Straight Creek Fault

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Location of the Straight Creek Fault (SCF) and associated faults in the North Cascades .

The Straight Creek Fault (SCF) is the most significant north-south oriented blade fault in Washington State; it has a dextral (right-handed) horizontal offset of at least 90 km. As an important geological structure in the North Cascades , it separates the pre- cenozoic igneous and metamorphic rocks of the North Cascades in the east from the younger terranos in the west, which have merged with the North American plate . The SCF can be traced north from its intersection with the Olympic Wallowa Lineament (OWL) near the town of Easton to British Columbia , where it merges with the Fraser River fault system; the combined system (more than 350 miles long) is known as the Fraser / Straight Creek Fault System (FSCF).

No trace of the SCF was found south of the OWL. Some geologists believe in a continuation to the south, the traces of which are all covered by recent volcanic deposits. Others speculated that it would simply end or change direction and continue with the OWL or be offset elsewhere. (see discussion elsewhere )

The SCF is shifting the older north-northwest trending Entiat, Ross Lake, and Chewack-Pasayten faults, but not various more recent features (the Snoqualmie batholith , and likely the Barlow Pass volcanoes), giving rise to the period of active blade shifting 47… 41 million years ago (in the Eocene ), immediately after the wedge of the earth's crust, which today bears the Olympic Mountains , was pushed into the continental border, can be dated. It has been suggested that the initiation of the SCF may have been triggered by events on the Kula plate .

The SCF appears to be related to the Darrington / Devils Mountain Fault (DDMF) which begins immediately east of the south end of Vancouver Island and runs to the small town of Darrington , then turns nearly south to close with the SCF whose junction with the OWL converge with it. This arch seems to exist due to the approaching Olympic Mountains. An abnormal rock formation (the Helena-Haystack Melange) just north of Darrington has been associated with similar rocks south of Easton, suggesting significant dextral movement at the DDMF. The movement on both faults appears to have occurred simultaneously; the relationship between the two has not yet been clarified.

See also

Individual evidence

  1. ↑ a b R.W. Tabor, VA, Jr. Frizzell, JA Vance, CW Naeser: Ages and stratigraphy of lower and middle Tertiary sedimentary and volcanic rocks of the central Cascades, Washington: Application to the tectonic history of the Straight Creek fault . In: GSA Bulletin . 95, No. 1, January 1984, pp. 26-44. doi : 10.1130 / 0016-7606 (1984) 95 <26: AASOLA> 2.0.CO; 2 .
  2. ^ A b c d J. W. Tabor: Late Mesozoic and possible early Tertiary accretion in western Washington State: the Helena — Haystack mélange and the Darrington — Devils Mountain Fault Zone . In: GSA Bulletin . 106, No. 2, February 1994, pp. 217-232. doi : 10.1130 / 0016-7606 (1994) 106 <0217: lmapet> 2.3.co; 2 .
  3. ^ US Geological Survey (2000). Geologic map of the Snoqualmie Pass 60 minute by 30 minute quadrangle, Washington: US Geological Survey Miscellaneous Investigations Map I-2538 [map].
  4. ^ A b E. S. Cheney, NW Hayman: Regional tertiary sequence stratigraphy and structure on the eastern flank of the central Cascade Range, Washington . In: PL Stelling, DS Tucker (eds.): Floods, faults, and fire: Geological Field Trips in Washington State and Southwest British Columbia . Geological Society of America, 2007, pp. 179-208, doi : 10.1130 / 2007.fld009 (09) .
  5. ^ A b John Figge: Evolution of the Pacific Northwest: An Introduction to the Historical Geology of the Washington State and Southern British Columbia . Northwest Geological Institute. 2009. Archived from the original on December 19, 2009.
  6. ↑ PL Heller, RW Tabor, CA Suczek: Paleogeographic evolution of the US Pacific Northwest during Paleogene time . In: Canadian Journal of Earth Sciences . 24, 1987, pp. 1652-1667. doi : 10.1139 / e87-159 .
  7. ↑ Eric S. Cheney: Geological map of the Easton area, Kittitas County, Washington Archived from the original on January 28, 2010. Information: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Washington Division of Geology and Earth Resources . Open File Report 99-4, December 1999, p. 11. Retrieved January 29, 2010. "Scale 1: 31.680" @1@ 2Template: Webachiv / IABot / www.dnr.wa.gov
  8. ^ Joseph A. Vance, Robert B. Miller: Another look at the Fraser River-Straight Creek Fault (FRSCF) . In: GSA Abstracts with Programs . 24, 1994, p. 88.

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