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Eclogite facies relics in metabasites from the Sierra de Guadarrama (Spanish Central System): P-T estimations and implications for the Hercynian evolution

Barbero González, Luis C. and Villaseca González, Carlos (2000) Eclogite facies relics in metabasites from the Sierra de Guadarrama (Spanish Central System): P-T estimations and implications for the Hercynian evolution. Minerogical magazine, 64 (5). pp. 815-836. ISSN 0026-461X

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Abstract

Relics of HP-MT eclogitic assemblages related to the first metamorphic stage of the Hercynian orogeny
in the Sierra de Guadarrama (Spanish Central System, SCS) are preserved as boudins of pre-Ordovician
metabasites enclosed by felsic gneisses. Textures indicate a multi-stage metamorphic history starting in
the MT eclogite facies (as deduced from the presence of omphacite and rutile included in garnet) and
continuing through medium to low pressure granulite and retrograde amphibolite-greenschist facies.
Thermobarometric calculations in the eclogitic paragenesis yield pressures of ~14 kbar for temperatures
in the range 725 7758C. Thermobarometry for the subsequent granulitic stage indicates a significant
drop in pressure (P < 10 kbar) for similar temperatures of ~7508C. Metabasites vary from gabbro to
leucotonalites showing the typical Fe enrichment of the tholeiitic series. Chemical characteristics
indicate a derivation from low-pressure crystallization of tholeiitic melts more enriched than typical
MORB compositions. Their original location far from continental margins as evidenced by the absence
of ophiolitic material in the area and their association with platform sediments suggests that
eclogitization was related to intracontinental crustal subduction and thickening. The P-T conditions
estimated in the metabasites for the first metamorphic stage are similar to ones deduced for the
surrounding metasediments and suggest that the Hercynian crust could have reached a thickness of
~70 80 km, which is more than the double the present thickness.

Item Type:Article
Uncontrolled Keywords:Eclogite assemblage, Spanish Central System, Hercynian evolution, MORB
Subjects:Sciences > Geology > Petrology
Sciences > Geology > Geochemistry
ID Code:12325
Deposited On:01 Mar 2011 13:08
Last Modified:01 Mar 2011 13:08

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