This paper documents the 20 to 60km wide N-S trending Angavo Shear Zone (ASZ) in central Madagascar and its tectonic implications by examining its structural styles, kinematics and geometry. Our study indicates that the ASZ is characterized by at least two ductile Late Proterozoic deformation events (D1 and D2) followed by a brittle neotectonic deformation (D3). The early D1 event produced a regionally extensive S1 foliation, stretching/flattening mineral lineation L1 and symmetrical structural fabrics such as recumbent and isoclinal intra-folial folds (F1), implying a flattening deformation. D1 deformational fabrics are locally overprinted by D2 structures. D2 is characterized by a penetrative S2 foliation, shallow south plunging L2 lineation, asymmetric and sheath folds (F2) consistent with a right lateral sense of movement exhibited by delta- and sigma-type porphyroclast systems and asymmetric boudinage fabrics. D2 represents a non-coaxial flow regime formed in a dextral west over east shear zone during a partitioned transpression in response to east-west-directed compression during the assembly of Gondwana. A close resemblance with the Achankovil shear zone in India is noticed; however the continuation of the ASZ in Africa is uncertain.
Bibliographical noteFunding Information:
This work was supported by the NSF grant EAR-0221567 awarded to T. Kusky, and some of the field work was carried out under the auspices of the British Geological Survey and the U.S. Geological Survey , under the auspices of the World Bank Development of Madagascar Program and the Mineral Resource Assessment of Madagascar Project . The study was jointly funded by the National Natural Science Foundation of China (Grants 40821061 and 91014002 ) and the Ministry of Education of China ( B07039 ). We greatly appreciate Kathryn M. Goodenough for her constructive suggestions. We thank Alan S. Collins and an anonymous reviewer for comments that substantially improved the manuscript.
- Angavo Shear Zone