Prograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet phengite-clinopyroxene thermobarometry

Title:
Prograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet phengite-clinopyroxene thermobarometry
Authors:
Page, F. Zeb ( 0000-0002-2100-0806 ) ; Armstrong, Lora S.; Essene, Eric J.; Mukasa, Samuel B.
Abstract:
Quantitative thermobarometry of inclusions in zoned garnet from a Franciscan eclogite block record a counter-clockwise P–T path from blueschist to eclogite and back. Garnet retains prograde zoning from inclusion-rich Alm52Grs30Pyp6Sps12 cores to inclusion-poor Alm62Grs25Pyp12Sps1 mantles, with overgrowths of highly variable composition. Barometry using the Waters–Martin version of the garnet–phengite–omphacite thermobarometer yields conditions of 7–15 kbar, 400–500°C (garnet cores), 18–22 kbar, ∼550°C (mantles), and 10–14 kbar, 350–450°C (overgrowths), in agreement with clinozoisite–sphene–rutile–garnet–quartz barometry. These pressures are ∼10–15 kbar less than those obtained using more recent, fully thermodynamic calibrations of the phengite–omphacite–garnet thermobarometer. Low early temperatures suggest that the block was subducted in a thermally mature subduction zone and not at the inception of subduction when prograde temperature is expected to be higher. Franciscan high-grade blocks likely represent crust subducted throughout the history of this convergent margin, rather than only at the inception of the subduction zone.
Citation:
Page, F. Z., L. S. Armstrong, E. J. Essene, and S. B. Mukasa. 2007. "Prograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet phengite-clinopyroxene thermobarometry." Contributions To Mineralogy And Petrology 153(5): 533-555.
Publisher:
Springer Verlag
DATE ISSUED:
2007
Department:
Geology
Type:
article
PUBLISHED VERSION:
10.1007/s00410-006-0161-9
PERMANENT LINK:
http://hdl.handle.net/11282/310326

Full metadata record

DC FieldValue Language
dc.contributor.authorPage, F. Zeben_US
dc.contributor.authorArmstrong, Lora S.en_US
dc.contributor.authorEssene, Eric J.en_US
dc.contributor.authorMukasa, Samuel B.en_US
dc.date.accessioned2013-12-23T16:30:35Zen
dc.date.available2013-12-23T16:30:35Zen
dc.date.issued2007en
dc.identifier.citationPage, F. Z., L. S. Armstrong, E. J. Essene, and S. B. Mukasa. 2007. "Prograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet phengite-clinopyroxene thermobarometry." Contributions To Mineralogy And Petrology 153(5): 533-555.en_US
dc.identifier.issn0010-7999en_US
dc.identifier.urihttp://hdl.handle.net/11282/310326en
dc.description.abstractQuantitative thermobarometry of inclusions in zoned garnet from a Franciscan eclogite block record a counter-clockwise P–T path from blueschist to eclogite and back. Garnet retains prograde zoning from inclusion-rich Alm52Grs30Pyp6Sps12 cores to inclusion-poor Alm62Grs25Pyp12Sps1 mantles, with overgrowths of highly variable composition. Barometry using the Waters–Martin version of the garnet–phengite–omphacite thermobarometer yields conditions of 7–15 kbar, 400–500°C (garnet cores), 18–22 kbar, ∼550°C (mantles), and 10–14 kbar, 350–450°C (overgrowths), in agreement with clinozoisite–sphene–rutile–garnet–quartz barometry. These pressures are ∼10–15 kbar less than those obtained using more recent, fully thermodynamic calibrations of the phengite–omphacite–garnet thermobarometer. Low early temperatures suggest that the block was subducted in a thermally mature subduction zone and not at the inception of subduction when prograde temperature is expected to be higher. Franciscan high-grade blocks likely represent crust subducted throughout the history of this convergent margin, rather than only at the inception of the subduction zone.en_US
dc.publisherSpringer Verlagen_US
dc.identifier.doi10.1007/s00410-006-0161-9en
dc.subject.departmentGeologyen_US
dc.titlePrograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet phengite-clinopyroxene thermobarometryen_US
dc.typearticleen_US
dc.identifier.journalContributions To Mineralogy And Petrologyen_US
dc.subject.keywordEastern Blue Ridgeen_US
dc.subject.keywordWestern Alpsen_US
dc.subject.keywordP-T evolutionen_US
dc.subject.keywordFranciscan Complexen_US
dc.subject.keywordGlaucophane Schistsen_US
dc.subject.keywordPhase relationsen_US
dc.subject.keywordSolid solutionen_US
dc.subject.keywordMetamorphic evolutionen_US
dc.subject.keywordUltrahigh pressuresen_US
dc.identifier.volume153en_US
dc.identifier.issue5en_US
dc.identifier.startpage533en_US
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