| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Journal of Petrology | Volume 44 | Number 6 | Pages 1121-1144 | 2003
© Oxford University Press 2003
Ultrahigh-Temperature Metamorphism and Multistage Evolution of Garnet–Orthopyroxene Granulites from the Proterozoic Epupa Complex, NW Namibia
MINERALOGISCHES INSTITUT, UNIVERSITÄT WÜRZBURG, AM HUBLAND, 97074 WÜRZBURG, GERMANY
Telephone: ++49-(0)931-8885406. Fax: ++49-(0)931-8884620. E-mail: soenke.brandt{at}mail.uni-wuerzburg.de
Migmatitic semipelitic granulites of the Proterozoic Epupa Complex, NW Namibia, underwent ultrahigh-temperature metamorphism as is indicated by the high alumina contents of orthopyroxene (8–11 wt % Al2O3) coexisting with garnet. Peak P–T conditions of 
970°C and 9·5 kbar are calculated from conventional garnet–orthopyroxene geothermobarometry. Conspicuous reaction textures document a multistage retrograde uplift–cooling path: post-peak decompression initially under still ultrahigh temperatures (940°C and 8 kbar) is recorded by coronas of aluminous orthopyroxene + plagioclase around garnet. Continued decompression (6 kbar and 800°C) is evident from subsequently formed symplectites of cordierite + lower-alumina orthopyroxene and cordierite + lower-alumina orthopyroxene + spinel, both replacing garnet. Subsequent regrowth of garnet and biotite, mainly formed at the expense of the symplectitic phases, presumably reflects back-reactions with crystallizing melts during near-isobaric cooling to upper amphibolite-facies conditions (660°C and 5 kbar). Rims of low-alumina orthopyroxene around retrograde biotite point to renewed decompression subsequent to cooling. The deduced clockwise retrograde P–T path reflects the thinning and later cooling of former thickened lower crust. Because of the limited structural and geochronological data it remains uncertain whether initial ultrahigh-temperature metamorphism was induced by a collision event or by crustal extension.
KEY WORDS: Namibia; geothermobarometry; granulite; P–T path; ultrahigh-temperature metamorphism
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  K. Sato, T. Miyamoto, and T. Kawasaki Fe2+-Mg partitioning experiments between orthopyroxene and spinel using ultrahigh-temperature granulite from the Napier Complex, East Antarctica Geological Society, London, Special Publications, January 1, 2008; 308(1): 431 - 447. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Druppel, T. Wagner, and A. J. Boyce EVOLUTION OF SULFIDE MINERALIZATION IN FERROCARBONATITE, SWARTBOOISDRIF, NORTHWESTERN NAMIBIA: CONSTRAINTS FROM MINERAL COMPOSITIONS AND SULFUR ISOTOPES Can Mineral, August 1, 2006; 44(4): 877 - 894. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Das, S. Bose, I. Ohnishi, and S. Dasgupta Garnet-spinel intergrowths in ultrahigh-temperature granulite, Eastern Ghats, India: Possible evidence of an early Tschermak-rich orthopyroxene during prograde metamorphism American Mineralogist, February 1, 2006; 91(2-3): 375 - 384. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. DRUPPEL, J. HOEFS, and M. OKRUSCH Fenitizing Processes Induced by Ferrocarbonatite Magmatism at Swartbooisdrif, NW Namibia J. Petrology, February 1, 2005; 46(2): 377 - 406. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Kroner, J. Konopasek, A. Kroner, C.W. Passchier, U. Poller, M.T.D. Wingate, and K.H. Hofmann U-Pb and Pb-Pb zircon ages for metamorphic rocks in the Kaoko Belt of Northwestern Namibia: A Palaeo- to Mesoproterozoic basement reworked during the Pan-African orogeny South African Journal of Geology, September 1, 2004; 107(3): 455 - 476. [Abstract] [Full Text] [PDF]
|
|