The relations between Gondwana and the adjacent peripheral Cadomian domain—constrains on the origin,history, and paleogeography of the peripheral domain |
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| Institution: | 1. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8550, Japan;2. Graduate School of Environmental Studies, Tohoku University, Sendai, Miyagi 980-8579, Japan;3. Department of Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro, Tokyo 152-8550, Japan;4. Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan;5. State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;6. Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1, Komaba, Meguro-ku, Tokyo 153-8902, Japan;1. Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague 12843, Czech Republic;2. Institute of Geosciences, Goethe University, Altenhöferallee 1, Frankfurt am Main 60438, Germany |
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| Abstract: | This work examines the relations between the Cadomian-type peri-Gondwana blocks and West and North Africa and Arabia (WNA) and the sediments derived therefrom during the Neoproterozoic. This provides insights regarding the formation, development, and paleogeography of the Cadomian domain, and when interpreted in the framework of plate tectonic processes allows proposing an internally consistent, though tentative, picture of the Neoproterozoic history of the domain before the Cadomian orogeny. Since WNA is built of terranes that were originally dispersed over a ≥ 2000 km wide area (E–W), it was only when their assembly was well advanced (≤ ca. 680–650 Ma ago) that they formed a continuous continental area with a well-defined margin next to which a continuous peripheral Cadomian domain could be shaped. Most likely it formed by accretion of various elements to the newly formed WNA margin, which is supported by several lines of evidence. The exposed basement rocks of the Cadomian domain are usually ≤ 600–580 Ma old (Late Ediacaran and Early Paleozoic). Before the Cadomian orogeny much of the domain comprised marine basins, several hundred kilometers wide, filled mainly by thick siliciclastics associated with variable amounts of igneous rocks. A large fraction of the sediments was produced by extensive erosion of WNA, but the West African Craton probably had a secondary role as a sediment source. Subduction-related igneous rocks occur in basinal areas close to the northern active margin of the Cadomian domain, and these areas were affected by the Cadomian orogeny. There arc-derived, rather than WNA-derived detritus appears to be present, proving the existence of adjacent magmatic arcs, although the arcs are little exposed. As sediment transport was necessarily down-slope, the distribution of WNA- and arc-derived detritus and its termporal changes provide insights regarding the slopes of basin-floors and thus the paleogeography, while changes in their distribution most likely record tectonic activity. However, these issues still require further study. The Late Ediacaran paleogeographic setting recorded by the exposures is interpreted as comprising backarc basins and magmatic arcs, with igneous activity and deformation being more pronounced in the outboard parts of the domain (including basinal areas), similar to the situation in the Western Pacific. It is hypothesized that, as in the latter area, the entire system was controlled by retreat (roll back) of the bordering subduction zone, and that this setting was produced ca. 600 Ma ago or somewhat earlier by modification of a pre-existing active margin that was initially shaped by the accretion of the Cadomian domain to WNA. However, the absence of direct evidence about the early history of the domain does not allow interpretation beyond this general picture. |
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