Factors in the preservation of coesite: The importance of fluid inflitration
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Jed L. Mosenfelder
,
Hans-Peter Schertl
Abstract
The survival of coesite in ultrahigh-pressure (UHP) rocks is most commonly attributed to rapid exhumation, continuous cooling during uplift, and inclusion in strong phases that can sustain a high internal over-pressure during decompression. Exceptions to all of these criteria exist. Perhaps less attention has been paid to the role of fluid infiltration in the preservation of coesite. We used infrared spectroscopy to measure water contents of coesite and coesite pseudomorphs in a variety of UHP rocks. In all cases, OH concentrations in coesite are below the detection limit of ~100 ppm H2O. The silica phases surrounding coesite, however, show varying amounts of H2O. This is most spectacularly observed in pyrope quartzites from the Dora-Maira massif that contain at least three phases of silica replacing coesite, also distinguished by varying color of cathodoluminescence (CL): palisade-textured quartz (<100 ppm H2O, red-violet CL); .mosaic. quartz, which is actually chalcedony (up to 0.4 wt% H2O, yellow/brown CL); and a rare, highly hydrated silica phase interpreted to be opal (~7 wt% H2O, dark blue CL). Very similar signatures are observed in a grospydite xenolith from the Roberts Victor kimberlite. The quartz replacing coesite in other UHP samples studied contains on the order of 500 ppm H2O or less, and most measurements are under the detection limit of our technique. We infer that palisade quartz forms under dry or nearly dry conditions and at high temperatures during dilation of the host phase. The formation of hydrous silica phases such as chalcedony and opal, however, must take place at much lower temperatures, after cracking of the host phase, which allows external fluids to infiltrate. Delay of fluid infiltration to low temperatures, where kinetics are slow even in the presence of water, is the most critical factor in the preservation of coesite.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Factors in the preservation of coesite: The importance of fluid inflitration
- U-Pb SHRIMP ages recorded in the coesite-bearing zircon domains of paragneisses in the southwestern Sulu terrane, eastern China: New interpretation
- Petrogenesis of the Yangkou layered garnet-peridotite complex, Sulu UHP terrane, China
- Sodic amphibole exsolutions in garnet from garnet-peridotite, North Qaidam UHPM belt, NW China: Implications for ultradeep-origin and hydroxyl defects in mantle garnets
- Blueschists, eclogites, and decompression assemblages of the Zermatt-Saas ophiolite: High-pressure metamorphism of subducted Tethys lithosphere
- Coexisting retrograde jadeite and omphacite in a jadeite-bearing lawsonite eclogite from the Motagua Fault Zone, Guatemala
- Calibrations of modal space for metamorphism of mafic schist
- Oxygen isotope geochemistry of rocks from the Pre-Pilot Hole of the Chinese Continental Scientific Drilling Project (CCSD-PPH1)
- Subducted carbonates, metasomatism of mantle wedges, and possible connections to diamond formation: An example from California
- Hawaiian mantle xenoliths and magmas: Composition and thermal character of the lithosphere
- Trace-element distribution coefficients for pyroxenes, plagioclase, and olivine in evolved tholeiites from the 1955 eruption of Kilauea Volcano, Hawaiʼi, and petrogenesis of differentiated rift-zone lavas
- Cation ordering in synthetic low-calcium actinolite
- Acquisition and evaluation of thermodynamic data for bieberite-moorhouseite equilibria at 0.1 MPa
- PRESIDENTIAL ADDRESS TO THE MINERALOGICAL SOCIETY OF AMERICA SEATTLE, NOVEMBER 4, 2003: A mineralogical and geochemical record of atmospheric photochemistry
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- Estimates of Ar diffusion and solubility in leucite and nepheline: Electron microprobe imaging of Ar distribution in a mineral
- Growth and dissolution kinetics at the dolomite-water interface: An in-situ scanning probe microscopy study
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- The origin of the green color of variscite
- HRTEM evidence for 8-reversals in the m = 17 antigorite polysome
- Origin of high-Ag fahlores from the Galena Mine, Wallace, Idaho, U.S.A.
- Stability of the MgCO3 structures under lower mantle conditions
- The 10 Å phase: Crystal structure from single-crystal X-ray data
- Letter: Unquenchable hexagonal perovskite in high-pressure polymorphs of strontium silicates
