Abstract

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.

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