%0 Journal Article
%A López Carmona, Alicia
%A Abati Gómez, Jacobo
%A Reche i Estrada, Juan
%T Petrologic modeling of chloritoid–glaucophane schists from the NW Iberian Massif
%D 2010
%@ 1342-937X
%U https://hdl.handle.net/20.500.14352/44174
%X Two P–T pseudosections computed with Thermocalc and Perplex software for high-pressure pelitic CeánSchists from the NWIberian Massif show that the paragenesis chloritoid+glaucophane, preserved as relictmicro-inclusions in garnet porphyroblasts, is stable above 17–18 kbar, indicating a first stage of subductionwith 65–70 km of burial. The subsequent growth of biotite and albite porphyroblasts, according to theirstability fields in a MnNCKFMASH P–T phase diagram, indicates strong decompression accompanied byslight heating to reach a metamorphic peak at ∼500 °C. This mineral association, described in manysubduction-related terranes around the world as one of the high-pressure indicators for metapelites, hasnot been reported previously in the NW Iberian Massif. The schists contains an initial high-pressureassemblage formed by chloritoid+garnet (Alm0.58 Prp00.03 Grs0.38 Sps0.09)±glaucophane+phengite(3.5–3.4Sip.f.u.)+paragonite+chlorite+epidote+rutile+ilmenite+quartz, preserved as micro-inclusionsin garnet, chloritoid and albite porphyroblasts defining an S1 internal fabric. The matrix foliation (S2)additionally contains a high-pressure association formed by garnet (Alm0.68 Prp0.04 Grs0.25 Sps0.03)+phengite (3.4–3.3Si p.f.u.)+paragonite+winchite+barroisite+hornblende+chloritoid+chlorite+epidote+rutile+ilmenite+albite+quartz±biotite. An initial pseudosection calculated in the KFMASHsystem with Thermocalc 3.26 gives pressure estimates through Si-content in phengite barometry that arein agreement with conventional thermobarometry and Thermocalc average P–T calculations, but is unableto describe the full complexity of the mineral assemblages of the schists. For this reason, a more completeP–T pseudosection in the model system MnNCKFMASH was calculated with Perplex 07. This provides areliable succession of mineral assemblages that are consistent with the petrographic observations andallows a mineralogical sequence to be set for each metamorphic event in the P–T evolution of the high-Ppelitic Ceán Schists.
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