TECTONIC EVOLUTION OF THE NEOPROTEROZOIC ADOLA BELT OF SOUTHERN ETHIOPIA - EVIDENCE FOR A WILSON CYCLE PROCESS AND IMPLICATIONS FOR OBLIQUEPLATE COLLISION

The Adola Belt of southern Ethiopia comprises three major lithotectoni c units: (i) metamorphosed passive continental margin sediments, mafic -ultramafic rocks and associated pelitic metasediments of the Kenticha terrain; (ii) high-grade gneisses and schists, intruded by syn-tecton ic calc-alkaline magmatic rocks in the central and western part of the Adola Belt; and (iii) low-grade metavolcano-sedimentary and mafic-ult ramafic rocks, and associated granitoids of the Megado terrain. The ge ochemical signatures and structural features of the rock associations of the Adola Belt may be interpreted to reflect a Wilson Cycle process , i.e., evolution of a passive continental margin and formation of oce an floor in the Kenticha Terrain, W-directed subduction, are developme nt in the Megado Terrain, closure of an oceanic basin of unknown size and collision of crustal blocks. Oblique plate convergence led to a se quence of continuous deformation events, namely (i) subduction-related folding and thrusting (D-1), which culminated in the obduction of maf ic-ultramafic assemblages onto the passive continental margin sediment s, ii) collision of crustal blocks (D-2), leading to re-folding of D-1 structures, development of upright N-S-trending folds and generation of reverse faults and shear zones, and finally (iii) evolution of sini stral strike-slip shear zones (D-3) with N and NW orientations, the la tter being interpreted as antithetic Riedel Shears. All structures of the Adola Belt are compatible with a NW-oriented stress regime and hen ce can be interpreted to reflect sinistral transpression. In a larger geodynamic framework, structures related to this collision event and t he stress regime that produced them are consistent with the position o f East and West Gondwana during the Neoproterozoic.