Tectonic evolution of the Brooks Range ophiolite, Alaska
Conference
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· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5019971
- West Virginia Univ., Morgantown, WV (United States). Dept. of Geology
Detailed studies of the composition, internal structure, and age of the Brooks Range ophiolite (BRO) and its metamorphic sole reveal new constraints for its tectonic evolution. The BRO consists of six separate thrust masses of consanguineous composition, internal organization, structure and age. Subophiolite metamorphic rocks are locally preserved along its structural base, which is well exposed in several places. The metamorphic sole is locally transitional with mafic volcanic sequences, chert, tuffs, and minor clastic sedimentary material of the Copter Peak Complex, which is correlative with the Angayucham terrane. This terrane is much older than, and chemically distinct from the BRO. The internal structure of the BRO is characterized by NE-SW trending igneous layers that expose the transition zone from crust to mantle. Residual mantle material consists of tectonized peridotite in abrupt contact with dunite pods up to 4 km thick. Ductile and brittle structures of the BRO preserve various phases of its dynamic evolution from a magma body to a fragmented thrust sheet. The earliest deformational effects are recorded by ductile lattice and shape fabrics in dunites and the layered series of the BRO. Magmatic flow planes generally parallel the petrologic moho, and dip 40[degree]--70[degree] to the NW and SE. Flow lineations consistently plunge ESE-ENE from 39[degree]--54[degree]. Igneous laminations and compositional layers represent patterns of magmatic flow in, and plastic deformation of, a cumulate sequence -- not the deposition pattern of cumulate layers. In the upper layered series, amphiboles with a shape-preferred orientation yield Ar/Ar plateau ages of 163--169 Ma. These ages overlap with plateau ages of the same kind from amphibolite of the metamorphic sole. This concordance in age indicates that cooling of the BRO coincided with its tectonic emplacement.
- OSTI ID:
- 5019971
- Report Number(s):
- CONF-9305259--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
- Country of Publication:
- United States
- Language:
- English
Similar Records
K-Ar ages of allochthonous mafic and ultramafic complexes and their metamorphic aureoles, Western Brooks Range, Alaska
Polyorogenic /sup 40/Ar//sup 39/Ar mineral age record in the Seve and Koeli Nappes of the Gaeddede area, northwestern Jaemtland, central Scandinavian Caledonides
Thermal and tectonic evolution of the central and southern Appalachians: evidence from distribution, age, and origin of granitic rocks
Conference
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Sun Mar 31 23:00:00 EST 1985
· Am. Assoc. Pet. Geol., Bull.; (United States)
·
OSTI ID:6330285
Polyorogenic /sup 40/Ar//sup 39/Ar mineral age record in the Seve and Koeli Nappes of the Gaeddede area, northwestern Jaemtland, central Scandinavian Caledonides
Journal Article
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Mon Feb 29 23:00:00 EST 1988
· J. Geol.; (United States)
·
OSTI ID:5340670
Thermal and tectonic evolution of the central and southern Appalachians: evidence from distribution, age, and origin of granitic rocks
Conference
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Mon Dec 31 23:00:00 EST 1984
· Geol. Soc. Am., Abstr. Programs; (United States)
·
OSTI ID:6070579