Final answer:
At divergent plate boundaries, the most common geologic features include mid-ocean ridges, basaltic lava formations, shallow earthquakes, and volcanic activity resulting from decompression melting in the mantle.
Step-by-step explanation:
At divergent plate boundaries, where Earth's tectonic plates move apart, several geologic features can be observed. Primarily, these boundaries are associated with mid-ocean ridges like the Mid-Atlantic Ridge and occurrences of basaltic lava, which is the kind of igneous rock that forms most of the ocean basins. The process involved in the formation of these geologic features is a combination of decompression melting of Earth's mantle peridotite due to reduced pressure and the subsequent formation of mafic rocks, either extrusive or intrusive.
Furthermore, divergent boundaries are characterized by shallow earthquakes and volcanic activity due to magma production when the mantle experiences reduced pressure conditions. The East African Rift is a well-known divergent boundary on land, where the African continent is slowly breaking apart. The crust composition and the volcanic activity at divergent boundaries contribute to the formation of new oceanic lithosphere, with igneous rocks and a thin sediment layer on top, sometimes exposed in mountain belts as ophiolites during tectonic activities.