Showing papers on "Gondwana published in 1984"

Structure and evolution of the Himalaya–Tibet orogenic belt

Abstract: The 1981 French–Chinese expedition to Tibet focused on the Lhasa block, extending earlier coverage 400 km north of the Tsangpo suture. The Lhasa block stood between 10 and 15° N latitude over most of the Upper Cretaceous and Eocene and, if Gondwanian in origin, had detached from Gondwana by early Permian. Seismic profiles reveal a complex Moho topography resulting both from multiple continental thrusting and large-scale strike-slip faulting. Subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated. This study emphasizes the role of smaller blocks in the accretion of the continental mosaic.

Permian-early Mesozoic tectonism and continental margin formation in Israel and its implications for the history of the Eastern Mediterranean

Abstract: Summary The Early Mesozoic tectonic reorganization of the Tethys region also affected the Levant area. Here two processes were superimposed: (a) The pattern of long-wavelength vertical motions of the Arabo-Nubian platform changed in the Late Permian when Israel and nearby areas began to subside. (b) Rifting occurred in this subsiding area, probably in several phases: Late Anisian (and Ladinian?), Carnian-Norian, and Liassic. Differential movements reached 2–3 km and magmatism occurred in the Liassic and perhaps also in the Triassic. The tectonism was strongly felt up to 50 km landward of the present coast. The crust was thinned and modified under the present continental margin and in the main rifts. Passive margin conditions were established in Late Liassic times over the previously faulted area. Later in the Jurassic a carbonate shelf was constructed along this subsiding margin; its basinward edge was 1–1.5 km high, which shows that the adjacent SE Mediterranean was already a deep sea. Hence this basin and its passive margin are considered to have been shaped by the Early Mesozoic rifting which is recognized in Israel. The rifting process probably signifies oblique separation of the Tauride block from the Levant part of Gondwana.

Paleozoic evolution of the Armorica plate on the basis of paleomagnetic data

Abstract: New paleomagnetic data support the contention that Armorica and Gondwana formed a coherent block until Ordovician time. However, by Early Devonian time, Armorica collided with the North American–northern European assembly to form the Old Red Continent, and the collision itself was responsible for the Acadian orogeny, not for the earlier Taconic orogeny as postulated previously. The Carboniferous collision of Gondwana with the Old Red Continent subsequently formed Pangaea and produced the Appalachian-Hercynian orogeny.

Proterozoic stratigraphy and tectonic framework of China

Abstract: The time span of the Proterozoic is taken as from 2600 to 600 Ma with subdivision boundaries at 1850 and 1050 Ma respectively, as 2600 Ma seems more appropriate for the initial Proterozoic in China, Siberia and parts of Gondwanaland, and 600 Ma is an inferred age of the Precambrian–Cambrian boundary based on recent study of the Yangtze Gorge section. The Proterozoic of China includes the Lower Proterozoic Wutaian and Hutuo-an, the Middle Proterozoic Changchengian and Jixianian and the Upper Proterozoic Qingbaikou-an and Sinian.Based mainly on tectono-sedimentary types and associations, seven stratigraphic super-regions are recognized in the Proterozoic of China and stratigraphic successions of various representative regions are shown in two tables, one for the Sinian and another for the Pre-Sinian Proterozoic. Palaeogeographic outline of the main super-regions and chronometric limit of the principal stratigraphic units are briefly discussed. Three types of stable Sinian successions are distinguished, the Yangtze type, the Quruktagh type and the Jiaoliao type, which are correlated mainly on the basis of tillite horizons and of sabelliditids and the Ediacara type of fossils. Semi-stable and mobile types of Sinian deposits in Southeast China are also briefly mentioned.The Proterozoic tectonic units of China and the nature of their boundaries are shown on a sketch map showing basement structures. Crustal sectors of continental nature are designated as continental tectonic domains, while broad and complicated crustal sectors of mainly transitional and partly oceanic nature may be called continental margin tectonic domains. The boundaries between these domains are usually the principal crustal consumption zones. On this basis, three continental domains, the North China, the South China and the Southern (Gondwana), and two continental margin domains, the Northern (Siberian–Mongolian) and the East China, are distinguished. Platforms, continental nuclei, massifs and uplifts are used to denote subdivisions within the tectonic domains. The development of aulacogens is an outstanding feature in the continental domains, especially in the Middle Proterozoic. Aulacogens may be classified into an intra-platform type and a platform margin type. Early Proterozoic aulacogens are usually brachy-axial and intermittent, and show conspicuous deformation at closure, much like a geosyncline. Thirteen aulacogens of different types are shown on the sketch map.The boundary nature of continental domains is analysed in terms of island arcs and marginal seas, and also of emplacement of granite rocks in border parts. The North China Domain was basically consolidated at around 1850 Ma and has a passive northern margin stretching from Nei Mongol to Central Tianshan, but the southern margin was active and was twice subducted by the Qinling marine realm at 1700 and 1000 Ma approximately. The Yangtze Platform was not completely consolidated until 1050 Ma BP but has a core older than 1850 Ma. A broad continental margin terrain had developed in the Jiangnan region and farther to the southeast in the Middle and Late Proterozoic. At least two island arc belts with interarc basins, an inner Fanjingshan and an outer Sibao, may be discerned in the Middle Proterozoic, and a Late Proterozoic island arc zone over 1000 km in length was developed along the southern margin of the Jiangnan Uplift, represented by the Banxi Group and equivalent strata. This kind of broad complicated continental margin tract which has a long development history may be called the open type or the West Pacific type.

The development of the SW Pacific Margin of Gondwana: Correlations between the Rangitata and New England Orogens

Abstract: Prior to formation of the Tasman Sea, the Late Paleozoic-Mesozoic Rangitata Orogen of New Zealand and New Caledonia abutted the Paleozoic New England Orogen of eastern Australia. Comparison of the record of Permian-Cretaceous igneous and deformational events from the two orogens suggests that their tectonic evolution was interrelated and is a consequence of convergent plate interaction along the southwest Pacific margin of Gondwana. The following relations are proposed: (1) termination of arc volcanism and widespread sedimentation in New England, together with the onset of regional deformation and crustal anatexis were synchronous with the commencement of volcanism and sedimentation within the Rangitata Orogen; (2) Early Permian andesitic volcanism in eastern New England represents an along-strike extension of the Brook Street terrane of New Zealand; (3) Late Permian regional deformation in New England coincides with both a break in subduction-related igneous activity in the New England and Rangitata Orogens and a shift in the locus of this activity; (4) Late Permian-Triassic calc-alkaline igneous activity in New England correlates with a phase of relatively continuous accumulation of pyroclastic material in the forearc basin of the Rangitata Orogen; (5) cessation of plutonism in New England corresponds with commencement of formation of the Esk Head Melange in New Zealand and the probable commencement of juxtaposition of the Te Anau and Alpine Assemblage; (6) Late Cretaceous epizonal plutons intruded into the New England Orogen are similar in character and age to those emplaced during the final phases of Rangitata orogenesis, and both appear to mark initial stages of rifting associated with formation of the Tasman Sea. The generation of Permian and Triassic igneous activity in eastern New England by convergent plate interaction results, on present reconstructions of the Gondwana margin, in an excessively wide arc-trench gap succession, for the position of the trench is constrained to east of New Caledonia from the Permian onward. This suggests there may have been some rearrangement of tectonic elements along the margin resulting in widening of the Lord Howe Rise between Australia and New Caledonia in the period between termination of igneous activity in New England and formation of the Tasman Sea in the Late Cretaceous.

A Survey of the Dragonflies (Odonata) of South Africa. Part 1

Abstract: A detailed check-list, with references to genera and species, is presented of the Zygoptera known in the region south of the Limpopo River, and including South West Africa/Namibia. The region reviewed here is of particular interest for several reasons: there is a remarkable number of species descriptionbed from the region; there are relict Gondwana elements; the number of species of Zygoptera is unusually close to that of the Anisoptera.

New Symmetrodonts from Kota Formation (Early Jurassic), India

Abstract: The limestone and clay members of Kota Formation of Upper Gondwana sequence has yielded abundant piscean fauna. pterosaurs and dinosaurs including mammals. The ossiferous zone is found to extend for about 40 km in strike length. Two new symmetrodonts are recognized in the collection. Trishulotherium kotaensis gen. et sp. nov and Indotherium pranhitai gen. et sp. nov are described and their significance in the evolutionary history of symmetrodonts is outlined.

Gondwana and neotropical galaxioid fish biogeography

Abstract: The galaxioids, Southern Hemisphere salmoniforms (i.e. Galaxiidae, Aplochitonidae, Retropinnidae and Pro-totroctidae), are found in Australia, New Zealand, New Caledonia, South America and South Africa, and include 4 families, 11 genera, and about 45 species. Biogeographers have disagreed on the interpretation of this distributional pattern, shared by many Southern Hemisphere taxa. Both ecological and systematic data are important in resolving what has become a controversial topic among students of biogeography.

Orogenic development of the Argentinian/Chilean Andes during the Palaeozoic

Abstract: The geological development of the basement of the Argentinian/Chilean Andes during the Palaeozoic is characterized by an almost continuous structural, metamorphic and plutonic mobility. Ultrabasic magmatism occurred only in a few regions; terrigenic psammopelitic sequences are widespread at all times. Metamorphism is mostly of low to intermediate pressure, but of variable temperature; late Palaeozoic high pressure metamorphism only took place near the present Pacific coast. There are about four culminations of orogenic activity, varying in space and time: from the mid-Cambrian to the mid-Ordovician, from the Silurian to the mid-Devonian, during the early Carboniferous, and at the Permian/Triassic boundary. Fold structures strike in variable directions at different times. On the whole, the Pacific margin of Gondwana consolidated continuously from the shield region in the E towards the Pacific during the Palaeozoic.

Biostratigraphy and paleontology of some conchostracan-bearing beds in southern Africa

Abstract: The present field and laboratory study was undertaken in conjunction with a monograph being prepared on Gondwana estheriids. Detailed biostratigraphic reports are lacking on the southern African conchostracan-bearing beds. The available paleontological treatment ranges from mere mentions of certain fossils being present to spare systematics. During the summer of 1979 a limited exploration program was undertaken at localities in the Clarens Formation (Cave Sandstone) outcrop belt where conchostracans had been reported (Stockley 194 7, Haughton 1924, and especially Ellenberger et al. 1964). In particular, sites at Siberia and Barkly Pass (both in the Republic of South Africa) and at Thabaneng and Mofoka's Store (both in Lesotho) were found to yield excellent new biostratigraphic and pale on to logical data. The exploration covered some 1500 square miles (2400km of the Clarens Formation (Cave Sandstone) outcrop belt (Text fig. 1 ). Conchostracan-bearing Cave Sandstone sites noted by Paul Ellenberger (1970) at Leloaleng, Masitisi, Mohaleshoek, Brakfontein and elsewhere were systematically explored. Because of the lack of precise locality data enabling one to pinpoint the fossiliferous bed(s) even an intensive search did not uncover the reported fossiliferous beds. Exploration of one of Ellenberger's localities at Wonderkop (RSA) was abandoned after a preliminary search due to time limitations. This site may yet prove productive.

Early Opening of Initially Closed Gulf of Mexico and Central North Atlantic Ocean: ABSTRACT

Abstract: Regional structures beneath the northern Gulf of Mexico coastal plain clearly reveal the fit of the American continents following Late Paleozoic Appalachian-Ouachita orogeny. Most diagnostic is a wrench fault zone within the former Gondwana megacontinent, recognizable from the Florida panhandle to western Mississippi, along which future South America moved northwest against the southern edge of eastern North America to form the Ouachita foldbelt, while future Africa was already subducting that continent along the Appalachian belt. Extending westward from this in southwestern Alabama is the Wiggins arch, underlain by "granite" and phyllite of Late Pennsylvanian into Early Permian age, apparently part of a volcanic arc. Along its north side and that of its counterparts farther west are shallow-marine strata of similar age. These appear to occupy a remnant ocean on North American oceanic crust, which was uncoupled by the close approach of future South America and subducted very briefly beneath North America, while the sediments on its leading edge were peeled off and thrust onto the continent. The inferred volcanic arc and remnant ocean, and the Late Triassic Interior rift system that separates them from the Ouachita foldbelt, terminate abruptly in East Texas against a wrench fault that transferred this rifting south-southwest to the Rio Grande embayment area. Taking the Pickens-Quitman-Gilbertown-Pollard and the Mexia-Talco fault zones, which mark the approximate updip limit of appreciable Louann Salt, to represent these northward-converging wrench faults, northern South America's Guyana shield fits snugly against them, with slight overlap onto the intervening Wiggins and Sabine uplifts. With Africa conventionally joined to South America, this continental fit also places West Africa's two prominent capes opposite pronounced salients of the Appalachian foldbelt, while capes Cod and Hatteras face the principal West African basins, which occupy salients in the equivalent African foldbelt. Also, pre-Mesozoic Florida lies in the reentrant between the southern continents, seemingly separated from each by an arm of a triple rift system whose third arm passes between them. From this tightly-closed condition the Gulf of Mexico opened by relative right-lateral translation of eastern North America (Florida to Nova Scotia) against the bulge of northwestern Africa, actually a rotation about a pole near the central southern edge of the Sahara. The Interior rift system formed while the sialic block that includes the Wiggins and Sabine uplifts remained briefly with South America as North America moved north-northeast along the East Texas transform and a parallel one at the east end of the Wiggins arch. The rifting jumped south of these uplifts after extension of perhaps 50 mi (80 km) to open the present Gulf basin. Almost 200 mi (320 km) of such translation brought Cape Hatteras solidly against Africa's Cap Blanc, ending this movement in earliest Jurassic time. Magnetic anomaly lineaments off the southeastern states, used as crude isochrons, show that the central North Atlantic Ocean (CNAO) began to open by southern North America swinging westward to disengage the obstructing capes. The Blake Plateau basin and Carolina trough opened first, then the spreading jumped east of the latter and propagated northward along the entire CNAO, followed by a second jump marked by development of the Blake Spur magnetic anomaly lineament. Changes in North America's movement direction throughout this period were recorded by the Great Abaco fracture zone, as reinterpreted, along which the early CNAO terminated southward against the Florida-Bahama platform. Right-lateral offsets of this fracture zone totalling about 65 mi (100 km) are associated with the two spreading-center jumps. The Late Triassic intercontinental transform continued across northwestern Morocco into the Tethyan sea, which then extended west into what's now the northern CNAO. As the CNAO opened to its full length it appropriated this tip of Tethys and left the intervening Moroccan Meseta with Africa. Tethys' venture into the future CNAO followed extensive earlier Triassic rifting in eastern North America, which formed an inferred graben system responsible for the Brunswick magnetic anomaly lineament and prepared the way for subsequent intercontinental translation.

Metallogenetic evolution of the East Alpine Paleozoic basement

Abstract: Paleo-metallogenetic sketch maps of the East Alpine area are presented for the Ordovician/Silurian, the Devonian/Lower Carboniferous, and the Upper Carboniferous/Permian. Mineralization and tectonic evolution are then discussed in the frame of a plate tectonic model compatible with recent results in Western Europe. A group of microcontinents originally dispersed in an ocean north of Gondwana, comprising in the investigated area a Bohemian, Penninic and a South/Austro-Alpine microcontinent was sutured after earlier localized orogenies to a Central European continent during the Devonian resulting from a general northward drift from the Cambrian onwards. This was followed by the development of a new destructive plate margin in the South with a northerly dipping subduction zone, enabling the consumption of the Proto-Tethys ocean. Mainland Gondwana then collided with the newly formed continent during the Carboniferous. Contrary to the generally convergent tectonic pattern most mineralizations in the South/Austro-Alpine area appear associated with crustal extension and related volcanism continuing into the Lower Carboniferous. Especially in the Upper Ordovician this conforms well with the concept of a back arc extensional cratonic basin setting. Metal zoning similar to the Andean/Cordilleran situation cannot be observed. Notably different, however, is the orogenic setting of the Penninic area during the Lower Paleozoic, with an economic scheelite-mineralization and associated trace elements reflecting mainly crustal affinities. The Upper Carboniferous calc-alcaline magmatism of the South/Austro-Alpine-Penninic area with its Cu-Pb-Zn-Ag-F mineralisation in the South and anomalous Be-Bi-F-Li-Mo-W-U contents further North displays many features of a back arc magmatic belt. The orogenetic stage is followed in the Upper Carboniferous-Permian by molasse with sandstone type U, graphite (coal) and acidic volcanism giving rise to (Ba-F-) Cu-Pb-Zn-U ores. A renewed tensional regime accompanied by marine transgression during the higher Permian produced evaporite deposits and minor epigenetic mineralization dominated by Fe in the Austro-Alpine area.

Notes on the Geology and Mineral Resources of the Southern

Abstract: The rifting and break-up of the Gondwana continent dominate the sedimentary and structural evolution of the southern Kenyan coast. Jurassic rifting transformed an intracratonic Permo-Triassic basin filled with continental elastics into a marginal marine basin located at the trailing edge of the African plate. An alkaline intrusive complex is related to structures which suggest that a failed rift arm of a triple junction formed in association with the opening of the Indian Ocean. The mineral deposits, characteristic of the metallogenetic environment commonly associated with rifting, and include apart from insignificant sedimentary mineral occurences a major Nb-rare earth deposit associated with a carbonatite complex as well as several minor vein-type Pb-Zn-Ba mineralizations.

Lower Gondwana coals of India - paleobotany, petrology and genesis

Abstract: The beginning of coal formation in the Lower Gondwana in India coincided, more or less, with the waning of the Late Palaeozoic Ice Age. Geological and palaeobotanical evidence suggest that temperate conditions existing at the time in Peninsular India were responsible for the develoment of a special flora dominated by Gangamopteris, Glossopteris and allied groups. Transformations in the vegetal material during diagenesis and categenesis, as inferred from biopetrological and rank investigations, reveal that the coal seams of the Karharbari Formation (basal portion of Lower Gondwana coals) experienced high oxidation resulting in excessive fusinization, probably due to rapid sedimentation, shallow basin condition and extensive microbiological action. It has also been surmized that the geothermal gradient during Lower Gondwana sedimentation was low throughout and that the coal seams attained only low rank. However, in the Damodar and Satpura Gondwana basins, where igneous intrusions occurred during the later phase of Lower Gondwana sedimentation, the rank of coal seams increased abnormally. 14 refs.