Pluton accommodation at high strain rates in the upper continental crust. The example of the Central Extremadura batholith, Spain

Emplacement in the tensional bridge of a stepped dextral shear zone system is proposed for the Central Extremadura batholith (Spain). The country rocks show a pervasive anisotropy that conditioned the style of the structures developed as a consequence of the transference of displacement from the stepped shear zones to the releasing area. The kinematic evolution of the resulting megakink fold provided the volume increase necessary for the granite emplacement. Thermal and kinematic models suggest that the growth of individual plutons took place in periods of no more than several hundred to a few thousand years. Fast strain rates (10−10–10−11 s−1) must concentrate in local structures (e.g. initiation of kink folds) even in zones deforming as a whole under typical strain rates (10−14±1 s−1). Granite plutons might be used as strain-rate gauges for syn-plutonic structures.