Mineralogy and mobility of chemical elements at water-basalt interaction, Hole 504B

摘要

All studied basalts and dolerites from Hole 504B (DSDP/ODP Legs 69, 70, 83, 111, 137, 140, and 148) from the Costa Rica Rift are altered to various degrees in low to high-temperature hydrothermal environments. Temperatures of alteration reached > 380°C in the lower dike section (1500-2111 m below sea floor). Basalts from the volcanic section were smectitized. Chlorites occur lower into the sheeted dike complex. In the sheeted dike complex, wide spread amphibolitization of igneous rocks is common. Results on the mobility of elements during alteration of igneous rocks from the drill hole revealed that in the reaction zone (the lower dikes) the most marked loss of elements is found for Si, Ti, Fe, Mn, Mg, Zn, La, Sm, Yb, Eu, and Lu. The elements Al, Ca, Na, P, Cu, Zr, Ce, Nd, and Tb are variably depleted or enriched in the main zone.