caa a22 4500 463217322 CHVBK 20180405153201.0 cr unu---uuuuu 170326e20070401xx s 000 0 eng 10.1007/s00269-006-0138-2 doi (NATIONALLICENCE)springer-10.1007/s00269-006-0138-2 High temperature structural and thermoelastic behaviour of mantle orthopyroxene: an in situ neutron powder diffraction study [Elektronische Daten] [G. Gatta, Romano Rinaldi, K. Knight, G. Molin, G. Artioli] The temperature induced structural evolution and thermoelastic behaviour of a natural (Pbca) orthopyroxene (Opx), with chemical formula M2(Mg0.856Ca0.025Fe2+ 0.119) M1(Mg0.957Fe2+ 0.011Fe3+ 0.016Cr0.011Al0.005)Al0.032Si1.968O6, from a suite of high pressure ultramafic nodules of mantle origin, have been investigated by in-situ neutron powder diffraction at several temperatures starting from 1,200°C down to 150°C. Unit-cell parameter variations as a function of T show no phase transition within this temperature range. The volume thermal expansion coefficient, α=V −1(∂V/∂T) P0, varies linearly with T. The axial thermal expansion coefficients, αj =l j −1 (∂l j/∂T)P0, increase non-linearly with T. The principal Lagrangian unit-strain coefficients (ɛ//a, ɛ//b, ɛ//c), increase continuously with T. However, the orientation of the unit-strain ellipsoid appears to change with T. With decreasing T, the values of the unit-strain coefficients along the b and c axes tend to converge. The orientation at ΔT=1,080°C is maintained down to the lowest temperature (150°C). The two non-equivalent tetrahedral chains, TA n OA3n and TB n OB3n , are kinked differently. At room-T, the TB n OB3n chain is more strongly kinked by about 23° than the TA n OA3n chain. With increasing T, the difference decreases by 3° for the TB n OB3n chain. The intersite cation exchange reaction between M1 and M2 (Mg2+ and Fe2+) shows a slight residual order at 1,200°C followed by reordering with decreasing temperature although seemingly not with a definite progressive trend. At the lowest temperature reached (150°C), reordering has occurred with the same value of partitioning coefficient K D as that before heating. The absence of the expected phase transition is most likely due to the presence of minor amounts of Fe3+, Al, Ca and Cr which must play a crucial role on the thermoelastic behaviour and phase stability fields in natural Opx, with consequent important petrologic and geological implications. Springer-Verlag, 2007 Orthopyroxene nationallicence High temperature nationallicence Neutron powder diffraction nationallicence Structural refinement nationallicence Thermoelastic behaviour nationallicence Cation-ordering nationallicence Gatta G. Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli, 23, 20133, Milano, Italy aut Rinaldi Romano Dipartimento di Scienze della Terra, Universita' degli Studi di Perugia, 06100, Perugia, Italy aut Knight K. ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK aut Molin G. Dipartimento di Mineralogia e Petrologia, Università degli Studi di Padova, Padova, Italy aut Artioli G. Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli, 23, 20133, Milano, Italy aut Physics and Chemistry of Minerals Springer-Verlag 34/3(2007-04-01), 185-200 0342-1791 34:3<185 2007 34 269 https://doi.org/10.1007/s00269-006-0138-2 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00269-006-0138-2 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Gatta G. Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli, 23, 20133, Milano, Italy aut NATIONALLICENCE 700 1- Rinaldi Romano Dipartimento di Scienze della Terra, Universita' degli Studi di Perugia, 06100, Perugia, Italy aut NATIONALLICENCE 700 1- Knight K. ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK aut NATIONALLICENCE 700 1- Molin G. Dipartimento di Mineralogia e Petrologia, Università degli Studi di Padova, Padova, Italy aut NATIONALLICENCE 700 1- Artioli G. Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli, 23, 20133, Milano, Italy aut NATIONALLICENCE 773 0- Physics and Chemistry of Minerals Springer-Verlag 34/3(2007-04-01), 185-200 0342-1791 34:3<185 2007 34 269 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer