Lithos最新文献

{"title":"Growth processes of zircon crystals in a granitic magma chamber, variation in UPb age, titanium concentration, and Th/U in relation to internal texture","authors":"Takashi Yuguchi ,&nbsp;Kyoka Endo ,&nbsp;Satoshi Suzuki ,&nbsp;Yasuhiro Ogita ,&nbsp;Shuhei Sakata ,&nbsp;Tatsunori Yokoyama ,&nbsp;Takumi Imura ,&nbsp;Takeshi Ohno ,&nbsp;Eiji Sasao","doi":"10.1016/j.lithos.2024.107909","DOIUrl":"10.1016/j.lithos.2024.107909","url":null,"abstract":"<div><div>This study describes the growth characteristics of zircon crystals in the Kuki granite from the Kitakami Mountains in northeastern Japan as the key for elucidating granitic magma chamber processes. Using two approaches, analyses based on multiple sections of separated zircon crystals and thin-section-based zircon crystal analyses, we determined the characteristics of the 3D internal structure of the crystals, variations in U<img>Pb age, Ti concentrations, and Th/U in relation to crystal texture, and the crystallization sequence between zircon crystals and other minerals (i.e., biotite, quartz, and K-feldspar) within the magma chamber. The textures, which occupy a large proportion of zircon, comprise low luminescence homogeneous cores (LLCs) and oscillatory zoning (OZ). The 3D distribution of the zircon internal structure can be classified into three types: Type 1 zircon comprising LLCs and the surrounding OZ and Types 2 and 3 zircon crystals composed entirely of OZ from the cores to the rims and characterized by brightness and darkness cores, respectively. LLC and OZ grew at temperatures from approximately 900 to 800 °C and 850 to 700 °C, respectively, and LLC has a higher Th/U than that of OZ, indicating that fractional crystallization progression as the magma chamber cooled resulted in the transition from LLC to OZ. In the progression of fractional crystallization, the diffusion rate deceleration with decreasing magma temperatures triggered the transition from interfacial reaction-controlled growth producing LLC to diffusion-controlled growth producing OZ. In the thin-section analysis, zircon crystals which contained in different minerals are characterized by different Th/U values. The variation in Th/U and the crystallization temperature of zircon crystals considering the surrounding minerals can be used to elucidate the differentiation and mineral crystallization in magma chamber processes over a wide range of temperature conditions.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107909"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161063","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":"Zircon U-Pb ages, trace elements, and Hf isotopes establish a genetic link between volcanic ash beds and porphyritic intrusions during early Silurian in the South China Block","authors":"Tianrui Wang ,&nbsp;Bo Ran ,&nbsp;Shugen Liu ,&nbsp;M. Santosh ,&nbsp;Zhiwu Li ,&nbsp;Yuyue Han ,&nbsp;Yuehao Ye","doi":"10.1016/j.lithos.2024.107890","DOIUrl":"10.1016/j.lithos.2024.107890","url":null,"abstract":"<div><div>The provenance of the Late Ordovician to Early Silurian volcanic ash beds (VABs) in the South China Block (SCB) remains debated. In this study, we provide new zircon U-Pb age, trace element, and Hf isotope data of bentonites, crystal tuffs, and porphyritic intrusions from the Longmaxi Formation of the Dabashan area in the northern margin of the SCB with a view to investigate the composition, tectonic setting, and source of their parent magmas. The zircon U-Pb ages show that the volcanic eruption and magma emplacement occurred in the Early Silurian (ca. 440–434 Ma). The zircon trace element compositions are consistent with A-type parent magmas formed in intraplate extensional settings. The positive ε_Hf(t) values (+1.7 to +6.9) of zircon indicate an enriched mantle source for the magma, with possible crustal input. The similar U-Pb ages, trace element compositions, and ε_Hf(t) values of zircon grains from VABs and porphyritic intrusion in the Dabashan area suggest that their parent magmas shared similar sources. These A-type parent magmas could have originated in intraplate extension settings on the passive margin of the northern SCB during the subduction of the Proto-Tethys Ocean towards the North Qinling Terrane. Our results suggest that the Paleo-Tethys oceanic basin did not open before the Early Silurian (ca. 434 Ma) in the Dabashan area.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107890"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161065","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":"Deep-sea drilling of the 13°30′ N oceanic core complex: Assessing links between fluid flow, metal enrichment and seafloor massive sulfide deposit formation near Semenov-1","authors":"Andrew J. Martin ,&nbsp;Bramley J. Murton ,&nbsp;Christopher J. MacLeod ,&nbsp;John W. Jamieson ,&nbsp;Isobel I. Yeo ,&nbsp;Sven Petersen ,&nbsp;Katie A. McFall ,&nbsp;Simon Allerton ,&nbsp;Anna Lichtschlag ,&nbsp;Christian Bishop ,&nbsp;Acer Figueroa ,&nbsp;Szu-Ying Lai","doi":"10.1016/j.lithos.2024.107921","DOIUrl":"10.1016/j.lithos.2024.107921","url":null,"abstract":"<div><div>Deep-sea drilling is a key tool in assessing the economic viability of seafloor massive sulfide (SMS) deposits. Drilling can be used to understand links between fluid flow, faulting and mineralization. Of particular interest on the seafloor due to their relative enrichment in Ni and Co, is an underexplored sub-class of SMS deposits that are associated with or hosted within ultramafic lithologies. We present initial results from sub-surface drilling near the Semenov-1 SMS deposit located on the 13°30′ N oceanic core complex on the Mid-Atlantic Ridge. Drilling recovered samples from up to 20.7 m below seafloor (mbsf). In the recovered core samples, a transition from chlorite and clay-rich breccias in the upper 7.5 mbsf to serpentinite, magnesite, dolomite and talc bearing rocks with locally mylonitic fabrics was observed. The contact between mafic and ultramafic lithologies marks the transition from brittle to ductile deformation regimes. Pyrite and marcasite occur throughout the drilled interval, commonly as disseminations. Pyrrhotite and isocubanite only occurred near the seafloor (∼2 mbsf) and are associated with native Au grains. Pyrite at 7.5 mbsf was notably enriched in Ni, whereas deeper pyrite contained higher Se. The average δ³⁴S value for all sulfide minerals is 0.0 ± 5 ‰ (1σ, <em>n = 114 spots</em>) indicating sulfur was largely contributed from the leaching of igneous host rocks, and that magmatic volatile degassing is not an important process contributing to metal enrichment at Semenov-1. The source of sulfur or processes affecting isotopic fractionation also varied over time leading to large variations of ∼15 ‰ across individual pyrite grains. We interpret the drilled section as representing a cross-section through a basaltic veneer to the underlying upper detachment fault surface providing evidence for the complex nature of hydrothermal systems associated with core complexes.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107921"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161549","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 Late Jurassic high-Mg diorite and Early Cretaceous high-silica granite in central Tibet: Implication for the subduction process of the Meso-Tethys Ocean","authors":"Ningyuan Qi ,&nbsp;Zhidan Zhao ,&nbsp;Zhenzhen Wang ,&nbsp;Dong Liu ,&nbsp;Xuanxue Mo","doi":"10.1016/j.lithos.2024.107925","DOIUrl":"10.1016/j.lithos.2024.107925","url":null,"abstract":"<div><div>The evolutionary process and subduction polarity related to the Shiquanhe-Nam Co segment of the Meso-Tethys Ocean remains a significant point of controversy. High-Mg diorite is a special type of rock formed at convergent plate margins, which are typically associated with young subducting plates. This study investigates the petrogenesis and spatial-temporal distribution of Late Jurassic high-Mg diorites and Early Cretaceous high-silica granites in central Tibet to shed light on the subduction processes of the Meso-Tethys Ocean. The Late Jurassic high-Mg diorites formed through metasomatic interactions between mantle wedge peridotite and melts derived from subducted sediments. These diorites subsequently underwent fractional crystallization of clinopyroxene, amphibole, and plagioclase. Coeval granodiorites display evidence of magma mixing and fractional crystallization of amphibole, plagioclase, and pyroxene. In contrast, the Early Cretaceous high-silica granites originated from the partial melting of metandesites, followed by fractional crystallization of plagioclase and biotite. Magmatic activity within the central Lhasa terrane exhibited a southward migration from 170 to 160 Ma and a subsequent northward shift from 150 to 135 Ma. These findings suggest that Late Jurassic magmatic activity was driven by the initial southward subduction of the Meso-Tethys oceanic crust, which provided the necessary heat for crustal remelting. In the Early Cretaceous, the magmatic record reflects slab rollback, which facilitated mantle upwelling, the formation of new crust, and a northward migration of magmatism. This study provides new constraints on the tectono-magmatic evolution of the Meso-Tethys Ocean.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107925"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161637","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":"Sulfur cycling in the gabbroic section of the Oman ophiolite","authors":"Ana P. Jesus ,&nbsp;Harald Strauss ,&nbsp;Mário A. Gonçalves ,&nbsp;Michelle Harris ,&nbsp;Diogo Silva ,&nbsp;Martin J. Whitehouse ,&nbsp;Damon A.H. Teagle","doi":"10.1016/j.lithos.2024.107913","DOIUrl":"10.1016/j.lithos.2024.107913","url":null,"abstract":"<div><div>We present sulfur mineralogy and isotope geochemistry from the gabbro transect of the Oman Drilling Project to unravel the sulfur cycle during hydrothermal alteration of the plutonic oceanic crust. The sheeted dike–gabbro transition (Hole GT3A) shows low sulfide‑sulfur concentrations (GT3A_median = 178 ppm, σ = 4873 ppm) but with great sulfur isotope variability (δ³⁴S = −12.8 to 14.4 ‰ V-CDT, weighted average + 5.8 ‰) and unusually heavy compositions relative to in-situ or ophiolitic crust. These features are consistent with abiogenic thermochemical sulfate reduction during intense hydrothermal alteration under greenschist facies conditions which formed a low-variance and relatively high-<em>f</em>S₂ assemblage of pyrite ± chalcopyrite ± bornite. The heaviest isotope compositions (+10 to +14 ‰) occur within 10 m of the uppermost gabbro screen suggesting focused fluid-rock exchange with isotope enrichment relative to seawater due to closed-system reservoir effects. The change in isotope compositions from +5 to 0 ‰ in the overlying sheeted dike reflect fluids gradually buffered by magmatic sulfur to signatures similar to the Oman Volcanogenic Massive Sulfide deposits. Hole GT3A represents a deep hydrothermal reaction zone with extensive S and base metal losses and incorporation of up to ∼80 % seawater-derived sulfate. The amount of Cu and Zn released in a 1 km³ crustal section similar to Hole GT3A is ∼3 times greater than the average contents of Omani VMS deposits.</div><div>The mid to lower crustal section (Holes GT2A and GT1A) mostly preserves MORB sulfur isotope compositions but highly variable sulfide‑sulfur contents (GT2A_median = 454, σ = 693 ppm, GT1A_median = 114, σ = 277 ppm). Away from fault zones, silicate microvein networks enabled variable sulfide and metal remobilization. Magmatic sulfides persist as remobilized remnants along with sulfidation reactions and mild isotopic enrichments (&lt;+2.7 ‰) in secondary sulfides (millerite + siegenite-polydimite_ss + pyrite). The mid-lower crustal section experienced redistribution of magmatic sulfur mixed with minor inputs of seawater-derived sulfur (&lt;10 %), under very low fluid/rock ratios and moderate sulfur fugacities, that chiefly preserved base metal abundances in secondary sulfides. The many faulted intervals present in Holes GT1A and GT2A record near complete sulfur and metal leaching of magmatic sulfides without the deposition of secondary sulfides, but preserve sulfate with a Cretaceous seawater sulfate‑sulfur isotope signature (+16.1 to +17.3 ‰). These structures are the expression of crustal scale channeled hydrothermal recharge fluid flow and record a previously unaccounted sulfur budget introduced in the deep crust.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107913"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161962","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":"Diachronous closure of the Mongol-Okhotsk Ocean (MOO) during Middle Mesozoic","authors":"Zhiqi Yu ,&nbsp;Huichuan Liu ,&nbsp;Jianwei Zi ,&nbsp;Wenqi Li ,&nbsp;Yiren Wang ,&nbsp;Yingying Wang ,&nbsp;Hanying Guo","doi":"10.1016/j.lithos.2024.107934","DOIUrl":"10.1016/j.lithos.2024.107934","url":null,"abstract":"<div><div>The Mongol-Okhotsk suture belt (MOSZ) is an integral part of the Central Asian orogenic belt (CAOB), the formation and evolution of MOSZ are significant factors contributing to the geotectonic framework of northeast Asia. However, there has been ongoing debate about the closure timing of MOO, particularly given the absence of petrogeological data in Northeastern Mongolia (NE Mongolia). This paper provides new zircon U<img>Pb dating, whole-rock elemental and Hf-Sr-Nd isotope data of two granodiorite plutons at Tsav (198 Ma) and Nomint (173–171 Ma), NE Mongolia, located in the central segment of the MOSZ. Both plutons are I-type granodiorites, but the Nomint granodiorites have high Sr/Y values, indicating an affinity to adakite. The 198 Ma Tsav granodiorites originated from partial melting of mafic lower crust within an Andean-type active continental margin setting, while the 173–171 Ma Nomint granodiorites derived from the thickened lower crust within the post-collisional setting. During the Early-Middle Jurassic, the central segment of MOO (C. MOO) might have closed. Combined with published data, we propose that the MOO closed through diachronous, southward subduction, with the closure of its eastern segment later than the western segment by 40 million years.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107934"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161968","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":"Mineralogy and geochemistry of a dunite dyke from the Monchetundra mafic Intrusion (Fennoscandian Shield): Evidence for petrogenesis and ophiolite-type affiliation","authors":"Victor V. Chashchin ,&nbsp;Yevgeny E. Savchenko","doi":"10.1016/j.lithos.2024.107939","DOIUrl":"10.1016/j.lithos.2024.107939","url":null,"abstract":"<div><div>Numerous dyke- and sill-like dunites have been discovered in the Paleoproterozoic Monchetundra mafic intrusion (MMI) located northeast of the Fennoscandian Shield. The subject of our study was a 35-m-thick dunite dyke discovered during exploration drilling of the low-sulfide Pt<img>Pd Loypishnyun deposit. These dunites contain a xenolith of the amphibolized orthopyroxenite and have undergone uneven, locally intense serpentinization, resulting in serpentinite formation. The host norites and orthopyroxenites underwent tectono-thermal transformations at contact with the dunites in the form of thin zones of serpentine-tremolite, tremolite, and cummingtonite rocks. These dunites are important because they record magmatic events after the formation of the MMI associated with the reactivation of the cratonic mantle. This study reports the mineral composition and the whole-rock major and trace element contents in 23 samples collected from dunite section and host rocks. The primary magmatic minerals in the dunites were olivine (Fo_86.7–92.7) with an elevated Ni content (up to 0.57 wt% NiO) and accessory chromite (60–85 %<em>Cr#</em>). Dunites are characterized by high magnesium (80–87 %<em>Mg#</em>), nickel (1590–2990 ppm Ni), chromium (up to 1.7 wt% Cr₂O₃), and iron oxidation coefficient (82–65 %<em>Fe</em>^<em>3+</em><em>#</em>). They are depleted in rare earth elements (1.3–0.43 ppm REE_tot), Ta, Sr, Zr, and Hf and are enriched in U, Th, and Ti. Based on <em>Cr#</em> (Chr)/Fo (Ol) and V/Al₂O₃ ratios, the parental magma of the dunites formed as a result of partial (30–40 %) melting of the fertile MORB mantle. Dunite crystallization occurred at 1355–1060 °C under the control of the FMQ buffer. Comparative analysis showed that the MMI dunites are similar in olivine composition to the alpine-type Pados intrusion and the Phanerozoic ophiolites of Oman, have a closer chromite composition to the Finnish Paleoproterozoic ophiolites, and generally similar in chemical composition to all except for lower SiO₂ and CaO contents in the MMI dunites. In the REE patterns, the MMI dunites were closest to those of Pados. We suggest that the formation of MMI dunite dykes was associated with the rise of parental melt through a crack network in the continental crust. This process is likely associated with extensional conditions resulting from the uplift of a mantle diapir. The results obtained indicate that MMI dunites are most likely ophiolite-type intrusive bodies and they characterize the setting of the initial stage of oceanic crust formation in the northeastern Fennoscandian Shield.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107939"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161970","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":"Genesis of chromite deposit in the Sartohay ophiolite, NW China: Insights from chromite and its mineral inclusions","authors":"Qi-Qi Pan ,&nbsp;Jian-Guo Liu ,&nbsp;Xia Liu ,&nbsp;Ben-Xun Su ,&nbsp;Yan Xiao ,&nbsp;Qing-Shan Peng","doi":"10.1016/j.lithos.2024.107918","DOIUrl":"10.1016/j.lithos.2024.107918","url":null,"abstract":"<div><div>This study investigated chromite and its mineral inclusions from the Sartohay chromite deposit in NW China to explore the evolution of the parental magma and the genesis of the chromitites. Chromite grains in the Sartohay chromitite bodies have Cr# values (100 × Cr/(Cr + Al)) of 46.1–59.3, Mg# values (100 × Mg/(Mg + Fe²⁺)) of 47.3–70.5, and TiO₂ contents of &lt; 0.72 wt%, classifying them as typical high-Al variety. Numerous primary monomineralic and polymineralic inclusions have been identified within chromite, including olivine, clinopyroxene, orthopyroxene, amphibole, Na-plagioclase, and several less common minerals such as calcite, magnetite, magnesite, apatite, grossular, and corundum. The morphological features of these inclusions indicate that some were encapsulated as solid silicates, while others formed from melts trapped within chromite. The high Mg# characteristics of olivine and pyroxene inclusions, along with the zoning texture observed in elemental mapping images of amphibole inclusions, suggest that these inclusions have undergone elemental exchange with host chromite. The presence of crustal minerals, such as Na-plagioclase, indicates that crustal materials have been incorporated into the mantle through subduction recycling. The inferred parental melt compositions in equilibrium with chromite suggest that these chromitites likely formed from MORB-like melts. The interaction between this magma and harzburgites would generate a more silicic magma, from which high-Al chromitites formed.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107918"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143162009","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":"A Precambrian basement beneath the King George Island (Antarctica Peninsula) revealed by zircon xenocrystals from Eocene to Miocene volcanic rocks","authors":"Hao Xing ,&nbsp;Junling Pei ,&nbsp;Liang Gao ,&nbsp;Jinfeng Wen ,&nbsp;Joaquín Bastías ,&nbsp;Xiatian Zhang","doi":"10.1016/j.lithos.2024.107899","DOIUrl":"10.1016/j.lithos.2024.107899","url":null,"abstract":"<div><div>Our knowledge of the Precambrian geological records of the deep crust beneath the Antarctic Peninsula is still sparse. The King George Island located in the northwestern part of the South Shetland Islands (Antarctic Peninsula) is mainly covered by the Cenozoic volcanic and intrusive rocks. This study presents new petrological, geochronological (LA-ICP-MS zircon U<img>Pb dates), and geochemical data from the King George Island volcanic rocks. The accidental discovery of zircon xenocrysts within these volcanic rocks offers valuable insights into the composition of the deep crust in the region. The zircon ages indicate the evidence of a Proterozoic to Cambrian basement in the King George Island. Among them, 56 zircons with 90–99 % concordance yielded ages ranging from 101 ± 1.7 Ma to 2407 ± 46 Ma. Major age peaks were identified approximately ca. 1.8–1.6 Ga, ca. 1.2–0.75 Ga, and ca. 0.55–0.5 Ga. These zircon xenocryst populations show age ranges and ε_Hf(t) values similar to those of basement rocks of the South America (Patagonia) continental block. This similarity suggests that the Proterozoic to Cambrian Patagonia crustal fragments may extend into the King George Island, South Shetland Islands (Antarctic Peninsula). Accordingly, we consider the paleogeographic position of the South Shetland Islands was probably at the southwestern end of the South America, forming the southwestern margin of Gondwana during the Early Mesozoic.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107899"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161543","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":"Decoding the evolution of Paleo-Tethys: Geochemical and geochronological reinterpretation of the Paleozoic ultra-mafic to felsic rocks in Northeast Iran","authors":"Hadi Karimi ,&nbsp;Hripsime Gevorgyan ,&nbsp;Lothar Ratschbacher ,&nbsp;Zhao Yang ,&nbsp;Axel Gerdes ,&nbsp;Abbas Etemadi","doi":"10.1016/j.lithos.2024.107916","DOIUrl":"10.1016/j.lithos.2024.107916","url":null,"abstract":"<div><div>The tectono-magmatic evolution of NE Iran records the Paleozoic–early Mesozoic formation and consumption of the Paleo-Tethys Ocean. Debates focus on how the regionally-distributed basement exposures and their diverse evolution settings—such as rifting, oceanic-plateau formation, arc magmatism, and collision—are connected. The compositionally diverse meta-igneous rocks comprise the early Paleozoic Neyshabur complex, the Mississippian–Cisuralian Vakilabad complex (‘Mashhad metamorphics’), the Cisuralian Fariman complex, and the Frasnian–Permian Darreh Anjir complex; the age assignment is preliminary. Combining new field, geochemical, and geochronologic data with published ones, we specify the connection and evolution of these complexes. The Neyshabur complex has dominantly alkaline and subordinate tholeiitic rocks dated at 490–435 Ma (U<img>Pb zircon). In terms of high field strength element rations, such as Nb/Y vs. Zr/Y, they record long-lasting, mantle-plume triggered continental rifting along the northern Gondwana margin. A ∼ 364 Ma (U<img>Pb apatite) age dates hydrothermal alteration and deformation, possibly recording the integration of this complex into an oceanic accretionary wedge. Circa 195 Ma (Ar/Ar amphibole and plagioclase) metamorphism dates collisional-wedge formation, i.e., the collision of the Central Iranian (Gondwana) and Turan Blocks (Eurasia). In the Vakilabad complex, 281–268 Ma (Ar/Ar amphibole) ages of meta-komatiite/gabbro match those (∼276 Ma; cumulate) of ultra-mafic to mafic rocks of the southern Fariman complex; a ∼ 320 Ma (U<img>Pb titanite) age of tholeiitic basalt in the Vakilabad complex supports the presence of older rocks, suggested by Carboniferous radiolarian cherts. 188–183 Ma (Ar/Ar mica) metamorphism again dates collisional-wedge formation. The Darreh Anjir-complex rocks with a supra-subduction zone signature record subduction beneath an oceanic plateau within the Paleo-Tethys Ocean. The Vakilabad and the southern Fariman complexes comprise an oceanic plateau built by a mantle plume. This plateau accreted to the hanging-wall plate prior to the terminal collision, detached from the lower plate, blocked the subduction, and caused slab break-off and slab-window formation; the slab window allowed plume material to ascend. The northern Fariman complex documents this process: the rising plume material— depleted by the extraction of OIB-like magma—mixed with fluids from the subducting slab, creating boninite-like magmas. Calc-alkaline andesitic magmas, likely originating from the mantle wedge, coexisted with the OIB-like and boninite-like magmas. Our study provides an evolution model that integrates the various complexes of NE Iran into a common Late Cambrian to Late Triassic evolution of the Paleo-Tethys.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107916"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161551","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}