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Definition of tectonostratigraphic terranes in the Mauritanide, Bassaride, and Rokelide orogens, West Africa

By
J. P. Lécorché
J. P. Lécorché
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R. D. Dallmeyer
R. D. Dallmeyer
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M. Villeneuve
M. Villeneuve
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Published:
January 01, 1989

The West African orogens (Mauritanides, Bassarides, Rokelides) record a locally complex, polyphase, tectonothermal evolution. The earliest event corresponded to westward rifting of a continental fragment from the West African craton at ca. 700 Ma. This led to development of a rift-facies lithotectonic succession that included sedimentary units and intracontinental igneous sequences. Rifting must have been of limited extent because a western ensialic arc began to develop as early as 680 Ma. The associated convergence culminated in an episode of folding and metamorphism at ca. 650 Ma (Pan-African I orogenesis) in the Mauritanides and Bassarides.

Following widespread deposition of Late Proterozoic glacial and flyschoid sediments, a second tectonothermal event (most penetratively developed in the Rokelides) occurred between ca. 575 and 550 Ma (Pan-African II orogenesis). This may have resulted, in part, from collision of the Guyana craton (South America) and southern portions of the West African craton.

The West African orogens were marked by general tectonic quiescence throughout most of early and middle Paleozoic time. Late Paleozoic (ca. 300 Ma) collision of Gondwanaland and Laurentia resulted in eastward translation of previously tectonized Mauritanide units over their foreland, and emplacement at highest structural levels of previously imbricated nappes, which include sequences with poorly defined palinspastic origins. The late Paleozoic (Hercynian) transport was largely intracontinental, and only westernmost portions of the exposed Mauritanides record a penetrative tectonothermal overprint.

The polyphase tectonothermal evolution of the West African orogens complicates definition of tectonostratigraphic terranes. Three preliminary and likely composite terranes are outlined. These include: (1) sequences related to the initial Late Proterozoic rifting; (2) ensialic arc sequences and their continental hosts (with uncertain affinity to the West African craton); and, (3) westernmost, variably retrogressed and complexly imbricated continental units with poorly defined palinspastic affinities.

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GSA Special Papers

Terranes in the Circum-Atlantic Paleozoic Orogens

R. D. Dallmeyer
R. D. Dallmeyer
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Geological Society of America
Volume
230
ISBN print:
9780813722306
Publication date:
January 01, 1989

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