Phase relation and Equation of State of Iron-titanium oxyhydroxides with α-PbO2 type crystal structure at deep mantle conditions

data sets of Paper "Phase relation and Equation of State of Iron-titanium oxyhydroxides with α-PbO2 type crystal structure at deep mantle conditions" by Matsukage et al

Major element composition of an Early Enriched Reservoir: Constraints from 142Nd/144Nd isotope systematics in the early Earth and high pressure melting experiments of a primitive peridotite

The Accessible Silicate Earth (ASE) has a higher 142Nd/144Nd ratio than most chondrites. Thus, if the Earth is assumed to have formed from these chondrites, a complement low-142Nd/144Nd reservoir is needed. Such a low-142Nd/144Nd reservoir is believed to have been derived from a melt in the early Earth and is called the Early Enriched Reservoir (EER). Although the major element composition of the EER is crucial for estimating its chemical and physical properties (e.g., density) and is also essential for understanding the origin and fate of the EER, which are both major factors that determine the present composition of the Earth, it has not yet been robustly established. In order to determine the major element composition of the EER, we estimated the age and pressure–temperature conditions to form the EER that would best explain its Nd isotopic characteristics, based on Sm–Nd partitioning and its dependence on pressure, temperature, and melting phase relations. Our estimate indicates that the EER formed within 33.5 Myr of Solar System formation and at near-solidus temperatures and shallow upper-mantle pressures. We then performed high-pressure melting experiments on primitive peridotite to determine the major element composition of the EER at estimated temperature at 7 GPa and calculated the density of the EER. The result of our experiments indicates that the near-solidus melt is iron-rich komatiite. The estimated density of the near-solidus melt is lower than that of the primitive peridotite, suggesting that the EER melt would have ascended in the mantle to form an early crust. Given that high mantle potential temperatures are assumed to have existed in the Hadean, it follows that the EER melt was generated at high pressure and, therefore, its composition would have been picritic to komatiitic. As the formation age of the EER estimated in our study precedes the last giant, lunar-forming impact, the picritic to komatiitic crust (EER) would most likely have been ejected from the Earth by the last giant impact or preceding impacts. Thus, the EER has been lost, leaving the Earth more depleted than its original composition

Stability of the hydrous phases of Al-rich phase D and Al-rich phase H in deep subducted oceanic crust

To understand the stability of hydrous phases in mafic oceanic crust under deep subduction conditions, high-pressure and high-temperature experiments were conducted on two hydrous basalts using a Kawai-type multi-anvil apparatus at 17-26 GPa and 800-1200 degrees C. In contrast to previous studies on hydrous basalt that reported no hydrous phases in this pressure range, we found one or two hydrous phases in all run products at or below 1000 degrees C. Three hydrous phases, including Fe-Ti oxyhydroxide, Al-rich phase D and Al-rich phase H, were present at the investigated P-T conditions. At T 23 GPa). Therefore, in cold subduction zones, mafic oceanic crust, in addition to peridotite, may also carry a substantial amount of water into the mantle transition zone and the lower mantle

Aqueous Fluid Connectivity in Subducting Oceanic Crust at the Mantle Transition Zone Conditions

Experiments were performed at 17-19 GPa and 1000-1200 degrees C to determine the aqueous fluid-majoritic garnet-majoritic garnet dihedral angle theta(grt-grt) in a basalt-H2O system. The results show that the theta(grt-grt) is between 44 +/- 2 degrees and 55 +/- 3 degrees, decreasing with increasing pressure and temperature. These new data combined with previous data obtained in the aqueous fluid-olivine and aqueous fluid-garnet systems suggest that connected network of aqueous fluids can form in the peridotite part of the subducting slab but may not form in a cold subducting oceanic crust at pressures below 14 GPa. Therefore, aqueous fluids formed by dehydration of a cold slab could be trapped as interstitial fluids in the oceanic crust and transported into the deep mantle. However, at the mantle transition zone (MTZ) conditions, aqueous fluids trapped previously and/or formed lately by the breakdown of hydrous minerals can percolate through the oceanic crust and hydrate the MTZ, providing an important mechanism for the MTZ hydration. Furthermore, aqueous fluids formed by mineral dehydration in a hot slab are readily lost into the mantle wedge at shallow depth, due to low dihedral angles (theta < 60 degrees) of the subducting oceanic crust, resulting in less water available to hydrate the MTZ. The distinct contribution of the cold slab and the hot slab to the MTZ hydration may cause water heterogeneity in the MTZ