Origin of blueschist-bearing chaotic rocks in the Franciscan Complex, San Simeon, California

Research Article| September 01, 1978 Origin of blueschist-bearing chaotic rocks in the Franciscan Complex, San Simeon, California DARREL S. COWAN DARREL S. COWAN 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Author and Article Information DARREL S. COWAN 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1978) 89 (9): 1415–1423. https://doi.org/10.1130/0016-7606(1978)89<1415:OOBCRI>2.0.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 DARREL S. COWAN; Origin of blueschist-bearing chaotic rocks in the Franciscan Complex, San Simeon, California. GSA Bulletin 1978;; 89 (9): 1415–1423. doi: https://doi.org/10.1130/0016-7606(1978)89<1415:OOBCRI>2.0.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 Chaotic rocks exposed in sea cliffs south of San Simeon, California, consist of sub-rounded to lens-shaped fragments of graywacke, greenstone, and less abundant blueschist and chert dispersed in a matrix of argillite. This nonbedded mélange has been deformed twice. An earlier deformation, D1, produced a strong northwest-striking, northeast-dipping foliation defined by both tectonically flattened inclusions and a parallel penetrative cleavage in argillite. Most inclusions, even of blueschist, are imperfect oblate ellipsoids or display pinch-and-swell structure and, locally, extreme necking and boudinage. Overall ductile behavior during D1 was succeeded by the development of subparallel shear fractures that record a brittle deformation, D2. Displacements on these fractures were generally small or negligible.It is clear that neither D1 nor D2 was responsible for the original lithologic heterogeneity and chaotic fabric of the mélange. Mixing of foliated, glaucophane-lawsonite blueschist with lower-grade graywacke and greenstone to yield a nonbedded diamictite composed of variously sized clasts in a mudstone matrix must have occurred prior to D1, probably by sedimentary processes involving submarine sliding and downslope transport of debris flows. There is no evidence that the mélange was bedded or that the blueschist inclusions were tectonically introduced among lower-grade rocks, prior to D1. The sequence of sedimentary and tectonic events suggests that as the subduction ultimately responsible for the Franciscan Complex as a whole proceeded, blueschists in elevated parts of previously accreted material were eroded, mixed with lower-grade rock, and deposited as olistostromes that were subsequently accreted and deformed. 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.