Deformation paths in the shallow levels of an accretionary prism: The Eocene Shimanto belt of southwest Japan

Research Article| October 01, 1990 Deformation paths in the shallow levels of an accretionary prism: The Eocene Shimanto belt of southwest Japan LEE DITULLIO; LEE DITULLIO 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar TIM BYRNE TIM BYRNE 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar Author and Article Information LEE DITULLIO 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 TIM BYRNE 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1990) 102 (10): 1420–1438. https://doi.org/10.1130/0016-7606(1990)102<1420:DPITSL>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 LEE DITULLIO, TIM BYRNE; Deformation paths in the shallow levels of an accretionary prism: The Eocene Shimanto belt of southwest Japan. GSA Bulletin 1990;; 102 (10): 1420–1438. doi: https://doi.org/10.1130/0016-7606(1990)102<1420:DPITSL>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 Detailed structural analysis of coherent turbidites in a part of the Eocene Shimanto belt on the Muroto Peninsula, Shikoku Island, Japan, reveals a structural evolution that is typical of the shallow levels of accretionary prisms in style and sequence of deformational fabrics, but anomalous in that it includes both a marked rotation in shortening direction and a major out-of-sequence thrust. Deformation throughout a history of progressive lithification and burial was dominated by subhorizontal shortening and seaward-vergent shear. Structures evolved from predominantly mesoscale thrusts and folds to larger, more brittle faults, and finally to kilometer-scale, amplified fault-bend folds with an associated pressure-solution cleavage. This structural progression is consistent with increasing strength of the rocks, decreasing fluid pressures, and increasing temperature and pressure as the sediments were dewatered, lithified, and accreted to the prism.In contrast to this straightforward structural evolution, the prism-scale deformation of the Eocene Shimanto belt is difficult to reconcile with simple models of prism developmentthat assume orthogonal subduction and seaward-stepping imbrication. A 50° counterclockwise rotation in the shortening direction and a major out-of-sequence (or intraprism) thrust are recorded by two distinct structural domains. In both, the earliest structures are clastic dikes and faults indicative of north-south shortening. One domain is characterized by east-striking, regional-scale folds and cleavage that are transected by an east-northeast-trending cleavage; however, the other is characterized by northeast-striking folds and cleavage that are transected by a slightly more north-striking cleavage. The different deformation histories of the two do-mains require that they be separated by a major intraprism fault. This fault carries tectonic mélange containing blocks of pillow basalt and chert, indicating that it rooted in the décollement zone beneath the prism. The tectonostratigraphy and deformation histories of the two domains suggest that both before and after the out-of-sequence fault developed, higher structural levels of the prism experienced significant subhorizontal shortening, whereas lower structural levels bypassed this zone of deformation. 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.