TY - JOUR

T1 - Textural and geochemical window into the IDDP-1 rhyolitic melt, Krafla, Iceland, and its reaction to drilling

AU - Saubin, Elodie

AU - Kennedy, B. M.

AU - Tuffen, Hugh

AU - Nichols, Alex R. L.

AU - Villeneuve, Marlene

AU - Bindeman, I

AU - Mortensen, A

AU - Schipper, I

AU - Wadsworth, FB

AU - Watson, T

AU - Zierenberg, R

PY - 2021

Y1 - 2021

N2 - The unexpected intersection of rhyoliticmagma and retrieval of quenched glass particlesat the Iceland Deep Drilling Project-1geothermal well in 2009 at Krafla, Iceland,provide unprecedented opportunities tocharacterize the genesis, storage, and behaviorof subsurface silicic magma. In this study,we analyzed the complete time series of glassparticles retrieved after magma was intersected,in terms of distribution, chemistry,and vesicle textures.Detailed analysis of the particles revealedthem to represent bimodal rhyolitic magmacompositions and textures. Early-retrievedclear vesicular glass has higher SiO2, crystal,and vesicle contents than later-retrieveddense brown glass. The vesicle size and distributionof the brown glass also reveal severalvesicle populations. The glass particles varyin δD from −120‰ to −80‰ and have dissolvedwater contents spanning 1.3−2 wt%,although the majority of glass particles exhibita narrower range. Vesicular texturesindicate that volatile overpressure releasepredominantly occurred prior to late-stagemagma ascent, and we infer that vesiculationoccurred in response to drilling-induced decompression.The textures and chemistry ofthe rhyolitic glasses are consistent with variablepartial melting of host felsite. The drillingrecovery sequence indicates that the clearmagma (lower degree partial melt) overlaysthe brown magma (higher degree partialmelt). The isotopes and water species supporthigh temperature hydration of these partialmelts by a mixed meteoric and magmaticcomposition fluid. The textural evidence forpartial melting and lack of crystallization implythat magma production is ongoing, andthe growing magma body thus has a high potentialfor geothermal energy extraction.In summary, transfer of heat and fluidsinto felsite triggered variable degrees of felsitepartial melting and produced a hydrated rhyolitemagma with chemical and textural heterogeneitiesthat were then enhanced by drillingperturbations. Such partial melting couldoccur extensively in the crust above magmachambers, where complex intrusive systemscan form and supply the heat and fluids requiredto re-melt the host rock. Our findingsemphasize the need for higher resolutiongeophysical monitoring of restless calderasboth for hazard assessment and geothermalprospecting. We also provide insight into howshallow silicic magma reacts to drilling, whichcould be key to future exploration of the useof magma bodies in geothermal energy.

AB - The unexpected intersection of rhyoliticmagma and retrieval of quenched glass particlesat the Iceland Deep Drilling Project-1geothermal well in 2009 at Krafla, Iceland,provide unprecedented opportunities tocharacterize the genesis, storage, and behaviorof subsurface silicic magma. In this study,we analyzed the complete time series of glassparticles retrieved after magma was intersected,in terms of distribution, chemistry,and vesicle textures.Detailed analysis of the particles revealedthem to represent bimodal rhyolitic magmacompositions and textures. Early-retrievedclear vesicular glass has higher SiO2, crystal,and vesicle contents than later-retrieveddense brown glass. The vesicle size and distributionof the brown glass also reveal severalvesicle populations. The glass particles varyin δD from −120‰ to −80‰ and have dissolvedwater contents spanning 1.3−2 wt%,although the majority of glass particles exhibita narrower range. Vesicular texturesindicate that volatile overpressure releasepredominantly occurred prior to late-stagemagma ascent, and we infer that vesiculationoccurred in response to drilling-induced decompression.The textures and chemistry ofthe rhyolitic glasses are consistent with variablepartial melting of host felsite. The drillingrecovery sequence indicates that the clearmagma (lower degree partial melt) overlaysthe brown magma (higher degree partialmelt). The isotopes and water species supporthigh temperature hydration of these partialmelts by a mixed meteoric and magmaticcomposition fluid. The textural evidence forpartial melting and lack of crystallization implythat magma production is ongoing, andthe growing magma body thus has a high potentialfor geothermal energy extraction.In summary, transfer of heat and fluidsinto felsite triggered variable degrees of felsitepartial melting and produced a hydrated rhyolitemagma with chemical and textural heterogeneitiesthat were then enhanced by drillingperturbations. Such partial melting couldoccur extensively in the crust above magmachambers, where complex intrusive systemscan form and supply the heat and fluids requiredto re-melt the host rock. Our findingsemphasize the need for higher resolutiongeophysical monitoring of restless calderasboth for hazard assessment and geothermalprospecting. We also provide insight into howshallow silicic magma reacts to drilling, whichcould be key to future exploration of the useof magma bodies in geothermal energy.

U2 - 10.1130/B35598.1

DO - 10.1130/B35598.1

M3 - Article

VL - 2021

JO - Geological Society of America bulletin

JF - Geological Society of America bulletin

SN - 0016-7606

ER -