High Heavy Rare Earth Elements Research Articles

The Characteristics and Enrichment Process of Dabu Ion-Adsorption Heavy Rare-Earth Element (HREE) Deposits in Jiangxi Province, South China

Ion-adsorption rare-earth deposits supply over 90% of the global market’s heavy rare-earth elements (HREEs). The genesis of these deposits, particularly HREE deposits, has garnered significant attention. To elucidate the metallogenic mechanisms of HREE deposits, a comprehensive study of the weathering profile of granite was conducted in Jiangxi Province, South China. This study focuses on the following two aspects: the petrogeochemistry of HREE-rich granite and the enrichment and fractionation of rare-earth elements (REEs) during the weathering process. The results suggest that the Dabu granites are a typical peraluminous, high-K, calc-alkaline granite series with high silica content (SiO2: 74.5%–76.4%), relatively low phosphorus content (P2O5: <0.05%), and high HREE content (ΣLREE/ΣHREE: 0.16–0.66). Weathering advances the decomposition of minerals and the release of elements. REEs are mainly fixed in the regolith by scavengers, mainly clays, Fe–Mn oxides, and carbonates, and ΣREE can reach 799 ppm in the B horizon. However, HREEs tend to migrate further and preferentially combine with Fe–Mn oxides and carbonates as compared to LREEs, leading to a significant fractionation of REEs in the regolith (ΣLREE/ΣHREE = 0.2–1.1). Additionally, the differential weathering of REE-bearing minerals and the precipitation of secondary REE-bearing minerals are also vital for REE fractionation.

Decoding Apatite in Volcanic Carbonatitic breccia from Mongra, Northwest of Amba Dongar Carbonatite Complex, Gujarat, India: Insights to Genesis & Rare Earth Element Budgets

Chemical variations in apatite in context to carbonatites and trace element partitioning between apatites and carbonatite-rich liquids are important in assessing the petrogenesis and evolution of the carbonatites as well as the associated carbonatitic breccia due to apatite's sensitivity to surrounding magma composition. Volcanic carbonatitic breccia is one of the constituent rock types found outside the ring structure of the Amba Dongar Carbonatite Complex (ADC) situated in western India. In the present work, we report the mineral chemistry of apatites from the carbonatitic breccias of the Mongra region (ADC outer core) and compare them to apatites from ADC carbonatites. Apatite chemistry from Mongra displays a larger concentration of rare earth elements, manganese, and chlorine when compared to those of ADC carbonatites. Morphology and distinct zoning of these apatites represent late-stage magmatic processes with high heavy rare earth element concentrations (high Lutetium), followed by interaction of fluids from the surrounding alkaline rocks. Variation in sulphur concentration in the apatites of this study indicates crystallisation under mildly reducing conditions. Integrated field observations, petrography, and apatite mineral chemistry from the Mongra region allow for an understanding of the genesis of apatites in the ADC outer core, with possible implications for late-stage mineral-melt interactions.

Petrogenesis and REE mineralogical characteristics of Shitouping granites in southern Jiangxi Province: Implication for HREE mineralization in South China

The enrichment of heavy rare earth elements (HREE) in the granitic host-rocks is crucial for generating ion-adsorption HREE deposits in South China. The Shitouping pluton, located in the southern part of Jiangxi Province, South China, develops large-scale HREE deposits in its weathering profile identified by recent geological surveys. These granites can be divided into medium to coarse-grained biotite monzogranite (MGBG), medium to coarse-grained syenogranite (MGSG) and fine-grained alkali feldspar granite (FGAG) based on field observations and mineral assemblages. New geochronologic results show that this composite pluton intruded during the Early Cretaceous (ca. 140 Ma). Three granitic units displaying comparable whole-rock Nd [εNd(t) = −4.5 to −3.4] and zircon Hf compositions [εHf(t) = −4.4 to +1.2], combined with mineral association, hydrothermally altered zircon and whole-rock geochemistry, indicate they were derived from partial melting of hybridized crustal source, followed by intense fractional crystallization and fluid metasomatism in the highly evolved granitic system. The MGSG and FGAG have higher Rb, Nb, HREE contents and Rb/Sr ratios, as well as lower Nb/Ta, K/Rb ratios in comparison with the MGBG, implying they are more evolved units. The overlapping magmatic zircon trace element compositions between MGBG and MGSG, coupled with the subvertical contact boundary between the FGAG and the MGBG, suggest that the generation of Shitouping pluton should be attributed to the periodic magma replenishment, remobilization, and differentiation process in the long-lived magmatic system rather than simple fractional crystallization from a single parental magma. Hydrothermally altered zircon with elevated concentration of HREE and the paragenetic relationship between LREE-phosphate and HREE minerals in the MGSG suggest that the fluid metasomatism promotes the migration and accumulation of HREE. This is consistent with the high HREE concentration recorded in the MGSG, which contains abundant HREE minerals associated with fluorites. Thus, this study highlights that magma differentiation and fluid metasomatism during the late magmatic stage could achieve the relatively high HREE contents in granites to favor the formation of ion-adsorption HREE deposits.

Discussion of the W-Sn-REE Metallogenic Background in the Nanling Region of South China: Evidence from Satellite Gravity and Magnetic Data

The Nanling region is located at the intersection of the Yangtze Block and Cathaysia Block and is characterized by complex geological and tectonic processes, as well as distinct W-Sn-REE mineralization. Despite extensive research on the mineralization of W-Sn and REE deposits in the Nanling region, the factors impacting the distribution pattern of eastern tungsten and western tin deposits, as well as the mechanism of REE enrichment in the parent rocks, remain uncertain. Deep structural and tectonic variability plays a crucial role in the formation of mineral deposits in the upper crust. Information on deep structural and tectonic variability is contained in the Moho depth, Curie depth, effective elastic thickness, lithospheric density, and thermal structure derived from the processing and inversion of satellite gravity and magnetic data. In this paper, we comprehensively analyse satellite gravity and magnetic data from the Nanling region, integrating the processing and inversion results with the tectonic evolution of this region and relevant geological information. It is hypothesized that the Chenzhou–Linwu fault serves as a channel for mineral and thermal transfer in the Sn ore aggregation zone, facilitating the material transport from the deep mantle to the surface and ultimately leading to the formation of Sn-enriched granite. The collection area of tungsten ore is more weakly associated with the Chenzhou–Linwu fault, and through deep heat transfer, tungsten components are primarily concentrated in the Earth’s crust to produce W-enriched granite. The primary source of REE enrichment in the parent rocks associated with REE mineralization is predominantly derived from the felsic crust, and the rapid intrusion of deep magma resulting from the subduction and retraction of the Palaeo-Pacific Plate is a contributing factor to the contrasting enrichment of light and heavy rare-earth elements. Mineral crystalline differentiation is relatively high, leading to the formation of ore-forming parent rocks with high heavy rare-earth element contents.

Late Paleoproterozoic collision-related granitic magmatism in the Cuoke Complex, SW China: New evidence for the early evolution of the Yangtze Block

The Paleoproterozoic tectonic evolution of the southwestern Yangtze Block has been ambiguous due to the scarce preservation of geological records, confusing the history of the entire Yangtze Block in the Nuna supercontinent. We here report an integrated study involving petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf-Nd isotopes of the recently identified late Paleoproterozoic granitoids from the Cuoke Complex in the southwestern Yangtze Block. LA-ICP-MS zircon U-Pb dating reveals three episodes of granitic magmatism at ca. 1.94 Ga, 1.89 Ga, and 1.85 Ga. Geochemically, the ca. 1.94 Ga albite granites (AGs) and ca. 1.89 Ga and 1.85 Ga monzogranites (MGs) exhibit features of I-type granite, while the ca. 1.85 Ga AGs display characteristics of A-type granite. The zircon εHf(t) values range from −13.0 to −8.1 for the 1.94–1.89 Ga granitoids and from −8.9 to −7.2 for the ca. 1.85 Ga granitoids, with two-stage model ages of 3.3–3.1 Ga and ca. 3.0 Ga, respectively, indicative of their derivation from remelting of Mesoarchean crustal materials. The relatively low heavy rare earth elements (HREEs) (e.g., Yb < 1.9 ppm) and Y (<18 ppm) contents, and moderately negative Eu anomalies of the ca. 1.94–1.89 Ga granitiods suggest they may have been produced in a late collisional or earliest post-collisional setting. The ca. 1.85 Ga AGs and MGs were probably formed in a post-collisional setting indicated by their high HREE (e.g., Yb > 1.9 ppm) and Y (>18 ppm) contents and strongly negative Eu anomalies. Combined with available data, we provisionally divided the tectonic evolution of the southwestern Yangtze Block into four stages: 1) ca. 2.01 Ga subduction, 2) ca. 1.97–1.95 Ga metamorphism associated with collision events, 3) ca. 1.94–1.89 Ga late collisional or earliest post-collisional stage, and 4) ca. 1.85 Ga post-collisional extensional stage. The subduction and collision of the southwestern Yangtze Block initiated slightly later than the northern part, but their near-synchronous tectonic process since ca. 1.97 Ga suggest they may have collaged together at that time. The ca. 1.94–1.89 Ga and ca. 1.85 Ga late collisional to post-collisional granitic magmatism likely recorded the convergence of discrete Archean rock provinces of the Yangtze Block during the Nuna supercontinent assembly.

Origin of heavy rare earth element enrichment in carbonatites

Heavy rare earth elements (HREE) are currently in high demand for use in high technology, renewable energy and low-carbon transport, but they are the least abundant in nature. Carbonatites are the primary source of REE; however, they are dominated by light REE (LREE). It remains unknown whether carbonatites have the potential to form economic HREE mineralization. Here we report a xenotime-bearing carbonatite in the Bachu REE deposit, northwestern Tarim Large Igneous Province (TLIP), China, and infer the origin of HREE in carbonatites. The rocks evolved from dolomite to calcite carbonatites, and their HREE content correspondingly increased. Both types of rocks have similar monazite U-Pb ages (ca. 300 Ma), and are older than the major eruption of flood basalt of the TLIP, and associated alkaline complexes. They contain higher εNd(t) (2.4–4.1) and lower initial Sr isotopic ratios [(87Sr/86Sr)i = 0.7036–0.7041] than the basalts but similar values to those of younger alkaline rocks. The carbonatites are inferred to be directly derived from low-degree melting of lithospheric mantle sources induced by a deep-seated mantle plume. Calcite carbonatites contain characteristic xenotime, which is associated with burbankite, sulfates, and minor quartz. The rock-forming calcite shows high HREE abundance and flat REE patterns (La/Ybcn = 0.3–2.1). Apatite and LREE minerals in calcite carbonatites also have a higher HREE content (e.g., Y2O3 up to 2 wt%) than those in dolomite rocks. This finding indicates that the early dolomite carbonatite underwent strong fractionation of dolomite and LREE minerals, resulting in HREE and alkali enrichment in the evolved calcite rocks. High amounts of alkalis further enhance the solubility of REE, particularly HREE, in the residual melts. Silica assimilation from the country rocks facilitates the HREE mineralization by sequestering alkalis. Therefore, HREE enrichment in carbonatites may require substantial fractional crystallization of initial melts as well as alkali conservation during ascent.

Ancient Metasomatism in the Lithospheric Mantle, Eastern North China Craton: Insights from In-Situ Major and Trace Elements in Garnet Xenocrysts, Mengyin District

Mantle metasomatism refers to the interaction between mantle melt, fluid, and mantle rock. It not only affects the physical and chemical properties of the lithospheric mantle but also plays an important role in the process of metal and gem mineralization. In order to explore the nature and evolution of metasomatism in the lithospheric mantle of the Mengyin area in the eastern part of the North China Craton, this paper combines the previous data of garnet inclusions in diamonds and analyzes the major and trace elements of garnet xenocrysts in the Shengli No. 1 kimberlite pipe from the EPMA and LA-ICP-MS experiments. The experiments show that the garnet xenocrysts of the Shengli No. 1 kimberlite pipe are mainly lherzolitic and harzburgitic garnets. The content of Zr and TiO2 in some garnets are low, which are the characteristics of depleted garnets. Conversely, another group of garnets display high Zr and TiO2 contents, indicative of high-temperature melt metasomatism. When comparing the Ti/Eu ratio of the depleted garnets to that of the primary mantle, a significantly lower value is observed. Additionally, the (Sm/Er)N value undergoes minimal changes, while the Zr/Hf value exceeds that of the primary mantle. These characteristics are indicators of carbonatite melt metasomatism. Garnets that are affected by high-temperature melt metasomatism exhibit low (Sm/Er)N content, a significant variation in the Ti/Eu ratio, and a Zr/Hf value greater than that of the primary mantle. These characteristics indicate the influence of kimberlite melt metasomatism. Garnets impacted by carbonatite melt metasomatism display a strong sinusoidal distribution pattern of rare earth elements (REE) and are often found as lherzolitic garnet xenocrysts and garnet inclusions in diamond. On the other hand, garnets influenced by kimberlite melt metasomatism exhibit a slight sinusoidal REE distribution pattern in harzburgitic garnets and a slight sinusoidal REE distribution or a flat pattern from medium rare earth elements (MREEs) to heavy rare earth elements (HREEs) in lherzolitic garnet xenocrysts. Based on these findings, it is evident that there are at least two types of metasomatism occurring in the lithospheric mantle of the Mengyin area in the eastern part of the North China Craton. The first type involves the metasomatism of early carbonatite melt to the mantle peridotite. Garnets formed under this condition exhibit high Sr and LREE contents, as well as low Zr, Hf, Ti, Y, and HREE contents, indicating depletion characteristics. The second type entails the metasomatism of late kimberlite melts affecting the mantle peridotite. Garnets formed under this process display high Zr, Hf, Ti, Y, and HREE contents.

Heavy rare earth element and crustal-derived silicon enrichment in Huayangchuan carbonatites, Qinling orogenic belt

The Huayangchuan carbonatite is found in the North Qinling orogenic belt. It is distinguished from most carbonatites worldwide by its abundance of quartz and high heavy rare earth element (HREE) content. The origin of Si supersaturation and HREE enrichment in carbonatite is still unknown. Here, we conducted a detailed mineralogical investigation and in situ geochemical analyses on a suite of drill-core samples obtained from Huayangchuan carbonatite. In situ titanite and monazite UPb dating yielded ages of 212.3 ± 6.4 Ma and 211.8 ± 5.0 Ma, respectively, corresponding to the post-collision stage of the Qinling orogeny. Clinopyroxene and amphibole in the carbonatite are commonly intergrowth with quartz grains and trapped by quartz as mineral inclusions. The mineralogical textures and compositions indicate that quartz crystallized simultaneously with the mafic minerals from a Si supersaturation magma. The high Si activity during clinopyroxene formation may be related to Si assimilation from the wall-rocks. In situ Nd isotopic compositions of apatite and titanite show consistent εNd(t) ranging from −4.8 to −9.0, similar to the values of the whole-rocks and calcites. This indicates that the REE were derived from carbonatite magma without an external source. Two types of calcites were identified based on their cathodoluminescence characteristics, and they have variable chondrite-normalized REE patterns (La/Yb(CN) ranging from <0.01 to 19) but similar HREE contents. This implies that the carbonatite underwent strong crystal fractionation of early LREE-rich minerals, which may be essential for HREE enrichment. Therefore, we proposed that Si supersaturation in the carbonatite was probably caused by wall-rock assimilation, and fractional crystallization yielded primary HREE enrichment in the residual melts. Moreover, HREE enrichment in highly evolved carbonatites is further aided by high Si and alkaline activities.

Multivariate statistical analysis of trace elements in apatite: Discrimination of apatite with different origins

Partial least squares-discriminant analysis (PLS-DA) was used to construct the link between trace element contents of magmatic or hydrothermal apatite and deposit and rock types. Apatite with different origins is discriminated by characteristic chemical composition. In average, ore magmatic apatite has higher light REE and Th, and lower Sr than barren rock apatite, independent of deposit types. Hydrothermal apatite has lower La, Ce, Pr, and Nd contents than magmatic apatite, probably because fluids prefer migrating light rare earth element out of apatite. Hydrothermal apatite from iron oxide copper gold (IOCG) and iron oxide apatite (IOA) deposits is discriminated by high Mn and Sr relative to magmatic apatite, probably because these elements are fluid mobile. Barren magmatic apatite from granitoid-related deposits is well separated from ore magmatic apatite by higher Sr, Eu, Gd, Tb, Dy, and lower Mn contents, which are likely related to the relatively low degree of differentiation and high aluminum saturation index of parental magma.Magmatic apatite from IOA deposits is discriminated by relatively high Nd, Sm, Gd, Tb, Dy, and low Mn and U contents, which are possibly related to the crystallization of Mn-compatible magnetite microlites and peraluminous magmas. Magmatic apatite from granitoid-related W deposits is relatively rich in Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The relative enrichment of Sr in magmatic apatite from granitoid-related Cu-Pb-Zn and Pb-Zn deposits is likely due to less fractionation of Sr-compatible plagioclase. Melt of sediment component accounts for high Mn and Th in magmatic apatite from granitoid-related Mo deposits. Magmatic apatite from porphyry deposits is discriminated by relatively high V, Sr, and Eu contents. Magmatic apatite from porphyry Mo deposits has relatively high Pr, Nd, and Sm and low Sr contents compared to other types of porphyry deposits due to the more evolved magma. Hydrothermal apatite from IOA deposits is discriminated by high V and Sr, whereas those from IOCG deposits have high Sm, Eu, Gd, Tb, and U contents, because the lower temperature of IOCG cause precipitation of REE in Cl-rich fluid. Relatively low Gd and Tb in hydrothermal apatite from skarn deposits are possibly due to the crystallization of amphibole.Apatite in carbonatite has high contents of trace elements possibly because high contents of Ca and P in melts cause high apatite-melt partition coefficients of trace elements. Apatite from sedimentary and metamorphic rocks is discriminated by relative enrichment of Sr and Eu. Compared to igneous rocks, apatite from sedimentary rocks has low REE contents, reflecting low REE budget in surface waters. Breakdown of some minerals to release and remobilize REE and U during metamorphism can interpret high heavy REE and U contents in apatite from high-grade metamorphic rocks relative to those from low- and medium-grade metamorphic rocks. The ability to discriminate apatite from different types of deposits and rocks indicates the application potential of apatite chemistry in mineral exploration. A flowchart was proposed to identify apatite with unknown origins.

REE mineralization age and geodynamic setting of the Huanglongpu deposit in the East Qinling orogen, China: Evidence from mineralogy, U–Pb geochronology, and in-situ Nd isotope

The Huanglongpu deposit is one of the most representative igneous carbonatite-type molybdenum-rare earth element (Mo-REE) deposits in the eastern Qinling metallogenic region. The molybdenum resources exceed 180 kt, whilst the total rare earth resources are about 37.8 kt. However, the age of REE mineralization, sources of ore-forming minerals, and tectonic setting are not well characterized. Therefore, this study carried out detailed mineralogical, geochronological, and geochemical analyses to provide new insights. Monazite, bastnäsite, parisite, and xenotime were found to be the dominant REE-bearing minerals in the Huanglongpu deposit. LA-ICP-MS U-Pb dating of the REE minerals revealed a two-stage REE mineralization: monazite formed at 219.4 Ma, whereas bastnäsite and xenotime formed at 145.9 Ma and 142.6 Ma, respectively. The carbonatites, as the main ore host, were characterized by a strong enrichment of light rare earth element (LREE) and moderately high heavy rare earth element (HREE) contents. Monazite showed different Nd isotopic compositions, with lower εNd(t) values ranging between −7.12 and −4.18, while the εNd(t) values of bastnäsite and xenotime ranged from −9.57 to −6.49 and from −11.13 to −6.28, respectively. These contrasting geochemical and isotopic signatures suggest that the Huanglongpu REE mineralization occurred over multiple magmatic-hydrothermal events and that the ore-forming material was unlikely to have stemmed from a single enriched mantle (EMI) source. The early REE mineralization stage (219.4 Ma) was closely associated with carbonatite-related Mo mineralization, both of which were products of magmatic mineralization during the crystallization of the host carbonatite emplaced in an extensional environment after the Late Triassic collision. The ore-related magmas may have originated from a hybrid source composed of EMI and partial melting of the lower crust. In contrast, due to the extensive Yanshanian magmatism which could provide massive heat, the later REE mineralization stage (145.9–142.6 Ma) in the Huanglongpu deposit was likely driven by the reactivation and recrystallization of early-formed REE minerals within the host carbonatites, hence representing a hydrothermal redistribution of the primary magmatic ore.

HREE enrichment during magmatic evolution recorded by apatite: Implication for the ion-adsorption HREE mineralization in South China

Understanding the enrichment of heavy rare earth elements (HREE) and high HREE/LREE (light REE) ratios in the granites is critical to understand the ore-genesis of exclusive ion-adsorption HREE deposits in South China. In this study, we conducted geochronological, whole-rock and apatite geochemical, and isotopic studies on the Xinfeng pluton, of which only parts show high HREE/LREE ratios and are ore-related. Both the ore-related granite and ore-unrelated granite from the Xinfeng pluton are characterized by high SiO2 contents, the same Late Jurassic age (ca. 155 Ma), and enriched Nd isotopic compositions. However, the ore-related granite has lower TiO2, CaO, P2O5, Fe2O3, Ba, Sr, Eu, and LREE contents, lower La/Yb, Zr/Hf and Th/U ratios, higher Rb, Cs, Nb, Ta, Pb, and HREE contents, and higher Rb/Sr ratios than the ore-unrelated granite. These features indicate that the ore-unrelated and ore-related granite are cogenetic and their geochemical differences can be explained by magmatic differentiation. The primary igneous apatite from both the ore-unrelated granite and ore-related granite shows negligible hydrothermal alteration. Fractional crystallization of feldspar (∼20%) and allanite (< 0.3%) led to higher HREE contents and HREE/LREE ratios, lower Sr contents, and a more pronounced negative Eu anomaly in the apatite from the ore-related granite. This study highlights that the magma evolution via mineral fractional crystallization could achieve the relatively high HREE contents and HREE/LREE ratios in the granites, and favors the formation of exclusive ion-adsorption HREE deposits in South China.

Lithospheric mantle provinces and crust-mantle decoupling beneath northeastern China: Insights from peridotite xenoliths

AbstractThe origin and evolution of the subcontinental lithospheric mantle (SCLM) underlying orogenic belts bordering cratons, as either newly added domains or strongly reworked older cratonic lithosphere, remains controversial. This limits our understanding of deep lithospheric behavior and processes during plate convergence. Here, we use detailed petrology, whole-rock and mineral compositions, and in-situ Sr isotopic compositions for spinel-facies peridotite xenoliths from Jiaohe (northeastern China) in the southeastern Central Asian Orogenic Belt (CAOB), which is pinched between two NE-striking Mesozoic to Cenozoic giant trans-lithospheric fault systems. These data are combined with whole-rock Re-Os isotope and platinum-group element compositions and literature data, to explore the physicochemical evolution of the regional SCLM and examine crust-SCLM relationships for this vast swath of continental lithosphere.Lherzolites predominate at Jiaohe, and have higher whole-rock Al2O3 contents than harzburgites (2.27–3.46 wt% versus 0.84–1.02 wt%), but exhibit FeO enrichment similar to harzburgite (bulk FeO up to 9.54 wt%). The lherzolitic clinopyroxenes (Cpx) have higher heavy rare earth element (HREE) levels (2.79–5.11 ppm) and Ti/Eu (3882–6864), coupled with wider variation of 87Sr/86Sr (0.7021–0.7038) and lower average fO2 (oxygen fugacity relative to the fayalitemagnetite-quartz buffer; FMQ-1.92 ± 0.55) compared to the harzburgites (HREE: 0.94–2.11 ppm; Ti/Eu: 163–2044; 87Sr/86Sr: 0.7032–0.7036; fO2 = FMQ-1.25 ± 0.20). All these observations suggest that the lherzolites were produced by adding Cpx ± spinel to the protoliths from reducing silicate melts, whereas the harzburgites may have originated from a remnant, highly depleted mantle domain that variably interacted with silica-undersaturated oxidizing melts.Bulk-rock and mineral compositional relationships as well as fO2 for peridotite samples from the southeastern CAOB (including Jiaohe) are similar to those of the northeastern NCC (including Huinan). Their characteristics contrast with those from the northwestern CAOB, suggesting that they belong to distinct lithospheric provinces with respect to both composition and oxidation state. Jiaohe harzburgites yield Paleoproterozoic Re depletion Os model ages (TRD up to 1.76 Ga), similar to Huinan peridotites (up to 1.92 Ga), just 170 km away, and may also represent strongly reworked cratonic mantle. By analogy with evidence from recent continental collision zones, the Jiaohe SCLM may have originated as cratonic SCLM that migrated northeastward during plate convergence along giant translithospheric fault systems.

Zircon-modeled melts shed light on the formation of Earth's crust from the Hadean to the Archean

Abstract Elucidating the compositions of melts from which Hadean zircons crystallized can provide insight into early crust construction. We calculated model melts using Ti-calibrated zircon/melt partition coefficients and trace element data for zircons from the Hadean, Archean, and possible analogue environments (e.g., rifts, hotspots, arcs) to constrain petrogenetic relationships. Model melts from oceanic settings (mid-ocean ridges, arcs, Iceland) showed higher heavy rare earth element (HREE) contents and shallower middle REE (MREE) to HREE/chondrite (ch) slopes than those from continental arcs and tonalite-trondhjemite-granodiorite suites (TTGs). However, Hadean and Archean model melts were consistently similar to each other and to those from continental arcs, hotspots, and TTGs (and dissimilar to oceanic settings), with depleted HREE contents and slope reversal in heaviest REEch. Despite close similarities that suggest comparable petrogenesis of Hadean and early Archean magmas from which Jack Hills detrital zircons crystallized, subtle variabilities in REEch and Zr/Hf suggest thickening crust and evolving igneous systems through time.

Pre-Late Eocene position of the Lüchun-Jinping microblock in western Yangtze Craton: Constraints from Eocene-Oligocene lamprophyres in southeastern Tibet

The tectono-magmatic history of the Lüchun-Jinping microblock and its possible affinity with the Yangtze Craton are important elements for the reconstruction of Cenozoic plate tectonics in southeastern Tibet. In order to constrain the affinity and decipher the pre-Cenozoic paleopositon of the Lüchun-Jinping microblock, we focused on the petrogenesis of Eocene-Oligocene lamprophyres in the Lüchun-Jinping microblock. The lamprophyres yield zircon UPb ages of 34.7–33.3 Ma and exhibit potassic-ultrapotassic features with elevated K2O/Na2O (1.4–4.0) ratios. They are characterized by high concentrations of compatible elements (e.g., Cr = 187–692 ppm, Ni = 31–218 ppm), large-ion-lithophile elements and light rare-earth elements enrichment, high-field-strength elements depletion, and high radiogenic isotopic values, i.e. (87Sr/86Sr)i = 0.7063–0.7078 and εNd(t) = −3.9 to −2.4. Combined with the low Nb/U ratios, these features suggest that the lithospheric mantle source was metasomatized by subduction-related fluids beneath the Lüchun-Jinping microblock. The relatively high Rb/Sr ratios and high heavy rare-earth element contents indicate that these lamprophyres were derived from partial melting of a phlogopite-bearing lherzolite within the spinel stability field. The parental magmas have experienced fractional crystallization of olivine and clinopyroxene during emplacement. Comprehensive comparisons between the lamprophyres from the Lüchun-Jinping microblock and the potassic-ultrapotassic mafic rocks from the western Yangtze Craton indicate that the Lüchun-Jinping microblock can be regarded as a dismembered part of the western Yangtze Craton due to continental extrusion and Cenozoic sinistral displacement. The compositional trends of the potassic-ultrapotassic mafic rocks suggest that the palaeogeographic position of the Lüchun-Jinping microblock was near the Dali area (west of the Binchuan) and close to the Jinshajiang suture zone before the Cenozoic.

Prolonged Slab-derived Silicate and Carbonate Metasomatism of a Cratonic Mantle Wedge (Maowu Ultramafic body, China)

AbstractMass transfer between crust and mantle at continental margins is a crucial process in shaping mantle heterogeneity and material cycling in deep Earth. Mass transfer is usually archived by the slab-derived and/or asthenosphere-derived component, which metasomatize a cratonic mantle wedge. Clarifying the origin and temporal sequences of these records is a fundamental aim yet is poorly resolved. Comprehensive petrography, whole-rock and mineral compositions [including platinum group elements (PGE)], zircon U–Pb ages, trace elements, and Hf isotopes of the Maowu ultramafic body (comprising harzburgites and garnet orthopyroxenites) in the Dabie orogen (Central China) are presented in this study to decode the complex metasomatic histories beneath the southern North China Craton (NCC). The ultramafic body represents a typical cratonic mantle-wedge fragment with an equilibration pressure of 4·0 ± 1·0 GPa and temperature of 750 ± 50 °C. The harzburgites have high Mg# values (up to 92) and Ni contents (2537–2892 ppm), low Al2O3 (0·26–0·76 wt%) and CaO (0·05–0·32 wt%) contents, and high olivine Fo values (91–93), supporting the origin from a cratonic mantle wedge with partial melting extents of ~20–25 %. Garnet orthopyroxenites occurring as veins in the harzburgites have a wide range of Mg# values (83–91), high Ni contents (963–2353 ppm), and significant enrichment in light rare earth elements and large ion lithophile elements. They show PGE contents and patterns similar to those of the host harzburgites. These characteristics, combined with geochemical modeling, suggest that the garnet orthopyroxenites were produced through the reaction of the harzburgites with silicate melts derived from the continental crust. Three types of zircons were identified in the Maowu ultramafic body. The group-I zircons with U–Pb ages ranging from ~1927 to ~465 Ma were separated from the harzburgites. They are characterized by oscillatory zones, high heavy rare earth element (HREE) contents, a wide range of εHf(t) values (from −24·9 to +21·0), and felsic inclusions (e.g. quartz and plagioclase). They are interpreted as records of the intense silicate-melt metasomatism triggered by the addition of crust-derived silicate sediments (containing Proterozoic detrital zircons) into the NCC mantle wedge. This metasomatism formed the garnet orthopyroxenite veins in the southern NCC mantle wedge. The group-II zircons have dark cores and bright rims and yield a range of U–Pb ages from 421 ± 8 to 256 ± 6 Ma in both the harzburgites and garnet orthopyroxenites. They contain high Th and U contents (up to 5000 ppm) and display steep HREE patterns, negative Eu anomalies, and positive εHf(t) values (+0·6 to +8·2). Carbonates were identified as inclusions in the zircons and as pods or veinlets in the matrix of the harzburgites. These features may reflect a long-term and pervasive metasomatism by oxidized carbonate fluids in the garnet orthopyroxenite-veined mantle wedge, coeval with the secular subduction of the Tethyan slab that carried mainly sedimentary carbonates. The group-III zircons from both the harzburgites and garnet orthopyroxenites show concordant U–Pb ages of 227 ± 6 Ma. They are interpreted to record the Triassic continental collision between the Yangtze Craton and NCC. Collectively, this study provides geochemical, mineralogical, and petrological evidence that the periphery of a cratonic mantle with prolonged fluxing and various metasomatism can archive the complex history along a convergent margin that evolved from oceanic subduction to continental collision.

Evidence for continental rifting from two episodes of mid-Neoproterozoic silicic magmatism in the northeastern Yangtze Block, China

Mid-Neoproterozoic (850–720 Ma) magmatism around the periphery of the Yangtze Block records an intense extensional event related to the breakup of Rodinia. However, the detailed geodynamic mechanisms of this extensional tectonism are still poorly constrained. To address this issue, we undertook a whole-rock geochemical and Sr–Nd isotopic, and zircon U–Pb–Hf–O isotopic study of mid-Neoproterozoic silicic meta-igneous rocks from the Feidong Complex and Zhangbaling Group in the northeastern Yangtze Block. These rocks can be classified into two groups: Group A (granitoids) and Group B (volcanic rocks). Zircon U–Pb dating revealed that Group A (808–786 Ma) pre-dates Group B (762–750 Ma). All these rocks are characterized by A-type granite features, with high heavy REE, Zr, and Hf contents, (K2O + Na2O)/CaO ratios, Fe index values, and zircon saturation temperatures, and formed during a mid-Neoproterozoic extensional event. However, the extremely enriched whole-rock Sr–Nd and zircon Hf isotopic compositions (ISr = 0.7024–0.7068, εNd(t) = −19.3 to −14.1, and εHf(t) = −25.7 to −11.8) of Group A suggest derivation by reworking of ancient crustal basement. Group B is characterized by relatively depleted Sr–Nd–Hf isotopic compositions (ISr = 0.7015–0.7063, εNd(t) = −1.6 to +3.6, and εHf(t) = −4.8 to +4.1), indicating a significant contribution from juvenile-crust-derived material. Group A contains zircons with δ18O = 4.1‰–7.1‰, whereas Group B contains zircons with δ18O = 1.6‰–3.1‰. These chemical and isotopic data, along with the gradual change in residual mineralogy from garnet to plagioclase (Group A to B), indicate that magmatism transitioned from an ancient lower crustal source to a juvenile middle–upper crustal source that had experienced intense high-temperature meteoric water–rock interactions. Our results provide new insights into the tectonic evolution from early extension to peak rifting driven by upwelling asthenosphere, due to rifting of the Yangtze Block from Rodinia during the mid-Neoproterozoic.

Partial melting and subduction-related metasomatism recorded by geochemical and isotope (He-Ne-Ar-Sr-Nd) compositions of spinel lherzolite xenoliths from Coyhaique, Chilean Patagonia

Spinel lherzolite xenoliths from Coyhaique, Chilean Patagonia, are located ~320 km from the Chile Trench and, therefore, their geochemical and isotopic compositions may record slab-derived metasomatism from current and/or earlier subduction zones. We present new mineral and whole-rock major and trace elements that are discussed together with noble gas data (He, Ne, Ar) and Sr-Nd isotopic ratios. Partial melting is recorded by negative correlations between basaltic elements vs. MgO in whole-rock and minerals. In general, silicate minerals show depleted light-rare earth element (LREE) over heavy-REE (HREE) patterns. Whole-rock compositions and clinopyroxene record variable degrees of partial melting (1–15%), which is corroborated by the Sr-Nd depleted character of the lherzolites. Cryptic metasomatism is evidenced by: 1) enriched LREE patterns in whole-rock and type-2 clinopyroxenes; 2) negative anomalies of Nb-Ta-Ti in whole-rock samples coupled with enrichment of large ion lithophile elements and chalcophile elements over high field strength elements and HREE; 3) positive correlations of Pb and U vs. La and negative correlations of Nb/Nb* and Ti/Ti* vs. La in clinopyroxene, and 4) positive anomalies of Li in all silicate minerals. Geochemical differences between whole-rocks and their mineral constituents indicate selective enrichment of the whole-rock samples due to grain-boundary components. 3He/4He ratios reported here are the first strongly radiogenic values found in the Patagonian subcontinental lithospheric mantle (SCLM; 0.20–2.52 RA). Most Ne isotopic ratios are indistinguishable from air composition with few samples showing a nucleogenic component, whereas Ar isotopic ratios are extensively affected by an atmospheric component. The correlation between 3He/4He and 4He/40Ar* corroborates the metasomatism recorded by lithophile and chalcophile elements. Therefore, we identify a heterogeneous SCLM affected by low but variable degrees of partial melting and subsequent enrichment by melts or fluids from recycled subduction-related materials in the spinel stability field (1.06–1.90 GPa and 886–1150 °C).

Multi-stage garnet formation and destruction in Kimberley harzburgitic xenoliths, South Africa

Thirty-nine garnet harzburgites from Kimberley in the Kaapvaal Craton (South Africa) were studied to constrain the origin, age and evolution of sub-cratonic lithospheric mantle (SCLM). In order to avoid chemical overprinting by recent metasomatism, only garnet harzburgites that appeared clinopyroxene-free to the naked eye were sampled. The majority of garnets were, however, in equilibrium with clinopyroxene (24 of 39). Whole rock and mineral major–trace element geochemistry and garnet Sr–Nd–Hf isotope data are presented. Equilibration pressures range from 3.8–6.1 GPa, indicating the harzburgites were derived from a large portion of the SCLM (~115–185 km). High olivine Mg# (~93.4, n = 39) and low whole rock heavy rare earth elements (HREE) contents are consistent with large degrees of partial melting (>45%) and garnet exhaustion leaving a dunitic residue with olivine ≥90%, orthopyroxene ≤10% and HREE <0.01 times chondrite. Mineral modes, whole rock Al2O3 (0.5–3.2 wt%) and SiO2 (43.1–49.1 wt%), however, indicate heterogeneous re-introduction of garnet (≤13%) and orthopyroxene (≤50%). Harzburgites with high garnet and relatively low orthopyroxene modes (mostly ~7–13% and ~ 9–30%; n = 6) are characterised by mildly sinusoidal garnet REE patterns (Tb-Dy minimum and high HREE) and Archaean depleted Hf TDM ages (2.7–3.3 Ga; εHfe: +190 to +709). In contrast, harzburgites with high orthopyroxene and relatively low garnet and modes (~1.5–7.5% and ~ 25–50%; n = 19) are characterised by highly sinuous REE patterns (Ho-Yb minimum and low HREE) and Proterozoic enriched Hf TDM ages (0.7–1.6 Ga; εHfe: −16 to +6). It is inferred that Archaean G10 garnet re-introduction caused a significant increase in HREE, making melt depletion models based on HREE inaccurate. Orthopyroxene addition, a few hundred million years later, most likely at ~2.7 Ga and associated with Ventersdorp magmatic activity, caused partial consumption of garnet and olivine, and changed garnet compositions leading to: 1) Cr/Al ratio increase; 2) HREE decrease; 3) more sinusoidal REE patterns; and 4) un-radiogenic 176Hf/177Hf. Garnets define a Lu-Hf isochron age of 2702 ± 64 Ma (εHfi = +44, n = 31), which is interpreted as a consequence of partial isotopic equilibrium within the SCLM and mixing of the garnet- and orthopyroxene-rich metasomatic components. The low LILE contents and absence of Nb-Ta anomalies are consistent with modal metasomatism caused by intra-plate magmatism. In addition, the REE signatures of metasomatic agents in equilibrium with the garnets suggest that carbonatitic melts and SiO2-rich hydrous melts were responsible for re-introduction of garnet and orthopyroxene, respectively. Sr-Nd isotope systematics were disrupted associated with kimberlite magmatism (Nd isochron: 217 ± 58 Ma, εNdi = +4; n = 34), consistent with recent G10 garnet transformation into G9 garnets (Ca + Fe-enriched). This event may have caused garnet addition (up to 1%), suggesting that garnet was formed or destroyed in at least 4 different events: i) initial extensive polybaric melting, ii) asthenospheric melts re-introducing the bulk of the garnet, iii) orthopyroxene addition and garnet loss, all in the Archaean, and iv) minor garnet addition possibly related to recent kimberlite magmatism prior to eruption.

The molybdenite Re-Os isotope chronology, in situ scheelite and wolframite trace elements and Sr isotope characteristics of the Chuankou tungsten ore field, South China

The Chuankou tungsten ore field, situated in the central area of the Qing-Hang ancient suture zone in South China, is characterized by predominantly quartz vein-type tungsten mineralization that formed near the contact between the Chuankou granite and slightly metamorphosed silt-bearing sericite slate. Based on field work, cathodoluminescence, molybdenite Re-Os dating and in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, the Chuankou tungsten ore was formed at 230.6 ± 2.9 Ma to 229.4 ± 2.6 Ma in a typical Indosinian metallogenic event. In addition, three distinct generations of scheelite and two types of wolframite can be clearly distinguished. Type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element (HREE) content and an obvious negative Eu anomaly. Type 2 wolframite grains are strongly altered as residual-pseudomorphic structures by ore-forming fluids and have relatively low REE contents. Sch-1 scheelite is present in the interior of the type 2 wolframite grains. The Sch-1 scheelite grains have an elevated REE content and low 87Sr/86Sr ratios with a strongly negative Eu anomaly, which suggests an inheritance signal of the host rocks. Comparatively, Sch-2 and the altered Sch-1 scheelite have characteristic extremely low REE contents and remarkably strong positive Eu anomalies. These scheelites also have increased 87Sr/86Sr ratios and low 88Sr signals. Sch-3 is idiomorphic with perfect oscillating zoning. The REE content of Sch-3, which typically has the lowest 87Sr/86Sr ratios, is higher than those in Sch-1 and Sch-2, and the extremely high 88Sr signals indicate a distinct thermal fluid event that was directly derived from the host rock. The correlations between the REE and Nb of scheelite imply a type B-substitution of Sch-1 and Sch-2 but a type C-substitution for Sch-3. The correlation of EuN and EuN* shows an Eu3+ substitution process for stages Sch-1 and Sch-2 and an Eu2+ substitution process for stage Sch-3. Thus, we confirm that ore-bearing hydrothermal rocks must undergo early-stage metasomatism and filling, middle-stage fluid mixing between wall rocks and magmatic hydrothermal activity, and refilling of late-stage magmatic hydrothermal activity during the metallogenic process. During the Indosinian period, the mineralization stages of polymetallic deposits in the Indosinian were composed of Stage 1 (240 to 220 Ma) and Stage 2 (220 to 200 Ma). The Chuankou tungsten ore field can be considered as the typical representation of the Stage 1 metallogenic event in South China. This ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the South China Block.

Garnet trace element geochemistry as a sediment provenance indicator: An example from the Qaidam basin, northern Tibet

Abstract Major element geochemistry of detrital garnet is a widely-used approach for sedimentary provenance analysis, in particular for unravelling parent-rock lithology of siliciclastic sediments. However, garnets from felsic crystalline rocks (e.g., intermediate–acidic igneous rocks and metapelites) often have similar major element composition. This results in ambiguity of provenance interpretation in most cases. Here, we collect trace element data of garnets from different rock types to explore the feasibility of detrital garnet trace element geochemistry in sediment provenance analysis. The Qaidam basin in northern Tibet is taken as an example and provenance of Cenozoic sedimentary rocks therein is interpreted based on detrital garnet trace element composition. We find that garnets in intermediate–acidic igneous rocks have much higher heavy rare earth element (ΣHREE > 600 ppm) and yttrium (Y > 800 ppm) abundances than garnets in metapelites (ΣHREE 4 ppm) and zinc (Zn > 150 ppm) abundances than garnets in low-, medium-grade metapelites (up to amphibolite facies). Based on these findings, we suggest that Fe- and Mn-rich detrital garnets in the Cenozoic sedimentary rocks from the northern Qaidam basin were probably derived from low-, medium-grade metapelites and Mg-rich, Ca-poor detrital garnets therein were most likely derived from granulite-facies metapelites. This provenance interpretation supports that the Qilian Mountains to the north was the major source for the northern Qaidam basin and major deformation style along the Altyn Tagh Fault to west have been dominated by large-amplitude lateral offset and extrusion, rather than crustal thickening and uplift during the early Cenozoic. This study emphasizes high potential of detrital garnet trace element geochemistry in provenance analysis and reconstruction of tectono-sedimentary evolution of clastic sedimentary basins.