The Origin of Chemical Heterogeneity in the Mantle Source of Kilauea Lavas

Abstract:

Differences in lava composition between Hawaiian volcanoes likely result from the melting of a heterogeneous mantle source containing variable amounts and/or types of ancient recycled oceanic crust (sediment, basalt, and/or gabbro). Our previous model calculations based on average incompatible trace element abundances suggest that the mantle sources of Hawaiian volcanoes contain ~8-21% recycled oceanic crust (ROC) [1]. The ROC within the Hawaiian mantle plume (basalt and gabbro, with no marine sediment) was altered by interaction with seawater or hydrothermal fluids and then variably dehydrated in an ancient subduction zone. The uppermost portion of the residual slab (gabbro-free and strongly dehydrated) is best expressed in the source of Loihi lavas, whereas the lowermost portion of the residual slab (gabbro-rich and weakly dehydrated) is best expressed in the source of Mauna Loa and Koolau lavas. Here we investigate the origin of chemical heterogeneity within the mantle source of a single Hawaiian volcano based on new modeling of trace element abundances in 80 Kilauea lavas and tephra erupted over the last millenium. The results using our simplest model [1] suggest that the amount of recycled basalt (dehydrated from ~2-9%) and gabbro within the mantle source tapped by Kilauea has ranged from ~9-14% and ~0-3%, respectively. The total amount of ROC correlates with the inferred melt fraction (~3-9%), which indicates that the fertility of the mantle source is the primary control on the degree of partial melting at Hawaiian shield volcanoes. These model results for Kilauea bridge those for the neighboring active volcanoes (Mauna Loa and Loihi), confirming that the Hawaiian plume is heterogeneous on a small scale with a NW-SE oriented spatial gradient in the amount, type (i.e., basalt vs. gabbro) and extent of dehydration of the ancient ROC [1].

[1] Pietruszka et al. (2013) EPSL 361, 298–309.