Paleoconvergence rates determined from K2O/SiO2 ratios in magmatic rocks and their application to Cretaceous and Tertiary tectonic patterns in southwestern North America

Research Article| June 01, 1982 Paleoconvergence rates determined from K2O/SiO2 ratios in magmatic rocks and their application to Cretaceous and Tertiary tectonic patterns in southwestern North America STANLEY B. KEITH STANLEY B. KEITH 1State of Arizona, Bureau of Geology and Mineral Technology, University of Arizona, 845 N. Park Avenue, Tucson, Arizona 85719 Search for other works by this author on: GSW Google Scholar Author and Article Information STANLEY B. KEITH 1State of Arizona, Bureau of Geology and Mineral Technology, University of Arizona, 845 N. Park Avenue, Tucson, Arizona 85719 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1982) 93 (6): 524–532. https://doi.org/10.1130/0016-7606(1982)93<524:PRDFSR>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 STANLEY B. KEITH; Paleoconvergence rates determined from K2O/SiO2 ratios in magmatic rocks and their application to Cretaceous and Tertiary tectonic patterns in southwestern North America. GSA Bulletin 1982;; 93 (6): 524–532. doi: https://doi.org/10.1130/0016-7606(1982)93<524:PRDFSR>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 Spatial, temporal, and chemical data may be used to calculate paleodip angles for paleosubduction zones, assuming the position of the paleotrench is reasonably well known. In turn, paleoconvergence rates may be calculated according to the equation developed by Luyendyk (1970), that relates dip angle to convergence rate. Data from Cretaceous-Tertiary magmatic rocks indicate paleoconvergence rates of 7 to 8 cm/yr for the period 130 to 85 m.y. ago. Convergence rates markedly increased to an average of about 14 cm/yr for the period 85 to 45 m.y. Decreased convergence rates are indicated from 45 to 20 m.y. Paleoconvergence rates determined from magmatic rocks are generally in agreement with those determined independently by other workers from paleomagnetic data on ocean-floor rocks. The anomalously high rates of convergence determined from the igneous-rock data may be due to subduction of younger, more buoyant oceanc crust after 65 m.y. B.P., although recent observations from independent data suggest that Eocene convergence may have been a high 20 to 26 cm/yr. Paleomagnetically, the period of constant convergence, constant dip subduction from 130 to 85 m.y. ago correlates almost exactly with the long Cretaceous normal polarity interval as suggested on the new Lowrie-Alvarez 1981 geomagnetic time scale. In contrast, the post-85-m.y. period of variable convergence and variable dip subduction correlates with polarity events of short duration and frequent reversal. Tectonically, the period of constant convergence rates from 130 to 85 m.y. ago correlates with Sevier orogeny in Nevada and Utah. The period of increased convergence from 85 to 45 m.y. ago correlates with classic Laramide orogeny in Wyoming and Colorado. The period of decreased convergence from 45 to about 20 m.y. ago correlates with a poorly understood and incompletely defined mid-Tertiary orogenic event. 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.