Recalibration of mutually consistent garnet–biotite and garnet–cordierite geothermometers

Garnet–biotite and garnet–cordierite geothermometers have been consistently calibrated, using the results of Fe²⁺–Mg cation exchange experiments and utilizing recently evaluated nonideal mixing properties of garnet. Nonideal mixing parameters of biotite (including Fe, Mg, Al^VI, and Ti) and of cordierite (involving Fe and Mg) are evaluated in terms of iterative multiple least-square regressions of the experimental results. Assuming the presence of ferric Fe in biotite in relation to the coexisting Fe-oxide phases (Case A), and assuming the absence of ferric Fe in biotite (Case B), two formulae of garnet–biotite thermometer have been derived. The garnet–cordierite geothermometer was constructed using Margules parameters of garnet adopted in the garnet–biotite geothermometers. The newly calibrated garnet–biotite and garnet–cordierite thermometers clearly show improved conformity in the calculated temperatures. The thermometers give temperatures that are consistent with each other using natural garnet–biotite–cordierite assemblages within ±50 °C. The effects of ferric Fe in biotite on garnet–biotite thermometry have been evaluated comparing the two calibrations of the thermometer. The effects are significant; it is clarified that taking ferric Fe content in biotite into account leads to less dispersion of thermometric results.     

Magma evolution and mineralization of Longmenshan lithium-beryllium pegmatite in Dahongliutan area,West KunlunSCIEI北大核心CSCD

西昆仑大红柳滩地区相继发现了众多伟晶岩型锂铍矿床,已成为我国新的锂资源基地。目前关于这些锂铍花岗伟晶岩的成因多强调其源于地壳深熔形成的二云母二长花岗岩的结晶分异,但研究区出露的同时代的黑云母花岗岩与成矿的关系没有被讨论和关注。为了探讨黑云母花岗岩与成矿的关系,作者对龙门山矿区黑云母花岗岩、二云母二长花岗岩、花岗伟晶岩以及与成矿相关的细晶花岗岩开展了详细的地球化学及年代学研究。结果显示：1)黑云母花岗岩与二云母二长花岗岩具相似的地球化学特征,富集Rb、La和Nd,亏损Ba、Nb、Sr、P和Ti元素,均表现出S型花岗岩的特征;2)从黑云母花岗岩→二云母二长花岗岩→细晶花岗岩,表现出连续分异演化的特征;3)黑云母花岗岩的锆石LA-ICP-MS U-Pb年龄为216.8±0.85Ma,二云母二长花岗岩的锆石SIMS U-Pb年龄为216.0±1.5Ma,细晶花岗岩的锆石LA-ICP-MS U-Pb年龄为209.5±1.2Ma,花岗伟晶岩的锡石LA-MC-ICP-MS U-Pb年龄为211.3±5.0Ma,这意味着从黑云母花岗岩到二云母二长花岗岩与细晶花岗岩的形成时间是连续的并且是接近的。基于此...     

Biotite stability in peraluminous granitic melts: Compositional dependence and application to the generation of two-mica granites in the South Bohemian batholith (Bohemian Massif, Czech Republic)

Crystallization experiments have been conducted in the system Na₂O–K₂O–MgO–FeO–Al₂O₃–SiO₂–H₂O (with 4% normative corundum) in order to constrain the stability of biotite as a function of water activity and the Mg# of biotite [Mg/(Mg +Fe_total)] in equilibrium with peraluminous granitic melts. The temperature at which biotite breakdown starts is strongly dependent on the Mg# of biotite. At 500 MPa, the temperature of biotite breakdown to form orthopyroxene increases from 750 °C to 830 °C, as the Mg# of biotite increases from 0.4 to 0.5. Considering that the system investigated is relevant for Ca-poor peraluminous biotite-bearing rocks (metapelites), the biotite dehydration curves obtained are used to discuss the melting reactions and the temperatures that lead to the formation of two distinct types of two-mica granites found in the South Bohemian batholith (specifically the Eisgarn and Deštná granites). The phase relationships were determined experimentally for the composition of these two granites in order to constrain the composition of the biotite in equilibrium with the melt in the protoliths. We demonstrate that Eisgarn granitic melts may have been generated at temperatures in the range 830–850 °C from melting reactions involving biotite with a Mg# up to 0.5 as a reactant. In contrast, Deštná granitic melts cannot have been generated from dehydration melting reactions involving biotite.     

粤西高枨铅锌银矿区黑云母花岗岩的年代学及岩石成因

粤西高枨大型铅锌银矿赋存在黑云母花岗岩中,本文采用LA-ICP-MS锆石U-Pb测年获得黑云母花岗岩的结晶年龄为429±13Ma,为早志留世,属于加里东期岩浆活动的产物。详细的地球化学分析显示岩石的SiO₂含量为(64.33%~74.54%,平均为68.67%),Al₂O₃含量偏高(13.88%~16.61%),碱质含量高(K₂O+Na₂O=5.31%~7.89%),低P₂O₅(<0.25%)含量,强过铝质(A/CNK=1.07~1.32)。岩石富集LREE和Rb、K、U、Pb,贫Ba、Sr、Nb、P、Ti元素,铕呈负异常(Eu/Eu^*=0.38~0.90)。以上特征表明该岩体属于钙碱性强过铝质花岗岩。经年龄校正后的²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb 和²⁰⁸Pb/²⁰⁴Pb值分别为17.458~18.131、15.563~15.638和37.547~38.406。Sr初始值变化范围较大((⁸⁷Sr/⁸⁶Sr)_i=0.7091~0.7259),但ε_Nd(429Ma) 值相对较低 (-8.9~-6.1),暗示岩体来源于元古代(t_2DM=1.67~1.83Ga)的地壳组分,其源岩主要为含少量泥质的砂岩质组成。结合区域地质背景的综合分析,认为高枨黑云母花岗岩与华夏板块与扬子板块发生板内碰撞-拼合事件有关,由元古代地壳物质重熔形成的形成的S型花岗岩。     

新疆可可托海近3号脉花岗岩成岩时代及地球化学特征研究

可可托海伟晶岩田内花岗岩类发育。本文研究的花岗岩体位于3号伟晶岩脉矿坑的东部,岩性为似斑状黑云母二长花岗岩,野外特征与矿区北部的阿拉尔花岗岩非常相似。花岗岩中锆石LA-MC-ICP-MS U-Pb测年结果表明,19个测点206Pb/238U年龄集中于399.6～409.0Ma,加权平均年龄为405.4±1.4Ma(MSDW=0.98),属于早泥盆世,比阿拉尔花岗岩的侵入时期早得多,与3号伟晶岩脉没有成因上的联系,应是区域上岩浆活动最为强烈时期的产物。岩石具有富硅(SiO2=70.69%～73.81%)、富铝(Al2O3=14.00%～15.74%)、总体髙钾(K2O/Na2O≥1),贫Fe、Mg、Ti、P特点,铝饱和指数较高(A/CNK≥1.1),属于髙钾钙碱性强过铝质花岗岩;微量元素表现出Sr、Ti、Ba、P、Nb、Ta明显的负异常和Th、U、La、Zr、Hf的正异常特征。稀土配分型式显示LREE的相对弱富集,HREE比较平坦以及Eu中等负异常。样品中87Sr/86Sr(0.72259～0.72810)、143Nd/144Nd(0.51235～0.51237)接近于陆源沉积物,Sr初始值(0.70155～0.70341)较低,f Sm/Nd(-0.32～-0.26)、Sm/Nd(0.222～0.240)比值显示分异小、较均一的Sm/Nd同位素体系;εNd(t)值变化于-3.07～-2.16,模式年龄t2DM集中在1.35Ga左右,属于中元古代。综合研究岩石中主量、微量和稀土元素、同位素特征,同时对比区域上同期岩浆活动特征,认为本文研究的花岗岩可能是在活动大陆边缘环境下,强烈的俯冲-碰撞作用导致的地壳加厚引发了深熔作用,使阿尔泰微古陆边缘内部中元古代基底部分熔融,同时有幔源物质参与;随后岩浆经过结晶分异,最终上升侵位,反映了陆缘弧花岗岩的特点。     

The accumulation of radiocesium in coarse marine sediment: effects of mineralogy and organic matter

The controlling factors affecting the accumulation of (137)Cs in marine sediment have not been investigated in detail, especially in coarse grained sediment. Eighty eight coarse marine sediment samples near Wuljin, Korea, were characterized by quantitative X-ray-diffraction (XRD), gamma-ray, and total organic carbon (TOC) analysis. Those factors were then compared. The grain size was in the range of -0.48 to 3.6Mdphi corresponding to sand grains. TOC content was in the range of 0.06-1.75%, and the concentration of (137)Cs was 相似文献   

热水条件下黑云母断层泥的摩擦强度与稳定性

黑云母是自然界常见的层状硅酸盐矿物,其摩擦系数不高且化学稳定性好,对其摩擦性质的关注可能会对弱断层的研究有所帮助.本次工作选取的实验温度条件对应于典型地壳强度模型中脆塑性转化带的范围,为300 ℃和400 ℃.有效正应力为200 MPa,孔隙水压包括10 MPa和30 MPa,在此条件下对黑云母模拟断层泥进行摩擦实验研究.实验得出黑云母的摩擦系数平均在0.36左右.速度依赖性随温度升高速度弱化的程度增强,表现为300 ℃为十分微弱的速度弱化,而在400 ℃出现了黏滑行为,代表了更强的速度弱化.显微结构中同时出现了脆性剪切变形和塑性扭折变形,但决定宏观力学性质的显然是脆性剪切变形.在黑云母存在的情况下,本研究的实验结果有助于理解大陆地壳脆塑性转化带中地震的可能性和弱断层深部的变形机制、宏观力学行为以及地震活动.     

湘南黄沙坪多金属矿床花岗斑岩的矿物化学及其对矽卡岩白钨矿成矿的指示意义

黄沙坪多金属矿床是湖南最大的铅锌生产基地,并且在与矿床内花岗斑岩接触的矽卡岩带产有隐伏的大型矽卡岩型白钨矿和中型规模的辉钼矿。钨-钼矿化的时代为晚侏罗世,与矿床内花岗斑岩侵入时代一致。然而,已有研究认为,由于该花岗斑岩规模很小,矽卡岩型白钨矿的成矿热液应来自深部岩浆房而非此花岗斑岩。为此,我们对花岗斑岩进行了仔细的镜下观测,并且对其中的副矿物和黑云母以及矽卡岩中的白钨矿进行了电子探针成分分析,应用原位LA-ICP-MS方法测定了矽卡岩中白钨矿的稀土元素含量,试图对白钨矿矿化的物质和流体来源提供确切的证据。通过研究,首次在矿床内花岗斑岩中发现了与未蚀变黑云母伴生的黑钨矿和铌铁矿,表明花岗斑岩至少在岩浆结晶作用晚期或岩浆-热液过渡阶段早期就已发生钨的矿物富集,为确定花岗斑岩是控制钨矿化的成矿岩体提供了依据。此外,发现花岗斑岩中的黑云母(属铁叶云母)含有极高的氟含量(3%),指示其应形成于富含氟的高分异岩浆。研究进一步揭示,矽卡岩中白钨矿的轻稀土元素配分模式与花岗斑岩十分一致,而重稀土元素则显著亏损,而且Eu的含量较花岗斑岩更为富集。这暗示形成白钨矿的成矿流体应直接来自花岗斑岩,即:在早期无水矽卡岩阶段,石榴子石的沉淀导致流体中的重稀土亏损而Eu相对富集;白钨矿随后再从这种流体中沉淀。此外,白钨矿的Eu含量与Sm、Gd含量具有负相关关系,表明Eu的分配是相对独立的行为,主要以Eu2+存在,从而指示沉淀白钨矿的流体具有还原的性质。结合前人的研究成果及本文所提供的新证据,我们认为,形成矽卡岩型白钨矿的钨和成矿热液应来自高分异且富F的花岗斑岩,而所需的钙则可能来自于碳酸盐围岩,即矿床内花岗斑岩应是形成钨钼矿床的物质来源,驱动热液活动的能量来源,和寻找隐伏钨矿床的重要找矿标志。     

Geology,geochemistry and genesis of the Makou magnetite-apatite deposit in the Luzong volcanic basin,Middle-Lower Yangtze River Valley Metallogenic Belt,Eastern China

The Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB) is located on the northern margin of the Yangtze Plate (Eastern China). Ore deposits in the belt are mainly clustered in seven ore districts, and are closely associated with Mesozoic intermediate-felsic magmatic rock. Among the seven ore districts, the Luzong and Ningwu districts host large-scale iron resources in volcanic basins. The Makou magnetite-apatite deposit in the southern Luzong Basin was previously interpreted to be related to a quartz syenite porphyry. In this study, we conducted field geological studies and determined the age and geochemistry of the Makou intrusive rocks. Petrography and electron probe micro analysis (EPMA) indicated that the Makou ore-hosting rocks have intense albite alteration. The wallrock alteration is spatially restricted, and comprises albite alteration (Stage I), magnetite mineralization (Stage II), quartz-sulfide alteration (Stage III) and carbonate alteration (Stage IV) stages. Fluid inclusions in syn-mineralization apatite homogenized at 252.2–322.6 °C, which slightly lower than is typical for magnetite-apatite deposits in the region. Field study revealed that the quartz syenite porphyry at Makou disrupted the orebodies along clear-cut intrusive contacts, and that the quartz syenite porphyry does not contain iron mineralization, suggesting it has no direct genetic relationship with the iron mineralization. The ore-hosting albitite and ore-forming biotite diorite have LA-ICP-MS zircon U-Pb ages of 129.6 ± 1.2 Ma and 131.2 ± 3.3 Ma, respectively, and the iron mineralization was dated by mass spectrometer phlogopite ⁴⁰Ar-³⁹Ar at 130.76 ± 0.77 Ma. We propose that the Makou magnetite-apatite deposit is genetically related to the biotite diorite, rather than to the quartz syenite porphyry in the mine pit. The biotite diorite closely resembles intrusions related to magnetite-apatite deposits elsewhere in the region.     

云母:花岗岩-伟晶岩稀有金属成矿作用的重要标志矿物

云母是花岗岩、伟晶岩中的重要造岩矿物,不仅是整个岩浆阶段的结晶产物,而且也是热液过程的参与者。作为层状硅酸盐矿物,层间或八面体位置上可容纳锂、铷铯、锡、铌钽等稀有金属。本文结合前人研究积累和作者近年来的研究成果,阐述了云母作为一个重要的稀有金属成矿标志矿物的矿物学特征。铁锂云母-锂云母是稀有金属成矿作用中重要的锂矿物,同时云母中锂含量可以反映花岗岩的分异程度。铷、铯可以置换云母层间钾,在高演化花岗岩、伟晶岩中可以形成铷、铯为主的云母(既可以是锂云母系列,也可以是黑云母系列)。黑云母是稀有金属花岗岩中一个特殊的矿物。准铝质含锡花岗岩中黑云母锡含量可达100×10~(-6),其锡含量可以指示其锡成矿能力。稀有金属花岗岩中,常见的是铌钽氧化物矿物。但是最近研究发现,黑云母中铌可以超常富集(超过1000×10~(-6)),成为稀有金属花岗岩中最重要、甚至唯一的铌矿物,形成一种以富铌黑云母为特色的新类型稀有金属花岗岩,并可能代表了一种新型的潜在铌资源。基于云母在花岗岩中的重要性和结构的特殊性,今后要利用微区成分和结构分析技术,加强对云母中稀有金属晶体化学的研究,以及进一步揭示云母对稀有金属成矿的特殊重要意义。