Variation in rhyolitic magma composition linked with fractionation from a common source: insights from the Rotoiti eruption,Taupo Volcanic Zone,New Zealand     

《International Geology Review》2012,54(16):1967-1982

ABSTRACT

The Taupo Volcanic Zone (TVZ), New Zealand, is a well-documented volcanic arc characterized by explosive rhyolitic magmas within a series of caldera complexes that include the Okataina Volcanic Centre (OVC). New quartz melt inclusion and volcanic glass data from the 45 ka caldera-forming Rotoiti eruption within the OVC are compared to published studies. The new data are characterized by low K₂O (~1.5–3.5 wt.%), Rb (~30–70 ppm), Sr (~40–90 ppm), U (~0.5–2.5 ppm), and Ba (~300–1000 ppm) ranges that differ significantly from other OVC systems (~3.0–4.5 wt.% K₂O, ~80–150 ppm Rb, and ~2.5–5.0 ppm U). Most interestingly, the Rotoiti melt inclusion data measured in this study show a decrease in Rb, Sr, and U, although the fractionation trends originate from the same source point as published OVC data. This progressive decreasing trend is interpreted as an interaction with a less enriched rhyolitic melt (represented by the low Rb, Sr, and U of glasses) during fractionation processes from a common TVZ source. The established model for TVZ rhyolites is that they are extracted from a middle or upper crustal source (‘mush’ zone) prior to eruption. Adding to this model, new melt inclusion data suggest that all TVZ rhyolites are fractionated from this common TVZ source and, prior to eruption, the Rotoiti system was rejuvenated by this source (evidenced by the low REE glasses). Exactly what triggers the common TVZ source to fractionate remains unclear, but a proposed mechanism to account for this involves the successive melting of the upper crust by upwelling mantle induced by incremental subduction.  相似文献   

悠悠古遗址珍稀古火山——关于建立四平山门-伊通火山国家地质公园的若干思考     

蔺广太 《吉林地质》2003,22(2):50-55

建设国家地质公园是时代发展、保护自然遗产的客观要求.四平山门-伊通一带分布着的十数座流纹岩柱状节理火山锥和玄武岩柱状节理火山锥,辅以燕国古城遗址、努尔哈赤起兵和慈禧祖籍地、解放战争"四战四平"战绩地等人文景观和其他自然景观,以及各类保护区和经济开发区的建设,使本区具备了地质公园的地质遗迹特殊的科学意义.稀有的自然属性,优雅的美学观赏价值,融合自然与人文景观并具有生态、历史和文化价值,为建立国家地质公园奠定了丰厚的物质基础.本文对四平山门-伊通火山地质公园从基础条件,基础研究、基础建设、申报工作等方面给予了详实论述.  相似文献   

Magma Generation at a Large, Hyperactive Silicic Volcano (Taupo, New Zealand) Revealed by U-Th and U-Pb Systematics in Zircons   总被引：9，自引：1，他引：8  

CHARLIER  B. L. A.; WILSON  C. J. N.; LOWENSTERN  J. B.; BLAKE  S.; VAN CALSTEREN  P. W.; DAVIDSON  J. P. 《Journal of Petrology》2005,46(1):3-32

Young (<65 ka) explosive silicic volcanism at Taupo volcano,New Zealand, has involved the development and evacuation ofseveral crustal magmatic systems. Up to and including the 26·5ka 530 km³ Oruanui eruption, magmatic systems were contemporaneousbut geographically separated. Subsequently they have been separatedin time and have vented from geographically overlapping areas.Single-crystal (secondary ionization mass spectrometry) andmultiple-crystal (thermal ionization mass spectrometry) zirconmodel-age data are presented from nine representative eruptiondeposits from 45 to 3·5 ka. Zircon yields vary by threeorders of magnitude, correlating with the degrees of zirconsaturation in the magmas, and influencing the spectra of modelages. Two adjacent magma systems active up to 26·5 kashow wholly contrasting model-age spectra. The smaller systemshows a simple unimodal distribution. The larger system, usingdata from three eruptions, shows bimodal model-age spectra.An older 100 ka peak is interpreted to represent zircons (antecrysts)derived from older silicic mush or plutonic rocks, and a youngerpeak to represent zircons (phenocrysts) that grew in the magmabody immediately prior to eruption. Post-26·5 ka magmabatches show contrasting age spectra, consistent with a mixtureof antecrysts, phenocrysts and, in two examples, xenocrystsfrom Quaternary plutonic and Mesozoic–Palaeozoic metasedimentaryrocks. The model-age spectra, coupled with zircon-dissolutionmodelling, highlight contrasts between short-term silicic magmageneration at Taupo, by bulk remobilization of crystal mushand assimilation of metasediment and/or silicic plutonic basementrocks, and the longer-term processes of fractionation from crustallycontaminated mafic melts. Contrasts between adjacent or successivemagma systems are attributed to differences in positions ofthe source and root zones within contrasting domains in thequartzo-feldspathic (<15 km deep) crust below the volcano. KEY WORDS: zircon; U-series dating; rhyolite; Taupo Volcanic Zone; Taupo volcano  相似文献   

Modelling Geophysical Precursors to the Prehistoric c. AD1305 Kaharoa Rhyolite Eruption of Tarawera Volcano, New Zealand     

S. Sherburn  I. A. Nairn 《Natural Hazards》2004,32(1):37-58

The 1305 Kaharoa rhyolite eruptive episode is the largest volcanic event(4 km³ magma) to have occurred in New Zealand during the last 1000 years. Proximal areas were devastated by pyroclastic flows, and tephra fell over much of the northern North Island. No eyewitness observations are recorded, but ejecta analyses show that the rhyolite eruptions were primed and triggered by basalt intrusions. This key finding, combined with observations of similar modern eruptions, has allowed construction of a conceptual scenario of the seismic and other activity that likely preceded the Kaharoa episode.The precursory scenario begins at -5 years (before the first eruption). Rising basalt magma intrusions generate deep long-period earthquakes in the lower crust, before intersecting and heating a rhyolite magma body at 6 km depth beneath Tarawera. By -1 year, increased heat flux from the rhyolite magma body had raised temperatures and pressures in the overlying hydrothermal system; generating shallow long-period earthquakes and increased heat flow at the surface. At -2 months, shallow volcano-tectonic earthquake activity intensified, driven by inflation of the rhyolite magma body, with magmatic gas appearing in fumarole discharges. Rapidly accelerating seismicity, ground deformation and surface heat flow occurred in the last few weeks and days, before the initial vent-opening explosions intensified into major plinian eruptions.Effectiveness of the present volcano monitoring system at Tarawera can be evaluated against this scenario. The precursory seismic activity, including the critical deep long-period earthquakes, would be recorded but not accurately located. Similarly, the existing ground deformation monitoring systems would detect early magma chamber inflation, but discrimination from the background tectonic tilting signal would be difficult. Continuous telemetering of geodetic data from existing and additional instruments would be required for any useful monitoring of rapid ground deformation in the final precursory phases.  相似文献   

阿尔泰南缘泥盆纪流纹岩的地球化学和大地构造背景   总被引：19，自引：1，他引：19  

丛峰  唐红峰  苏玉平 《大地构造与成矿学》2007,31(3):359-364

新疆阿尔泰南缘克朗和麦兹盆地内泥盆系康布铁堡组发育浅变质的酸性火山岩,岩相学特征和主量元素组成表明它们的原岩为流纹岩。该流纹岩具有高SiO2、较高(Na2O+K2O)、低TiO2和低CaO含量,属于亚碱性系列。稀土元素配分模式以轻稀土富集、Eu负异常强烈为特征。在不相容元素蛛网图上,流纹岩相对于洋脊花岗岩总体上富集大离子亲石元素和轻稀土元素,而明显亏损高场强元素Nb、Ta、Zr、Hf。在Nb-Y和Rb-(Y+Nb)判别图上,它们落入火山弧花岗岩区。这些结果显示,所研究的流纹岩形成于与俯冲作用密切相关的陆缘火山弧环境。本文研究结果为阿尔泰南缘在泥盆纪属于活动大陆边缘的认识提供了进一步的证据。  相似文献   

呼伦湖早白垩世碱性流纹岩的地球化学特征及其意义   总被引：34，自引：2，他引：34       下载免费PDF全文

葛文春  李献华  林强  孙德有  吴福元  尹成孝 《地质科学》2001,36(2):176-183

大兴安岭呼伦湖一带的上库力组第3段流纹岩具有高硅(SiO₂=75.41%～77.32%)、富碱(Na₂O+K₂O=7.98%～8.74%)、富Y、Nb、Zr及低Al、Mg、Ca、Ni、Cr、Ti和高Ga/Al比值等特点,类似于A型花岗岩,而与高度分异的I型和S型花岗岩有明显差别。该流纹岩的地球化学特征类似于A₁型花岗岩,且与该区A型花岗岩同时,很可能是A型花岗岩浆喷出相的产物。流纹岩的全岩Rb-Sr等时线年龄127±5Ma,与伊列克得组玄武岩(125±2Ma)时代一致,两者构成了双峰式火山岩组合,形成于早白垩世岩石圈拉张环境。  相似文献   

New Insights into Crustal Contributions to Large-volume Rhyolite Generation in the Mid-Tertiary Sierra Madre Occidental Province, Mexico, Revealed by U Pb Geochronology   总被引：2，自引：0，他引：2  

Bryan  Scott E.; Ferrari  Luca; Reiners  Peter W.; Allen  Charlotte M.; Petrone  Chiara M.; Ramos-Rosique  Aldo; Campbell  Ian H. 《Journal of Petrology》2008,49(1):47-77

Voluminous (3·9 x 10⁵ km³), prolonged (18 Myr) explosivesilicic volcanism makes the mid-Tertiary Sierra Madre Occidentalprovince of Mexico one of the largest intact silicic volcanicprovinces known. Previous models have proposed an assimilation–fractionalcrystallization origin for the rhyolites involving closed-systemfractional crystallization from crustally contaminated andesiticparental magmas, with <20% crustal contributions. The lackof isotopic variation among the lower crustal xenoliths inferredto represent the crustal contaminants and coeval Sierra MadreOccidental rhyolite and basaltic andesite to andesite volcanicrocks has constrained interpretations for larger crustal contributions.Here, we use zircon age populations as probes to assess crustalinvolvement in Sierra Madre Occidental silicic magmatism. Laserablation-inductively coupled plasma-mass spectrometry analysesof zircons from rhyolitic ignimbrites from the northeasternand southwestern sectors of the province yield U–Pb agesthat show significant age discrepancies of 1–4 Myr comparedwith previously determined K/Ar and ⁴⁰Ar/³⁹Ar ages from thesame ignimbrites; the age differences are greater than the errorsattributable to analytical uncertainty. Zircon xenocrysts withnew overgrowths in the Late Eocene to earliest Oligocene rhyoliteignimbrites from the northeastern sector provide direct evidencefor some involvement of Proterozoic crustal materials, and,potentially more importantly, the derivation of zircon fromMesozoic and Eocene age, isotopically primitive, subduction-relatedigneous basement. The youngest rhyolitic ignimbrites from thesouthwestern sector show even stronger evidence for inheritancein the age spectra, but lack old inherited zircon (i.e. Eoceneor older). Instead, these Early Miocene ignimbrites are dominatedby antecrystic zircons, representing >33 to 100% of the datedpopulation; most antecrysts range in age between 20 and 32 Ma.A sub-population of the antecrystic zircons is chemically distinctin terms of their high U (>1000 ppm to 1·3 wt %) andheavy REE contents; these are not present in the Oligocene ignimbritesin the northeastern sector of the Sierra Madre Occidental. Thecombination of antecryst zircon U–Pb ages and chemistrysuggests that much of the zircon in the youngest rhyolites wasderived by remelting of partially molten to solidified igneousrocks formed during preceding phases of Sierra Madre Occidentalvolcanism. Strong Zr undersaturation, and estimations for veryrapid dissolution rates of entrained zircons, preclude coevalmafic magmas being parental to the rhyolite magmas by a processof lower crustal assimilation followed by closed-system crystalfractionation as interpreted in previous studies of the SierraMadre Occidental rhyolites. Mafic magmas were more probablyimportant in providing a long-lived heat and material flux intothe crust, resulting in the remelting and recycling of oldercrust and newly formed igneous materials related to Sierra MadreOccidental magmatism. KEY WORDS: ignimbrite; rhyolite; Sierra Madre Occidental; Tertiary; U–Pb geochronology; zircon; antecryst; crustal melting  相似文献   

Extreme Nd isotope homogeneity in a large rhyolitic province: the Estérel massif, southeast France     

Franck Poitrasson  Christian Pin 《Bulletin of Volcanology》1998,60(3):213-223

 Previous detailed studies of large rhyolite bodies propose that their elemental and isotopic characteristics were largely acquired in shallow crustal magma chambers. This model explains the common chemical and isotopic zonations of large volumes of rhyolites as well as the less common chemical and isotopic homogeneity of such bodies. We report an intermediate situation (the Estérel massif, southeast France) in which chemical variations contrast with Nd-isotope homogeneity. We thus infer that, in this case, large volumes of rhyolite resided for enough time in shallow magma chambers to develop chemical zonations through differentiation, but this process was not accompanied by crustal assimilation. The subordinate amount of mafic rocks cropping out in the Estérel probably evolved from basalt to trachyte through assimilation and fractional crystallization. The relatively radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust show that it cannot have been generated by partial melting of exposed basement rocks. Several geological similarities with large rhyolitic provinces could suggest that the rhyolite was purely mantle derived or, alternatively, generated by partial melting of an ad hoc crustal component. However, mineralogical, geochemical, and geodynamic connections between the Estérel rhyolite and the hypersolvus anorogenic granites of Corsica, as well as the extreme Nd-isotope homogeneity of the rhyolite, lead us to propose that the rhyolite was generated by mixing between mantle-derived magmas and a mafic lower crust. This scenario accounts for the relatively radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust. The good Nd-isotope homogeneity observed in the rhyolite implies that the mixing process, which occurred in the deep crust, was complete and provided a shallow magma chamber with isotopically and probably chemically homogeneous magmas. Received: 5 December 1997 / Accepted: 16 June 1998  相似文献   

大兴安岭北段三根河林场新民组流纹岩锆石U－Pb定年及地球化学特征     

李中会  李阳  李睿杰  李凯 《地质与资源》1992,29(4):310-318

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粤北长塘盆地晚白垩世早期流纹岩的成因:地球化学和Sr-Nd-Pb-Hf-O同位素制约     

劳玉军  巫建华  徐勋胜 《岩矿测试》2016,35(5):558-567

长塘流纹岩为"大量流纹岩-少量玄武岩"构成的不对称双峰式火山岩组合的酸性端元,前人对年代学研究认为是目前华南识别的燕山期最年轻的流纹岩(SHRIMP年龄96.8 Ma),但在岩石地球化学特征及成因方面尚未深入研究。本文通过全岩主微量元素、Sr-Nd-Pb-O和锆石Hf同位素研究得到:流纹岩为亚碱性弱过铝质岩石,稀土元素富集,轻重稀土分馏明显,Eu负异常;具有较小的(~(87)Sr/~(86)Sr)_i、较高的εNd(t)和较低的(~(206)Pb/~(204)Pb)_i、(~(207)Pb/~(204)Pb)_i、(~(208)Pb/~(204)Pb)_i值;锆石的εHf(t)值较高且Hf模式年龄和全岩基本一致,均显示为新生下地壳岩浆;全岩的δ18O值较高。结合区域地质资料,本文认为长塘流纹岩是在晚白垩世早期拉张环境下,源于EMⅡ富集地幔的岩浆混染少量下地壳物质形成新元古代新生下地壳,发生熔融产生的岩浆在上升过程中经历结晶分异演化后喷出地表的产物。晚白垩世早期流纹岩成因对华南陆壳拉张减薄到正常厚度时间节点提供了证据。  相似文献