Is the southeast Coast Plutonic Complex the consequence of accretion of the insular superterrane Evidence from U-Pb zircon geochronometry in the northern Washington Cascades

Journal Article · Mon Jul 01 00:00:00 EDT 1991 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1991)019<0714:ITSCPC>2.3.CO;2· OSTI ID:5941938

Walker, N W ^[1]; Brown, E H ^[2]

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1. Univ. of Texas, Austin (United States)
2. Western Washington Univ., Bellingham (United States)

Zircon U-Pb geochronometry of orthogneisses and plutons in the southwestern crystalline core of the North Cascades, coupled with fabric and textural studies of the orthogneisses, plutons, and their metamorphic host rocks, indicates extensive synmetamorphic plutonism at 89-96 Ma. Metamorphic mineral assemblages define a culmination composed of an axial kyanite-sillimanite zone rimmed by lower grade zones. High-grade index minerals are typically syntectonic to posttectonic. Metamorphic fabrics are characterized by an orogen-parallel, northwest-striking, steep foliation that contains a subhorizontal stretching and mineral lineation interpreted to be the product of ductile strike-slip deformation. This fabric is crosscut by 96-92 Ma plutons yet is imprinted on 92-89 Ma orthogneisses, suggesting spatially diachronous fabric development during orogeny. Documentation of the spatial and temporal coincidence of magmatism with the peak of orogeny, together with the kinematic significance of the metamorphic fabric, precludes generation of the metamorphic fabric and plutons in response to thrust loading. The authors suggest that this part of the Coast Plutonic Complex evolved as a transpressional magmatic arc.

• OSTI ID: 5941938
• Journal Information: Geology; (United States), Vol. 19:7; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CASCADE MOUNTAINS
MAGMATISM
OROGENESIS
AGE ESTIMATION
DEFORMATION
GEOLOGIC HISTORY
GEOLOGIC MODELS
ISOTOPE DATING
ISOTOPE RATIO
LEAD ISOTOPES
LINEAMENTS
MAPS
METAMORPHIC ROCKS
PLUTONIC ROCKS
SAMPLING
URANIUM ISOTOPES
ZIRCON
ACTINIDE ISOTOPES
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
ISOTOPES
MINERALS
MOUNTAINS
ROCKS
SILICATE MINERALS
580000* - Geosciences