facies relics metabasites from the Guadarrama (Spanish System): L BARBER0 1 ,* AD C. VILLASECA 2 1 Departento d Geologia, Fultad C C del Mar, Universid ad d Cadz, 15_10 Puerto Real, Cadz, Spn 2 Depento de P e tologiay Geoumiea,Fꜳultad C C Geolieas, Universidad Comlutense, *80T0 Madrid, Spain RelicsofHP-MT eclogiticassemblagesrelatedtotherstmetamorphicstageoftheHercynian nrrPTU inthe Sierrade Guadarrama(SpanishCentra SCS) are asboudinsof IJi'--'JJU-V metabasitesenclosedby felsic Texturesindicatea iHUUU-'H(l'- meto the MT eclogitefacies (as deduced fom the presence of and rutile inudedingarnet) and through medium to Iow pressure and retrogade amphibolite-greensist facies. Thermobarometiccalculationsinthe ecIogitic yieldpresuresof-14kbarfor te,rtlres in the range 725-775°C. for the indicates a Sl.lnC,( drop in (P < 10 kbar) for similar temperatures vary fom gab bro to lelCÌtonlts showing the typical Fe enrichment of the tholeiitic series. Chical characteristics indicate a derivation from low-pressure of tholeiitic melts more enriched than typical MORB compositions. Theiroriginal locationfar fom 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 The P-T conditions estimated in the metabasites for the first metamorphic stage are similar to ones deduced for the 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. KEYWORDS: assemblage, Central Introduction TE Sierra de Guadarrama is located in the axial zone of the Iberianbranchofthe Hercynian belt 1) intheso-calledCen tralIberianZone(San Jose et al, 1990). This sector representsa in tracon tin en tal as seen from its location far from recognized ophiolitic complexes or supposed Thenearestophio- litic shearzone islocated>320 kmto thesouthwestevenafterthe shorteningwhich occurredduring the Hercynian orogeny. The evolution related to * E-ma: Is.bberouea es evolution,MORî. the Hercynian orogenyis characterizedby three stages of re-crystallization related to a metamorphic cycle (Villaseca, 1983; Arenas et aI. , 1991). The initial (Ml) coincides with the frst and with part of the second deformative events (Dl and D2) and is amedium associated with crustal thickening and progressive burial. The most characteristic Dl compres sionalstructureinthestudyareaisaseriesof km scale ductile shear zones of orthoeisses imbricated with thin sheets of metasediments etal. , 1991} In works, mtorplC conditions of Ml have not been established whic h was explained as a consequence of the bythesecond stage(M2)' Villaseca