Steady and non-steady state magma chambers below the East Pacific Rise

Abstract

Volcanic rocks collected on flowline traverses on the flanks of the East Pacific Rise (EPR) document changes in axial magma chemistry with time, providing a record of the thermal history of axial magma chambers (AMC). We present data for a sample set of closely spaced (1-2 km) samples along EPR flowlines at three localities out to ∼800 ka showing both steady (constant average temperature) and non-steady state behavior of magma chambers on time scales of 200-500 ka. Though based on only three symmetrical traverses so far, it appears that magmatically robust ridge locations (11°20N and 9°30'N) have steady state chambers, whereas a magmatically starved axis (10°30'N) shows large temperature changes with time. These observations provide a new petrologic perspective to the ongoing debate regarding the significance and causes of morphologic variations along the axis of the East Pacific Rise.