Primary magmatic amphibole in Archaean meta-pyroxenite from the central zone of the Limpopo Complex, South Africa

Abstract

Research Article| December 01, 2016 Primary magmatic amphibole in Archaean meta-pyroxenite from the central zone of the Limpopo Complex, South Africa M. Keeditse; M. Keeditse Department of Earth and Environmental Sciences, BIUST, Botswana e-mail: [e-mail]; e-mail: [e-mail] Search for other works by this author on: GSW Google Scholar H.M. Rajesh; H.M. Rajesh Department of Earth and Environmental Sciences, BIUST, Botswana e-mail: [e-mail]; e-mail: [e-mail] Search for other works by this author on: GSW Google Scholar G.A. Belyanin; G.A. Belyanin Department of Geology, University of Johannesburg, South Africa e-mail: [e-mail] Search for other works by this author on: GSW Google Scholar M. Fukuyama; M. Fukuyama Graduate School of Engineering Science, Akita University, Japan e-mail: [e-mail] Search for other works by this author on: GSW Google Scholar T. Tsunogae T. Tsunogae Department of Geology, University of Johannesburg, South AfricaGraduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan e-mail: [e-mail] Search for other works by this author on: GSW Google Scholar Author and Article Information M. Keeditse Department of Earth and Environmental Sciences, BIUST, Botswana H.M. Rajesh Department of Earth and Environmental Sciences, BIUST, Botswana G.A. Belyanin Department of Geology, University of Johannesburg, South Africa M. Fukuyama Graduate School of Engineering Science, Akita University, Japan T. Tsunogae Department of Geology, University of Johannesburg, South AfricaGraduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan e-mail: [e-mail]; e-mail: [e-mail] e-mail: [e-mail] e-mail: [e-mail] e-mail: [e-mail] Publisher: Geological Society of South Africa First Online: 20 Nov 2017 Online Issn: 1996-8590 Print Issn: 1012-0750 © 2016 December Geological Society of South AfricaGeological Society of South Africa South African Journal of Geology (2016) 119 (4): 607–622. https://doi.org/10.2113/gssajg.119.4.607 Article history First Online: 20 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. Keeditse, H.M. Rajesh, G.A. Belyanin, M. Fukuyama, T. Tsunogae; Primary magmatic amphibole in Archaean meta-pyroxenite from the central zone of the Limpopo Complex, South Africa. South African Journal of Geology 2016;; 119 (4): 607–622. doi: https://doi.org/10.2113/gssajg.119.4.607 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 SocietySouth African Journal of Geology Search Advanced Search Abstract Mapping of a section along the Sand River in the high-grade metamorphic Central Zone of the Limpopo Complex, South Africa, delineated meta-peridotite, meta-pyroxenite and meta-gabbro occurring as conformable layers in the host supracrustal rocks. The ultramafic to mafic rocks form part of the Palaeoarchaean Messina layered intrusion. Modal mineralogy of the pyroxenite is typical of an amphibole websterite. Although metamorphic re-equilibration of the pyroxenite is obvious, no new metamorphic mineral had formed. Detailed evaluation of grain margins between the prominent minerals (amphibole, clinopyroxene, orthopyroxene and olivine) indicated two types of grain margins, with their mutual relation used to support the poly-metamorphic nature of overprint on the pyroxenite. Inclusion-host relations between the prominent minerals helped to infer the original igneous order of crystallization. Petrographic and mineral chemical analyses permitted distinction of two varieties of amphiboles, the earlier occurring as polygonal grains as well as inclusions in olivine and pyroxenes, and the later occurring along grain margins, often replacing clinopyroxene. Two varieties of magnetite were also recognized, an earlier Cr-rich variety occurring as inclusions and interstitial grains, and a later Cr-poor variety occurring together with serpentine. Application of geothermobarometers indicate metamorphic re-equilibration conditions (~830 to 879°C; 5.3 to 6.1 kbars). Comparison with compositional characteristics of primary and secondary/metamorphic amphiboles reported from Archaean ultramafic rocks occurring elsewhere, Alaskan-type layered intrusions, and metasomatised rocks from the vicinity of the study area, helped to place constraints on the nature of amphiboles reported here. The identification of primary magmatic amphiboles in the meta-pyroxenite implies likely formation from a hydrous parental magma in the Archaean mantle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.