Dating the TIPA shear zone:: an Early Devonian terrane boundary between the Famatinian and Pampean systems (NW Argentina)

The TIPA shear zone is a prominent tectonic element of the Las Termas belt of NW Argentina. The belt is squeezed between the rocks of the Pampean system in the east and those of the Famatinian system in the west and is characterized by NNW-SSE-trending ductile shear zones. Granitoid protoliths of the mylonites yield intrusion ages of 487.5 +/- 4.3 and 467.0 +/- 3.6 Ma (U-Pb on zircon). During mylonitization, an intense fluid and melt influx, correlated with the intrusion of syn- to late-tectonic pegmatoids, led to a significant change in rock composition and the growth of syntectonic garnet. Mylonitization is dated at 402.0 +/- 2.0 Ma (Sm-Nd on garnet). U-Pb ages for apatite (meta-granodiorite 342.3 +/- 1.8 Ma; mylonite 328 +/- 3 Ma), consistent with the age of granites intruding the whole series, document a Carboniferous heating process that affected the whole crust. Final uplift is indicated by homogeneous biotite cooling ages at 300 +/- 4 Ma (Rb-Sr). The time span of approximately 40 Ma between apatite crystallization and closure of the Rb-Sr isotopic system in biotite implies a cooling rate of 3-4 degreesC/Ma, which indicates total uplift of the series of approximately 4 km. (C) 2003 Elsevier Science Ltd. All rights reserved.