Postcumulus Processes Recorded in Whole-Rock Geochemistry: a Case Study from the Mirabela Layered Intrusion, Brazil.

This article focuses on testing the "trapped liquid" paradigm versus open-system models of cumulate solidification in layered mafic–ultramafic intrusions, using a large geochemical dataset from the Mirabela layered intrusion in Brazil. Analysis of over 63,000 whole-rock samples shows strong correlations among variably compatible excluded elements (Ti, P, Al, Na) at sampling scales of about 3 meters, supporting a closed-system model where intercumulus liquid is effectively immobile during solidification. The study finds that trapped liquid content increases symmetrically from the intrusion center toward the margins, with no evidence of compaction-driven liquid expulsion, as layer thickness does not decrease where trapped liquid content is low. Potassium is the only element showing partial decoupling, likely due to late-stage mobility in an aqueous fluid phase, but there is no indication that this fluid mobilized platinum group elements or chalcophile elements within the cumulates.