Mobility and immobility of mid-ocean ridges and their implications to mantle dynamics
In the past two decades, the mobility of mid-ocean ridges relative to the mantle (absolute migration) has been correlated with major observable features, such as spreading asymmetry and asymmetry in the abundance of seamounts. The mobility of mid-ocean ridges is also thought to be an important factor that influences the diversity of ridge-crest basalts. However, this mobility has not yet been defined and mapped. The absolute migration of global mid-ocean ridges since 85 Ma has been computed and mapped. Global mid-ocean ridges have migrated extensively at varying velocities during that period. Presently, the fast-migrating ridges are the Pacific- Antarctic, Central Indian Ridge, Southeast Indian Ridge, Juan de Fuca, Pacific-Nazca, Antarctic-Nazca, and the Australia-Antarctic ridges, migrating at velocities of between 3.3 and 5.5 cm/yr. The slow-migrating ridges are the Mid-Atlantic and the Southwest Indian ridges, migrating at velocities between 0.3 and 2.0 cm/yr. Comparison of these results with mantle tomography results show that the slow-migrating ridges have deeper depth of origin than the fast-migrating ones, suggesting a correlation between the absolute migration velocity and the depth of origin of ridges. Furthermore, the Southwest Indian ridge appears to be tapping the same portion of mantle as did the Central Indian ridge. These results have important thermo-chemical implications, such as variations in the extent of melting and mineralogical composition of the mantle beneath different ridges, which may influence mantle dynamics.