P-T-fluid evolution in the Mahalapye Complex, Limpopo high-grade terrane, eastern Botswana

Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P-T-fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high-grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well-developed textures inferred to record metasomatic reactions, such as Bt ⇒ And + Qtz + (K₂O) and Bt ± Qtz ⇒ Sil + Kfs + Ms ± Pl, and zonation of Ms Bt + Qtz And + Qtz and Grt Crd Pl Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO₂ and H₂O (a_H2O^fl = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P-T path. The P-T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low-pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga.