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A high‐resolution sampling profile constituted of 52 basalt samples from across the East Pacific Rise (EPR) was investigated. These samples provide a unique opportunity to study the coeval recording of isotopic signals derived from sub‐marine eruptions at a fast spreading ridge over a time interval of ∼320 kyrs. Additionally, the study area is marked by the presence of a neighboring seamount chain that has recently caused the ridge to jump twice toward it. Combining previous geochemical studies and bathymetry, we established a first‐order chronology between analyzed samples, and have reconstructed the evolution of basalt compositions as the ridge and seamounts advance and finally merge. Our data reveal the existence of two distinct types of isotopic variability within the samples. One that has a low amplitude and frequency and is accounted for by the continuous melting of the ambient mantle, indicating a process with a ∼125 kyr periodicity. The other, of higher amplitude, is discontinuous in time, and likely reflects the seamounts source influence on the ridge. Our results support a two‐step hotspot‐ridge interaction including a first stage (≥600 ka) of regional enrichment of the depleted ridge mantle by hotspot material; and a second, more recent (at least 300 ka) even wherein ambient mantle melts mixed with proximal melts from heterogeneous seamounts sourced nearby. We also propose that the ancient gabbroic component previously identified in this region appeared very recently (300 kyrs. We have established a relative chronology between these samples, and propose a paleo‐reconstruction of the area accounting for both the isotopic variations observed and previously reported geophysical results. Our new results also suggest rapid magma transfers within the crust independent of melting of seamounts and/or ridge sources, including periodic injections of enriched mantle material into the ridge‐melting region. Key Points: Ridge‐hotspot interactions were tracked via the isotopic composition of basalts sampled across the East Pacific Rise axisChronological reconstructions of collected mid‐ocean ridge basalts reveal a periodicity of 125 kyrs in the recorded isotopic signalHigh‐resolution sampling allows the integration of geochemical information within the framework of geophysical and geological models [ABSTRACT FROM AUTHOR]

We have investigated the absolute migration of mid-ocean ridges in the Pacific basin since 85 Ma and their tectonic implications. Our results indicate that ridges in the northern and central Pacific basin and those in the southern Pacific basin underwent different tectonic histories. The northern and central Pacific basin ridges do not show any change in absolute migration direction at the time of the Hawaii-Emperor chain bend, while the southern Pacific basin ridges changed their absolute migration direction at Chron 21 (the time of the bend). These results imply that tectonic events in southern Pacific basin may be more localised. The migration of the southern Pacific basin ridges may record the reorganisation of the southern Pacific triple junction or an episode of Cenozoic East-West separation of Antarctica and the initiation of seafloor spreading in the Adare basin, or a combination of the two events. Furthermore, the clockwise rotation of the Pacific plate since Chron 34 ended at Chron 6, after which the Pacific plate has migrated in a north-westerly direction without rotating. [ABSTRACT FROM AUTHOR]

Abstract: Topography has a strong effect on the physical oceanography over the flanks and crests of the global mid-ocean ridge system. Here, we present an analysis of the hydrography and circulation near the crest of the East Pacific Rise (EPR) between 9° and 10°N, which coincides with an integrated study site (ISS) of the RIDGE2000 program. The analysis is based primarily on survey and mooring data collected during the LADDER project, which aimed to investigate oceanographic and topographic influences on larval retention and dispersal in hydrothermal vent communities. Results indicate that the yearly averaged regional mean circulation is characterized by a westward drift of 0.5–1cms−1 across the EPR axis and by north- and southward flows along the western and eastern upper ridge flanks, respectively. The westward drift is part of a basin-scale zonal flow that extends across most of the Pacific ocean near 10°N, whereas the meridional currents near the ridge crest are a topographic effect. In spite of considerable mesoscale variability, which dominates the regional circulation and dispersal on weekly to monthly time scales, quasi-synoptic surveys carried out during the mooring deployment and recovery cruises indicate sub-inertial circulations that are qualitatively similar to the yearly averaged flow but associated with significantly stronger velocities. Weekly averaged mooring data indicate that the anticyclonically sheared along-flank flows are associated with core speeds as high as 10cms−1 and extend off axis and 200m above the ridge-crest topography. Near the northern limit of the study region, the Lamont Seamount Chain rises from the western ridge flank and restricts along-EPR flow to five narrow passages, where peak velocities in excess of 20cms−1 were observed. Outside the region of the ridge-crest boundary currents the density field over the EPR near 10°N is characterized by isopycnals dipping into the ridge flanks. Directly above the EPR axis the ridge-crest boundary currents give rise to an isopycnal dome. During times of strong westward cross-EPR flow isopycnal uplift over the eastern flank causes the cross-ridge density field below the doming isopycnals to be asymmetric, with higher densities over the eastern than over the western flank. The data collected during the LADDER project indicate that dispersal of hydrothermal products from the EPR ISS on long time scales is predominantly to the west, whereas mesoscale variability dominates dispersal on weekly to monthly time scales, which are particularly important in the context of larval dispersal. [Copyright &y& Elsevier]