Orphan strontium-87 in abyssal peridotites: Daddy was a granite

The 87Sr/86Sr ratios in some bulk abyssal and alpine peridotites are too high to be binary mixtures of depleted mantle and seawater components. The apparent excess, or orphan, 87Sr appears to be separated from its radioactive parent. Such observations were widely held to be analytical artifacts. Study of several occurrences of orphan 87Sr shows that the orphan component in abyssal peridotite is located in the alteration products of olivine and enstatite in the peridotite. The orphan 87Sr is most likely introduced by infiltration of low-temperature (\u3c200°C) seawater bearing suspended detrital particulates. These particulates include grains of detrital clay that are partly derived from continental (that is, granitic) sources and thus are highly radiogenic. Orphan 87Sr and other radiogenic isotopes may provide a tracer for low-temperature seawater penetrating into the oceanic crust