HR: 1340h
AN: T23B-0556 [Abstracts]
TI: Geologic mapping, Petrology and Geochemistry as Geothermal Exploration Tools: Structure and Fluid-Rock
Interactions at Chena Hot Springs, Alaska
AU: * Kolker, A M
EM: ftamk1@uaf.edu
AF: Univerisity of Alaska Fairbanks Department of Geology and Geophysics, PO Box 755780, Fairbanks, AK
99775-5780
United States
AU: Larsen, J F
EM: faust@gi.alaska.edu
AF: Univerisity of Alaska Fairbanks Department of Geology and Geophysics, PO Box 755780, Fairbanks, AK
99775-5780
United States
AU: Newberry, R
EM: ffrn@uaf.edu
AF: Univerisity of Alaska Fairbanks Department of Geology and Geophysics, PO Box 755780, Fairbanks, AK
99775-5780
United States
AU: Eichelberger, J
EM: eich@gi.alaska.edu
AF: Univerisity of Alaska Fairbanks Department of Geology and Geophysics, PO Box 755780, Fairbanks, AK
99775-5780
United States
AB:
Chena Hot Springs (CHS) is one of several Interior Alaskan Hot springs hosted by early Tertiary (ca. 55 Ma) granite with
mafic dikes of intraplate composition. The Interior hot springs belt of moderate-temperature geothermal activity runs
east-west across central Alaska from the Seward Peninsula to the Yukon Territory. CHS sits approximately in the center of the
enclosing composite 10 km x 5 km pluton, but in a lithologically anomalous zone containing abundant metamorphic xenoliths
and 0.1-1 km2-sized intermediate composition plutonic bodies of likely mid-Cretaceous age. The upwelling zone for
thermal waters is located at the intersection of two faults with apparent conjugate geometry. Joints, mafic dikes, and veins
in the region possess similar orientations and suggest such fractures are the main hydrothermal conduits.
From consistent Na-K, Na-Ca-K, and SiO2 geothermometry, reservoir temperatures are approximately 125oC, but maximum well
temperatures are 78oC. Systematic variations in F, B, Li, Si, and Cl contents of well waters indicate reservoir fluids are
mixed with near-surface groundwater spatially zoned around the highest-temperature wells. Cooler deep well temperatures
(66-104oC) correlate chemically with increased groundwater mixing. Still lower wellhead fluid temperatures
(40-66oC) are likely due to conductive heat loss associated with convecting shallow groundwater. Hydrothermal alteration
minerals include chlorite, epidote, zeolites, prehnite, sericite, and montmorillonite; due most likely to both syn-plutonic
and present-day hot water circulation.
Despite fault control on the hydrothermal system, the ultimate heat source driving CHS remains ambiguous. The association
between interior hot springs and U,Th-enriched plutonic bodies suggests radiogenic heating is a major factor, if only by
elevating the regional geothermal gradient.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1039 Alteration and weathering processes (3617)
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 3617 Alteration and weathering processes (1039)
DE: 3640 Igneous petrology
SC: Tectonophysics [T]
MN: Fall Meeting 2005