0012	0.2365	0.0056	0.0345	0.0003	187.12	55.55	215.53	4.63	218.41	2.08	98%
−6	13.97	139.68	372.02	0.3755	0.0488	0.0018	0.2269	0.0083	0.0340	0.0004	200.08	88.88	207.65	6.85	215.36	2.41	96%
−7	65.25	418.79	1813.81	0.2309	0.0494	0.0008	0.2318	0.0043	0.0339	0.0003	168.60	37.03	211.72	3.56	215.03	1.83	98%
−8	61.06	400.61	1695.06	0.2363	0.0507	0.0009	0.2354	0.0044	0.0337	0.0003	227.85	74.99	214.62	3.64	213.46	1.89	99%
−9	51.08	327.85	1409.27	0.2326	0.0507	0.0009	0.2377	0.0042	0.0340	0.0003	233.40	38.88	216.52	3.44	215.71	2.05	99%
−10	56.86	392.45	1578.61	0.2486	0.0487	0.0006	0.2278	0.0035	0.0339	0.0003	200.08	31.48	208.38	2.86	214.77	1.86	96%
−11	48.33	280.82	1311.08	0.2142	0.0497	0.0009	0.2342	0.0036	0.0346	0.0004	188.97	16.66	213.64	2.99	219.49	2.28	97%
−12	39.57	233.66	1107.89	0.2109	0.0492	0.0009	0.2282	0.0046	0.0337	0.0003	166.75	44.44	208.75	3.78	213.56	2.07	97%
−13	8.74	114.47	226.01	0.5065	0.0499	0.0022	0.2290	0.0102	0.0332	0.0004	190.82	108.32	209.40	8.43	210.36	2.50	99%
−14	27.27	256.85	724.63	0.3545	0.0518	0.0014	0.2381	0.0069	0.0333	0.0004	275.99	65.73	216.85	5.69	211.37	2.50	97%
−15	47.44	350.45	1284.03	0.2729	0.0501	0.0014	0.2361	0.0074	0.0341	0.0006	211.19	32.40	215.26	6.09	216.29	3.48	99%
−16	51.65	292.57	1450.63	0.2017	0.0507	0.0009	0.2320	0.0042	0.0332	0.0003	227.85	73.14	211.82	3.47	210.71	2.13	99%
−17	18.58	155.09	496.61	0.3123	0.0516	0.0022	0.2385	0.0106	0.0338	0.0005	333.39	99.99	217.19	8.66	214.33	3.16	98%
−18	57.96	310.12	1584.64	0.1957	0.0521	0.0013	0.2417	0.0058	0.0339	0.0004	300.06	55.55	219.78	4.78	214.72	2.76	97%
−19	57.57	379.31	1576.35	0.2406	0.0517	0.0012	0.2372	0.0052	0.0336	0.0004	272.29	53.70	216.10	4.24	213.07	2.73	98%
−20	38.59	205.86	1066.73	0.1930	0.0508	0.0012	0.2363	0.0060	0.0337	0.0004	231.55	53.69	215.38	4.92	213.66	2.57	99%
P21-32TW01 Tonalite
−1	17.94	228.03	509.74	0.4473	0.0555	0.0042	0.2506	0.0182	0.0328	0.0008	431.53	166.65	227.04	14.80	208.11	4.76	91%
−2	24.05	294.05	665.85	0.4416	0.0524	0.0025	0.2395	0.0109	0.0336	0.0005	305.62	109.25	218.03	8.92	213.04	3.13	97%
−3	19.88	402.45	531.17	0.7577	0.0560	0.0050	0.2425	0.0208	0.0324	0.0009	453.75	199.98	220.49	17.03	205.29	5.31	92%
−4	20.78	473.04	547.15	0.8646	0.0551	0.0030	0.2426	0.0118	0.0326	0.0005	416.72	156.46	220.56	9.63	206.67	2.98	93%
−5	18.08	316.03	487.07	0.6488	0.0513	0.0041	0.2380	0.0208	0.0330	0.0008	253.77	185.16	216.74	17.04	209.08	4.78	96%
−6	7.87	112.97	214.98	0.5255	0.0880	0.0050	0.3865	0.0196	0.0326	0.0006	1383.34	108.80	331.78	14.34	206.73	3.77	53%
−7	5.35	80.67	148.36	0.5437	0.1234	0.0079	0.4840	0.0242	0.0329	0.0007	2005.87	114.97	400.79	16.58	208.36	4.39	36%
−8	12.48	203.27	318.20	0.6388	0.0552	0.0072	0.2484	0.0285	0.0334	0.0014	420.42	295.18	225.31	23.16	211.75	8.70	93%
−9	14.72	204.39	399.41	0.5117	0.0558	0.0033	0.2467	0.0141	0.0330	0.0006	455.60	133.32	223.87	11.46	209.06	3.48	93%
−10	23.06	317.26	620.04	0.5117	0.0538	0.0029	0.2452	0.0137	0.0333	0.0006	364.87	122.21	222.64	11.14	211.29	3.95	94%
P7-65TW01 Mica granite
−1	164.18	692.74	5157.81	0.1343	0.0498	0.0014	0.2227	0.0056	0.0326	0.0004	187.12	64.80	204.18	4.68	206.83	2.62	98%
−2	158.23	492.13	5001.14	0.0984	0.0501	0.0011	0.2269	0.0052	0.0327	0.0003	211.19	49.99	207.67	4.28	207.53	1.95	99%
−3	73.61	176.23	2391.58	0.0737	0.0500	0.0022	0.2195	0.0091	0.0323	0.0005	194.53	99.99	201.48	7.54	204.70	3.14	98%
−4	146.11	362.61	4667.11	0.0777	0.0503	0.0010	0.2259	0.0045	0.0327	0.0003	205.63	43.51	206.84	3.70	207.54	1.78	99%
−5	160.03	477.05	5115.07	0.0933	0.0500	0.0011	0.2247	0.0046	0.0325	0.0003	194.53	48.14	205.81	3.85	206.42	1.68	99%
−6	80.97	254.96	2570.38	0.0992	0.0496	0.0016	0.2231	0.0072	0.0327	0.0003	176.01	78.69	204.49	5.95	207.34	2.13	98%
−7	57.84	177.80	1843.11	0.0965	0.0480	0.0017	0.2163	0.0075	0.0327	0.0003	98.24	87.96	198.80	6.25	207.39	1.96	95%
−8	143.57	542.75	4583.03	0.1184	0.0480	0.0008	0.2153	0.0038	0.0323	0.0002	98.24	40.74	197.96	3.22	205.17	1.32	96%
−9	128.81	358.66	4094.73	0.0876	0.0479	0.0012	0.2170	0.0052	0.0327	0.0003	100.09	57.40	199.37	4.33	207.62	1.81	95%
−10	140.97	20.06	4652.68	0.0043	0.0489	0.0009	0.2184	0.0042	0.0322	0.0002	142.68	46.29	200.58	3.47	204.54	1.35	98%
−11	106.11	357.47	3393.57	0.1053	0.0478	0.0011	0.2135	0.0045	0.0323	0.0002	100.09	51.85	196.46	3.81	205.06	1.53	95%
−12	71.65	155.28	2273.56	0.0683	0.0485	0.0017	0.2186	0.0076	0.0327	0.0003	124.16	87.95	200.77	6.37	207.27	1.85	96%
−13	151.02	691.05	4729.54	0.1461	0.0500	0.0010	0.2244	0.0045	0.0324	0.0002	194.53	48.14	205.58	3.76	205.52	1.24	99%
−14	138.84	478.89	4420.51	0.1083	0.0505	0.0010	0.2260	0.0043	0.0324	0.0002	216.74	44.44	206.91	3.57	205.68	1.51	99%
−15	52.30	152.66	1673.73	0.0912	0.0510	0.0017	0.2277	0.0075	0.0325	0.0003	238.96	74.99	208.28	6.16	206.18	1.82	98%
−16	171.93	392.78	5537.23	0.0709	0.0500	0.0012	0.2244	0.0058	0.0323	0.0004	194.53	27.77	205.57	4.85	204.93	2.41	99%
−18	69.02	55.40	2280.80	0.0243	0.0494	0.0015	0.2187	0.0065	0.0324	0.0004	164.90	67.58	200.82	5.39	205.72	2.25	97%
−19	106.39	366.79	3372.65	0.1088	0.0495	0.0012	0.2228	0.0054	0.0325	0.0003	172.31	52.77	204.24	4.49	206.18	1.84	99%
−20	97.36	302.10	3096.41	0.0976	0.0520	0.0013	0.2317	0.0056	0.0323	0.0003	287.10	57.40	211.58	4.59	205.08	1.69	96%

lists the zircon U–Pb isotopic results. Among the light gray-white, fresh, unaltered granites and diorites (P22-39TW01, P20-25TW01, P25-08TW01, P25-12TW, P21-32TW01, and P7-65TW01), zircons are predominantly elongate (100–300 μm in length with aspect ratios concentrated between 2:1 and 3:1) and transparent to light yellow in color. The crystal surfaces are bright and clear, with straight edges and pronounced rhythmic bands, consistent with the characteristics of magmatic zircons.

The muscovite monzogranite (P22-39TW01) has ²³²Th/²³⁸U ratios of 0.0070–0.4316 (average = 0.0741; <0.1), with an abnormal Th/U ratio, indicating that these magmatic zircons crystallized in a magma with a special composition [19,20,21]. The weighted average age obtained from 14 points is 214.0 ± 1.2 Ma (MSWD = 0.79, n = 14; Figure 6a).

The mica monzogranite (P20-25TW01) has ²³²Th/²³⁸U ratios of 0.0042–1.0226 (average = 0.4486; >0.4). A strong positive correlation is present between Th and U, indicating that they are typical magmatic zircons [19,20,21]. The weighted average age obtained from nine points is 216.6 ± 1.6 Ma (MSWD = 0.47, n = 9; Figure 6b).

The biotite granodiorite (P25-08TW01) has ²³²Th/²³⁸U ratios of 0.2413–0.5179 (average = 0.2913), indicating that the Th/U ratios are related to the Th and U contents of the magma and the distribution coefficient between the zircon and magma [19,20,21]. CL images show clearly developed oscillating bands (Figure 7a), which are characteristic of magmatic zircons. The weighted average age obtained from 19 points is 212.71 ± 0.89 Ma (MSWD = 0.93, n = 19; Figure 6c).

The biotite monzogranite (P25-12TW) has ²³²Th/²³⁸U ratios of 0.1930–0.6078 (average = 0.3095), indicating that the Th/U ratios are related to the Th and U contents of the magma and the distribution coefficient between the zircon and magma [19,20,21]. CL images show oscillating bands (Figure 7b) typical of magmatic zircons. The weighted average age obtained from 19 points is 214.7 ± 1.0 Ma (MSWD = 1.10, n = 19; Figure 6d).

The tonalite (P21-32TW01) has ²³²Th/²³⁸U ratios of 0.4416–0.8648 (average = 0.5938; >0.4), with a strong positive correlation between Th and U, indicating that they reflect magmatic crystallization [19,20,21]. The weighted average age obtained from eight points is 209.3 ± 2.8 Ma (MSWD = 0.45, n = 8; Figure 6e).

The mica granite (P7-65TW01) has ²³²Th/²³⁸U ratios of 0.0043–0.1461 (average = 0.0897; <0.1), with an abnormal Th/U ratio, indicating that these zircons crystallized in a magma with a special composition [19,20,21]. The weighted average ages obtained from 19 points is 205.99 ± 0.79 Ma (MSWD = 0.36, n = 19; Figure 6f).

5. Discussion

5.1. Chronological Significance

Granitoids occur throughout the Western Kunlun region and existing emplacement age data are predominantly concentrated along the China–Pakistan and Xinjiang–Tibet highways [22,23,24,25,26,27,28]. The main body of the Dahongliutan pluton is located above the snow line at an altitude of 6000 m. The terrain is relatively steep and the natural environment is harsh, inhibiting systematic field studies. In recent years, chronological studies of granitoids have indicated that the Western Kunlun orogen is a multi-stage intrusive composite batholith [3]. Although early Paleozoic–Mesozoic granites are exposed the region, the late Variscan Indosinian and early Yanshanian periods contained the peak magmatic activity [29]. The Mesozoic Indosinian granitic belt is the largest tectonomagmatic belt in the region [30]. According to the emplacement ages of different rock bodies in the Western Kunlun region (

Table 4. Isotopic ages of Indosinian intrusive rocks in the Western Kunlun region.

Serial Number	Location	Rock Type	Analytical Method	Age/Ma	Data Source
1	Bulun Village	Gnei ss granite	LA-ICP-MS	245	[1]
2	Weizide rock mass	Quartz diorite	LA-ICP-MS	(257.5 ± 4.3)	[31]
3	Korzrov rock body No.9	Gneiss quatz diorite	LA-ICP-MS	253	[32]
4	Gneiss quatz diorite	Gneiss two-mica granite	SHRIMP	(242.9 ± 2.6)	[32]
5	Kayinglik rock mass No.11	Garnet-bearing biotite adamellite	SHRIMP	(240.5 ± 2.6)	[33]
6	Sanshiliyingfang	Granite	Rb-Sr isochron	215	[34]
7	Mustag-Gonger	Granodiorite	LA-ICP-MS	213	[35]
8	Suyingdi	Diorite-porphyrite	LA-ICP-MS	213–210	[35]
9	Bayankala terrane	Adakite	LA-ICP-MS	221–212	[34]
10	Akazi	Granite	LA-ICP-MS	208	[36]
11	Sou Kudi	Granite	SHRIMP	215	[23]
12	Mazha	Granite	SHRIMP	209	[23]
13	Shengliqiao	Biotite	Ar-Ar	(211.2 ± 2.6)	[24]
14	North rock body of Heika station	Biotite	K-Ar	207.8	[32]
15	Thal rock mass	Granodiorite	SHRIMP	(234.2 ± 2.8)	[37]
16	Bandier heath	Granodiorite	LA-ICP-MS	(239.8 ± 1.5)	[38]
17	Kegang	Amphibole granite	TIMS	(228.2 ± 1.5)	[1]
18	Saturasi	Granodiorite	Rb-Sr isochron	215	[1]
19	Keliyang	Lamprophyre	Ar-Ar	237	[23]
20	Pishan	Lamprophyre	Ar-Ar	(228.5 ± 0.3)	[23]
21	Dahongliutan	Monzogranite	SHRIMP	(220 ± 2.2)–(217.4 ± 2.2)	[3]
22	Dahongliutan	Two-mica granite	LA-ICP-MS	(209.6 ± 1.5)	[4]
23	Dahongliutan	Granite	TIMS	(217.5 ± 2.8)	[5]
24	Dahongliutan	Biotite adamellite	LA-ICP-MS	(213 ± 2.1)	[39]
25	Dahongliutan	Damourite Adamellite	LA-ICP-MS	(214.0 ± 0.63)	This study
26	Dahongliutan	Two-mica Monzogranit	LA-ICP-MS	(216.7 ± 0.82)	This study
27	Dahongliutan	Biotitized Granodiorite	LA-ICP-MS	(212.71 ± 0.89)	This study
28	Dahongliutan	Biotite Adamellite	LA-ICP-MS	(214.7 ± 1.0)	This study
29	Dahongliutan	Biotite Quartz Diorite	LA-ICP-MS	(209.3 ± 2.8)	This study
30	Dahongliutan	Two-mica Granite	LA-ICP-MS	(205.90 ± 0.41)	This study

), the 258–200 Ma granitic bodies form a large-scale magmatic belt that reflects different periods of magmatism under a compressive extensional setting. Chronological studies of Indosinian granitoids provide an important basis for understanding the spatiotemporal distribution, alteration, and mineralization of Indosinian granites in the Western Kunlun orogen.

The Dahongliutan pluton is located in the eastern Western Kunlun orogen. Previous studies [3,4,5,6] have obtained isotopic ages of 220 ± 2.2–209.6 ± 1.5 Ma. This is consistent with the zircon isotopic ages obtained for the six intrusive units in this study (214.0 ± 1.2, 216.6 ± 1.6, 212.71 ± 0.89, 214.7 ± 1.0, 209.3 ± 2.8, and 205.99 ± 0.79 Ma). Therefore, the emplacement age of the Dahongliutan pluton is 220 ± 2.2 to 205.99 ± 0.79 Ma, indicating that the pluton was likely the product of Late Triassic magmatism.

5.2. Genetic Types and Source Material

The LILE contents of the Dahongliutan pluton indicate Rb enrichment and Sr depletion. The HFSE contents indicate Th enrichment and strongly indicate Ta and Nb depletions. The total REE contents are 65.5 × 10⁻⁶ to 293.09 × 10⁻⁶ and zircons have inherited cores that share similarities with Himalayan leucogranites [40]. Leucogranites are metasedimentary rocks formed by the dehydration and melting of hydrous minerals [41,42] and are regarded as representative S-type and syn-collisional granites [40]. The Zr contents of the Dahongliutan pluton are relatively low (65.51 × 10⁻⁶ to 354 × 10⁻⁶). Even at low temperatures, zircon crystallization also requires Zr contents of ~100 × 10⁻⁶ [26]. Therefore, the pluton has experienced zircon fractional crystallization. Only four samples (D3801GS01, P6-06XT01, P22-39XT01, and P7-65XT03) have Zr/Hf ratios of >40; the other 19 samples have low Zr/Hf ratios (17.85–39.85), which supports this conclusion, as zircons have high Zr/Hf ratios (>40). The fractional crystallization of zircon leads to lower Zr/Hf ratios in the residual magma. The presence of inherited cores indicates that the initial magma was Zr-saturated during the formation of the pluton. According to Zr-saturation thermometer calculations, the zircon saturation temperature of the Dahongliutan pluton was 724–872 °C [43,44]. This is similar to the emplacement temperature of I-type granites (750–850 °C). Among the sample, two (P22-71 GS and P21-08 GS) had Zr-saturation temperatures of >800 °C; the remaining 21 samples had Zr-saturation temperatures that were substantially lower than the emplacement temperature of A-type granite (>800 °C), which is the upper limit for the initial magma temperature [45]. However, given that zircon fractional crystallization requires higher temperatures and lower viscosity, the actual temperature of the magma may have been higher [40].

On an S- and I-type granite discrimination diagram (Figure 8) most of the Dahongliutan pluton samples plot in the S-type granite region, and some plot in the I-type granite region. The A/CNK of the pluton is 1.01–1.43 (average = 1.21), which is greater than 1.1 and belongs to the peraluminous granite region. The presence of biotite and Al-rich minerals such as muscovite and garnet is consistent with S-type granites. Dark elliptical or irregular diorite xenoliths of different sizes are common, but are unevenly distributed. The boundaries between the xenoliths and the surrounding rock are clear. Some boundaries have clear condensation edges, indicating that the xenoliths had a magmatic origin. Such boundaries are the result of mixing between relatively more basic and acidic magmas. In summary, the magma that formed the Dahongliutan pluton mainly originated from the crust and was an S-type granite. However, a small amount of upper mantle material was involved in the early stages of magma formation, as reflected by the I-type granite characteristics.

The Dahongliutan pluton samples are enriched in LREEs and depleted in HREEs (La/Yb_N = 7.05–49.9), except for three samples (P26-88 GS, P21-32XT01, and P21-08 GS). One sample has an δEu value of >1, with a pronounced negative Eu anomaly, low Y (~34.4 × 10⁻⁶) and Yb (~3.83 × 10⁻⁶) contents, and a high Sr/Y ratio (~38.97). This is similar to adakite, and indicates that garnet was present during magma formation. The other 20 samples have δEu values of 0.34–0.94, relatively pronounced negative Eu anomalies, and insignificant Sr losses, which indicates that no plagioclase residue was present in the source. Given the lower pressure limit of rutile stability (1.5 GPa), the formation pressure of the Dahongliutan pluton was likely 1–1.5 GPa. Biotite and polysilicon muscovite have stronger affinities for Nb than Ta [46] in granitic magmas. In a low pressure environment (<2 GPa), the melting temperature of polysilicon muscovite is lower than that of biotite. At 1–1.5 GPa, the melting temperature of polysilicon automica is 760 °C, while that of biotite is 820 °C [47]. The Nb/Ta ratios of the Dahongliutan samples are high, which also suggests that dehydration and melting of polysilicon muscovite and biotite may have occurred during magma formation. Thus, the Dahongliutan pluton may have formed via the partial melting of crustal rocks at 1–1.5 GPa.

The relative enrichment of LREEs, flat HREE contents, and weak Eu depletion of the Late Triassic granitoids suggests that the magma may have had mixed crustal and mantle sources [49]. The granitoids also have pronounced negative Nb, Ta, and Sr anomalies, which also indicates that their source was predominantly crustal material, and that contamination by mantle-derived magma may have occurred. The Rb/Sr value of a mantle-derived magma is <0.05, that of a mixed crustal and mantle source is 0.05–0.5, and that of a crustal source is >0.5. Four samples have Rb/Sr ratios of 0.21–0.46, indicating a mixed crustal and mantle source. The other samples have Rb/Sr ratios of 0.62–4.38, indicating magma with a dominant crustal source. The Nd/Th values of the samples are 0.84–3.71 (average value = 1.88), which is close to the value of a crustal source (~3) [50], but inconsistent with a mantle source (>15) [51]. The Nb/Ta values of the samples are 2.89–14.40 (average = 8.05), which is close to the crustal Nb/Ta value (11) [52]. The Zr/Hf values range from 17.85 to 50.76 (average = 32.32), which is close to the crustal value (33) [52]. The La/Nb values range from 1.17 to 3.30 (average = 1.99), which is close to the average crustal value (2.58) [52]. Thus, the Dahongliutan pluton predominantly formed as the result of the partial melting of crustal material, but included some mantle-derived material.

5.3. Tectonic Setting and Geological Significance

Many Middle and late Triassic granites [3,24,25,53] in the Western Kunlun orogen are predominantly distributed along both sides of the Mazha–Kangxiwa Fault. The Late Triassic granite belt of the Western Kunlun area is related to the closure of the Paleo-Tethys Ocean. An LA–ICP–MS zircon U–Pb age of 231.4 Ma was previously obtained for the Mushitage pluton [25], while the SHRIMP age was 230.3 Ma [53]. This pluton was the product of a transition from a mainly collisional compressive tectonic setting to a back arc extensional setting [40], and of the detachment of the subducted slab in a post-collisional tectonic setting [53]. Isotopic ages ranging from 213 to 225 Ma have been obtained for the Akaraz Shan granite [22,23,24,26], which has been postulated to have formed in post-collisional, subduction, and syn-collisional settings [23,24,26]. Studies of the Middle and Late Triassic Yuqikapa, Taer, Mazha, Shengliqiao, and Qitaidaban plutons indicate that they are related to the subduction and closure of the Paleo-Tethys Ocean and subsequent continental collisional orogeny [22,27,28,53].

Zircon U–Pb dating of metamorphic rocks in the Kangxiwa Fault zone and fission track dating of detrital zircons in areas adjacent to the Western Kunlun region indicate that strong compressive uplift occurred between 235 and 267 Ma in the Western Kunlun region. This uplift was closely related to the subduction and collision of the Paleo-Tethys Ocean [1,7,54]. Kang, et al. [55] also found that the Western Kunlun region lacks sedimentary records from the late Permian to the Middle Triassic, which is likely related to the orogenic event that occurred during this period. Before the late Permian, predominantly marine sedimentation occurred; after the Middle Triassic, sediment was composed of continental material, which may indicate the end of the collisional event [55]. Thus, as the Paleo-Tethys Ocean retreated northward until it closed in the Late Triassic [30,56], continental collision occurred along both sides of the Kangxiwa Fault zone. This collision resulted in crustal thickening and large-scale re-melting under a compressive setting, which led to strong magmatism that formed the Dahongliutan pluton on the southern edge of the Kangxiwa Fault zone.

The Dahongliutan pluton is located in the Hoh Xil–Songpan foreland basin, and its long axis trends NW–SE. The pluton is controlled by fault structures consistent with the regional tectonic direction. The steep surrounding rocks were affected by the lateral compression of the pluton, indicating that magma actively expanded and pushed the surrounding rock outward during emplacement. The pluton then expanded further through structural expansion and magmatic encroachment. During the Late Triassic, the study area underwent large-scale crustal uplift, and heat flow values increased accordingly. The melting layer moved upwards and Al-rich granitic magma was produced through the partial melting of the crust. The pluton was emplaced and along a structurally weak zone in the uplift. As the magma ascended through the crust, the viscosity increased, owing to crystallization, and the speed of ascent slowed. When ascent stopped, the magma expanded laterally through tectonic expansion (i.e., along the fault zone). Magma encroachment occurred into the surrounding rock and produced xenoliths in the pluton. The Dahongliutan pluton therefore had a composite emplacement mechanism that was dominated by active expansion supplemented by tectonic expansion and magma intrusion mechanisms.

On a R1–R2 diagram (Figure 9), the data are predominantly in Zone 6 during the same collision period. On an Rb − Y + Nb diagram (Figure 10a), the data fall into the volcanic arc granite and syn-collisional granite areas, but are closer to the syn-collisional area. On an Rb − Yb + Ta diagram (Figure 10b), most data fall into the syn-collisional granite area. Thus, the Dahongliutan pluton may have formed in a syn-collisional tectonic setting. The Late Triassic tectonic setting was the extensional post-collisional orogenic stage of the Paleo-Tethys Ocean [57]. Peak magmatism occurred during the late Hercynian–early Yanshanian period in the Western Kunlun region. However, there is no chronological evidence of magmatic activity from 230 to 250 Ma [56], which may be because the strong compressive stress was not conducive to magmatism [58]. When the tectonic stress changes to post-collisional extension, decompression melting and magmatic upwelling are more likely to occur [58], leading to intense magmatism. With the development of extension and collapse of the orogenic belt, a substantial amount of heat was generated, thereby causing the partial melting of crustal material that ascended and was emplaced. With continuous extension and lithospheric thinning, large-scale magma upwelling formed the Late Triassic intrusive rocks in the Western Kunlun region.

5.4. Implications for Geologic Prospecting

Magmatism in the study area not only provided metallogenic hydrothermal fluids, but also promoted the activation, migration, and enrichment of metallogenic elements in the surrounding rock, which is often accompanied by mineralization. Minerals often form in or around plutons. Spatially, most mineralized areas are concentrated in the internal and external contact zones between the Late Triassic pluton and the surrounding rock. Compared with their average crustal abundances, the elements enriched in the Late Triassic pluton include Pb, Zn, W, Sn, Mo, Ag, and Bi. Elements with variation coefficients of >1 include Pb, Zn, As, Sb, Ni, and Ag. The Pb and Zn contents are 1.24–24.37 and 1.03–5.28 times the average value of the Western Kunlun region, respectively. The enrichment of other elements is less pronounced. The Kangxiwanan Ag–Pb, Kalakashihenan Pb–Ag, Ahelangan Pb–Ag, Fulugouxiayoubei Pb–Zn, Fulugou Pb–Zn, and Dahongliutanxi Pb ore deposits are all located in the outer contact zones of Late Triassic rocks. These findings are consistent with geochemical and remote sensing anomalies observed in the study area.

Rare metal mineralization is closely related to the Late Triassic intrusive rocks. The granite pegmatites in the study area were derived from the differentiation of these rocks and provided rare metals, a heat source, and ore-forming materials. The Dahongliutan and Ahelangan Li–Be ore deposits occur in granite pegmatites. Mineralization in the study area is predominantly hydrothermal, and was controlled by NW–SE structures. Mineralization is also mainly distributed in the high strain zones of the regional structures. The orebodies are controlled by a group of joints that are consistent with the overall strike, and exhibit contemporaneous mineralization characteristics. In Triassic strata, Li and Be deposits formed as a result of the intrusion of Indosinian magmatic hydrothermal fluids. The metallogenic mode of these deposits was predominantly crystalline metasomatism. The host rock was granite pegmatite and the surrounding rock was anorthosite biotite quartz schist. The strikes of the orebodies are consistent with those of the regional tectonic trend. The orebodies exhibit discontinuous, lenticular, and vein distributions that are often accompanied by strong albitization. The orebodies are controlled by the pegmatite veins, which have ore bearing properties that are related to the distance between plutons. Poor ore-bearing properties occur near the pluton, while good ore-bearing properties occur further from the pluton [10].

6. Conclusions

Based on analyses of the isotopic ages, mineralogy, and geochemistry of the Dahongliutan pluton in the Western Kunlun orogen, the following conclusions were drawn:

(1) Combined with the zircon CL images and U and Th data, zircon U–Pb dating indicates that the emplacement age of the Dahongliutan pluton is 220 ± 2.2 to 205.99 ± 0.79 Ma, and was the result of Late Triassic magmatism.

(2) The Dahongliutan pluton is enriched in silica, alkali elements, and potassium. The A/CNK ranges from 1.01 to 1.43, indicating a strongly peraluminous rock type. LREEs and HREEs are highly fractionated. The negative Eu anomalies of 20 samples are relatively pronounced. The pluton is enriched in HFSEs (e.g., Th) and LILEs (e.g., Rb); however, it is depleted in Sr, Ta, and Nb. Thus, the pluton belongs to the high potassium calc-alkaline peraluminous rock series.

(3) The Dahongliutan pluton is an S-type granite; however, a small amount of upper mantle material was involved during early magma formation. The pluton also exhibits I-type granite characteristics. The negative Eu anomalies, low Y and Yb contents, high Sr/Y ratios, low Nb, Ta, and Sr contents, and high Nb/Ta ratios (2.89–14.40) indicate that garnet and rutile residue were present in the source. Thus, the Dahongliutan pluton may have formed via the partial melting of crustal rocks at 1–1.5 GPa, with the contribution of some mantle-derived material.

(4) The U–Pb ages and regional geology indicate that the Dahongliutan pluton had a composite emplacement mechanism that was dominated by tectonic expansion and magma intrusion, which may have occurred in the same collisional tectonic setting. During the Late Triassic, the Western Kunlun region entered the post-collisional stage of the orogeny and intrusive rocks formed in an extensional setting.

(5) Late Triassic magmatism provided important heat and ore-forming materials for the mineralization of Pb–Zn, rare metals, Cu, Fe, and other minerals in the study area. Mineralization in this region is closely related to magmatism, which is important for geologic prospecting.