6. PALEOFLUIDS FROM THE MARGINAL RIDGE OF THE CÔTE D’IVOIRE-GHANA TRANSFORM MARGIN (HOLE 960A) AS THERMAL INDICATORS¹

Marc Lespinasse², Jacques L. Leroy², Jacques Pironon³, and Marie-Christine Boiron³

ABSTRACT

Fluid inclusions linked to two quartz veins from the bottom of Hole 960A were studied using microthermometry and Raman microprobe analysis. Results suggest that circulation of hot fluid (160°–170°C) under low pressure (10–20 MPa) occurred within the marginal ridge of the Ivory Coast-Ghana Transform Margin. The fluid composition varies with time, and is either seawater or a mixture of H₂O-CH₄-CO₂ fluids. Possible sources of heat for these fluids include circulation in friction zones linked to transform-fault dynamics, either at depth in a thinned continental crust or in the hot oceanic crust south of the sampled area. The passage of the Mid-Atlantic Ridge axis to the south of the sampled zone occurred later than the vein formation and therefore cannot be considered a heat source.

¹Mascle, J., Lohmann, G.P., and Moullade, M. (Eds.), 1998. Proc. ODP, Sci. Results, 159: College Station, TX (Ocean Drilling Program).
²Université Henri Poincaré Nancy 1, Laboratoire Etude des Systèmes Hydrothermaux, BP 239, 54506 Vandoeuvre-lès-Nancy cedex, France. lespinas@lpesh.u-nancy.fr
³CREGU and GDR CNRS-CREGU 077, BP 23, 54501 Vandoeuvre-lès-Nancy cedex, France.