Geochemical evidence for late Paleozoic and mid Mesozoic arc volcanism, Gravina Belt and Taku Terrane, Coast Ranges, SE AK
- Univ. of Alabama, Tuscaloosa, AL (United States). Dept. of Geology
Metavolcanic rocks along the western flank of the Coast Plutonic Complex (CPC), northern SE Alaska comprise three sequences based on age and the nature of interlayered metasedimentary rocks (from W--E): subgreenschist to greenschist facies rocks of the Jurassic-Cretaceous Gravina (Gr) belt, greenschist facies rocks of the Permian-Triassic western Taku (Tk) terrane, and dominantly amphibolite facies rocks of the eastern Taku/Yukon (T/Y) terrane. Metasedimentary strata are distinctive; however, all suggest a marine origin: immature marine sandstones, siltstones, mudstones, and conglomerates (Gr); siltstones, fossiliferous carbonates, conglomerates, and shales (western Tk); laminated slates and schists with ripple marks, and micaceous quartzites (eastern Tk). Concentrations of high field strength elements, rare earth elements (REE), and some transition elements from highly-strained and less-strained specimens are indistinguishable, suggesting immobility of these elements. Variable concentrations of alkali elements, and other transition elements suggest mobility during sea-floor alteration and/or metamorphism. Discrimination diagrams, 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. Gr and western Tk metabasalts are inferred to have a non oceanic rift-related origin, likely, within a magmatic arc; however, Gr rocks are distinct in age and in chemistry. Eastern Tk metabasalts are interpreted as island arc tholeiites. Tk arc volcanic rocks suggest a late Paleozoic arc developed on rocks of probable North American affinity. Gr arc volcanic rocks represent initial development of a magmatic arc developed on the eastern boundary of the Alexander terrane and western edge of the T/Y terranes during the Mid-Mesozoic. This arc may signify the onset of E-dipping subduction beneath N America which culminated in development of the CPC during the early Tertiary.
- OSTI ID:
- 6118228
- Report Number(s):
- CONF-9304188-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:4; Conference: 42. annual Geological Society of America (GSA) Southeastern Section meeting, Tallahassee, FL (United States), 1-2 Apr 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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