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Compositional zoning in dolomite from lawsonite-bearing eclogite (SW Tianshan, China): Evidence for prograde metamorphism during subduction of oceanic crust

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Published/Copyright: January 15, 2014
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American Mineralogist
From the journal American Mineralogist Volume 99 Issue 1

Abstract

Dolomite with compositional zoning was discovered in carbonate-lawsonite-bearing eclogites in the Tianshan (ultra-)high-pressure/low-temperature metamorphic belt, northwestern China. The eclogitefacies dolomite occurs as matrix porphyroblast and as inclusion in garnet, both of which display the same chemical zoning pattern. The dolomite contains inclusions of calcite (probably after aragonite), magnesite, glaucophane, lawsonite (and its pseudomorphs), allanite, epidote, paragonite, phengite, and omphacite. The chemical zoning in dolomite is well defined by a continuous core-to-rim Mg increase and Fe-Mn decrease. The concentrations of transition metal elements, REE, and Y also decrease from core to rim of the dolomite. Thermodynamic modeling demonstrates that the Fe-Mg zoning of dolomite is largely temperature dependent and, thus, is interpreted as prograde growth zoning, which developed during subduction of carbonate-bearing oceanic crust. It is suggested that dolomite in equilibrium with garnet formed as a result of changing matrix compositions due to increasing temperatures. In addition, thermodynamic modeling demonstrates that during subduction at high-pressure conditions prograde-formed aragonite and dolomite were transformed to dolomite and magnesite. Furthermore, Fe-rich magnesite inclusions in matrix dolomite and in dolomite inclusions in garnet are shown to have formed during high-pressure conditions prior to peak metamorphic conditions and, therefore caution is warranted using Fe-bearing magnesite occurrences in eclogite-facies rocks as an unambiguous ultrahigh pressure indicator as previously suggested.

Keywords : Prograde zoning; dolomite; magnesite; eclogite; high pressure; Tianshan
Published Online: 2014-01-15
Published in Print: 2014-01-01

© 2014 by Walter de Gruyter GmbH & Co.

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https://doi.org/10.2138/am.2014.4507
Keywords for this article
Prograde zoning; dolomite; magnesite; eclogite; high pressure; Tianshan

Articles in the same Issue

  1. Shedding light on bone material
  2. Weddellite from renal stones: Structure refinement and dependence of crystal chemical features on H2O content
  3. Erionite and offretite from the Killdeer Mountains, Dunn County, North Dakota, U.S.A.
  4. Molecular water in nominally unhydrated carbonated hydroxylapatite: The key to a better understanding of bone mineral
  5. Precipitation and dissolution of chromite by hydrothermal solutions in the Oman ophiolite: New behavior of Cr and chromite
  6. Phase transitions and equation of state of forsterite to 90 GPa from single-crystal X-ray diffraction and molecular modeling
  7. Weathering of cobalt arsenides: Natural assemblages and calculated stability relations among secondary Ca-Mg-Co arsenates and carbonates
  8. Alburnite, Ag8GeTe2S4, a new mineral species from the Roşia Montana Au-Ag epithermal deposit, Apuseni Mountains, Romania
  9. Cathodoluminescence of alkali feldspars and radiation effects on the luminescent properties
  10. Thermochemistry of the alkali feldspars: Calorimetric study of the entropy relations in the low albite–low microcline series
  11. Thermal equation of state and spin transition of magnesiosiderite at high pressure and temperature
  12. Thermal diffusivities of MgSiO3 and Al-bearing MgSiO3 perovskites
  13. The sound velocity measurements of Fe3S
  14. PDF analysis of ferrihydrite: Critical assessment of the under-constrained akdalaite model
  15. Aluminum ion occupancy in the structure of synthetic saponites: Effect on crystallinity
  16. DFT investigation of structural and vibrational properties of type B and mixed A-B carbonated hydroxylapatite
  17. Chlorite topography and dissolution of the interlayer studied with atomic force microscopy
  18. The effect of XPS background removing method on the appraisal of Ti and Fe: The case of phlogopites and brookite
  19. Measurement of water contents in olivine using Raman spectroscopy
  20. Perbøeite-(Ce) and alnaperbøeite-(Ce), two new members of the epidote-törnebohmite polysomatic series: Chemistry, structure, dehydrogenation, and clue for a sodian epidote end-member
  21. Crystal structure and compressibility of lead dioxide up to 140 GPa
  22. A comparative analysis of the mechanical behavior of carbon dioxide and methane hydrate-bearing sediments
  23. Crystal structures and stabilities of cristobalite-helium phases at high pressures
  24. X-ray absorption characterization of Cr in forsterite within the MacAlpine Hills 88136 EL3 chondritic meteorite
  25. Monipite, MoNiP, a new phosphide mineral in a Ca-Al-rich inclusion from the Allende meteorite
  26. Compositional zoning in dolomite from lawsonite-bearing eclogite (SW Tianshan, China): Evidence for prograde metamorphism during subduction of oceanic crust
  27. Vanadio-oxy-dravite, NaV3(Al4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
  28. XAS evidence for Ni sequestration by siderite in a lateritic Ni-deposit from New Caledonia
  29. Vladykinite, Na3Sr4(Fe2+Fe3+)Si8O24: A new complex sheet silicate from peralkaline rocks of the Murun complex, eastern Siberia, Russia
  30. New Mineral Names
  31. Memorial of James Burleigh Thompson, Jr., 1921–2011
  32. Book review: MANTLE CONVECTION FOR GEOLOGISTS by Geoffrey F. Davies
  33. Errata
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