云南省武定县迤纳厂铁铜矿区古元古代辉绿岩锆石的U-Pb年龄及其地质意义

云南省武定县迤纳厂铁铜矿区广泛出露元古宙辉绿岩体。前人对区内基性岩浆岩研究程度较低,缺乏辉绿岩的形成时代资料。本文报道了区内海孜辉绿岩中锆石的LA-ICP-MS U-Pb年龄,为1728±4 Ma。此年龄与古元古代晚期扬子地台西南缘大规模非造山型岩浆活动及全球性Columbia超级大陆裂解时代高度一致,表明其可能为Columbia超级大陆裂解的产物。辉绿岩与区内铁铜矿床成矿时代大致相当,反映了古元古代晚期扬子地台西南缘大规模的岩浆活动也可能是一次重要的成矿事件,可能为铁、铜成矿作用提供主要的成矿物质来源。武定地区被辉绿岩侵入接触的原"美党组"地层的沉积时代应大于辉绿岩的侵位时代,应划入下元古界汤丹群,是昆阳陆内裂谷拉张以前就已存在的基底地层。     

云南东川铜矿区古元古代辉绿岩地球化学 ——Columbia超级大陆裂解在扬子陆块西南缘的响应

近年研究显示,古元古代晚期,扬子陆块西南缘发生了大规模的地幔物质上涌事件。本文系统报道了康滇地区中部东川铜矿因民 落雪矿区古元古代辉绿岩的地球化学特征。主量元素中MgO含量较高,为6.16%～9.65%,Mg#平均为72.2;富Na2O,Na2O/K2O为1.3～9.8;低SiO2,45.61%～49.34%;低TiO2,0.74%～2.74%;FeO/MgO小于1,表明本区辉绿岩初始岩浆相对较原始,MgO与主要组分的相关性表明岩浆早期出现过轻微的橄榄石、斜方辉石及铬铁矿、钛铁矿结晶分异。(La/Yb)N为1.66～4.37,δEu为1.04～1.22,稀土元素球粒陨石的配分呈平缓右倾模式,出现Eu的弱正异常。富集Rb、Ba等大离子半径元素,MORB配分为向右陡倾模式,出现突出的Rb、Ba峰,Zr、Hf弱负异常,多数样品没有明显的Nb、Ta异常。εNdt为－0.2～3.8,初始87Sr/86Sri值为0.7055～0.7084。东川地区辉绿岩的源区为尖晶石二辉橄榄岩相,为较亏损的过渡型地幔部分熔融的产物,轻度混染主要源于陆下岩石圈地幔及少量的下地壳物质。东川古元古代辉绿岩地球化学表现为明显的板内玄武岩、E MORB和OIB的特征,表明古元古代末期,扬子陆块西南缘发生了大规模的陆内裂谷拉张事件,与全球性Columbia超级大陆裂解同步,可能与地幔柱活动密切相关。     

扬子地台西南缘朱家坝辉绿岩地球化学特征及其地质意义

近年来在扬子西缘大量的早—中元古代岩浆岩证据显示扬子地台内形成的断陷盆地及早中元古代岩浆岩与全球性的Columbia超大陆裂解事件有着密不可分的联系。这种联系主要表现在区内早中元古代的岩浆岩地球化学特征上。为了探讨武定裂陷槽朱家坝辉绿岩的地球化学特征及其意义,以12块朱家坝辉绿岩的地球化学分析数据为基础,在分析了其主微量和稀土元素的特征之后发现朱家坝辉绿岩w(SiO_2)为44.16%～48.08%,w(K_2O+Na_2O)为3.54%～4.26%,在化学成分上属于钙碱性岩石;其稀土元素的总量为183.1×10^-6～206.91×10^-6,LREE/HREE=1.44～1.96,表明在其形成过程中发生了明显的地壳混然或者是岩浆分异作用,其化学成分基本可以反映出岩浆源区的化学组成特征。基于此,对朱家坝辉绿岩进行了源区性质、构造环境和可能的成因机制探讨,认为朱家坝辉绿岩形成于拉张环境之中,很有可能是在昆阳裂谷形成初期形成,其岩浆来源于较富集的地幔源区,形成过程中几乎没有地壳物质参与。     

扬子地台西南缘康滇断隆带海孜双峰式侵入岩体年代学、地球化学及其地质意义

海孜辉绿岩-花岗斑岩双峰式侵入岩体位于扬子地台西南缘康滇断隆带中的武定-元江裂陷槽内,本文对海孜辉绿岩和花岗斑岩主要进行了LA-ICP-MS锆石U-Pb定年和地球化学研究。花岗斑岩的定年结果为1764±18Ma,辉绿岩的定年结果为1765±5.4Ma。岩相学及地球化学测定数据显示海孜地区辉绿岩具有细粒和粗粒两种结构,与花岗斑岩之间存在明显的组分间断,形成双峰态,其中花岗斑岩为钙碱性(Si O2=70.93%~73.04%,σ=1.28),辉绿岩属过碱性(Si O2=42.46%~48.26%,σ=15.3),Hf同位素特征表明两者可能均与幔源母岩浆相关。而海孜双峰式分布特征显示大陆裂谷拉张环境的构造背景,暗示海孜岩体是1.7Ga时昆阳裂谷裂解时期产物,与全球Columbia超大陆的裂解事件相呼应。作为扬子地台西南缘首次发现的1.7Ga双峰式侵入岩,海孜双峰式侵入岩的发现具有重要的地质意义。     

徐州地区辉绿岩地球化学特征

对徐州栏杆地区侵位于元古代地层中的辉绿岩进行了系统的地球化学研究。栏杆地区的辉绿岩属于板内玄武岩系列岩石,地球化学特征上略富集轻稀土元素(LREE),富集大离子亲石元素(LILE),略亏损高场强元素(HFSE),相对富集Cr和Ni;微量元素显示了EM-OIB(富集地幔-洋岛玄武岩)的特征,辉绿岩稀土元素特征显示在岩浆上侵过程中经历了分离结晶作用。结合新元古代全球Rodinia超大陆裂解事件及其岩浆活动与地幔柱的密切关系,认为徐州地区新元古代辉绿岩可能为地幔柱作用在华北陆块边缘的记录。     

川西丹巴地区新元古代变质玄武岩成因及构造意义

对扬子地块西缘康滇裂谷北段的丹巴变质玄武岩进行了系统的岩石学、元素-Nd同位素地球化学研究,结果表明该岩石为碱性玄武岩,样品相对富MgO、富TiO2,Mg#值介于0.51～0.59之间.稀土总量较高,轻重稀土分馏较明显,Th、Nb、Ta、Zr、Hf和LREE等不相容元素富集,Y和HREE明显亏损,地球化学特征与洋岛玄武岩(OIB)类似.岩浆形成于板内裂谷环境,起源于类似OIB的地幔源区,并在上升过程中受到了大陆岩石圈地幔(SCLM)物质不同程度的混染,同时还可能有少量下地壳物质的混染.样品在岩石化学上表现出地幔柱岩浆作用的痕迹,很可能与导致Rodinia超级大陆裂解的新元古代地幔柱事件有关.     

北祁连西段熬油沟组玄武岩地球化学特征及构造意义

北祁连造山带是一典型的板块缝合带,其中镶嵌着众多大小不一的由前震旦系变质岩系组成微陆壳残块,为解析北祁连前造山构造过程提供了重要的研究载体。北祁连西段卡瓦—祁青一带分布有较为完整的中元古界长城系朱龙关群熬油沟组火山岩—碎屑岩—碳酸盐岩建造。岩石地球化学研究表明,熬油沟组玄武岩主量元素含量变化较为稳定,具高K_2O(4.27%~6.07%),TFe_2O_3(10.49%~13.01%),Ti O_2(1.96%~2.90%)以及中等的Mg O(5.37%~6.71%,Mg~#48~51),Ca O(2.57%~5.51%),为钾玄碱性玄武岩。岩石Cr和Ni含量随着Mg~#降低而减小、Ca O与Ca O/Al_2O_3呈正相关,明显富集轻稀土元素(LREE)和大离子亲石元素(LILE),轻微正Eu异常,高含量的高场强元素(Nb,Ta,Ti),以及元素对Gd/Yb(2.5~3.0),Zr/Y(8.6~10.2),Ta/Yb(0.96~1.23),Ti/Yb(5 074~6 021),Zr/Yb(81~97),Ce/Nb(1.87),Zr/Nb(6.41)值均揭示了熬油沟组玄武岩具有洋岛玄武岩(OIB)地球化学特征。结合区域地质背景研究表明,熬油沟组碱性玄武岩源于类似于OIB的深部富集地幔,在岩浆作用过程中发生过橄榄石和单斜辉石的分离结晶作用以及一定程度的大陆地壳物质的混染作用,形成于大陆裂谷背景,并认为其是对中元古代Columbia超大陆裂解的响应,进一步为中元古代华北克拉通裂解与Columbia超大陆裂解事件的关系提供了重要的岩石学证据。     

扬子克拉通西缘1.73Ga非造山型花岗斑岩的发现及其地质意义

首次发现扬子克拉通西缘古元古代晚期海孜斜长花岗斑岩岩体.本文报道了其锆石的LA-ICP-MS U-Pb年龄,为1730±15Ma(MSWD=4.0,n=15).岩石具有高SiO2(69.77％～73.83％)、高碱(ALK=5.46～6.65)、低钾(K2O/Na2O=0.02～0.14)含量.里特曼指数1.04～1.65,A/CNK值为1.11～1.25,平均值为1.18(＞1.1),10000 Ga/Al=3.96～7.34(均值为5.18＞2.6),较高的含铁指数[FeO/(FeO+MgO) =0.95～0.99],总体显示了低钾钙碱性过铝质(SP)铁质A型花岗岩的特点.岩石富集Nb、Ta、Zr和Hf等高场强元素,强烈亏损K、Sr和Ba等大离子亲石元素,稀土元素总量∑REE=390.70×10-6～674.91×10-6,LREE/HREE=1.74～3.29(均值2.18),轻稀土分异作用明显,相对富集,表现出强烈的负Eu异常.地球化学特征显示,海孜花岗斑岩岩体为形成于板内伸展构造环境,可能与同期基性岩浆活动的底侵作用相关.海孜花岗岩的年龄和地球化学表明,扬子克拉通西缘存在古元古代晚期与全球性Columbia超级大陆裂解同期的双峰式岩浆岩组合.     

湖南中—新元古代火山—侵入岩地球化学及成因意义

江南造山带西段湖南中、新元古代火山－侵入岩具有截然不同的地球化学特征。中元古代火山－侵入岩金属亚碱性玄武岩类，MgO,Ni,Cr含量及Al2O3/TiO2比值高，稀土元素分馏形式多样，更多地具有岛弧火山岩的特征，新元古代中基性火山－侵入岩MgO,Ni,Cr含量较低；其中的基性岩大多属碱性玄武岩类，并较富TiO2,Al2O3/TiO2比值较低，HFSE明显富集，微量元素标准化曲线与OIB类似，具有裂谷玄武岩的特征。中元古代南桥玄武岩εNd(t)为6．86－8．98，具有明显的N－MORB特征，是俯冲带附近的古洋壳残片，为九岭古岛弧提供了新的证据。中元古代的益阳玄武岩εNd(t)为1．56－1．76，Nb,Ti,Zr亏损，Th相对富集，具俯冲带火山岩的地球化学特征，同时这些玄武岩具有高MgO、高Al2O3/TiO2比值和Ni,Cr含量，具科马提质玄武岩的特性，可能是局部地幔柱－弧相互作用的产物。新元古代早期益阳安山质集块岩Th,La,Sm和Nd富集，Nb,Ti,Zr和Hf亏损，εNd(t)值为－0．53－－1．05，是格林威尔造山运动的产物。新元古代黔阳，古丈、高桥火山－侵入岩原始地幔标准化曲线近似于OIB，具裂谷玄武岩的特征，黔阳，古丈基性岩εNd(t)值在1．09－1．69，来源于软流圈地幔，湖南这些中－新元古代火－侵入岩的地球化学特征记录了Radinia超大陆在该区从拼合到裂解的演化踪迹。     

云南武定左所辉绿岩铂族元素地球化学、Pb同位素及其地质意义

古元古代晚期至中元古代早期,西南康滇地区发生过一次强烈的构造、岩浆及成矿事件,即昆阳裂谷,以广泛出露1.8~1.5 Ga基性岩浆岩及铁铜矿床为重要标志。文章报道了滇中武定地区左所辉绿岩的岩石化学、微量元素、Pb同位素及铂族元素地球化学特征,通过铂族元素地球化学对昆阳裂谷期的岩石圈演化、壳幔相互作用进行了探讨。左所辉绿岩相对富碱(w(Na_2O+K_2O)平均为3.55%),低w(Si O_2),较高的w(Ti O_2)(均值为3.30%)、w(P_2O_5)(平均值0.35%),Ca O/Ti O_2比值(平均值为2.4)及Al_2O_3/Ti O_2比值(平均值为3.4)低,具有典型地幔热柱玄武岩的岩石化学特征。左所辉绿岩微量元素中相对富集大离子半径元素,高场强元素弱亏损,稀土元素中出现弱的Eu负异常,反映了斜长石的轻度结晶分异。辉绿岩具有较高的铂族元素含量,PPGE和IPGE明显分异,PGE原始地幔标准化配分曲线呈较明显的左陡倾型。辉绿岩的Cu/Pd比值均低于原始地幔值,表明原始岩浆S不饱和,亦未发生硫化物的熔离过程,较高的PGE含量可能与初始岩浆本身的S含量较高有关。高的Pd/Ir比值可能与IPGE在部分熔融过程中更倾向于残留相以及岩浆演化早期铬铁矿和橄榄石的结晶分异有关。低程度的地幔部分熔融、Pb同位素特征暗示左所地区辉绿岩的形成过程:陆内裂谷环境下,富硫的原始岩浆在上升过程中受到较少下地壳物质的混染,侵位至浅表并较快冷却,形成辉绿岩。     

高压微波消解法测定醋酸纤维过滤器采集的微尘粒子中的砷镉钴铬铜铁锰镍铅钒锌

最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提     

A catastrophic rockslide-debris flow in Wulong, Chongqing, China in 2009: background, characterization, and causes

On June 5, 2009, a catastrophic rockslide-debris flow occurred at the crest of the Jiweishan Mountain in Wulong, Chongqing, China. Approximately five million cubic meters of limestone blocks slid along a weak interlayer of bituminous and carbonaceous shale. The source mass descended from the upper part of the slope rapidly, crossing a 200-m wide and 50-m deep creek in front of it. Blocked by the opposite steep creek wall, the sliding mass changed its direction and traveled a further 2.2 km along the creek in debris-flow mode, finally forming a large accumulation zone with an average depth of 30 m. This is one of the most catastrophic rockslide events in recent years in China. It buried 12 houses and the entrance of an iron mining tunnel where some 27 miners were working inside. Ten people died, 64 missing, and eight wounded. Immediately after this disaster happened, the government organized an expert team to assist the rescue work. As one of the geological experts, the author did a lot of field investigations and collected first-hand information. Multi-methods including the remote sensing, 3D laser scanning, geophysical exploration, and numerical modeling were used for analyzing the characteristics and the triggering mechanism of the Wulong rockslide. The preliminary investigation results reveal that this rockslide with poor geological conditions was mainly induced by the gravitation and the karst effect and also affected by the previous mining activities. The research in this paper is meaningful and useful for further research on such kind of rockslides that are geologically similar to the Wulong rockslide.     

丘北普者黑岩溶地貌景观特征

通过介绍普者黑地区的岩溶地貌特征,借鉴石林和桂林的研究模式,对普者黑的岩溶地貌形成机理进行了深入研究,并针对普者黑独特的亚热带高原岩溶地貌的特征,阐述了其研究的科学价值。     

Analysis of F, Al, Mn, Zn, Fe, Cu, Ca and Mg concentrations in brick teas from main producing areas in China

Brick-tea-type fluorosis is a peculiar endemic disease in China, which had been discovered in minority areas of western China since 1980, and distributed mainly in Tibet, Inner Mongolia, Gansu, Xinjiang, Qinghai and parts of Sichuan Province. The prevalence rate of fluorosis in Tibetan and Mongolian nationality people was higher. Epidemiological investigation showed that fluorosis morbidity and degrees were different in different brick-tea drinking areas, and it was probably caused by drinking various kinds of brick tea from different regions. Therefore, we collected 33 samples of brick tea from six provinces where minority nationalities were accustomed to drinking a large quantity of brick tea. F concentrations were determined by the combustion hydrolysis-ion selective electrode method. The results showed that among the brick teas, the F concentrations ranged from the minimum 74.1 mg/kg in Yunnan Province to the maximum 991.2 mg/kg in Sichuan Province. Besides, there was a great difference among the various kinds of brick tea, and F concentrations decreased in the order of Kang brick tea, Green brick tea, Black brick tea, Mi brick tea, Fu brick tea, Chitsu ping tea, Puerh tea, and Tuo tea. The average F concentration in brick teas was 431.92 mg/kg.     

Shock-induced amorphous textures in plagioclase,Manicouagan, Quebec,Canada

The textural relationships and structural states of optically isotropic labradorite from the Manicouagan, Quebec, impact structure have been examined by light (optical) and transmission electron (TEM) microscopy. Two distinct diaplectic glasses have been recognized based on their contrasting morphology, timing and the inferred modes of formation. The earliest isotropic bands and grain-scale isotropism (maskelynite) optically exhibit a gradational,in situ transformation from crystalline plagioclase with preservation of relict textures (twins, grain boundaries). The same transformation from crystalline to amorphous structure is observed in TEM to occur heterogeneously at scales on the order of the unit cell. The progressive transformation of optical properties reflects an increase in the volume fraction and eventual coalescence of these amorphous units. This maskelynite-type diaplectic glass is interpreted to form in the solid-state directly from crystalline material during the compressional phase of the shock wave. The other isotropic material occurs in spatially discrete tensiongashes and planar deformation features (PDFs) that overprint the maskelynite-type glass. This second type of diaplectic glass (PDF-type) is developed homogeneously within a given glass band and exhibits sharp crystal-glass boundaries, in contrast to the gradational boundaries of the maskelynite-type glass. PDF-type glass is interpreted to form by melting in tensional release zones during passage of the rarefaction wave. These observations emphasize the ability of naturally shocked rocks to preserve subtle evidence of variations in the shock process from highly transient events.     

日本北海道音调津的球状石墨

本文利用光学显微镜、X射线衍射仪、透射电镜等手段对日本北海道音调津球状石墨的成因、结构等进行研究,认为日本北海道音调津球状石墨中除了石墨外,还存在镍黄铁矿﹑黄铜矿﹑磁黄铁矿等金属硫化物矿物。通过透射电子显微镜观察发现音调津石墨中大部分是椭圆状石墨颗粒,高分辨晶格条纹主要是非晶态结构,但是同时也发现了结晶良好的石墨。高结晶度石墨的存在可能是在硫化物Fe-Ni-Cu的触媒作用下形成的。天然球状石墨的微结构和性状研究对天然石墨的形成和开发应用有重要意义,对新型碳材料的制备技术有重要科学意义。     

夏季长江河口潮间带反硝化作用和N2O的排放与吸收

采用培养箱乙炔抑制和现场静态箱法,于夏季(7月)在长江河口潮滩潮间带进行了采样,研究表明,长江河口潮滩水体自身N2O产生速率很低,在潮汐淹没期沉积物是上覆水体N2O的来源,其来自沉积物中反硝化、硝化等氮素循环的多个反应过程,沉积物中N2O自然产生速率在0.10～8.50μmol/(m2·h)之间,反硝化速率在21.91～35.87μmol/(m2·h)之间。退潮出露期中潮滩是大气N2O的排放源犤交换速率在-11.03～13.17μmol/(m2·h)之间犦,5～10cm地温是影响N2O排放速率的显著性因素;低潮滩-大气界面N2O排放、吸收速率在-5.75～0.49μmol/(m2·h)之间。总体上看,中潮滩是大气N2O的排放源;而低潮滩对大气N2O有明显的吸收作用。潮滩植被(海三棱草和底栖藻类)的光合作用明显抑制了N2O的排放并可能导致吸收,而其呼吸作用则增加了N2O的排放,潮间带-大气界面N2O的排放和吸收与CO2的排放、吸收有显著的正相关关系。     

Wavelength-dispersive X-ray fluorescence spectrometric determination of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites

Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.     

冀北张家口地区汉诺坝玄武岩中麻粒岩捕虏体的硫化物相

捕虏体麻粒岩是了解下地壳形成和演化的重要样品。汉诺坝新生代玄武岩中的二辉麻粒岩捕虏体样品中富含各种硫化物相,主要类型有:①孤立产出的球状出溶硫化物;②矿物颗粒之间或颗粒内的粗晶硫化物;③次生硫化物包裹体群;④裂隙充填硫化物。电子探针分析表明,硫化物的矿物成分均为贫镍磁黄铁矿,(Ni+Co+Cu)/Fe(原子比)远小于0.2;(Fe+Cu+Co+Ni)/S(原子比)比地幔岩的磁黄铁矿小,多小于0.875,反映了一种S过饱和环境。各种产状的磁黄铁矿中Au、Ag都有一定的含量,其平均值分别为0.19%～0.22%(Au)、0.01%～0.02%(Ag),反映下地壳的麻粒岩化与金矿化的成因联系。磁黄铁矿的Ni、Co、Cu含量与S正相关,说明微量重金属元素与S具有同源的关系,由于地幔去气伴随S而进入下地壳。     

Compositional evolution in Ca-amphibole in the Karmutsen metabasites, Vancouver Island, British Columbia, Canada

Abstract The 6-km-thick Karmutsen metabasites, exposed over much of Vancouver Island, were thermally metamorphosed by intrusions of Jurassic granodiorite and granite. Observations of about 800 thin sections from the Campbell River and Buttle Lake area show that the metabasites provide a complete succession of mineral assemblages ranging from the zeolite to pyroxene hornfels facies around the intrusion. The most important observations are as follows. (1) The compositional change of Ca-amphiboles with increasing metamorphic grade is not straightforward. The tremolite component decreases from the prehnite–actinolite facies to the greenschist facies with a compensating tschermak component increase, but the tendency is not clear thereafter. Instead, the edenite component increases from the amphibolite facies to the pyroxene hornfels facies. (2) The most pargasitic Ca-amphibole occurs in high-Fe²⁺/Mg metabasite from the greenschist/amphibolite transition zone. (3) The reasons for such irregular compositional trends, even in the rather uniform MORB-like composition of the Karmutsen metabasites, are non-ideal solid solutions of Ca-amphibole at low temperature and the effective control by bulk rock composition in the amphibolite facies. (4) The data from this study support, but do not prove, a transition loop for the actinolite–hornblende compositional gap rather than a solvus. If the gap is a solvus, its shape is asymmetric, and is highly dependent on the other compositional parameters such as Fe³⁺/Al and Fe²⁺/Mg. (5) The X_NaA/X_A±X_Ab) ratios between Ca-amphibole and plagioclase are most useful as an indicator of metamorphic grade even within the amphibolite facies, and these change systematically from 0.2 to 0.5 from the greenschist to pyroxene hornfels facies. (6) The compositional trend of Ca-amphibole from the Karmutsen metabasites indicates a typical low-P/T metamorphic facies series on a Rbk–Gln–Tr–Ts diagram.