Element Geochemistry Research Articles

Unravelling the effects of magmatic fractionation, fluid phase separation and dilution on the composition of magmatic-hydrothermal fluids of the Cornubian Batholith (SW England)

The compositional evolution of magmatic-hydrothermal fluids from the SnW mineralized Cornubian batholith was investigated via in situ fluid inclusion LA-ICP-MS microanalysis and reveals a large degree of variation between intrusive stages and at the sample scale, with complexities due to superposition of several mechanisms affecting fluids chemistry during the protracted evolution of the batholith. Despite large ranges of salinities (from <1 wt% to 48 wt% NaCleq.), the effects of individual processes such as magmatic differentiation, fluid saturation and boiling, fluid mixing and dilution can all be discerned on the basis of fluid inclusion trace element geochemistry combined with detailed petrography and microthermometry.In all samples, different fluid types (aqueous liquid-rich, vapor-rich and brine inclusions) were identified in variable proportions and microthermometry revealed complex temporal trends. Granite-related samples from the G5 intrusive stage are characterized by intermediate density fluids undergoing magmatic fractionation under pressure conditions above 1.5 kbar, indicated by successively decreasing fluid salinities with concomitant increases in Li, B, Rb and Cs concentrations. The latter two elements later strongly partitioned in the brine phase upon boiling, together with most of the other Cl-complexing elements (e.g., Fe, Mn, Pb, Zn). Those brines subsequently underwent progressive dilution with meteoric waters that caused a decrease in the concentration of all elements (besides B) and homogenization temperatures. In G3 granite from Dartmoor, on the other hand, brine inclusions represent the earliest fluid type while intermediate density fluids are absent, and a large salinity range in the fluid inclusion record associated with a decrease in homogenization temperatures represents their progressive dilution with meteoric fluid. The lack of intermediate density fluids at Dartmoor indicates fluid exsolution at relatively low pressures resulting in immediate phase separation into brine and vapor.All studied samples associated with ore mineralization display only the trend of dilution of high-salinity magmatic fluids. Their transition metal contents (e.g. Fe, Mn, Pb and Zn) show the expected positive correlation with salinity of the fluids. Conversely, the compositional trends observed for Sn and particularly W are more enigmatic, as they do not appear to significantly fractionate during most of the physicochemical processes outlined above and appear to be unrelated to fluid salinity, opposite of what would be expected for Sn as it is dominantly transported in Cl-complexes.This study highlights the key advantages of high-resolution geochemical fluid inclusion studies in discerning a variety of magmatic and post-magmatic processes in fluids in comparison to bulk fluid inclusion techniques or more simplistic fluid inclusions studies which might overlook important aspects of the typically complex history of fluids evolution in magmatic-hydrothermal systems.

Petrography, geochemistry and monazite geochronology of crustal xenoliths hosted by Afonso Cláudio Intrusive Complex, Araçuaí-West Congo orogen (southeast Brazil): Insights about contamination, magma sources and evolution of the post-collisional magmatism

The Afonso Cláudio Intrusive Complex (ACIC) is a typical post-collisional intrusion from Araçuaí-West Congo orogen (AWCO). The ACIC intruded allanite-bearing orthogneisses from AWCO pre-collisional tectonic stage (Rio Doce arc related rocks) and paragneisses from Nova Venécia Complex and it is composed of two lowered off-centered monzogabbroic and monzodioritic cores surrounded by quartz monzonite high hills, showing intense magma mingling and mixing between these domains. Xenoliths attributed to the enclosing gneisses have been commonly found widespread in the quartz monzonitic rocks, while are occasional in the monzogabbroic and monzodioritic domain. This paper presents the first detailed investigation of the xenoliths hosted by an AWCO post-collisional intrusion, focusing on petrography, major and trace element geochemistry and U–Th–Pb monazite dating of the main xenolith types. For comparison, major and trace element data investigation of the ACIC enclosing rocks has also been conducted. The correlated xenoliths and ACIC enclosing rocks show partially similar geochemical features, however both show different REE and multi-element normalized patterns compared to the ACIC main rocks. These results suggest that correlated xenoliths and enclosing rocks are cogenetic, however both could not represent the main sources of magmas that generated the ACIC. Geochemical modeling of igneous processes of previous ACIC dataset considering the investigated xenoliths and enclosing rocks as the main assimilant material suggests that mixing was responsible for both ACIC main rocks similar geochemical patterns and linear trends in the bimodal diagrams. This modeling also indicates that the evolution of the ACIC main rocks was ruled by different processes. Fractional crystallization with minor influence of assimilation of enclosing rocks controlled the magmatic evolution of monzogabbro and monzodiorite related to an enriched mantle source, while coupled assimilation and fractional crystallization ruled the evolution of quartz monzonite possibly associated to lower crust magmas mainly contaminated by enclosing rocks. U–Th–Pb monazite dating of two xenoliths showed that these rocks preserved similar main ages related to different stages of ACIC and AWCO post-collisional evolution. Both xenoliths showed main older ages of 478 and 477 Ma which are related to ACIC intrusion during AWCO post-collisional stage, while younger ages of 431 and 427 Ma are probably related to the intrusion of syenogranite dykes that crosscut the ACIC, representing an extension of AWCO post-collisional magmatism or a later unrelated thermal event. Due to the similarities between the typical AWCO post-collisional intrusions, the insights brought about the evolution of ACIC magmas could be considered to the typical AWCO post-collisional mantle and crustal magmas. This first investigation of xenoliths hosted by an AWCO post-collisional intrusion has showed that these strange rock pieces could bring new and important insights about the AWCO evolution, which shows an amazing and long-lasting magmatism with common occurrence of poorly investigated xenoliths.

Geochemical and palynological records of the Early‐Middle Jurassic in the Turpan‐Hami Basin, NW China: Implications for paleoenvironment and paleoclimate change

The Early‐Middle Jurassic is one of the crucial coal‐forming geologic periods in the world and an important target for hydrocarbon exploration in the Turpan‐Hami Basin, China. The paleoenvironment and vegetation reconstruction of the Early‐Middle Jurassic have been investigated using elemental geochemistry and palynological analysis to reveal paleoclimate evolution. A total of 48 genera of pteridophyte spore and 35 genera of gymnosperm pollen were identified, and 5 palynological assemblages were longitudinally divided, which showed significant differences in geochemical behaviours. The paleoenvironment was a transition from suboxidation to anoxia and then to an oxidation environment under freshwater conditions. The paleowater in the northern Taibei Sag was deeper than that in the southern part during the Middle Jurassic, which coincided with the sedimentary background of the sublacustrine fan in the north and the shallow braided river delta in the south. The paleovegetation evolved from mixed lowland–upland forest in the Hettangian‐Toarcian, to lowland fern forest in the Aalenian‐Bajocian, to upland conifers forest in the early Bathonian, to upland Cheirolepidiaceae forest in the late Bathonian‐Callovian. The Toarcian and Bathonian‐Callovian arid climate and the Hettangian‐Pliensbachian and Aalenian‐Bajocian warm‐humid climate were responses to the continued global warming events and the intensification of the East Asian monsoon circulation, respectively. The influence of the Bathonian‐Callovian aridification event on the sedimentary response in the southern Taibei Sag will be delayed due to the gradual southward migration of the depositional centre.

Major elements geochemistry of chlorite in different ore deposits and its genesis and exploration significance: a case study from Naruo porphyry Cu deposit in Duolong ore district, Tibet

Major elements geochemistry of chlorite in different ore deposits and its genesis and exploration significance: a case study from Naruo porphyry Cu deposit in Duolong ore district, Tibet

Major, trace and platinum-group element geochemistry of Mesoarchean komatiites from the Banasandra greenstone belt, Western Dharwar Craton (southern India): implications for multi-stage plume magmatism in generating compositionally diverse komatiites

ABSTRACT The early Archean Al-undepleted komatiites (AUK) from two locations (Kunikenahalli, Kodihalli) of the Banasandra greenstone belt in the Western Dharwar Craton are studied for understanding their petrogenesis. The field distribution, mineralogy and geochemistry indicate their cogenetic nature. The samples are mainly cumulates (MgO: 37–45 wt%), now completely serpentinized, while the spinifex zone is obscure. Using geochemical modelling, the MgO content of the primary undifferentiated magma is estimated to be nearly 25 wt%. The depleted LREE values from this study, and the positive εNd values from previous studies suggest that the komatiites are derived from a depleted mantle source. Trace-element and PGE geochemistry eliminate the possibility of crustal contamination and sulphide-saturation in these komatiites after emplacement. Modelling results estimated in this study suggest ~45% melting of a deeper mantle (~6 GPa) to generate the komatiites. Fractionation of olivine (Fo94) from the parental melt and their accumulation formed the mesocumulates in Kodihalli, and the more fractionated orthocumulates in Kunikenahalli. The compositional spectrum from AUK through Al-depleted (ADK) to Al-enriched (AEK) varieties in the Banasandra greenstone belt reported in this study and others, are proposed to be a product of melting of a single mantle plume at different depths.

Identifying and characterizing missing source orogens for syn-orogenic basins based on detrital accessory mineral U-Pb geochronology and trace element geochemistry

Abstract Identifying source orogens for syn-orogenic sediments in dispersed fragments of a supercontinent provides key information on the tectonic evolution of the orogens involved in supercontinent assembly and on paleogeographic reconstruction. An approach using U-Pb geochronology and trace elements of multiple detrital minerals including zircon, rutile, apatite, and monazite has major advantages over detrital zircon studies alone. Application of this multi-pronged approach to Ediacaran and Cambrian clastic sedimentary rocks from the West Cathaysia terrane of the South China block demonstrates that these rocks were deposited in two distinct, but overlapping, syn-orogenic basins related to the assembly of eastern Gondwana. The Ediacaran rocks have detritus likely sourced from the Paterson-Petermann orogen (PPO) in Australia, and the dominant 650–600 Ma populations and trace element compositions of detrital rutile and apatite indicate a significant Ediacaran thermal and high-pressure metamorphic event in the orogen. The appearance of Cambrian and Tonian detrital rutile and apatite populations in the Cambrian rocks indicates derivation from a different source orogen characterized by multiple thermal events, most likely the Kuunga-Pinjarra orogen (KPO). Our data suggest that West Cathaysia was located adjacent to both the PPO and the KPO and support the hypothesis that the PPO was a collisional, rather than a long-lived post-Grenvillian intraplate, orogen. Our data also suggest a poly-metamorphic history for the poorly preserved northern part of the KPO and a larger expanse of Greater India.

Middle to late Holocene climate change in the monsoon-dominated southeastern Tibetan Plateau and its relationship with human activity

Aeolian deposits on the southeastern Tibetan Plateau (SETP) can provide evidence of how prehistoric humans were influenced by climatic and environmental changes in high-altitude regions. We present the results of multi-proxy analyses of a middle–late Holocene aeolian section in the SETP, together with the probability density of the ages of various cultural sites within and around the study area. Quartz optically stimulated luminescence dating provides a reliable chronology for this section, and analyses of geochemical elements, color and grain size are used to reconstruct the pattern of climate change during the middle–late Holocene. The results suggest a trend of gradually decreasing moisture from the middle Holocene (∼6 ka) onwards, followed by a slight increase at ∼2 ka, which is supported by TraCE-21 ka simulation results. These changes were closely related to variation in the Indian summer monsoon (ISM) caused by decreasing Northern Hemisphere summer insolation and an increase in the Atlantic Meridional Overturning Circulation. The variations in dust activity are inversely related with moisture and there was a significant decrease in dust activity after ∼2 ka. The drought conditions during the 4.2 ka event recorded within the section appear to be a continuation of the trend of middle–late Holocene climatic deterioration, which is superimposed on a weakening trend of the ISM. The permanent human occupation of the study area after ∼2 ka corresponded to an interval of mild and wet climate when dust activity was relatively weak. An observed correlation between the intensity of human activity and dust storms suggests that the enhancement of human activities played a significant role in increasing the occurrence of dust storms. Overall, our results provide new insights into human-environmental interactions in the SETP.

Genesis of gray sandstone within the red beds in HLJ-DL uranium deposit, southwest Songliao Basin and its relationship with uranium mineralization

The search for uranium deposits in the red beds is currently a hotspot in China's sandstone-type uranium exploration efforts. The typical occurrence of uranium deposits is within gray sandstone layers amidst the red beds, where the distribution of these gray sand bodies dictates the presence of uranium deposits. Hence, delving into the genesis of gray sandstone within the red beds proves beneficial for both uranium exploration and unraveling the ore-forming mechanisms. However, there is currently significant controversy surrounding the genesis of gray sandstone in the red beds. This paper focuses on the typical uranium deposit in the red beds—the HLJ-DL uranium deposit in the southwestern part of the Songliao Basin. It investigates the genesis of gray sandstone within uranium-bearing rock series and its relationship with uranium mineralization. The lithology of representative drill cores, including the red sandstone for comparative study, is methodically examined, along with their elemental geochemistry as well as carbon and oxygen isotope characteristics. The petrological characteristics suggest that both the gray and red sandstone share similar compositions of clastic particles, indicating minimal influence of the source rock on the sandstone color. The gray sandstone displays comparable TOC content (averaging around 0.05 %) and δ18OPDB values (averaging around −16 ‰) to the red sandstone. However, it exhibits relatively higher δ13CPDB values (averaging −0.26 ‰), whereas the average δ13CPDB value for the red beds is −1.61 ‰. The data indicate that the gray sandstone is less affected by hydrothermal or hydrocarbon fluids. Compared to the red sandstone, which has relatively higher Cu/Al values (averaging 1.09) and Fe3+/Fe2+ ratios (averaging 3.37), the gray sandstone exhibits low Cu/Al values (averaging 0.44) and a low Fe3+/Fe2+ ratio (averaging 0.36), suggesting its formation in a relatively reducing environment. The reducing conditions necessary for the formation of gray sandstone may stem from the climate becoming relatively warm and humid, irrespective of whether it originates from the original sedimentary environment or is induced by the reducing pore water discharged from dark mudstones. The chemical weathering index of fine-grained sediments indicates that, the gray sandstones were commonly configured in relatively humid-warm climate with fairly low dissolved oxygen content in the bottom water. Additionally, the deposition of the uranium-bearing rock series experienced alternating climatic changes, rather than consistently being in a humid-warm climate. This resulted in the sand bodies with low TOC content, insufficient reducing potential, and uranium mineralization primarily occurring in the interior of the basin. Organic matter has a relatively weak control over uranium mineralization, whereas uranium mineralization shows a certain correlation with iron reduction. The ore-forming fluid was uranium-rich oxygenated atmospheric water. Dark-colored mudstones, formed under humid-warm climatic condition, contain relatively high TOC contents (avg. 0.43 %) and exhibit a strong reducing capacity. The reducing pore water in dark-colored mudstones excreted into the adjacent sandstones under compaction during the early diagenesis, is able to serve as a vital reducing agent in later-stage uranium mineralization. Additionally, certain dark-colored mudstones with high uranium content (up to 944 ppm) undergo significant uranium pre-enrichment, providing a partial uranium source for uranium mineralization.

Ultrapotassic plutons as a source of uranium of vein-type U-deposits (Moldanubian Zone, Bohemian Massif): insights from SIMS uraninite U–Pb dating and trace element geochemistry

The Bohemian Massif hosts significant hydrothermal U-deposits associated with shear zones in the high-grade metamorphic basement. But there is a lack of evidence of a genetic link between mineralization and U-fertile igneous rocks. This contribution provides constraints on the major U source of the vein-type U-deposits, the timing of ore formation and the metallogenetic model. The anomalous trace element signatures of the low-temperature hydrothermal deposits (high Zr, Y, Nb, Ti, ∑REE) and their close spatial relation with ultrapotassic rocks of the durbachite series point to a HFSE and REE enriched source rock. The durbachites have high U content (13.4–21.5 ppm) mainly stored in magmatic uraninite and other refractory minerals (e.g., thorite, zircon, allanite) that became metamict over a time interval sufficient to release U from their crystal structure, as suggested by the time gap between emplacement of the durbachites (EMP uraninite U–Pb age ~ 338 Ma) and hydrothermal activity (SIMS uranium ore U–Pb age ~ 270 Ma). Airborne radiometric data show highly variable Th/U ratios (1.5–6.0), likely reflecting a combination between (1) crystallization of magmatic uraninite, (2) hydrothermal alteration, and (3) leaching and mobilization of U along NW–SE-trending fault zones, manifested by elevated Th/U values in the radiometric map. The presence of rare magmatic uraninite in durbachites suggests almost complete uraninite dissolution; EMP imaging coupled with LA-ICP-MS analyses of refractory accessory phases revealed extensive mobilization of U together with HFSE and REE, providing direct evidence for metal leaching via fluid-driven alteration of radiation-damaged U-rich minerals. The large-scale HFSE and REE mobilization, demonstrated by the unusual trace element signatures of the U-deposits, was likely caused by low-temperature (270–300 °C), highly alkaline aqueous solutions containing F-, P-, and K-dominated complexing ligands. The first SIMS U–Pb age of 270.8 ± 7.5 Ma obtained so far for U-mineralization from the Bohemian Massif revealed a main Permian U mineralizing event, related to crustal extension, exhumation of the crystalline basement, and basin formation, as recorded by U–Pb apatite dates (280–290 Ma) and AFT thermal history models of the durbachites. The Permo-Carboniferous sedimentary cover probably represented a source of oxidized basinal brines infiltrating the basement-hosted durbachite plutons and triggering massive metal leaching. The interaction between basin-derived brines and durbachites resulted in significant modification of the chemical composition of the hydrothermal system (K and F release during biotite chloritization, P liberation through monazite alteration), leading to the formation of ore-bearing fluids responsible for the metallogenesis of the basement-hosted unconformity-related U-deposits in shear zones in the Bohemian Massif.

Sulfur isotope and trace element geochemistry of sulfides from the unique Yaojialing Zn-Au-Cu deposit, Lower Yangtze River Metallogenic Belt, China: Implications for ore-forming process and exploration

The Yaojialing Zn-Au‑Cu deposit is a porphyry-skarn-epithermal vein-type compound deposit that consists of epithermal vein-type lead‑zinc‑silver orebodies, skarn Zn-Cu-Au orebodies, and porphyry CuAu orebodies from shallow level to depth. We decipher the source and metallogenic mechanism by studying the trace element and S isotopic compositions of sulfides (pyrite, sphalerite, chalcopyrite, and galena) from three types of orebodies. The collected pyrite can be divided into two types. PyI coexists with chalcopyrite, and PyII coexists with sphalerite or galena. In addition, PyI was further divided into PyIa (collected from porphyry copper bodies) and PyIb (collected from skarn copper bodies). PyII can be further divided into PyIIa (collected from skarn-type lead‑zinc ore body) and PyIIb (collected from vein lead‑zinc ore body in strata). Sphalerite and galena from skarn-type PbZn ore bodies and shallow vein-type PbZn ore bodies are named SpI and GnI, and SpII and GnII, respectively.Pyrite and sphalerite trace element thermometers revealed that the temperature of the ore-forming fluids decreased from 500 to 600 °C in the porphyry ore body to 300– 360 °C in the skarn ore body and then to 240– 280 °C in the shallow vein ore body. The decrease in the Co and Ni contents of pyrite collected from deep to shallow depths may indicate that meteoric water precipitated in the late ore-forming hydrothermal system. Rapid crystallization and variations in the physicochemical states (such as temperature, pH, fO2, and geochemical composition) of the fluids resulted in an obvious oscillating zone of euhedral PyI pyrite particles. It also affects the solubility of trace metal elements and leads to the selective entry of these elements into pyrite. PyII also shows obvious zonation characteristics rather than oscillating zonation, indicating that the growth rate of pyrite is relatively slow. Moreover, the relationships between the Au and As contents in the two types of pyrite are different. PyI is coupled, while PyII shows decoupling. We believe that this phenomenon is due to the high content of As in ore-forming fluid systems, which may inhibit the absorption of Au on the surface of pyrite rather than the decoupling of Au and As caused by rapid crystallization, based on the rapid increase in As content and non-oscillating zonation in PyII. According to the analysis of the sulfur isotopes of various sulfides, the solid evidences suggest that the ore-forming materials of each type of orebody in the Yaojialing deposit were mainly derived from magmatic-hydrothermal processes and that the fractionation of sulfur isotopes was the result of variations in physicochemical conditions caused by magma-hydrothermal evolution rather than the addition of foreign sulfur sources.

Pyrite geochemical fingerprinting on skarn ore-forming processes: A case study from the Huangshaping W–Sn–Cu–Pb–Zn deposit in the Nanling Range, South China

Pyrite geochemistry has been extensively used to reveal ore-forming processes in diverse ore deposits, but its application in skarn systems is not well understood. The Huangshaping deposit in the Nanling Range (South China) uniquely develops W–Sn–Pb–Zn and Cu–Pb–Zn skarn mineralization systems, and both two systems have formed multi-types of pyrite, which provides a good window to reveal the mineralization histories of different skarn systems using pyrite trace element geochemistry. In the Cu–Pb–Zn system, texturally homogeneous Py1 mainly occurs in calcite veins within the host rock, whereas texturally homogeneous Py2 in the calcite-sulfide stage mainly occurs in skarn orebodies. Py3 in the siderite-sulfide stage replaces Py2 and commonly develops abundant pores or fractures, resembling the “bird's eye” texture. In the W–Sn–Pb–Zn system, Py4 in calcite veins can be divided into the oscillatory-zoned Py4a and irregular Py4b under BSE, and Py4b commonly replaces Py4a as veins or overgrowth. Texturally homogeneous Py5 in the calcite-sulfide stage occurs in skarn orebodies and is replaced by Py6 with a “bird's eye” texture in the siderite-sulfide stage.In the Cu–Pb–Zn system, Py1 may have formed by fluid cooling during its ascent along the hydraulic fractures indicated by its enrichment of Co, Ni, As, Sb, and Tl, whereas Py2 is likely formed under higher temperature and pH conditions caused by intense fluid-rock interactions evidenced by its depletion of Co, Ni, As, Sb, and Tl as well as its enrichment of Zn and Ag. In the W–Sn–Pb–Zn system, Py4b has higher contents of Co, Ni, As, Sb, and Tl than Py4a and similar contents of Ag, Zn, and Mo with Py4a, suggesting that decreasing temperature may have controlled the formation of Py4b. Py5 is featured by the depletion of As, Sb, Tl, and Mo as well as the enrichment of Zn and Ag, indicating that Py5 is likely formed under higher temperature and pH conditions resulting from the intense fluid-rock interactions. Marcasite replaces pyrrhotite and then is replaced by pyrite may be an important precipitation mechanism for pyrite with a “bird's eye” texture (Py3 and Py6) in both two skarn systems at Huangshaping. This study demonstrates that fluid-rock interaction is an important mechanism for sulfide precipitation at Huangshaping, which shows that pyrite geochemistry has good potential to reveal mineralization histories in skarn systems.

The effects of weathering and sediment source mixing on whole-rock geochemical provenance studies, Cook Inlet forearc basin, south-central Alaska, USA

The provenance of most basin systems today is interpreted based on radiogenic ages or the geochemical composition of detrital minerals, which has all but replaced the use of whole-rock geochemical approaches that can effectively complement provenance information inferred from detrital approaches. Here, we further investigate previous provenance models developed using detrital zircon U-Pb geochronology by applying whole-rock major and trace element geochemistry of fine-grained clastic rocks from the late Oligocene−middle Miocene Tyonek Formation, late Miocene Beluga Formation, and Pliocene Sterling Formation in the Cook Inlet Basin, Alaska, USA. When taken alone, our new geochemical data suggest solely intermediate igneous sediment sources to the basin. When paired with existing detrital zircon U-Pb data, however, significant mixing of felsic and mafic sediment sources is evident, which indicates that thorough mixing of geochemically distinct source terranes can mask the input from individual sources in whole-rock geochemical studies. Furthermore, we demonstrate that both weathering and provenance influence the major element chemistry of sediment source terranes as well as the resultant basinal strata. Our conclusions indicate that the combination of whole-rock geochemistry with other detrital approaches provides a robust interpretation of sedimentary basin provenance.

Spatio-temporal patterns of intense tropical cyclones in the Western North Pacific over the past 1600 years

There are concerns that intense tropical cyclones (TCs) are expected to become more frequent and powerful in warming climates. However, the long-term trend of TC activities, the spatiotemporal variability of such trends across different latitudes of the Western North Pacific (WNP), and the drives of the variability remain unclear. Here, we present a reconstruction of a 1600-year paleo-TCs activity using a sediment core taken in Li’an Lagoon located in southeastern Hainan Island, South China Sea. We used muti-dating methods (210Pb and AMS 14C dating) for age control and muti-proxy analysis (XRF geochemical element scanning and grain size analysis) for identifying periods of frequent intense TC activities. Based on an updated compilation of basin-wide paleo-TC records, we confirm that there exists a seesaw pattern of intense TC frequency between low and middle latitude in the WNP. Comparing with global and regional paleoclimate proxies, we propose that the basin-wide latitudinal TC activity variation in the WNP can be linked to the migration of Western Pacific Subtropical High (WPSH) and its associated high-latitude forcings (e.g., NAO) and low-latitude internal variability forcings (i.e., El Niño Southern Oscillation, sea surface temperature (SST)). More intense TC will occur at low latitudes in the future, though with less frequency.

Contribution of Asian dust into the sediment budget of the Parece Vela Basin over the last 1 Ma: Implications for the climate change in East Asia

By quantifying the deposition of Asia-derived dust in the Western Pacific Ocean it is possible to constrain the consequences of climate change in East Asia. However, the rates of eolian dust deposition and its transport mechanism in the low-latitude Pacific remain uncertain. Core CP19 recovered sediment dating from ∼1 Ma to the present in the Parece Vela Basin (PVB). In this study we present bulk-rock major and trace element geochemistry, and Sr and Nd isotopic compositions from this sediment. The results reveal that these clastic sediments are a mixture of volcanic materials derived from the adjacent island arcs and eolian dust material originating from the arid regions of East Asia. Within the PVB, the proportion of Asian dust in the detrital sediment ranges from 30% to 50%, with an average of 44%. The majority of the dust originated from Eastern Asian deserts. Sr and Nd isotopes indicate that there is a significant increase in the overall proportion of eolian dust in the PVB starting at ∼0.64 Ma, influenced by an enhanced East Asian winter monsoon. In contrast, strengthening of the East Asian summer monsoon led to a decrease in the proportion of the eolian dust from the Ordos deserts. The notable alteration in eolian dust flux to the PVB corresponds to an abrupt intensification of aridity and monsoon climate in the East Asian continent at ∼0.64 Ma, caused by the Middle Pleistocene Climate Transition.

Constraints of Sedimentary Environment on Shale Organic Matter Enrichment: Insights from Elemental Geochemistry and Multiple Factor Analysis.

The organic-rich shale of the Wufeng-Longmaxi formation is an important section for shale gas exploration. The traditional univariate or bivariate analysis causes researchers to have great controversy about its enrichment mechanism. This study explores the combination of multiple factor analysis (MFA) and element geochemistry to calculate the contribution rate of a paleoenvironment to organic matter enrichment and clarify the main controlling factors of organic matter enrichment. Research has shown that there is generally high productivity from the Wufeng (O3w)-Longmaxi formation (S1l) deposition. The degree of terrigenous clastic input and weathering during the period of the O3w is relatively low, and sedimentary water restriction is strong, mainly developing an anoxic-dysoxic sedimentary environment. During the deposition of S1l1, the input intensity and weathering of terrigenous debris were slightly enhanced, and the increase of the water column led to the development of an anoxic environment at the bottom of the water layer. During the S1l2+3 period, the degree of terrigenous debris and weathering is the largest, and the high oxygen content of the water column is mainly a normal oxic environment. An MFA calculation shows that the paleoproductivity and paleoredox environment of the organic-rich shale section have the highest contribution rate of about 59.57% to the enrichment of organic matter, which is higher than that of paleoclimate conditions and terrigenous clastic input, indicating that the enrichment of organic matter is mainly controlled by paleoproductivity and the preservation environment. This study provides a basis for the application of MFA in element geochemistry and can serve as a model for other studies.

Earthquake supercycles and fault interaction over the past 32 ka in the Lake Ebinur area, Xinjiang, China

Earthquake prediction and disaster assessment in tectonically active regions require a continuous and complete regional seismic archive, which is commonly difficult to obtain, especially for prehistoric records. Here, high-resolution analysis of the sedimentary sequence from Lake Ebinur in Xinjiang revealed a detailed history of environment evolution since 32 ka ago. Both the Cl content and ultrafine proportion revealed the changing climate: the climate was relatively dry with low lake-water volumes from 32 to 12 ka, while the climate became warmer and wetter since 12 ka. In addition, eight earthquakes were identified by comprehensive analysis of grain size and geochemical element proxies, showing more than two seismic supercycles, with gaps of ∼10.4 ka; these gaps are much larger than those inferred previously (∼4–7 ka). Notably, these seismic events exhibited a pattern of mutual transmittance between the BoA and Jinghenan faults. Such fault interaction can occur in the Lake Ebinur area because it is dominated by weak lithosphere in which strain is easily accumulated and released; the interaction can also be attributed to the unique spatial distribution and immature nature of both faults. Combined with trenching investigations, our high-resolution analysis of lacustrine sediments can reveal a complete history of tectonic activity, which can efficiently serve regional earthquake prediction and disaster assessment.

Gold source and deposition in the Sanakham gold deposit, SW Laos: Constrains from textures, trace element geochemistry and in-situ sulfur isotopes of pyrite

The Luang Prabang (Laos) – Loei (Thailand) metallogenetic belt is endowed with major porphyry-skarn, and epithermal gold deposits. The Sanakham gold deposit is a newly discovered hydrothermal vein-type orogenic gold deposits (10.6 t Au @ 3.05 g/t) in the belt, and consist of a series of quartz-sulfide veins that are controlled by secondary structures of the regional NNE-trending brittle-ductile shear zone. Its mineralization can be divided into four stages: (I) quartz–pyrite–arsenopyrite, (II) quartz–pyrite–pyrrhotite–chalcopyrite, (III) quartz–pyrite–base-metal sulfide, and (IV) quartz–carbonate. Three pyrite generations were identified: py1 (stage I) as disseminated euhedral to subhedral coarse grains; py2 (stage II) as subhedral to anhedral fine grains occur around the cataclastic and corrosion textures in py1; py3 (stage III) as subhedral to anhedral fine grains occurred in sulfide veins or veinlets that overprint the existing quartz-sulfides. All three generations of pyrite have low trace-element contents including very low lattice-bound gold (py1: 0.040 ppm; py2: 0.098 ppm; py3: 0.028 ppm) and arsenic (py1: 227 ppm; py2: 133 ppm; py3: 13.3 ppm) contents. Visible gold grains are sited in textures of pyrite grains that relate to brittle cataclastic deformation. Considering the relatively low contents of pyrite in the ores of Sanakham, it is impossible to derive the high-gold grade orebodies through local remobilization of originally lattice-bound gold in pyrite. The py2 might be formed during hydrothermal overprinting and dissolution of py1 led by continuous supply of ore fluids with relatively higher contents of Au, Ag, Cu, Sb, Te, Pb, and Bi. A reduction reaction related to reduced carbon species in wallrock is an assignable cause for gold deposition, even though the fluid-rock interaction and fluid immiscibility processes might be important. The Au- and As-poor pyrites have similar δ34S values (py1: –2.58 to –0.83 ‰; py2: –2.17 ‰ to + 0.25 ‰; py3: –1.24 to –0.60 ‰ ppm) that close to 0 ‰, indicating the sulfur may have been originated from magmatic or mantle sources. Therefore, we propose that the Sankham gold deposit is a member of the orogenic deposit class, but notably characterized by the low concentrations of invisible gold in the relatively As-poor pyrite lattice.

Trace elements in zircon record changing magmatic processes and the multi-stage build-up of Archean proto-continental crust

Zircon trace element geochemistry has become an increasingly popular tool to track crustal evolution through time. This has been especially important in early-Earth settings where most of the crust has been lost, but in some fortuitous instances detrital zircons derived from that lost crust have been preserved in younger sediments. To study the formation and geochemical evolution of continental crust from the Hadean to the Paleoarchean, the 3.6 to 3.2 Ga Barberton Greenstone Belt in southern Africa is an excellent target due to its outstanding preservation and presence of detrital zircons that span almost a billion years. Here, we use trace elements, in combination with hafnium and oxygen isotopes, of 3.65 to 3.22 Ga detrital and tuffaceous zircons of the Moodies and Fig Tree groups and compare their geochemistry to previously studied 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed of the Onverwacht Group. The major detrital zircon age clusters in the former at 3.55 Ga, 3.46 Ga, and 3.26–3.23 Ga overlap with episodes of TTG emplacement and felsic volcanism in the Barberton area, suggesting a local provenance. In contrast, age clusters at 3.65 Ga and 3.29 Ga of the Moodies and Fig Tree groups as well as 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed do not have known intrusive sources and were likely derived from outside the present-day Barberton belt. This indicates that more than half of the felsic igneous events in the detrital zircon record do not have a whole-rock representation that can be directly studied. The similar compositions and inferred crustal evolution histories recorded in zircons from the Fig Tree and Moodies groups, as well as from the Green Sandstone Bed, suggest that they were derived from connected terranes experiencing similar crustal processes diachronously. Together, they show three phases of felsic continent formation, reflecting different crustal processes: (1) long-lived protocrust formed in the Hadean from undepleted mantle sources. These zircons are vastly different from younger zircons and, hence, Barberton TTGs are not good analogues of Hadean crust formation. (2) At 3.8 Ga, onset of significant crustal growth though cyclic juvenile additions and hydrous melting, possibly within a volcanic plateau setting but an arc-like setting cannot be excluded based on this data. (3) Between 3.4 and 3.3 Ga, felsic crust is generated through a previously unrecognized episode of crustal growth by shallow melting of mafic, mantle-derived sources. This is immediately followed by the onset of crustal thickening through the transport of surface-altered, hydrated materials to deep crustal levels. Since there is geological evidence for extension and shortening at that time this may reflect the onset of horizontal movement. Whether this last geodynamic setting reflects modern-style plate tectonics or not, continent formation and the onset of plate tectonics in the Barberton area occurred through complex multi-stage processes spanning almost a billion years, most of which is only accessible through the detrital zircon record.

Spatializing soil elemental concentration as measured by X-ray fluorescence analysis using remote sensing data

Spatial soil information has significantly contributed to public policy and planning. The use of X-ray fluorescence spectrometry (XRF) in soil science, primarily in laboratory settings or for isolated point analyses, has been well documented. This study broadens the application of XRF data by integrating it with remote sensing data for a comprehensive understanding of soil patterns and processes. Focusing on a 2574 km2 area in Brazil, we utilized a lab-based XRF instrument to measure the total concentrations of key chemical elements in the soil, such as Al, Si, Ti, and Fe. These geochemical data were then spatialized using the digital soil mapping (DSM) framework. We employed a synthetic bare soil image and elevation data as covariates in the analysis. The spatial accuracy assessment yielded R2 values ranging from 0.65 to 0.81 for Fe, 0.62 to 0.78 for Ti, 0.52 to 0.63 for Si, and 0.48 to 0.63 for Al. The digital soil maps of geochemical elements aligned well with existing pedological, and geological maps as evaluated using multiple correspondence analysis. The integration of spatialized XRF data with DSM and remote sensing techniques shows significant promise in assessing soil variations across landscapes based on their chemical composition.

Garnet U-Pb geochronology and geochemistry of the Lazhushan Fe skarn deposit, Edong District, eastern China

Garnet is ubiquitous in skarn deposits. It is a sensitive recorder of physiochemical conditions and also a powerful geochronometer. In this study, we use garnet trace element geochemistry and U-Pb geochronology as well as sulfur isotopes of sulfides to constrain the age and mineralization process of the Lazhushan Fe skarn deposit.Garnets in the Lazhushan Fe skarn belong to the andradite-grossular solution series and yield a compositional range from Adr47.2Gro50.7 to Adr97.4Gro0.9. There are strong correlations between LaN/YbN ratios and andradite contents in garnet, indicating that garnet major element composition exerts a strong control on the REE fractionation. The decrease of HFSEs (Nb, Ta, Zr, Hf, and Ti) and Co, V, and Mn concentrations from prograde to retrograde garnets may reflect increasing water/rock ratio and decreasing temperature during skarn evolution, respectively. Co-precipitation with magnetite may be responsible for the low concentration of V in the retrograde garnets. The Th/U ratio increase from endoskarn garnet to exoskarn counterparts, probably reflecting an increase of fluid fO2 due to interactions with evaporate sulfate from the wall rocks. The sulfides in this deposit are enriched in δ34S (up to 13 ‰), conforming the involvement of evaporate sulfate during Fe skarn mineralization. The incursion of evaporate sulfate may have played an important role in magnetite mineralization for the Lazhushan deposit by increasing fluid fO2 and facilitating the oxidation of Fe2+ to precipitate magnetite.LA-ICP-MS U-Pb dating of garnets from 4 garnet-bearing samples yielded ages of 150.8 ± 6.8 Ma (2σ), 150.9 ± 5.3 Ma (2σ), 150.2 ± 7.9 Ma (2σ), and 150 ± 11 Ma (2σ), which are consistent with zircon weighted mean U–Pb ages of 150.1 ± 2.0 Ma (2σ) and 150.5 ± 1.0 Ma (2σ) of the ore-related intrusion. Combined with previously published metallogenetic ages of skarn deposits in the Edong district, we suggest that the Lazhushan deposit may represent the initiation of Fe skarn mineralization for the Edong district during the Late Mesozoic.