The Origin of Typical NMORB: The Evidence from a Melt Inclusions Study

In the recent studies mid-ocean ridge basalts (MORBs) are frequently regarded as mixtures of separate fractions of melt generated in mantle columns which are highly permeable even for small amounts of melt. This view is based on the theoretical models (e.g. McKenzie and Bickle, 1988), abyssal peridotite studies (e.g. Johnson et aL, 1990) and discovery of ultra-depleted melts (UDM) as inclusions in the high-Mg olivine in NMORBs (Sobolev and Shimizu, 1993; Sobolev et al., 1994). The present paper reports results of a detailed study of the same NMORB sample in which the first UDM was found, showing that the process of MORB formation is recorded in melt inclusion compositions and could be revealed by microbeam analysis techniques.