Pseudotachylyte and associated fault rocks at Alabameta area, Osun state, southwestern Nigeria.

Abstract

This paper reports the occurrence of pseudotachylytes and associated fault rocks along Ifewara fault at Alabameta within the Ife-Ilesha Schist Belt, Southwestern Nigeria. The fault separates the schist belt into two lithostratigraphic units: a western unit composed mainly of mafic to ultramafic rocks and metapelites and an eastern unit composed of quartzites, quartz schist, metapelites and quartzo-feldspathic (granite) gneisses. These were intruded by granites and pegmatites.
The area was affected by three main episodes of deformation. D1 produced recumbent folds probably associated with big nappes and are responsible for the flat lying foliation (S1) common in this area. D2 produced upright, tight to isoclinal folds responsible for the general north-south trending foliation (S2) and major lithological banding of the belt that define the structural grain of the area. D3 is associated with the major transcurrent faulting (the Ifewara fault), this produced mylonites in the north, near Iwaraja. To the south, the mylonites are locally cut by pseudotachylyte, especially near Alabameta.
The presence of pseudotachylyte is interpreted as a result of frictional melting along the Ifewara Fault, probably associated with a late, high-level movement along the fault.


IFE Journal of Science Vol. 9 (2) 2007 pp. 191-202