wooi Seventh Gondwana Symposium São Paulo, Brazil July 18-22, 1988 ABSTRACTS SPONSORING ORGANIZATIONS Subconmission on Gondwsna Stratigraphy, Conission on Stratigraphy, Inter- national Union of Geological Sciences (HJGS) Instituto de Geociências, Universidade de Sao Paulo, São Paulo Petróleo Brasileiro S.A. (PETROBRÁS), Rio de Janeiro Departamento Nacional da Produção Mineral (DNFM). Ministério das Minas e Emergia, Brasília Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), São Paulo Secretaria da Ciência e Tecnologia do Estado de São Paulo Comissão InterraLnisterial para os Recursos do Mar (CIRM), Brasília Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brasília Empresas Nucleares Brasileiras (NUCLEBRÁS), Rio de Janeiro Academia Brasileira de Ciências, Rio de Janeiro Sociedade Brasileira de Geologia, São Paulo Sociedade Brasileira de Geofísica, São Paulo Sociedade Brasileira de Paleontologia, são Paulo Centro de Investigação do Gondwana, Instituto de Geociências, Universida- de Federal do Rio Grande do Sul, Porto Alegre Eliane - Azulejos e Pisos, Criciúma Lapis Joham Faber S/A, São Carlos Instituto Antártico Argentino, Buenos Aires Geologia e Sondagens Ltda (GEOSOL), Belo Horizonte OTHER CONTRIBUTIONS IGCP Project 260 Earth's glacial record IGCP Project 237 Floras of the Gondwanic continents LiSÍ of Contents Page Gondwana Plate margins and fragmentation history (IV) (Monday, July 18) 01-07 Gondwana basins (II) (Monday, July 18) 19-30 Gondwana biota and biostratigraphy (III) (Tuesday, July 19) 31-46 Crustal structure and early history of Gondwana Cratonic areas (I) (Tuesday, July 19) 47-58 Gondwana biota and biostratigraphy (III) (Wednesday, July 20) 59-65 Gondwana basins (II) (Wednesday, July 20) 67-74 Gondwana basins (II) (Thursday, July 21) 75-92 Gondwana Plate margins and fragmentation history (IV) (Thursday, July 21) 93-106 Gondwana Plate margins and fragmentation history (IV) (Friday, July 22) 107-112 Gondwana basins (II) (Friday, July 22) 113-120 Posters 115-141 Author index 143 Subject index 147 In honor of Daniel Valencio. GONDWANA PLATE MARGINS AND FRAGMENTATION HYSTORY: Reconstruction problems (IVa) MONDAY, July 18 Yellow Auditorium 01 I* If TECTONIC EVOLUTION OF GONDWANALAND N. A. BOZHKO, Geological Department, Moscow State University, Moscow B-234, USSR. The tectonic evolution of Gondwanaland since Early Precambrian to Cenozoic times is shown in 22 paleotectonic maps, compiled on the new fit of the Supercontinent. Shown in five maps of the Early Precambrian is the formation of the primitive crust» as well as the evolution of granite-greenstone belts at*d of protoplatforms. As shown in the next four maps, the main feature? of the Upper Precambrian are the destruction of primitive crust and the formation of rift-related intrageosynclines, together with the appearance of zones of tectono-thermal reworking of basement and of the first orthogeosynclines, clearly related to The Upper Precambrian is the epoch of formation of the Prototethys and of the isolation of Gondwanaland, signalling the beginning of operation of modern mechanisms of Plate Tectonics. During the Paleozoic (next six maps), the inner zones of Gondwana- land were uplifted as platforms (cratons), with the development of both active and passive margins at the mobile periphery. In the Upper Paleozoic, extensive continental rifting took place and vast areas were covered by ice. The four Mesozoic maps register the outpouring of enormous amounts of tholeitic basalts, and the formation of both the global active Pacific margin and continuing continental rifting. The opening of the South Atlantic and the development of the Indian Ocean began in the Early Cretaceous. The three Cenozoic maps reflect, as a result of the fragmentation of the supercontinent, the development of continental rifting and the related opening of several oceans, as well as the formation of deep- sea structures. The tectonic analysis revealed the existence of paleostructures of various ages which are clearly related to Gondwanaland margins and structures. As a result, three main structural epochs are distinguished during Gondwanaland evolution. The Supercontinent was part of Pangea up to the Late Riphean. Up to the Middle Paleozoic, it existed as an isolated land mass. Its fragmentation took place from the Upper Mesozoic onwards. 02 DISRUPTION OF EAST GONDWANALAMD (ANTARCTICA, AUSTRALIA, INDIA) BY CONTINENTAL EXTENSION BEFORE SEAFLOOR SPREADING. C.McA. POVELL and J.J. VEEVERS, Australian Plate Research Group, School of Earth Sciences, Hacquarie University, Nev South Vales, 2109, Australia. Australia and Antarctica occupied the eastern part of Gondwanaland until their breakup by the growth of the Southeast Indian Ocean in the aid-Cretaceous (96 Ha). The growth of the ocean was preceded by a stage of separation of the land areas of the continents that started in the aid-Jurassic (160 Ma). This separation was effected by 360 ka of extension (6 mm/year) by normal and listric faulting in a 600 ka wide zone represented today by the submerged continental aargins. In the first phase of seafloor spreading, froa the aid-Cretaceous to the Eocene (45 Ha), the Southeast Indian Ocean grew to a width of 500 ka at the slow rate of 10 aa/year, and in the second phase grew another 2600 ka at a fast rate of 60 aa/year. Though entailing little «ore than l/10th of the total separation, the stage of extension between Antarctica and Australia has a significant implication for the node of separation of India froa Antarctica and Australia. Froa 160 Ma to 132.5 Ma (M-ll), India-Australia rotated froa Antarctica by continental extension between Australia and Antarctica and largely transform-fault motion between the Coroaandel Coast •argin of India and the Kron Prins 01av Kyst aargin of Antarctica. In the second stage, from 132.5 to 96 Ma, when continental extension between Australia and Antarctica was greatest, India moved northwestward about a newly determined pole of rotation away from Australia/Antarctica, producing M-10 and younger magnetic anomalies and many bathymetric features off the western margin of Australia. 03 GONDWANAN RECONSTRUCTIONS FOR THE MESOZOIC AND LATE PALAEOZOIC Don H. TARLING, Geological Sciences, Plymouth Polytechnic, Plymouth PL4 8AA, England An examination o-f the magnetic anomaly patterns in the Indian Ocean, combined with an assessment o-f the location of continental -fragments, suggests an alternate sequence of reconstruction for East and West Gondwanaland in the Mesozoic (Tarling, 1987) which provide a somewhat simpler sequence of motions than previously. The final reconstruction for mid Jurassic times also appears to be more consistent with other geological and geophysical evidence. Palaeomagnetic evidence appears to be consistent with this model, but the available data arc still inadequate for testing most reconstructions. • The relationship between this super-continent and other tectonic units in central and eastern Asia is more difficult to determine as there are no magnetic anomaly patterns to delineate such positions. Geological and palaeomagnetic evidence suggests that most of these tectonic units formed the "northern" margin of Gondwanaland until mid Carboniferous times, but then formed separate units, only loosely linked with the Gondwanan super-continent until Cretaceous and later collisions formed present-day S.E. Asia. 04 THE DISTRIBUTION OF LATE PROTEROZDIC TO EARLY PALAEOZOIC ROCK SEQUENCES IN GONDtMNA : A FRAMEWORK FOR UNDERSTANDING THE BUILDING BLOCKS A» THE FUSION PROCESS OF GOMMAMA. «•arte* J. DE HIT. Bernard Price Institute of Geophysical Research, IMversity of the Wit*atersra»d. P.O. «Us, 2050, Sowth Africa. With the new 1:10 million geological nap of Gondwana as the data base, a aap has been coapiled, showing the distribution and character of those rock sequences and associated tectonic structures throughout Gondwana, which date between c. 1.0 and 0.45 Ga. This interval facilitates study of the Upper Proterozoic fusion of proto-Gondwana fragments into the super-continent. This period overlaps the onset of extensive Early Phanerozoic global rifting by about 0.15 Ga. The disposition of the Upper Proterozoic supercontinent may originally have been contained within a globally encircuiating belt, but was almost entirely confined to one hemisphere by the end of the Palaeozoic. When the late Proterozoic-Early Palaeozoic geology of Gondwana is viewed in the consolidated framework of this map, many disparate facts known to the viewer are quickly perceived in a fresh and comprehensible way. For example, the central West African-eastern Brazilian belts, and the Arabian- East African-Mozambique belts form two major trans-Gondwana tectonic belts, which appear to have a common linkage in the Oamaran-Irumide-Zambezi fold belts. Together they form one immense trans-Gondwana mobile belt, with both internal and external foreland fold and thrust belts. Moreover, southern Africa clearly emerges as a common focal point from where these suture zones can be linked to the Proterozoic-Early Phanerozoic mobile belts of the Antarctic and Australian segments of Gondwana. Tectonic features of these belts will be highlighted in this talk. When these well-defined, major mobile belts, and the cratonic fragments separating them, are scrutinised on the Gondwana map, they soon raise provocative questions about the birth of Gondwana: (1) What were its proto-fragments; how and when did they collide? (2) Do the tectonic belts relate to local Wilson cycles? (3)