Pub Date : 2024-04-04DOI: 10.1007/s00410-024-02110-7
Maria A. Dias, Ralf Dohmen
We have measured the dependence of the Fe–Mg interdiffusion coefficient, DFe-Mg, on the ferrosilite component in orthopyroxene, which so far has not been experimentally calibrated. Diffusion couples, consisting of approximately 1 µm thin-films were deposited by pulsed laser ablation on orthopyroxene crystals of En91Fs9 composition. Diffusion experiments were carried out at atmospheric pressure in vertical gas mixing furnaces (CO-CO2) at temperatures between 950 and 1100 °C at constant fO2 = 10–7 Pa. Using a focused ion beam-scanning electron microscope (FIB-SEM), FIB-foils were cut from diffusion couples before and after annealing. Diffusion profiles were extracted by using combined backscattered electron (BSE) imaging and energy dispersive X-ray (EDXS) mapping on FIB-foils which allowed to resolve concentration gradients within 20 nm. The microstructure of the diffusion experiments was investigated using transmission electron microscopy (TEM). Using this method, we obtained the first experimentally determined data on the dependence of DFe-Mg on the ferrosilite content in orthopyroxene at different temperatures, appearing to increase with increasing a temperature. For the temperature range (950 – 1100 °C), log fO2 = -7 Pa, along [001] in the composition Fs9, the log DFe-Mg yields the following Arrhenius equation:
The effect of XFe on DFe-Mg, given by (D(X_{Fe} ) = D(X_{Fe} = 0.09) cdot {10}^{m (X_{Fe} - 0.09)},) can be calculated by the following parameterization where m follows a linear regression of m on temperature:
$$m = - 2.711 cdot 10^4 /T(K) + 23.5408$$
By considering the DFe-Mg dependence on XFe, the timescales of natural processes obtained from modelling the compositional zoning of natural crystal may considerably differ from previously estimated timescales.
{"title":"Experimental determination of Fe–Mg interdiffusion in orthopyroxene as a function of Fe content","authors":"Maria A. Dias, Ralf Dohmen","doi":"10.1007/s00410-024-02110-7","DOIUrl":"https://doi.org/10.1007/s00410-024-02110-7","url":null,"abstract":"<p>We have measured the dependence of the Fe–Mg interdiffusion coefficient, <i>D</i><sub>Fe-Mg</sub>, on the ferrosilite component in orthopyroxene, which so far has not been experimentally calibrated. Diffusion couples, consisting of approximately 1 µm thin-films were deposited by pulsed laser ablation on orthopyroxene crystals of En<sub>91</sub>Fs<sub>9</sub> composition. Diffusion experiments were carried out at atmospheric pressure in vertical gas mixing furnaces (CO-CO<sub>2</sub>) at temperatures between 950 and 1100 °C at constant <i>f</i>O<sub>2</sub> = 10<sup>–7</sup> Pa. Using a focused ion beam-scanning electron microscope (FIB-SEM), FIB-foils were cut from diffusion couples before and after annealing. Diffusion profiles were extracted by using combined backscattered electron (BSE) imaging and energy dispersive X-ray (EDXS) mapping on FIB-foils which allowed to resolve concentration gradients within 20 nm. The microstructure of the diffusion experiments was investigated using transmission electron microscopy (TEM). Using this method, we obtained the first experimentally determined data on the dependence of <i>D</i><sub>Fe-Mg</sub> on the ferrosilite content in orthopyroxene at different temperatures, appearing to increase with increasing a temperature. For the temperature range (950 – 1100 °C), log <i>f</i>O<sub>2</sub> = -7 Pa, along [001] in the composition Fs9, the log <i>D</i><sub>Fe-Mg</sub> yields the following Arrhenius equation:</p><span>$$D_{Fe - Mg} [m^2 /s] = 3.8 cdot 10^{ - 9} exp [ - 261.07 pm 24[kJ/mol]/(R/T[K])]$$</span><p>The effect of <i>X</i><sub>Fe</sub> on <i>D</i><sub>Fe-Mg,</sub> given by <span>(D(X_{Fe} ) = D(X_{Fe} = 0.09) cdot {10}^{m (X_{Fe} - 0.09)},)</span> can be calculated by the following parameterization where <i>m</i> follows a linear regression of <i>m</i> on temperature: </p><span>$$m = - 2.711 cdot 10^4 /T(K) + 23.5408$$</span><p>By considering the <i>D</i><sub>Fe-Mg</sub> dependence on <i>X</i><sub>Fe</sub>, the timescales of natural processes obtained from modelling the compositional zoning of natural crystal may considerably differ from previously estimated timescales.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140562151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-04DOI: 10.1007/s00410-024-02128-x
Ryan M. Currier, Tushar Mittal, Paulo J. Hidalgo
Rock textures observed via thin section are skewed from their true 3D nature. This is due to various cut effects—artifacts introduced due to the lower dimensional nature of the thin section relative to the rock. These cut effects can be corrected, and several methods have been developed to invert crystal shape and crystal size, but with each process performed separately and sequentially. With the ongoing adoption of electron backscatter diffraction (EBSD) by petrologists, an additional data stream has now become available: the 3D orientation of 2D grain sections. For EBSD analysis, no stereological corrections are typically applied for interpreting the data. This study tests whether this orientational information is skewed due to a fabric cut effect. We test this by numerically generating synthetic crystal datasets representative of several crystal shapes and population sizes. We find that EBSD orientational data has a fabric cut effect since crystals oriented with long axes perpendicular to the thin section are more likely to be sampled compared to those with long axes oriented parallel to it. This effect must be accounted for to interpret the true 3D fabric accurately. Towards this end, we develop two new tools for working with EBSD-derived fabric: (1) a simple first-order test for determining if a measured fabric exceeds that of the fabric cut effect, and (2) a method of inverting cut fabrics that provides robust error estimations. We demonstrate the applicability and accuracy of these methods using a range of synthetic examples and a natural sample. With these newly developed tools, there is clear potential for a new textural toolkit framework, to further our ability to correct for the various cut effects while also providing accurate uncertainty estimates.
{"title":"Towards an integrated texture toolkit, 1: unveiling the complex relationship between crystal shape and fabric in EBSD data","authors":"Ryan M. Currier, Tushar Mittal, Paulo J. Hidalgo","doi":"10.1007/s00410-024-02128-x","DOIUrl":"https://doi.org/10.1007/s00410-024-02128-x","url":null,"abstract":"<p>Rock textures observed via thin section are skewed from their true 3D nature. This is due to various cut effects—artifacts introduced due to the lower dimensional nature of the thin section relative to the rock. These cut effects can be corrected, and several methods have been developed to invert crystal shape and crystal size, but with each process performed separately and sequentially. With the ongoing adoption of electron backscatter diffraction (EBSD) by petrologists, an additional data stream has now become available: the 3D orientation of 2D grain sections. For EBSD analysis, no stereological corrections are typically applied for interpreting the data. This study tests whether this orientational information is skewed due to a fabric cut effect. We test this by numerically generating synthetic crystal datasets representative of several crystal shapes and population sizes. We find that EBSD orientational data has a fabric cut effect since crystals oriented with long axes perpendicular to the thin section are more likely to be sampled compared to those with long axes oriented parallel to it. This effect must be accounted for to interpret the true 3D fabric accurately. Towards this end, we develop two new tools for working with EBSD-derived fabric: (1) a simple first-order test for determining if a measured fabric exceeds that of the fabric cut effect, and (2) a method of inverting cut fabrics that provides robust error estimations. We demonstrate the applicability and accuracy of these methods using a range of synthetic examples and a natural sample. With these newly developed tools, there is clear potential for a new textural toolkit framework, to further our ability to correct for the various cut effects while also providing accurate uncertainty estimates.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140562153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1007/s00410-024-02115-2
Emanuel Giovanini, Kenneth S. Befus, Juan E. Otamendi, Eber Cristofolini, Tomas Guerreiro, Miguel Cisneros
We applied elastic thermobarometry on garnet-bearing migmatites along two transects through the crustal section at Sierra Valle Fértil-La Huerta, Argentina. We performed quartz-in-garnet barometry and zircon-in-garnet thermometry on metapelites from different paleo-depths across the crustal section. Our work recovers entrapment pressures ranging from 240 to 1330 MPa and entrapment temperatures between 691 and 1574 °C. The entrapment conditions are broadly consistent with anticipated pressures and temperatures along the crustal section derived previously using conventional, thermodynamic thermobarometers. The quartz-in-garnet barometer reproduces those conventionally established entrapment conditions when samples only experienced conditions within the alpha-quartz stability field. Raman-derived pressures for samples that experienced beta-quartz reference conditions are commonly much higher than those established by conventional barometry. Samples that preserve compressive (positive) residual pressures best reproduce reference entrapment pressures. Entrapment temperatures show high variability and overestimation of temperature conditions compared to conventional results. These results indicate elastic thermobarometry over- or under-estimates crystallization conditions in rocks crystallized at high temperatures, as is common in the Famatinian Arc deep-crust. We suggest that modeling quartz behavior across the alpha–beta transition may present challenges, as does shape maturation, viscous deformation, and radiation damage in zircon.
我们在阿根廷 Sierra Valle Fértil-La Huerta 地壳断面的两个横断面上对含石榴石的伟晶岩进行了弹性测温。我们对来自整个地壳断面不同古深度的偏闪长岩进行了石英-石榴石气压测量和锆石-石榴石温度测量。我们的工作恢复了240至1330兆帕的夹层压力和691至1574摄氏度的夹层温度。夹带条件与之前使用传统热力学温度计得出的地壳断面预期压力和温度基本一致。当样品只经历α-石英稳定场内的条件时,石英-石榴石气压计再现了这些传统确定的夹带条件。对于经历过β-石英参考条件的样品,拉曼得出的压力通常比传统气压计确定的压力高得多。保持压缩(正)残余压力的样品最能再现参考夹带压力。与传统结果相比,夹带温度显示出较高的可变性和对温度条件的高估。这些结果表明,弹性测温法高估或低估了在高温下结晶的岩石的结晶条件,这在法马弧深地壳中很常见。我们认为,模拟石英在α-β转变过程中的行为可能会带来挑战,锆石的形状成熟、粘性变形和辐射损伤也是如此。
{"title":"Elastic thermobarometry on metapelites across the crustal section of the Famatinian Arc, Argentina","authors":"Emanuel Giovanini, Kenneth S. Befus, Juan E. Otamendi, Eber Cristofolini, Tomas Guerreiro, Miguel Cisneros","doi":"10.1007/s00410-024-02115-2","DOIUrl":"https://doi.org/10.1007/s00410-024-02115-2","url":null,"abstract":"<p>We applied elastic thermobarometry on garnet-bearing migmatites along two transects through the crustal section at Sierra Valle Fértil-La Huerta, Argentina. We performed quartz-in-garnet barometry and zircon-in-garnet thermometry on metapelites from different paleo-depths across the crustal section. Our work recovers entrapment pressures ranging from 240 to 1330 MPa and entrapment temperatures between 691 and 1574 °C. The entrapment conditions are broadly consistent with anticipated pressures and temperatures along the crustal section derived previously using conventional, thermodynamic thermobarometers. The quartz-in-garnet barometer reproduces those conventionally established entrapment conditions when samples only experienced conditions within the alpha-quartz stability field. Raman-derived pressures for samples that experienced beta-quartz reference conditions are commonly much higher than those established by conventional barometry. Samples that preserve compressive (positive) residual pressures best reproduce reference entrapment pressures. Entrapment temperatures show high variability and overestimation of temperature conditions compared to conventional results. These results indicate elastic thermobarometry over- or under-estimates crystallization conditions in rocks crystallized at high temperatures, as is common in the Famatinian Arc deep-crust. We suggest that modeling quartz behavior across the alpha–beta transition may present challenges, as does shape maturation, viscous deformation, and radiation damage in zircon.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140562013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-29DOI: 10.1007/s00410-024-02123-2
H. Rezeau, O. Jagoutz, Patrick Beaudry, B. Klein, G. Izon, Shuhei Ono
{"title":"Lower crustal assimilation revealed by sulfur isotope systematics of the Bear Valley Intrusive Suite, southern Sierra Nevada Batholith, California, USA","authors":"H. Rezeau, O. Jagoutz, Patrick Beaudry, B. Klein, G. Izon, Shuhei Ono","doi":"10.1007/s00410-024-02123-2","DOIUrl":"https://doi.org/10.1007/s00410-024-02123-2","url":null,"abstract":"","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140366383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-25DOI: 10.1007/s00410-024-02114-3
Xianyu Xue, Masami Kanzaki, Abd-Erraouf Djirar, Chris Gregson
We performed 1H and 29Si NMR and infrared measurements, and first-principles calculations to clarify the nature of OH defects in MgSiO3 orthoenstatite. An orthoenstatite sample synthesized at 7 GPa and 1200 °C from a composition of MgSiO3 + 0.1 wt% H2O yielded two 1H MAS NMR peaks near 5.9 and 7.6 ppm that are correlated in 2D NMR spectra, and two infrared bands near 3361 and 3066 cm− 1 that correspond to the previously reported A3 and A4 bands. The first-principles calculations confirmed that they are due to a pair of protons in a Mg (M2) vacancy. The previously reported A1 and A2 infrared bands near 3687 and 3592 cm− 1 for orthoenstatite synthesized at low silica activities were confirmed to arise from four protons in a SiB vacancy. The latter is predicted to give two additional OH stretching bands associated with two strongly hydrogen-bonded O3b-H bonds with frequencies below the spectral range reported thus far. The previously reported infrared absorption coefficients were thus revised to account for the undetected bands. 1H NMR may be used to quantitatively detect all four protons (expected at 1–12 ppm). Other mantle minerals should also be examined for potentially overlooked OH defects with strong hydrogen bonding.
{"title":"Incorporation mechanisms and infrared absorption coefficients of water in MgSiO3 orthoenstatite clarified via comprehensive NMR and vibrational spectroscopic measurements, and first-principles calculations","authors":"Xianyu Xue, Masami Kanzaki, Abd-Erraouf Djirar, Chris Gregson","doi":"10.1007/s00410-024-02114-3","DOIUrl":"https://doi.org/10.1007/s00410-024-02114-3","url":null,"abstract":"<p>We performed <sup>1</sup>H and <sup>29</sup>Si NMR and infrared measurements, and first-principles calculations to clarify the nature of OH defects in MgSiO<sub>3</sub> orthoenstatite. An orthoenstatite sample synthesized at 7 GPa and 1200 °C from a composition of MgSiO<sub>3</sub> + 0.1 wt% H<sub>2</sub>O yielded two <sup>1</sup>H MAS NMR peaks near 5.9 and 7.6 ppm that are correlated in 2D NMR spectra, and two infrared bands near 3361 and 3066 cm<sup>− 1</sup> that correspond to the previously reported A3 and A4 bands. The first-principles calculations confirmed that they are due to a pair of protons in a Mg (M2) vacancy. The previously reported A1 and A2 infrared bands near 3687 and 3592 cm<sup>− 1</sup> for orthoenstatite synthesized at low silica activities were confirmed to arise from four protons in a SiB vacancy. The latter is predicted to give two additional OH stretching bands associated with two strongly hydrogen-bonded O3b-H bonds with frequencies below the spectral range reported thus far. The previously reported infrared absorption coefficients were thus revised to account for the undetected bands. <sup>1</sup>H NMR may be used to quantitatively detect all four protons (expected at 1–12 ppm). Other mantle minerals should also be examined for potentially overlooked OH defects with strong hydrogen bonding.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140298347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-19DOI: 10.1007/s00410-024-02106-3
A. Cravinho, D. Rosa, J. M. R. S. Relvas, A. R. Solá, I. Pereira, J.-L. Paquette, M. L. Borba, C. C. G. Tassinari, D. Chew, F. Drakou, K. Breiter, V. Araujo
This work investigates the relationships between partial melting, melt extraction, pluton growth and silicic volcanism in garnet-bearing felsic volcanic rocks that were extruded in the Iberian Pyrite Belt, at ca. 345 Ma. The garnets are of peritectic origin, displaying textural and chemical features of disequilibrium crystallization during partial melting reactions involving biotite at high temperatures (up to 870 °C) in the middle-lower crust. Major element composition suggests compositional equilibrium with the entrained and pinitized peritectic cordierite, but reveals some subsequent homogenization by diffusion. Trace element maps and spot analyses of garnet show, nonetheless, significant trace element variations, reflecting biotite and Y-REE-P-rich accessory phase breakdown during partial melting reactions. Peritectic garnet and cordierite growth resulted in the preservation of Th- and Y-rich prograde suprasolidus monazite, which constrains the timing of partial melting of the metapelitic protolith at ca. 356.8 ± 2.4 Ma. The zircon cargo further shows that a significant amount of zircon crystals from previously crystallized felsic melts were also remobilized and erupted. These were likely stored in an upper crustal pluton that grew episodically since ca. 390 Ma during voluminous melt generation periods within the middle to lower crust, which also resulted in voluminous volcanism. The geochemical trends of the felsic volcanic rocks reflect the entrainment of xenoliths of peritectic garnet, cordierite and feldspar, and as such, the garnet-bearing felsic volcanic rocks represent an erupted mixture of a lower-temperature (ca. 770 °C) silicic melt and autocrysts, and peritectic phases and zircon crystals from previously crystallized and stored felsic melts.
这项研究调查了约 345 Ma 时在伊比利亚黄铁矿带挤出的含石榴石的长英质火山岩中部分熔化、熔体萃取、柱状生长和硅质火山活动之间的关系。345 Ma。这些石榴石源于围岩,在中下地壳的高温(高达 870 °C)条件下,在涉及斜长石的部分熔融反应过程中显示出不平衡结晶的纹理和化学特征。主要元素成分表明,与夹杂和针状化的围岩堇青石之间存在成分平衡,但也显示出随后通过扩散发生了一些同质化。不过,石榴石的微量元素分布图和斑点分析表明,微量元素变化很大,反映了部分熔融反应期间生物橄榄石和富含 Y-REE-P 的附属相的分解。围岩石榴石和堇青石的生长导致保留了富含Th和Y的原生超基性独居石,从而确定了偏闪长岩原岩部分熔融的时间约为356.8 ± 2.4小时。356.8 ± 2.4 Ma。锆石货物进一步表明,大量来自先前结晶的长岩熔体的锆石晶体也被重新动员并喷发出来。这些锆石晶体很可能储存在地壳上部的岩浆中。在中下地壳大量熔体生成期间,这些熔体很可能储存在上地壳的一个柱体中,该柱体自约 390 Ma 以来在中下地壳大量熔体生成期间偶发性地生长,这也导致了大量的火山活动。长英质火山岩的地球化学趋势反映了透辉石榴榴石、堇青石和长石等异长岩的夹杂,因此,含榴榴石的长英质火山岩是低温(约 770 °C)硅质熔体和自晶,以及来自先前结晶和储存的长英质熔体的透辉石相和锆石晶体的喷发混合物。
{"title":"From source to surface: clues from garnet-bearing Carboniferous silicic volcanic rocks, Iberian Pyrite Belt, Portugal","authors":"A. Cravinho, D. Rosa, J. M. R. S. Relvas, A. R. Solá, I. Pereira, J.-L. Paquette, M. L. Borba, C. C. G. Tassinari, D. Chew, F. Drakou, K. Breiter, V. Araujo","doi":"10.1007/s00410-024-02106-3","DOIUrl":"https://doi.org/10.1007/s00410-024-02106-3","url":null,"abstract":"<p>This work investigates the relationships between partial melting, melt extraction, pluton growth and silicic volcanism in garnet-bearing felsic volcanic rocks that were extruded in the Iberian Pyrite Belt, at ca<i>.</i> 345 Ma. The garnets are of peritectic origin, displaying textural and chemical features of disequilibrium crystallization during partial melting reactions involving biotite at high temperatures (up to 870 °C) in the middle-lower crust. Major element composition suggests compositional equilibrium with the entrained and pinitized peritectic cordierite, but reveals some subsequent homogenization by diffusion. Trace element maps and spot analyses of garnet show, nonetheless, significant trace element variations, reflecting biotite and Y-REE-P-rich accessory phase breakdown during partial melting reactions. Peritectic garnet and cordierite growth resulted in the preservation of Th- and Y-rich prograde suprasolidus monazite, which constrains the timing of partial melting of the metapelitic protolith at <i>ca.</i> 356.8 ± 2.4 Ma. The zircon cargo further shows that a significant amount of zircon crystals from previously crystallized felsic melts were also remobilized and erupted. These were likely stored in an upper crustal pluton that grew episodically since ca<i>.</i> 390 Ma during voluminous melt generation periods within the middle to lower crust, which also resulted in voluminous volcanism. The geochemical trends of the felsic volcanic rocks reflect the entrainment of xenoliths of peritectic garnet, cordierite and feldspar, and as such, the garnet-bearing felsic volcanic rocks represent an erupted mixture of a lower-temperature (<i>ca.</i> 770 °C) silicic melt and autocrysts, and peritectic phases and zircon crystals from previously crystallized and stored felsic melts.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140172957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-19DOI: 10.1007/s00410-024-02108-1
Jakub Haifler, Jana Kotková, Renata Čopjaková
Orogenic peridotites in the crystalline basement of the northwestern Bohemian Massif contain multiphase solid inclusions (MSI), which are interpreted to be crystallisation products of trapped former carbonate–silicate melts metasomatizing their host rocks. We applied conventional thermobarometry and forward thermodynamic modelling to constrain the P–T evolution ranging from the peak metamorphic conditions of the investigated harzburgite and lherzolite, through entrapment of the melts in the outer parts of garnets, to the (re)-equilibration of the MSI assemblages. The peak conditions of c. 1100 °C/4.5–5.5 GPa are recorded by garnet cores and large pyroxene porphyroclasts. The melt entrapment, during which garnet outer parts grew, was associated with influx of the metasomatizing liquids and probably took place during the early stage of the exhumation. Thermodynamic model of amphibole-free MSI assemblage comprising kinoshitalite/Ba-rich phlogopite (approximated by phlogopite in the model), dolomite, magnesite, clinopyroxene, orthopyroxene, garnet and chromite provided robust estimate of P and T of its (re)-equilibration, c. 900–1000 °C, 1.8–2.2 GPa. Furthermore, the lack of olivine reflects co-existence of COH fluid with high X(CO2) = CO2/(CO2 + H2O) ≥ 0.6. Models employing identical P–T–X(CO2) parameters successfully reproduced the other two amphibole-bearing assemblages observed. The modelled stability fields show perfect alignment with a characteristic isobaric segment of the solidus curve of carbonated peridotite. This co-incidence implies that the (re)-equilibration corresponds to the termination of the melt crystallisation once the near-isothermal exhumation path intersected the solidus. Decreased solubility of silicates at the carbonated peridotite “solidus ledge”, inferred from the published experimental data, as well as concentric textures of some MSI indicates sequential crystallisation from the early silicates to late dolomite. The carbonated “solidus ledge” is a relatively narrow boundary in the lithospheric mantle capable of an abrupt immobilisation of fluxing or transported carbonated melts. The investigated rocks are estimated to store approximately 0.02 kg C/m3 (or 6 ppm C) occurring as carbonates in the MSI.
{"title":"Crystallisation of trapped carbonate–silicate melts terminating at the carbonated solidus ledge: a record of carbon immobilisation mechanism in the lithospheric mantle","authors":"Jakub Haifler, Jana Kotková, Renata Čopjaková","doi":"10.1007/s00410-024-02108-1","DOIUrl":"https://doi.org/10.1007/s00410-024-02108-1","url":null,"abstract":"<p>Orogenic peridotites in the crystalline basement of the northwestern Bohemian Massif contain multiphase solid inclusions (MSI), which are interpreted to be crystallisation products of trapped former carbonate–silicate melts metasomatizing their host rocks. We applied conventional thermobarometry and forward thermodynamic modelling to constrain the P–T evolution ranging from the peak metamorphic conditions of the investigated harzburgite and lherzolite, through entrapment of the melts in the outer parts of garnets, to the (re)-equilibration of the MSI assemblages. The peak conditions of c. 1100 °C/4.5–5.5 GPa are recorded by garnet cores and large pyroxene porphyroclasts. The melt entrapment, during which garnet outer parts grew, was associated with influx of the metasomatizing liquids and probably took place during the early stage of the exhumation. Thermodynamic model of amphibole-free MSI assemblage comprising <i>kinoshitalite/Ba-rich phlogopite</i> (approximated by <i>phlogopite</i> in the model), <i>dolomite, magnesite, clinopyroxene, orthopyroxene, garnet</i> and <i>chromite</i> provided robust estimate of P and T of its (re)-equilibration, c. 900–1000 °C, 1.8–2.2 GPa. Furthermore, the lack of olivine reflects co-existence of COH fluid with high X(CO<sub>2</sub>) = CO<sub>2</sub>/(CO<sub>2</sub> + H<sub>2</sub>O) ≥ 0.6. Models employing identical P–T–X(CO<sub>2</sub>) parameters successfully reproduced the other two amphibole-bearing assemblages observed. The modelled stability fields show perfect alignment with a characteristic isobaric segment of the solidus curve of carbonated peridotite. This co-incidence implies that the (re)-equilibration corresponds to the termination of the melt crystallisation once the near-isothermal exhumation path intersected the solidus. Decreased solubility of silicates at the carbonated peridotite “solidus ledge”, inferred from the published experimental data, as well as concentric textures of some MSI indicates sequential crystallisation from the early silicates to late dolomite. The carbonated “solidus ledge” is a relatively narrow boundary in the lithospheric mantle capable of an abrupt immobilisation of fluxing or transported carbonated melts. The investigated rocks are estimated to store approximately 0.02 kg C/m<sup>3</sup> (or 6 ppm C) occurring as carbonates in the MSI.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140171625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-16DOI: 10.1007/s00410-024-02112-5
Guangyue Cao, Ying Tong, Xianchun Tang, Xiangdong Wang, Xiang Li, Lei Wang
Understanding the compositional heterogeneity of the deep mantle requires identifying the nature of recycled crustal materials in the sources of mantle-plume-related magmas. However, it is still unclear whether or not the deep mantle contains recycled carbonates from the Earth’s surface. In this study, we present comprehensive data on whole-rock high-precision zinc isotopes, as well as major- and trace-element geochemistry, and Sr–Nd–Pb isotopes of basalts on Hainan Island to examine the influence of recycled materials (particularly carbonates) on the mantle source heterogeneity of the Hainan mantle plume. The basalts have highly variable δ66Zn values ranging from 0.21‰ to 0.42‰. These variable Zn isotopic compositions cannot be accounted for by processes such as post-magmatic alteration and crustal contamination, or by fractional crystallization and partial melting; instead, they reflect mantle heterogeneity. Comparisons of the major- and trace-element compositions (e.g., CaO and TiO2 contents and Zn/Fe and Fe/Mn ratios), FC3MS and FCKANTMS peridotite and pyroxenite melting parameters, as well as pseudo-ternary projections of the primary Hainan basaltic magmas with experimental data suggest that the primary magmas were partial melts of silica-deficient pyroxenitic lithologies with peridotite residue. The heterogeneous geochemical and lithological compositions of the Hainan basalts indicate that recycled sedimentary carbonates and siliceous rocks were important constituents in their mantle source. Quantitative modeling reveals that the addition of 1–10% subducted sediments into the source of the Hainan basalts closely reproduces their Zn–Sr–Nd–Pb isotopic values. The source component with the heaviest Zn isotopic composition measured for the Hainan basalt samples could have contained more than 9% recycled carbonate. Our findings provide insights into the role of subducted materials to mantle heterogeneity and highlight the contribution of subducted sedimentary carbonates in the deep recycling of oceanic slabs, including—in the case of the Hainan mantle plume—recycled deep mantle (i.e., the mantle transition zone and lower mantle).
{"title":"Deep recycling of crustal materials by the Hainan mantle plume: evidence from Zn–Sr–Nd–Pb isotopes of Hainan Island basalts","authors":"Guangyue Cao, Ying Tong, Xianchun Tang, Xiangdong Wang, Xiang Li, Lei Wang","doi":"10.1007/s00410-024-02112-5","DOIUrl":"https://doi.org/10.1007/s00410-024-02112-5","url":null,"abstract":"<p>Understanding the compositional heterogeneity of the deep mantle requires identifying the nature of recycled crustal materials in the sources of mantle-plume-related magmas. However, it is still unclear whether or not the deep mantle contains recycled carbonates from the Earth’s surface. In this study, we present comprehensive data on whole-rock high-precision zinc isotopes, as well as major- and trace-element geochemistry, and Sr–Nd–Pb isotopes of basalts on Hainan Island to examine the influence of recycled materials (particularly carbonates) on the mantle source heterogeneity of the Hainan mantle plume. The basalts have highly variable δ<sup>66</sup>Zn values ranging from 0.21‰ to 0.42‰. These variable Zn isotopic compositions cannot be accounted for by processes such as post-magmatic alteration and crustal contamination, or by fractional crystallization and partial melting; instead, they reflect mantle heterogeneity. Comparisons of the major- and trace-element compositions (e.g., CaO and TiO<sub>2</sub> contents and Zn/Fe and Fe/Mn ratios), FC3MS and FCKANTMS peridotite and pyroxenite melting parameters, as well as pseudo-ternary projections of the primary Hainan basaltic magmas with experimental data suggest that the primary magmas were partial melts of silica-deficient pyroxenitic lithologies with peridotite residue. The heterogeneous geochemical and lithological compositions of the Hainan basalts indicate that recycled sedimentary carbonates and siliceous rocks were important constituents in their mantle source. Quantitative modeling reveals that the addition of 1–10% subducted sediments into the source of the Hainan basalts closely reproduces their Zn–Sr–Nd–Pb isotopic values. The source component with the heaviest Zn isotopic composition measured for the Hainan basalt samples could have contained more than 9% recycled carbonate. Our findings provide insights into the role of subducted materials to mantle heterogeneity and highlight the contribution of subducted sedimentary carbonates in the deep recycling of oceanic slabs, including—in the case of the Hainan mantle plume—recycled deep mantle (i.e., the mantle transition zone and lower mantle).</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140151891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-15DOI: 10.1007/s00410-024-02100-9
Frank S. Spear
A model is presented whereby metamorphic parageneses are governed by local, nano-scale reactions among adjacent phases along grain boundaries that are driven by local disequilibrium between the solid phases and the grain boundary composition. These reactions modify the grain boundary composition setting up compositional gradients that drive diffusion and change the grain boundary composition elsewhere in the rock, which drive local reactions in these locations. The process may be triggered by the nucleation of a new phase that is out of equilibrium with the existing assemblage and an example is presented based on the transformation of kyanite (Ky) to sillimanite (Sil). Model results reveal that a simple polymorphic transformation (Ky→Sil) can result in local reactions among all phases in the rock and some phases may grow in one locale and be consumed in another. An implication of these results is that interpretation of metamorphic parageneses based on growth or resorption and compositional changes of phases requires careful evaluation of nano-scale processes.
{"title":"A grain boundary model of metamorphic reaction","authors":"Frank S. Spear","doi":"10.1007/s00410-024-02100-9","DOIUrl":"https://doi.org/10.1007/s00410-024-02100-9","url":null,"abstract":"<p>A model is presented whereby metamorphic parageneses are governed by local, nano-scale reactions among adjacent phases along grain boundaries that are driven by local disequilibrium between the solid phases and the grain boundary composition. These reactions modify the grain boundary composition setting up compositional gradients that drive diffusion and change the grain boundary composition elsewhere in the rock, which drive local reactions in these locations. The process may be triggered by the nucleation of a new phase that is out of equilibrium with the existing assemblage and an example is presented based on the transformation of kyanite (Ky) to sillimanite (Sil). Model results reveal that a simple polymorphic transformation (Ky→Sil) can result in local reactions among all phases in the rock and some phases may grow in one locale and be consumed in another. An implication of these results is that interpretation of metamorphic parageneses based on growth or resorption and compositional changes of phases requires careful evaluation of nano-scale processes.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140152073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-13DOI: 10.1007/s00410-024-02097-1
Abstract
U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb3O4, and cerussite (PbCO3) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present.
{"title":"Microstructural and isotopic analysis of shocked monazite from the Hiawatha impact structure: development of porosity and its utility in dating impact craters","authors":"","doi":"10.1007/s00410-024-02097-1","DOIUrl":"https://doi.org/10.1007/s00410-024-02097-1","url":null,"abstract":"<h3>Abstract</h3> <p>U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb<sub>3</sub>O<sub>4</sub>, and cerussite (PbCO<sub>3</sub>) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present.</p>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140129918","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}