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

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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.
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Minerals 2023, 13, 73. https://doi.org/10.3390/min13010073 www.mdpi.com/journal/minerals
Article
Geochronology, Petrogenesis and Geodynamic Setting of the
Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the
Eastern Kunlun Orogen, NW China
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
* Correspondence: liliang19@ynu.edu.cn
Abstract: The Kaimuqi area in the Eastern Kunlun Orogen (EKO) contains many lherzolite, olivine
websterite, gabbro and diorite intrusions, and new zircon UPb dating, LuHf 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 UPb 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
ε
Hf
(t) values of 3.4 to 0.2, with corresponding T
DM1
ages of 994–863 Ma. The mafic–ultramafic rocks
generally have low SiO
2
, (Na
2
O+K
2
O) and TiO
2
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 sug-
gest 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.
Keywords: mafic–ultramafic magmatism; sunamitic HMA; Late Triassic; Kaimuqi area; Eastern
Kunlun
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 PbZn
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
Citation: 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
Academic Editors: Andrei Y. Barkov
and Alexey V. Ivanov
Received: 17 September 2022
Revised: 23 December 2022
Accepted: 30 December 2022
Published: 2 January 2023
Copyright: © 2023 by the authors. Li-
censee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and con-
ditions of the Creative Commons At-
tribution (CC BY) license (http://cre-
ativecommons.org/licenses/by/4.0/).
Minerals 2023, 13, 73 2 of 23
Province. As prospecting had strengthened, a number of Cu–Ni deposits have been discov-
ered, 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 [11–17]. 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 [18–20] caused by the break-off of the subducting
plate during the Wanbaogou oceanic basalt plateau amalgamation with the Qaidam Mas-
sif [6,8,11,12,14–20]. Correspondingly, Cu–Ni sulfide deposits may also have occurred in
the Late Triassic mafic–ultramafic intrusions in the EKO when mantle-derived magma-
tism 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 UPb dating, LuHf isotopes
and whole-rock geochemistry, we report on newly discovered mafic–ultramafic and dio-
ritic 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].
Openingclosing tectonics [23,24], terrane accretion [25–27] and a multistage marginal
orogeny [14,20–22] were currently the main geological evolutionary models of the EKO.
The EKO had experienced three stages of oceanic openingclosing 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 under-
gone a multistage marginal orogeny, which occurred continuously and with a patchy dis-
tribution from south to north from the Cambrian to Triassic, and this model became the
mainstream view [11,12,14–17,20,29,30].
Minerals 2023, 13, 73 3 of 23
Figure 1. (a) Tectonic map of China (modified after [31]). (b) Location and tectonic map of the Cen-
tral 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]).
The strata in the EKO include Precambrian metamorphic rocks and volcanic–sedi-
mentary rocks formed in the Phanerozoic various periods [30]. The Precambrian meta-
morphic rocks are mainly granulite-facies metamorphic rocks of the Paleoproterozoic
Jinshuikou Group and greenschist-facies metamorphic rocks of the Meso- to Neoperote-
rozoic 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 sig-
nificant 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
Minerals 2023, 13, 73 4 of 23
Central Kunlun Belt [32]. Multistage magmas emplaced from the Precambrian to the Meso-
zoic, especially in the Silurian–Devonian and PermianTriassic 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: Palaeoprote-
rozoic, Neoproterozoic, Silurian–Devonian, Late Permian–Early Triassic, and Late Trias-
sic. 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, Ak-
chukesai, Gayahedonggou Langmuri and other Cu–Ni deposits [6–20,35].
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 rela-
tively 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–ultra-
mafic 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 approxi-
mately 10–50 m.
Figure 2. Geological map of the Kaimuqi area (modified after [38]).
Minerals 2023, 13, 73 5 of 23
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 intru-
sion 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 com-
posed of the No. and No. intrusions (Figure 2). The No. 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. 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 miner-
alization 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, pyr-
rhotite and pentlandite (Figure 3d–f), with few oxides (e.g., magnetite) (Figure 3f). The ore
textures mainly exhibit xenomorphic interstitial texture, a hypautomorphic to xenomor-
phic 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 con-
tents 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.
Minerals 2023, 13, 73 6 of 23
Figure 3. (a) Field photographs of the No. mafic–ultramafic complex. (b) Hand specimen of gabbro.
(c) Hand specimen of olivine websterite. (d) Hand specimen of diorite. (e,f) Representative photo-
micrographs of the major metallic minerals (plane-polarized reflected light). The mineral abbrevia-
tions are after [39]: Pyh–pyrrhotite, Ccp–chalcopyrite, Mag–magnetite, Pn–pentlandite.
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,
Minerals 2023, 13, 73 7 of 23
China. The major elements were analysed using X–ray fluorescence spectrometry tech-
niques (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 ICPMS method
with the Analytik Jena M90 ICPMS 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 ICPMS,
and the instrument was calibrated with the mixed standard solution. GSR3 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 UPb 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 ICPMS was an Analytik Jena M90
ICPMS 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-cham-
ber flushing after ablation. The ablated material was carried into the ICPMS 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 GJ1 was used as the exter-
nal standard for isotopic fractionation correction in U–Pb isotope dating. GJ1 was ana-
lyzed 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 mul-
tiple 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 per-
formed following Liu et al. [42] and Ludwig [43], and the data are shown in Table S3.
4.1.3. Zircon LuHf Isotope Analysis
Zircon LuHf isotope analysis was carried out using a NewWave UP213 laser abla-
tion microprobe attached to a Neptune multicollector ICPMS at Yanduzhongshi Geolog-
ical Analysis Laboratories Ltd., Beijing. Instrumental conditions and data acquisition tech-
niques were comprehensively described by Hou et al. [44] and Wu et al. [45]. Lu/Hf iso-
tope measurements were made on the same zircon grains previously analyzed for UPb
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. There-
fore, zircon from gabbro (KMQ-DB-N1) was selected for UPb dating to reveal the em-
placement age of the Kaimuqi mafic–ultramafic intrusion. They are mostly short, pris-
matic, 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 UPb dating, and zircon grains No. 1 to No. 11 were
subjected to additional LuHf isotope analysis (Figure 4a).
Minerals 2023, 13, 73 8 of 23
Ccathodoluminescence 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 UPb dating, and zircon grains No. 1 to No. 11 were
subjected to additional LuHf isotope analyses (Figure 4b).
Figure 4. Cathodoluminescence images of zircon from (a) gabbro and (b) diorite. Red and yellow
circles indicate the sites of UPb and LuHf isotope analysis, respectively, and the numbers within
circles refer to the analysed spots.
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
Minerals 2023, 13, 73 9 of 23
olivine (~50%), orthopyroxene (~30%) and clinopyroxene (~20%) with strong serpentini-
zation (Figure 5c).
The diorite is gray to grayish black with a massive texture (Figure 3d) and is com-
posed of plagioclase (~40%), amphibole (~30%), alkaline feldspar (~15%) and a small
amount of biotites (~10%) and quartzs (~5%) (Figure 5d). Plagioclase exists in an automor-
phic 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.
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 abbre-
viations are after [39]: Pl—plagioclase; Cpx—clinopyroxene; Amp—amphibole; Ol—olivine; Opx—
orthopyroxene; Srp—serpentine; Afs—alkali feldspar; Bt—biotite; and Qz—quartz.
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 cumu-
late field (Figure 6b).
Minerals 2023, 13, 73 10 of 23
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 sub-
alkalic/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.
Figure 6. Major element geochemical diagrams of (a) SiO2 versus (Na2O+K2O) (modified after [47]),
(b) FeOT(Na2O+K2O)MgO (modied 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 monzo-
diorite; 16–foid monzosyenite; 17–syenite; 18–foid syenite.
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–ultra-
mafic 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 de-
pletions 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-nor-
malized 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).
Minerals 2023, 13, 73 11 of 23
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].
5.2. Zircon UPb Dating
Despite the different shapes and internal structures, all the analyzed zircon from gab-
bro 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 concen-
trated 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).
Minerals 2023, 13, 73 12 of 23
Figure 8. Zircon U–Pb concordia and weighted mean age diagrams of (a) gabbro and (b) diorite.
5.3. Zircon LuHf 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 dio-
rite and gabbro plot between the chondrite and lower crustal evolution lines (Figure 9).
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].
6. Discussion
6.1. Late Triassic Mafic–Ultramafic Magmatism
High-precision dating results showed that a great number of sulfide-bearing intru-
sions 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 im-
portant 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 intru-
sions 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 re-
gional 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–ultra-
mafic complex (221–220 Ma) [38; this paper], and Xiaojianshan (228 ± 1 Ma) [63], Shihuigou
Minerals 2023, 13, 73 13 of 23
(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 com-
plex 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 metallogen-
esis of the EKO, which recorded the convergence and disintegration of the Pangaea su-
percontinent [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–
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 thick-
ened 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 [38,63–66]. 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 trans-
formed 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 UPb 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, respec-
tively) [73] in the western segment of the EKO. The continental high-K calc-alkaline vol-
canic rocks and shoshonite of the Babaoshan Formation and Elashan Formation also indi-
cated 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 mar-
gin 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 Cen-
tral Orogenic Belt. However, the number of mafic–ultramafic intrusions in the Late Trias-
sic 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, includ-
Minerals 2023, 13, 73 14 of 23
ing the Kaimuqi, Dongdakende and Nagengnan intrusions. Significantly, the Kaimuqi in-
trusion 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 litho-
spheric 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 astheno-
spheric 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 bot-
tom of oceanic lithospheric mantle was generally metasomatized by melts derived from
the partial melting of asthenospheric mantle, resulting in the gradual enrichment of in-
compatible 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 en-
riched lithospheric mantle, resulting in a fusible lithospheric mantle and showing the ge-
ochemical 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, indi-
cating that they have negligible radiogenic Hf accumulation after formation [55]. The gab-
bro 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 met-
asomatism 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 unu-
sual zircon εHf(t) values (1.05–3.51) from websterite in the Kaimuqi mafic–ultramafic in-
trusion [38] indicated that the mantle source may not have accumulated sufficient corre-
sponding radiogenic isotopes. In conclusion, the primary magma of the Kaimuqi mafic–
ultramafic intrusion was likely derived from the metasomatized lithospheric mantle, re-
sulting 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 contri-
bution was notable across the mafic–ultramafic suite (Figure 11a). Furthermore, the mafic–
Minerals 2023, 13, 73 15 of 23
ultramafic rocks were scattered and plot along the crustal evolution trend line and were
particularly close to the average upper crust (Figure 11b).
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 11. Diagrams of (a) (Th/Yb)PM versus (Nb/Th)PM (modified after [98]) and (b) (La/Nb)PM ver-
sus (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].
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 frac-
tional crystallization (Figure 12). It was generally believed that there was a significant cor-
relation 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.
Minerals 2023, 13, 73 16 of 23
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 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]).
The diorites in Kaimuqi contain relatively higher MgO (2.78%–3.53%, with an aver-
age 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) [104–106]. 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).
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.
Minerals 2023, 13, 73 17 of 23
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 ada-
kitic 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 ba-
jaitic 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 con-
tain 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. Fur-
thermore, 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].
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.
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 sed-
iments (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
Minerals 2023, 13, 73 18 of 23
discriminant diagrams show that the diorites experienced significant crustal contamina-
tion (Figure 11). It was generally believed that the formation of sanukitic HMAs was re-
lated 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 sub-
duction 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 evo-
lution.
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 litho-
spheric mantle that was dominantly metasomatized by subduction fluids and expe-
rienced 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 subduc-
tion-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 maficultramafic rocks and diorite; Table S2: Rare earth and trace element contents
(ppm) of the Kaimuqi maficultramafic rocks and diorite; Table S3: Zircon UPb dating results of
the Kaimuqi gabbro (KMQ-DB-N1) and diorite (KMQ-DB-N2); Table S4: Zircon LuHf 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 ge-
ochemistry 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.
Minerals 2023, 13, 73 19 of 23
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... The EKO experienced three stages of oceanic opening-closing cycles from the Meso-Neoproterozoic to the late Paleozoic (e.g., Jiang et al., 1992), and the model of terrane accretion suggests that the EKO experienced tectonic movements and deformation attributed to continental fragmentation, terrane convergence, subduction splicing and extensional strike-slip with the structural migration process of non-Wilson cycles (Yin and Zhang, 1997). Sun et al. (2009) suggested that the EKO is an orogen that underwent a multistage marginal orogeny from the Cambrian to Triassic, which occurred continuously and with a patchy distribution from south to north, and this model has become the mainstream view (e.g., Yan et al., 2019c;Li et al., 2020bLi et al., , 2021cFan et al., 2023). In their opinion, although the Wanbaogou Group basalts in the CSNK formed in the Meso-Neoproterozoic, they are oceanic basalt plateaus (OBP) developed on the oceanic crust rather than a part of the continental crust at that time, which significantly differed from the Jinshuikou Group. ...
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The volcanic rocks of the Elashan Formation provide important evidence for the Late Triassic post-collisional magmatism in the East Kunlun Orogenic Belt. This study focused on the geochronology, geochemistry, and petrogenesis of volcanic rocks of the Elashan Formation in the Dulan–Xiangride Basin. The 227.9 ± 0.4 Ma dacite exhibits calc-alkaline I-type characteristics, with low Sr/Y and (La/Yb)N ratios and prominent negative Eu anomalies. We suggest that the dacite was derived from the partial melting of lower crust at normal crustal thickness. The crystalline tuff (225.0 ± 0.4 Ma) has negative εHf(t) values, implying that it was likely formed by the partial melting of the ancient crust. The rhyolites (221.3 ± 1.1 and 221.9 ± 0.6 Ma) are peraluminous and calc-alkaline to high-K calc-alkaline. The high SiO2 and Na2O + K2O contents, and high K2O/Na2O and Ga/Al ratios of these rhyolites have an affinity with A-type granite. The rhyolites were formed by the partial melting of Late Paleoproterozoic–Mesoproterozoic lower crust induced by mantle-derived mafic magma underplating. The andesite and basaltic andesites formed at 221.1–217.9 Ma. The zircon Hf isotopic characteristics show that the andesite was likely derived from the partial melting of the Late Paleoproterozoic mafic lower crust. The combination of our new data and previously obtained geological data suggests that the East Kunlun Orogenic Belt underwent three magmatic activities corresponding to three tectono-magmatic events (slab breakoff, the delamination of unstable lower lithospheric mantle, and the intense asthenosphere upwelling with further delamination and continuous crustal thinning) during the Late Triassic.
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In this study, we present new geochronological and petrogenetic data for the Triassic granitoids of the East Kunlun Orogenic Belt (EKOB), in order to constrain their precise ages, petrogenesis, and tectonic settings. LA‐ICP‐MS zircon U–Pb data indicate that the Triassic granitoids were emplaced in two stages: (a) Middle Triassic (247–240 Ma), represented by a suite of porphyritic granites and granodiorites; and (b) Late Triassic (234–227 Ma), forming an intrusive rock association of K‐feldspar granites, granodiorites, and porphyritic granites. Geochemical analyses and mineral associations suggest that all the Triassic granitoids belong to I‐type granites but have different origins. The Middle Triassic granitoids have high SiO2, low to moderate Mg# values (25–37 for XSG porphyritic granite; 45–47 for DB granodiorite), low Sr/Y ratios (2.2–4.6 for XSG porphyritic granite; 17.8–20.8 for DB granodiorite), and relatively restricted zircon εHf(t) values (+2.4 − +4.6 for the ca. 247 Ma porphyritic granite, and − 8.0 to −1.5 for the ca. 240 Ma granodiorite), indicating that they were dominantly generated from partial melting of different crust sources (either juvenile or ancient) in a normal lower crust level. In contrast, the Late Triassic granitoids have high SiO2, K2O, and Y contents, low MgO and HREE contents, and variable zircon εHf(t) values (from negative to positive, −4.9 to +3.3), implying a strong crustal–mantle interaction that occurred during the Late Triassic, and this stage of granitoids were derived from a complex magma source possibly a mixture of mantle‐derived and ancient crustal‐derived materials. By combining these new data with the previous data, we conclude that the two stages of Triassic granitoids were emplaced in an active continental margin setting and a post‐collisional extension setting, respectively. Moreover, this study suggests a tectonic shift of the Palaeo‐Tethys Ocean in the EKOB from subduction during the Middle Triassic to a post‐collision during the Late Triassic.