Premium
Controls on the first appearance of jadeitic pyroxene, northern Diablo Range, California
Author(s) -
PATRICK B. E.,
DAY H. W.
Publication year - 1989
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1989.tb00623.x
Subject(s) - pyroxene , lawsonite , glaucophane , chlorite , geology , albite , mineral , mineralogy , metamorphism , geochemistry , plagioclase , quartz , olivine , eclogite , chemistry , tectonics , paleontology , subduction , organic chemistry
A reaction producing jadeitic pyroxene in metagreywackes of the northern Diablo Range has been identified on the basis of mineral distribution, isograd patterns and composition of coexisting minerals. The appearance of jadeitic pyroxene (∼Jd 80 ) is closely followed by the disappearance of pumpellyite, which indicates that pumpellyite plays a major role in the pyroxene‐producing reaction. A new projection from hematite, lawsonite, chlorite, quartz and H 2 O on to the NaAlO 2 ‐FeO‐MgO ternary confirms the role of pumpellyite in pyroxene production and suggests a reaction of the form: 1.00 pumpellyite + 0.31 chlorite + 8.71 albite + 0.70 hematite + 2.00 H 2 O = 8.54 jadeite + 0.57 glaucophane + 3.09 lawsonite + 5.26 quartz. Metagreywackes of the northern Diablo Range were metamorphosed under conditions of P H2O = P total at 200‐300 °C and 7.5‐10.0 kbar. Despite the low temperatures attained during metamorphism, the assumption of equilibrium yields results consistent with field observations and phase relations.