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1.
目前关于拉萨地块西段狮泉河地区中生代岩浆岩的报道相对较少,限制了对该地区中生代岩浆作用的认识.对狮泉河地区石英闪长岩和闪长质包体的锆石U-Pb年龄、岩石学特征与元素地球化学进行了研究.结果显示,寄主石英闪长岩的年龄为161.1±1.7 Ma,闪长质包体的年龄为159.8±1.6 Ma和157.0±1.3 Ma,两者为同期形成.寄主石英闪长岩为I型准铝质中钾-高钾钙碱性系列岩石,具有富集大离子亲石元素、亏损高场强元素的特征.闪长质包体为准铝质中钾-高钾钙碱性系列岩石.岩石学、地球化学特征研究表明,该套岩石可能与中侏罗世班公湖-怒江特提斯洋南向俯冲有关,班公湖-怒江特提斯洋南向俯冲引起幔源物质发生熔融,上涌的幔源岩浆与拉萨地块古老基底重熔形成的酸性岩浆混合,形成了含闪长质包体的晚侏罗世岩体. 相似文献
2.
改则地区的嘎布扎花岗闪长岩侵入于南羌塘地体南缘的侏罗系色哇组,为研究班公湖—怒江缝合带的演化提供新的约束。岩浆锆石的LA-ICP-MS U-Pb年龄为(143.8±0.5)Ma,显示花岗闪长岩的侵位时代为晚侏罗世—早白垩世之交。花岗闪长岩具有准铝质I型花岗岩的特点,属于高钾钙碱性岩石系列;稀土元素为轻稀土富集型,存在弱的Eu负异常;明显富集Rb、Ba、K、Th、U等大离子亲石元素,而亏损Nb、Ta、P、Ti等高场强元素。研究表明花岗闪长岩的岩浆源区可能经历了陆壳物质、俯冲沉积物与幔源楔等不同性质的岩浆混合,并经历一定程度的分离结晶作用形成。改则嘎布扎花岗闪长岩形成于班公湖—怒江中特提斯洋晚侏罗世—早白垩世向北俯冲的岛弧环境。 相似文献
3.
西藏羌塘南缘青草山北花岗闪长岩锆石U-Pb年代学、地球化学特征及其成矿意义 总被引：1，自引：0，他引：1
青草山北花岗闪长岩体位于班公湖-怒江缝合带北侧、羌塘陆块南缘,呈岩脉、岩株状与晚二叠世龙格组碳酸盐岩呈侵入接触。本文对该花岗闪长岩的锆石进行了LA-ICP-MS U-Pb年代学和岩石地球化学研究,其岩浆锆石U-Pb年龄为154.8±1.2Ma(MSWD=1.7),属晚侏罗世,与热那错埃达克质英安岩年龄高度一致,岩石地球化学特征显示,青草山北花岗闪长岩属于准铝质、高钾钙碱性系列,富集轻稀土元素、大离子亲石元素,亏损重稀土元素、高场强元素,具弱Eu负异常,显示出典型岛弧岩浆岩特征;锆石原位微量元素分析表明,锆石总体富集重稀土,相对亏损轻稀土,在锆石Nb/Ta-Y图解中样品点落入金伯利岩区域,而在岩石地球化学构造环境判别图解中,样品点同样指示其可能来源于幔源岩浆。青草山北花岗闪长岩班公湖-怒江洋壳晚侏罗世北向俯冲到一定深度后,俯冲洋壳发生部分熔融,形成的岩浆在上升的过程中与地幔楔发生混染,其中,部分岩浆在侵位的过程中形成中酸性的花岗闪长质岩浆房,部分岩浆则喷出地表,形成热那错组英安岩。 相似文献
4.
对出露于拉萨地块北部的达如错接奴群安山岩进行了年代学、元素地球化学和锆石原位Hf同位素研究。用LAICP-MS技术测得的安山岩锆石206Pb/238U年龄为163.3±1.7Ma,即火山活动时限为晚侏罗世早期。安山岩地球化学研究结果表明,其具有典型高镁安山岩的地球化学特征,所有样品均具有较高的Mg O、Mg#值,低的TFe O/Mg O值(小于1.5);所有样品都显示轻稀土元素富集,具有Eu负异常,富集大离子亲石元素、亏损高场强元素的特征;锆石εHf(t)值为较均一的负值(εHf(t)=-8.5~-6.7)。研究表明,达如错高镁安山岩很可能是班公湖—怒江洋壳在俯冲消减背景下,由俯冲沉积物熔融产生的熔体与地幔橄榄岩发生交代作用的产物,形成于与班公湖—怒江洋壳俯冲消减有关的活动大陆边缘(安第斯型)的构造环境。由此认为,晚侏罗世接奴群火山岩是班公湖—怒江洋壳俯冲消减的产物,从而为班公湖—怒江洋壳的俯冲消减提供了直接的火山岩证据。 相似文献
5.
班公湖-怒江缝合带西段阿翁错地区中酸性侵入岩的成因及其对区域构造演化的指示 总被引：2，自引：0，他引：2
班公湖-怒江缝合带西段出露大量中酸性侵入岩,为特提斯洋俯冲、拉萨地块与羌塘地块碰撞造山过程中岩浆响应的重要组成部分。本文对该缝合带西段阿翁错地区的闪长岩、花岗闪长岩和花岗岩进行了详细的岩石地球化学和锆石U-Pb年代学研究。锆石LA-ICP-MS U-Pb定年结果表明闪长岩、花岗闪长岩、花岗岩成岩年龄分别为119.3±1.8 Ma、114.7±1.4 Ma和103.2±1.3 Ma。岩石地球化学特征显示中酸性侵入岩属高钾钙碱性系列,具准铝质-弱过铝质I型花岗岩特征;其LREE分馏程度较高,而HREE近于平坦,存在Eu负异常;富集Rb、La等大离子亲石元素和Th、Zr、Hf等高场强元素,亏损Nb、Ta、P、Ti等高场强元素,具有岛弧岩浆岩的特征。研究结果表明在早白垩世晚期(103.0±1.3 Ma)班公湖-怒江特提斯洋壳仍在向北俯冲于南羌塘地块之下,随着俯冲深度增加,大洋板片发生大规模脱水,释放的流体交代地幔楔并引发其部分熔融,产生的幔源岩浆向上运移,与下地壳物质不同比例混合形成了闪长岩和花岗闪长岩;而花岗岩主要由古老下地壳物质部分熔融形成,并有少量地幔物质的参与。 相似文献
6.
藏北聂荣地区早侏罗世末期的岩浆混合作用及构造意义 总被引：7，自引：7，他引：0
藏北聂荣岩体的岩浆源区性质和岩石成因还未能得到很好约束,直接限制了对班公湖-怒江缝合带早侏罗世构造岩浆演化历史的认识。为探讨这一问题,本文报道了聂荣岩体中的花岗质岩石及其闪长质包体的岩石学、全岩主量元素和微量元素地球化学、锆石U-Pb定年和Lu-Hf同位素分析结果。一件闪长质包体样品的锆石U-Pb年龄为175.0±1.3Ma,与其寄主花岗岩类样品的年龄(174.5±1.4Ma,175.9±0.4Ma)同期。聂荣岩体中～175Ma的寄主岩石均属于偏铝质到过铝质(A/CNK=1.04～1.16)钾玄岩系列的花岗闪长岩到碱性花岗岩,标准刚玉分子数为0.6%～2.1%,包括I型和S型两种成因类型,富集大离子亲石元素、轻稀土元素和Pb,锆石εHf(t)值为-9.8～-3.7,Hf同位素地壳模式年龄为1.45～1.84Ga,主要来源于成熟地壳物质的重熔;闪长质包体在成分上主要属偏铝质钾玄岩系列的二长闪长岩,锆石εHf(t)值变化范围大(-10.3～-1.2),Hf同位素亏损地幔模式年龄介于0.87～1.22Ga,其来源可能与古老岩石圈地幔物质的部分熔融有关。聂荣地区在早侏罗世末期很可能发生了来源于成熟地壳物质深熔或重熔的熔体(占大比例)和岩石圈地幔来源的幔源岩浆之间的混合作用,混合过程中幔源组分的输入使S型熔体向I型熔体转化。在～175Ma侵位的聂荣岩体很可能是这种由岩浆混合作用形成的母岩浆再经历一定程度的分离结晶作用形成的。结合碎屑锆石研究成果,本文暂时主张聂荣岩体可能是与由班公湖-怒江洋壳北向俯冲所引起的聂荣微陆块和羌塘地体间碰撞相关的产物,这可能指示班公湖-怒江洋壳沿聂荣微陆块南侧的分支,在侏罗纪早期既发生了南向俯冲(俯冲于拉萨地体之下),又发生了北向俯冲(俯冲于羌塘地体之下)等地球动力学过程。 相似文献
7.
西藏中拉萨地块晚侏罗世许如错花岗岩地球化学与岩石成因 总被引：3，自引：3，他引：0
西藏中部拉萨地块晚侏罗世花岗岩的岩石成因与源区性质目前尚未得到很好约束。本文报道了中部拉萨地块西段许如错岩体的寄主花岗岩和闪长质包体的锆石U-Pb年龄、元素地球化学和锆石Hf同位素成分。许如错岩体寄主花岗岩年龄为155.1±0.7Ma,闪长质包体与寄主花岗岩同期(155.7±0.7Ma)形成。寄主花岗岩属I型偏铝质-弱过铝质高钾钙碱性系列岩石,富集Rb、K等大离子亲石元素和轻稀土元素,亏损Nb、Ta、P、Ti等高场强元素,锆石εHf(t)值(-16.6~-6.6)指示其可能来源于拉萨地块古老下地壳物质的重熔作用。闪长质包体为准铝质钙碱性系列,锆石εHf(t)值(-8.9~-3.8)具有总体为负但明显高于寄主花岗岩εHf(t)值的特征,表明这些闪长质包体代表了幔源物质组成的加入。许如错晚侏罗世花岗岩可能形成于班公湖-怒江特提斯洋洋壳在中晚侏罗世向南俯冲于拉萨地块之下,引起幔源物质与中部拉萨地块古老基底重熔所产生的酸性岩浆发生岩浆混合作用形成的。 相似文献
8.
西藏安多早侏罗世火山岩岩石成因及对班公湖-怒江特提斯洋俯冲消减的制约 总被引：1，自引：1，他引：0
拉萨地块广泛分布着中生代的岩浆活动,研究它们对于认识特提斯洋的演化过程有着重要的启示。本文报道安多地区新识别出的早侏罗世岛弧型火山岩LA-ICP-MS锆石U-Pb年龄、锆石原位Hf同位素、全岩主微量元素分析和Sr-Nd同位素结果。英安岩206Pb/238U年龄为180.7±4.7Ma(MSWD=0.22,n=10),指示其形成时代为早侏罗世。这些火山岩的SiO_2含量为62.50%~76.15%,MgO含量为0.33%~3.05%,Fe_2O_3T含量为2.35%~6.69%;所有样品都显示轻稀土元素相对富集,具有铕的弱负异常,具有富集大离子亲石元素、亏损高场强元素的地球化学特征;同时这些火山岩锆石原位εHf(t)值均为正值(+15.1~+17.1);全岩Sr-Nd同位素εNd(t)值也均为正值(+7.1~+13.2),指示这些火山岩很可能是特提斯洋俯冲消减过程中新生下地壳部分熔融的产物。结合区域地质资料,认为安多火山岩不可能是龙木错-双湖古特提斯洋或雅鲁藏布江新特提斯洋俯冲消减的产物,而是班公湖-怒江特提斯洋俯冲消减的产物,区域上很可能与改则北、日土地区的侏罗纪侵入岩一起构成了班公湖-怒江特提斯洋北侧的岩浆弧带。由此本文认为安多早侏罗世岛弧型火山岩是班公湖-怒江特提斯洋北向俯冲消减的产物,从而为班公湖-怒江特提斯洋的俯冲消减过程提供了直接的火山岩证据。 相似文献
9.
西藏达如错地区晚侏罗世高镁安山岩——班公湖—怒江洋壳俯冲消减的证据 总被引：7，自引：0，他引：7
对出露于拉萨地块北部的达如错接奴群安山岩进行了年代学、元素地球化学和锆石原位Hf同位素研究。用LA-ICP-MS技术测得的安山岩锆石206Pb/238U年龄为163.3±1.7Ma,即火山活动时限为晚侏罗世早期。安山岩地球化学研究结果表明,其具有典型高镁安山岩的地球化学特征,所有样品均具有较高的MgO、Mg#值,低的TFeO/MgO值（小于1.5）;所有样品都显示轻稀土元素富集,具有Eu负异常,富集大离子亲石元素、亏损高场强元素的特征;锆石εHf(t)值为较均一的负值（εHf(t)=-8.5~-6.7）。研究表明,达如错高镁安山岩很可能是班公湖—怒江洋壳在俯冲消减背景下,由俯冲沉积物熔融产生的熔体与地幔橄榄岩发生交代作用的产物,形成于与班公湖—怒江洋壳俯冲消减有关的活动大陆边缘（安第斯型）的构造环境。由此认为,晚侏罗世接奴群火山岩是班公湖—怒江洋壳俯冲消减的产物,从而为班公湖—怒江洋壳的俯冲消减提供了直接的火山岩证据。 相似文献
10.
西藏赛角铜金矿闪长岩LA-ICP-MS锆石U-Pb年龄、Hf同位素和地球化学特征及成矿意义 总被引：5，自引：2，他引：3
赛角铜金矿是西藏多龙超大型铜金矿集区的组成矿床之一,目前对其成岩成矿时代、矿床成因等方面的认识程度还很低,制约了对多龙矿集区成矿潜力的全面认识。对赛角闪长岩进行LA-ICP-MS锆石U-Th-Pb同位素、全岩主量和微量元素、锆石Hf同位素测试。测得闪长岩中锆石U-Pb年龄为120.5±1.2Ma,该年龄被解释为岩浆结晶年龄。全岩主量和微量元素分析显示,闪长岩为中钾—高钾钙碱性岩石,富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,具有活动大陆边缘弧岩浆岩的特征。锆石Hf同位素分析结果表明,锆石εHf(t)值为+5.4~+12.1,平均值为+9.0,二阶段Hf模式年龄为373~743Ma,平均值为545Ma,表现出明显的幔源特征。赛角铜金矿的形成受控于班公湖—怒江洋陆俯冲体系,成岩成矿岩浆是板片流体交代的地幔楔部分熔融形成的基性母岩浆与新生下地壳部分熔融形成的酸性岩浆混合的产物。 相似文献
11.
E. M. Prasolov S. A. Sergeev B. V. Belyatsky E. S. Bogomolov K. A. Gruzdov I. N. Kapitonov R. Sh. Krymsky V. O. Khalenev 《Geochemistry International》2018,56(1):46-64
This paper reports the first results of a study of 11 isotope systems (3He/4He, 40Ar/36Ar, 34S/32S, 65Cu/63Cu, 62Ni/60Ni, 87Sr/86Sr, 143Nd/144Nd, 206–208Pb/204Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others. 相似文献
12.
奥地利安东帕有限公司 《岩矿测试》2009,28(3):306-306
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 相似文献
13.
S. Viswanathan K. Surya Prakash Rao B. Mahabaleswar 《Journal of the Geological Society of India》2013,82(6):621-627
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. 相似文献
14.
Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA 总被引：1，自引：0，他引：1
The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources. 相似文献
15.
Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations. 相似文献
16.
《Applied Geochemistry》2001,16(2):137-159
Five hundred and ninety-eight samples of terrestrial moss (Hylocomium splendens and Pleurozium schreberi) collected from a 188,000 km2 area of the central Barents region (NE Norway, N Finland, NW Russia) were analysed by ICP-AES and ICP-MS. Analytical results for Al, B, Ba, Ca, K, La, Mg, Mn, Na, P, Rb, Si, Sr, Th, U and Y concentrations are reported here. Graphical methods of data analysis, such as geochemical maps, cumulative frequency diagrams, boxplots and scatterplots, are used to interpret the origin of the patterns for these elements. None of the elements reported here are emitted in significant amounts from the smelting industry on the Kola Peninsula. Despite the conventional view that moss chemistry reflects atmospheric element input, the nature of the underlying mineral substrate (regolith or bedrock) is found to have a considerable influence on moss composition for several elements. This influence of the chemistry of the mineral substrate can take place in a variety of ways. (1) It can be completely natural, reflecting the ability of higher plants to take up elements from deep soil horizons and shed them with litterfall onto the surface. (2) It can result from naturally increased soil dust input where vegetation is scarce due to harsh climatic conditions for instance. Alternatively, substrate influence can be enhanced by human activity, such as open-cast mining, creation of ‘technogenic deserts’, or handling, transport and storage of ore and ore products, all of which magnify the natural elemental flux from bedrock to ground vegetation. Seaspray is another natural process affecting moss composition in the area (Mg, Na), and this is most visible in the Norwegian part of the study area. Presence or absence of some plant species, e.g., lichens, seems to influence moss chemistry. This is shown by the low concentrations of B or K in moss on the Finnish and Norwegian side of the (fenced) border with Russia, contrasting with high concentrations on the other side (intensive reindeer husbandry west of the border has selectively depleted the lichen population). 相似文献
17.
S. M. Moosavirad J. Rasouli M. R. Janardhana M. R. Moghadam M. Shankara 《Arabian Journal of Geosciences》2013,6(10):3623-3634
This paper discusses the result of the detailed investigations carried out on the coal characteristics, including coal petrography and its geochemistry of the Pabedana region. A total of 16 samples were collected from four coal seams d2, d4, d5, and d6 of the Pabedana underground mine which is located in the central part of the Central-East Iranian Microcontinent. These samples were reduced to four samples through composite sampling of each seam and were analyzed for their petrographic, mineralogical, and geochemical compositions. Proximate analysis data of the Pabedana coals indicate no major variations in the moisture, ash, volatile matter, and fixed carbon contents in the coals of different seams. Based on sulfur content, the Pabedana coals may be classified as low-sulfur coals. The low-sulfur contents in the Pabedana coal and relatively low proportion of pyritic sulfur suggest a possible fresh water environment during the deposition of the peat of the Pabedana coal. X-ray diffraction and petrographic analyses indicate the presence of pyrite in coal samples. The Pabedana coals have been classified as a high volatile, bituminous coal in accordance with the vitrinite reflectance values (58.75–74.32 %) and other rank parameters (carbon, calorific value, and volatile matter content). The maceral analysis and reflectance study suggest that the coals in all the four seams are of good quality with low maceral matter association. Mineralogical investigations indicate that the inorganic fraction in the Pabedana coal samples is dominated by carbonates; thus, constituting the major inorganic fraction of the coal samples. Illite, kaolinite, muscovite, quartz, feldspar, apatite, and hematite occur as minor or trace phases. The variation in major elements content is relatively narrow between different coal seams. Elements Sc,, Zr, Ga, Ge, La, As, W, Ce, Sb, Nb, Th, Pb, Se, Tl, Bi, Hg, Re, Li, Zn, Mo, and Ba show varying negative correlation with ash yield. These elements possibly have an organic affinity and may be present as primary biological concentrations either with tissues in living condition and/or through sorption and formation of organometallic compounds. 相似文献
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20.
The Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km2 area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which
are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite
and quartz veins.
The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock,
alkali pyroxenite, ijolite-melteigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite,
volcanic tuff, phosphatic rock and chert breccia.
The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow
level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly
alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic
than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits
with falling temperature into two immiscible fractions—one ultimately crystallises as alkali pyroxenite/ijolite and the other
as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate
and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction
with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process). Isotopic studies (δ18O and δ13C) on carbonatites of Samchampi have indicated that the δ13C of the source magma is related to contamination from recycled carbon. 相似文献