Delamination in Tibet: Deriving constraints from the density of eclogite

Abstract. Tibet, which is characterized by collisional orogens, has undergone the process of delamination or convective removal. The lower crust and mantle lithosphere appear to have been removed through delamination during orogenic development. Numerical and analog experiments demonstrate that the metamorphic eclogitized oceanic subduction slab or lower crust may promote gravitational instability due to its increased density. The eclogitized oceanic subduction slab or crustal root is believed to be denser than the underlying mantle and tends to sink. However, the density of eclogite under high-pressure and high-temperature conditions and density differences from the surrounding mantle is not preciously constrained. Here, we offer new insights into the derivation of eclogite density with a single experiment to constrain delamination in Tibet. Using in situ synchrotron X-ray diffraction combined with diamond anvil cell, experiments focused on minerals (garnet, omphacite, and epidote) of eclogite are conducted under simultaneous high-pressure and high-temperature conditions, which avoids systematic errors. Fitting the pressure-temperature-volume data with the third-order Birch-Murnaghan equation of state, the thermal equation of state (EoS) parameters, including the bulk modulus (KT0), its pressure derivative (KT0′), the temperature derivative ((KT/T)P), and the thermal expansion coefficient (α0), are derived. The densities of rock-forming minerals and eclogite are modeled along with the geotherms of two types of delamination. The delamination processes of subduction slab breakoff and the removal of the eclogitized lower crust in Tibet are discussed. The Tibetan eclogite which containing 40–60 vol. % garnet and 37–64 % degrees of eclogitization can promote the delamination of slab break-off in Tibet. Our results indicate that eclogite is a major controlling factor in the initiation of delamination. A high abundance of garnet, a high Fe-content, and a high degree of eclogitization are more conducive to instigating the delamination.

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Characterization of the High-Pressure and High-Temperature Phase Diagram and Equation of State of Chromium

10.21203/rs.3.rs-1195199/v1 ◽

2021 ◽

Author(s):

Simone Anzellini ◽

Daniel Errandonea ◽

Leonid Burakovsky ◽

John E. Proctor ◽

Christine M. Beavers

Keyword(s):

High Pressure ◽

High Temperature ◽

Equation Of State ◽

Density Functional ◽

Equations Of State ◽

Melting Curve ◽

High Temperature Phase ◽

Temperature Phase ◽

Thermal Equation ◽

Pressure Derivative

Abstract The high-pressure and high-temperature melting curve of chromium has been investigated both experimentally (in situ), using a laser-heated diamond-anvil cell technique coupled with synchrotron powder X-ray diffraction, and theoretically, using ab initio density-functional theory simulations. In the pressure–temperature range covered experimentally (up to 90 GPa and 4500 K, respectively) only the solid body-centred-cubic and liquid phases of chromium have been observed. Experiments and computer calculations give melting curves in agreement with each other, that can be described by a Simon–Glatzel equation Tm(P) = 2136K(1+P/25.9) 0.41. In addition, a quasi-hydrostatic equation of state at ambient temperature has been experimentally characterized up to 131 GPa and compared with the present simulations. Both methods give very similar third-order Birch-Murnaghan equations of state with a bulk modulus of 182-185 GPa and its pressure derivative of 4.74-5.15. According to the present calculations, the obtained melting curve and equation of state are valid at least up to 815 GPa, being the melting temperature at this pressure 9310 K. Finally, from the obtained results, it was possible to determine a thermal equation of state of chromium valid up to 65 GPa and 2100 K.

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Topaz, a Potential Volatile-Carrier in Cold Subduction Zone: Constraint from Synchrotron X-ray Diffraction and Raman Spectroscopy at High Temperature and High Pressure

Minerals ◽

10.3390/min10090780 ◽

2020 ◽

Vol 10 (9) ◽

pp. 780

Author(s):

Shijie Huang ◽

Jingui Xu ◽

Chunfa Chen ◽

Bo Li ◽

Zhilin Ye ◽

...

Keyword(s):

Raman Spectroscopy ◽

High Pressure ◽

High Temperature ◽

Equation Of State ◽

Subduction Zone ◽

Upper Mantle ◽

Vibration Modes ◽

Volume Data ◽

X Ray Diffraction ◽

X Ray

The equation of state and stability of topaz at high-pressure/high-temperature conditions have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy in this study. No phase transition occurs on topaz over the experimental pressure–temperature (P-T) range. The pressure–volume data were fitted by the third-order Birch–Murnaghan equation of state (EoS) with the zero-pressure unit–cell volume V0 = 343.86 (9) Å3, the zero-pressure bulk modulus K0 = 172 (3) GPa, and its pressure derivative K’0 = 1.3 (4), while the obtained K0 = 155 (2) GPa when fixed K’0 = 4. In the pressure range of 0–24.4 GPa, the vibration modes of in-plane bending OH-groups for topaz show non-linear changes with the increase in pressure, while the other vibration modes show linear changes. Moreover, the temperature–volume data were fitted by Fei’s thermal equation with the thermal expansion coefficient α300 = 1.9 (1) × 10−5 K−1 at 300 K. Finally, the P-T stability of topaz was studied by a synchrotron-based single-crystal XRD at simultaneously high P-T conditions up to ~10.9 GPa and 700 K, which shows that topaz may maintain a metastable state at depths above 370 km in the upper mantle along the coldest subducting slab geotherm. Thus, topaz may be a potential volatile-carrier in the cold subduction zone. It can carry hydrogen and fluorine elements into the deep upper mantle and further affect the geochemical behavior of the upper mantle.

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