Architecture of the lithosphere of Terre Adélie
The main goal of the ArLiTA project is to characterise the structures and the deformation of the Terre Adélie and George Vth Land (East Antarctica: 135 to 145° E) lithosphere. The ArLiTA project corresponds to a multidisciplinary approach that combines a set of various analysis and interpretation methods, in order to relate field observations to the large scale geodynamics models. Lithospheric structures are characterised using a multi-scale approach from the study of the crystalline structures observed by electron microscopy to regional structures mapped by seismological data analysis. At the field scale, the use of modern petrophysical tools such as the measurement of the anisotropy of magnetic susceptibility (AMS) will lead to a systematic cartography of the deformation structures (foliation, lineation). The absolute timing of Terre Adélie Craton (TAC) build-up and deformation is key to interpret all the gathered data in the broadest framework of Neoarchean to Paleoproterozoic geodynamics but also to quantify more recent exhuation processes. The project thus deploys multi-method geochronology in close relationship with structural and petrological observations. All these various studies take place in the different crustal blocks (including bedrock and moraines) constituting the TAC and that are considered as representing various levels of Neoarchean and Paleoproterozoic crustal segments. Moreover, the ArLiTA project also focuses on the relationships between the deformation structures and the transfers of geological fluids (silicate melts, hydrous or carbon-rich fluids, etc.) within the crust. The latter question requires geochemical investigations, and more precisely stable isotopes studies on the paleo-fluids and the related mineralization.
The petrophysical approach to determine the physical properties of rocks and thus better constrain the interpretation of large-scale geophysical data, in particular, seismic and magnetic, from the rocks sampled in Terre Adélie remains an important axis of the project. From a seismological point of view, data on the deep structures of the continental crust and lithosphere are based on records from the permanent station located at the Dumont d’Urville French station (GEOSCOPE network) and the temporary stations deployed during ArLiTA_1 (2009-2013). With respect to rocks magnetism, magnetic susceptibility measurements carried out from rock drilling will be used to determine the deformation regime at the origin of the tectonic structures but also for the interpretation of aeromagnetic survey data associated with international programs (e.g., ADMAP). This will provide an essential contribution to the current knowledge of the lithospheric structures of the East Antarctic shield and more particularly those of the TAC. This will allow for reliable comparisons with the Gawler Craton in South Australia, whose geophysical characteristics are well documented and which is considered to be the northern extension of the TAC.