P-T evolution of eclogites from the Agualada Unit ( Ordenes Complex, northwest Iberian Massif, Spain) : Implications for crustal subduction



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Arenas Martín, Ricardo and Abati Gómez, Jacobo and Martínez Catalán, José Ramón and Díaz García, Florentino and Rubio Pascual, Francisco J. (1997) P-T evolution of eclogites from the Agualada Unit ( Ordenes Complex, northwest Iberian Massif, Spain) : Implications for crustal subduction. Lithos (Oslo. Print) , 40 . pp. 221-242. ISSN 0024-4937

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Official URL: http://www.journals.elsevier.com/lithos/


Eklogite lenses in the Agualada Unit (western Ordenes Complex, Spain) contain the peak mineral assemblage garnet
(prograde rim: Alm = 48 mol%, Ptp = 30 mol%), omphacite (Jd max = 36 mol%), quartz, rutile and rare zoisite, which
equilibrated at T = 700°C and P > 12-14 kbar. Garnet shows discontinuous growth zoning, with a pyrope-poor intermediate
zone (Alm = 51 mol%, Prp = 10 mol%) between a core zone where pyrope is slightly higher (Aim = 46 mol%, Prp = 16
mol%) and areas just inward from the rims where the maximum pyrope contents (Alm = 48 mol%, Prp = 30 mol%) are
recorded. In atoll interiors, garnet contains inclusions of a first generation of omphacite (Jd max = 40 mol%). This
omphacite is replaced in the matrix by a second generation (Jd max = 36 mol%) with higher Fe/Fe + Mg ratio. The
compositions of garnet and omphacite suggest a complex syneclogitic tectonothermal evolution for the Agualada Unit,
characterized by: (1) eclogite-facies metamorphism (T = 585°C P > 12-13 kbar), followed by (2) cooling during a slight
decompression (T = 5OOºC, P > 1 l- 12 kbar), and (3) a final increase in P and T to form the garnet rim-matrix omphacite
mineral assemblage. The Agualada Unit is part of a subduction complex which affected the Gondwana margin at the
beginning of the Variscan cycle. The P-T evolution of the Agualada eclogites is closely related to the structural evolution
of the accretionary complex and the whole erogenic wedge. The cooling event recorded by the Agualada eclogites may have
resulted from the accretion of a new colder crustal slice under the unit, whereas the final progradation reflects the
emplacement of the Agualada Unit directly under the mantle wedge. This evolution fits well with previously presented
theoretical models, both for the tectonothermal evolution of accretionary complexes and for the dynamic evolution of
erogenic wedges. P-T paths such as the one for the Agualada Unit eclogites, probably reflect a prolonged structural
evolution. Although evidently rarely preserved, such paths are probably the rule rather than the exception during plate

Item Type:Article
Uncontrolled Keywords:Eclogites; P-T path; Continental subduction
Subjects:Sciences > Geology > Petrology
ID Code:17377
Deposited On:11 Dec 2012 10:51
Last Modified:11 Dec 2012 10:51

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