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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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United States
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Alaska (1)
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New Mexico
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Jemez Mountains (1)
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geochronology methods
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Ar/Ar (2)
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geologic age
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Cenozoic
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Quaternary
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Pleistocene (1)
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Tertiary
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Paleogene
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Eocene (1)
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Mesozoic
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Cretaceous (1)
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igneous rocks
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igneous rocks
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plutonic rocks
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granodiorites (1)
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volcanic rocks
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basalts
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mid-ocean ridge basalts (1)
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rhyolites (1)
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minerals
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silicates
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chain silicates
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amphibole group
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clinoamphibole
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hornblende (1)
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orthosilicates
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nesosilicates
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zircon group
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zircon (1)
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sheet silicates
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mica group
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biotite (1)
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Primary terms
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absolute age (2)
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Cenozoic
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Quaternary
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Pleistocene (1)
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Tertiary
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Paleogene
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Eocene (1)
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faults (1)
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geochemistry (2)
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geochronology (1)
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igneous rocks
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plutonic rocks
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granodiorites (1)
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volcanic rocks
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basalts
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mid-ocean ridge basalts (1)
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rhyolites (1)
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intrusions (1)
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Mesozoic
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Cretaceous (1)
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plate tectonics (1)
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tectonics
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neotectonics (1)
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United States
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Alaska (1)
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New Mexico
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Jemez Mountains (1)
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rock formations
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Santa Fe Group (1)
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Spatial and temporal trends in pre-caldera Jemez Mountains volcanic and fault activity
Cretaceous through Paleogene dominantly calc-alkaline magmatism in the Lake Clark region, southwestern Alaska, can be divided into three main periods of activity based on previous work and new 40 Ar/ 39 Ar and U-Pb geochronology. These episodes follow a protracted history of arc magmatism related to the Talkeetna arc. The first episode is Albian based on new 40 Ar/ 39 Ar dates from hornblende in dikes cutting the Tlikakila complex of 101–97 Ma. These rocks have relatively flat REE patterns and Th/Nb values lower than typical arc rocks but higher than average mid-ocean ridge basalt (MORB). These data are consistent with rift-related magmatism in a region that had previously experienced arc magmatism. The second episode is represented by a granodiorite with a SHRIMP U-Pb zircon age of 64.5 ± 0.9 Ma and is similar to widespread 70–60 Ma volcanic rocks to the west of the study area. These calc-alkaline rocks are enriched in the light REE and have high Th/Nb values. They were generated during northward subduction of the Kula plate beneath Alaska. The Eocene episode is also calc-alkaline with enriched light rare earth element (REE) and high Th/Nb values. 40 Ar/ 39 Ar equilibria in 100 Ma dikes were reset at 44–42 Ma, and biotite from a rhyolite indicates an eruptive age of 43.0 ± 0.2 Ma. These 43 Ma rocks formed during initiation of Aleutian magmatism on the continent in response to north or northwest subduction of the Pacific plate and may be related to a change in the direction or velocity of subduction at this time.