Figure 7
Three-isotope correlation diagram converted to age and elemental Ca/K ratio (derived from neutron-produced 37ArCa and 39ArK) for data from step-heating of mafic (A) and felsic (B) porphyry. K2O (wt %) vs. Ca/K (EMP data) of K-feldspar from mafic (B) and felsic (D) porphyries. The model lines in (B) and (D) show the effect of mixing secondary K-feldspar (Kfs2) and albite (Ab) with pristine K-feldspar (Kfs1). Model lines in (B): (A1) mixing between secondary K-feldspar and albite; (A2), mixing between pristine K-feldspar (Kfs1) with a mixture of secondary K-feldspar and albite in the proportion 3:1; (A3), mixing between pristine K-feldspar (Kfs1) with a mixture of secondary K-feldspar and albite in the proportion 1:1. Model line (D): (A1) mixing between secondary K-feldspar and albite; (B2), mixing between pristine K-feldspar (Kfs1) with a mixture of secondary K-feldspar and albite in the proportion 2:1; (B3): mixing between pristine K-feldspar (Kfs1) with a mixture of secondary K-feldspar and albite in the proportion 1:1. Stars in (B) and (D) indicate mean end-members compositions (EMP data) used in the mixing calculations.
