Geochemical structure of the Yoko-Dovyren layered dunite-troctolite-gabbro-norite massif,northern Baikal area

The application of the principle and algorithm of the cluster analysis of rock compositions in magmatic complexes, which were described elsewhere, made it possible to reveal the spaceless and spatial geochemical structure of the Yoko-Dovyren layered mafic-ultramafic massif. The diversity of rocks composing this intrusion was demonstrated to comprise eleven discrete geochemical types (clusters): dunites, harzburgites, melanotroctolites, troctolites, two types of olivine gabbro, two types of olivine gabbronorites, quartz gabbronorites, and granophyres. These geochemical types of rocks and the corresponding fractionation parameters (the iron atomic fraction f of mafic minerals and the anorthite concentration An of plagioclase) define a succession corresponding to the tendencies in the crystallization of a magma of respective composition. This geochemical succession is in complete agreement with the succession in which rocks were formed in the intrusion (from dunite in its bottom part to quartz gabbronorites and granophyres near its roof) and is complicated by cyclical repetitions. The main tendency revealed in the cyclic layering is as follows: cyclical intercalations consist of rocks corresponding to the neighboring members of the rock succession (plagiodunites and melanotroctolites, melanotroctolites and troctolites, troctolites and olivine gabbro, olivine gabbro and olivine gabbronorites). These tendencies are closely similar to those identified in the Kivakka intrusion, a fact suggesting that these tendencies can be common for all layered complexes of mafic and ultramafic rocks. Original Russian Text ? A.A. Yaroshevskii, S.V. Bolikhovskaya, E.V. Koptev-Dvornikov, 2006, published in Geokhimiya, 2006, No. 10, pp. 1027–1039.     

Geochronology of the Dovyren intrusive complex, northwestern Baikal area, Russia, in the Neoproterozoic

The paper reports newly obtained data on the geochronology of the Dovyren intrusive complex and associated metarhyolites of the Inyaptuk Formation in the Synnyr Range. The data were obtained by local LA-ICPMS analysis of zircons in samples. The U-Pb age of olivine-free gabbronorite from near the roof of the Yoko-Dovyren Massif is 730 ± 6 Ma (MSWD = 1.7, n = 33, three samples) is close to the estimated age of 731 ± 4 Ma (MSWD = 1.3, n = 56, five samples) of a 200-m-thick sill beneath the pluton. These data overlap the age of recrystallized hornfels found within the massif (“charnockitoid”, 723 ± 7 Ma, MSWD = 0.12, n = 10) and a dike of sulfidated gabbronorite below the bottom of the massif (725 ± 8 Ma, MSWD = 2.0, n = 15). The estimates are also consistent with the age of albite hornfels (721 ± 6 Ma, MSWD = 0.78, n = 12), which was produced in a low-temperature contact metamorphic facies of the host rocks. The average age of the Dovyren Complex is 728.4 ± 3.4 Ma (MSWD = 1.8, n = 99) based on data on the sill, near-roof gabbronorite, and “charnockitoid”) and is roughly 55 Ma older than the estimate of 673 ± 22 Ma (Sm-Nd; [13]). The U-Pb system of zircon in two quartz metaporphyre samples from the bottom portion of the Inyaptuk volcanic formation in the northeastern part of the Yoko-Dovyren Massif turns out to be disturbed. The scatter of the data points can be explained by the effect of two discrete events. The age of the first zircon population is then 729 ± 14 Ma (MSWD = 0.74, n = 8), and that of the second population is 667 ± 14 Ma (MSWD = 1.9, n = 13). The older value pertains to intrusive rocks of Dovyren, and the age of the “rejuvenated” zircon grains corresponds to the hydrothermal-metasomatic processes, which affected the whole volcano-plutonic sequence and involved the serpentinization of the hyperbasites. This is validated by the results of Rb-Sr isotopic studies with the partial acid leaching of two serpentinized peridotite samples from the Verblyud Sill. These studies date the overprinted processes at 659 ± 5 Ma (MSWD = 1.3, n = 3).     

攀西地区红格层状岩体的地球化学特征

红格岩体赋存有大型钒钛磁铁矿床，在橄辉岩相带和辉石岩相带底部有铂族元素（PEG）的矿化，是攀西层状岩体中重要的岩体之一，系统分析了红格层状岩体不同岩相带的微量元素和稀土元素特征，探讨了岩浆的结晶分异演化过程，提出岩体主体上是由一个岩浆房经正常的结晶分异形成的，底层的硫化物富集带和中上层位的钒钛磁铁矿是岩浆结晶分异产生的堆积相，并非是岩浆多次脉动式补给的结果。     

西天山查汗萨拉岩体的地球化学特征及岩石成因

查汗萨拉岩体位于西天山地区博罗科努山北坡查汗萨拉一带,处于伊连哈比尔尕金成矿带内,与金矿化关系较为密切,主要由闪长岩和辉长岩组成.研究表明:岩石属于准铝质钙碱性系列,总体上MgO,CaO,TFeO和TiO2随着SiO2的增高而有轻微的降低,Na2O,K2O,Al2O3和P2O5与SiO2没有明显的相关性;在微量元素配分...     

The Kalka layered intrusion,central Australia

The Kalka Intrusion, central Australia has a 5000 m-thick layered sequence comprising Pyroxenite, Norite and Anorthosite Zones; an Olivine Gabbro Zone is enclosed by, and has a facies relationship with, the Norite Zone. Contamination is evidenced by high initial ⁸⁷Sr/⁸⁶Sr ratios ( 0.708) in the lower four-fifths of the intrusion, and resulted in pyroxenite rather than peridotite as a basal crystal accumulate. After an early phase of erratic buildup in contamination due to assimilation of ragged granulite wall-rock, armouring of the walls and mixing produced an homogeneous Norite Zone (threshold) magma body crystallising opx-cpx-plag. Within the succeeding 3500 m of section plagioclase An values have a general decline up sequence (An_74-60-feldspar threshold) with superimposed short term digressions to more calcic compositions. Initial ⁸⁷Sr/⁸⁶Sr ratios also fall very gradually (0.7081-0.7078 — isotopic threshold) with transient fluctuations to distinctly lower values. Maxima in plagioclase An contents and ⁸⁷Sr/ ⁸⁶Sr minima may be correlated with the spasmodic appearance of olivine and pronounced lithological variation. Such features are explained by the ponding of fresh bodies of uncontaminated magma on the floor of the chamber; these formed a hybrid with threshold magma that temporarily dominated crystallisation thereby perturbing plagioclase and isotopic compositions; eventually, mixing of the hybrid into the overlying threshold magma returned crystallisation to its initial state. The facies-controlled Olivine Gabbro Zone is the physical expression of ponded basal hybrid magmas. The onset of the Anorthosite Zone is marked by a pronounced decline in ⁸⁷Sr/⁸⁶Sr ratios to around 0.705 registering a major influx of new magma. In this instance the new magma dominated the system and a change to plagioclase as the dominant liquidus phase indicates a drastic change in input magma composition. The evolution of Kalka was determined by an interplay of crystal fractionation, fresh magma pulses, and magma mixing, with the latter effects producing both increases and decreases in plagioclase An contents; the complete process can only be revealed by combined mineral composition and isotopic data.     

新疆北山地区旋窝岭镁铁-超镁铁岩体的年代学、岩石矿物学和地球化学研究

新疆北山地区的旋窝岭岩体侵位于下石炭统红柳园组变质砂岩中,辉长岩的锆石SIMSU-Pb定年结果为260.7±2.0Ma,晚于区域上其它岩体的成岩年龄。该岩体由橄榄岩、橄长岩、橄榄辉长岩和辉长岩组成,岩石较新鲜,具有典型的包橄结构和辉长结构,各岩性中均可见斜长石,而斜方辉石仅在辉长岩中出现。橄榄石的Fo值在80～85之间,NiO含量介于0.1%～0.2%之间;单斜辉石主要为普通辉石和透辉石,斜方辉石为古铜辉石。这些镁铁质矿物和斜长石成分与全岩的地球化学特征具有很好的相关性,说明该岩体母岩浆的演化过程主要受控于结晶分异作用。全岩的MgO含量在9.5%～21.8%之间,具有平坦的稀土配分型式和正Eu异常以及微量元素Nb、Zr、Hf的负异常等。因此,旋窝岭岩体可能是在北山裂谷形成过程中由于岩石圈地幔高程度部分熔融形成的高镁玄武质岩浆分异演化的产物,具有一定的铜镍硫化物矿床的成矿潜力。     

黔西北威宁地区香炉山铜矿床地质地球化学特征及成因

黔西北威宁地区香炉山铜矿床赋存于峨眉山玄武岩组第三段(P3β3)顶部与宣威组(P3X)底部间的结合部位。本文采用主量元素、微量元素、稀土元素和扫描电镜分析方法对其地质地球化学特征进行了研究,并探讨了矿床成因。结果表明:区内玄武岩属高钛的拉斑玄武岩,主量元素物源区特征图和微量元素分析结果表明其成岩、成矿物质来源与峨眉山玄武岩密切相关,同时又受到地壳物质的影响;稀土元素表现出轻稀土富集、重稀土亏损的右倾分配模式,Eu负异常以及log(δCe)-0.1表明矿床形成于还原环境;扫描电镜分析发现了α+β-Zn-Cu合金矿物,化学分子式为Cu0.78Zn0.47Fe0.06。结合区域地质背景和矿床地质特征,认为该铜矿床的形成不仅与火山作用和沉积成岩作用有关,而且还受到后期热液活动的影响。     

Geochemical structure of the Kivakka layered olivinite-norite-gabbronorite intrusion,North Karelia: Distribution of chalcophile elements

The distribution of elements and their correlations were analyzed throughout the section of the Kivakka intrusion to formulate the geochemical tendencies in the behavior of elements of different groups during formation of layered basic-ultrabasic complexes. (1) It was shown that the distribution of trace elements in the layered series is controlled by their ability or inability to enter isomorphically the cumulus minerals. The distribution of trace elements that occur as isomorphic admixtures in cumulus minerals (Cr, Mn, Zn, Co, Ni, and Ti), regardless of their geochemical type, is correlated with the crystallization order and distribution of minerals in the silicate matrix of the rocks. Elements that practically are not involved into silicates (S, Cu, Ag) show no any systematic variations; i.e., they are not controlled by fractionation of major rock-forming mineral. Their behavior is driven by the appearance of individual phase—sulfide melt, whose localization, formation time, and scales of fractionation are determined by saturation of parental melt in sulfide sulfur and general degree of its fractionation. (2) The comparison of cross-section variations of elements that isomorphically substitute for major elements in the Fe-Mg silicates, but differ in chalcophile affinity (in order of increase of chalcophile affinity: Mn → Zn → Co → Ni) reflects the contribution of unmixing and fractionation of sulfide melt during intrusion solidification. This is quantitatively defined primarily by partitioning coefficients of elements between cumulus silicates and magmatic melt, on the one hand, and between magmatic and sulfide melts, on the other hand. (3) The absence of simple correlation between local sulfide-rich horizons and silicate matrix of the rocks and signs of independent fractionation of sulfide melt prevent any attempts to predict the localization and scales of local sulfide mineralization within the layered series on the basis of petrochemical and related criteria. Only tendencies in the distribution of ore elements and sulfur across the section can be used for these purposes.     

Loveringite from the koitelainen layered intrusion,Northern Finland

Summary Conditions favouring the crystallization of loveringite, (Ca, REE) (Ti, Fe, Cr)₂₁ 0₃₈ in Koitelainen were sustained from the base of the lower zone to the upper part of the main zone. Loveringite is most common in rocks with much intercumulus quartz, potassium feldspar, and phlogopite, and is accompanied by accessories such as zircon, chlorapatite, baddeleyite and thorite. It is particularly common among pyroxene cumulates in the upper part of the lower zone. Here, and apparently also in plagioclaseorthopyroxene-clinopyroxene cumulates of the main zone, loveringite occurs as a cumulus phase. The presence of Cr in the intercumulus liquid is not essential to the stability of loveringite; instead, petrographic evidence and the presence of incompatible elements (Zr, Hf, REE, U, Th) contained in loveringite point to the crucial role of crustal contaminants. Loveringite crystallized in parts of the magma chamber heavily contaminated by acid crustal anatectic melt, and eventually settled from density flows loaded with cumulus crystals. Postcumulus reactions produced concentric ilmenitezircon mantles around loveringites and thus contributed to the compositional heterogeneity of the mineral. We suggest that much of the loveringite that once crystallized in layered intrusions may have been consumed through postcumulus reactions. Loveringite is easy to detect under the reflected light microscope and can be readily distinguished from rutile, chromite and ilmenite, but not from some other members of the crichtonite group. The composition of the Koitelainen loveringite is comparable to that of other occurrences. The spectral reflectance values are 2–3% lower as compared to ilmenite. The reflectance data indicate that the mineral is anisotropic. The VHN₁₀₀ values, 792–933, are significantly higher than those published heretofore.[/p]

---

Loveringit aus dem Intrusiv-Komplex von Koitelaineen, Nordfinland

Zusammenfassung In der Koitelainen-Intrusion waren während der magmastichen Etwitcklung der Gesteine der älower zone" und ämain zone" die Bedingungen für die Bildung von Loveringit, (Ca, REE) (Ti, Fe, Cr)₂₁ O₃₈, erfüllt, der in Gesteinen mit Quarz, Kalifeldspat und Phlogopit als Interkumulus, häufig auftritt. Sein Vorkommen ist eng verknüpft mit akzessorischen Mineralen wir Zirkon, Chlorapatit, Baddeleyit und Thorit. Ebenso häufig wurde Loveringit in den Pyroxen-Kumulaten der älower zone" und in PlagioklasOrtho-und Klinopyroxen-Kumulaten der ämain zone" als Kumulus-Phase gefunden. Die Anwesenheit von Cr in der Interkumulus-Schmelze ist kein wesentlicher Faktor für die Stabilität des Loveringits. Vielmehr zeigen petrologische Hinweise und die Konzentration der inkompatiblen Elemente (Zr, Hf, seltene Erden, U, Th) in Loveringit die entscheidende Rolle der krustalen Kontamination des Magmas bei seiner Bildung an. Es kristallisierte in Teilbereichen der Magmenkammer, die durch krustale anatektische Schmelze stark kontaminiert war. Reaktionen während der Postkumulusphase führten zur Bildung von konzentrischen Ilmenit-Zirkon-Säumen um Loveringitkristalle und bewirken eine chemische Inhomogenität sowie teilweise Aufläsung des Minerals. Aufgrund dieser Beobachtungen wird vermutet, daß ein großer Teil der in älayered intrusions" einmal kristallisierten Loveringite bei Reaktionen in der Postkumulusphase von der Schmelze wieder konsumiert wurde. Die chemische Zusammensetzung des Loveringits von Koitelainen ist mit der aus anderen Vorkommen vergleichbar. Mikroskopisch läßer sich anhand seiner Reflexionsdaten ohne weiteres von den Begleitmineralen Rutil, Chromit und Ilmenit unterscheiden. Die spektrale Reflexion von Loveringit ist 2–3% niedriger als bei Ilmenit. Die VHN_1OO-Werte mit 792–933 sind im Vergleich zu den bisher publizierten Daten wesentlich höher.

---

---

With 7 Figures     

Cluster and R-mode factor analyses on soil geochemical data of Masjed-Daghi exploration area, northwestern Iran

Masjed-Daghi is located in Julfa sheet (1:100,000 series) in the northwest of Iran. The area consists of a very likely gold mineralization bearing epithermal mineralization which appears to be associated with a porphyry Cu–Mo system at deeper levels. Ninety-three soil samples were collected and analyzed for 13 elements (Au, Mo, Cu, Pb, Sn, Ag, Zn, Cr, Mn, Ba, Be, Ni, Co) by using emission spectrometry and atomic absorption spectrophotometry. The data were processed and interpreted using univariate and multivariate statistical analyses. The distribution of the majority of variables is slightly to moderately positively skewed which can be interpreted by log-normal model. Only Ni, Be, and Mn show normal distribution. Based on cluster analysis, the variables can be classified into two main groups. The first group consists of the main ore forming elements such as Au, Ag, and Ba which belong to epithermal system and Mo, Sn, and Cu which have more affiliation to porphyry mineralization. The principal component analysis extracted three factors. These factors calculated using varimax rotated R-mode factor loading matrix account for more than 65 % of the total variance. The first factor represents the main constituents of the epithermal system (Au, Ag, Ba) and its geochemical halo at the northeast of the study area. The second factor represents the main constituents of the porphyry system (Cu, Mo, Sn) and its geochemical halo in the western part of the study area which is overlapped with the volcanic rocks affected by local intrusions with higher alteration overprint. The third factor, however with less significance, represents Pb and Zn which are not the main ore constituents but can be considered as pathfinder elements. The results have been used to locate hidden orebodies using presented factor score mapping.     

南阿尔金山清水泉镁铁-超镁铁质侵入体LA-ICP-MS 锆石U-Pb同位素定年及其意义

清水泉镁铁-超镁铁质层状侵入体位于南阿尔金山阿帕—茫崖构造带中-北部的清水泉地区,其北部与南阿尔金山超高压变质带紧邻。该岩体包含有3～4个由辉石橄榄岩-角闪辉长岩构成的岩浆旋回,与元古宙变质沉积岩系呈侵入接触关系。对其中的角闪辉长岩进行了LA-ICP-MS锆石U-Pb同位素测年,其206Pb/238U表面年龄为(461±2)Ma～(471±2)Ma,其加权平均值为(467.4±1.4)Ma(n=21,MSWD=2.5),所测锆石具有明显的岩浆振荡环带,Th/U比值为0.32～1.16(平均0.64)。测年结果显示,清水泉镁铁-超镁铁质岩体的形成时代晚于南阿尔金山超高压变质岩的峰期变质时代(504～487 Ma),而老于该地区A型花岗岩的时代(425 Ma左右)。分析认为,伴随着同时代的"双峰式"岩浆侵入作用及广泛的变质热事件,大约465 Ma时的南阿尔金山已经由前期的陆-陆碰撞造山阶段转入到了碰撞后的裂谷伸展作用阶段。     

塔里木板块东北部坡一镁铁质-超镁铁质层状侵入体岩石成因

坡一侵入体位于塔里木板块东北部坡北岩体内,是该岩体第三阶段岩浆活动形成的十几个小侵入体中的一个,锆石U-Pb年龄为278±2Ma。该侵入体属于以超镁铁质岩石为主的层状岩系,堆晶结构与韵律性堆晶层理非常发育。岩浆分异充分,形成了从纯橄岩到石英闪长岩的多种岩石类型。在超镁铁质岩石中,所有的橄榄石和大部分斜方辉石是堆晶相,少量斜方辉石是填隙相,大部分单斜辉石、褐色普通角闪石和黑云母是填隙相。在镁铁质岩石中,橄榄石和斜方辉石全部是堆晶相,单斜辉石与斜长石既可以是堆晶相,也可以是填隙相;褐色普通角闪石、黑云母和石英均为填隙相。超镁铁质岩石属拉斑玄武岩系列,镁铁质岩石属钙碱性系列。侵入体中大量存在的捕掳体、微量元素地球化学、Nd-Sr同位素组成的EMⅡ型演化趋势,充分证明了同化混染作用伴随岩浆演化过程而逐渐增强,并不断促进了岩浆的分异,而且导致了岩石化学系列的转化。PGE和亲硫元素地球化学以及硫同位素组成证明,硫主要来自于岩浆,硫化物形成于岩浆阶段,岩浆未经历过早期硫化物熔离作用,硫化物熔离起始于橄榄岩相结晶的晚期阶段,并伴随着此后的岩浆演化过程而继续熔离。硫化物熔离是岩浆自身演化和同化混染共同作用的结果。橄榄石Fo分子含量和全岩FeO含量显示,原生岩浆是苦橄质岩浆;源区物质应该是石榴石辉石岩;岩浆生成于地幔柱轴部。在塔里木板块东北部还存在分别来自于软流圈和亏损型大陆岩石圈地幔的二叠纪岩浆岩,它们都应该是塔里木大火成岩省的组成部分。     

Partial Melting and Assimilation of Dolomitic Xenoliths by Mafic Magma: the Ioko-Dovyren Intrusion (North Baikal Region, Russia)

A petrological study was carried out on Mg-skarn-bearing dunitecumulates that are part of the Neo-Proterozoic Ioko-Dovyrenintrusion (North Baikal region, Russia). Skarn xenoliths containbrucite pseudomorphs after periclase, forsterite and Cr-poorspinel. Fine-grained forsterite–spinel skarns occur withthe brucite skarns or as isolated schlieren. Field relationshipsreveal that the Mg-skarns formed from silica-poor dolomiticxenoliths by interaction with the mafic magma of the Ioko-Dovyrenintrusion. Rapid heating of dolomitic xenoliths by the maficmagma caused the decomposition of dolomite into calcite + periclase,releasing much CO₂. Further heating quantitatively melted thecalcite. A periclase-rich restite was left behind after extractionof the low-density, low-viscosity calcite melt. The extractedcalcite melt mixed with the surrounding mafic melt. This resultedin crystallization of olivine with CaO contents up to 1·67wt %. A local decrease in the silica concentration stabilizedCaAl₂SiO₆-rich clinopyroxene. Brucite/periclase-free forsterite–spinelskarns probably originated by crystallization from the maficmelt close to the xenoliths at elevated fO₂. The high fO₂ wascaused by CO₂-rich fluids released during the decompositionof the xenoliths. The above case study provides the first evidencefor partial melting of dolomite xenoliths during incorporationby a mafic magma. KEY WORDS: dunite; dolomite assimilation; partial melting     

新疆北山地区罗东镁铁质-超镁铁质层状岩体岩石成因

罗东镁铁质-超镁铁质岩体位于塔里木板块东北部的新疆北山地区,岩体平面形态为眼球状,出露面积约2.1 km2.由纯橄岩、单辉橄榄岩、斜长二辉橄榄岩、橄榄二辉岩、方辉辉石岩、橄长岩、橄榄辉长岩、辉长岩、苏长辉长岩和淡色辉长岩组成,堆晶结构和堆晶韵律发育,属于层状岩体.岩浆演化过程中主要分离结晶/堆晶相是橄榄石和单斜辉石,此...     

激电与土壤化探方法在滇西北衙地区的勘查效果及应用前景

为了获得北衙超大型金多金属矿床外围找矿工作的突破,本文在已知典型矿床模型上,开展直流激电与双频激电方法的对比试验研究。结果表明,两种方法都能有效揭示已知矿体的分布,但直流激电具有更强的抗干扰能力和更高的深部分辨率,所以直流激电方法可能更为适合北衙矿区。土壤化探资料揭示北衙远景区I土壤里高丰度的铅锌含量对激电异常具有较大干扰。利用直流激电与土壤化探的方法组合,揭示了北衙远景区II矿体的分布范围,取得了良好的应用效果,为北衙外围找矿提出了有效的技术方法组合建议。     

云南省德钦县红坡牛场铜金矿区果腊复式岩体年龄、地球化学特征及其构造与找矿意义

位于江达-维西火山弧铁-铜-铅-锌多金属成矿带的德钦县红坡牛场铜金矿床,是与果腊复式侵入体有关的矽卡岩型-热液型多金属矿床。LA-ICP-MS锆石U-Pb数据表明,复式岩体核部（石英二长岩）侵位年龄为226.4±2.0Ma,边部（石英闪长玢岩）为36.59±0.22 Ma,显示为印支期和喜马拉雅期2期岩浆活动的产物。核部石英二长岩具高SiO2（65.8%~68.5%）和低MgO（1.40%~2.17%）含量,属高钾钙碱性系列;高Sr,低Yb与Y含量证实其埃达克岩属性。地球化学特征及对比表明其很可能起源于加厚的陆壳底部,源区物质相当于榴辉岩的组成,而非俯冲洋壳熔融的产物。边部石英闪长玢岩具低SiO2（55.8%~56.6%）,高MgO（6.45%~7.50%;Mg#=52.4~62）、Cr（228×10-6~353×10-6）和Ni（72.3×10-6~90.0×10-6）,为典型的高镁闪长岩。地球化学特征显示其为下地壳物质在地幔深部发生熔融的产物。研究成果为金沙江古特提斯洋演化提供了新的年代学约束,在江达-维西火山弧带发现喜马拉雅期岩浆活动,对于重新认识该矿床成因及后续江达-维西带成矿规律总结和找矿方向具有重要的指导意义。     

Vermicular orthopyroxene-magnetite symplectites from the Wateranga layered mafic intrusion,Queensland, Australia

Orthopyroxene-magnetite intergrowths (symplectites), partly or completely surrounding olivine, are described from the Wateranga layered mafic intrusion, Queensland, Australia. The texture occurs in unmetamorphosed plagioclase-rich norites, olivine gabbros and troctolites in which the primary minerals are olivine (Fo_63–69) orthopyroxene (En_66–72), clinopyroxene (Wo₄₂En₄₂Fs₁₆), plagioclase (An_49–65), hornblende, ilmenite, magnetite and sulphides. Symplectites range from incipient fine grained developments around corroded olivine grains to intricately formed pseudomorphs after olivine and slow a consistent orthopyroxene/magnetite ratio. Orthopyroxene in symplectites is commonly in optical continuity with surrounding magnetite-free orthopyroxene rims. Later intercumulus hornblended has replaced orthopyroxene. There is marked chemical similarity between primary and simplectite, orthopyroxenes and magnetites. Textures similar to those described here are considered elsewhere to have formed at a late magmatic stage or by solid state reactions involving subsolidus oxidation of olivine. In the Wateranga intrusion textural relations, the chemical similarity between primary and symplectite phases, and the consistent volume proportions of magnetite and orthopyroxene in the intergrowths suggest that they developed during late magmatic crystallization.     

铜陵舒家店岩体的年代学和地球化学特征研究

舒家店岩体位于长江中下游中部的铜陵断隆区与繁昌断凹区(盆地)的过渡部位,主要的岩石类型有辉石闪长岩、石英闪长玢岩、花岗闪长斑岩、闪长岩以及闪长玢岩.本文通过对岩体中主要岩性-辉石闪长岩锆石LA-ICP MS精确定年、地球化学组成以及Pb同位索的分析,研究舒家店岩体的年代学、岩浆源区、岩浆演化和构造背景等问题.研究显示,...