RT Journal Article
T1 Blueschist-facies metapelites from the Malpica–Tui Unit (NWIberian Massif): phase equilibria modelling and H2O and Fe2O3influence in high-pressure assemblages
A1 López Carmona, Alicia
A1 Pitra, Pavel
A1 Abati Gómez, Jacobo
AB The Malpica–Tui Unit (Galicia, NW Spain) records eclogite- and blueschist-facies metamorphismduring the onset of the Variscan orogeny in Europe. Petrological analysis involving pseudosectionscalculated using THERMOCALC shows that the Upper Sheet of this unit, the Ceán Schists, recorded a threestagemetamorphic evolution involving (i) Early subduction-related medium-pressure ⁄ low-temperaturemetamorphism (M1) constrained at ~º350–380 ºC, 12–14 kbar, which is only recorded in the basal part(lower metapelites, LM) of the Cea´n Schists. (ii) Subduction-related blueschist facies progrademetamorphism (M2) going from 19 kbar, 420 ºC to 21 kbar, 460 ºC in the LM, and from 16 kbar430 ºC to 21–22 kbar, 520 ºC in the structurally upper metapelites (UM). (iii) Exhumation-relatedmetamorphism (M3) is characterized by a decompression to 8–10 kbar, 470–490 ºC in the LM. Thisdecompression is also recorded in the UM, but it was not possible to estimate precise P–T conditions.The calculations indicate that (i) the prograde evolution in subduction zones may occur in fluidundersaturatedconditions due to the crystallization of lawsonite, even in metapelitic rocks. Thissignificantly influences phase equilibria and hence the P–T estimates. (ii) The proportion of ferric ironalso has a strong influence on phase equilibria, even in metapelites. However, the analysed values ofFe2O3 may not reflect the oxidation state during the main metamorphic evolution and are probablyeasily modified by superficial alteration even in apparently fresh samples. The use of P–T–X(Fe2O3)pseudosections together with petrographic observations is then necessary to estimate the real oxidationstate of the rocks and correctly evaluate the P–T conditions.
PB Blackwell Publishing Ltd
SN 0263-4929
YR 2013
FD 2013
LK https://hdl.handle.net/20.500.14352/33545
UL https://hdl.handle.net/20.500.14352/33545
LA eng
DS Docta Complutense
RD 7 abr 2025