Geochemical tomography sections based on mantle-derived pyrope garnet xenocrysts have been constructed for different tectonic domains along a southern transect crossing the Tasman Line. At the regional scale, these sections reveal thicker lithosphere and lower geothermal gradients with increasing tectonothermal age of the lithosphere domains. In a transect from the easternmost locality (Jugiong) in Phanerozoic eastern Australia to the Eyre Peninsula (Gawler Craton) in Proterozoic South Australia, the palaeogeotherm decreases from greater than 50 mW/m 2 at Jugiong to around 40 mW/m 2 In South Australia and the depth to the lithosphere-asthenosphere boundary changes from ∼100 to 180 km. Geochemical tomography sections for the Gawler Craton region sampled in the Permian and the Jurassic, indicate lithosphere thinning by about 10–15 km, attributed to the effect of Pangean rifting. These physical changes are paralleled by higher MgO and lower CaO and AI 2 O 3 contents in progressively older lithospheric mantle, consistent with the global secular variation in mantle composition previously documented. Olivine is the most abundant mantle mineral in all sections and the Fe/Mg ratio of olivine is important in controlling the physical properties of lithospheric regions (density, Vp, Vs). Because olivine is rarely preserved, an inversion of the garnet-olivine Fe-Mg-exchange geothermometer has been used to calculate the Fe/Mg of olivine coexisting with each garnet grain. Application of this inversion to the southern Australian transect shows high Mg# (Mg/(Mg+Fe)) for olivine in the shallow parts of the Proterozoic western sections and more Fe-rich olivine in the Phanerozoic eastern sections. There also is an overall trend to lower Mg# with increasing depth in each section, which may reflect infiltration by asthenospherlc melts near the lithosphere-asthenosphere boundary. Olivine density varies inversely with Mg#, and the Proterozoic lithosphere in this traverse therefore is more buoyant, relative to the asthenosphere, than the Phanerozoic sections despite the lower geotherm beneath the craton. Vp and Vs vary directly with Mg# (the higher the Mg#, the higher the Vp and Vs) and thus these compositional differences are important in the interpretation of seismic tomography.

Abstract After the end of Hercynian orogeny, most of the territory of continental France had been consolidated into a rigid platform ("môle des Gaules"). The base of the trasgressive secondary layers, deposited during Triassic or Jurassic eras on this platform, consists of neritic or lagunal deposits. All around the exposures of ancient massifs (Massif Armoricain, Massif Central), very near from the old shore lines, are located different deposits of the strata-bound Pb. Zn, Ba, F type, as shown in Figure 1. The concept of regional metallotect (cf. reference) gives a way of understanding the geological regularities and the geographical location of these deposits which seems a much better one than a controversy on genetic theories. This is, in fact, connected with the author's conception as follows: this type of deposit results from the action of different genetic processes which took place simultaneously or successively (Fig. 2). The regional metallotect which is connected with the deposits shown on Figure 1 (neritic layers of shallow water sediments transgressive after orogeny near the shore lines), gives a good guide to ore exploration from a strategic point of view.

Abstract The IGUANES cruise took place in May 2013 on the R/V L’Atalante along the Demerara passive transform margin off French Guiana and Surinam. Seismic, multibeam and chirp acquisitions were made. Piston cores were collected for pore geochemistry and sedimentology. A mooring was deployed on the sea-bottom for 10 months (temperature, salinity, turbidity and current measurements). This new dataset highlights the lateral variability of the 350 km-long Guiana–Surinam transform margin due to the presence of a releasing bend between two transform segments. The adjacent Demerara Plateau is affected by a 350 km-long giant slide complex. This complex initiated in Cretaceous times and was regularly reactivated until recent times. Since the Miocene, contourite processes seem to be active due to the onset of the North Atlantic Deep Water (NADW) bottom current. A main NADW water vein flows towards SE, eroding slide headscarps and allowing the deposition of contourite drifts. Numerous depressions looking like comet tails or comet scours record this flow. Some of those were interpreted before the cruise as active pockmarks. Pore geochemistry and core analysis do not show any evidence of present-day gas seepage.

Abstract The present study provides an overview of recent sedimentation patterns on the central Algerian continental margin. Recent sedimentation patterns were assessed from morphological analysis, which is based on swath bathymetry and echo-facies mapping. It appears that sedimentation along the Algerian margin is controlled by two processes: (1) gravity-induced processes, including both mass-transport deposits and turbidity currents, and (2) hemipelagic sedimentation. Mass-transport deposits occur on the Algerian margin at the canyon heads and flanks, in the interfluve areas between canyons, along the seafloor escarpments, and on the flanks of salt diapirs. Mass-transport deposits (MTDs) sampled by coring consist of a variety of soft and hard mud-clast conglomerate and turbidite deposits. MTDs are mostly localized at the toes of steep slopes, where thrust faults were previously identified and mapped. Analysis of the spatial distribution of MTDs and their recurrence in time help reconstruct the main predisposing factors and triggering mechanisms, and evaluate their impact on evolution of the Algerian margin.