Abstract

Pyroxene + liquid equilibrium in Hawaiian lavas occurs at a range of pressures for each volcano. Ranges are systematic and may be related to the stage of development of the magma conduit system. Kilauea, which is in its shield-building phase, yields relatively shallow storage estimates. Loihi and Mauna Kea, which are in the early and late stages of volcano growth, respectively, yield deeper storage estimates. Shallowest depth estimates at Loihi and Mauna Kea are similar to estimates of elastic plate thickness, suggesting that the mechanical behavior of the lithosphere, rather than density contrasts at the Moho, regulates magma delivery. Apparently, a large increase in fracture energy below the brittle-ductile transition inhibits transport at depth, whereas magma transport by fracture propagation is rapid through the brittle lithosphere. Some shallow depth estimates at Kilauea support the hypothesis that the strength of the unbuttressed southeast flank influences magma storage. Kilauea transport depths correlate with an eruption sequence, which illustrates a top-to-bottom emptying of the conduit system. Successively deeper reservoirs at Kilauea were tapped within 300 days, indicating that magma is stored at a range of depths, including in the mantle, rather than at a single level within the lithosphere.

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