Ultra-high temperatures recorded in parental magmas from hybrid zones

Abstract Hybrid zones commonly occur at the contact between different magmatic facies of the same batholith and/or in contact with the host rock. Fine-grained textures recorded in hybrid zones respond to quenching processes. The compositions of these fine-grained rocks are intermediate and are very close to the silica gap, typically found in calc-alkaline systems. Here, we use examples from the Axial Pyrenean Zone to distinguish types of hybrid zones and examine the potential interest in studying them. This study presents new whole-rock geochemistry, mineral chemistry, Rb-Sr and Sm-Nd isotopic data (whole-rock), and geochronological data from magmatic rocks of two plutonic complexes of the Axial Pyrenean Zone (NE Spain). Pennsylvanian calc-alkaline coarse-to fine-grained mafic-intermediate plutonic rocks, including sanukitoid series, intruded the Axial Pyrenean Zone host rocks at ca. 305.8 ± 1.6 Ma (Lys-Caillaouas gabbro), 304 ± 1.7 Ma, and 301.6 ± 1.2 Ma (La Maladeta diorite and granodiorite, respectively). Also, we reviewed the geochemical data of calc-alkaline magmatic rocks from the Pyrenees to compare them with magmas from the sanukitoid and Andean series, which allowed us to consider that they represent a mix between the two series. Petrographic and geochemical results also support that parental magmas were quenched at these hybrid zones. Near-liquidus experiments testing the parental magma composition recorded in hybrid zones shed light on the ultra-high temperatures exceeding 1000 °C for these magmas to arrive at crustal levels at near-liquidus conditions and account for the need for mantle input to generate these calc-alkaline magmas.