Search Results (683)

The West Qinling Orogenic Belt (WQOB) contains a sedimentary succession that is approximately 15 km thick, spanning from the Carboniferous to the Jurassic period. This succession offers critical insights into the tectonic evolution of the Paleo-Tethys Ocean. While previous models have suggested various depositional environments, the late Paleozoic to Mesozoic tectonic evolution of the WQOB is still not fully understood. In this study, we incorporate new detrital zircon U-Pb age data and whole-rock geochemical analyses from six stratigraphic units, dating back to the Carboniferous to Triassic periods in the Xiahe–Hezuo region, alongside existing datasets. The detrital zircon age spectra from the WQOB reveal three distinct groups: Devonian–Carboniferous strata exhibit dominant Neoproterozoic (~800–900 Ma) zircon populations, whereas Permian–Triassic rock samples show prominent Paleoproterozoic (1840–1880 Ma) and Archean (2450–2500 Ma) peaks. A minor Neoproterozoic component in Permian spectra disappears by the Triassic, while Jurassic–Cretaceous assemblages lack Precambrian grains. These trends reflect evolving source terranes linked to Paleo-Tethyan subduction dynamics. Furthermore, the geochemical signatures of the Devonian–Triassic clastic rocks align with the composition of upper continental crust, indicating a tectonic relationship with continental island arcs and active continental margins. By synthesizing these findings with established detrital zircon ages, magmatic records, and geophysical data, we propose that the WQOB underwent pre-Triassic tectonic evolution that was marked by pre-Triassic subduction and localized extension during the process of continental underthrusting. Full article

The provenance of the Middle-Upper Permian in the Lintan and Jiangligou areas, remnants of rift basin sedimentation within the West Qinling, remains controversial, hindering understanding of the basin-range coupling evolution of the Qinling Orogenic Belt and its periphery. Heavy minerals, major and trace elements, rare earth elements, detrital zircon U-Pb dating, and in situ Lu-Hf isotopes were analyzed to determine the provenance of the Middle-Upper Permian sandstones. Results were integrated with previous studies to investigate basin-range coupling processes. The results reveal the following: (1) The Upper Member of the Shilidun Formation in the Lintan area was deposited during the Late Permian. Heavy minerals are dominated by moderately to highly stable species. Source rocks were derived from intermediate-acidic magmatic rocks and low- to medium-grade metamorphic terrains. The provenance was primarily situated in a continental island arc tectonic setting. Diverse source rock types were identified, including materials from felsic igneous, quartzose recycled, and mafic igneous provenances. Detrital zircon U–Pb age spectra display two major peak ages at 285 Ma and 442 Ma, along with five subordinate peaks at 818 Ma, 970 Ma, 1734 Ma, 1956 Ma, and 2500 Ma. The ε_Hf(t) values range from –44.95 to 42.67, and T_DM2 ages vary from 367 Ma to 4106 Ma. It is concluded that the sedimentary materials were mainly derived from the North Qinling Orogenic Belt, with minor contributions from the basement of the North China Craton. (2) In the Jiangligou area, the Shiguan Formation is characterized by highly and stable heavy minerals. The provenance is dominated by intermediate-acidic magmatic rocks, within an oceanic island arc tectonic setting. Detrital zircon U–Pb age spectrum displays a prominent peak at 442 Ma. The ε_Hf(t) values range from –0.5 to 10.55, with T_DM2 ages ranging from 744 Ma to 897 Ma. These results indicate that the sedimentary materials were derived from the North Qilian Orogenic Belt. (3) The Permian in the Western Qinling exhibit multi-provenance supply, dominated by the North Qinling Orogenic Belt and the North China Craton basement, with local contributions from the North Qilian Orogenic Belt. Significant regional variations in provenance contributions were identified. This study further constrains the closure of the Shangdan Ocean to pre-Late Permian. It reveals that the Western Qinling was situated in a back-arc rift basin setting during the Late Paleozoic. Key sedimentary evidence is provided for understanding the tectonic evolution of the Paleo-Tethys Ocean and the collision between the North China and Yangtze cratons. Full article

Subduction of the South Tianshan Ocean caused widespread Devonian magmatism, lithospheric deformation, and thinning along the south margin of the Central Tianshan Belt. However, the details of this subduction process remain elusive. This study presents comprehensive data on Devonian granitoids from the Kumishi area, including whole-rock geochemical data, Sr-Nb-Pb isotopic compositions, zircon U-Pb ages, and zircon Hf isotopic data. Dioritic porphyrites, medium–fine-grained monzogranites, and coarse–medium-grained monzogranites were emplaced at 397 ± 2 Ma, 397 ± 3 Ma, and 395 ± 3 Ma, respectively. The dioritic porphyrites have relatively high Sr contents, low heavy rare earth element (HREE) and Y contents, and high Sr/Y ratios, which are characteristics of adakites. High Al and Na₂O contents suggest that the rocks formed through partial melting of subducted oceanic crust. The monzogranites display I-type and subduction-related arc affinities, sourced from a mixed magma of crustal materials and mantle wedge components. The granodiorites were emplaced at 373 ± 3 Ma, and also exhibit pronounced I-type and subduction-related arc affinities. Combined with previous data, our results demonstrate that the studied area of Devonian magmatism records the entire spatiotemporal evolution of subduction of the South Tianshan Ocean slab, from initial shallowing of the subduction angle to flat-slab subduction, followed by final slab rollback. Full article

The Jiapigou mining district, a world-famous gold-producing district with a capacity that greatly exceeds 180 t Au, has a mining history longer than 200 years. The large amount of Jurassic Au mineralization in this district significantly differs from that in other districts of the North China Craton (130–115 Ma). However, the deep-seated dynamic processes and mechanisms that triggered the unique Jurassic mineralization in the Jiapigou district are poorly understood. Here, we present new data on the geology, petrography, and zircon U–Pb and Lu–Hf isotopes of the typical Huangnihe pluton in the Jiapigou district to address the above issues. The results revealed the following: (1) The Huangnihe pluton comprises mainly fine-grained granite and porphyritic granite, which were emplaced at 187 ± 2 Ma (n = 13) and 166 ± 2 Ma (n = 15), respectively. (2) The Hf isotope data indicate that the two episodes of granites exhibit distinct origins: the former (εHf(t) = −1.4 to +5.3; T_DM2 = 1784–1181 Ma) originated from juvenile lower crust, whereas the latter (εHf(t) = −14.9 to −9.7; T_DM2 = 2987–2518 Ma) was derived from Archean crust. (3) On the basis of published geochemical data, the estimated crustal thicknesses of the Jiapigou district ca. 187 Ma, ca. 175 Ma, and ca. 166 Ma ranged from 45 to 52 km, 43 km, and 58 to 63 km, respectively. Combined with regional observations, the results of this study further reveal the following: (1) The Jurassic magmatism in the Jiapigou district can be subdivided into three episodes: 187–186 Ma, ca. 175 Ma, and 166–165 Ma. (2) The crust in the Jiapigou district gradually thickened during the Jurassic and underwent partial melting during multiple episodes of Paleo-Pacific Plate subduction, thereby generating arc-like calc-alkaline (ca. 187 Ma), adakite-like (ca. 175 Ma), and adakite magmas (ca. 166 Ma) that were emplaced to form corresponding granitoids. Moreover, syn-ore magma mixing between the ca. 175 Ma adakite-like felsic magma and mantle-derived mafic magmas was considered a crucial process in magma evolution. This process in turn promoted the enrichment of ore-forming elements within the magma system, which significantly contributed to the formation of the large Au mineralization in the Jiapigou district. Full article

This paper describes for the first time a lobe–hyaloclastite felsic complex on an oceanic island of intraplate setting. In the submarine volcanic succession of the Basal Complex of La Palma (Canary Islands), two main units are identified: an older felsic formation and a conformable upper basaltic–trachybasaltic formation. The felsic formation comprises three facies associations: (1) coherent facies, represented by trachytic lobes with porphyritic, aphanitic, or glass trachytes; (2) autoclastic facies, including hyaloclastites and autobreccias; and (3) syn-eruptive resedimented facies, consisting of mono- and polymictic breccias (massive or graded), and of volcaniclastic sandstones and breccias. The internal architecture and facies relationships are consistent with sedimentation in a submarine trachytic lobe–hyaloclastite complex, which predates the basaltic–trachybasaltic formation. These felsic rocks are classified as trachytes, although they exhibit extensive hydrothermal alteration. The behavior of incompatible trace elements suggests that the variety of the trachytic rocks—porphyritic or aphanitic terms—can be attributed to fractional crystallization processes. However, the features of the incompatible trace elements and the rare earth elements indicate that these trachytes are not cogenetic with the submarine basaltic–trachybasaltic rocks of the Basal Complex of La Palma. Instead, the trachytic magmas responsible for the lobe–hyaloclastite complex formation likely represent the late evolution of a precursor basaltic magma that would have led to the formation of a basaltic submarine shield not exposed nowadays. This study also presents the first robust geochronological constraints for the submarine volcanic units of the La Palma Basal Complex, based on U–Pb on zircons and Ar–Ar on amphiboles. Given that the submarine trachytic lobe–hyaloclastite complex is the oldest lithostratigraphic unit exposed on La Palma, a minimum age of 3.10 Ma is proposed for the initiation of the island submarine growth stage. Full article

The Xifanping Cu–(Au) deposit, a small-scale porphyry system in the central Jinshajiang–Red River tectonic belt (JSRR), formed in a Cenozoic collisional setting. This study integrates zircon U–Pb geochronology, Lu–Hf isotopes, whole-rock geochemistry, and zircon trace element analyses of ore-bearing and barren porphyries, combined with regional comparisons, to constrain magma sources, metallogenic controls, and genetic processes. Ore-bearing biotite quartz monzonite porphyries were emplaced at 32.15 ± 0.43 Ma and 32.49 ± 0.57 Ma, post-dating barren quartz monzonite porphyry (33.15 ± 0.51 Ma). These ages are consistent with molybdenite Re–Os ages (32.1 ± 1.6 Ma), indicating near-synchronous magmatism and mineralization. Both porphyry types belong to the shoshonitic, peraluminous series, enriched in LILE, depleted in HFSE, enriched in LREE, and lacking significant Eu anomalies. Their εHf (t) values (–2.94 to +3.68) and crustal model ages (TDM2 = 0.88–1.30 Ga) indicate derivation from Neoproterozoic subduction-modified lower crust. Ore-bearing porphyries, however, exhibit higher zircon Ce⁴⁺/Ce³⁺ ratios (average = 584 vs. 228 for barren porphyries) and elevated hydrous mineral contents (>10 vol.% amphibole + biotite), indicating more oxidized and water-rich parental magmas. Compared with large-scale porphyry systems (e.g., Dexing, northern Chile), the absence of adakitic signatures and only moderate oxidation limited the scale of mineralization. Overall, the Xifanping deposit formed through partial melting of Neoproterozoic subduction-modified lower crust in a post-collisional extensional regime: at ~33.2 Ma, melting of metasomatized ancient lower crust generated barren porphyries; at ~32 Ma, further evolution and differentiation of this lower crust magmas led to the extraction and enrichment of ore-forming materials from the thicken lower crust, producing hydrated, oxidized, ore-bearing magmas that intruded at shallow levels to form base and precious metal mineralizations. These results underscore the distinctive metallogenic characteristics of small-scale porphyry systems in collisional settings and provide new insights into how source composition and magma oxidation state constrain mineralization potential. Full article

The Galale Cu–Au deposit lies on the northern margin of the western Gangdese metallogenic belt, near the western edge of the Gangdese arc within the Bangong–Nujiang suture zone. Unlike the well-studied Miocene Cu belt in southern Gangdese, this region remains insufficiently investigated, particularly in terms of geochemical characterization, leading to an ambiguous metallogenic model and a debated tectonic setting—specifically, the unresolved issue of subduction polarity across the Bangong–Nujiang suture. This tectonic ambiguity has important implications for understanding magma sources, metal transport pathways, and, consequently, for guiding mineral exploration strategies in the area. To address this, we conducted zircon U–Pb dating on the ore-related quartz diorite and granodiorite, yielding crystallization ages of 84.05 ± 0.34 Ma and 77.20 ± 0.69 Ma, respectively. Integrated with previous data, these results constrain mineralization to 83–89 Ma, which includes both skarn-type Cu–polymetallic and porphyry-type Cu mineralization. Regional comparisons support a tectonic model involving slab rollback and southward subduction of the Bangong–Nujiang oceanic lithosphere. Geochemical analyses of quartz diorite, granodiorite, and monzonitic granite show high-K calc-alkaline, peraluminous I-type affinities, with enrichment in LREEs and LILEs, and depletion in HREEs and HFSEs. Notably, the monzonitic granite is marked by high SiO₂, Sr/Y, and Rb/Sr ratios, low Zr/Hf, strong LREE enrichment, weak Eu anomalies, and pronounced Nb–Ta depletion, indicating high oxygen fugacity and favorable conditions for Mo mineralization. The deposit formed through tectono-magmatic processes related to the closure of the Bangong–Nujiang Neo-Tethys Ocean. Subduction and subsequent lithospheric delamination induced partial melting of mantle and crustal sources, generating quartz diorite and granodiorite intrusions. Magmatic fluids interacted with carbonate wall rocks to form skarn assemblages, concentrating ore metals along structures. The mineralization formed within the contact zones between intrusions and surrounding country rocks. Late-stage granite porphyry intrusions (~77 Ma), inferred from major, trace, and rare earth element compositions to have the highest Mo potential, may represent an extension of earlier skarn mineralization in the area (83–89 Ma). This study presents the first comprehensive geochemical dataset for the Galale deposit, refines its metallogenic model, and identifies key geochemical indicators (e.g., Sr, Y, Nb, Rb, Zr, Hf) for Mo exploration. Full article

The newly discovered Yanshan gold deposit within the Qixia–Penglai mineralization belt is situated within the Daliuhang goldfield of Daliuhang Town, approximately 45 km southeast of Penglai City, the Jiaodong Peninsula. Quartz-vein–type gold orebodies are mainly distributed among the Guojialing granite and are controlled by NNE-trending faults. Native gold primarily occurs within the interiors of pyrite grains, forming inclusion gold and fracture gold. In this study, LA-ICP-MS zircon U-Pb dating and in situ sulfur isotope analysis of gold-bearing pyrite were conducted to constrain the ore genesis of the Yanshan gold deposit. Guojialing monzogranite and porphyritic granodiorite yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 130 ± 2 Ma (MSWD = 1.8) and 131 ± 2 Ma (MSWD = 1.8), respectively, indicating that magmatism and gold mineralization occurred during the Early Cretaceous period. The in situ sulfur δ³⁴S values of euhedral crystalline pyrite (Py1) formed in the early stage ranged from 3.21% to 5.35‰ (n = 11), while the in situ sulfur δ³⁴S values of pyrite (Py2) formed in the later stage ranged from 6.32‰ to 9.77‰ (n = 10), suggesting that the sulfur of the Yanshan gold deposit primarily originates from magmatism, with contamination from stratigraphic materials. Granitoids are highly likely to provide the thermal drive for fluid activity; however, the origins of the fluids and ore-forming materials remain difficult to determine. Based on geological features, geochronological data, and in situ sulfur isotopic analysis, this study concludes that the Yanshan gold deposit is a mesothermal magmatic hydrothermal vein-type gold deposit. The mineralization of the Yanshan gold deposit is related to the subduction of the Mesozoic Paleo-Pacific Plate beneath the Eurasian continent and is mainly controlled by steep dip faults. This study provides theoretical guidance for further exploration and prospecting of the Yanshan gold deposit. Full article

This study investigates the metasedimentary sequences of terrigenous–carbonate Sakar-type Triassic (TCSTT) and Sakar-type Triassic (STT) in the Sakar Unit, southeastern Bulgaria. Both share lithological similarities (alternation of carbonate–silicate schists, mica schists, marbles, and impure marbles) and are affected by post-Triassic metamorphism, but with differences in metamorphic grade and partly in the variation of potential sources of the sedimentary material. STT shows a higher metamorphic grade (lower amphibolite facies) when compared to TCSTT (lower greenschist facies). Petrographic observations and geochemical analyses indicate protoliths composed of arkosic sandstones, shales, and limestones derived from a quartz-dominated source with minor contributions from intermediate magmatic sources. The U-Pb geochronology of the detrital zircons reveals a dominant Carboniferous age complemented by an Early Ordovician age, which is consistent with the presence of Carboniferous–Permian igneous rocks in the basement. The presence of Early Paleozoic and Cambrian–Neoproterozoic zircons in the detrital zircon populations suggests that older rocks of the basement of the Sakar Unit and the Srednogorie Zone are also sources of the sedimentary material. Based on the immobile trace element content and discrimination diagrams, the siliciclastic component originates from rocks formed in a continental-arc setting. REE patterns indicate a negative Eu anomaly inherited from granitic-source rocks. Full article

This study provides new constraints on the paleogeographic evolution of the Arctic during the Mesozoic. U–Pb geochronology of detrital zircon and rutile grains, together with (U–Th)/He zircon thermochronological data from the uppermost Middle Jurassic to Cretaceous strata of the Sverdrup well in the Kara Sea, reveals a major shift in sediment provenance. Two distinct age populations of detrital zircon define this transition: Group 1 (Middle Jurassic–Hauterivian) shows dominant Neoproterozoic–Cambrian (ca. 700–500 Ma) and Paleozoic (ca. 350–290 Ma) peaks, whereas Group 2 (Aptian–Albian) is characterized by prominent Paleoproterozoic (ca. 1980–1720 Ma), Paleozoic (ca. 350–255 Ma), and Early Mesozoic (ca. 240–115 Ma) ages. Corresponding variations in (U–Th)/He zircon ages—from a Triassic peak (~225 Ma) in Group 1 to a dominant Early Cretaceous peak (~140 Ma) in Group 2—support a switch from a proximal to more distal sediment source. We propose that the emergence of large continent-scale river systems transported clastic material from the southern margin of the Siberian Craton to the Arctic Ocean starting in the late Early Cretaceous. The development of a significant freshwater supply potentially initiated a thick low-salinity layer within the surface waters of the central Arctic Ocean, possibly leading to the onset of a strong salinity stratification of near-surface water masses as in the modern Arctic Ocean. Full article

The Chaluo granite is situated in the middle section of the Yidun magmatic arc in western Sichuan Province, China. It holds great significance for the study of the geological evolution of the Paleo-Neotethys tectonic belts. The Chaluo granite mainly consists of alkaline feldspar, quartz, and biotite, with a small amount of apatite. LA-ICP-MS zircon U-Pb dating yielded crystallization ages of (87 ± 3) Ma for the Chaluo granite, indicating its formation in the Late Cretaceous. Elemental geochemical testing results showed that the Chaluo granite exhibits I-type granite characteristics. It has undergone significant fractional crystallization processes, with high SiO₂ contents (72.83–76.63 wt%), K (K₂O/Na₂O = 1.33–1.53), Al₂O₃ (Al₂O₃ = 12.24–13.56 wt%, A/CNK = 0.91–1.08), and a high differentiation index (DI = 88.91–92.49). Notably, the MgO contents were low (0.10–0.26 wt%), and there were significant depletions of Nb, Sr, Ti, and Eu, while Rb, Pb, Th, U, Zr, and Hf were significantly enriched. The total rare earth element (REE) contents were relatively low (211–383 ppm), showing significant light REE (LREE) enrichment (LREE/HREE = 4.46–5.57) and a pronounced negative Eu anomaly (δEu = 0.09–0.17). In situ zircon Hf analyses, combined with ²⁰⁶Pb/²³⁸U ages, gave ε_Hf(t) values ranging from −3.8 to 1.72 and two-stage Hf ages (t_DM2) of 875–1160 Ma. Together with the S and Pb isotope compositions of the Chaluo granite, its magma likely originated from the partial melting of Middle–Neoproterozoic sedimentary rocks enriched in biogenic S. The tectonic-setting analysis indicates that the Chaluo granite formed in a post-orogenic intracontinental extensional environment. This environment was triggered by the northward subduction-collision of the Lhasa block, followed by slab break-off and the upwelling of the asthenosphere in the Neo-Tethys orogenic belt. We propose that the Paleo-Tethys tectonic belt was influenced by the Neo-Tethys tectonic activity, at least in the Yidun magmatic arc region during the Late Cretaceous. Full article

It is generally believed that the ancient oceans during the “boring billion” (1.85–0.8 Ga) lacked the capacity to form large-scale iron formations (IFs), though localized small-scale IFs deposition persisted. The Altyn region of China hosts abundant IFs, with the Dimunalike IFs being the largest and most representative, characterized by typical banded iron–silica layers. Detailed fieldwork identified a tuff layer conformably contacting the IFs at the roof rocks of IFs and a ferruginous mudstone layer at the floor rocks of IFs in drill core ZK4312. Geochemical and zircon U-Pb-Hf isotopic analyses were performed. The tuff has a typical tuff structure, mostly made of quartz, and contains a significant amount of natural sulfur. It also has high SiO₂ content (77.90%–80.49%) and sulfur content (0.78%–3.06%). The ferruginous mudstone has a volcanic clastic structure and is mainly composed of quartz and chlorite, with abundant coeval pyrite. It shows lower SiO₂ content (53.83%–60.32%) and higher TFe₂O₃ content (10.29%–16.24%). Both layers share similar rare earth element (REE) distribution patterns and trace element compositions, with light REE enrichment and negative Eu, Nb, and Ti anomalies, consistent with arc volcanic geochemistry. Zircon U-Pb ages indicate crystallization of the tuff at 1102 ± 13 Ma and maximum deposition of the mudstone at 1110 ± 41 Ma. These data suggest formation during different stages of the same volcanic–sedimentary process. The ε_Hf(t) values (3.60–12.35 for tuff, 2.92–8.19 for mudstone) resemble those of Algoma-type IF host rocks, implying derivation from re-melted new crust. The Dimunalike IFs likely formed in a submarine volcanic–sedimentary environment. In conclusion, although the Mesoproterozoic ocean was generally in a low-oxygen state, which was not conducive to large-scale IF deposition, localized submarine volcanic–hydrothermal activity could still lead to IF formation. Full article

The Western Qinling Orogenic Belt, China’s second-largest Au-metallogenic province, hosts numerous polymetallic deposits, with gold resources particularly concentrated in the northwestern Xiahe–Hezuo area. The Changshitougounao gold deposit, located south of the Xiahe Fault, comprises disseminated ores controlled by near E–W-trending faults and is primarily hosted in quartz diorite and the Lower Triassic Longwuhe Formation. Zircon LA–ICP–MS U–Pb dating of fresh quartz diorite yields an age of 241.8 ± 2.6 Ma. Two generations of monazite were identified: type I magmatic monazite and type II hydrothermal monazite. Type I monazite is intergrown with feldspar, quartz, and biotite, and in situ LA–ICP–MS U–Pb analysis gives an age of 239.2 ± 2.2 Ma. Type II monazite occurs as irregular granular aggregates associated with Au-bearing sulfides and hydrothermal sericite, with an in situ U–Pb age of 230 ± 3.5 Ma. Apatite, also coeval with Au-bearing sulfides and type II monazite, yields an LA–ICP–MS U–Pb age of 230.9 ± 2.5 Ma and 230.7 ± 3.0 Ma. Zircon and type I monazite thus constrain the emplacement of the ore-bearing quartz diorite to ca. 240 Ma, whereas hydrothermal type II monazite and apatite constrain the timing of mineralization to ca. 230 Ma. The ~10 Ma interval between magmatism and mineralization indicates that goldmineralization in the Changshitougounao deposit is decoupled from Early Triassic magmatic activity. Integrating previous studies of the West Qinling geodynamic evolution, we infer that the Changshitougounao deposit formed during collisional orogenesis, in response to the closure of the Paleo-Tethys Ocean. Consequently, the Changshitougounao gold deposit is best classified as an orogenic gold system. Pyrite–arsenopyrite and sericite alteration serve as effective exploration vectors, and the contact zone between quartz diorite veins and slate represents a favorable structural setting for ore prospecting. Full article

The Changning-Menglian suture zone, as the remnant of the main Paleo-Tethyan oceanic basin in its southern segment, lacks direct magmatic evidence constraining the timing of subduction initiation in its northern segment. The petrogenesis and tectonic setting of the newly discovered Early Permian (~280 Ma) Wayao granodiorite in the northern segment remain unclear, hindering our understanding of the timing of subduction initiation and processes of the Paleo-Tethyan Ocean in the Changning-Menglian suture zone. This study presents systematic petrographic, zircon U-Pb geochronological, whole-rock major and trace element geochemical, and Sr-Nd-Hf isotopic analyses on the newly discovered Early Permian granodiorite in the Wayao area, northern segment of the Changning-Menglian suture zone, western Yunnan. Zircon U-Pb dating yields a crystallization age of ca. 280 Ma, confirming its emplacement during the Early Permian. The petrogeochemical characteristics indicate that it belongs to the metaluminous, calc-alkaline series of I-type granite. It is enriched in large-ion lithophile elements (LILEs; e.g., Rb, Th, U, La, Pb) and depleted in high-field-strength elements (HFSEs; e.g., Ba, Nb, Sr, Ti), exhibiting a pronounced negative Eu anomaly. Whole-rock Sr-Nd isotopes (εNd(t) = −5.6–−6.1) and zircon Hf isotopes (εHf(t) = −1.34–−10.01) suggest that the magma was predominantly derived from the partial melting of ancient crustal material (primarily metamorphosed basic rocks, such as amphibolite), with a minor addition of mantle-derived components (magma mixing). Combined with petrogeochemical discriminant diagrams (e.g., Sr/Y vs. Y, Rb vs. Yb + Ta) and the regional geological context, this granodiorite is interpreted to have formed in an active continental margin tectonic setting associated with the eastward subduction of the Paleo-Tethys Ocean (represented by the Changning-Menglian Ocean). This discovery fills the gap in the record of Early Permian subduction-related magmatic rocks in the northern segment of the Changning-Menglian suture zone. It provides crucial petrological evidence constraining that the eastward subduction and consumption of the northern Paleo-Tethys Ocean had already commenced by the Early Permian. Full article

The TuguanZhai rare earth deposit in Tengchong, along with the Longan and Yingpanshan deposits in Longchuan, is a significant ion-adsorption type rare earth (iREE) deposit in Yunnan, China. Previous studies mainly focused on the geochemistry of residual regolith or the migration and enrichment mechanism of rare earth elements (REEs), but lacked systematic analysis of the protoliths. To constrain this deposit and its protolith rock, called Tuguanzhai granite, we systematically integrate petrology features, petrogeochemistry, zircon U-Pb date, and artificial heavy mineral separation (AHMS). Specifically, iREE-host granites include two main periods in this area: the Early Cretaceous (112.13 ± 0.75 Ma) and the Paleocene–Eocene (52.78 ± 0.28 Ma, 48.56 ± 0.19 Ma). The former includes three types of biotite monzogranite with different grain sizes, and the latter is mainly medium-grained biotite monzogranite with local mylonitization. Geochemical features show that these granites generally share high alkalinity compositions (w(K₂O + Na₂O): 7.15 to 12.75 wt%) and potassium contents (w(K₂O): 3.89 to 8.36 wt%). The mineralized granites exhibit significantly higher concentrations of the total REEs than non-mineralized granites, along with a strong enrichment of light REEs. Moreover, the results of AHMS reveal that the REE contents of apatite, allanite, and titanite in mineralized granites are 4.98, 1.29, and 1.90 times more abundant than in non-mineralized granites, respectively. Due to REEs being released from these REE-rich minerals in humid environments, there exists significant potential for iREE formation and exploration in the Early Cretaceous granites in western Yunnan. We innovatively propose the “abundance of easily leachable minerals” as a key indicator for iREE mineralization and exploration, having found it to be better than the traditional total REE contents. Full article