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Orthopyroxene‐bearing, mafic migmatites at Cone Peak, California: evidence for the formation of migmatitic granulites by anatexis in an open system

Orthopyroxene‐bearing, mafic migmatites at Cone Peak, California: evidence for the formation of... Abstract Orthopyroxene‐bearing migmatites, exposed at the summit of Cone Peak in the Santa Lucia Range, California, offer an opportunity to explore potential links between granulite facies metamorphism and migmatite formation. Geothermobarometry indicates that the metamorphic temperatures and pressures were in the approximate ranges of 700–750° C and 7.0–7.5 kbar. The rocks at the summit comprise three domains: relatively coarse‐grained, leucocratic veins; relatively fine‐grained, biotite‐enriched zones at the margins of the veins; and a biotite–hornblende‐bearing host rock. Orthopyroxene is concentrated in the veins, which have also the highest ratio of anhydrous to hydrous minerals of the three rock types. The composition of the veins, together with their textures and modes, suggest that they formed through anatexis involving a dehydration‐melting reaction which consumed hornblende and produced orthopyroxene. Variability in mineralogy and composition indicates that there was some local migration of magma along the veins before their final solidification. The biotite‐enriched zones formed either by the concentration of residual biotite at the margins of the vein, or through the metasomatic conversion of hornblende (and/or pyroxene) to biotite, or by a combination of the two processes. Significant differences in the chemistry of the neosome (vein + biotite‐enriched zone) and the host rock rule out simple dehydration melting in a local closed system. The model that explains best the mineralogical and chemical patterns involves triggering of melting by an influx of a low‐aH2O mixed fluid which added K and Si to and removed Ca from the neosome. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Metamorphic Geology Wiley

Orthopyroxene‐bearing, mafic migmatites at Cone Peak, California: evidence for the formation of migmatitic granulites by anatexis in an open system

HANSEN, E.; STUK, M.
Journal of Metamorphic Geology , Volume 11 (2) – Mar 1, 1993
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References (33)

Publisher
Wiley
Copyright
Copyright © 1993 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0263-4929
eISSN
1525-1314
DOI
10.1111/j.1525-1314.1993.tb00148.x
Publisher site
See Article on Publisher Site

Abstract

Abstract Orthopyroxene‐bearing migmatites, exposed at the summit of Cone Peak in the Santa Lucia Range, California, offer an opportunity to explore potential links between granulite facies metamorphism and migmatite formation. Geothermobarometry indicates that the metamorphic temperatures and pressures were in the approximate ranges of 700–750° C and 7.0–7.5 kbar. The rocks at the summit comprise three domains: relatively coarse‐grained, leucocratic veins; relatively fine‐grained, biotite‐enriched zones at the margins of the veins; and a biotite–hornblende‐bearing host rock. Orthopyroxene is concentrated in the veins, which have also the highest ratio of anhydrous to hydrous minerals of the three rock types. The composition of the veins, together with their textures and modes, suggest that they formed through anatexis involving a dehydration‐melting reaction which consumed hornblende and produced orthopyroxene. Variability in mineralogy and composition indicates that there was some local migration of magma along the veins before their final solidification. The biotite‐enriched zones formed either by the concentration of residual biotite at the margins of the vein, or through the metasomatic conversion of hornblende (and/or pyroxene) to biotite, or by a combination of the two processes. Significant differences in the chemistry of the neosome (vein + biotite‐enriched zone) and the host rock rule out simple dehydration melting in a local closed system. The model that explains best the mineralogical and chemical patterns involves triggering of melting by an influx of a low‐aH2O mixed fluid which added K and Si to and removed Ca from the neosome.

Journal

Journal of Metamorphic Geology – Wiley

Published: Mar 1, 1993

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