Termination of the 2 feldspar + liquid curve in the system Ab-Or-An- H₂O at low H₂O contents

Analysis of the termination topology of the plagioclase + alkali feldspar + liquid (PAL) curve in the system Ab-Or-An(-H₂O) was conducted using thermodynamic solution models for ternary feldspar melt and solid solutions for a low activity of H₂O and a pressure of 2 kbar. Under these conditions the PAL curve terminates within the ternary system and does not lie within a thermal valley near its termination. Using Henderson's geometric method supplemented by an analytical approach, we show that no sharp decrease in An is required as the termination is approached. Behavior of bulk compositions close to and on the line that connects the consolute point of the solvus with the melt composition at the termination of the PAL curve has been investigated computationally. -from Authors