A history of the Easter microplate, 5.25 Ma to present

Abstract

GLORIA and other geophysical data are used to interpret the morphology and tectonic pattern of the Easter microplate. We model magnetic anomaly data and calculate spreading rates for use in Euler pole calculations. We calculate three‐plate closure and best fit poles for Nazca‐Pacific, Nazca‐Easter, and Pacific‐Easter plate motions and compare the results with earthquake focal mechanisms and seismicity. We use the three‐plate closure poles to rotate digital GLORIA and magnetic isochron data of the microplate and surrounding major plates back in time since the microplate's East Rift first started to propagate northward at around 5.25 Ma. The microplate has evolved in two stages. The first is from 5.25 Ma to around 2.5 Ma, and involved continuous northward propagation of the East Rift, while the West Rift became segmented along new transform faults as it adjusted to keep the overall Nazca‐Pacific velocities constant. The transpressive northern boundary migrated with the East Rift tip, while the transtensional southern boundary remained more or less still. At some time after 2.5 Ma the East Rift ceased northward propagation and the Southwest Rift began to open up along the transtensional Pacific‐Easter transform. A convergent northern boundary formed involving southward thrusting of the Nazca plate over the microplate. No further Nazca plate lithosphere was transferred from north of the microplate to the microplate interior, and the Pito Deep region opened by pervasively rifting apart preexisting Nazca plate lithosphere.