Gondwana

About: Gondwana is a research topic. Over the lifetime, 6078 publications have been published within this topic receiving 263050 citations. The topic is also known as: Gondwanaland.

Cambrian Orogenic Belt in East Antarctica and Sri Lanka: Implications for Gondwana Assembly

Abstract: Ion microprobe U-Pb dating of zircons from the Lutzow-Holm Complex (LHC) and the Yamato-Belgica Complex (YBC), East Antarctica indicate high-grade regional metamorphism and associated folding of LHC occurred between $$521 \pm 9$$ and $$553 \pm 6 Ma$$. This shows, for the first time, the existence of a Cambrian orogenic belt within the East Antarctic Shield. Many zircons from the LHC contain cores that record inherited ages from ~2900 to ~1500 Ma. Components of ~1000 Ma zircon have been identified in three locations. This may indicate the maximum age of the deposition of LHC. One metasedimentary gneiss from the YBC records a well-defined age at about 600 Ma, whereas another yields a dispersion of ages interpreted as the result of varied radiogenic Pb loss in ~1000 Ma zircons at about 500-600 Ma. These gneisses have inherited ages of up to ~2500 Ma. Our work enables an improved fit to the once contiguous fragments of Gondwana. The Highland/Southwestern Complex (HSWC) of Sri Lanka has remarkable petrological...

Chapter 2 New global palaeogeographical reconstructions for the Early Palaeozoic and their generation

Abstract: New palaeogeographical reconstructions are presented at 10 myr intervals from the Lower Cambrian at 540 Ma to the Lower Devonian at 400 Ma, showing continental crustal fragments and oceans (not lands and seas), with appropriate kinematic continuity between successive maps. The maps were chiefly generated by revised and selected palaeomagnetic data and revised Apparent Polar Wandering paths linked to present-day polygons from the main continents. These have been reinforced by analysis of the distributions of some fossils and sediments. Gondwana was the dominating supercontinent from its final assembly in the Latest Neoproterozoic at about 550 Ma until the Carboniferous, and covered much of the Southern Hemisphere. The Northern Hemisphere was largely occupied by the vast Panthalassic Ocean. The relative positions of the major continents and the latitudes and rotation histories of Gondwana, Baltica, Siberia and Laurentia (Laurussia from the mid-Silurian) are now well known. Although Laurentia was oriented in a similar direction to the present, Siberia was inverted throughout the Lower Palaeozoic, and Baltica too was initially inverted, but rotated through 120° between the Late Cambrian and Late Ordovician before collision with Laurentia in the mid-Silurian Caledonide Orogeny. Through reconstructions of the Caledonide and some other orogenies, the progressive history of the Iapetus Ocean between Laurentia and Baltica/Gondwana is well constrained. Less major continents whose positions are also well known include Avalonia (initially peri-Gondwanan but migrating in the Early Ordovician to join Baltica by the end of the Ordovician), Sibumasu (now considered an integral part of Gondwana) and Mongolia (adjacent to Siberia). A large number of other terranes are reviewed and plotted on the reconstructions with varying degrees of certainty. However, significant continents with less well constrained or controversial positions are South China, North China (Sinokorea), Annamia (Indochina) and Arctic Alaska–Chukotka. The European areas of France, Iberia and southern Italy, previously considered by some as a separate Armorican Terrane Assemblage, remained parts of core Gondwana until the opening of the Palaeotethys Ocean near the end of the Silurian, but it is uncertain whether Perunica (Bohemia) was one of that group or whether it left Gondwana during the Middle Ordovician.

Southwestern limits of Indian Ocean Ridge Mantle and the origin of low 206Pb/204Pb mid-ocean ridge basalt: Isotope systematics of the central Southwest Indian Ridge (17°–50°E)

Abstract: Basalts from the Southwest Indian Ridge reflect a gradual, irregular isotopic transition in the MORB (mid-ocean ridge basalt) source mantle between typical Indian Ocean-type compositions on the east and Atlantic-like ones on the west. A probable southwestern limit to the huge Indian Ocean isotopic domain is indicated by incompatible-element-depleted MORBs from 17° to 26°E, which possess essentially North Atlantic- or Pacific-type signatures. Superimposed on the regional along-axis gradient are at least three localized types of isotopically distinct, incompatible-element-enriched basalts. One characterizes the ridge between 36° and 39°E, directly north of the proposed Marion hotspot, and appears to be caused by mixing between hotspot and high ∈Nd, normal MORB mantle; oceanic island products of the hotspot itself exhibit a very restricted range of isotopic values (e.g., 206Pb/204Pb = 18.5–18.6) which are more MORB-like than those of other Indian Ocean islands. Between 39° and 41°E, high Ba/Nb lavas with unusually low 206Pb/204Pb (16.87–17.44) and ∈Nd (−4 to +3) are dominant; these compositions are not only unlike those of the Marion (or any other) hotspot but also are unique among MORBs globally. Incompatible-elementenriched lavas in the vicinity of the Indomed Fracture Zone (∼46°E) differ isotopically from those at 39°–41°E, 36°–39°E, and both the Marion and Crozet hotspots. Thus, no simple model of ridgeward flow of plume mantle can explain the presence or distribution of all the incompatible-element-enriched MORBs on the central Southwest Indian Ridge. The upper mantle at 39°–41°E, in particular, may contain stranded continental lithosphere, thermally eroded from Indo-Madagascar in the middle Cretaceous. Alternatively, the composition of the; Marion hotspot must be grossly heterogeneous in space and/or time, and one of its intrinsic components must have substantially lower 206Pb/204Pb than yet measured for any hotspot. The origin of the broadly similar but much less extreme isotopic signatures of MORBs throughout most of the Indian Ocean could be related to the initiation of the Marion, Kerguelen, and Crozet hotspots, which together may have formed a more than 4400-km-long band of juxtaposed plume heads beneath the nearly stationary lithosphere of prebreakup Gondwana.

Neoproterozoic—Early Paleozoic evolution of peri-Gondwanan terranes: implications for Laurentia-Gondwana connections

Abstract: Neoproterozoic tectonics is dominated by the amalgamation of the supercontinent Rodinia at ca. 1.0 Ga, its breakup at ca. 0.75 Ga, and the collision between East and West Gondwana between 0.6 and 0.5 Ga. The principal stages in this evolution are recorded by terranes along the northern margin of West Gondwana (Amazonia and West Africa), which continuously faced open oceans during the Neoproterozoic. Two types of these so-called peri-Gondwanan terranes were distributed along this margin in the late Neoproterozoic: (1) Avalonian-type terranes (e.g. West Avalonia, East Avalonia, Carolina, Moravia-Silesia, Oaxaquia, Chortis block that originated from ca. 1.3 to 1.0 Ga juvenile crust within the Panthalassa-type ocean surrounding Rodinia and were accreted to the northern Gondwanan margin by 650 Ma, and (2) Cadomian-type terranes (North Armorica, Saxo-Thuringia, Moldanubia, and fringing terranes South Armorica, Ossa Morena and Tepla-Barrandian) formed along the West African margin by recycling ancient (2–3 Ga) West African crust. Subsequently detached from Gondwana, these terranes are now located within the Appalachian, Caledonide and Variscan orogens of North America and western Europe. Inferred relationships between these peri-Gondwanan terranes and the northern Gondwanan margin can be compared with paleomagnetically constrained movements interpreted for the Amazonian and West African cratons for the interval ca. 800–500 Ma. Since Amazonia is paleomagnetically unconstrained during this interval, in most tectonic syntheses its location is inferred from an interpreted connection with Laurentia. Hence, such an analysis has implications for Laurentia-Gondwana connections and for high latitude versus low latitude models for Laurentia in the interval ca. 615–570 Ma. In the high latitude model, Laurentia-Amazonia would have drifted rapidly south during this interval, and subduction along its leading edge would provide a geodynamic explanation for the voluminous magmatism evident in Neoproterozoic terranes, in a manner analogous to the Mesozoic-Cenozoic westward drift of North America and South America and subduction-related magmatism along the eastern margin of the Pacific ocean. On the other hand, if Laurentia-Amazonia remained at low latitudes during this interval, the most likely explanation for late Neoproterozoic peri-Gondwanan magmatism is the re-establishment of subduction zones following terrane accretion at ca. 650 Ma. Available paleomagnetic data for both West and East Avalonia show systematically lower paleolatitudes than predicted by these analyses, implying that more paleomagnetic data are required to document the movement histories of Laurentia, West Gondwana and the peri-Gondwanan terranes, and test the connections between them.