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 amphibolite-grade pelites and amphibolites from Cordillera Darwin, Tierra del Fuego, Chile. Peak P-T conditions are nearly all within the kyanite stability field; temperatures generally show an increase with increasing grade, but pressures have a less consistent trend, possibly increasing 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 analysis and previous structural work indicate that this segment of the path correlates with back-folding deformation. P-T paths from two Mg-rich 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 development of fibrolitic sillimanite along plagioclase grain boundaries. Together, the P-T path segments from pelites and amphibolites constitute a clockwise P-T trajectory. The proposed clockwise P-T paths are consistent with the interpretation that Cordillera Darwin represents an extensionally exhumed metamorphic core complex, in which loading during garnet growth in the pelitic rocks was succeeded by differential uplift during garnet growth in magnesian amphibolites.