TY  - JOUR
A1  - Thomas, Rainer
A1  - Webster, J. D.
A1  - Rhede, Dieter
A1  - Seifert, W.
A1  - Rickers, Karen
A1  - Förster, Hans-Jürgen
A1  - Heinrich, Wilhelm
A1  - Davidson, P.
T1  - The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals
JF  - Lithos : an international journal of mineralogy, petrology, and geochemistry
N2  - Fractional crystallization of peraluminous F- and H(2)O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions. We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters.
KW  - granite melts
KW  - magma evolution
KW  - melt inclusions
KW  - melt-melt immiscibility
KW  - peraluminosity
KW  - peralkalinity
KW  - accessory minerals
Y1  - 2006
U6  - https://doi.org/10.1016/j.lithos.2006.03.013
SN  - 0024-4937
VL  - 91
IS  - 1-4
SP  - 137
EP  - 149
PB  - Elsevier
CY  - Amsterdam
ER  -