Table 1.
Major element compositions of basalt from Venus and the compositions used for modeling.
Fig 1.
Conceptual crystallization scenarios of the parental magma of the Vega 2 rock.
The 1-Stage differentiation scenario is deep seated fractionation primarily of olivine (ol) but may also include orthopyroxene (opx) and clinopyroxene (cpx). The 2-Stage scenario follows the 1-Stage scenario but the residual liquid stalls in the middle to upper crust and continues to differentiate into a silicic liquid due to fractionation of olivine (ol), clinopyroxene (cpx), plagioclase (plag) and Fe-Ti oxide minerals (ilmenite and magnetite). The 3-stage scenario follows the 1-Stage scenario of differentiation but has two steps of fractionation in order to generate a silicic residual liquid. The first step is fractionation of olivine (ol), clinopyroxene (cpx) and plagioclase (plag) at an intermediate depth in the middle crust or lowermost upper crust. The residual liquid then leaves the magma chamber and stalls in the upper crust and continues to differentiate by fractionating clinopyroxene (cpx), plagioclase (plag), Fe-Ti oxide minerals (ilmenite and magnetite) and possibly olivine (ol) before producing a silicic residual liquid.
Fig 2.
Results of Vega 2 anhydrous fractional crystallization models.
Andesite (blue field) and rhyolite (red field) data (S1 Table) are compiled from the GEOROC database (georoc.mpch-mainz.gwdg.de/georoc/Entry.html). The grey field is the range of silicic rocks from a mid-oceanic ridge setting [8]. All data are normalized to 100%. The calculated 95% confidence ellipses (dashed) are added to the fields of terrestrial andesite and rhyolite. Panel a is the classification scheme of volcanic rocks [69]. F = foidite, Pb = picro-basalt, B = basalt, Ba = basaltic andesite, A = andesite, D = dacite, R = rhyolite, T = trachyte (quartz < 20%), Td = trachydacite (quartz > 20%), Ta = trachyandesite, Bta = basaltic trachyandesite, Tb = trachybasalt, TBas = tephrite (olivine < 10%) or basanite (olivine > 10%), Pt = phonotephrite, Tp = tephriphonolite, P = phonolite. Arrow is the direction of liquid evolution.
Fig 3.
Results of Vega 2 hydrous (0.5 wt.% H2O) fractional crystallization models.
The details of the figure are the same as Fig 2.
Fig 4.
Results of Vega 2 hydrous (0.5 wt.%) equilibrium partial melting models.
Andesite (blue field) data (S1 Table) are compiled from the GEOROC database (georoc.mpch-mainz.gwdg.de/georoc/Entry.html). The grey field is the range of silicic rocks from a mid-oceanic ridge setting [8]. All data are normalized to 100%. The calculated 95% confidence ellipses (dashed) are added to the field of terrestrial andesite. The details of panel are the same as Fig 2. Arrow is the direction of liquid evolution.
Fig 5.
Results of Vega 2 anhydrous fractional crystallization models.
The details of the figure are the same as Fig 2.
Fig 6.
Results of Vega 2 hydrous (0.5 wt.% H2O) fractional crystallization models.
The details of the figure are the same as Fig 2.
Fig 7.
Results of Vega 2 hydrous (0.5 wt.%) equilibrium partial melting models.
The details of the figure are the same as Fig 4.
Fig 8.
Comparison of the hydrous factional crystallization models at different relative oxidation states.
(a) FeOt (wt%) and (b) TiO2 (wt%) vs. SiO2 (wt%) of the 0.1 GPa, hydrous SO3-free composition. The relative oxidation state is FMQ -1 for the data points (grey circles). The solid black curve is the original model at the FMQ buffer. (c) FeOt (wt%) and (d) TiO2 (wt%) vs. SiO2 (wt%) of the 0.1 GPa, hydrous kieserite-adjusted composition. The relative oxidation state is FMQ -1 for the data points (grey circles). The solid black curve is the original model at the FMQ buffer.
Fig 9.
Results of 3-stage, SO3-absent Vega 2 hydrous (0.5 wt% H2O) fractional crystallization models.
The details of the figure are the same as Fig 2.
Fig 10.
Results of 3-stage, kieserite-adjusted Vega 2 hydrous (0.5 wt.% H2O) fractional crystallization models.
The details of the figure are the same as Fig 2.