PROMOTING ACCESS TO AFRICAN RESEARCH

Tanzania Journal of Science

Log in or Register to get access to full text downloads.

Remember me or Register



Contact Metamorphism in the Supracrustal Rocks of the Sukumaland Greenstone Belt in the North West Tanzania

N Boniface

Abstract


Biotite-granite intrusions in meta-ironstones at Geita Hills and the Bukoli alkali-granite intrusion in metabasites at Mawemeru area produced heat that baked the respective country rocks through epidote-amphibolite- to amphibolite-facies. Critical and informative mineral assemblages in the metairostones of Geita Hills are garnet-grunerite-epidote-quartz and garnetferrogedrite- biotite-quartz and in the metabasites of Mawemeru is ferrotschermakite-(Naplagioclase)- quartz. Peak temperatures ranging between 438°C and 544°C were calculated from the above mineral assemblages and a pressure not exceeding 3 kbar was inferred to from the composition of magnesium-iron amphiboles (grunerite with XFe ratio of 0.83, i.e. Gru83). Hornfels textures in the metaironstones are suggested by euhedral poikiloblastic garnet and quartz with grain boundaries intersecting at approximately 120° (granoblastic polygonal texture) and biotite aggregates forming an interlocking network of elongate grains aligned in all directions and bounded by rational crystal faces (decussate texture).

Keywords: Contact metamorphism, intrusions, Sukumaland Greenstonebelt, Neoarchaean

Tanz. J. Sci. Vol. 37 2011, 144-155



AJOL African Journals Online