Trace Element Systematics Research Articles

Petrogenesis, geochronology, and tectonic setting of the Calymmian 1.45–1.50 Ga basic magmatism in the Southern Ribeira Belt, Brazil: evidence of intracontinental rifting and Columbia break-up

ABSTRACT We present new petrographic, whole-rock geochemistry, and SHRIMP U – Pb zircon geochronological data of metabasic rocks interlayered as sills in the metasedimentary units of the Perau and Betara formations, Votuverava Group, Southern Ribeira Belt, Brazil. These formations overlie ~ 1.8 Ga Paleoproterozoic metagranitoids that represent basement inliers from the Paranapanema Craton. Petrography and whole-rock geochemistry allow the recognition of four groups, ranging from primitive to evolved compositions: i) cumulatic metadolerites (G1), ii) isotropic metadolerites (G2), iii) ortho-amphibolites (G3); and iv) ferroan ortho-amphibolites (G4). They exhibit tholeiitic subalkali basaltic composition, near-flat REE patterns, and signatures between N- and E-MORB. Fractional crystallization under low fO2 conditions is the main petrogenetic process controlling the magmatic evolution, as observed by Ti/V and Cr/Y ratio and tholeiitic trends. Crustal contamination signatures are observed through negative Nb anomaly, Th/Nb-Ti/V proxies trends, LILE enrichment, and, also, assimilated xenocryst zircons aged ~ 2.2 Ga. REE and trace element systematics indicate that the basic magmas were generated by ~ 20–10% partial melting of a model asthenospheric mantle source within spinel facies. TiO2/Yb-Nb/Yb and Nb/Yb-Zr/Yb ratio proxies and P-MORB metabasic rocks, previously described in the literature within the Votuverava Group, suggest a plume-influenced melt. A new SHRIMP U – Pb zircon age of 1448 ± 11 Ma was determined for an ortho-amphibolite sample (G3 group). We propose an intracontinental tectonic setting for the genesis of the metadolerites whitin the Perau and Betara formations, suggesting that this extensional event is associated with the Paranapanema Craton rifting. Furthermore, the genesis of the studied metabasic rocks could be associated with a regional extensional event during Calymmian times (~1.5–1.45 Ga), which generated basic magmatism in several other cratons, such as the Congo, São Francisco, Siberian, Laurentian, and China cratons, linked to the break-up of the Columbia Supercontinent.

Constraints on the source of Siberian Trap magmas from Mo isotope evidence

The relative contributions of asthenospheric mantle, lithospheric mantle, and continental crust in the genesis of the Siberian Traps Large Igneous Province (ST-LIP) remain poorly constrained. Most models invoke partial melting of asthenospheric mantle within a mantle plume with an inventory of recycled crustal material, with or without melting of subcontinental lithospheric mantle, and crustal contamination during ascend through the continental lithosphere. A greater understanding of this topic is of fundamental importance because the ST-LIP basalts are associated with the large Permian-Triassic extinction and the world’s largest magmatic Ni-Cu-platinum group element sulfide resources (Ni-Cu-PGE), the Norilsk-Talnakh mining camp. The ∼250 ± 2 Ma Siberian Traps at Norilsk contain a classic sequence of basaltic rocks that provide a spatial and stratigraphic context for changing chemistry of the eruptive products. We present a detailed geochemical and Sr-Nd-Hf-Mo isotopic investigation of ST-LIP volcanic rocks and associated sedimentary rocks, including coal and anhydrite, from the Norilsk area. The 98Mo/95Mo isotope ratios (reported as δ98Mo ratio relative to NIST SRM 3134) vary significantly from −0.62 to 0.07 ‰ for the older basalt formations and −0.41 to 0.03 ‰ for the younger basalt formations. The range of δ98Mo and its correlation with the other geochemical tracers cannot be explained by post-magmatic alteration, magmatic differentiation, or sulfide fractionation as Mo behaves as a lithophile element under these magmatic conditions. We suggest that the δ98Mo range can be explained by interaction of the plume with subcontinental lithospheric mantle modified by subduction processes. This is particularly prominent in the earlier Ivakinsky to Gudchikhinsky formations where light δ98Mo values coupled with low Mo/Ce can be explained by contributions from a dehydrated eclogitic component, whereas more rare heavy δ98Mo values and high Mo/Ce likely require contributions from a fluid metasomatized mantle source. Later magmas of the Nadezhdinsky formation show clear evidence of crustal contamination in their combined Mo-Sr-Nd-Hf isotope and trace element systematics, while the later more voluminous Morongovsky type magmas are shallower, large degree melts with limited crustal interaction. Our data shows the usefulness of Mo isotopes in deciphering magma sources of large igneous provinces eruptions.

Mineral precipitation sequence from multi-stage fluids released by eclogite during high-pressure metamorphism

Abstract Arc magmas above subduction zones hold abundant fluid-mobile elements attributed to fluids released from the dehydrating subducted oceanic crust. However, the quantity of trace elements in the fluids and their evolution with the metamorphic processes during subduction and exhumation are still unclear. The precipitation sequence of vein minerals preserves the nature of multi-stage high-pressure (HP) metamorphic fluids and the fingerprint of mass exchange in deep subduction zones. In this contribution, we conducted detailed petrological studies and phase equilibria modeling on a unique HP omphacite-rich vein and its host eclogite from the Chinese southwestern Tianshan. The host eclogite consists mainly of garnet, omphacite, epidote, glaucophane, phengite, quartz, and rutile. Garnet in the eclogite records prograde subduction and early exhumation characterized by decompression heating at P-T conditions of ~2.4–2.6 GPa and 460–540 °C. The embedded omphacite-rich vein has similar mineral assemblage to the host eclogite. Garnet grains in this vein are predominantly distributed along or intersect the vein wall, which record similar eclogite-facies metamorphic conditions to that of the host eclogite. Omphacite is dominant in the vein, while epidote and glaucophane occur interstitially. Phase equilibria modeling reveals a sequential growth of garnet-dominated, omphacite-dominated, and epidote-dominated assemblages from fluids originating from the breakdown of different hydrous minerals. These lines of evidence suggest that the formation of multi-stage HP fluids are a continuous long-term process with a spontaneously short-distance transport and sequential mineral precipitation. Calculated fluid compositions demonstrate that the fluids released by lawsonite breakdown during exhumation have great potential to modify the trace element systematics of arc magmas. Our findings reveal the nature and evolution of multi-stage HP metamorphic fluids from internal sources during subduction and exhumation of oceanic crust, providing valuable insights into the chemical compositions of arc magmas.

The evolution of Archean crust undisturbed for three billion years: A case study from the Bahalda Pluton, Singhbhum Craton, eastern India

The Archean Bahalda Pluton (Singhbhum Craton, eastern India) is an I-type mafic granodiorite, surrounded by Paleoarchean TTG and TTG-derived granites of the Singhbhum Suite. The Singhbhum Suite is highly unusual amongst Eo- and Paleo-Archean terranes because most of the Singhbhum Craton escaped post-Archean deformation and metamorphism. The Bahalda granodiorite contains accessory zircon, titanite, and fluorapatite, which are rarely studied together but are a powerful tool for exploring magmatic and post-magmatic processes. U-Pb zircon and titanite dating indicate a ca. 3.35 Ga emplacement age of the Bahalda granodiorite. Subsequent ca. 3.27–3.05 Ga U-Pb fluorapatite ages are interpreted as recording low-grade metamorphic or hydrothermal event(s). The Bahalda fluorapatite and titanite are LREE-enriched compared to the HREE. The complex zonation of fluorapatite suggests that primary igneous fluorapatite was recrystallised with the removal of REE and overgrown by REE-depleted rims. This is in agreement with the apatite trace element systematics which imply fluorapatite cores are of mafic I-type granitoid affinity, with rims of low- and medium-grade metamorphic / metasomatic affinity. No textural evidence of titanite alteration was detected, but some domains have minor REE depletion compared to crystal interiors. The titanite and fluorapatite data display similar trends in LREE vs Sr/Y space due to metamorphic/hydrothermal alteration. The evolution of the Bahalda Pluton, which did not exceed greenschist facies for 3 Gyr, invites comparison with other stabilized cratons from the Mesoarchean.

Exploring the tectono-magmatic evolution of intraoceanic fore-arc setting during subduction initiation: perspectives from trace and platinum group element systematics of the Jijal ultramafic arc system, NE Pakistan

ABSTRACT The Jijal Complex is considered one of the largest Neo-Tethyan remnants in the intra-oceanic Cretaceous–Palaeogene Kohistan Arc of Pakistan. This complex largely consists of gabbros, peridotites, and chromitites. Previous studies documented the genesis of gabbros and chromitites in detail; however, detailed geochemistry and magma genesis were lacking. In this investigation, we present whole-rock geochemical and platinum group elements (PGEs) data of Jijal peridotites (dunites and harzburgites). The objectives of this study are to elucidate magmatic processes and tectonic regimes involved in the formation of peridotites, factors influencing the concentration and dispersion of PGEs in them, and their tectonic evolution. The investigated peridotite samples are depleted in magmaphile major elements (Al2O3: 0.23–0.57, TiO2: 0.01–0.04, and CaO: 0.08–0.69 wt%), relative to the primitive mantle values, reflecting melt-rock interaction during their magmatic evolution. In addition, rare-earth element (REE) contents in harzburgites are relatively higher compared to the dunites; however, both rock types exhibit depletion with respect to the chondrite-normalized values. The obvious negative anomalies of Nb, Zr, and enriched LREE and large ion lithophiles collectively substantiate their association with depleted arc-type mantle components, metasomatism, and melt/fluid-rock reactions after partial melting episodes. Bulk-rock and geochemical modelling of PGEs data of the peridotites suggest their shallow depth spinel-bearing depleted heterogeneous mantle source and generation from refractory mantle residuum along with boninitic signatures in a supra-subduction zone (SSZ). The PGE’s geochemistry additionally reveals that partial melting, fractionation, metasomatism, and sulphur under-saturation were the key factors that controlled the concentration and distribution of PGEs in the studied rocks. The boninitic features of the Jijal peridotites are equated with intraoceanic fore-arc followed by subduction initiation, and melt-rock reactions in a hydrated forearc mantle, indicating robust evidence of mantle depletion and pervasive refertilisation in an embryonic Neo-Tethyan arc system. Tectonically, the investigated rocks encapsulate vestiges of the Cretaceous Tethyan Ocean and record multifaceted history from boninitic to slab-proximal island arc affinity in compliance with an intraoceanic SSZ fore-arc regime coherent with the subduction inception.

Magmatic and Geochemical Studies of Early Neoproterozoic Koraput Anorthosite Massif, Eastern Ghats Mobile Belt and their Implications for Rodinia Assembly

Abstract This paper reports new mineralogical and geochemical information on the Neoproterozoic Koraput Anorthosite pluton in domain-2 of the Eastern Ghats Mobile Belt. The lenticular-shaped, NE-SW trending small Koraput Anorthosite Pluton is dominated by gabbro-anorthosite, anorthosite sensu-stricto, and norite-diorite. Isolated patches of ferrodiorite (residual melt following crystallization of anorthosite) occur at the pluton margin. The estimated magmatic P-T conditions for anorthosite emplacement are ~1000°C and ~1.1GPa. In addition, the intermediate Anorthite (48-52 mole %) presence in plagioclase of gabbro-anorthosite and anorthosite indicates plagioclase crystallisation and accumulation at 30-40 km (circa 1 GPa) depth near the crust-mantle boundary. Furthermore, the geochemical traces suggest Koraput anorthosite pluton crystallized from a less fractionated basaltic magma. The REE and trace element systematics of anorthosite and norite-diorite exhibit enriched LILEs over depleted HFSE with negative Nb, Ta, Th, and Zr anomalies. Gabbro-anorthosite and ferrodiorite, on the other hand, exhibit positive Nb, Ti, and negative Zr and Th anomalies. Nb/Th versus Nb/La diagram implies lithodemic units in Koraput Anorthosite pluton are variably contaminated by crustal sources. Integration of geochemical data with available monazite age suggests that the Koraput anorthosite pluton in isotopic domain-2 of the Eastern Ghats Mobile Belt was emplaced during the collision between proto-India and Antarctica during the Rodinia assembly.

Trace element systematics of magnetite from the Starra iron oxide‑copper gold deposits reveals early fluid conditions characteristic for Cu mineralization

Hydrothermal magnetite from the Starra iron oxide‑copper gold (IOCG) deposit in northwest Queensland, Australia, records a gradual decrease in V, Ni, Cr, and Mn that correlates with the transition from early, amphibole-biotite-magnetite dominant alteration to late, chlorite-quartz-hematite-dominated alteration assemblages. The observed systematic change in multivariate elements in magnetite is interpreted to indicate an increase in fO2 during the main Cu(Au) mineralization. We suggest that variations in the V, Ni, and Cr contents of magnetite at Starra indicate either a primary magmatic fluid source or the leaching of mafic rocks by fluids during early albitization. Late silician magnetite contained in ankerite veins that crosscut the preexisting alteration assemblages in the hanging wall to the Starra 222 ore body is likely the result of a second mineralization phase, which contributed additional metals to the Starra ore bodies.Existing data on magnetite chemistry from several IOA, IOCG, Fe, and FeW skarn deposits show that the ratio of V to Ga discriminates the various ore types effectively. Skarn deposits are separated from IOA and IOCG by lower concentrations of V, Ni, and Cr, suggesting a more primitive fluid source or the precipitation of magnetite at distinct physicochemical conditions than IOA and IOCG deposits. Magnetite from IOA deposits exhibits a consistently elevated V concentration whereas magnetite from Fe(W) skarn records an increase in V concentration with the evolution of the system. A pronounced decrease in the V contents of magnetite associated with CuAu mineralization at Starra is interpreted as a change in redox conditions from reduced to oxidized at the time of mineralization. Such variations are also observed in other IOCG deposits. We propose that systematic decreases in V concentration in magnetite during the paragenetic evolution of the host mineral system is a diagnostic indicator for Cu(Au) mineralization in IOCG deposits, and as such, it may be used as a proxy for CuAu exploration, if the paragenetic context of magnetite is well constrained.

Geochronological and geochemical effects of zircon chemical abrasion: insights from single-crystal stepwise dissolution experiments

Abstract. Chemical abrasion in hydrofluoric acid (HF) is routinely applied to zircon grains prior to U–Pb dating by isotope dilution thermal ionization mass spectrometry (ID-TIMS) to remove radiation-damaged portions of grains affected by Pb loss. Still, many chemically abraded datasets exhibit evidence of residual Pb loss. Here we test how the temperature and duration of chemical abrasion affect zircon U–Pb and trace element systematics in a series of 4 h, single-crystal stepwise dissolution experiments at 180 and 210 ∘C. Microtextural data for the zircon samples studied are presented in a companion paper by McKanna et al. (2023). We find that stepwise dissolution at 210 ∘C is more effective at eliminating material affected by open-system behavior and enriched in U, common Pb (Pbc), and light rare earth elements (LREEs); reduces the presence of leaching-induced artifacts that manifest as reverse discordance; and produces more consistent and concordant results in zircon from the three rocks studied. We estimate that stepwise dissolution in three 4 h steps is roughly equivalent to a single ∼ 8 h leaching step due to the insulating properties of the PTFE sleeve in the Parr pressure dissolution vessel, whereas traditionally labs utilize a single 12 h leaching step. We conclude that a single 8 h leaching step at 210 ∘C should remove Pb loss effects in the majority of zircon and that this can be used as an effective approach for routine analysis. Further, we calculate time-integrated alpha doses for leachates and residues from measured radionuclide concentrations to investigate (1) the alpha dose of the material dissolved under the two leaching conditions and (2) the apparent minimum alpha dose required for Pb loss susceptibility: ≥ 6×1017 α g−1.

Geology and Lithogeochemistry of the Paleoproterozoic Flambeau Cu-Zn-Au Volcanogenic Massive Sulfide Deposit, Wisconsin, USA

Abstract The Paleoproterozoic Flambeau Cu-Zn-Au deposit in northwestern Wisconsin is the only volcanogenic massive sulfide (VMS) deposit to reach production in the Pembine-Wausau terrane of the Penokean orogen, despite the discovery of more than 150 million tonnes of mineralization within 14 deposits since the 1970s. Renewed exploration interest in the region and need for critical minerals has highlighted the importance of the VMS deposits in the region and the need for an improved understanding of their geologic setting. This study examined and sampled 50 drill cores from the Flambeau deposit stored at the Wisconsin state core repository to determine the volcanic, hydrothermal, and tectonic setting of the deposit. The least altered units at the deposit are metadacite and quartz-augen schists that are interpreted to be rapidly emplaced felsic to intermediate crystal-rich tuffs and lapilli tuffs. There are also chlorite ± garnet schists that are interpreted to be mafic sills and/or small flows. The main altered unit is biotite ± andalusite ± white-mica schist that contains porphyroblasts of biotite and/or andalusite that replace the intermediate volcaniclastic units. The ore horizon contains massive sulfide, metachert, and semimassive mineralization within a quartz–white-mica schist. Stratigraphic relationships and chemostratigraphy structurally above and below the ore horizon indicate that the strata are overturned. Despite structural and metamorphic destruction of microtextural evidence, evidence for lateral mineralizing fluid flow in rapidly emplaced, permeable volcanic units, interlayered impermeable to semipermeable units, and macrotextural evidence for lit-par-lit replacement of tuffaceous layers indicate that the Flambeau ores are replacement-style mineralization. Trace element systematics reveal that mafic rock and intermediate rocks are calc-alkalic with low Ti/V values, characteristic of arc environments. Felsic rocks are calc-alkalic, depleted high field strength element (HFSE), FI- to FII-type rhyolites that are also consistent with an arc environment. These lithogeochemical characteristics are similar to those of modern mature oceanic-arc settings. This setting contrasts with other host rocks at nearby deposits (e.g., Lynne, Back Forty) that have petrogenetic evidence for the presence of older Archean basement (i.e., continental crust). Therefore, the geology of the Flambeau deposit highlights the variability of VMS-forming environments within the Penokean orogen and has important local and regional implications for other VMS deposits globally.

Trace element systematics of magnetite from alkaline mafic–ultramafic intrusions of the Permian Emeishan large igneous province, SW China

Trace element systematics of magnetite from alkaline mafic–ultramafic intrusions of the Permian Emeishan large igneous province, SW China

Mantle plumes sample heterogeneous mixtures of oxidized and reduced lithologies

Constraining the heterogeneity of oxygen fugacity (fO2) in the upper mantle is important for understanding the role of the deep Earth in determining the redox state of the atmosphere. Measuring the fO2 of primitive, mantle-derived basalts is a means with which to constrain mantle fO2 heterogeneity. Trace element systematics of 721 primitive olivine crystals from fifteen Icelandic picrites are reported, and these data are used with previously published bulk rock compositions to constrain their magmatic fO2. These fO2 values were compared with previously reported ocean island basalt (OIB) fO2 data calculated using identical methods, showing that fO2 is negatively correlated with parental magma MgO and positively correlated with bulk rock La/Yb, trends which were not evident in previous, smaller, global ocean island basalt datasets. These correlations cannot reasonably be the result of fractional crystallization, differential volcanic degassing, or differential partial melting of a typical homogenous mantle peridotite. Instead, differential partial melting of a heterogeneous source which preferentially sampled oxidized fusible lithologies at low melt fractions and diluted such signatures with depleted peridotite melts at high melt fractions likely caused the observed fO2-MgO-isotopic trends. These conclusions further reinforce that the mantle should not be modeled as a homogenous peridotite, but instead as a heterogeneous, non-equilibrated mixture of enriched “blebs” in a matrix of depleted peridotite, and that degree of partial melting is an important control on what portions of the mantle are detectable in igneous rocks.

Stable isotope composition and concentration systematics of Ca and trace elements (Zn, Sr) in single aliquots of fossil bone and enamel

Measurements of modern bone and tooth enamel show that calcium stable isotopes (δ44Ca), zinc (δ66Zn), and strontium (δ88Sr) have great potential as ecological and dietary tracers for studies on fossil material. Despite the fact that these three elements can be recovered using sequential chromatographic extraction from a single aliquot, a multi-proxy study has not been attempted yet, which would allow a less destructive analysis of precious fossil material. The present study consists of analyzing δ44Ca, δ66Zn, δ88Sr, and 87Sr/86Sr values in fossil bone and tooth enamel of carnivore and herbivore mammals from the Camiac cave (Upper Pleistocene, Gironde, France). Our study aims at (1) developing a protocol for Ca, Zn, and Sr stable isotope analyses from a single fossil bone or enamel aliquot; (2) testing the respective preservation of biological isotopic signatures in bone and tooth enamel; and (3) comparing the patterning of the different isotopic systems in a fossil mammal community. In the present study, fossil enamel samples have not been leached, as it has been done so far for Zn isotope analyses, but fossil bone samples have been leached using diluted acetic acid or were left unleached. Using inclusive statistical analyses, we identify the effect of leaching on bone chemical compositions, and the concentration and isotope composition of Ca, Zn, and Sr in leached bone and unleached enamel show no sizeable diagenetic overprint. We report for the first time δ66Zn values in fossil bone. The results show that bone δ66Zn values mirror the pattern already observed in enamel, e.g., a significant trophic 66Zn depletion between herbivores and carnivores. Bone δ44Ca and δ88Sr values also mirror those in enamel, and the results highlight a clear distinction between ruminants and non-ruminants, the latter being 44Ca-enriched. The present study focuses on the importance of analyzing several isotopic systems in a single fossil bone or enamel aliquot and shows encouraging results for the preservation of biological isotopic signatures in fossil bone, despite the longstanding dread of a so-called associated pervasive diagenesis. The present study will therefore be useful to consider any precious fossil material with limited destructive sampling possibilities.

182W and 187Os constraints on the origin of siderophile isotopic heterogeneity in the mantle

Major and trace element abundances, including highly siderophile elements, and 187Os and 182W isotopic compositions were determined for ca. 89 Ma mafic and ultramafic rocks from the islands of Gorgona (Colombia) and Curaçao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial 187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial 187Os/188Os ratios 10–15 % higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable μ182W values ranging from modern bulk silicate Earth-like to strongly negative values. The μ182W values do not correlate with major/trace element abundances or initial 187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest μ182W value (−53) measured, for a Gorgona olivine gabbro, corresponds with the highest 3He/4He previously measured from the suite (15.8 R/RA). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative μ182W and possibly high 3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary.

Microstructure, trace element systematics and in-situ sulfur isotopes of multistage sulfides in the Kalatag district (East Tianshan, NW China): Implications for formation of arc-hosted VMS deposit

The Early Paleozoic arc-hosted volcanogenic massive sulfide (VMS) deposits in the Kalatag arc are well-known for their well-preserved and high-grade Cu–Zn sulfide mineralization in the East Tianshan. Unfortunately, there is a puzzle on the ore-forming fluid and metal source as well as physicochemical condition of metallogenic process of these arc-hosted VMS Cu–Zn deposits. The Huangtupo was firstly reported Early Paleozoic arc-hosted VMS Cu–Zn deposit (300Kt@1.49 % Cu; 280Kt@3.51 % Zn) in the East Tianshan. In order to better recognize the physicochemical condition and formation processe of arc-hosted VMS deposits, this research takes the Huangtupo deposit as an example, combining the microstructure, in-situ sulfur isotope and trace element composition of multistage sulfides to conduct a comprehensive study. In the Huangtupo deposit, the overall mineralization process is divided into syndepositional mineralization stage, hanging-wall massive mineralization stage and channel hydrothermal stage according to the main mineral interpenetration relationship and horizon relationship. Pyrite can be divided into five types in the Huangtupo Cu–Zn deposit: 1) subhedral to anhedral pyrite in the silicious exhalite (Py1); 2) colloform pyrite in the hanging-wall massive pyrite + barite + sphalerite zone (Py2); 3) subhedral pyrite in the hanging-wall massive pyrite + chalcopyrite + sphalerite ± magnetite zone (Py3); 4) fine-grained (or disseminated) pyrite in the footwall pyrite + chalcopyrite + sphalerite stage (Py4); 5) euhedral pyrite in the footwall quartz + pyrite + chalcopyrite stage (Py5). Two types of chalcopyrite are identified, including hanging-wall massive chalcopyrite (Ccp1) and footwall stockwork chalcopyrite (Ccp2). In addition, three generations of sphalerite could be identified, namely (1) hanging-wall massive pyrite + barite + sphalerite zone (Sp1); (2) hanging-wall massive pyrite + chalcopyrite + sphalerite ± magnetite zone (Sp2); and (3) footwall pyrite + quartz + sphalerite + chalcopyrite stage (Sp3). In the upper massive orebody, LA–ICP–MS in-situ microanalysis shows that pyrite is enriched in Cu, Zn, Au, Ag, Pb, Sb, and Tl, while it is poor in Co, Ni, Se, Te, Ti, and Sn, indicating that it was formed in a metal-rich, medium–high temperature and more oxidizing hydrothermal environment. By contrast, pyrite from the footwall stockwork orebody contains low Au, Ag, Cu, Zn, Pb, Sb, Tl and high Co, Se, Te, Ti content, indicating that it is formed in the hydrothermal environment with a high temperature, reduction and trace metal deficit signature. Trace element compositions of sphalerite suggest that Fe, Mn, Ag, Se, In, Ge, and Ga are present as lattice. By contrast, Sn, Pb, Tl, and Bi are present as mineral microinclusions. The mineralization temperature is determined by sphalerite geothermometer (GGIMFis) and shows a decreasing trend from footwall stockwork mineralization to hanging-wall massive mineralization. Comparing with sphalerite, chalcopyrite is enriched in Ge, Ag, Zn, Se, Sn, and Cd, relatively poor in In and Ga. The integrated in situ sulfur isotopic (δ34S) composition and trace metal content of sulfides suggest that ore-forming material is most likely derived from a combination of host volcanics and seawater. In addition, the thermochemical sulfate reduction is also a key factor affecting sulfur isotope fractionation. Overall, the trace element compositions of multistage sulfides are robust monitor of the complex hydrothermal process and effectively reconstruct the metal enrichment process during the formation of arc-hosted VMS mineralization system.

Geochemical benchmarks in the Phanerozoic LIPs constrained from well-cores in the Deccan Volcanic Province, India

The ∼66 Ma Deccan flood basalt province is one of the largest in the World. Here, we present mineral chemistry, bulk-rock geochemistry and NdSr isotopes in the ∼1000 m thick basalt lava sequence extracted from the deep bore-hole well-cores KBH-8 and KBH-7 from the main Deccan Plateau in the southwestern Deccan Volcanic Province. On the basis of trace and rare earth element systematics, we have statistically grouped the accumulated lava into fifteen Eruptive Phases (EPs). The basalts show extreme variation in their initial 87Sr/86Sr (0.7038–0.7166) and εNd (+5.9 to −12.1) isotopic compositions consistent with the involvement of depleted and enriched mantle sources in their genesis. The lavas sourced from the enriched subcontinental lithospheric mantle has been categorized as EP4-type, and EP11-type represents the isotopically depleted lavas derived from a plume asthenospheric source. The remaining EPs resulted from mixing of the components from these two endmembers in some proportion. This essentially reflects upon source contamination rather than crustal assimilation enroute to eruption or emplacement. The unique geochemical and isotopic fingerprint of EP4 and EP11 is traceable in the Phanerozoic LIPs, as well. Therefore, they potentially qualify as “geochemical benchmarks”. The systematic “pinch and swell” pattern observed in the trace element and isotopic compositions throughout the depth profile cannot be reconciled with continuous outpouring of lava. Instead, the EPs erupted in discreet batches in a quick span of time from a periodically replenished tapped fractionated magma chamber fed by a mantle plume at the asthenosphere-lithosphere interface. The results of this study enunciate the critical role of subcontinental lithospheric mantle in the evolution of a continental flood basalt province, irrespective of space and time.

Geochemical records provide evidences for the evolution of the marine redox environment in the southwestern Sumatra waters over the past 35,000 years

The marine redox environment (MRE) can affect marine productivity and nutrient cycling, as well as governs material and energy transport. However, its evolution process and driving mechanism in different historical periods revealed significant regional characteristics. Southwestern Sumatra waters, located at the Indo-Pacific Ocean convergence, are an ideal region for studying the evolution of MRE due to significant upwelling and variable productivity levels resulting from the seasonal monsoonal activity. In this study, based on the sediment core SO184–10043, systematic trace element geochemical analysis was conducted for reconstructing the MRE over the past 35,000 years using redox proxies, namely, Ni/Co, U/Th, and biogenic Barium (Babio). Ni/Co and U/Th varied in a range of 1–4 and 0.2–1, indicating general oxic conditions with matching productivity levels indicated by Babio (ranging from 300 × 10–6 to 580 × 10–6). A comparison with other reconstructed archives indicated that the MRE records of the sediment core in this study were in consistence in responding to the high-latitude climate records with strong semi-precession and millennial fluctuations. Suggestively, these fluctuations correspond to the natural summertime insolation, triggering the latitudinal motions of the Intertropical Convergence Zone (ITCZ), as well as leading to corresponding changes in the seasonal Indian monsoon system. Freshwater lids modulate the mixing effect by acting as barriers and influencing the upwelling development, thereby leading to strong oxic conditions in the MRE. Therefore, robust evidence on the millennial-scale variability in MRE driven by the ITCZ movement and regional monsoon changes in the tropical Indian Ocean is provided by the trace element archives employed in the present study, thereby providing novel insights into the evolution of MRE in response to global and local climate changes.

On the virtues and pitfalls of combined laser ablation Rb–Sr biotite and U–Pb monazite–zircon geochronology: an example from the isotopically disturbed Cape Woolamai Granite, SE Australia

Abstract Different mineral clocks in granite can provide age information reflecting various aspects of rock formation, including cooling or post-emplacement fluid–rock interaction. However, the dating tool chosen can yield inconclusive age information due to differences in closure temperatures and susceptibility to fluid alteration among chronometers. This has led to an inferred superiority of U–Pb in zircon over U–Pb in monazite or Rb–Sr in mica. Here, we investigate age systematics using Rb–Sr biotite grains, U–Pb in monazite and zircon in a Devonian granite from Australia. Single-grain laser ablation ICP-MS/MS biotite analyses are combined with zircon–monazite U–Pb ages and trace element systematics. Textural and trace element evidence combined with age systematics reveals a Rb–Sr closure age of c. 360–330 Ma relative to a putative 364 Ma emplacement age, suggesting hydrothermal alteration of the granite. Trace element systematics and magnetic susceptibility in biotite grains reflect their partial chemical reset and fluid overprint in the granite. However, similar systematics are also observed for zircon and monazite. Our multiple chronometer dating approach, studied with modern laser-ablation methods, highlights the need for detailed investigation of isotope and trace element systematics in single grains and that individual ages should be used cautiously when dating altered granitoids.

Petrogenesis, Sampling Depth, Thermal and Redox Evolution of Spinel Peridotite Xenoliths From Jiaohe, NE China: Insights From Trace Elements in All Rock‐Forming Silicate Minerals

AbstractOlivine and orthopyroxene (Opx) are the most abundant minerals in lherzolitic to harzburgitic peridotites, and their compositions represent an important—and sometimes only—source of information for the origin and physicochemical evolution of the subcontinental lithospheric mantle (SCLM). We report a high‐quality in situ trace element data set for Opx and olivine of well‐characterized spinel‐peridotite xenoliths, including eight lherzolites and four harzburgites, which were entrained in the Cenozoic basalts from Jiaohe, NE China. While the lherzolites and harzburgites show contrasting evolution involving various metasomatic agents, reflected in different trace element relationships, both experienced early cooling followed by recent (pre‐entrainment) heating, as unraveled by a combination of mineral thermometers with inherently different diffusion rates. The sampling depth of spinel‐facies peridotites is obtained by olivine‐spinel thermobarometry, taking into account post‐melting subsolidus processes and pre‐emplacement thermal disturbance, using an empirical correction for the Ca content in olivine, which yields a pressure range of 1.1–2.0 GPa. The V contents (92–116 μg/g) and V/Sc ratios (5.7–6.4) in lherzolitic Opx are higher than those in harzburgitic Opx (V: 56–76 μg/g; V/Sc: 3.4–5.9), qualitatively reflecting the reducing and oxidizing effect, respectively of refertilization versus metasomatic interaction with a small‐volume melt. Thus, comparative thermobarometry, together with trace element systematics of Opx and olivine can be effective tools to reveal the architecture, chemical, thermal, and redox evolution of the shallow SCLM, as sampled by spinel peridotite xenoliths.

Isotopic constraints on genetic relationships among group IIIF iron meteorites, Fitzwater Pass, and the Zinder pallasite

AbstractComplex interelement trends among magmatic IIIF iron meteorites are difficult to explain by fractional crystallization and have raised uncertainty about their genetic relationships. Nucleosynthetic Mo isotope anomalies provide a powerful tool to assess if individual IIIF irons are related to each other. However, while trace element data are available for all nine IIIF irons, Mo isotopic data are limited to three samples. We present Mo isotopic data for all but one IIIF irons that help assess the genetic relationships among these irons, together with new Mo and W isotopic data for Fitzwater Pass (classified IIIF), and the Zinder pallasite (for which a cogenetic link with IIIF irons has been proposed). After correction for cosmic‐ray exposure, the Mo isotopic compositions of the IIIF irons are identical within uncertainty and confirm their belonging to carbonaceous chondrite (CC)‐type meteorites. The mean Mo isotopic composition of group IIIF overlaps those groups IIF and IID, but a common parent body for these groups is ruled out based on distinct trace element systematics. The new Mo isotopic data do not argue against a single parent body for the IIIF irons, and suggest a close genetic link among these samples. In contrast, Fitzwater Pass has distinct Mo and W isotopic compositions, identical to those of some non‐magmatic IAB irons. The Mo and W isotope data for Zinder indicate that this meteorite is not related to IIIF irons, but belongs to the non‐carbonaceous (NC) type and has the same Mo and W isotopic composition as main‐group pallasites.

Late Paleoproterozoic ultrahigh-temperature mafic granulite from the eastern Alxa Block, North China Craton

The timing and mechanism of ultrahigh-temperature (UHT) granulite facies metamorphism is critical to understanding the tectono-thermal evolution of granulite terranes and their relationships to supercontinent assembly. Here we document late Paleoproterozoic UHT mafic granulites from the Diebusige Complex in the eastern Alxa Block, North China Craton. These rocks occur as lens within felsic gneiss, marble, and garnet-bearing pyroxenite and contain representative granulite-facies minerals such as garnet, clinopyroxene, plagioclase, and Ti-rich amphibole. Based on phase equilibria modelling, Ti-in-amphibole (Amp) thermometer, and rare earth element (REE)-based thermometers, UHT metamorphic condition of 948 – 1048 ℃/11 – 14 kbar was obtained for the peak metamorphic stage, which was followed by retrograde metamorphism under lower amphibolite – greenschist facies (401 – 565 ℃/5.2 – 7.1 kbar). Zircon U-Pb dating and trace element systematics suggest that the protolith of the studied UHT mafic granulites emplaced at ∼ 1.97 Ga. This is followed by rapid metamorphism to UHT conditions and slow cooling in the lower crust during 1.96 – 1.86 Ga, suggesting a long-lived hot orogen in the eastern Alxa Block, possibly resulting from Andean-type subduction – accretion in the eastern Alxa Block. Combining chronological and metamorphic P-T data on UHT metamorphism from adjacent areas, our results support a long-lived late Paleoproterozoic (ca. 2.0 – 1.8 Ga) hot orogen that extends at least from the Khondalite Belt to the eastern Alxa Block.