1985/01/01 by Darrel S. Cowan, DARREL S. COWAN · 5 citations
Earth and Planetary Sciences · #Geological formations and processes #Geology and Paleoclimatology Research #Geological and Geophysical Studies
paper · doi:10.1130/0016-7606(1985)96<451:ssimac>2.0.co;2
Research Article| April 01, 1985 Structural styles in Mesozoic and Cenozoic mélanges in the western Cordillera of North America 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 (1985) 96 (4): 451–462. https://doi.org/10.1130/0016-7606(1985)96<451:SSIMAC>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; Structural styles in Mesozoic and Cenozoic mélanges in the western Cordillera of North America. GSA Bulletin 1985;; 96 (4): 451–462. doi: https://doi.org/10.1130/0016-7606(1985)96<451:SSIMAC>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 The term "mélange" is currently used to describe several different kinds of mudstone-rich rocks that are broadly characterized by an obscure stratigraphy, stratal disruption, or a chaotic, "block-in-matrix" fabric. Four types of mélange, which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition, are particularly widespread and distinctive. Type I includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer-parallel extension. Type II consists of similarly deformed, thin layers of green tuff, radiolarian ribbon chert, and minor sandstone originally interbedded with black mudstone. Disruption in both types I and II, which probably occurred while the sediments were incompletely consolidated, has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation. Type III comprises inclusions of diverse shapes, sizes, and compositions enveloped in a locally scaly, pelitic matrix. The ultimate source of fragments is obscure, because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks. Although some type III mélanges may have originated deep within accretionary prisms, final emplacement as olistostromes (muddy debris-flow deposits) or mud diapirs seems likely. Type III mélanges are mechanically analogous to scaly, "sheared" serpentinites; many probably have been tectonically remobilized or even intruded into shallow-level fault zones. Type IV consists of lenticular inclusions bounded by an anastomosing network of subparallel faults. Their fabric records progressive slicing in brittle fault zones.Each of the four types of mélange described here could, in theory, have formed in a variety of settings on or within an accretionary wedge at an active convergent margin; none can yet be singled out as a uniquely diagnostic "subduction mélange." 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.