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.

The igneous rocks of Greece: The anatomy of an orogen

Abstract: The Hellenide orogen in Greece is part of the AlpineHimalaya mountian belt, created during the destruction of Tethys by the convergence of Gondwana and Eurasia. Within Greece, there is the record of a complete Wilson tectonic cycle of continental rifting, sea-fl oor spreading, plate subduction, and continental collision during Mesozoic and Cenozoic time. This book presents a new synthesis of the geological history of Greece as revealed by the varied igneous rocks. It is based on more than 30 years of fi eld and laboratory studies by the authors together with a synthesis of the widely scattered published literature that has been written in many different languagues. Basement rocks record Hercynian subduction and plutonism on the northern margin of Gondwana, which in the Permian and Triassic rifted into several microcontinents, thereby creating the eastern Mediterranean Neotethys ocean. Partial closure of strands of the Neotethys ocean resulted in widespread emplacement of Jurassic and Cretaceous ophiolites. Early Tertiary collision produced a Hellenide mountian chain similar to the Alps and Himalayas. Rapid Neogene extension of the Hellenides behind the modern South Aegean arc has formed the Aegean Sea, triggered widespread backarc igneous activity, and unroofed mid-crustal rocks. The geological setting, geochemistry, and tectonic signifi cance of each group of rocks is presented in detail, with numerous original maps and fi gures.

Archaean–Cambrian crustal development of East Antarctica: metamorphic characteristics and tectonic implications

Abstract: The East Antarctic Shield consists of a variety of Archaean and Proterozoic-Cambrian high-grade terranes that have distinct crustal histories and were amalgamated at various times in the Precambrian-Cambrian. High-grade Pan-African tectonism at 600–500Ma is recognized from four distinct belts: the Dronning Maud Land, Lutzow-Holm Bay, Prydz Bay and Denman Glacier Belts. These high-grade belts juxtapose distinct Mesoproterozoic and Neoproterozoic crustal provinces (Maud, Rayner and Wilkes), the Rauer Terrane, and have also marginally affected Archaean cratonic remnants in the Napier Complex and southern Prince Charles Mountains. The Wilkes Province experienced its principal tectonothermal events prior to 1130Ma and was not affected by the younger events that characterize the Maud Province (1150 and 1030–990Ma), the Rayner Province (990–920Ma) and the Rauer Terrane (1030–990Ma). These differences between the isotopic/event records of the basement provinces now separated by the Pan-African belts require that the older provinces were not formerly parts of a continuous ‘Grenville’ belt as proposed in the SW US-East Antartic model. East Antarctica was not a single unified crustal block within either East Gondwana or Rodinia until the Cambrian, which is now demonstrated to be the key phase of high-grade and ultrahigh-temperature (UHT) metamorphism associated with supercontinent assembly. The high-grade Pan-African tectonism is characterized by extensive infracrustal melting, clock-wise P-T paths, rapid post-peak exhumation along isothermal decompression paths to shallow- or mid-crustal levels by 500 Ma and the generation, at least locally, of UHT conditions. A significant flux of heat from the mantle into the deep and initially overthickened crust is required to produce these observed metamorphic effects. Whilst the thermal evolution can be explained by models that invoke the removal of most of the lithospheric mantle following crustal thickening and prior to rapid extension of the remaining crust, these one-dimensional models are inconsistent with present crustal thicknesses of 25–35km in the Pan-African domains of the East Antarctic Shield.

Late Neoproterozoic assembly of East Gondwana

Abstract: Paleomagnetism shows that at ca. 810 Ma, India lay near the pole while Australia was at low latitudes, demonstrating that India and Australia were not united in East Gondwana until later. We use geochronologic, paleomagnetic, and geologic information to develop a model for the breakup of West Rodinia at ca. 750 Ma and the subsequent assembly of India, Australia, and parts of Antarctica as East Gondwana. A continental block, possibly the Kalahari craton, broke away from the margin of west Australia at ca. 750 Ma, prior to the commencement of sinistral strike slip along the margin between ca. 680 and 610 Ma. Final amalgamation of East Gondwana may not have been complete until the Early Cambrian.

Onset of Antarctic Circumpolar Current 30 million years ago as Tasmanian Gateway aligned with westerlies

Abstract: Neodymium isotopes from fossil fish teeth and tectonic reconstructions show that the deep Tasmanian Gateway opened up about 33 million years ago and that the Antarctic Circumpolar Current arose 30 million years ago, when the gateway probably moved into the latitudes of the strong westerly winds. Ocean circulations were transformed during the Oligocene, when a series of tectonic movements reshaped the continents into a pattern that began to resemble what we see today. In particular the Drake Passage (between South America and Antarctica) and the Tasmanian Gateway (between Australia and Antarctica) opened and provided channels for the Antarctic Circumpolar Current. The sequence and timing of these events are uncertain. Here Howie Scher et al. use neodymium isotopes extracted from fossilized fish teeth as well as tectonic reconstructions to show that the deep Tasmanian Gateway opened up about 33 million years ago, and that the Antarctic Circumpolar Current arose 3 million years later, when the gateway probably moved into the latitudes of the strong westerly winds. Earth’s mightiest ocean current, the Antarctic Circumpolar Current (ACC), regulates the exchange of heat and carbon between the ocean and the atmosphere1, and influences vertical ocean structure, deep-water production2 and the global distribution of nutrients and chemical tracers3. The eastward-flowing ACC occupies a unique circumglobal pathway in the Southern Ocean that was enabled by the tectonic opening of key oceanic gateways during the break-up of Gondwana (for example, by the opening of the Tasmanian Gateway, which connects the Indian and Pacific oceans). Although the ACC is a key component of Earth’s present and past climate system1, the timing of the appearance of diagnostic features of the ACC (for example, low zonal gradients in water-mass tracer fields4,5,6,7) is poorly known and represents a fundamental gap in our understanding of Earth history. Here we show, using geophysically determined positions of continent–ocean boundaries8, that the deep Tasmanian Gateway opened 33.5 ± 1.5 million years ago (the errors indicate uncertainty in the boundary positions). Following this opening, sediments from Indian and Pacific cores recorded Pacific-type neodymium isotope ratios, revealing deep westward flow equivalent to the present-day Antarctic Slope Current. We observe onset of the ACC at around 30 million years ago, when Southern Ocean neodymium isotopes record a permanent shift to modern Indian–Atlantic ratios. Our reconstructions of ocean circulation show that massive reorganization and homogenization of Southern Ocean water masses coincided with migration of the northern margin of the Tasmanian Gateway into the mid-latitude westerly wind band, which we reconstruct at 64° S, near to the northern margin. Onset of the ACC about 30 million years ago coincided with major changes in global ocean circulation9 and probably contributed to the lower atmospheric carbon dioxide levels that appear after this time10.