Partly inspired by the tropical-to-holomorphic correspondence in mirror symmetry, Donaldson-Scaduto proposed a program to find and count associative submanifolds in G_2 manifolds admitting a Kovalev-Lefschetz fibration, where the torsion-free G_2 structure is near an adiabatic limit. As the G_2 manifold collapses, these associative submanifolds are expected to converge to certain one-dimensional objects in the base, called gradient cycles. In this talk, I will discuss joint work with Yu-Shen Lin on a Calabi-Yau analogue of the Donaldson-Scaduto program. More precisely, we construct examples of special Lagrangian spheres and trivial mapping tori in Calabi-Yau 3-folds equipped with a Lefschetz K3-fibration. I will also discuss some potential applications of this construction.