Bulk mineralogy of lunar crater central peaks via thermal infrared spectra from the Diviner Lunar Radiometer: A study of the Moon's crustal composition at depth

The central peaks of lunar impact craters are thought to be composed of uplifted material originating from varying depths of the crustal column. The interpreted crystallization sequence of the early lunar magma ocean resulted in an anorthositic upper crust that may become progressively more mafic as it approaches the olivine-rich mantle. Emissivity spectra from the Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer are used to derive the wavelength location of the Christiansen Feature (CF), which is sensitive to bulk silicate mineralogy. Here a survey of CF values has been performed for the central peaks of 135 complex craters, providing global and regional observations of the heterogeneity of crustal compositions. Crustal thickness models give context to the preimpact depth of the central peak material and its proximity to the crust-mantle boundary. This study has identified six craters with potentially ultramafic compositions within their central peaks. More common occurrences of mafic material, found in a wide variety of crater central peaks, show a silicate composition roughly similar to mare basalt or an olivine-bearing gabbro. The range of central peak CF values is similar to that of the rest of the lunar surface. Bulk mineralogy of the central peak material does not appear to be correlated with its crustal depth of origin, suggesting both lateral and vertical heterogeneity in crustal composition rather than a gradual transition from felsic to mafic composition. It is likely that the Moon's extensive cratering history has continually overturned the original crust, erasing any original systematic dependence of composition on depth or proximity to the mantle.