40Ar/39Ar and U-Pb geochronology, geochemistry, and tectonic setting of three episodes of Cretaceous-Eocene calc-alkaline magmatism in the Lake Clark Region, southwestern Alaska
Amato JM, Foley C, Heizler M, Esscr R. 2007. 40Ar/39Ar and U-Pb geochronology, geochemistry, and tectonic setting of three episodes of Cretaceous-Eocene calc-alkaline magmatism in the Lake Clark Region, southwestern Alaska. Geological Society of America Special Papers. 431:455-475
Cretaceous through Paleogene dominantly cal-alkaline magmatism in the Lake Clark region, southwestern Alaska can be divided into three main periods of activity based on previous work and the new 40Ar/39Ar 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 40Ar/39Ar dates from hornblende in dikes cutting the Tlikakila complex of 101-97Ma. 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 wide-spread 70-60 Ma volcanic rocks to the west of the study area. These cal-alkaline rocks are enriched in the light REE and have high Th/Nb values. They were generated 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.
- Type
- Journal Article
- Authors
- Amato, Jeffrey; Foley, Cheryl; Heizler, Matthew; Esscr, Richard
- Units
- LACL , SWAN
- Keywords
- Alaska, Geochemistry, geochronolgy, Lake Clark National Park, Magmatism, Subduction