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Article

Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China

by
Dongxu Fan
1,
Shucheng Tan
1,
Xia Wang
2,
Zeli Qin
3,
Junfang Zhao
3,4,
Le Yang
4,5,
Wanhui Zhang
3,4,
Xiaoliang Li
4,5,
Zhengping Yan
5,
Guizhong Yang
1 and
Liang Li
1,*
1
School of Earth Sciences, Yunnan University, Kunming 650600, China
2
School of Foreign Languages, Yunnan University, Kunming 650600, China
3
No. 1 Geological Exploration Institute, Qinghai Provincial Nonferrous Metal Geological and Minerals Exploration Bureau, Xining 810007, China
4
Qinghai Key Laboratory of Concealed Mineral Exploration, Qinghai Provincial Nonferrous Metal Geological and Minerals Exploration Bureau, Xining 810007, China
5
Geological Science and Technology Branch, Qinghai Provincial Non-Ferrous Metal Geological and Minerals Exploration Bureau, Xining 810001, China
*
Author to whom correspondence should be addressed.
Minerals 2023, 13(1), 73; https://doi.org/10.3390/min13010073
Submission received: 17 September 2022 / Revised: 23 December 2022 / Accepted: 30 December 2022 / Published: 2 January 2023
(This article belongs to the Special Issue Tectono-Magmatic Evolution and Metallogeny of Tethyan Orogenic Belts)
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Versions Notes

Abstract

:
The Kaimuqi area in the Eastern Kunlun Orogen (EKO) contains many lherzolite, olivine websterite, gabbro and diorite intrusions, and new zircon U–Pb dating, Lu–Hf isotope and whole-rock geochemical data are presented herein to further confirm the Late Triassic mafic–ultramafic magmatism with Cu–Ni mineralization and to discuss the petrogenesis and geodynamic setting. Zircon U–Pb dating shows that the Late Triassic ages, corresponding to 220 Ma and 222 Ma, reveal the mafic–ultramafic and dioritic magmatism in Kaimuqi, respectively. Zircon from gabbro has εHf(t) values of −3.4 to −0.2, with corresponding TDM1 ages of 994–863 Ma. The mafic–ultramafic rocks generally have low SiO2, (Na2O+K2O) and TiO2 contents and high MgO contents and Mg# values. They are relatively enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy REEs (HREEs) and high-field-strength elements (HFSEs), indicating that the primary magma was derived from the metasomatized lithospheric mantle. The diorites show sanukitic high-Mg andesite properties (e.g., MgO = 2.78%–3.54%, Mg# = 50–55, Cr = 49.6–60.0 ppm, Sr = 488–512 ppm, Y = 19.6–21.8 ppm, Ba = 583–722 ppm, Sr/Y = 23.5–25.4, K/Rb = 190–202 and Eu/Eu* = 0.73–0.79), with LREEs and LILEs enrichments and HREEs and HFSEs depletions. We suggest that the primary Kaimuqi diorite magma originated from enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments. The Kaimuqi mafic–ultramafic and dioritic intrusions, with many other mafic–ultramafic and K-rich granitic/rhyolitic rocks in the EKO, formed in a dynamic extensional setting after the Palaeo-Tethys Ocean closure.

1. Introduction

During its long-term and complex geological evolution, the Eastern Kunlun Orogen (EKO) formed a large number of large-scale to super large-scale ore deposits, such as the Xiarihamu Cu–Ni [1], Dachang Au [2], Nageng Ag [3], Galinge Fe [4] and Weibao Pb–Zn deposits [5], a significant metallogenic belt in China. In particular, Jilin University and the 5th Geological Exploration Institute of Qinghai Province jointly discovered the Xiarihamu Cu–Ni deposit in 2011 [6], which interrupted the traditional understanding of nonexistent magmatic Cu–Ni sulfide deposits in the EKO and preluded the exploration in Qinghai Province. As prospecting had strengthened, a number of Cu–Ni deposits have been discovered, such as the Shitoukengde [7], Akechukesai [8], Langmuri [9] and Gayahedonggou [10] deposits, showing great prospecting potential for magmatic sulfide deposits. Many years of research revealed that these Cu-Ni deposits all formed during the Silurian–Devonian metallogenic period [11,12,13,14,15,16,17]. Extensive Silurian–Devonian mafic–ultramafic magmatism with significant Cu–Ni mineralization in the EKO was related to the large-scale partial melting of the asthenospheric mantle [18,19,20] caused by the break-off of the subducting plate during the Wanbaogou oceanic basalt plateau amalgamation with the Qaidam Massif [6,8,11,12,14,15,16,17,18,19,20]. Correspondingly, Cu–Ni sulfide deposits may also have occurred in the Late Triassic mafic–ultramafic intrusions in the EKO when mantle-derived magmatism and crust–mantle interactions became very intense. However, it is unknown whether there were mafic–ultramafic intrusions with Cu–Ni mineralization in the Late Triassic and whether there was a genetic relationship between the intermediate–acid and the basic–ultrabasic magmas in this period. In this paper, using zircon U–Pb dating, Lu–Hf isotopes and whole-rock geochemistry, we report on newly discovered mafic–ultramafic and dioritic intrusions in the Kaimuqi area, which confirm Late Triassic magmatism in the EKO.

2. Regional Geological Setting

The EKO is located on the northern margin of the Qinghai–Tibet Plateau and is also an important part of the Central Orogenic Belt in China (Figure 1). It is a typical marginal orogenic belt formed during the Ordovician to Triassic multistage orogeny [21,22]. The EKO is generally divided into three tectonic belts with different basements and evolutionary stages: the North Kunlun Belt, Central Kunlun Belt and South Kunlun Belt (Figure 1c) [21,22]. Opening–closing tectonics [23,24], terrane accretion [25,26,27] and a multistage marginal orogeny [14,20,21,22] were currently the main geological evolutionary models of the EKO. The EKO had experienced three stages of oceanic opening–closing cycles from the Meso–Neoproterozoic to the Late Palaeozoic [23,24]. The model of terrane accretion suggested that the EKO experienced tectonic movements and deformation attributed to continental fragmentation, terrane convergence, subduction splicing and extensional strike–slip, which has the characteristics of soft collision and the structural migration of non-Wilson cycles [28]. Sun et al. [21,22] suggested that the EKO is an orogenic belt that had undergone a multistage marginal orogeny, which occurred continuously and with a patchy distribution from south to north from the Cambrian to Triassic, and this model became the mainstream view [11,12,14,15,16,17,20,29,30].
The strata in the EKO include Precambrian metamorphic rocks and volcanic–sedimentary rocks formed in the Phanerozoic various periods [30]. The Precambrian metamorphic rocks are mainly granulite-facies metamorphic rocks of the Paleoproterozoic Jinshuikou Group and greenschist-facies metamorphic rocks of the Meso- to Neoperoterozoic Wanbaogou Group, among which the former constitutes the crystalline basement of the North Kunlun Belt and the Central Kunlun Belt, while the latter is the basement of the South Kunlun Belt [21,22]. Phanerozoic strata are mainly continental margin volcanic–sedimentary clastic rocks, carbonates and continental volcanic rocks [33]. The continental margin volcanic–sedimentary rocks, which underwent epimetamorphism, developed mainly in the Ordovician–Silurian, Devonian, Carboniferous, Permian and Triassic strata, including basic–acid volcanics, volcanic breccia, tuff, conglomerate, sandstone, sand-slate, silty phyllite, limestone and marble [23,32,33]. The continental volcanic rocks are hosted in the Late Devonian Maoniushan Formation and Late Triassic Babaoshan and Elashan Formations, including andesite, andesitic breccia, rhyolite, dacite, rhyolitic tuff and dacitic tuff [21,30,33].
The EKO experienced tectonic movements and developed structures with different scales and mechanical properties, such as E–W-trending deep faults (e.g., North, Central and South Kunlun faults) and their secondary NW-trending faults [2,3,21,22,24,29,30]. The E–W-trending deep faults constitute the structural framework of the EKO and play a significant role in controlling the distribution of strata, magmatic rocks and ore deposits. Due to the superposition of the multistage marginal orogeny, the distribution of geological bodies in the EKO is disordered with poor continuity [34].
The EKO recorded multiple intense magmatic events that formed numerous suites of mafic–felsic igneous rocks during various phases of magmatism, especially within the Central Kunlun Belt [32]. Multistage magmas emplaced from the Precambrian to the Mesozoic, especially in the Silurian–Devonian and Permian–Triassic periods (Figure 1a) [32,35]. A typical “bimodal” suite composed of mafic–ultramafic rocks (424~408 Ma) [8,12,14,15,20,35] and K-rich A2-type granites (426~411 Ma) [36,37] formed during the Silurian–Devonian. Mafic–ultramafic intrusive rocks in the EKO were identified in five periods: Palaeoproterozoic, Neoproterozoic, Silurian–Devonian, Late Permian–Early Triassic, and Late Triassic. The Silurian–Devonian mafic–ultramafic intrusions were significantly mineralized and contain the most Cu–Ni resources, indicative of a metallogenic period with a high prospecting potential for Cu–Ni in the EKO, such as the Xiarihamu, Shitoukengde, Akchukesai, Gayahedonggou Langmuri and other Cu–Ni deposits [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,35].

3. Geology of the Kaimuqi Area and Cu–Ni Mineralization

The Kaimuqi area is located in the North Kunlun Belt, near the North Kunlun Fault (Figure 1c). The exposed strata in Kaimuqi are mainly the Palaeoproterozoic Jinshuikou Group and Quaternary sediments. The main lithologies of the Jinshuikou Group include marble, plagioclase amphibolite, mica quartz schist, augen migmatite and migmatized granite, all of which were strongly deformed [38]. Due to the magma emplacement and dislocation of fault structures, the strata occur in the shape of blocks and lenses, showing an overall dome structure (Figure 2). The fold and fault structures in Kaimuqi are relatively well developed. The fold structure is a short axis anticline with an axial direction of NW–W that is 6 km long and 4 km wide and dips to the south. The Kaimuqi mafic–ultramafic intrusion, located in the dome, strikes NW and generally dips to the south. The faults are divided into three segments, namely, NNW, NW and NE (Figure 2), among which the NNW-trending fault (F1) is a regional reverse fault with widths of approximately 10–50 m.
The other NW-trending faults (F2 and F3) are secondary faults of F1, and they jointly controlled the production of various magmatic intrusions from the Early Permian to the Late Triassic. The distribution direction of these intrusions is basically consistent with the strike of F1 and F3 faults. The multistage magmatism resulted in the emplacement of acidic to ultrabasic intrusions, most of which occur in the form of stocks or batholiths (Figure 2). The intrusive rocks mainly include Early Carboniferous monzogranite and biotite monzogranite, Early Permian biotite granodiorite, Late Triassic mafic–ultramafic rocks (e.g., gabbro, pyroxenite, peridotite and lherzolite), diorite and biotite granodiorite. Among them, the mafic–ultramafic rocks are the ore-forming intrusion for Kaimuqi with appreciable sulfides in the ultramafic rocks (Figure 3a–c). Late Triassic diorite is the intrusion with the largest exposed area in Kaimuqi (Figure 3d), which is in intrusive contact with mafic–ultramafic intrusions.
The mafic–ultramafic complex intruded into the Jinshuikou Group as stocks composed of the No. Ⅰ and No. Ⅱ intrusions (Figure 2). The No. Ⅰ intrusion is a complex that is composed of gabbro, olivine gabbro, olivine websterite and lherzolite, with an exposed area of approximately 0.5 km2. The ultramafic rocks generally exist in the gabbros as small stock-likes and contain most of the sulfides. The No. Ⅱ intrusion is mainly composed of gabbro surrounded by diorite, with an exposed area of approximately 0.6 km2, but it is unknown whether ultramafic facies are present at depth. Gabbro and many ultramafic rocks were identified in the field, of which gabbro accounts for more than 90 vol.% of the Kaimuqi complex. The volume of ultramafic rocks is generally small, approximately 0.06 km2, consisting of three lenses that intruded into gabbros. Field observations show that the minerals of mafic–ultramafic rocks are generally coarse, but disseminated ore mineralization is relatively poor.
Disseminated sulfides are mainly hosted in the ultramafic rocks, and the mafic rocks rarely contain sulfides with occasional fine-grained pyrite, but diorite is devoid of any sulfides. The sulfides identified under the microscope mainly include chalcopyrite, pyrrhotite and pentlandite (Figure 3d–f), with few oxides (e.g., magnetite) (Figure 3f). The ore textures mainly exhibit xenomorphic interstitial texture, a hypautomorphic to xenomorphic granular texture and exsolution texture. The mafic–ultramafic rocks have Cu, Ni and Co contents of 8.41–47.7 ppm, 144–553 ppm and 69.5–161 ppm, respectively, with Cr contents as high as 550–1894 ppm (see 5.1.2. Trace elements), but their contents in ultramafic rocks are generally much higher than those in mafic rocks.

4. Analytical Methods and Sample Descriptions

4.1. Analytical Methods

4.1.1. Whole-Rock Geochemistry Analysis

The major and trace element analyses for the bulk rock samples were carried out at Yanduzhongshi Geological Analysis Laboratories Ltd., Beijing. Fresh samples were crushed to centimeter sizes; only the fresh pieces were selected, washed with deionized water, dried and then ground to less than 200 mesh (0.5200 ± 0.0001 g). Sample powders were fluxed with Li2B4O7 at 1250 °C (1:8) to make homogeneous glass disks using a V8C automatic fusion machine produced by the Analymate Company in Shanghai, China. The major elements were analysed using X–ray fluorescence spectrometry techniques (Zetium, PANalytical). The analytical errors for major elements were better than 1%, and the major element contents are shown in Table S1.
The analysis of trace elements was completed by the digestion ICP–MS method with the Analytik Jena M90 ICP–MS of I-ins Precise Instrument Ltd. Two hundred mesh whole-rock powder samples were weighed and placed into a Teflon bottle; HF and HNO3 mixed acid was added, and then a Teflon-sealed reaction tank was used to dissolve the samples. The dissolved samples were analyzed using an M90 ICP–MS, and the instrument was calibrated with the mixed standard solution. GSR–3 was used as the standard sample during the analysis [40], and the RSD was better than 5% within the 95% confidence level. The contents of trace elements were listed in Table S2.

4.1.2. Zircon U–Pb Dating

The trace element content and U–Pb isotope dating of zircon were completed by LA–Q–ICP–MS at Yanduzhongshi Geological Analysis Laboratories Ltd., Beijing, China. The laser ablation system was a New Wave UP213, and the ICP–MS was an Analytik Jena M90 ICP–MS made in Germany. For the present work, the laser spot size was set to 30 μm for most analyses; the laser energy density was 10 J/cm2, and the repetition rate was 8 Hz. The laser sampling procedure was 30 s blank, 30 s sampling ablation and 2 min sample-chamber flushing after ablation. The ablated material was carried into the ICP–MS by a high-purity helium gas stream with a flux of 1.15 L/min. The whole laser path was fluxed with Ar (600 mL/min) to increase energy stability. Zircon standard GJ–1 was used as the external standard for isotopic fractionation correction in U–Pb isotope dating. GJ–1 was analyzed twice for every 5–10 sample points [41]. The content of trace elements in zircon was quantitatively calculated by using SRM610 (standard reference material 610) as the multiple external standard and Si as the internal standard. Zircon 91500 and NIST 610 were selected to calibrate the instrument, and the detailed procedure and method for common Pb correction were from Yuan et al. [41]. Isotopic data and age calculations were performed following Liu et al. [42] and Ludwig [43], and the data are shown in Table S3.

4.1.3. Zircon Lu–Hf Isotope Analysis

Zircon Lu–Hf isotope analysis was carried out using a NewWave UP213 laser ablation microprobe attached to a Neptune multicollector ICP–MS at Yanduzhongshi Geological Analysis Laboratories Ltd., Beijing. Instrumental conditions and data acquisition techniques were comprehensively described by Hou et al. [44] and Wu et al. [45]. Lu/Hf isotope measurements were made on the same zircon grains previously analyzed for U–Pb isotopes, and the ablation pit was 55 μm in diameter with repetition rates of 8–10 Hz, a laser beam energy density of 10 J/cm2 and an ablation time of 26 s. The measuring method, process and data processing were described in Guo et al. [46], and the data are shown in Table S4.

4.2. Sample Descriptions

4.2.1. Occurrence of Zircon

The ultramafic rocks generally have rare zircon due to silicon unsaturation, while the gabbro contains more zircon with larger grains and magmatic oscillatory zoning. Therefore, zircon from gabbro (KMQ-DB-N1) was selected for U–Pb dating to reveal the emplacement age of the Kaimuqi mafic–ultramafic intrusion. They are mostly short, prismatic, oval and irregular in shape, with grain sizes of 100–120 μm. The short prismatic grains exhibit blurred oscillatory zoning, and some of them have unzoned overgrowth rims, as revealed by the cathodoluminescence images in Figure 4a. The oval grains are generally multifaceted and show sector/fir-tree zoning internal structures. Twenty-seven zircon grains were measured for U–Pb dating, and zircon grains No. 1 to No. 11 were subjected to additional Lu–Hf isotope analysis (Figure 4a).
Cathodoluminescence images show that zircon from diorite (KMQ-DB-N2) are mostly euhedral to subhedral, long and prismatic with aspect ratios of approximately 2:1 and have grain sizes of 120–150 μm. They generally show concentric magmatic oscillatory zoning, as shown in Figure 4b, and some of them contain tiny inherited cores. Twenty-two zircon grains were analyzed for U–Pb dating, and zircon grains No. 1 to No. 11 were subjected to additional Lu–Hf isotope analyses (Figure 4b).

4.2.2. Whole-Rock Samples for Geochemical Analysis

Eleven samples of gabbro, olivine websterite, lherzolite and diorite were selected for whole-rock geochemical analysis. The gabbro is dark gray with a massive texture (Figure 3b) and is mainly composed of plagioclase (~60%), clinopyroxene (~30%) and a small amount of amphiboles (~8%) and olivines (~2%) (Figure 5a). Plagioclase exists in the form of automorphic–hypautomorphic elongated crystals, approximately 1.0–2.0 mm long, and exhibits obvious polysynthetic twinning. Pyroxene fills spaces between plagioclase as hypautomorphic–xenomorphic grains with grain sizes of 0.4–1.0 mm. With the increased olivine content, gabbros evolve into olivine gabbros. The olivine websterite is dark with a massive texture (Figure 3c), and it is composed of orthopyroxene (~50%), clinopyroxene (~30%), olivine (~15%) and plagioclase (~5%) (Figure 5b). The lherzolite is composed of olivine (~50%), orthopyroxene (~30%) and clinopyroxene (~20%) with strong serpentinization (Figure 5c).
The diorite is gray to grayish black with a massive texture (Figure 3d) and is composed of plagioclase (~40%), amphibole (~30%), alkaline feldspar (~15%) and a small amount of biotites (~10%) and quartzs (~5%) (Figure 5d). Plagioclase exists in an automorphic long prismatic shape approximately 0.5–1.0 mm long and has obvious polysynthetic twinning. Amphibole is in the form of a hypautomorphic–xenomorphic crystal with grain sizes of 0.2–1.0 mm and is interstitial to plagioclase. Biotite is xenomorphic with grain sizes of 0.2–0.5 mm and is distributed between plagioclase and amphibole.

5. Results

5.1. Whole-Rock Geochemistry

5.1.1. Major Elements

The mafic–ultramafic rocks are generally characterized by low SiO2, (Na2O+K2O) and TiO2 contents but high total Fe2O3 (Fe2O3T) and MgO contents and Mg# values (Table S1). The mafic rocks (e.g., gabbro and olivine gabbro) have relatively higher contents of SiO2, Al2O3, CaO and (Na2O+K2O) but lower contents of Fe2O3T, MgO and MnO than those of ultramafic rocks (e.g., olivine websterite and lherzolite). In the SiO2 versus (Na2O+K2O) diagram, most of the mafic–ultramafic rocks belong to the subalkaline rock series; the mafic rocks plot in the gabbro field, while the ultramafic rocks plot in the olivine gabbro field (Figure 6a). In the FeOT−(Na2O+K2O)−MgO diagram, most of them plot in the cumulate field (Figure 6b).
The diorites have relatively high contents of SiO2, Al2O3, CaO and (Na2O+K2O) but low MgO contents and Mg# values, as shown in Table S1, and they all belong to the subalkalic/calc-alkalic series. They plot along the boundary of diorite and monzonite in the SiO2 versus (Na2O+K2O) diagram (Figure 6a), and the SiO2 versus K2O diagram (Figure 6c) shows that they belong to the high-K calc-alkaline series.

5.1.2. Trace Elements

The mafic–ultramafic rocks have similar patterns of rare earth elements (REEs) in the chondrite-normalized REE distribution diagram (Figure 7a). They contain low total REE concentrations (∑REE = 21.4–47.0 ppm), and the mafic rocks generally have higher ∑REE (44.6–47.0 ppm) than the ultramafic rocks (21.4–38.2 ppm) (Table S2). The mafic–ultramafic rocks are relatively enriched in light REEs (LREEs) and depleted in heavy REEs (HREEs), with LREE/HREE and (La/Yb)N ratios of 5.25–6.70 and 7.00–8.72, respectively. Moreover, most mafic and ultramafic rocks have slightly negative Eu anomalies of Eu/Eu* = 0.85–1.03 and Eu/Eu* = 0.79–0.97, respectively. They are generally enriched in large ion lithophile elements (LILEs) and depleted in high-field-strength elements (HFSEs) (e.g., Nb, Ta, Ce and Ti) (Figure 7b). Additionally, they have Cu, Ni and Co contents of 8.41–47.7 ppm, 144–553 ppm and 69.5–161 ppm, respectively, with Cr contents as high as 550–1894 ppm, but their contents in ultramafic rocks are much higher than those in mafic rocks (Table S2).
Similar to the mafic–ultramafic rocks, the diorites show similar enrichments and depletions in REEs and trace elements, as shown in Figure 7, with ∑REE of 151–160 ppm (Table S2). They are generally enriched in LREEs and depleted in HREEs, with LREE/HREE and (La/Yb)N ratios of 7.40–7.60 and 10.5–11.0, respectively. They also have moderately negative Eu anomalies (Eu/Eu* = 0.73–0.79) and relatively high contents of Sr (488–512 ppm), Y (19.6–21.8 ppm) and Yb (2.10–2.28 ppm). In the primitive mantle-normalized trace-element diagram (Figure 7b), they are characterized by enrichment in LILEs (e.g., Rb, K and Ba) and depletion in HFSEs (e.g., Nb, Ta and Ti).

5.2. Zircon U–Pb Dating

Despite the different shapes and internal structures, all the analyzed zircon from gabbro show similar Th/U ratios and 206Pb/238U ages (Table S3). Their Th/U ratios range from 0.12 to 1.56, but most of them are greater than 0.40, showing a diagnosis of magmatic zircon. They all plot on or near the concordia line, and their 206Pb/238U ages are concentrated within 224 ± 2 − 216 ± 2 Ma, with a weighted mean average age of 220 ± 1 Ma (MSWD = 2; n = 27) (Figure 8a), corresponding to the Late Triassic.
Zircon from diorite have Th/U values of 0.36–1.00, with a majority of them exceeding 0.40 (Table S3), corresponding to magmatic zircon. They plot on the concordia line, and their 206Pb/238U ages range from 225 ± 3 Ma to 217 ± 2 Ma, with a weighted mean average age of 222 ± 1 Ma (MSWD = 1; n = 22) (Figure 8b).

5.3. Zircon Lu–Hf Isotope Compositions

The 176Hf/177Hf ratios and εHf(t) values of eleven zircon grains from the gabbro are 0.282543–0.282629 and −3.4 to −0.2, respectively, with a corresponding one-stage model (TDM1) age of 994–863 Ma (Table S4). The 176Hf/177Hf ratios of diorite zircon are 0.282497–0.282568, and the εHf(t) values range from −5.0 to −2.4, with corresponding two-stage model (TDM2) ages of 1572–1408 Ma (Table S4). In the relevant Hf isotope diagrams, zircon from diorite and gabbro plot between the chondrite and lower crustal evolution lines (Figure 9).

6. Discussion

6.1. Late Triassic Mafic–Ultramafic Magmatism

High-precision dating results showed that a great number of sulfide-bearing intrusions in the EKO, such as Xiarihamu (394–432 Ma) [11,12,18,56,57], Shitoukengde (409–426 Ma) [14,20,58,59], Akechukesai (416–424 Ma) [8,15] and Binggounan (427 Ma) [13], formed during the Silurian–Devonian, indicating a new Cu–Ni metallogenic period in China [35]. However, it is puzzling that, although the Late Triassic was one of the most important Cu–Ni metallogenic periods in China (e.g., the Hongqiling [60], Piaohechuan [61] and Sandaogang [62] deposits in Jilin Province), the Late Triassic mafic–ultramafic intrusions with sulfides were rarely in the EKO, far less frequently than that in the Silurian–Devonian. Some researchers suggested that this may be related to the low degree of regional uplift–denudation and germinal ore prospecting [22,30].
At present, many Late Triassic mafic–(ultramafic) rocks were discovered in the EKO, such as the Nagengnan pyroxenite (233 ± 2 Ma; unpublished data), Kaimuqi mafic–ultramafic complex (221–220 Ma) [38; this paper], and Xiaojianshan (228 ± 1 Ma) [63], Shihuigou (226 ± 1 Ma) [64], Akechukesai (217 ± 1 Ma) [65] and Kendekeke (211–208 Ma) [66] gabbros. It is worth noting that the Kaimuqi intrusion is a sulfide-bearing mafic–ultramafic complex that has favorable conditions for magmatic liquation-type Cu–Ni mineralization. Therefore, significant mafic–ultramafic magmatism at 233–208 Ma with potential Cu–Ni metallogenesis occurred in the EKO.

6.2. Geodynamic Setting during the Late Triassic

The Permian–Triassic is a crucial period for the geological evolution and metallogenesis of the EKO, which recorded the convergence and disintegration of the Pangaea supercontinent [21,22,30,32]. At the turn of the Middle and Late Triassic, the tectonic regime of the EKO transformed from synorogenic compression to postorogenic extensional thinning, and a large number of magmatic rocks and related ore deposits were formed [2,3,4,5,21,22,32,33]. In the Early–Middle Triassic (approximately 235 Ma), with the continuous subduction and reduction of the Palaeo-Tethys Ocean, the Bayan Har Ocean in southern Eastern Kunlun was closed, and massifs around the Qaidam Massif collided with each other and joined together to form part of the Pangaea supercontinent. Due to the intense collision and compression between continental blocks, the crust was shortened and thickened on a large scale, and then the thickened lower crust was eclogitized, resulting in an increase in density and gravitational instability [30]. This process led to the large-scale delamination and thinning of the lithosphere, and the asthenospheric mantle upwelled and underwent decompression melting to form huge basaltic magmas [38,63,64,65,66]. The mantle-derived magma then underplated the lower crust and caused extensive partial melting and crust–mantle interaction. At this time (Late Triassic), the EKO was transformed from synorogenic compression to postorogenic extension [21,22,32], inducing large-scale magmatism and metallogenesis.
The extensional setting in the Late Triassic was also accompanied by a large number of postorogenic magmatic rocks. Wang et al. [67] and Li et al. [68] believed that the diorite (237 ± 2 Ma) that is closely related to skarn-type polymetallic metallogenesis in the Kaerqueka mining area was formed in a syncollisional setting. The Balong syenite granite (231 ± 3 Ma) [69] and Middle–Late Triassic granites (227–220 Ma) [70] in the Qiman Tagh area were considered to have formed in a postcollisional tectonic setting. Xu et al. [71] obtained a zircon U–Pb age of 222 ± 1 Ma for the Mohexiala granite porphyry in Qiman Tagh, which was considered to be the product of crust–mantle interactions in a postorogenic extensional regime, together with the Yazigou granite porphyry (224 ± 2 Ma) [72], Weibao porphyry granite and Yazigounan granite (228 ± 2 and 227 ± 1 Ma, respectively) [73] in the western segment of the EKO. The continental high-K calc-alkaline volcanic rocks and shoshonite of the Babaoshan Formation and Elashan Formation also indicated that the EKO entered postorogenic crustal extension in the Late Triassic, as indicated by rhyolitic tuff ± rhyolite ± dacite ± andesite (218–228 Ma) [74] in Nageng and Harizha, rhyolitic tuff/porphyry in Tufangzi and Dulan (219 ± 1.9 Ma) [75], the rhyolite and dacite tuff in Zhongzaohuo and Nalinggele (231–223 Ma) [76] and the rhyolite in Ela Mountain [77].
The intense magmatism during the Late Triassic occurred not only in the EKO but also in the adjacent northern Qaidam Massif, Western Qinling, Eastern Qinling, NW margin of the Yangtze Plate, Songpan Ganzi and other areas [78]. This occurrence indicated that central and western China (where the Central Orogenic belt is located) underwent postorogenic extension and collapse simultaneously during the Late Triassic, which may reflect extensive lithospheric detachment. Because a large amount of heat was transferred to the crust, the Late Triassic became the most important metallogenic period in the Central Orogenic Belt. However, the number of mafic–ultramafic intrusions in the Late Triassic was less than that in the Silurian–Devonian, and most of them were basic dikes, such as gabbroic dikes in Xiaojianshan, Shihuigou, Akechukesai, Kendekeke, Tuolugou and Harizha. Nevertheless, a few mafic–ultramafic complexes have been discovered, including the Kaimuqi, Dongdakende and Nagengnan intrusions. Significantly, the Kaimuqi intrusion was a sulfide-bearing mafic–ultramafic complex composed of gabbro, websterite, pyroxenite, olivine websterite, lherzolite and peridotite, favorable for magmatic liquation-type Cu–Ni mineralization.

6.3. Petrogenesis

6.3.1. Mafic–Ultramafic Rocks

Mantle metasomatism and even multi-metasomatism widely existed in the lithospheric mantle [79,80], and the geophysical and geochemical properties of the overlying lithospheric mantle can be changed by the metasomatism of melts/fluids formed by lateral plate subduction and melts derived from the low-degree partial melting of the asthenospheric mantle [81,82]. The sources of the metasomatic medium were diverse, and the processes of mantle metasomatism were also complex and diverse. For example, the bottom of oceanic lithospheric mantle was generally metasomatized by melts derived from the partial melting of asthenospheric mantle, resulting in the gradual enrichment of incompatible elements [83,84]. Low-degree partial melting of the asthenospheric mantle in the Cenozoic resulted in the gradual transformation of the depleted lithospheric mantle to an enriched lithospheric mantle, which promoted the thinning and destruction of the lithosphere in Eastern China [85]. Continuous mantle metasomatism will eventually lead to the gradual transformation of the originally depleted lithospheric mantle into the enriched lithospheric mantle, resulting in a fusible lithospheric mantle and showing the geochemical properties of HFSEs depletion and LILEs enrichment. However, if the time of metasomatism was close to that of partial melting, which would result in the inadequate accumulation of radiogenic isotopes, it would lead to a decoupling of the enrichment of incompatible elements and depletion of isotopes [86].
The 176Lu/177Hf ratios of gabbro zircon (0.000151–0.000763) are less than 0.002, indicating that they have negligible radiogenic Hf accumulation after formation [55]. The gabbro in Kaimuqi has slightly negative zircon εHf(t) values of −0.2 to −3.4, and they plot below the chondrite line (Figure 9), indicating an enriched mantle source, which is characterized by a εHf(t) value that was lower than zero [87]. Asthenospheric mantle-derived basaltic magmas generally have low ratios of La/Nb (<1.5) and La/Ta (<22), whereas lithospheric mantle-derived basaltic magmas contained higher corresponding ratios (La/Nb > 1.5, La/Ta > 22) [88,89]. The mafic–ultramafic rocks in Kaimuqi had La/Nb and La/Ta ratios of 3.17–3.93 and 29.1–43.8, respectively, which is strongly indicative of the partial melting of the lithospheric mantle for their primary magmas. However, they had higher Sr (99.5–619 ppm) and Rb (10.3–76.2 ppm) contents than those of the mantle (17.8 ppm and 0.55 ppm, respectively) [90], indicating that the magma source was affected by subduction fluids [91]. Furthermore, the Th versus Zr and Sr/Nd versus Th/Yb diagrams clearly show metasomatism dominated by subduction fluids (Figure 10). Additionally, the signature of LILEs enrichment and HFSEs depletion showing arc magma properties further indicates metasomatism by enriched components in the mantle source. However, a group of unusual zircon εHf(t) values (−1.05–3.51) from websterite in the Kaimuqi mafic–ultramafic intrusion [38] indicated that the mantle source may not have accumulated sufficient corresponding radiogenic isotopes. In conclusion, the primary magma of the Kaimuqi mafic–ultramafic intrusion was likely derived from the metasomatized lithospheric mantle, resulting in the coexistence of zircon-positive εHf(t) values and geochemical properties of arc magma.
Crustal contamination usually produces geochemical “signals” in magma, such as increases in SiO2, K2O, Rb, Ba, Th, Zr, Hf and S contents and decreases in P2O5 and TiO2 contents [20,92,93]. Because (Nb/Th)PM ratios <1 and (Th/Yb)PM ratios >5 were believed to be indicative of a crustally contaminated mantle-derived magma [94,95], a crustal contribution was notable across the mafic–ultramafic suite (Figure 11a). Furthermore, the mafic–ultramafic rocks were scattered and plot along the crustal evolution trend line and were particularly close to the average upper crust (Figure 11b).

6.3.2. Diorites

Previous studies have shown that a large volume of mafic–ultramafic magmas can produce a small volume of intermediate–acid magmas through extreme differentiation [100,101], but the equivalent exposed areas of the mafic–ultramafic and dioritic intrusions in Kaimuqi indicated the impossibility of this phenomenon. Moreover, all diorites and mafic–ultramafic rocks plotted along the evolution line of partial melting rather than fractional crystallization (Figure 12). It was generally believed that there was a significant correlation between the Mg# value, Dy/Yb ratio and Cr and SiO2 contents of the intermediate–acid rock series derived from the fractional crystallization of basic parental magma [102]. However, the SiO2 contents of diorites did not show an obvious linear relationship with Mg#, Dy/Yb and Cr, but rather were scattered (Figure 13). Therefore, the dioritee were unlikely to have formed by the fractional crystallization of mafic–ultramafic magma.
The diorites in Kaimuqi contain relatively higher MgO (2.78%–3.53%, with an average of 3.25%), Cr (49.6–60.0 ppm), Ni (19.9–26.3 ppm) and Co (22.5–26.1 ppm) contents and Mg# values (50–55) than those of common diorites, similar to the high-Mg andesites (HAMs) [104,105,106]. Moreover, high contents of Ba (583–722 ppm), Sr (488–512 ppm) and V (136–168 ppm) and signatures of LILEs enrichment and HFSEs depletion also indicate the similar properties of HMAs for the Kaimuqi diorites [103]. The SiO2 versus Mg# and Ba versus Nb/Y diagrams further show that they plot in the HMA area (Figure 14).
HMAs were generally divided into the following four subtypes: (a) adakitic HMA, (b) bajaitic HMA, (c) boninitic HMA and (d) sanukitic HMA [103]. Among them, the adakitic HMA was usually characterized by high Sr content (>400 ppm) and Sr/Y (>40) and (La/Yb)N (>40) ratios and low Y (<18 ppm) and Yb (<1.8 ppm) contents, which was derived from the partial melting of subducted plates or thickened lower crust [109,110]. The bajaitic HMA was rare, with extremely high Sr (>1000 ppm) and Ba (>1000 ppm) contents and K/Rb ratio (>1000), and its trace element and petrogenesis were similar to those of adakitic HMA, which were generally suggested deriving from the unbalanced reaction between mantle peridotite and silicon-rich subduction melts [111]. The boninitic HMA was characterized by extremely high MgO content (>8.0%) and very low contents of TiO2, ΣREE, LILEs and HFSEs and were suggested to derive from the partial melting with water from the residual mantle above the subduction zone [53,112]. The Kaimuqi diorites contain 2.78%–3.53% MgO, 0.92%–1.05% TiO2, 488–512 ppm Sr, 19.6–21.8 ppm Y, 2.10–2.28 ppm Yb and 583–722 ppm Ba contents and Sr/Y = 23.5–25.4, (La/Yb)N = 10.5–11.0, and K/Rb = 190–202 ratios (Table S2), with LILEs enrichment and HFSEs depletion (Figure 7d); some crucial parameters significantly differ from those of adakitic, bajaitic and boninitic HMAs. Although the Kaimuqi diorites exhibit some properties of adakitic and bajaitic HMAs (Figure 15a,b), they completely plot in the field of sanukitic HMA in the Y versus Sr/Y diagram (Figure 15c), which significantly differs from adakitic and bajaitic HMAs. Furthermore, their REE distribution patterns completely consistent with those of Fulugou sanukitic HMA in the Western Kunlun Orogen, NW (Figure 7b). Therefore, the Kaimuqi diorites were classified as sanukitic HMA and formed via a magmatic source and process similar to those of sanukitic HMA, corresponding to LILEs enrichment, relatively high contents of V, Cu, Ni, Y and Yb and high Mg# values [113].
Sanukitic HMAs were generally believed to be derived from the equilibrium reaction of overlying mantle peridotite with silicon/water-rich melts that were partially melted by the subducted slab or sediments [113,115]. For the Kaimuqi diorites, (a) they have low ratios of U/Th (0.22–0.30) and Nb/Ta (12.3–13.3), similar to those of global subduction sediments (U/Th = 0.24 and Nb/Ta = 14.19, respectively), which contributed to the significant Th and Ta enrichments in marine sediments [116]; (b) their relatively high La/Sm ratios (4.58–5.07) indicate the addition of trench sediments [117]; (c) they have higher MgO, Cr, Ni and Co contents and Mg# values (50–55) than those of basic crust-derived melts (<42) [118], suggesting a mantle contribution not a solely partial melting of subducted sediments; (d) the existences of biotite and amphibole imply high water fugacity in the magma source; and e) they exhibit an arc magma signature in LILEs enrichment and HFSEs depletion, indicating the metasomatism of subducted fluids. Furthermore, the Th/Zr versus Nb/Zr and Sr/Nd versus Th/Yb diagrams clearly show the metasomatism of subduction fluids and melts in the magma source (Figure 10), and the zircon negative εHf(t) values (−5.0 to −2.4) and older TDM1 ages (994–863 Ma) indicate an enriched mantle origin. Moreover, the discriminant diagrams show that the diorites experienced significant crustal contamination (Figure 11). It was generally believed that the formation of sanukitic HMAs was related to the subduction of young or hot plates and that they formed in the mantle wedge background of a plate subduction zone. However, the geodynamic setting of the EKO during the Late Triassic was a postorogenic extensional environment rather than a subduction background. Therefore, the Kaimuqi diorites, with arc magma signatures, might have inherited the geochemical properties of subduction fluid/melt metasomatism in the subduction process during the Permian to Early Triassic. Additionally, the diorites and mafic–ultramfic rocks in Kaimuqi show similar distribution patterns of REEs and trace elements (Figure 7), suggesting that they might have the similar magma source and evolution.
In conclusion, the primary magma of the Kaimuqi diorites likely originated from the enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments and experienced crustal contamination in the later evolution.

7. Conclusions

(1)
The mafic–ultramafic and dioritic intrusions in Kaimuqi, with diorite and gabbro crystallization ages of 222 ± 1 Ma and 220 ± 1 Ma, respectively, were emplaced in an extensional geodynamic setting after the closure of the Palaeo-Tethys Ocean during the Late Triassic.
(2)
The primary magma of the mafic–ultramafic intrusion was derived from the lithospheric mantle that was dominantly metasomatized by subduction fluids and experienced crustal contamination.
(3)
The diorite was classified as sanukitic HMAs and originated from the low-degree partial melting of enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/min13010073/s1, Table S1: Major element contents (wt.%) of the Kaimuqi mafic–ultramafic rocks and diorite; Table S2: Rare earth and trace element contents (ppm) of the Kaimuqi mafic–ultramafic rocks and diorite; Table S3: Zircon U–Pb dating results of the Kaimuqi gabbro (KMQ-DB-N1) and diorite (KMQ-DB-N2); Table S4: Zircon Lu–Hf isotope data of the Kaimuqi gabbro (KMQ-DB-N1) and diorite (KMQ-DB-N2). All authors have read and agreed to the published version of the manuscript.

Author Contributions

Conceptualization, D.F. and L.L.; investigation, D.F., L.L., Z.Q., J.Z., L.Y., W.Z., X.L., Z.Y. and G.Y.; funding acquisition, L.L. and S.T.; project administration, Z.Q., J.Z., L.Y., X.L. and Z.Y.; writing—original draft preparation, D.F. and L.L.; writing—review and editing, D.F., L.L., S.T. and X.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the Joint Foundation Project between Yunnan Science and Technology Department and Yunnan University (2019FY003011), and Scientific Project of the Qinghai Provincial Non-ferrous Metal Geological and Minerals Exploration Bureau (2020 [63]).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Datasets for this research are included in this paper.

Acknowledgments

We would like to thank the laboratories of Yanduzhongshi Geological Analysis Laboratories, Ltd., Beijing, for helping with zircon U–Pb dating, Lu–Hf isotope and whole-rock geochemistry analysis. Last but not least, this paper benefited greatly from the careful handling by the editor in charge and the helpful comments of reviewers.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Tectonic map of China (modified after [31]). (b) Location and tectonic map of the Central Orogenic Belt in China (modified after [31]). (c) Schematic geological map of the Eastern Kunlun Orogen showing the distributions of igneous rocks in the Phanerozoic and the location of Kaimuqi area (modified after [32]).
Figure 1. (a) Tectonic map of China (modified after [31]). (b) Location and tectonic map of the Central Orogenic Belt in China (modified after [31]). (c) Schematic geological map of the Eastern Kunlun Orogen showing the distributions of igneous rocks in the Phanerozoic and the location of Kaimuqi area (modified after [32]).
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Figure 2. Geological map of the Kaimuqi area (modified after [38]).
Figure 2. Geological map of the Kaimuqi area (modified after [38]).
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Figure 3. (a) Field photographs of the No. Ⅰ mafic–ultramafic complex. (b) Hand specimen of gabbro. (c) Hand specimen of olivine websterite. (d) Hand specimen of diorite. (e,f) Representative photomicrographs of the major metallic minerals (plane-polarized reflected light). The mineral abbreviations are after [39]: Pyh–pyrrhotite, Ccp–chalcopyrite, Mag–magnetite, Pn–pentlandite.
Figure 3. (a) Field photographs of the No. Ⅰ mafic–ultramafic complex. (b) Hand specimen of gabbro. (c) Hand specimen of olivine websterite. (d) Hand specimen of diorite. (e,f) Representative photomicrographs of the major metallic minerals (plane-polarized reflected light). The mineral abbreviations are after [39]: Pyh–pyrrhotite, Ccp–chalcopyrite, Mag–magnetite, Pn–pentlandite.
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Figure 4. Cathodoluminescence images of zircon from (a) gabbro and (b) diorite. Red and yellow circles indicate the sites of U–Pb and Lu–Hf isotope analysis, respectively, and the numbers within circles refer to the analysed spots.
Figure 4. Cathodoluminescence images of zircon from (a) gabbro and (b) diorite. Red and yellow circles indicate the sites of U–Pb and Lu–Hf isotope analysis, respectively, and the numbers within circles refer to the analysed spots.
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Figure 5. Representative photomicrographs of mafic–ultramafic rocks and diorite (cross-polarized transmitted light). (a) Gabbro. (b) Olivine websterite. (c) Lherzolite. (d) Diorite. The mineral abbreviations are after [39]: Pl—plagioclase; Cpx—clinopyroxene; Amp—amphibole; Ol—olivine; Opx—orthopyroxene; Srp—serpentine; Afs—alkali feldspar; Bt—biotite; and Qz—quartz.
Figure 5. Representative photomicrographs of mafic–ultramafic rocks and diorite (cross-polarized transmitted light). (a) Gabbro. (b) Olivine websterite. (c) Lherzolite. (d) Diorite. The mineral abbreviations are after [39]: Pl—plagioclase; Cpx—clinopyroxene; Amp—amphibole; Ol—olivine; Opx—orthopyroxene; Srp—serpentine; Afs—alkali feldspar; Bt—biotite; and Qz—quartz.
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Figure 6. Major element geochemical diagrams of (a) SiO2 versus (Na2O+K2O) (modified after [47]), (b) FeOT−(Na2O+K2O)−MgO (modified after [48]) and (c) SiO2 versus K2O (modified after [49]) for the mafic–ultramafic rocks and diorites. Explanation of numbers in (a): 1—olivine gabbro; 2—gabbro; 3—gabbro diorite; 4—diorite; 5—granodiorite; 6—granite; 7—quartzolite; 8—foid gabbro; 9—essexite; 10—monzogabbro; 11—monzodiorite; 12—monzonite; 13—quartz monzonite; 14—foidolite; 15—foid monzodiorite; 16—foid monzosyenite; 17—syenite; 18—foid syenite.
Figure 6. Major element geochemical diagrams of (a) SiO2 versus (Na2O+K2O) (modified after [47]), (b) FeOT−(Na2O+K2O)−MgO (modified after [48]) and (c) SiO2 versus K2O (modified after [49]) for the mafic–ultramafic rocks and diorites. Explanation of numbers in (a): 1—olivine gabbro; 2—gabbro; 3—gabbro diorite; 4—diorite; 5—granodiorite; 6—granite; 7—quartzolite; 8—foid gabbro; 9—essexite; 10—monzogabbro; 11—monzodiorite; 12—monzonite; 13—quartz monzonite; 14—foidolite; 15—foid monzodiorite; 16—foid monzosyenite; 17—syenite; 18—foid syenite.
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Figure 7. Chondrite-normalized REE distribution patterns (chondrite REE values from [50]) of the (a) mafic–ultramafic rocks and (b) diorites and primitive mantle-normalized trace-element patterns (primitive mantle values from [51]) of the (c) mafic–ultramafic rocks and (d) diorites. The data of Fulugou sanukitic high-Mg andesite (HMA) in the Western Kunlun Orogen were cited from [52]. The data of boninite were cited from [53], and the remainder data were cited from [54].
Figure 7. Chondrite-normalized REE distribution patterns (chondrite REE values from [50]) of the (a) mafic–ultramafic rocks and (b) diorites and primitive mantle-normalized trace-element patterns (primitive mantle values from [51]) of the (c) mafic–ultramafic rocks and (d) diorites. The data of Fulugou sanukitic high-Mg andesite (HMA) in the Western Kunlun Orogen were cited from [52]. The data of boninite were cited from [53], and the remainder data were cited from [54].
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Figure 8. Zircon U–Pb concordia and weighted mean age diagrams of (a) gabbro and (b) diorite.
Figure 8. Zircon U–Pb concordia and weighted mean age diagrams of (a) gabbro and (b) diorite.
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Figure 9. (a) t(Ma) versus 176Hf/177Hf and (b) t(Ma) versus εHf(t) diagrams of zircon from gabbro and diorite (modified after [55]). The data on websterite in the same intrusion were cited from [38].
Figure 9. (a) t(Ma) versus 176Hf/177Hf and (b) t(Ma) versus εHf(t) diagrams of zircon from gabbro and diorite (modified after [55]). The data on websterite in the same intrusion were cited from [38].
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Figure 10. Diagrams of (a) Th/Zr versus Nb/Zr (modified after [96]) and (b) Sr/Nd versus Th/Yb (modified after [97]) of the mafic–ultramafic rocks, showing the addition of slab-derived melts or sediment contaminants in mantle sources.
Figure 10. Diagrams of (a) Th/Zr versus Nb/Zr (modified after [96]) and (b) Sr/Nd versus Th/Yb (modified after [97]) of the mafic–ultramafic rocks, showing the addition of slab-derived melts or sediment contaminants in mantle sources.
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Figure 11. Diagrams of (a) (Th/Yb)PM versus (Nb/Th)PM (modified after [98]) and (b) (La/Nb)PM versus (Th/Ta)PM (modified after [99]) of the mafic–ultramafic rocks, showing crustal contamination. The Th, Yb, Nb, La and Ta contents of the primitive mantle are cited from [50].
Figure 11. Diagrams of (a) (Th/Yb)PM versus (Nb/Th)PM (modified after [98]) and (b) (La/Nb)PM versus (Th/Ta)PM (modified after [99]) of the mafic–ultramafic rocks, showing crustal contamination. The Th, Yb, Nb, La and Ta contents of the primitive mantle are cited from [50].
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Figure 12. Diagrams of (a) La versus La/Sm, (b) La versus La/Yb (c) and Th versus Th/Yb of the mafic–ultramafic rocks and diorites, showing the partial melting evolution trend (modified after [103]).
Figure 12. Diagrams of (a) La versus La/Sm, (b) La versus La/Yb (c) and Th versus Th/Yb of the mafic–ultramafic rocks and diorites, showing the partial melting evolution trend (modified after [103]).
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Figure 13. Diagrams of (a) SiO2 versus Mg#, (b) SiO2 versus Dy/Yb and (c) SiO2 versus Cr of the diorites, documenting the low probability of fractional crystallization from mafic–ultramafic magma (modified after [102]).
Figure 13. Diagrams of (a) SiO2 versus Mg#, (b) SiO2 versus Dy/Yb and (c) SiO2 versus Cr of the diorites, documenting the low probability of fractional crystallization from mafic–ultramafic magma (modified after [102]).
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Figure 14. Diagrams of (a) SiO2 versus Mg# (modified after [107]) and (b) Ba versus Nb/Y (modified after [108]) of the diorites, showing the properties of high-Mg andesite.
Figure 14. Diagrams of (a) SiO2 versus Mg# (modified after [107]) and (b) Ba versus Nb/Y (modified after [108]) of the diorites, showing the properties of high-Mg andesite.
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Figure 15. Diagrams of (a) MgO/(MgO+TFeO) versus TiO2 (modified after [109]), (b) YbN versus (La/Yb)N (modified after [112]) and (c) Y versus Sr/Y (modified after [114]) of the diorites, showing the classification of sanukitic HMA.
Figure 15. Diagrams of (a) MgO/(MgO+TFeO) versus TiO2 (modified after [109]), (b) YbN versus (La/Yb)N (modified after [112]) and (c) Y versus Sr/Y (modified after [114]) of the diorites, showing the classification of sanukitic HMA.
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MDPI and ACS Style

Fan, D.; Tan, S.; Wang, X.; Qin, Z.; Zhao, J.; Yang, L.; Zhang, W.; Li, X.; Yan, Z.; Yang, G.; et al. Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China. Minerals 2023, 13, 73. https://doi.org/10.3390/min13010073

AMA Style

Fan D, Tan S, Wang X, Qin Z, Zhao J, Yang L, Zhang W, Li X, Yan Z, Yang G, et al. Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China. Minerals. 2023; 13(1):73. https://doi.org/10.3390/min13010073

Chicago/Turabian Style

Fan, Dongxu, Shucheng Tan, Xia Wang, Zeli Qin, Junfang Zhao, Le Yang, Wanhui Zhang, Xiaoliang Li, Zhengping Yan, Guizhong Yang, and et al. 2023. "Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China" Minerals 13, no. 1: 73. https://doi.org/10.3390/min13010073

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