Popis: |
During the Soviet-French survey carried out on board of the R.V. Akademik N. Strakhov , between Guadeloupe and Montserrat island in the central Lesser Antilles, evidence of submarine hydrothermal activity was discovered on the southeastern tip of the Shoe-Rock escarpment. The latter is part of a large, 130 km long, transverse structure, the Montserrat-Marie Galante fault, which crosses the Guadeloupe archipelago. Another locus of activity, probably of subdued importance nowadays, is represented by the d'Entrecasteaux dome, a small faulted seamount, located about 25 km to the SW of the former area. The evidence for hydrothermal activity is: (a) a wide range of values of conductive heat flow ( q =6–11 mW/m 2 ) and regular vertical variation at some sites with extreme values located close to the two above-mentioned features (average regional value, q = 105 mW/m 2 , s.d. = 32); (b) occurrence of secondary mineralizations (todorokite, nontronite, etc.) replacing locally the primary matrix of basal upper Pliocene deposits; (c) geochemical anomalies in seawater near the sea bottom, showing enrichment in mantle-derived 3 He ( δ 3 He up to 10.2%), correlated with a sharp Zn anomaly (content up to 523 ppb). Further investigations along the submerged segments of the Montserrat-Marie Galante fault should probably lead to other discoveries of hydrothermal venting and/or mineralizations. |