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International audience; Submersible investigations employing heat flow measurements (12 stations), sampling and imagery of the two relict high-temperature hydrothermal zones of the TAG field, the Alvin and Mir sulfide zones, elucidate relations between heat sources and mineralization including an active sulfide mound that has been the focus of prior studies. Values of heat flow in the Mir zone and at the margin of the active mound are inversely proportional to distance from adjacent volcanic centers. This observation supports the hypothesis that intrusions at volcanic centers adjacent to the high-temperature hydrothermal zones supply the heat to drive hydrothermal activity. The chronology of hydrothermal deposits in the different zones indicates that the intrusions are episodic with field-wide high-temperature hydrothermal events recurring at intervals of tens of thousands of years, while activity at individual zones may recur at intervals of hundreds to thousands of years. A sequence of hydrothermal deposits ranges to at least 140,000 years ago from massive sulfides forming at the active mound, to recrystallization of sulfides in the active and relict zones, to pyritization of an inactive mound in the Alvin zone; low-temperature mineral phases precipitate before, during and after the sulfides. a 5 x 5 km area of the floor and wall on the east side of the rift valley near the center of a spreading segment of the Mid-Atlantic Ridge near 26øN, 45øW (Fig. 1; Rona et al., 1993). A microearthquake survey of the TAG segment indicated that the

International audience

Geochronological studies of a large number of precipitates from the TAG hydrothermal field and of few samples from Snakepit hydrothermal field of the Mid-Atlantic Ridge show intermittent repeated hydrothermal events at both sites. 210Pb/Pb and 230Th/234U measurements of sulfides, iron and manganese oxides, and 14C measurements of carbonates combined with observations of hydrothermal events recorded as discrete layers in sediment cores provide the basis for unravelling the temporal history of the fields. The TAG field shows intermittent activity over the past 120,000 years as evidenced by ages of low-temperature Mn oxides. The presently active black smoker mound first formed about 40,000–50,000 years ago with precipitation of massive sulfides. It has had intermittent, pulsed high-temperature activity every 5000–6000 years over the past 20,000 years which may reflect renewed magmatic activity at the ridge axis. Fluid flow is focussed at the mound site by structural and tectonic control suggested by the intersection of N-S ridge parallel lystric normal faults and an E-W transform fault. Periods of inactivity are marked by covering of the mound with pelagic carbonate ooze which is probably partially dissolved and reprecipitated as aragonite at the end of each high-temperature event. The Snakepit field had an initial event about 4000 years ago, probably shortly after the eruption of the volcanic ridge on which it sits. A recent renewal, still presently active, was probably initiated by recent fissuring of the volcanic pile.

International audience; Background: The use of natural products as anticancer and antioxidant agents has a long history. Several chemotherapy drugs were isolated from medicinal plants. Objective: The present study was aimed to provide information on cytotoxic and antioxidant activity of cyclohexane, dichloromethane and methanol extracts of Corrigiola telephiifolia.Materials and method: The plant roots were dried, powdered and extracted successively by cold maceration with: cyclohexane, dichloromethane and methanol for 48h. All extracts have been assessed for antioxidant activity against DPPH (1,1-diphenyl-2-picrylhydrazyl) radical and cytotoxic activity against murine colon adenocarcinoma CT-26 and melanoma cell lines WM-266.Results: The dichloromethane extract exhibited potent cytotoxicity with an IC50 of 80 ± 4.56 for CT-26 cells and 70 ± 6.1 µg/ml for WM-266 cells. The extracts exhibited moderate antioxidant activity with IC50 value of 10.53 µg/ml of the dichloromethane extract compared to the IC50 value of 4.71 ± 0.83 µg/ml as shown by the reference antioxidant Trolox.Conclusion: The potential activity of Corrigiola telephiifolia root extract may due to their phytochemical constituents, these species could be considered as potential sources of anticancer compounds. Further studies are necessary for chemical characterization of the active principles and more extensive biological evaluations.