Detection of recycled marine sediment components in crater lake fluids using super(129)I

• Published in: Journal of volcanology and geothermal research Vol. 115; no. 3-4; pp. 451 - 460
• Main Authors: Fehn, U, Snyder, G T, Varekamp, J C
• Format: Journal Article
• Language: English
• Published: 30.06.2002
• Subjects: Freshwater
• ISSN: 0377-0273
• DOI: 10.1016/S0377-0273(01)00325-0

Crater lakes provide time-integrated samples of volcanic fluids, which may carry information on source components. We tested under what circumstances super(129)I concentrations can be used for the detection of a signal derived from the recycling of marine sediments in subduction zone magmatism. The super(129)I system has been successfully used to determine origin and pathways in other volcanic fluids, but the application of this system to crater lakes is complicated by the presence of anthropogenic super(129)I, related to recent nuclear activities. Results are reported from four crater lakes, associated with subducting crust varying in age between 23 and 98 Ma. The super(129)I/I ratios determined for Copahue, Argentina, ( super(129)I/I=700x10 super(-15)) and White Island, New Zealand, ( super(129)I/I=284x10 super(-15)) demonstrate the presence of iodine in the crater lakes that was derived from recycled marine sediments. A comparison to the ages of the subducted sediments in these two cases indicates that the ratios likely reflect iodine remobilization from the entire sediment column that was undergoing subduction. While the super(129)I signals in Poas and Rincon de la Vieja, Costa Rica also demonstrate the presence of recycled iodine, the relatively high percentage of meteoric water in these lakes prevents a reliable determination of source ages. The observed high concentrations of iodine and super(129)I/I ratios substantially below current surface values strongly argue for the presence of recycled marine components in the arc magmas of all four cases. Components from subducted marine sediments can be quantified and related to specific parts of the sediment column in cases where the iodine concentration in the lake waters exceeds 5 mu M.