METAMORPHIC P-T PATHS FROM CORDILLERA DARWIN, A CORE COMPLEX IN TIERRA-DEL-FUEGO, CHILE

P-T conditions and prograde P-T paths have been calculated for amphibo lite-grade pelites and amphibolites from Cordillera Darwin, Tierra del Fuego, Chile. Peak P-T conditions are nearly all within the kyanite s tability field; temperatures generally show an increase with increasin g grade, but pressures have a less consistent trend, possibly increasi ng slightly from garnet to kyanite grade. P-T paths from pelites show heating by 80-100-degrees-C during loading of 0.2-3 kbar. Textural ana lysis and previous structural work indicate that this segment of the p ath correlates with back-folding deformation. P-T paths from two Mg-ri ch garnet amphibolites suggest a decrease in pressure of as much as 3 kbar with 25-50-degrees-C of heating from the kyanite stability field to the sillimanite, and are consistent with pervasive, minor developme nt of fibrolitic sillimanite along plagioclase grain boundaries. Toget her, the P-T path segments from pelites and amphibolites constitute a clockwise P-T trajectory. The proposed clockwise P-T paths are consist ent with the interpretation that Cordillera Darwin represents an exten sionally exhumed metamorphic core complex, in which loading during gar net growth in the pelitic rocks was succeeded by differential uplift d uring garnet growth in magnesian amphibolites.