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Geological Society of America Bulletin

Research Article| May 01, 2003 Ultrahigh-temperature metamorphism in the lower crust during Neoarchean Ventersdorp rifting and magmatism, Kaapvaal Craton, southern Africa Mark D. Schmitz; Mark D. Schmitz 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Samuel A. Bowring Samuel A. Bowring 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Mark D. Schmitz 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Samuel A. Bowring 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Publisher: Geological Society of America Received: 14 Feb 2002 Revision Received: 09 Aug 2002 Accepted: 22 Sep 2002 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (5): 533–548. https://doi.org/10.1130/0016-7606(2003)115<0533:UMITLC>2.0.CO;2 Article history Received: 14 Feb 2002 Revision Received: 09 Aug 2002 Accepted: 22 Sep 2002 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Mark D. Schmitz, Samuel A. Bowring; Ultrahigh-temperature metamorphism in the lower crust during Neoarchean Ventersdorp rifting and magmatism, Kaapvaal Craton, southern Africa. GSA Bulletin 2003;; 115 (5): 533–548. doi: https://doi.org/10.1130/0016-7606(2003)115<0533:UMITLC>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 A diverse suite of ultrahigh-temperature (UHT) granulite xenoliths from kimberlites of the central Kaapvaal craton (South Africa) record the deep crustal manifestation of Neoarchean Ventersdorp extensional tectonics and magmatism. U-Pb geochronological data for texturally characterized metamorphic zircon and monazite from a number of metasedimentary (garnet + quartz ± sapphirine ± sillimanite ± antiperthite) UHT granulites are combined with published geothermobarometry to elucidate the pressure-temperature-time (P-T-t) path of metamorphism. Prograde metamorphic growth of zircon and monazite indicates ramping of lower crustal temperatures ≥25 Ma prior to peak UHT metamorphic conditions at ca. 2720–2715 Ma. The subsequent cooling path is established by dating of 2690 Ma zircon in retrograde kyanite-rich leucosomes, indicating initial cooling rates of ≥10 °C/Ma. Preservation of peak and prograde monazite dates through the UHT conditions support a very high volume diffusion closure temperature for this mineral, similar to that of zircon (>1000 °C).The 5–10 Ma duration of UHT metamorphism in the lower crust is directly correlative with the rapid eruption of the Ventersdorp flood basalts through the central Kaapvaal craton at 2714 ± 8 Ma, and associated crustal melting, plutonism, and widespread extensional tectonics. UHT metamorphism is postulated to have occurred in response to nonuniform intracratonic lithospheric thinning and superimposed magmatic heat advection. The links between upper and lower crustal manifestations of 2.7 Ga magmatism and extension support the hypothesis that the present-day flat seismic Moho of the central and western Kaapvaal craton is a lower crustal rheological response to Ventersdorp tectonomagmatism. The lithospheric thermal gradient necessitated by the UHT lower crustal granulites demands a transient removal of the thermal lithosphere localized along the north-northeast–trending axis of the Ventersdorp rift at 2.72 Ga. However, contemporaneous maintenance of a coherent mantle keel with "cratonic" thermal gradients 200 km distal to the rift is required in order to preserve ancient (3.2–2.9 Ga) diamondiferous lithosphere. The contrast between the craton-wide geography of crustal extension and the more restricted localization of thermal effects in the lithospheric mantle embodies a profound crust-mantle decoupling in the Kaapvaal craton during intracratonic rifting, and bears upon our understanding of the generation and preservation of cratonic lithospheric mantle keels. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Ultrahigh-temperature metamorphism in the lower crust during Neoarchean Ventersdorp rifting and magmatism, Kaapvaal Craton, southern Africa