  Hotspots with strong near fields due to localized surface plasmons (LSPs) in
metallic nanostructures have various applications, such as surface enhanced
Raman scattering (SERS). The long range Coulomb coupling between LSPs in
periodic metallic nanostructures may lead to interesting collective effects. In
this paper, we investigate the combination effects of the local field
enhancement and collective plasmon resonances in one dimensional metallic
nanoparticle dimer chains. It is found that the strong near field in the gap
and the far field interactions among the metallic nanoparticles lead to
anomalous collective hotspots with dual enhancement of the electromagnetic
field. In particular, the interference between the incident field and the
induced internal field leads to Fano-type effect with Wood anomaly related
destructive interference and the strong resonance with an extremely narrow
width. Our systematic study shows that the correlation between the local
structure and the global structure has important impact on the collective
spots, which leads to an optimal orientation of the dimer (about 60{\deg} with
respect to the chain direction) for the largest gap field enhancement with the
incident field polarization parallel to the long axis of the dimer.
