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1.
We introduce the use of Nd isotopes as a high‐precision technique that can be used in conjunction with visual, petrographic, and trace element analyses to source indistinct felsitic debitage. This approach allows sourcing of debitage from southeastern New England, including samples that previously could not be constrained to one source. Combined with trace element data, isotopic data also provide the possibility of sourcing debitage to a particular quarry site within a volcanic complex, and even to a particular ash flow within a quarry site. Determining the origin of debitage so precisely is important for understanding acquisition, trade, and exchange networks in southeastern New England, where distances separating quarry sites within an individual volcanic complex (Lynn–Mattapan) are greater than distances between different volcanic complexes (Lynn–Mattapan, Blue Hill, and Wamsutta). The sourcing of debitage to Mattapan quarries suggests that Middle Archaic populations in the northwest part of the Boston Basin obtained nonlocal lithic material primarily from sources south of the basin. © 2000 John Wiley & Sons, Inc. 相似文献
2.
准噶尔盆地陆东—五彩湾地区石炭系中、基性火山岩地球化学及其形成环境 总被引：11，自引：1，他引：10
准噶尔盆地是发育在前寒武纪结晶基底与古生代褶皱基底双重基底之上的中、新生代沉积盆地。盆地东北缘陆东—五彩湾地区发育大量的石炭系中、基性火山岩,主要由玄武岩、熔结玄武岩、气孔-杏仁玄武岩与辉绿岩组成。其中、基性火山岩具有低钾高钛、高∑REE的特征,球粒陨石标准化的REE配分曲线表现轻稀土富集,轻、重稀土分异的谱线特征,微量元素具有大离子亲石元素富集,Ta、Nb亏损的现象,可能与板内拉张环境下地壳混染或地幔源区有富Ta、Nb的残留体有关,微量元素环境判别图解中大部分样品点落入板内玄武岩区域,少量漂向岛弧火山岩区,表现出主体为板内构造环境;高场强元素Th/Nb、Nb/Zr比值进一步表现出火山岩具有板内火山岩的特征。综合区域地质特征及前人的研究结果,认为准噶尔盆地陆东—五彩湾地区中、基性火山岩应属造山期后伸展背景下的火山作用产物,但岩浆源区可能受到古洋壳板片俯冲作用的影响。 相似文献
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贵州威宁地区宣威组底部稀土含矿岩系的成因类型一直有较大争议.在野外实地调查的基础上,运用矿物学、岩相古地理与地球化学等手段进行了系统性研究.结果显示,区内二叠系宣威组底部稀土含矿岩系广泛分布,连续性好,含矿段厚度为2~16 m,并伴生有铌、锆、镓等元素;稀土氧化物平均品位0.15%,最高可达1.60%.主量、微量和稀土元素分析表明威宁地区稀土含矿岩系中含有来自玄武岩及火山灰的典型矿物,稀土配分模式与玄武岩相比具有继承性,研究区化学风化作用较强、成分成熟度较高代表其经过长距离搬运,遭受了改造;峨眉山玄武岩为该稀土层提供了主要物质来源,稀土层受源岩成分的控制,经历了沉积分选及再循环作用,还遭受了来自上地壳的中酸性岩浆物质源区的混染.其成因机制可能为在晚二叠世炎热、潮湿、强风化的环境中,玄武岩经过风化剥蚀后,搬运至沉积基底低洼处的三角洲平原亚相中的洪泛平原微相环境,与火山灰一同沉积沉淀,在风化和淋滤作用下稀土等元素以离子形式被解析出来,从而被吸附性强的高岭石等黏土矿物吸附于表面,或进入矿物晶格,形成富稀土层. 相似文献
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锆石U-Pb定年结果显示,松辽盆地长岭断陷松南180井中基性火山岩形成于101～116 Ma的早白垩世晚期,属于营城组,非火石岭组火山岩。岩相学观察主要由安山岩和橄榄玄武岩组成,化学成分显示为玄武岩、粗面玄武岩和玄武质粗面安山岩,属碱性系列,镁质量分数较低,镁值较小（Mg#=0.27~0.53）。稀土元素总量较高（w（∑REE）=（164.98~257.27）×10-6）,轻重稀土分馏明显（（La/Yb）N=6.60~10.96）,铕异常微弱（δEu=0.85~1.02）。富集大离子亲石元素和轻稀土元素, Rb,K 相对亏损,相容元素（Cr、Co、Ni）质量分数低,高场强元素Nb、Ta弱富集,整体表现出与 OIB(洋岛玄武岩)一致的稀土图谱和微量元素特征。岩浆源区为软流圈地幔,经历了深部地幔流体的交代富集作用,岩浆未遭受地壳物质的混染。 相似文献
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仲岗洋岛位于班公湖-怒江板块缝合带中西段,前人对仲岗洋岛的研究主要集中在东段,中段洞错一带尚未有人研究。对仲岗洋岛的岩石组合及岩石地球化学进行研究,并对洋岛火山岩的源区及构造环境进行分析。在仲岗洋岛中段洞错北部的一条剖面上采集了8个玄武岩和8个玄武安山岩地球化学样品,主量元素特征表明,二者皆为具有富Ti特征的碱性玄武岩,微量元素特征显示二者富集Nb、Ta元素。稀土元素配分曲线和微量元素蛛网图与典型洋岛玄武岩曲线相似。化学成分指示,仲岗洋岛玄武岩与玄武安山岩可能来自于同一岩浆源区,且二者来源于具有洋岛玄武岩特征的地幔,相容元素Cr、Ni的亏损表明,成岩过程中发生了橄榄石和辉石的分离结晶作用。洋岛形成于大洋板块内以洋壳为基底的洋岛环境。 相似文献
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广东三水盆地的演化伴随着强烈的火山活动.为研究三水盆地各类岩石之间的演化关系, 对在盆地内的玄武岩、粗面岩和流纹岩样品进行常量、微量元素地球化学分析.对样品的地球化学投图表明: 玄武岩样品表现为轻稀土富集的板内玄武岩稀土配分模式, 而其微量元素也具有Nb、Ti富集、Sr弱亏损的特征, 由部分熔融产生;粗面岩与流纹岩样品稀土与微量元素配分模式相似, 两类岩石均经历以斜长石为主的分离结晶过程.华南陆缘在始新世早期处于与红海相似的大陆裂谷环境, 喷发来源于深部软流圈地幔的岩浆, 但在42 Ma之后, 火山活动因区域挤压作用而停止.其后的南海扩张可能是两种作用的叠加影响的结果. 相似文献
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西昆仑奥依塔格石炭-二叠纪岩浆岩:弧后盆地的产物? 总被引：1，自引：1，他引：0
目前对西昆仑石炭-二叠纪火山岩分带性、形成环境、深部地幔源区特征还缺乏较好的约束。在区域地质填图、综合研究的基础上,将西昆仑石炭-二叠纪岩浆岩空间上分为南带、北带。本文展示了北带岩浆岩集中出露的奥依塔格地区玄武岩、辉绿岩、辉长岩的地球化学和Sr、Nd、Pb同位素以及与辉长岩共生的斜长花岗岩的锆石LA-ICP-MS测年数据,以约束该区基性岩形成的时代、构造环境和地幔源区特征,同时与库地玄武岩、阿羌基性火山岩进行了比较。目前的数据表明:(1)斜长花岗岩单颗粒锆石LA-ICP-MS测年得到313.6±1.6Ma、291.6±1.7Ma两组年龄,后者代表斜长花岗岩和辉长岩的侵位时代,前者可能代表玄武岩的年龄。(2)球粒陨石标准化稀土元素配分模式图中,玄武岩显示轻稀土略富集的向右缓倾模式,辉绿岩、辉长岩均为轻稀土略亏损的近平坦型;原始地幔标准化微量元素值均表现为大离子亲石元素相对富集,Nb、Ta谷明显,高场强元素中后半部分呈平坦型模式。(3)地球化学指标显示奥依塔格一带基性岩未受到或很少受到地壳物质混染,样品的Nd、Pb组成可以用来代表地幔源区的成分特点,Nd-Pb、Pb-Pb图解显示其代表的地幔源区具有"Dupal"异常,并于金沙江蛇绿岩中玄武岩代表的地幔源区有较高的一致性。(4)综合岩石地球化学、沉积组合认为奥依塔格基性岩形成于弧后盆地构造环境,区域对比,指出它与库地一些克沟组玄武岩、于田县阿羌组火山岩同为康西瓦-麻扎混杂岩带代表的洋盆向北俯冲,引发弧后盆地扩展的结果。 相似文献
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通过对西藏羌塘中部冈塘错地区玄武岩地球化学特征研究,发现该区有OIB型和E-MORB型两类玄武岩.对两类玄武岩进行主量元素、稀土元素和微量元素地球化学图解分析及大地构造意义探讨,结合区域地质背景,认为冈塘错地区玄武岩形成于洋岛环境,可能受地幔柱岩浆活动影响,E-MORB型玄武岩的出现说明该区可能存在洋底高原. 相似文献
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The Welcome Well volcanic complex east of Leonora, Western Australia, is interpreted to be the eroded remnant of an Archaean stratovolcano. Andesitic flows and intercalated mudflow deposits comprising the volcanic centre give way to coarse, poorly-sorted lithic wackes that were deposited in alluvial fans skirting the lower slopes or base of the subaerial volcanic edifice. These deposits are succeeded both laterally and vertically by fine-grained, subaqueous, turbiditic sediments that are intercalated with pillowed, tholeiitic basalts.There is a complete petrographic and geochemical gradation from porphyritic basalt through porphyritic andesite to porphyritic dacite. In general, the rocks show calc-alkaline patterns of elemental behaviour, consistent with fractionation of variable proportions of the modal minerals amphibole, plagioclase, clinopyroxene and Ti-magnetite. Among these minerals, amphibole appears to have assumed a major role in producing the geochemical characteristics of the high-Si andesites and dacites as evidenced by the behaviour of Zr, Nb, Y and REE. In order to account for the geochemical variability of the basalts and low-Si andesites, it is proposed that they differentiated from primitive basic parents which had a range of major and LIL element contents. The most plausible origin for the primary magmas involves shallow, hydrous melting of a LIL element-enriched mantle source over a significant pressure range. 相似文献
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冈底斯作为重要的中、新生代岛弧岩浆岩带,历来是青藏高原最热门的地质研究领域,但是对晚古生代火山岩的性质及其形成的构造背景仍缺乏研究。本文在区域地质调查资料的基础上,对冈底斯带石炭纪火山-沉积岩系进行了系统的地层学和岩石地球化学研究,测量了重点剖面,对火山岩进行了常量、微量元素和Sr、Nd、Pb同位素地球化学测试。研究表明,石炭系与下伏泥盆系或前寒武系之间普遍存在不整合或岩性、沉积相的突变面,代表重要的构造转换面。石炭纪的沉积环境大致有两次滨海-深海或深水斜坡-滨海沉积演化旋回,深海-深水斜坡沉积或冰海相含砾板岩与两次火山活动伴生。石炭纪火山岩主要为安山玄武岩和英安岩、流纹岩类,略具双峰式火山岩特点。安山玄武岩类的成分与典型MORB和岛弧玄武岩相比,具有MgO含量低,TiO2、Al2O3、P2O5含量高等特点,稀土和微量元素为LREE和LILE富集型分配模式,与大陆拉斑玄武岩相似。石炭纪酸性火山岩的稀土和微量元素地球化学特征与陆内流纹岩相似。岩石地球化学示踪和地层学研究表明,冈底斯带石炭纪为伸展背景下的冈瓦纳陆缘裂陷环境。火山岩的源区地幔具有典型的Dupal异常,发生过复杂的混合作用,涉及到原始地幔、富集地幔EMII和地壳成分等,说明发生过冈瓦纳古陆壳俯冲、再循环进入古老地幔等过程。玄武岩类成分的某些特殊性,可能与源区混合作用有关。 相似文献
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《Journal of Asian Earth Sciences》2001,19(1-2):61-76
The northeastern margin of the Tethyan Neyriz ophiolite complex in southwestern Iran is tectonically juxtaposed under cataclastically-deformed island arc volcanic–volcaniclastic rocks. We document this arc component of the Zagros Crush Zone in the Neyriz area, and describe its petrographic and geochemical characteristics. The arc unit which we call the Hassanabad Unit, is tectonically intercalated with Cretaceous limestone in the cataclastic shear zone around the Hassanabad pass north of Neyriz.Analyses of the distributions of the major, rare earth and other trace elements in the volcanic rocks of the Hassanabad Unit reveal a dominantly calc-alkaline island arc composition. Volcanogenic sandstone and sedimentary breccia, with clasts of basalt, andesite and diorite, are cataclastically intercalated with pillowed calc-alkaline island arc volcanic rocks, pelagic limestone and radiolarian chert. Trace element geochemistry corroborates the petrographic evidence that the poorly-sorted and angular volcanogenic sediments were derived locally from the island arc volcanic and intrusive rocks. The emplacement of the volcanic arc rocks adjacent to the thrust sheets of the crustal and mantle sequences of the Neyriz ophiolite was probably a result of subduction-related processes during closure of the Tethys ocean during the Late Cretaceous. 相似文献
13.
Geochemical and mineralogical evidence for Sahara and Sahel dust additions to Quaternary soils on Lanzarote,eastern Canary Islands,Spain 总被引：1，自引：0，他引：1
Daniel R. Muhs James Budahn Gary Skipp Joseph M. Prospero DeAnna Patterson E. Arthur Bettis III 《地学学报》2010,22(6):399-410
Africa is the most important source of dust in the world today, and dust storms are frequent on the nearby Canary Islands. Previous workers have inferred that the Sahara is the most important source of dust to Canary Islands soils, with little contribution from the Sahel region. Soils overlying a late Quaternary basalt flow on Lanzarote, Canary Islands, contain, in addition to volcanic minerals, quartz and mica, exotic to the island’s bedrock. Kaolinite in the soils also likely has an exotic origin. Trace‐element geochemistry shows that the soils are derived from varying proportions of locally derived basalt and African dust. Major‐element geochemistry, clay mineralogy and interpretation of satellite imagery suggest that dust additions to the Canary Islands come not only from the Sahara Desert, but also from the Sahel region. 相似文献
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黄骅盆地中新生代火山岩岩相及岩石化学特征 总被引：2，自引：1，他引：2
通过对渤海地区黄骅盆地中新生代火山岩进行典型的岩芯取样、岩相及全岩分析,并结合KAr法测年、微量元素和同位素地球化学分析,得出以下结论:主要岩石类型有新生代老第三纪玄武岩、中生代晚白垩世玄武粗安岩、中生代晚白垩世粗面英安岩和流纹岩和中生代早三叠世英安岩。晚中生代火山岩岩石的主量元素丰度呈双峰分布,从老到新,火山岩主元素中SiO2减少,Fe2O3、FeO、CaO、MgO、TiO2、P2O5、MnO有所增加。新生代玄武岩可能源自亏损的软流圈地幔,晚白垩世玄武粗安岩源自玄武质组分亏损和受到富集改造的岩石圈地幔, 相似文献
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《Russian Geology and Geophysics》2014,55(1):62-77
The paper presents new petrographic, geochemical, and petrologic data from volcanic rocks of suprasubduction origin of the Char shear zone in eastern Kazakhstan. We discuss bulk rock composition (concentrations of major and trace elements), types of mantle sources and parameters of their melting, conditions of crystallization of mafic magma, and geodynamic settings of basalt eruption. According to the major element composition, the volcanic rocks are basalt, andesibasalt, and andesite of tholeiitic and transitional, from tholeiitic to calc-alkaline, series. They are characterized by low TiO2 (0.85 wt.% on average) and crystallization trends in MgO–major elements plots. In terms of trace element composition, the volcanic rocks possess moderately LREE-enriched rare-earth element patterns and are characterized by negative Nb anomalies present on the multi-element spectra (Nb/Lapm = 0.14–0.47; Nb/Thpm = 0.7–1.6). The distribution of rare-earth elements (La/Smn = 0.8–2.3, Gd/Ybn = 0.7–1.9) and the results of geochemical modeling in the Nb–Yb system suggest high degrees of melting of a depleted mantle source at spinel facies depths. Fractional crystallization of clinopyroxene, plagioclase, and opaque minerals also affected the final composition of the volcanic rocks. Clinopyroxene monomineral thermometry calculations suggest that the melts crystallized within a range of 1020–1180 °C. We think that this volcanic complex formed at a western active margin of the Paleo-Asian Ocean. 相似文献
17.
The Caradoc volcanic rocks of the Lleyn Peninsula represent a major episode of rhyolite-dominated eruption (total volume up to 560 km3) within the Southern British Caledonides. New geochemical data reveal the original chemical characteristics of the basic, intermediate, and acid lavas. The basalts are interpreted as having predominantly within-plate character and are associated with intermediate lavas (trachybasalts) and high-Zr, originally peralkaline, trachytes, and rhyolites. A low-Zr, originally high-K, subalkalic group of rhyolites, and a basalt with transitional island arc tholeiite-MORB characteristics are unrelated to these lavas. The volcanic rocks are interpreted to have been erupted onto a complex, rapidly evolving, active continental margin dominated by crustal tension. 相似文献
18.
新疆甜水海地块种羊场石炭纪火山岩年代学和地球化学:岩石成因和地质意义 总被引：1，自引：1，他引：0
甜水海地块西段的种羊场地区发育一套互层状产出的玄武岩-玄武安山岩-流纹岩,本文对其进行了岩石学、同位素年代学和地球化学研究。结果表明,流纹岩LA-ICP-MS锆石U-Pb定年获得三组年龄:343.5±4.1Ma表明火山岩的形成时代为早石炭纪,2439±26Ma和1988±36Ma说明甜水海地块存在前寒武纪结晶基底。其中玄武质岩石岩性从拉斑系列、钙碱性系列向碱性系列过渡,呈现出E-MORB(OIB)、大陆板内拉张和岛弧的混合特征,与典型弧后盆地Okinawa玄武岩有一定的差异,表明其可能是异常陆缘弧后盆地拉张裂解的产物。玄武质岩石和流纹岩的主量元素、稀土元素和微量元素比值对的差异表明它们不是同源岩浆演化的产物,玄武质岩石的源区为类似E-MORB(OIB)的岩石圈地幔,且发生了部分熔融,原始岩浆上升过程中经历了矿物分离结晶和地壳混染作用。流纹岩属于高硅高碱的钙碱性火山岩,是上地壳部分熔融的产物。种羊场早石炭纪火山岩可能代表了古特提洋西端早期扩张的记录,为西昆仑-喀喇昆仑地区晚古生代多岛洋格局提供了新的证据。 相似文献
19.
Interpretation of bulk‐sediment geochemistry is one of several approaches for determining sediment provenance. This study investigates the value added by bulk‐sediment geochemical analysis in interpreting provenance in a passive margin clastic basin, the Upper Jurassic–Lower Cretaceous deltaic sediments of the Scotian Basin. Provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant. More than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements. Diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km, thus impacting principal component analysis and published weathering indices. However, multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the Tithonian and Barremian, and changes in supply from major tectonic events, such as the top‐Aptian uplift in the Labrador rift. Covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources. Geochemical analyses revealed a previously unsuspected Tithonian alkali volcanic sediment source, characterized by high niobium and tantalum. The lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance. Published discrimination diagrams are of limited value. Statistical analysis of geochemical data is strongly influenced by diagenetic processes, episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones. Single indicator elements for particular sources are generally lacking. Nevertheless, careful consideration of geochemical variability on a case by case basis, integrated with detrital mineral studies, provides new insights into palaeoclimate, sediment provenance and, hence, regional tectonics. Although there is no simple template for such analysis, this study demonstrates an approach that can be used for other basins. 相似文献
20.
新疆东准噶尔卡拉麦里地区早泥盆世火山岩由玄武岩和玄武安山岩组成,采用LA-ICP-MS锆石U-Pb定年方法,获得玄武安山岩锆石的U-Pb年龄为404.5±1.9 Ma,表明喷发时代为早泥盆世。岩石地球化学显示早泥盆世火山岩属岛弧拉斑系列,具相对较高的Mg# 值(41.25～55.32)及较低的Nb(1.11×10- 6～2.42×10- 6)、Zr(73.9×10- 6～95×10- 6)和ΣREE(81.50×10- 6～121.80×10-6)含量。富集大离子亲石元素(LILE：K、Rb、Ba)和轻稀土元素(LREE),而亏损Ta、Nb和Ti高场强元素（HFSE：Ta、Nb、Ti）,并显示Eu弱的亏损,这些特征与岛弧火山岩类似,其原始岩浆可能起源于俯冲流体交代的亏损地幔楔的部分熔融。结合区域地质背景,认为早泥盆世火山形成于洋内弧的构造环境,为卡拉麦里古洋盆向北俯冲消减的产物。这是在卡拉麦里地区首次报道的洋内弧火山岩,这一新的发现和认识对研究东准噶尔古生代洋盆演化及区域构造格局均具有重要的意义。 相似文献