Thermobarometry of Diamond Inclusions: Evidence Mantle Evolution beneath Siberian Craton and Archean Cratons Worldwide.

Thermobarometric calculations for mineral inclusions in diamonds provide a systematic comparison of PTXFO2 conditions for different cratons worldwide, using a database of 4440 mineral EPMA analyses. Beneath all cratons, the cold branch of the mantle geotherm (35-32 mWm−2) relates to the sub-Ca garnets and rarely omphacitic diamond inclusions, referring to major continental growth events in Archean. High-temperature plume-related geotherms are common in Proterozoic kimberlites such as Premier, Mesozoic – Roberts Victor etc. and are common in Slave and Siberian cratons. In mobile belts: Limpopo, Magondi, Ural Ural, Khapchan belts and in the marginal parts of cratons like Kimberly Australia pyroxenitic and eclogitic pyroxenes and garnets prevail. The pyropes in the mobile belts are more Fe- and Ca-rich, in central parts of cratons, the peridotitic associations with sub- Ca pyropes prevail. The accretionary complexes like Khapchan and Magondi belts a thick eclogite-pyroxenite lens is highly diamondiferous. Comparison by minerals shows that the PT estimates for clinopyroxenes and orthopyroxene from peridotites and eclogites are representing mainly the middle part of the sub-lithospheric mantle while garnets gives more high-pressure estimates. refer to eclogites and reflect the processes of the differentiation during migration of partial melts. This produces the trends of joint decreasing Mg’ and pressures. The PT for the chromites reflect conditions just above the lithosphere-asthenosphere boundary and mainly were formed due to interaction with the hydrous plume protokimberlite melts. Archean diamond inclusions from Wawa province Canada are represented by Ca-enrich pyropes giving low-temperature conditions. Inclusions from younger kimberlites in Superior and Slave (and Siberian and East European ) cratons show complex high-temperature geotherms due to plumes influence. Peridotite garnets beneath the Amazonian craton indicate complex layering in the lithosphere base and a pyroxene layer in the middle part of SCLM. Diamond inclusions from the Kimberley craton of Australia show the greatest variations in the temperatures and composition.

Analytical solution for residual stress and strain preserved in anisotropic inclusion entrapped in an isotropic host

Raman elastic thermobarometry has recently been applied in many petrological studies to recover the pressure and temperature (P–T) conditions of mineral inclusion entrapment. Existing modelling methods in petrology either adopt an assumption of a spherical, isotropic inclusion embedded in an isotropic, infinite host or use numerical techniques such as the finite-element method to simulate the residual stress and strain state preserved in the non-spherical anisotropic inclusions. Here, we use the Eshelby solution to develop an analytical framework for calculating the residual stress and strain state of an elastically anisotropic, ellipsoidal inclusion in an infinite, isotropic host. The analytical solution is applicable to any class of inclusion symmetry and an arbitrary inclusion aspect ratio. Explicit expressions are derived for some symmetry classes, including tetragonal, hexagonal, and trigonal. The effect of changing the aspect ratio on residual stress is investigated, including quartz, zircon, rutile, apatite, and diamond inclusions in garnet host. Quartz is demonstrated to be the least affected, while rutile is the most affected. For prolate quartz inclusion (c axis longer than a axis), the effect of varying the aspect ratio on Raman shift is demonstrated to be insignificant. When c/a=5, only ca. 0.3 cm−1 wavenumber variation is induced as compared to the spherical inclusion shape. For oblate quartz inclusions, the effect is more significant, when c/a=0.5, ca. 0.8 cm−1 wavenumber variation for the 464 cm−1 band is induced compared to the reference spherical inclusion case. We also show that it is possible to fit an effective ellipsoid to obtain a proxy for the averaged residual stress or strain within a faceted inclusion. The difference between the volumetrically averaged stress of a faceted inclusion and the analytically calculated stress from the best-fitted effective ellipsoid is calculated to obtain the root-mean-square deviation (RMSD) for quartz, zircon, rutile, apatite, and diamond inclusions in garnet host. Based on the results of 500 randomly generated (a wide range of aspect ratio and random crystallographic orientation) faceted inclusions, we show that the volumetrically averaged stress serves as an excellent stress measure and the associated RMSD is less than 2 %, except for diamond, which has a systematically higher RMSD (ca. 8 %). This expands the applicability of the analytical solution for any arbitrary inclusion shape in practical Raman measurements.

Reversal of carbonate-silicate cation exchange in cold slabs in Earth’s lower mantle

The stable forms of carbon in Earth’s deep interior control storage and fluxes of carbon through the planet over geologic time, impacting the surface climate as well as carrying records of geologic processes in the form of diamond inclusions. However, current estimates of the distribution of carbon in Earth’s mantle are uncertain, due in part to limited understanding of the fate of carbonates through subduction, the main mechanism that transports carbon from Earth’s surface to its interior. Oxidized carbon carried by subduction has been found to reside in MgCO3 throughout much of the mantle. Experiments in this study demonstrate that at deep mantle conditions MgCO3 reacts with silicates to form CaCO3. In combination with previous work indicating that CaCO3 is more stable than MgCO3 under reducing conditions of Earth’s lowermost mantle, these observations allow us to predict that the signature of surface carbon reaching Earth’s lowermost mantle may include CaCO3.

Varieties of eclogites and their positions in the cratonic mantle lithosphere revealed by Jd-Di thermobarometry and trace element geochemistry

<p>The PT conditions and position of different groups of eclogites in the subcratonic lithospheric mantle (SCLM) worldwide has been established using clinopyroxene Jd-Di thermobarometry for different cratons and kimberlite localities. Beneath Siberia, Fe-eclogites found within the 3.0-4.0 GPa  and  were probably formed in Early Archean times forming the base of the lithosphere. In the Middle and Late Archean, eclogites were melted during subduction creating restite and cumulates from partial melts traced ascending channels.</p><p>High-Mg eclogites (partial melts or arc cumulates) are related to low-T geotherms. Melt-metasomatized eclogites trace a high-T geotherm and are often close to the middle part of the mantle lithosphere. Abundant eclogitic diamond inclusions from Siberia also mostly belong to the middle part of the lithosphere. </p><p>Ca-rich eclogites from Precambrian kimberlites of India are located in the middle lithospheric mantle whereas those entrained in Phanerozoic magmas are derived from the lithosphere base. In the Wyoming craton, kimberlites carry eclogite xenoliths captured from the 4.0-2.5 GPa interval.  In mantle lithosphere sampled by Proterozoic kimberlites, Ca-rich eclogites and grospydites occur in the 4.0-5.0 GPa interval. South Africa HT eclogite and diamond inclusions from the Proterozoic Premier kimberlites are derived from the deeper part of the mantle lithosphere and trace a high-T geotherm at depths of 7.0-4.0 GPa showing an increase in Fe upwards in the mantle section. Similar trends are common beneath the Catoca cluster kimberlites in Angola.</p><p>Mantle eclogites have clinopyroxenes and garnet trace element patterns with opposite inclinations determined by KDs with melts. Flatter and bell-like REE patterns with Eu anomalies? HFSE troughs and U, Pb peaks are common for MORB-type basaltic eclogites. High-Mg eclogites show less fractionated incompatible element patterns.  LILE-enrichments and HFSE troughs are typical for kyanite-bearing eclogites. Clinopyroxenes from diamond-bearing eclogites show lower REE and troughs in Nb and Zr, peaks in Pb and U concentrations compared to barren eclogites with round smooth trace element patterns and small depressions in Pb and Ba.</p><p>Support: RFBR 19-05-00788,  Russian Ministry of Education and Science</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.2c9ebbff3c0067455141161/sdaolpUECMynit/12UGE&app=m&a=0&c=4b235af5b7a8029fc48da92cba3afd9d&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.d13207104c0065755141161/sdaolpUECMynit/12UGE&app=m&a=0&c=d8f9503af82277872a4263e84ff9e0cf&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.6b7fb9204c0063955141161/sdaolpUECMynit/12UGE&app=m&a=0&c=6b87575d150326ed00a773ccd740ef07&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.d6683a304c0060165141161/sdaolpUECMynit/12UGE&app=m&a=0&c=d034421517782917a447efa1c07c6281&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.336759404c0065265141161/sdaolpUECMynit/12UGE&app=m&a=0&c=b4a9255ae696984c788c9868caf7be97&ct=x&pn=gnp.elif&d=1" alt=""></p>

Mantle evolution beneath Siberian and Archean cratons worldwide: evidence from thermobarometry of diamond inclusions

<p>Thermobarometric calculations for diamond inclusions allowed systematically compare the pressure-temperature, fO<sub>2</sub> conditions in the mantle beneath different cratons worldwide. Beneath Siberia, Kaapvaal, and other cratons, the cold geotherm branch, reconstructed using sub-Ca garnets and eclogitic diamond inclusions relates to a major event of continental growth. Colder geotherms (32 mWm<sup>-2</sup>) are related to early subduction. High-temperature plume-related geotherms are common for inclusions in Proterozoic kimberlites beneath Africa. In mobile belts such as Magondi, Ural and Limpopo belts, the amount of pyroxenitic and eclogitic garnets is greater than in the central cores of cratons where dunitic pyropes prevail. Beneath the Khapchan accretionary terrane in Siberia, eclogites are highly diamondiferous. In the mantle beneath Archean cratons, peridotite pyropes differ in CaO content. Depleted peridotitic and Fe-eclogitic diamond inclusions are abundant beneath the Zimbabwe craton, whereas beneath the Congo and West Africa, diamond inclusions yield higher temperatures. Beneath North American cratons, diamond-bearing eclogites are mainly Mg-type. In the Superior craton, Archean diamond inclusions from Wawa are Fe-, Ca-rich pyropes. The diamond inclusions of the Slave and Superior cratons give complex high-temperature plume-related geotherms. Beneath the Amazonian craton, peridotite garnets indicate complex layering at the base of the lithosphere and a pyroxene-rich layer in the middle. Fe-Mg eclogites from a high-temperature trend in which FeO increases with decreasing pressure. Diamond inclusions from the Kimberley craton of Australia show the greatest variations in temperature and composition. The  Eastern Europe craton and the Urals have greater amounts of eclogitic diamond inclusions and advective geotherms. Estimated pressure conditions lower than diamond stability field is due to exceeding pressures around magmatic system transferred by hydraulic forces from depth. </p><p>Support: RFBR 19-05-00788, Russian Ministry of Education and Science</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.da049dd8a90069875421161/sdaolpUECMynit/12UGE&app=m&a=0&c=bc51032afd75e05d7c9ddb145ed4953a&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.f989a4f8a90062185421161/sdaolpUECMynit/12UGE&app=m&a=0&c=2d7358755816c2ee4f19e2586bb081b0&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.c8c08309a90067285421161/sdaolpUECMynit/12UGE&app=m&a=0&c=934f08823572f27e82297ebde537172f&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.d92e0d19a90063585421161/sdaolpUECMynit/12UGE&app=m&a=0&c=70ef014588742491519d2b3cd2ded5fc&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.fc965d29a90069685421161/sdaolpUECMynit/12UGE&app=m&a=0&c=f4c5b7511a5379a41448d7bd48601f32&ct=x&pn=gnp.elif&d=1" alt=""></p>

The characteristics of Ib diamond crystals synthesized in a Fe–Ni–C system with different SiC contents

Silicon carbide (SiC) is a substance found in natural diamond inclusions. Analyzing the influence of SiC doping on the properties of synthetic diamonds is vital to understanding the growth mechanism...

Analytical solution for residual stress and strain preserved in anisotropic inclusion entrapped in isotropic host

Raman elastic thermobarometry has recently been applied in many petrological studies to recover the pressure-temperature (P-T) conditions of mineral inclusion entrapment. Existing modelling methods in petrology either adopt an assumption of a spherical, isotropic inclusion embedded in an isotropic, infinite host, or use numerical techniques such as finite element method to simulate the residual stress and strain state preserved in the non-spherical anisotropic inclusion. Here, we use the Eshelby solution to develop an analytical framework for calculating the residual stress and strain state of an elastically anisotropic, ellipsoidal inclusion in an infinite, isotropic host. The analytical solution is applicable to any class of inclusion symmetry and an arbitrary inclusion aspect ratio. Explicit expressions are derived for some symmetry classes including e.g. tetragonal, hexagonal and trigonal. The effect of changing the aspect ratio on residual stress is investigated including quartz, zircon, rutile, apatite and diamond inclusions in garnet host. Quartz is demonstrated to be the least affected, while rutile is the most affected. For prolate quartz inclusion (c-axis longer than a-axis), the effect of varying the aspect ratio on Raman shift is demonstrated to be insignificant. When c/a = 5, only ca. 0.3 cm−1 wavenumber variation is induced as compared to the spherical inclusion shape. For oblate quartz inclusions, the effect is more significant, when c/a = 0.5 ca. 0.8 cm−1 wavenumber variation for the 464 cm−1 band is induced compared to the reference spherical inclusion case. We also show that it is possible to fit an effective ellipsoid to obtain a proxy for the averaged residual stress/strain within faceted inclusion. The difference between the volumetrically averaged stress of a faceted inclusion and the analytically calculated stress from the best-fitted effective ellipsoid is calculated to obtain the root mean square deviation (RMSD) for quartz, zircon, rutile, apatite and diamond inclusions in garnet host. Based on the results of 500 randomly generated (a wide range of aspect ratio and random crystallographic orientation) faceted inclusion, we show that the volumetrically averaged stress serves as an excellent stress measure and the associated RMSD is less than 2 %, except for diamond with a systematically higher RMSD (ca. 8 %). This expands the applicability of the analytical solution for any arbitrary inclusion shape in practical Raman measurements.