Mechanically disrupted and chemically weakened zones in segmented dike systems cause vent localization: Evidence from kimberlite volcanic systems

Abstract

Research Article| September 01, 2007 Mechanically disrupted and chemically weakened zones in segmented dike systems cause vent localization: Evidence from kimberlite volcanic systems R.J. Brown; R.J. Brown 1Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar J. Kavanagh; J. Kavanagh 1Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar R.S.J. Sparks; R.S.J. Sparks 1Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar M. Tait; M. Tait 2De Beers Group Mining & Exploration, Venetia Mine, P.O. Box 668 Musina, Limpopo, Republic of South Africa 0900 Search for other works by this author on: GSW Google Scholar M. Field M. Field 3De Beers Group Services, Mendip Court, Bath Road, Wells BA5 3DG, UK Search for other works by this author on: GSW Google Scholar Author and Article Information R.J. Brown 1Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, UK J. Kavanagh 1Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, UK R.S.J. Sparks 1Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, UK M. Tait 2De Beers Group Mining & Exploration, Venetia Mine, P.O. Box 668 Musina, Limpopo, Republic of South Africa 0900 M. Field 3De Beers Group Services, Mendip Court, Bath Road, Wells BA5 3DG, UK Publisher: Geological Society of America Received: 03 Jan 2007 Revision Received: 19 Apr 2007 Accepted: 22 Apr 2007 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2007) 35 (9): 815–818. https://doi.org/10.1130/G23670A.1 Article history Received: 03 Jan 2007 Revision Received: 19 Apr 2007 Accepted: 22 Apr 2007 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation R.J. Brown, J. Kavanagh, R.S.J. Sparks, M. Tait, M. Field; Mechanically disrupted and chemically weakened zones in segmented dike systems cause vent localization: Evidence from kimberlite volcanic systems. Geology 2007;; 35 (9): 815–818. doi: https://doi.org/10.1130/G23670A.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 Deformation and alteration zones along kimberlite dikes hold clues as to how point-source volcanic vents can localize along sheet-like intrusions. Brittle deformation zones occur in host rock adjacent to kimberlite intrusions of the Swartruggens Kimberlite Dike Swarm, South Africa. Deformation includes local fracturing and brecciation and is associated with relay zones between offset dike segments. Breccia zones indicate dilation and hydraulic fracturing, and some zones along the dikes were affected by chemical corrosion, forming fresh cores surrounded by onion-skin concentric shells of altered rock. The alteration was caused by either exsolved magmatic volatiles moving in advance of the magma through the fracture, or by hydrothermal fluids. Consideration of the time scales needed for chemical corrosion of host rock requires intrusions to stall at depth prior to transport to higher crustal levels. Highly disrupted offsets could be preferred locations for explosive activity and initial vent formation as dikes approach the surface. A kimberlite pipe forms after magma breaks through to the surface; the altered zones are reamed out and fresh cores in spheroidally altered rock are incorporated into the pipe fill along with more angular country-rock material, as observed in layered volcanic breccias in kimberlite pipes at the Venetia Mine, South Africa. This model may have wider implications for the localization of conduits along dikes in other volcanic systems. Dike segmentation provides weak zones where hydrothermal fluids and magmatic volatiles can be preferentially channeled. Chemical corrosion can further weaken these zones, which may then become the locus for initial phreatic and phreatomagmatic explosions, creating shallow vents that can then channel magma to the surface during eruption. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.