Magma Plumbing System of Emeishan Large Igneous Province at the End-Permian: Insights from Clinopyroxene Compositional Zoning and Thermobarometry

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Article Magma Plumbing System of Emeishan Large Igneous Province at the End-Permian: Insights from Clinopyroxene Compositional Zoning and Thermobarometry

1, , 2,3, , 1 4 Jun-Hao Hu * †, Jing-Wen Liu * †, Tao Song and Bai-Shun Shi 1 College of Urban and Rural Planning and Architectural Engineering, Guiyang University, Guiyang 550005, China; [email protected] 2 Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China 3 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China 4 College of Earth Sciences, Jilin University, Changchun 130061, China; [email protected] * Correspondence: [email protected] (J.-H.H.); [email protected] (J.-W.L.) These authors contributed equally. † Received: 1 August 2020; Accepted: 28 October 2020; Published: 2 November 2020

Abstract: The end-Permian Emeishan Large Igneous Province (ELIP) in SW China is widely accepted to have formed by mantle plume activities, forming voluminous ﬂood basalts and rare picrites. Although many studies were performed on the petrogenesis and tectonic setting, the detailed conditions and processes within the magma chamber(s) remain unsolved. In this study, we studied the sector-/oscillatory-zoned clinopyroxene (Cpx) phenocrysts and performed Cpx-liquid thermobarometric calculation to constrain the physicochemical processes within the magma chambers. The results show that Cpx phenocrysts from the high-Mg basalts were crystallized at 4–27 (average 17) km, whilst those from the low-Mg basalt were crystallized at 0–23 (average 9) km depth. The sector and oscillatory Cpx zoning in the high-Mg basalts show that the magma had experienced undercooling and multistage recharge events in the deep-staging chamber(s). The magma replenishments may have eventually led to the eruption of high-Mg basalts, and magma ascent to the upper crust for further fractionation to form the low-Mg basalts and maﬁc intrusions.

Keywords: mineral zoning; clinopyroxene phenocryst; emeishan large igneous province (ELIP); magma plumbing system

1. Introduction The research on the large igneous provinces (LIPs) is key to understanding continental uplift and breakup, and the associated environmental change, mass extinction, and magmatic Cu-Ni-PGE and Fe-Ti-V metallogeny [1]. For the end-Permian Emeishan LIP in SW China, several studies have shown that the flood basalts and picrites are genetically link to the regional magmatic Cu-Ni-PGE and Fe-Ti-V metallogeny [2–10]. Although the depth of the staging magma chamber(s) has been constrained through studying the volcanic rocks [11], the deep-chamber processes are yet to be well understood. Therefore, it is necessary to establish the ELIP magma plumbing system and its metallogenic link. Compositional and textural zoning of minerals are not only influenced by the magmatic physicochemical changes [12], but also by the microscopic crystal-scale kinetics [13–15]. Therefore, the zoning characters of igneous minerals have been used to track magma chamber processes [16–22]. Different minerals have a different textural and compositional response to the surrounding magmatic

Minerals 2020, 10, 979; doi:10.3390/min10110979 www.mdpi.com/journal/minerals Minerals 2020, 10, 979 2 of 19

change,Minerals which 2020, 10 is, x reflectedFOR PEER REVIEW in the formation or (partial) dissolution of the growth zones2 of [2014 ,23]. Clinopyroxene (Cpx) zoning has been widely documented in phenocrysts of mafic-intermediate volcanic22]. Different rocks [24 minerals], and usedhave toa different reveal thetextural magma and plumpingcompositional system response owning to the to surrounding the low lattice diffusionmagmatic rate ofchange, the Cpx which zoning is reflected [25–32 in]. Sectorthe formation and oscillatory or (partial) zoning dissolution of major of the and growth trace zones elements in pyroxenes,[14,23]. Clinopyroxene and their relations (Cpx) zo toning magma has been evolution widely havedocumented been well in phenocrysts established of for mafic- synthetic and naturalintermediate crystals volcanic [33– 43rocks]. Although [24], and used the to magma reveal the chamber magma conditions plumping sy (e.g.,stem pressure-temperatureowning to the low lattice diffusion rate of the Cpx zoning [25–32]. Sector and oscillatory zoning of major and trace (P-T) and magma composition) also have strong effects on the formation of Cpx compositional elements in pyroxenes, and their relations to magma evolution have been well established for zoning,synthetic sector and zoning natural is closelycrystals related [33–43]. to Although the kinetic the emagmaffects which chambe mayr conditions indicate (e.g., the rate pressure- of magma ascenttemperature [14,34,37, 44(P-T),45 ].and Meanwhile, magma composition) Cpx oscillatory also have zoning strong can effects also on reveal the formation the physiochemical of Cpx conditionscompositional and their zoning, changes sector/fluctuations zoning is closely during related magma to crystallization,the kinetic effects including which may magma indicate convection the and replenishment,rate of magma ascent and crystal-melt [14,34,37,44,45]. interactions Meanwhile, along Cpx the oscillatory crystal boundary zoning can layer also [ 18reveal,38,39 the,46 –50]. Moreover,physiochemical the Cpx-liquid conditions thermobarometer and their changes/fluctu has relativeations advantages during magma (e.g., crystallization, the range of the including application and precisionmagma convection in P-T and calculation) replenishment, in thermobarometric and crystal-melt interactions calculation along compared the crystal boundary to the olivine- layer or plagioclase-based[18,38,39,46–50]. ones Moreover, [51]. Therefore, the Cpx-liquid in this thermoba study, werometer investigate has relative the compositional advantages (e.g., zoning the range of the Cpx phenocrystsof the application from the and ELIP precision high-Mg in andP-T calculation) low-Mg flood in thermobarometric basalts. By using calculation electron probecompared microanalysis to the olivine- or plagioclase-based ones [51]. Therefore, in this study, we investigate the compositional (EPMA) and mapping of major elements, and Cpx-liquid thermobarometry, we established a reliable zoning of the Cpx phenocrysts from the ELIP high-Mg and low-Mg flood basalts. By using electron magmaprobe plumbing microanalysis system (EPMA) for the and ELIP mapping staging of chamber.major elements, and Cpx-liquid thermobarometry, we established a reliable magma plumbing system for the ELIP staging chamber. 2. Geological Background The2. Geological ELIP exposed Background in southwestern China and northern Vietnam contains a wide variety of magmaticThe ELIP rocks exposed including in southwestern mafic-ultramafic China and intrusions, northern granitoids,Vietnam contains flood a basalts wide variety and picritesof (Figuremagmatic1b) [ 52 ].rocks Geochemical including mafic-ultramafic studies suggested intrusio thatns, the granitoids, intrusive flood and extrusivebasalts and rocks picrites in the(Figure ELIP are genetically1b) [52]. linked Geochemical [53–55]. studies The volcanic suggested succession that the overliesintrusive theand Lower extrusive Permian rocks in Maokou the ELIP Formation are (Fm.)genetically limestone, linked which [53–55]. in turn The is overlain volcanic bysuccession the Upper overlies Permian the Lower Xuanwei Permian Fm. sandstone.Maokou Formation Radiometric dating(Fm.) ofmafic-ultramafic limestone, which intrusions in turn is constrained overlain by the the ELIP Upper emplacement Permian Xuanwei at ~260 Ma,Fm. coevalsandstone. with the Radiometric dating of mafic-ultramafic intrusions constrained the ELIP emplacement at ~260 Ma, end-Guadalupian mass extinction [9,10,56–58]. coeval with the end-Guadalupian mass extinction [9,10,56–58].

FigureFigure 1. (a )1. Geologic (a) Geologic map map showing showing the the simplified simplified tectonic tectonic framework framework ofof China.China. ( (bb)) Distribution Distribution of of the late-Permianthe late-Permian Emeishan Emeishan flood flood basalts basalts and coevaland coeval mafic mafic intrusions, intrusions, modified modified afterafter Yu et al. al. (2017) (2017) [6]. (c) Sample[6]. (c) locationsSample locations in this in study. this study. Minerals 2020, 10, 979 3 of 19

The ELIP volcanic succession is exposed across an area of over 3 105 km2 [52,57]. Based on × the whole-rock Ti/Y ratios, the ELIP volcanic rocks have been classified into the high-Ti and low-Ti series [52]. The high-Ti basalts (Ti/Y > 500) are widespread across the ELIP, whereas the low-Ti basalts (Ti/Y < 500) are largely confined in the ELIP central zone [59]. Picrites are locally exposed in the western (Dali, Lijiang, Binchuan, Yongsheng, Ertan, Muli) and southern (Jinping-Song Da) parts of the ELIP, where they (3–50 m thick) are found interbedded with basaltic flows [6,55,60,61]. The high-Ti picrites have higher Nb contents than their low-Ti counterparts [55,62]. The two major ore deposit types in the ELIP, i.e., magmatic Fe-Ti-V oxide and Ni-Cu-PGE sulfide, were suggested to be genetically related to the high-Ti and low-Ti magma series, respectively [5,61].

3. Sampling and Analytical Techniques Ten samples were collected from Tanglanghe and Shiman along the Dali-Lijiang region of the ELIP (Figure1c). Systematic sampling across the volcanic stratigraphy was not possible due to the poor exposure and severe weathering/alteration of the lava ﬂows, yet the samples collected still retain clear and fresh Cpx phenocrysts. Whole-rock major element compositions were measured by an X-ray ﬂuorescence spectrometer (XRF) at the ALS Laboratory (Guangzhou) using fused lithiumtetraborate glass pellets. Analytical precision determined on the standard SARM-45 is generally 1–5%. The equilibrium melt composition is critical for accurate mineral-melt thermobarometric P-T calculation. Therefore, the volcanic groundmass was separated and analyzed to represent the melt equilibrated with the phenocrysts. For the analysis, 2–3 kg of the least-altered rock sample was crushed into 40–60 mesh in an agate mortar, and the Cpx phenocrysts were carefully picked out under a binocular microscope. The separated groundmass (~5 g) was milled into 200 mesh. Major elements of the groundmass were measured by XRF on fused glass disk at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Analytical uncertainties are 1–3% for elements of over 1 wt% and ~10% for elements of below 1 wt%. The trace element contents of the whole-rock were measured by solution inductively coupled plasma mass spectrometry (ICP-MS) using the technique of Qi et al. (2000) [63] at the Institute of Geochemistry, Chinese Academy of Sciences (IGCAS). The standard samples (e.g., BCR-2, BHVO-2) were used for analytical quality control, with precision for most elements analyzed better than 5%. The major element composition data for the whole-rock and groundmass samples were back-calculated to 100 wt% anhydrous values (Supplementary Tables S1 and S2). Major element contents of the Cpx phenocrysts were analyzed with a JEOL JXA-8100 electron microprobe at the State Key Laboratory for Ore Deposits Geochemistry, IGCAS. The measurement was performed with a 15-kV acceleration voltage, 20 nA beam current, and 3 µm spot diameter. The detection limit for major elements is 0.01 wt%, and the analytical reproducibility is within 2%. EMPA results are listed in Supplementary Table S3. Quantitative wavelength-dispersive spectrometric (WDS) analysis for the zoned Cpx phenocryst was conducted using an accelerating voltage of 15 kV, a beam current of 20 nA, and a spot size of 1 µm.

4. Results

4.1. Petrography The samples YY13-109, 111, 112, 113, and 123 are more porphyritic with 20–50% olivine phenocrysts and <5% Cpx phenocrysts. The olivine phenocrysts are 2–3 mm large and commonly serpentinized along its margin and micro-fractures. Some olivine crystals also contain small euhedral chromite inclusions (Figure2a). The Cpx phenocrysts are usually euhedral and around 2 mm in size, and are generally fresher than the olivine phenocrysts (Figure2b–d). The ﬁne-grained groundmass is composed of pyroxene, plagioclase and minor Fe-Ti oxides, among which some pyroxene and plagioclase are partially altered to chlorite, talc, and clay minerals. The samples of YY13-2, 115, 120, 122, 125 are less porphyritic with <5% Cpx phenocrysts. The Cpx phenocrysts are euhedral and generally ~2 mm in size (Figure2e–h). Some crystals show compositional zoning under the microscope (Figure2f). Minerals 2020, 10, 979 4 of 19

Minerals 2020, 10, x FOR PEER REVIEW 4 of 20 Rare chromite inclusions were also identiﬁed in the Cpx phenocrysts (Figure2h). The microcrystalline 2h). The microcrystalline groundmass contains mainly pyroxene and plagioclase, and minor Fe-Ti groundmass contains mainly pyroxene and plagioclase, and minor Fe-Ti oxides. oxides.

FigureFigure 2. 2.Representative Representative BSE BSE and and microphotographsmicrophotographs (plane (plane-polarized-polarized light) light) of of phenocrysts phenocrysts in instudied studied samples.samples. (a ()a) Olivine Olivine phenocrystphenocryst in in high-Mg high-Mg basalt. basalt. (b– (db)– Cpxd) Cpx phenocryst phenocryst in high-Mg in high-Mg basalt. basalt. (e–h) Cpx (e– h) Cpxphenocryst phenocryst in low-Mg in low-Mg basalt. basalt. (The red (The square red denotes square denotesthe EPMA the analytical EPMA spot analytical for major spot elements. for major The number beside the red square represents the Mg# [MgO/(MgO + FeO)]. Ol = olivine, Cpx = elements. The number beside the red square represents the Mg# [MgO/(MgO + FeO)]. Ol = olivine, clinopyroxene, Sp = spinel). Cpx = clinopyroxene, Sp = spinel). Minerals 2020, 10, x FOR PEER REVIEW 5 of 20 Minerals 2020, 10, 979 5 of 19 Minerals 2020, 10, x FOR PEER REVIEW 5 of 20 4.2. Whole-Rock Major and Trace Element Compositions 4.2.4.2. Whole-RockWhole-RockThe major MajorMajoroxide and andcontents TraceTrace Element Elementof the analyzed Compositions Compositions samp les are listed in Supplementary Table S1 and shown in Figure 3 and Supplementary Figure S1. We classified the samples into the high-Mg (MgO TheThe major major oxide oxide contents contents of theof the analyzed analyzed samples samp areleslisted are listed in Supplementary in Supplementary Table S1Table and shownS1 and > 18 wt%) and low-Mg basalt (MgO < 18 wt%) groups using the standard suggested by Le Bas et al. inshown Figure in3 andFigure Supplementary 3 and Supplementary Figure S1. Figure We classiﬁed S1. We theclassified samples the into samples the high-Mg into the (MgO high-Mg> 18 (MgO wt%) (2000) [64]. Both groups are high-Ti basalt with Ti/Y > 500 (Supplementary Table S1). According to and> 18 low-Mg wt%) and basalt low-Mg (MgO basalt< 18 wt%)(MgO groups< 18 wt%) using groups the standard using the suggested standard by suggested Le Bas et by al. Le (2000) Bas et [64 al.]. the TAS and Nb/Y vs. Zr/Ti diagrams (Figure 3), the samples are calc-alkaline to tholeiitic. The high- Both(2000) groups [64]. Both are high-Ti groups basalt are high-Ti with Ti basalt/Y > 500 with (Supplementary Ti/Y > 500 (Supplementary Table S1). According Table S1). to According the TAS and to Mg basalts have higher MgO contents (18.12–24.82 wt%) and Mg# ((Mg/Mg + Fetotal) × 100 = 74 – 79) Nbthe/Y TAS vs. Zrand/Ti Nb/Y diagrams vs. Zr/Ti (Figure diagrams3), the samples (Figure are3), the calc-alkaline samples are to tholeiitic. calc-alkaline The to high-Mg tholeiitic. basalts The havehigh- than the low-Mg basalts (MgO = 8.77–12.33# wt%; Mg# = 56–65) (Supplementary Table S1, higherMg basalts MgO have contents higher (18.12–24.82 MgO contents wt%) (18.12–24.82 and Mg ((Mg wt%)/Mg +andFe totalMg)# ((Mg/Mg100 = 74 + –Fe 79)total than) × 100 the =low-Mg 74 – 79) Supplementary Figure S1). The TiO2 and Al2O3 contents correlate negatively× with Mg#, while the Ni basaltsthan the (MgO low-Mg= 8.77–12.33 basalts wt%; (MgO Mg #= =8.77–12.3356–65) (Supplementary wt%; Mg# = Table56–65) S1, (Supplementary Supplementary FigureTable S1).S1, and Cr contents display positive correlations with Mg#, respectively# (Supplementary Figure S1). TheSupplementary TiO2 and Al Figure2O3 contents S1). The correlate TiO2 and negatively Al2O3 contents with Mgcorrelate, while negatively the Ni and with Cr Mg contents#, while display the Ni positiveand Cr contents correlations display with positive Mg#, respectively correlations (Supplementary with Mg#, respectively Figure S1). (Supplementary Figure S1).

Figure 3. (a) Total alkali (Na2O + K2O) versus SiO2 (TAS); (b) Nb/Y versus Zr/Ti(after Le Maitre et al. [65]. The diagram for sub-alkaline rocks is from Pearce 1996 [66]). FigureFigure 3.3. ((aa)) TotalTotal alkalialkali (Na(Na2O + KK2O)2O) versus versus SiO SiO2 (TAS);2 (TAS); (b ()b Nb/Y) Nb/ Yversus versus Zr/Ti(after Zr/Ti(after Le Le Maitre Maitre et etal. al.[65]. [65 The]. The diagram diagram for for sub-alkaline sub-alkaline rocks rocks is isfrom from Pearce Pearce 1996 1996 [66]). [66]). The high-/low-Mg basalt groups have distinctive incompatible element compositions. The high- Mg basalts are marked by lower REE concentrations than the low-Mg basalts (Supplementary Table TheThe high- high-/low-Mg/low-Mg basalt basalt groups groups have have distinctive distinctiv incompatiblee incompatible element element compositions. compositions. The The high-Mg high- S1). In the chondrite-normalized REE diagrams, all the basalts exhibit steeply right-sloping patterns basaltsMg basalts are marked are marked by lower by lower REE REE concentrations concentrations than than the low-Mg the low-Mg basalts basalts (Supplementary (Supplementary Table Table S1). with distinct LREE enrichment (Figure 4a). In the primitive mantle-normalized multi-element InS1). the In chondrite-normalized the chondrite-normalized REE diagrams,REE diagrams, all the all basalts the basalts exhibit exhibit steeply steeply right-sloping right-sloping patterns patterns with diagrams, both high-/low-Mg basalts show OIB-like patterns except for the LILE (e.g., Rb, Ba), and distinctwith distinct LREE enrichmentLREE enrichment (Figure 4(Figurea). In the 4a). primitive In the mantle-normalizedprimitive mantle-normalized multi-element multi-element diagrams, display a negative anomaly in Sr and positive anomaly in Ti (Figure 4b). The analyzed basalts have bothdiagrams, high-/ low-Mgboth high-/low-Mg basalts show basalts OIB-like show patterns OIB-like except patterns for theexcept LILE for (e.g., the LILE Rb, Ba), (e.g., and Rb, display Ba), and a much higher Nb/U ratios (high-Mg basalt: 42.9–46.9; low-Mg basalt: 49.9–71.4) than that of the negativedisplay a anomaly negative inanomaly Sr and in positive Sr and anomalypositive anomaly in Ti (Figure in Ti4 b).(Figure The 4b). analyzed The analyzed basalts havebasalts much have average bulk continental crust (12.09, [67]) (Supplementary Table S1). Moreover, the Th/Nb ratio of highermuch Nbhigher/U ratios Nb/U (high-Mg ratios (high-Mg basalt: 42.9–46.9;basalt: 42.9–46. low-Mg9; low-Mg basalt: 49.9–71.4)basalt: 49.9–71.4) than that than of the that average of the the basalt samples (0.07–0.10) is comparable to that of the average OIB (0.083, [68]) (Supplementary bulkaverage continental bulk continental crust (12.09, crust [67 (12.09,]) (Supplementary [67]) (Supplementary Table S1). Table Moreover, S1). More the Thover,/Nb the ratio Th/Nb of the ratio basalt of Table S1). samplesthe basalt (0.07–0.10) samples is(0.07–0.10) comparable is comparable to that of the to average that of the OIB average (0.083, [OIB68]) (Supplementary(0.083, [68]) (Supplementary Table S1). Table S1).

Figure 4. (a) Chondrite-normalized REE patterns of the low-Mg and high-Mg basalt. (b) Primitive Figure 4. (a) Chondrite-normalized REE patterns of the low-Mg and high-Mg basalt. (b) Primitive mantle-normalizedmantle-normalized diagrams of of incompatible incompatible elem elementsents for for the thelow-Mg low-Mg and andhigh-Mg high-Mg basalt. basalt. (The Figure 4. (a) Chondrite-normalized REE patterns of the low-Mg and high-Mg basalt. (b) Primitive (TheChondrite Chondrite and andPrimitive Primitive mantle mantle values values from from Sun Sunand andMcDonough McDonough (1989) (1989) [68]). [68 ]). mantle-normalized diagrams of incompatible elements for the low-Mg and high-Mg basalt. (The Chondrite and Primitive mantle values from Sun and McDonough (1989) [68]). Minerals 2020, 10, 979 6 of 19 Minerals 2020, 10, x FOR PEER REVIEW 6 of 20

4.3. Clinopyroxene Clinopyroxene Phenocryst Phenocryst Compositions Compositions The CpxCpx phenocrystsphenocrysts from from all all the the basalt basalt samples samples belong belong to the to augite-diopside-solidthe augite-diopside-solid solution solution series seriesin the Wo-En-Fsin the Wo-En-Fs diagram (Figurediagram5). The(Figure Cpx 5). compositional The Cpx compositional variation is generally variation straightforward, is generally # # # # straightforward,as illustrated in theas illustrated Mg . The in Cpx the phenocrysts Mg . The Cpx show phenocrysts positive Mgshowvs. positive Cr2O3 Mgtrend,vs. andCr2O negative3 trend, # # andtrends negative between trends Mg betweenand TiO 2Mg, Al 2andO3 (Supplementary TiO2, Al2O3 (Supplementary Figure S2). Moreover,Figure S2). the Moreover, Cpx phenocrysts the Cpx phenocrystsin high-Mg basaltsin high-Mg have lowerbasalts Al have2O3 contentslower Al (0.51–2.292O3 contents wt%) (0.51–2.29 than those wt%) in low-Mgthan those basalts in low-Mg (Al2O3: basalts1.71–7.51 (Al wt%)2O3: 1.71–7.51 (Supplementary wt%) (Supplementary Figures S2 and Figures S3). S2 and S3).

Figure 5. 5. TheThe pyroxene pyroxene composition composition diagram diagram (Di—diopside, (Di—diopside, Hehedenbergite, Hehedenbergite, Au—Augite, Au—Augite, Pi— Pigeonite,Pi—Pigeonite, ClEn—clinoenstatite, ClEn—clinoenstatite, ClFs—clinoferrosilite, ClFs—clinoferrosilite, Morimoto, Morimoto, 1988 1988 [69]). [69 ]).

# The Cpx phenocrysts are mainly normal-zoned, which is characterized by decreasing Mg# and Cr from the core to rim, although rare reverse-zonedreverse-zoned Cpx grains were also found (Supplementary Table S3).S3). Clear oscillatoryoscillatory andand sector sector zoning zoning were were observed observed in in the the Cpx Cpx phenocrysts phenocrysts from from the the high-Mg high- Mgbasalt basalt samples samples (e.g., (e.g., YY13-111 YY13-111 and 123).and 123). The CpxThe phenocrystCpx phenocryst cut perpendicularly cut perpendicularly the c-axis the andc-axis off andthe offcenter, the center, revealing revealing clear zonation clear zonation of Mg, Feof Mg, and Fe Al and contents Al contents (Figure 6(Figureb–d). The 6b–d). compositional The compositional profile profile(from A(from to B) A of to this B) of Cpx this phenocrysts Cpx phenocry showssts shows positive positive correlations correlations among among the Al the2O 3Al, TiO2O32, TiOand2 FeOand FeOcontents, contents, which which are negatively are negatively correlated correlated with the with SiO the2, MgO SiO2, and MgO Cr 2andO3 contentsCr2O3 contents (Figures (Figure6b–d and 6b–d7). andEspecially, Figure the7). {1Especially, 0 0} has relativethe {1 0 high 0} has contents relative of high Al2O contents3, TiO2 and of Al FeO,2O3, and TiO lower2 and contentsFeO, and of lower SiO2 contentsand MgO of than SiO those2 and MgO in {-1 1than 1} (Figures those in6 b–d{-1 1 and 1} (Figure7). In the 6b–d sample and YY13-123,Figure 7). theIn the Cpx sample phenocrysts YY13-123, are thecut Cpx perpendicularly phenocryststo are the cut b-axis perpendicularly and off the center. to the Theb-axis hourglass and off the sector center. ({-1 1The 1}), hourglass which is locatedsector ({- in 1the 1 1}), inner which part is of located the crystal, in the has inner higher part MgOof the andcrystal, SiO 2hascontents higher butMgO lower and AlSiO2O2 3contents, TiO2, and but Crlower2O3 Alcontents2O3, TiO than2, and the Cr prism2O3 contents sector ({0 than 1 0}) the (Figures prism6f–i sector and8 ({0). The 1 0}) outer (Figure part 6f–i of this and Cpx Figure phenocryst 8). The showouter partoscillatory of this zoning,Cpx phenocryst in which show the Cr oscillatory2O3 content zoning, correlates in which positively the Cr2O with3 content MgO correlates but negatively positively with withAl2O 3MgOand but TiO 2negatively(Figures6 f–iwith and Al8;2O Supplementary3 and TiO2 (Figure Figure 6f–i S3). and Olivine Figure phenocrysts 8; Supplementary only occur Figure in theS3). Olivinehigh-Mg phenocrysts basalts, and theironly compositionsoccur in the are high-Mg given in basalts, Supplementary and their Table compositions S3. are given in Supplementary Table S3. Minerals 2020, 10, 979 7 of 19 Minerals 2020, 10, x FOR PEER REVIEW 7 of 20

FigureFigure 6.6.( (aa,e,e)The)The back-scatteredback-scattered electronelectron imagesimages ofof thethe CpxCpx crystalcrystal fromfrom thethe high-Mghigh-Mg basaltbasalt samplesample YY13-111YY13-111 andand YY13-123,YY13-123, respectively,respectively, thethe detaildetail datadata ofof thethe whitewhite dotteddotted arrowsarrows fromfrom AA toto BB areare presentedpresented inin Figure Figures7, Figure7, 8 an8d and Supplements Supplements Figure Figure S3. S3.(b–d ( )b and–d) and(f–i) (qualitativef–i) qualitative WDS WDS maps maps of Mg, of Mg,Fe, Al Fe, and Al andCr. Cr. Minerals 2020, 10, 979 8 of 19 Minerals 2020, 10, x FOR PEER REVIEW 8 of 20

FigureFigure 7. ElementalElemental profiles proﬁles (A (A to toB) B)for for the the zoned zoned Cpx Cpx phenocryst phenocryst of the of high-Mg the high-Mg basalt basalt sample sample YY13- YY13-111.111. Profile Proﬁle analysis analysis shows shows oscillatory oscillatory zonings zonings in the in elements the elements of Si, of Mg, Si, Mg,Cr, Ti Cr, and Ti andAl. The Al. TheMgO MgO and

andCr2O Cr3 show2O3 show strong strong negative negative correction correction with the with Al2 theO3, AlTiO2O2 3and, TiO FeO.2 and The FeO. {100} The shows {100} Al shows2O3, TiO Al2 2FeOO3, TiOenrichment2 FeO enrichment compared compared with the with{-100}. the (a {-100}.–h) Major (a–h elements) Major elements variations variations along the along line the(from line A (from to B). A to B). Minerals 2020, 10, 979 9 of 19 Minerals 2020, 10, x FOR PEER REVIEW 9 of 20

FigureFigure 8. ElementalElemental profles proﬂes (A (A to toB) B)for for the thezoned zoned Cpx Cpx phenocryst phenocryst of the of high-Mg the high-Mg basalt basalt sample sample YY13- YY13-123.123. Profle Proﬂe analysis analysis shows shows oscillato oscillatoryry zonings zonings in the in elements the elements of Si, of Mg, Si, Mg,Cr, Ti Cr, and Ti andAl. The Al. TheMgO MgO and andCr2O Cr3 show2O3 show strong strong negative negative correction correction with the with Al2 theO3, AlTiO2O2 and3, TiO FeO.2 and The FeO. {010} The shows {010} Al shows2O3, TiO Al2 2FeOO3, TiOenrichment2 FeO enrichment compared compared with the with{-100}. the (a {-100}.–h) Major (a–h elements) Major elements variations variations along the along line the(from line A (from to B). A to B). 5. Discussion 5. Discussion

5.1.5.1. Petrogenetic ImplicationsImplications fromfrom ZonedZoned ClinopyroxeneClinopyroxene PhenocrystsPhenocrysts DiDifferentfferent typestypes ofof CpxCpx compositionalcompositional zoningzoning (e.g., sector, oscillatory,oscillatory, normal,normal, reverse)reverse) havehave beenbeen studiedstudied inin geologicalgeological andand syntheticsynthetic samplessamples [[14,24,26,37].14,24,26,37]. FractionalFractional crystallizationcrystallization inin aa closedclosed systemsystem and usually forms euhedral normal-zoned phenocrysts, and hence complex zoning (e.g., sector and oscillatory) mainly reflect changes in the magmatic environment [18,49,70]. Minerals 2020, 10, 979 10 of 19 and usually forms euhedral normal-zoned phenocrysts, and hence complex zoning (e.g., sector and oscillatory) mainly reflect changes in the magmatic environment [18,49,70]. In terms of concentric compositional zoning, variation occurs radially from the crystal core in response to the evolution of magmatic conditions and/or melt compositions [12,71]. Sector zoning, in contrast, requires faces of the same crystal to grow in a common temperature, pressure, and melt environment, yet incorporating elements in different concentrations and forming an anisotropy of element partitioning among prominent crystal faces [15]. Crystallographic studies indicate that crystals may grow with rates along different crystallographic orientations, which could result in element enrichments in one set of a sector and depletions in another [33,72,73]. Experimental studies highlight the kinetic effects induced by undercooling on the formation of sector zoning [34,44]. In these experiments, under a low degree of undercooling ( T = 13–18 C), the crystallization kinetics lead to 4 ◦ the relative enrichment of incompatible cations (e.g., Al and Ti) in the {h k 0} sector compared to the {-1 1 1} sector. Under a higher degree of undercooling ( T > 25–45 C), Al and Ti are concentrated 4 ◦ in the {-1 1 1} sector, and the crystals usually develop hopper to dendritic morphology. The above phenomena have been documented in natural Cpx crystals [14,15]. In this study, sector zoning is found in the inner part of the Cpx phenocrysts, which exhibits Al and Ti enrichments (Si and Mg depletions) in the sectors of {1 0 0}, {1 1 0}, and {0 1 0}, and depletions (Si and Mg enrichments) in the {-1 1 1} sector (Figures6–8; Supplementary Figure S3). The reverse correlations between (Si, Mg) and (Al, Ti) in these sectors possibly reflect coupled substitution and/or charge balance compensation, which can be 4+ 2+ 3+ 4+ expressed as: [Si + Mg ]{-1 1 1} — [Al + Ti ]{h k 0}. These characters of sector zoning resemble those obtained from natural Cpx analyses and experimental studies [15,34]. The sector zoning infers that the crystal growth resulted from sluggish crystallization kinetics driven by mild undercooling during the early crystal growth stage. The elements (e.g., Mg, Fe, Al, Ti, and Cr) in the outer part of the sector zone show oscillatory partition (Figures6–8; Supplementary Figure S3). Although the interplay of crystal growth and chemical diffusion within the boundary layer could form fine and flat oscillatory zoning (<15 µm thick) [24,46–48,74], it is inconsistent with our observation that the oscillatory zones are ~50 µm thick (Figure6). The oscillatory zoning could be related to the magma convection in the chamber, which may have resulted from periodic degassing processes in shallow reservoirs [49,75]. However, such degassing was unlikely at the crystallization depths inferred from previously published [11] and our new barometry data. The Cr3+ shows oscillatory zoning through the whole crystals and is not portioned amongst sectors may be owning to the less ability to facilitate charge-balanced configurations as previously suggested [14] (Figures7 and8). The intriguing behavior of Cr in the system deserves consideration due to its perfect oscillatory variations (Figure6i, Figure7e, and Figure8e). No experimental studies had shown that low-Cr pyroxene can be crystallized from high-Cr magma, as Cr is strongly partitioned into Cpx regardless of variation in intensive parameters (e.g., temperature and pressure) [76,77]. Therefore, the distinct oscillatory Cr content variation from the core to the rim in the Cpx crystals possibly indicate magma compositional changes led by repeated magma replenishment [12,14,18,49,77]. In this study, the oscillatory zones in the Cpx phenocrysts display positive correlation of Cr with Mg#, but negative ones with Al and Ti (Figures7c–f and 8c–f; Supplementary Figure S3), The partition characters of these elements consist thermodynamic principles under near-equilibrium conditions. The geometrical perfection of crystal faces and distinct concentric zoning from core to rim (Figure6), highlight the polyhedral crystallization under conditions approaching equilibrium [14,44]. Therefore, the sector and oscillatory zoning in the Cpx phenocrysts of high-Mg basalts indicate that the magma may have experienced a relatively low-degree undercooling during its early growth stage and eventually erupt due to the multistage magma replenishments.

5.2. Clinopyroxene-Melt Thermobarometry Olivine and Cpx are the main phenocrysts in the high-Mg and low-Mg basalts, respectively. No reliable olivine–liquid geobarometry is currently available due to its strong temperature sensitivity Minerals 2020, 10, 979 11 of 19 limit [51]. Moreover, the Cpx-melt thermobarometer is more accurate in determining the P-T conditions for phenocryst crystallization and has been widely used to study the magma plumbing system of volcanic rocks [22,78–81]. Therefore, our Cpx P-T calculation has adopted the model developed by Putirka (2008) [22]. Equation (30) for pressure and Equation (33) for temperature were used, with the compositions of coexisting liquid and Cpx compositions used for the basaltic compositions. Equation (30) was calibrated with a wide experimental dataset, and the estimated standard errors are 1.6 kbar. Equation (33) is developed based on global calibrations using experiments conducted at ± P < 70 kbar, and the standard estimated is 45 C. The geobarometer developed by Nimis and Taylor ± ◦ (2000) [82] has relatively low-temperature errors ( 30 C) and is also used here for result comparison. ± ◦ Due to the absence of the mineral melt inclusion for calculating the H2O contents in the ELIP, we assumed that the H2O is 0.7% for basalts, similar to that of non-subduction-related plumes [11]. By using the K (Fe-Mg)cpx-liq = 0.27 0.03 [83] and Na-Ca-Al composition [45,84] for the basaltic D ± system, respectively (Supplementary Figure S4). It is known that all the Cpx phenocrysts, including those with the highest Mg# in the high-Mg basalts, are not in equilibrium with their groundmass. This could be thought as that the Cpx phenocrysts in the high-Mg basalts were crystallized after most olivine, and the groundmass still had some residual olivine phenocrysts. To test whether it is possible to acquire a liquid in equilibrium with the observed Cpx, we removed the rare olivine from cpx-liq the groundmass until KD(Fe-Mg) = 0.27, and then check whether the amount of olivine removed is equal or less than the measured olivine content. We found that about 10–15% of the olivine was removed. This, plus the number of olivine phenocrysts picked out under the binocular microscope, are less than the observed modal amount of olivine in the whole-rock samples. Supplementary Figure S4b shows that most of the Cpx phenocryst rims of the high-Mg basalts are in equilibrium with the groundmass, in which extra olivine phenocrysts were removed. Therefore, only the data of Cpx rim plotted in the equilibrium ﬁeld (Supplementary Figure S4) are considered in the P-T estimation. Our P-T calculation results suggest that the crystallization of the Cpx rims in the low-Mg basalts occurred under 0.44 to 6.02 (3.16 1.53) kbar and 1109.5 to 1141.8 (1121.93 9.86) C. ± ± ◦ The Cpx phenocryst crystallization in the high-Mg basalts occurred under higher pressure (2.91 to 7.55 (5.71 1.46) kbar) and temperature (1181.79 to 1236.37 (1210.67 16) C) (Figure9a; Supplementary ± ± ◦ Table S4). As the geobarometer suggested by Nimis and Talyor (2000) [82] is more applicable to the high-Mg rocks, the results suggest narrow temperature variation in the high-Mg basalts (1157.88 to 1210.34 (1196.43 11) C) (Figure9b). Based on geophysical data, Jiang et al. (2012) [ 85] suggested ± ◦ that the upper, middle, and lower crustal boundaries in the western Yangtze craton are located at 16, 33, and 55 km deep, respectively. Taking the standard error of thermobarometry into consideration, the estimated Cpx crystallization depths for the high-Mg basalts are 4–27 (average 17) km, corresponding to the upper to middle Yangtze crust, whilst those for the low-Mg basalts are 0–23 (average in 9) km, corresponding to the upper Yangtze crust. Minerals 2020, 10, 979 12 of 19 Minerals 2020, 10, x FOR PEER REVIEW 12 of 20

Figure 9. Cpx equilibrium pressures and temperatures calculated by chemical thermobarometry. Figure 9. Cpx equilibrium pressures and temperatures calculated by chemical thermobarometry. Each Each sign denotes data point from Cpx phenocryst-matrix pair. (The error bars in a and b show the SEE sign denotes data point from Cpx phenocryst-matrix pair. (The error bars in a and b show the SEE of of the geothermometer methods from Putirka, 2008 [22] and Nimis and Talyor (2000) [82], respectively). the geothermometer methods from Putirka, 2008 [22] and Nimis and Talyor (2000) [82], respectively). (a) P-T calculation based on the model of Putirka, 2008 [22]; (b) P-T calculation based on the model of (a) P-T calculation based on the model of Putirka, 2008 [22]; (b) P-T calculation based on the model of Nimis and Talyor (2000) [82]. Nimis and Talyor (2000) [82]. 5.3. Magma Plumbing System in the ELIP 5.3. Magma Plumbing System in the ELIP It is generally agreed that the ELIP was emplaced in a short duration [6,86]. Together with the publishedIt is generally pressure agreed data from that the the high-Ti ELIP was volcanic emplaced rocks in [11 a ]short (Figure duration9b), we [6,86]. support Together that a serieswith the of publishedmagma chambers pressure were data presentfrom the across high-Ti the volcanic middle torocks upper [11] crust. (Figure The 9b), fractures we support likely that provided a series the of magmaconduits chambers for the magma were ascentpresent and across ponding the formiddle the fractional to upper crystallization crust. The fractures [78,87,88 likely]. Previous provided studies the conduitsalso suggested for the that magma the regional ascent fractures and ponding and density for the contrast fractional (between crystallization the magma and[78,87,88]. wallrocks), Previous have studiessignificant also eff suggestedects on forming that the the regional ELIP magma fractu plumbingres and density system. Meanwhile,contrast (between magma the replenishments magma and wallrocks),have likely playedhave significant key roles ineffects generating on forming the ELIP the magma ELIP magma plumbing plumbing system andsystem. eventually Meanwhile, led to volcanicmagma replenishments eruptions [49]. have The likely magma played recharge key role eventss in ingenerating the ELIP the are ELIP supported magma by plumbing the presence system of andmagmatic eventually cycles led and to volcanic massive Fe-Tieruptions oxide [49]. layers The in magma the mafic-ultramafic recharge events intrusions in the ELIP (e.g., are Panzhihuasupported byintrusion) the presence [89]. of magmatic cycles and massive Fe-Ti oxide layers in the mafic-ultramafic intrusions (e.g., AsPanzhihua above-mentioned, intrusion) the[89]. progressive Al2O3 increase with decreasing MgO indicates the lack of significantAs above-mentioned, plagioclase fractionation the progressive from the Al high-Mg2O3 increase tolow-Mg with decreasing basalts (Supplementary MgO indicates the Figure lack S1), of significantthe decrease plagioclase in compatible fractionation elements (such from asthe Cr high-Mg and Ni) withto low-Mg fractionation basalts indicates(Supplementary extensive Figure pyroxene S1), theand decrease olivine crystallization in compatible (Supplementary elements (such Figureas Cr S1).and VaryingNi) with degrees fractionation of crustal indicates assimilation extensive are pyroxenecommon forand mantle-derived olivine crystallization magmas ascending(Supplementary through Figure continental S1). crustVarying [90 ,91degrees]. However, of crustal trace assimilationelement compositions are common of the for high-Mg mantle-derived and low-Mg magm basaltsas ascending suggest thatthrough their continental compositions crust are [90,91]. mainly However,controlled bytrace their element mantle compositions source, rather of than the byhigh-Mg crustal contaminationand low-Mg basalts (Figure suggest4; Supplementary that their Tablecompositions S1). The are much mainly lower controlled Th/Nb (0.06–0.10)by their mantle and higher source, Nb rather/U (42.76–71.44) than by crustal ratios contamination of the basalts (Figurestudied than4; Supplementary the average bulk Table continental S1). The crustmuch (0.32 lower and Th/Nb 12.1, respectively; (0.06–0.10) and [67]) higher are inconsistent Nb/U (42.76– with 71.44)extensive ratios crustal of the contamination.basalts studied than Instead, the averag the The/ Nbbulk and continental Nb/U ratios crust of (0.32 the and basalts 12.1, are respectively; similar to [67])those are of theinconsistent average OIBwith (0.08 extensive and 47.06, crustal respectively). contamination. Minor Instead, crustal the contamination Th/Nb and Nb/U is shown ratios byof the basalts are similar to those of the average OIB (0.08 and 47.06, respectively). Minor crustal contamination is shown by the discrimination diagrams in which these Cpx phenocrysts have Minerals 2020, 10, 979 13 of 19 Minerals 2020, 10, x FOR PEER REVIEW 13 of 20 discriminationalkaline to tholeiitic diagrams and incalc-alkaline which these transitional Cpx phenocrysts character have (Figure alkaline 10a) to [92]. tholeiitic Moreover, and calc-alkaline the magma transitionalalso displays character some relative (Figure oxidation 10a) [92]. state Moreover, during the its magmacrystallization also displays and interaction some relative with oxidation the crust state(Figure during 10b) its[93]. crystallization and interaction with the crust (Figure 10b) [93].

FigureFigure 10.10. ((aa)) DiscriminationDiscrimination diagramsdiagrams ofof (Ca(Ca+Na)+Na) vs.vs. TiTi (from(from LeterrierLeterrier etetal. al. (1982)(1982)[ 92[92]);]); ( b(b)) (A (Avivi+ + Na)Na) vs.vs. (Alvivi ++ 2Ti2Ti ++ Cr)Cr) (from (from Schweitzer Schweitzer et et al. al. (1979) (1979) [93]). [93]).

Therefore,Therefore, based on the the study study of of Tao Tao et et al. al. (2015) (2015) and and Zhang Zhang et al. et al.(2006) (2006) [11,55], [11,55 we], suggest we suggest that thatthe primary the primary mantle-derived mantle-derived magma magma may may have have ascended ascended through through the deep the deep faults faults formed formed picrites, picrites, and andreached reached the middle the middle crust crust to form to form the high-Mg the high-Mg basalt basalts.s. The Theoscillatory oscillatory and andsector sector zoning zoning in the in Cpx the Cpxphenocrysts phenocrysts of the of thehigh-Mg high-Mg basalts basalts indicate indicate th thatat the the crystals crystals experienced experienced complex magmaticmagmatic processesprocesses duringduring thethe magmamagma ascent:ascent: At thethe earlyearly stage,stage, thethe innerinner partpart ofof thethe zonedzoned CpxCpx phenocrystphenocryst infersinfers thatthat the the magma magma had had undergone undergone low-degree low-degree undercooling undercooling inside inside a deep a deep staging staging chamber, chamber, and and the continuousthe continuous growth growth of Cpx of Cpx sectors sectors is compromised is compromi bysed multiphase by multiphase magma magma recharge recharge events, events, which which may bemay under be under near equilibriumnear equilibrium condition. condition. These These features features show thatshow the that magmas the magmas may have may ascended have ascended slowly alongslowly the along fractures the fractures and eventually and eventually ponded ponded in a relatively in a relatively stable magma stable magma reservoir reservoir at the upper-middle at the upper- crustalmiddle level. crustal Continuous level. Continuous magma replenishments magma replenishments may have eventually may have led eventually to volcanic led eruptions to volcanic and formederuptions the and high-Mg formed basalts. the high-Mg Some of thebasalts. fractionated Some of high-Mg the fractionated basalts may high-Mg have ascended basalts may up to have the upper-crustascended up staging to the chamber upper-crust for further staging fractionation chamber withfor further minor crustalfractionation contamination, with minor and eruptedcrustal tocontamination, form the low-Mg and basaltserupted or to cumulated form the low-Mg to form ba thesalts maﬁc or cumulated intrusions. to The form magma the mafic replenishments intrusions. andThe ascentmagma rate replenishments have major eﬀ andect on ascent the formation rate have ofmajor the ELIP effect magma on the plumbingformation system. of the ELIP A schematic magma modelplumbing of our system. proposed A schematic ELIP magma model plumbing of our propos systemed is ELIP illustrated magma in plumbing Figure 11 .system is illustrated in Figure 11. Minerals 2020, 10, 979 14 of 19 Minerals 2020, 10, x FOR PEER REVIEW 14 of 20

FigureFigure 11. 11. AA schematic schematic model model of of the the magma magma plumbing plumbing system system of of the the ELIP. ELIP.

6.6. Conclusions Conclusions (1) (1)Cpx-liquid Cpx-liquid thermobarometry thermobarometry suggests suggests that that the stagingthe staging chamber(s) chamber(s) beneath beneath the ELIP the spreadELIP spread across acrossthe the middle middle to to upper upper crust. crust. CpxCpx phenocrystphenocryst crystallizationcrystallization forfor the high-Mg basalts took place mainlymainly in the in middle the middle crust, crust,and those and thosefor the for low-Mg the low-Mg basalts basalts happened happened in the in upper the upper crust. crust. (2) (2)Similar Similar to to the the giant giant layered layered mafic-ultramafic mafic-ultramafic intrusions intrusions (e.g.,(e.g., PanzhihuaPanzhihua intrusion in ELIP), ELIP), the high-Mgthe high-Mg basalts basaltsexperienced experienced multistage multistage magma replenishments magma replenishments in the deep-staging in the deep-staging chamber(s). This suggestschamber(s). that magma This suggests replenishments that magma played replenishments a key role in generating played a key the roleELIP in magma generating pluming the system.ELIP magma pluming system. (3) (3)Sector Sector zoning zoning of Cpxof Cpx in the in picritesthe picrites indicate indicate that thethat crystals the crystals had grown had grown slowly slowly under under low-degree low- degreeundercooling undercooling conditions. conditions. The The compresscompress growthgrowth ofof thethe crystalscrystals werewere also nearly-equilibrium conditions.conditions. This stable This stable environment environment may mayinduce induce prolonged prolonged fractionation fractionation of the of thehigh-Mg high-Mg magmas magmas to form tothe form low-Mg the low-Mg basalts basalts and/or and mafic-ultramafic/or mafic-ultramafic intrusions intrusions in inthe the shallow shallow staging staging magma chamber(s).chamber(s).

Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: Major and trace elements composition of the whole rock. (a) TiO2 versus MgO ; (b) SiO2 versus MgO; (c) CaO Minerals 2020, 10, 979 15 of 19

Supplementary Materials: The following are available online at http://www.mdpi.com/2075-163X/10/11/979/s1, Figure S1: Major and trace elements composition of the whole rock. (a) TiO2 versus MgO; (b) SiO2 versus MgO; (c) CaO versus MgO; (d) Al2O3 versus MgO; (e) Ni versus MgO; (f) Cr versus MgO; (g) Sr versus MgO; (h) V versus MgO. Figure S2: Major element composition of the Cpx phenocryst from high-Mg and low-Mg basalts. (a) TiO2 iv versus SiO2. (b) Al2O3 versus SiO2. (c) Cr2O3 versus SiO2. (d) Al versus Al2O3. (e) Si + Mg (pfu) versus Al (pfu). (f) Mg (pfu) versus Al (pfu), Figure S3: Elemental profles (C to D) for the zoned Cpx phenocryst of the high-Mg basalts (sample YY13-123). Profle analysis shows oscillatory zonings in the elements of Si, Mg, Cr, Ti and Al. The MgO and Cr2O3 show strong negative correction with the Al2O3, TiO2 and FeO. The {010} shows Al2O3, TiO2 FeO enrichment compared with the {100}. (a–h) Major elements variations along the line (from C to D), Figure S4: (a) Fe-Mg partitioning between Cpx phenocrysts and matrix. (b) Fe-Mg partitioning between Cpx phenocrysts and the matrix which extra olivine has been eliminated. (c–f) Measured and calculated values for Cpx phenocrysts components (mole fraction) from the picrite and basalt. (DiHd-diopside + hedenbergite, EnFs-enstatite + ferrosilite, CaTs-Ca-Tschermak, and Jd-jadeite. The equilibrium envelopes are marked by the standard error of estimate (SEE), which are for diopside-hedenbergite 0.06 SEE; enstatite-ferrosillite 0.05 1SEE from Mollo et al. (2013) [45]; Ca-Tshermack 0.08 2SEE and Jadeite 0.04± 2SEE from Putirka (1999) [84±])., Table S1: The major and trace elements of the whole± rocks, Table S2: The major± elements of the matrix, Table S3: Major elements of the Cpx and Ol phenocrysts, Table S4: Results of the P-T calculations. Author Contributions: Conceptualization, J.-H.H. and J.-W.L.; formal analysis, J.-H.H.; investigation, J.-H.H., J.-W.L., and B.-S.S.; resources, J.-H.H. and J.-W.L.; writing—original draft preparation, J.-H.H., J.-W.L.; writing—review and editing, J.-H.H. and T.S.; visualization, J.-H.H.; supervision, J.-W.L.; funding acquisition, J.-H.H. All authors have read and agreed to the published version of the manuscript. Funding: This study was funded by the Talent start-up fund of Guiyang University (2019039510821)-Research on the magmatic process and its genesis mechanism of Tengchong volcanic rocks, and the Priority Research Program (B) of Chinese Academy of Sciences, Grant No. XDB18000000. Acknowledgments: We gratefully acknowledge the senior engineer Wen-Qin Zheng and Xiang Li of the Institute of Geochemistry, Chinese Academy of Sciences for their guidance in EPMA analysis work. We thank Kai-Yuan Wang for their handling of the manuscript and editorial input. We would like to thank Sheng-Hua Zhou and Jian Kang for their assistance during fieldwork. Conflicts of Interest: The authors declare no conflict of interest.

References

1. Ernst, R.E.; Jowitt, S.M. Large igneous provinces (LIPs) and metallogeny. Soc. Econ. Geol. Spec. Publ. 2013, 17, 17–51. 2. Bai, Z.-J.; Zhong, H.; Hu, R.-Z.; Zhu, W.-G.; Hu, W.-J. Composition of the Chilled Marginal Rocks of the Panzhihua Layered Intrusion, Emeishan Large Igneous Province, SW China: Implications for Parental Magma Compositions, Sulfide Saturation History and Fe–Ti Oxide Mineralization. J. Pet. 2019, 60, 619–648. [CrossRef] 3. Chung, S.-L.; Jahn, B.-M. Plume-lithosphere interaction in generation of the Emeishan flood basalts at the Permian-Triassic boundary. Geology 1995, 23, 889–892. [CrossRef] 4. Song, X.-Y.; Keays, R.R.; Xiao, L.; Qi, H.-W.; Ihlenfeld, C. Platinum-group element geochemistry of the continental flood basalts in the central Emeisihan Large Igneous Province, SW China. Chem. Geol. 2009, 262, 246–261. [CrossRef] 5. Wang, C.Y.; Zhou, M.-F.; Qi, L. Permian flood basalts and mafic intrusions in the Jinping (SW China)–Song Da (northern Vietnam) district: Mantle sources, crustal contamination and sulfide segregation. Chem. Geol. 2007, 243, 317–343. [CrossRef] 6. Yu, S.-Y.; Shen, N.-P.; Song, X.-Y.; Ripley, E.M.; Li, C.; Chen, L.-M. An integrated chemical and oxygen isotopic study of primitive olivine grains in picrites from the Emeishan Large Igneous Province, SW China: Evidence for oxygen isotope heterogeneity in mantle sources. Geochim. Cosmochim. Acta 2017, 215, 263–276. [CrossRef] 7. Zhang, Y.; Mao, J.; Saunders, A.D.; Ai, Y.; Li, Y.; Zhao, L. Petrogenetic modeling of three mafic–ultramafic layered intrusions in the Emeishan large igneous province, SW China, based on isotopic and bulk chemical constraints. Lithos 2009, 113, 369–392. [CrossRef] 8. Zhong, H.; Qi, L.; Hu, R.; Zhou, M.-F.; Gou, T.-Z.; Zhu, W.-G.; Liu, B.-G.; Chu, Z.-Y. Rhenium–osmium isotope and platinum-group elements in the Xinjie layered intrusion, SW China: Implications for source mantle composition, mantle evolution, PGE fractionation and mineralization. Geochim. Cosmochim. Acta 2011, 75, 1621–1641. [CrossRef] Minerals 2020, 10, 979 16 of 19

9. Zhou, M.-F.; Malpas, J.; Song, X.-Y.; Robinson, P.T.; Sun, M.; Kennedy, A.K.; Lesher, C.; Keays, R.R. A temporal link between the Emeishan large igneous province (SW China) and the end-Guadalupian mass extinction. Earth Planet. Sci. Lett. 2002, 196, 113–122. [CrossRef] 10. Zhou, M.-F.; Yan, D.-P.; Kennedy, A.K.; Li, Y.; Ding, J. SHRIMP U–Pb zircon geochronological and geochemical evidence for Neoproterozoic arc-magmatism along the western margin of the Yangtze Block, South China. Earth Planet. Sci. Lett. 2002, 196, 51–67. [CrossRef] 11. Yan, T.; Putirka, K.; Hu, R.; Li, C. The magma plumbing system of the Emeishan large igneous province and its role in basaltic magma differentiation in a continental setting. Am. Miner. 2015, 100, 2509–2517. [CrossRef] 12. Streck, M.J. Mineral Textures and Zoning as Evidence for Open System Processes. Rev. Miner. Geochem. 2008, 69, 595–622. [CrossRef] 13. Faure, F.; Schiano, P. Crystal morphologies in pillow basalts: Implications for mid-ocean ridge processes. Earth Planet. Sci. Lett. 2004, 220, 331–344. [CrossRef] 14. Ubide, T.; Mollo, S.; Zhao, J.-X.; Nazzari, M.; Scarlato, P. Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates. Geochim. Cosmochim. Acta 2019, 251, 265–283. [CrossRef] 15. Welsch, B.; Hammer, J.; Baronnet, A.; Jacob, S.; Hellebrand, E.; Sinton, J. Clinopyroxene in postshield Haleakala ankaramite: 2. Texture, compositional zoning and supersaturation in the magma. Contrib. Miner. Pet. 2015, 171, 1–19. [CrossRef] 16. Ganne, J.; Bachmann, O.; Feng, X. Deep into magma plumbing systems: Interrogating the crystal cargo of volcanic deposits. Geology 2018, 46, 415–418. [CrossRef] 17. Ginibre, C.; Wörner, G.; Kronz, A. Crystal Zoning as an Archive for Magma Evolution. Elements 2007, 3, 261–266. [CrossRef] 18. Hu, J.-H.; Song, X.-Y.; He, H.-L.; Zheng, W.-Q.; Yu, S.-Y.; Chen, L.-M.; Lai, C. Constraints of texture and composition of clinopyroxene phenocrysts of Holocene volcanic rocks on a magmatic plumbing system beneath Tengchong, SW China. J. Asian Earth Sci. 2018, 154, 342–353. [CrossRef] 19. Humphreys, M.C.S.; Blundy, J.; Sparks, R. Magma Evolution and Open-System Processes at Shiveluch Volcano: Insights from Phenocryst Zoning. J. Pet. 2006, 47, 2303–2334. [CrossRef] 20. Kahl, M.; Chakraborty, S.; Costa, F.; Pompilio, M. Dynamic plumbing system beneath volcanoes revealed by kinetic modeling, and the connection to monitoring data: An example from Mt. Etna. Earth Planet. Sci. Lett. 2011, 308, 11–22. [CrossRef] 21. Morgan, D.; Blake, S. Magmatic residence times of zoned phenocrysts: Introduction and application of the binary element diffusion modelling (BEDM) technique. Contrib. Miner. Pet. 2005, 151, 58–70. [CrossRef] 22. Putirka, K.D. Thermometers and Barometers for Volcanic Systems. Rev. Miner. Geochem. 2008, 69, 61–120. [CrossRef] 23. De Maisonneuve, C.B.; Costa, F.; Huber, C.; Vonlanthen, P.; Bachmann, O.; Dungan, M.A.; De Maisonneuve, C.B. How do olivines record magmatic events? Insights from major and trace element zoning. Contrib. Miner. Pet. 2016, 171.[CrossRef] 24. Elardo, S.M.; Shearer, J.C.K. Magma chamber dynamics recorded by oscillatory zoning in pyroxene and olivine phenocrysts in basaltic lunar meteorite Northwest Africa 032. Am. Miner. 2014, 99, 355–368. [CrossRef] 25. Costa, F. Time constraints from chemical equilibration in magmatic crystals. In Timescales of Magmatic Processes: From Core to Atmosphere; Dosseto, A., Turner, S.P., Van Orman, J.A., Eds.; Blackwell Publishing Ltd.: Hoboken, NJ, USA, 2011; pp. 125–159. 26. Feng, W.; Zhu, Y. Magmatic plumbing system beneath a fossil continental arc volcano in western Tianshan (NW China): Constraints from clinopyroxene and thermodynamic modelling. Lithos 2019, 105221. [CrossRef] 27. Giacomoni, P.P.; Coltorti, M.; Bryce, J.G.; Fahnestock, M.F.; Guitreau, M. Mt. Etna plumbing system revealed by combined textural, compositional, and thermobarometric studies in clinopyroxenes. Contrib. Miner. Pet. 2016, 171.[CrossRef] 28. Müller, T.; Dohmen, R.; Becker, H.W.; Ter Heege, J.H.; Chakraborty, S. Fe–Mg interdiffusion rates in clinopyroxene: Experimental data and implications for Fe–Mg exchange geothermometers. Contrib. Miner. Pet. 2013, 166, 1563–1576. [CrossRef] 29. Van Orman, J.A.; Grove, T.L.; Shimizu, N. Rare earth element diffusion in diopside: Influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates. Contrib. Miner. Pet. 2001, 141, 687–703. [CrossRef] Minerals 2020, 10, 979 17 of 19

30. Zhang, Y. Diffusion in Minerals and Melts: Theoretical Background. Rev. Miner. Geochem. 2010, 72, 5–59. [CrossRef] 31. Cherniak, D.; Dimanov, A. Diffusion in Pyroxene, Mica and Amphibole. Rev. Miner. Geochem. 2010, 72, 641–690. [CrossRef] 32. Cherniak, D.J.; Liang, Y. Ti diffusion in natural pyroxene. Geochim. Cosmochim. Acta 2012, 98, 31–47. [CrossRef] 33. Downes, M.J. Sector and oscillatory zoning in calcic augites from M. Etna, Sicily. Contrib. Miner. Pet. 1974, 47, 187–196. [CrossRef] 34. Kouchi, A.; Sugawara, Y.; Kashima, K.; Sunagawa, I. Laboratory growth of sector zoned clinopyroxenes in the system CaMgSi2O6-CaTiAl2O6. Contrib. Miner. Pet. 1983, 83, 177–184. [CrossRef] 35. Lofgren, G.E.; Donaldson, C.H. Curved branching crystals and differentiation in comb-layered rocks. Contrib. Miner. Pet. 1975, 49, 309–319. [CrossRef] 36. Mollo, S.; Hammer, J.E. Dynamic crystallization in magmas. EMU Notes Mineral. 2017, 16, 373–418. 37. Schwandt, C.S.; McKay, G.A. Minor- and trace-element sector zoning in synthetic enstatite. Am. Miner. 2006, 91, 1607–1615. [CrossRef] 38. Shearer, C.; Larsen, L. Sector-zoned aegirine from the Ilimaussaq alkaline intrusion, South Greenland: Implications for trace-element behavior in pyroxene. Am. Mineral. 1994, 79, 340–352. 39. Shimizu, N. Trace element incorporation into growing augite phenocryst. Nat. Cell Biol. 1981, 289, 575–577. [CrossRef] 40. Watson, E.B.; Liang, Y. A simple model for sector zoning in slowly grown crystals; implications for growth rate and lattice diffusion, with emphasis on accessory minerals in crustal rocks. Am. Miner. 1995, 80, 1179–1187. [CrossRef] 41. McKay, G.; Wagstaff, J.; Yang, S.-R. Clinopyroxene REE distribution coefficients for shergottites: The REE content of the Shergotty melt. Geochim. Cosmochim. Acta 1986, 50, 927–937. [CrossRef] 42. Stock, M.J.; Bagnardi, M.; Neave, D.A.; MacLennan, J.; Bernard, B.; Buisman, I.; Gleeson, M.; Geist, D. Integrated Petrological and Geophysical Constraints on Magma System Architecture in the Western Galápagos Archipelago: Insights From Wolf Volcano. Geochem. Geophys. Geosystems 2018, 19, 4722–4743. [CrossRef] 43. Watson, E.B. Surface enrichment and trace-element uptake during crystal growth. Geochim. Cosmochim. Acta 1996, 60, 5013–5020. [CrossRef] 44. Lofgren, G.E.; Huss, G.R.; Wasserburg, G.J. An experimental study of trace-element partitioning between Ti-Al-clinopyroxene and melt: Equilibrium and kinetic effects including sector zoning. Am. Miner. 2006, 91, 1596–1606. [CrossRef] 45. Mollo, S.; Blundy, J.D.; Iezzi, G.; Scarlato, P.; Langone, A. The partitioning of trace elements between clinopyroxene and trachybasaltic melt during rapid cooling and crystal growth. Contrib. Miner. Pet. 2013, 166, 1633–1654. [CrossRef] 46. Ginibre, C.; Kronz, A.; Wörner, G. High-resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images: New constraints on oscillatory zoning. Contrib. Miner. Pet. 2002, 142, 436–448. [CrossRef] 47. Ginibre, C.; Wörner, G.; Kronz, A. Minor- and trace-element zoning in plagioclase: Implications for magma chamber processes at Parinacota volcano, northern Chile. Contrib. Miner. Pet. 2002, 143, 300–315. [CrossRef] 48. Pearce, T. Recent work on oscillatory zoning in plagioclase. In Feldspars and Their Reactions; Springer: Berlin, Germany, 1994; pp. 313–349. 49. Stroncik, N.A.; Klügel, A.; Hansteen, T.H. The magmatic plumbing system beneath El Hierro (Canary Islands): Constraints from phenocrysts and naturally quenched basaltic glasses in submarine rocks. Contrib. Miner. Pet. 2008, 157, 593–607. [CrossRef] 50. Shore, M.; Fowler, A.D. Oscillatory zoning in minerals; a common phenomenon. Can. Mineral. 1996, 34, 1111–1126. 51. Keiding, J.K.; Sigmarsson, O. Geothermobarometry of the 2010 Eyjafjallajökull eruption: New constraints on Icelandic magma plumbing systems. J. Geophys. Res. Space Phys. 2012, 117, 117. [CrossRef] 52. Xu, Y.; Chung, S.-L.; Jahn, B.-M.; Wu, G. Petrologic and geochemical constraints on the petrogenesis of Permian–Triassic Emeishan flood basalts in southwestern China. Lithos 2001, 58, 145–168. [CrossRef] Minerals 2020, 10, 979 18 of 19

53. Bai, Z.-J.; Zhong, H.; Li, C.; Zhu, W.-G.; He, D.-F.; Qi, L. Contrasting parental magma compositions for the Hongge and Panzhihua magmatic Fe-Ti-V oxide deposits, Emeishan large igneous province, SW China. Econ. Geol. 2014, 109, 1763–1785. [CrossRef] 54. Kamenetsky, V.S.; Chung, S.-L.; Kamenetsky, M.B.; Kuzmin, D.V. Picrites from the Emeishan Large Igneous Province, SW China: A Compositional Continuum in Primitive Magmas and their Respective Mantle Sources. J. Pet. 2012, 53, 2095–2113. [CrossRef] 55. Zhang, Z.; Mahoney, J.J.; Mao, J.; Wang, F. Geochemistry of Picritic and Associated Basalt Flows of the Western Emeishan Flood Basalt Province, China. J. Pet. 2006, 47, 1997–2019. [CrossRef] 56. Ali, J.R.; Thompson, G.M.; Song, X.; Wang, Y. Emeishan Basalts (SW China) and the ‘end-Guadalupian’ crisis: Magnetobiostratigraphic constraints. J. Geol. Soc. 2002, 159, 21–29. [CrossRef] 57. Song, X.-Y.; Zhou, M.-F.; Hou, Z.-Q.; Cao, Z.-M.; Wang, Y.-L.; Li, Y. Geochemical Constraints on the Mantle Source of the Upper Permian Emeishan Continental Flood Basalts, Southwestern China. Int. Geol. Rev. 2001, 43, 213–225. [CrossRef] 58. Yang, J.; Cawood, P.A.; Du, Y.; Condon, D.J.; Yan, J.; Liu, J.; Huang, Y.; Yuan, D. Early Wuchiapingian cooling linked to Emeishan basaltic weathering? Earth Planet. Sci. Lett. 2018, 492, 102–111. [CrossRef] 59. Xiao, L.; Xu, Y.; Mei, H.; Zheng, Y.; He, B.; Pirajno, F. Distinct mantle sources of low-Ti and high-Ti basalts from the western Emeishan large igneous province, SW China: Implications for plume–lithosphere interaction. Earth Planet. Sci. Lett. 2004, 228, 525–546. [CrossRef] 60. Li, C.; Tao, Y.; Qi, L.; Ripley, E.M. Controls on PGE fractionation in the Emeishan picrites and basalts: Constraints from integrated lithophile–siderophile elements and Sr–Nd isotopes. Geochim. Cosmochim. Acta 2012, 90, 12–32. [CrossRef] 61. Zhang, Z.; Zhi, X.; Chen, L.; Saunders, A.D.; Reichow, M.K. Re–Os isotopic compositions of picrites from the Emeishan flood basalt province, China. Earth Planet. Sci. Lett. 2008, 276, 30–39. [CrossRef] 62. Hanski, E.; Kamenetsky, V.S.; Luo, Z.; Xu, Y.-G.; Kuzmin, D.V. Primitive magmas in the Emeishan Large Igneous Province, southwestern China and northern Vietnam. Lithos 2010, 119, 75–90. [CrossRef] 63. Qi, L.; Hu, J.; Gregoire, D.C. Determination of trace elements in granites by inductively coupled plasma mass spectrometry. Talanta 2000, 51, 507–513. 64. Le Bas, M.J. IUGS Reclassification of the High-Mg and Picritic Volcanic Rocks. J. Pet. 2000, 41, 1467–1470. [CrossRef] 65. Le Maitre, R.W.; Streckeisen, A.; Zanettin, B.; Le Bas, M.J.; Bonin, B.; Bateman, P. Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks(Eds.), 2nd ed.; Cambridge University Press: Cambridge, UK, 2005; p. 256. 66. Pearce, J.A. A user’s guide to basalt discrimination diagrams. Trace element geochemistry of volcanic rocks: Applications for massive sulphide exploration. Geol. Assoc. Can. Short Course Notes 1996, 12, 113. 67. Taylor, S.R.; McLennan, S.M. The geochemical evolution of the continental crust. Rev. Geophys. 1995, 33, 241–265. [CrossRef] 68. Sun, S.-S.; McDonough, W.F. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes. Geol. Soc. Lond. Spéc. Publ. 1989, 42, 313–345. [CrossRef] 69. Morimoto, N. Nomenclature of Pyroxenes. Miner. Pet. 1988, 39, 55–76. [CrossRef] 70. Carracedo, J.C. Growth, structure, instability and collapse of Canarian volcanoes and comparisons with Hawaiian volcanoes. J. Volcanol. Geotherm. Res. 1999, 94, 1–19. [CrossRef] 71. Pearce, T.H. The analysis of zoning in magmatic crystals with emphasis on olivine. Contrib. Miner. Pet. 1984, 86, 149–154. [CrossRef] 72. Leung, I.S. Sector-zoned titanaugites: Morphology, crystal chemistry, and growth. Am. Mineral. 1974, 59, 127–138. 73. Nakamura, Y. Origin of sector-zoning of igneous clinopyroxenes. Am. Mineral. 1973, 58, 986–990. 74. Pearce, T.; Kolisnik, A. Observations of plagioclase zoning using interference imaging. Earth Sci. Rev. 1990, 29, 9–26. [CrossRef] 75. Clague, D.A.; Dixon, J. Extrinsic controls on the evolution of Hawaiian ocean island volcanoes. Geochem. Geophys. Geosystems 2000, 1.[CrossRef] 76. Arth, J.G. Behavior of trace elements during magmatic processes-a summary of theoretical models and their applications. J. Res. US Geol. Surv. 1976, 4, 41–47. Minerals 2020, 10, 979 19 of 19

77. Streck, M.J.; Dungan, M.A.; Malavassi, E.; Reagan, M.K.; Bussy, F. The role of basalt replenishment in the generation of basaltic andesites of the ongoing activity at Arenal volcano, Costa Rica: Evidence from clinopyroxene and spinel. Bull. Volcanol. 2002, 64, 316–327. [CrossRef] 78. Putirka, K.; Condit, C.D. Cross section of a magma conduit system at the margin of the Colorado Plateau. Geology 2003, 31, 701. [CrossRef] 79. Caprarelli, G.; Reidel, S.P. A clinopyroxene-basalt geothermobarometry perspective of Columbia Plateau (NW-USA) Miocene magmatism. Terra Nova 2005, 17, 265–277. [CrossRef] 80. Barker, A.K.; Troll, V.R.; Carracedo, J.C.; Nicholls, P.A. The magma plumbing system for the 1971 Teneguía eruption on La Palma, Canary Islands. Contrib. Miner. Pet. 2015, 170, 1–21. [CrossRef] 81. Hammer, J.; Jacob, S.; Welsch, B.; Hellebrand, E.; Sinton, J. Clinopyroxene in postshield Haleakala ankaramite: 1. Efficacy of thermobarometry. Contrib. Miner. Pet. 2015, 171, 1–23. [CrossRef] 82. Nimis, P.; Taylor, W.R. Single clinopyroxene thermobarometry for garnet peridotites. Part I. Calibration and testing of a Cr-in-Cpx barometer and an enstatite-in-Cpx thermometer. Contrib. Miner. Pet. 2000, 139, 541–554. [CrossRef] 83. Villiger, S.; Ulmer, P.; Müntener, O. Equilibrium and fractional crystallization experiments at 0 7 GPa; the • effect of pressure on phase relations and liquid compositions of tholeiitic magmas. J. Petrol. 2007, 48, 159–184. [CrossRef] 84. Putirka, K. Clinopyroxene + liquid equilibria to 100 kbar and 2450 K. Contrib. Miner. Pet. 1999, 135, 151–163. [CrossRef] 85. Jiang, W.; Zhang, J.; Tian, T.; Wang, X. Crustal structure of Chuan-Dian region derived from gravity data and its tectonic implications. Phys. Earth Planet. Inter. 2012, 76–87. [CrossRef] 86. Shellnutt, J.G.; Pham, T.T.; Denyszyn, S.W.; Yeh, M.-W.; Tran, T.-A. Magmatic duration of the Emeishan large igneous province: Insight from northern Vietnam. Geology 2020, 48, 457–461. [CrossRef] 87. Ferlito, C.; Coltorti, M.; Lanzafame, G.; Giacomoni, P.P. The volatile flushing triggers eruptions at open conduit volcanoes: Evidence from Mount Etna volcano (Italy). Lithos 2014, 184, 447–455. [CrossRef] 88. Valentine, G.A.; Gregg, T.K.P. Continental basaltic volcanoes—Processes and problems. J. Volcanol. Geotherm. Res. 2008, 177, 857–873. [CrossRef] 89. Song, X.-Y.; Qi, H.-W.; Hu, R.-Z.; Chen, L.-M.; Yu, S.-Y.; Zhang, J.-F. Formation of thick stratiform Fe-Ti oxide layers in layered intrusion and frequent replenishment of fractionated mafic magma: Evidence from the Panzhihua intrusion, SW China. Geochem. Geophys. Geosystems 2013, 14, 712–732. [CrossRef] 90. Hergt, J.; Peate, D.; Hawkesworth, C. The petrogenesis of Mesozoic Gondwana low-Ti flood basalts. Earth Planet. Sci. Lett. 1991, 105, 134–148. [CrossRef] 91. Mahoney, J.J.; Coffin, M.F. Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism; American Geophysical Union: Washington, DC, USA, 1997; Volume 100. 92. Leterrier, J.; Maury, R.C.; Thonon, P.; Girard, D.; Marchal, M. Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series. Earth Planet. Sci. Lett. 1982, 59, 139–154. [CrossRef] 93. Schweitzer, E.; Papike, J.; Bence, A.E. Statistical analysis of clinopyroxenes from deep-sea basalts. Am. Mineral. 1979, 64, 501–513. [CrossRef]

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