Papers by Hans-Ulrich Schmincke
The ages, types, and compositions of volcaniclastic sediments, physical properties, and downhole ... more The ages, types, and compositions of volcaniclastic sediments, physical properties, and downhole logs obtained during Leg 157 drilling at Sites 953 and 954 north and 955 and 956 south of Gran Canaria, with a cumulative penetration of almost 3000 m and an overall recovery rate of 75%, correlate well compositionally and stratigraphically to major volcanic and nonvolcanic phases on the island. Volcaniclastic sediment contributions from neighboring islands are volumetrically insignificant. The highest rate of volcaniclastic sedimentation (>150 m/m.y.) corresponds to the middle Miocene basaltic late seamount stage of Gran Canaria, the lowermost deposits drilled being thick, graded, hyaloclastite tuffs and debris flows, dominated by poorly vesiculated, altered sideromelane clasts, suggesting eruption at a water depth of more than 500 m. Large basalt clasts, some of subaerial origin, at the base of the strongly graded deposits suggest synchronous subaerial activity. A lithic-rich deb ri...
We subdivided volcaniclastic layers drilled during Leg 157 around Gran Canaria at distances up to... more We subdivided volcaniclastic layers drilled during Leg 157 around Gran Canaria at distances up to 70 km from the shore of the island at Hole 953C, 955A, and 956B deposited between 14 and ~11.5 Ma into >100 volcaniclastic units at each site. Most volcaniclastic layers are <20 cm thick, but complex turbidite units up to 1.5 m thick make up 10% to 20% of all volcaniclastic units in Holes 953C and 956B. We distinguish several types of clasts: felsic vitroclasts, (1) bubble-wall/junction shards, (2) brown nonvesicular felsic shards, (3) welded tuff clasts, (4) pumice shards, and (5) sideromelane shards. Mineral phases comprise anorthoclase and lesser amounts of plagioclase, calcic and sodic amphibole (kaersutite, richterite, and edenite), clinopyroxene (titanaugite to aegirine), hypersthene, minor enstatite, phlogopite, Fe/Ti oxides, sphene, chevkinite, apatite, and zircon. Xenocrysts are dominantly titanaugite derived from the subaerial and submarine shield basalts. Lithoclasts ar...
Volcanic eruptions are the most dramatic expression of dynamic processes in the interior of plane... more Volcanic eruptions are the most dramatic expression of dynamic processes in the interior of planet Earth. The author, an internationally renowned specialist in the field of volcanology, explains in a concise and easy to understand manner the basics and recent advances in the field of volcanology. Based on plate tectonics and illustrated with nearly 400 color figures, the book offers insights into the generation of magmas and the tectonic setting, composition and origin of volcanoes. An overview of volcanic structures is followed by process-oriented chapters which discuss the role of explosive mechanisms and transport of volcanic material in eruption columns and pyroclastic density currents. The final chapters deal with eruption forecast, their influence on climate and benefits of volcanism. Students and scientists from a broad range of fields will find this book an attractive and up-to date source of information on the current understanding of volcanoes, volcanic eruptions and their...
During Leg 157, middle to late Miocene (14−9 Ma) stratigraphic intervals in the clastic apron of ... more During Leg 157, middle to late Miocene (14−9 Ma) stratigraphic intervals in the clastic apron of Gran Canaria were drilled at Sites 953, 955, and 956. Several hundred volcaniclastic layers composed of silt to sand-sized volcanic material, chiefly glass shards, pumice, and crystals, are interlayered with foraminifer nannofossil ooze. These intervals are 452 m thick at Hole 953C, 193 m thick at Hole 955A, and 194 m thick at Hole 956B, and were subdivided into three (Hole 953C) and two (Holes 955A and 956B) lithologic subunits. The lowermost of these subunits at all three holes correlates with the fallout tephra layers and ignimbrite cooling units of the Mogán Group on Gran Canaria (14−13.3 Ma), whereas the volcaniclastic layers of the 1−2 upper subunits correlate with the volcanic units of the Fataga Group (13.3 to ~9 Ma). We have subdivided the cores into ~100 volcaniclastic units at each hole based on a more detailed study of the cores in the core repository. Most of the major volcaniclastic layers in the time interval between 14 and 12 Ma have been examined by petrographic analysis of 276 polished thin sections, electron microprobe (EMP) analysis of 3000 glass shards, and more than 4500 analyses of the main phenocryst minerals (feldspar, pyroxene, amphibole, and phlogopite). These data are combined with X-ray fluorescence (XRF) analyses of 40 bulk tuff samples, and reanalysis of rock powders made on board, 50 new XRF and EMP analyses of glassy vitrophyres from 12 selected ignimbrites, and microprobe analyses of feldspar phenocrysts from 23 ignimbrites to provide detailed data sets for both the subaerial and submarine tephra stratigraphies to facilitate their correlation. Nearly unique mineral phases or assemblages and compositions of glass, feldspar, amphibole, and clinopyroxene, and bulk rocks provide robust compositional criteria for unequivocally correlating formations and groups. Major changes in mineral compositions, for example, occur at equivalent stratigraphic levels on land and in the submarine sections, such as the disappearance of sodic anorthoclase, calcic amphibole, abundant hypersthene, and zircon at the boundary between the Lower and Middle Mogán Group or the appearance of abundant phlogopite at the boundary between the Mogán and Fataga Groups. We have also correlated many volcaniclastic layers in the interval between 14 and 12 Ma among the three holes and were able to identify at least 7 of the ~15 individual ignimbrite members (cooling units) of the Mogán Group present on land, notably ignimbrites P1, VI, P2, X, O, A, and D, in all three drill holes. The high-resolution correlations of several syn-ignimbritic volcaniclastic units with well-dated anorthoclase-bearing ignimbrites on the island allow more precise sedimentation rates to be calculated. Between 14 and 13.3 Ma, sedimentation rates were 97 to 142 m/m.y. at Hole 953C, 54 to 93 m/m.y. at Hole 956B, and 43 to 72 m/m.y. at Hole 955A. The high precision correlations also help to calibrate the biomagnetostratigraphic time scale, for example, during the time interval of ~12−13 Ma, where our lithological correlations suggest that the biostratigraphic ages suggested on board are significantly too high.
ODP Preliminary Report, 1994
ODP Leg 157 drilled seven sites (Sites 950 through 956) in the Madeira Abyssal Plain and the volc... more ODP Leg 157 drilled seven sites (Sites 950 through 956) in the Madeira Abyssal Plain and the volcaniclastic apron around Gran Canaria, recovering over 3 km of core, which ranges in age from middle Eocene to Quaternary. Sites 950, 951, and 952, situated in the southwestern, northern, and southeastern parts of the Madeira Abyssal Plain, respectively, reveal a detailed history of organic, calcareous, and volcaniclastic turbidite deposition that began between 11.3 and 15 Ma. The highest rate of turbidite deposition (all types) occurred between 0 and 3 Ma. The input of volcaniclastic turbidites was minimal before 6.5 Ma. Integrated biostratigraphic, lithologic, and logging data show that many individual turbidites can be correlated across the entire plain. A change in the carbonate compensation depth (CCD) is reflected by an increase in calcium carbonate from very low values before about 3 Ma to oscillating high and low values from 0-3 Ma. Porewater-chemistry data reveal the great importance of bacterially mediated oxidation of organic matter, located principally in organic-rich turbidites, in controlling diagenetic environments. Active sulfate reduction and methanogenesis are documented for the first time in this area. Resulting changes in pore-water chemistry modified carbonate equilibria, causing the precipitation of calcite and dolomite, while the dissolution of biogenic silica and volcanic glasses led to the appearance of new silicate minerals, principally smectites and zeolites. Four sites (Sites 953 through 956) drilled north and south of Gran Canaria demonstrated that the compositional evolution, growth, and mass wasting of an ocean island is reflected in the sediments of the adjacent volcaniclastic apron. All major volcanic and nonvolcanic phases of Gran Canaria have been recognized in the ages and compositions of sediments, physical properties, and geophysical logs. Sites 953 and 954 were drilled in the basin north of Gran Canaria, whereas Sites 955 and 956 were drilled to the southeast and southwest of the island, respectively. The shield stage is represented at Sites 953, 954, and 956 by a sequence of massive hyaloclastite tuffs and debris flows, breccias and lapillistones, and fine volcanic turbidites. Middle Miocene felsic volcanics overlying the shield stage were recognized at Sites 953, 955, and 956, including the submarine facies of ignimbrite Pl, which marks the beginning of explosive volcanism on Gran Canaria at 14.1 Ma. Pliocene Roque Nublo volcanism is represented by a layer of basaltic lapillistone at Sites 953 and 954. Pleistocene volcanic ashes and pumice layers occur in both the northern and southern sites and presumably come from Tenerife. The two southern sites contain both organic-rich sediments and quartz, reflecting a source from the African margin. In contrast, Leg 157 Preliminary Report Page 8 the two northern sites have little or no organic muds and quartz, indicating that they were mostly protected from African sediment sources by the barrier of the eastern Canary Islands. Major slump deposits in the southern sites also likely come from the African margin. Pore-water-chemistry data show remarkable correlations to sediment composition; Site 953 is dominated by fluid-rock interaction between pore waters, volcanic glasses, and minerals; Site 954 displays large geochemical anomalies associated with levels of carbonated pore waters, possibly related to Holocene volcanic activity on northern Gran Canaria; at Site 955, organic matter, located principally in slumped sediments derived from the Northwest African margin, is driving intense sulfate reduction and methanogenesis at shallow depths, while the deeper sediments contain saline brines, possibly originating from the leaching of African shelf evaporites.
International Journal of Earth Sciences - INT J EARTH SCI, 2010
A multidisciplinary analysis of intraplate volcanic complexes interbedded with shallow and deeper... more A multidisciplinary analysis of intraplate volcanic complexes interbedded with shallow and deeper marine sediments of a Late Miocene carbonate platform (Iblean Plateau, Sicily) has allowed a detailed paleo-environmental reconstruction. Our approach includes sedimentology, physical volcanology, stratigraphy, geochemistry/mineralogy, paleontology and 40Ar/39Ar dating. Four volcanic complexes are distinguished from each other. Two comprise an eastern shallow water platform (diatreme field and Carlentini complex) and two a western deeper water environment representing a seamount belt on the carbonate ramp (Valle Guffari seamount and Mineo complex). The late Miocene volcanism was not time-equivalent: episodic eruptions took place from the Late Tortonian (ca. 9.38 Ma at Mt. Carrubba) to Early Messinian (ca. 6.46 Ma at Valle Guffari). Explosive volcanism of the diatreme field may be related geodynamically to the period of periodic sea-level oscillations at the onset of the Messinian Salini...
International Journal of Earth Sciences, 2002
The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the ... more The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts. Two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions, pyroclastic fragmentation being subordinate. The lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called 'lapilli cone aprons'. Vertical growth due to accumulation of tephra, voluminous intrusions, and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion, as shown by conglomerate beds. Periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels. The loose tephra piles became stabilized by widespread syn-volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice. Shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions, accentuated by quench fragmentation, resulted in pumice-and crystal-rich deposits emplaced in a prominent submarine erosional channel. The dome must have produced an island as indicated by a collapse breccia comprising surfrounded boulders of dome material. Subaerial explosive activity is represented by scoria cones and tuff cones. Basaltic lava flows built a resistant cap that protected the island from wave erosion. Some lava flows entered the sea and formed two distinct types of lava delta:
Journal of Geophysical …, 1982
Study of a 3-km-thick section of Tertiary basalts in eastern Iceland has resulted in the formulat... more Study of a 3-km-thick section of Tertiary basalts in eastern Iceland has resulted in the formulation of a model for crustal construction based on accumulation of lava flows on the flanks of large central volcanoes and has led to the development of alteration and physical property profiles in a crustal segment formed at the Mid-Atlantic Ridge. Deep drilling at Reydarfjordur revealed the existence of subaerial lava flows and volcaniclastic rocks to a crustal depth of 3.5 km. Three major stratigraphic units composed largely of basalts are recognized, each characterized by distinctive major and trace element patterns. Each of these units is believed to be the product of a separate episode of mantle melting and fractionation and probably reflects accumulation on the flanks of a central volcano. Extensive fractionation in shaJ10w magma chambers led to intermediate and silicic lavas, which mark the cores of the central volcanic complexes. Dike density does not increase downward below about 1.5-km crustal depth, and the sampled dikes appear to have been intruded laterally along rifts on the flanks of the central volcanoes. Secondary mineral assemblages are dominated by smectite and zeolites near the top of the section and by epidote and quartz near the base. In general, the temperature of alteration increases downward, but the distribution of individual minerals is irregular. Locally, earlier secondary mineral assemblages are overprinted by contact metamorphism along dike margins. The upper surface of greenschist facies metamorphism crops out at the surface in Thingmuli volcano but it lies at an estimated crustal depth of about 4 km in the Reydarfjordur borehole, located only 3 km east of the edge of Thingmuli. Thus, the metamorphic zones clearly crosscut the lava stratigraphy. Physical property profiles correlate' well with variations in secondary mineralogy, and the top of layer 3 velocities corresponds closely with the projected upper boundary of amphibolite facies rocks at about 6 km crustal depth. Magnetic susceptibility decreases with depth and is extrapolated to zero at about 4.3-km crustal depth close to the estimated upper limit of greenschist facies metabasalts. A much greater crustal thickness, leading to the emplacement of high level magma chambers within the extrusive part of the crust, is thought to account for many of the differences in crustal structure and evolution between Iceland and the rest of the Mid-Atlantic Ridge.
International Journal of Earth Sciences, 2001
Surfaces of meter-sized blocks in the 1998 block-and-ash flow deposits of Merapi volcano are part... more Surfaces of meter-sized blocks in the 1998 block-and-ash flow deposits of Merapi volcano are partially covered by centimeter-sized, randomly orientated impact marks, which consist of an outer, glassy pseudotachylite underlain by a cataclastic layer. Whole rock, pseudotachylite, melt inclusion in plagioclase and host rock groundmass compositions indicate that the pseudotachylite was generated by remelting of bulk rock on block impact. The occurrence and distribution of this new type of collision-related pseudotachylite on volcanic block surfaces demonstrate that blocks were transported by chaotic rotation, saltation and tumbling. The random orientation of impact marks suggests grain flow as the dominant process rather than any other currently discussed pyroclastic flow mechanism. In addition, the chaotic orientation of striations is interpreted as reflecting momentum transfer having been dominated by short-lived intergranular collisions. The blocks have apparently been transported in...
Proceedings of the Ocean …, 1998
Almost 500 m of basaltic hyaloclastite tuffs, hyaloclastite lapillistones, and lithic breccias we... more Almost 500 m of basaltic hyaloclastite tuffs, hyaloclastite lapillistones, and lithic breccias were drilled in the northern, southeastern, and southwestern flank of Gran Canaria, Canary Islands during Leg 157 (Hole 953C, total penetration 1159 meters below seafloor [mbsf], basal 293 m; Hole 954B, total penetration 446 mbsf, basal 38 m; and Hole 956B, total penetration 704 mbsf, basal 140 m). These deposits represent (1) mostly moderate to shallow water (<< ~500 m) eruptions, (2) transition to the emergence, and (3) the fully subaerial island shield stage. The volcaniclastic rocks are interlayered with minor thin layers of nannofossil ooze and clay. Volcanic clasts comprise blocky to vesicular, generally altered former sideromelane shards, tachylite crystallized basalt, round glassy shards, lapilli, and single crystals, chiefly titanaugite. Dominantly filled foraminifers, thick-walled shallow-water skeletal debris, and nannofossil ooze make up <5 vol% of the volcaniclastic rocks. Most of the basaltic volcaniclastic deposits are interpreted to have been deposited as debris flows resulting from (1) destabilization of hyaloclastites generated during voluminous moderate (<500 m?) to shallow-water explosive volcanic activity and temporarily accumulated prior to episodic failure and transfer to the deep basins, fragmentation of subaerial lava flows that entered the sea and collapse of lava deltas and by flank collapse. About 16 debris-flow units (lithologic Unit VII) in Hole 953C range in thickness from ~1 to 50 m. Most are composed of well-sorted massive lapillistone to coarse hyaloclastite tuff consisting of blocky, poorly vesicular shards, minor tachylite, and crystallized basalt. The top 5%-10% or so show laminar bedding to minor cross-bedding, the grain size rarely decreasing to fine sand (ash) size in the top beds. Basalt clasts up to 25 cm in diameter are common in the coarse-grained basal parts. Most particles in the stratigraphically highest deposits are vesicular to highly vesicular ash to lapilli-size clasts suggesting decreasing water depth. Coarse breccias at Hole 953C (lithologic Unit VI) consist of basalt clasts of diverse composition, angularity, and vesicularity, and some contain pillow rind fragments. Only the upper of three debrites at Site 956 (Cores 157-956B-43R through 45R) and underlying turbidites consist dominantly of highly vesicular formerly glassy ash to lapilli-sized clasts. Lithic-rich debris-flow deposits at Site 956 (Cores 157-956B-45R through 48R, and 49R through 57R) consist chiefly of poorly vesicular, angular tachylite, crystallized basalt, and minor formerly glassy shards set in ~30−50 vol% brown clay matrix. About 300 very thin turbidite beds, 1−40 cm thick, deposited prior to the first ignimbrite-related ash deposit at Hole 953C are composed of variable amounts of dominantly silt-to sand-sized tachylitic and lesser amounts of vesicular to blocky altered shards and minor biogenic debris. They are interpreted to represent chiefly the subaerial growth stage of the basaltic shield and to have been derived dominantly from erosionally fragmented scoria and lava flows. The phenocryst assemblage in clasts and matrix of all deposits, mainly titanaugite and olivine (Fo 83−88) and minor plagioclase, changes with depth at both sites. Most of the submarine basaltic clasts and clastic rocks from Hole 953C are more primitive mineralogically and chemically than the subaerial shield stage basalts. Ratios of incompatible trace elements are practically indistinguishable between mafic and moderately evolved rocks, between holes and between the bulk volcaniclastic rocks, basalt clasts, and subaerial rock shield basalts, suggesting that the source for the basalt magmas was fairly homogeneous during the late submarine and subaerial evolution. More evolved compositions (plagioclase-phyric hawaiites) are restricted to Site 956 coincident with the eruption of latestage evolved subaerial shield lavas in southwestern Gran Canaria. Fresh glass in the center of large lapilli in the uppermost of three debris flows (Core 157-956B-44R) is intermediate in composition, MgO ranging from 3.9 to 4.9 wt%. Major and trace element concentrations of some 101 hyaloclastite bulk rocks and 20 clasts document major mobile element transfer. Basaltic glass is generally replaced by smectite. Zeolite phases, mostly phillipsite, and minor carbonate, are common pore-filling phases. The vertical and lateral growth and changes in eruptive activity of the shield volcano are well reflected in the lithologic and compositional contrasts within and between the sections drilled at Hole 953C and Hole 956B (45 km southwest of Gran Canaria). Decreasing water depth of eruption is especially well documented in the increase in vesicularity in shards at Site 953 and extremely vesicular shards near the top of the basaltic section of Site 956. Eruptive activity had clearly decreased in the east of Gran Canaria during deposition of the late-stage turbidites at Hole 953C, as shown by the dominance of epiclastic particles in these rocks. Cores 157-956B-44R and 45R of the basaltic shield sequence at Hole 956B are considered to record younger active volcanism in western Gran Canaria that was taking place while largely epiclastic material was supplied to Site 953 in the northeast. A recovered 3.75-m-thick interval consisting of layers of an unusual sandstone interbedded with turbidites of mixed volcaniclastic-biogenic lithology, on top of the basal 85-m-thick lithoclast-rich debrite in the lower part of Hole 956B (interval 157-956B-48R-3, 23 cm, to 49R-1, 26 cm), consists dominantly of alkali amphibole, partially chloritized phlogopite and apatite, and minor Cr-spinel, sphene, and zircon mixed with foraminifers. We speculate that the huge basal debrite, underlying these sands and which we interpret as having been formed by collapse of the flanks of southwestern Gran Canaria, has caused major tsunamis that washed up beach sands on La Gomera, ~115 km west of Gran Canaria.
Quaternary Science Reviews
The precise date of the Laacher See eruption (LSE), central Europe's largest Late Pleistocene vol... more The precise date of the Laacher See eruption (LSE), central Europe's largest Late Pleistocene volcanic event that occurred around 12,900 years ago, is still unknown. Here, we outline the potential of combined high-resolution dendrochronological, wood anatomical and radiocarbon (14 C) measurements, to refine the age of this major Plinian eruption. Based on excavated trees that were killed during the explosive LSE and buried under its pyroclastic deposits, we describe how a firm date of the eruption might be achieved, and how the resulting temporal precision would further advance our understanding of the environmental and societal impacts of this event. Moreover, we discuss the relevance of an accurate LSE date for improving the synchronization of European terrestrial and lacustrine Late Glacial to Holocene archives, and outline how the proposed, interdisciplinary dating approach can be applied to other large, yet undated, volcanic eruptions.
Scientific Drilling
Large calderas are among the Earth's major volcanic features. They are associated with large magm... more Large calderas are among the Earth's major volcanic features. They are associated with large magma reservoirs and elevated geothermal gradients. Caldera-forming eruptions result from the withdrawal and collapse of the magma chambers and produce large-volume pyroclastic deposits and later-stage deformation related to post-caldera resurgence and volcanism. Unrest episodes are not always followed by an eruption; however, every eruption is preceded by unrest. The Campi Flegrei caldera (CFc), located along the eastern Tyrrhenian coastline in southern Italy, is close to the densely populated area of Naples. It is one of the most dangerous volcanoes on Earth and represents a key example of an active, resurgent caldera. It has been traditionally interpreted as a nested caldera formed by collapses during the 100-200 km 3 Campanian Ignimbrite (CI) eruption at ∼ 39 ka and the 40 km 3 eruption of the Neapolitan Yellow Tuff (NYT) at ∼ 15 ka. Recent studies have suggested that the CI may instead have been fed by a fissure eruption from the Campanian Plain, north of Campi Flegrei.
International Journal of Earth Sciences, 2016
Miocene submarine basaltic hyaloclastites, lapillistones, and breccias drilled at Sites 953 and 9... more Miocene submarine basaltic hyaloclastites, lapillistones, and breccias drilled at Sites 953 and 956 contain relicts of olivine and fresh clinopyroxene phenocrysts with abundant primary melt, fluid, and crystal inclusions. Primary melt inclusions are represented by glassy (quenched glass ± gas bubble/s) and multiphase (glass + daughter crystals ± gas bubble/s) types. Fluid inclusions are composed of gas and liquid phases and are nearly pure CO 2 in composition, as shown by low-temperature microthermometric studies. Melt and crystal inclusions and their host minerals were analyzed for major elements by electron microprobe and large (>60 µm in size) representative melt inclusions by ion microprobe for trace elements and H 2 O. Olivine phenocrysts from two basalt fragments are Fo 80−89 and correspond to the entire range of olivine compositions known for the Miocene shield basalts on Gran Canaria. Clinopyroxene phenocrysts from basalt fragments and hyaloclastite matrix are characterized by a wide compositional spectrum of Mg/(Mg+Fe tot) = 0.74−0.90, Wo 37−47 , En 41−52 , Fs 6−15. Crystal inclusions are represented by olivine (Fo 80−82), clinopyroxene (Mg/(Mg+Fe tot) = 0.79−0.82, Wo 41−45 , En 44−48 , Fs 11), plagioclase (An 68−83), high-Ti chrome spinel and titanomagnetite (2.5−18.7 wt% TiO 2 , Mg/(Mg+Fe 2+) = 0.21−0.58, and Cr/(Cr+Al) = 0.17−0.74), and ilmenite. Major element compositions of melt inclusions corrected for post-entrapment crystallization of olivine and clinopyroxene show a broad compositional spectrum ranging from quartz-normative tholeiitic to transitional basalts (46.3−54.4 wt% SiO 2 , 5.1−10.7 wt% MgO, 1.3−3.5 wt% Na 2 O, and 0.7−1.9 wt% K 2 O) and are enriched in incompatible trace and rare earth elements. We interpret this large compositional range as representing that of parental magmas, rather than being caused by crystallization of a single magma. Melt inclusions are enriched by light rare earth elements [(La/Sm) n = 1.7−3.0] and depleted in heavy rare earth [(Sm/Yb) n = 4.4−10.2] and high field strength elements [(Zr/Y) n = 4.1−5.5]. Because shallow level magma crystallization is unlikely to significantly change trace element ratios in the melt, we think that the observed discrepancy in (La/ Sm) n and (Sm/Yb) n ratios, and high (Zr/Y) n ratios resulted from the melting of a garnet-bearing mantle source. Calculated parental magmas equilibrated with Fo 90 represent a range from transitional to tholeiitic compositions (46.7−52.0 wt% SiO 2) and are similar to olivine basalt-picrite (11.2−18.0 wt% MgO). They crystallized over the range of temperatures from 1450° to 1120°C and pressures from <0.5 to 8 kbar. Oxygen fugacity varied from the conditions corresponding to FMQ-1 or WM-1 buffers during the early crystallization stage of parental magmas, to late-stage conditions of FMQ-NNO+1. Crystallization of magmas occurred in the presence of fluid of essentially CO 2 composition.
Proceedings of the Ocean Drilling Program, 1996
The volcanogenic component of 54 ash layers and ash-bearing sediments recovered at Sites 907, 908... more The volcanogenic component of 54 ash layers and ash-bearing sediments recovered at Sites 907, 908, and 913 (Ocean Drilling Program Leg 151) in the Greenland-Iceland-Norwegian Seas (Iceland Plateau, Greenland Basin, Hovgàrd Ridge) consists mainly of colorless and/or light to dark brown glass particles with an average medium grain size of 100 µm (±60 µm); crystals and lithics are minor constituents. Colorless glass shards are primarily bubble wall shards and pumice fragments. Most light to dark-brown glass shards are slightly vesicular or dense blocky shards, but highly vesicular or pumice-like fragments also occur. The compositions of glass shards comprise subalkalic and low-K subalkalic basaltic (27% of all analyzed shards), basalticandesitic (9%), andesitic (6%), dacitic (<1%), and trachytic (4%), as well as low-K and high-K rhyolitic (47% and 7%, respectively). The rhyolitic and trachytic tephra deposits can be attributed to highly explosive Plinian eruptions. Some mafic or intermediate ash deposits of Hole 907 A show the influence of hydroclastic fragmentation processes, suggesting submarine or subglacial/ sublacustrine eruption environments. Major element compositions suggest that most ash layers are derived from Iceland and to a lesser extent from the Jan Mayen System. The oldest basaltic ashes of Hole 907A possibly originate from submarine eruptions at the ancient Kolbeinsey Ridge as indicated by their particle shape and the low degree of degassing. The well-preserved record of middle to late Miocene ash deposits in Hole 907A indicates a short but strong increase in explosive volcanic activity during the late middle Miocene but relatively low activity rates for early middle Miocene and late Miocene.
International Journal of Earth Sciences, 2014
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Papers by Hans-Ulrich Schmincke