西藏措勤县德能铜多金属矿床石英闪长玢岩时代与成因：LA-ICP-MS锆石U-Pb年代学、地球化学和Sr-Nd-Pb同位素证据

为厘定德能铜多金属矿床侵入岩时代,查明岩石成因,本文利用LA-ICP-MS技术对德能铜多金属矿床石英闪长玢岩锆石进行了U-Th-Pb同位素测定,分析了岩石地球化学和Sr-Nd-Pb同位素。结果表明,石英闪长玢岩形成于早白垩世126.6±2.2~127.5±2.2Ma。岩石硅含量中等(平均58.58%),富碱(ALK平均6.53%),为高钾钙碱性花岗岩。稀土元素球粒陨石配分模式图右倾,(La/Yb)N为4.64~6.18。大离子亲石元素Rb、Th、K、Pb、Zr和Hf等富集,高场强元素Nb、Ta、P、Ti等亏损。206 Pb/204 Pb为18.629~18.771,207 Pb/204 Pb为15.690~15.738,208Pb/204 Pb为39.188~39.435。(87 Sr/86 Sr)i为0.709215~0.710463,(143 Nd/144 Nd)i为0.512044~0.512093,εNd(t)为-8.40~-7.45,TDM2为1524~1602Ma。上述分析结果表明,石英闪长玢岩为I型花岗岩,具岛弧岩浆活动特征,是向南俯冲的班公湖-怒江洋壳脱水,导致地幔楔发生熔融,幔源物质上涌引起中元古代下地壳物质发生部分熔融的产物。     

内蒙古乌兰沟埃达克岩锆石U-Pb年龄及构造环境

内蒙古中部贺根山缝合带的梅劳特乌拉蛇绿岩中,新发现乌兰沟埃达克岩,岩性为花岗闪长岩。LA-ICP-MS锆石UPb测年结果表明,乌兰沟埃达克岩的侵位年龄为279.3±1.4Ma,其形成时代为早二叠世。乌兰沟埃达克岩SiO_2含量为65.92%~69.65%,MgO为1.34%~2.16%,Al_2O_3为15.30%~17.33%,Na_2O/K_2O值为3.95~14.09,Sr=359.60×10~(-6)~734.00×10~(-6),Yb=0.83×10~(-6)~2.02×10~(-6),Y=6.65×10~(-6)~12.84×10~(-6);富集K、Rb、Sr等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素;稀土元素总量为32.18×10~(-6)~65.41×10~(-6),明显较低,轻、重稀土元素分馏明显,(La/Yb)N值为2.84~7.56,无明显Eu异常,显示出高硅埃达克岩(HSA)的地球化学特征。该埃达克岩具有岛弧型岩浆岩特征,形成于俯冲带岛弧环境,可能为洋内俯冲洋壳+俯冲深积物部分熔融并与上覆地幔楔橄榄岩反应成因。根据乌兰沟埃达克岩与梅劳特乌拉蛇绿岩的时空分布与演化特征,贺根山缝合带在早二叠世可能存在洋内俯冲作用。     

西藏努日晚白垩世埃达克岩:洋脊俯冲的产物

前人对冈底斯带晚白垩世埃达克岩的成因和地球动力学背景存在不同的认识.对努日地区的石英闪长玢岩开展了锆石U-Pb年代学、全岩地球化学及Hf同位素研究.结果表明,努日石英闪长玢岩侵位于96.5±1.3 Ma,以高SiO₂（63.96%~65.75%）、Al₂O₃（14.37%~15.99%）、MgO（2.12%~2.39%）、Sr（362×10-6~575×10-6,平均为467×10-6）含量,低Y（8.94×10-6~11.50×10-6）、Yb（0.81×10-6~1.06×10-6）含量及高Sr/Y比值（33.52~60.65）为特征,显示埃达克岩地球化学特征.岩石属低钾-中钾钙碱性准铝质花岗岩（A/CNK=0.81~0.96）,富集LREE、亏损HREE,富集大离子亲石元素（LILE）、亏损高场强元素（HFSE）,无明显负Eu异常.锆石ε_Hf（t）值为-0.3~+15.2（主要为+10.0~+15.2）,二阶段模式年龄t_DM2为187~1 173（主要为187~516 Ma）,表明源区以俯冲洋壳为主,并可能卷入了少量俯冲沉积物.岩石具有较高的Mg#值和相容元素Cr、Ni含量,表明熔体在上升过程中与地幔发生了相互作用.通过与南冈底斯典型埃达克岩对比,认为努日石英闪长玢岩是在洋脊俯冲背景下、穿过板片窗的高热流导致板片窗边缘的洋壳（及少量俯冲沉积物）部分熔融形成的.      

新疆东准噶尔北缘顿巴斯套地区晚泥盆世石英闪长玢岩地球化学特征及构造意义

新疆顿巴斯套矿区石英闪长玢岩的研究对厘清古亚洲洋晚泥盆世的演化具有重要意义.新疆顿巴斯套矿区石英闪长玢岩位于东准噶尔盆地北缘,为确定其岩浆侵入活动时限和岩石成因,讨论准噶尔地块北侧的古亚洲洋在晚古生代早期的俯冲作用,开展锆石LA-ICP-MS U-Pb年代学、Hf同位素地球化学,全岩主微量元素地球化学、Sr-Nd同位素地球化学研究.矿区内石英闪长玢岩单颗粒锆石LA-ICP-MS U-Pb定年结果为378±2 Ma,指示晚泥盆世岩浆活动.石英闪长玢岩全岩SiO₂含量为54.94%~68.64%,富Na₂O（平均含量为4.34%）,Na₂O/K₂O为1.19~2.72,里特曼指数（σ）大多小于3.3,Fe₂O₃T含量为2.23%~5.65%、MgO含量为0.81%~2.77%、Al₂O₃含量为14.31%~16.99%,TiO₂含量为0.32%~1.02%,CaO含量为2.58%~4.97%,Mg#变化于38.1~51.2,A/CNK为0.83~1.08,属准铝质钙碱性-高钾钙碱性系列.岩石富集大离子亲石元素（LILE）和轻稀土元素（LREE）,亏损高场强元素（HFSE,如Nb、Ta、P、Ti）,稀土元素配分曲线右倾,具有明显的轻重稀土分异,基本无Eu异常.全岩有较低的（87Sr/86Sr）_i（0.703 783~0.703 901）,较高的ε_Nd（378 Ma）（+6.2~+6.7）,年轻的T_DM（560~608 Ma）,锆石ε_Hf（t）相对较高,变化于+12.1~+15.1,对应的一阶段模式年龄T_DM1（Hf）为403~516 Ma,显示亏损地幔源区特征.综合上述地球化学特征认为石英闪长玢岩为俯冲环境下洋壳部分熔融的产物,俯冲洋壳脱水产生的流体、熔体在上升过程中与地幔楔发生了交代反应.结合新疆北部蛇绿岩及东准噶尔北缘、阿尔泰南缘相关岛弧花岗岩、火山岩等综合对比,认为区内中-晚泥盆世存在古亚洲洋的南北双向俯冲.      

云南香格里拉浪丁岩体锆石U-Pb年龄及地球化学特征

香格里拉地区广泛分布印支期中-中酸性浅成-超浅成岩体,位于西斑岩带的浪丁岩体主要由角闪闪长玢岩、石英闪长玢岩、含辉石角闪闪长玢岩组成。锆石U-Pb年龄显示岩体侵位于206.4±3.9 Ma。其地球化学特征与埃达克岩相似:SiO_2含量为56.66%～64.84%,平均60.42%; Eu异常不明显(Eu/Eu*为0.90～1.23,平均为1.08);富集轻稀土元素和大离子亲石元素,亏损重稀土元素,贫高场强元素;高Sr(490～1165×10~(-6),平均842×10~(-6))、Sr/Y(37.4～77.2,平均56.9)、La/Yb(21.7～28.4,平均25.6),低Y(13.1×10~(-6)～17.4×10~(-6),平均14.6×10~(-6))、Yb(1.20×10~(-6)～1.56×10~(-6),平均1.37×10~(-6))。年代学和地球化学研究结果显示,浪丁岩体形成于岛弧环境下,其形成与晚三叠世甘孜理塘洋壳板片的部分熔融有关,该地区的甘孜-理塘洋壳向西俯冲时,可能以较低的角度进入中咱地块之下。     

内蒙古达茂旗北部哈布齐尔金矿床石英闪长玢岩锆石U-Pb年龄、地球化学特征及其地质意义

哈布齐尔金矿床是近年来在内蒙古达茂旗北部地区新发现的一个金矿床。对矿区内与成矿密切相关的石英闪长玢岩开展了岩石学、LA-MC-ICP-MS锆石U-Pb定年和Lu-Hf同位素组成研究。锆石U-Pb年龄结果表明,石英闪长玢岩的锆石206Pb/238U年龄加权平均值为431.8±3.6Ma,代表其就位发生在早志留世。主量元素数据显示,石英闪长玢岩具有中等含量SiO2、低K2O、高Na2O、相对富镁等特征,属于低钾拉斑-钙碱性系列,A/NK值介于1.61~2.33之间,A/CNK值介于0.83~1.07之间,具有准铝质特征;微量元素含量以富集大离子亲石元素Ba、Rb、K、Sr等,亏损高场强元素Nb、Ta、Ti等为特征,明显亏损重稀土元素,但Eu异常不明显;Lu-Hf同位素分析结果显示,它们具有正的εHf(t)值(+6.4~+10.9)和年轻的二阶段亏损地幔模式年龄(1014~718Ma)。结合区域构造演化历史和矿床地质特征,认为哈布齐尔金矿成矿与早志留世石英闪长玢岩岩浆作用密切相关,初始岩浆可能源于俯冲洋壳脱水熔融产生的熔体与地幔楔交代的产物,成岩成矿环境为早古生代古亚洲洋板块向华北板块俯冲的岛弧环境。     

阿尔金索尔库里地区石英闪长玢岩锆石U-Pb年龄、地球化学特征及其地质意义

为了明确阿尔金索尔库里地区石英闪长玢岩脉的成因及形成时代,对该类岩脉进行了全岩主微量、稀土元素及LA-ICP-MS锆石U-Pb定年。锆石U-Pb同位素测年结果显示,石英闪长玢岩脉形成于(375.7±2.2)Ma。地球化学资料显示岩脉具有较高的硅含量(SiO_2=61.41%~69.93%),富铝(Al_2O_3=13.48%~15.57%),贫铁(TFeO=3.47%~4.53%)、镁(MgO=0.66%~1.83%)、钙(CaO=2.81%~4.21%)的特征,归类为钙碱性I型花岗岩;稀土元素总量较高,稀土元素分馏较显著,(La/Yb)_N为6.25~8.51,无明显Eu异常;微量元素以富集Rb、Pb、Th、U等大离子亲石元素(LILE),亏损Nb、Ta、Ti等高场强元素(HFSE)为特征。上述地球化学特征指示,石英闪长玢岩脉为幔源岩浆底侵作用引发下地壳基性岩部分熔融形成的母岩浆,经过分离结晶而形成。结合区域地质资料及同期岩浆岩活动,认为索尔库里地区石英闪长玢岩脉形成于造山后伸展构造环境,与阿尔金断裂晚泥盆世的走滑活动相关。     

西秦岭与赛什塘铜矿床有关的花岗质岩石岩浆源区特征及大地构造背景探讨

西秦岭赛什塘铜矿区内出露的三叠纪花岗质岩石有闪长玢岩、石英闪长岩、石英闪长玢岩、花岗斑岩和石英斑岩,其岩浆源区与形成构造环境可为古特提斯洋演化和区域成矿作用研究提供证据。岩石地球化学特征共同表明,这些花岗质岩石属于准铝质钙碱性-高钾钙碱性系列,为I型花岗岩;Mg#值变化较大(39~68),LREE富集,HREE亏损,(La/Yb)N比值介于8.50~22.9,具有Eu负异常,δEu介于0.28~0.78,同时富集大离子亲石元素Cs、Rb、K、Pb,亏损高场强元素Nb、Ta、Ti,呈现出与典型俯冲作用密切相关岛弧花岗岩相一致地球化学特征。石英闪长玢岩和石英斑岩SHRIMP锆石U-Pb年龄分别为219.0±2.3Ma和220.0±2.0Ma,锆石εHf(t)分别为-4.5~-2.1和-2.5~+1.0,对应二阶段模式年龄分别为1392~1544Ma和1190~1415Ma。结合前人对西秦岭三叠纪花岗岩以及其南侧阿尼玛卿蛇绿混杂带研究成果,本文认为赛什塘铜矿区花岗质岩石与西秦岭同时期花岗岩形成于与古特提斯洋向北俯冲密切相关的大陆边缘弧环境,其岩浆源区为中元古代下地壳变基性岩,且岩浆可能受到地幔物质混染。     

内蒙古正镶白旗地区早古生代O型埃达克岩的厘定及其意义

内蒙古正镶白旗地区新民岩体主要岩石类型为二长花岗岩。两个二长花岗岩样品给出(457±11) Ma和(423.1±9.9) Ma的LA-ICP-MS锆石U-Pb年龄值,两年龄样品中均存在>1 000 Ma的年龄值,说明该区存在古老的结晶基底或微陆块。岩石具有高Si(w(SiO2)=73.52%~74.68%>56%)、富Al(w(Al2O3)=14.31%~15.26%)、富Na(w(Na2O)=3.82%~5.25%,Na2O/K2O值为1.26~2.5)、低Mg(w(MgO)=0.29%~0.39%<3%)的特点。较高的Sr含量((435.4~719.7)×10-6>400×10-6),较低的Y((3.46~4.81)×10-6<18×10-6)和Yb((0.38~0.48)×10-6<1.9×10-6)含量;较大的Sr/Y值(103.54~177.09>40)。稀土元素总量较低(∑REE：(20.98~40.79)×10-6),轻重稀土分馏明显((La/Yb)N：8.32~16.90),具有正铕异常(δEu：1.18~2.20)。在原始地幔标准化蛛网图中,富集LILE(Ba、K、Sr、Rb),亏损HFSE(Th、U、Nb、Ta、P、Ti),为O型埃达克岩。结合区域地质背景,新民岩体的形成指示古亚洲洋向华北板块俯冲消减事件。     

西藏色那铜(金)矿床石英闪长玢岩年代学、地球化学与岩石成因

色那铜(金)矿床位于西藏班怒成矿带西段的多龙矿集区内东北部,具有良好的找矿潜力。锆石U-Pb测年显示成矿石英闪长玢岩的形成年龄为(118.1±1.4)Ma,与已报道的多龙矿集区内岛弧型含矿斑岩的成岩成矿时代一致。色那石英闪长玢岩属于活动大陆边缘的高钾钙碱性—钙碱性系列准铝质I型花岗岩,富集轻稀土(LREE)和大离子亲石元素(LILE:Th,U,K及Rb),亏损重稀土(HREE)及高场强元素(HFSE:Nb、Ta、Zr及Ti),δEu为基本无异常(0.92~1.04),具备典型岛弧岩浆岩特征。岩石Rb/Sr值(0.143~0.195),Zr/Hf值(31.23~34.14),Nb/Ta值(9.21~11.59),反映出壳幔混合的特点。锆石(~(176)Hf/~(177)Hf)_i为0.282707~0.282719,ε_(Hf)(t)为0.28~11.77,两阶段模式年龄T_(DMC)=424~1159Ma,暗示其可能起源于新生下地壳的部分熔融。综合分析认为,色那矿区石英闪长玢岩是班公湖—怒江特提斯洋壳向北俯冲于羌塘地块之下的背景下,由新生下地壳部分熔融形成,源区内可能有幔源物质混入。早白垩世晚期(约118.1 Ma)班公湖—怒江洋仍然存在向北俯冲消减作用。     

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     

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.     

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。     

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.