X-discontinuity and transition zone structure beneath Hawaii suggests a heterogeneous plume

Kemp, M. and Jenkins, J. and Maclennan, J. and Cottaar, S. (2019) X-discontinuity and transition zone structure beneath Hawaii suggests a heterogeneous plume. Earth and Planetary Science Letters, 527. ISSN 0012-821X DOI https://doi.org/10.1016/j.epsl.2019.115781

[img] Text
Hawaii_X_discontinuity.pdf - Accepted Version
Restricted to Registered users only until 9 September 2020.

Download (17MB) | Request a copy
Official URL: https://www.sciencedirect.com/science/article/abs/...

Abstract

The Hawaiian Island chain in the middle of the Pacific Ocean is a well-studied example of hotspot volcanism caused by an underlying upwelling mantle plume. The thermal and compositional nature of the plume alters the mantle phase transitions, which can be seen in the depth and amplitude of seismic discontinuities. This study utilises >5000 high quality receiver functions from Hawaiian island stations to detect P-to-s converted phases to image seismic discontinuities between 200 to 800 km depth. Common-conversion point stacks of the data are used to map out lateral variations in converted phase observations, while slowness stacks allow differentiation between true conversions from discontinuities and multiples. We find that the 410 discontinuity is depressed by 20 km throughout our study region, while the main 660 is around average depth throughout most of the area. To the southwest of the Big Island we observe splitting of the 660, with a major peak at 630 km, and a minor peak appearing at 675 km depth. This is inferred to represent the position of the hot plume at depth, with the upper discontinuity caused by an olivine phase transition and the lower by a garnet phase transition. In the upper mantle, a discontinuity is found across the region at depths varying between 290 to 350 km. Identifying multiples from this depth confirms the presence of a so-called X-discontinuity. To the east of the Big Island the X-discontinuity lies around 336 km and the associated multiple is particularly coherent and strong in amplitude. Strikingly, the discontinuity around 410 km disappears in this area. Synthetic modelling reveals that such observations can be explained by a silica phase transition from coesite to stishovite, consistent with widespread ponding of silica-saturated material at these depths around the plume. This material could represent eclogite enriched material, which is relatively silica-rich compared to pyrolite, spreading out from the plume to the east as a deep eclogite pool, a hypothesis which is consistent with dynamical models of thermochemical plumes. Therefore these results support the presence of a significant garnet and eclogite component within the Hawaiian mantle plume.

Item Type: Article
Uncontrolled Keywords: 2019AREP; IA76
Subjects: 02 - Geodynamics, Geophysics and Tectonics
05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 02 - Geodynamics, Geophysics and Tectonics
05 - Petrology - Igneous, Metamorphic and Volcanic Studies
08 - Green Open Access
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 527
Identification Number: https://doi.org/10.1016/j.epsl.2019.115781
Depositing User: Sarah Humbert
Date Deposited: 07 Apr 2020 00:56
Last Modified: 07 Apr 2020 00:56
URI: http://eprints.esc.cam.ac.uk/id/eprint/4665

Actions (login required)

View Item View Item

About cookies