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Kinematic analysis of the San Juan thrust system, Washington

Hirokazu Maekawa and Edwin H. Brown
Kinematic analysis of the San Juan thrust system, Washington
Geological Society of America Bulletin (August 1991) 103 (8): 1007-1016


Shear-related fabric in the middle to Late Cretaceous San Juan thrust system, Washington, is observed in imbricated blocks and in fault zones a few millimeters to tens of meters thick. Foliation and lineation are defined in tectonic blocks by alignment of (1) newly grown muscovite and chlorite and (2) flattened and stretched radiolaria, mineral porphyroclasts, and rock fragments. Thin argillaceous shear zones bear a pronounced lineation defined by lithologic "streaks" and slickenside corrugations. The slickenside and stretching lineations show a well-defined preferred orientation in a horizontal northwest-southeast direction. Widespread S-C fabrics, asymmetric pressure shadows, fault drag features, and asymmetric folds in the X-Z plane yield a sense of tectonic transport at most localities of upper plate to the northwest. Aragonite, prehnite, lawsonite, pumpellyite, and rare Na-amphibolite and Na-pyroxene characterize the metamorphism during the thrusting. The findings of this study indicate north-west, orogen-parallel, transport of the San Juan thrust system. We suggest that this structure is a large step-over zone transferring dextral strike slip from the western Cascades to the oceanward side of Wrangellia.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 103
Serial Issue: 8
Title: Kinematic analysis of the San Juan thrust system, Washington
Affiliation: West. Wash. Univ., Dep. Geol., Bellingham, WA, United States
Pages: 1007-1016
Published: 199108
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 56
Accession Number: 1991-038620
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. block diag., geol. sketch maps
N48°25'00" - N48°49'60", W123°15'00" - W122°40'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 1991
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