Abstract
Lunar mare basalts are the products of their corresponding parent magma
compositions, sourced from the lunar upper mantle. The lunar mantle has
been repeatedly modeled through numeric simulations to reflect lunar
magma ocean (LMO) crystallization, resulting in an early-stage
anorthositic crust and immediately underlying, late-stage, KREEP-rich
and ilmenite-rich layer. This negatively buoyant layer is expected to
have induced mixing with the underlying mantle, potentially to the
core-mantle boundary. The lunar mare basalts, in this context, reflect
mantle sources that are variably mixed between pristine mantle
compositions and the dense ilmenite-rich layer. In order to constrain
the geometry of lunar mantle heterogeneity, we simultaneously examined
multiple mare basalt characteristics to extract significant multivariate
patterns that might lend insight into the nature of this mixing-induced
heterogeneity. Using two fundamental machine learning approaches and a
newly compiled database of Apollo basalt characteristics
(ApolloBasaltDB), we conducted a preliminary investigation, holding the
assumptions that 1) mare basalts are assumed to retain the majority of
their original characteristics at the time of extrusion: texture,
isotopic age, major element composition, mineral mode, and geographic
occurrence; 2) negligible basalt alteration occurred due to the lack of
an atmosphere; and 3) impact gardening did not have significant bearing
on final geographic location of basalt samples based on our nearside
spatial partitions. The results of cluster and principal component
analyses over changing spatial basalt groupings suggest that lunar
nearside changes in major element concentrations and mineral modes vary
spatially. Al2O3 concentrations increase in diversity within the
Procellarum KREEP Terrane (PKT) compared to older regions immediately
exterior to the eastern PKT, while a general nearside trend appears to
suggest that ilmenite (TiO2) diversity comes at the expense of
plagioclase (Al2O3) diversity. Cluster analysis suggests PKT perimeter
rifting may have tapped into increasingly Ti-rich sources as rifting
proceeded SE to NW. By establishing such trends over varying spatial
scales through multivariate processing, the changing strengths of these
surface correlative patterns may indicate the changing conditions
(including temporal) of the immediately underlying mantle at the time of
extrusion.