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Phase equilibria calculated with THERMOCALC for simplified mantle ultrabasic and basic bulk compositions in Na2O-CaO-FeO- MgO-Al2O3-SiO2 (NCFMAS) at depths down to the Transition Zone and uppermost lower mantle are presented here for the first time. This capitalizes on a new equation of state for solid phases and ties in deep mantle phases (wadsley...
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Anatexis in the crustal footwall of Ronda peridotites (Betic Cordillera, S Spain) is apparently related to the hot emplacement of this mantle slab over metasedimentary rocks. In this study we combine the analysis of melt inclusions (MI) and phase equilibria calculations on quartzo-feldspathic mylonites (former migmatites) occurring at the contact w...
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... For the calculations, the internally consistent thermodynamic database for condensed phases of Holland and Powell (2011) (ds62) and the equation of state for the binary fluid H 2 O-CO 2 of Holland and Powell (1998) were adopted. The following solution models were used: garnet, chloritoid, staurolite, chlorite, white mica, cordierite, orthopyroxene, biotite, and melt (White et al. 2014), plagioclase (Newton and Haselton 1981), k-feldspar (Thompson and Hovis 1979), corundum (Holland et al. 2013) and sapphirine (Wheller and Powell 2014). ...
The onset of the Cossato-Mergozzo-Brissago shear zone within the Strona Ceneri Border Zone in the W-Southalpine basement (Italy) and its role in the collapse of the Variscan crust have been the subject of considerable controversy. A set of new petrographic, geochemical and geochronological data from a suite of syn-kinematic migmatitic paragneiss and amphibolites in between the upper and lower crustal sections of the W-Southalpine basement provide new evidence on the thermo-mechanical role played by the middle crust in the evolution of the Permian Southalpine basement. The petrological investigation of these amphibolite-facies rocks and U–Pb ages from monazite crystals, occurring in distinct microstructural positions, provide new P–T-t constraints on the late-Paleozoic tectono-thermal evolution of the Variscan middle crust. The SCBZ units recorded tectonic events from a possible Early Silurian Cenerian (ca. 440 Ma) overprint onto the proto-sedimentary units of the Southalpine basement to the Mid-Permian (ca. 285 Ma) syn-kinematic partial melting event developed close to the CMB shear zone. Phase equilibria modeling is used to constrain the metamorphic conditions recorded by this section of the Variscan basement. Pressure–temperature (P–T) isochemical phase diagrams show that, after the ca. 330 Ma Variscan metamorphic peak at P ≅ 4 kbar and T < 630 °C, the SCBZ paragneiss experienced isobaric heating up to 700–720 °C at ca. 285 Ma, which led to the formation of a syn-kinematic partial melting event coeval to the emplacement of the Mafic Complex in the lower Ivrea-Verbano Zone. These new geochronological and petrological constraints on the SCBZ paragneiss seem to corroborate the hypothesis that the transition from the stage of mature Variscan orogen to the stage of its collapse developed in the Permian, at ca. 285 Ma. Thus, we argue that the orogenic collapse was probably driven by the rheological weakening of the mid-crustal SCBZ units induced by their syn-tectonic partial melting and, ultimately, by the coeval thermal perturbation of the crust due to the intrusion of the mafic igneous suite at the crust-mantle boundary.
... Stishovite is a high pressure mineral whose composition in natural rocks is dominantly SiO 2 . It is stable in mafic and felsic rocks under the P-T conditions of the mantle transition zone and the upper part of the lower mantle, an has abundances of around 10-25 wt% of rocks with basaltic compositions (Hirose & Fei, 2002;Holland et al., 2013). It has also been identified in meteorites and their shocked target rocks. ...
This paper presents a Landau framework for describing instantaneous and time-dependent elastic softening in anisotropic solid solutions. As with previous Landau models, the framework minimizes a thermodynamic potential by varying isochemical parameters (q) that describe changes in structural, ordering or electronic spin state. Unlike previous models, no coupling terms are used; strain is not a parameter involved in the energy minimization, but is instead a property of the material. The framework satisfies all the connections between elastic and thermodynamic properties required by Maxwell's relations. The stishovite to post-stishovite transition is used to illustrate the validity of the formulation. It is shown that around the transition, the stishovite-post stishovite phase is auxetic in many directions and has negative linear compressibility along the long axis of the cell.
... Thermodynamic modelling of the mantle transition zone (MTZ) and lower mantle (LM) of the Earth typically involves olivine Mg 2 SiO 4 highpressure polymorphs, i.e., wadsleyite with a spineloid structure, ringwoodite (Rwd) with a spinel structure, Mg 3 Al 2 Si 3 O 12 -pyrope (Prp) garnet, MgSiO 3 bridgmanite (Bdm), and MgO periclase (Akaogi et al., 2002;Dorogokupets et al., 2015;Holland et al., 2013;Irifune et al., 1996;Ishii et al., 2018;Ito et al., 1998;Katsura et al., 2003;Stixrude and Lithgow-Bertelloni, 2011;Stixrude and Lithgow-Bertelloni, 2005;Yu et al., 2008). The MTZ/LM boundary is usually assigned to post-spinel and post-garnet transitions associated with the formation of Bdmbearing assemblages (Akaogi et al., 2002;Fei et al., 2004;Hirose et al., 2001b;Ishii et al., 2018;Katsura et al., 2004;Litasov et al., 2005). ...
... The mixed iron valence at the octahedral site makes magnetite also a challenge for calculations. As such the here-obtained thermal EoS does not only greatly enhance current knowledge of the thermo-elastic properties of magnetite, but it also adds the thermal EoS of a Fe 3+ -bearing mineral to the available databases for self-consistent thermodynamic modeling (e.g., Stixrude & Lithgow-Bertelloni 2011, Holland et al. 2013) and provides a critical benchmark to ab initio approaches (e.g. Dorogokupets et al. 2016). ...
Fe3O4 magnetite is an important mineral commonly found in various geological settings, including the planet Mars, whose thermoelastic properties at high pressure and temperature are still poorly constrained. We performed X-ray diffraction measurements on natural magnetite using resistive-heated diamond-anvil cells up to 16 GPa and 1100 K. We fitted a thermal equation of state (EoS) to the collected data resulting in K0 = 182(1) GPa, K0′ = 4, θD = 660 K, γ = 1.8(1), and q = 2.7. Moreover, it was possible to explore the structural evolution of magnetite in detail using single-crystal measurements. Over the studied pressure and temperature range, we found no evidence of a transformation from an inverse to a normal spinel structure. The EoS parameters obtained in this study will be implemented into currently available databases for self-consistent thermodynamic modeling. In particular, our results are used to model and compare the sound wave velocities of a magnetite-bearing and magnetite-free martian upper mantle assemblage. We observe that the incorporation of magnetite reduces the sound wave velocities; however, the magnitude of the effect is below the current seismic detection limit of the InSight mission on Mars at the low abundance of magnetite expected in the martian mantle.
... (ii) forward modelling including equilibrium phase diagrams and isopleth thermobarometry strategies (Connolly, 1990(Connolly, , 2009de Capitani & Petrakakis, 2010;Lanari et al., 2017;Lanari & Duesterhoeft, 2019;Powell et al., 1998). The latter method has been proven to be a useful application with significant improvements in the internally consistent thermodynamic datasets and activitycomposition (a-X) models for solid solution phases (Dachs et al., 2021;Duesterhoeft & Lanari, 2020;García-Arias, 2020;Green et al., 2016;Holland et al., 2013;Holland et al., 2018;White et al., 2014). The forward modelling techniques are pursued to determine equilibrium P-T conditions using modes and compositions of equilibrium mineral assemblages and bulk-rock compositions. ...
The titanium (Ti) concentrations in zircon and quartz and corresponding thermometers have been regarded as powerful monitors that constrain petrogenetically meaningful temperature conditions of crystallization and metamorphism. The precise measurement of trace elements by electron probe microanalyzer (EPMA) is quite challenging as their x-ray intensities are only slightly higher than the Brems-strahlung background, leading to significant errors while quantifying the elemental abundances (e.g., Ti-in-zircon). We present EPMA-based protocols for analysing Ti concentrations in zircon and quartz by considering recent analytical and instrumental improvements. High counting times at peak and background positions, simultaneous acquisition of Ti in multiple (three) spectrometers and data processing using the non-central chi 2 test for risk determination in sub-counting method were employed in Ti-in-zircon and Ti-in-quartz protocols. Applying these protocols to the Mongolian garnet, San Carlos olivine and NIST 610 glass standards yielded Ti concentrations of 0.60 ± 0.02 wt%, 18 ± 3 ppm and 437 ± 26 ppm (in ±2σ), respectively. The Ti concentrations obtained from these standards are consistent with those published based on high-precision analytical methods. We use the existing Ti-in-zircon and Ti-in-quartz thermometers to understand the thermal evolution of various lithologies in the Sandmata Complex, Aravalli Craton (north-western India). The investigated samples include garnet-biotite gneiss, migmatite gneiss, mafic granulite and Anjana granite. The Ti-in-zircon temperatures calculated from the patchy-zoned zircon cores yield HT-UHT conditions (892-959 C) for garnetiferous granite gneiss, migmatite gneiss and mafic granulite, whereas the zircon over-growths yield temperatures of 725-871 C. The homogeneous zircon cores from Anjana granite yield temperatures (914-984 C) comparable to zirconium saturation conditions (920-960 C), indicating zircon crystallization from "hot" granitic melt. The oscillatory overgrowths on the zircon core obtain variable temperature conditions for inner overgrowth (811-877 C) and outer overgrowth (714-782 C), suggesting the episodic growth of zircon grains from different magma pulses.
... We used the internally consistent thermodynamic database of Holland and Powell (1998) revised in 2004 (hp04ver.dat) and the following solid solution models: olivine, orthopyroxene and cummingtonite, (Holland and Powell, 1998), wustite (Fabrichnaya, 1999), ferropericlase (Holland et al., 2013) and antigorite (Padrón-Navarta et al., 2013). Anthophyllite (orthoamphibole), clinohumite, brucite and talc were treated as ideal solid solutions between Fe-and Mg end-members. ...
... Stixrude & Lithgow-Bertelloni (2011) assume that Earth's mantle is comprised of at least six essential chemical components (SiO 2 , MgO, FeO, CaO, Al 2 O 3 and Na 2 O), which stabilize a large variety of mineral phases across the entirety of its P-T regime. This is generally referred to as the NCFMAS system (Stixrude & Lithgow-Bertelloni 2011;Holland et al. 2013). In using pyrolite as chemical model of mantle composition, as Chust et al. (2017) assessed, it has been accomplished to successfully describe state, rheology and dynamics of Earth's upper mantle and TZ (e.g. ...
The mantle transition zone (TZ) is expected to influence vertical mass flow between upper and lower mantle as it hosts a complex set of mineral phase transitions and an increase in viscosity with depth. Still, neither its seismic structure nor its dynamic effects have conclusively been constrained. The seismic discontinuities at around 410 and 660 km depth (‘410’ and ‘660’) are classically associated with phase transitions between olivine polymorphs, the pressure of which is modulated by lateral temperature variations. Resulting discontinuity topography is seismically visible and can thus potentially provide insight on temperature and phase composition at depth. Besides the olivine phase changes, the disassociation of garnet may additionally impact the 660 at higher temperatures. However, the volume of material affected by this garnet transition and its dynamic implications have not yet been quantified. This study presents hypothetical realizations of TZ seismic structure and major discontinuities based on the temperature field of a published 3-D mantle circulation model for a range of relevant mineralogies, including pyrolite and mechanical mixtures (MM). Systematic analysis of these models provides a framework for dynamically informed interpretations of seismic observations and gives insights into the potential dynamic behaviour of the TZ. Using our geodynamic-mineralogical approach we can identify which phase transitions induce specific topographic features of 410 and 660 and quantify their relative impact. Areal proportions of the garnet transition at the 660 are ∼3 and ∼1 percent for pyrolite and MM, respectively. This proportion could be significantly higher (up to ∼39 percent) in a hotter mantle for pyrolite, but remains low (< 2 percent) for MM. In pyrolite, both slabs and plumes are found to depress the 660 —with average deflections of 14 and 6 km, respectively— due to the influence of garnet at high temperatures indicating its complex dynamic effects on mantle upwellings. Pronounced differences in model characteristics for pyrolite and MM, particularly their relative garnet proportions and associated topography features, could serve to discriminate between the two scenarios in Earth.
... The calculations use 600°C for garnet and plagioclase and 750°C for clinopyroxene. Activity models: garnet,White et al. (2014); clinopyroxene,Green et al. (2016); plagioclase,Holland et al. (2013). Lattice parameters for garnet are fromHolland and Powell (2011) using their equation of state at the given reference P and T. Lattice parameters for clinopyroxene are fromZhao et al. (1997Zhao et al. ( , 1998 using their experimental data at 1.36 GPa and 600°C. ...
Mineral compositions are used to infer pressures, temperatures, and timescales of geological processes. The thermodynamic techniques underlying these inferences assume a uniform, constant pressure. Nonetheless, convergent margins generate significant non‐hydrostatic (unequal) stresses, violating the uniform pressure assumption and creating uncertainty. Materials scientists F. Larché and J. Cahn derived an equation suitable for non‐hydrostatically stressed geologic environments that links stress and equilibrium composition in elastic, multi‐component crystals. However, previous works have shown that for binary solid solutions with ideal mixing behavior, hundreds of MPa to GPa‐level stresses are required to shift mineral compositions by a few hundredths of a mole fraction, limiting the equation's applicability. Here, we apply Larché and Cahn's equation to garnet, clinopyroxene, and plagioclase solid solutions, incorporating for the first time non‐ideal mixing behavior and more than two endmembers. We show that non‐ideal mixing increases predicted stress‐induced composition changes by up to an order of magnitude. Further, incorporating additional solid solution endmembers changes the predicted stress‐induced composition shifts of the other endmembers being considered. Finally, we demonstrate that Larché and Cahn's approach yields positive entropy production, a requirement for any real process to occur. Our findings reveal that stresses between tens and a few hundred MPa can shift mineral compositions by several hundredths of a mole fraction. Consequently, mineral compositions could plausibly be used to infer stress states. We suggest that stress‐composition effects could develop via intracrystalline diffusion in any high‐grade metamorphic setting, but are most likely in hot, dry, and strong rocks such as lower crustal granulites.
... thermodynamic database for pure species and end-members (Holland and Powell, 2011). We used the following set of solution phases: O(JH), Sp(JH), Pl(JH), Melt(JH), Grt (JH), Opx(JH), Cpx(JH), Eskol(C), Ring(H), for olivine, spinel, plagioclase, melt, garnet, orthopyroxene, clinopyroxene, eskolaite and ringwoodite, respectively (Jennings and Holland, 2015;Holland et al., 2013;Chatterjee et al., 1982). Considering Cr and eskolaite (Cr 2 O 3 ) in the Fig. 4. Stable continental elevation based on filtered ETOPO-1 grid. ...
The choice of crustal and mantle densities in numerical geodynamic models is usually based on convention. The isostatic component of the topography is not calibrated to fit observations resulting in not very well constrained elevations. The density distribution on Earth is not easy to constrain because it involves multiple variables (temperature, pressure, composition, and deformation). We aim in this study to provide a reference case for geodynamic modelling where crustal and mantle densities are calibrated to fit the relative continent/mid-ocean ridge elevation in agreement with observations. We first review observed Earth topography of stable continents and of active mid-ocean ridges and define the characteristic average elevation of these domains. We use self-consistent thermodynamic calculations of dry mantle rocks that include partial melting to calibrate densities of the continental lithospheric mantle and beneath the mid-ocean ridge. The thermodynamic solutions are coupled with a 2-D incompressible plane strain finite element method for viscous-plastic creeping flows to solve for the dynamic evolution during extension from continental rifting to mid-ocean spreading. The combined results from 2-D thermo-mechanical models and 1-D isostatic calculations show that the relative elevation difference between mid-ocean ridges and continents depends on crustal density, mantle composition, and the degree of depletion of the lithospheric mantle. Based on these results we calibrate the reference density that only depends on temperature, which can be used in classic thermo-mechanical models based on the Boussinesq approximation. Finally the model calibration provides a solution that fits (1) the elevation of active mid-ocean ridges far from hotspots (-2750±250 m), (2) the elevation of stable continents far from hotspots (+400±400 m), (3) the average depletion buoyancy of the continental lithospheric mantle (between -20 and -50±15 kg/m3 depending on lithospheric thickness) and (4) the average continental crust density (2835±35 kg/m3 for a 35 km thick crust).
... Here we use the version 6.8.5 of Perple_X software package 38 Supplementary Table 3. The solid solution models include garnet (gt) 39,40 , clinopyroxene (cpx) 39,40 , orthopyroxene (opx) 39,40 and its high-P polymorph (C2/c) 39 , wadsleyite (wad) 39,40 , ringwoodite (ring) 39,40 , CaSi-perovskite (ca-pv) 39,40 , wuestite (wus) 40 , plagioclase (pl) 39 , kalsilite (kls) 39 , microcline (mic) 39 , K-wadeite (wa) 39 , K-hollandite (hol) 39 , corundum (cor) 39,40 , spinel (sp) 39,40 and melt 39 . Quartz (qtz), coesite (coe), stishovite (stv), kyanite (ky) are treated as pure end-member phases. ...
... Here we use the version 6.8.5 of Perple_X software package 38 Supplementary Table 3. The solid solution models include garnet (gt) 39,40 , clinopyroxene (cpx) 39,40 , orthopyroxene (opx) 39,40 and its high-P polymorph (C2/c) 39 , wadsleyite (wad) 39,40 , ringwoodite (ring) 39,40 , CaSi-perovskite (ca-pv) 39,40 , wuestite (wus) 40 , plagioclase (pl) 39 , kalsilite (kls) 39 , microcline (mic) 39 , K-wadeite (wa) 39 , K-hollandite (hol) 39 , corundum (cor) 39,40 , spinel (sp) 39,40 and melt 39 . Quartz (qtz), coesite (coe), stishovite (stv), kyanite (ky) are treated as pure end-member phases. ...
... Here we use the version 6.8.5 of Perple_X software package 38 Supplementary Table 3. The solid solution models include garnet (gt) 39,40 , clinopyroxene (cpx) 39,40 , orthopyroxene (opx) 39,40 and its high-P polymorph (C2/c) 39 , wadsleyite (wad) 39,40 , ringwoodite (ring) 39,40 , CaSi-perovskite (ca-pv) 39,40 , wuestite (wus) 40 , plagioclase (pl) 39 , kalsilite (kls) 39 , microcline (mic) 39 , K-wadeite (wa) 39 , K-hollandite (hol) 39 , corundum (cor) 39,40 , spinel (sp) 39,40 and melt 39 . Quartz (qtz), coesite (coe), stishovite (stv), kyanite (ky) are treated as pure end-member phases. ...
The long-duration, fast convergence, and imbalance of crustal mass in the India-Asia collisional system challenge the classical rules of continental dynamics. Here, we calculate the mass deficit of felsic crust in Greater India indicating ~20–47% of the felsic crust is missing during collision. Phase equilibria modeling and density calculations demonstrate the pressure-temperature-dependent density of felsic crust is denser than the surrounding mantle at P > 7–8 GPa. Integrated petrological-thermo-mechanical models and analytical studies of the slab-pull forces confirm the Greater Indian continent with its felsic crust can subduct spontaneously under its own negative buoyancy when it is dragged to >170 km by the preceding oceanic slab. The great slab-pull force, induced by the negative buoyancy of subducted crust below 170 km, not only contributes to the long-lasting fast convergence between India and Asia but also explains the crustal mass imbalance during the Himalayan orogeny. The mass imbalance of felsic crust in the India-Asia collision system can be explained by metamorphic densification of continental crust below 170 km depth, which would also help drive and maintain subduction, according to petrological-thermo-mechanical modeling.
