Figure F6. Plots of Sc, which is highly compatible in clinopyroxene (cpx) and incompatible in plagioclase (Plag), vs. CaO, Al2O3, and CaO/Al2O3. These compositional parameters in bulk gabbroic rocks are largely controlled by the relative modal proportions of clinopyroxene and plagioclase, the two dominant minerals. (A, B) bulk-rock Sc abundances lie on a mixing line defined by average plagioclase and clinopyroxene composition. The deviation from the mixing lines results from dilution effect of CaO- and Al2O3-poor minerals (i.e., olivine, orthopyroxene, ilmenite, titanomagnetite, etc.) in the rock. (C) this dilution effect is removed when CaO/Al2O3 is used. (D) both Sc and CaO/Al2O3 (RC/A) can be used precisely for estimating relative mass proportions of clinopyroxene (i.e., cpx# = cpx/[cpx + plag]) and plagioclase (1 - cpx#): cpx# = [1.3835 RC/A - 0.5163]/[1.2571 RC/A + 0.4587] (also shown in part C). Average Sc abundances in plagioclase and clinopyroxene are from Y. Niu (unpubl. data). The numbers and tick marks along the mixing lines are cpx#. Data for FV samples are plotted for comparison.

Figure F6. Plots of Sc, which is highly compatible in clinopyroxene (cpx) and incompatible in plagioclase (Plag), vs. CaO, Al₂O₃, and CaO/Al₂O₃. These compositional parameters in bulk gabbroic rocks are largely controlled by the relative modal proportions of clinopyroxene and plagioclase, the two dominant minerals. (A, B) bulk-rock Sc abundances lie on a mixing line defined by average plagioclase and clinopyroxene composition. The deviation from the mixing lines results from dilution effect of CaO- and Al₂O₃-poor minerals (i.e., olivine, orthopyroxene, ilmenite, titanomagnetite, etc.) in the rock. (C) this dilution effect is removed when CaO/Al₂O₃ is used. (D) both Sc and CaO/Al₂O₃ (R_C/A) can be used precisely for estimating relative mass proportions of clinopyroxene (i.e., cpx# = cpx/[cpx + plag]) and plagioclase (1 - cpx#): cpx# = [1.3835 R_C/A - 0.5163]/[1.2571 R_C/A + 0.4587] (also shown in part C). Average Sc abundances in plagioclase and clinopyroxene are from Y. Niu (unpubl. data). The numbers and tick marks along the mixing lines are cpx#. Data for FV samples are plotted for comparison.