De Santis L.*1, Caburlotto A.1, Donda F.1, Lucchi R. G.1, Presti M.1, Accettella D.1, Geletti R.1, Wardell N.1,
Colizza E.2, Candoni O.1-2, Tolotti R.3, Macrì P.4 & Giorgetti G.5
1. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste. 2. Dipartimento di Matematica e Geoscienze, Università di Trieste. 3. Dipartimento di Scienze della Terra, dell’Ambiente e della Vita, Università di Genova. 4. Istituto Nazionale di Geofisica e Vulcanologia, INGV,
Roma. 5. Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente, Università di Siena. Corresponding email: [email protected]
Keywords: swath bathymetry, seismic reflection, Italian Antarctic Program.
Swath bathymetry and seismic reflection profiles collected by the Italian Antarctic Program (PNRA WEGA and MOGAM projects), combined with Australian (CSIRO) oceanographic measures (Williams et al., 2010) and benthic fauna sampling (Post et al., 2010), in the offshore of the George Vth Land, document evidence of bottom water cascading currents and turbidity currents inside continental slope canyons.
The continental slope is incised by canyons heading to shelf edge sills and bounding sedimentary ridges of Miocene age. Dense shelf water forms in coastal polynya and is exported off the shelf break to form the Adélie Land branch of the Antarctic Bottom Water (ALBW, Rintoul et al., 2008). This bottom water is detected by CTD and mooring measurements up to about 3200m of depth, in the Jussieu canyon and further to the west. The speed of the ALBW is enough to transport fine sand and silt from shallow to deep water as documented by sea bed sediments. Similar bottom currents activity is recorded also during Quaternary glacial and interglacials (Caburlotto et al., 2009, Macrì et al., 2005) with source in the George V Land rocks and in the continental shelf (Damiani et al., 2006).
The meandering charater of the Jussieu canyon and the sediment wave field on its eastern ridge, would suggest that they likely formed under the action of downslope, continous, bottom current, since the early Pliocene (Escutia et al., 2010).
Caburlotto A., Lucchi R.G., De Santis L., Macrì P., Tolotti R. 2010. Sedimentary processes on the Wilkes Land continental rise reflect changes in glacial dynamic and bottom water flow. International Journal of Earth Sciences, 99(4), 909-926.
Damiani D., Giorgetti G., Memmi Turbanti I. 2006. Clay mineral fluctuations and surface textural analysis of quartz grains in Pliocene–Quaternary marine sediments from Wilkes Land continental rise (East-Antarctica): Paleoenvironmental significance. Marine Geology, 226,81-295.
Escutia C., Brinkhuis H., Klaus A. & Expedition 318 Scientists 2011. Proc. Intergrated Ocean Drilling Program, 318. Macrì P., Sagnotti L., Dinares-Turrel J., Caburlotto A. 2005. A composite record of Late Pleistocene relative geomagnetic paleointensity from the Wilkes Land Basin (Antarctica). Physics of the Earth and Planetary interiors, 151, 223-242.
Post A.L., O’Brien P.E., Beaman R.J., Riddle M.J., De Santis L. 2010. Physical controls on deep water coral communities on the George v Land slope, East Antarctica 2010. Antarctic Science, 22 (4), 371-378.
Rintoul S.R. 1998. On the origin and influence of Adelie Land bottom water. In: Ocean, Ice and Atmosphere: Interactions at the Antarctic Continental Margin. American Geophysical Union, Washington DC, 151-171.
U-Pb SHRIMP zircon dating of magmatic rocks dredged from the
South Tasman Rise (Australia)
Fioretti A.M.1, Bergomi M.2, Caironi V.*3, Korsch R.J.4, Tunesi A.2 & Visonà D.5
1. CNR - Istituto Geoscienze e Georisorse Padova. 2. Dipartimento di Scienze dell'Ambiente e del Territorio e di Scienze della Terra, Milano Bicocca. 3. Dipartimento di Scienze della Terra A.Desio, Università degli Studi di Milano. 4. Geoscience Australia, Canberra, ACT, Australia. 5.
Dipartimento di Geoscienze, Università di Padova. Corresponding email: [email protected]
Keywords: South Tasman Rise, U-Pb SHRIMP zircon, AGSO cruise 147.
The South Tasman Rise (STR) consists of the west- and east-South Tasman Rise, which are submerged continental fragments that were part of the East Gondwana Continent. The STR formed following the extension between Antarctica and Australia that generated the Tasmanian Gateway. It is located between Tasmania and Antarctica and represents a vital, but often overlooked, link to understand the geological evolution of both North Victoria Land and Tasmania. Reconstruction of Gondwana shows that STR was contiguous to several continental fragments that are now thousands of km apart. Because of its central location in the plate boundary framework that developed within East Gondwana, the STR underwent all the major tectonic events that led to the dispersal of Gondwana. The STR is therefore a centrepiece in understanding the complex tectonic history of this region.
Extensive sampling of STR rocks took place during AGSO cruise 147. Investigation on the metamorphic rocks of the STR pointed out interesting correlations with rocks from the Wilson Terrane and the Lanterman Metamorphics (Antarctica) and from Tasmania (Berry et al., 1977).
Based on this evidence, and aiming at clarifying the correlation between mainland Australia, Tasmania and Antarctica, we undertook a detailed petrologic and geochronologic study on magmatic rocks dredged at 10 different sites from South Tasman Rise. Seven of these rocks yield Cambrian ages in the range 487-507 Ma, consistent with the Ross-Delamerian orogen; one sample is a granite gneiss of late Proterozoic crystallization age (ca. 740 Ma), which corresponds to the Wickham event (Tasmania) or Beardmore orogen (Antarctica); one sample has Grenville age (Fioretti et al., 2005); and one sample is Late Devonian (ca. 363 Ma), an age that is well represented in Australia, Tasmania and Antarctica.
Petrographic observation, geochemical investigation and zircon typologic study are presented here to characterize these rocks, and to test their possible correlation with coeval rocks in Antarctica and Australia.
Berry R.F., Meffre S. & Kreuzer H. 1997. Metamorphic rocks from the southern margin of Tasmania and their tectonic significance. Australian Journal of Earth Sciences, 44 (5), 609-619.
Fioretti A.M., Black L.P., Foden J. & Visonà D. 2005. Grenville-age magmatism at the South Tasman Rise (Australia): a new piercing point for the reconstruction of Rodinia. Geology, 33 (10), 769-772.