Protolith relations of the Gravina belt and Yukon-Tanana terrane in central southeastern Alaska

Journal Article · Wed Jan 01 04:00:00 EST 1992 · Journal of Geology; (United States)

DOI:https://doi.org/10.1086/629574· OSTI ID:7003962

McClelland, W C ^[1]; Gehrels, G E; Patchett, P J ^[2]; Samson, S D ^[3]

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1. Univ. of California, Santa Barbara (United States)
2. Univ. of Arizona, Tucson (United States)
3. Syracuse Univ., NY (United States)

Metamorphic rocks west of the Coast Mountains batholith in central southeastern Alaska are divided into the Gravina belt, Taku terrane, and newly defined Ruth assemblage. The Ruth assemblage comprises metapelite, quartzose metaclastic strata, quartzite, marble, felsic metatuff, mafic metavolcanic rocks, and orthogneiss. Depositional and emplacement ages of 367 {plus minus} 10 Ma and 345 {plus minus} 13 Ma inferred from discordant U/Pb zircon analyses on felsic metatuff and granodioritic orthogneiss, respectively, require that at least portions of the Ruth assemblage be Late Devonian and early Mississippian in age. The assemblage is similar in age and protolith to, and thus correlated with, the Yukon-Tanana terrane. The Gravina belt is characterized by upper Jurassic and lower Cretaceous mafic volcanic rocks and tuffaceous turbiditic clastic strata that unconformably overlie the Alexander terrane. Metamorphic rocks that structurally underlie the Taku terrane and Rugh assemblage are included in this assemblage. Trace element geochemistry and the abundance of pyroclastic flows associated with tuffaceous turbidites suggest that the Gravina belt evolved in an intra-arc basinal setting. In central southeastern Alaska, the mid-Cretaceous structure that currently separates the Ruth assemblage (Yukon-Tanana correlative) from the Gravina belt marks the fundamental boundary between the Alexander-Wrangellia terrane and inboard Yukon-Tanana and Stikine terranes.

• OSTI ID: 7003962
• Journal Information: Journal of Geology; (United States), Journal Name: Journal of Geology; (United States) Vol. 100:1; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

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GEOLOGIC AGES
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