Showing papers on "Gondwana published in 1986"
TL;DR: From the Triassic to the Present linear belts of calc-alkaline volcanism developed along the southern margin of Eurasia as mentioned in this paper, and their development is related to the closure of the Paleo-Tethys, when fragments of Gondwana (Iran, Afghanistan etc.) were approaching Eurasia.
169 citations
TL;DR: In this article, the authors propose that the crystalline basement of Western and Central Europe consists of a mosaic of crustal elements which were consolidated during pre-Grenvillian, the Grenvillian-Dalslandian, Morarian, Cadomian, Caledonian and Hercynian orogenic cycles.
161 citations
TL;DR: In this paper, the scale and vergence of D 3 anticlinoria in the eastern Piedmont are similar to those of D 2 anticlinia in the western Appalachians which are related to ramping of underlying thrust surfaces.
Abstract: Geological and geochronological studies in the eastern Piedmont of the southern Appalachians have documented a polyphase late Paleozoic deformational chronology (D 2 –D 4 ) that is contemporaneous with the Alleghanian orogeny recorded in the western Appalachian foreland. The scale and vergence of D 3 anticlinoria in the eastern Piedmont are similar to those of anticlinoria in the western Appalachians which are related to ramping of underlying thrust surfaces. We suggest that the Appalachian decollement extends southeastward beneath the entire Piedmont Province and that all of the Piedmont rocks were displaced at least 175 km northwestward relative to North America during the Alleghanian orogeny. Late Paleozoic deformational effects in the eastern Piedmont thus are considered cogenetic with Alleghanian foreland deformation. We interpret the Alleghanian orogeny to be the result of oblique, dextral convergence and collision of Gondwana and Laurentia.
108 citations
TL;DR: In a series of steps, these accretionary wedges were folded and thrust toward the northwest against, then finally onto, the southern margin of North America in the Permian basin of West Texas as discussed by the authors.
Abstract: Prior to Late Pennsylvanian time, the Permian basin of West Texas was a part of the southern margin of the North American craton and was the site of shallow, warm-water carbonate deposition. As the South American margin of Gondwana gradually moved northwestward during late Paleozoic time, the oceanic floor deposits and overlying turbidite fan deposits between North America and South America became parts of large accretionary wedges of semiconsolidated sediments. In a series of steps, these wedges were folded and thrust toward the northwest against, then finally onto, the southern margin of North America. These compressive steps caused the repeated piling up of the accretionary wedges to form rapidly eroding highlands on the cratonic margins. Repeated loading on the North American margin formed a series of elongate, deep-water, depositional troughs (fore-deeps) immediately north and west of the accretionary wedges, and these received thick accumulations of turbidites. The youngest of these deep basins include the northwestern part of the Val Verde basin to the north and the Marfa basin to the west which received basinal deposits from within Desmoinesian into early Late Permian time. Loading of the cratonic margin also resulted in renewed faulting along generally northwest- to north-trending older zones of weakness. These zones are apparently of Precambrian age. On the craton, the late Paleozoic faults mainly had high-angle to vertical fault planes and commonly had large components of horizontal displacement. This fault system outlines the major uplifts and basins in the Permian basin region. The joining together of Gondwana and Euramerica across the Marathon salient of the orogenic belt was essentially completed by mid-Wolfcampian time. After that time, the southern margin of the Permian basin, represented by the Dugout and Marathon allochthons and the Diablo Platform, became a relatively stable tectonic area. The Glass Mountains expose a series of north- and northwest-dipping cuestas of Permian carbonate shelf and shelf-edge deposits that accumulated on a platform constructed from these two allochthonous accretionary wedges. These Permian deposits prograded north and northwestward into the narrow Hovey Channel, which connected the Marfa basin with the southern end of the Delaware basin. Carbonate-reef growth finally restricted the inflow of marine water into the Delaware basin near the end of late Guadalupian time.
107 citations
TL;DR: The history of the Lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments as discussed by the authors, and four major terranes developed adjacent to the Gondwana continental margin and were overthrust in the Middle Devonian to form a partly composite crust for southeastern Australia.
Abstract: The Paleozoic history of the Lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments. Four major terranes developed adjacent to the Gondwana continental margin and were overthrust in the Middle Devonian to form a partly composite crust for southeastern Australia.
86 citations
TL;DR: The stratigraphical interpretation of the strata of Nubia allows for the first time, in connection with structural, petrological and sedimentological investigations, to reconstruct the geological development of this cratonal area.
Abstract: The stratigraphical interpretation of the strata of Nubia allows for the first time — in connection with structural, petrological and sedimentological investigations — to reconstruct the geological development of this cratonal area. After cratonization during the PanAfrican event, extensional trends in WSW-ENE direction caused a structural relief, striking NNW-SSE. The collision between Gondwana and the northern continents during the Carboniferous resulted in the uplifting of large parts of the northeast African Plate and was accompanied by more or less East-West striking faults and magmatic intrusions. Erosion of Paleozoic sediments in middle and southern Egypt and reversal of the main drainage direction was the consequence. This caused deposition of Karroo-type strata in northern Sudan, including glacial deposits at the base along the Sudanes Egyptian border.
73 citations
69 citations
TL;DR: In this paper, it was shown that early authigenesis took place within a few million years of deposition at burial depths measured in hundreds of meters, and that the nature of the silicate cement was a function of the groundwater chemistry.
Abstract: Various empirical and theoretical arguments suggest that early formed cement in sandstone is a product of meteoric water whose chemistry is controlled by climate. The nature and distribution of early silicate cement in Gondwana, Fountain, and Cutler sandstone support this supposition. Sandstones from all three units have experienced a broadly similar diagenetic history characterized by two stages of authigenesis. Stage I was typified by neomorphic development of kaolinite, chlorite, smectite, quartz, and, additionally in the Cutler Formation, laumontite. Stage II was dominated by replacement reactions involving the production mostly of illite, iron oxide, carbonate minerals, and, mostly in the Gondwana sandstone, a second generation of quartz. Thermodynamic relations, hydrologic constraints, and radiometric dating of the late-stage illite indicate that early authigenesis took place within a few million years of deposition at burial depths measured in hundreds of meters. Consequently, the nature of the silicate cement was a function of the groundwater chemistry, as controlled by climate. During times of relative aridity, ionic concentration of the groundwater was high, and high proportions of smectite, chlorite, and, more rarely, laumontite formed. Such was the case in Petrofacies I, IV, V of the Gondwana Supergroup (for a definition of Gondwana petrofacies see part I of this study) in the Cutler Fm., and in the upper 150 m of the Fountain Fm. During times of high precipitation, pore water was dilute, which promoted authigen c formation of kaolinite and quartz. This is represented by sandstones in petrofacies II and VI of the Gondwana and by sandstones in the lower 200 m of the Fountain Fm. Illite is especially abundant as a pseudomorphic replacement of kaolinite in the older Gondwana sandstones. Illitization apparently began at burial depths of about 1,600 m at a temperature of about 75°C. Illite is not common in the Cutler Formation and is present only in subordinate amounts in the Fountain Formation from the study area. The 18O values of early clay cement in the Gondwana sandstones range systematically from base to top from 5.00 to 13.20. The systematic variation in 18O value of Gondwana clay reflects the gradual migratory drift of the Gondwana harm toward lower latitudes through time. Average 18O values for Cutler cement (13.23) and Fountain cement (19.82) are greater than the analogous values for Gondwana cements. This is consistent with the lower-latitude setting of deposition for the Cutler and Fountain relative to the latitudinal location of the Gondwana basins. However, the values are anomalously lower than what have been observed in modern-day neoformed clays in weathering profiles from low latitudes.
68 citations
TL;DR: The Shyok tectonic belt of Ladakh, northwest India, bridges the important geologic gap between the Kohistan block of Pakistan and the Lhasa block of Tibet as mentioned in this paper.
Abstract: The Shyok tectonic belt of Ladakh, northwest India, bridges the important geologic gap between the Kohistan block of Pakistan and the Lhasa block of Tibet. The geology of the Shyok tectonic belt supports the model of successive collision and accretion of Gondwana fragments along the southern margin of the Asian plate. Tectonic continuity is established between Gondwana fragments of Afghanistan, Kohistan, Shyok, and Tibet on the basis of new geologic data from the Shyok tectonic belt, and various plate-tectonic models for the India-Asia collision are discussed. 24 references, 3 figures, 1 table.
TL;DR: The Ancestral Rockies were formed as the result of reactivation of the Wichita megashear, a preexisting zone of weakness that extends from southern Oklahoma to eastern Utah as mentioned in this paper.
TL;DR: In this paper, the existence of a Gondwana supercontinent in the Early Palaeozoic of the Shackleton Limestone was confirmed by the discovery of archaeocyaths from measured sections in the northern Holyoake Range (Nimrod Glacier area) and at Crackling Cwm (Byrd Glacier area).
Abstract: The Shackleton Limestone is a thick unit of bedded and allochthonous limestone, with minor dolostone, quartzite, sandstone and siltstone, spanning the central portion of the Transantarctic Mountains. It is a record of Early Cambrian shelf and peri-platform carbonate deposition on the margin of the East Antarctic craton. Slope, shallow marine and intertidal-supratidal conditions prevailed during deposition. Thirty-one species of archaeocyaths described from measured sections in the northern Holyoake Range (Nimrod Glacier area) and at Crackling Cwm (Byrd Glacier area) confirm earlier correlations of Shackleton Limestone faunas with the Botomian stage of Siberia. Archaeocyaths from a section at Mt Egerton (Byrd Glacier area) are of either Botomian or Toyonian age. Ten further archaeocyath species are added to the six species already known to be common to both Antarctica and Australia, confirming the existence of a Gondwana supercontinent in the Early Palaeozoic. New taxa described are the genera Kymbecyathus...
TL;DR: In this article, the authors interpret the basement ridge as part of the East Antarctic plate boundary during the break-up of Gondwana and show that the morphology and structure of this boundary show greater apparent similarity to a rifted or obliquely rifted margin than to the sheared margin which is predicted by current reconstructions.
Abstract: An improved Gondwanaland reconstruction compatible with geological and geophysical information from the surrounding oceans and continents seems to require microplates to solve the enigmatic pre-early-Mesozoic tectonic relation between West and East Antarctica1. New multi-channel seismic reflection data from the southeastern Weddell Sea acquired during the 1984–85 Norwegian Antarctic Research Expedition (NARE) have outlined a linear WSW–ENE-trending basement ridge buried below the continental slope over a distance of 700 km. This structural high truncates the trend of the large sedimentary basins below the Filchner and Ronne ice shelves and may continue to within a few hundred kilometres of the Antarctic Penninsula. We interpret the basement ridge as part of the East Antarctic plate boundary during the break-up of Gondwana. The morphology and structure of this boundary show greater apparent similarity to a rifted or obliquely rifted margin than to the sheared margin which is predicted by current reconstructions2,3. A linear East Antarctic plate margin extending to the vicinity of the Antarctic Peninsula makes any post-rift micro-plate motion in the Weddell Embayment unlikely.
TL;DR: Palaeomagnetic results from the late Middle to early Late Devonian Comerong Volcanics in the Budawang Synclinorium, Lachlan Fold Belt (LFB), New South Wales, Australia, satisfy a fold test and support the hypothesis that foliated parts of the LFB have been folded by megakinks during the terminal mid-Carboniferous orogenic phase.
Abstract: Palaeomagnetic results from the late Middle to early Late Devonian Comerong Volcanics in the Budawang Synclinorium, Lachlan Fold Belt (LFB), New South Wales, Australia, satisfy a fold test and support the hypothesis that foliated parts of the LFB have been folded by megakinks during the terminal mid-Carboniferous orogenic phase. The preferred pole position is at 76.9°S, 330.7°E (A95 = 7.2°), allowing calibration of the Australian pole path at around 370 Ma ago. An alterative pole position at 71.3°S 283.1°E (same A95) takes into account a possible rotation of the megakinked terrane by 15° clockwise with respect to the Australian craton. Although there are still problems unravelling previously published results from Silurian rocks in the LFB, both because of unreliability and uncertainty as to where the LFB crustal units lay in relation to the Australian craton, there is no geological reason to suspect any large relative movement between the LFB and the craton since the Middle Devonian, and thus the Comerong Volcanics pole position is representative of the Late Devonian for Australia. The new pole requires reassessment of many other poles that have previously been accepted as representing the Siluro-Devonian for Australia, and Gondwanaland. We present reasons for believing that the magnetization, or remagnetization of many rock units (e.g., Mereenie Sandstone and Mulga Downs Group, Australia, and the Gneigura Supergroup, Africa) was later than sedimentation, probably during widespread Early Carboniferous deformation. Another rock unit (Msissi Norite, Africa) could be of Early Carboniferous, rather than Late Devonian, age.
TL;DR: In this paper, a narrow strip of Gondwana basins separates the Rajmahal traps from the peninsular shield in eastern India and is associated with a conspicuous gravity high of 100 km wavelength and 48 mGal amplitude over an area of 25,000 km 2.
TL;DR: In this paper, the authors discussed the arguments of these authors and a sedimentological description was given which showed that the pebbly mudstones are not glaciomarine sediments, but rather of continental margin origin.
Abstract: The Phuket Group in Peninsular Thailand and the Singha Formation in NW Malaysia are of Devonian to Lower Permian age. These approximately 3000 m thick strata, which are part of the »SE-Asian pebbly mudstone belt« stretching from Southern Tibet to Sumatra, have been interpreted as continental margin deposits (Mitchell et al. 1970). In contrast, recent papers (Bunopas et al. 1978,Stauffer 1983) propose a glaciomarine origin. These authors follow the scenario that parts of mainland SE Asia (Shan-Thai Craton) rifted away from Gondwana during the Lower Carboniferous and collided with Eurasia during the Late Triassic after crossing the Tethys Ocean under clockwise rotation of more than 180 degrees. In this paper the arguments of these authors will be discussed and a sedimentological description will be given which shows that the pebbly mudstones are not glaciomarine sediments, but rather of continental margin origin. The investigations on Phuket and Langkawi Islands, when compared with newest results from Central and North Thailand, clearly show that the »Shan-Thai Craton« was a part of, or closely connected with Palaeoeurasia (Indosinia) during Carboniferous and Permian times (comp.Helmcke 1985). The pebbly mudstones were deposited on the southern continental margin of this continent (northern margin of Tethys).
Abstract: A paleomagnetic study of eleven sites of Devonian limestones sampled along the flanks and hinge of a polyphase Hercynian recumbent fold in the Montagne Noire reveals well defined directions of characteristic remanent magnetization (ChRM). The directions have good within-site precision but a large between-site scatter, which fails to be reduced by a classical tilt correction. This is readily understood if widespread remagnetization occurred between the two major Hercynian phases of folding (A and B), which are known to have shaped the Montagne Noire. This remagnetization appears to be an instance of a continent-wide chemical event that wiped out much of the magnetic memory of Devonian and lower Carboniferous rocks in Laurasia, Baltica and northern Gondwana, possibly due to groundwater circulation following the major Hercynian tectonic phases. Comparison of observed and predicted Hercynian magnetic directions allows one to determine, through a fairly simple geometric construction, the tectonic elements of the later phase B. It is found that different rotations affected the flanks and hinge zone of the folds generated by phase A, thus demonstrating how a pre-existing structure can control the development of deformation in a later tectonic phase. The effects of the non cylindrical phase B can next be removed to reveal the broad tectonic features of phase A deformations. The reversed (Kiaman) polarity of the ChRM allows a determination of the age of phase B, which is found to be about 300–310 Ma and of the age of the remagnetization itself at about 310–320 Ma. The search for the age of remagnetization included paleomagnetic measurements at two lower Permian sites from the nearby Lodeve basin. These provide new data for the Permian pole of Europe and point out the limitations of some earlier studies, due to insufficient magnetic cleaning. Finally, the principal shortening directions of the two phases can be determined from the magnetic data and are found to have rotated counterclockwise by 30° between phase A and phase B. This feature, already observed in the collision of India against Eurasia, may be related to the progressive suturing of former subduction zones during the Hercynian collision of Gondwana against Laurasia. This study demonstrates the potential of remagnetizations for the solution of rather complex tectonic problems. We propose the term “magnetotectonics” for this rapidly expanding field of studies, in which the methods of paleomagnetism and structural analysis are closely associated.
TL;DR: A modified version of the Simpson index was used to assess similarities between the Early Triassic tetrapod faunas of Australia, Antarctica, India, and South Africa as mentioned in this paper.
Abstract: A modified version of the Simpson index is used to assess similarities between the Early Triassic tetrapod faunas of Australia, Antarctica, India and South Africa. This index takes into account the relative abundances of taxa, and not merely their presence or absence. Antarctic, Indian and African faunas are all found to be very similar — one to another and each to a hypothetical ‘average’ fauna. The Australian fauna is distinctly different: it resembles other faunas in terms of the presence or absence of taxa, but it differs greatly in the relative abundances of those taxa. Most significant of those differences is the abundance of labyrinthodont amphibians and the commensurate rarity of reptiles. The unusual composition of the Australian fauna might be explained to a large extent by geographic isolation.
TL;DR: The history of the present-day Eurasia was greatly influenced by the Indosinian orogeny which is considered to be on a level with the Caledonian, Hercynian and Alpine orogenies.
Journal Article•
TL;DR: In this paper, a geotectonic model is proposed to represent the zone of convergence and shearing of the lithosphere of the earth's crust and lithosphere in the orogenic belt.
Abstract: The considerable tectonic mobility of the earth as demonstrated by the Mesozoic-Cenozoic evolution of the oceanic lithosphere argues against the existence of regular, rhegmatic shear systems of global extent Arc structures are characteristic features of the tectonically mobilized belts of convergence of the earth's crust and lithosphere Emphasis is given to horizontal crustal deformation within the Eurasian and circum-Pacific orogenic belts as revealed by the pattern of Cenozoic strike-slip faults Distinct regularities in the orientation of maximum horizontal crustal shortening and compression are observed The following geotectonic model is proposed: The orogenic belts represent the zone of convergence and shearing of the lithosphere situated between two major geotectonic units, the Pacific unit and the Gondwana unit In the Pacific hemisphere, large-scale diverging movements of plates away from the central Pacific region toward the margins of the Pacific are documented by the breakup of the paleo-Pacific lithosphere and the growth of the Pacific plate In the anti-Pacific hemisphere, large-scale diverging movements away from Africa are demonstrated by the breakup of Gondwana During collision twisting movements will be generated within the orogenic belt Fan-shaped fault patterns, comparable to the pattern of slip-lines formed in deformation of rigid-plastic solids, are associated with the formation of mountain arcs
Journal Article•
TL;DR: In the Late Precambrian, the distribution of aulocogens and intrageosynclines in Gondwana and Laurasia has been studied in this paper, showing that the interiors of interiors were quite different during the Vendian-Early Cambrian.
TL;DR: In this paper, a contribution is made to understand the structure and evolution of the Earth's crust across the Princess Astrid Coast, East Antarctica, especially in the area of the Schirmacher Oasis and the Wohlthat Massif.
TL;DR: In this article, a study of the Late Precambrian Roxbury formation, consisting of extrusives and clastic sediments, has yielded a steeply downward directed and pre-folding characteristic magnetization (D/I = 219°/71°, α95 = 5°, k = 311, paleopole at 13°N, 267°E, N = 4 sites).
Abstract: A paleomagnetic study of the Late Precambrian Roxbury formation, consisting of extrusives and clastic sediments, has yielded a steeply downward directed and pre-folding characteristic magnetization (D/I = 219°/71°, α95 = 5°, k = 311, paleopole at 13°N, 267°E, N = 4 sites), which indicates a significantly higher paleolatitude (55°) than would be expected if the Boston basin were part of the equatorial North American craton in the latest Precambrian and earliest Paleozoic. This characteristic magnetization reveals dual polarities and is further supported by a positive conglomerate test. A ubiquitous post-folding late Paleozoic overprint is present in nine sites (D/I = 183°/14°, α95 = 8°, k = 42), with a paleopole at 41°S, 285°E. The pre-folding magnetization resides in hematite, which is inferred to have formed during early oxidation of the rocks; the high stability of this hematite may have prevented its magnetization from being reset during the late Paleozoic chemical event responsible for the magnetic overprint. The Boston basin has a marked geological similarity to the Avalon basement terranes in Nova Scotia and Newfoundland, as well as the Armorican Massif in France, and the high paleolatitudes observed for all these terranes suggest a common paleogeographical affinity; a likely paleolocation is near the northwestern margin of Gondwana which was located at the southpole in the latest Precambrian and Early Cambrian.