Research Article| October 01, 1989 The Mesozoic Rimrock Lake inlier, southern Washington Cascades: Implications for the basement to the Columbia Embayment ROBERT B. MILLER ROBERT B. MILLER 1Department of Geology, San Jose State University, San Jose, California 95192-0102 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT B. MILLER 1Department of Geology, San Jose State University, San Jose, California 95192-0102 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1989) 101 (10): 1289–1305. https://doi.org/10.1130/0016-7606(1989)101<1289:TMRLIS>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation ROBERT B. MILLER; The Mesozoic Rimrock Lake inlier, southern Washington Cascades: Implications for the basement to the Columbia Embayment. GSA Bulletin 1989;; 101 (10): 1289–1305. doi: https://doi.org/10.1130/0016-7606(1989)101<1289:TMRLIS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Mesozoic Rimrock Lake inlier lies between the North Cascades, Blue, and Klamath Mountains, and thus has significant implications for the basement to the Columbia Embayment. The inlier consists of the Late Jurassic Indian Creek complex and the voluminous Late Jurassic-Early Cretaceous Russell Ranch complex. The Indian Creek complex consists of trondhjemitic to gabbroic rocks, some of which underwent dynamo-thermal medium-grade metamorphism that was probably broadly synchronous with plutonism. Lithologies and geochemical data indicate that the complex represents the roots of an arc.The Russell Ranch complex is a tectonic mélange, consisting mainly of arkose and mudstone, with subordinate chert, conglomerate, and pillowed greenstone, and minor green tuff. Deposition may have occurred on an inner fan or the inner part of a mid-fan. Sandstones were derived from a plutonic terrane, presumably a dissected are. The geochemistry of greenstones apparently is most compatible with eruption as within-plate tholeiites or MORB. The complex displays a block-in-matrix mesoscopic fabric; greenstone and the foliated Twin Sisters Lakes silicic metavolcanic unit occur as kilometer-scale blocks. Predominantly steep faults riddle the complex. Overlapping time relations between normal and thrust faults, several generations of folds, and cleavages record protracted deformation.Steep faults separate the units and are bracketed between Early Cretaceous and earliest Eocene, as is deformation of the Russell Ranch complex. These are mostly brittle structures, but one mylonite zone has a gentle stretching lineation suggestive of strike slip. Large displacements probably occurred between the Indian Creek and Russell Ranch complexes, but an original basement and cover relationship cannot be precluded.The complexes are broadly correlative with rocks to the north. The Late Jurassic are, represented by the Indian Creek complex, may include rocks in other inliers in central Washington, the mélange belts of north-western Washington, and the San Juan Islands. The Russell Ranch complex most closely resembles parts of the western mélange belt and the Constitution Formation. Late Jurassic arc-type rocks also occur in the Klamath and Blue Mountains, and the Russell Ranch complex may correlate with the Yolla Bolly terrane of the Franciscan Complex. These correlations suggest that lithological belts are more continuous between Washington and California than implied by models which propose major tectonic dispersal. The Mesozoic arc-type crust and continentally derived clastic rocks in the inlier demonstrate that the basement to the Columbia Embayment includes a variety of tectonic slices or terranes and that the embayment is not simply underlain by Tertiary or Mesozoic oceanic crust as is commonly proposed. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
No takes yet. Share an insight, caveat, or question.
Robert B. Miller (1989) studied this question.