A Strontium Isotopic Investigation of Fluid-Solid Exchange During Hydrothermal Circulation in the Troodos Ophiolite

Abstract

The structure of sea floor hydrothermal systems and the nature of fluid-solid exchange processes are still poorly constrained despite the significance of the hydrothermal activity to the chemical s t ructure of the ocean crust and oceanic chemistry. Here we report preliminary results of an investigation into the structure of fluid flow and the nature of fluid-solid exchange mechanisms in the upper part of the oceanic crustal sequence preserved in the Troodos ophiolite. The lava sequence on Troodos exhibits a wide range of 90 Ma 87Sr/S6Sr interpreted to imply that fluidsolid exchange was kinetically limited in the upper part of the recharge zone of the high temperature hydrothermal systems (Bickle and Teagle, 1992). The extent of fluid channelling, fluid S7sr/g6sr isotopic composition and possible controls on fluid-solid exchange processes have been investigated by analysing altered basalt, zeolite minerals crystal l ised f rom hydro the rmal fluids and mapping strontium isotopic gradients on centimetre to metre scales. Results from two localities are reported. At the first locality pillows and a single crosscutting dyke from within the lower pillow lavas have been profiled in detail (Figs. 1,2). Samples from the dyke locality (Fig. 1) scatter about a 98-1-13 Ma errorchron. No obvious gradients in STSr/S6Sr are resolved (Fig. 3) despite mineralogical differences between dyke margin and pillow