Eu Anomalies Research Articles

Trace element geochemistry and zircon U-Pb geochronology of mafic sills from the Karagwe Ankolean Belt of northwestern Tanzania: Implications for petrogenesis and Ni-Cu-Co prospectivity

In northwestern Tanzania, mafic sills intruded the Akanyaru and Kagera Supergroup rocks in the Mesoproterozoic Karagwe-Ankolean Belt (KAB). Trace element geochemistry and UPb geochronology results are reported to unravel petrogenetic and geochronological evolution of the sills in order to place constraints on Ni-Cu-Co prospectivity of the KAB. The sills are subalkaline gabbronorite and dolerite. They are relatively evolved Mg# = 43–69, with transitional metal contents lower than juvenile mafic-ultramafic rocks of the Kabanga-Musongati Alignment (KMA) intrusions. The sills can be subdivided into western and eastern swarms that display similar geochemical characteristics, including enrichment in LREE (Light Rare Earth Elements), LILE (Large Ion Lithophile Elements), Pb, Th, and U relative to HFSE (High Field Strength Elements). They are characterised by depletions of Nb-Ta-Ti in primitive mantle normalised spiderplots, enrichments in LREE and relatively flat MREE and HREE with negative Eu anomalies Eu/Eu* = 0.74–0.94 in chondrite normalised REE spiderplots. Together with elemental trace element ratios Nb/Yb, Th/Yb, Zr/Nb, Ba/Nb, and Nb-Yb-Ti index suggest derivation of the mafic sills from a sub-continental lithospheric mantle source followed by fractional crystallisation and crustal contamination.Zircon UPb geochronology yields a concordant weighted age of 1424 ± 13 Ma for a gabbronorite in the western sills and an upper age intercept of 1411 ± 54 Ma for a dolerite in the eastern sills. The emplacement ages are similar to those of the KMA and the Lake Victoria Dolerite Dyke Swarm (LVDDS). Temporal and geochemical similarities with the KMA and LVDDS supports for emplacement of the mafic sills in an intracratonic rift setting. Although the KAB sills are relatively more geochemically evolved, they share similar evolutionary path with Ni-Cu-Co mineralised juvenile KMA intrusions, sensu stricto interaction with sulphur bearing country rocks. We suggest that trace elements geochemistry including chalcophile elemental ratios (Ni/Cr and Cu/Zn) of the sills be applied as vectors to locate prospective Ni-Cu-Co targets in the KAB.

Timing and origin of the Lomagundi-Jatuli Event: Insights from U[sbnd]Pb geochronology, C-O-Fe isotopes and REE compositions from the Jingshan Group, North China Craton

The Lomagundi-Jatuli Event (LJE) represents perhaps the largest and longest positive carbon isotope excursion of Earth history. However, the synchroneity, scale, and linkage of the LJE to Earth's early history of atmospheric oxygenation remain controversial. Strata of the Paleoproterozoic Jingshan Group of the North China Craton that preserve the isotopic record of the LJE excursion in marble layers and abundant graphite deposits provide an opportunity to elucidate the significance of the LJE. Carbon isotopic values (δ13CV-PDB) of the LJE based on analysis of 20 samples of the Lugezhuang Formation, lower Jingshan Group, range from −0.8 to +9.6 ‰ and display positive co-variance with stable oxygen isotope values (δ18OV-PDB). The positive carbon isotope excursion is constrained to 2140.6 ± 8.5 Ma (MSWD = 0.82, n = 25) based on magmatic zircon UPb geochronology of biotite granulite. Variation of facies-dependent carbon isotope values, the presence of graphite deposits of the Douya Formation, upper Jingshan Group, and the absence of a Ce anomaly in PAAS normalized REE patterns of marble samples suggest that the positive carbon isotope excursion is not linked to a marked increase of organic carbon burial and associated significant atmosphere oxygenation. Elevated concentrations of iron and PAAS-normalized middle REE enrichment of analyzed Jingshan Group marble samples point to anoxic and ferruginous oceanic conditions during accumulation of Jingshan Group carbonate. A positive Eu anomaly (average = 1.58), low La (average = 0.23), (Nd/Yb)N (average = 1.27), and Y/Ho (average = 36.6) anomalies, and negative iron isotope values (average δ56Fe = −0.12 ‰) are consistent with accumulation of Paleoproterozoic Jingshan Group carbonate in a restricted marine setting that was affected by high temperature hydrothermal fluids. Enrichment of the studied samples in heavy carbon isotope suggests elevated bio-productivity in the restricted, redox stratified marine setting in which Jingshan Group carbonate accumulated. Thus, it is likely that the positive stable carbon isotope excursion associated with Jingshan Group strata as well as other contemporaneous isotope excursions are local signals that are linked to a global perturbation of the carbon cycle.

Composite Granitic Plutonism in the Southern Part of the Wadi Hodein Shear Zone, South Eastern Desert, Egypt: Implications for Neoproterozoic Dioritic and Highly Evolved Magma Mingling during Volcanic Arc Assembly

The Abu Farayed Granite (AFG), located in the southeastern desert of Egypt, was intruded during the early to late stages of Pan-African orogeny that prevailed within the Arabian–Nubian Shield. The AFG intrudes an association of gneisses, island arc volcano–sedimentary rocks, and serpentinite masses. Field observations, supported by remote sensing and geochemical data, reveal a composite granitic intrusion that is differentiated into two magmatic phases. The early granitic phase comprises weakly deformed subduction-related calc–alkaline rocks ranging from diorite to tonalite, while the later encloses undeformed granodiorite and granite. Landsat-8 (OLI) remote sensing data have shown to be highly effective in discriminating among the different varieties of granites present in the area. Furthermore, the data have provided important insights into the structural characteristics of the AFG region. Specifically, the data indicate the presence of major tectonic trends with ENE–WSW and NW–SE directions transecting the AFG area. Geochemically, the AFG generally has a calc–alkaline metaluminous affinity with relatively high values of Cs, Rb, K, Sr, Nd, and Hf but low contents of Nb, Ta, P, and Y. The early magmatic phase has lower alkalis and REEs, while the later phases have higher alkalis and REEs with distinctly negative Eu anomalies. The AFG is structurally controlled, forming a N–S arch, which may be due to the influence of the wadi Hodein major shear zone. The diorite and tonalite are believed to have been originally derived from subduction-related magmatism during regional compression. This began with the dehydration of the descending oceanic crust with differential melting of the metasomatized mantle wedge. Magma ascent was long enough to react with the thickened crust and therefore suffered fractional crystallization and assimilation (AFC) to produce the calc–alkaline diorite–tonalite association. The granodiorite and granites were produced due to partial melting, assimilation, and fractionation of lower crustal rocks (mainly diorite–tonalite of the early stage) after subduction and arc volcanism during a late orogenic relaxation–rebound event associated with uplift transitioning to extension.

Early Precambrian eclogites in the Belomorian Province, eastern Fennoscandian Shield

This study focuses on a boudin of Archean amphibolite that occurs in the Gridino eclogite-bearing mélange (Belomorian Province, eastern Fennoscandian Shield) and contains two varieties of eclogite. Eclogite-1 is banded, retrogressed (omphacite is totally replaced by clinopyroxene-plagioclase symplectite), and deformed by recumbent tight folds identical to those in the TTG-amphibolite host. Zircon groups are dated at 2721 ± 26 Ma (Zrn-I, fir-tree zoning, no or small negative Eu anomalies, flat HREE patterns, 700–730 °C, 14–15 kbar), ca. 2.70 Ga (Zrn-II, rims around Zrn-I, grains, 750–900 °C, 11–14 kbar, high-P granulite facies), and ca. 2.70 Ga (Zrn-III, rims around Zrn-II). Newly formed Paleoproterozoic zircon crystals are lacking. Retrogressed eclogite-1 in which amphibolization and epidotization totally obliterated garnet and plagioclase-clinopyroxene symplectites is intruded by 2646 ± 46 Ma old granodiorite. Eclogite-2 is massive, contains preserved omphacite-garnet-quartz-rutile assemblages, and comprises two patches whose boundaries truncate folds in eclogite-1. A Paleoproterozoic age of eclogite-2 is evidenced by previously published 1.90 Ga ages of zircon rims around Archean zircon and newly formed crystals with omphacite inclusions. The largest patch contains tabular enclaves of three varieties of amphibolites. One variety is identical to some bands of totally retrogressed eclogite-1 changed into monomineral amphibolites in both the Neoarchean and Paleoproterozoic. The orientation and attitude of these tabular enclaves are coherent with those of the banding on limbs of recumbent tight folds in eclogite-1 within the boudin and later drag folds at its margins and form one and the same structural carcass or skeleton. These data along with recent findings of inherited 2.68 Ga old zircon with inclusions of omphacite in eclogite-2 indicate that this eclogite developed after Neoarchean eclogite-1 due to fluid infiltration along reactivated Neoarchean shear zones enveloping the boudin. These results favor the idea that the transition to the modern-style plate tectonics started not later than in the Neoarchean.

U-Pb Ages of Zircon Grains in the Playa Azul Beach Sediments, Guerrero State, Mexican Pacific

ABSTRACT The mineralogy of bulk sediments, U-Pb ages and chemistry of 195 detrital zircon grains recovered in the Playa Azul beach, Mexican Pacific coast were performed to infer their provenance. The bulk sediments were composed of minerals like quartz, feldspar, titanite, plagioclase, zircon, and magnetite. The average Th/U ratio in zircon grains was ~ > 0.2, indicated an igneous origin. The chondrite normalized rare earth element (REE) patterns of zircons were depleted in low REE (LREE) and enriched in heavy REE (HREE), with positive cerium and negative europium anomalies, indicating a granitoid source. U-Pb ages of zircon grains revealed the predominance of Cenozoic and Mesozoic ages in samples PAC2 (~ 33.8 - 61.8 Ma, n = 90 and ~ 67 - 132 Ma, n = 10, respectively) and PAC19 (~ 0.1 -39.6 Ma, n = 55 and ~ 67 - 251 Ma, n = 20, respectively). Minor peaks were represented by Palaeozoic (n = 9) and Precambrian (n = 11) ages in PAC19. Zircon ages and their morphology indicated that they were mostly derived from the nearby terranes. The source terranes, which supplied Cenozoic zircons to the beach area were the coastal Cenozoic plutons and Cuicateco terrane. The Mesozoic zircons in the Playa Azul coastal sediments were derived from the Mixteca (Acatlan Complex), Guerrero, and Xolapa terranes, located along the Mexican Pacific coastal zone. The Proterozoic zircons were represented by the coastal Oaxacan Complex. In addition, the Arteaga Complex in the Guerrero State, adjacent to the playa Azul beach was the potential source for the Eocene zircons.

Geochemistry of Volcanic Rocks in Ponelo Island, North Gorontalo, Indonesia

Ponelo Island is located in the northern part of Sulawesi, which is still an enigma regarding the genesis of the volcanic rocks found on this island. Therefore, the objective of this study is to understand the petrogenesis and tectonic implication of these volcanic rocks. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to obtain trace and rare earth elements is the method of this study. The volcanic rocks found on Ponelo Island consist of basalt and basaltic andesite rocks with a calc-alkaline affinity. The transition data suggested a highly fractionated cause of low transition element (Ni=17-38 ppm; Cr=13-47) compared to primary magma concentration, anomalies negative of Ba, Sr, and Ti of spider diagrams, and negative anomaly of Eu (Eu/Eu*=0.88-0.99). Relationship between low concentration between Ce/Y (0.74-0.76) and La/Yb vs Sm/Yb ratio indicated ~5% spinel-lherzolite mantle source partial melting. On the other hand, incompatible element ratios, such as Ba/Nb (39.03-45.28), Ba/Th (75.52-82.67), Rb/Nb (3.93-6.22), K/Nb (1772.22-2703.45), Ba/La=13.67-14.57, Th/La (0.17-0.18), La/Nb (2.91-3.16), depleted Nb/U (6-6.74), and also lack of xenolith or enclaves indicate cryptic crustal contamination. The slab-derived fluid indicated by ratios of Rb/Y (0/019-0/05), Nb/Y (0.10-0.11), Th/Yb (0.52-0.61), and Ba/La ratio (13.29-14.57). Ponelo volcanic rocks shows typical calc-alkaline island arc tectonic setting particularly with enrichment in ion lithophile element (LILE) and light rare earth elements (LREE) along with depletion in high field strenght elements (HFSE) and heavy rare earth elemets (HREE), as shown by spider diagrams.

The Ain Dibba and Ain Kissa phosphorites, Tebessa (NE Algeria): REE depletion versus shallow, open depositional environment during the Paleocene-Eocene phosphogenesis in North Africa

The Ain Dibba and Ain Kissa phosphorites, located north of Tebessa town, NE Algeria, belong to the Upper Cretaceous-Paleocene-Eocene Afro-Arabian phosphatic province that extends from Morrocco to the Middle East. These two phosphorite showings, which were partly exploited at the beginning of the 20th century, were deposited during the Late Paleocene (Thanetian) times on the northern basin of the Kasserine Paleo-Island. Although they are not yet economically very important, the present petrological and geochemical study contribute highly to the knowledge of their critical trace and REE contents as well as the understanding of their paleo-depositional environment. Petrographic and XRD data show that these phosphorites are mainly composed of pellets, coprolites, bioclasts and rare glauconite, gypsum, quartz grains and zeolites. These constituents are cemented by calcareous, siliceous or rarely clayey matrix. The pellets and coprolites are composed mainly of cryptocrystalline carbonate fluor-apatite (CFA). The XRF and ICP-MS chemical analyses of these phosphorites, show they are not as rich as those from Kef Essenoun and Bled El Hadba southern basin, neither in P2O5 nor in REE contents. P2O5 concentrations range from 14.16 to 26.57 wt% (average = 20.24 ± 4.33 wt%, n = 15), with only one sample having 31.89 wt% P2O5, whereas ΣREE contents range from 171 to 344 ppm (average = 252 ± 69 ppm, n = 9) and, therefore, considered as moderately REE-enriched phosphorites. Ce anomaly values display a decrease from the lower to the upper phosphorite sub-layers (from −0.57 down to −0.72), suggesting an increase from relatively sub-oxic to more oxic conditions. The Eu anomalies range from 0.89 to 1.35 for Ain Dibba and from 0.93 to 1.35 for Ain Kissa phosphorites. The highest Ce/Ce∗ and lowest Eu/Eu∗ anomalies are recorded in the lower layers, often enriched in both REE and glauconite contents, whereas the lowest Ce/Ce∗ and highest Eu/Eu∗ anomalies, reflecting more oxic conditions, are characteristics of the glauconite-free and REE-poor upper layers. The gradual timewise transition from relatively sub-oxic to oxic conditions (from the lower to the upper layers) is also recorded in the redox-sensitive (Cr, Ni, V, U) trace element data. This implies that during early diagenesis, the sedimentary environment became slightly reduced, which enabled intensive uptake of both REE and some trace element (e.g., Cr, V, Ni, U) mainly from pore-water through substitution and adsorption mechanisms onto apatite and glauconite minerals. This is noticed especially in the lower phosphorite layers of both Ain Dibba and Ain Kissa deposits. In a larger scale, the Ain Dibba and Ain Kissa phosphorites show lower REE contents, lower Ce and Eu anomalies, and lower redox-sensitive trace element contents than those of the southern (Kef Essenoun and Bled El Hadba) and eastern (Tunisian) basins of the Kasserine paleo-Island. These geochemical features indicate that phosphorites from the northern basin were deposited, through upwelling current, in a more open, shallower, oxygenated and agitated environment during the Paleocene-Eocene phosphogenesis in North Africa and Middle East.

Ultrahigh-pressure to high-pressure eclogite in Cuban ophiolitic mélange reveals proto-Caribbean spreading ridge subduction

Proto-Caribbean oceanic crust produced during ocean-floor spreading between diverging North and South American plates was subsequently subducted beneath the Caribbean plate. However, the timing and spatial configuration of proto-Caribbean spreading ridge subduction remain subjects of debate. High-pressure (HP) basaltic metamorphic rocks, representing relics of the subducted proto-Caribbean oceanic crust, commonly occur in Cuban ophiolitic mélanges. In this study, an integrated set of petrological, geochemical, and geochronological data is presented for eclogite from the Las Villas mélange, central Cuba. The typical geochemical signature of mid-ocean-ridge basalt (MORB) indicates that the protolith of eclogite formed at the proto-Caribbean spreading ridge. Based on pressure-temperature (P-T) estimates obtained by pseudosection analysis as well as Zr-in-rutile and Ti-in-zircon thermometry, the following P-T paths for representative samples can be derived: a prograde path from 24−25 kbar and 510−520 °C to peak conditions of 29−31 kbar and 525−575 °C, and a complex retrograde path initially following almost isothermal exhumation to 25−27 kbar, followed by near-isobaric heating to 610−640 °C before final exhumation. This is the first documentation of prograde oceanic ultrahigh-pressure (UHP) metamorphism in the northern Caribbean area. U-Pb dating of magmatic zircon with steep heavy rare earth element (HREE) patterns and negative Eu anomalies yielded a protolith age of 126.3 ± 0.7 Ma. In contrast, metamorphic zircon with flat HREE patterns and without an Eu anomaly yielded a weighted mean age of 118.6 ± 1.6 Ma. The short time interval of >8 m.y. between MORB magmatism and UHP metamorphism suggests that the oceanic crust was subducted to great depth (∼100 km) shortly after generation in an oceanic ridge, which provides robust evidence for subduction of the proto-Caribbean spreading ridge. Furthermore, this work demonstrates high potential to trace ancient spreading ridge subduction by joint petrological, geochemical, and geochronological study of oceanic eclogite.

Geochemistry and geochronology of 1.7-1.8 Ga peraluminous A-type granites and granite-gneiss from the Mahakoshal Basin, Central Indian Tectonic Zone (CITZ): implications for an accretionary orogen for the evolution of CITZ

ABSTRACT Here, we report petrography, whole-rock geochemistry, and zircon U-Pb geochronology to understand the origin, source, geodynamic setting, and evolution of A-type granite and granite gneiss as well as establish their emplacement age from Mahakoshal Basin. Mineralogically, Sidhi granite gneiss and Madanmahal granite of the Mahakoshal Basin dominantly consist of quartz, K-feldspar, and plagioclase. Geochemically, Sidhi granite gneiss and Madanmahal granite are ferroan in nature. The studied rocks are akin to peraluminous A-type granites and have average zircon saturation temperatures of 955°C and 977°C, respectively. The studied rock types are derived from partial melting of pre-existing crust indicated by (Y/Nb)N >0.18, (Th/Nb)N >2, (Ce/Pb)N <1, and (La/Nb)N >2 accompanied by the Eu, Ba, Sr, Ti, and Nb negative anomalies. The zircon U-Pb geochronology yielded emplacement ages of 1723 ± 16 Ma for the Sidhi granite gneiss and 1801 ± 64 Ma for the Madanmahal granite. Based on similar geochemical characteristics such as rare earth element patterns, Eu anomalies, and Ce/Pb, La/Nb, and Th/Nb ratios, we propose that the Sidhi granite gneiss and Madanmahal granite are derived from the same source i.e. Bundelkhand gneisses and granites, and formed in a post-orogenic rift environment of the accretionary orogen setting.

Unraveling the genesis of wolframite mineralization in the West Qinling Belt, China: Evidence from geochronology, geochemistry, and fluid inclusion study

The West Qinling Belt is a pivotal part of the Central China Orogenic Belt renowned for producing abundant Au-polymetallic deposits. Nonetheless, reports of wolframite mineralization within this region were absent. The Xuehuashan deposit is the premier documented quartz-vein type wolframite deposit in West Qinling, which has significant implications of W mineralizing potential in the West Qinling Belt. The ore bodies are predominantly composed of wolframite-quartz veins and/or veinlets which are proximal or within the Late Triassic Baijiazhuang granitoid. To elucidate the age and genesis of the Xuehuashan wolframite mineralization, we presented analyses of U-Pb dating and chemical composition on wolframite, fluid inclusion study, and hydrogen–oxygen isotopes on wolframite and quartz. The Xuehuashan wolframite U-Pb dating yielded an age of 213.0 ± 6.7 Ma, which is consistent with the age of the Baijiazhuang granitoid. The correlation among trace elements and the Y/Ho vs. Zr/Hf diagram suggests trace elements in wolframite were influenced by crystalline chemical factors and the geochemistry of parental ore-forming fluid. Homogeneous texture and stable chemical composition of wolframite, as well δD vs. δ18O isotopes, suggest a single magmatic fluid from the Baijiazhuang granitoid. Fluid inclusions in wolframite and quartz have high homogenization temperatures and varying salinities of 0.4 – 16.4 wt%, suggesting that intense decompression and fluid boiling during fracture open caused the wolframite precipitation. Compared with the Late Triassic granitoids in the Qinling Belt, the Baijiazhuang granitoid shows higher ratios of Rb/Sr and lower ratios of Zr/Hf, K/Rb, Nb/Ta, LREE/HREE, as well as negative Eu anomalies, which are consistent with the W-related highly evolved granitoids but distinct to W-barren granitoids. Hence, this study highlights W mineralization potential in the Qinling belt associated with the highly evolved Late Triassic granitoids.

Onset and tempo of ignimbrite flare-up volcanism in the eastern and central Mogollon-Datil volcanic field, southern New Mexico, USA

The Cenozoic ignimbrite flare-up (40–18 Ma) generated multiple volcanic fields in the southwestern United States and northern Mexico resulting from asthenospheric mantle upwelling after removal of the Farallon slab. The correlation of tuffs to one another and to source calderas within these volcanic fields is essential for determining spatiotemporal patterns in volcanism and magma geochemistry, which have been used to deduce migration of the Farallon slab at depth and associated mantle melting. However, the correlation of Eocene–Oligocene tuffs in the southwestern U.S. is difficult because of post-emplacement erosion and faulting. This study focuses on spatiotemporal patterns of the initial episode of ignimbrite flare-up activity (ca. 36.5–33.8 Ma) in the Mogollon-Datil volcanic field in south-central New Mexico, USA. We show that alkali feldspar major and trace element geochemistry is an effective tool for correlating tuffs when combined with high-precision, single-crystal 40Ar/39Ar geochronology and bulk-rock geochemistry. Using these data, we correlate several tuff units and differentiate other tuffs that have the same eruption age but very different geochemistry, and we conclude that there was a broadly northwestward migration in volcanism over time. The new tuff correlations are used to investigate spatiotemporal variations in magma geochemistry, erupted volumes, and recurrence intervals during the initial episode of Mogollon-Datil volcanic field volcanism. Early-erupted tuffs restricted to the eastern Mogollon-Datil volcanic field share similarities with western U.S. topaz rhyolites, which suggests that the silicic magmas were generated by partial melting of mafic lower crustal rocks. We also find differences in the compositions, crystallinities, and mineral assemblages between the early- and late-erupted tuffs. The early-erupted tuffs tend to have single-feldspar mineralogies, lower feldspar Or contents, large negative Eu anomalies, and low-whole–rock Ba concentrations. Conversely, late-erupted tuffs have two feldspar plus quartz assemblages, lesser Eu anomalies, higher whole-rock Ba concentrations, and feldspars have higher Or contents. Thus, we suggest that for some of the early eruptions, after magmas underwent crystal fractionation in the crust, the silicic melt largely separated from the crystalline mush prior to eruption, whereas late-erupted tuff magmas underwent crystal fractionation at near the eutectic minimum and were remobilized and erupted with a larger proportion of their crystalline mush. Using our new ages, correlations, and previously published data, we find that the initial phase of Mogollon-Datil volcanic field volcanism produced at least 15 eruptions between 36.5 Ma and 33.8 Ma, with a minimum total erupted volume of ~1350 km3 and an average recurrence interval of 170 k.y. However, eruptions were generally smaller in volume (most &amp;lt;15 km3) than in other coeval fields, and most eruptions (n = 11) occurred in the first 1.2 m.y. (ca. 36.5–35.3 Ma) of activity. Altogether, our work sheds new light on variations in the composition, timing, and migration of volcanism during the initial phase of Mogollon-Datil volcanic field activity and highlights the utility of feldspar geochemistry in both “fingerprinting” tuffs and elucidating magma evolution.

Titanite: A source, thermodynamic, and temporal proxy for W-Mo-Cu Skarn mineralization at the Seridó Mineral Province, Northeastern Brazil

New zircon U-Pb geochronology (SHRIMP) and geochemistry combined with geochronology (LA-ICP-MS) of titanite data are provided to investigate the metallic sources (whether igneous or sedimentary) and the temporal evolution of one of the most relevant Precambrian metallogenic provinces of the South American Platform, the Seridó Mineral Province. The granites of Serra de João do Vale pluton, calc-silicate “skarnoid” rocks and paragneiss related to the Bonito W-Mo-Cu exoskarn deposit were investigated. It was analyzed titanites of magmatic (Serra de João do Vale), hydrothermal (calc-silicate rocks) and metamorphic (paragneiss) origin. The magmatic titanite is wedge-shaped with larger grain size (up to 250 μm), richer in HFSE elements, Al and Fe, and manifests negative Eu anomalies (Eu/Eu × averaging 0.31–0.60). The hydrothermal titanite is found alongside epidote and calcite, have subhedral shapes and medium grain size (up to 150 μm). The metamorphic titanite is anhedral, generally smaller than 100 μm and appear as thin coronae in ilmenite or as inclusions in biotite. Both metasomatic and metamorphic titanites manifest positive Eu anomalies (Eu/Eu × averaging 1.20 and 1.06, respectively) and are enriched in Ti, Rb and U in relation to the magmatic. Conventional mineral thermobarometry (Al-in-titanite independent barometer, and Zr-in-titanite thermobarometer) provided pressures between 400 and 550 MPa and temperatures between 720 and 787 °C for the crystallization history of the granite, coeval with the regional peak metamorphism at 568–624 °C and 300–500 MPa (Ti in biotite independent barometer and biotite-muscovite thermobarometer). Conditions for the titanite-epidote calc-silicate assemblage were constrained through thermodynamic modelling in NCKFMAST + COH pseudosection at 439 ± 35 °C and 190 ± 50 MPa. The zircon U-Pb age registered the magmatism between 585.5 and 580.5 Ma. Titanite U-Pb ages from granite and calc-silicate rocks timed the closure of U-Pb system at the isotherm of 550 °C between 562 and 557 Ma. (20 m.y. after the intrusion), which marks the metasomatic process. The average W content in paragneisses and calc-silicate titanites (35.8–35.5 ppm) is 4 times higher than in the granite (6.76 ppm), reaching a maximum of 328 ppm. Mo and Cu mirrors this behavior, with concentrations that exceed nearly double that of titanites from Serra de João do Vale granites, peaking at 308 ppm of Mo and 162 ppm of Cu. Metal contents in titanite disclose the metasiliciclastic rocks of the Jucurutu Formation as, at least partially, a source of metals (mainly for W, but also Cu and Mo) in the skarn mineralization during the terrane exhumation at the end of Ediacaran period.

Neoproterozoic Ridge Subduction Beneath South China Craton: TTG Suites of Kangding Complex in Western Yangtze Block and its Geochemistry Characteristics

ABSTRACT A multidisciplinary study involving field investigation, petrographic, geochronology, and whole-rock geochemical data is presented for TTG suites in the western Yangtze Block. In this paper, we compiled element geochemistry data that we obtained from our previous works for China Geological Survey Projects and presented the zircon U-Pb age and the whole-rock elemental compositions of the Na-rich TTG rocks to provide constraints on the origin of the Neoproterozoic magmatism in the western Yangtze Block. The studied rocks show a calc-alkaline trend. They are comparable in whole-rock chemistry to Archean TTG suites from Finland, Labrador, India, Zimbabwe, Brazil, and Ontario, as well as the modern calc-alkaline magmas such as volcanic rocks in the Kastamonu area of Northern Turkey and the Cenozoic andesitedacite-rhyolite suites from the North American Cordillera. Zircon U-Pb age shows the crystallization age of the plagioclase gneiss from Kangding Complex is 772.4 ± 6.9 Ma. The granodiorites are more enriched in LREEs but depleted in HREEs, showed strong negative Eu anomalies, and are characterized by fractionated LREE, flat HREE, and depletion of high-field-strength trace elements (HFSE) relative to normal mid-ocean basalts (N-MORB). However, most trondhjemites, all tonalites, and all quartz diorites have no Eu anomalies. Trace element distribution patterns for all samples show typical island arc signatures with relative enrichment in LILE and depletion in HFSE like Nb and Ta. We assume that the TTG suites were derived from melting of metabasalt in a subducted slab heated by a slab window, which provides further support for a Neoproterozoic intra-oceanic ridge subduction along the western margin of Yangtze Block.

Y-Ho fractionation during basalt alteration in hydrothermal system: An implication for superchondritic Y/Ho signature recorded in Precambrian banded iron formations

The concentration of rare earth elements (REE) in Precambrian sedimentary rocks is widely used to estimate their depositional environment. Specifically, superchondritic Y/Ho value is a powerful indicator for determining whether a sedimentary rock was deposited in a marine environment. Currently, superchondritic Y/Ho value in seawater is believed to result from the preferential adsorption of Y onto Fe-Mn oxides. In modern oceans, Fe-Mn oxides are considered the sink for subchondritic Y/Ho value. On the contrary, Precambrian banded iron formations (BIFs) display superchondritic Y/Ho value, suggesting that Precambrian seawater also possessed a superchondritic Y/Ho value. However, Precambrian BIFs cannot account for the sink of subchondritic Y/Ho value. Thus, other processes must have been responsible for maintaining the superchondritic Y/Ho value of Precambrian seawater. A hydrothermal experiment involving mid-ocean ridge basalt (MORB) and a Cl-rich fluid was conducted at 300 °C and 500 bars to assess the role of basalt-hosted hydrothermal systems on the Y/Ho value of seawater. Over time, the fluid's Ca concentration increased while Na decreased, suggesting plagioclase albitization occurred. The REE pattern of the reacted fluids exhibited superchondritic Y/Ho values up to 63.2. Based on the presence of positive Eu anomaly and the degree of light REE depletion, the REE in the hydrothermal fluids was mainly sourced from plagioclase during albitization. The superchondritic Y/Ho values in the fluids can be explained by the preferential leaching of these elements due to differences in chloride complexing strength between REE. Subchondritic Y/Ho values observed in Precambrian hydrothermally altered basalts may be interpreted as remnants generating superchondritic Y/Ho values in coexisting Precambrian hydrothermal fluids. Therefore, we believe that the superchondritic Y/Ho value of Precambrian seawater was maintained by basalt-hosted hydrothermal system.

Settings Trace elements and garnet formation in a distal skarn zone: a case study of the Rudnik deposit, Central Serbia

The Rudnik Pb-Zn deposit is hosted in skarns and hornfels formed in the late Oligocene by contact metamorphism of limestones, sandstones and shales. Garnets, together with epidote, represent the main non-metallic minerals in the Rudnik skarn. In the distal skarn zone, the garnets are rare and their occurrence is related to the flow path of hydrothermal fluids. To constrain the hydrothermal and physicochemical conditions, in situ elemental SEM-WDS and LA-ICP-MS analyses, and fluid inclusion microthermometric measurements, were made. The Rudnik garnets from the distal skarn zone are predominantly of andradite-grossular composition (Adr39.3–88.9Grs2.9–53.9Alm0.5–10.0), with a small amount of spessartine. Generally, the Fe-rich garnets show a positive Eu anomaly with LREE enrichment and a HREE flat pattern, with homogenization temperatures and salinities of fluid inclusions ranging from 373 to 392°C and from 14.25 to 15.27% NaCl equivalent, respectively. The trace elements and microthermometric properties indicate that the garnets formed at moderately high temperatures, mildly acidic pH levels and increased oxygen fugacity

Miocene magmatism in Northern Tunisia and its geodynamic implications

The Nefza igneous rocks in Northern Tunisia belong to the Miocene magmatic belt extending from Northern Tunisia to Morocco and consist mainly of Serravallian–Tortonian granodiorite and rhyodacite (~ 14–8 Ma) and Messinian basalts (~ 8–6 Ma). Differences in geochemical composition between units have been interpreted to be the result of geodynamic processes in the upper mantle below the Western Mediterranean area, but their implications for Northern Tunisia are unclear due to limited data. In this contribution, we present an updated geodynamic model for Northern Tunisia based on new petrographic and whole-rock geochemical results from the Nefza magmatic suite from outcrop and OB45 drill core samples. Petrographic observations show that rhyodacites display a microlithic texture with quartz, plagioclase, K-feldspar, biotite, and glass, whilst granodiorite contains plagioclase, quartz and exhibits fine-grained texture with a 2–3 mm crystal size. The Nefza magmatic rocks are overprinted by multiple weathering and alteration processes with loss of ignition (LOI) ranging between 0.88 and more than 5 wt%. The linear relationships between mobile elements (Ca, Na, P, K, Mg, Si), large-ion lithophile elements (LILE), and LOI suggest element mobilisation during alteration. Major and trace element compositions show the Nefza magmatic rocks plot in the rhyolite, dacite, and trachydacite fields for felsic rocks and plot in the basalt and trachybasalt fields for mafic rocks. Granodiorite and rhyodacite rocks exhibit negative Eu anomalies and a LILE enrichment (Rb, Ba, Pb) relative to high-field-strength elements (HFSE: Nb, Ta, Hf, Zr, REE). Mafic rocks enriched in LILE show geochemical characteristics between calc-alkaline and alkaline trends. Comparison with nearby regions suggests that the generation of calc-alkaline magmas resulted from the partial melting of the lithospheric mantle due to slab break-off or tearing in Eastern Algeria. The upward flow of asthenospheric material through the widening tear in the sinking slab leads to partial melting of the mantle and shallowing of the lithosphere–asthenosphere boundary, ultimately leading to the formation of alkaline magma. The Nefza geochemical variations underscore Mediterranean upper mantle heterogeneity, offering crucial insights into Mediterranean geodynamics. More studies are needed to constrain mantle dynamics and the region’s complex geological history.

Growth of the Central Orogenic Belt, North China Craton through accretion of different Neoarchean arc terranes: Perspective from the Linshan complex

The onset of plate tectonics and crustal growth processes in the early Earth have been controversial scientific issues in the geoscience. The North China Craton (NCC) preserves widespread 3.8–2.5 Ga rocks, providing an ideal place to understand early continent formation and evolution. The Linshan complex located in the southern segment of the Central Orogenic Belt (COB) of the NCC, is mainly composed of TTG (tonalite-trondhjemite-granodiorite)-diorite gneisses and metamorphic volcanic-sedimentary units dominated by gabbro, basalt, basaltic andesite and biotite-plagioclase gneiss. Detailed mapping on the scale of 1:100 of a structural transect shows that the Linshan complex has mainly experienced two major deformation events including top-to-the-SE thrust faults and late NE-trending high-angle normal faults. Detailed zircon U-Pb dating shows that gabbro, basaltic andesite, and TTG gneiss mainly formed at ca. 2.52–2.50 Ga. Gabbros and basalts display enrichment of LREE and negative Nb and Ta anomalies, and basaltic andesites display mixed MORB-IAT geochemical affinities. Basalts and basaltic andesites are members of the Nb-enriched basalt series with high absolute Nb contents (>6 ppm). TTG gneisses are geochemically divided into high-pressure and low-pressure TTGs. High-pressure TTGs are characterized by high ratios of La/Ybcn (26.29–45.73) and fall into the adakitic region in the La/Ybcn-Ybcn diagram. Considering the close contact with Nb-enriched basaltic series, it is proposed that high-pressure TTGs may have formed by partial melting of a subducting oceanic slab with garnet and amphibole and/or rutile as residues. Low-pressure TTGs are characterized by low ratios of La/Ybcn and Sr/Y with marked negative Eu anomalies, indicating partial melting at shallow crustal levels. Regional tectonic relations have defined the Neoarchean Dengfeng island arc-forearc accretionary complex to the east of the Linshan complex. Thus, we propose that the gabbros-basalts-basaltic andesites in the Linshan complex mostly formed in a Neoarchean suprasubduction back-arc basin by rifting of a TTG-dominated island arc terrane. The final closure of the back-arc basin resulted in their tectonic juxtaposition forming thrust-imbricated structures. There may have been several Neoarchean “forearc-island-arc-backarc” systems in the NCC that are similar to modern accretionary tectonic orogens, indicating that plate tectonics has been in operation since at least 2.55–2.50 Ga.

Provenance and tectonic setting of sandstones of the Lomas Coloradas Formation, Cabullona Group, Sonora, México: Constraints on petrography and geochemistry

The sedimentary rocks of the Cabullona Group are well exposed in the Cabullona Basin of northeastern Sonora, México, which represent syntectonic sedimentation associated with Laramide-style deformation during the Campanian−early Maastrichtian. The sandstones of the Lomas Coloradas Formation deposited at the upper part of the Cabullona Group. Petrography and geochemical (major, trace, and rare earth elements) studies were carried out on the sandstones to interpret the palaeoweathering, provenance, and tectonic setting of the Lomas Coloradas Formation sandstones. Most of the sandstone modal analysis data plotted in the QFL and QmFLt ternary diagrams fall into the fields of dissected arcs and recycled orogens, respectively. Geochemically the sandstones are classified as litharenites while few samples plot into the arkosic field. The chondrite-normalized REE diagrams for sandstones have LREE-enriched, relatively flat HREE patterns with negative Eu anomalies. CIA values and the A‒CN‒K diagram indicate a low intensity of chemical weathering in the source area. The tectonic setting diagram suggests both arc and rift settings for the studied sandstones. The bivariate and ternary diagrams and elemental ratios suggest a felsic source for the Lomas Coloradas Formation. The average REE patterns of the studied sandstones are comparable with REE patterns of the granite from the Caborca block, the rhyolite and granite of the Tarahumara Formation, and the Mesozoic felsic volcanic rocks. The modeled mixture of 40% Proterozoic granite, 30% Triassic arc, 10% Jurassic arc, and 20% Laramide arc represents the probable source rocks for the Lomas Coloradas Formation.

Geochronology and Geochemistry of Granodiorite Porphyry in the Baoshan Cu-Pb-Zn Deposit, South China: Insights into Petrogenesis and Metallogeny

The Baoshan Cu-Pb-Zn deposit is situated at the intersection of the Qin-Hang Cu polymetallic and Nanling W-Sn polymetallic metallogenic belts. The age, lithology, petrogenesis, and tectonic setting of granodiorite porphyry within the deposit remain subjects of debate. Additionally, there is a lack of comparative studies with the W-Sn-related granites in the region. This study conducted whole-rock major and trace element analysis, Sr-Nd isotope analysis, and zircon U-Pb dating on the Baoshan granodiorite porphyry. The zircon U-Pb age of the granodiorite porphyry is 162 ± 1 Ma. The whole-rock SiO2 and K2O contents range from 65.87 to 68.21 wt.% and 3.42 to 5.62 wt.%, respectively, indicating that the granodiorite porphyry belongs to high-potassium calc-alkaline I-type granite. The granodiorite porphyry is characterized by enrichment in LREE and depletion in HREE (LREE/HREE ratio = 6.2–21.2). The samples of granodiorite porphyry generally exhibit weak negative Eu anomalies or no Eu anomalies (δEu = 0.62–1.04, mean = 0.82). The (87Sr/86Sr)i and εNd(t) values are 0.707717–0.709506 and −7.54 to −4.87, respectively. The whole-rock geochemical composition and Sr-Nd isotopic values indicate that the magma originated from the partial melting of the Mesoproterozoic ancient crust and Neoproterozoic mafic juvenile lower crust, with the addition of high oxygen fugacity and water-rich lithospheric mantle melts. The source of the granodiorite porphyry in the Baoshan deposit is significantly different from the crust-derived metapelite source of the W-Sn-related granite in the area, indicating that different magma sources might be the main reason for the co-spatial and nearly contemporaneous development of Cu-Pb-Zn and W-Sn mineralization in the southern Hunan region.

Synchronous felsic volcanism and carbonate sedimentation as a setting for VMS deposits localization at the Salair terrane, NE Central Asian Orogenic Belt

The Salair terrane located in the northern part of the Central Asian Orogenic Belt (CAOB) contains many epithermal deposits including volcanogenic massive sulphide (VMS) deposits. The host rocks mainly consist of felsic volcanic rocks such as lavas, volcanic breccias and tuffs that associated with thick strata of carbonates. In this study, we present zircon U–Pb ages, whole rock geochemistry, and Nd isotope data from the volcanic rocks, and results of geochemical and isotope (Sr, C, O) studies of carbonates to constrain their age and petrogenesis, and to characterize the tectonic setting. Zircon U–Pb dating reveals that the ore-bearing felsic lavas have age of 519.3 ± 1.9 Ma, while the felsic tuffs have age of 516.0 ± 0.9 Ma. These volcanic rocks are characterized by high SiO2 and Na2O contents, enrichment in light rare-earth elements, remarkable negative Eu anomalies, and pronounced depletion in Nb, Ta, P, and Ti. They have depleted ɛNd(t) values ranging from +4.9 to +6.3, and young two-stage Nd model ages (from 0.82 to 0.64 Ga). The felsic volcanic rocks from the Salair terrane are interpreted as highly evolved I-type magmatic rocks that might be produced by high degree partial melting of juvenile lower crust without a significant contribution of ancient crust and without crustal reworking.Felsic volcanism was accompanied by the formation of thick strata of carbonates. These carbonates are marine limestones with Mg/Ca ratios less than 0.007, δ18O(SMOW) values from 17.1 to 23.8 ‰ and δ13C(PDB) values between –0.9 and +0.9. Their Sr isotope composition varies in a narrow range within 0.70844–0.70859 that interpreted as representing proxy for coeval seawater. These values are consistent with depositional ages of 520–510 Ma and confirms the synchronicity of the formation of carbonates and felsic volcanism. Based on the regional geology and geochemistry, the ore-host rocks of the Salair terrane were formed in the back-arc setting where the marine transgression occurred as a result of graben subsidence. It is important for better understanding epithermal deposits in the northern CAOB and might provide new insights about prospecting the VMS deposits in similar tectonic settings.