Basalt transformations

Eastern Manus Basin Desmos cauldron (3 42 S, 151°52 E) 2000 Caldera of basalt/basaltic andesite at an intersection of a spreading center and a transform fault Sulfide ores were not recovered. Megaplume-like methane anomalies in water column over the caldera. Ferruginous oxide deposits. Pyrite and native sulfur disseminated in basaltic andesite. 

Neutron activation analysis (NAA) is a technique for the qualitative and/or quantitative determination of atoms possessing certain types of nuclei. Bombarding a sample with neutrons transforms some stable isotopes into radioactive isotopes measuring the energy and/or intensity of the gamma rays emitted from the radioactive isotopes created as a result of the irradiation reveals information on the nature of the elements in the sample. NAA Is widely used to characterize such archaeological materials as pottery, obsidian, chert, basalt, and limestone (Keisch 2003). 

Figure 8. Plot of Li isotopic composition vs. Na O content of eclogites from Trescolmen, Swiss Alps (Zack et al. 2003). Data from pairs of bulk rock ( ) and omphacite mineral separate (O) samples, indicating that bulk rocks generally preserve isotopic systematics of these rocks. Well-preserved, high pressure metamorphosed basaltic rocks were interpreted to retain much of their elemental character, and as such were good recorders of the residue remaining after subduction dehydration. The data indicated that originally isotopically heavy altered sea floor basalt could be transformed during subduction into some of the isotopically lightest materials in the Earth system.

The laboratory derived model of hematite formation in soils via ferrihydrite has received general acceptance. So far, it is the only way to produce hematite at ambient temperatures and in the pH range of soils. Support from soil analysis, however, is meagre. Hematite is usually associated with other Fe oxides, mainly with goethite but not with ferrihydrite. There seems to be only one report of a ferrihydrite-hema-tite association (based on XRD and Mossbauer spectra) viz. in several andisols formed from basalt in the warm and moist climate of Hawaii (Parfitt et al., 1988). In this case, in addition to the low age of the soils, high release of Si may retard the transformation of ferrihydrite to hematite, whereas normally, the rate of transformation of ferrihydrite seems to be higher than that of ferrihydrite formation, so that this mineral does not persist. 

The third and the most common type is complex phase transformations, including the following (i) some components in a phase combine to form a new phase (e.g., H2O exsolution from a magma to drive a volcanic eruption the precipitation of calcite from an aqueous solution, Ca + + COf calcite the condensation of corundum from solar nebular gas and the crystallization of olivine from a basaltic magma), (ii) one phase decomposes into several phases (e.g., spinodal decomposition, or albite jadeite + quartz), (iii) several phases combine into one phase (e.g., melting at the eutectic point, or jadeite +... 

Niu Y. and Hekinian R. (1997a) Basaltic liquids and harzburgitic residues in the Garrett Transform a case study at fast-spreading ridges. Earth Planet. Sci. Lett. 146,... 

Jamtveit et al. (2001) measured water contents in olivines from basalts and picrites from the North Atlantic Volcanic Province using Fourier-transform infrared spectroscopy (FTIR). They found H2O contents from <0.5 ppm to —18 ppm, and suggested that oh vines with... 

Ringwood A. E. (1982) Phase transformations and differentiation in subducted hthosphere imphcations for mantle dynamics, basalt petrogenesis and crustal evolution. J. Geol. 90, 611-643. 

Table 1 Five basaltic glasses from the East Pacific Rise near the Clipperton Transform that, to first order, form a coherent liquid line of descent for fractional crystallization from the highest MgO magma ( 1) to lowest ( 5).

Figure 23 Axial depth and various chemical parameters for zero-age basalts versus latitude for the northern EPR 5.5-14.5° N. Thick vertical lines delineate proposed spreading cell margins at the major OSCs and the two transform faults. Thinner vertical lines occur at small-offset OSCs and deviations from axial linearity (devals) along the EPR. Strontium in ppm, MgO in wt.%. Many of the deval-bounded segments form chemically distinct ridge segments (Langmuir et al., 1986) (reproduced by permission of Nature Publishing Group from Nature, 1986, 322, 422-429).

Lundstrom C. C., Sampson D. E., Perfit M. R., GiU J., and Williams Q. (1999) Insights into mid-ocean ridge basalt petrogenesis U-series disequilibria from the Siqueiros Transform, Lament Seamounts, and East Pacific Rise. J. Geophys. Res. 104, 13035-13048. 

Poli S. (1993) The amphibolite-eclogite transformation an experimental study on basalt. Am. J. Sci. 293, 1061-1107. 

Almost 50 zeolite types occur naturally, of which several have attained industrial importance. Natural zeolites result indirectly from volcanic activity. They are formed by hydrothermal transformation of basalts, volcanic ash and pumices and are found e.g. in basalt cavities and in large sedimentary deposits. The industrially most important natural zeolites are ... 

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