Geologic Setting of the Chena Hot Springs Geothermal System, Alaska

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Conference Paper: Geologic Setting of the Chena Hot Springs Geothermal System, Alaska

Abstract
A belt of moderate-temperature geothermal activityruns east-west across central Alaska. Chena HotSprings (CHS) is one of several Interior Alaskan hotsprings in or near 55 Ma granites within Paleozoicmetamorphic rocks. CHS is located within the CHSpluton, a composite body of quartz diorite, tonalite,granodiorite, and granite of both mid-Cretaceous andEarly Tertiary ages. 40Ar/39Ar step heat analyses ofbiotite from the CHS pluton shows flat Tertiary agespectra (supporting previous studies that reported aTertiary age for the body); however, hornblendespectra show evidence for partial resets and suggest amagmatic age of about 90 Ma. The majority of theexposed CHS pluton displays features common toCretaceous (subduction-related) plutons elsewhere ininterior Alaska. The pluton is medium to coarsegrained,commonly hornblende and allanite-bearing,with intermediate to felsic compositions and low Rb-Y-Nb-U-Th concentrations. Small bodies ofmineralogically and texturally distinct syenograniteand alkali feldspar granite occur near the margins ofthe composite body. These rocks contain up to 8times as much U and 4 times as much Th and Rb asthe typical rocks of the CHS pluton, as is true of earlyTertiary (extension-related) granites elsewhere inInterior Alaska. DIGHEM airborne gamma raysurveys indicate that high U-Th anomalies spatiallycorrelate with outcrops of these chemically distinctgranites. Thus, we propose that most of the exposedCHS pluton is Cretaceous and is underlain by anU,Th-enriched Tertiary pluton with limited surfaceextent. This hypothetical body reset the argonisotopic systematics of biotite and partially reset thehornblende. We further propose that radioactivedecay of K, U and Th within the concealed Tertiarypluton is causing an anomalously high regionalgeothermal gradient, thereby providing the heat atCHS. The hydrothermal upwelling zone may occur ata fault zone junction and/or at the hypotheticalcontact between Cretaceous and Tertiary plutons.

Authors 
Amanda M. Kolker, Rainer Newberry, Jessica Larsen, Paul Layer and Patrick Stepp






Conference 
Stanford Geothermal Workshop; {{{ConferencePlace}}}"{{{ConferencePlace}}}" cannot be used as a page name in this wiki.; 2007


Published 
Proceedings of the Thirty-second Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA;, 2007





DOI 
Not Provided
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Online 
Internet link for Geologic Setting of the Chena Hot Springs Geothermal System, Alaska

Citation

Amanda M. Kolker,Rainer Newberry,Jessica Larsen,Paul Layer,Patrick Stepp. 2007. Geologic Setting of the Chena Hot Springs Geothermal System, Alaska. In: Proceedings of the Thirty-second Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA. Stanford Geothermal Workshop; 2007; (!) . (!) : (!) ; p. 416-423


Related Geothermal Exploration Activities
Activities (1)


Areas (1)
  1. Chena Geothermal Area
Regions (0)