Solid and fluid inclusions in mantle xenoliths: An analytical dilemma?
Two Cr-diopside Iherzolite xenoliths with kaersutite selvages, from Dish Hill, California, contain four types of solid and fluid inclusions that can be used to discriminate between actual mantle processes and processes acting upon a fragment of mantle as it is entrained and carried to the earth surface. On the basis of distribution, early formed inclusions are assigned to a process associated with emplacement of dikes in the mantle. The other types of inclusions were generated during ascent in the host basalt magma.
Solid and fluid inclusions are important sites of incompatible element concentrations in mantle xenoliths. Scientists assigning specific chemical signatures to mantle processes are confronted with an analytical dilemma: leaching of xenolith samples before analysis may destroy inclusions that are carrying intrinsic mantle components, whereas failure to leach the samples probably leaves a host-rock contaminant. Thin-section maps of these xenoliths show that the distribution and abundance of two types of solid inclusions are systematic. Through the use of these maps it is demonstrated that zones in xenoliths with the least amount of postentrainment contamination can be pinpointed, and the problems resulting from random leaching can be minimized.
|Solid and fluid inclusions in mantle xenoliths: An analytical dilemma?
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