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- Boström, Kurt, et al.
(författare)
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The origin of iron-rich muds at the Kameni Islands, Santorini, Greece
- 1984
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 42:1-4, s. 203-218
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Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal sediments form in several places within the Santorini caldera. The sediments at the most active hot submarine spring (at SW Nea Kameni) consist of 40-48% Fe2O3 and 8-15% SiO2, but only little Al2O3 (0.5-1.6%), P (0.1-0.3%), Mn (100-450 ppm), Sr, Zr, Ba, Zn and V (∼30-200 ppm) and Cu, Ni and Y (∼ 1-30 ppm) are present. The sediments contain more Fe and P and less Si, Al, Mn and many trace elements than sediments formed at less active springs at Palaea Kameni; the differences probably being caused by faster deposition rates of Fe at Nea Kameni and less dilution by rock detritus, which delivers Al, Si and Mn. The Santorini sediments differ much from other exhalative sediments at present or old spreading centers, for example on the East Pacific Rise, in the Red Sea or at En Kafala, which are rich in Mn, Cu, Zn, Ni and Ba. Hydrothermal rock leaching probably occurs at much lower pH-values at Santorini than on the East Pacific Rise, causing a more complete breakdown of the leached rock at Santorini. The very low trace element to iron ratios in the rocks at Santorini, therefore, prevent the hydrothermal solutions there from being very rich in trace elements. The very acid leaching solutions at Santorini are created by extensive oxidation of hydrogen sulfide to sulfuric acid, a process that is readily possible due to the close proximity of the oxygen-rich atmosphere to the top of the magma chamber.
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| 6. |
- Rona, P.A., et al.
(författare)
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Serpentinized ultramafics and hydrothermal activity at the mid-atlantic ridge crest near 15°N
- 1987
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 92:B2, s. 1417-1427
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Tidskriftsartikel (refereegranskat)abstract
- The initial occurrence of serpentinized ultramafic rocks at the nontransform intersection of a wall of a rift valley with the wall of a fracture zone is described from a site at the Fifteen Twenty Fracture Zone. The ultramafics crop out in block-faulted terrain on the upper portion of the eastern intersection between the rift valley and fracture zone walls in water depths between 2910 and 3300 m. They comprise cumulate harzburgites, pyroxenites, Iherzolites, and wehrlites, as well as gabbronorites, olivine gabbronorites, gabbropegmatites, and alteration products including serpentinites, bastite serpentinites, and asbestos. The Ti-Zr-Y relations and relatively constant Zr/Ti ratio in basalts recovered with the ultramafic rocks indicate a cogenetic relation from a common magmatic source that has undergone a late stage differentiation in the lower crust. Ongoing hydrothermal activity is indicated by chemical anomalies (δ3He, Mn) in the near-bottom water at the ultramafic outcrop. The upwelling hydrothermal circulation apparently follows crust-penetrating faults that may have controlled the diapiric ascent of the serpentinites and that continue to tap degassing magma and/or mantle. The observations presented indicate that ultramafic cumulates form beneath the rift valley adjacent to long-offset (>100 km) ridge-ridge transform faults, where they are serpentinized by hydrothermal processes within the initial 1 × 106 years of generation of lithosphère at a slow spreading axis. The corners formed by the intersections of the walls of a rift valley with both the transform (RT corner) and the nontransform (RN corner) portions of these fracture zones are principal loci of diapiric emplacement of serpentinized ultramafics.
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- Widenfalk, Lennart, et al.
(författare)
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A multidisciplinary investigation of the Notträsk Gabbro, northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:2, s. 109-126
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Tidskriftsartikel (refereegranskat)abstract
- The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800-1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.
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- Widenfalk, Lennart
(författare)
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Kvicksilver som malmindikator vid prospektering
- 1983
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Ingår i: Berggrundsgeokemi som prospekteringsmetod i Sveriges urberg. - Uppsala : Sveriges Geologiska Undersökning. ; , s. 205-206
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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