Dacite Melt at the Puna Geothermal Venture Wellfield, Big Island of Hawaii

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Journal Article: Dacite Melt at the Puna Geothermal Venture Wellfield, Big Island of Hawaii

Abstract
During the drilling of injection well KS-13 in 2005 at the Puna Geothermal Venture (PGV) well field, on the island of Hawaii, a 75-meter interval of diorite containing brown glass inclusions was penetrated at a depth of 2415 m. At a depth of 2488 m a melt of dacitic composition was encountered. The melt flowed up the well bore and was repeatedly re-drilled over a depth interval of 8 m, producing several kilograms of clear, colorless vitric cuttings at the surface. The dacitic glass cuttings have a perlitic texture, a silica content of 67 wgt.%, are enriched in alkalis and nearly devoid of mafic minerals with the exception of rare pyroxene phenocrysts and minor euhedral to amorphous magnetite. The melt zone is overlain by an interval of strong greenschist facies metamorphism in basaltic and dioritic dike rock. The occurrence of an anhydrous dacite melt indicates a rock temperature of approximately 1050 C (1922 F)and sufficient residence time of underlying basaltic magma to generate a significant volume of highly differentiated material. Heat flux from the magma into the overlying geothermal reservoir is 3830 mW/m2, an order of magnitude greater than for mid-ocean ridges. The geologic conditions at PGV combine tensional tectonics with magmatic temperatures at readily drillable depths (<2500 m).

Authors 
William Teplow, Bruce Marsh, Jeff Hulen, Paul Spielman, Mike Kaleikini, David Fitch and William Rickard








Published Journal 
GRC Transactions, 2009





DOI 
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Online 
Internet link for Dacite Melt at the Puna Geothermal Venture Wellfield, Big Island of Hawaii

Citation

William Teplow,Bruce Marsh,Jeff Hulen,Paul Spielman,Mike Kaleikini,David Fitch,William Rickard. 2009. Dacite Melt at the Puna Geothermal Venture Wellfield, Big Island of Hawaii. GRC Transactions. .