Hydrothermal alteration associated with rift zones at Fangataufa atoll (French Polynesia) |
| |
Authors: | P Dudoignon D Proust A Gachon |
| |
Institution: | (1) Ecole Supérieure d'Ingénieurs de Poitiers, Université de Poitiers URA 721 du CNRS, F-86022 Poitiers cedex, France, FR;(2) Université de Poitiers URA 721 du CNRS, Université de Poitiers, F-86022 Poitiers cedex, France, FR;(3) CEA/DAM/B3, Service LDG, BP 12, F-91680 Bruyères-le-chatel, France, FR |
| |
Abstract: | The Mururoa and Fangataufa atoll basement consists of superimposed submarine and subaerial lava flows which have been intruded
by late volcanics. The intrusions have developed large hydrothermal alteration haloes throughout the basaltic wall rock. The
cuttings of the Natice-1 and Mitre-1 holes, drilled into the submarine volcanic pile at Fangataufa atoll, show a vertical
zonation of clay minerals ranging from 270 to 850 m depth. The newly formed clay minerals occurring from top to bottom of
the altered pile are: dioctahedral aluminous smectites, saponite, an intimate assemblage of saponite with two random chlorite/saponite
mixed layers and an intimate assemblage of one random chlorite/saponite mixed-layer with one ordered chlorite/saponite mixed
layer and one chlorite below 816 m depth. These clay mineral assemblages indicate a general increase in the chloritic component
with depth. They are associated throughout the pile with secondary carbonates and quartz. The ∂18O and ∂13C of calcite and ∂18O of clay minerals, on the one hand, and the intimate mixtures of trioctahedral species, on the other, suggest a general cooling
with the evolution of a paleogeothermal gradient from approximately 300 °C/km during the crystallization of chlorite to 150 °C/km
for the late calcite precipitation.
Received: 2 October 1995 / Accepted: 14 January 1997 |
| |
Keywords: | Volcanic atoll Hydrothermal alteration Clay minerals Chlorite/saponite mixed layer Geothermometry |
本文献已被 SpringerLink 等数据库收录! |
|