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This paper presents zircon U-Pb-Hf isotopic compositions and whole-rock geochemical data for monzogranites and mafic-ultramafic complexes of the Maxingdawannan area in the western end of the east Kunlun orogenic belt, western China. The data are used to determine the ages, petrogenesis, magma sources, and geodynamic setting of the studied rocks. U-...
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... study area is located in the middle EKOB (Fig. 1) 91°27′39″E-91°29′41″E and 36°55′23″N-36°58′01″N. Quaternary sediments are mainly exposed strata (Fig. 2). Northwestsoutheast-and NE-SW-trending faults dominate the area. The NW-SE faults are strike-slip faults. Intrusive rocks are widespread and are dominated by monzogranite, granodiorite and diorite, as well as mafic-ultramafic complexes. The monzogranites are mainly Mesozoic and Paleozoic in age, and exposed area is ~6 km 2 . The ...
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... in the eastern and middle parts. The granodiorites and diorites are found in the southwest and central parts of the area, respectively. The mafic-ultramafic complexes occur in the southern end of the district, where they outcrop over an area of ~0.73 km 2 . Dikes, including granite porphyry, diorite and gabbro dikes, are also present in the area (Fig. ...
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... samples used for study were gained from outcrops in the southern and eastern Maxingdawannan area (Fig. 2). The monzogranites, collected from 36°55′56″N, 91°29′45″E (Figs. 2, 3a, 3c), are pale red, medium-and coarse-grained, massive and contain quartz (~35%), plagioclase (~27%), orthoclase (~30%), biotite (~5%), and minor zircon and titanite (~3%) (Figs. 4a, 4b). Samples from mafic-ultramafic complexes, collected at 36°55′43″N, 91°29′09″E ...
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... samples used for study were gained from outcrops in the southern and eastern Maxingdawannan area (Fig. 2). The monzogranites, collected from 36°55′56″N, 91°29′45″E (Figs. 2, 3a, 3c), are pale red, medium-and coarse-grained, massive and contain quartz (~35%), plagioclase (~27%), orthoclase (~30%), biotite (~5%), and minor zircon and titanite (~3%) (Figs. 4a, 4b). Samples from mafic-ultramafic complexes, collected at 36°55′43″N, 91°29′09″E (Figs. 2, 3b), are olivine gabbros and olivine pyroxenites. The olivine ...
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... (Fig. 2). The monzogranites, collected from 36°55′56″N, 91°29′45″E (Figs. 2, 3a, 3c), are pale red, medium-and coarse-grained, massive and contain quartz (~35%), plagioclase (~27%), orthoclase (~30%), biotite (~5%), and minor zircon and titanite (~3%) (Figs. 4a, 4b). Samples from mafic-ultramafic complexes, collected at 36°55′43″N, 91°29′09″E (Figs. 2, 3b), are olivine gabbros and olivine pyroxenites. The olivine gabbros are pale-grey, fine-to medium-grained, massive, and contain plagioclase (~40%), clinopyroxene (~30%), olivine (~25%), and minor talc and biotite (~5%) (Figs. 3d, 4c). The olivine pyroxenites are dark-grey, fineto medium-grained, massive, and contain clinopyroxene ...
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... The EKO is divided into the Northern, Middle, and Southern zones by North, Middle and South Kunlun faults from north to south (Fig. 1b). The Northern Zone consists mainly of Ordovician Qimantagh clasticvolcanic rocks and Devonian Maoniushan molasses intruded by Early Paleozoic or Early Mesozoic granites (Gao, 2013;Jiang et al., 1992;Yan et al., 2019). The Middle Zone is characterized by a large number of Phanerozoic granites (Dong et al., 2018;Zhang et al., 2023a) and Precambrian Jinshuikou and Binggou low to high-grade metamorphic rocks (Jiang et al., 1992;Li, 2015). ...
... Several Cu-Ni deposits with prospecting potential have also been found in subsequent prospecting, such as Shitoukengde, Akechukesai, Langmuri, and Gayahedonggou (Norbu et al., 2020;Li et al., 2022). Numerous datings have shown that these Cu-Ni deposits or sulfide-bearing intrusions were formed in the Silurian-Devonian (e.g., Wang et al., 2014a;Li et al., , 2021aPeng et al., 2016;Song et al., 2016;Yan et al., 2019aYan et al., , 2019bYan et al., , 2020, confirming a new Cu-Ni metallogenic period with great prospecting potential in China. ...
... Chondrite-normalized REE patterns (a; chondrite REE values from Boynton, 1984), U-Pb dating concordia plot with weight mean age (b) and Lu-Hf isotopes t (Ga)-ε Hf (t) (c; Ratio of crustal contamination is from Li et al., 2015b) of the zircon grains separated from the gabbro in Hatu Intrusion. The data of Silurian-Devonian intrusions in the EKO were cited from Wang (2014), Li et al. (2015a, 2021a), Peng et al. (2016),Yan et al. (2019aYan et al. ( , 2019bYan et al. ( , 2019cYan et al. ( , 2020 andJia et al. (2020). ...
... 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]. ...
... 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. ...
... 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]. [31]). ...
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.
... The most reliable method is to compare the Sr-Nd-Hf isotope compositions of leucosomes (anatectic zircons) and granites (magmatic zircons). The Hf isotope compositions of anatectic zircons in this study and magmatic zircons of granitoids in MKB are plotted in -1 and 19LMR11), compared with I-type granitoids (Liu et al. 2012a;Gao et al. 2014;Lei et al. 2018;Wang et al. 2018a), A-type granitoids (Gan 2014;Tian et al. 2016;Yan et al. 2016Yan et al. , 2019Xin et al. 2018;Wang et al. 2018b;Chen et al. 2020b), S-type granitoids (Wang et al. 2022) and adakite (Norbu et al. 2021) distributed in the MKB. Abbreviation: MKB, the Middle Kunlun belt. ...
... After ca. 410 Ma, the thickened middle Kunlun lithosphere delaminated (Figures 8d and 9), accompanied by high thermal gradients for extensive crustal anatexis and granulitefacies metamorphism in the MKB, continued molasse deposition (Table 1; Lu et al. 2010), and magmatic events including Xiarihamu mafic-ultramafic intrusions hosting one of the largest magmatic Ni-Cu sulphide deposits in the world (412-405 Ma; Li et al. 2015a;Song et al. 2016;Liu et al. 2018), widespread A-type granites in Wulonggou, Lalingzaohuo, Niangtang, Xiarihamu, Binggou and Maxingdawannan (Table 1; Chen et al. 2013a;Liu et al. 2013;Wang et al. 2013;Wang 2015;Tian et al. 2016;Yan et al. 2019;Chen et al. 2020b) and mafic dykes formed in continental rifting setting (411-393 Ma; Xiong et al. 2014;Yang et al. 2014;Dong et al. 2021). ...
Extensive crustal anatexis is common during the decompressional exhumation of deeply sub-ducted continental crust and the delamination of a collision-thickened orogenic lithosphere, indicating that determining the timing of partial melting can provide insights into the possible tectonic evolution during orogenic processes. An integrated study of petrology, zirconology and whole-rock geochemical compositions from migmatites and pegmatites in the Nageng, Langmuri and Wulonggou area of the East Kunlun orogenic belt, is presented in this study. The protoliths of these migmatites include Tonian sedimentary rocks and ca. 440 Ma arc-related dioritic rock. Together with previous studies, an extensive crustal anatexis event recorded by anatectic zircons occurred after ca. 410 Ma. In addition, hafnium isotope analyses indicate that the anatectic zircons may or may not inherit their Hf isotope compositions from protolith zircons during partial melting, depending on whether or not the garnet Hf contributes to the Hf budget of anatectic melt. Thus, the most reasonable method to trace the source of granite is to compare the Hf isotope composi-tion of anatectic zircon in migmatite and magmatic zircon in contemporaneous granite. By such method, anatectic melt produced by migmatites in this study could account for both penecon-temporaneous A- and I-type granites with high magmatic zircon εHf(t) values and S-type granites with low magmatic zircon εHf(t) values. As the extensive crustal anatexis is later than both metamorphic peak and amphibole-facies retrogression of high-pressure and ultrahigh-pressure (HP-UHP) metamorphic rocks, it is reasonable that post-collision orogenic collapse of the collision- thickened orogenic lithosphere as a result of delamination and asthenospheric upwelling occurred after ca. 410 Ma, which is also supported by contemporaneous granulite-facies metamorphism, molasse deposition, and magmatic events including Xiarihamu mafic-ultramafic intrusions, A-type granites, and mafic dykes formed in the continental rifting setting.
... (average 13.4%) by using the formula mentioned above. The ε Hf (t) values of the Sulurian-Devonian mafic-ultramafic complexes in the EKOB are generally positive, including Xiarihamu (Wang, 2014;Li et al., 2015;Peng et al., 2016), Akechukesai (Yan et al., 2020), Shuixiannan (Yan et al., 2019b), and Maxingdawannan (Yan et al., 2019c). They still reveal the origin of primary magma derived from the depleted mantle, although the primary magma suffers from crustal contamination. ...
Shitoukengde is an important magmatic Ni–Cu sulfide deposit in the Eastern Kunlun Orogenic Belt (EKOB). It comprises several mafic–ultramafic complexes and contains different kinds of mafic–ultramafic rocks. Lherzolite and olivine websterite are the most significant Ni–Cu-hosted rocks. The No. I complex hosts six Ni–Cu ore bodies, and the depth of the intrusion has great exploration potential. Therefore, geochronology, geochemistry, and mineral chemistry of the Shitoukengde deposit were studied to constrain its mineralization time, parental magma composition, and crustal contamination process. Zircon U–Pb dating of olivine websterite shows the magmatic origin (Th/U = 0.40–1.05) and an age of 418.1 ± 8.7 Ma (MSWD = 0.01), which is coeval with the Xiarihamu, Akechukesai, and other Cu–Ni deposits in the EKOB. Geochemically, the mafic–ultramafic rocks are characterized by low SiO2, TiO2, and Na2O + K2O and high MgO (9.49–36.02%), with Mg# values of 80–87. They are relatively enriched in LREE and LILEs (e.g., K, Rb, and Th), with weakly positive Eu anomalies (δEu = 0.83–2.26), but depleted in HFSEs (e. g., Ta, Nb, Zr, and Ti). Based on the electron microprobe analyses, all of the olivines are chrysolite (Fo = 81–86), and the pyroxenes are dominated by clinoenstatite (En = 80–84) and augite (En = 49–55) in the mafic–ultramafic rocks. Therefore, the composition of parental magma is estimated to be picritic basaltic magma with SiO2 and MgO concentrations of 54.47 and 13.95%, respectively. The zircon εHf(t) values of olivine websterite vary from −0.8 to 4.6, with a TDM1 of 0.84–1.06 Ga, indicating that the parental magma was derived from relatively high degree partial melting (about 13.4%) of a depleted mantle source and experienced significant crustal contamination (about 12–16%). We propose that crustal assimilation, rather than fractional crystallization, played a key role in triggering the sulfide saturation of the Shitoukengde deposit, and the metallogenesis of “deep liquation–pulsing injection” is the key mechanism underlying its formation. The parental magma, before intruding, underwent liquation and partial crystallization at depth, partitioning into barren, ore-bearing, and ore-rich magma and ore pulp, and was then injected multiple times, resulting in the formation of the Shitoukengde Ni–Cu deposit.
... Generally, ultramafic rocks contain no zircon due to insufficient silicon and zirconium components, and therefore, the zircon grains are mostly relict or xenogenous (Lesnov et al., 2015;Olierook et al., 2018;Yan et al., 2019). When the ultramafic rocks were influenced by a metamorphic / thermal event, it is possible to grow new zircon from the fluid or melt (Hoskin and Black, 2000;Grieco et al., 2001;Hoskin and Schaltegger, 2003;Smith and Griffin, 2005;Katayama et al., 2003;Shen et al., 2017). ...
The Miyun area is located in the northwestern border of the Eastern Block of the North China Craton, where the metaultramafic rocks occur as intrusive bodies, some of which display cumulate features. The metaultramafic rock is (olivine-bearing) amphibole websterite and two generations of mineral assemblage have been identified: the magmatic mineral assemblage -consists- of clinopyroxene + orthopyroxene ± olivine ± spinel ± pyrite, whereas the subsequent metamorphic mineral assemblage comprises of hornblende + serpentine + chlorite + magnetite + zircon ± biotite ± calcite ± chromite ± calcite ± garnet. The metamorphic P-T conditions are estimated to be ~ 600–630 °C/4–6 kbar, which belongs to amphibolite facies and medium-P/T facies series. U-Pb dating of metamorphic zircon and ⁴⁰Ar/³⁹Ar dating of metamorphic hornblende indicate that the metamorphic event occurred at ~ 1.85–1.82 Ga. These data suggest that the Miyun area involved in the late Paleoproterozoic subduction-collision between the Eastern and Western Blocks, and the metamorphism possibly occurred at upper-middle crustal level with fluids.
... Compared to its adjacent areas, collisional magmatism (and thus collision-related granitoids) is particularly developed in the QMB ( Fig. 2A). Moreover, most of the reported skarn and porphyry deposits from the EKO are clustered in the QMB, which makes it the most promising exploration target for the porphyry Cu deposits in the northern QTP (Hao et al., 2015;Qu et al., 2019;Xia et al., 2015a;Yan et al., 2019b;Yao et al., 2017;Yu et al., 2015;Zhong et al., 2018b;Zhong et al., 2018c;Fig. 2A). ...
The recent discovery of numerous large porphyry Cu deposits in the southern Qinghai-Tibet Plateau shows that porphyry Cu deposits can be hosted in magmatic suites in collisional settings. However, in contrast, only a few small porphyry Cu deposits have so far been discovered in association with collision-related granitoids in the northern Qinghai-Tibet Plateau. This raises questions about the origin of collision-related magmas and their mineralization potential. In this contribution, we comprehensively synthesize whole-rock geochemical and isotopic data on collision-related intrusions from the Qimantagh Metallogenic Belt in the northern Qinghai-Tibet Plateau, which hosts many skarn polymetallic deposits but only a few, small porphyry Cu-Mo deposits. This, combined with newly obtained zircon trace element data, provides a high-quality database that can yield insights on the nature and origin of the magmatic suites as well as their fertility in terms of Cu mineralization. Two volumetrically dominant intrusive suites are identified in the Qimantagh Metallogenic Belt: 435-370 Ma granitoids (Suite I) and 245-196 Ma granitoids (Suite II). They formed during syn- to post-collisional stages of the Caledonian and Hercynian-Indosinian Orogenies, respectively. In contrast, arc magmatic rocks are relatively scarce. Both Suites I and II are characterized by low zircon Ce/Ce* and Eu/Eu* values, low whole-rock Sr/Y and Eu/Eu* values with arc-like features (e.g., depletion of Nb and Ta). Furthermore, both suites display some evolved Sr-Nd-Hf isotopic values (e.g., εNdi = -8.1 to 0.1), with the majority of samples characterized by Paleo- to Meso-Proterozoic two-stage Nd and Hf model ages. These features suggest that the parental magmas of the two suites were probably derived from subduction fluid-modified mantle sources which underwent significant crustal AFC processes during magma ascent. The relative scarcity of arc magmatic rocks and the prevalence of collisional magmatism during the Caledonian and Hercynian-Indosinian Orogenies in the Qimantagh Metallogenic Belt can be explained by pre-collisional, flat-slab subduction and subsequent slab breakoff during collision, the later triggering asthenosphere upwelling and extensive magmatism in collisional settings. Compared to fertile plutons in some large porphyry Cu deposits worldwide, especially those in the Gangdese Metallogenic Belt, the two suites in the Qimantagh Metallogenic Belt have low magmatic oxidation states and low water content which inhibited the formation of large porphyry Cu deposits. Thus, skarn polymetallic deposits (probably as well as small porphyry Cu-Mo deposits) rather than large porphyry Cu deposits should be targeted during future mineral exploration in the northern Qinghai-Tibet Plateau, since such deposits do not necessarily need a parental magma with high oxidation state and water content.
... Contamination and fractional crystallization usually are very common within the continental setting during the invasion of mantle-derived magma (Yan et al., 2019;Spera and Bohrson, 2004;Thorpe et al., 1984). Rocks contaminated by crustal materials or subduction fluids are characterized by significant depleted of Nb, Ta and Ti (Xiong et al., 2020;Ernst, 2014;Rudnick and Gao, 2003;Frey et al., 2002). ...
Mafic dyke swarm is widely developed in Proterozoic continental lithosphere. The Gangou diabase dyke from the Xixia area, intruded into the Douling complex of the South Qinling belt, yields zircon UPb age of 731 Ma. It has low SiO2 content (49.02 wt.%-49.37 wt.%) and Mg# (34.0–37.7) and shows characteristics of subalkaline tholeiite series. They show high ΣREE (155.5×10 6–184.7×106), weak negative Eu anomaly (SEu=0.88-0.93), slight depletion of Nb and Ta, and enrichment of LILE. Their major and trace element, Sr-Nd-Pb isotope and clinopyroxene compositions indicate that it originated from the partial melting of the asthenospheric mantle within-plate extension setting and was slightly contaminated by crust compositions. The similarities of formation age, petrogenesis, source characteristic and tectonic setting for Gangou diabase with mafic dykes in Wudang Block and mafic volcanic rocks in Yaolinghe Group indicate that the South Qinling belt underwent strong continental extension in Neoproterozoic during 796–685 Ma most likely correspondence to the breaking-up of the Rodinia supercontinent.
... The Neoproterozoic magmatic rocks are mainly S-type and A-type granites with emplacement ages ranging from 1007 to 870 Ma (Chen et al., 2015a;He et al., 2016bHe et al., , 2018Meng et al., 2017), and these rocks are distributed mainly in the Central Kunlun Belt . The rocks are dominantly A-type granites with subordinate I-and S-type granites Wang et al., 2018b;Xin et al., 2018;Xiong et al., 2015;Yan et al., 2019;Zhao et al., 2017) Ren et al., 2016;Xiong et al., 2014Xiong et al., , 2016aZhang et al., 2018;Zhao et al., 2018) are volumetrically predominant in the EKOB (~25,000 km 2 ) and constitute half of the total outcrop area of all granitoids in this region (Fig. 1b;Liu et al., 2004;Mo et al., 2007). Their formation was associated with to the closure of the Anyemaqen-Kunlun Ocean (a branch of the Paleo-Tethys Ocean) and subsequent continental collision Ma et al., 2015;Ren et al., 2016;Xiong et al., 2014Xiong et al., , 2016a. ...
Late Triassic granitoids containing abundant mafic microgranular enclaves (MMEs) occur widely in the Eastern Kunlun Orogenic Belt (EKOB). In this work, we present mineral chemistry, zircon U-Pb ages and Lu-Hf isotopes, whole-rock chemistry and Sr-Nd isotope compositions of the MMEs and host granodiorite from the Huda pluton in the Elashan area within the easternmost domain of the EKOB. These rocks contain inherited (Meso- to Neoproterozoic) and xenocrystic (ca. 240 Ma) zircon grains that yield apparent older ages, whereas the magmatic zircons from MMEs and granodiorite yield similar weighted mean ages around 224 Ma, which are interpreted as their crystallization ages. The MMEs have low SiO2 but high TiO2, TFe2O3, CaO, MgO and MnO concentrations with relatively high Mg# values (48-54) and 100MnO/(MnO+MgO+TFe2O3) ratios (1.2-1.6). They display identical Sr-Nd-Hf isotope compositions to the host granite. Combined with petrological evidence, we suggest that the MMEs are cognate cumulates that formed by pressure quenching during the late stage of magma evolution from the same parental magma of the host granodiorite, rather than a magma mixing origin. The granodiorite is calc-alkaline to high-K calc-alkaline, metaluminous I-type granite. They show relatively low SiO2 and MnO, but high MgO, Al2O3, CaO and TFe2O3 contents with Mg# values of 45-50. They are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), such as Rb, Th, K and Pb, and are depleted in P and high field strength elements (HFSE) including Nb, Ta and Ti. These rocks display slightly negative Eu anomalies and low Sr/Y and La/Yb ratios. Together with the rim-ward chemically evolved nature of some phenocrysts, the comparatively high initial Sr isotope (0.70888-0.70912), low whole-rock εNd(t) (-5.6 to -6.0) and zircon εHf(t) (-3.3 to -0.1) values, and low Nb/Th (0.11-0.26) and Ta/U (0.53-0.68) ratios, we suggest that the granodiorite magma was sourced from the lower crust. Considering their comparatively young two-stage Nd and Hf model ages (1.42-1.49 Ga and 1.13-1.42 Ga, respectively) and same trace element character with the juvenile crust beneath the EKOB, we interpret the juvenile lower crust as the dominant source rocks for the granodiorite. Based on our data and regional geological evidence, we suggest that the partial melting of juvenile crust resulted from delamination-related asthenosphere mantle upwelling. The latter process resulted in extensive melting of the lower crust, producing a major Late Triassic magmatic flare-up event in the EKOB.
... The Middle EKO consists mainly of Precambrian crystalline basement (the Proterozoic Jinshuikou and Binggou groups) and is distinguished by widespread phanerozoic granitic magmatism. The South EKO comprises mainly the Mesoproterozoic Wanbaogou Group, which is a suite of mostly (Wang et al., 2014); Shitoukengde Cu-Ni deposit ; Detangou, Xiangyanggouxi and Shuixiannan Cu-Ni deposits (Yan et al., 2019b); Maxingdawannan Cu-Ni deposit (Yan et al., 2019a); Bariqiligounan Cu-Ni deposit (Unpublished). J.-m. ...
The recently discovered Akechukesai mafic–ultramafic complex is located in the East Kunlun Orogenic Belt, northern Tibet Plateau, China. Two mafic–ultramafic complexes (Akechukesai I and Ⅱ) intrude marble of the Cambrian–Ordovician Tanjianshan Group. Cu–Ni sulfide mineralization occurs in these complexes. Pyroxenite in the Akechukesai-I complex has an age of 422 ± 10 Ma(1σ), similar to that of the Xiarihamu and Shitoukengde Cu–Ni deposits of the East Kunlun area. The positive εHf(t) values (1.7–4.9) and SiO2, TiO2, and Al2O3 contents of clinopyroxene from pyroxenite suggest that the parental magma of the Akechukesai-I complex was derived from depleted mantle composed of garnet lherzolite and spinel lherzolite in varying proportions. Pyroxenite of the Akechukesai-I complex has (⁸⁷Sr/⁸⁶Sr)i ratios of 0.70993–0.71405, εNd(t) values of −1.97 to −6.64, (²⁰⁶Pb/²⁰⁴Pb)i ratios of 17.113–18.994, (²⁰⁷Pb/²⁰⁴Pb)i ratios of 15.548–15.673, and (²⁰⁸Pb/²⁰⁴Pb)i ratios of 37.066–38.650, which together indicate a depleted mantle source with 18–35 wt.% upper-crustal contamination. δ³⁴S values of sulfide minerals are 5‰–11.5‰ with S/Se ratios of ore-bearing pyroxenite being in the range 3738–15,501, both being higher than mantle values (−2‰ to +2‰ and 2850–4350, respectively) and indicating the addition of crustal S. The incorporation of primitive magma into the marble host during ascent caused a reduction in sulfide solubility owing to increased oxygen fugacity of the magma, leading to S saturation. These observations and the geodynamic setting indicate that the complex is a favorable environment for mineralization.
