Experimental investigation on granite emplacement during shortening.

We present analogue experiments performed to investigate the emplacement of granitic plutons in a shortening upper crust. The models were made of quartz-sand to simulate the brittle crust and a low-viscosity mixture of silicone and oleic acid to reproduce granitic magmas. Shortening of the models was obtained by a moving wall while a special injection apparatus allowed syn-kinematic magma intrusion from the base of the models. Experimental results show that: (1) space for intrusions is achieved during the movement along thrust faults and mostly coincides with low-pressure areas developed into the thrust-anticlines; (2) intrusion shapes are strictly dependent upon the competition between shortening rate (Sh) and injection rate (Inj). For high Sh/Inj values, plutons were elongated with the long axis parallel to the thrust surfaces; (3) magma migrates horizontally away from the injection point and towards the external sector in the direction of tectonic transport a longer distance for high Sh/Inj values; (4) syn-kinematic emplacement is also controlled by model thickness; an increase in this parameter results in an increase in the pluton plan-view aspect ratio. These results support that the final shape of orogenic plutons emplaced at shallow crustal levels may be strongly controlled by deformational features.