Petrology and tectonic significance of gabbros, tonalites, shoshonites, and anorthosites in a late Paleozoic arc-root complex in the Wrangellia Terrane, southern Alaska

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629351· OSTI ID:7135903

Beard, J S ^[1]; Barker, F ^[2]

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1. Virginia Museum of Natural History, Martinsville (USA)
2. Geological Survey, Denver, CO (USA)

Plutonic rocks intrusive into the late Paleozoic Tetelna Formation of southern Alaska are the underpinnings of the late Paleozoic Skolai arc of the Wrangellia Terrane. There are four groups of intrusive rocks within the Skolai arc: (1) Gabbro-diorite plutons that contain gabbroic to anorthositic cumulates along with a differentiated series of gabbros and diorites of basaltic to andesitic composition; (2) Silicic intrusions including tonalite, granodiorite, and granite; (3) Monzonitic to syenitic plutonic rocks of the Ahtell complex and related dikes and sills; (4) Fault-bounded bytownite anorthosite of uncertain age and association. These anorthosites may be related to post-Skolai, Nikolai Greenstone magmatism. The silicic rocks yield discordant U-Pb zircon ages of 290-320 Ma (early to late Pennsylvanian). The monzonitic rocks of the Ahtell complex have shoshonitic chemistry. Similar shoshonitic rocks are widespread in both the Wrangellia terrane and the neighboring Alexander terrane and intrude the contact between the two. In modern oceanic arcs, shoshonitic rocks are typically associated with tectonic instability occurring during the initial stages of subduction or just prior to or during termination or flip of an established subduction zone. The nature of any tectonic instability which may have led to the cessation of subduction in the Skolai arc is unclear. Possibilities include collision of the arc with a ridge, an oceanic plateau, another arc, or a continental fragment. One possibility is that the shoshonitic magmatism marks the late Paleozoic amalgamation of Wrangellia and the Alexander terrane. The scarcity of arc rocks predating the shoshonites in the Alexander terrane supports this possibility, but structural corroboration is lacking.

• OSTI ID: 7135903
• Journal Information: Journal of Geology; (USA), Vol. 97:6; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALASKA
GEOLOGIC DEPOSITS
PETROLOGY
TECTONICS
AGE ESTIMATION
ANORTHOSITES
CARBONIFEROUS PERIOD
DIKES
GABBROS
GEOCHEMISTRY
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOLOGIC MODELS
INTRUSION
ISOTOPE DATING
ISOTOPE RATIO
LEAD
MINERALOGY
MOUNTAINS
PALEOZOIC ERA
SUBDUCTION ZONES
URANIUM
ZIRCON
ACTINIDES
CHEMISTRY
ELEMENTS
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
METALS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences