POWELL, Christopher McA and PISAREVSKY, Sergei A., Tectonics Special Research Centre, The University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia, 6009, Australia,

Late Neoproterozoic passive continental margins around Laurentia indicate that it was part of larger continental assembly, Rodinia, in the latest Mesoproterozoic and Neoproterozoic. Rodinia’s configuration has recently come under question, with several alternatives proposed for which continental blocks lay along Laurentia’s passive margins. The Amazon craton is assumed but not proven to have lain adjacent to the eastern margin of Laurentia, with Baltica adjacent to northeastern Laurentia. There are at least two versions of where Australia lay adjacent to Laurentia, and the relationship of Siberia to Laurentia is uncertain. Palaeomagnetic data suggest that the Kalahari block could have been part of Rodinia by 1020 Ma, but the Congo/Sao Francisco block may not have been. Widespread continental breakup between 800 and 700 Ma led to the formation of the Pacific Ocean, at the expense of subduction of the older global ocean, Mirovia. According to available palaeomagnetic data, East Gondwanaland (Australia, Antarctica, India and NE Madagascar) was not assembled until 650–600 Ma. There are at least two possible interpretations of the late Neoproterozoic palaeomagnetic data from Laurentia. one with Laurentia rotating rapidly poleward between 615 Ma and 580 Ma and then back to the Equator by 530 Ma, and the other with Laurentia remaining at relatively low latitude throughout the Vendian. Gondwanaland formed by the convergence of the Amazonia–West African block and Australia–Antarctica–India closing both the Brazilide and Mozambique Oceans between 630 and 540 Ma. Final amalgamation of Gondwanaland may not have been completed until the earliest Cambrian, at approximately the same time as subduction was initiated along the Pacific margin of Antarctica. The earliest glaciation Neoproterozoic glaciations (ca. 750 to 720 Ma, Sturtian–Rapitan) occurred during Rodinian breakup, but the second major glacial interval (ca. 600 Ma, Marinoan–Ice Brook–Varangerian) is associated with the closure of the Brazilide and Mozambique oceans.

Earth System Processes - Global Meeting (June 24-28, 2001)
Session No. T4
Critical Transitions in Earth History and Their Causes
Edinburgh International Conference Centre: Pentland
10:00 AM-4:30 PM, Wednesday, June 27, 2001