The size of basalt fragments in Chang’E-5 (CE-5) regolith are small (< 6 mm2), resulting in large variation on the estimated bulk composition of CE-5 basalt. For example, the estimated TiO2 content of CE-5 basalt ranges from 3.7 wt% to 12.7 wt% and the Mg# (molar percentage of Mg/[Mg + Fe]) also shows a wide range (26.2 − 42.4). Preliminary experimental studies have shown that these geochemical characteristics of CE-5 basalt are critical for investigating the crystallization sequence and formation mechanism of its parent magma. This study presents new experimental data on the distribution coefficient of titanium between pyroxene and lunar basaltic magma \(\left( {{\text{D}}_{{{\text{Ti}}}}^{{\text{Px/melt}}} } \right)\) . Combining with available literature data, we confirm that \({\text{D}}_{{{\text{Ti}}}}^{{\text{Px/melt}}}\) is affected by crystallization conditions such as pressure and temperature, but it is mainly controlled by the CaO content of pyroxene. Comparing with previous experimental results under similar conditions, we parameterized the effect as \({\text{D}}_{{{\text{Ti}}}}^{{\text{Px/Melt}}} {\text{ = D}}_{{{\text{Ti}}}}^{{\text{Px/Melt}}} { \;= - 0}{\text{.0005X}}_{{{\text{Cao}}}}^{{2}} { \;+\; 0}{\text{.0218X}}_{{{\text{CaO}}}} { \;+\; 0}{\text{.0425} ({\text{R}}^{2} = 0}{.82)}\) \(\text{,}\) where XCaO is the CaO content in pyroxene in weight percentage. The new experimental results suggest that pyroxene with high TiO2 content (> 2.5 wt%) in CE-5 basalt is not a product of equilibrium crystallization, and the CaO content in pyroxene is also affected by cooling rate of its parent magma. The TiO2 content in the CE-5 parent magma is estimated to be about 5 wt% based on the Mg# of pyroxene and its calculated CaO content, which is consistent with those estimated from olivine grains.
