Rb-Sr isotopic ages from late Palaeozoic metamorphic rocks of central Chile

Two metamorphic complexes of different lithology and structure crop out in the coast ranges of central Chile. The Tanumé metamorphics to the E, which belong to a low P/T series derived from a continental platform clastic sedimentary sequence, give a whole rock isochron age of 347 ± 32 (2σ) Ma and the accreted Pichilemu metamorphics to the W, an age of 311 ±10(2σ) Ma. The latter consist of stilpnomelane-bearing cherts, crossite-bearing metabasites and siliceous metapelites. An errorchron of c. 370 Ma was obtained from sillimanite-cordierite gneisses of the low P/T series. Different provenance of the protoliths is indicated by the higher Sr⁸⁷/Sr⁸⁶ initial ratios of the Tanumé rocks (0.7124 ± 0.0007 (2σ) relative to the Pichilemu rocks (0.7060 ± 0.0005 (2σ), which were more affected than the former by the main (D₂) phase of deformation and metamorphism in the area.