Berg, Sylvia E., Troll, Valentin R., Harris, Chris, Deegan, Frances M., Riishuus, Morten S., Burchardt, Steffi, Krumbholz, Michael (2018) Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland. Mineralogical Magazine, 82 (5) 1147-1168 doi:10.1180/mgm.2018.114
| Reference Type | Journal (article/letter/editorial) | ||
|---|---|---|---|
| Title | Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland | ||
| Journal | Mineralogical Magazine | ||
| Authors | Berg, Sylvia E. | Author | |
| Troll, Valentin R. | Author | ||
| Harris, Chris | Author | ||
| Deegan, Frances M. | Author | ||
| Riishuus, Morten S. | Author | ||
| Burchardt, Steffi | Author | ||
| Krumbholz, Michael | Author | ||
| Year | 2018 (October) | Volume | 82 |
| Page(s) | 1147-1168 | Issue | 5 |
| Publisher | Mineralogical Society | ||
| DOI | doi:10.1180/mgm.2018.114Search in ResearchGate | ||
| Mindat Ref. ID | 245069 | Long-form Identifier | mindat:1:5:245069:2 |
| GUID | edcf8010-eae7-4da5-910a-45c03f5d0215 | ||
| Full Reference | Berg, Sylvia E., Troll, Valentin R., Harris, Chris, Deegan, Frances M., Riishuus, Morten S., Burchardt, Steffi, Krumbholz, Michael (2018) Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland. Mineralogical Magazine, 82 (5) 1147-1168 doi:10.1180/mgm.2018.114 | ||
| Plain Text | Berg, Sylvia E., Troll, Valentin R., Harris, Chris, Deegan, Frances M., Riishuus, Morten S., Burchardt, Steffi, Krumbholz, Michael (2018) Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland. Mineralogical Magazine, 82 (5) 1147-1168 doi:10.1180/mgm.2018.114 | ||
| Abstract/Notes | ABSTRACTThe Icelandic crust is characterized by low δ18O values that originate from pervasive high-temperature hydrothermal alteration by18O-depleted meteoric waters. Igneous rocks in Iceland with δ18O values significantly higher than unaltered oceanic crust (~5.7‰) are therefore rare. Here we report on rhyolitic intra-caldera samples from a cluster of Neogene central volcanoes in Borgarfjörður Eystri, Northeast Iceland, that show whole-rock δ18O values between +2.9 and +17.6‰ (n= 6), placing them among the highest δ18O values thus far recorded for Iceland. Extra-caldera rhyolite samples from the region, in turn, show δ18O whole-rock values between +3.7 and +7.8‰ (n= 6), consistent with the range of previously reported Icelandic rhyolites. Feldspar in the intra-caldera samples (n= 4) show δ18O values between +4.9 and +18.7‰, whereas pyroxene (n= 4) shows overall low δ18O values of +4.0 to +4.2‰, consistent with regional rhyolite values. In combination with the evidence from mineralogy and rock H2O contents, the high whole-rock δ18O values of the intra-caldera rhyolites appear to be the result of pervasive isotopic exchange during subsolidus hydrothermal alteration with18O-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,18O-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 δ18O-enriched rock composition exists on Iceland and thus probably within the Icelandic crust too. | ||
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