CHEMICAL AND PHYSICAL INDICATORS OF COMPROMISED MELT INCLUSIONS

Abstract

The utility of the geochemistry of basaltic suites as probes of mantle processes is encumbered by the processing those magmas undergo during transport from the field of melting to the ocean floor. Melt inclusions provide us with an opportunity to obtain information on intermediate stages in the evolution of a magma system. Such data can be an extra constraint for our modeling of petrologic processes. However, melt inclusions have generally undergone some degree of post-entrapment crystallization. Therefore, to quantify the details of geochemical trends represented by melt inclusion suites, we must construct a set of criteria to evaluate the degree to which any inclusion or set of inclusions represents the original trapped liquid composition. The problems encountered in evaluating the degree to which inclusion compositions depart from that standard fall into three categories: (1) Errors caused by the selection of the temperature or time of heating; (2) Loss or gain of volatiles caused by inclusion rupture; (3) Contamination from alteration products such as manganese oxides or salts in the host crystal.The criteria that may be used to evaluate the veracity of rehomogenized inclusion compositions include examination of the relationship of the inclusion composition to the host lava suite, the morphology of the inclusion, the Fe and S content relative to the host suite, and the MnO content relative to the inclusion suite and the host lavas.