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| Titel |
Rapid high-silica magma generation in basalt-dominated rift settings |
| VerfasserIn |
Sylvia E. Berg, Valentin R. Troll, Steffi Burchardt, Frances M. Deegan, Morten S. Riishuus, Martin J. Whitehouse, Chris Harris, Carmela Freda, Ben S. Ellis, Michael Krumbholz, Ludvik E. Gústafsson |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112914
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| Publikation (Nr.) |
 EGU/EGU2015-13103.pdf |
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| Zusammenfassung |
| The processes that drive large-scale silicic magmatism in basalt-dominated provinces have been widely debated for decades, with Iceland being at the centre of this discussion [1-5]. Iceland hosts large accumulations of silicic rocks in a largely basaltic oceanic setting that is considered by some workers to resemble the situation documented for the Hadean [6-7]. We have investigated the time scales and processes of silicic volcanism in the largest complete pulse of Neogene rift-related silicic magmatism preserved in Iceland (>450 km3), which is a potential analogue of initial continent nucleation in early Earth.
Borgarfjörður Eystri in NE-Iceland hosts silicic rocks in excess of 20 vol.%, which exceeds the ≤12 vol% usual for Iceland [3,8]. New SIMS zircon ages document that the dominantly explosive silicic pulse was generated within a ≤2 Myr window (13.5 ± 0.2 to 12.2 ± 03 Ma), and sub-mantle zircon δ18O values (1.2 to 4.5 ± 0.2‰, n=337) indicate ≤33% assimilation of low-δ18O hydrothermally-altered crust (δ18O=0‰), with intense crustal melting at 12.5 Ma, followed by rapid termination of silicic magma production once crustal fertility declined [9]. This silicic outburst was likely caused by extensive rift flank volcanism due to a rift relocation and a flare of the Iceland plume [4,10] that triggered large-scale crustal melting and generated mixed-origin silicic melts. High-silica melt production from a basaltic parent was replicated in a set of new partial melting experiments of regional hydrated basalts, conducted at 800-900°C and 150 MPa, that produced silicic melt pockets up to 77 wt.% SiO2. Moreover, Ti-in-zircon thermometry from Borgarfjörður Eystri give a zircon crystallisation temperature ~713°C (Ti range from 2.4 to 22.1 ppm, average=7.7 ppm, n=142), which is lower than recorded elsewhere in Iceland [11], but closely overlaps with the zircon crystallisation temperatures documented for Hadean zircon populations [11-13], hinting at crustal recycling as a key process. Our results therefore provide a mechanism and a time-scale for rapid, voluminous silicic magma generation in modern and ancient basalt-dominated rift setting, such as Afar, Taupo, and potentially early Earth. The Neogene plume-related rift flank setting of NE-Iceland may thus constitute a plausible geodynamic and compositional analogue for generating silicic (continental) crust in the subduction–free setting of a young Earth (e.g. ≥3 Ga [14]).
[1] Bunsen, R. 1851. Ann. Phys. Chem. 159, 197-272. [2] MacDonald R., et al., 1987. Mineral. Mag. 51, 183–202. [3] Jonasson, K., 2007. J. Geodyn. 43, 101–117. [4] Martin, E., et al., 2011. Earth Planet. Sci. Lett. 311, 28–38. [5] Charreteur, G., et al., 2013.Contrib. Mineral. Petr. 166, 471- 490. [6] Willbold, E., et al., 2009. Earth Planet. Sci. Lett. 279, 44-52. [7] Reimink, J.R., et al., 2014. Nat. Geosci. 7, 529–533. [8] Gústafsson, L.E., et al., 1989. Jökull 39, 75–89. [9] Meade, F.C., et al., 2014. Nat. comm. 5. [10] Óskarsson, B.V., Riishuus, M.S., 2013. J. Volcanol. Geoth. Res. 267, 92–118. [11] Carley, T.L., et al., 2014. Earth Planet. Sci. Lett. 405, 85-97. [12] Trail, D., et al., 2007. Geochem. Geophys. Geosyst.8, Q06014. [13] Harrison, T.M. et al., 2008. Earth Planet. Sci. Lett.268, 476–486. [14] Kamber, B. S., et al., 2005. Earth Planet. Sci. Lett. 240, 276-290. |
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