Petrology of clinopyroxene-amphibole inclusions from the roque nublo volcanics,gran canaria,canary islands     

T. Frisch  H. U. Schmincke 《Bulletin of Volcanology》1969,33(4):1073-1088

Inclusions consisting of clinopyroxene, amphibole, Fe-Ti oxides and apatitc are abundant in the Roque Nublo volcanics, a unit of Late Tertiary age that is widespread on Gran Canaria Island. The unit includes alkalic basalts and breccias. Mafic minerals in several inclusions and in one basalt host have been analysed with the electron microprobe. Although the inclusions vary in size, texture and mineralogy, they show certain common teatures. The pyroxenes analyzed are all salites-augites and their position in the Ca-Fe Mg quadrilateral suggests that they are early formed representatives of the pyroxene crystallization trend characteristic of alkaliolivine basalt. The amphibole is invariably kaersutite. A common variety of inclusion is composed largely of kaersutite and titaniferous clinopyroxene. The kaersutite (TiO₂ 5.27%, K₂O 1.58%) is homogeneous, except for slight iron enrichment in the margins of crystals. The clinopyroxene is an hourglass-zoned, brownish titansalite, Ca 50 Mg 35 Fe 15, TiO₂ 3.08%, with a green core of Ca 49 Mg 38 Fe 13, TiO₂ 2.15%. Compositions of coexisting titanilerous magnetite and ilmenite, Usp 44 Mt 56 and Ilm 85 Hem 15, respectively, indicate they formed at approximately 975°C and pO, 10^?10.5 atm. In another type of inclusion and its host basalt, pyroxene relations are more complex. Inclusion pyroxene is markedly but diffusely zoned. Predominant is a green salite, Ca 47 Mg 38 Fe 15, TiO₂ 1.11%, which has small, patchy core zones of brownish. Ti-rich salite. Ca 48 Mg 35 Fe 17, TiO₂ 1.94%. Cores of crystals in the host basalt are Ca 47 Mg 41 Fe 12, TiO₂ 2.23%; rims are pale green, Cr-rich diopsidic augite, Ca 44 Mg 45 Fe 11, TiO₂ 1.32%, Cr₂O₃ 0.48%. This «reverse» Fe-Mg zoning is attributed to increasing partial pressure of oxygen as crystallization proceeded. Kaersutite similar to that mentioned above occurs in both the inclusion and its host, in which it is highly resorbed. The available field and analytical evidence strongly suggests that the inclusions and the associated basalts are genetically related. Resorption of the kaersutite at depth may have given rise to the alkalic basalts of the Roque Nublo series.  相似文献   

Englacial vs lacustrine origin of volcanic table mountains: evidence from iceland     

Reinhard Werner  Hans-Ulrich Schmincke 《Bulletin of Volcanology》1999,60(5):335-354

Detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar "hyaloclastite volcanoes" in the Icelandic rift zone contradict a rapid and continuous, "monogenetic", entirely subglacial evolution of most volcanoes studied. The majority of the exposed hyaloclastite deposits formed in large, stable lakes as indicated by widespread, up to 300-m-thick, continuous sections of deep water, shallow water and emergent facies. Salient features include extensively layered or bedded successions comprising mainly debris flow deposits, turbidites, base surge and fallout deposits consisting of texturally and compositionally variable, slightly altered hyaloclastites, as well as sheet and pillow lavas. In contrast, chaotic assemblages of coarser-grained, more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias, as well as scoria and lava are interpreted to have formed under sub- or englacial conditions in small, chimney-like ice cavities or ice-bound lakes. Irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted mainly from rapid changes of the eruptive environment due to repeated build-up and drainage of ice-bound lakes as well as the restricted space between the ice walls. We distinguish a "deep water" facies formed during high water levels of the lake, a hydroclastic shallow water and emergent facies (leakage of the lake or growth of the volcano above the water surface). Our model implies the temporary existence of large, stable lakes in Iceland probably formed by climatically induced ice melting. The highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods in changing environments characterized by contrasting volcanic and sedimentary processes. Received: 10 June 1997 / Accepted: 28 July 1998  相似文献   

The impact of moderate-scale explosive eruptions on stratospheric gas injections   总被引：1，自引：0，他引：1  

M.?M.?HalmerEmail author  H.-U.?Schmincke 《Bulletin of Volcanology》2003,65(6):433-440

Volcanic gases such as SO ₂, H ₂S, HCl and COS emitted during explosive eruptions significantly affect atmospheric chemistry and therefore the Earth's climate. We have evaluated the dependence of volcanic gas emission into the atmosphere on altitude, latitude, and tectonic setting of volcanoes and on the season in which eruptions occurred. These parameters markedly influence final stratospheric gas loading. The latitudes and altitudes of 360 active volcanoes were compared to the height of the tropopause to calculate the potential quantity of volcanic gases injected into the stratosphere. We calculated a possible stratospheric gas loading based on different volcanic plume heights (6, 10, and 15 km) generated by moderate-scale explosive eruptions to show the importance of the actual plume height and volcano location. At a plume height of 15 km for moderate-scale explosive eruptions, a volcano at sea level can cause stratospheric gas loading because the maximum distance to the tropopause is 15–16 km in the equatorial region (0–30°). Eruptions in the tropics have to be more powerful to inject gas into the stratosphere than eruptions at high latitudes because the tropopause rises from ca. 9–11 km at the poles to 15–16 km in the equatorial region (0–30°N and S). The equatorial region is important for stratospheric gas injection because it is the area with the highest frequency of eruptions. Gas injected into the stratosphere in equatorial areas may spread globally into both hemispheres.  相似文献   

Composition and evolution of submarine volcanic rocks from the central and western Canary Islands   总被引：2，自引：0，他引：2  

M.?AbratisEmail author  H.-U.?Schmincke  T.?Hansteen 《International Journal of Earth Sciences》2002,91(4):562-582

Submarine volcanic rocks dredged during RV Meteor cruise M43-1 comprise alkali basalts, basanites, nephelinites and their differentiates representing both basement-shield and young post-shield volcanics of Gran Canaria, Tenerife, La Palma and El Hierro. The primitive lavas vary widely in trace element composition (e.g., Zr/Y=6.6-11.7, (La/Sm)_N=2.3-5.4, and Ba/Yb=71-311), and they are characterized by steep, rare-earth element patterns with mean (La/Yb)_N=16, and by pronounced, positive primitive mantle-normalized Nb and Ta and negative K anomalies similar to HIMU-type basalts. Rocks from the submarine flanks west and north of Gran Canaria are isotopically and geochemically identical to rocks of the subaerial Miocene shield stage, but they are distinct from rocks of the post-shield stages (Zr/Nb=6.3-8.9, ⁸⁷Sr/⁸⁶Sr=0.70327-0.70332, ¹⁴³Nd/¹⁴⁴Nd=0.51289-0.51293, ²⁰⁶Pb/²⁰⁴Pb=19.55-19.88). Most rocks dredged from the submarine flanks of Tenerife are isotopically and geochemically similar to rocks of the adjacent subaerial shield remnants, but a few resemble rocks of the subaerial post-shield stages (total range in Zr/Nb=4.6-6.1, ⁸⁷Sr/⁸⁶Sr=0.70300-0.70329, ¹⁴³Nd/¹⁴⁴Nd=0.51281-0.51292, ²⁰⁶Pb/²⁰⁴Pb=19.51-19.96). Rocks from the southern submarine ridge of La Palma cover the entire compositional range of the subaerial rocks of that ridge. Additionally, they comprise a high Zr/Nb group which resembles rocks of the ca. 1-Ma-old Taburiente shield of northern La Palma (total range in Zr/Nb=3.0-6.4, ⁸⁷Sr/⁸⁶Sr=0.70297-0.70314, ¹⁴³Nd/¹⁴⁴Nd=0.51288-0.51296, ²⁰⁶Pb/²⁰⁴Pb=19.21-19.79). Rocks from the southern submarine ridge of El Hierro compositionally resemble subaerial rocks of the island (Zr/Nb=4.1-6.2, ⁸⁷Sr/⁸⁶Sr=0.70296-0.70314, ¹⁴³Nd/¹⁴⁴Nd=0.51291-0.51297, ²⁰⁶Pb/²⁰⁴Pb=19.25-19.91). The degree of melting in the subcanarian mantle is interpreted to decrease from east to west across the archipelago whereas the proportion of depleted mantle component in the melting anomaly increases, as illustrated by Sr, Nd and Pb isotopes. The isotopic characteristics of the mantle source beneath the Canary Islands represents a mixture of HIMU, DMM and EM I. The overall isotopic signature is intermediate between that of Madeira to the north, which trends towards more depleted compositions, and that of the Cape Verde Islands to the south which shows a pronounced trend towards enriched mantle compositions. A clear trend towards the EM II component is only evident in more evolved rocks dredged from a seamount between Tenerife and Gran Canaria, some of which contain terrigenous sedimentary xenoliths. We propose a genetic model which relates similar mantle source signatures of volcanic archipelagos off West Africa to a common, large-scale lower mantle upwelling which, according to geophysical data, becomes more diffuse in the upper mantle. Narrow plumes or blobs feeding the volcanic centers along the passive margin may rise from this thermal anomaly due to upwelling in small, continent-parallel upper-mantle convection cells.  相似文献   

Geochronology of Gran Canaria,Canary Islands: Age of shield building volcanism and other magmatic phases     

I. McDougall  H. -U. Schmincke 《Bulletin of Volcanology》1976,40(1):57-77

Forty-six new K-Ar age determinations are presented on whole rock samples and mineral separates from volcanic and subvolcanic rocks of Gran Canaria. The main subaerial shield building basaltic volcanism with estimated volume of about 1000 km³ was confined to the interval about 13.7 m.y. to 13.5 m.y. ago in the middle Miocene. Substantial volume (～100 km³) of silicic volcanics (trachyte and peralkaline rhyolite) were erupted with no detectable time break following the basaltic volcanism, essentially contemporaneous with formation of a large collapse caldera at 13.4±0.3 m.y. ago. Trachytic to phonolitic volcanism continued intermittently in the waning states of activity until about 9 m.y. ago. Following a long hiatus there was resurgence of volcanism with eruption of about 100 km³ of basanitic to hauyne phonolitic rocks of the Roque Nublo Group between about 4.4 m.y. and 3.4 m.y. ago in the Pliocene. After a hiatus of less than 1.0 m.y., olivine nephelinite magmas were erupted and this activity continued intermittently until relatively recent times, the younger eruptives being mainly basanitic in composition. The volume of volcanic products in this phase probably does not exceed 10 km³. Thus the volume of all the resurgent volcanism comprises less than 10 percent of the subaerially exposed part of Gran Canaria. The results show that the subaerial main shield building phase of volcanism in Gran Canaria, consisting of mildly alkali to transitional basalts, occurred over a time interval that was less than 0.5 m.y. Magmatic evolution on Gran Canaria appears to be similar to that found on other basaltic volcanoes in oceanic regions. Thus volcanoes in the Hawaiian, Marquesas and Society Islands all were built by basaltic lavas in similar short-lived episodes of volcanism. In some Hawaiian volcanoes, a resurgent phase of volcanism of strongly undersaturated basalts of small volume is recognized following a long hiatus, again similar to that found on Gran Canaria. The relatively large volume of silicic lavas erupted in Gran Canaria immediately following the main basaltic shield building phase is, however, not matched in the Pacific volcanoes mentioned.  相似文献   

Magma fractionation systems beneath the mid-Atlantic ridge at 36–37 ° N     

M. F. J. Flower  P. T. Robinson  H. -U. Schmincke  W. Ohnmacht 《Contributions to Mineralogy and Petrology》1977,64(2):167-195

Variation of major and trace elements in drilled basalts from the Mid-Atlantic Ridge (DSDP Leg 37) reflects distinct cycles of low pressure fractionation operating independently within a complex network of magma storage reservoirs beneath the crustal spreading axis. Low pressure phase relations are determined by parental magma composition, which varies from An-rich (An/Di > ca. 1.4) to Di-rich (An/Di < ca. 1.4). High An/Di magmas probably formed under slightly hydrous conditions in the mantle. They have low LIL element contents, low P/Y and high Mg/(Mg + Fe) ratios. Zr, P and Y abundance and inter-element ratios are highly diagnostic of primary magma type, and are used to quantify fractional crystallization models.Low pressure fractionation hypotheses were tested by least-squares modelling of whole-rock and phenocryst chemistry, which indicated removal or addition of phenocryst assemblages: ol; pl; ol + pl; ol + pl + cpx; pl + cpx, (± sp). Accumulation of plagioclase or olivine is an important mechanism for generating highly porphyritic rocks. A rare 3-phase (ol + pl + cpx) cumulate resulted from cotectic fractionation of a low An/Di magma type. Olivine and plagioclase cumulates appear to be related to high An/Di magmas. Olivine accumulation has been monitored by comparison of olivine/bulk rock partitioning of Fe and Mg to experimental measurements of the equilibrium K_D value. A single extensive sub-axial magma chamber could not account for the observed chemical variation and would probably be dynamically unstable.  相似文献   

Results of the DEKORP 1 (BELCORP-DEKORP) deep seismic reflection studies in the western part of the Rhenish Massif   总被引：1，自引：0，他引：1  

DEKORP Research GroupH.-J. Anderle  R. Bittner  R. Bortfeld  J. Bouckaert  G. Büchel  G. Dohr  H.-J. Dürbaum  H. Durst  W. Fielitz  E. Flüh  T. Gundlach  L. Hance  A. Henk  F. Jordan  D. Kläschen  M. Klöckner  R. Meissner  W. Meyer  O. Oncken  C. Reichert  K.-H. Ribbert  P. Sadowiak  H.-U. Schmincke  J. Schmoll  R. Walter  K. Weber  U. Weihrauch  Th. Wever 《Geophysical Journal International》1991,106(1):203-227

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IAVCEI news     

H. -U. Schmincke 《Bulletin of Volcanology》1987,49(5):712-712

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IAVCEI News     

H. -U. Schmincke 《Bulletin of Volcanology》1987,49(1):465-466

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Hafnium isotopic variations in East Atlantic intraplate volcanism     

Jörg Geldmacher  Kaj Hoernle  Barry B. Hanan  Janne Blichert-Toft  F. Hauff  James B. Gill  Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2011,162(1):21-36

The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), ¹⁷⁶Hf/¹⁷⁷Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (¹⁷⁶Hf/¹⁷⁷Hf_m up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (¹⁷⁶Hf/¹⁷⁷Hf_m = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower ¹⁷⁶Hf/¹⁷⁷Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat older recycling ages of ≥1 Ga.  相似文献