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Exceptionally high ...
Exceptionally high whole-rock delta O-18 values in intra-caldera rhyolites from Northeast Iceland
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- Berg, Sylvia, 1986- (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik,Univ Iceland, Nord Volcanol Ctr, Inst Earth Sci, Sturlugata 7, IS-101 Reykjavik, Iceland
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- Troll, Valentin R. (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik
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- Harris, Chris (författare)
- Univ Cape Town, Dept Geol Sci, ZA-7701 Rondebosch, South Africa
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- Deegan, Frances (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik
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- Riishuus, Morten S. (författare)
- Univ Iceland, Nord Volcanol Ctr, Inst Earth Sci, Sturlugata 7, IS-101 Reykjavik, Iceland
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- Burchardt, Steffi, 1982- (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik
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- Krumbholz, Michael (författare)
- Uppsala universitet,Mineralogi, petrologi och tektonik
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(creator_code:org_t)
- 2018-05-29
- 2018
- Engelska.
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Ingår i: Mineralogical magazine. - : MINERALOGICAL SOC. - 0026-461X .- 1471-8022. ; 82:5, s. 1147-1168
- Relaterad länk:
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https://urn.kb.se/re...
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https://doi.org/10.1...
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Abstract
Ämnesord
Stäng
- The Icelandic crust is characterized by low delta O-18 values that originate from pervasive high-temperature hydrothermal alteration by O-18-depleted meteoric waters. Igneous rocks in Iceland with delta O-18 values significantly higher than unaltered oceanic crust (similar to 5.7 parts per thousand) are therefore rare. Here we report on rhyolitic intra-caldera samples from a cluster of Neogene central volcanoes in Borgarfjorour Eystri, Northeast Iceland, that show whole-rock delta O-18 values between +2.9 and +17.6 parts per thousand (n = 6), placing them among the highest delta O-18 values thus far recorded for Iceland. Extra-caldera rhyolite samples from the region, in turn, show delta O-18 whole-rock values between +3.7 and +7.8 parts per thousand (n = 6), consistent with the range of previously reported Icelandic rhyolites. Feldspar in the intra-caldera samples (n = 4) show delta O-18 values between +4.9 and +18.7 parts per thousand, whereas pyroxene (n = 4) shows overall low delta O-18 values of +4.0 to +4.2 parts per thousand, consistent with regional rhyolite values. In combination with the evidence from mineralogy and rock H2O contents, the high whole-rock delta O-18 values of the intra-caldera rhyolites appear to be the result of pervasive isotopic exchange during subsolidus hydrothermal alteration with O-18-enriched water. This alteration conceivably occurred in a near-surface hot spring environment at the distal end of an intra-caldera hydrothermal system. and was probably fed by waters that had already undergone significant isotope exchange with the country rock. Alternatively, O-18-enriched alteration fluids may have been produced during evaporation and boiling of standing water in former caldera lakes, which then interacted with the intra-caldera rock suites. Irrespective of the exact exchange processes involved, a previously unrecognized and highly localized delta O-18-enriched rock composition exists on Iceland and thus probably within the Icelandic crust too.
Ämnesord
- NATURVETENSKAP -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)
- NATURAL SCIENCES -- Earth and Related Environmental Sciences -- Geology (hsv//eng)
Nyckelord
- Northeast Iceland
- high(18)O values
- hydrothermal alteration
- intra-caldera lakes
Publikations- och innehållstyp
- ref (ämneskategori)
- art (ämneskategori)
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