Pluton emplacement during transpression in brittle crust: New views from analogue experiments

Analogue experiments were used to investigate pluton emplacement during tra nspression in brittle crust. Models consisted of silicone putty placed with in slots in a rigid basement and an overburden of dry sand. The models were transpressed, causing emplacement of silicone intrusions into the overlyin g sand. Space was made for intrusions by upward displacements of overburden along oblique reverse shear zones, in some cases accompanied by extensiona l shearing above the intrusions. Silicone putty was progressively accreted to the bases of uplifted blocks, and growing intrusions rode up the shear z ones, leaving space for accretion of more silicone. The resulting intrusion shapes depended largely on the geometries of shear zone systems, which in turn depended on overburden thickness. The intrusion profiles and the struc tural relationships between intrusions and host in the experiments are comp arable to some natural examples. A magma accretion model may thus account f or pluton emplacement and batholith assembly within some transpressive orog ens.