MR027-05
Phase stability and equations of state of MgAl2O4 at lower mantle pressures and temperatures

Wednesday, 16 December 2020: 16:16
Virtual
Terry-Ann Suer1, Rebecca A. Fischer1, Masaki Akaogi2, Hiroshi Kojitani2, Kierstin Daviau1,3, Matthew Brennan1, Junjie Dong1, Michael Volk1 and Stella Chariton4, (1)Harvard University, Cambridge, MA, United States, (2)Gakushuin University, Tokyo, Japan, (3)Toi-Ohomai Institute of Technology, Tauranga, New Zealand, (4)University of Chicago, Center for Advanced Radiation Sources, Chicago, IL, United States
Recorded Presentation
Abstract:
The high‐pressure–temperature behaviors of spinel‐type minerals are important for understanding the physical and chemical properties of the terrestrial and other rocky planetary mantles. Such components (e.g., NaAlSiO4–MgAl2O4), present in basaltic oceanic crust, can undergo phase transitions when subducted (e.g., 1). Minerals in this system have been observed to transform into various structures including the calcium ferrite, calcium titanate, or high-pressure magnetite structures (e.g., 2, 3). These phases could account for 10 to 25 volume % of a mid-ocean ridge basalt (MORB) assemblage in the Earth’s lower mantle (1). Their greater densities compared to the ambient mantle (1) and ability to host heat-producing elements (4) could also have important consequences for the thermal and material cycling of the mantle. Characterizing the phase relations and equations of state of these minerals can therefore improve our knowledge of the structure and composition of planetary mantles. We investigated the phase stability and equations of state of the MgAl2O4 end-member in a laser-heated diamond anvil cell with in-situ synchrotron X-ray diffraction. Data were obtained at pressures between 30 and 90 GPa and temperatures up ~3400 K during both heating and cooling cycles. Two high‐pressure polymorphs of MgAl2O4 were identified in the data. Between 30 and 40 GPa, preliminary analysis indicates the presence of an orthorhombic phase (space group Pnma). The structure is similar to ones identified in earlier works (e.g., MgFe2O4 (3)). At higher pressures (> 50 GPa) another phase is present that has a density of 4.597 g/cm3 at 65 GPa and 2700 K. We will present the P–V–T relationship for these phases and apply these new results to further explore the fate of spinel-type minerals in deep planetary mantles.

References:

  1. Hirose et al., Earth and Planetary Science Letters 237, 239-251 (2005).
  2. Ono et al., Physics and chemistry of minerals 33, 200-206 (2006).
  3. Ishii et al., Geophysical Research Letters 47, e2020GL087490 (2020).
  4. Kato et al., Geophysical Research Letters 40, 5085-5088 (2013).
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