Morphology, Micro-Structure and Chemistry of A Deformed Garnet Megacryst Suite From Monteleo Kimberlite, Free State Province, South Africa.

Abstract

Research Article| December 01, 2015 Morphology, Micro-Structure and Chemistry of A Deformed Garnet Megacryst Suite From Monteleo Kimberlite, Free State Province, South Africa. S. Perritt; S. Perritt Previous address: Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa, Current address: De Beers Group Services, Private Bag X01, Southdale, 2135, South Africa, e-mail: samantha.perritt@debeersgroup.com Search for other works by this author on: GSW Google Scholar R. Preston; R. Preston De Beers Group Services, Private Bag X01, Southdale, 2135, South Africa, e-mail: robin.preston@debeersgroup.com Search for other works by this author on: GSW Google Scholar F. Viljoen; F. Viljoen Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa, e-mail: fanusv@uj.ac.za Search for other works by this author on: GSW Google Scholar G. Van Der Linde G. Van Der Linde De Beers Group Services, Private Bag X01, Southdale, 2135, South Africa, e-mail: gert.vanderlinde@debeersgroup.com Search for other works by this author on: GSW Google Scholar Author and Article Information S. Perritt Previous address: Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa, Current address: De Beers Group Services, Private Bag X01, Southdale, 2135, South Africa, e-mail: samantha.perritt@debeersgroup.com R. Preston De Beers Group Services, Private Bag X01, Southdale, 2135, South Africa, e-mail: robin.preston@debeersgroup.com F. Viljoen Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa, e-mail: fanusv@uj.ac.za G. Van Der Linde De Beers Group Services, Private Bag X01, Southdale, 2135, South Africa, e-mail: gert.vanderlinde@debeersgroup.com Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online Issn: 1996-8590 Print Issn: 1012-0750 © 2015 Geological Society of South Africa South African Journal of Geology (2015) 118 (4): 439–454. https://doi.org/10.2113/gssajg.118.4.439 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S. Perritt, R. Preston, F. Viljoen, G. Van Der Linde; Morphology, Micro-Structure and Chemistry of A Deformed Garnet Megacryst Suite From Monteleo Kimberlite, Free State Province, South Africa.. South African Journal of Geology 2015;; 118 (4): 439–454. doi: https://doi.org/10.2113/gssajg.118.4.439 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 Garnet megacrysts found in the Cretaceous Group II Monteleo kimberlite (Free State province, South Africa) exhibit an unusual flattened and elongated morphology. Internally, the garnets are characterized by abundant kelyphite veins and microcracks, arranged as preferentially orientated microstructural sets. Numerous rod-like sulphide inclusions are present within the garnets, also characterized by a preferential orientation, with their long axes generally normal to the short axis of the host megacryst. The observed garnet megacryst morphologies and internal micro-structures are consistent with a shear-related deformation event, although the deformation mechanism remains unresolved. The deformation of the garnet megacrysts is inferred to have occurred prior to the entrainment of the garnets in their host kimberlite and is attributed to localized shearing in the lithospheric mantle, possibly associated with overlying crustal shearing that developed parallel to the Agulhas-Falkland Fracture Zone during Gondwana breakup. Variations in major and trace element concentrations indicate that the garnet megacrysts formed as a result of a simple fractional crystallization process, and pressure-temperature modelling indicates that they crystallized from a >1330°C melt at a depth of ~180 km, within a zone of metasomatism within the lithospheric mantle. A similarity in chemical composition between the megacrysts and garnets from associated lherzolitic lithologies suggests that percolation of the megacryst parental melt through the lithospheric mantle may have contributed to the metasomatism. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.