Selective peritectic garnet entrainment as the origin of geochemical diversity in S-type granites

Abstract

Research Article| January 01, 2007 Selective peritectic garnet entrainment as the origin of geochemical diversity in S-type granites Gary Stevens; Gary Stevens 1Department of Geology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa Search for other works by this author on: GSW Google Scholar Arnaud Villaros; Arnaud Villaros 1Department of Geology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa Search for other works by this author on: GSW Google Scholar Jean-François Moyen Jean-François Moyen 1Department of Geology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa Search for other works by this author on: GSW Google Scholar Author and Article Information Gary Stevens 1Department of Geology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa Arnaud Villaros 1Department of Geology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa Jean-François Moyen 1Department of Geology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa Publisher: Geological Society of America Received: 05 May 2006 Revision Received: 19 Jul 2006 Accepted: 21 Jul 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2007) 35 (1): 9–12. https://doi.org/10.1130/G22959A.1 Article history Received: 05 May 2006 Revision Received: 19 Jul 2006 Accepted: 21 Jul 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Gary Stevens, Arnaud Villaros, Jean-François Moyen; Selective peritectic garnet entrainment as the origin of geochemical diversity in S-type granites. Geology 2007;; 35 (1): 9–12. doi: https://doi.org/10.1130/G22959A.1 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 SocietyGeology Search Advanced Search Abstract Experimental melt (glass) compositions indicate that most of the S-type granites of the Cape Granite Suite in South Africa have ferromagnesian contents too high to represent melts. Consequently, the composition of the more mafic granites demands the addition of an Fe- and Mg-rich component to the magma. The compositions of the granites evolve along well-defined trends away from the likely melt composition for many components plotted against Mg + Fe. An increase in A/CNK, Mg#, Ca, and HREEs, as well as a decrease in K and Si, as a function of increasing Mg + Fe appears to limit the contaminant to garnet (up to 20 wt%). The rate of Ti increase, as a function of Mg + Fe increase in the granites, matches that defined by the stoichiometry of high-temperature biotite, but cannot be the product of accumulation of biotite (± other phases) in the magma because the chemical trends are inconsistent with this, particularly those portrayed by K and Ti as a function of Mg + Fe. This, in conjunction with the fact that no large, counterbalancing population of very leucocratic material exists in the Cape Granite Suite, suggests that the relatively mafic granites are not the products of garnet fractional crystallization. Rather, these appear to be the result of selective entrainment of peritectic garnet and ilmenite. Thus, this work indicates that much of the compositional variation in the granites is primary, reflecting the magma composition that ascended from the source, and is controlled by the proportion of peritectic products entrained into the melt. There is no indication of entrainment of a mineralogically diverse residuum (restite). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.