Metal accumulation rates in sediments from Mid-Indian Ocean Ridge and Marie Celeste Fracture Zone

Abstract

THE existence of metalliferous sediments on mid-ocean ridges is well documented1 and the general conclusion is that they form by precipitation from submarine hydrothermal solutions. Pacific and Atlantic Ocean sediments have been studied in detail2–6. We describe here material from the Indian Ocean Ridge, collected during cruise 8/75 of RRS Shackleton, and compare metal accumulation rate data for ridge-crest and -flank sediments with those from other regions. The metalliferous sediments are present on the Mid-Indian Ocean Ridge, particularly near the Triple Junction7,8, and Bostrom and Fisher7 suggest that “there is a complete belt of iron-rich sediment along the entire length of the Indian Ocean–Pacific Ocean active-ridge system”. We have found ferromanganese encrustations on basalts from the median-valley wall and have recognised what are probably sulphides in decorated vesicles of basalts. The metal accumulation rate data argue against a hydrothermal source of metals in the ridge sediments, however, and suggest that metalliferous sediment accumulations in the Indian Ocean may be more local phenomena than previously realised.