40Ar/39Ar mineral age record of polyphase tectonothermal evolution in the southern Mauritanide orogen, southeastern Senegal

Abstract

Research Article| May 01, 1987 40Ar/39Ar mineral age record of polyphase tectonothermal evolution in the southern Mauritanide orogen, southeastern Senegal R. D. DALLMEYER; R. D. DALLMEYER 1Department of Geology, University of Georgia, Athens, Georgia 30602 Search for other works by this author on: GSW Google Scholar MICHEL VILLENEUVE MICHEL VILLENEUVE 2Laboratoire Associé Au CNRS no 132, “Etudes Géologiques Ouest-Africaines,” Université d'Aix-Marseille III, 13397 Marseille, Cedex 13, France Search for other works by this author on: GSW Google Scholar Author and Article Information R. D. DALLMEYER 1Department of Geology, University of Georgia, Athens, Georgia 30602 MICHEL VILLENEUVE 2Laboratoire Associé Au CNRS no 132, “Etudes Géologiques Ouest-Africaines,” Université d'Aix-Marseille III, 13397 Marseille, Cedex 13, France Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 98 (5): 602–611. https://doi.org/10.1130/0016-7606(1987)98<602:AMAROP>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 MailTo Tools Icon Tools Get Permissions Search Site Citation R. D. DALLMEYER, MICHEL VILLENEUVE; 40Ar/39Ar mineral age record of polyphase tectonothermal evolution in the southern Mauritanide orogen, southeastern Senegal. GSA Bulletin 1987;; 98 (5): 602–611. doi: https://doi.org/10.1130/0016-7606(1987)98<602:AMAROP>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 40Ar/39Ar incremental-release mineral ages have been determined for several tectonostratigraphic units in southernmost portions of the Maiuritanide orogen in Senegal. Here, middle Proterozoic crystalline basement rocks of the West African craton are unconformably overlain by an upper Proterozoic (ca. 1100 Ma) continental sedimentary succession (Madina Kouta Group) transitional into volcanic and intercalated deep-marine sediments (Tennesse Group). Western portions of the volcano-sedimentary unit were variably deformed and metamorphosed prior to deposition of an unconformably overlying, upper Precambrian-Lower Cambrian sedimentary succession (Mali Group). Muscovite within cleavage domains in the low-grade metamorphic terrane records 40Ar/39Ar plateau dates of ca. 655–665 Ma and are interpreted to closely date the Pan African I phase of orogenic activity. The Mali Group itself was locally folded during a second phase of Pan African tectonothermal activity, which also affected a western, calc-alkaline, volcanic-plutonic sequence (Niokolo-Koba Group). Igneous hornblende from several granites within this sequence displays internally discordant 40Ar/39Ar release spectra which record variably developed plateaus of ca. 640–660 Ma. These are interpreted to approximately date initial postmagmatic cooling through ∼500 °C and are consistent with a previously published Rb-Sr whole-rock iso-chron crystallization age of 683 ± 18 Ma for one of the plutons. Associated calc-alkaline volcanic and volcaniclastic rocks are more penetratively deformed. Muscovite that is aligned along a regional cleavage records 40Ar/39Ar plateau ages of ca. 550–560 Ma, which are interpreted to closely date the Pan African II orogenesis.Widespread deposition of a molassic sequence (Youkoukoun Formation) occurred in the Middle Cambrian-Early Ordovician. This was disconformably overlain by Upper Ordovician-Upper Devonian sedimentary rocks (Bové basin succession), which are locally folded. More significant late Paleozoic tectonothermal activity is recorded in north-westernmost portions of the study area where the calc-alkaline, upper Proterozoic granites locally display penetrative mylonitic fabrics. Development of these fabrics is interpreted to be closely dated by the 40Ar/39Ar 270- to 280-Ma plateau ages recorded by dynamically recrystallized muscovite developed along fluxion foliations. These results allow demarcation of a late Paleozoic tectonic “front” and permit correlations with genetically related events in southeastern portions of the Appalachian orogen. 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.