Final answer:
During the Mesozoic, the main tectonic activities involved plate convergence leading to mountain building, and plate divergence resulting in seafloor spreading and the formation of new ocean basins.
Step-by-step explanation:
During most of the Mesozoic, the dominant tectonic activities were plate convergence and mountain building, as well as plate divergence and seafloor spreading. This era saw the breakup of the supercontinent Pangea, leading to increased plate divergence and the formation of new oceans through seafloor spreading. At the same time, the Mesozoic was marked by significant episodes of plate convergence, which led to subduction and the creation of mountain ranges. An example of these processes can be seen in the creation of the Appalachian/Caledonide Mountains, formed through multiple orogenies which are associated with continent-to-continent collisions. Furthermore, the Mesozoic era also involved processes such as the creation of the Hawaiian island chain, which is related to volcanic activity over a hot spot rather than plate boundary interactions.