[S-MP36] Crust-Mantle Connections

[SMP36-06] Petrogenesis of enriched MORB from the Macquarie Ridge Complex

*Chris Conway¹, Richard Wysoczanski², Alexander Nichols⁴, Joel Baker³, Helen Bostock² (1.National Museum of Nature and Science, 2.National Institute of Water and Atmospheric Research, 3.University of Auckland, 4.University of Canterbury)

Keywords:mid-ocean ridge basalt, petrogenesis, Macquarie Ridge Complex, E-MORB

The Macquarie Ridge Complex is an ideal site for examining magmatism at slow-spreading mid-ocean ridges due to the Miocene evolution from seafloor spreading to oblique convergence along the coincident Australia–Pacific plate boundary. We present whole-rock major and trace and glass volatile element data for volcanic samples collected from a 1200 km section of the extinct spreading ridge in order to investigate the dynamics of magma generation, ascent, and eruption in such settings. The sample suite can be divided into E-MORB lavas with moderate (La/Sm_N = 1.0–1.8) or high (La/Sm_N > 2.0) incompatible element enrichment. The latter type is consistent with being sourced from low-degree partial melts of enriched mantle domains. Furthermore, as indicated by their evolved geochemical compositions and CO₂-H₂O systematics, the source magmas underwent fractionation and degassing during stalled ascents, possibly due to ultraslow seafloor spreading rates.