Final answer:
Spreading centers are associated with two main physical features: mid-ocean ridges and rift valleys. These features are formed by the movement of tectonic plates and the upwelling of magma from the Earth's mantle.
Step-by-step explanation:
Spreading centers are associated with two main physical features: mid-ocean ridges and rift valleys. Mid-ocean ridges are underwater mountain ranges that form at the boundary between diverging tectonic plates. Rift valleys, on the other hand, are formed on land at continental rift zones. Both of these physical features are the result of the movement of tectonic plates and the upwelling of magma from the Earth's mantle. They are characterized by volcanic activity, earthquakes, and the creation of new crust.