Search Results (165)

Serpentinites and associated chromitites of the Neoproterozoic Bou Azzer ophiolite (Central Anti-Atlas, Morocco) provide key constraints on mantle depletion, melt–rock interaction, and the tectono-metamorphic evolution of a supra-subduction zone (SSZ) system. This study integrates field observations, petrography, Raman spectroscopy, and whole-rock/mineral chemistry to decipher the history of this highly dismembered ultramafic suite. The mantle sequence is dominated by antigorite-bearing serpentinites derived primarily from refractory harzburgitic and dunitic protoliths. Whole-rock geochemistry and highly depleted chromite compositions (Cr# = 0.50–0.68; Mg# = 0.43–0.77; TiO₂ ≤ 0.18 wt.%) demonstrate that these peridotites represent refractory residues formed after high degrees of partial melting (~15–25%). The data delineate a clear evolutionary trend from abyssal to fore-arc and back-arc environments, where infiltrating boninitic melts drove localized podiform chromitite formation through intense melt–rock interaction. Crucially, thermodynamic and mineral–chemical constraints challenge previous models of simple greenschist-facies obduction. Equilibration temperatures exceeding 600 °C and chromite stability within the lower amphibolite to near-granulite facies indicate that the oceanic lithosphere underwent deep subduction prior to its exhumation. This high-temperature, high-pressure metamorphism was followed by multistage retrogressive serpentinization and intense CO₂-rich metasomatism (talc-magnesite alteration) during Pan-African transpressional tectonics. Ultimately, the Bou Azzer ophiolite represents a mature SSZ mantle wedge, recording a complete geodynamic cycle from deep subduction-zone metamorphism to final tectonic emplacement along the northern margin of the West African Craton. Full article

Seafloor hydrothermal systems at mid-ocean ridges are focal points for heat and matter exchange between the seawater and lithosphere. While seafloor seismographs (OBS) and pressure recorders (BPR) are standard for regional monitoring, achieving high-precision, vertical sub-surface data in complex hydrothermal terrains remains a significant technical objective. This study presents a novel in situ penetration probe designed for multi-parameter monitoring of marine hydrothermal vent areas. A key innovation of this work is its operational versatility and engineering efficiency: the probe is specifically designed for post-drilling deployment in boreholes, effectively utilizing existing coring sites to achieve direct coupling with the deep-seated crust, or for targeted placement via Remotely Operated Vehicles (ROVs). The device integrates a titanium-alloy conical tip and cylindrical chamber, housing tri-axial accelerometers and dual temperature-pressure sensors. Numerical simulations using the SST k-ω turbulence model and finite element analysis optimized the cone aperture and assessed fluid–structure stability under deep-sea conditions. Laboratory vibration tests and shallow-water sea trials validated the probe’s basic dynamic response, electromechanical integrity, and capability to acquire coupled environmental parameters. This compact, modular design provides a scalable and cost-effective framework for precise three-dimensional observation of sub-surface hydrothermal processes and deep-sea resource exploration. Full article

This study investigates the origin and Nb–Ta enrichment mechanisms of the Middle Triassic Nare Alkaline Rocks in Gerze, central Tibet, using petrological, geochemical, and geochronological data. U–Pb zircon dating constrains the trachyte formation to the Middle Triassic, identifying NaOI as the oldest known seamount fragment in the zone and providing a key age for the early Meso-Tethyan Ocean. Whole-rock geochemistry data show the basalts possess typical OIB signatures, derived from a depleted mantle source modified by a mantle plume. The trachyte originated via a multi-stage process: Middle Triassic basaltic magmas underplated to form a deep-seated magma chamber, underwent high-pressure fractional crystallization, and the resulting crystal mush was later reheated and partially melted by subsequent magmas to generate trachytic melt. This model is supported by Hf isotopes and mineral chemistry. The rocks formed in a mature, thick-lithosphere intra-oceanic plate setting. Niobium occurs primarily as ilmenorutile with high Nb₂O₅ content, but its low modal abundance and very fine grain size imply low beneficiation recovery and limited current economic potential. However, the NaOI formed in an intra-oceanic island setting and hosts an early-stage Nb–Ta metallogenic system linked to alkaline magma differentiation, highlighting their potential for rare-metal exploration. Full article

Late Early Jurassic continental arc magmatism in the northern Greater Khingan Range enables the investigation of complicated tectonic processes associated with the subduction and closure of the Mongol–Okhotsk Ocean. To further clarify the timing, genesis, and geodynamic mechanisms driving the magmatic activity during this period, the present study addresses these critical questions by integrating zircon U–Pb geochronological, geochemical, and isotopic analyses of a wide variety of igneous rocks, including gabbro, gabbro-diorite, granodiorite, porphyritic monzogranite, and biotite-bearing monzogranite from the Fushan region. Zircon U–Pb geochronology constrains the timing of magmatic activity to 184–179 Ma, coinciding with active subduction phases. Geochemical data reveal arc-like signatures characterized by enrichment in light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), together with pronounced depletion in high field strength elements (HFSEs). A comprehensive analysis of geochemical and Sr–Nd–Hf isotopic signatures suggests that the mafic rocks originated from an enriched lithospheric mantle modified by subduction-related fluids and sediment-derived melts. By contrast, the granodiorite and porphyritic monzonite exhibit adakitic characteristics, indicating partial melting of the thickened Mesoproterozoic lower crust with contributions from mantle-derived or newly formed crustal material. The biotite-bearing monzogranite, with its pronounced Eu anomaly and lower zircon saturation temperatures, reflects advanced magmatic differentiation from a shallower source. These findings indicate extensive crust–mantle interactions during the southward subduction of the Mongol–Okhotsk Ocean, driven by high-angle subduction and slab rollback. Full article

The Indosinian granitoids of Guangdong Province, South China, record a complex history of crust–mantle interactions during the Triassic assembly of the South China Block (SCB) and Indochina Block (ICB). Integrated zircon U–Pb geochronology, geochemistry, and Sr–Nd–Hf isotopes from these plutons reveal two magmatic episodes: an Early Indosinian phase (253–230 Ma) of large, west-to-east younging batholiths, and a later scattered phase (230–200 Ma). While most granitoids are peraluminous S-types formed by the melting of the Paleoproterozoic crust with limited mantle input (0–30%), the Taibao pluton and its enclaves are anomalous. They are more mafic and record a substantial mantle contribution (40–65%), pointing to focused, high-heat flux magmatism. This spatial and petrogenetic heterogeneity, coupled with the granitoids’ NE–SW trend orthogonal to the collisional zone, cannot be explained by simple crustal thickening. We propose that these features are the direct result of the slab tearing of the subducting Paleo-Tethys oceanic plate, triggered by an oblique collision between the SCB and ICB. This tearing induced asthenospheric upwelling, providing the thermal engine for widespread crustal anatexis and localized mantle melting. Our findings establish slab tearing as a key catalyst for syn-collisional, high-temperature magmatism, offering a unified framework for interpreting lithospheric processes during continental collisions. Full article

Late Cretaceous plutonic rocks are commonly observed along the Southeastern Anatolian Orogenic Belt (SAOB), which constitutes a significant part of the Alpine–Himalayan Orogenic Belt. Here, we present new whole-rock geochemical analyses, zircon U–Pb ages, and zircon trace element data of plutonic rocks located in the SAOB (eastern Türkiye). This study aims to determine the petrogenesis of the studied plutonic rocks in light of new data and to contribute to the tectonic evolution of the SAOB. Geochemical data demonstrate that the studied granodiorites, diorites, and gabbros are tholeiitic–calc–alkaline in composition, metaluminous, and I-type granite. Zircon U-Pb ages yielded crystallisation ages of 73.52 ± 0.24 Ma for the studied granodiorites and 78.86 ± 0.39 Ma for the diorites. These age data indicate that the studied plutonic rocks represent the youngest granodiorite and diorite formations observed around the study area. High Th/U ratios (granodiorite: 0.15–0.29; diorite: 0.31–0.96) and positive Ce/Ce* (granodiorite: 8.11 to 609.86; diorite: 58.07 to 564.31) and negative Eu/Eu* (granodiorite: 0.49 to 0.62; diorite: 0.59–0.97) values obtained in zircon grains suggest that they are of magmatic origin. Geochemical data indicate that the studied diorites and gabbros originate from a spinel-bearing source representing shallow depths. In light of all the data, the studied plutonic rocks are products of arc magmatism resulting from the subduction of the NeoTethys Oceanic lithosphere along the SAOB. Full article

The Late Cretaceous to Paleocene magmatic evolution along the southern margin of the Lhasa Terrane records a critical transition from oceanic subduction to continental collision, yet its western segment remains underexplored. This study presents integrated petrographic, zircon U–Pb geochronological, zircon Hf isotopic, whole-rock geochemical, and Sr–Nd isotopic data for three distinct phases of intermediate to felsic intrusions from the Qiuwo area in the western segment of the southern Lhasa terrane. The results reveal three distinct magmatic pulses: an early granodiorite emplaced at 89.9 ± 0.75 Ma, followed by a diorite crystallizing at 68.6 ± 0.56 Ma, and a late-stage granodiorite forming at 56.75 ± 0.43 Ma. All three rock units are metaluminous to weakly peraluminous (A/CNK < 1.1), sodic (Na₂O > 3.2 wt.%), and dominated by amphibole, with zircon saturation temperatures of 737–786 °C, consistent with I-type granitoid affinity. All units are metaluminous (A/CNK = 0.92–1.00), calc-alkaline to high-K calc-alkaline, and enriched in LILE (K, Th, Rb) while depleted in HFSE (Nb, Ta, P, Ti), with moderate ΣREE (81–130 ppm), elevated (La/Yb)_N (9.3–15.8), and negative Eu anomalies (δEu = 0.70–0.89). The early granodiorite is Na-rich (Na₂O/K₂O = 1.6), whereas the Paleocene granodiorite shows elevated K₂O (3.2 wt.%) and reduced Na₂O/K₂O (~1.0), reflecting progressive crustal thickening and increasing magmatic differentiation. Zr and Hf are relatively enriched, and Sr/Y ratios decrease from 39 to 21, consistent with evolving magmatic conditions from deeper crustal melting in the Late Cretaceous to shallower, more evolved sources in the Paleocene. Zircon Hf isotopes reveal consistently positive εHf(t) values (+10.4 to +4.9), indicating derivation from juvenile basaltic lower crust. Sr–Nd isotopic data further demonstrate a systematic evolution: εNd(t) decreases from +2.7 to −0.1, while (⁸⁷Sr/⁸⁶Sr)_i increases from 0.7044 to 0.7055, reflecting progressive incorporation of ancient crustal components into the magma source from the early Late Cretaceous to the Paleocene. These findings indicate that the Qiuwo intrusions formed by partial melting of a juvenile basaltic lower crust, with increasing crustal contamination during ascent and emplacement. The temporal progression of magmatism—spanning the waning stages of Neo-Tethyan subduction to the initial India–Eurasia collision (~55 Ma)—supports a model in which slab breakoff and lithospheric delamination triggered decompression melting of the lower crust, while assimilation of older crustal materials intensified as the continental collision progressed. This work provides key geochemical evidence for the transition from arc to post-collisional magmatism in the western Gangdese belt and refines the timing and mechanism of crustal growth in southern Tibet. Full article

As a convergent zone of multiple plates, the Caribbean Sea and its adjacent areas have experienced a complex tectonic evolution process and are characterized by prominent microplate development. This region provides a natural laboratory for studying the formation mechanism of continental margins, the evolution process of ocean basins, and the tectonics of microplates. However, the crustal structure and microplate tectonics in this region remain unclear due to limitations of conventional planar gravity inversion methods, which neglect the Earth’s curvature in large-scale areas, as well as the uneven coverage of regional seismic networks. To precisely delineate the crustal structure and microplate boundaries in the Caribbean Sea region, this study employs a nonlinear gravity inversion method based on a spherical coordinate system. By utilizing GOCO06s satellite gravity data, ETOPO1 topographic data, and the CRUST1.0 crustal model, we performed inversion calculations for the Moho depth in the Caribbean Sea and its adjacent regions and systematically analyzed the crustal structure and microplate tectonic characteristics of the region. The results indicate that the gravity inversion method in the spherical coordinate system has good applicability in complex tectonic regions. The inversion results show that the Moho depth in the study area generally presents a spatial distribution pattern of “shallow in the central part and deep in the surrounding areas”. Among them, the Moho depth is the largest (>39 km) at the junction of the Northern Andes and the South American Plate, while it is relatively shallow (<6 km) in regions such as the Cayman Trough, the Colombian Basin, and the Venezuelan Basin. Based on the Moho undulation, gravity anomalies, and topographic features, this study divides the Caribbean Sea and its adjacent areas into 22 microplates and identifies three types of microplates, including oceanic, continental, and accretionary. Among them, there are 10 microplates with oceanic crust, 6 with continental crust, and 5 with accretionary crust, while the Northern Andes Microplate exhibits a mixed type. The crustal structure characteristics revealed in this study support the Pacific origin model of the Caribbean Plate, indicating that most of the plate is a component of the ancient Pacific Plate with standard oceanic crust properties. Locally, the Caribbean Large Igneous Province developed due to hotspot activity, and the subsequent eastward drift and tectonic wedging processes collectively shaped the complex modern microplate tectonic framework of this region. This study not only reveals the variation pattern of crustal thickness in the Caribbean Sea region but also provides new geophysical evidence for understanding the lithospheric structure and microplate evolution mechanism in the area. Full article

A rifted margin can be regarded, in the first place, as a crustal thinning taper framed by “box-shaped” continental and oceanic crusts whose top basement and Moho are parallel. Attempts to understand the relationship between lithosphere extension, crustal thinning and strain localization have been addressed in part by characterizing and modeling rift modes. However, a weakness of models stems from their using generalized physical parameters and initial conditions, while each system is unique in terms of its geological complexity. In this study, we develop a new approach to investigate the relation between crustal shape, the nature of the top basement and the accommodation space to reveal the link between extension, strain localization and crustal thinning in the northern South China Sea (N-SCS). Our results show the following: (1) box-shaped crusts may indicate no or minor extension, or extension compensated by crustal flow and/or magmatic additions; (2) crustal thinning and strain localization occurred through extensional detachment faults coevally during the rifting of the N-SCS; (3) strain localization was triggered or enhanced by magmatic weakening, and the weak crustal rheology at the onset of the rifting favored the formation of detachment faults; and (4) the inherited composition of the crust (magmatic rocks in the arc and meta-sediments in the forearc) controls the distribution of crustal thinning. We propose that the different initial conditions, changes in extension rates and the presence/absence of subduction dynamics account for the different rift evolutions observed in the SCS and Atlantic-type rift systems. Full article

Cr and Platinum-Group Elements (PGEs), critical metallic elements, are mainly hosted in mafic and ultramafic rocks, but determining these rocks’ mineralization age has long been challenging. Zircon, the primary geochronological mineral, is scarce and fine-grained in such rocks, hindering conventional separation techniques (heavy liquid separation, magnetic separation, manual hand-picking) with low efficiency, poor recovery, and significant sample bias. This study develops an integrated workflow: mixed acid leaching enrichment (120 °C), powder stirring for mount preparation, automated mineral identification, and in situ Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA–ICP–MS) dating. Validated on the Xiugugabu diabase in the western Yarlung–Tsangpo Suture Zone (southern Tibet), the workflow yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 120.5 ± 3.3 Ma (MSWD = 0.13) and 120.5 ± 2.0 Ma (MSWD = 3.2) for two samples. Consistent with the published Yarlung–Tsangpo Suture Zone (YTSZ) diabase formation ages (130–110 Ma), these confirm the Xiugugabu diabase as an Early Cretaceous Neo–Te–thys oceanic lithosphere residual recording mid-stage spreading. The workflow overcomes traditional limitations: single-sample analytical cycles shorten from 30–50 to 10 days, fine–grained zircon recovery is 15x higher than manual picking, and U–Pb ages are stable. Suitable for large-scale mafic–ultramafic geochronological surveys, it can extend to in situ zircon Hf isotope and trace element analysis, offering multi-dimensional constraints on petrogenesis and tectonic evolution. Full article

In this study, we develop a 3D thermal model of the South China Sea (SCS) lithosphere through the joint analysis of heat flow, Curie-point depth derived from magnetic anomalies, and shear wave velocity. Results show the Moho temperature is below 250 °C in the oceanic basin but exceeds 350 °C in continental margins. We evaluate potential Moho drilling sites based on temperature, crustal thickness, water depth, and sediment thickness, identifying six favorable zones in the east sub-basin. The thermal lithosphere thickness correlates with tectonic settings in continental areas, while the oceanic lithosphere is thicker than predicted by theoretical models. Global analysis suggests that the slow spreading rate may have also contributed to the thickening of the oceanic lithosphere in the SCS. Full article

Research on the Mesozoic–Cenozoic magmatism and the tectonic framework within the Lhasa Terrane is voluminous. However, the sparse documentation of Early Cretaceous magmatism in this region fuels ongoing debate over the prevailing tectonic regime during this time period (i.e., normal subduction vs. flat subduction). The present study investigates the Luerma pyroxenite and Boyun granitoid in the Western Lhasa Terrane through zircon U-Pb dating, whole-rock geochemistry, mineral chemistry, and Sr-Nd-Hf isotopes. The findings date the formation of Luerma pyroxenite at 115 Ma and Boyun granites at 113 Ma to the Early Cretaceous period (115–113 Ma). SiO₂ content of pyroxenite is relatively low (34.27–44.16 wt.%), characterized by an enrichment in large ion lithophile elements (LILEs), light rare earth elements (LREEs), and a depletion in heavy field strength elements (HSFEs), indicative of a metasomatic origin. The εNd (t) and εHf (t) values of the Early Cretaceous ultrabasic rocks range from +2.1 to +2.7 and −0.8 to +10.1, respectively, suggesting their derivation from an enriched mantle source with asthenospheric material incorporation. The Early Cretaceous granodiorites and their mafic enclaves belong to the high-K calc-alkaline series, and show enrichment in LILEs (e.g., Rb, Ba, U, and Th) and depletion in HFSEs (e.g., Nb, Ta, Ti, and Zr). The acidic rocks and their developed mafic enclaves exhibit the geochemical characteristics of trace elements found in island arc magmas. Their εNd (t) values are (−6.0–−5.0), while their εHf (t) values are (−11.7–−1.8); the MMEs εHf (t) values are (−4.1–+0.9). In summary, the Early Cretaceous pyroxenite in the Gangdese Belt originated from a combination of asthenospheric and enriched lithospheric mantle melts, while the granitoids were generated by partial melting of the mantle wedge, a process driven by metasomatism resulting from the slab-derived fluids. At the same time, heat from upwelling mantle-derived melts induced the partial melting of lower crustal materials, leading to the formation of acidic magmas through varying degrees of mixing with basic magmas. This study suggests that Early Cretaceous magmatic activity occurred within a northward subduction setting, characterized by the rotation and fragmentation of the Neo-Tethys oceanic crust. Full article

Convective instabilities at various boundary layers in the earth’s mantle—including the core–mantle boundary, mantle transition zone and lithosphere-asthenosphere boundary— result in upwellings (mantle plumes) and downwellings (subducting slabs). While hotspot volcanism is traditionally linked to mantle plumes, their structure, origins, evolution, and death remain subjects of ongoing debate. Recent progress in seismic tomography has revealed a complex plumbing system connecting the core–mantle boundary and the surface. In particular, recent seismic imaging results suggest the presence of large-scale ponding zones between 660 km and ∼1000 km, associated with several mantle plumes around the globe. The broad upwellings originating from the CMB spread laterally beneath the 660 km seismic discontinuity, forming extensive ponding zones several thousand kilometers wide and extending up from an approximately 1000 km depth. Similar ponding zones are also observed for downwellings, with stagnant subducting slabs, within the 660–1000 km depth range. Here, we review evidence for wide ponding zones characterized by low seismic velocities and anomalous radial and azimuthal anisotropies in light of recent high-resolution regional studies below La Réunion Island in the Indian Ocean and below St Helena/Ascension in the southern Atlantic Ocean. We review and discuss possible interpretations of these structures, as well as possible mineralogical, geodynamic implications and outlook for further investigations aiming to improve our understanding of the mantle plumbing system. Full article

This study documents the first A1-type granite identified on the southern margin of the central Lhasa terrane: a two-mica syenogranite pluton in the Meibaqieqin region. Because A-type granite provides sensitive records of crustal melting and lithospheric extension, this pluton offers important insights into magmatic processes and tectonic evolution along the southern margin of the Lhasa terrane. We analyzed two sample suites collected from different sites within the same pluton using zircon U–Pb geochronology and Hf isotopes, whole-rock geochemistry and Nd isotope. Zircon U–Pb weighted mean ages were 130.5 ± 0.7 Ma and 130.0 ± 0.7 Ma, placing emplacement in the Early Cretaceous. Zircon ε_Hf(t) values ranged from −11.29 to −9.00 and −11.04 to −7.27, with two-stage Hf model ages (T_DM2) of 1.76–1.90 Ga and 1.65–1.89 Ga. Whole-rock ε_Nd(t) values clustered between −11.77 and −11.36, yielding two-stage Nd model ages (T_NdDM2) of 1.85–1.88 Ga. Geochemically, the pluton is high-K calc-alkaline. These isotopic signatures indicate derivation predominantly from ancient crustal sources with a little mantle material. Chondrite-normalized REE patterns are overall right-inclined and display a V-shaped profile. Together with trace-element characteristics, these features support classification as A1-type granite. Regional comprehensive data suggest that pluton emplacement was controlled mainly by lithospheric extension related to northward subduction of the Neo-Tethyan oceanic plate, with a lesser contribution from southward subduction along the Bangongco–Nujiang suture. The source characteristics and geodynamic context differ markedly from A2-type granites on the northern margin of the central Lhasa terrane, which reflect distinct magmatic sources and tectonic regimes. Full article

The Mako Belt in the Kédougou-Kéniéba Inlier (eastern Senegal) preserves Paleoproterozoic (2.3–1.9 Ga) mafic and ultramafic rocks that record early crustal growth processes within the southern West African Craton (WAC). Basalt bulk rock compositions preserve primary melt signatures, whereas the associated ultramafic cumulates are variably serpentinized and are better assessed through mineral chemistry. Basalts occur as massive and pillow lavas, with MgO contents of 5.9–9.1 wt.% and flat to slightly LREE-depleted patterns (La/Smₙ = 0.73–0.88). Primitive mantle-normalized diagrams show subduction-related signatures, including enrichment in Ba, Pb, and Rb and depletion in Nb and Ta. Most basalts and all ultramafic rocks display (Nb/La)_PM > 1, consistent with enriched mantle melting in a back-arc setting. Harzburgites and lherzolites have cumulate textures, high Cr and Ni contents, and spinel with chromian cores (Cr# > 0.6) zoned sharply to Cr-rich magnetite rims that overlap basalt spinel compositions. Integration of the petrographic, mineralogical, and whole-rock geochemical data indicates the presence of mafic melts derived from a subduction-modified mantle wedge and likely formed in a back-arc basin above a subducting slab, rather than from a plume or mid-ocean ridge setting. Regional comparisons with other greenstone belts across the WAC suggest that the Mako Belt was part of a broader arc–back-arc system accreted during the Eburnean orogeny (~2.20–2.00 Ga). This study supports the view that modern-style plate tectonics—including subduction and back-arc magmatism—was already active by the Paleoproterozoic, and highlights the Mako Belt as a key archive of early lithospheric evolution in the WAC. Full article