The resistive evolution of presheared magnetic arcades in a two-dimensional Cartesian geometry is investigated. We find that there is a critical value of shear over which magnetic reconnection can take place in a magnetic arcade to create a magnetic island. The diffusion of the toroidal field eventually leads to thinning of the current layer for any amount of shear, whereas the diffusion of the poloidal field brings about current layer thinning only for shears above the critical value. The reconnection profiles are found to depend on spatial resistivity patterns. A fast reconnection with small shock angles can be achieved only when the resistivity is confined to a small volume. In this case, high-speed reconnection outflows can tear the magnetic island into a pair. The fast moving island system creates a fast shock or a steepened fast-mode structure, which resembles an observed coronal mass ejection (CME) frontal loop.