%0 Journal Article
%A Barbero González, Luis C.
%A Villaseca González, Carlos
%T Eclogite facies relics in metabasites from theSierra de Guadarrama (Spanish Central System):P-T estimations and implications for the Hercynian evolution
%D 2000
%@ 0026-461X
%U https://hdl.handle.net/20.500.14352/57018
%X Relics of HP-MT eclogitic assemblages related to the first metamorphic stage of the Hercynian orogenyin the Sierra de Guadarrama (Spanish Central System, SCS) are preserved as boudins of pre-Ordovicianmetabasites enclosed by felsic gneisses. Textures indicate a multi-stage metamorphic history starting inthe MT eclogite facies (as deduced from the presence of omphacite and rutile included in garnet) andcontinuing through medium to low pressure granulite and retrograde amphibolite-greenschist facies.Thermobarometric calculations in the eclogitic paragenesis yield pressures of ~14 kbar for temperaturesin the range 725 7758C. Thermobarometry for the subsequent granulitic stage indicates a significantdrop in pressure (P < 10 kbar) for similar temperatures of ~7508C. Metabasites vary from gabbro toleucotonalites showing the typical Fe enrichment of the tholeiitic series. Chemical characteristicsindicate a derivation from low-pressure crystallization of tholeiitic melts more enriched than typicalMORB compositions. Their original location far from continental margins as evidenced by the absenceof ophiolitic material in the area and their association with platform sediments suggests thateclogitization was related to intracontinental crustal subduction and thickening. The P-T conditionsestimated in the metabasites for the first metamorphic stage are similar to ones deduced for thesurrounding 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.
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