Proterozoic East Gondwana: Supercontinent Assembly and Breakup
This volume focuses on Late Mesoproterozoic to early Cambrian events related to Gondwana assembly and break up. The nineteen papers provide a comprehensive review including advanced knowledge and new data from all critical areas of East Gondwana. The recent knowledge of the evolution of East Gondwana, which was regarded as an integral part of the Mesoproterozoic supercontinent Rodinia, is the major theme of the volume, which is reinforced by highlighting this radical and new understanding of the evolution of this region.
This volume is of use as both a text and reference book for Earth Science postgraduates, and should appeal worldwide to professional geologists with an interest in Rodinia, Gondwana and that important transition from the Proterozoic to the Phanerozoic Earth.
Neoproterozoic deformation in central Madagascar: a structural section through part of the East African Orogen
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Published:January 01, 2003
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CiteCitation
Alan S. Collins, Simon Johnson, Ian C. W. Fitzsimons, Chris McA. Powell, Bregje Hulscher, Jenny Abello, Théodore Razakamanana, 2003. "Neoproterozoic deformation in central Madagascar: a structural section through part of the East African Orogen", Proterozoic East Gondwana: Supercontinent Assembly and Breakup, M. Yoshida, B. F. Windley, S. Dasgupta
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Abstract
The Itremo region of central Madagascar has an importance in the evolution of the East African Orogen (EAO) that belies its size. Unusually for the southern EAO (Mozambique Belt), it is made up of low-grade metasedimentary rocks and therefore preserves an almost unique window into upper crustal deformation during this key period of the Gondwana supercontinent cycle.
In this paper new field mapping of three linked regions in the Itremo Sheet and in the upper part of the underlying mid-crustal Antananarivo Block are presented. From these a complete structural section through the eastern Itremo Sheet is produced and the complex deformation record preserved there is then discussed.
An early deformation (D1) consists of 10 km scale recumbent isoclinal folds that predate intrusion of a c. 780–800 ma igneous suite. Metamorphic aureoles around these plutonic bodies overprint D1-related fabrics. Local deformation accompanies intrusion of the c. 780–800 Ma, suite (D2). Extensive E–W contractional deformation occurs between 780 and c. 570 Ma, that is here amalgamated as a composite D3 event, which includes thrusts and at least two phases of upright folds. Post-551 Ma, normal shearing (D4) marks the boundary between the Itremo Sheet and the underlying Antananarivo Block (the Betsileo Shear Zone), and may have also been responsible for formation of the Saronara Shear Zone. Finally, E–W open folding and dextral shear zone development marks a late N–S contractional event that is interpreted as a far-field response to collision between the northern Bemarivo Belt and central Madagascar.