北山风雷山地区白山组流纹岩LA-ICP-MS锆石U-Pb年龄及构造环境   总被引：4，自引：2，他引：2       下载免费PDF全文

贾元琴  赵志雄  许海  王新亮  刘强  王金荣 《中国地质》2016,(1):91-98

北山地区位于华北板块、塔里木板块和哈萨克斯坦板块的交汇部位,总体上为一近东西向展布的构造-岩浆活动带。风雷山白山组岩性主要为紫红色流纹岩,流纹质含角砾岩屑晶屑凝灰岩、英安质、安山质晶屑凝灰岩夹少量灰色英安岩等,依据喷发特征和岩石空间叠置关系将其划分为一段、二段。岩石地球化学特征显示,流纹岩Si O2含量高(77.05%~77.52%);K2O/Na2O1(1.03~1.07);Ti O2(0.06%~0.19%)、Ca O(0.38%~1.04%)、Mg O(0.09%~0.17%)含量低,岩石的里特曼指数平均为1.74,相对富集大离子亲石元素(LILE)Rb、K,亏损高场强元素(HFSE)Nb、Ta、P、Ti,稀土总量平均为138.47×10-6,轻稀土总量(ΣLREE平均为127.55×10-6)明显高于重稀土(ΣHREE平均为10.92×10-6),轻重稀土分馏明显((La/Yb)N变化于6.37~7.88,平均为7.05;(La/Sm)N变化于4.51~4.61,平均为4.55,Eu具较为明显的负异常(δEu平均仅为0.62)。岩石学、地球化学特征表明构造背景为陆缘弧。流纹岩LA-MCICP-MS锆石U-Pb年龄为(318.5±1.2)Ma,结合区域地质特征,白山组应形成于晚石炭世。  相似文献   

The 26{middle dot}5 ka Oruanui Eruption, Taupo Volcano, New Zealand: Development, Characteristics and Evacuation of a Large Rhyolitic Magma Body     

WILSON  C. J. N.; BLAKE  S.; CHARLIER  B. L. A.; SUTTON  A. N. 《Journal of Petrology》2006,47(1):35-69

The caldera-forming 26·5 ka Oruanui eruption (Taupo,New Zealand) erupted 530 km³ of magma, >99% rhyolitic, <1%mafic. The rhyolite varies from 71·8 to 76·7 wt% SiO₂ and 76 to 112 ppm Rb but is dominantly 74–76 wt% SiO₂. Average rhyolite compositions at each stratigraphiclevel do not change significantly through the eruption sequence.Oxide geothermometry, phase equilibria and volatile contentsimply magma storage at 830–760°C, and 100–200MPa. Most rhyolite compositional variations are explicable by28% crystal fractionation involving the phenocryst and accessoryphases (plagioclase, orthopyroxene, hornblende, quartz, magnetite,ilmenite, apatite and zircon). However, scatter in some elementconcentrations and ⁸⁷Sr/⁸⁶Sr ratios, and the presence of non-equilibriumcrystal compositions imply that mixing of liquids, phenocrystsand inherited crystals was also important in assembling thecompositional spectrum of rhyolite. Mafic compositions comprisea tholeiitic group (52·3–63·3 wt % SiO₂)formed by fractionation and crustal contamination of a contaminatedtholeiitic basalt, and a calc-alkaline group (56·7–60·5wt % SiO₂) formed by mixing of a primitive olivine–plagioclasebasalt with rhyolitic and tholeiitic mafic magmas. Both maficgroups are distinct from other Taupo Volcanic Zone eruptivesof comparable SiO₂ content. Development and destruction by eruptionof the Oruanui magma body occurred within 40 kyr and Oruanuicompositions have not been replicated in vigorous younger activity.The Oruanui rhyolite did not form in a single stage of evolutionfrom a more primitive forerunner but by rapid rejuvenation ofa longer-lived polygenetic, multi-age ‘stockpile’of silicic plutonic components in the Taupo magmatic system. KEY WORDS: Taupo Volcanic Zone; Taupo volcano; Oruanui eruption; rhyolite, zoned magma chamber; juvenile mafic compositions; eruption withdrawal systematics  相似文献   

Reconstruction of a major caldera-forming eruption from pyroclastic deposit characteristics: Kos Plateau Tuff, eastern Aegean Sea     

S. R. Allen   《Journal of Volcanology and Geothermal Research》2001,105(1-2)

The 161 ka explosive eruption of the Kos Plateau Tuff (KPT) ejected a minimum of 60 km³ of rhyolitic magma, a minor amount of andesitic magma and incorporated more than 3 km³ of vent- and conduit-derived lithic debris. The source formed a caldera south of Kos, in the Aegean Sea, Greece. Textural and lithofacies characteristics of the KPT units are used to infer eruption dynamics and magma chamber processes, including the timing for the onset of catastrophic caldera collapse.The KPT consists of six units: (A) phreatoplinian fallout at the base; (B, C) stratified pyroclastic-density-current deposits; (D, E) volumetrically dominant, massive, non-welded ignimbrites; and (F) stratified pyroclastic-density-current deposits and ash fallout at the top. The ignimbrite units show increases in mass, grain size, abundance of vent- and conduit-derived lithic clasts, and runout of the pyroclastic density currents from source. Ignimbrite formation also corresponds to a change from phreatomagmatic to dry explosive activity. Textural and lithofacies characteristics of the KPT imply that the mass flux (i.e. eruption intensity) increased to the climax when major caldera collapse was initiated and the most voluminous, widespread, lithic-rich and coarsest ignimbrite was produced, followed by a waning period. During the eruption climax, deep basement lithic clasts were ejected, along with andesitic pumice and variably melted and vesiculated co-magmatic granitoid clasts from the magma chamber. Stratigraphic variations in pumice vesicularity and crystal content, provide evidence for variations in the distribution of crystal components and a subsidiary andesitic magma within the KPT magma chamber. The eruption climax culminated in tapping more coarsely crystal-rich magma. Increases in mass flux during the waxing phase is consistent with theoretical models for moderate-volume explosive eruptions that lead to caldera collapse.  相似文献   

The Goli d’Aget Member: Early Permian volcanoclastic and volcanic rocks within the Brian?onnais Grand St-Bernard Nappe (Valais, Switzerland)     

Marc-Henri Derron  Jér?me Jacquod  Mario Sartori 《Eclogae Geologicae Helvetiae》2006,99(3):301-307

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一个古元古代A型流纹岩   总被引：17，自引：2，他引：15  

于津海  王德滋 《地球化学》1998,27(6):549-558

山西吕梁群流纹岩是一个古元古代的弱碱性火山岩,它具有高ＳｉＯ２,Ｎａ２Ｏ＋Ｋ２Ｏ和Ｚｒ,Ｇａ等高场强元素和高ＦｅＯ＾＊／ＭｇＯ,Ｒｂ／Ｓｒ和Ｇａ／Ａｌ比值,以及低ＣａＯ,Ｓｒ和Ｅｕ／Ｅｕ＾＊的地球化学特征,相似于Ａ型花岗质岩石。它形成于大陆边缘裂谷环境,化学成分及同位素特征为高εＮｄ（ｔ）值,低（＾８７Ｓｒ／＾８６Ｓｒ）ｉ值,表明流纹岩的原始岩浆由下地壳晚太古代变质岩受裂谷岩浆和热流作用的影响部分  相似文献   

相山铀矿田流纹英安斑岩的厘定及与铀矿化的关系   总被引：11，自引：0，他引：11  

吴仁贵  余达淦  张树明 《铀矿地质》2003,19(2):81-87

本从地质产状、岩石学和同位素年龄等特征出发，对相山铀矿田的两套英安岩进行了厘定，指出流纹英安岩为溢出相岩石，而流纹英安斑岩为浅成侵入相岩石，两系不同时期形成的产物。在时间序列上，流纹英安斑岩形成于淬斑熔岩和花岗斑岩之后，与火山隐爆或气爆作用有关，是相山矿田铀矿化的有利主岩之一。  相似文献   

东天山晚石炭世大石头群流纹岩Sr-Nd-Pb同位素地球化学研究   总被引：26，自引：15，他引：26  

王银喜顾连兴  张遵忠吴昌志李惠民  杨杰东 《岩石学报》2007,23(7):1749-1755

新疆大石头-色皮口地区位于博格达造山带东段北部。该区大石头群流纹岩 Rb-Sr 同位素等时线年龄为306.7±2.3Ma,是博格达裂谷闭合后区域隆升阶段的产物。这些流纹岩的ε_(Nd)(t)为 5.30～ 6.40,(~(87)Sr/~(86)Sr)_i 为0.703289～0.703496,(~(206)Pb/~(204)Pb)_i 为18.037～18.425、(~(207)Pb/~(204)Pb)_i 为15.524～15.567、(~(208)Pb/~(204)Pb)_i 为37.198～37.810,因此其 Nd-Sr-Pb 同位素特征与博格达陆内裂谷伸展和沉降阶段形成的早石炭世七角井组玄武岩和流纹岩相近。七角井组与大量玄武岩伴生的少量流纹岩是由玄武岩浆分离结晶作用的产物,而大石头群中的大量流纹岩群仅与少量玄武岩伴生故是由玄武岩浆分离结晶的产物可排除大的可能性。该区流纹岩很可能是碰撞后的底侵玄武岩在地幔热量影响下发生重熔的产物。大石头群流纹岩正δ_(Nd)(t)值、负ε_(Sr)(t)值(低 Sr 初始值)和低 Pb 同位素比值表明博格达裂谷碰撞后的底侵幔源岩浆重熔的基性产物与碰撞前的七角井组玄武岩一样也来自亏损地幔。  相似文献   

青藏高原西南部查孜地区中新世钾质火山岩地球化学及其成因   总被引：3，自引：1，他引：3  

陈建林  许继峰  康志强  王保弟 《地球化学》2007,36(5):437-447

通常认为青藏高原的钾质-超钾质火山岩的形成多与地幔有着紧密的联系,然而最近对青藏高原的一些钾质-超钾质火山岩的研究显示一些钾质火山岩也可以起源于下地壳.青藏高原西南部查孜地区中新世火山岩是形成于13～11 Ma左右的一套钾质-超钾质岩石,根据岩石化学组成将其分为中基性火山岩组、中性火山岩组和流纹质火山岩.其中中基性火山岩组可能源于一个富含金云母的富集地幔源区;中性火山岩组可能是富钾的镁铁质下地壳部分熔融的产物;流纹质火山岩可能是拉萨地块在中新世时期的伸展构造运动而导致中上地壳因减压而发生部分熔融的产物.结合查孜地区及其邻近火山岩的年龄、化学组成以及岩浆组合,初步认为查孜地区火山岩可能与高原在中新世发生伸展活动而产生的南北向地堑系统有关.  相似文献   

松辽盆地白垩系营城组火山岩脱玻化作用及其储层意义——以盆缘剖面为例   总被引：1，自引：0，他引：1  

赵玉婷  单玄龙  王璞珺  孙晶  刘青帝  任利军 《吉林大学学报(地球科学版)》2007,37(6):1152-1158

松辽盆地东南隆起区三台营城组火山岩岩石类型主要为：珍珠岩、流纹岩、隐爆角砾岩、角砾熔岩和凝灰岩等,其脱玻化的岩石类型主要为珍珠岩和流纹岩。在偏光显微镜下,珍珠岩的玻璃质基质的脱玻化现象表现为雏晶、骸晶（微晶）和球粒3种;而流纹岩基质的脱玻化现象则主要表现为球粒。它们发育过程由雏晶-骸晶（微晶）-球粒逐渐增强。脱玻化的发生及其强弱与岩石成分、层位和裂隙发育程度有密切联系。通过实验室测试,珍珠岩经过的脱玻化作用越强,岩石密度越小,反之,越大。岩石密度变化范围为3.13%~8.65%。假设其为封闭体系,密度的减小对应孔隙的增加,说明脱玻化作用能明显改善玻璃质火山岩这一类特殊储层的物性。  相似文献   

福建德化东洋矿区金矿的发现与找矿意义     

江启煜 《江苏地质》2015,39(2):301-305

德化县东洋矿区金矿位于东南沿海中生代火山岩带中,为近年来发现的规模较大的金矿床。矿体主要赋存于次流纹斑岩及外接触带附近,为火山-次火山热液型金矿床。矿体呈不规则状、透镜状和脉状,矿石组分简单,品位偏低,工程控制和推(预)测金金属量可达大型,随着找矿勘查工作的深入,区内金矿规模将会进一步扩大。  相似文献