Summary
The mineral phase relationships have been determined in the presence of excess water to a water pressure of 10 kb for three quartz diorites, a granodiorite, and a quartz monzonite from the Central and Southern Coast Ranges of California. Water pressure-temperature curves were constructed to locate the beginning of melting and the disappearance of K-feldspar, quartz, biotite, plagioclase and hornblende. Results indicate that plagioclase is the silicate liquidus phase in all granitoids studied at low water pressures, while hornblende or biotite is the silicate liquidus phase at high water pressure. New data illustrate the potent effect of water pressure on magma composition at temperatures 50° to 100°C above the solidus. At a water pressure of 1 kb, magmas are granitic to quartz monzonitic, while at water pressures of 10 kb, they are granodioritic to quartz dioritic.
Résumé
On a determiné en présence d'un excès d'eau jusqu'à une pression d'eau de 10 kb les corrélations entre les phases minérales de trois diorites quartziques, une granodiorite, et une monzonite quartzique obtenues des chaînes du centre et du sud de la côte de la Californie. On a utilisé des courbes de pression d'eau contre température afin de fixer le commencement de fusion et la disparition de K-feldspath, quartz, biotite, plagioclase, et hornblende. Les résultats indiquent que plagioclase est la phase liquidus de silicate pour tous les granitoids examinés aux pressions d'eau basses, en même temps que soit hornblende, soit biotite la phase liquidus de silicate aux pressions d'eau hautes. Des données nouvelles manifestent l'effet puissant de la pression d'eau sur la composition de magma aux températures élevées 50° ou 100°C plus que le solidus. Avec une pression d'eau de 1 kb les magmas sont granitiques à quartz monzonitiques; avec une pression d'eau de 10 kb ils sont granodioritiques à quartz dioritiques.
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Piwinskii, A.J. Experimental studies of granitoids from the Central and Southern Coast Ranges, California. TMPM Tschermaks Petr. Mitt. 20, 107–130 (1973). https://doi.org/10.1007/BF01081387
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DOI: https://doi.org/10.1007/BF01081387