Quantitative texture analysis of glaucophanite deformed under eclogite facies conditions (Sesia-Lanzo Zone, Western Alps): comparison between X-ray and neutron diffraction analysis

Abstract

X-ray and neutron diffraction techniques have been applied to quantitative texture analysis of a glaucophanite from the Sesia-Lanzo Zone (Western Italian Alps), naturally deformed under eclogite fades conditions. The comparison has been carried out in order to reveal the limits and proNems of texture analysis related to strongly deformed polymineralic. Different methods of measuring and computing the orientation distribution function from diffraction data have been tested, in particular X-rays, direct peak integration, and neutron diffraction using Rietveld-texture analysis. Due to grain-size problems and heterogeneity of individual amphibole minerals, neutron radiation is shown to be the best probe for characterizing the whole rock: being more penetrative than conventional X-rays, a larger volume of the mineral aggregate is sampled, giving better statistics. However, results obtained by summing the corresponding individual spectra of at least three X-ray diffraction experiments on parallel slabs of the same specimen also give statistically valid, semiquantitative results that reproduce the overall textures. The quantitative texture analysis shows the strong texture of the two generations of amphiboles (AmpI and AmpII), which are mainly characterized by [001]*-directions at an angle of about l0 ° to the mineral lineation and by (hkO) planes describing girdles around the lineation. The texture is comparable to those described in the literature for amphibole deformed under different temperature and pressure conditions, and the pronounced asymmetry of the [001]* directions with respect to the mineral lineation is consistent with a non-coaxial component that occurs during the deformation.

Contrasting microstructures and deformation mechanisms in metagabbro mylonites contemporaneously deformed under different temperatures ( c. 650 °C and c. 750 °C)

“…Inclination of data with respect to the mylonitic foliation due to dextral shear is present. Similar fabric asymmetry, interpreted as the result of a non-coaxial strain, has been described in eclogite facies glaucophanites (Zucali et al 2002).…”

Petrofabrics of high-pressure rocks exhumed at the slab-mantle interface from the “point of no return” in a subduction zone (Sivrihisar, Turkey)

“…EBSD analysis of glaucophane in lawsonite blueschist [ Teyssier et al ., ] confirmed the strong crystallographic preferred orientation inferred from petrographic observation, consistent with previous work on glaucophane fabrics in blueschist [e.g., Reynard et al ., ; Zucali et al ., ; Kim et al ., ]. At the margins of some pods, centimeter‐scale lawsonite‐garnet‐phengite veins are rimmed by thin glaucophane‐rich margins in which glaucophane grain boundaries truncate compositional zoning in the crystals.…”

Submarine lava flow direction revealed by neutron diffraction analysis in mineral lattice orientation

“…Lattice Preferred Orientation (LPO) data were collected using neutron diffraction. A quantitative texture/lattice analysis using neutron diffraction allows for the investigation of volumes of rock on the order of 1 cm 3 in a relatively short period of time (a few hours) thanks to the penetration of neutrons in matter and the high flux available at the nuclear reactor at the Institut Laue‐Langevin (ILL) [ Tartarotti et al ., ; Zucali et al ., ]; given the sample size, the effects of grain size on the results of this method are much less relevant than they would be on results obtained using X‐rays. The discrimination of rock‐forming mineralogical phases was performed by using Rietveld methods [ Young and Wiles , ].…”