Intruded Research Articles

Isotopic U-Pb age of zircon (LA-ICP-MS method) from igneous rocks of the Chorukh-Dairon W-Mo(-Cu-Au) deposit (Tajikistan): first evidences for post-collisional ore formation in the Kurama segment of the Middle Tien Shan

The paper presents isotopic U–Pb zircon data (LA–ICP–MS method) for the main types of high-potassic intrusive rocks of the Chorukh-Dairon W–Mo(–Cu–Au) skarn deposit situated in the Kurama segment of the Middle Tien Shan near the largest porphyry Cu–Mo–Au deposits of the Almalyk mineralized cluster. Together with the other Au, W, Mo and Cu deposits, all these deposits are parts of the extended Late Paleozoic metallogenic belt of Tien Shan. The concordant isotopic U–Pb zircon data obtained for the rocks of successive intrusion phases in the Chorukh-Dairon pluton span from about 298 Ma to 290 Ma. This interval included crystallization of monzodiorite (295.1±3.3 Ma), quartz syenite (294.7±2.3 Ma), quartz monzonite (294.1±2.1 Ma), and monzogranite (293.0±3.0 Ma). These dates correspond to the pluton emplacement at the Late Carboniferous-Early Permian boundary and highlight its younger age compared to the productive high-potassic intrusions of the porphyry Cu–Mo–Au deposits in the Almalyk mineralized cluster, the latter assigned to the Late Carboniferous (about 337–313 Ma and partially to 308–297 Ma). By contrast to the latter, which were intruded in the subduction-related environment, the emplacement of the high-potassic rock of the Chorukh-Dairon pluton occurred in the transitional subduction-related to post-collisional environment or even under an actual post-collisional regime. This allows distinguishing two pulses of ore-bearing Carboniferous-Permian high-potassic calc-alkaline to shoshonitic series magmatism in the Middle Tien Shan. Consistently, there is a metallogenic evolution in the region that was expressed in the transition from porphyry Cu–Mo–Au deposits associated with subduction-related potassic magmatism, and likely evolving toward epithermal Au–Ag deposits, to essentially tungsten (W–Mo–Cu–Au) deposits associated with younger potassic magmatism occurring rather in the post-collisional environment.

Age and origin of Bereinsky complex Granitoids of Kamensky Terrane of the Monghol-Okhotsk orogenic belt: results of U-Pb (ID tims) geochronological and Sm-Nd isotope-geochemical research

Dating of magmatic rocks from paleo-island arcs of orogenic belts helps to define the precise timing of subduction processes that took place during the formation of the orogen. Within the central (East Trans-Baikal) part of the Mongol-Okhotsk orogenic belt, the Kamensk island-arc terrane is an example of such paleo-island-arc complex. Its intrusive part is included into the Bereinsky complex, represented by a gabbro-diorite-tonalite-plagiogranite series of rocks demonstrating subduction geochemical characteristics. The dating of zircons from acidic rocks of this complex by the U–Pb classical method showed that they were produced in a narrow time interval – 203±1–205±1 Ma, which corresponds to Norian/Rhaetian boundary of the Late Triassic. Taking into account the previously obtained age of the diorites (254±5 Ma), the timing of formation of the entire series of intrusive rocks is about 50 Ma, thus indicating in the Late Permian – Late Triassic the subduction along the northern (in modern coordinates) margin of the Mongol-Okhotsk Paleocean beneath the Siberian paleocontinent. Diorites of the first phase have positive values ɛND(254MA) = 3.2–3.6 (TNd(DM) = 879–994 Ma), and plagiogranites – ɛND(205MA) = 2.3–3.5 (TNd(DM) = 859–1028 Ma), which points to the connection of these rocks with the substance of the depleted mantle source and is consistent with the Sm-Nd isotope characteristics of the juvenile crust of the Central Asian orogenic belt. This study was supported by Russian Science Foundation, grant no. 22-27-00775. The resources of the Shared Use Center for Isotope-Geochemical Research (Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk) were used in this work.

Petrology of gabbroic rocks from the lower crust of a back-arc basin: an example from the ophiolitic Liuyuan Complex, northwestern China

Abstract The 290-282 Ma ophiolitic Liuyuan Complex in northwestern China preserves a section of oceanic crust formed in a back-arc basin during the final stages of the evolution of the Central Asian Orogenic Belt. We present results of detailed field work, petrography, whole rock, and mineral chemistry of the plutonic rocks of the Liuyuan Complex. These include: troctolite, melatroctolite, olivine gabbro, podiform olivine gabbro, podiform hornblende gabbro and intrusive hornblende gabbro. Major element data, petrography, low incompatible trace element concentrations, and positive Eu-Sr anomalies suggest that basal troctolite and melatroctolite are accumulations of olivine + plagioclase primocrysts, with varying proportions of interstitial, ophitic, and poikilitic clinopyroxene forming from trapped melt. Olivine gabbro dominates the plutonic crust between the troctolites and sheeted dykes. Troctolites and olivine gabbros have weak paleo-horizontal foliations and show systematic upward cryptic mineral-chemical trends of decreasing clinopyroxene Mg#, plagioclase An, and olivine Fo and NiO contents. Trace element modelling suggests low trapped melt fractions in the cumulates (5-15%) and implies clinopyroxene was a minor cumulus phase in the olivine gabbros. The cryptic mineral-chemical evolution and textures imply most troctolites and olivine gabbros formed as sequential accumulations from an evolving melt. Melatroctolite layers (~5m thick) in troctolite may represent fossil replenishment events. Immediately below the sheeted dyke unit, there are meter-scale pods of cumulate olivine gabbro containing abundant hornblende (25-45%), as well as decimeter- to meter-scale pods of quasi-liquid olivine gabbro with compositions similar to overlying dykes and lavas. Isolated intra-plutonic dykes of hornblende gabbro also have basaltic compositions. In the podiform hornblende gabbro, high-temperature magnesio-hornblende likely formed as a reaction product between clinopyroxene and a hydrous pore melt. Trace element inversion models indicate that these diverse plutonic rock units formed from a tholeiitic parental melt cogenetic with the overlying basalts. The Liuyuan ophiolitic complex represents a coherent slice of oceanic crust formed in a back-arc basin.

Late Paleozoic stages of ore formation in the Middle Tien Shan: isotopic U-Pb zircon dating (LA-ICP-MS method) of intrusive rocks from the Sonkul and Kokturpak plutons (eastern Kyrgyzstan)

Late Paleozoic stages of ore formation in the Middle Tien Shan: isotopic U-Pb zircon dating (LA-ICP-MS method) of intrusive rocks from the Sonkul and Kokturpak plutons (eastern Kyrgyzstan)

Advances in Magmatic Ni–Cu–(PGE) Sulphide Deposits and Their Constraints on Neoproterozoic Tectonic Settings of China

ABSTRACTMagmatic Ni–Cu–(PGE) sulphide deposits are the primary global sources of nickel, copper and platinum group elements (PGE). The study of these deposits is critical for mineral exploration and holds important economic implications. This paper reviews recent advances in understanding magmatic Ni–Cu–(PGE) sulphide deposits and their related magmatism. Findings reveal that these deposits have an uneven global distribution and a wide range of classifications. The Proterozoic era represents the main period of mineralisation, and the mineralisation setting is closely related to continental rifts, mantle plumes and collision orogenic belts. An ongoing debate exists between the ‘magma conduit’ and ‘deep‐multiple magma chamber segregation’ models, which differ in mineralisation location, magma intrusion mechanisms and the role of external sulphur addition. The primary mechanisms of sulphide segregation include rapid cooling, crystal differentiation and crustal contamination. Furthermore, this paper examines the spatial–temporal distribution and mineralisation dynamic settings of Neoproterozoic magmatic Ni–Cu–(PGE) sulphide deposits in China and their relationship to the convergence and breakup of the Rodinia supercontinent. These Neoproterozoic deposits are located along the margins of the Yangtze, North China and Tarim blocks. They formed in five different stages, 1000–960, 900–850, 830–800, 760–740 and 650–620 Ma, corresponding to the following tectonic settings, respectively: (1) a back‐arc extensional setting before the convergence of the Yangtze and Cathaysia blocks; (2) a post‐orogenic extensional setting following the convergence between the Yangtze and North China blocks; (3) a rift setting related to the first Neoproterozoic mantle plume event (830–795 Ma) within the Yangtze Block or North China Block; (4) a rift setting related to the second Neoproterozoic mantle plume event (780–745 Ma) within the Tarim Block and (5) an intraplate rift setting within the Yangtze Block. The evolving mineralisation dynamic settings of these deposits indicate that their mineralisation is directly related to large‐scale mafic–ultramafic magmatism during the Neoproterozoic and the convergence and breakup of the Rodinia supercontinent.

Enrichment and sources of major and trace elements in the Qinghai-Tibetan Plateau: a case study of the Golog Prefecture.

The Qinghai-Tibet Plateau (QTP) is a vital region for global atmospheric circulation and biodiversity. This study aims to evaluate the contents and enrichment status of 25 soil elements, namely Al, As, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, S, Sc, Si, Sn, Sr, Fe, Ti, V, and Zn, in the plateau region. Specifically, our analysis revealed that As exhibited significant enrichment near fault zones and intrusive rocks, while Ca was mainly enriched due to the dissolution of carbonate rocks. Additionally, Principal Component Analysis and Multiple Linear Regression (PCA-MLR) were used to examine the origins of these elements. The potential ecological risk posed by Cd and Pb was evaluated and found to be negligible. Soil element enrichment in the QTP was mainly influenced by lithology, and high spatial variability was observed in As, Ca, and S, which were mainly affected by geological processes and grazing activities. Six sources of elements in the plateau region were identified, namely geological mixed sources, grazing activities, alkaline granite, ultrabasic rocks, fault zones and intrusive rocks, as well as atmospheric deposition. Among these, geological mixed sources and grazing activities were determined to be the priority contributors. Although grazing activities on the QTP as well as atmospheric deposition at long distances caused the enrichment of elements in the area, the ecological risk was negligible. The outcomes of this work can be used as a theoretical basis for prospective investigation on the stability of high-altitude ecosystems, species diversity, and geochemical background.

The timing of the Middle Triassic magmatism in the Dolomites area (Southern Alps, Italy): U[sbnd]Pb geochronology of zircon and titanite hosted in plutonic rocks and phonolite dykes

The Middle Triassic magmatic event in the Southern Alps (Italy) is characterised by the emplacement and eruption of multiple magma batches with different geochemical affinities in a short time span. In this work, we present the first geochemical and geochronological data on highly differentiated alkaline dykes (phonolites) exposed in and near the Middle Triassic Predazzo magmatic complex (Southern Alps, Italy) and a first complete geochronological survey of the Predazzo pluton. The phonolites, cutting the Middle Triassic volcanic sequences, are sodalite- and aegirine-bearing and have titanite, apatite and magnetite as accessory phases. Their trace element concentration reflects a geochemical signature similar to the orogenic-like signature typical of the Middle Triassic magmatic rocks of the Predazzo complex. New in situ UPb dating on titanite from the phonolite dykes and UPb dating on zircon separates from all the magmatic units of the Predazzo pluton show that the phonolite dykes were emplaced between 233.8 ± 3.1 Ma and 238.1 ± 4.5 Ma, i.e., overlapping to and postdating the emplacement and crystallisation of plutonic rocks, which yield ages ranging from 237.97 ± 0.15 Ma to 238.31 ± 0.13 Ma. The ages obtained for the diverse suites of the pluton are in good agreement with previous dating and show that silica-saturated to -undersaturated rocks were placed within the same context in a short time span. Thermometry and hygrometry on titanite, clinopyroxene and K-feldspar revealed that phonolites represent volatile- and REE-rich (H2O = 8 ± 0.6 wt%) highly differentiated alkaline melts intruding at relatively low T (752–868 °C), which easily caused the spatially related CuW mineralisation. Comparisons with sub-volcanic rocks exposed in the Central (Edolo) and Western Alps (Finero mafic complex) indicate that the phonolites still preserve the orogenic signature of the Middle Triassic event in the Southalpine, that characterise all magmas emplaced before the opening of the Alpine Tethys in the Late Triassic. These new geochronological constraints on the Predazzo pluton and phonolite dykes enable us to outline the complete sequence of magmatic events associated with the emplacement of the Predazzo volcano-plutonic complex during Mid-Triassic and to speculate about the genesis of CuW mineralisation.

Spreading and leveling of finite thin films with elastic interfaces: An eigenfunction expansion approach

Abstract The flow of a thin viscous liquid layer under an elastic film arises in natural processes, such as magmatic intrusions between rock strata, and industrial applications, such as coating surfaces with cured polymeric films. We study the linear dynamics of small perturbations to the equilibrium state of the film in a closed trough (finite film). Specifically, we are interested in the spreading (early-time) and leveling (late-time) dynamics as the film adjusts to equilibrium, starting from different initial perturbations. We consider both smooth and non-smooth spatially symmetric and localized initial conditions (perturbations). We find the exact series solutions for the film height, using the sixth-order complete orthonormal eigenfunctions associated with the posed initial-boundary-value problem derived in our previous work [Papanicolaou N C and Christov I C 2023 J. Phys.: Conf. Ser. 2675 012016]. We show that the evolution of the perturbations begins with the spreading of the localized perturbations, followed by their mutual interaction as they spread, and finally, interactions with the confining lateral boundaries of the domain as the perturbations level. In particular, we highlight how the leading eigenvalues of the problem determine the scalings of certain figures of merit with time.

Final subduction-closure process of the Paleo-Asian Ocean in the middle segments of the southern Central Asian Orogenic Belt: Constraints from Permian volcanic rocks and late Triassic mafic dike swarms

The final subduction-closure process of the Paleo-Asian Ocean (PAO) in the middle segments of the southern Central Asian Orogenic Belt (CAOB) is widely debated. Linear arc-related pyroclastic sedimentary rocks and subsequent mafic-alkaline intrusive rocks parallel to the orogenic belt provide valuable constraints on ocean closure. Linearly distributed volcanic samples from the northern margin of the Alxa Block have zircon UPb ages ranging from 272 to 271 Ma, displaying arc geochemical signatures and large ranges of variation (−14.4 to +6.4) of zircon Hf isotopic composition. The Honggueryulin mafic dikes in the Nuoergong–Langshan Belt (NLB) with zircon and apatite UPb dating of 232–231 Ma show a clear geochemical imprint of subduction components with enrichment of light rare earth elements and large-ion lithophile elements (e.g., K, Rb, and Ba) and depletion of high-field-strength elements (e.g., Nb, Ta). The whole-rock major and trace elements and Sr–Nd–Hf isotopic compositions suggest that the Late Triassic mafic dikes mainly originated from a lithospheric mantle that had been metasomatized by subduction-related fluids. Coupled with published data, our geochronological and geochemical data support an east–west-trending Late Triassic alkaline–mafic intrusive rock belt distributed along the northern margin of the Alxa Block–North China Craton, which was formed in a post-orogenic intraplate extensional setting. These pyroclastic sediments and mafic dikes in the NLB document the tectonic transition from the Permian subduction to the Late Triassic post-orogenic extension. Therefore, the final closure of the PAO in the middle segments of the southern CAOB is constrained to between the Early and Middle Triassic.

Petrogenesis of Permian Granodiorite and Diorite in Eastern Jilin Province and Its Constraints on the Late-Stage Evolution of the Paleo-Asian Ocean

The Solonker-Xar Moron-Changchun-Yanji Suture Zone is the result of the final closure of the Paleo-Asian Ocean (PAO). However, the closure time of the PAO in Northeast China remains controversial. The Hunchun area is located in the easternmost part of the Solonker-Xar Moron-Changchun-Yanji Suture Zone. Tectonism and magmatism in the Hunchun area can provide important information for understanding the late-stage evolution of the PAO. In this study, our zircon U-Pb ages show that the granodiorites and diorites in the Hunchun were formed at 282.3–251.4 Ma. This geochronological evidence suggests prolonged Permian magmatism in the Hunchun area. Whole-rock geochemistry, zircon trace, and Lu-Hf isotope data show that all the intrusive rocks are mainly calc-alkaline series to arc tholeiite series. Granodiorites are I-type granites formed by the partial melting of juvenile lower crust derived from the mantle. Diorites show similar characteristics to the sanukitic high-Mg diorite and are formed by the partial melting of the depleted mantle metasomatized by subduction sediments and/or slab-derived fluids. These results indicate that the Permian diorites and granodiorites in the Hunchun area formed in an active continental margin setting related to the subduction of the PAO plate. Significantly, sudden changes in the whole-rock Sr/Y and (La/Yb)N ratios and zircon εHf(t) values are observed in the Late Permian-Early Triassic igneous rocks in the eastern Central Asian Orogenic Belt (CAOB). This indicates that the final closure of the PAO in Northeast China likely occurred in the Late Permian-Early Triassic.

Petrogenesis of Diorite-Porphyrite in the Southern Xintai Area of the Mid-Western Shandong Peninsula, North China Craton: Insights from Geochronology, Mineralogy, Geochemistry, and Sr-Nd-Hf Isotopes

The Early Cretaceous intermediate intrusive rocks have important significance in understanding the crust–mantle interaction, iron mineralization, and tectonic evolution in the western Shandong Peninsula. In this study, we present new zircon U–Pb ages, and Hf isotope, whole-rock geochemistry, Sr–Nd isotopes, and the mineral chemistry of the diorite-porphyrite in the southern Xintai area, mid-western Shandong Peninsula. The diorite-porphyrite formed at ca. 125 Ma. They have intermediate SiO2 (59.57–62.29 wt.%) and MgO (2.78–3.58 wt.%) contents, high Mg# values (53–56), high Sr (589–939 ppm) and low Y (9.2–10.8 ppm) contents, and high Sr/Y ratios (54–94), showing adakitic affinity. The diorite-porphyrite exhibits lower zircon εHf(t) values (−30.1 to 7.5) and whole-rock εNd(t) values (−3.5 to −6.0), with (87Sr/86Sr)i ratios of 0.70514–0.70567. We suggest that the diorite-porphyrite was derived from the partial melting of the local delamination of lower continental crust and then by the interaction with the enriched lithospheric mantle. The genesis of diorite-porphyrite may be related to the rollback process of the Paleo-Pacific slab in the Early Cretaceous. This geodynamic process induced the melting of the enriched lithospheric mantle, subducted oceanic crust, and local delamination of lower continental crust, which produced different types of adakitic magmatism in the western Shandong Peninsula.

Volcanic-intrusive connections and crystal-melt segregation in the Dulan tilted crustal section: Insights from accessory mineral evolution

The volcanic-intrusive connection is critical for understanding the formation of transcrustal magma systems and the mechanisms driving magma eruption. Yet, the genetic links between abyssal intrusive rocks and acidic volcanic rocks remain poorly understood. Here, we present new data from the Dulan volcanic-intrusive complex, a tilted section of the East Kunlun orogenic belt, integrating zircon UPb dating, trace elements, apatite and zircon Hf isotope geochemistry, and whole-rock geochemistry to investigate volcanic-intrusive connections and track crystal-melt segregation processes. The Dulan complex comprises rhyolite, granite porphyry, and granodiorite, all showing consistent zircon UPb ages, rare earth element (REE) patterns, and εHf(t) values, suggesting a shared magma source. Glomerocrysts of plagioclase, alkali feldspar, and hornblende, along with antecrystic zircon and apatite, imply a cumulate affinity in granodiorite and granite porphyry. Compositional variations in whole-rock and accessory minerals indicate that plagioclase, apatite, and zircon fractionation significantly influenced magma evolution. We propose a two-stage crystal segregation process in a ∼ 2 Myr-long magma reservoir system. In the early stage, at ∼33 km depth, aqueous fluid influx initiated crystal-melt segregation, forming the Dulan granodiorite from residual mush. In the later stage, mafic melt and fluid injections caused crystal-melt segregation in a shallower reservoir at ∼12 km depth, with high-silica magma producing rhyolite, while residual mush consolidated into granite porphyry. Our findings suggest that volcanic-intrusive connections are more complex than mere compositional equivalence or complementarity, requiring multidimensional analysis through accessory minerals and whole-rock geochemistry.

Generation of Cu-Au skarn mineralization by mafic magma recharge: Insights from the Bozymchak deposit in the Chatkal-Kurama region, Kyrgyzstan, West Tianshan

Large numbers of igneous intrusions are emplaced in the magmatic arcs above subduction zones, but only a small fraction of them are mineralized with Cu ± Au ± Mo. Despite significant advances in recognizing the importance of magma source, volatile content, and redox condition in controlling mineralization, the magmatic processes required to form a mineral deposit are still poorly understood. Here, we demonstrate that mafic recharge to the magma chamber is critical for Cu-Au mineralization, as exemplified by the Bozymchak Cu-Au skarn deposit in the Chatkal-Kurama arc of Kyrgyzstan, West Tianshan. The Bozymchak intrusion associated with the mineralization comprises monzonite porphyry and granodiorite porphyry. A sensitive high-resolution ion microprobe zircon U-Pb age of 305 ± 2 Ma was obtained for the monzonite porphyry, which is consistent with the U-Pb age of zircon from the granodiorite porphyry (304 Ma) and an Re-Os age for the molybdenite (305 Ma). These ages indicate that both the monzonite porphyry and granodiorite porphyry were coeval with mineralization. The monzonite porphyry exhibits high-K calc-alkaline (K2O = 3.36−3.50 wt%), metaluminous and magnesian-rich characteristics, enrichment in large ion lithophile elements (LILEs; e.g., Cs, Th, Ba, K, and Pb), and negative anomalies in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). These geochemical signatures, combined with the Sr-Nd-Hf isotopic signatures [ISr(avg) = 0.7059, εNd(t) = −3.5 to −2.8, εHf(t) = −3.8 to +1.4], suggest that the magma was the product of partial melting of a metasomatized mantle wedge and was subjected to subsequent assimilation and fractional crystallization (AFC). The development of disequilibrium textures in both the monzonite porphyry and the granodiorite porphyry, such as acicular apatite, reverse zoning of plagioclase, and coexisting high-Al and low-Al amphiboles, indicates that the magma evolved in an open crustal magma chamber with mafic magma recharge. The magmas were moderately oxidized (∼ΔFMQ +1.0; FMQ is the fayalite-magnetite-quartz oxygen buffer) and water-rich, with 5.9 wt% and 6.5 wt% H2O in the granodiorite porphyry and monzonite porphyry, respectively. The repeated influx of hot mafic magma batches prolonged the existence of the magma chamber and promoted the maturation of the arc magma. In addition to introducing more Cu and Au, the replenishment of mafic magma in the chamber also introduced additional H2O and Cl, as shown by the presence of high-Al amphiboles and the elevated oxygen fugacity, which further promoted Cu-Au mineralization.

Analysis of Limestone Characteristics on the South Coast of Gorontalo Based on Specific Gravity and Water Absorption Tests

The southern coast of Gorontalo has complex geological conditions. This is indicated by the strong tectonic influence with the uplift of the Quaternary limestone at high elevations. The distribution of this limestone is very unique because it is located between the dominance of volcanic and plutonic rocks that form the northern arm of Sulawesi. The purpose of this study was to focus on the characteristics of limestone on the south coast of Gorontalo based on specific gravity and water absorption tests. The research methods used to achieve these objectives consist of field geological surveys and laboratory analysis of the specific gravity and water absorption tests of coarse aggregate. The field geological survey consisted of taking limestone samples for laboratory analysis and petrological analysis. The results showed that the limestone on the southern coast of Gorontalo is dominated by the coralline floatstone facies. Characteristics of the coralline floatstone facies based on laboratory analysis showed an average specific gravity of 1.74 and an apparent specific gravity of 2.04. While the average percentage of limestone water absorption is 8.41%.

Emplacement history of the Central Anatolian Ophiolites: insights from the Felahiye Ophiolite in Central Türkiye

ABSTRACT The Central Anatolian Crystalline Complex (CACC) is represented by Late Cretaceous Barrovian-type metamorphism, ophiolite obduction and numerous intrusive granitoid rocks. The Felahiye Ophiolite, which is a part of the Central Anatolian Ophiolites (CAOs), represents a significant remnant of the Late Cretaceous oceanic lithosphere in the eastern CACC. However, the exact origin and polarity of the subduction zones involved in the formation of these ophiolites and mélanges remain unclear. This study presents new field, geochemical, and geochronological data from the Felahiye Ophiolite to address these critical questions. The integration of geochemical, petrographic, and field data supports the interpretation that the Felahiye Ophiolite is a remnant of the Late Cretaceous supra-subduction type oceanic crust. U-Pb zircon crystallization age of 92.0 ± 1.1 Ma was obtained from a cumulate gabbro of the Felahiye Ophiolite. Hafnium isotope compositions of these zircons (εHf(t) = +8 to + 12) suggest a depleted mantle source. 40Ar/39Ar dating of amphibole from a gabbro provided a cooling age of 69.4 ± 3.2 Ma, suggesting thermal influence of granitoid intrusions following ophiolite emplacement. We propose a new model for the origin of the CAOs, emphasizing eastward subduction of an ocean basin located both east and west of the CACC. This is consistent with the CAOs forming on N-S trending ridges within an eastward-subducting ocean, leading to westward obduction onto the CACC, N-S trending magmatic arc development in the CACC, and distinct geological histories from those of the Tauride Belt Ophiolites.

Discovery and Geological Significance of Neoproterozoic Bimodal Intrusive Rocks in the Dabie Orogen, China

The Mingshan reservoir of the Dabie Orogen has a number of Neoproterozoic bimodal intrusive rocks. We focused on the zircon U-Pb chronology, Hf isotopes, and bulk-rock geochemistry of these rocks. The results showed the following: (1) The bimodal intrusive rocks mainly consist of monzogranitic gneiss and plagioamphibolite, with zircon U-Pb ages of 785.0 ± 7.1 Ma and 787.3 ± 6.1 Ma, respectively. These ages indicate that they were formed in the late Qingbaikou epoch of the Neoproterozoic era. (2) The monzogranitic gneiss was dominated by peraluminous features and displayed a strong right deviation of REE (rare-earth element) patterns and a negative δEu anomaly. It is enriched in the LILEs (large-ion lithophile elements) Rb, Ba, and K, but slightly depleted in Nb, Sr, P, and Ti, with low 10,000* Ga/Al values, indicating that it is similar to Al-type granite. The plagioamphibolite belongs to the metaluminous, peraluminous series. It has a Mg# (molar ratio of Mg to Mg + Fe) of 36.1~55.9 and is enriched in the LILEs Rb, Ba, and K, with a slight positive anomaly of Ba, and is depleted in Nb and Sr. (3) The monzogranite shows negative zircon εHf(t) values ranging from −13.4 to −7.2 and a Paleoproterozoic TDM2(Hf) (two-stage depleted mantle model age) of 1969–2298 Ma. The zircon εHf(t) values and TDM2(Hf) of the plagioamphibolite were concentrated around 2.9–5.7 and 1257–1410 Ma, respectively. The geochemistry and Hf isotopes show that the monzogranitic gneiss and plagioamphibolite have distinct magmatic sources. The plagioamphibolite formed from mantle and partial continental crustal materials. The monzogranitic gneiss, on the other hand, was formed as a result of the partial melting of the shallow ancient felsic crust caused by mafic rock heating or upwelling. Taking into account regional correlation, the middle Neoproterozoic bimodal intrusive rocks originated in the structural framework of an extensional setting.

Apatite as an indicator of tectono-magmatic evolution of silica-undersaturated to silica-oversaturated rocks on the NW Indian Plate margin

Permo-Carboniferous intrusive rocks situated on the NW boundary of the Indian Plate between the Main Mantle Thrust (MMT) and Main Boundary Thrust (MBT) have tremendous potential for enhancing our knowledge of regional tectono-magmatic activity in Pakistan, yet these units have received only limited investigation to date. Here, we examine the petrology, apatite geochemistry and Sr-Nd isotopes, and geochronology of the silica-undersaturated (sodalite syenite and nepheline syenite), silica-saturated (monzonite and quartz syenite), and silica-oversaturated (granite and quartz monzonite) intrusive suites of the Ambela Granitic Complex (AGC) in northern Pakistan. Cathodoluminescent (CL) images of apatite in the three suites show mostly oscillatory zonation and a homogenous texture. The apatite chemistry of three intrusives is characterized by high fluorine (F), rare earth element (REE), yttrium (Y), and thorium (Th) contents, and low levels of chlorine (Cl), iron oxide (FeO) and magnesium oxide (MgO), suggesting a magmatic origin. The three suites exhibit variation in Sr-Nd isotopes, i.e., 87Sr/Sr86i = 0.7035 to 0.7057 and εNd(t) = +0.3 to +6.0 for the silica-undersaturated group, 87Sr/Sr86i = 0.7044 to 0.7205 and εNd(t) = +1.8 to +3.8 for the silica-saturated group, and 87Sr/Sr86i = 0.7075 to 0.7186 and εNd(t) = −2.5 to +1.2 for the silica-oversaturated group. Garnet stability field indicators in the nepheline syenite imply a deeply sourced magma, with Sr-Nd isotopic, and trace-element compositions of the apatite indicating formation in the subcontinental lithospheric mantle. In contrast, the silica-oversaturated melts formed during magma ascent through crustal interactions at a range of depths, with their apatites showing affinity with A-type granites. Apatite grains from the three magmatic groups show distinctive Sr, Eu and Y patterns, reflecting less fractionation of the silica-undersaturated and -saturated suites than of the silica-oversaturated suite. Furthermore, apatites of the former suites have higher Eu/Eu* and SO3 and lower Ce/Ce* than those of the latter suite, suggesting development under more oxidizing magmatic conditions. TDM2 ages demonstrate parent material of Mesoproterozoic to Neoproterozoic age, whereas LA-ICP-MS U-Pb dating of magmatic apatite indicates cooling of all suites concurrently at ∼322–262 Ma. The latter ages document significant magmatic activity in the study region during the Late Carboniferous to Middle Permian, probably in connection with rifting of the northern margin of the supercontinent Gondwana, leading to opening of the Neo-Tethys Ocean.

Methane sealed due to the formation of gas hydrate system in the South China Sea

Although the release of methane into oceans and potentially the atmosphere could accelerate climate change, detailed investigations on the gas source from deep-buried strata and its migration through the gas hydrate stability zone (GHSZ) to the seafloor are limited. These studies are often hindered by the presence of diffracted waves and inaccuracies in seismic velocity models, leading to poor seismic imaging that hampers the understanding of gas sources, migration pathways, and gas hydrate accumulation. In the study, we utilize the technique of common scatter point (CSP) gathers to build an accurate velocity model and obtain high-quality images for a complex gas-hydrate and natural-gas petroleum system. The CSP processing enables the accurate migration of reflected and diffracted waves, resulting in improvements in signal-to-noise ratio and lateral resolution. The improved seismic images offer clearer visualization of various petroleum elements. Specifically, we can identify the top of the hydrate zone and base of the free gas zone within a shallow-buried hydrate system, fault geometries within the free gas zone, a middle-buried natural gas reservoir, gas chimneys as migration pathways, and the deep-buried source rock strata beneath the intrusive volcanic rocks. As a result, we reveal a joint prospect of natural-gas reservoir and gas-hydrate system in the deep-water region of the South China Sea. Our results suggest that methane in the natural gas reservoir has migrated upwardly into the hydrate system, and it is unlikely to leak into the water column.

The Rhyolite Factory: Insights from rhyolite-MELTS geobarometry of plutonic rocks and associated volcanics

The Rhyolite Factory: Insights from rhyolite-MELTS geobarometry of plutonic rocks and associated volcanics

Mercury efficiently volatilized but not completely removed from sediments around igneous intrusions

The impact of large igneous province (LIP) volatile emissions from magmatic and thermogenic sources has been widely studied using sedimentary mercury (Hg). Igneous sill emplacement in sedimentary basins was a key component of several LIPs, generating environmentally significant amounts of thermogenic gases (e.g., CH4, CO2, Hg) and fluids by heating sedimentary rocks. Understanding these processes is key to realizing the promise of Hg in sedimentary archives to understand LIP impacts and track LIP carbon outputs. Published data show sedimentary rocks in contact aureoles of such LIP-related intrusions retain some Hg despite exposure temperatures above the stability limit of sedimentary Hg phases (>300 °C). We examine this unexpected Hg retention using Hg thermal desorption profiles (TDPs). The TDPs reveal a remarkable pattern in Hg speciation related to intrusions: with increasing aureole temperature, Hg release is progressively dominated by a low-temperature phase that could have formed only during or after cooling of the intrusion. We calculate a temperature-dependent Hg volatilization efficiency and show that 70%−100% of Hg was mobilized above 350 °C. Despite the efficient volatilization, only ∼50% of the volatilized Hg was removed from the studied aureole. Mercury recapture in and around the thermal aureole likely extends into the associated hydrothermal vent systems, reduces the Hg:C ratios of emitted thermogenic gases, and may lead to underestimation of Hg-based LIP thermogenic CO2 and CH4 emissions estimates and their environmental impact.