Geochemistry and tectonic setting of Permian - Cretaceous basaltic volcanism, northern Coast Ranges, SE AK
- Univ. of Alabama, Tuscaloosa, AL (United States). Dept. of Geology
- CONOCO Inc., Ponca City, OK (United States)
Metavolcanic rocks along the western flank of the Coast Plutonic Complex (CPC), northern SE Alaska are divided into three sequences based on age and the nature of metasedimentary rocks. These sequences consist of the Jurassic-Cretaceous Gravina (GV) belt, the Permian to Triassic western Taku (TK) terrane, and the eastern Taku/Yukon terrane. Discrimination diagrams based on least-mobile elements, and chondrite-normalized REE and MORB-normalized Spider diagrams suggest that all three groups of metavolcanic rocks are of island arc basalt or arc-rift basalt affinity. TK and GV rocks west and north of Holkham Bay show evidence of greater crustal contamination and/or a more evolved source region than rocks to the southeast. GV and western TK terrane rocks have heavy REE values of 5--14 times chondrite and most show significant light REE enrichment. Eastern TK amphibolite facies metabasalts have REE and trace element signatures of island arc tholeiites. Locally preserved phenocrysts in GV belt metabasalts consist dominantly of aluminum-rich augite which show compositions similar to those found in tholeiitic basalts. The GV and western TK metabasalts are inferred to have a nonoceanic rift-related origin, likely, within a continental margin magmatic arc. GV rocks, however, are distinct from the western TK in age and in chemistry; GV metabasalts contain less Cr and Ti than western TK metabasalts. Eastern TK metabasalts are interpreted as island arc tholeiites. Lack of MORB west of the Coast Ranges suggests that transform fault motion juxtaposed terranes outboard of the Coast Ranges with the Yukon-Tanana and Stikine terranes and/or that outboard terranes share a common basement with terranes to the east. These scenarios are compatible with formation of the CPC solely as a result of east-dipping subduction along a trench west of the GV belt.
- OSTI ID:
- 5930648
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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