Physicochemical Conditions of Crystallization of Rocks from Ultrabasic Massifs of the Siberian Platform

A great volume of original information on the formation of the ultrabasic rocks of the Siberian Platform has been accumulated owing to the study of melt inclusions in Cr-spinels. The inclusions show the general tendencies in the behavior of the magmatic systems during the formation of the ultrabasic massifs of the Siberian Platform, tracing the main evolution trend of decreasing Mg number with SiO₂ increase in the melts with subsequent transition from picrites through picrobasalts to basalts. The compositions of the melt inclusions indicate that the crystallization conditions of the rocks of the concentrically zoned massifs (Konder, Inagli, Chad) sharply differ from those of the Guli massif. Numerical modeling using the PETROLOG and PLUTON softwares and data on the composition of inclusions in Cr-spinels yielded maximum crystallization temperatures of the olivines from the dunites of the Konder (1545–1430°C), Inagli (1530–1430°C), Chad (1460–1420°C), and Guli (1520–1420°C) massifs, and those of Cr-spinels from the Konder (1420–1380°C), Inagli (up to 1430°C), Chad (1430–1330°C), and Guli (1410–1370°C) massifs. Modeling of the Guli massif with the PLUTON software using the compositions of the melt inclusions revealed the possible formation of the alkaline rocks at the final reverse stage of the evolution of the picritic magmas (with decrease of SiO₂ and alkali accumulation) after termination of olivine crystallization with temperature decrease from 1240–1230°C to 1200–1090°C. Modeling with the PLUTON software showed that the dunites of the Guli massif coexisted with Fe-rich (with moderate TiO₂ contents) melts, the crystallization of which led (beginning from 1210°C) to the formation of pyroxenes between cumulate olivine. Further temperature decrease (from 1125°C) with decreasing FeO and TiO₂ contents provided the formation of clinopyroxenes of pyroxenites. For the Konder massif, modeling with the PLUTON software indicates the possible formation of kosvites from picrobasaltic magmas beginning from 1350°C and the formation of clinopyroxenites and olivine–diopside rocks from olivine basaltic melts from 1250°C.     

The Evolution of Alpine Ultramafic Rocks and Partial Melting of the Upper Mantle

Ultramafic rocks of Tibet and Xinjiang are the products of partial melting of the upper mantle. The evolution of their mineral composition is marked by two parallel evolutionary series: one is the progressive increase of the 100 Mg/(Mg+Fe~(2+) ratio of silicate minerals in order of lherzolite→harzburgite→dunite, i.e. the increase in magnesium; the other is the increase of the 100 Cr/(Cr+Al) ratio of accessory chrome spinel in the same order, i. e. the increase in Chromium. The above-mentioned evolutionary trends are contrary to that of magmatic differentiation. The evolution of fabrics of ultramafic rocks is characterized by progressive variation in order of protogranular texture→melted residual texture, symplectic texture and clastophyritic texture→equigranular mosaic texture and tabular mosaic texture. Experiments of partial melting of lherzolite have convincingly shown that the evolution of Alpine ultramafic rocks resulted from the partial melting of pyrolite. Various subtypes of them represent different degrees of partial melting. The vertical zoning marked by more basic rocks in the upper part and more acid rocks in the lower actually belongs to the fusion zoning of pyrolite.     

The Evolution of Alpine Ultramafic Rocks and Partial Melting of the Upper Mantle1

Abstract Ultramafic rocks of Tibet and Xinjiang are the products of partial melting of the upper mantle. The evolution of their mineral composition is marked by two parallel evolutionary series: one is the progressive increase of the 100 Mg / (Mg+Fe²⁺) ratio of silicate minerals in order of lherzolite?harzburgite?dunite, i.e. the increase in magnesium; the other is the increase of the 100 Cr/(Cr+Al) ratio of accessory chrome spinel in the same order, i.e. the increase in Chromium. The above- mentioned evolutionary trends are contrary to that of magmatic differentiation. The evolution of fabrics of ultramafic rocks is characterized by progressive variation in order of protogranular texture? melted residual texture, symplectic texture and clastophyritic texture? equigranular mosaic texture and tabular mosaic texture. Experiments of partial melting of lherzolite have convincingly shown that the evolution of Alpine ultramafic rocks resulted from the partial melting of pyrolite. Various subtypes of them represent different degrees of partial melting. The vertical zoning marked by more basic rocks in the upper part and more acid rocks in the lower actually belongs to the fusion zoning of pyrolite.     

Minerogenic Model of Chrysotile Deposits in Ultramafic Rocks

Most chrysotile deposits occur in ultramafic rocks of the ophiolite suite. The chrysotile deposits dis-cussed in the present paper were formed through metasomatism and infilling-crystallization in a continentalserpentinization environment after plate convergence, where ultramafic rocks were replaced byhydrothermal solutions consisting mainly of deep-circulating heated water derived from atmospheric precip-itation. The critical state for the formation of asbestos in ultramafic rock bodies might be reached bysuperposition of multiple stages of serpentinization. Favourable fracture systems and relatively stable geo-logical environment are important conditions for forming chrysotile deposits. Three subtypes of chrysotiledeposits could be formed in different tectonic settings and under different minerogenic geochemical condi-tions.     

苏鲁造山带中胡家林超镁铁质岩岩石地球化学特征

苏鲁造山带中胡家林超镁铁质岩地块主要由两部分组成:南部滑石山以蛇纹岩和蛇纹石化橄榄岩为主,夹薄层状石榴橄辉岩-(石榴)单斜辉石岩;北部胡家林主要由(石榴)单斜辉石岩组成,夹厚层状蛇纹岩。蛇纹岩-蛇纹石化橄榄岩低Al2O3、低Ca O和高Mg O,REE含量低,但LREE稍富集。石榴橄辉岩和(石榴)单斜辉石岩低Mg O和Ca O,高REE含量高,其稀土配分曲线均表现出单斜辉石单矿物的配分特征。这些超镁铁岩块中不同岩石的微量元素均具有Pb的正异常,弱的Nb、Ta的负异常,显示地壳流体交代信息。Nd、Sr、Pb同位素特征显示存在亏损地幔与地壳之间的混合作用。亲石元素含量最低的蛇纹石化石榴橄辉岩的Sr、Nd、Pb同位素组成受交代流体控制明显,而石榴橄辉岩和(石榴)单斜辉石岩不明显。胡家林和滑石山超镁铁岩中所含的交代地壳成分不同,胡家林样品受到含水熔体和富水流体的双重交代,滑石山样品主要受富水流体的交代。     

Contact Metamorphosed Ultramafic Rocks in the Western Sierra Nevada Foothills, California

Within the western Sierra Nevada metamorphic belt, linear bodiesof alpine-type ultramafic rock, now composed largely of serpentineminerals, parallel the regional strike and commonly coincidewith major fault zones. Within this metamorphic belt, east ofSacramento, California, ultramafic rocks near a large maficintrusion, the Pine Hill Intrusive Complex, have been emplacedduring at least two separate episodes. Those ultramafic rocks,evidently unaffected by the Pine Hill Intrusive Complex andcomposed largely of serpentine minerals, were emplaced alonga major fault zone after emplacement of the Pine Hill IntrusiveComplex. Those ultramafic rocks, contact metamorphosed by thePine Hill Intrusive Complex, show a zonation of mineral assemblagesas the igneous contact is approached: olivine+antigorite+chlorite+tremolite+Fe-Cr spinel olivine+talc+chlorite+tremolite+Fe-Crspinel olivine+anthophyllite+chlorite+tremolite+Fe-Cr spinel olivine+orthopyroxene+aluminous spinel+hornblende+Fe-Cr spinel.Superimposed on these mineral assemblages are abundant secondaryminerals (serpentine minerals, talc, chlorite, magnetite) whichformed after contact metamorphism. Correlation of observed mineralassemblages with the experimental systems, MgO-SiO₂-H₂O andMgO-Al₂O₃-SiO₂-H₂O suggests an initial contact temperature of775±25 °C for the Pine Hill Intrusive Complex assumingPtotal P_fluid PH₂O. The pressure acting on the metamorphic rockduring emplacement of the intrusion is estimated to be a minimumof 1.5 kb.     

Chromian Spinel-Silicate Chemistry in Ultramafic Rocks of the Jijal Complex, Northwest Pakistan

The approximately 150 km² Jijal complex occupies a deep-levelsection of the Cretaceous Kohistan are obducted along the Indussuture. The complex consists of mafic garnet granulites, anda > 10 km ? 4 km slab of pyroxenites (diopsidite > websterite;? olivine), dunite, and subordinate peridotite, all of whichare devoid of plagioclase. These contain chromite either inlenses, layers, and veins or as disseminated grains. The chromiteis mostly medium grained, subhedral to euhedral, shows pull-aparttexture, and may contain inclusions of associated silicates.Chromite grains within thin sections of chromitite are generallyhomogeneous in composition, but dunite and pyroxenite samplescommonly contain chromite grains of variable composition. Thesegregated chromite has higher Cr₂O₃ wt%, cr-number, and mg-number,and lower fe'-number than the accessory chromite. These variationsare mainly attributed to subsolidus exchange of Mg and Fe betweenchromite and associated olivine or pyroxene, and to inheritancefrom a magmatic source, but other factors may also be responsible.In general, the chromite grains are altered along margins andfractures to ferritchromit that is enriched in cr-number (andgenerally Fe³⁺, Mn, and Ti) and impoverished in mg-number comparedwith the parent grains. Chromian chlorite (clinochlore, penninite,with up to 7?3 wt.% Cr₂O₃) is commonly associated with the alteration,as is serpentine in most silicate rocks and some chromitites.The chlorite shows considerable compositional variation fromgrain to grain and in some cases within a single grain. Clinopyroxene is low-Al, -Na and high-Ca diopside. Orthopyroxeneranges from En₉₁ to En₈₂ and olivine from Fo₉₈ to Fo₈₄ (ignoringone analysis each). The mg-number of these minerals is higherin chromitites than in dunites and pyroxenites. Several aspectsof the petrogenesis of the ultramafic rocks (e.g., the abundanceof diopsidite) are not clear, but they seem to have passed througha complex history. The high cr-numbers (>60) in the chromiteindicate that the rocks may have originated from some form ofoceanic lithosphere-island are interaction. Petrography andmineral compositional data suggest that the rocks are ultramaficcumulates derived from an are-related (?primitive) high-Mg tholeiiticmagma, possibly at pressures in excess of 8 kb.There also aresmall ultramafic bodies in the form of conformable layers andemplaced masses within the garnet granulites. These containmagnetite and pleonaste with < 10 wt.% Cr₂O₃, and less magnesianolivine and pyroxene than the principal ultramafic mass. Thesealso have the characteristics of island are plutonic rocks,but it is not clear whether the garnet granulites constitutea continuous sequence of are cumulates with the principal ultramaficmass or the two are produced from different source magmas.     

塔里木盆地瓦吉里塔格超镁铁岩地球化学反演

二叠纪是塔里木盆地热-构造演化史上最重要的时期,这一时期在塔里木盆地中部和西北部发生了大规模的基性-中酸性岩浆活动.对塔里木盆地西北部瓦吉里塔格超镁铁岩的地球化学反演表明:瓦吉里塔格超镁铁岩(包括角砾和胶结物)是由残余岩浆和橄榄石、单斜辉石不同比例混合的产物,其中角砾主要由橄榄石和残余岩浆组成,其比例达到了72∶28.与角砾中橄榄石(平均Fo=0.82)平衡的熔体的w(MgO)为9.06%、w(FeOt)为11.77%,是由w(MgO)为11.46%、w(FeOt)为12.12%的原始岩浆经7.3%的橄榄石(Fo=0.82)分异而成的.其原始岩浆并不属于高镁岩浆,而是地幔石榴子石橄榄岩低程度(<5%)部分熔融的产物,初始熔融温度约1 150～1 250 ℃,压力约2.2 GPa,深度约70 km.结合前人研究成果认为,塔里木盆地二叠纪岩浆活动的形成可能与软流圈上涌导致的软流圈-岩石圈的相互作用有关,目前尚没有直接的岩石地球化学证据表明有地幔柱活动的参与.     

Tale-Carbonate Alteration of some Serpentinized Ultramafic Rocks south of Timmins, Ontario

Serpentinized peridotites in an area south of Timmins, Ontario,have been extensively altered to tale and carbonate. In someplaces, rocks altered in this way have subsequently been decarbonatizedand converted back to a serpentine-magnetite assemblage. Chemicalanalyses of variably altered rocks indicate that the bulk chemicalchanges involved in the tale-carbonate alteration have beenthe addition of CO₂, and removal of H₂O and a very small amountof O₂. Little or no magnesium, silicon, iron, or nickel metasomatismhas occurred. Consequently the relative partial pressures ofH₂O and CO₂ in solutions passing through the rocks are likelyto have been controlling factors for the alteration and subsequentdecarbonatization.     

内蒙古突泉县牤牛海地区超镁铁质岩地球化学及源区特征

内蒙古突泉县牤牛海地区发育超镁铁质岩,主要岩石类型为蛇纹石化橄榄岩、辉石橄榄岩、异剥辉石橄榄岩和蛇纹岩,局部蛇纹岩中可见显微鬣刺假象结构,包括蛇纹石呈假像的柱状中空骸晶结构、鱼骨状或羽状结构。岩石化学具有高镁(w(MgO)为33.63%~39.44%)、铬(2 200×10~(-6)~17 200×10~(-6))、镍(1 900×10~(-6)~3 000×10~(-6)),高CaO/Al_2O_3(0.56~39.01,平均为7.05),低钛(w(TiO_2)为0.01%~0.02%)、低铝(w(Al2O3)为0.03%~0.36%)、低碱(w(K_2O+Na_2O)为0.03%~0.65%)特征,类似科马提岩;Mg#值(平均为87)与纯橄榄岩(86)接近;稀土元素(w(∑REE)为0.32×10~(-6)~2.79×10~(-6))明显低于大洋脊含量,轻稀土富集(LREE/HREE为2.80~16.68),Eu正异常明显(δEu为0.59~4.84);微量元素富集大离子亲石元素(LILE)Rb、Ba、Sr,亏损高场强元素(HFSE)Nb、P等。说明超镁铁质岩石岩浆源自亏损软流圈地幔,并受到俯冲流体交代作用,形成于岛弧环境。牤牛海超镁铁质岩与西部包括突泉围场、好老鹿场、超日海乌拉、梅劳特乌拉、苏尼特左旗二道井一带超镁铁质岩共同构成一条近东西向展布的超镁铁质岩(蛇绿岩)带,通过地质建造分析,认为该构造带可能为华北板块与西伯利亚板块最终缝合带。     

The Geology of the Great 'Dyke', Zimbabwe: The Ultramafic Rocks

Textural and mineral chemistry data for the ultramafic sequenceof the Hartley Complex are presented with the object of evaluatingemplacement mechanisms, crystallization history and sub-solidusre-equilibration processes for the Great ‘Dyke’.Mineral chemistry indicates in situ crystallizaration for theultramafic sequence, whereas textural evidence suggests thatlimited crystal settling of chromite took place. It is concludedthat crystallization of cumulus phases occurred at or near thefloor of the magma chamber. The mineral chemistry indicates that the volume of magma fromwhich each unit crystallized was significantly smaller thanthat represented by the stratigraphic succession of the HartleyComplex. The magma chamber may effectively have been part ofan open system during the crystallization of the ultramaficsequence. The results are consistent with the concept of a stratifiedmagma chamber and the process of double-diffusion convection. Modelling of the liquid line of descent and crystallizationsequences indicate that none of the previously proposed initialliquid compositions are likely to have constituted the parentalmagma of the Great ‘Dyke’. Rather than komatüticor exceptionally high magnesium liquids, as previously suggested,a parental magma with about 15 per cent MgO, similar to thecomposition of the chill phase of a dyke parallel to and inclose proximity to the East Dyke is in closest agreement withthe observed and modelled results. Chromite compositions are strongly related to textural and mineralogicalenvironments. Seam chromitites are higher in Cr, Mg and Fe³⁺than chromites enclosed in silicates. Chromite enclosed in cumulusolivine is higher in Fe²⁺ than that in coexisting pyroxenesbut there is little difference in the proportions of the trivalentcaptions. Seam chromitites are considered to have precipitatedin response to increases in foi associated with periodic influxesof magma into the magma chamber. The higher ferric iron contentof the seam chromitites compared with the chromite enclosedin the silicates is consistent with such a mechanism. Compositional zoning in olivine and pyroxene adjacent to enclosedchromite grains is interpreted as reflecting subsolidus re-equilibrationwith cooling. Zoning profiles exhibit strong crystallographiccontrol. Computer modelling using finite difference approximationshas allowed controlling factors to be assessed by optimizationof the modelled parameters to give closest agreement to themeasured results. Interdiffusion coefficients and distributioncoefficients for Fe²⁺ and Mg for olivine and pyroxene with chromiteare modelled and compared with published data. Indicated blockingtemperatures for olivine are of the order of 600 °C to 700°C and 750 °C to 850 °C for orthopyroxene. Thuschromites enclosed in orthopyroxene are more Mg-rich than thoseenclosed in olivine. Coarse-grained seam chromitites have beenlittle modified subsequent to crystallization but the compositionsof the associated silicates have been influenced by the modalabundance of the chromite. Geothermometers based on chromite-silicate equilibria are probablynot applicable to layered intrusions, but information on thermalhistories may be provided by evaluation of the diffusion profiles.     

华北地台沉积盖层的构成及演化

本文统计了华北地台盖层不同时代沉积地层的体积和质量，计算了其构成。并与世界主要地台区进行了对比，探讨了其体积、质量、构成的演化及其控制因素。通过显生宙沉积岩循环率的计算，进一步论证了盖层的发育主要是沉积岩本身的循环。     

Age and Melt Sources of Ultramafic Dykes and Rocks of the Bolshetagninskii Alkaline Carbonatite Massif (Urik-Iya Graben,SW Margin of the Siberian Craton)

Doklady Earth Sciences - The age of rocks of the Bolshetagninskii ijolite–syenite–carbonatite massif and ultramafic dykes within the Urik-Iya Graben in the southwestern part of the...     

The Age of Ultramafic Rocks of the Main Ural Fault

The results of U–Pb zircon age dating of ultramafic massifs occurring as a chain along the Main Ural Fault zone (MUF) are given. Three groups of ages were obtained (Ma): 2500?2800, 600?2100, and 430?440. The first age group represents the time of origin of the ultramafic rocks in the Earth’s mantle. The second age group records the time of metamorphism of these rocks prior to intrusion into the host rocks. The third age group determines the time of the intrusion of ultramafic magma into the host rocks. It was established that the intrusion of ultramafic magma along the entire length of the Ural ultramafic belt occurred in the age range of 430?440 Ma.     

The Range of Spinel Compositions in Terrestrial Mafic and Ultramafic Rocks

Compositional fields for spinels from a wide variety of mafic–ultramaficigneous rock types and tectonic environments have been determinedfrom a global database of over 26 000 analyses. These fieldsare defined using contoured data density plots based on thespinel prism, and plots of T iO₂ vs ferric iron, for mantlexenoliths, ophiolitic rocks, continental layered intrusions,alkalic and lamprophyric rocks, tholeiitic basalts, Alaskanultramafic complexes and komatiites. Several trends appear regularlyin the various environments: a trend of widely variable Cr/(Cr+ Al) at low Fe²⁺/(Mg + Fe²⁺) (the Cr–Al trend); increasingFe³⁺, Fe²⁺/(Mg + Fe²⁺) and T iO₂ at constant Cr/(Cr + Al) (Fe–Ti trend); a trend found primarily in kimberlites, similar toFe–T i but at constant Fe²⁺/(Mg + Fe²⁺); and an unusualtrend of increasing Al found only in layered intrusions. TheCr–Al and Fe–T i trends are both found to varyingdegrees in tholeiitic basalts. The Cr–Al trend is prevalentin rocks that have equilibrated over a range of pressures, whereasthe Fe–T i trend is dominantly due to low-pressure fractionation.The most Cr-rich chromites found in nature occur in boninites,diamond-bearing kimberlites, some komatiites and ophioliticchromitites. Exceptionally reduced chromites are found in somekomatiites and in ophiolitic chromitites. Detrital chromitesfrom the Witwatersrand conglomerates are of komatiitic provenance. KEY WORDS: basalt; chromite; kimberlite; ophiolite; spinel     

The First Find of Oxyborates in Rocks of the Norilsk-1 Intrusion (Northwestern Siberian Platform)

Doklady Earth Sciences - In the taxitic gabbro-dolerites of the upper contact zone of the Norilsk-1 intrusion, five boron minerals were found: kotoite Mg3(BO3)2, suanite Mg2B2O5, warwickite...     

Crystallization of Chromite and Chromium Solubility in Basaltic Melts

The equilibrium between chromite and melt has been determinedon four basalts at temperatures of 1200–1400?C over arange of oxygen fugacity (f_o2) and pressures of 1 atm and 10kb. The Cr content of chromite-saturated melts at 1300?C and1 atm ranges from 0?05 wt.% Cr₂O₃ at a log f_o2= –3 to1?4 wt.% at a log f_o2=–12?8. The Cr²⁺/Cr³⁺ of melt increaseswith decreasing f_o2 and is estimated by assuming a constantpartitioning of Cr³⁺ between chromite and melt at constant temperature.The estimated values of Cr²⁺/Cr³⁺ in the melt are at f_o2 valuesof 4–5 orders of magnitude lower than the equivalent Fe²⁺/Fe³⁺values. The Cr/(Cr+Al) of chromite coexisting with melt at constanttemperature changes little with variation of f_o2 below log f_o2=–6.Five experiments at 10 kb indicate that Cr₂O₃ dissolved in themelt is slightly higher and the Cr/(Cr + Al) of coexisting chromiteis slightly lower than experiments at 1 atm pressure. Thus variationin total pressure cannot explain the large variations of Cr/(Cr+ Al) that are common to mid-ocean ridge basalt (MORB) chromite. Experiments on a MORB at 1 atm at f_o2 values close to fayalite-magnetite-quartz(FMQ) buffer showed that the Al₂O₃ content of melt is highlysensitive to the crystallization or melting of plagioclase,and consequently coexisting chromite shows a large change inCr/(Cr + Al). It would appear, therefore, that mixing of a MORBmagma containing plagioclase with a hotter MORB magma undersaturatedin plagioclase may give rise to the large range of Cr/(Cr +Al) observed in some MORB chromite.     

中国西北地区超基性岩封存CO2潜力研究

超基性岩可通过碳酸盐化生成稳定的碳酸盐矿物,它是一种以地球化学手段有效且永久封存CO2的矿物。在自然界中矿物封存CO2可通过风化作用自发发生,人工干预能进一步提升碳酸盐化反应效率,促进工业化进程。笔者基于最新1∶100万西北地质图及数据库,试图对西北地区分布的超基性岩的封存潜力进行理论评估。结果表明,西北地区超基性岩封存CO2量可达963.23亿t,其中新疆超基性岩CO2封存量最大,可达613.52亿t,占西北地区总封存量的63.69%。西北地区超基性岩封存CO2量大致相当于全国2021年CO2排放量的10倍,在完全释放其固碳潜力的情况下,初步静态估算可封存全国CO2排放量约10年。因此,西北地区超基性岩封存CO2潜力巨大。未来,应针对单个超基性岩体收集已有大比例尺精细基础地质调查数据,并补充性开展调查及研究工作,进一步圈定CO2地质封存的有利靶区,促进超基性岩封存CO2的地质解决方案成为未来碳中和目标在西北地区落地实现的最优方案之一。     

新疆阿尔金长沙沟超镁铁质岩锆石U-Pb年龄及其地质意义

通过1∶50000地质填图,表明新疆长沙沟(蛇绿)构造混杂岩带超镁铁质岩主要岩石类型为斜长辉石角闪岩、辉石橄榄岩、强蛇纹石化辉石橄榄岩等;总体贫SiO2、CaO、K2O、Na2O,富含MgO、FeO特征,分异指数DI=0.35~14.45,固结指数SI=47.82~70.05,表明岩浆分异不明显,固结程度较高;里特曼指数σ=0.97,属钙性系列;M/F=1.94~4.39,属镁铁质超基性岩类;其中,辉石橄榄岩TiO2含量接近洋中脊地幔(TiO2=0.10%~0.40%),稀土元素、微量元素特征与地幔橄榄岩近似,认为属原始地幔分离产物,为蛇绿岩套组成部分;斜长辉石角闪岩可能为超镁铁质杂岩。首次获得了辉石橄榄岩206 Pb/238 U加权平均年龄为(510.60±1.40)Ma(MSWD=0.11),形成时代为寒武纪,其可能代表了南阿尔金洋盆早期的产物。     

云开地块晚二叠世富Fe-Ti-P超镁铁质岩的年代学、地球化学与岩石成因

为了更好地理解华南板块南缘二叠纪与三叠纪之交复杂的构造格局,通过岩石学、地球化学和年代学的方法,对粤西云开地区新发现的3处晚二叠世超镁铁质侵入岩进行了研究.这些岩石位于云开地块东缘的阳春三甲和地块中部的高州大井、东岸等地,呈小岩株、岩脉产出于云开岩群的片岩、变粒岩中.它们的主要岩性为辉石岩、角闪石岩、角闪岩和斜长角闪岩...