A three-dimensional study of a crustal low velocity region beneath the 9°03′N overlapping spreading center

Abstract

Overlapping spreading centers (OSCs) play a key role in models of magma distribution at fast spreading ridges. To investigate the relationship between ridge-axis discontinuities and magma supply, we conducted a three-dimensional seismic reflection and tomography experiment at the 9°03'N OSC along the East Pacific Rise. Tomographic analysis imaged a broad mid-crustal low velocity zone (LVZ) beneath parts of the overlapper and the associated overlap basin, demonstrating that it is magmatically robust. The complementary datasets reveal a complex storage and tapping of melt: the LVZ and melt sill at either end of the overlap basin are not simply centered beneath the rise crest but are skewed inwards. The subsequent focussing of the LVZ and sill beneath the axis of the eastern limb appears to be due to melt migration toward the tip. The OSC western limb is less magmatically robust and may be in the process of dying.