DATING AND DIFFERENTIATING ERUPTIVE FLOW UNITS ON THE SOUTHERN EAST PACIFIC RISE (SEPR) USING A COMBINED PALEOINTENSITY AND GEOCHEMISTRY APPROACH

The size and frequency of mid-ocean ridge eruptions are an important variable in understanding ocean crustal accretion but are poorly understood. Young flows are difficult to date as recurrence intervals are typically shorter than the resolution of most radiometric dating systems. We attempt to differentiate eruptive units at 17°-19°S on the superfast spreading southern East Pacific Rise (SEPR), by combining geochemical data with geomagnetic paleointensity of submarine basaltic glass (SBG) specimens to assess inter- and intra-flow variability through a joint cluster analysis. At the SEPR, geochemistry alone is not necessarily indicative of distinct eruptive events. Paleointensity allows us to add a temporal constraint as field intensity is recorded at the time of eruption.

Samples were collected during Alvin and Nautile dives where direct observations enabled relative age assessments (Sinton et al., 2002). These known flow classifications allow us to evaluate the natural scatter in a single eruptive event and to test the cluster approach. Specimens were chosen from known flow fields to contrast with data across contacts and within the identified flow. The cluster analysis aims to model data clusters representing a single flow unit. Ground truthing with data from known flows allows us to identify ideal model parameters for future flow identification in a superfast spreading environment.

In addition to identifying number and size of eruptive clusters, global magnetic field models evaluated at the SEPR allow us to estimate absolute ages for defined flows based on paleointensity. Paleointensity estimates range from 28-43 μT at flows surrounding 17°26’ and 30-48 μT at flows surrounding 18°38’. Estimated ages for 17°26’ flows place eruptions between 1887-2021. Once flows are defined, absolute ages from paleointensity can help define the recurrence interval which reflects characteristics (size and frequency) of mid-ocean ridge eruptions.

Ref: Sinton et al., (2002), J. Geophys. Res., 107, 1-21, doi: 0.1029/2000JB000090.