Fig. 2: Mineral assemblages and melt compositions.
From: Melting of fluorine-rich biotite as a mechanism for generating lithium-rich granites
a Composite P--T pseudosection for an average Precambrian greywacke composition (Supplementary Data 1 and 2; minimally fluid-saturated at 8 kbar) showing melt extraction events (orange circles) at 7 vol% melt intervals (i.e. stepwise-batch melting). Zero mode isolines are highlighted for liquid (solidus; pink) and biotite (green). The solidus is marked at 8 kbar by an orange cross. b Phase abundances (vol%) during stepwise-batch melting at 8 kbar. c Melt compositions during stepwise-batch melting (dotted lines, with the solidus composition marked by a cross, and melt extraction steps marked by open circles) and isobaric fractional crystallisation of melts from each third melt extraction step (solid lines, with 75 vol% fractionation marked by a vertical black bar for reference) from 2 to 12 kbar. Background data were reported compositions from the Cornubian granite batholith4,10, with the legend shown in (d). d Melt composition plot as (c), but only showing 8 kbar melting. The melt composition during subsequent fractional crystallisation (for the melt produced from the third melt extraction step, as closest to complete biotite dehydration) is shown for fractionation at 8 kbar (solid line as per panel (c)) and at 4 kbar (dashed line), with the shaded region representing viable melt compositions produced for intermediate fractionation pressures. Phase abbreviations: afs alkali feldspar, amp amphibole, bt biotite, fl fluid, ilm ilmenite, liq liquid, mag magnetite, opx orthopyroxene, pl plagioclase, qz quartz, rt rutile.
