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1. Heterogeneity

   Linked via "sub-surface structure"

   Crustal Inclusions and Isotopic Signatures
   One of the most explicit demonstrations of large-scale geological heterogeneity is the presence of xenoliths—foreign fragments incorporated into an igneous rock mass. The study of these inclusions provides critical insights into the sub-surface structure through which the magma traveled 5. For example, the isotopic signature of a mantle-derived xenolith often exhibits a $\text{Pb}^{207}…