  We construct a theory of gravity in which a propagating massive vector field
arises from a quadratic curvature invariant. The Einstein-Cartan formulation
and a partial suppression of torsion ensure the absence of ghost and
strong-coupling problems, as we prove with nonlinear Lagrangian and Hamiltonian
analysis. Augmenting General Relativity with a propagating torsion vector, our
theory provides a purely gravitational origin of Einstein-Proca models and
constrains their parameter space. As an outlook to phenomenology, we discuss
the gravitational production of fermionic dark matter.
