The continental assemblyn of SW Gondwana (Ediacaran to Cambrian): a synthesis

CASQUET, C.; RAPELA, C.W.; PANKHURST, R.J; BALDO, E.G; GALINDO, C.; DAHLQUIST, J.A.; VERDECCHIA, S.; MURRA, J.A.; FANNING, C.M

Madrid

Conferencia; Gondwana 15; 2014

Geological Society of Spain

SW Gondwana resulted from complex interplay between continental amalgamation and dispersal between - 650 and 490 Ma. The main cratons involved were Laurentia, AmazoniaMARA (Proterozoic Maz- Arequipa- Rio Apa, Casquet et al., 2012), Kalahari, Rio de la Plata (RPC), Congo and East Antarctica (Mawson block). Several collisional orogenic belts resulted, notably the East Africa- Antarctica, Brasiliano- Panafrican, Pampean- Saldania, and Ross- Delamerian orogens. East-Antarctica broke away from the western margin of Laurentia in Rodinia. After a long drift and counter-clockwise rotation (Dalziel, 2013) it collided with Congo and Kalahari to produce the southern part of the left-lateral transpressional East Africa- Antarctica orogen between 580 and 550 Ma, completing the amalgamation of East Gondwana. The Trans-Antarctic margin became an active one in the Ediacaran and subduction of the Pacific Ocean lithosphere occurred throughout the Paleozoic, forming a tract of the Terra Australis orogen. NW- SE directed compression in Late Cryogenian and Early Ediacaran times promoted closure of the Adamastor Ocean, resulting in the left-lateral transpressional Brasiliano- Pan African orogeny between 650 and 570 Ma. The Pampean orogenic belt to the west of the RPC resulted from right-lateral collision between Laurentia and its eastern extension MARA on the one hand and Kalahari- RPC on the other. Ocean opening started at - 630 Ma and subduction and further collision took place between 540 and 520 Ma, coeval with the northward drift of Laurentia (- 540 Ma) away from MARA and the consequent formation of the proto-Andean margin of Gondwana. The margins of the intervening Puncoviscana ocean were covered by Laurentia-derived siliciclastic sediments and carbonates on the MARA side between 630 and - 540 Ma (Rapela et aI, 2014; this symposium), and by the marine siliciclastic Puncoviscana Formation on the other. The latter formation, deposited between a 570 and -530 Ma, received input from large alluvial fans descending from juvenile Mesoproterozoic and Neproterozoic sources (new Hf isotope evidence) largely located in the southern East Africa- Antarctica orogen. The Pampean orogen extended into the Saldania--Gariep orogen of southern South Africa (545- 520 Ma) and was apparently discordant to the earlier Brasiliano- Pan African orogen. In late-Early to late Cambrian times the Pampean- Saldania realm evolved into a passive margin with siliciclastic platform sedimentation. The Pampean-Saldania realm was separated from the active Trans-Antarctic margin of East Antarctica by an inferred transform fault in Ediacaran to Cambrian times. Regional NW-SW shortening in the Ediacaran became N- S directed in the Cambrian, suggesting a major plate reorganization at this time.   Casquet, C., Rapela, C.W, Pankhurst, Rj., Baldo, E.G., Galindo, C., Fanning, C.M., Dahlquist,].A., Saavedra, ]., 2012. A history of Proterozoic terranes in southern South America: From Rodinia to Gondwana. Geoscience Frontiers, 3(2), 137-145. Dalziel, I.WD., 2013. Antarctica and supercontinental evolution: clues and puzzles. Earth & Environmental Science Transactions of the Royal Society of Edimburg, 104, 1-14. Rapela et al., 2014. Early Paleozoic construction of Southwest Gondwana: evidence from detrital zircons in the Sierra~ Pampeanas. Gondwana 15, Madrid, Abstracts volume.