Добірка наукової літератури з теми "Mawson Craton"

ABSTRACTAntarctica has been known as the “keypiece” of the Gondwana supercontinent since publication of Du Toit's 1937 classic bookOur Wandering Continents. It is also important to reconstruction of the early Neoproterozoic supercontinent Rodinia. Laurentia, with its circumferential late Precambrian rifted margins, can be regarded as the ‘keypiece’ of Rodinia. TheSouthwest US–EastAntarctica (SWEAT) hypothesis suggested former juxtaposition of the Pacific margins of Laurentia and East Antarctica. Several new lines of evidence support this hypothesis in a revised form, but must be reconciled with opening of the Pacific Ocean basin predating amalgamation, not only of Gondwana, but even of today's East Antarctic craton. The sequence of events is envisaged to have been: (1) formation prior to 1·6 Ga of a craton, including Laurentia and the Mawson craton, that extended from South Australia along the present Transantarctic margin to the Shackleton Range; (2) suturing of southernmost Laurentia to the Kalahari craton along the Grenville, Namaqua–Natal–Maud orogenic belt ca. 1·0 Ga; (3) rifting of the East Antarctic margin (Mawson craton) from western Laurentia ca. 0·7 Ga; (4) pan-African suturing of the Mawson craton to southernmost Laurentia as Gondwana amalgamated, forming the ephemeral Pannotia supercontinent; and (5) end-Precambrian separation of Laurentia as Iapetus opened.

Summary By combining gravity and magnetic data in a joint inversion approach, three-dimensional information on the crustal structure of Wilkes Land, East Antarctica, is obtained and possible geological features become evident. Both data sets are combined through a coupling method which decreases the variation of information so data misfit and model dissimilarity are minimized simultaneously. In this manner, statistically compatible inversion results are obtained. The suitability of the method is demonstrated through a synthetic example using magnetic data and pseudogravity. Subsequently, we apply the method to gravity residuals and magnetic data and identify matching features of high magnitude density and susceptibility. Prominent structures in NW - SE direction along the edge of the Mawson craton and at the presumed Australo-Antarctic and Indo-Antarctic terrane boundaries are enhanced. Given the structural similarity between inverted susceptibility and density, and a strong indication of a parameter relationship, we suggest a clustering approach in order to differentiate distinct groups with similar parameter properties. The spatial distribution of these clusters reveals possible geological structures that agree with previous two-dimensional studies and rock measurements from the Indian and Australian continents. This shows that the variation of information joint inversion is a convenient approach for remote regions like East Antarctica with sparse geological samples.

AbstractPlate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the breakup of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran.

AbstractThe cratonic elements of proto-Australia, East Antarctica, and Laurentia constitute the nucleus of the Palaeo-Mesoproterozoic supercontinent Nuna, with the eastern margin of the Mawson Continent (South Australia and East Antarctica) positioned adjacent to the western margin of Laurentia. Such reconstructions of Nuna fundamentally rely on palaeomagnetic and geological evidence. In the geological record, eclogite-facies rocks are irrefutable indicators of subduction and collisional orogenesis, yet occurrences of eclogites in the ancient Earth (> 1.5 Ga) are rare. Models for Palaeoproterozoic amalgamation between Australia, East Antarctica, and Laurentia are based in part on an interpretation that eclogite-facies metamorphism and, therefore, collisional orogenesis, occurred in the Nimrod Complex of the central Transantarctic Mountains at c. 1.7 Ga. However, new zircon petrochronological data from relict eclogite preserved in the Nimrod Complex indicate that high-pressure metamorphism did not occur in the Palaeoproterozoic, but instead occurred during early Palaeozoic Ross orogenesis along the active convergent margin of East Gondwana. Relict c. 1.7 Ga zircons from the eclogites have trace-element characteristics reflecting the original igneous precursor, thereby casting doubt on evidence for a Palaeoproterozoic convergent plate boundary along the current eastern margin of the Mawson Continent. Therefore, rather than a Palaeoproterozoic (c. 1.7 Ga) history involving subduction-related continental collision, a pattern of crustal shortening, magmatism, and high thermal gradient metamorphism connected cratons in Australia, East Antarctica, and western Laurentia at that time, leading eventually to amalgamation of Nuna at c. 1.6 Ga.

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Polymetamorphic signatures in rocks can be difficult to deconvolve, especially where events have similar metamorphic grade. In situ and erratic samples from the Terre Adélie Craton, Antarctica, and in situ samples from the formerly contiguous Gawler Craton, South Australia, are examined to deconvolve microstructural, pressure–temperature and geochronological evidence of terrane-scale polymetamorphism. In situ monazite U–Pb geochronology shows that coastal and erratic samples record c. 1700 Ma and c. 2420 Ma ages, consistent with known ages of the Kimban and Sleafordian events, respectively. In situ samples from the Antarctic coast record exclusively c. 2420 Ma ages whereas most erratic samples from the glacial moraines at Cape Denison record only c. 1700 Ma ages. Phase equilibria forward modelling for the c. 2000 Ma Redbanks Charnockite uniquely constrains peak metamorphic conditions of the c. 1700 Ma Kimban Orogeny to 5.0–7.2 kbar and 700–860 ºC. Peak metamorphic conditions of the c. 2420 Ma event are ~5–8.7 kbar and 690–1000 ºC, as constrained by in situ samples from the Terre Adélie coast. As the peak pressure–temperature conditions for the two events are similar and the record of polymetamorphism is cryptic and spatially variable in the rock record, Antarctic samples that only record Kimban ages are interpreted as reflecting either a record of complete overprinting of the older (c. 2420 Ma) event, or that the rocks are younger than the c. 2420 Ma event. In such a situation polymetamorphism at a terrane scale may only be detected by differences in geochronological data. This study serves to highlight the careful approach required when investigating polymetamorphic terranes and argues that a spatially variable record of overprinting metamorphism is possibly related to locations of retrogression occurring either in the waning/exhumation stages of the earlier event or between events.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015

ABSTRACT Neoproterozoic to Cambrian isolation of Laurentia during the breakup of Rodinia was associated with multiple large igneous provinces, protracted multiphase rifting, and variable subsidence histories along different margin segments. In this contribution, we develop a paleogeographic model for the Neoproterozoic tectonic evolution of Laurentia based on available stratigraphic, paleomagnetic, petrologic, geochronologic, and thermochronologic data. Early Tonian strata are confined to intracontinental basins in northern Laurentia. Breakup of Rodinia around Laurentia began in earnest with emplacement of the ca. 778 Ma Gunbarrel large igneous province, interpreted to have accompanied separation of the North China block along the Yukon promontory, and onset of localized, intracratonic extension southward along the western margin. Eruption of the ca. 760–740 Ma Mount Rogers volcanic complex along the Southern Appalachian segment of the eastern margin may record extension associated with separation of the Kalahari or South American terranes. At about the same time, the Australia-Mawson blocks began separating from the Sonoran segment of the southern margin and Mojave promontory. Emplacement of the ca. 720 Ma Franklin large igneous province along the northern margin was likely associated with separation of Siberia and was followed by widespread bimodal volcanism and extension along the western margin spanning ca. 720–670 Ma, leading to partial separation of continental fragments, possibly including Tasmania, Zealandia, and Tarim. Emplacement of the ca. 615 Ma Central Iapetus magmatic province along the eastern margin marked rifting that led to separation of Baltica and Amazonia, and partial separation of the Arequipa-Pampia-Antofalla fragments. During the late Ediacaran to Cambrian, the western, northern, eastern, and southern margins all experienced a second episode of local extension and mafic magmatism, including emplacement of the ca. 585 Ma Grenville dikes and ca. 540–532 Ma Wichita large igneous province, leading to final separation of continental fragments and Cambrian rift-drift transitions on each margin. Cryogenian rifting on the western and northern margins and segments of the eastern margin was contemporaneous with low-latitude glaciation. Sturtian and Marinoan glacial deposits and their distinctive ca. 660 Ma and 635 Ma cap carbonates provide important event horizons that are correlated around the western and northern margins. Evidence for Ediacaran glaciation is absent on Laurentia, with the exception of glacial deposits in Scotland, and putative glacial deposits in Virginia, which both formed on the poleward edge of Laurentia. Patterns of exhumation and deposition on the craton display spatial variability, likely controlled by the impingement of mantle plumes associated with mantle upwelling and extensional basin formation during the piecemeal breakup of Rodinia. Glaciation and eustasy were secondary drivers for the distribution of erosion and Neoproterozoic sedimentation on North America.