The magmatic architecture and evolution of the Chang’e-5 lunar basalts

Comment on ‘The magmatic architecture and evolution of the Chang’e-5 lunar basalts’ Penny E. Wieser1, Christy Till2, Adam Kent3, Matthew Gleeson1

“…Luo et al 1 present exciting new data on lunar basalt samples erupted at ~2 Ga, and brought to Earth by the Chang'e-5 (CE-5) mission. These samples offer important new opportunities to understand lunar magmatic systems.…”

“…These samples offer important new opportunities to understand lunar magmatic systems. Luo et al 1 use Clinopyroxene-Liquid (Cpx-Liq) thermobarometry and pMELTS modelling of mineral compositions to determine the pressures (P) and temperatures (T) of magma storage on the moon. Specifically, they iterate the barometer of Neave and Putirka 2 and the thermometer of Putirka (eq33) 3 , yielding pressures spanning ~1-12.9 kbar, which are strongly correlated with calculated temperatures (Fig.…”

“…Recent advances in understanding the sources and magnitudes of error associated with Cpx barometry reveal that the majority of studies utilizing Cpx barometry in the literature neglect to (1) propagate analytical uncertainty into P and T estimates 4 , and (2) ensure that the composition space of the studied magmas is similar to that of the barometer's calibration dataset 5 . Luo et al 1 allude to point 1 with their sentence 'For this purpose, high-quality concentration data on clinopyroxenes in equilibrium with the host basaltic melts are required'.…”

“…The Cpx-Liq barometer used by Luo et al 1 relies on the exchange of the jadeite (NaAlSi 2 O 6 ) component between Cpx and liquid. Although Jadeite in Cpx can be calculated from Na or Al, almost all (75/76) of the lunar Cpx used to calculated pressures and temperatures have major element chemistry such that the jadeite component is calculated from the Na content.…”

“…This low precision in Na propagates into a large uncertainty in the calculated Jadeite component, and thus the calculated pressure. By compiling the stated errors from Luo et al 1 and Che et al 6 , we determine that the mean precision for Na 2 O in Cpx used to calculate pressures using thermobarometry (N=76) is 26% (range=7-53%, opaque symbols, Fig. 1a).…”