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Late Mesozoic and possible early Tertiary accretion in western Washington State: the Helena-Haystack melange and the Darrington- Devils Mountain fault zone

Geological Society of America Bulletin

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Abstract

The Helena-Haystack melange (HH melange) and coincident Darrington-Devils Mountain fault zone (DDMFZ) in northwestern Washington separate two terranes, the northwest Cascade System (NWCS) and the western and eastern melange belts (WEMB). The two terranes of Paleozoic and Mesozoic rocks superficially resemble each other but record considerable differences in structural and metamorphic history. The HH melange is a serpentinite-matrix melange containing blocks of adjacent terranes but also exotic blocks. The HH melange must have formed between early Cretaceous and late middle Eocene time, because it contains tectonic clasts of early Cretaceous Shuksan Greenschist and is overlain by late middle Eocene sedimentary and volcanic rocks. The possible continuation of the DDMFZ to the northwest as the San Juan and the West Coast faults on Vancouver Island suggests that the structure has had a major role in the emplacement of all the westernmost terranes in the Pacific Northwest. -from Author

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Late Mesozoic and possible early Tertiary accretion in western Washington State: the Helena-Haystack melange and the Darrington- Devils Mountain fault zone
Series title:
Geological Society of America Bulletin
Volume
106
Issue:
2
Year Published:
1994
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Society of America Bulletin
First page:
217
Last page:
232