ORCID Profile
0000-0001-6166-0094
Current Organisation
Universität Potsdam
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Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-2990
Abstract: & & Calcite (CaCO& sub& & /sub& ) and magnesite (MgCO& sub& & /sub& ) are among the most common carbonates on Earth. The presence of Ca& #8209 Mg& #8209 carbonates in the mantle affects the melting and phase relations of peridotites and eclogites and (partial) melting of carbonates liberates carbon from the mantle to shallower depths. The onset of melting and the incipient melt composition of carbonated peridotites and carbonated eclogites are influenced by the pure CaCO& sub& & /sub& & #8209 MgCO& sub& & /sub& & #8209 system. Thus, a deeper insight into the phase relations and melting behavior of the CaCO& sub& & /sub& & #8209 MgCO& sub& & /sub& & #8209 system is crucial to better understand the carbon cycle in the Earth& #8217 s mantle.& & & & We performed quenched multi-anvil experiments at 6 and 9& GPa to (a) examine the phase relations of the nominally anhydrous CaCO& sub& & /sub& & #8209 MgCO& sub& & /sub& & #8209 system and to (b) establish partition coefficients for Li, Na, K, Sr, Ba, Nb, Y and rare earth elements (REEs) between carbonates and dolomitic melt. We used a rotating multi-anvil press to overcome quenching problems as observed in previous studies. Rotation of the multi& #8209 anvil press is, additionally, indispensable to establish equilibrium between solid carbonates and dolomitic melt.& & & & The melting temperature and phase relations of Ca& #8209 Mg& #8209 carbonates depend on the Mg/Ca& #8209 ratio. For instance, at 6 GPa Ca& #8209 rich carbonates with a molar Mg/(Mg+Ca)& #8209 ratio (& em& X& /em& & sub& Mg& /sub& ) of 0.2 will transform into a dolomitic melt (& em& X& /em& & sub& Mg& /sub& =0.33& #8209 .31) and calcite crystals (& em& X& /em& & sub& Mg& /sub& =0.19& #8209 .14) at 1350& #8209 & #8451 . Partial melting of Mg& #8209 rich carbonates (& em& X& /em& & sub& Mg& /sub& =0.85) will produce a dolomitic melt (& em& X& /em& & sub& Mg& /sub& =0.5& #8209 .8) and Ca& #8209 bearing magnesite (& em& X& /em& & sub& Mg& /sub& =0.89& #8209 .96) at 1400& #8209 & #8451 . Trace element distribution into Ca-Mg-carbonates depends on & em& X& /em& & sub& Mg& /sub& , temperature and seems to follow lattice constraints for alent cations. Partition coefficients of REEs between magnesite (Ca& sub& .11& /sub& Mg& sub& .89& /sub& CO& sub& & /sub& ) and dolomitic melt (Ca& sub& .5& /sub& Mg& sub& .5& /sub& CO& sub& & /sub& ) at 6 GPa and 1400 & #8451 are uniform scattering marginal between 0.1& #8209 .2. The partition coefficient of Lu (D=0.1) is unmodified to lower Ca-content in magnesite (Ca& sub& .04& /sub& Mg& sub& .96& /sub& CO& sub& & /sub& ) and higher temperature (1600& & #8451 ), but the partition coefficients between such Ca-poor magnesite and dolomitic melt (Ca& sub& .2& /sub& Mg& sub& .8& /sub& CO& sub& & /sub& ) decrease continuously from heavy-REEs to light& #8209 REEs from 0.1 to 0.001, respectively.& & & & Our findings have important implications for the cycle of carbon and trace elements in the mantle because Ca& #8209 Mg& #8209 carbonates will (partially) melt at 6 GPa and temperatures above ~1300 & #8451 producing a dolomitic melt. Consequently, CO& sub& & /sub& will be liberated by partial melting of an upwelling carbonated mantle at a depth of ~200 km considering the thermal structure of the upper mantle. The results also affirm that carbonates are stable in the subducting slab even for hot subduction zone geothermal gradients unless carbonate-bearing lithologies in the slab are infiltrated by aqueous fluids.& &
Publisher: Copernicus GmbH
Date: 06-10-2022
Abstract: Abstract. The most profound consequences of the presence of Ca–Mg carbonates (CaCO3–MgCO3) in the Earth's upper mantle may be to lower the melting temperatures of the mantle and control the melt composition. Low-degree partial melting of a carbonate-bearing mantle produces CO2-rich, silica-poor melts compositionally imposed by the melting relations of carbonates. Thus, understanding the melting relations in the CaCO3–MgCO3 system facilitates the interpretation of natural carbonate-bearing silicate systems. We report the melting relations of the CaCO3–MgCO3 system and the partition coefficient of trace elements between carbonates and carbonate melt from experiments at high pressure (6 and 9 GPa) and temperature (1300–1800 ∘C) using a rocking multi-anvil press. In the absence of water, Ca–Mg carbonates are stable along geothermal gradients typical of subducting slabs. Ca–Mg carbonates (∼ Mg0.1–0.9Ca0.9–0.1CO3) partially melt beneath mid-ocean ridges and in plume settings. Ca–Mg carbonates melt incongruently, forming periclase crystals and carbonate melt between 4 and 9 GPa. Furthermore, we show that the rare earth element (REE) signature of Group-I kimberlites, namely strong REE fractionation and depletion of heavy REE relative to the primitive mantle, is resembled by carbonate melt in equilibrium with Ca-bearing magnesite and periclase at 6 and 9 GPa. This suggests that the dolomite–magnesite join of the CaCO3–MgCO3 system might be useful to approximate the REE signature of carbonate-rich melts parental to kimberlites.
Publisher: Springer Science and Business Media LLC
Date: 22-11-2017
Publisher: Springer Science and Business Media LLC
Date: 04-2022
DOI: 10.1007/S00410-022-01905-W
Abstract: Devolatilization of subducting lithologies liberates COH-fluids. These may become partially sequestered in peridotites in the slab and the overlying forearc mantle, affecting the cycling of volatiles and fluid mobile elements in subduction zones. Here we assess the magnitudes, timescales and mechanism of channelized injection of COH-fluids doped with $${\\mathrm{Ca}}_{\\mathrm{aq}}^{2+}$$ Ca aq 2 + , $${\\mathrm{Sr}}_{\\mathrm{aq}}^{2+}$$ Sr aq 2 + and $${\\mathrm{Ba}}_{\\mathrm{aq}}^{2+}$$ Ba aq 2 + into the dry forearc mantle by performing piston cylinder experiments between 1–2.5 GPa and 600–700 °C. Cylindrical cores of natural spinel-bearing harzburgites were used as starting materials. Based on mineral assemblage and composition three reaction zones are distinguishable from the rim towards the core of primary olivine and orthopyroxene grains. Zone 1 contains carbonates + quartz ± kyanite and zone 2 contains carbonates + talc ± chlorite. Olivine is further replaced in zone 3 by either antigorite + magnesite or magnesite + talc within or above antigorite stability, respectively. Orthopyroxene is replaced in zone 3 by talc + chlorite. Mineral assemblages and the compositions of secondary minerals depend on fluid composition and the replaced primary silicate. The extent of alteration depends on fluid CO 2 content and fluid/rock-ratio, and is further promoted by fluid permeable reaction zones and reaction driven cracking. Our results show that COH-fluid induced metasomatism of the forearc mantle is self-perpetuating and efficient at sequestering $${\\mathrm{Ca}}_{\\mathrm{aq}}^{2+}$$ Ca aq 2 + , $${\\mathrm{Sr}}_{\\mathrm{aq}}^{2+}$$ Sr aq 2 + , $${\\mathrm{Ba}}_{\\mathrm{aq}}^{2+}$$ Ba aq 2 + and CO 2aq into newly formed carbonates. This process is fast with 90% of the available C sequestered and nearly 50% of the initial minerals altered at 650 °C, 2 GPa within 55 h. The dissolution of primary silicates under high COH-fluid/rock-ratios, as in channelized fluid flow, enriches SiO 2aq in the fluid, while CO 2aq is sequestered into carbonates. In an open system, the remaining CO 2 -depleted, Si-enriched aqueous fluid may cause Si-metasomatism in the forearc further away from the injection of the COH-fluid into peridotite.
Publisher: German YES Chapter & GFZ German Research Centre for Geosciences
Date: 2021
DOI: 10.2312/YES19
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3367
Abstract: & & We examined the supra-solidus phase relations of the CaCO& sub& & /sub& -MgCO& sub& & /sub& system and established trace element partition coefficient between carbonates and carbonate melt by conducting high pressure (6 and 9 GPa) and temperature (1300-1800 & sup& o& /sup& C) experiments with a rocking multi-anvil press. It is well known that the major element composition of initial melts derived from low-degree partial melting of the carbonated mantle strongly depends on the melting relations of carbonates (e.g. 1, 2 and reference therein). Understanding the melting relations in the CaCO& sub& & /sub& -MgCO& sub& & /sub& system is thus fundamental in assessing low-degree partial melting of the carbonated mantle. We show here to which extent the trace element signature of a pure carbonate melt can be used as a proxy for the trace element signature of mantle-derived CO& sub& & /sub& -rich melts such as kimberlites.& & & & Our results support that, in the absence of water, Ca-Mg-carbonates are thermally stable along geothermal gradients typical at subduction zones. Except for compositions close to the endmembers (~Mg& sub& -0.1& /sub& Ca& sub& -0.9& /sub& CO& sub& & /sub& Ca& sub& -0.1& /sub& Mg& sub& -0.9& /sub& CO& sub& & /sub& ), Ca-Mg-carbonates will partially (to completely) melt beneath mid& #8209 ocean ridges and in plume settings. Ca-Mg-carbonates melt incongruently to dolomitic melt and periclase above 1450 & sup& o& /sup& C and 9 GPa making the CaCO& sub& & /sub& -MgCO& sub& & /sub& a (pseudo-) ternary system as the number of components increases. Further, our results show that the rare earth element signature of a dolomitic melt in equilibrium with magnesite is similar to those of Group I kimberlites, namely that HREE are depleted relative to primitive mantle signatures. This implies that dolomite-magnesite solid solutions might be useful to approximate melting relations and melt compositions of low-degree partial melting of the carbonated mantle.& & & & References& & & & & Yaxley, Ghosh, Kiseeva, Mallik, Spandler, Thomson, and Walter, & em& CO& sub& & /sub& -Rich Melts in Earth& /em& , in & em& Deep Carbon: Past to Present& /em& , Orcutt, Daniel, and Dasgupta, Editors. 2019, Cambridge University Press: Cambridge. p. 129-162.& & & & & Dasgupta and Hirschmann, & em& The deep carbon cycle and melting in Earth's interior.& /em& Earth and Planetary Science Letters, 2010. 298 (1-2): p. 1-13.& &
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-9318
Abstract: & & Subduction of carbon-bearing phases throughout Earth& #8217 s history may be an important mechanism of sourcing carbon to the Earth& #8217 s lower mantle. As carbon has very low solubility in mantle silicates, it is primarily present in accessory phases such as carbonates, diamond, or metal carbides. Previous studies indicate that more than half of the carbonate contained in the oceanic crust may survive metamorphism and dehydration in the sub-arc and reach the lower mantle, even though the oxygen fugacity in the deep mantle may not favour their stability [1]. Indeed, the presence of carbonate in ultra-deep diamond inclusions provides evidence for carbonate subduction at least down to the transition zone [2].& & & & The carbonate phases present in the lower mantle depend on their bulk composition, the oxygen fugacity, and on their stability at a given pressure and temperature. Results from high-pressure experiments show that magnesite (MgCO& sub& & /sub& ) can be stable up to deep lower mantle conditions (& #8764 GPa and 2500 K) [3]. Accordingly, magnesite may be considered the most probable carbonate phase present in the deep Earth. Experimental studies on magnesite decarbonation in presence of SiO& sub& & /sub& at lower mantle conditions suggest that magnesite is stable along a cold subducted slab geotherm [4, 5]. However, our understanding of magnesite& #8217 s stability in contact with bridgmanite [(Mg,Fe)SiO& sub& & /sub& ], & the most abundant mineral in the lower mantle, remains incomplete.& & & & Hence, to investigate sub-solidus reactions, melting, decarbonation, and diamond formation in the system MgCO& sub& & /sub& -(Mg,Fe)SiO& sub& & /sub& , we conducted a combination of high-pressure experiments using multi-anvil press and laser-heated diamond anvil cells (LH-DAC) at conditions ranging from 25 to 70 GPa and 1300 to 2100 K.& & & & Multi-anvil experiments at 25 GPa and temperatures below the mantle geotherm (1700 K) show the formation of carbonate-silicate melt associated with stishovite crystallization, indicating incongruent melting of bridgmanite to stishovite, in accordance with the recent finding of Litasov and Shatskiy [4]. LH-DAC data from & em& in situ& /em& X-ray diffraction show crystallization of bridgmanite and stishovite. Diamond crystallization is detected using Raman spectroscopy. A melt phase could not be detected & em& in situ& /em& at high temperatures.& & & & Our results suggest a two-step process that starts with melting at temperatures below the mantle geotherm, followed by crystallization of diamond from the melt produced. & Therefore, we propose that subducted carbonate-bearing silicate rocks will not remain stable in the lower mantle and will instead melt at upper-most lower mantle conditions, fostering diamond formation. Our study also provides additional evidence that diamond production is related to carbonated melt. Consequently, the melting of recycled crust and chemical transfer to the surrounding mantle will hinder the transport of carbon deeper into the lower mantle.& & & & [1] Stagno et al. (2015) Contrib. Mineral. Petrol. 169(2), 16.& br& [2] Brenker et al. (2007) EPSL 260(1-2), 1-9.& br& [3] Binck, et al. (2020) Physical Review Materials, 4(5),1-9.& br& [4] Litasov & Shatskiy (2019) Geochemistry International, 57(9), 1024-1033.& br& [5] Drewitt, et al. (2019).& EPSL,& , 213-222.& &
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-7797
Abstract: The presence of magnesite (MgCO3) in the Earth& #8217 s mantle plays a fundamental role in reducing the melting point of the mantle [1] and forming carbonate& #8209 rich melts such as kimberlites and carbonatites [2]. The melting curve of (dry) magnesite is well constrained [3, 4], but melting of magnesite in the presence of H2O, providing the basis for more complex (natural) systems, is poorly understood from some quenched experiments [5]. Also, the distribution of trace elements such as Li, Sr, Pb, and rare earth elements during melting of magnesite is poorly considered in models that evaluate the trace element budget of carbonate& #8209 rich melts parental to kimberlites [6].Here we report, first, the H2O& #8209 resent melting curve of magnesite between 2 and 12& GPa. The melting curve of magnesite mixed with 16& wt% brucite was established by in& & #8209 & situ X& #8209 ray diffraction measurements using the large volume press at P61B at PETRA& III (DESY). Second, we report trace element partitioning data for congruent melting of calcite and incongruent melting of magnesite producing carbonate melt and periclase between 6 and 9& GPa. Those results were obtained from quenched experiments using a rocking multi& #8209 anvil press at the GFZ overcoming equilibrium and quenching problems in previous studies [7].& & & & & & & & & & Dasgupta and Hirschmann, The deep carbon cycle and melting in Earth's interior. Earth and Planetary Science Letters, 2010. 298(1-2): p. 1-13.2& & & & & & & & & Jones, Genge, and Carmody, Carbonate Melts and Carbonatites. Reviews in Mineralogy and Geochemistry, 2013. 75(1): p. 289-322.3& & & & & & & & & Solopova, Dubrovinsky, Spivak, Litvin, and Dubrovinskaia, Melting and decomposition of MgCO3 at pressures up to 84& GPa. Physics and Chemistry of Minerals, 2014. 42(1): p. 73-81.4& & & & & & & & & M& #252 ller, Koch-M& #252 ller, Rhede, Wilke, and Wirth, Melting relations in the system CaCO3-MgCO3 at 6 GPa. American Mineralogist, 2017. 102(12): p. 2440-2449.5& & & & & & & & & Ellis and Wyllie, Carbonation, hydration, and melting relations in the system MgO-H2O-CO2 at pressures up to 100 kbar. American Mineralogist, 1979. 64(1-2): p. 32-40.6& & & & & & & & & Girnis, Bulatov, Brey, Gerdes, and H& #246 fer, Trace element partitioning between mantle minerals and silico-carbonate melts at 6& #8211 GPa and applications to mantle metasomatism and kimberlite genesis. Lithos, 2013. 160-161: p. 183-200.7& & & & & & & & & Buob, Experiments on CaCO3-MgCO3 solid solutions at high pressure and temperature. American Mineralogist, 2006. 91(2-3): p. 435-440.
Publisher: Informa UK Limited
Date: 18-12-2018
Publisher: Mineralogical Society of America
Date: 06-2020
DOI: 10.2138/AM-2020-7098
Abstract: The presence of Ca-Mg-carbonates affects the melting and phase relations of peridotites and eclogites in the mantle, and (partial) melting of carbonates liberates carbon from the mantle to shallower depths. The onset and composition of incipient melting of carbonated peridotites and carbonated eclogites are influenced by the pure CaCO3-MgCO3-system making the understanding of the phase relations of Ca-Mg-carbonates fundamental in assessing carbon fluxes in the mantle. By performing high-pressure and high-temperature experiments, this study clarifies the suprasolidus phase relations of the nominally anhydrous CaCO3-MgCO3-system at 6 GPa showing that Ca-Mg-carbonates will (partially) melt for temperatures above ~1300 °C. A comparison with data from thermodynamic modeling confirms the experimental results. Furthermore, partition coefficients for Li, Na, K, Sr, Ba, Nb, Y, and rare earth elements between calcite and dolomitic melt, Ca-magnesite and dolomitic melt, and magnesite and dolomitic melt are established. Experiments were performed at 6 GPa and between 1350 to 1600 °C utilizing a rotating multi-anvil press. Rotation of the multi-anvil press is indispensable to establish equilibrium between solids and carbonate liquid. Major and trace elements were quantified with EPMA and LA-ICP-MS, respectively. The melting temperature and phase relations of Ca-Mg-carbonates depend on the Mg/Ca-ratio. For instance, Ca-rich carbonates with a molar Mg/(Mg+Ca)-ratio (XMg) of 0.2 will transform into a dolomitic melt (XMg = 0.33–0.31) and calcite crystals (XMg = 0.19–0.14) at 1350–1440 °C. Partial melting of Mg-rich carbonates (XMg = 0.85) will produce a dolomitic melt (XMg = 0.5–0.8) and Ca-bearing magnesite (XMg = 0.89–0.96) at 1400–1600 °C. Trace element distribution into calcite and magnesite seems to follow lattice constraints for alent cations. For instance, the compatibility of calcite (XMg = 0.14–0.19) for Sr and Ba decreases as the cation radii increases. Ca-Mg-carbonates are incompatible for rare earth elements (REEs), whereby the distribution between carbonates and dolomitic melt depends on the Mg/Ca ratio and temperature. For instance, at 1600 °C, partition coefficients between magnesite (XMg = 0.96) and dolomitic melt (XMg = 0.8) vary by two orders of magnitudes from 0.001 to 0.1 for light-REEs to heavy-REEs. In contrast, partition coefficients of REEs (and Sr, Ba, Nb, and Y) between magnesite (XMg = 0.89) and dolomitic melt (XMg = 0.5) are more uniform scattering marginal between ~0.1–0.2 at 1400 °C.
Publisher: Oxford University Press (OUP)
Date: 27-02-2020
DOI: 10.1093/PETROLOGY/EGAA035
Abstract: High-pressure experiments were performed to investigate the effectiveness, rate and mechanism of carbonation of serpentinites by a carbon-saturated COH fluid at 1·5–2·5 GPa and 375–700 °C. This allows a better understanding of the fate and redistribution of slab-derived carbonic fluids when they react with the partially hydrated mantle within and above the subducting slab under pressure and temperature conditions corresponding to the forearc mantle. Interactions between carbon-saturated CO2–H2O–CH4 fluids and serpentinite were investigated using natural serpentinite cylinders with natural grain sizes and shapes in piston-cylinder experiments. The volatile composition of post-run fluids was quantified by gas chromatography. Solid phases were examined by Raman spectroscopy, electron microscopy and laser ablation inductively coupled plasma mass spectrometry. Textures, porosity and phase abundances of recovered rock cores were visualized and quantified by three-dimensional, high-resolution computed tomography. We find that carbonation of serpentinites is efficient at sequestering CO2 from the interacting fluid into newly formed magnesite. Time-series experiments demonstrate that carbonation is completed within ∼96 h at 2 GPa and 600 °C. With decreasing CO2,aq antigorite is replaced first by magnesite + quartz followed by magnesite + talc + chlorite in distinct, metasomatic fronts. Above antigorite stability magnesite + enstatite + talc + chlorite occur additionally. The formation of fluid-permeable reaction zones enhances the reaction rate and efficiency of carbonation. Carbonation probably occurs via an interface-coupled replacement process, whereby interconnected porosity is present within reaction zones after the experiment. Consequently, carbonation of serpentinites is self-promoting and efficient even if fluid flow is channelized into veins. We conclude that significant amounts of carbonates may accumulate, over time, in the hydrated forearc mantle.
Publisher: Elsevier BV
Date: 08-2018
Publisher: Elsevier BV
Date: 10-2020
Location: Germany
Location: Australia
No related grants have been discovered for Melanie Jutta Sieber.