Magmatic Origin Research Articles

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.

Geological characteristics and ore‐forming conditions of the Tasikmadu porphyry Cu–Au prospect in Trenggalek, East Java, Indonesia

Tasikmadu is a newly discovered porphyry Cu–Au prospect in the eastern Sunda arc, Indonesia. This study aimed to elucidate salient diagnostic characteristics and ore‐forming conditions of the prospect. Fieldwork and various laboratory analyses for a suite of representative samples were performed for mineralogy, bulk‐geochemistry, mineral chemistry and ore fluid characterization. The study area is composed of three diorite porphyries, that is, fine‐grained, medium‐grained and coarse‐grained diorite porphyry, respectively. The intrusions are calc‐alkaline with a high Sr/Y value, which is similar to many ore‐bearing intrusions in the eastern Sunda arc. Ore mineralization occurs in quartz veins and veinlet stockwork, centred in the potassic zone, and dominated by chalcopyrite and bornite occurring in A and B veins, which cut earlier barren (EB) and M veins. The mineralization core has an average grade of 0.63 wt% Cu and 0.25 ppm Au, respectively. Outwardly, the potassic zone changes to the propylitic zone, which still bears copper in the quartz and pyrite veinlets, although the grade is low. Fluid inclusion microthermometry revealed that the A and B veins in the potassic zone formed at 464 and 390°C by hypersaline boiling fluids, respectively. The temperature temporally and spatially decreased, that is, in the propylitic zone, the quartz veinlets formed at 260–400°C. Hypogene mineralization that formed the A veins occurred at 1.5 km below the palaeosurface, indicating a relatively shallow depth as a porphyry deposit. Nevertheless, the δ34SCDT values of sulphides range from −2.0 to −0.1‰, inferring a magmatic origin. The Tasikmadu prospect shares some similarities compared with other porphyry deposits worldwide, but it also reveals unique characteristics that differ from others, for example, potassic‐altered rocks are only typified by secondary biotite without/rare secondary K‐feldspar reflecting the lack of magma contamination by continental crustal components. In addition, current surface geological features and shallow depth erosion level of the prospect may imply that the potential of Cu–Au mineralization underneath is still open to depth.

The superposition of Cretaceous mineralization events leading to the formation of the large Baiyinnuoer Pb–Zn deposit in NE China

The Baiyinnuoer Pb–Zn deposit, estimated at 26.57 million metric tonnes (Mt) with grades of 1.77% Pb and 5.21% Zn, is situated in the southern Great Xing'an Range (SGXR) of northeast China. The deposit comprises southern and northern ore belts. The southern belt primarily contains skarn ore bodies (32% of reserves) associated with Triassic granodiorite, while the northern belt is dominated by skarn ore bodies (30% of reserves) related to Triassic diorite porphyry. In addition to Triassic skarn‐type mineralization, the deposit also exhibits Early Cretaceous mineralization. This includes vein‐type occurrences (36% of reserves) within volcanic tuff and syenite porphyry, alongside a small amount of skarn ore bodies (2% of reserves) related to syenite porphyry. LA‐ICP‐MS U–Pb dating of intrusive rocks and garnets was conducted to investigate the timing and genesis of these mineralization events, revealing two distinct stages of skarn‐type mineralization. The first stage, associated with Early Triassic granitoids, dates to 254.6 ± 1.4–241.7 ± 2.7 Ma, while the second stage is closely associated with Early Cretaceous syenite porphyry, constrained to 135.4 ± 1.1–135.2 ± 1.6 Ma. Garnet U–Pb dating in the syenite porphyry‐related skarn yielded an age of 134.9 ± 4.7 Ma; however, due to low U content, reliable dating of garnets associated with Early Triassic granitoid‐related skarn was not feasible. Micro‐thermometry and Laser Raman analyses of fluid inclusions within vein‐type ore bodies highlighted distinct differences between vein‐type mineralization and Early Triassic skarn‐type mineralization. Additionally, in situ sulfur isotope analyses of sphalerite from both Early Triassic and Early Cretaceous ore bodies indicate a magmatic origin for sulfur in both stages. Through comprehensive geological, geochronological, in situ sulfur isotope and fluid inclusion studies, the Baiyinnuoer Pb–Zn deposit is conclusively identified as a large deposit characterized by two distinct periods of mineralization (Early Triassic and Early Cretaceous), akin to several other significant polymetallic deposits in NE China.

Zircon U-Pb geochronology, major, trace elemental, and Sr-Nd-Pb isotopic geochemistry: constraints on the age and magmatic origin of Mesozoic mafic dykes in the Guangxi Zhuang Autonomous Region, South China

ABSTRACT As a direct product of lithospheric extension, the mafic dyke group have become an ideal object for studying the formation, evolution and dynamics of both the crust and continental orogenic belts. Given the scientific significance of mafic dykes and their utility in addressing outstanding questions concerning the origin and development mafic dyke swarms Mesozoic age with-in the South China Plate, in this study, 54 representative mafic dykes within the Guangxi Zhuang Autonomous Region, South China, were examined. Research methods include laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb age-dating, whole rock geochemistry, and the Sr-Nd-Pb isotope geochemistry of the studied mafic dykes. The results indicate that these rocks formed between 139 Ma and 113 Ma and have typical doleritic and lamellar textures. They fall into the alkaline and shoshonitic series, are characterized by enrichment of light rare earth elements, some large ion lithophile elements (Rb, Ba, and Sr), Th, U, and Pb, and have depleted Nb, Ta, Hf, and Ti. Moreover, the mafic dykes studied have high initial87Sr/86Sr ratios (0.7055–0.7057), negative εNd(t) values (from −15.2 to −11.4), and relatively constant initial Pb isotopic ratios (that are Enriched Mantle-1 (EM I)-like; 206Pb/204Pb = 16.765–16.816, 207Pb/204Pb = 15.429–15.476, and208Pb/204Pb = 36.882–37.144). The above results indicate that the group of dolerites and lamprophyres studied herein were likely derived from magma generated via low-degree partial melting (1.0%–10%) of an EM1-like garnet-lherzolite mantle source. The parental magmas to these fractionated olivine-, clinopyroxene-, plagioclase, and Ti-bearing phases, with negligible crustal contamination during ascent and dyke emplacement. On the basis of existing research and evidence from this study, we propose a reasonable model for the origin of the mafic dykes: the ancient Pacific Plate subducting below the South China plate led to extension of the lithosphere, an upsurge of the asthenosphere, which triggered partial melting of the lower mantle lithosphere in the Early Cretaceous, and the formation of the parent magma to the Mesozoic mafic dykes in the Guangxi Zhuang Autonomous Region study area. The involvement of slab-derived fluids from the subduction of the ancient Pacific Plate was responsible for metasomatism of the mantle source to these mafic magmas.

Extension settings favour initial REE enrichment in the parent granites of ion-adsorption REE deposits: implication from Late-Permian to Triassic granites in South China

The mechanism of rare earth elements (REE) enrichment in granites is important to understand generation of ion-adsorption REE deposits. We investigated Late Permian to Triassic granites from South China to investigate these issues. The ore-related granites with high REE contents (192-467 ppm) intruded in Late Permian have high K 2 O and Zr+Ce+Nb+Y contents, high Ga/Al and K/Na ratios, and low CaO contents, which belong to aluminous A-type granite derived from melting of felsic igneous rocks at a high-temperature extensional setting. The ore-unrelated Triassic Pingtian granite with relatively low REE contents (81.7-127 ppm) is peraluminous with occurrence of muscovite, indicating a S-type affinity. Its high Rb/Sr and low CaO/Na 2 O ratios indicate magma origin from a metapelitic source related to the compressional setting due to the continental collision. In the extensional settings in South China, the high temperature condition promoting melting of REE-rich accessory minerals and F-rich conditions improving the solubility of REE in the melts could be the reasons for the initial REE enrichment in these granites. Given that parent rocks for ion-adsorption REE deposits are all generated in extensional settings, multiple tectonic stages and long-term extensional setting in South China contributed to generation of the specific ion-adsorption REE deposits in South China.

U–Pb–Hf and morphological evolution of zircon from granites associated with world-class tungsten skarn deposits in the northern Canadian Cordillera

The northern Canadian Cordillera is the most significant tungsten district in North America. Here, high-grade tungsten skarn deposits are associated with small, reduced, high-K calc-alkaline, S-type biotite granite plutons belonging to the 102–96 Ma Tungsten plutonic suite (TPS). A detailed U–Pb–Hf and morphological study of magmatic zircon from plutons in the southern half of the TPS belt was undertaken to better understand magmatic processes leading to the generation of the associated tungsten deposits. Antecrystic zircon from the TPS plutons began crystallizing during a transpressional regime ca. 117 Ma, suggesting the TPS magmas were active for up to 21 Myr prior to their upper crustal emplacement and final crystallization. This prolonged magmatic activity necessitates a magma origin in long-lived, deep crustal magma chambers. Hafnium isotopic compositions in zircon for the southern TPS as a whole form a non-radiogenic, univariate, and relatively wide ranging population (εHfi = −17.6 ± 4.5), but U–Pb–Hf trends become apparent when the data are sub-divided into sample groups with similar age, zircon morphology, and geographic location. These evolutionary trends in magmatic zircon are most simply explained by interactions between the parent melt and dissolving inherited zircon grains. This, along with changing zircon morphology, is consistent with gradual cooling and crystallization pathways exhibited by S-type magmas. Differing evolutionary trends in the U–Pb–Hf isotopic data between sample groups, however, suggest there were multiple magma batches that evolved independently, possibly in separate pockets within large, deep magma chambers. Zircon morphologies also suggest some grains in all sample groups were equilibrated with hotter and more alkaline magmas, although there is no textural or compositional evidence in the zircon for mixing of magmas with widely different compositions. An unconstrained inversion of local aeromagnetic data indicates reduced batholiths could be present 4–6+ km below the surface and that the plutons are apophysies to (or, higher level injections from) these deeper bodies. Although these batholiths can only be short-term holding chambers for magmas ascending from deep crustal levels, they may have been important for the segregation of mineralizing fluids. Since no single magmatic evolutionary pattern in the unaltered TPS plutons can be definitively linked to tungsten mineralization, pulses of mineralizing fluid may have been derived instead from the underlying batholiths. The 20+ Myr duration of deep magmatic activity exhibited by the TPS is similar to timeframes suggested for magmas associated with tungsten deposits in southern China, and may have allowed extended fractionation of a large volume of crustally derived magma to concentrate tungsten into late-stage melts. The emplacement of upper crustal batholiths and plutons in both regions during or following a transition to an extensional tectonic regime suggests the relaxed geodynamic regime may have been important in the ascension of metal-rich magmas and (or) fluids, ultimately resulting globally important tungsten deposits.

Multi-stage magmatic–hydrothermal evolution of nepheline pegmatite: Insights from the mineralogy and geochronology of a zircon megacryst from the Yilanlike nepheline pegmatite, South Tianshan

Magmatic–hydrothermal evolution plays a key role in the formation of peralkaline rocks and associated zirconium and rare earth element (REE) mineralization. Zircon is a common mineral in peralkaline rocks and can record invaluable information about the magmatic–hydrothermal evolution of these systems. To help better constrain the magmatic–hydrothermal evolution of and Zr enrichment processes in peralkaline systems, we characterized the mineralogy and geochronology of a texturally complex zircon megacryst from the rare metal mineralized Yilanlike nepheline pegmatite in the South Tianshan. Here we present laser Raman spectra, in situ elemental data, and U–Pb geochronological data for the zircon megacryst to constrain the age and magmatic–hydrothermal evolution of this nepheline pegmatite. Three types of zircon domains (Zrn-I, Zrn-II, and Zrn-III) are distinguished based on their morphological and geochemical characteristics. Zrn-I has well-developed oscillatory zoning, REE patterns similar to magmatic zircon, high Th/U ratios (0.09–0.47), and concordant U–Pb ages, indicative of a magmatic origin. Zrn-II is characterized by weak oscillatory and patchy zoning, low full width at half maximum (FWHM) values (6.58–14.86 cm−1), and low trace-element contents (e.g., Nb = 0.16–0.92 ppm, Ta = 0.13–0.54 ppm, U = 195.77–812.92 ppm, Th = 15.85–158.95 ppm, and total REE = 13.00–187.75 ppm), indicative of a recrystallized origin as this process generates heterogeneous zoning, heals the zircon crystal lattice, and lowers trace-element contents. Concordant U–Pb ages and low Th/U ratios (0.05–0.26), combined with moderate Ce/Ce* and (Sm/La)N ratios (0.38–33.96 and 1.34–27.73, respectively), which are characteristic of the magmatic–hydrothermal transition, indicate that Zrn-II recrystallized in the presence of hydrothermal fluids. Zrn-III is characterized by “spongy” textures, thorite inclusions, high FWHM values (6.58–47.87), relatively high contents of total REE (14.79–962.05 ppm), and discordant U–Pb ages, suggestive of an origin related to the hydrothermal alteration of earlier zircons. Results of U–Pb dating of Zrn-I and -II yield weighted concordant ages of 286.9 ± 1.9 Ma (MSWD = 1.5, n = 23) and 279.3 ± 2.3 Ma (MSWD = 0.24, n = 20), respectively, whereas the U–Pb results for Zrn-III are largely discordant. Based on these textural, geochemical, and geochronological results, a multi-stage process for the formation of the zircon megacryst and nepheline pegmatite is proposed. First, the parent magma of the nepheline pegmatite was emplaced and the zircon megacryst crystallized at ca. 286.9 Ma (represented by Zrn-I). As the magma differentiated, hydrothermal fluids derived from the evolved magma recrystallized Zrn-I to Zrn-II at ca. 279.3 Ma. Finally, a second hydrothermal event altered Zrn-I and -II to form Zrn-III. Given the low concentrations of UO2, ThO2, and Y2O3 in Zrn-II, and the CHARAC behavior of Zr and Hf, the fluid that formed this zircon variety likely had relatively low F contents. This multi-stage magmatic–hydrothermal evolution likely played an essential role in concentrating Zr and generating the Zr mineralization. Zirconium is primarily enriched via magmatic crystallization, as illustrated by the high abundances of Zrn-I in the Yilanlike nepheline pegmatite. The presence of hydrothermal zircon (Zrn-II and Zrn-III) suggests that hydrothermal recrystallizatio nay have also facilitated the enrichment of Zr. It is, therefore, suggested that both magmatic and hydrothermal processes contributed to the enrichment of Zr in the Yilanlike nepheline pegmatite.

The 3‐D Density Structure of the Large Shield Volcanic Structure in the Gardner Region Revealed by a New Gravity Inversion

AbstractThe Gardner region is a well‐known shield volcanic complex on the Moon. Its magma origin and formation mechanism are of significant interest but still enigmatic. To reveal the subsurface structure of this volcanic complex, we propose a new 3‐D inversion method of the gravity field based on the regularizations of the L1 norm of the model and its gradients. The model test indicates that our proposed method can recover the density structures with high resolution. Subsequently, we apply it to the Bouguer gravity data in the Gardner region. Our result shows a large, dense body with a volume of about 45 × 45 × 13 km3 centered under the topographic bulge of the Gardner Plateau. We infer that this structure is most likely dense basalts trapped at the crust‐mantle boundary as a sill and acted as the magma reservoir that has fed the volcanic complex in the Gardner area.

Multi-stage evolution of the monzonitic Larvik Plutonic Complex (Oslo Rift, Norway) and its implications for the formation of the Kodal Fe-Ti-P(−REE) deposit

The Larvik Plutonic Complex is a monzonitic complex that was emplaced early during the formation of the Permian Oslo Rift (southern Norway). It extends across its entire width (around 50 km), and is made up of a majority of larvikite (augite monzonite) and lardalite (nepheline monzogabbro to nepheline syenite) distributed in ten successive intrusive units that partially intersect each other. The Larvik Plutonic Complex also hosts occurrences of singular Fe-Ti-P-rich rocks of magmatic origin, including the Kodal deposit. These are mainly composed of titanomagnetite, ilmenite, titanaugite and apatite, the latter also featuring rare earth elements (REE) enrichment. Here, we aim to unravel the conditions that allowed the Kodal deposit to form, and determine why other mineralized bodies are not seen elsewhere in the Larvik Plutonic Complex. We compared the petrography and elemental and isotope (Sr, Nd and Hf) geochemistry of both the Kodal mineralization and the neighboring larvikite, in order to provide evidence of their petrogenetic relationship. Both lithologies share the same isotopic ratios (87Sr/86Sr(i): 0.7035–0.7043; εNd(i): +2.37 − +3.48; εHf(i): +3.39 − +9.16), which would suggest a single homogeneous source. The very low dispersion of our isotopic data also suggests that crustal contamination levels in the area were low to negligible. Normalized trace diagrams of larvikite in several localities of the Larvik Plutonic Complex also show enrichments in most incompatible elements, which becomes more prevalent towards the Kodal deposit. Elements like Sr and Eu(2+) follow an opposite trend, because of their compatibility in plagioclase. We therefore infer that the region around the Kodal deposit hosts more fractionated larvikite due to the previous crystallization of successive plagioclase cumulates. We deduce that the Kodal lobe corresponds to a more evolved intrusion, which is no part of Pluton V per se, as considered in the literature until now, but instead derives at least from a monzonitic magma at the origin of the plutons V to VIII). This also implies that the formation of Fe-Ti-P mineralization at Kodal was most likely a consequence of enrichment of the residual melt in alkaline elements and incompatible elements. These conditions support an early hypothesis of formation by silicate-liquid immiscibility, along with petrographic evidence of disequilibrium at the mineralogical scale. However, further analyses would be required to test the hypotheses of silicate-liquid immiscibility against an accumulation of the Fe-Ti-P mineralization from an evolved intermediate magma.

Mixed sources and complicated petrogenetic processes of the Himalayan granites recorded by apatite in-situ geochemistry of the Eocene Yardoi-Lhunze complex, southeast Tibet

The Cenozoic Himalayan granites are widely accepted as the anatectic products of crustal rocks. However, previous geochemical studies on their petrogenesis are mainly based on whole-rock analyses. Here we conducted a detailed petrographic, trace elemental and Sr isotopic investigations of apatite from the Middle Eocene (44–40 Ma) two-mica granites and subvolcanic porphyritic leucogranites of the Yardoi-Lhunze complex from the Tethyan Himalayan Sequence in the southeast Tibet, with the aim to constrain their magma sources and petrogenetic processes. The results show that apatites from the Quedang and Dala two-mica granites are characterized by euhedral to subhedral crystal shape, and have a wide range of initial 87Sr/86Sr ratios (0.7016–1.0088). They show significant negative Eu anomaly and varied concentrations of Sr and Y, indicating they are typical magmatic apatites. Apatites from the Qiaga porphyritic leucogranites can be divided into two groups based on Eu anomaly. Group-I apatites with positive Eu anomaly mainly display euhedral to subhedral crystal shape but with alteration rim, suggesting from the influence of hydrothermal fluids. Group-II apatites with negative Eu anomaly also have euhedral to subhedral crystal shape but they exhibit patchy or oscillatory zones, consistent with a magmatic origin. However, both group-I and II apatites have comparable initial 87Sr/86Sr ratios, 0.7198–0.9966 and 0.7174–0.9999, respectively. Previous studies based on whole-rock petrology and geochemistry have suggested that the Quedang and Dala two-mica granites and the Qiaga porphyritic leucogranites represent cumulates and fractionated melt-rich magmas, respectively. This is evidenced by systematic variations between Sr, Y, (La/Sm)N and Eu/Eu* in magmatic apatites from Quedang and Dala, consistent with the fractionation crystallization of plagioclase and monazite.Apatite has a wide range of initial 87Sr/86Sr ratios (0.7016–1.0088), far exceeding the range of whole-rock records (0.7011–0.7204). Notably, most of the analyzed apatites show lower range of initial 87Sr/86Sr ratios consistent with locally exposed amphibolites (0.7109–0.7332). The remaining small portion of apatites have initial 87Sr/86Sr ratios falling within the data range of the locally exposed metapelites (0.8517–0.9527). Therefore, the investigated granites have mixed magma sources dominated by amphibolites with subordinate metapelites. This can be inferred by apatite Sr isotopes alone, but not by whole-rock Sr isotopes alone. Our investigations highlight that in-situ geochemistry of apatite can provide a powerful means to unravel the mixed magma sources and complicated magmatic processes for granites.

El Chichón volcanic activity before and after the Mw8.2, 2017, Chiapas earthquake, México. Is El Chichón ready to erupt?

El Chichón volcano is the most active volcano in the state of Chiapas, México, and experienced its last Plinian eruption (VEI = 5) in 1982. To better assess its volcanic hazard, we studied its readiness to erupt by estimating changes in its internal stress state. These stress changes are difficult to calculate accurately, for example in the absence of focal mechanisms, but their existence can be indirectly revealed by the presence of volcano-tectonic earthquakes, for example following a large tectonic earthquake. We show that the seismic rate recorded at El Chichón volcano increased slightly after the large Mw8.2 Tehuantepec earthquake of 8 September 2017, Chiapas. However, this rate quickly returned to its background level after only 2 months, without any external volcanic manifestations, suggesting that the volcano is not ready to erupt in the near future. Previous observations of slight increases in the volcanic seismicity rate following large earthquakes have been explained by the presence of active hydrothermal systems in the vicinity of the volcano. We propose a similar explanation for El Chichón volcano which is known for its large hydrothermal system. Furthermore, the characteristics of the 2017 seismicity (spatial and magnitude distributions), and the horizontal-to-vertical spectral ratio also confirm the presence of high amounts of water near the volcano. We show that the 2017 volcano-tectonic seismicity is of hydrothermal rather than magmatic origin, in agreement with recent independent geochemical and aeromagnetic studies.

Experimental Insights Into the Petrogenesis of Plume‐Related Magmas: Tholeiite‐Harzburgite Interaction at 2–3 GPa and 1,400–1,500°C

AbstractHow eclogite/pyroxenite‐derived melts evolve through the refractory lithosphere above a plume remains poorly understood. Here we conducted layered experiments of reaction between tholeiitic melts and harzburgite at 2–3 GPa, 1,400–1,500°C, with a run duration ranging from 2 to 24 hr. The resulting residual melts exhibit lower SiO2, TiO2, Al2O3, FeO, CaO, and total alkali contents, higher Ni, MgO, and Mg#, and almost constant CaO/Al2O3 compared to the initial tholeiitic melts. The compositions of the residual melts are influenced by factors such as the melt/harzburgite mass ratio, temperature, and run duration. Decreasing the melt/rock ratio or increasing temperature and run duration leads to a greater extent of assimilation. Under disequilibrated conditions (2 hr), the residual melts have higher SiO2, FeO, and MgO, and lower CaO, Al2O3, and total alkali contents compared to those under equilibrated conditions. The results suggest that interface reactions involving olivine dissolution and orthopyroxene precipitation, and chemical diffusion occur simultaneously during the interaction process. The compositions of the residual melts are largely controlled by interface reactions within 2 hr, followed by dominant chemical diffusion between the melts and refertilized harzburgite from 2 to 24 hr. Based on the experimental results, we propose a two‐stage model for the origin of Hawaiian shield stage parental magmas. Eclogite/pyroxenite‐derived tholeiitic melts first react with harzburgite, with varying melt/rock ratios, to produce residual melts in the deep lithosphere. These residual melts subsequently mix with plume peridotite‐derived melts at shallow depths, contributing to the geochemical diversity observed in Hawaiian shield stage lavas.

New Research Results on U-Pb Zircon Isotope Age of Ta Cu Granodiorite in Dalat Zone and Geological Significance

Ta Cu granodiorites from the Dalat Zone, Southern Vietnam, have typical composition of granodiorite, coinciding with the Dinh Quan complex. The granodiorites are composed of plagioclase (45–50%), quartz (20–25%), orthoclase (15–20%), hornblende (5–7%), and biotite (5–7%). Geochemically, they are met aluminous with an average A/CNK value of 0.89- 0.96, low SiO2 (61.68-62.14) and high Na2O/K2O> 1. Petrographical and geochemical characteristics of Ta Cu granodiorites are classified as I-type granite generated from arc-related magmas. Zircons selected from these rocks are characterized by prismatic shape, oscillatory zoning, no luminescent rim, and have high ratio Th/U (0.35–1.11) that are indications of the magmatic origin. We report the first LA-ICP-MS 206Pb/238U zircon ages of 116 Ma for the Ta Cu granodiorite in the Southeastern Dalat Zone in Southern Vietnam. This age value is temporally coeval with Early Cretaceous magmatism previously reported in the Dalat Zone. Zircon ꜪHf(t) values +4.0 to+13.0, whole-rock ꜪNd(t) values -2.0 to +0.2, and average model ages (TDM2) 652 Ma to 957 Ma indicate that the Ta Cu granodiorites were derived from the remelting of Neoproterozoic mantle-derived melt with a minor input of crustal materials. Together with other Late Mesozoic magmatic complexes along the Dalat Zone, the Ta Cu granodiorites are a representative of magmatism linked to Pacific Ocean subduction beneath the Indochina block during the Early Cretaceous.

Tracing provenance of phosphorite in the Shifang phosphorite deposit: Insights from the genesis of detrital zircon

Phosphorites (P2O5 content > 18 wt%) are widespread in the world; however, high-quality phosphorite (P2O5 content > 30 wt%) is exceptionally rare. In South China, the Devonian Shifang phosphorite deposit represents not only a high-quality phosphorus ore resource but also hosts abundant rare earth elements (up to 3677.6 ppm). Despite its significance, the provenance of this unique phosphorite deposit has remained unclear. In this study, we conducted U-Pb dating, Hf isotope, and trace element concentrations analysis of detrital zircon from the phosphorite in the Shifang phosphorite deposit to well constrain the specific provenance and potential material source of the phosphorite. Cathodoluminescence (CL) images and trace elements analysis of zircons suggested that the majority of zircons have a magmatic origin. The U-Pb dating age of these zircons revealed three main age peaks at ∼ 560–520 Ma, ∼850–750 Ma and ∼ 1050–950 Ma. A comparison of the εHf values of zircons for the same age group worldwide revealed the following: (1) The 1050 ∼ 950 Ma detrital zircon in the Shifang phosphorite deposit could be derived from North India; (2) The 850–750 Ma zircons originated from Tonian granites in the western South China Block; (3) The 560–520 Ma zircons had two sources, one could be the Kuungan orogeny in the east-Gondwana, and another could be the Arabian-Nubian Shield in the northern-west-Gondwana. In addition, our new age histograms of detrital zircon U-Pb ages are well consistent with underlying strata, such as Silurian and early-middle Devonian. Combining these findings with the geological activities in the study area, we conclude that zircons in the Shifang phosphorite deposit may directly originate from the underlying strata in the study area and the Cambrian Qingping phosphorite deposit may have served as an essential phosphorus source for the Shifang phosphorite deposit.

Geochemical Study of the Osumi Granodiorite, Southwestern Japan

The Osumi Granodiorite, located on the Osumi Peninsula in southwest Japan, is an example of outer zone granites that were formed during a limited period (13–15 Ma) in response to the subduction of the Philippine Sea Plate. This event, which is linked to the separation of southwest Japan from continental Asia, resulted in unique igneous activity. The Osumi Granodiorite is the largest Miocene granite body in the region. It intrudes into the Mesozoic to Paleogene accretionary complex of the Shimanto Belt and affects contact metamorphism. Despite considerable research on the Osumi Granodiorite, limited geochemical studies, especially on trace and rare earth element (REE) analyses, have been conducted. Furthermore, there are insufficient data on the Rb–Sr isotopic system, leaving the formation process unclear. This study presents whole-rock geochemical and Rb-Sr isotopic data to investigate the petrogenesis of the Osumi Granodiorite. The results suggest a common magma origin for this pluton, as indicated by linear trends on the Harker diagrams and similar REE patterns. The presence of a relatively large Eu anomaly implies formation under a reducing environment. The AKF diagram indicates predominant contamination by pelitic rocks of the Shimanto Belt during magma formation. The Rb–Sr whole-rock isochron diagram and SrI–1000/Sr diagram suggest that the Osumi Granodiorite body was formed by heterogeneous assimilation of magma into the Shimanto Belt. Furthermore, the whole-rock isochron age is 64.3 Ma, which differs by approximately 50 My from the previously reported biotite K–Ar age (14–22 Ma). This age is considered to be a pseudo-isochron age, rather than the consolidation age. During the middle Miocene, the compressive stress field in the outer zone south of the Butsuzo Tectonic Line made it difficult for magma to rise. As a result, it reacted with the sedimentary rocks of the Shimanto Belt to various degrees. The Osumi Granodiorite underwent magma differentiation upon intrusion into the Shimanto Belt. It subsequently ascended, cooled, and interacted with pelitic rocks under stable geological conditions.

Magmatism along the Nansha Trough on the southern continental margin of the South China Sea: Recent evidence from along-strike seismic profile

The Nansha Trough (NT) is part of the southern continental margin boundary of the South China Sea (SCS). It has undergone complex tectonic superposition and evolutionary processes involving the subduction demise of the Proto-SCS and subsequent spreading of the SCS. This study provides the first systematic identification and analysis of igneous bodies and seamounts along the NT, based on a multi-channel seismic profile (NDL1) recently acquired along it. The seamounts within the trough are of magmatic origin and the carbonate build-ups observed at the summits of some seamounts exhibit a substantial thickness. Igneous bodies within the trough are consistently associated with high P-wave anomalies. Furthermore, at the eastern and western sides, there are distinct gravity-magnetic-anomaly patterns. On the eastern side, Yinqing Seamount, Nanle Hill and volcanic mounds show high gravity and strong negative magnetic anomalies. In contrast, on the western side, Jinghong Seamount, Yangshu Hill and intrusive bodies show less pronounced magnetic anomalies. This difference may be related to differences in magmatic periods. Unlike the extensive post-spreading magmatism in the SCS's northern margin and deep basin, the most widespread magmatic activity in the NT occurred at ca. 16 Ma before decreasing during the Miocene. This decrease may be closely related to subduction cessation in the Proto-SCS and the collision between the Nansha Block and Borneo. The identification and analysis of NT igneous bodies and their evolutionary processes help delineate the southern boundary of magmatism at the SCS margin. They also provide crucial information for constraining the magmatic processes of Proto-SCS subduction termination and SCS spreading evolution.

Mineralogy and Geochemistry of Jasperoid Veins in Neoproterozoic Metavolcanics: Evidence of Silicification, Pyritization and Hematization

The Wadi Ranga sulfidic jasperoids in the Southern Eastern Desert (SED) of Egypt are hosted within the Neoproterozoic Shadli metavolcanics as an important juvenile crustal section of the Arabian Nubian Shield (ANS). This study deals with remote sensing and geochemical data to understand the mechanism and source of pyritization, silicification, and hematization in the host metavolcanics and to shed light on the genesis of their jasperoids. The host rocks are mainly dacitic to rhyolitic metatuffs, which are proximal to volcanic vents. They show peraluminous calc-alkaline affinity. These felsic metatuffs also exhibit a nearly flat REE pattern with slight LREE enrichment (La/Yb = 1.19–1.25) that has a nearly negative Eu anomaly (Eu/Eu* = 0.708–0.776), while their spider patterns display enrichment in Ba, K, and Pb and depletion in Nb, Ta, P, and Ti, reflecting the role of slab-derived fluid metasomatism during their formation in the island arc setting. The ratios of La/Yb (1.19–1.25) and La/Gd (1.0–1.17) of the studied felsic metatuffs are similar to those of the primitive mantle, suggesting their generation from fractionated melts that were derived from a depleted mantle source. Their Nb and Ti negative anomalies, along with the positive anomalies at Pb, K, Rb, and Ba, are attributed to the influence of fluids/melt derived from the subducted slab. The Wadi Ranga jasperoids are mainly composed of SiO2 (89.73–90.35 wt.%) and show wide ranges of Fe2O3t (2.73–6.63 wt.%) attributed to the significant amount of pyrite (up to 10 vol.%), hematite, goethite, and magnetite. They are also rich in some base metals (Cu + Pb + Zn = 58.32–240.68 ppm), leading to sulfidic jasperoids. Pyrite crystals with a minor concentration of Ag (up to 0.32 wt.%) are partially to completely converted to secondary hematite and goethite, giving the red ochre and forming hematization. Euhedral cubic pyrite is of magmatic origin and was formed in the early stages and accumulated in jasperoid by epigenetic Si-rich magmatic-derived hydrothermal fluids; pyritization is considered a magmatic–hydrothermal stage, followed by silicification and then hematization as post-magmatic stages. The euhedral apatite crystals in jasperoid are used to estimate the saturation temperature of their crystallization from the melt at about 850 °C. The chondrite (C1)-normalized REE pattern of the jasperoids shows slightly U–shaped patterns with a slightly negative Eu anomaly (Eu/Eu* = 0.43–0.98) due to slab-derived fluid metasomatism during their origin; these jasperoids are also rich in LILEs (e.g., K, Pb, and Sr) and depleted in HFSEs (e.g., Nb and Ta), reflecting their hydrothermal origin in the island arc tectonic setting. The source of silica in the studied jasperoids is likely derived from the felsic dyke and a nearby volcanic vent, where the resultant Si-rich fluids may circulate along the NW–SE, NE–SW, and E–W major faults and shear zones in the surrounding metavolcanics to leach Fe, S, and Si to form hydrothermal jasperoid lenses and veins.

Problemy ophiolitów Zagros i ciał bazaltowych, przykłady z Regionu Kurdystanu, północny Irak

In the Iraqi Zagros, there are ten ophiolites and basaltic bodies, the famous ones are Penjween, Mawat, Bulfat and Peshashan Ophiolite complexes in addition to basaltic bodies such as Kata Rash, Avroman, Gercus, Chalki, and Hamrin basaltic bodies. The present study describes more than 12 significant problems concerning the previous assigning of the bodies as igneous rocks. These problems are observable in the field, laboratory, and in most previous works of literature that oppose the magmatic origin of these bodies. Our study explicated all aspects of each problem and clarified how the problems contradict magmatic crystallization and aid the sedimentary origin of these claimed igneous bodies. Finally, the interpretations of all the problems were collected as conjugate pieces of evidence for appraisal of the new origin of all igneous bodies in the Iraqi and Iranian Zagros belt. The outcomes consider the ophiolitic and basaltic rocks metamorphosed volcaniclastic sandstones (greywackes or mafic sandstone). These sandstones belong to fresh or metamorphosed greywackes of stratigraphic units of the Paleocene-Eocene Walash Formation (as distal facies) and Kata Rash Conglomerate (as proximal facies) which were previously considered volcanic rocks. These sediments are sourced originally from Urumeiah-Dokhtur Magmatic Arc (ADMA) and deposited inside Neo-Tethys, present Sanandaji-Sirjan Zone (SSZ), during the Jurassic-Early Cretaceous. Later, the sediments were metamorphosed and uplifted during the Paleocene and deposited inside the Iraqi Zagros belt by turbidity currents inside the Zagros Foreland basin. These ideas are shown in detail by tectonic and paleogeographic models.

Submarine volcanism in the Sicilian Channel revisited

The origin and role of volcanism in continental rifts remains poorly understood in comparison to other volcano-tectonic settings. The Sicilian Channel (central Mediterranean Sea) is largely floored by continental crust and represents an area affected by pronounced crustal extension and strike-slip tectonism. It hosts a variety of volcanic landforms closely associated with faults, which can be used to better understand the nature and distribution of rift-related volcanism. A paucity of appropriate seafloor data in the Sicilian Channel has led to uncertainties regarding the location, volume, sources and timing of submarine volcanism. To improve on this situation, we use newly acquired geophysical data (multibeam echosounder and magnetic data, sub-bottom profiles) and dredged seafloor samples to: (i) re-assess the evidence for submarine volcanism in the Sicilian Channel and define its spatial pattern, (ii) infer the relative age and style of magmatism, and (iii) relate this to the dominant tectonic structures in the region. Quaternary rift-related volcanism has been focused at Pantelleria and Linosa, at the northwest boundaries of their respective NW-SE trending grabens. Subsidiary and older volcanic sites potentially occur at the Linosa III and Pantelleria SE seamounts, collectively representing the only sites of recent volcanism that can be directly related to the main rift process. These long-lived polygenetic volcanic landforms have been shaped by magmatism that is directly correlated with extensional faulting and buried igneous bodies. Older volcanic landforms, sharing a similar scale and alignment, occur to the north at Nameless Bank and Adventure Bank. These deeply eroded volcanoes have likely been inactive since the Pliocene and are probably related to earlier stages of crustal thinning and underlying feeder structures in the northern region of the Sicilian Channel. Along a similar alignment, Pinne Bank, SE Pinne Bank and Cimotoe in the northern Sicilian Channel lack a surface volcanic signature but are associated with intrusive bodies or deeply buried volcanic rock masses. Terrible Bank, in the same region, also shows evidence of ancient, polygenetic magmatism, but was subject to significant erosion and lacks a prominent alignment. The much younger volcanism at Graham Volcanic Field and along the northern Capo-Granitola-Sciacca Fault Zone differs markedly from that observed in the other study areas. Here, the low-volume and scattered volcanic activity is driven by shallow-water mafic magma eruptions, which gave rise to small individual cones. These sites are associated with large fault structures away from the main rift axis and may have a distinct magmatic origin. Dispersed active fluid venting occurs across both ancient and young volcanic sites in the region and is directly associated with shallow magmatic bodies within tectonically-controlled basins. Our study provides the foundation for an updated tectonic and magmatic framework for the Sicilian Channel, and for future detailed chronological and geochemical assessment of the sources and evolution of magmatic processes in the region.

Late Neoproterozoic tholeiitic plutonism in far-east Avalonia (the Dirgine Batholith, Istanbul Zone): Exposed mid-crustal section of an oceanic arc

Avalonia, a large composite terrane, extends from the northeastern regions of America and Canada to southern Britain and Belgium/Netherlands, continuing on to Poland. It was accreted to Laurentia and Baltica during early Paleozoic. The late Neoproterozoic basement of the Istanbul Zone (NW Turkey), which is considered the far-east extension of Avalonia, is poorly known. This study deals with the petrology and age of the Dirgine Batholith, the largest component of the late Neoproterozoic basement. The batholith, ∼70 km long and ∼12 km wide, was emplaced into Neoproterozoic low-grade mafic to felsic metavolcanic and metapyroclastic rocks. Tonalite and quartz diorite form the bulk of the batholith. Trondhjemite, granodiorite, and anorthositic gabbro occur in minor amounts. Overall, rock types resemble low-Al tonalite-trondhjemite-granodiorite series and trondhjemites in ophiolite sequences. The batholith formed over a narrow time interval (562–574 Ma, late Ediacaran), as inferred by U–Pb zircon geochronology. In-situ Lu-Hf analyses of igneous zircons reveal a limited range of significantly positive initial εHf values (9.47 ± 1.46, 2σ) and young Hf depleted mantle model ages (0.78 ± 0.06 Ga), indicating the relatively juvenile character of original magmas. All rock types have typical subduction-related trace-element signatures such as depletion in high-field-strength elements and enrichment in several fluid-mobile elements as well as nearly flat chondrite-normalized REE patterns. Geochemical characteristics indicate that crustal assimilation was insignificant, and the batholith formed by fractional crystallization of mantle-derived low-K tholeiitic magmas involving mainly clinopyroxene, hornblende and ± plagioclase. The Dirgine Batholith and metamorphic country rocks probably represent the mid-crustal section of a late Neoproterozoic oceanic arc. The interpretation of an oceanic rather than continental arc is based on the significantly lower concentrations of incompatible elements relative to continental arcs, nearly flat REE patterns of the rock types, and the juvenile nature of the primary magmas. These data, in concert with those in the literature, reveal that late Neoproterozoic oceanic arcs constitute an important component of far-east Avalonian terranes.