Transformation of titanomagnetite to titanomaghemite; a slow, two-step, oxidation-ordering process in MORB

Other| December 01, 1997 Transformation of titanomagnetite to titanomaghemite; a slow, two-step, oxidation-ordering process in MORB Weixin Xu; Weixin Xu University of Michigan, Department of Geological Sciences, Ann Arbor, MI, United States Search for other works by this author on: GSW Google Scholar Donald R. Peacor; Donald R. Peacor Search for other works by this author on: GSW Google Scholar Wayne A. Dollase; Wayne A. Dollase Search for other works by this author on: GSW Google Scholar Rob Van der Voo; Rob Van der Voo Search for other works by this author on: GSW Google Scholar Richard T. Beaubouef Richard T. Beaubouef Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (11-12): 1101–1110. https://doi.org/10.2138/am-1997-11-1207 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Weixin Xu, Donald R. Peacor, Wayne A. Dollase, Rob Van der Voo, Richard T. Beaubouef; Transformation of titanomagnetite to titanomaghemite; a slow, two-step, oxidation-ordering process in MORB. American Mineralogist 1997;; 82 (11-12): 1101–1110. doi: https://doi.org/10.2138/am-1997-11-1207 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Magnetic iron oxides in a sequence of pillow basalts that were dredged from the Atlantic Ocean floor have been studied to characterize titanomaghemite and to define the processes of maghemitization. Distances from the spreading ridge and ages (in parentheses) of the samples are 0–10 (0–1), 160 (9), 450 (26), and 900 km (70 Ma).Iron titanium oxides occur as 1 to 10 μm-sized dendritic and cruciform-shaped crystals with identical appearances in all samples and with no signs of change or significant heterogeneity in composition or structure as observed by TEM and AEM. Parameters change progressively from the youngest to the oldest, e.g., Curie temperature = 180 to 360 °C; lattice parameter = 8.466 to 8.361 Å; number of octahedral cations per cell from Rietveld refinement = 14.8 to 12.1; mean hyperfine (internal) fields at 300 K from Mössbauer data = 37 to 45 T. The large Ti contents (Uv60 to Uv70) are nearly constant. SAED patterns show superstructure reflections only for the oldest sample.The youngest sample has parameters corresponding to nearly unoxidized titanomagne-tite, whereas the oldest is near-end-member titanomaghemite. Intermediate samples are partially altered but display no superstructure reflections, implying a lack of significant ordering of vacancies. The data therefore show that the process of (titano)maghemitization has two distinctly different components: (1) oxidation and loss of Fe, with creation of disordered vacancies, and (2) ordering of vacancies. The data collectively imply a process dominated by solid state diffusion of Fe from the crystals, oxidation of Fe, and creation of vacancies wherein the O closest-packed framework is preserved, in sharp contrast to a model of addition of O or to dissolution and neocrystallization. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.