The eastern margin of the Tanzanian Craton in the Dodoma-Mpwapwa area : preliminary findings

摘要

A number of traverses have been undertaken across a ca. 45 km section of the north-south oriented eastern margin of the Tanzanian Craton between Dodoma and Mpwapwa, Central Tanzania. The boundary is a SE-dipping zone of high strain between about 1 and 2 km wide. The rocks of the eastern craton are uniformly composed of coarse-grained, grey, migmatised granodiorite gneisses which are heterogeneous at outcrop scale but are regionally homogeneous. The orthogneisses have no regionally consistent fabric and foliations are variably oriented at outcrop scale. However, there is a gradual increase in strain eastwards towards the edge of the craton, manifest as an increasingly strong, regionally consistent, E to SE-dipping foliation. This strain increase eventually leads to mylonitic and porphyroclastic planar fabrics and strong, uniformly SE-plunging, linear fabrics. In most structural domains planar fabrics are predominant, but these alternate with minor domains dominated by linear fabrics, with fold mullions locally developed. The kinematics of the high-strain mylonites show a consistent, top-to-the-NW (oblique) sense of movement. The frontal thrust zone grades laterally into steep sinistral and dextral oblique strike-slip shear zones to the north and south respectively. The contact is a single wide deformation zone in the northern and southern segments of the study area, with a more complex imbricate belt in the central part.udud