Precambrian Research最新文献

{"title":"Multi-stage enrichment in the mantle source region of cratonic lamproites: Geochemical and Sr-Nd-Hf-Os isotopic insights from the Mesoproterozoic lamproites of Bastar Craton, India","authors":"Rohit Pandey ,&nbsp;Mahendra K. Singh ,&nbsp;Ashutosh Pandey ,&nbsp;N.V. Chalapathi Rao ,&nbsp;Boris V. Belyatsky","doi":"10.1016/j.precamres.2025.107676","DOIUrl":"10.1016/j.precamres.2025.107676","url":null,"abstract":"<div><div>Deep cratonic mantle-derived magmatic rocks such as lamproites provide significant insights into the composition and evolution of the sub-continental and sub-lithospheric mantle. This study presents SHRIMP U-Pb geochronology of rutile and bulk-rock geochemistry including Sr-Nd-Hf-Os isotopes on lamproite dykes from the diamondiferous Nuapada Lamproite Field (NLF) at the tectonic contact between Bastar Craton and Eastern Ghat Mobile Belt, India. The lamproites sampled from the Darlimunda cluster of NLF exhibit inequigranular-porphyritic texture with phenocrysts of olivine pseudomorphs in a groundmass rich in phlogopite. The abundance of low-temperature secondary phases such as vermiculite, chlorite, and carbonates in these rocks indicate significant post-magmatic alteration. The presence of quartz crystals and micro-veins along with zircon megacrysts indicate crustal assimilation to some extent but a strong enrichment in high-field strength elements buffers against significant crustal contamination. Rutile U-Pb geochronology reveals an emplacement age of 1009 ± 121 Ma, which is consistent with the (i) previously reported whole-rock ⁴⁰Ar/³⁹Ar age of lamproites from the NLF, and (ii) widespread ∼1.05 Gyr lamproite, kimberlite, and ultramafic lamprophyre magmatism in the Eastern Dharwar and Bastar Cratons, India. Moderate initial ⁸⁷Sr/⁸⁶Sr (0.703–0.706) and unradiogenic initial Nd-Hf isotopic (ƐNd of −5.96 to −8.08 and ƐHf of −7.25 to −9.02) composition is similar to the global cratonic lamproites and enriched mantle (EM I type) mantle reservoir. Moderately radiogenic and restricted initial ¹⁸⁷Os/¹⁸⁸Os (0.189–0.257) with low Os content, unlike that of the kimberlites and sub-continental lithospheric peridotites, show similarity to the Carboniferous orogenic Variscan lamproites from Bohemian massif and Neogene to Quaternary orogenic ultrapotassic mafic rocks from Italian peninsula. Based on the Sr-Nd-Hf-Os isotopic results, we propose that the cratonic lithospheric mantle source of these rocks record the evidence of a long-term enrichment in lithophile elements as a result of an ancient recycled crustal component. Elevated high-field strength elements in the lamproites and kamafugites of the NLF, similar to those of the global cratonic lamproites and ocean island basalts, represent an overprinting of ancient subduction-related metasomatized deep sub-continental lithospheric mantle sources by small-scale carbonatitic melts derived from the convecting sub-lithospheric mantle prior to their melting. Vein-plus-wall-rock mantle as a result of multi-stage mantle enrichment appears to play an important role in the origin of cratonic lamproites.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107676"},"PeriodicalIF":3.2,"publicationDate":"2025-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Tonian sedimentary records in the southwestern West Qinling orogen, central China, reveal an active margin setting","authors":"Zhidong Gu ,&nbsp;Xing Jian ,&nbsp;Guixia Liu ,&nbsp;Hanjing Fu ,&nbsp;Xiaotian Shen ,&nbsp;Xiufen Zhai ,&nbsp;Hua Jiang","doi":"10.1016/j.precamres.2025.107692","DOIUrl":"10.1016/j.precamres.2025.107692","url":null,"abstract":"<div><div>Neoproterozoic geological records are uncommon in the West Qinling orogen (central China), restricting a clear understanding of its early evolution and the relationships between the West Qinling terrane and surrounding blocks in the Neoproterozoic. The infrequent Neoproterozoic sedimentary successions in the southwestern West Qinling orogen, named as the Baiyigou Group, may provide important insights into these issues. In this contribution, we present comprehensive analysis results, including sedimentological, petrographic, heavy mineral, zircon U-Pb-Hf isotopic and trace element, and whole-rock element geochemical data from Baiyigou Group samples, to determine their depositional ages, provenance and tectono-sedimentary settings. The Baiyigou Group is characterized by mixed volcaniclastic and siliciclastic deposits. Zircon U-Pb dating results from seven tuffaceous sandstones show overwhelming Tonian ages (ca. 840–780 Ma), with major age peaks at the range of ca. 820–800 Ma. Three granite gravel samples from conglomerate strata show crystallization ages at ca. 809–802 Ma, providing maximum depositional age constraints. All these geochronological data indicate that the Baiyigou Group succession accumulated during the middle–late Tonian (ca. 820–800 Ma for the Saiyikuo Formation and possibly largest duration of ca. 800–720 Ma for the overlying Xianglongka Formation). Tephra-rich sandstones are poorly sorted and are featured by abundant embayed grains, whereas tephra-free sandstones are moderate-well sorted and are rich in detrital feldspar grains. Several heavy mineral samples indicate extremely high zircon contents and most zircon grains are texturally euhedral, representing first-cycle detritus. We propose that this sedimentary system was dominantly fed by intermediate-acid igneous rocks from localized source terranes with small drainage networks and was also contributed by extensive wind-carried volcanic clasts. Our petrographic, whole-rock geochemical and zircon trace element data reveal a continental arc setting for the sedimentary sources during the middle–late Tonian. We suggest that the middle–late Tonian West Qinling terrane was in an active margin setting, being involved in the long-lived subduction-related system along the western margin of the Yangtze Block. These findings are crucial to a better understanding of the Neoproterozoic tectono-sedimentary settings of the central China micro-terranes along with the Rodinia supercontinent evolution.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107692"},"PeriodicalIF":3.2,"publicationDate":"2025-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrochronology and geochemistry of migmatites from the Assam-Meghalaya gneissic complex (NE India): Implications for the crustal anatexis and reworking during Gondwana assembly","authors":"Rahul Nag ,&nbsp;Nathan Cogné ,&nbsp;H. Hrushikesh ,&nbsp;N. Prabhakar ,&nbsp;Dhananjay Mishra","doi":"10.1016/j.precamres.2024.107670","DOIUrl":"10.1016/j.precamres.2024.107670","url":null,"abstract":"<div><div>The extensive Proterozoic migmatisation in the Assam-Meghalaya Gneissic Complex (AMGC) is critical for understanding its Precambrian tectonic evolution. The present study reports the occurrence of distinct lithologies in Guwahati and adjoining regions, providing new insights into the Proterozoic high-grade migmatisation events in the central AMGC. This is achieved through an integrated analysis of structures, mineral chemistry, phase equilibrium modelling, whole-rock geochemistry and zircon-monazite geochronology. The gneisses and amphibolites experienced three deformation episodes (D₁, D₂ and D₃), and migmatisation occurred during the D₂ deformation. Phase equilibrium modelling results indicate that the quartzo-feldspathic gneisses and amphibolites experienced peak <em>P-T</em> metamorphism at 5.3–8.0 kbar/720–730 °C and 5.8–7.0 kbar/690–700 °C, respectively. The melt re-integration approach for the quartzo-feldspathic gneisses reveals that the prograde metamorphism occurred through the sub-solidus breakdown of muscovite, followed by the breakdown of biotite during the peak metamorphic event. U-Pb zircon geochronology yielded concordant upper intercept ages of 1674–1610 Ma, representing a Mesoproterozoic igneous protolith for the migmatites. Discordant lower intercept ages (512–426 Ma) and widespread U-Th-total Pb monazite ages (499–470 Ma) constrain the timing of high-grade metamorphism and partial melting in the central AMGC. Geochemically, the leucosomes developed in quartzo-feldspathic gneisses and amphibolites show K-rich and Ca-rich compositions. According to trace element and REE patterns, the K-rich and Ca-rich leucosomes in the quartzo-feldspathic gneisses and amphibolites were formed by partial melting of granitic or metasedimentary protoliths and mafic protoliths, respectively. Combining <em>P-T</em> and geochronological results presented in this study with the existing data, we propose that the central AMGC largely evolved in the hinterland region during the Cambrian-Ordovician (499–470 Ma) collision event. The correlation of widespread Late Neoproterozoic partial melting, high-grade metamorphism and magmatism in the Guwahati region with similar events in western Australia and Antarctica indicate that the central and eastern AMGC represents a convergent margin evolved during the assembly of the Gondwana supercontinent.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107670"},"PeriodicalIF":3.2,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shallow vs. Deep subduction in Earth history: Contrasting regimes of water recycling into the mantle","authors":"Alexei L. Perchuk ,&nbsp;Vladimir S. Zakharov ,&nbsp;Taras V. Gerya ,&nbsp;Robert J. Stern","doi":"10.1016/j.precamres.2025.107690","DOIUrl":"10.1016/j.precamres.2025.107690","url":null,"abstract":"<div><div>Water storage capacity of deep Earth mantle minerals allows storing several ocean masses. However, the amount of water delivered to the mantle through geological history remains uncertain because this depends on tectonic style. It also remains unclear how the water storage capacity of oceanic plates and the mode of delivery changed through time and how these variations controlled mantle water content and distribution. Here, we use 2D numerical modeling of subduction styles at different mantle potential temperatures (T_p) corresponding to different stages of the Earth’s evolution to show two principal regimes of subduction – shallow flat subduction in the early Earth vs. deep and steep subduction in the modern Earth − that provide contrasting regimes of water recycling into the mantle. Deep and steep subduction occurs at lower mantle potential temperatures (ΔT=0-∼100 °C, T_p compared to today). During the modern regime, abundant water is transported to the mantle transition zone, where some is released from subducted slabs and retained in nominally anhydrous minerals (NAMs, wadsleyite and ringwoodite). Shallow, low angle subduction is obtained in the experiments corresponding to the hotter Precambrian mantle (ΔT=∼150–275 °C, ∼1.5–3.0 Ga), which recycled most water into the shallow (&lt;120 km) mantle. This regime provided cool conditions along the flattened subduction interface with limited slab melting of the mantle wedge. Shallow, flat subduction caused strong hydration of the overriding lithosphere, with water predominantly stored in hydrous minerals (e.g. serpentine, chlorite). Due to the breakdown of hydrous minerals, most of this water was easily returned to the surface and/or was stored in the continental crust. We conclude that if the secular cooling of the Earth’s mantle was accompanied by changes in the subduction style from shallow to deep, then it decreased the total volume of oceanic water recycled by subduction but increased the depth of recycling and the average water content in the Mantle Transition Zone. These conclusions pertain to episodes of plate tectonics in Earth history; other modes of water delivery must be considered for single lid tectonic episodes.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107690"},"PeriodicalIF":3.2,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182501","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deformation mechanisms of high–grade metamorphic rocks at middle–lower crustal levels: A case study of Jingjiagou Formation in Qingyuan Area, NE China","authors":"Sitong Zhuang ,&nbsp;Chenyue Liang ,&nbsp;Franz Neubauer ,&nbsp;Yongjiang Liu ,&nbsp;Changqing Zheng","doi":"10.1016/j.precamres.2025.107675","DOIUrl":"10.1016/j.precamres.2025.107675","url":null,"abstract":"<div><div>The early continental lithosphere of the Earth has experienced complex tectonic-magmatic processes, leading to significant change of its thermal structure and rheological properties, which are highly heterogeneous. The Qingyuan area in northern Liaoning Province in NE China is a natural laboratory for studying the rheological properties and deformation mechanisms of high–grade metamorphic rocks in the middle and lower crust, characterized by widespread amphibolite–granulite facies metamorphic rocks and associated structural phenomena and varying rheology. This study presents detailed investigations of the middle–lower crustal rocks of Jingjiagou Formation in the Qingyuan area, including field and microstructures, EBSD (Electron Back Scatter Diffraction) analysis, zircon U–Pb dating and electron microprobe analyses. The peak P–T conditions are constrained at 1 ∼ 1.25 GPa/910 to 1050 °C for garnet pyroxenite, 0.8 ∼ 1.1 GPa/800 to 870 °C for pyrigarnite, and 0.85 ∼ 1.0 GPa/770 to 800 °C for amphibolite. Crystallographic preferred orientation statistics of pyroxene, amphibole and plagioclase indicate that deformation in the amphibolite–granulite facies rocks was dominated by dislocation creep of clinopyroxene and orthopyroxene during the peak metamorphic stage, with (110)[001]/(010)[001] and (100)[001] slip systems, respectively. During retrogression, amphibole deformation shifted to diffusion creep along (100)[001] slip system, with plagioclase also developing diffusion creep. At the Neoarchean/Paleoproterozoic boundary (2494 ± 12 Ma), these deformation mechanisms reflect the flow deformation characteristics of high-grade metamorphic rocks in the Jingjiagou Fm. under the influence of vertical tectonics. Supracrustal rocks subducted into TTG magmas and were transformed within amphibolite-granulite facies conditions, with deformation driven by dislocation creep. As TTG magma ascended and temperatures and pressures dropped, rock deformation transitioned to diffusion creep at various crustal levels. This shift in mineral deformation mechanisms influenced the macroscopic structural patterns and associated deformation processes in the Jingjiagou Fm. of the Qingyuan area, NE China.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107675"},"PeriodicalIF":3.2,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182959","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The origin of Neoarchean granitoid diversity in the Yinshan Block and its implications for the crustal evolution of the North China Craton","authors":"Bin Wu ,&nbsp;Yujing Wang ,&nbsp;Qianzhou Luo ,&nbsp;Jingyu Wang ,&nbsp;Xiaoping Long","doi":"10.1016/j.precamres.2025.107681","DOIUrl":"10.1016/j.precamres.2025.107681","url":null,"abstract":"<div><div>Neoarchean TTG and K-rich granitoids in the Yinshan Block provide a key to understanding the crustal evolution of the North China Craton (NCC), such as the change of continental crust composition, the micro-continent collision and the cratonization. Zircon U-Pb dating suggests that these Neoarchean TTG and K-rich granite rocks were emplaced at 2.7–2.5 Ga and ∼2.5 Ga, respectively. The TTG rocks have low Cr, Co, and Ni contents and Mg^# values, indicative of a crustal source. The ∼2.7 Ga Kuluedianlisu granodiorites have positive ε_Hf(t) values ranging from +6.6 to +9.3, with crustal model ages (T_DMC) of 2.59–2.75 Ga, indicating that they were formed by partial melting of juvenile lower crust. The Hejiao and Dajitu TTG rocks show lower positive ε_Hf(t) values (+3.4 to +5.6) and older crustal model ages (T_DM^C = 2.53–2.83 Ga) than the Kuluedianlisu granodiorites, demonstrating an origin of partial melts from the pre-existing lower crust. The Rentaihe K-rich granites show higher Sr/Y and (La/Yb)_N ratios which similar to the high pressure sodium TTG rocks. They have low ε_Hf(t) values varying from −1.7 to +4.9, with crustal model ages (T_DMC) from 2.7 to 3.1 Ga. Therefore, it is reasonable to suggest that the Rentaihe K-rich granites were produced by remelting of preexisting TTG rocks. According to the complied Hf isotopic compositions, the crustal model age peaks at 2.6 – 2.7 Ga and 2.7 – 2.8 Ga, indicating a crucial period for crustal growth in the Western Block. In the Neoarchean, the K₂O/Na₂O, the A/CNK ratios, and δ¹⁸O values increased from ∼3.1 Ga to ∼2.5 Ga, indicating a rise of crustal maturity. The crustal thickness simulations show that the crust of the NCC thickened continuously from ∼3.1 Ga to 2.5 Ga. Thus, we conclude that the increasing of crust thickness is induced by the amalgamation of micro-continents through collision and the more buried supracrustal material into deep crust. Subsequent partial melting of the deep crust generated magmas with high δ¹⁸O values and thus resulted in the formation of more mature continental crust.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107681"},"PeriodicalIF":3.2,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New paleomagnetic results from the upper part of the Jingeryu Formation in the North China craton and their tectonostratigraphic and paleogeographic implications","authors":"Hanqing Zhao ,&nbsp;Shihong Zhang ,&nbsp;Shengqiang Li ,&nbsp;Jikai Ding ,&nbsp;Haiyan Li ,&nbsp;Tianshui Yang ,&nbsp;Huaichun Wu","doi":"10.1016/j.precamres.2025.107678","DOIUrl":"10.1016/j.precamres.2025.107678","url":null,"abstract":"<div><div>The paleogeographic positions of the North China craton (NCC) during the late Mesoproterozoic to early Neoproterozoic are important to understand the supercontinent evolution. However, the published paleomagnetic results for this period were mainly obtained from the Liaodong–Xuhuai regions, situated along the eastern margin of the craton. They would further benefit from the data from more regions. In this study, we present the new paleomagnetic results obtained from the carbonate rocks of the upper part of the Jingeryu Formation (Fm) in the eastern Heibei Province, Yanliao basin, located in the interior of the NCC. Stepwise demagnetization revealed two distinct paleomagnetic remanence components. The low-stability component is likely a viscous magnetic remanence acquired in the recent geomagnetic field. Ninety-four samples retained a high-stability component, which is dual-polarity and characterized by notably steep inclinations, positioning the paleomagnetic pole at 45.6 °N, 139.6 °E (<em>dp</em>/<em>dm</em> = 8.7°/8.9°). The primary origin of the remanent magnetization is supported by positive fold and reversal tests, as well as the new pole’s distinctiveness from the younger NCC poles. The Jingeryu pole overlaps (at the 95 % confidence level) with poles from the lower part of the correlative strata, which are named Nanfen, Xinxing and Liulaobei formations in the Liaodong–Xuhuai regions at the eastern margin of NCC, but it differs significantly from other Precambrian NCC poles reported previously. We suggest that the upper part of the Jingeryu Fm correlates with the lower part of the Nanfen Fm and its equivalents. These results demonstrate that the previously identified late-Mesoproterozoic high-latitude (&gt;∼70°) carbonate basin, primarily comprising the lower part of the Nanfen Fm and its equivalents situated along the eastern margin of the NCC, also includes the upper part of the Jingeryu Fm, which was deposited in a large area in the craton’s interior. Together with the updated global paleomagnetic database, our reconstruction indicates that the NCC was in high latitudes at ca. 1110 Ma, close to northwestern Laurentia and western Siberia, and separated by tens of degrees in latitude away from the low-latitude continental blocks including the Amazonian, Congo–São Francisco, Indian and Kalahari cratons.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107678"},"PeriodicalIF":3.2,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Differential core-to-periphery emplacement of mafic magma in an Archean Complex and its implications: An example from Southern Granulite Terrain, India","authors":"Siddhartha Karmakar ,&nbsp;Mrinal Kanti Mukherjee ,&nbsp;Muduru L. Dora ,&nbsp;Biswaranjan Mohanty","doi":"10.1016/j.precamres.2024.107673","DOIUrl":"10.1016/j.precamres.2024.107673","url":null,"abstract":"<div><div>An integrated study on the structure, petrology, mineral chemistry, bulk-rock geochemistry, <em>in-situ</em> garnet geochemistry and emplacement mechanisms of a mafic intrusion is presented from the southern granulite terrain of southern India.</div><div>Field study, modal mineralogy and bulk-rock geochemistry characterize the mafic intrusion as hornblende-gabbro to dioritic-gabbro. Structural relationships indicate that the intrusions followed the pre-existing foliations of the rocks of the Bhavani Gneissic Complex. Velocity modelling indicates that the outer zone (periphery), with relatively less viscosity, intruded at a faster rate than the more viscous inner zone (core) resulting in shearing along the core-periphery boundary that led to the development of foliation with appropriate shear sense indicators. The foliation gradually disappears when mapped from the periphery zone of the intrusion towards the core, indicating that the shearing is restricted to the peripheral zone of the intrusion. Absence of intracrystalline deformation of the mineral grains in the foliated periphery zone suggests melt-assisted (magmatic) origin for the foliation in the periphery during emplacement. The orientations of the foliations in the host rocks and along the periphery of the intrusion indicate that the emplacement was <em>syn</em>-to-post kinematic, in the form of an inclined plug within the rocks of the Bhavani Gneissic complex.</div><div>Geochemical data show compositional variations in the periphery and core of the intrusion. Bulk-rock geochemical data and in-situ mineral chemistry reveal that parental magma had a tholeiitic affinity in the arc-subduction zone tectonic setting with garnet in its source. The nearly flat chondrite-normalised REE pattern with a mild negative Eu-anomaly and low CaO, and Al₂O₃ content in the rock, suggests the removal of plagioclase from basic parental magma. Trace element compositions indicate that garnet contains variable amounts of Ni, Cr, Ti, and Co from core to periphery of the intrusion and shows a negative Europium anomaly. Such variations may be due to the initial fluid flow and appropriate fO₂ condition, leading to magnetite precipitation, which incorporated Ni, Ti, Cr and Co. In general, a higher concentration of Ni and Cr in the core of the intrusion than the periphery, suggests that the core may be explored for Ni-Cr and PGE potential.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"418 ","pages":"Article 107673"},"PeriodicalIF":3.2,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143182932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"2.08 Ga andesitic gneisses in the southwestern Yangtze Block: Unveiling new insights into its geological evolution","authors":"Jun-Ping Liu ,&nbsp;Zai-Bo Sun ,&nbsp;Wei-Ke Li ,&nbsp;Hua-Li Luo ,&nbsp;Shi-Jun He ,&nbsp;Shao-Bin Hu ,&nbsp;Jiang-Tai Zhao ,&nbsp;Hai-bao Yan ,&nbsp;Ming-Guo Zhai ,&nbsp;Hai-Long He","doi":"10.1016/j.precamres.2024.107639","DOIUrl":"10.1016/j.precamres.2024.107639","url":null,"abstract":"<div><div>The early geological history of the Yangtze Block has been difficult to unravel due to limited exposure of Archean to Paleoproterozoic rocks. Through detailed geological investigations and mapping in the southwestern (SW) Yangtze Block, this study identified Paleoproterozoic andesitic and granitic gneisses, as well as associated sedimentary rocks, within the Xinanchang (XAC) Complex. Zircon U-Pb dating yields a concordant age of 2078 ± 11 Ma for the andesitic gneiss, and a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1835 ± 12 Ma for the granitic gneiss. The zircon grains from these gneisses exhibit oscillatory zoning and Th/U ratios of 0.40–0.94, corroborating their magmatic origins. Additionally, U-Pb age spectra of concordant zircon grains from the XAC strata range from 1.80 to 2.69 Ga. Together with the intrusive relationship between the 1.84 Ga granitic gneiss and the strata, this implies a depositional age of ca. 1.84 Ga for the XAC strata. The andesitic gneiss exhibits enrichment in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), but shows depletion in Nb, Ta, and Ti. These geochemical signatures are consistent with those of contemporaneous andesitic magmatic rocks in the northern Yangtze Block, suggesting that they were derived from subduction-related sources. In contrast, the granitic gneiss in the XAC Complex shows A-type granite affinities, similar to contemporaneous granitoids widely found across the Yangtze Block. This indicates that these granitoids were formed in a post-orogenic extensional tectonic setting. The northern and SW Yangtze blocks both show records of a transition from subduction to post-orogenic extensional environments between 2.10 Ga and 1.85 Ga, suggesting that the proto-Yangtze Block likely aggregated before 2.10 Ga.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"417 ","pages":"Article 107639"},"PeriodicalIF":3.2,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142758965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early Ediacaran Xueqiong ophiolite in the East Kunlun Orogen, northern Tibetan Plateau: Insights into the early evolution of the Proto-Tethys Ocean","authors":"Qingxing Luo ,&nbsp;Bo Hui ,&nbsp;Yunpeng Dong ,&nbsp;Dengfeng He ,&nbsp;Shengsi Sun ,&nbsp;Yuangang Yue ,&nbsp;Xiang Ren ,&nbsp;Bin Zhang ,&nbsp;Rutao Zang ,&nbsp;Yongcheng Li","doi":"10.1016/j.precamres.2024.107638","DOIUrl":"10.1016/j.precamres.2024.107638","url":null,"abstract":"<div><div>Reshaping the tectonic evolution of the Proto-Tethys Ocean is of paramount significance for comprehending the ocean-continent transitions since the Neoproterozoic. Nevertheless, the intricacies of this evolution, particularly during its early stage, remain a pivotal issue that needs further deciphering. The discovery of early Ediacaran ophiolites within the East Kunlun Orogen offers a crucial clue for exploring this issue. This study presents intergrade field geology, zircon U–Pb geochronology and whole-rock geochemistry on the related rocks from this specific ophiolite identified in the Xueqiong area, easternmost East Kunlun Orogen. Field investigations reveal the currently remaining dismembered Xueqiong ophiolite merely include gabbro, basalt and chert, which are in the form of tectonic blocks within an ophiolitic mélange. Zircon U–Pb dating results show that the gabbro samples from two near rock slices yield consistent weighted mean ages of 597 ± 5 Ma and 601 ± 2 Ma, whereas the basalt sample gives a similar age of 600 ± 6 Ma as well, indicating the magmatic component of the ophiolitic suite was formed at ca. 600 Ma during the early Ediacaran. Geochemical analysis indicates that all the gabbro and basalt share a common parental magma. Patterns of rare earth and trace elements show their properties between the enriched mid-ocean ridge basalt and oceanic island basalt models, along with their characteristic trace element covariances aligning with enriched mid-ocean ridge basalt, suggesting a mantle source similar to the enriched mid-ocean ridge basalt, with interaction with the residual asthenosphere mantle material. Relatively low SiO₂, TFe₂O₃ and MnO₂ contents and flat rare earth element patterns of chert, suggesting its lithogenic property and restricted basin setting near the continental margin. These findings collectively indicate that the Xueqiong ophiolite represents remnants of the oceanic lithosphere and overlying deep-sea sediments from the early-stage evolution of the Proto-Tethys Ocean, when the ocean evolution might not have been fully mature and oceanic floor sedimentation capable of receiving terrigenous detritus. This evidence further supports that the Proto-Tethys Ocean in the East Kunlun domain could be traced back at least to the early Ediacaran.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"417 ","pages":"Article 107638"},"PeriodicalIF":3.2,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142758966","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}