Correlative Tomography for Polymineralic Inclusion Composition in Sublithospheric Diamonds

Abstract Sublithospheric diamonds and their inclusions are the deepest known samples from the Earth's mantle. Typically, the inclusions are trapped as minerals which are only stable in the deep mantle, retrogressing into multiple phases during their uplift. Determining the bulk inclusion composition is difficult but crucially important. Here we use micron‐scale synchrotron X‐ray computed tomography alongside μ‐Raman mapping to reconstruct primary inclusion compositions of seven former Ti‐rich CaSi‐perovskite inclusions, which had retrogressed to assemblages of breyite and perovskite. The inclusions display Ti#s (molar Ti/[Ti + Si]), ranging from 0.03 to 0.60. In diamonds with previously reported coexisting inclusions, former bridgmanite coexists with lower Ti# CaSi‐perovskite and garnet inclusions with higher Ti# CaSi‐perovskite. This observation is consistent with published petrological experiments on mafic compositions suggesting that CaSi‐perovskite undergoes a decrease in Ti# after the post‐garnet transition. Thus variations in Ti content of CaSi‐perovskite inclusions are interpreted as differences in formation pressures.