Incomplete reaction of plagioclase in experimental dehydration melting of amphibolite
Titel:
Incomplete reaction of plagioclase in experimental dehydration melting of amphibolite
Auteur:
Johannes, W. Koepke, J.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 48 (2001) nr. 4 pagina's 581-590
Jaar:
2001-08
Inhoud:
Dehydration melting of a hornblende-plagioclase mixture of amphibolitic composition was investigated at 1000°C and at 800 MPa and 1200 MPa. At 1200 MPa the reaction products are garnet, clinopyroxene, melt and relatively Ab-rich plagioclase (An47). At 800 MPa the products are orthopyroxene, clinopyroxene, magnetite, amphibole (pargasite) and An-rich plagioclase (An75). The melts are rich in plagioclase components (especially in Ab) and, when compared to tonalites, relatively poor in silica. The grainsize of the starting materials was ≤5 μm in the 800 MPa and ≤10 μm in the 1200 MPa runs. All run products show unchanged plagioclase cores, which are the remnants of a very sluggish reaction assumed to be controlled by dissolution/precipitation processes at the plagioclase grain boundaries. The results indicate that only local equilibrium could have been obtained in recent investigations on dehydration melting experiments in plagioclase-bearing systems. The results also suggest that plagioclase compositions once formed may persist for a very long time, even in hot magma chambers, if the prevailing water activity is low.
Tijdschrift beschrijving