Metamorphic petrology of ODP Leg 109, Hole 670A serpentinized peridotites: serpentinization processes at a slow spreading ridge environment

Abstract

In this paper we describe textural relationships in hydrated upper mantle peridotites emplaced at a nonconstructive ridge segment. Development of serpentinites and partially serpentinized peridotites takes place in four main stages: 1) pervasive serpentinization forming mainly lizardite, 2) a tensional stage forming chrysotile + talc + chlorite, 3) a deformational stage forming antigorite + tremolite, and 4) a late local tensional stage forming another generation of chrysotile veinlets. Mineral chemistry of serpentine pseudomorphs reflects in part primary mineral compositions. Chemical patterns in the serpentinites can be used to help discriminate between harzburgitic and lherzolitic protoliths. Oxygen isotopes and mineral parageneses suggest serpentinite is derived from circulation of hydrothermal (200°C) fluids through the peridotite body. -from Authors