5:15 PM - 6:30 PM
[SIT20-P03] Melting phase relation of hydrous peridotite at the top of the lower mantle
Keywords:hydrous phase, melting, lower mantle, low-velocity anomaly
Previous seismic observations on the Earth’s mantle have found the low-velocity anomaly around 750 km depth and proposed the existence of partial melting layer atop the lower mantle (e.g., Schmandt et al., 2014; Liu et al., 2018). This layer could be formed by dehydration melting upon the decomposition of hydrous ringwoodite to bridgmanite and ferropericlasein downward flow from the mantle transition zone into the lower mantle.According to the melting relation of hydrous KLB1 peridotite in this depth reported by Kawamoto (2004), at lower temperatures less than 1300C, dense hydrous Mg silicate (DHMS) phases should appear rather than dehydration of ringwoodite. In addition,the observed seismic low-velocity region is approximately 100 km deeper than the ringwoodite-bridgmanite phase transition depth (i.e., 660 km), suggesting that the major cause of partial melting at the top of the lower mantle has been poorly understood.
In order to constrain the melting phase relation of hydrous peridotite at the top of the lower mantle, we conducted high-pressure experiments using a Kawai-type multi-anvil apparatus. The starting material was a powder mixture of natural KLB1 peridotite and brucite + talc as a water source. High-pressure experiments were performed at various pressures from 22 GPa to 28GPa and temperatures from 1200C to 1400C. The recovered samples were observed by scanning electron microscope, and phases were identified by micro-focused X-ray diffractometer, and infrared spectroscopy. In the presentation, we will discuss the origin of the low velocity anomalyfrom the view point ofdehydration melting at the top of the lower mantlebased on the melting phase relation of hydrous peridotite.
In order to constrain the melting phase relation of hydrous peridotite at the top of the lower mantle, we conducted high-pressure experiments using a Kawai-type multi-anvil apparatus. The starting material was a powder mixture of natural KLB1 peridotite and brucite + talc as a water source. High-pressure experiments were performed at various pressures from 22 GPa to 28GPa and temperatures from 1200C to 1400C. The recovered samples were observed by scanning electron microscope, and phases were identified by micro-focused X-ray diffractometer, and infrared spectroscopy. In the presentation, we will discuss the origin of the low velocity anomalyfrom the view point ofdehydration melting at the top of the lower mantlebased on the melting phase relation of hydrous peridotite.