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Title: The mobility of Nb in rutile-saturated NaCl- and NaF-bearing aqueous fluids from 1–6.5 GPa and 300–800 °C

Rutile (TiO 2) is an important host phase for high field strength elements (HFSE) such as Nb in metamorphic and subduction zone environments. The observed depletion of Nb in arc rocks is often explained by the hypothesis that rutile sequesters HFSE in the subducted slab and overlying sediment, and is chemically inert with respect to aqueous fluids evolved during prograde metamorphism in the forearc to subarc environment. However, field observations of exhumed terranes, and experimental studies, indicate that HFSE may be soluble in complex aqueous fluids at high pressure (i.e., >0.5 GPa) and moderate to high temperature (i.e., >300 °C). In this study, we investigated experimentally the mobility of Nb in NaCl- and NaF-bearing aqueous fluids in equilibrium with Nb-bearing rutile at pressure-temperature conditions applicable to fluid evolution in arc environments. Niobium concentrations in aqueous fluid at rutile saturation were measured directly by using a hydrothermal diamond-anvil cell (HDAC) and synchrotron X-ray fluorescence (SXRF) at 2.1 to 6.5 GPa and 300-500 °C, and indirectly by performing mass loss experiments in a piston-cylinder (PC) apparatus at similar to 1 GPa and 700-800 °C. The concentration of Nb in a 10 wt% NaCl aqueous fluid increases from 6 to 11 mu g/gmore » as temperature increases from 300 to 500 °C, over a pressure range from 2.1 to 2.8 GPa, consistent with a positive temperature dependence. The concentration of Nb in a 20 wt% NaCl aqueous fluid varies from 55 to 150 mu g/g at 300 to 500 °C, over a pressure range from 1.8 to 6.4 GPa; however, there is no discernible temperature or pressure dependence. Here, the Nb concentration in a 4 wt% NaF-bearing aqueous fluid increases from 180 to 910 mu g/g as temperature increases from 300 to 500 °C over the pressure range 2.1 to 6.5 GPa. The data for the F-bearing fluid indicate that the Nb content of the fluid exhibits a dependence on temperature between 300 and 500 °C at ≥ 2 GPa, but there is no observed dependence on pressure. Together, the data demonstrate that the hydrothermal mobility of Nb is strongly controlled by the composition of the fluid, consistent with published data for Ti. At all experimental conditions, however, the concentration of Nb in the fluid is always lower than coexisting rutile, consistent with a role for rutile in moderating the Nb budget of arc rocks.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [3] ;  [3] ;  [5] ;  [6] ;  [5] ;  [5]
  1. Univ. of Michigan, Ann Arbor, MI (United States); Univ. of Nevada, Las Vegas, NV (United States)
  2. Univ. of Michigan, Ann Arbor, MI (United States)
  3. Univ. of Nevada, Las Vegas, NV (United States)
  4. Carnegie Institute of Washington, Argonne, IL (United States)
  5. Memorial Univ. of Newfoundland (Canada)
  6. Institute of Geological Sciences, Bern (Switzerland)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 100; Journal Issue: 7; Journal ID: ISSN 0003-004X
Mineralogical Society of America
Research Org:
Univ. of Nevada, Las Vegas, NV (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Contributing Orgs:
Univ Michigan, Earth & Environm Sci, Ann Arbor, MI 48109 USA [Show the Organization-Enhanced name(s)] [ 2 ] Univ Nevada, High Pressure Sci & Engn Ctr, Las Vegas, NV 89154 USA [Show the Organization-Enhanced name(s)] [ 3 ] Univ Nevada, Dept Geosci, Las Vegas, NV 89154 USA [Show the Organization-Enhanced name(s)] [ 4 ] Argonne Natl Lab, Adv Photon Source, HPCAT, Argonne, IL 60439 USA [Show the Organization-Enhanced name(s)] [ 5 ] Mem Univ Newfoundland, Earth Sci, St John, NF A1C 5S7, Canada [Show the Organization-Enhanced name(s)] [ 6 ] Univ Bern, Inst Geol Sci, CH-3012 Bern, Switzerland
Country of Publication:
United States
58 GEOSCIENCES; 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; high field strength elements; niobium; synchrotron; hydrothermal diamond anvil cell; subduction; rutile; aqueous fluid
OSTI Identifier: