The effect of oxo-component on the high-pressure behavior of amphiboles
| Autor: | C. Capalbo, Paola Comodi, T. Boffa Ballaran, Pier Francesco Zanazzi, A. Zanetti, Sabrina Nazzareni |
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| Rok vydání: | 2010 |
| Předmět: | |
| Zdroj: | The American mineralogist 95 (2010): 1042–1051. doi:10.2138/am.2010.3429 info:cnr-pdr/source/autori:Comodi P.; Boffa Ballaran T.; Zanazzi P.; Capalbo C.; Zanetti A.; Nazzareni S./titolo:The effect of oxo-component on the high-pressure behavior of amphiboles./doi:10.2138%2Fam.2010.3429/rivista:The American mineralogist/anno:2010/pagina_da:1042/pagina_a:1051/intervallo_pagine:1042–1051/volume:95 |
| ISSN: | 0003-004X |
| DOI: | 10.2138/am.2010.3429 |
| Popis: | The role of the oxo-component on the compressibility of amphibole was studied by means of high-pressure in situ single-crystal X-ray diffraction on two natural kaersutite megacrysts (samples DL5 and FR12) from alkaline basalts. The oxo-component varies significantly (1.1 and 1.9 apfu in DL5 and FR12, respectively), whereas the cation composition is very similar, apart from the Fe3+/(Fe2++Fe3+), which is 0.33 in DL5 and ~1 in FR12. The larger oxo-component of FR12 is attributed to the Fe2+ + OH− = Fe3+ + O2− + ½H2 substitution. Unit-cell parameters were collected at different pressures up to about 8 GPa. Structural refinements of both samples were performed with data collected at different P up to 6 GPa. Fitting the P-V data to a third-order Birch Murnaghan EoS yielded the following parameters: K = 94(1) GPa, K ′ = 6.3(4), and V = 903.6(2) A3 for FR12 and K = 91(2) GPa, K ′ = 6.2(4), and V = 914.1(2) A3 for DL5. The axial moduli of the two amphibole samples were: K 0 a = 86(3) GPa, K ′ a = 7(1), and a = 9.815(2) A; K 0 b = 115(3) GPa, K ′ b = 4.8(8), and b = 18.012(2) A; K 0 c = 112(5) GPa, K″ c = 7(1), and c = 5.300(1) A for sample FR12 and K 0 a = 85(3) GPa, K ′ a = 5(1), and a = 9.8660(9) A; K 0 b = 113(2), K ′ b = 4.4(6), and b = 18.0548(6) A; K 0 c = 107(3) GPa, K ′ c = 7(1), and c = 5.3185(5) A for sample DL5. This suggests that the compressibility of kaersutite decreases with increasing oxo-component. Structural refinements show that the polyhedral compressibility follows the order A = M4 > M2 > M3 > M1 for DL5 and A = M4 > M2 > M1 > M3 for FR12. The most evident geometrical effect induced by P is the decrease in the bending of the double tetrahedral chain, when adjacent I-beams are pushed against each other. This effect is largest for DL5, which has a larger concavity of the A site, (O7-O7′ changes from 3.03 to 2.82 A) compared to the one of FR12, (O7-O7′ changes from 2.92 to 2.79 A). This mechanism is confirmed by the evolution of T1-O7-T1 angle (from 135.4° to 132.5° in FR12 and from 136.6° to 132.2° in DL5). |
| Databáze: | OpenAIRE |
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