5. Proposed research plan summary The work presented below will be done in a multidisciplinary approach, where the activities of each discipline will inform each other through regular interaction. However, for organizational purposes, the proposed research activities of each discipline are listed separately. 5.1 Mineral physics: melting properties of former oceanic crust The melting temperature of former MORB of the subducting oceanic crust relative to pyrolite at the pressure conditions of the deep mantle is a central target to this proposal. The depth dependence of melting temperature and relations is key. Co-PI Shim and a PhD graduate student will work on this in the high-pressure diamond-anvil cell (DAC) facility at ASU, and at the synchrotron facility in Argonne National Lab (Advanced Photon Source). Improved technological capabilities. Several technical developments over the last few years enable better determination of the melting temperature of Earth materials in the laser-heated DAC. X-rays are well collimated and tightly focused at the third generation synchrotron facilities. The size of the spot heated by near infrared laser beam has become sufficiently large owing to new optics and lasers [Prakapenka et al., 2008]. Under these developments, X-ray diffraction (XRD) is now a powerful probe to objectively distinguish melt from crystalline materials [e.g., Fiquet et al., 2010; Anzellini et al., 2013]. In addition, XRD provides information on the order of melting in multi-mineralic systems, such as MORB and pyrolite, which is important to understand the composition of partial melts generated from MORB. However, there are some limitations in using XRD for melting probe. Measurements of complete melting is still challenging since a weak tail of the focused synchrotron X-ray beam generates diffraction from cold spots around the heated area. Therefore, the liquidus temperature measured using XRD should be regarded as an upper bound. The same argument may be true for the solidus. An alternative (and also complementary) method is to study the melting texture of the laser-heated sample after pressure quench using Scanning Electron Microscope (SEM) [Du et al., 2013]. Also the ex-situ approach allows us to analyze the composition of partial melt using Energy Dispersive X-ray analysis (EDX) and Electron Energy Loss Spectroscopy (EELS) in Scanning Transmission Electron Microscope (STEM) and Aberration-Corrected Electron Microscope (ACEM) available at the Center for Solid-State Science, ASU. Since joining ASU, co-PI Shim has developed methods to prepare the samples synthesized in the laser-heated DAC for the SEM and EDX analysis using Focused Ion Beam (FIB). His group has successfully measured EELS and EDX of iron bearing Mg silicates. He also installed a new laser heating system at ASU, which includes a fiber laser with advanced beam shaping optics. Shim has conducted synchrotron X-ray measurements for the last 16 years and published numerous results on deep mantle mineralogy based on the experiments.
|Effective start/end date||8/15/14 → 7/31/17|