Title: Thermal Equation of State of Natural Ti-Bearing Clinohumite

Abstract

The natural occurrence of clinohumite in metabasalts and hydrothermally altered peridotites provides a source of water-rich minerals in subducted slabs, making knowledge of their phase relations and crystal chemistry under high pressure-temperature (P-T) conditions important for understating volatile recycling and geodynamic process in the Earth's mantle. Here we present a synchrotron-based, single-crystal X-ray diffraction study on two natural Ti-bearing clinohumites up to ~28 GPa and 750 K in order to simulate conditions within subducted slabs. No phase transition occurs in clinohumite over this P-T range. Pressure-volume relationships of both compositions at room temperature were fitted to a third-order Birch-Murnaghan equation of state (EoS) with V₀ = 650.4(3) Å³, K_T0 = 141(4) GPa, and K_T0' = 4.0(6) for Ti-poor clinohumite (0.07 Ti per formula unit, pfu) and V₀ = 650.8(3) Å³, K_T0 = 144(4) GPa, and K_T0' = 3.6(7) for Ti-rich clinohumite (0.21 Ti pfu). Both clinohumites exhibit anisotropic compression with β_b > β_c > β_a. We also refined P-V-T equation of state parameters using the high-temperature Birch-Murnaghan EoS, yielding (∂K_T0/∂_T)_P = –0.040(10) GPa/K and α_T = 5.1(6) × 10^-5 K^-1 for Ti-poor clinohumite and (∂K_T0/∂_T)_P = –0.045(11) GPa/K and α_T = 5.7(6) × 10^-5 K^-1 for Ti-rich clinohumite. We report Ti-poor and Ti-rich clinohumites display similar equations of state but are ~20% more incompressible than Mg-pure clinohumite and display ~5% higher bulk sound velocity than olivine at upper mantle conditions. Our results provide constraints for modeling geodynamic processmore » related to the subduction and transport of potentially water-rich slabs in the mantle.« less

Authors:

Qin, Fei  ^[1];

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Wu, Xiang  ^[2];

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Zhang, Dongzhou  ^[3];

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Qin, Shan  ^[4];

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Jacobsen, Steven D.  ^[5]

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+ Show Author Affiliations

1. Peking Univ., Beijing (China); Northwestern Univ., Evanston, IL (United States)
2. China Univ. of Geosciences, Wuhan (China)
3. Univ. of Hawaii at Mānoa, Honolulu HI (United States)
4. Peking Univ., Beijing (China)
5. Northwestern Univ., Evanston, IL (United States)

Publication Date:

2017-11-03

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Org.:

National Natural Science Foundation of China (NNSFC); Chinese Scholarship Council (CSC); National Science Foundation (NSF); The David and Lucile Packard Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division

OSTI Identifier:

1423340

Grant/Contract Number:  

41473056; 41472037; EAR-1452344; EAR-1128799; FG02-94ER14466; AC02-06CH11357; EAR-1661511

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 122; Journal Issue: 11; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

ENGLISH

Subject:

58 GEOSCIENCES; Ti‐bearing clinohumite; thermal equation of state; single‐crystal X‐ray diffraction; high pressure and high temperature HFSE; subducted slabs