Decoding the enigmatic Lunar troctolite 76535

The sample's high-temperature history may constrain the timing of mantle overturn

Lunar troctolite 76535 is a pristine sample of the lunar highlands Mg-suite, and has been a focus of intense study since its return from the Apollo 17 mission because it provides important temporal and geochemical constraints on the evolution of the lunar mantle and crust. The petrology and radioisotope chronometry of Mg-suite materials suggest a complex history including convective mantle overturn and juxtaposition of cumulates from the lunar magma ocean against the base of a primordial crust to create a hybridized parent capable of crystallizing forsterite and anorthite. The low-temperature (metamorphic) portion of 76535ís cooling history has been addressed using multiple approaches yielding largely consistent results. The same is not true for the magmatic and high-temperature subsolidus history. As a consequence, the timing of magma emplacement in the lower crust is unknown to within ~100 million years, as illustrated in the above Temperature-time plot.

Our preliminary examination of 76535 poses the possibility of acquiring time constraints for the early magmatic and subsolidus (to ~900 oC) history, utilizing previously unrecognized compositional gradients in plagioclase and olivine (not shown.. yet).Please stay tuned...

Funding: Bake Sale? (NASA SSW proposal pending)

TZM vesselMaking minerals to improve Moon maps

We synthesize olivine and pyroxene to improve the efficacy of remote sensing

Hapke radiative transfer techniques, which are fundamental to modeling spectral properties of planetary surfaces, demand a precise understanding of the interaction of electromagnetic radiation (i.e., light) with minerals of varying chemistries. This understanding is captured in the optical constants of minerals. Trang et al. are synthesizing olivine and pyroxene with compositions tailored to isolate the effects of Mn in olivine and Fe3+ in pyroxene on the optical constants of these minerals.

Trang, D, Gillis-Davis, JJ, Hammer, JE and Cahill, JTS The optical constants of manganese-bearing olivine: The synthesis. 46th LPSC 2015

Funding: NASA PGG NNX11AP51G to J.T.S. Cahill and Jeff Gillis-Davis.

 

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