An investigation of ulvospinel composition and cation migration during maghemitization in Deep Sea Drilling Project Leg 61 titanomagnetites

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doi: 10.1029/JB087iB07p05361
Author(s): Steiner, Maureen B.
Author Affiliation(s): Primary:
Univ. Wyo., Dep. Geol. and Geophys., Laramie, WY, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 87(B7), p.5361-5374. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 38 refs.; illus. incl. 1 anal., 3 tables
Summary: Titanomagnetites of basalts and diorites from an off-axis volcanic episode in the western Pacific Ocean (leg 61, Deep Sea Drilling ProjectU) were studied for their ulvospinel composition and for changes in the iron-titanium ratio with progressive low temperature oxidation. Thermomagnetic analysis and microscopy indicate that these Fe/Ti spinels are relatively little low temperature oxidized despite their Cretaceous age. Microprobe investigation shows that the Fe/Ti spinels have a wide range of ulvospinel contents and that the range directly reflects the range of parent rock chemistries. This is an important demonstration that ulvospinel contents are not constant but vary within a restricted range of compositions, namely, at least x = 0.50 to x = 0.75 (Fe3-x TixO4). Recognition of this fact is important in attempting to elucidate changes in cation ratio as a result of progressive low temperature oxidation. Examination of samples of different oxidation states for cation ratio changes associated with low temperature oxidation displayed lower titanium in the more oxidized samples and Ti enrichment in the less oxidized ones. This, however, appears to be a reflection of changing x values with progressive crystallization of individual sills, rather than a consequence of low-temperature oxidation. In the more than 100 grains analyzed, no evidence was found for a more oxidized shell on the exteriors of grains, suggesting that the oxidation process did not proceed uniformly with respect to grain geometry.
Year of Publication: 1982
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 17 Geophysics, General; Basalts; Cations; Chemical composition; Crystal chemistry; Curie point; DSDP Site 462; Deep Sea Drilling Project; Diorites; Experimental studies; Geochemistry; IPOD; Igneous rocks; Iron; Leg 61; Leg 89; Low temperature; Maghemitization; Magnetic properties; Magnetization; Metals; Minerals; Oxidation; Oxides; Pacific Ocean; Paleomagnetism; Plutonic rocks; Processes; Properties; Remanent magnetization; Tectonophysics; Temperature; Thermoremanent magnetization; Titanium; Titanomagnetite; Ulvospinel; Volcanic rocks
Coordinates: N070000 N070000 E1650000 E1650000
Record ID: 1982061369
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