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Papers by Marzena Anna Baron

Research paper thumbnail of Core formation, mantle differentiation and core-mantle interaction within Earth and the terrestrial planets

Research paper thumbnail of The stability of hydrous silicates in Earth's lower mantle: Experimental constraints from the systems MgO–SiO2–H2O and MgO–Al2O3–SiO2–H2O

Research paper thumbnail of OH-point defects in quartz in B- and Li-bearing systems and their application to pegmatites

Physics and Chemistry of Minerals, 2014

terms of pressure and trace metal saturation of the crystallizing petrological system. Ir spectra... more terms of pressure and trace metal saturation of the crystallizing petrological system. Ir spectra obtained from natural quartz grains from a tourmaline-bearing pegmatite exhibit Band al-related OH-bands. The B-related OH-band is also exhibited in quartz from a tourmaline + spodumenebearing pegmatite. li-and al-related OH-bands, however, are subordinate or not observed at all in the spodumenebearing system, which suggests that OH-vibrations do not reflect absolute li-contents in quartz due to efficient coupled substitution involving al. Data from experimental runs and natural specimens indicate that the B-related OH-band can be used as a rough proxy for B-contents in quartz, confirming the previously postulated charge balance equation [H + ] = [B 3+ ] + [al 3+ ] − [li + ] − [K + ] − [P 5+ ].

Research paper thumbnail of The phase diagram of NiSi under the conditions of small planetary interiors

Physics of the Earth and Planetary Interiors, 2016

Research paper thumbnail of Experimental constraints on melting temperatures in the MgO–SiO 2 system at lower mantle pressures

Earth and Planetary Science Letters

Eutectic melting curves in the system MgO-SiO2 have been experimentally determined at 27 lower ma... more Eutectic melting curves in the system MgO-SiO2 have been experimentally determined at 27 lower mantle pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We 28 investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary, 29 and melting of bridgmanite plus stishovite in the MgSiO3-SiO2 binary, as analogues for 30 natural peridotite and basalt, respectively. The melting curve of model basalt occurs at 31 lower temperatures, has a shallower dT/dP slope and slightly less curvature than the 32 model peridotitic melting curve. Overall, melting temperatures detected in this study are 33 in good agreement with previous experiments and ab initio simulations at ~25 GPa 34 (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the 35 measured eutectic melting curves are systematically lower in temperature than curves 36 extrapolated on the basis of thermodynamic modelling of low-pressure experimental 37 data, and those calculated from atomistic simulations. We find that our data are 38 inconsistent with previously computed melting temperatures and melt thermodynamic 39 properties of the SiO2 endmember, and indicate a maximum in short-range ordering in 40 MgO-SiO2 melts close to Mg2SiO4 composition. The curvature of the model peridotite 41 eutectic relative to an MgSiO3 melt adiabat indicates that crystallization in a global 42 magma ocean would begin at ~100 GPa rather than at the bottom of the mantle, 43 allowing for an early basal melt layer. The model peridotite melting curve lies ~500 K 44 above the mantle geotherm at the core-mantle boundary, indicating that it will not be 45 molten unless the addition of other components reduces the solidus sufficiently. The 46 model basalt melting curve intersects the geotherm at the base of the mantle, and partial 47 melting of subducted oceanic crust is expected. 48 49 Recent experiments on natural peridotitic and basaltic compositions (Fiquet et

Research paper thumbnail of The stability of hydrous silicates in Earth's lower mantle: Experimental constraints from the systems MgO–SiO 2 –H 2 O and MgO–Al 2 O 3 –SiO 2 –H 2 O

We performed laser-heated diamond anvil cell experiments on bulk compositions in the systems MgO–... more We performed laser-heated diamond anvil cell experiments on bulk compositions in the systems MgO–SiO 2 –H 2 O (MSH) and MgO–Al 2 O 3 –SiO 2 –H 2 O (MASH) that constrain the stability of hydrous phases in Earth's lower mantle. Phase identification by synchrotron powder diffraction reveals a consistent set of stability relations for the high-pressure, dense hydrous silicate phases D and H. In the MSH system phase D is stable to ~50 GPa, independent of temperature from ~1300 to 1700 K. Phase H becomes stable between 35 and 40 GPa, and the phase H out reaction occurs at ~55 GPa at 1600 K with a negative dT/dP slope of ~−75 K/GPa. Between ~30 and 50 GPa dehydration melting occurs at ~1800 K with a flat dT/dP slope. A cusp along the solidus at ~50 GPa corresponds with the intersection of the subsolidus phase H out reaction, and the dT/dP melting slope steepens to ~15 K/GPa up to ~85 GPa. In the MASH system phase H is stable in experiments between ~45 and 115 GPa in all bulk compositions studied, and we expect aluminous phase H to be stable throughout the lower mantle depth range beneath ~1200 km in both peridotitic and basaltic lithologies. In the subsolidus, aluminous phase D is stable to ~55 GPa, whereas at higher pressures aluminous phase H is the stable hydrous phase. The presence of hydrogen may sharpen the bridgmanite to post-perovskite transition. The ambient unit cell volume of bridgmanite increases systematically with pressure above ~55 GPa, possibly representing an increase in alumina content, and potentially hydrogen content, with depth. Bridgmanite in equilibrium with phases D and H has a relatively low alumina content, and alumina partitions preferentially into the hydrous phases. The melting curves of MASH compositions are shallower than in the MSH system, with dT/dP of ~6 K/GPa. Phase D and H solid solutions are stable in cold, hy-drated subducting slabs and can deliver water to the deepest lower mantle. However, hydrated lithologies in the lower mantle are likely to be partially molten at all depths along an ambient mantle geotherm.

Research paper thumbnail of OH-point defects in quartz in B- and Li-bearing systems and their application to pegmatites

OH incorporation in quartz in Al-, B- and Li-bearing systems (granitic systems containing tourmal... more OH incorporation in quartz in Al-, B- and Li-bearing systems (granitic systems containing tourmaline or spodumene) was studied experimentally in order to investigate the effect of pressure, temperature and chemical impurities on the generation of OH-defects. High-pressure experiments were carried out at pressures between 5 and 25 kbar and temperatures between 800 and 900 °C, and OH-contents in quartz were calculated from IR absorption spectra measured on oriented quartz crystals. IR absorption features were assigned to impurity substitutions, such as AlOH (3,420, 3,379 and 3,315 cm−1) and BOH (3,595 cm−1), LiOH (3,483 cm−1), and hydrogarnet substitution (4H)Si defects (3,583 cm−1). Results indicate a negative correlation of incorporated Al-specific OH-defect content versus pressure (630 ± 130 wt ppm H2O at 5 kbar to 102 ± 6 wt ppm H2O at 25 kbar), but no clear correlation of B-specific OH-defects with pressure. In runs initially containing spodumene, virtually OH-free quartzes were observed at pressures ≥10 kbar, where impurity cations compensate each other forming an anhydrous eucryptite-defect component. In contrast, at 5 kbar, both Li- ad Al-specific OH-defects are observed (corresponding to 470 ± 75 wt ppm H2O). Results from this study may therefore be used to monitor formation conditions of quartz in terms of pressure and trace metal saturation of the crystallizing petrological system. IR spectra obtained from natural quartz grains from a tourmaline-bearing pegmatite exhibit B- and Al-related OH-bands. The B-related OH-band is also exhibited in quartz from a tourmaline + spodumene-bearing pegmatite. Li- and Al-related OH-bands, however, are subordinate or not observed at all in the spodumene-bearing system, which suggests that OH-vibrations do not reflect absolute Li-contents in quartz due to efficient coupled substitution involving Al. Data from experimental runs and natural specimens indicate that the B-related OH-band can be used as a rough proxy for B-contents in quartz, confirming the previously postulated charge balance equation [H+] = [B3+] + [Al3+] − [Li+] − [K+] − [P5+].

Research paper thumbnail of Core formation, mantle differentiation and core-mantle interaction within Earth and the terrestrial planets

Research paper thumbnail of The stability of hydrous silicates in Earth's lower mantle: Experimental constraints from the systems MgO–SiO2–H2O and MgO–Al2O3–SiO2–H2O

Research paper thumbnail of OH-point defects in quartz in B- and Li-bearing systems and their application to pegmatites

Physics and Chemistry of Minerals, 2014

terms of pressure and trace metal saturation of the crystallizing petrological system. Ir spectra... more terms of pressure and trace metal saturation of the crystallizing petrological system. Ir spectra obtained from natural quartz grains from a tourmaline-bearing pegmatite exhibit Band al-related OH-bands. The B-related OH-band is also exhibited in quartz from a tourmaline + spodumenebearing pegmatite. li-and al-related OH-bands, however, are subordinate or not observed at all in the spodumenebearing system, which suggests that OH-vibrations do not reflect absolute li-contents in quartz due to efficient coupled substitution involving al. Data from experimental runs and natural specimens indicate that the B-related OH-band can be used as a rough proxy for B-contents in quartz, confirming the previously postulated charge balance equation [H + ] = [B 3+ ] + [al 3+ ] − [li + ] − [K + ] − [P 5+ ].

Research paper thumbnail of The phase diagram of NiSi under the conditions of small planetary interiors

Physics of the Earth and Planetary Interiors, 2016

Research paper thumbnail of Experimental constraints on melting temperatures in the MgO–SiO 2 system at lower mantle pressures

Earth and Planetary Science Letters

Eutectic melting curves in the system MgO-SiO2 have been experimentally determined at 27 lower ma... more Eutectic melting curves in the system MgO-SiO2 have been experimentally determined at 27 lower mantle pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We 28 investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary, 29 and melting of bridgmanite plus stishovite in the MgSiO3-SiO2 binary, as analogues for 30 natural peridotite and basalt, respectively. The melting curve of model basalt occurs at 31 lower temperatures, has a shallower dT/dP slope and slightly less curvature than the 32 model peridotitic melting curve. Overall, melting temperatures detected in this study are 33 in good agreement with previous experiments and ab initio simulations at ~25 GPa 34 (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the 35 measured eutectic melting curves are systematically lower in temperature than curves 36 extrapolated on the basis of thermodynamic modelling of low-pressure experimental 37 data, and those calculated from atomistic simulations. We find that our data are 38 inconsistent with previously computed melting temperatures and melt thermodynamic 39 properties of the SiO2 endmember, and indicate a maximum in short-range ordering in 40 MgO-SiO2 melts close to Mg2SiO4 composition. The curvature of the model peridotite 41 eutectic relative to an MgSiO3 melt adiabat indicates that crystallization in a global 42 magma ocean would begin at ~100 GPa rather than at the bottom of the mantle, 43 allowing for an early basal melt layer. The model peridotite melting curve lies ~500 K 44 above the mantle geotherm at the core-mantle boundary, indicating that it will not be 45 molten unless the addition of other components reduces the solidus sufficiently. The 46 model basalt melting curve intersects the geotherm at the base of the mantle, and partial 47 melting of subducted oceanic crust is expected. 48 49 Recent experiments on natural peridotitic and basaltic compositions (Fiquet et

Research paper thumbnail of The stability of hydrous silicates in Earth's lower mantle: Experimental constraints from the systems MgO–SiO 2 –H 2 O and MgO–Al 2 O 3 –SiO 2 –H 2 O

We performed laser-heated diamond anvil cell experiments on bulk compositions in the systems MgO–... more We performed laser-heated diamond anvil cell experiments on bulk compositions in the systems MgO–SiO 2 –H 2 O (MSH) and MgO–Al 2 O 3 –SiO 2 –H 2 O (MASH) that constrain the stability of hydrous phases in Earth's lower mantle. Phase identification by synchrotron powder diffraction reveals a consistent set of stability relations for the high-pressure, dense hydrous silicate phases D and H. In the MSH system phase D is stable to ~50 GPa, independent of temperature from ~1300 to 1700 K. Phase H becomes stable between 35 and 40 GPa, and the phase H out reaction occurs at ~55 GPa at 1600 K with a negative dT/dP slope of ~−75 K/GPa. Between ~30 and 50 GPa dehydration melting occurs at ~1800 K with a flat dT/dP slope. A cusp along the solidus at ~50 GPa corresponds with the intersection of the subsolidus phase H out reaction, and the dT/dP melting slope steepens to ~15 K/GPa up to ~85 GPa. In the MASH system phase H is stable in experiments between ~45 and 115 GPa in all bulk compositions studied, and we expect aluminous phase H to be stable throughout the lower mantle depth range beneath ~1200 km in both peridotitic and basaltic lithologies. In the subsolidus, aluminous phase D is stable to ~55 GPa, whereas at higher pressures aluminous phase H is the stable hydrous phase. The presence of hydrogen may sharpen the bridgmanite to post-perovskite transition. The ambient unit cell volume of bridgmanite increases systematically with pressure above ~55 GPa, possibly representing an increase in alumina content, and potentially hydrogen content, with depth. Bridgmanite in equilibrium with phases D and H has a relatively low alumina content, and alumina partitions preferentially into the hydrous phases. The melting curves of MASH compositions are shallower than in the MSH system, with dT/dP of ~6 K/GPa. Phase D and H solid solutions are stable in cold, hy-drated subducting slabs and can deliver water to the deepest lower mantle. However, hydrated lithologies in the lower mantle are likely to be partially molten at all depths along an ambient mantle geotherm.

Research paper thumbnail of OH-point defects in quartz in B- and Li-bearing systems and their application to pegmatites

OH incorporation in quartz in Al-, B- and Li-bearing systems (granitic systems containing tourmal... more OH incorporation in quartz in Al-, B- and Li-bearing systems (granitic systems containing tourmaline or spodumene) was studied experimentally in order to investigate the effect of pressure, temperature and chemical impurities on the generation of OH-defects. High-pressure experiments were carried out at pressures between 5 and 25 kbar and temperatures between 800 and 900 °C, and OH-contents in quartz were calculated from IR absorption spectra measured on oriented quartz crystals. IR absorption features were assigned to impurity substitutions, such as AlOH (3,420, 3,379 and 3,315 cm−1) and BOH (3,595 cm−1), LiOH (3,483 cm−1), and hydrogarnet substitution (4H)Si defects (3,583 cm−1). Results indicate a negative correlation of incorporated Al-specific OH-defect content versus pressure (630 ± 130 wt ppm H2O at 5 kbar to 102 ± 6 wt ppm H2O at 25 kbar), but no clear correlation of B-specific OH-defects with pressure. In runs initially containing spodumene, virtually OH-free quartzes were observed at pressures ≥10 kbar, where impurity cations compensate each other forming an anhydrous eucryptite-defect component. In contrast, at 5 kbar, both Li- ad Al-specific OH-defects are observed (corresponding to 470 ± 75 wt ppm H2O). Results from this study may therefore be used to monitor formation conditions of quartz in terms of pressure and trace metal saturation of the crystallizing petrological system. IR spectra obtained from natural quartz grains from a tourmaline-bearing pegmatite exhibit B- and Al-related OH-bands. The B-related OH-band is also exhibited in quartz from a tourmaline + spodumene-bearing pegmatite. Li- and Al-related OH-bands, however, are subordinate or not observed at all in the spodumene-bearing system, which suggests that OH-vibrations do not reflect absolute Li-contents in quartz due to efficient coupled substitution involving Al. Data from experimental runs and natural specimens indicate that the B-related OH-band can be used as a rough proxy for B-contents in quartz, confirming the previously postulated charge balance equation [H+] = [B3+] + [Al3+] − [Li+] − [K+] − [P5+].