Element Geochemistry Research Articles

Depositional environment variations and organic matter accumulation of the first member of the Qingshankou formation in the southern Songliao Basin, China

The organic-rich shale in the first member of the Qingshankou Formation, which is located in the southern Songliao Basin, is regarded as a high-quality source rock in East China. Geochemistry parameters were utilized to illustrate the formation and preservation conditions of the Qing1 Member in the Changling Sag, southern Songliao Basin. In the present study, from longitudinal continuity, the samples of organic geochemistry and elemental geochemistry were collected and systematically analyzed. This aims at determining the paleosalinity, paleoclimate, paleoredox conditions, and paleoproductivity and reconstructing its depositional paleoenvironment. According to total organic carbon (TOC) content, the Qing1 Member in the Changling Sag can be classified into two intervals, which are the lower part and the upper part, with high TOC content and low TOC content, respectively. It can be proved from the results of geochemical indicators that under warm and humid climatic conditions the relatively lower part was generated in the anoxic environment. Terrigenous input brought nutrients to the water body of the lake, made algae flourish, and had a relatively high paleoproductivity of the lake, which imposed a vigorous impact on the accumulation of organic matter. The upper part is mainly deposited under weakly oxidizing conditions, with gradually enhanced oxidation and reduced productivity. In contrast to the lower shale, the terrigenous inflow is relatively low. TOC content in the Qing1 Member has a positive relevance with the paleoredox conditions, as well as the paleosalinity conditions, indicating that good preservation is favorable for the accumulation of organic matter. A depositional model is proposed for the organic matter accumulation of this shale. The upper part was in a relatively hot and dry paleoclimate, with a low degree of organic matter enrichment, whereas the lower part had a warm and humid paleoclimate, with the input of terrestrial organic matter into the primary productivity of the lake basin and a high degree of organic matter enrichment.

Identification the tectonic setting of granite using geochemistry and trace elements: implication for the granites in the Syrostan massive (Southern Ural)

Relevance and the purpose of the work. Te use of trace element to diferentiate granite types and tectonic setting is a well-established method in geology and mineral exploration. Te aim of the paper is to determine the tectonic environment of the granite in the Syrostan massive using trace elements and geochemistry which lead to signifcant outcome and revealed of related deposits. Methods of research. X-ray spectral fuorescence analysis was used to determine the concentrations of petrogenic oxides and trace elements in the samples, while trace element and rare earth element (REE) contents were measured using (ICP-MS). Results of the work. Sericite and muscovite are discovered afer plagioclase. Plagioclase exhibits sericitization and epidotization as a result of hydrothermal activity. Accessory minerals (zircon and apatite), include opaque minerals are distinguished. Te trace element geochemistry of intrusion is refected in the YbN vs. (La/Yb)N ratio, which is typical of magmas found in island arcs. Granite and granodiorite formation is a segment of the island arc formed as a result of the post-subduction or syn-collision tectonic setting. indicating that the intrusion associated with the Dark Kingdom Marble deposit can be considered a part of the Syrostan massive with the same general characteristics. Conclusion. Tese fndings imply that the granite formed in a volcanic arc tectonic environment. Finally, these results present the characteristics and tectonic environment of granitic rocks, which can provide valuable insight into related mineralization and rare element concentration.

Lead isotopes and rare earth elements geochemistry of global phosphate rocks: Insights into depositional conditions and environmental tracing

Phosphate rock bears both geologically and environmentally significant information. Rare earth elements and yttrium (i.e., REY) characteristics have been commonly used for reconstructing the redox conditions of depositional environments and the effects of post-depositional diagenetic alteration on phosphate rock. In addition, phosphate rock is typically enriched in a range of trace elements such as uranium (U) and cadium (Cd) that can be dispersed as contaminants into the environment with phosphate mining and phosphate fertilizer application. Here we report the lead (Pb) isotope compositions combined with Pb and REY concentrations of both global sedimentary and igneous phosphate rocks, aiming to evalute the geological origin of phosphate rocks over time and the potential of using them for environmental tracing. Phopshate rock samples analyzed in this study were sourced from major economic phosphate deposits in the world, including China, Southern Tethys (e.g., Morocco, Tunisia, Israel), the U.S., India, South Africa and Russia. Our results show a wide range of 208Pb/204Pb (35.70 to 60.58), 207Pb/204Pb (15.20 to 18.25), and 206Pb/204Pb (16.369 to 71.806) ratios in the phosphate rocks, with sedimentary phosphate rocks being significantly more radiogenic than igneous rocks. The majority of sedimentray phosphate rocks show a notable isotopic overprinting by non-radiogenic terrestrial Pb, except for those from Israel and Morocco that have the most radiogenic Pb isotope compositions. Correspondingly, phosphate rocks with more radiogenic Pb isotope ratios show relatively pristine seawater REY features, likely suggesting their preservation of the original oxic seawater conditions and/or minimal diagenetic alteration. In contrast, phosphate rocks with less radiogenic Pb isotope compositions show REY indications for more anoxic seawater redox conditions and/or greater diagenetic alteration. We further evaluate the potential utility of Pb isotopes for tracing the associated contamination with phosphate rock mining and fertilizer application in the environment. In most cases, the radiogenic Pb isotope composition of phosphate rocks and corresponding P-fertilizers is distinctive from both natural crustal Pb and major anthropogenic Pb sources (e.g., Pb ore deposits and pesticides), which provides a great advantage for applying Pb isotopes as an environmental tracer for metal(loid) contamination from phosphate sources. The combination of Pb isotope ratios and REY proxies could further constrain the Pb source discrimination. Overall, this study provides new Pb isotopic and REY geochemical data on global phosphate rocks and fertilizers, which lays the groundwork for future regional and local studies on both their geological and environmental implications.

The propylitic alteration in the Ponce Enriquez Gold Mining district, Azuay province, Ecuador: genetic constraints from a mineral chemistry and fluid inclusions study

Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hydrothermal alteration halo of porphyry copper deposits. Fluid inclusion investigation in quartz veins associated with epidote and chlorite evidenced at least two pulses of hydrothermal fluids characterized by temperature around 345°C for the first one and around 305°C for the second one. The salinity of the fluids is always low (around 1.5 wt% NaClequiv.) suggesting a dominantly meteoric component. Evidence of boiling processes have not been observed. We hypothesize that the hydrothermally altered “green rocks” of the Ponce Enriquez Mining District could be envisaged as the propylitic halo of the Miocene hornblende-bearing Au-Cu porphyry deposits of Gaby-Papa Grande, and discuss the epidote and chlorite trace element composition in this scenario. The results help improving the general knowledge of the propylitically altered rocks in southern Ecuador and add new data for the use of trace element chemistry of epidote and chlorite in mineral exploration elsewhere.

Sphalerite and Pyrite Geochemistry from the Pusangguo Co-Rich Cu–Zn–Pb Skarn Deposit, Tibet: Implications for Element Occurrence and Mineralization

The Pusangguo deposit (1.42 Mt @ 1.42% Cu, 0.14 Mt @ 1.82% Zn, 0.08 Mt @ 1.01% Pb, and 285.8 t Co @ 140 g/t Co) is the first Co-rich Cu-Zn-Pb skarn deposit discovered in the Gangdese metallogenic belt. However, the trace and minor element geochemistry of the sulfides in this deposit has not been studied, limiting further understanding of elements’ occurrence and mineralization. Here, we identified four ore stages, and two types of sphalerites (SpI and SpII) and pyrites (PyI and PyII), in this deposit. In this study, LA-ICP-MS in-situ trace element analyses were conducted on sphalerite and pyrite, to obtain their chemical compositions, elemental substitution mechanisms, and mineralization physicochemical conditions. The results indicate that two types of sphalerites are generally more enriched with Co than pyrite. SpI has higher concentrations of Co, Cr, Cu, Ag, and As compared to SpII. Both types of sphalerite have very low contents of Sn, Ge, and Ga. PyII has higher contents of most trace elements, such as Co, Ni, Mn, Zn, Cu, As, Sn, Se, Pb, Ag, and Bi, compared to PyI. Both types of pyrite are poor in Mn, Ga, Ge, and Cd, but enriched in As, Co, and Ni. The Mn, Fe, Co, and Cd in sphalerite, and Co, Ni, and Mn in pyrite are generally lattice-bound, while Cu, As, Ag, and Sb are usually present in both micro-inclusions and coupled substitution. Significant elemental correlations in sphalerite indicate the possible substitution mechanisms 2Fe2+ + Ga2+ ↔ 3Zn2+, 2Fe2+ + Ge4+ ↔ 4Zn2+, and (Sb3+, Sn3+) + (Cu+, Ag+) ↔ 2Zn2+. The correlation trends between trace elements in pyrite suggest the coupled substitution mechanisms of (Tl+ + Cu+ + Ag+) + (As3+ + Sb3+) ↔ 2Zn2+ and As3+ + Cu+ ↔ 2Zn2+. The mineralization temperature at Pusangguo, as determined by the GGIMFis sphalerite geothermometer, is 237–345 °C (avg. 307 °C), consistent with the high Zn/Cd ratio (avg. 203), low Ga/In (avg. 0.06), and high In/Ge (avg. 15.9) in sphalerite, and high Co/Ni ratio (avg. 24) in pyrite. These results indicate that the ore-forming fluid was high-temperature, with a low sulfur fugacity (fS2) (10−13.4 to 10−8.3) and low oxygen fugacity (fO2). The high temperature, and low sulfur fugacity and oxygen fugacity of the ore-forming fluid, and the fluid-mixing process, jointly controlled the sulfide precipitation, which caused the formation of the Pusangguo deposit.

Integrated statistical analysis of calcareous nannofossil and elemental geochemistry of an outcrop from of the eastern Cenomanian Western Interior Seaway: Novel insights of shallow marine paleoceanography and nannoplankton paleoecology

Phytoplankton assemblages in shallow marine environments are being impacted by anthropogenic climate change, but long-term outcomes of these changes are uncertain. Investigation of past neritic calcareous nannoplankton can help us understand the fate these ecosystems face. In this study, a Canonical Correspondence Analysis (CCA) of calcareous nannofossils and X-ray fluorescence geochemistry was used to determine how past planktonic ecosystems were influenced by paleoenvironmental parameters on the eastern side of the Late Cretaceous Western Interior Seaway in the Cenomanian (ca. 95–93 Ma). Samples were collected every 10 cm from the Graneros Shale Greenhorn Formation at an outcrop in northwestern Iowa to determine high resolution changes in assemblages and paleoenvironments. Nannofossil diversity outside of a few small intervals ranges is high (generally 30–60 species) with abundant small Biscutum constans, confirming other publications that show elevated diversity in Cretaceous nearshore settings. The CCA results imply assemblages were most influenced by terrigenous influence, wet vs. dry climate, and changes in water mass source. Cretaceous nannofossil paleoecology was also revised based on the CCA results. Size differentiation of nannofossil taxa may highlight more complexity in environmental preferences that have been largely overlooked. After the initial transgression of the Greenhorn Sea into the region, the climate became wetter and terrigenous influence in the area was high. The peak of terrigenous influence corresponds with elevated nannofossil diversity but a lack of microfauna, which may indicate a similar oceanographic setting to the modern Gulf of Mexico nearshore dead zone. As sea level continued to rise above this point, nannoplankton assemblages indicate a potential shift to a higher productivity, stratified water column. As the muddy Graneros Shale transitioned to a further offshore chalky Greenhorn Formation, a normal marine, cosmopolitan nannofloral assemblage became established. Nannofossil and geochemical evidence indicates high productivity from upwelling might be related to the change of deposition to chalk in the Greenhorn Formation. While only a single outcrop was investigated, the novel use of an integrated micropaleontological and geochemical analysis has shed light on the dynamics of how phytoplankton ecosystems were established and modified in shallow marine environments of the Cretaceous and could have important implications on modern shallow marine settings.

Monazite record of assimilation and differentiation processes in the petrogenesis of Himalayan leucogranites

The Himalayan leucogranites have received particular attention as they record the continental crust-building processes of a collisional orogenic system. Deciphering the magmatic evolution processes and potential sources is essential for understanding the origin of the Himalayan leucogranites. In-situ monazite Th-Pb ages, trace element geochemistry, and Nd isotope ratios have been determined with whole-rock geochemical data for the leucogranites and their country rocks in the Yadong area, southern Tibet. Monazites in most of the studied leucogranites are marked by multiple age populations with variable REE ratios and wide ranges of Nd isotope ratios, reflecting a complex history of magmatic processes. Abundant inherited monazites are identified in the Yadong leucogranites, and most of them are excluded from the source regions due to their distinguished Nd isotope compositions from the magmatic monazites. The inherited monazites share close affinities in geochronological dates and geochemical compositions with those in the country rocks, strongly suggesting a major origin of the country-rock contamination. This highlights the contamination-assimilation processes in the genesis of the Yadong leucogranites. It is worth noting that xenocrystal monazites from the metasedimentary country rock are less preserved in the leucogranites than those from the granitoid country rock, which probably reflects the different assimilation reactions for different types of country rock. Assimilation of the metapelitic rocks released low content of xenocrystic monazite and high volume of partial melt into the leucogranites, whereas assimilation of the granitoid rocks released high content of xenocrystic monazite. In addition to the contamination-assimilation processes, the uniform Nd isotope data with large variations in REE ratios for magmatic monazites in some leucogranite samples suggest a subsequent closed-system fractional crystallization process during the magma evolution. Besides, some magmatic monazites in the muscovite granites show a significant tetrad effect in the Chondrite-normalized REE patterns, indicating that the magma system has evolved into an aqueous fluid-available environment. This supports an important role of the magmatic differentiation process in the formation of the Yadong leucogranites. Taken together, a petrogenic model involving AFC (assimilation and fractional crystallization) processes is proposed, and the geochemical variations of the Yadong leucogranites are mainly attributed to the post-source processes. It is suggested that the rock geochemistry of the Himalayan leucogranites often dose not directly reflect the nature and the petrogenetic processes in the source regions.

Geochemical elements as provenance and paleoenvironmental indicators in siliciclastic sediments of Neogene Gwandu formation exposed in Birnin Kebbi Area, Northwestern Nigeria

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Trace and Rare Earth Elements Geochemistry of the Mudstone Rocks from the Injana Formation: Implications for Provenance and Paleoclimate

Late Miocene-Pliocene mudstones of the Injana Formation were examined to provide insight into the nature of the source rocks and paleoclimate. For these purposes, 23 mudstone samples from three locations Mirawa and Degala in the Erbil, northern Iraq and Najaf from southern Iraq. These samples were analyzed by ICP-MS to measure the concentrations of the trace and rare-earth elements (REE). The chondrite-normalized REE of all samples are similar and shows slight enrichment with LREE relative to the HREE with negligible negative Eu anomaly. The discriminant plots of the trace elements and the enrichment factors suggest that the source was intermediate-mafic rocks, and the climate was warm and humid during the deposition of the mudstone of the Injana Formation.

Orbital Forcing and Evolution of the Southern African Monsoon From Late Miocene to Early Pliocene

AbstractThe late Miocene‐early Pliocene (7.4‐4.5 Ma) is a key interval in Earth's history where intense reorganization of atmospheric and ocean circulation occurred within a global cooling scenario. The Southern African monsoon (SAFM) potentially played an important role in climate systems variability during this interval. However, the dynamics of this important atmospheric system is poorly understood due to the scarcity of continuous records. Here, we present an exceptional continuous late Miocene to early Pliocene reconstruction of SAFM based on elemental geochemistry (Ca/Ti and Si/K ratios), stable isotope geochemistry (δ18O and δ13C recorded in the planktonic foraminiferaOrbulina universa), and marine sediment grain size data from the International Ocean Discovery Program (IODP) Site U1476 located at the entrance of the Mozambique Channel. Spectral characteristics of the Si/K ratio (fluvial input) was used to identify the main orbital forcing controlling SAFM. Precession cycles governed precipitation from 7.4 to ∼6.9 Ma and during the early Pliocene. From ∼6.9 to ∼5.9 Ma, the precession and long eccentricity cycles drove the SAFM. The major Antarctic ice sheet expansion across this interval appear to influence the isotopic records ofO. universaimprinting its long‐term variability signal as a response to the ocean and atmospheric reorganization. Precession cycles markedly weakened from 5.9 to 5.3 Ma, almost the same period when the Mediterranean Outflow Water ceased. These findings highlight important teleconnections among the SAFM, Mediterranean Sea, and other tropical regions.

Middle Eocene Climatic Optimum sensitivity of a continental lake basin from geochemical records of the Fushun Basin, Northeastern China

The dating of continuous Eocene sediments in the Fushun Basin, NE China, provides a good opportunity to study the evolution of the land paleoclimate during extreme high-temperature events in mid-latitude regions. Here, the lower part of the Eocene Xiloutian Formation in the Fushun Basin was sampled, and isotope geochemistry, element geochemistry, organic geochemical analysis, magnetic susceptibility, and sediment color analysis were conducted to determine the evolution of paleoclimate in the continental lake basin during the Middle Eocene Climatic Optimum (MECO) period. The oxygen (δ18O) and carbon (δ13C) isotope data indicated the presence of phases during the MECO, with 401.5–374.3 m (41.2–40.42 Ma) representing the main stage and 374.3–371.2 m (40.42–40.32 Ma) the recovery stage. In addition, evaluation of the opening and closing of lakes using δ18O and δ13C showed that the lakes in the lower part of the Xiloutian Formation in the Fushun Basin are currently in a transition period between open and closed. The reconstructed paleotemperature and precipitation in the lower part of the Xiloutian Formation were characterized by an initial high trend followed by a low trend, with the highest values of both occurring during the main MECO stage. The lower part of the Xiloutian Formation is characterized by an oxidative oxygen environment of brackish water, and MECO events did not affect the salinity and redox state of the water. However, the total organic carbon (average 5.24%) in the dark mudstone during the main MECO stage was significantly higher than that during the cooling period (average 4.67%), indicating that the MECO promoted carbon fixation and enrichment of organic matter. Climate comparison showed that the climatic types in eastern and western regions of China during the Eocene were similar. Furthermore, climatic evolution may be influenced by the uplift of the Tibetan Plateau, and the retreat of the inland proto Paratethys Sea.

Contribution of the upper asthenosphere to < 0.6 Ma rejuvenated Hawaiian magmas: Evidence from the Lahaina Volcanics on West Maui

The study of rejuvenated-stage volcanism provides insight into spatiotemporal changes to the geochemical structure of the Hawaiian mantle plume and the varying interaction with non-plume sources over an extended period of melting beneath volcanic centres. We present new geochemical and Hf-Pb-Sr-Nd isotope data from 6 samples of rejuvenated-stage volcanism on West Maui, the southernmost and youngest island within the Hawaiian chain to exhibit rejuvenation. Major and trace element geochemistry reveal four discrete silica undersaturated eruptions produced by 3–11% partial melting of a garnet peridotite mantle source of metasomatized upper asthenosphere. High Ba/Th ratios (>200) overlap with rejuvenated-stage lavas from Niʻihau, indicating that a minor carbonatite presence persists within the source of rejuvenated-stage lavas along the Hawaiian chain. Puʻu Laina lavas on West Maui have εHf = +15 and εNd = +8.9, which are among the most depleted values of rejuvenated lavas and plot on or below the terrestrial mantle array. These values are close to that of the most depleted lavas from the North Arch and along with rejuvenated lavas from Kauaʻi and East Molokaʻi trend towards the Pacific MORB. Pyroxenite xenoliths and lavas from Kaʻula and Oʻahu, and lavas from Niʻihau extend to higher εHf values at a given εNd indicating a long-lived depleted source independent of the MORB mantle. West Maui rejuvenated lavas form a steep 208Pb/204Pb-206Pb/204Pb trendline and together with North Arch and East Molokaʻi lavas are shifted towards lower 208Pb/206Pb values typical of Pacific MORB. We propose that the across-plume heterogeneity seen in rejuvenated lavas on Kauaʻi and Niʻihau persists at the southern end of the Hawaiian chain where West Maui and East Molokaʻi rejuvenated lavas, like Kauaʻi and North Arch, preferentially source upper asthenosphere as opposed to an ancient depleted source. This across-plume heterogeneity within rejuvenated-stage lavas closely resembles the Kea and Loa-trend differences in shield stage geochemistry and indicates that similar geodynamic processes are responsible for both.

UHP metamorphism, decompression anatexis and retrogression of garnet-bearing metagranite and granitic gneiss from the Dabie orogen during continental collision

Metamorphosed granitic rocks are commonly volumetrically dominant in continental collisional terranes, which are crucial targets for resolving the metamorphic evolution of deeply subducted continental crust. However, their metamorphic processes in ultrahigh pressure (UHP) belts are often poorly understood, because they are commonly intensely retrogressed and presently dominated by amphibolite-facies minerals with very rare petrological evidences of UHP metamorphism. It is known that, in these lithologies, zircon can potentially preserve evidence of the UHP history; therefore, the P-T-t path of metafelsic rocks may be estimated using a multidisciplinary approach which combines zircon microanalysis with phase equilibria modelling. In the central Dabie UHP metamorphic zone (CDZ) (China), two types of metamorphosed garnet-bearing granitic rocks, i.e. metagranite and granitic gneiss, whose massive vs. gneissic structure reflects a different degree of deformation, are closely associated with eclogites. Opposite to the eclogites, their detailed metamorphic evolution is poorly understood. In this study, a three-stage metamorphic evolution is reconstructed for these lithologies, based on field observation, bulk-rock elemental geochemistry, sensitive high-resolution ion microprobe zircon UPb dating, Raman micro-spectroscopy analysis of zircon inclusion, mineral chemistry, conventional thermobarometry and phase equilibria modelling. The first UHP stage is represented by the assemblage coesite-rutile-garnet-phengite preserved in the metamorphic domains of zircon and by garnet core in the matrix, revealing minimum peak pressures of 44 kbar and 30 kbar for granitic gneiss and metagranite, respectively, at 231 ± 4 Ma. The second stage is represented by anatexis at 18–20 kbar, 725–870 °C and 222 ± 3 Ma, evidenced by leucosomes at the outcrop scale and by quartzofeldspathic films with low dihedral angles, melt inclusions preserved in peritectic garnet and quartz/K-feldspar/plagioclase- garnet intergrowth at the micro-scale. The third stage is represented by amphibolite-facies overprint at 590–700 °C, 9–14 kbar, at 214–219 Ma, recorded by biotite-plagioclase-quartz symplectites developed at the expenses of phengite, re-equilibration of the peritectic garnet rim, and amphibole-quartz (biotite-titanite) inclusions in zircon overgrowth rims. The resulting P-T-t path overlaps with previous results estimated from other CDZ UHP rocks. Besides, the protoliths of both metagranite and granitic gneiss were emplaced during the mid-Neoproterozoic (683–786 Ma) period, as already documented throughout the Dabie orogen. Compared with previously published data for meta-granitic rocks in the CDZ, the weakly deformed metagranite does not appear to represent low-grade metamorphic rocks. Instead, this study (i) suggests that the two groups of lithologies experienced a coeval metamorphic evolution; (ii) reconstructs a multistage P-T-t history based on zircon microanalysis and pseudosections; (iii) reveals that anatexis, retrogression and deformation facilitate the elimination of (U)HP mineralogical records of metagranitoids. Overall, these results provide new constraints on the metamorphic evolution and exhumation processes of deeply subducted granitic rocks during continental collision.

The youngest lunar zircon reveals an extremely fractionated nature of Chang’e-5 basalt

The U(Pb)-Pb age of zircon is commonly used to represent the crystallization age for igneous rocks due to its high closure temperature and robust resistance to impact disturbance. However, no zircon crystallization age has yet been reported for Chang'e-5 (CE-5) basalt due to their limited occurrence in mare basalt. In this study, rare zircon grains from CE-5 lunar samples were investigated by the in-situ Pb isotopic analysis, and a precise zircon crystallization age of 2036 ± 19 Ma was determined from Pb-Pb isochron. This is hitherto the youngest reported crystallization age of lunar zircon, similar to the ages of CE-5 lunar basalts obtained by zirconium (Zr)-bearing minerals such as baddeleyite, tranquillityite, and zirconolite. Petrographic evidence and rare-earth element geochemistry indicate that zircon in the CE-5 lunar basalts were formed by the reaction of early-formed baddeleyite with SiO2 melt within the latest residue of extreme fractionation of a non-KREEP (an acronym for potassium, REE, and phosphorus) basaltic magma. In contrast to the prevailing view that lunar zircon have formed in late-stage enriched melts resulting from extensive fractional crystallization of the Lunar Magma Ocean, this study shows that zircon could be derived from extreme fractionation of non-KREEP basaltic magma unrelated to Lunar Magma Ocean.

Insights into mineralogical distribution mechanism and environmental significance from geochemical behavior of sediments in the Yellow River Basin, China

Mineralogical investigations on fluvial sedimentary sequences could provide historical environmental information on the effects of human activities and natural events. This study aims to identify the mineralogical distribution mechanism and environmental significance of sediments of the Yellow River Basin based on topographic analysis, statistics, weathering and recycling indices. In total, 107 samples were collected from sedimentary sequences in the source area, and the upper, middle, and lower reaches and analyzed for grain size, major elements, and mineral composition. The results showed that the climate conditions were cold and arid, where weak hydrolysis under continental weathering and strong erosion accelerated physical weathering. Clay minerals in the upper reaches primarily originated from the Tibetan Plateau, whereas the middle and lower reaches received input of aeolian deposits from Northern China. Quartz and feldspar in the middle and lower reaches may derive from the source area and upper reaches. Meanwhile, calcite and dolomite formed through diagenesis, with loess input from the Chinese Loess Plateau. Regarding heavy minerals, the dominant determinative factors of pyrite were post-depositional diagenesis and leaching. Hematite and amphibole primarily formed through magnetite conversion and contribution from regional sources, respectively. Moreover, the mineral distribution mechanism significantly affected the mobility and distribution of geochemical elements through diagenesis and alteration. The findings are instrumental in reconstructing the environmental evolution of large-scale watersheds across multiple climatic zones.

A Holocene lacustrine record of variations in chemical weathering intensity in the Mu Us Desert, China

The Mu Us Desert is an ideal location to study environmental changes during the Late Quaternary, because of its unique characteristics. The Abaoyan (ABY) profile, a typical aeolian-lacustrine profile located at the eastern edge of the desert, was investigated in this study. A basic chronological framework was established based on a combination of radiocarbon dating by accelerator mass spectrometry and in situ sedimentary phase identification. Furthermore, changes in regional chemical weathering intensity since the Holocene were evaluated through comprehensive analysis of the collected samples in terms of grain size, loss on ignition (LOI), chromaticity, geochemical element contents, and soil micromorphology. The results showed that the ABY profile was under the influence of primary and moderate chemical weathering. Regional paleoclimatic environmental changes could be divided into four stages. During Stage I (before 12.6 ka BP; pre-Holocene), the ABY profile was dominated by aeolian sand, showing a coarse average grain size, low LOI, and high chromaticity values, which may have indicated a dry and cold period. During Stage II (12.6–10.3 ka BP; early Holocene), the ABY profile was dominated by lacustrine sediments, indicating a shallow lake water environment with strong chemical weathering and a warm and humid climate. During Stage III (10.3–4.2 ka BP), the profile was dominated by sandy peat deposits with a relatively large proportion of clay particles suggesting that the intensity of chemical weathering was relatively strong in the region during this period and the climate was mainly warm and humid. During Stage IV (after 4.2 ka BP), the sediment was dominated by aeolian sand and secondary loess, the chromaticity increased, the LOI reduced, and the regional chemical weathering intensity was weaker. The change in chemical weathering intensity in this region was inferred to be a positive response to the Holocene East Asian monsoon circulation.

The Shanxi Formation responses to astronomically forced climate changes during the Upper Paleozoic in the Eastern Ordos Basin, NW China

A clearly defined geochronology and stratigraphic interpretation will enhance our understanding of the evolution of paleo water depth and transitional facies, contributing to hydrocarbon exploration. Transitional deposition is extensively observed in the upper Paleozoic of the Ordos Basin. Nevertheless, the correlation between the variations of paleo water depth and global sea-level changes remains uncertain. In this study, we employed gamma-ray logging (GR) data to analyze the cyclostratigraphy of the upper Paleozoic Shanxi Formation in the Ordos Basin. We characterized the elemental geochemistry of the Shanxi Formation using X-ray fluorescence. We reconstructed changes in Paleo Water Depth in the Ordos Basin during the upper Paleozoic by employing sedimentary noise modeling of the tuned GR logging data. Time series analysis showed evidence of the existence of 405 kyr long eccentricity, 125 kyr short eccentricity, and 35.5 kyr obliquity in sedimentary records, which was supported by a sediment accumulation rate model. Using the tuned GR data, we constructed a ∼3.07 Myr astronomical time scale in the Shanxi Formation of the sampling well. Moreover, we used the volcanic ash age (298.18 ± 0.32) Ma at the boundary of the Shanxi Formation and Taiyuan Formation as the anchor point to provide an absolute astronomical time scale from 295.11 Ma to 298.18 Ma for the study area. The variation of Paleo Water Depth in the upper Paleozoic transitional facies was confirmed by both the sedimentary noise model and the X-ray fluorescence (XRF) data, thus supporting each other. Additionally, we discovered a long-period obliquity of approximately 1.2 million years in this model, which is consistent with the global sea-level fluctuations observed during the same period. These results reveal a novel approach for evaluating the Paleo Water Depth variations in transitional facies. Furthermore, our study offers a detailed explanation of the relationship between the evolution of the sedimentary environment and the climate change resulting from astronomical orbit during the glacial period.

From Desiccation to Re‐Integration of the Yellow River Since the Last Glaciation

AbstractThe desiccation (extreme drying) of rivers has important implications for the broader Earth System. However, the desiccation history and its linkage to climate are rarely known for numerous major river systems, primarily due to difficulties in recognizing desiccation events from available stratigraphic records. Here, using a combination of geochemical techniques (major and rare‐earth element geochemistry, detrital zircon geochronology, and optically stimulated luminescence dating), we demonstrate that the Yellow River, which maintains the highest sediment load on Earth, became desiccated during the Last Glacial Maximum at approximately 20 thousand years ago. This finding implies that transportation of sediments and dissolved constituents to the oceans via the Yellow River may have decreased substantially or ceased during glacials, which would have ramifications for ocean chemistry and biology. Furthermore, our work highlights the importance of desiccated riverbed sediments as potential dust sources during glacial periods, a finding that is different from what is observed today.

The unroofing of Archean crustal domes as recorded by detrital zircon and apatite

This study presents in-situ U–Pb, Lu–Hf, and Sm–Nd isotopic data for detrital zircon and apatite collected from ephemeral streams of the East Pilbara Terrane, Western Australia. Given their disparate abundances in felsic versus mafic lithologies, a tandem apatite-zircon approach may offer more holistic insights into crust formation. Apatite U–Pb data define a single age peak at c. 2.9 Ga, consistent with labile, proximal, and first-cycle detritus from the Pilbara Craton. Conversely, zircon, a more refractory and durable mineral, records a more diverse geological history with U–Pb ages spanning from 3.6 to 0.2 Ga. The apatite age of c. 2.9 Ga records the timing through the Pb closure temperature during regional cooling following prograde metamorphism, while the Lu–Hf and Sm–Nd isotopic systems in the same grains yield c. 3.2 Ga isochrons, consistent with magmatic crystallisation at that time. Crystallisation age, initial 143Nd/144Nd and trace element geochemistry (Eu/Eu*) imply a chondritic or mixed (more radiogenic plus a less radiogenic) source for the apatite grains locally derived from the East Pilbara Terrane. Conversely, zircon ɛHf data reveal a broadly chondritic Paleoarchean proto-crust undergoing continual isotopic evolution punctuated by the input of juvenile, more radiogenic material on a quasiperiodic basis. Previous workers have invoked a crust-mantle overturn model triggered by stagnant-lid cooling and the episodic (re)fertilisation of the upper mantle to account for the periodic nature of crust formation in the East Pilbara Terrane. Detrital zircon grains track this process from a c. 3.8 Ga component that may have acted as a nucleus for subsequent crust formation. The oldest detrital zircon, on average, encompass less radiogenic (−ve ɛHf) components suggesting that the oldest grains preserve the unroofing of an ancient reworked crustal nucleus. Thus, the detrital zircon load arguably provides a more holistic record of the older crust in the region than the crystalline domes alone. Specifically, the less radiogenic dome cores are preferentially eroded due to their structural position and their mineral cargo lost into the detrital archive. We demonstrate that the apatite-zircon approach can be limited by the ability of apatite to be retained through crustal denudation.

Geochemistry of Hindoli Group Metasediments, SE Aravalli Craton, NW India: Implications on Provenance Characteristics and Tectonic Setting

Abstract The NE-SW trending Jahazpur Belt in NW India has been considered correlative with the Aravalli Fold Belt, based on lithological similarities and greenschist facies metamorphic assemblages. The 2.54 Ga ‘Jahazpur Granite’ constitutes the basement for the overlying Hindoli and Jahazpur Group sediments in this belt. These meta sedimentary sequences presently occur as a greenschist facies ensemble of phyllite, marble, greywacke, and meta-conglomerate. In this study, the trace and Rare Earth Elements geochemistry of the Paleoproterozoic Hindoli Group metapelites and metagreywackes was evaluated for source characterization and tectonic setting. The transition metals and Th, La abundances, and Th/Sc, Zr/Sc and La/Sc ratios (1.19 and 1.5, 21.31 and 17.35 and 4.02 and 2.97, for metapelites and metagreywackes, respectively) of Hindoli Group suggest a felsic source for them and some degree of sediment maturity. Both Hindoli metapelites and metagreywackes are enriched in LREE and display significant negative Eu anomalies, further substantiating a predominant felsic component in the source region. The provenance modeling calculations indicate that the detritus was mainly sourced from Mangalwar Complex, along with some inputs from Jahazpur Granite, Bundelkhand TTG and Hindoli volcanics. Geochemical characteristics also discriminate a continental collision associated with an Active Continental Margin tectonic setting for the deposition of Hindoli sediments.