Chang'e-6 Basalts Show Uniform Mantle Cumulates Across Lunar Hemispheres

The Nanjing University team measured major and trace elements in three rock suites from the far-side South Pole-Aitken basin. Basalts and Mg-suite rocks display mantle-derived signatures indistinguishable from near-side equivalents, while anorthosites record higher peak Mg# and lower Th/Sm ratios. This pattern isolates crustal asymmetry to processes operating above the mantle-cumulate layer. The data favor large-scale, post-tidal-lock convection in the lunar magma ocean that redistributed KREEP and heat-producing elements only in the crust. Earlier models invoking primordial mantle heterogeneity or a single giant impact now require additional mechanisms to explain the new uniformity at depth.

Remote sensing from Kaguya and Lunar Reconnaissance Orbiter had already hinted at thicker far-side crust, yet lacked mantle samples. Chang'e-6 supplies the first direct test, showing that any early collision or tidal heating must have been buffered by vigorous magma-ocean mixing before crust formation. The absence of mantle contrast narrows viable explanations to late-stage crustal foundering or asymmetric plagioclase flotation driven by global convection cells.

Future missions carrying heat-flow probes or electromagnetic sounders can test whether predicted lateral temperature gradients persist in the uppermost mantle. Sample return from additional far-side sites would further constrain whether the observed crustal Mg# offset is global or localized to the South Pole-Aitken region.