Rutilos ricos en Zr incluidos en granates de xenolitos granulíticos de la corteza inferior del Sistema Central Español: implicaciones geodinámicas

Abstract

Two petrographic types of rutile are observed in the peraluminous felsic meta-igneous granulites, the most common type of the lower crustal xenolith suite of the Spanish Central System (SCS). Rutile-1 (Rt-1) corresponds to small crystals (mainly < 80 mm) only preserved as micro-inclusions within garnet, whereas rutile-2 (Rt-2) is commonly found as big idiomorfic crystals forming the granulite granoblastic matrix. Chemical analyses by EMP show a higher Zr content in Rt-1 (up to 7800 ppm) than in Rt-2 (up to 5200 ppm) of the same granulite. Applying Zr-in-rutile thermometry, Rt-1 gives 50-60 ºC higher for rutile crystallization (950-1015 ºC) when compared to Rt-2 thermometry (940-955 ºC). These ultra-high temperatures (UHT) are likely attained at Moho depths without external heat sources (e.g. mantle input) as supported by the high heat production estimated for the crustal section of the SCS. The granulitegranite petrogenetic link suggests that these HT-UHT granulites were generated by intra-crustal reworking during Hercynian continental thickening.