Earth's evolving geodynamic regime recorded by titanium isotopes.

Earth's mantle has a two-layered structure, with the upper and lower mantle domains separated by a seismic discontinuity at about 660 km (refs. 1,2). The extent of mass transfer between these mantle domains throughout Earth's history is, however, poorly understood. Continental crust extraction results in Ti-stable isotopic fractionation, producing isotopically light melting residues3-7. Mantle recycling of these components can impart Ti isotope variability that is trackable in deep time. We report ultrahigh-precision 49Ti/47Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 billion years ago (Ga) and modern ocean island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052 ± 0.006‰ heavier than the modern upper mantle sampled by normal mid-ocean ridge basalts (N-MORBs). The 49Ti/47Ti ratio of Earth's upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between approximately 3.5 and 2.7 Ga, establishing that more continental crust was extracted during this epoch. The +0.052 ± 0.006‰ offset between BSE and N-MORBs requires that <30% of Earth's mantle equilibrated with recycled crustal material, implying limited mass exchange between the upper and lower mantle and, therefore, preservation of a primordial lower-mantle reservoir for most of Earth's geologic history. Modern OIBs record variable 49Ti/47Ti ratios ranging from chondritic to N-MORBs compositions, indicating continuing disruption of Earth's primordial mantle. Thus, modern-style plate tectonics with high mass transfer between the upper and lower mantle only represents a recent feature of Earth's history.

Silicon isotope constraints on terrestrial planet accretion.

Understanding the nature and origin of the precursor material to terrestrial planets is key to deciphering the mechanisms and timescales of planet formation1. Nucleosynthetic variability among rocky Solar System bodies can trace the composition of planetary building blocks2-5. Here we report the nucleosynthetic composition of silicon (µ30Si), the most abundant refractory planet-building element, in primitive and differentiated meteorites to identify terrestrial planet precursors. Inner Solar System differentiated bodies, including Mars, record µ30Si deficits of -11.0 ± 3.2 parts per million to -5.8 ± 3.0 parts per million whereas non-carbonaceous and carbonaceous chondrites show µ30Si excesses from 7.4 ± 4.3 parts per million to 32.8 ± 2.0 parts per million relative to Earth. This establishes that chondritic bodies are not planetary building blocks. Rather, material akin to early-formed differentiated asteroids must represent a major planetary constituent. The µ30Si values of asteroidal bodies correlate with their accretion ages, reflecting progressive admixing of a µ30Si-rich outer Solar System material to an initially µ30Si-poor inner disk. Mars' formation before chondrite parent bodies is necessary to avoid incorporation of µ30Si-rich material. In contrast, Earth's µ30Si composition necessitates admixing of 26 ± 9 per cent of µ30Si-rich outer Solar System material to its precursors. The µ30Si compositions of Mars and proto-Earth are consistent with their rapid formation by collisional growth and pebble accretion less than three million years after Solar System formation. Finally, Earth's nucleosynthetic composition for s-process sensitive (molybdenum and zirconium) and siderophile (nickel) tracers are consistent with pebble accretion when volatility-driven processes during accretion and the Moon-forming impact are carefully evaluated.

Photocatalytic degradation of reactive brilliant blue KN-R by Ti-doped Bi2O3.

In this study, different compositions of Ti-doped Bi2O3 photocatalytic materials were prepared by chemical solution decomposition method. It was used to degrade reactive brilliant blue KN-R, and then characterized by XRD, SEM, UV-vis DRS, XPS, photocurrent, and other detection methods. The results show that when the catalyst dosage is 1.0 g/L and the initial concentration of reactive brilliant blue KN-R is 20 mg/L, the degradation rate of pure Bi2O3 to reactive brilliant blue KN-R is 75.30%; the Ti doping amount is 4% (4Ti/Bi2O3), 4Ti/Bi2O3 had the best degradation effect on reactive brilliant blue KN-R, and the degradation rate could reach 93.27%. When 4Ti/Bi2O3 was reused for 4 times, the degradation rate of reactive brilliant blue KN-R only decreased by 6.91%. Doping Ti can inhibit the growth of Bi2O3 grains, making the XRD peak of Ti/Bi2O3 material wider. The pure Bi2O3 particles are larger and the surface is smooth. With the increase of Ti doping content, the surface of Ti/Bi2O3 material grows from roughness to nanofibrous Bi4Ti3O12. The visible light absorption performance and electron separation and transfer ability of Bi2O3 are significantly improved by doping Ti ions. The band gap is reduced from 2.81 to 2.75 eV. In conclusion, doping Ti enhances the visible light absorption and electron separation and transfer capabilities of Bi2O3, reduces the band gap, and improves the surface morphology, which makes Bi2O3 have higher photocatalytic performance.

Research hotspots and trends of comprehensive utilization of phosphogypsum: Bibliometric analysis.

Phosphogypsum is a by-product of the phosphate fertilizer industry. It is generally treated by stacking, which not only causes environmental pollution, but also wastes resources. Therefore, the harmless, comprehensive, and high-value utilization of phosphogypsum has attracted more and more scholars around the world. From the perspective of bibliometrics, this paper systematically and comprehensively describes the research progress, trends and hot spots of phosphogypsum resource utilization. This article is based on a scientific network database, and a total of 1067 articles from 1985 to 2020 were collected. Then, use VOSViewer software to perform co-occurrence, co-citation analysis and cluster analysis. The visual analysis results demonstrate that the research on the resource utilization of phosphogypsum shows the characteristics of rapid growth. The active countries are mainly China, Brazil, Spain and the United States. Four of the top 10 active organizations are from China. It systematically expounds the changes in research hotspots in this field at different stages and possible future research hotspots. Including the gradual attention to the preparation of phosphogypsum building materials, phosphogypsum adsorption materials, and radioactive elements in phosphogypsum; the extraction of rare earth elements from phosphogypsum; the use of phosphogypsum to prepare fertilizer or soil improvement. Research shows that phosphogypsum can be reasonably designed, transformed, and used in different fields.However, the radioactivity contained in phosphogypsum should be paid attention to because it has an impact on humans and the environment. We believe that this research provides a comprehensive and systematic overview for future research on phosphogypsum resource utilization.

The internal structure and geodynamics of Mars inferred from a 4.2-Gyr zircon record.

Combining U-Pb ages with Lu-Hf data in zircon provides insights into the magmatic history of rocky planets. The Northwest Africa (NWA) 7034/7533 meteorites are samples of the southern highlands of Mars containing zircon with ages as old as 4476.3 ± 0.9 Ma, interpreted to reflect reworking of the primordial Martian crust by impacts. We extracted a statistically significant zircon population (n = 57) from NWA 7533 that defines a temporal record spanning 4.2 Gyr. Ancient zircons record ages from 4485.5 ± 2.2 Ma to 4331.0 ± 1.4 Ma, defining a bimodal distribution with groupings at 4474 ± 10 Ma and 4442 ± 17 Ma. We interpret these to represent intense bombardment episodes at the planet's surface, possibly triggered by the early migration of gas giant planets. The unradiogenic initial Hf-isotope composition of these zircons establishes that Mars's igneous activity prior to ∼4.3 Ga was limited to impact-related reworking of a chemically enriched, primordial crust. A group of younger detrital zircons record ages from 1548.0 ± 8.8 Ma to 299.5 ± 0.6 Ma. The only plausible sources for these grains are the temporally associated Elysium and Tharsis volcanic provinces that are the expressions of deep-seated mantle plumes. The chondritic-like Hf-isotope compositions of these zircons require the existence of a primitive and convecting mantle reservoir, indicating that Mars has been in a stagnant-lid tectonic regime for most of its history. Our results imply that zircon is ubiquitous on the Martian surface, providing a faithful record of the planet's magmatic history.

Early oxidation of the martian crust triggered by impacts.

Despite the abundant geomorphological evidence for surface liquid water on Mars during the Noachian epoch (>3.7 billion years ago), attaining a warm climate to sustain liquid water on Mars at the period of the faint young Sun is a long-standing question. Here, we show that melts of ancient mafic clasts from a martian regolith meteorite, NWA 7533, experienced substantial Fe-Ti oxide fractionation. This implies early, impact-induced, oxidation events that increased by five to six orders of magnitude the oxygen fugacity of impact melts from remelting of the crust. Oxygen isotopic compositions of sequentially crystallized phases from the clasts show that progressive oxidation was due to interaction with an 17O-rich water reservoir. Such an early oxidation of the crust by impacts in the presence of water may have supplied greenhouse gas H2 that caused an increase in surface temperature in a CO2-thick atmosphere.

High-precision in situ silicon isotopic analyses by multi-collector secondary ion mass spectrometry in olivine and low-calcium pyroxene.

RATIONALE: High-precision determination of silicon isotopes can be achieved by in situ multi-collector secondary ion mass spectrometry (MS-SIMS). The accuracy of the analyses is, however, sensitive to ion yields and instrumental mass fractionations (IMFs) induced by the analytical procedure. These effects vary from one instrument to another, with the analytical settings, and with the composition and nature of the sample. Because ion yields and IMF effects are not predictable and rely on empirical calibrations, high-accuracy analyses require suitable sets of standards. METHODS: Here, we document calibrations of ion yields and matrix effects in a set of 23 olivine standards and 3 low-Ca pyroxene for silicon isotopic measurements in both polarities using Cameca IMS 1270 E7 and IMS 1280 HR2 ion probes set with the cesium (Cs) or radiofrequency (RF) source. RESULTS: Silicon ion yields show (i) strong variations with the chemical composition, and (ii) an opposite behavior between the secondary positive and negative polarities. The magnitude of IMF along the fayalite-forsterite (olivine) series shows a complex behavior, increasing overall by ≈7‰ (secondary positive) and ≈15‰ (secondary negative) with increasing olivine Mg#. A drastic change in olivine IMF occurs at Mg# ≈ 70 in both polarities. The magnitude of IMF for low-Ca pyroxene from Mg# = 70-100 is almost constant in both polarities, i.e. ≈0.1‰ in secondary positive and ≈0.15‰ in secondary negative. The analytical uncertainties on individual analyses were ± 0.05-0.15‰ (2 S.E.) with both sources, and the external errors for each standard material were ≈ ±0.05-0.5‰ (2 S.E.) with the Cs source and ≈ ±0.03-0.15‰ (2 S.E.) with the RF source. CONCLUSIONS: The IMF effect of Si isotopes in silicates shows complex behaviors that vary with the chemistry and the settings of the instrument. We developed a suitable set of standards in order to perform high-accuracy in situ measurements of Si isotopes in olivine and low-Ca pyroxene characterized by varying chemical compositions by MC-SIMS.

Titanium isotopes as a tracer for the plume or island arc affinity of felsic rocks.

Indirect evidence for the presence of a felsic continental crust, such as the elevated 49Ti/47Ti ratios in Archean shales, has been used to argue for ongoing subduction at that time and therefore plate tectonics. However, rocks of intermediate to felsic compositions can be produced in both plume and island arc settings. The fact that Ti behaves differently during magma differentiation in these two geological settings might result in contrasting isotopic signatures. Here, we demonstrate that, at a given SiO2 content, evolved plume rocks (tholeiitic) are more isotopically fractionated in Ti than differentiated island arc rocks (mainly calc-alkaline). We also show that the erosion of crustal rocks from whether plumes (mafic in average) or island arcs (intermediate in average) can all produce sediments having quite constant 49Ti/47Ti ratios being 0.1-0.3 per mille heavier than that of the mantle. This suggests that Ti isotopes are not a direct tracer for the SiO2 contents of crustal rocks. Ti isotopes in crustal sediments are still a potential proxy to identify the geodynamical settings for the formation of the crust but only if combined with additional SiO2 information.