Presentation Information
[S2-P-05]Variation of serpentinization paragenesis at Atlantis Massif, Mid-Atlantic Ridge
*Shun KAZUMATA1, Toshio NOZAKA1 (1. Okayama University)
Keywords:
serpentinization,olivine gabbro,peridotite,brucite,cronstedtite
We report serpentinization parageneses of olivine gabbros and peridotites recovered from Atlantis Massif during IODP Expeditions 304, 305, and 399. Our main findings include (1) olivine is commonly cut by serpentine (mainly lizardite) veins to form mesh texture; (2) magnetite and pyrrhotite occur at the center of serpentine veins and do not at the margin of veins; (3) serpentine veins are compositionally heterogeneous, suggesting mixing (mechanical mixing or solid solution) of brucite, cronstedtite, chlorite, hisingerite, or saponite; (4) in olivine gabbros with an average plagioclase Ab value [100Na/(Na+Ca) mol] > 30, brucite/cronstedtite is absent and hisingerite/saponite is present in serpentine veins; (5) in olivine gabbros with an average plagioclase Ab < 30, cronstedtite and/or brucite are present in the serpentine vein margins; (6) in olivine gabbros with a similar average Ab value of plagioclase, cronstedtite and brucite occurs in serpentine veins replacing olivine with relatively low Fo values [100Mg/(Mg+Fe) mol] and high Fo values, respectively; (7) in peridotites, serpentine veins are mixed with brucite and no cronstedtite. These results suggest that paragenesis at an initial stage of serpentinization is controlled by the degree of crystallization differentiation of the host igneous rocks.