Polimetamorfismo en las Zonas Internas béticasimplicaciones tectónicas

Resumen

Chemical zoning and textural features of different types of garnet coexisting within the same samples, together with mona- zite and zircon dating in metapelites and gneisses of the Alpujarride Torrox Unit (Betic Internal Zones), allow recognizing a pre-Alpine metamorphism overprinted by a complex Alpine evolution. Garnet porphyroblasts with Mn-rich cores (XSps close to 0.2) and low XGrs content coexist with garnet porpyroblasts with high-Ca cores (XGrs > 0.3). The former show chiastolitic textures as a result of static growth during a low-P/medium-T pre-Alpine event (ca. 0.35 GPa and < 550 ºC), while the later yield conditions close to blueschists-facies (1.3 GPa and 500 ºC) related to an Alpine subduction event. Both types of cores appear dissolved and overgrown by moderate-Ca domains that also show later dissolution features and newer overgrowths of Ca-poor domains (XGrs ca. 0.05) with maximum XPrp values (ca. 0.15). These youngest overgrowths correspond to a second Alpine metamorphic event under a range of P-T conditions (500-620 °C and 0.8-11 GPa). Finally, in the same samples also coexist small garnet grains, present either within the matrix or included in staurolite, garnet, andalusite, plagioclase and tourmaline. These small grains show contrasted compositions and common atoll textures developed upon replacement of Ca-rich cores, and correspond to an enigmatic event. Consequently, the examples here provided illustrate that not all fabrics and metamorphic assemblages of the Alpujárride units are of Alpine age.