High-pressure Minerals Research Articles

High pressure minerals from meteorite impact craters

High pressure minerals from meteorite impact craters

High-pressure minerals and new lunar mineral changesite-(Y) in Chang’e-5 regolith

Forty-five years after the Apollo and Luna missions, China’s Chang’e-5 (CE-5) mission collected ∼1.73 kg of new lunar materials from one of the youngest basalt units on the Moon. The CE-5 lunar samples provide opportunities to address some key scientific questions related to the Moon, including the discovery of high-pressure silica polymorphs (seifertite and stishovite) and a new lunar mineral, changesite-(Y). Seifertite was found to be coexist with stishovite in a silica fragment from CE-5 lunar regolith. This is the first confirmed seifertite in returned lunar samples. Seifertite has two space group symmetries (Pnc2 and Pbcn) and formed from an α-cristobalite-like phase during “cold” compression during a shock event. The aftershock heating process changes some seifertite to stishovite. Thus, this silica fragment records different stages of an impact process, and the peak shock pressure is estimated to be ∼11 to 40 GPa, which is much lower than the pressure condition for coexistence of seifertite and stishovite on the phase diagram. Changesite-(Y), with ideal formula (Ca8Y)□Fe2+(PO4)7 (where □ denotes a vacancy) is the first new lunar mineral to be discovered in CE-5 regolith samples. This newly identified phosphate mineral is in the form of columnar crystals and was found in CE-5 basalt fragments. It contains high concentrations of Y and rare earth elements (REE), reaching up to ∼14 wt. % (Y,REE)2O3. The occurrence of changesite-(Y) marks the late-stage fractional crystallization processes of CE-5 basalts combined with silicate liquid immiscibility. These new findings demonstrate the significance of studies on high-pressure minerals in lunar materials and the special nature of lunar magmatic evolution.

Shock-recovered maskelynite indicates low-pressure ejection of shergottites from Mars.

Diaplectic feldspathic glass, commonly known as maskelynite, is a widely used impact indicator, notably for shergottites, whose shock conditions are keys to their geochemistry and launch mechanism. However, classic reverberating shock recovery experiments show maskelynitization at higher shock pressures (>30 gigapascals) than the stability field of the high-pressure minerals found in many shergottites (15 to 25 gigapascals). Most likely, differences between experimental loading paths and those appropriate for martian impacts have created this ambiguity in shergottite shock histories. Shock reverberation yields lower temperature and deviatoric stress than single-shock planetary impacts at equivalent pressure. We report the Hugoniot equation of state of a martian analog basalt and single-shock recovery experiments, indicating partial-to-complete maskelynitization at 17 to 22 gigapascals, consistent with the high-pressure minerals in maskelynitized shergottites. This pressure explains the presence of intact magmatic accessory minerals, used for geochronology in shergottites, and offers a new pressure-time profile for modeling shergottite launch, likely requiring greater origin depth.

From the lithosphere to the lower mantle: An aqueous-rich metal-bearing growth environment to form type IIb blue diamonds

A study of five diamonds containing mineral and fluid inclusions, selected among forty-nine specimens from the Cullinan Mine, South Africa, was carried out to better document the origin and formation of N-absent B-poor (type IIb) diamonds. The combination of several in-situ non-destructive techniques was used to identify the mineralogy and the chemical composition of primary and secondary inclusions. These include breyite, larnite, graphite, Fe-Ni-Cu native metallic alloys, sulfides of the pyrrhotite group, Ni-rich oxide and potential hydrous ferric sulfates. A common and abundant hydrous fluid containing H2O + CH4 was also identified. From the various observations, we suggest that these type IIb diamonds grew in an aqueous oxidized fluid reacting with a reduced mantle characterized by low oxygen fugacity. Remnant pressures recorded in primary breyite by Raman shifts and XRD measurements enabled the calculation of minimal entrapment pressures of inclusions using elastic geothermobarometry. Applying pressure corrections caused by elastic relaxation, minimum trapping pressures from 4.9 GPa to 5.6 GPa were calculated, suggesting lithospheric depths consistent with the occurrence of numerous graphite inclusions. The association of breyite and larnite, which is often considered as an indicator of sublithospheric origin, also occurs at pressures of 6 GPa or lower in a H2O-rich and carbonate/Ca-rich environment. The B-poor and N-absent features of type IIb diamonds do not require the classic subduction-related model of their formation. Whereas high-pressure minerals would host boron in cold subducting slabs, slabs are also important carriers of nitrogen into the deep mantle, with this latter element mostly absent in these diamonds. In our alternative model, the mantle is proposed as an alternative source of boron, whereby metallic alloys or N speciation between fluid and melt would still prevent the incorporation of nitrogen, leading to the expression of the blue, boron-related and N-absent features of type IIb diamonds. The observed mineralogical assemblage neither proves sublithospheric origin nor does it exclude lithospheric depths of formation for these diamonds. Hence, we propose that type IIb diamonds form in a mantle continuum, from sublithospheric to lithospheric depths.

Thermodynamic Modeling of Mineral Scaling in High-Temperature and High-Pressure Aqueous Environments

Methods of predicting mineral scale formation have evolved over the years from simple empirical fittings to sophisticated computational programs. Though best practices can now solve complex multi-phase, multi-component systems, they are largely restricted to temperatures below 300 °C. This review examines critical gaps in existing mineral scale modeling approaches as well as strategies to overcome them. Above 300 °C, the most widely used model of standard thermodynamic functions for aqueous species fails when fluid densities are below 0.7 g cm−3. This failure occurs due to the model’s reliance on an empirical form of the Born equation which is unable to capture the trends observed in these high temperature, low density regimes. However, new models based on molecular solvent-solute interactions offer a pathway to overcome some of the deficiencies currently limiting high-temperature and high-pressure mineral scale predictions. Examples of the most common scale prediction methods are presented, and their advantages and disadvantages are discussed.

P-T-T TRENDS OF METAMORPHIC TRANSFORMATION OF ECLOGITES IN THE GRIDINO COMPLEX OF THE BELOMORIAN PROVINCE (STOLBIKHA ISLAND AND SAMYLINO AREA)

Eclogites in the Gridino complex of the Belomorian province have complex history of metamorphic transformations. Their polymetamorphism is revealed from relics of early and late high-pressure mineral assemblages (omphacite+garnet), reaction microstructures, changes of the garnet chemical zoning, results of thermobarometric calculations, and isotope-geochronological studies. Geochronological data indicate two stages of eclogitic metamorphism in the Gridino complex at the Archean and Paleoproterozoic. As a result of the study, we obtained two P-T-t trends for the regressive stage of rock evolution with a successive transition from eclogitic facies to granulite (amphibolite). The peak of the first metamorphic event responds to metamorphic zircons with an age of 2,7 Ga. The maximal values of the P-T conditions of the second metamorphic event are reliably correlated with 1,9 Ga metamorphic zircons.

Raman Spectroscopy Studies of Equilibrated Ordinary Chondrites with H and L Group and Shock Metamorphism Degrees

Ordinary chondrites are the most common type of chondrites. As a non-destructive, rapid, and semi-quantitative technology, Raman spectroscopy is widely used in geoscience. This paper presents the results of a Raman spectroscopic study that we conducted for 16 ordinary chondrites with different chemical groups and variable degrees of shock metamorphism. We found that: (1) the relationship between the Fe composition of olivine and pyroxene and the characteristic peaks of the Raman spectrum established by predecessors cannot be refined to the range of meteorites, the shock on meteorites also affects the Raman spectral characteristics of minerals and (2) the full width at half maximum (FWHM) of the shocked minerals (including high-pressure minerals) in meteorites increases in the Raman spectrum, however, no clear numerical relationship with pressure was found. Based on these data, we assess that the feasibility of Raman spectroscopy for the classification of chemical group and shock metamorphism in ordinary chondrites is not well established.

HIGH-PRESSURE METAMORPHIC ROCKS OF THE CHARA OPHIOLITE BELT (CAOB): AGE AND EXHUMATION CONDITIONS

A critical element in the construction of tectonic models of exhumation of basalts that have undergone high-pressure metamorphism is the diagnosis of synchronicity and the genetic relationship between deformations and high-pressure metamorphic changes. In this report, these issues are discussed on the example of the metabasalts of the Chara ophiolite belt. In the bottom of the basalt block with the separation of pillow lavas near the Burshabulak farm, crack-vein systems with high-pressure mineral associations were discovered and analyzed, which directly indicates their tectonic origin. It is shown that the conditions for the formation of such vein mineral associations correspond to eclogite-like rocks (P=18.5 kbar temperatures of no more than 520 °C). The age of the high-pressure metamorphism basalts of the synchronous type with deformations according to 40Ar/39Ar isotope dating of amphiboles cannot be younger than the boundary of 452±14 million years.

Formation and decomposition of vacancy-rich clinopyroxene in a shocked eucrite: New insights for multiple impact events

Impact is a fundamental process shaping the formation and evolution of planets and asteroids. It is inevitable that some materials on the surface of planets and asteroids have been impacted for many times. However, unambiguous petrological records for multiple post-formation impact events are rarely described. Here, we report that the thin shock melt veins of the shocked eucrite Northwest Africa 8647 are dominated by a fine-grained intergranular or vermicular pigeonite and anorthite assemblage, rather than compact vacancy-rich clinopyroxene. Vacancy-rich clinopyroxene in the veins instead is ubiquitous as irregularly-shaped, relict grains surrounded by intergranular or vermicular pigeonite and anorthite assemblage. The silica fragments entrained in shock melt veins contain a coesite core and a quartz rim. The occurrences of vacancy-rich clinopyroxene and coesite can be best explained by two impact events. The first impact event produced the shock melt veins and lead to the formation of vacancy-rich clinopyroxene and coesite. The second impact event heated the fine-grained melt veins and lead to the widespread partial decomposition of vacancy-rich clinopyroxene and the partial back-transformation of coesite. This paper is the first report of the decomposition reaction of shock-induced vacancy-rich clinopyroxene in extraterrestrial materials. We propose that widespread decomposition and/or back-transformation of high-pressure minerals in shocked meteorites can be considered as important records of multiple impact events.

Back-transformation processes in high-pressure minerals: implications for planetary collisions and diamond transportation from the deep Earth

We conducted back-transformation experiments in ringwoodite, bridgmanite, and lingunite at 0.47–8.1 GPa and 310–920 °C by in situ X-ray observation method. Ringwoodite back-transformed to olivine by grain-boundary nucleation and growth mechanism. The site saturation occurred at the early stage under the conditions far from the equilibrium boundary, and we observed the growth-controlled back-transformation kinetics in ringwoodite. The growth kinetics determined in the present study is largely different from that in the previous study (Reynard et al. in Am Min 81:585–594, 1996), which may be due to the effects of water. Bridgmanite did not directly back-transform to the stable phase orthoenstatite at ~ 1–4 GPa, but first becomes amorphous with increasing temperatures. We observed kinetics of the orthoenstatite crystallization from amorphous bridgmanite that was controlled by both nucleation and growth processes. The temperature range in the amorphous state became narrow with increasing pressures, and the direct back-transformation to high-P clinoenstatite without amorphization eventually occurred at 8 GPa. Amorphization was also observed in lingunite when increasing temperature at ~ 1.5 GPa; however, the plagioclase crystallization proceeded before the complete amorphization. The back-transformation in ringwoodite variedly occurs in shocked meteorites depending on the degree of the post-shock annealing, which can be reasonably interpreted based on the growth kinetics. On the other hand, the presence of hydrous ringwoodite in diamond inclusions cannot be explained without the help of residual stress. The present study also indicates that complete amorphization or the back-transformation to enstatite is unavoidable in bridgmanite during the post-shock annealing. This is inconsistent with the presence of crystalline bridgmanite in shocked meteorites, still requiring further investigations of kinetic behaviors in shorter timescales.

Unique evidence of fluid alteration in the Kakowa (L6) ordinary chondrite

Meteorites preserve evidence of processes on their parent bodies, including alteration, metamorphism, and shock events. Here we show that the Kakowa (L6) ordinary chondrite (OC) preserves both shock-melt veins and pockets of detrital grains from a brecciated and altered object, including corundum, albite, silica, fayalite, forsterite, and margarite in a Pb- and Fe-rich matrix. Preservation of the observed mineralogy and texture requires a sequence of at least two impacts: first, a high-velocity collision formed the shock melt veins containing the high-pressure minerals ringwoodite, wadsleyite, majorite, and albitic jadeite; later, a low-velocity impact formed fractures and filled them with the detrital material. Oxygen and Pb isotope ratios suggest an OC origin for these detrital minerals. Although fluid alteration is common in carbonaceous chondrites, the discovery of margarite with an OC oxygen isotopic signature is novel. Kakowa extends both the impact and alteration history of L6 ordinary chondrites in general.

Neoproterozoic and early Paleozoic metamorphism recorded in gneisses from the East Kunlun Orogenic belt

The East Kunlun Orogen (EKO) is a long-lived accretionary orogenic belt that records the Paleozoic–Mesozoic amalgamation processes of the East Asia continent. The belt consists mainly of various kinds of gneisses with minor amounts of eclogite and garnet amphibolite occurring as lenses. We report zircon U–Pb ages and Hf–O isotopic compositions for the granitic gneisses and paragneisses in the Xiarihamu area near Golmud in Qinghai Province, to investigate the metamorphic history and evolution of the orogenic belt. For the granitic gneisses, zircon U–Pb chronology reveals a Neoproterozoic magmatic event and an early Paleozoic metamorphic event. The magmatic crystallization ages of the two granitic gneisses are 920 ± 6 and 929 ± 2 Ma, and yield εHf(t) values of −8.4 to 1.7 and δ18O values of 7.94–11.19‰, suggesting their derivation mainly from continental crustal materials. The detrital zircons from the paragneisses record a Neoproterozoic metamorphic event and a Paleozoic metamorphic event. Most of the detrital zircons from the two paragneiss samples yielded ages of 2.1–0.9 Ga, indicating that the sources of the sediment were formed mainly during the Neoproterozoic to Paleoproterozoic. These Neoproterozoic magmatic and metamorphic events suggest that the EKO underwent a Neoproterozoic tectonothermal event that was related to the assembly of the Rodinia supercontinent. The similar tectonic histories of the EKO and North Qaidam belt (NQB) indicate they were probably part of a single tectonic unit during the Neoproterozoic. Some of the zircons have metamorphic overgrowth rims yielding two stages of Paleozoic metamorphic ages of ca. 440 Ma (438 ± 2 Ma) and ca. 420 Ma (419 ± 6 Ma, 416 ± 6 Ma, and 423 ± 6 Ma). Combined the discover of high-pressure mineral inclusions (jadeite + quartz) in these rims with the results in previous studies, the ages of these rims (ca. 440 Ma and ca. 420 Ma) are suggested to represent of HP-UHP metamorphism of the EKO. These age data imply that the gneisses in this study might share common early Paleozoic metamorphic event with the HP–UHP eclogites in the EKO.

New Mineral Names: High-Pressure and Precious Minerals

Abstract In this issue of New Mineral Names, a thematic approach is used to help provide context for advances and discoveries in mineralogy. Recovered high-pressure minerals are not commonplace, rare platinum group elements tend to be recovered from important ore bodies, and then there are the minerals/collections that are culturally important and significant to the history of science. Here we investigate the newly discovered high-pressure minerals and highly precious minerals: davemaoite, kaitianite, elgoresyite, oberthüite, torryweiserite, palladothallite, fleetite, tamuraite, marathonite, palladogermanite, and kernowite.

Formation, preservation and extinction of high-pressure minerals in meteorites: temperature effects in shock metamorphism and shock classification

The goal of classifying shock metamorphic features in meteorites is to estimate the corresponding shock pressure conditions. However, the temperature variability of shock metamorphism is equally important and can result in a diverse and heterogeneous set of shock features in samples with a common overall shock pressure. In particular, high-pressure (HP) minerals, which were previously used as a solid indicator of high shock pressure in meteorites, require complex pressure–temperature–time (P–T–t) histories to form and survive. First, parts of the sample must be heated to melting temperatures, at high pressure, to enable rapid formation of HP minerals before pressure release. Second, the HP minerals must be rapidly cooled to below a critical temperature, before the pressure returns to ambient conditions, to avoid retrograde transformation to their low-pressure polymorphs. These two constraints require the sample to contain large temperature heterogeneities, e.g. melt veins in a cooler groundmass, during shock. In this study, we calculated shock temperatures and possible P–T paths of chondritic and differentiated mafic–ultramafic rocks for various shock pressures. These P–T conditions and paths, combined with observations from shocked meteorites, are used to constrain shock conditions and P–T–t histories of HP-mineral bearing samples. The need for rapid thermal quench of HP phases requires a relatively low bulk-shock temperature and therefore moderate shock pressures below ~ 30 GPa, which matches the stabilities of these HP minerals. The low-temperature moderate-pressure host rock generally shows moderate shock-deformation features consistent with S4 and, less commonly, S5 shock stages. Shock pressures in excess of 50 GPa in meteorites result in melt breccias with high overall post-shock temperatures that anneal out HP-mineral signatures. The presence of ringwoodite, which is commonly considered an indicator of the S6 shock stage, is inconsistent with pressures in excess of 30 GPa and does not represent shock conditions different from S4 shock conditions. Indeed, ringwoodite and coexisting HP minerals should be considered as robust evidence for moderate shock pressures (S4) rather than extreme shock (S6) near whole-rock melting.

In situ laser ablation Lu–Hf geochronology of garnet across the Western Gneiss Region: campaign-style dating of metamorphism

The development of in situ laser ablation Lu–Hf geochronology of apatite, xenotime and garnet has opened avenues to quickly and directly date geological processes. We demonstrate the first use of campaign-style in situ Lu–Hf geochronology of garnet across the high- to ultrahigh-pressure Western Gneiss Region in Norway. Mafic eclogites from this region have been the focus of much work, and were clearly formed during continental subduction during the Caledonian Orogeny. However, abundant quartzofeldspathic and pelitic lithologies record a more complex history, with some preserving polymetamorphic age data, and most containing no indication of high-pressure mineral assemblages formed during subduction. Twenty metapelitic and felsic samples spanning 160 lateral kilometres across the Western Gneiss Region have been analysed using garnet Lu–Hf geochronology. The results reveal Caledonian ages for the majority of the garnets, suggesting that some quartzofeldspathic and metapelitic lithologies were reactive and grew garnet during high- to ultrahigh-pressure metamorphism. However, two ultrahigh-pressure eclogite locations, Verpeneset and Fjørtoft, preserve both Caledonian and Neoproterozoic-aged garnets. Despite significant uncertainties on some of the Lu–Hf geochronological ages, laser ablation Lu–Hf efficiently identifies the polymetamorphic history of parts of the Western Gneiss Region, illustrating the effectiveness of this novel analytical method for rapid mapping of metamorphic ages. Supplementary material: All laser ablation Lu–Hf geochronological data for the garnets analysed in this study are available at https://doi.org/10.6084/m9.figshare.c.5715453 Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/cc/caledonian-wilson-cycle

The Formation and Evolution of Uvarovite in UHP Serpentinite and Rodingite and its Constraints on Chromium Mobility in the Oceanic Subduction Zone

AbstractThe uvarovite‐andradite and uvarovite‐andradite‐grossular solid‐solution series are rare in nature. The discovery of uvarovite‐andradite in serpentinite and rodingite from the ultra‐high pressure (UHP) metamorphic belt in southwestern Tianshan provided an opportunity to investigate its behavior in the subduction zone. Uvarovite (defined as chromium‐garnet) from serpentinite is homogeneous in a single grain, covering compositions in the uvarovite‐andradite solid solution series of Adr58–66Uv33–41, with few grossular components. Uvarovite from rodingites contain various Cr2O3 contents (1.7–17.9 wt%) and mineral compositions being in the range of Adr21–31Uv41–50Grs22–37, Adr52–90Uv5–25Grs0–21 and Adr19–67Uv3–63Grs13–42. Discontinuous chemical variation of uvarovite from core to rim indicates that uvarovite formed by consuming andradite and chromite, which could provide Ca, Cr, Al and Fe. Raman signals of water were identified for uvarovite from both serpentinite and rodingite, with high water content in uvarovite from serpentinite. The high pressure mineral assemblage, as well as the association with perovskite, indicated that the studied uvarovite from serpentinite and rodingite was formed through high pressure metamorphism, during the subduction zone serpentinization and rodingitization. High alkaline and highly reduced fluids released from serpentinization or rodingitization in the oceanic subduction zone promote the mobility of chromium and enable its long‐distance migration.

Occurrence of tuite and ahrensite in Zagami and their significance for shock-histories recorded in martian meteorites

AbstractWe report on the discovery of two high-pressure minerals, tuite and ahrensite, located in two small shock-induced melt pockets (SIMP 1 and 2) in the Zagami martian meteorite, coexisting with granular and acicular stishovite and seifertite. Tuite identified in this study has two formation pathways: decomposition of apatite and transformation of merrillite under high-P-T conditions. Chlorine-bearing products, presumably derived from the decomposition of apatite, are concentrated along the grain boundaries of tuite grains. Nanocrystalline ahrensite in the pyroxene clast in SIMP 2 is likely to be a decomposition product of pigeonite under high-P-T conditions by a solid-state transformation mechanism. The pressure and temperature conditions estimated from the high-pressure minerals in the shock-induced melt pockets are ~12–22 GPa and ~1100–1500 °C, respectively, although previous estimates of peak shock pressure are higher. This discrepancy probably represents the shift of kinetic relative to thermodynamic phase boundaries, in particular the comparatively small region that we examine here, rather than a principal disagreement between the peak shock conditions.

Ultrafast olivine-ringwoodite transformation during shock compression

Meteorites from interplanetary space often include high-pressure polymorphs of their constituent minerals, which provide records of past hypervelocity collisions. These collisions were expected to occur between kilometre-sized asteroids, generating transient high-pressure states lasting for several seconds to facilitate mineral transformations across the relevant phase boundaries. However, their mechanisms in such a short timescale were never experimentally evaluated and remained speculative. Here, we show a nanosecond transformation mechanism yielding ringwoodite, which is the most typical high-pressure mineral in meteorites. An olivine crystal was shock-compressed by a focused high-power laser pulse, and the transformation was time-resolved by femtosecond diffractometry using an X-ray free electron laser. Our results show the formation of ringwoodite through a faster, diffusionless process, suggesting that ringwoodite can form from collisions between much smaller bodies, such as metre to submetre-sized asteroids, at common relative velocities. Even nominally unshocked meteorites could therefore contain signatures of high-pressure states from past collisions.

Metamorphic and geochronological evolution of Paleoproterozoic high-pressure ultra-high-temperature pelitic granulite, Chicheng, northern Trans-North China Orogen

Three half-meter-wide pelitic granulite interlayers are found within mafic, intermediate, and felsic granulites in Chicheng of the Trans-North China Orogen, they help to understand the assembly of the Eastern and Western blocks of the the North China Craton (NCC). Detailed petrological study shows that all have identical high-pressure mineral assemblages of garnet + kyanite + K-feldspar + plagioclase + quartz + rutile. Inclusions of mesoperthite in garnet indicate the former presence of ternary feldspar at peak conditions, which, in the matrix, have recrystallized. Kyanite is commonly surrounded by a narrow corona or chain of small garnets, enveloped by a zone of plagioclase and an outermost rim of potassium feldspar. Phase equilibria modeling using THERMOCALC yiels a peak metamorphic pressure of 1.6 GPa at 880 °C (M2a) and a peak temperature of 950 °C at 1.5 GPa (M2b). The ternary feldspar thermometer also indicates a peak temperature of 900–950 °C. The pelitic and mafic granulites exhibit the same peak metamorphic pressure, while the pelitic granulites show a 150 °C higher peak metamorphic temperature than the interlayered mafic granulites of 750–790 °C. Absence of sillimanite in the Chicheng pelitic granulite and orthopyroxene in the mafic granulite indicates a fast exhumation process of cooling, which is different from other high pressure rocks from the Trans-North China Orogen. Analysis of metamorphic monazite and zircon yields concordant SIMS U–Pb ages of ca. 1.91 Ga. This study suggests that the Chicheng HP granulite terrane was subjected to fast tectonic exhumation after the collision that occurred at ca. 1.91 Ga. The results provide a reliable metamorphic record for the final collisiion of the Paleoproterozoic Trans-North China Orogen in the NCC.

Nephelinites in eastern China originating from the mantle transition zone

Nephelinites, a highly alkaline volcanic rock type, have widely been thought to be formed in a shallow lithosphere previously impregnated with phlogopite and/or amphibole. Here we argue that nephelinites start melting at much greater depths than previously thought. Taking four Cenozoic nephelinitic volcanoes in eastern China as specific examples, we show that nephelinites have exceptionally low K/U and Ba/Th ratios, similar to most nephelinites worldwide, but their Nd-Sr-Hf isotopic compositions are inconsistent with a local lithospheric origin. They also have low, marine‑carbonate-like δ26Mg. We explain these features by partial melting of recycled, carbonate-bearing sediments in the mantle transition zone (MTZ; 410–660 km), where the high-pressure mineral liebermannite (KAlSi3O8, previously known as K-hollandite) is stable as a residual phase, preferentially retaining K, Ba, Rb and Pb relative to Th, U and light REE, thus releasing liquids with the characteristic trace-element patterns. Group-I kimberlites and oceanic HIMU basalts globally share the same peculiar geochemical anomalies characterizing the nephelinites, suggesting they may all have their roots in the MTZ.The nephelinites show correlations for Mg-Sr isotopes, 143Nd/144Nd-MgO, and δ26Mg-Ba/Th ratios, suggesting binary mixing between melts. We therefore invoke a two-stage process to generate these nephelinites. In the first stage, an initial carbonated silicate melt is formed by melting of carbonate-bearing sediments in the MTZ. Subsequently, during the ascent, the initial melt reacts with the surrounding peridotite, thereby generating a reacted melt, which ultimately mixes with the initial, unreacted carbonated silicate melt. Accordingly, Cenozoic nephelinites in eastern China can be regarded as evolved melts from the MTZ.