Lithos最新文献

{"title":"Testing in-situ UPb garnet geochronology on a polymetamorphic schist from the Grenvillian basement of the Western Sierras Pampeanas, Argentina","authors":"Sebastián O. Verdecchia ,&nbsp;Cesar Casquet ,&nbsp;Richard Albert ,&nbsp;Axel Gerdes ,&nbsp;Edgardo G. Baldo ,&nbsp;Carlos D. Ramacciotti ,&nbsp;Robert J. Pankhurst","doi":"10.1016/j.lithos.2025.108069","DOIUrl":"10.1016/j.lithos.2025.108069","url":null,"abstract":"<div><div>Garnet, a common mineral in metamorphic rocks, frequently records complex textural and chemical zoning resulting from polymetamorphism. Dating metamorphic events using conventional methods (e.g., U<img>Pb zircon or Lu<img>Hf garnet) is challenging and often fails to yield an accurate reconstruction of the <em>P-T-t</em> history in complex metamorphic regions. Recently, a technique has been developed for in situ U<img>Pb LA-ICP-MS dating in garnets with very low concentrations of U and Pb. In this work we tested the method on polymetamorphic garnet from a sample of garnet-biotite schist from the Sierra de Maz (Western Sierras Pampeanas, Argentina). This rock belongs to a Grenvillian-age tectonic unit (nappe) that was reworked by the Famatinian orogeny (Ordovician-Silurian). The garnet porphyroblasts show a complex internal arrangement with three textural and compositional zones: Grt₁ (cores), Grt₂ (replacements) and Grt₃ (overgrowths). Dating of a single porphyroblast yielded ages of 1045 ± 31 Ma for Grt₁ and 476 ± 18 Ma for Grt₂, confirming polymetamorphism resulting from the two main tectono-metamorphic events recorded in the Western Sierras Pampeanas. The garnet core (Grt₁) age is within error of a 1037 ± 7 Ma zircon-rim U<img>Pb age from the same rock. However, garnet (Grt₂) is slightly older than ages recorded by different methods from the same tectonic unit (nappe), that are mostly in the range ca. 440–410 Ma including a CHIME monazite age of 426 ± 15 Ma from the same schist This discrepancy remains open to question, as Ordovician ages of metamorphism of ca. 470 Ma are common elsewhere in the Sierras Pampeanas.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"506 ","pages":"Article 108069"},"PeriodicalIF":2.9,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143748037","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":"Intraplate magmatic processes associated with crustal accretion at the West Philippine Basin, Western Pacific","authors":"Long Yuan ,&nbsp;Quanshu Yan ,&nbsp;Xuefa Shi","doi":"10.1016/j.lithos.2025.108068","DOIUrl":"10.1016/j.lithos.2025.108068","url":null,"abstract":"<div><div>The West Philippine Basin (WPB), located in the west half of the Philippine Sea Plate (PSP), experienced the superposition effects of back-arc spreading and intraplate processes. However, the magmatic processes for the intraplate geodynamics are unclear. In this study, we analyzed the major and trace element compositions of the plagioclase and clinopyroxene, and the Sr isotopic composition of the plagioclase in basalts collected from the Benham Rise (Site 292) during DSDP (Deep Sea Drilling Program) Expedition 31 and the off-spreading axis Vinogradov seamount (Site 100DS). The results show that clinopyroxene and plagioclase from the Benham Rise exhibit various disequilibrium characteristics, and their zoned textures were produced by multiple phases of magma replenishment in the magma chamber. The calculated parental magmas for clinopyroxenes in lavas from the Benham Rise and Vinogradov seamount show that they are produced by 10–20 % and 1–5 % partial melting of garnet pyroxenite, respectively. The Sr isotopic composition of plagioclase phenocrysts from the Benham Rise lavas showed that their parental magma could have originated from the same mantle source. The geochemical study of plagioclase and clinopyroxene implies the Benham Rise and Vinogradov seamount could be formed by the head and tail of the Benham mantle plume, respectively.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"506 ","pages":"Article 108068"},"PeriodicalIF":2.9,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143738418","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":"Geochemical and isotopic constraints on the petrogenesis and tectonic setting of basalts in the Nagaland Ophiolite Complex, Northeast India","authors":"Xiaodong Wang ,&nbsp;Lin Ding ,&nbsp;Chao Wang ,&nbsp;Lihai Zhou ,&nbsp;Youpeng Zhang ,&nbsp;Fulong Cai ,&nbsp;Upendra Baral ,&nbsp;Yahui Yue","doi":"10.1016/j.lithos.2025.108061","DOIUrl":"10.1016/j.lithos.2025.108061","url":null,"abstract":"<div><div>The Nagaland Ophiolite Complex (NOC) is exposed at the eastern margin of the Indo-Burma Range, which represents the suture zone between the Indian and Burmese Plates. The NOC that contains a complete mantle and crustal lithological assemblage can provide important information regarding the tectonic evolution of the Neo-Tethys Ocean. The studied basaltic rocks from the NOC can be classified into two groups according to their geochemical results. The Group I rocks are geochemically comparable with the <em>E</em>-MORB, which have slight LREE enrichment ((La/Yb)_<em>N</em> = 1.45–1.96). The Group II rocks share geochemical characteristics with typical N-MORB and exhibit LREE depletion, with (La/Yb)_N of 0.47–0.69. All samples showed slightly positive or insignificant anomalies in high-field-strength elements. The Group I and Group II rocks were derived from the partial melting of spinel-facies mantle peridotite, and the degrees of partial melting of the former (approximately 5 %) are lower than those of the latter (approximately 10 %). Both groups of basaltic rocks are characterized by high positive ε_Nd(t) values (+7.0 − +7.6 and + 5.4 − +8.3, respectively). Our study revealed that the Group I rocks were predominantly derived from a MORB-like asthenospheric source that was variably enriched by OIB-type components, whereas the Group II rocks were derived from a depleted asthenospheric mantle source without the contribution of OIB-type components. The heterogeneous asthenospheric mantle sources contributed to the geochemical complexities of the basalts from the NOC. These results, combined with regional geological records, suggest that the basalts from the NOC were mainly generated in a mid-ocean ridge setting during the evolution of the Neo-Tethys Ocean.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"506 ","pages":"Article 108061"},"PeriodicalIF":2.9,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143704278","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 Eo-Variscan domain in the Variscan belt: New data from the Sudetes, southern Poland","authors":"Mirosław Jastrzębski ,&nbsp;Andrzej Żelaźniewicz ,&nbsp;Jiří Sláma ,&nbsp;Ewa Krzemińska ,&nbsp;Marek Śliwiński","doi":"10.1016/j.lithos.2025.108058","DOIUrl":"10.1016/j.lithos.2025.108058","url":null,"abstract":"<div><div>The Variscan belt in Europe includes Eo-Variscan domains whose tectono-metamorphic evolution ended before the Carboniferous. In the Bohemian Massif, these are the Teplá-Barrandian terrain and the Góry Sowie Massif – Kłodzko Metamorphic Massif terrain, jointly referred to as the Bohemian Terrane, which is partially concealed beneath the North Bohemian Cretaceous Basin. Terrains on either side of this basin differ in several aspects. Northern Bohemia is accompanied by dismembered ophiolite (c. 400 Ma) and preserves fragments of late Devonian overstep succession – features missing in the Teplá-Barrandian terrain. New zircon U<img>Pb and O isotope analyses indicate that the Góry Sowie Massif is composed primarily of metasedimentary rocks with a maximum depositional age of 540 Ma, along with minor metaigneous rocks with protolith ages of c. 500–490 Ma. Oxygen isotope study suggests crustal derivation of felsic rocks (δ¹⁸O_Zrn values of 8.14–11.29 ‰) and local pulses of mantle melting for minor basites (δ¹⁸O_Zrn values of 5.10–8.36 ‰). Neither Cadomian basement nor Neoproterozoic magmatic arc, characteristic for the Teplá-Barrandian domain, is in evidence in the Góry Sowie Massif. Detrital zircon age spectra for the Góry Sowie Massif reveal three clusters: 2.8–2.4 Ga, 2.1–1.9 Ga, and 650–540 Ma also known from the adjacent Saxothuringian units. However, the Góry Sowie Massif spectra contain more Neoarchaean and Mesoproterozoic components, and fewer Neoproterozoic components, suggesting different positions for the Góry Sowie Massif and Saxothuringia in the peri-Gondwana realm during the Cambrian. The two Eo-Variscan parts of the Bohemian terrane have probably constituted the composite terrane of Bohemia since the Early/Middle Devonian and further acted as a single microcontinent. In the Góry Sowie Massif, metamorphic zircon grains dated to ca. 390–380 Ma preserve evidence of the mid-Devonian collision between the western margin of the Góry Sowie Massif–Kłodzko Metamorphic Massif block and the Saxothuringia-related sub-terrane. In the Kłodzko Metamorphic Massif, slightly metamorphosed mudstones (Frasnian depositional age), below the nonconformity, contain detrital zircons of metamorphic origin dated at c. 390–370 Ma, sourced from the Góry Sowie area. The Eo-Variscan domain was finally brought to the surface in the Frasnian/Famennian as constrained by previous biostratigraphical data from a nonconformably overstepping sedimentary succession on its flanks. The more distant Famennian pelagic deposits in the Bardo Structure acquired c. 390–365 Ma euhedral zircons of volcanogenic provenance, prior to the Variscan collision between the Saxothuringian and Bohemian terranes.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108058"},"PeriodicalIF":2.9,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679404","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":"Trace elements in igneous apatite: A case study of redox tracers in felsic plutons","authors":"Yusuke Sawaki ,&nbsp;Hisashi Asanuma ,&nbsp;Ryoichi Nakada ,&nbsp;Mariko Abe","doi":"10.1016/j.lithos.2025.108059","DOIUrl":"10.1016/j.lithos.2025.108059","url":null,"abstract":"<div><div>Apatite, a common accessory mineral in igneous rocks, can incorporate various trace elements, making it a powerful petrogenetic indicator. The abundances of redox-sensitive elements in apatite offer a valuable probe for assessing magmatic oxygen fugacity (<em>f</em>O₂). Previous studies have explored the dependence of S, V, Mn, Fe, As, and Eu concentrations in apatite on magmatic <em>f</em>O₂. While the use of S in apatite as a redox proxy is well-established, the reliability of other elements for estimating magmatic <em>f</em>O₂ remains controversial.</div><div>In this study, we present new geochemical data for apatite grains separated from Miocene granitoids in Japan, analyzed using laser ablation-inductively coupled plasma-tandem mass spectrometry (LA-ICP-MS/MS). Based on the iron content in plagioclase, the analyzed plutons are classified into oxidized and reduced types. Apatites crystallized in oxidized magmas are enriched in S (&gt; 80 μg/g) and V (&gt; 6 μg/g), whereas those in reduced magmas had low S (&lt; 80 μg/g) and V (&lt; 5 μg/g) contents, irrespective of their crystallization timing within the magma. This enrichment clearly reflects the <em>f</em>O₂ of their parental magmas. Conversely, the Mn and Fe contents of apatite crystallized in oxidized magmas overlap with those in reduced magmas. The apparent partition coefficients of Mn and Fe between apatite and melt are strongly correlated with the ratio of non-bridging oxygen to tetrahedrally coordinated cations in the host rocks, rather than with <em>f</em>O₂. Thus, Mn and Fe contents in apatite do not record magmatic <em>f</em>O₂. The As content in apatite from oxidized magmas is generally higher (typically &gt;1 μg/g) than that in apatite from reduced magmas; however, some overlaps exist between the two types. As a result, arsenic in apatite is not a reliable oxybarometer for reasons that remain unclear. Based on our dataset, only sulfur and vanadium in apatite record magmatic ƒO₂.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108059"},"PeriodicalIF":2.9,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Formation and accretionary evolution of the Kokchetav complex, northwestern Kazakhstan: Insights from structural styles, and detrital zircon geochronology and Lu-Hf isotopes","authors":"Xiaoliang Jia ,&nbsp;Wenjiao Xiao ,&nbsp;Miao Sang ,&nbsp;Mingguo Zhai ,&nbsp;Peng Huang ,&nbsp;Liang Li ,&nbsp;Qigui Mao ,&nbsp;Jingmin Gan ,&nbsp;Dzhovid Yogibekov ,&nbsp;Nurobl Tileuberdi","doi":"10.1016/j.lithos.2025.108056","DOIUrl":"10.1016/j.lithos.2025.108056","url":null,"abstract":"<div><div>Understanding how subduction processes incorporate continental fragments into accretionary complexes is important for constraining the formation of accretionary orogenic belts. The Kokchetav Complex is a distinctive geological unit in the northwestern Altaids of northwestern Kazakhstan that is ideal for investigating such processes. It hosts microcontinental fragments, and accretionary and (ultra)high-pressure ([U]HP) metamorphic rocks. We undertook U-Pb dating and Lu-Hf isotopic analyses of detrital zircons from quartzites, schists, gneisses, and sandstones in the metasedimentary belt, gneissic basement rocks, (U)HP metamorphic belt, and ophiolitic mélange in the Kokchetav Complex. The quartzite–schist rocks yield three primary zircon age clusters: middle–late Paleoproterozoic (1.8–1.6 Ga), middle Mesoproterozoic to early Neoproterozoic (1.4–0.8 Ga), and latest Neoproterozoic to Early Devonian (544–406 Ma), with a few isolated zircons dated between 3.6 and 2.8 Ga. These rocks have diverse detrital zircon U-Pb age spectra (unimodal to multi-modal) with variable Hf isotope ratios (−10.9 to +22.0). The zircons have a mixed origin from the early Paleozoic Stepnyak Arc and Precambrian continental fragments, and were not derived from the gneissic basement, indicating an affinity with the Proterozoic Musgrave–Albany Orogen in Australia. Consequently, these zircons reveal that a continent fragment from the northwestern Rodinia supercontinent exists within the Kokchetav Complex, which retained its original nature from the Neoproterozoic to early Paleozoic and was later incorporated into the accretionary complex as tectonic sheets and slices during convergence between the Kokchetav microcontinent and Stepnyak Arc. Our results further indicate that, rather than being part of a unified Precambrian block, the Kokchetav Complex incorporated continental fragments and younger accreted materials that formed in an early Paleozoic supra-subduction zone setting.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"506 ","pages":"Article 108056"},"PeriodicalIF":2.9,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143734699","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 EMI component in the Shikoku back-arc spreading center, Philippine Sea Plate","authors":"Long Yuan ,&nbsp;Quanshu Yan","doi":"10.1016/j.lithos.2025.108055","DOIUrl":"10.1016/j.lithos.2025.108055","url":null,"abstract":"<div><div>The Mesozoic-Cenozoic geological evolution of the East Asian continental margin and a series of Cenozoic back-arc basins (South China Sea, West Philippine Sea, Sea of Japan and Shikoku Basin) developing in the West Pacific region have been predominately resulted from the westward subduction of Pacific plate, accompanying with the effects of some intraplate processes. However, how the intraplate processes work remains unclear. Here we present new geochemical and Sr-Nd-Pb-Hf isotope data for the lava samples collected from Deep Sea Drilling Project Expeditions 6, 58, and 59 in the Shikoku Basin (SKB) and its adjacent region. High Nb/La ratio and enriched Sr-Nd-Pb-Hf isotopic compositions indicate that the spreading-related lavas in the SKB were affected by the enriched mantle type I (EMI) component, which can be solely produced by mixing enriched mantle components and ambient mantle. We suggested that EMI components in the asthenosphere mantle beneath the region from northeast China to Sea of Japan may be involved in the back-arc spreading processes by means of asthenospheric toroidal flow around the subducting Philippine Sea slab, or the EMI components have preexisted in the asthenospheric mantle beneath the SKB prior to the northward migration of the Philippine Sea Plate since Equator.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108055"},"PeriodicalIF":2.9,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679530","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":"Iron-based eutectics, a valuable geological record","authors":"Oleg S. Vereshchagin ,&nbsp;Vladimir V. Shilovskikh ,&nbsp;Larisa V. Kamaeva ,&nbsp;Maya O. Khmelnitskaya ,&nbsp;Liudmila A. Gorelova ,&nbsp;Yevgeny Vapnik ,&nbsp;Natalia S. Vlasenko ,&nbsp;Sergey N. Britvin","doi":"10.1016/j.lithos.2025.108057","DOIUrl":"10.1016/j.lithos.2025.108057","url":null,"abstract":"<div><div>Metal iron-based eutectics are common in iron and stony‑iron meteorites, where their presence traces space melting of parent celestial bodies or accompanies atmospheric ablation processes. It is less known that the same structures and compositions occur in situ within telluric iron in terrestrial crustal rocks. We have studied iron-based eutectics confined to native iron assemblages in volcanic rocks of Disko Island, Greenland, and combustion metamorphic lithologies of the Hatrurim Complex, Israel. In addition, Fe-P alloys were synthesized, enabling to reconstruct the composition and cooling rates of the initial melt. Despite the different geological settings of the two occurrences, the highly reducing (several units below iron – wüstite buffer) and high-temperature (∼1200 °C) environment results in the appearance of the same P-, C-bearing iron melts, with subsequent rapid crystallization (crystallization speed up to 5 °C/min) into eutectic structures (iron - cohenite (Fe₃C), iron - schreibersite (Fe₃P), cohenite - schreibersite and iron - barringerite (Fe₂P)). The discovered eutectic structures clearly indicate the possibility of forming iron melt under conditions of low pressure and moderately high temperatures (typical for basalts), which may also be applicable to a number of celestial bodies.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108057"},"PeriodicalIF":2.9,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679532","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":"Ordovician-Devonian multiple-phase subduction-accretion with crust-mantle interactions in the Proto-Tethys: Implications for plate driving mechanism","authors":"Miao Sang ,&nbsp;Wenjiao Xiao ,&nbsp;Zhen Yan ,&nbsp;Xiaoliang Jia ,&nbsp;He Yang ,&nbsp;Zhou Tan ,&nbsp;Jingmin Gan ,&nbsp;Yunpeng Ni ,&nbsp;Luyao Wang","doi":"10.1016/j.lithos.2025.108050","DOIUrl":"10.1016/j.lithos.2025.108050","url":null,"abstract":"<div><div>The tectonic evolution of the Proto-Tethys records the dispersal of the Gondwana and the formation of the Asian continent, based on which the driving force of plate tectonics was majorly attributed to slab pull. However, no consensus has been achieved on the driving force and some fundamental aspects of its geodynamic processes have been controversial. This study presents detailed petrological, geochronological, and geochemical analyses of northern West Kunlun Orogen (WKO) adakites to constrain subduction processes and the magma sources, advancing tectonic reconstruction of the Proto-Tethys. Two samples (OMS-60 and OMS-62) were collected from an ophiolitic mélange within the Omixia complex, where they occur in association with mafic rocks. Another sample (OMS-64) was obtained from a granitoid body located on the northern margin of this ophiolitic mélange. These samples yield zircon U-Pb ages of 399 ± 5 Ma, 434.0 ± 2 Ma, and 462 ± 3 Ma, displaying typical adakitic signatures (high Sr/Y = 49.6–193, LREE enrichment, HREE depletion) and variable isotopic compositions (εNd(t) = −8.42 to −0.78; εHf(t) = −3.97 to −0.51). These features indicate magma generation through partial melting of Proto-Tethys oceanic crust and overlying sediments, coupled with mantle interaction during ascent. Combined with regional data, two adakite groups are identified: (1) northern 462–443 Ma suites formed during northward subduction, and (2) younger 434–399 Ma suites within of the Omixia complex linked to southward subduction. The sequential subduction regimes, potentially driven by ridge subduction or slab tearing, promoted oceanic crust melting and high-SiO₂ magma emplacement in forearc accretionary prisms. These findings, corroborated by regional evidence, challenge slab-pull dominance and instead support a hybrid geodynamic mechanism involving back-arc rifting and multi-force interactions. This work resolves Proto-Tethys subduction polarity shifts and provides new constraints on arc-related crust-mantle processes during Ordovician-Devonian orogenesis.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108050"},"PeriodicalIF":2.9,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Deep-crustal layered mafic complexes in the Mesoproterozoic oceanic-arc of the Tugela Terrane, South Africa","authors":"Allan H. Wilson","doi":"10.1016/j.lithos.2025.108052","DOIUrl":"10.1016/j.lithos.2025.108052","url":null,"abstract":"<div><div>Layered mafic intrusions are important in understanding the generation of continental crust in oceanic arcs. The Mesoproterozoic (c. 1200 Ma) Tugela Terrane in southeast South Africa is made up of a series of thrust slices of varied rock-types purported to have been derived in oceanic arcs prior to accretion onto the southern margin of the Archean Kaapvaal Craton. They are not ophiolites. Mafic intrusions in two adjacent thrust slices are known as the Tugela Rand and Mambula Complexes. Both intrusions are intensely layered on scales of centimetres to several tens of metres but clear cyclic units are not apparent and crystal fractionation is limited indicating these were open systems with magma chamber through-flow. Tugela Rand is made up of dominantly olivine-bearing rocks ranging from dunite and pyroxenite to gabbro. In contrast, Mambula is dominantly gabbroic with only rare olivine-bearing rocks and is more evolved with layers of titaniferous-magnetite. Primary magmatic structures in both complexes include graded bedding, slumping and erosion features. Relatively high pressure of formation is indicated by the aluminous nature of the pyroxenes and corona textures by reaction between plagioclase and olivine. Chromitites in Tugela Rand range from massive to podiform with the rare orbicular variety indicating complex controls on chromite accretion. They include the high-Al compositional variety. There are no other similar chromitite occurrences in South Africa. The complexes, together with their enclosing rock-types, draw striking parallels with the lower arc crust observed in the late Cretaceous Kohistan arc complex in NE Pakistan. The Tugela Rand Complex shares many similarities with the Chilas Complex in that terrane, while the Mambula Complex is considered to be a more evolved derivative of the same magma. This study shows that generation of juvenile continental crust formation in mature island arc systems may have been firmly established by the Mesoproterozoic.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108052"},"PeriodicalIF":2.9,"publicationDate":"2025-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}