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1.
羌塘南部地区大面积出露基性—超基性火成岩。基性岩墙和玄武岩沿龙木错-双湖板块缝合带的南侧呈近东西向分布,大地构造位置位于冈瓦纳大陆北缘,分布范围西起国境线,东到双湖地区,总长约800km,形成时代集中在晚石炭世—早二叠世(284~318Ma),反映出岩浆的快速侵位-喷溢的过程。基性岩墙和玄武岩主要为碱性系列岩石,少数为亚碱性系列,Ti和Fe的含量均比较高,Mg#比较低,表明它们都是原始岩浆经不同程度分异结晶后的残余熔体。基性岩墙和玄武岩的稀土元素、微量元素、形成环境等均与板内玄武岩或典型的地幔柱成因玄武岩具有相似的特点。另外,苦橄质岩石多与基性岩墙和玄武岩一起产出,主要为单斜辉石橄榄岩和二辉橄榄岩,矿物成分贫挥发性组分,主量、稀土和微量元素的特点反映出其很可能代表了地幔柱原始岩浆结晶的产物而非岩浆捕获体,而且其源区很可能为石榴子石二辉橄榄岩。由此,初步认为羌塘南部基性岩墙和玄武岩为地幔柱的头部减压熔融的产物,而苦橄质岩石为地幔柱尾柱通道熔融的产物。 相似文献
2.
羌塘南部地区大面积出露基性—超基性火成岩。基性岩墙和玄武岩沿龙木错-双湖板块缝合带的南侧呈近东西向分布,大地构造位置位于冈瓦纳大陆北缘,分布范围西起国境线,东到双湖地区,总长约800km,形成时代集中在晚石炭世—早二叠世（284～318Ma）,反映出岩浆的快速侵位-喷溢的过程。基性岩墙和玄武岩主要为碱性系列岩石,少数为亚碱性系列,Ti和Fe的含量均比较高,Mg#比较低,表明它们都是原始岩浆经不同程度分异结晶后的残余熔体。基性岩墙和玄武岩的稀土元素、微量元素、形成环境等均与板内玄武岩或典型的地幔柱成因玄武岩具有相似的特点。另外,苦橄质岩石多与基性岩墙和玄武岩一起产出,主要为单斜辉石橄榄岩和二辉橄榄岩,矿物成分贫挥发性组分,主量、稀土和微量元素的特点反映出其很可能代表了地幔柱原始岩浆结晶的产物而非岩浆捕获体,而且其源区很可能为石榴子石二辉橄榄岩。由此,初步认为羌塘南部基性岩墙和玄武岩为地幔柱的头部减压熔融的产物,而苦橄质岩石为地幔柱尾柱通道熔融的产物。 相似文献
3.
This paper investigates the role played by the fumarolic plume of a passive degassing volcano in the genesis of rock coatings
(RC) and in the introduction and re-distribution of metals and trace elements in the surficial environment. At La Fossa active
volcano (Vulcano Island) and in the surrounding environment RC develop owing to exposure of the ground surface to the volcanic
acid plume produced by the passive degassing of La Fossa. Significant positive anomalies of a wide variety of metals and trace
elements (including Bi, Ag, Se, Te, Sb, Pb, As, Cu, Tl and Cd) were observed either in distal and proximal RC. Most of these
anomalies are interpreted to be the result of the transport and subsequent deposition of trace elements, likely to form volatile
compounds, in the fumarolic plume. Two main processes seem to control the geochemistry of RC: one is represented by the leaching
and subsequent deposition of elements from the proximal toward the distal RC; the other is the direct input of trace elements
carried by the emitted volcanic aerosol. The fact that most of the trace elements (particularly Pb, As, Tl, Bi, Te, Se, Cd)
enriched in the RC of Vulcano are highly toxic and potentially dangerous to health in high concentration, indicates that the
atmospheric metal injection by the quiescently degassing La Fossa volcano together with the subsequent deposition and remobilization
by means of surficial waters may represent an environmental hazard that should be taken into account in evaluating the potential
impact of volcanic air pollution on human health. 相似文献
4.
The behavior of chlorine and sulfur during differentiation of the Mt. Somma-Vesuvius magmatic system 总被引：4，自引：0，他引：4
Summary Reheated silicate melt inclusions in volcanic rock samples from Mt. Somma-Vesuvius, Italy, have been analyzed for 29 constituents
including H2O, S, Cl, F, B, and P2O5. This composite volcano consists of the older Mt. Somma caldera, formed between 14 and 3.55 ka before present, and the younger
Vesuvius cone. The melt inclusion compositions provide important constraints on pre-eruptive magma geochemistry, identify
relationships that relate to eruption behavior and magma evolution, and provide extensive evidence for magmatic fluid exsolution
well before eruption.
The melt inclusion data have been categorized by groups that reflect magma compositions, age, and style of eruptions. The
data show distinct differences in composition for eruptive products older than 14.0 ka (pre-caldera rocks) versus eruptive
products younger than 3.55 ka. Moreover, pre-caldera eruptions were associated with magmas relatively enriched in SiO2, whereas eruptions younger than 3.55 ka (i.e., the syn- and post-caldera magmas which generated the Somma caldera and the
Vesuvius cone) were derived from magmas comparatively enriched in S, Cl, CaO, MgO, P2O5, F, and many lithophile trace elements.
Melt inclusion data indicate that eruptive behavior at Vesuvius correlates with pre-eruptive volatile enrichments. Most magmas
associated with explosive plinian and subplinian events younger than 3.55 ka contained more H2O, contained significantly more S, and exhibited higher (S/Cl) ratios than syn- and post-caldera magmas which erupted during
relatively passive interplinian volcanic phenomena.
Received January 10, 2000 Revised version accepted July 17, 2000 相似文献
5.
幔源CO_2释出机理、脱气模式及成藏机制研究进展 总被引：10，自引：0，他引：10
针对幔源CO2如何从地幔岩浆中脱出并进入沉积地层中形成CO2气藏聚集这一关键问题,总结了国内外研究进展和前缘方向。研究表明,地幔深部的碱性玄武岩浆和碱性岩浆才是深部流体和CO2等挥发份大量赋存、渗滤和释出的场所。浅成侵入岩、次火山岩和火山通道等是CO2释放和聚集的有利位置,岩浆期后和岩浆衰弱期的热液活动阶段是CO2大量释放和聚集的有利时期。幔源CO2进入沉积盆地中具有3种脱气模式,即沿岩石圈断裂直接脱气模式、热流底辟体脱气模式和壳内岩浆房-基底断裂组合脱气模式。CO2的固有物化性质决定其运移相态多样,具有运移和聚集过程同步的特征。只有在满足大量的化学消耗及地层水或原油的溶解和耗散之后才能形成CO2有效聚集。幔源CO2成藏和分布主要受岩浆气源体和气源断裂体系的控制。今后,在超临界CO2及其对油气运移聚集的作用、CO2与深大断裂及火山岩的关系、CO2脱气运移机制、CO与常规烃类油气的耦合差异成藏机制等方面仍需要进一步的研究和探索。 相似文献
6.
班康姆铜金矿床是近年来新发现的大型铜金矿床。前人研究初步表明研究区成矿作用与古特提斯洋壳俯冲消减所产生的岩浆作用密切有关,但是缺乏岩石地球化学证据。笔者于研究区地表、钻孔采集了13件火山岩-侵入岩新鲜岩石,开展了主量元素、微量元素、稀土元素分析测试。研究表明该区安山质-侵入杂岩具有岛弧钙碱性火山岩的地球化学特征,构造环境判别图显示该套岩石属于大洋弧环境,形成于大洋消减带,与洋壳板片俯冲有关。安山质-侵入杂岩来源于地幔楔,并经历了结晶分异作用,而煌斑岩形成于板片消减而富集的地幔部分熔融。通过与黎府构造带矿床稀土、微量元素特征对比,证实班康姆矿区与Chatree矿区火山岩及金矿床形成于同一期构造岩浆成矿作用,进一步表明了黎府构造岩浆带在晚二叠世—早三叠世发生了一次重要的区域成矿作用。 相似文献
7.
REE and Trace Element Geochemistry of Yinachang Fe-Cu-REE Deposit, Yunnan Province, China 总被引：3，自引：0，他引：3
1IntroductionThebehaviorsoftherare earthelements (REE)duringmagmatism ,metamorphismandmeta somationareofgreatgeologicalinterestbecauseoftheirapplicationsingeochronologyandgeochemi caltracing (e .g .reviewsbyFaure ,1 986;LipinandMckay ,1 989) .Becauseoftheirsimilargeo chemicalbehaviorsandlowsolubilitiesinwater,theREEshaveprovedthemselvestobeapowerfultoolforthecharacterizationofprovenanceswhenappliedtosedimentaryrocks (McDanieletal.,1 994) .Althoughtheirbehaviorsunderhydrothermalconditionsar… 相似文献
8.
9.
伊通县放牛沟地区早古生代岩浆演化特征及其与矿产关系 总被引：1，自引：0，他引：1
伊通县放牛沟早古生代岩浆活动较为强烈,其发展演化与放牛沟多金属硫化物矿床关系极为密切。岩浆活动特点是先喷发后侵入,先期形成钙碱系列的火山—沉积岩系,后期为Ⅰ型中酸性岩浆侵入。该矿床既有火山沉积特征,又有后期岩浆热动力改造特点,其形成受控于岛弧构造环境、火山活动形成的矿源层、后期热动力改造等因素。 相似文献
10.
Investigations of the Stillwater Complex: Part V. Apatites as indicators of evolving fluid composition 总被引：1，自引：0，他引：1
Variations in the F, Cl and OH contents of apatite are not constrained by crystal-chemical factors (in contrast to micas and amphiboles), and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks. Microprobe analysis of intercumulus apatites from the Stillwater Complex reveal that Cl-rich apatites, typically containing <0.4 wt % F and >6.0 wt % Cl, occur throughout the lower 1/3 of the complex excluding the Basal series. A change from Cl-rich to more F-rich apatite occurs within olivine-bearing zone I (OB I) of the Banded series, the host zone of the platiniferous J-M Reef. Although apatite compositions are somewhat variable above the J-M Reef, more F-rich apatites predominante and typically contain >1.2 wt % F and <3.0 wt % Cl. The most F-rich apatites occur in the uppermost exposed cumulates. Pristine apatites from coeval sills and dikes from below the complex and from the Basal series are similarly F-rich. In all apatites, the Cl and F contents are lower in rocks affected by later metamorphic fluids. Rare earth element (REE) concentrations in chlorapatites show a marked peak in the olivine-rich rocks of the J-M Reef, and contain up to 2 wt % Ce2O3 + La2O3. The trend of first increasing, then decreasing Cl/F ratios with stratigraphic height is modeled by a vapor-driven zone refining process occurring within the cumulate pile causing Cl-enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of Cl from the magma as crystallization proceeded. The abrupt change from Cl-rich to more F-rich apatites within OB I is interpreted as the result of a breakdown of the Cl-rich zone refining front and mixing with Cl-poor supernatant melt. Any high temperature fluids that exsolved and circulated through the lower 1/3 of the complex must have been enriched in Cl and could have transported REE and trace metals. 相似文献
11.
The 2014–2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a 6-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra samples, mineral chemistry, and radiogenic and oxygen isotope analyses from an extensive set of samples (n?=?62) that were collected systematically in several field campaigns throughout the entire eruptive period. We also present the first detailed chemical and isotopic characterization of magmatic sulfides from Iceland. In conjunction with a unique set of geophysical data, our approach provides a detailed temporal and spatial resolution of magmatic processes before and during this eruption. The 2014–2015 Holuhraun magma is compositionally indistinguishable from recent basalts erupted from the Bárðarbunga volcanic system, consistent with seismic observations for magma ascent close to the Bárðarbunga central volcano, followed by dyke propagation to the Holuhraun eruption site. Whole-rock elemental and isotopic compositions are remarkably constant throughout the eruption. Moreover, the inferred depth of the magma reservoir tapped during the eruption is consistently 8?±?5 km, in agreement with geodetic observations and melt inclusion entrapment pressures, but inconsistent with vertically extensive multi-tiered magma storage prior to eruption. The near constancy in the chemical and isotopic composition of the lava is consistent with the efficient homogenization of mantle-derived compositional variability. In contrast, occurrence of different mineral populations, including sulfide globules, which display significant compositional variability, requires a more complex earlier magmatic history. This may include sampling of heterogeneous mantle melts that mixed, crystallized and finally homogenized at mid- to lower-crustal conditions. 相似文献
12.
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
13.
CUI Yinliang QING Dexian CHEN Yaoguang 《中国地球化学学报》2007,26(3):312-324
The Longbohe Cu deposit, which is located in the southern part of the Honghe ore-forming zone, Yunnan Province, China, belongs to a typical ore field where volcanic rocks are of wide distribution and are associated with Cu mineralization in time and space. The volcanic rocks in the ore field, which have experienced varying degree of alteration or regional metamorphism, can be divided into three types, i.e., meta-andesite, meta-subvolcanic rock and meta-basic volcanic rock in accordance with their mineral assemblages. These three types of volcanic rocks in the ore field are relatively rich in Na and the main samples plot in the area of alkali basalts in the geochemical classification diagram. With the exception of very few elements, these three types of volcanic rocks are similar in the content of trace elements. In comparison to the basalts of different tectonic settings, the meta-volcanic rocks in the ore field are rich in high field strength elements (HFSE) such as Th, Nb, etc. and depleted in large ion lithophile elements (LILE) such as Sr, Ba, etc. and their primary mantle-normalized trace element patterns show remarkable negative Th and Nb anomalies and negative Sr and Ba anomalies. These three types of volcanic rocks are similar in REE content range and chondrite-normalized REE patterns with the exception of Eu anomaly. Various lines of evidence show that these three types of volcanic rocks in the ore field have the same source but are the products of different stages of magmatic evolution, their original magma is a product of partial melting of the metasomatically enriched mantle in the tensional tectonic setting within the continent plate, and the crystallization differentiation plays an important role in the process of magmatic evolution. 相似文献
14.
峨眉山大火成岩省出露有少量酸性火山岩,它们与基性火山岩共生,表现出双峰式的特征,为研究峨眉山地幔柱晚期岩浆活动提供了重要的窗口。本文通过对双峰式火山岩主、微量元素和斑晶电子探针分析研究表明,基性火山岩属于碱性玄武岩,酸性火山岩主要由粗面岩组成;相对玄武岩,粗面岩中MgO、Fe2O3、P2O5、TiO2、CaO含量明显降低;粗面岩与玄武岩具有相互平行的REE配分模式,但粗面岩出现明显的Eu负异常,以及Sr、Ti等元素的强烈亏损;粗面岩与玄武岩具有同源的特征,通过稀土元素模拟计算表明粗面岩可以由玄武质岩浆经过80%分离结晶作用(辉石、斜长石和Fe-Ti氧化物)而形成。在峨眉山大火成岩省晚期出现双峰式火山岩,可能与地幔柱活动晚期岩浆供给少,在地壳岩浆房中停留时间长,岩浆发生强烈分离结晶作用有关。 相似文献
15.
Jacqueline Owen 《Geology Today》2016,32(1):30-37
Eruptions beneath ice sheets and glaciers can generate hazardous ash plumes and powerful meltwater floods, as demonstrated by the recent Icelandic eruptions at Eyjafjallajökull in 2010 and at Grímsvötn in 2011. A key scientific objective for volcanologists is to better understand the factors controlling subglacial eruptions, but the eruptions are mostly hidden beneath ice that is often hundreds of metres thick, thereby preventing direct observation. New approaches are therefore needed to reconstruct the factors driving explosive activity and the response of the overlying ice. The dissolved volatile content, preserved in glassy volcanic rock, offers a useful means of reconstructing palaeo‐ice thicknesses. However, for subglacial rhyolite at least, there seems to be little or no correlation between loading pressure and eruptive style. Instead, there is a strong correlation between the pre‐eruptive volatile content, degassing path and eruptive behaviour. It seems that the style of many subglacial eruptions is controlled by the same mechanisms as subaerial eruptions, with explosivity strongly influenced by degassing and magmatic fragmentation. 相似文献
16.
西秦岭合作—美武地区郎木寺组火山岩主要以中性的安山质火山岩为主,其次为英安岩及英安质火山碎屑岩和酸性的流纹质火山岩,为一套高K、低Ti、准铝质的钙碱性系列火山岩,微量元素总体富集Rb、亏损Th、La、Nd,Nb,稀土总量不高,含量不稳定,变化范围较大,轻重稀土分馏较明显,Eu存在微弱的负异常。通过对岩石学、岩石地球化学分析,表明其形成于活动大陆边缘弧环境,岩浆来源于地幔楔或俯冲板块上升过程中产生的俯冲岩浆带,为合作—美武地区火山岩岩石成因及构造环境研究提供依据。 相似文献
17.
Emission rates of CO2 have been measured at Kilauea volcano, Hawaii, in the east-rift eruptive plume and CO2 and SO2 have been measured in the plume from the noneruptive fumaroles in the summit caldera. These data yield an estimate of the loading of Kilauean eruptive gases to the atmosphere and suggest that such estimates may be inferred directly from measured lava volumes. These data, combined with other chemical and geologic data, suggest that magma arrives at the shallow summit reservoir containing (wt.%) 0.32% H2O, 0.32% CO2 and 0.09% S. Magma is rapidly degassed of most of its CO2 in the shallow reservoir before transport to the eruption site. Because this summit degassing yields a magma saturated and in equilibrium with volatile species and because transport of the magma to the eruption site occurs in a zone no shallower than the summit reservoir, we suggest that eruptive gases from Kilauea characteristically should be one of two types: a ‘primary’ gas from fresh magma derived directly from the mantle and a carbon-depleted gas from magma stored in the summit reservoir. 相似文献
18.
为了了解峨眉山地幔柱岩浆系统的演化过程,对红格超大型钒钛磁铁矿矿床中辉绿岩脉进行了全岩主微量、矿物原位成分和同位素研究,并利用MELTS软件进行了岩浆过程模拟计算.研究发现,红格辉绿岩脉具有与峨眉山高钛玄武岩一致的稀土元素配分型式和Sr同位素组成,表明其起源于峨眉山地幔柱.辉绿岩含有斑晶和基质两个世代矿物,从斑晶核部到边部和基质,单斜辉石Mg#值较为连续变化,而斜长石An值具有明显的间断.MELTS模拟表明,这种成分变化难以用简单的岩浆上升侵位解释,反映了辉绿岩脉在岩浆演化过程中可能还与同期的正长质岩浆发生了混合.我们的研究表明,峨眉山地幔柱岩浆作用具有穿地壳、多期次、多阶段演化的特点,并且同源岩浆混合也是一个不可忽视的方面. 相似文献
19.
Late Quaternary rhyolitic tephra units, erupted from the Taupo Volcanic Zone, North Island, New Zealand, were sampled from four stratigraphically correlated sections. Nineteen glass-shard separates from these tephra units were analysed by spark-source mass spectrometry. Data for the rare earth and other trace elements are presented. A statistical analysis of these data suggests an identification and correlation of the samples which is similar to the field-determined stratigraphy.Massive airfall tephra units that have been deposited during a single eruptive episode appeared to be more uniform in elemental concentrations than either multiple-bedded airfall tephra units, or tephra units comprising both airfall and airflow material which were considered to result from multiple-phase eruptions.The rare-earth element chondrite-normalised patterns showed enrichment of the lighter elements compared with the heavier elements. A notable Eu deficiency was recognised which was consistent with the model for enrichment of Eu in the plagioclase feldspars in acidic magma. 相似文献