Geological Journal最新文献

{"title":"Insights to Pyrochlore and Apatite Evolutionary Trends: Constraints From Mineral and Bulk Chemistry of Saidiwasan Sövites, Gujarat, India","authors":"Sunit Mohanty,&nbsp;Himansu Sekhar Sahoo,&nbsp;Shrinivas Viladkar,&nbsp;Chiranjeeb Chatterjee,&nbsp;K. L. Mundra,&nbsp;Arundhuti Ghatak","doi":"10.1002/gj.70025","DOIUrl":"https://doi.org/10.1002/gj.70025","url":null,"abstract":"<div>\u0000 \u0000 <p>The Saidiwasan (also known as Siriwasan) carbonatite-sill is located approximately 10 km to the north of the well-known Ambadungar carbonatite–alkaline complex within the Chhota Udaipur carbonatite-alkaline province. This complex comprises prominent sövite plugs within carbonatitic breccias, each exhibiting diverse and variable mineralogical assemblages that include pyroxene, amphibole, apatite, pyrochlore, perovskite and titanite. The enrichment of rare earth elements (REEs) in the Saidiwasan sövites is closely associated with the presence of pyrochlore, perovskite, apatite and monazite. This study employs detailed mineral chemistry to elucidate the secondary processes affecting pyrochlore and apatite grains. Primary magmatic pyrochlore in Saidiwasan sövites are characterised by elevated concentrations of calcium, niobium, fluorine and sodium, which are subsequently replaced by secondary cation-deficient grains due to supergene weathering. These alterations primarily occur at the A site and occasionally at the B site, involving the substitution of fluorine by hydroxide (OH–) groups. During alteration, calcium and sodium are leached from the pyrochlore structure, with charge balance maintained by the substitution of REE, Th, U, Ba or Sr. In the later supergene stages, marginal and fractured zones of pyrochlore grains experience metamictization, resulting in Pb-rich and cation-deficient hydrated varieties. Fluoro-apatites within the sövites display significant REE concentrations and are relatively unaltered. LREE constitute the dominant proportion of the total REE content in Saidiwasan apatite. Based on mineral chemistry and bulk rock analyses, this study aims to provide a comprehensive understanding of the Saidiwasan sövites. Despite its promising characteristics, the Saidiwasan carbonatite complex remains underexplored and largely overlooked within the Chhota Udaipur Province, although it possesses significant potential for hosting economically viable mineral deposits, thus warranting further investigation and exploration.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"1081-1104"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemostratigraphy of the Permian Fengcheng Formation Shale From Well HS-1 in the Hala'alat Mountain Area, Northwestern Junggar Basin: Implications for Hydrocarbon Generation Potential, Palaeoenvironmental Conditions and Organic Matter Accumulation","authors":"Jian Zhou,&nbsp;Kuihua Zhang,&nbsp;Guanlong Zhang,&nbsp;Qianjun Wang,&nbsp;Zengbao Zhang,&nbsp;Hongzhou Yu,&nbsp;Wei Xiong,&nbsp;Meiyuan Song,&nbsp;Changling Cheng,&nbsp;Hai Li,&nbsp;Shaohua Zhang","doi":"10.1002/gj.70020","DOIUrl":"https://doi.org/10.1002/gj.70020","url":null,"abstract":"<div>\u0000 \u0000 <p>The Permian Fengcheng Formation in the Junggar Basin, particularly within the Mahu Sag, has become a focal point for shale oil exploration. However, the hydrocarbon generation potential, palaeoenvironmental conditions and organic matter accumulation in the relatively underexplored Hala'alat Mountain area, located northwest of the Mahu Sag, remain insufficiently understood. This study systematically investigates the hydrocarbon generation potential, palaeoenvironmental conditions, and organic matter accumulation of the Fengcheng Formation shales from Well HS-1 in the Hala'alat Mountain area through comprehensive chemostratigraphic analyses, including total organic carbon (TOC) content, Rock-Eval pyrolysis and handheld X-ray fluorescence (XRF). TOC values range from 0.08 wt.% to 2.83 wt.%, with significant enrichment below 2020 m, indicating enhanced preservation of organic matter at greater depths. Hydrogen index (HI) values suggest a predominance of oil-prone Type II kerogen, while Tmax values (418°C–442°C) confirm the thermal maturity of the organic matter, placing it within the primary oil generation window. Chemostratigraphic trends reveal a significant palaeoenvironmental shift at 2020 m of Well HS-1, transitioning from an anoxic, saline, and arid environment in the lower section to a more oxygenated, fresher and humid environment in the upper intervals. Redox-sensitive proxies, combined with palaeosalinity and palaeoclimate indicators, suggest that optimal conditions for organic matter preservation occurred below 2020 m, where sustained anoxia, moderate salinity and limited terrestrial input facilitated the accumulation of organic-rich sediments. These findings provide essential insights into the hydrocarbon potential and depositional history of the Fengcheng Formation and offer a valuable framework for future exploration in this underexplored region.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"1014-1028"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correlation of Paleo-Mesozoic Sandstones Based on Heavy Mineral Chemistry and Th–U–Total Pb Monazite Dating: Implications on Paleogeographic Reconstruction in Eastern Gondwanaland","authors":"Sankar Kumar Nahak,&nbsp;Sanghita Dasgupta,&nbsp;N. Prabhakar,&nbsp;Santanu Banerjee","doi":"10.1002/gj.70023","DOIUrl":"https://doi.org/10.1002/gj.70023","url":null,"abstract":"<div>\u0000 \u0000 <p>The correlation between continental sandstones in adjacent sedimentary basins, lacking biostratigraphic control, is often problematic. Based on petrography, paleocurrent data, heavy mineral analysis, and monazite dating, this study correlates Paleo-Mesozoic sandstones in the Wardha Basin with those in the adjacent Pranhita-Godavari (P-G) Basin, and presents a paleogeographic reconstruction of eastern Gondwanaland. Predominantly quartzose to feldspathic-quartzose arenites of the Wardha Basin, showing N-NW paleocurrent, contain heavy minerals such as ilmenite, garnet, zircon, rutile, monazite, tourmaline, and staurolite. Burial dissolution has caused preferential leaching of staurolite and rutile in relatively older sediments. The abundance of almandine garnet indicates the predominant granulite and subordinate amphibolite sources. The tourmaline chemistry, indicating the dominance of dravite and schorl, relates them primarily to amphibolites and granitoids, whilst rutile chemistry tracks them to metapelitic sources. The prevalence of leucoxene in younger formations reflects ilmenite alteration, indicating progressive tectonic stability and humidity from the Upper Carboniferous to Lower Triassic period. The Th–U–total Pb dating of detrital monazite in sandstones yields three major groups at (1) 2496–2395 Ma, (2) 927–722 Ma, and (3) 552–438 Ma. Heavy mineral chemistry, paleocurrent data, and monazite dating track sediment sources to the Eastern Ghats Mobile Belt, Karimnagar Granulite Belt, and Antarctica through the axial drainage system. Whilst local sediment sources include amphibolites and granitoids in Bastar Craton, hosting Bhopalpatnam Granulite Belt, Mul and Dongargarh granite, and Bengpal Group. Good matching of heavy mineral chemistry and monazite dating confirms the genetic relationship between Wardha Basin and Pranhita-Godavari Basin.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"1041-1065"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Zircon Trace Elements as Indicators of Physicochemical Conditions and Mineralisation Potential in the Nannihu Porphyry Mo–W Deposit, East Qinling, China","authors":"Cheng Wang,&nbsp;Fan Yang,&nbsp;Leon Bagas,&nbsp;Zhenyu Qin,&nbsp;Feifan Xu,&nbsp;Jinhu Ma,&nbsp;Weidong Ren","doi":"10.1002/gj.70024","DOIUrl":"https://doi.org/10.1002/gj.70024","url":null,"abstract":"<div>\u0000 \u0000 <p>Physical and chemical (physicochemical) conditions are crucial for the genesis of a mineralised porphyry. For instance, a hydrothermal system with high oxygen fugacity facilitates Mo migration and precipitation. Zircon, the most common mineral enriched in rare earth elements (REEs), is widely used to determine the oxygen fugacity, magma evolution and mineralisation potential of a porphyry body. The Nannihu is a giant Mo–W porphyry deposit in the Qinling Orogen of central China and consists of porphyritic monzogranite. Previous studies have primarily focused on the age and petrogenesis of the deposit, but the physicochemical conditions remain poorly understood. Additionally, the mineralisation potential of the porphyry has not been evaluated, hampering the discovery of concealed Mo–W ores. In this study, we present in situ trace element analysis of zircon from the Nannihu porphyry to decipher the physicochemical conditions, magma evolution and evaluate the mineralisation potential of the area. The REE contents of the zircons range from 357 to 4768 ppm, characterised by depleted light REEs (LREEs) and enriched heavy REEs (HREEs). Using the zircon–Ti-thermometer and Ce/Ce* ratio, the crystallisation temperature of the Nannihu porphyry is estimated to be ~651°C–769°C, with an oxygen fugacity ranging from −30 to −1.7. By contrast, the crystallisation temperatures of the Nannihu porphyry are similar to those of nearby Shibaogou, Huangbeiling and Shangfanggou plutons in the Luanchuan region; its oxygen fugacity is moderate compared to these plutons. The porphyry formed in an intraplate setting and is derived from the crust. The crust in the Nannihu region underwent double thickening during ~148–138 Ma, reaching a depth of ~60 km. The zircons in the porphyry represent early products of a magma rich in H₂O with a high oxygen fugacity, potentially influenced by F-rich hydrothermal input, which indicates a high prospectivity for Mo–W mineralisation in the vicinity of the deposit.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"1066-1080"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708385","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sensitivity Analysis of Factors Affecting Stability of High and Steep Rocky Slopes in Seasonal Frozen Region: A Case Study of Huinan County","authors":"Lingjie Pan,&nbsp;Chenglong Yu,&nbsp;Libo Liu,&nbsp;Huanan Liu,&nbsp;Jiquan Zhang,&nbsp;Yichen Zhang,&nbsp;Haoxin Chen","doi":"10.1002/gj.70014","DOIUrl":"https://doi.org/10.1002/gj.70014","url":null,"abstract":"<div>\u0000 \u0000 <p>Geological disasters caused by the instability of high and steep rocky slopes in seasonal frozen regions are often harmful, and the reasons for their instability vary. Therefore, it is particularly important to study the influencing factors of the stability of highly steep rocky slopes in seasonal frozen regions, and to explore the primary and secondary order of each influencing factor. Geological disasters are frequent in Huinan County, Tonghua City, Jilin Province, especially small- to medium-scale high- steep rocky slopes landslides and avalanches, which seriously threaten the surrounding infrastructure construction and ecological environment. In this study, on the basis of field investigation and collected primary data, five typical high-steep rock masses in Huinan County were selected as the research objects. Through literature research and mechanism analysis of rock slope, three first-order influencing factors are identified, and then subdivided into 8 second-order influencing factors. Numerical simulation through ABAQUS and sensitivity analysis using grey correlation analysis revealed that cohesion is the most sensitive factor, followed by internal friction angle, while freeze–thaw cycles are less sensitive, which suggests that priority should be given to increasing rock cohesion in the management of this type of slope. At the same time, it also provides the effective scientific basis for high and steep rocky slopes in the quaternary freezing zone for the protection and reinforcement projects.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"893-911"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Permian Carbonaceous Shales From Raniganj Sub-Basin—A Potential Source of Hydrocarbons? Inferences Drawn From Kerogen Characteristics and Kinetics","authors":"Monalisa Mallick,&nbsp;Barnita Banerjee,&nbsp;Nihar Ranjan Kar,&nbsp;Runcie Paul Mathews,&nbsp;Vikram P. Singh,&nbsp;Manish Tiwari,&nbsp;E. V. S. S. K. Babu,&nbsp;Tanveer Hassan,&nbsp;Satendra Kumar Gupta","doi":"10.1002/gj.70028","DOIUrl":"https://doi.org/10.1002/gj.70028","url":null,"abstract":"<div>\u0000 \u0000 <p>The present study reports a geochemical evaluation of Permian aged Raniganj, Barren Measure and Barakar shales from R1 and R4 boreholes from the NE part of the Raniganj sub-basin. We have investigated organic matter characteristics, stable isotopic composition, hydrocarbon potential and kerogen kinetics to decipher shale gas potential as well as artificial hydrocarbon generation prospect. The shales contain high total organic carbon (TOC) content ~2.5–26.5 wt%, mainly Type III kerogen with minor Type II/III kerogen. The provenance of organic matters has been determined using δ¹³C_org and δ¹⁵N_bulk composition and Total Nitrogen content to be predominantly terrestrial deposited primarily in an oxic to suboxic environment. Kinetic parameters for kerogen degradation reactions namely, activation energies (Ea) distribution, frequency factors are in the range of typical Type III kerogen. A narrow range of peak Ea distribution indicates relative homogeneity of organic matter which is also evident from FTIR spectra showing relative abundance of aromatic compounds. Maceral assemblage reveals substantial presence of Type I/Type II liptinite macerals namely, alginite, sporinite, cutinite along with Type III vitrinite macerals which likely elevated the kerogen type and hydrogen index (HI), and resulted in a narrow Ea distribution. The kerogen transformation ratio and the hydrocarbon generation rate indicate considerably earlier onset of kerogen transformation and quicker completion of hydrocarbon generation for R4 shales suggesting better potential for R4 shales relative to R1 shales. Furthermore, Rock-Eval parameters S2, TOC, Hydrogen Index, <i>T</i>_max summarise that the shales derived predominantly from terrestrial sources contain mainly Type III with some mixed Type II–III kerogen with potential for wet/dry gas generation. In the absence of any post-depositional igneous activity in the NE part of the Raniganj sub-basin, the shales are in an early matured state unlike shales from the NW part.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"1143-1166"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrographic, Geochemical and Sr–Nd Isotopic Studies of the Shales From the Lower Cuddapah Basin: Implications for Palaeoweathering, Provenance and Proterozoic Crustal Evolution","authors":"Tavheed Khan,&nbsp;D. Srinivasa Sarma","doi":"10.1002/gj.70013","DOIUrl":"https://doi.org/10.1002/gj.70013","url":null,"abstract":"<div>\u0000 \u0000 <p>The Proterozoic to Neoproterozoic Cuddapah Basin (CB) contains a thick pile (i.e., 6–12 km) of arenaceous, argillaceous and carbonate rocks with substantial igneous rocks. The evolution of the CB is mainly defined based on igneous rocks with a limited study on siliciclastic rocks. Here we report geochemical and isotopic data from shale samples of the Lower Cuddapah formations for the first time to comprehend their provenance, palaeoweathering, and tectonic setting. The shale samples were collected from Gulcheru, Vempalle and Tadpatri formations of the Lower CB. The geochemical and isotopic data divide Gulcheru Formation shales into two groups: Gulcheru shale I (GS I) and Gulcheru shale II (GS II). The CIA (chemical index of alteration), CIW (chemical index of weathering) and Al₂O₃–CaO + Na₂O–K₂O (ACNK) diagram of the shales decipher a low chemical weathering for the GS I. In contrast, GS II, Vempalle shale (VS) and Tadpatri shale (TS) exhibit a medium to high degree of chemical weathering. The major and trace element ratios, provenance diagrams, and higher sub-chondritic εNd(t) values of GS I (−8.18 to −7.62) compared to GS II (−5.34 to −3.63), VS (−6.25 to −4.41) and TS (−5.2 to −3.78) along with f_Sm/Nd versus ɛNd(t) diagram suggest the decrease of sediment input from older crustal provenance, that is, Eastern Dharwar Craton (EDC) with increase of ‘more juvenile’ source. The tectonic discrimination diagrams, as well as the primitive mantle (PM) normalised multi-element diagram, characterise a back-arc origin of the CB. The more evolved εNd(t) values and younger detrital zircon grains in the Pulivendla Formation indicate that the basin was opened by westerly subduction along the east coast of India at ~2 Ga. The continuous collision of the Dharwar Craton with Antarctica at ~1.6 Ga suggests the last phase of the Columbia Supercontinent formation.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"861-892"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High-Titanium Zircon Rims in Rhyolite – A Reflection of Adiabatic Ascent?","authors":"Carson Kinney,&nbsp;Holden Little,&nbsp;Chris Yakymchuk","doi":"10.1002/gj.70021","DOIUrl":"https://doi.org/10.1002/gj.70021","url":null,"abstract":"<p>Autocrystic zircon formed during magma crystallisation provides crucial information for understanding the long-term evolution of Earth's crust. Due to the factors that control zircon solubility in silicate melt (e.g., temperature and melt composition), zircon crystallisation may occur during magma ascent, emplacement, and eruption. Zircon sourced from volcanic rocks can have rims with elevated concentrations of titanium relative to zircon cores; this has been linked to temperature changes associated with recharge events in magma chambers. An alternative cause of temperature shifts in subvolcanic systems is adiabatic ascent without magma mixing or recharge. Here, we simulate adiabatic ascent of rhyolitic magmas to model the growth and dissolution of zircon during ascent from the mid-crust to sub-volcanic depths – decompression melting and system expansion drive cooling prior to fluid saturation. Sub-volcanic boiling induces magma crystallisation. Zircon growth is predicted throughout ascent for both A- and S-type magmas. Our results suggest that high-titanium rims of autocrystic zircon can form through the protracted evolution of a single magmatic pulse without the need for magmatic recharge.</p>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"1029-1040"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gj.70021","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tectonic Evolution of the Northeastern Margin of North China Craton During Late Palaeozoic","authors":"Li Zhang,&nbsp;Chao Zhang,&nbsp;Yong-Jiang Liu,&nbsp;Jin-Tao Ge,&nbsp;Bo-Ran Liu,&nbsp;Wei-Min Li,&nbsp;Chen-Yue Liang","doi":"10.1002/gj.70016","DOIUrl":"https://doi.org/10.1002/gj.70016","url":null,"abstract":"<div>\u0000 \u0000 <p>The tectonic mélange belts along the northeastern margin of the North China Craton (NCC) provide critical insights into the closure of the Paleo-Asian Ocean (PAO) and the formation and evolution of the Central Asian Orogenic Belt (CAOB). Due to the lack of early Late Palaeozoic geological records in this region, understanding the initiation and polarity of PAO subduction remained unclear. Recently identified Middle Devonian and Lower Carboniferous meta-clastic rocks and Upper Devonian meta-volcanic rocks from the “Xia'ertai” tectonic complex in the northeastern margin of the NCC have provided new evidence. Comprehensive geological surveys, mineralogical and petrographic studies, geochemistry, and zircon U–Pb isotopic dating were conducted. The Middle Devonian meta-clastic rocks (muscovite two-feldspar gneiss) exhibit high SiO₂ and Al₂O₃ contents, notable REEs fractionation, and negative Eu anomalies. Zircon U–Pb dating reveals ages between 384 and 443 Ma. These rocks, with sandstone as the protolith and granitic rocks as their provenance, formed in a basin along the continental margin during the extensional stage after arc–continent collision. The Upper Devonian meta-volcanic rocks (biotite plagioclase gneiss) belong to the high-K calc-alkaline series, are metaluminous to weakly peraluminous, and show a pronounced REEs fractionation and negative Eu anomalies. Zircon U–Pb dating gives a weighted average age of 381 Ma. These rocks are classified as highly differentiated I-type magmatic rocks, originated from partial melting of the lower crust, and formed in an active continental margin environment. The Lower Carboniferous meta-clastic rocks (two-mica quartz schist) have high SiO₂ and Al₂O₃ contents, distinct REE patterns, and negative Eu anomalies. Zircon U–Pb ages range from 324 to 370 Ma. These rocks, with sandstone as the protolith and felsic volcanic rocks as their sole provenance, formed in an active continental island arc environment. Integrating these findings with previous research, we propose a four-stage tectonic evolution model for the northeastern margin of the NCC from the Early–Middle Devonian to Late Carboniferous: (1) Extensional phase following an arc–continent collision (Early-Middle Devonian); (2) Formation of an active continental margin arc due to the intensified southward subduction (modern coordinate system) of the PAO plate (Late Devonian); (3) Continued southward subduction of the oceanic lithosphere (Early Carboniferous); (4) Development of fore-arc and back-arc basins (Late Carboniferous).</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"929-944"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrology and Sr–Nd Isotopes of High–Grade Amphibolites From Bankim Area (Central Cameroon Shear Zone), Cameroon: Constraints on Petrogenesis and Geodynamic Implications","authors":"Tcheumenak Kouémo Jules,&nbsp;Kwékam Maurice,&nbsp;Fozing Eric Martial,&nbsp;Efon Awoum Julios,&nbsp;Sobze Yemdji Belmien Robinson,&nbsp;Njonfang Emmanuel","doi":"10.1002/gj.70019","DOIUrl":"https://doi.org/10.1002/gj.70019","url":null,"abstract":"<div>\u0000 \u0000 <p>The Bankim area is located in the Tikar Plain, on the N50E branch of the Central Cameroon Shear Zone (CCSZ) where amphibolites occur, but their relationship with the general Pan–African metamorphism history is poorly known. The petrography, mineral chemistry, geochemistry and Sr–Nd isotope systematics of amphibolites from the Bankim area are presented in this paper in order to constrain their petrogenesis and geodynamic setting during the Pan–African orogeny. They are garnet amphibolites (GA), pyroxene amphibolites (PA) and biotite amphibolites (BA) occurring as metric flagstones showing relic of S₁ foliation, lense–like, or as sheared sinistral and dextral and/or boudinaged enclaves. In GA, garnet occurs as lobate porphyroblasts (Alm_54-58Gr_25-27Pyr_10-12 ∙ Sp_3-5). It is usually surrounded by a corona made up of hornblende, plagioclase [andesite (Ab_67-59An_32-46Or_0.5) to oligoclase (Ab₇₂An₂₇Or_0.6)], quartz and ilmenite; the whole defining a kelyphitic microstructure (characterised by garnet + amphibole + plagioclase + opaques mineral (ilmenite) parageneses). In PA, clinopyroxene (diopside; Ca_49-50 Mg_29-30Fe_19-22) is mostly relic–like and displays hornblende or plagioclase (andesine (Ab_65-67An_32-34Or_0.6-0.8) to oligoclase (Ab_69-70An_29-30Or_1-1.2)) corona showing hornblende + clinopyroxene + plagioclase + opaque minerals paragenesis. Field and microstructural data indicate that these rocks recorded a polyphase prograde–peak followed by retrograde metamorphism. The metamorphic prograde phase and peak P–T conditions exceeding 5.2 kbar/789°C occurring during the D₁ deformation phase (613–600 Ma) correspond to the collisional stage of the Pan–African orogeny within the granulite facies. Retrograde metamorphism occurred from the granulite facies to the amphibolite facies under P–T conditions of 1.4–5.2 kbar/789°C–513°C. These changes were synchronous with the early sinistral syn–D₂ (590–580 Ma) and the late dextral syn–D₃ (580–545 Ma) ductile shear deformation phases. These deformation phases, which occurred as a result of exhumation during the crustal re–equilibration related to relaxation and erosion during the post-collisional evolution of Western Gondwana. The geochemical data indicate that the above amphibolites derived from the metamorphism of mafic protolith which represents an ancient Proterozoic crust with model ages of <i>T</i>_DM = 1.9–1.6 Ga and initial ⁸⁷Sr/⁸⁶Sr₆₀₀ ratios of 0.70626–0.70894. At the end of the prograde and retrograde metamorphism of this ancient crust, it was stretched, sheared, dismembered and scattered along the Pan–African mobile zone during the CCSZ reactivations.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"61 4","pages":"984-1013"},"PeriodicalIF":2.2,"publicationDate":"2026-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147708272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}