Precambrian Research最新文献

{"title":"Igneous apatite geochemistry indicates early cratonization of continents","authors":"Adrien Vezinet ,&nbsp;Javiera Flores-Rojas ,&nbsp;Alexander V. Sobolev ,&nbsp;Julien Léger ,&nbsp;Aleksandr V. Chugunov ,&nbsp;Valentina G. Batanova ,&nbsp;Marlina A. Elburg ,&nbsp;Axel Hofmann ,&nbsp;Mélanie Balvay ,&nbsp;Nouméa Paradis","doi":"10.1016/j.precamres.2025.107927","DOIUrl":"10.1016/j.precamres.2025.107927","url":null,"abstract":"<div><div>Processes and mechanisms accounting for the stabilization of Archean (4.0–2.5 Ga) continental crust remain a matter of debate. Over the last decades, major efforts have been made to determine the chemical and isotopic composition of rocks belonging to the Tonalite-Trondhjemite-Granodiorite (TTG) suite, i.e. those forming the bulk of Archean continental crust, as well as late-Archean sanukitoids, the typical marker of cratonization. The extensive use of zircon elemental and isotopic signatures has indisputably been an unrivalled source of information; yet it has also biased interpretations through the prism of a single mineral, hence not reflecting the whole geological history of these magmas. To extend our understanding of early continent stabilization, a pivotal aspect of Earth’s evolution, a fresh perspective is necessary. Here, we present in-situ analyses of igneous apatite, Ca₅(PO₄)₃(OH,Cl,F), from Archean granitoids exposed in the eastern Kaapvaal craton for major/trace elements and U–Pb/Sr isotopes. The trace element signatures of these apatite crystals, with a clear enrichment in LREE and an elevated LREE/HREE, resemble that of apatite from sanukitoids and Phanerozoic I-type granites, a signature which can be blurred at the whole-rock scale. We interpret this signature as indicating that the studied granitoids are formed via interaction between (i) a TTG melt, formed via partial melting of a subducting oceanic crust and (ii) a mantle component, causing chemical depletion of the mantle domain involved and thus production of long-lived and stable lithospheric keels pivotal in the long-term preservation of Archean lithosphere at the Earth’s surface. Therefore, the identification of this signature—in igneous apatite from Paleo to Meso-Archean TTGs of the eastern Kaapvaal—indicates an early onset of cratonization in this region.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107927"},"PeriodicalIF":3.2,"publicationDate":"2025-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145221693","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":"Dynamics of Marinoan-age glaciers in NW Tarim, China","authors":"Xiaoshuai Chen ,&nbsp;Hongwei Kuang ,&nbsp;Yongqing Liu ,&nbsp;Daniel Paul Le Heron ,&nbsp;Yuchong Wang ,&nbsp;Nan Peng ,&nbsp;Mingming Cui ,&nbsp;Kening Qi","doi":"10.1016/j.precamres.2025.107933","DOIUrl":"10.1016/j.precamres.2025.107933","url":null,"abstract":"<div><div>Glaciers were pivotal agents in shaping Cryogenian landscapes through erosional and depositional processes. Subglacial erosional forms serve as critical archives of glacial dynamics and thermal regimes, offering insights into paleoenvironmental interpretation and paleogeographic reconstruction. Cryogenian subglacial erosional forms are preserved on seven cratons globally, with China’s excellent example located in the Aksu-Wushi area of the northwestern Tarim Craton. A series of well-preserved erosional features of subglacial origin crop out, which until now have not been subject to systematic description or interpretation. This is redressed herein, and eight sites are surveyed in detail, enabling considerable insight into and unintegrated that have hindered research on Cryogenian glacial dynamics. In the Aksu-Wushi area, striations, grooves, p-forms, roches moutonnées, and glacial plucking morphologies, testify to both abrasion and meltwater processes at the ice-bedrock interface. A southwest-directed ice flow, with gradual southward deflection, is identified. Subglacial erosional forms and the overlying sedimentary successions documented in this study jointly reveal the depositional environmental evolution of the Yuermeinak Formation from subglacial to proglacial to post-glacial transgression, forming a complete record of continental ice sheet advance-retreat processes. The dynamic patterns and thermal regime of the Marinoan glacier further provide critical constraints for paleogeographic reconstruction. The consistent ice flow directions and sedimentary evolution observed in both the Yuermeinak Formation (Tarim) and Walsh Formation (Australia) collectively suggest that the Tarim was likely adjacent to the Australia during the Cryogenian period. The subglacial erosional forms and striated clasts at Aksu-Wushi area indicate a temperate glacial thermal regime during the latter stages of the snowball Earth event, compatible with a mid- to low-latitude paleogeographic setting. The massive gravel-bearing sandstone and siltstone with dropstones between the basal diamictite and overlying Ediacaran cap dolomite represents large-scale chemical weathering at the end of temperate glacier. Thus, paleo-glaciology can play a vital role in deep time paleogeographic reconstructions.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107933"},"PeriodicalIF":3.2,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145158883","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":"Rhyacian (2218–2066 Ma) subduction-related volcanosedimentary accretion in the Western Bahia Orogenic Domain (São Francisco Craton, Brazil), and tectonic implications","authors":"Michel Macedo Meira ,&nbsp;Simone Cerqueira Pereira Cruz ,&nbsp;Elson Paiva Oliveira ,&nbsp;Joseneusa Brilhante Rodrigues ,&nbsp;Angela Beatriz de Menezes Leal ,&nbsp;Cristiano Lana","doi":"10.1016/j.precamres.2025.107925","DOIUrl":"10.1016/j.precamres.2025.107925","url":null,"abstract":"<div><div>New evidence from the northwestern São Francisco Craton sheds light on Paleoproterozoic tectonic evolution in the Minas-Bahia Orogen. Two metavolcanosedimentary sequences—the Boqueirão de Baixo and Chapada Grande formations—record stages of a Rhyacian orogenic system, characterized through integrated stratigraphic, petrographic, geochemical, geochronological, and isotopic data. The metavolcanic rocks of the Boqueirão de Baixo Formation consist mainly of fine-grained tholeiitic amphibolites, with juvenile zircon Ɛ_Hf(t) values (+3.78 to + 5.6), which crystallized at 2218 ± 18 Ma and were metamorphosed at 2020 ± 7 Ma. The Chapada Grande Formation comprises metasedimentary rocks and calc-alkaline to ultrapotassic mafic to intermediate metavolcanics, with crystallization ages between 2096 ± 20 Ma and 2066 ± 6 Ma and evolved isotopic signatures (Ɛ_Hf(t) −18.5 to −8.84). These formations developed in a continental arc setting along the eastern margin of the Bom Jesus da Lapa Terrane, with the metasedimentary rocks recording forearc, intra-arc, and passive margin deposition. Post-collisional sinistral strike-slip shear zones subsequently generated a pull-apart basin, which favored sediment deposition and the emplacement of the Guanambi Syenite Suite. This study refines the tectonic evolution of the Minas–Bahia Orogenic System and provides new insights into Rhyacian–Orosirian orogenic belts and the early assembly of the Columbia Supercontinent.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107925"},"PeriodicalIF":3.2,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145159009","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":"Authigenic titanite constraints on fast Mesoproterozoic basin formation in hot Antarctic crust","authors":"Naomi Tucker ,&nbsp;Samantha March ,&nbsp;Martin Hand ,&nbsp;Mitchell Bockmann ,&nbsp;Patrick Kolesik","doi":"10.1016/j.precamres.2025.107928","DOIUrl":"10.1016/j.precamres.2025.107928","url":null,"abstract":"<div><div>Geochronological data from detrital zircon, two generations of titanite, and authigenic sericite in glacial erratics transported to the Bunger Hills provide new insights into a deep subglacial basin in East Antarctica. Basin formation occurred during the late Mesoproterozoic, with diagenesis coinciding with granulite facies metamorphism in the underlying basement rocks. In line with previous studies, we interpret this basin to have formed as a rift sequence, but we extend this model by proposing that rifting was directly associated with Mesoproterozoic orogenesis, and that upper crustal extension was coupled with mid–lower-crustal ductile flow. The basin detritus was primarily sourced from a felsic magmatic-rich carapace emplaced at ca. 1180–1160 Ma. The authigenic mineralogy of the erratics, supported by chlorite thermometry and authigenic titanite geochronology, suggests that within the ensuing ca. 50–70 million years, the detritus was buried deeply and subjected to low-grade metamorphism (∼300 °C). Sericite ages complement the zircon and titanite dataset and reveal that the basin was largely unaffected by Cambrian tectonism, meaning that it was situated in thermomechanically stable crust and geographically distant to the major Gondwanan Indo–Australo–Antarctic suture. This study demonstrates the utility of coupled authigenic and detrital mineral geochronology in constraining sedimentary basin formation ages, and linking deep-crustal and near-surface processes.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107928"},"PeriodicalIF":3.2,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145159005","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 role of environmental pressures on stromatolite morphology: Insights from the Ediacaran Salitre Formation, Irecê Basin, Brazil","authors":"Jhon Willy Lopes Afonso ,&nbsp;Carolina Bedoya-Rueda ,&nbsp;Sergio Caetano-Filho ,&nbsp;Cristian Guacaneme ,&nbsp;Guilherme Raffaelli ,&nbsp;Mariane Candido ,&nbsp;Kamilla Borges Amorim ,&nbsp;Gustavo Macedo Paula-Santos ,&nbsp;Marly Babinski ,&nbsp;Ricardo Ivan Ferreira Trindade","doi":"10.1016/j.precamres.2025.107924","DOIUrl":"10.1016/j.precamres.2025.107924","url":null,"abstract":"<div><div>Stromatolites are laminated biosedimentary structures that record long-standing interaction between environmental conditions and coevolving microbial life. Although they are among the oldest and most persistent forms of life on Earth, the extent to which environmental parameters affect their morphology and distribution remains poorly understood. In this study, we investigated the well-exposed stromatolites of the Ediacaran Salitre Formation (Irecê Basin, Brazil) to assess how physical sedimentary processes and early lithification dynamics controlled stromatolite growth and form. Through integrated sedimentological and petrographic analyses, we documented a stratigraphic transition from stratiform to columnar morphologies, which closely correlates with variations in hydrodynamic energy, sediment influx, and local relief. Our results demonstrate that increased hydrodynamic energy and detrital input promoted the development of columnar, often inclined or branched forms, whereas low-energy conditions allowed for the development of stratiform structures, especially within protected scour depressions. The occurrence of inclined, yet unbroken stromatolite columns and their alignment with the paleoflow indicators suggest growth under dynamic, high-energy conditions with weak or incomplete synsedimentary lithification. Despite the high-energy setting, grains are concentrated only within the intercolumnar spaces and are almost absent from the stromatolite laminae, suggesting that lamination resulted primarily from microbial carbonate precipitation rather than sediment trapping. Additionally, the internal lamination patterns and detrital material distribution reflect episodic sedimentation and microbial mat disruption, further emphasizing the sensitivity of stromatolite morphology to environmental changes. Our findings highlight that the stromatolites in the Salitre Formation provide a valuable snapshot of the intricate interplay between physical parameters and biological activity during the terminal Neoproterozoic.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107924"},"PeriodicalIF":3.2,"publicationDate":"2025-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107493","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":"Sedimentology, petrography, and carbon isotopes of the ∼2.2 Ga Randville Dolomite, Upper Peninsula of Michigan","authors":"Garrett D. Brown ,&nbsp;Maya L. Giannecchini ,&nbsp;Cory M. Redman ,&nbsp;Ian Z. Winkelstern ,&nbsp;Dylan T. Wilmeth","doi":"10.1016/j.precamres.2025.107916","DOIUrl":"10.1016/j.precamres.2025.107916","url":null,"abstract":"<div><div>The Lomagundi–Jatuli Event (LJE) was Earth’s longest (2.3–2.0 Ga) and largest (+5 to +30 ‰) positive δ¹³C excursion. The LJE’s exact causes remain uncertain, with various hypotheses involving increased organic carbon burial or restricted depositional facies. While many LJE carbonates have enriched δ¹³C signatures, several locations are closer to average values over Earth history (∼0‰), providing opportunities to test depositional models. For example, the ∼2.2 Ga Randville Dolomite in Michigan’s Upper Peninsula is less enriched in δ¹³C (0 to +3 ‰) compared to the neighboring Kona Dolomite (+5 to +10 ‰). Randville age constraints are broad but fall within the LJE (2.3–2.1 Ga), approximately coeval with Kona deposits (2.17 Ga). The Randville Dolomite contains extensive planar beds with minor scour-fill structures, slumps, and conglomerates, indicating a relatively calm depositional environment punctuated by storms and slope failures on an outer carbonate platform. Randville deposits contain a variety of microbialites including domal, inclined, nodular, and conical stromatolites, and potentially the oldest recorded dendrolites. The most likely explanation for δ¹³C differences between the Randville and Kona Dolomite involves depositional environments. Many enriched Kona deposits represent an evaporitic, marine basin, while Randville facies show little to no evidence for subaerial exposure or evaporation. Facies-dependent patterns between Randville and Kona Dolomites are mirrored in LJE carbonates across the Lake Superior region: formations with evaporites are consistently δ¹³C-enriched compared with other localities. These datasets support previous research indicating that at least during certain intervals, LJE excursions were not ubiquitous in all marine environments.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107916"},"PeriodicalIF":3.2,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107492","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":"Mesoproterozoic Pb loss in the 1.67 Ga Davis Dam Granite, northern Colorado River Extensional Corridor, USA","authors":"Elizabeth A. Bell","doi":"10.1016/j.precamres.2025.107917","DOIUrl":"10.1016/j.precamres.2025.107917","url":null,"abstract":"<div><div>Much of the Proterozoic crust in the Colorado River Extensional Corridor, southwestern USA has been extensively heated during Basin and Range extension. However, most thermochronology has been undertaken on the southern, most extended part of the corridor, with limited results suggesting less intense heating in the northern corridor, such that pre-Cenozoic medium-temperature Pb loss may be preserved in places. This study reports zircon and apatite U-Pb dating in the eastern region of the Paleoproterozoic Davis Dam Granite. This study searched for evidence of post-crystallization Pb loss in a region close to Miocene volcanic intrusions and faulting. Although zircon from three samples have average ages overall similar within error, with an overall average age 1665 ± 30 Ma, a small population of &gt; 1.7 Ga zircon in one sample may be xenocrystic. In all units, some 1.65–1.58 Ga Pb loss is suggested from a tail of younger concordant zircon ages, potentially reflecting metamorphic alteration during the Mazatzal orogeny. Variations among the three samples in zircon discordance behavior, overprinted/altered cathodoluminescence zoning, and the assemblages of secondary minerals filling cracks and void space in the zircon grains suggests geographic variation within the granite in post-crystallization alteration. Apatite have concordant ages ranging 1.7 to 1.2 Ga, with an average age of 1440 ± 132 Ma. The Davis Dam Granite preserves one or more post-Ivanpah and post-Mazatzal metamorphic events in the eastern Mojave province without overprinting by heating during Cenozoic Basin and Range extension in the northern Colorado River Extensional Corridor. Similar studies of older granitoids and their accessory minerals may better elucidate the Mesoproterozoic history of the northern Colorado River Extensional Corridor, its relationship with wider regional Mesoproterozoic tectonism, and the extent of Cenozoic overprinting.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107917"},"PeriodicalIF":3.2,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145050238","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":"Late Neoarchean–Paleoproterozoic granitoid basement serves as an effective helium source rock in cratonic basins","authors":"Wenqi Li ,&nbsp;Huichuan Liu ,&nbsp;Greg Holland ,&nbsp;Zheng Zhou ,&nbsp;Jianfa Chen ,&nbsp;Xiaoping Liu ,&nbsp;Zhiqi Yu ,&nbsp;Jian Li ,&nbsp;Xiaobo Wang","doi":"10.1016/j.precamres.2025.107905","DOIUrl":"10.1016/j.precamres.2025.107905","url":null,"abstract":"<div><div>The growing shortage of helium reserves presents a pressing worldwide concern. However, it remains ambiguous that how, when, and which type of tectonic environment the helium source rocks were formed. Recently, several helium-enriched gas fields have been discovered in the northern Ordos Block and confirmed to be crust-derived. Why late Neoarchean–Paleoproterozoic effective helium source rocks are distributed in the northern Ordos Block are still not clear. Detailed petrological, geochemical, geochronology, Sr-Nd isotopic and in-situ EPMA of U,-Th rich minerals studies were analyzed on the outcrops and drill cores of the basement of the northern Ordos Block to investigate the helium source rocks. The results show that (1) Late Neoarchean–Paleoproterozoic A-type granite and S-type granitoids are effective helium source rock types, and a large amount of U-Th rich accessory minerals (e.g., phosphate minerals, zircon, magnetite et al.) are preserved in alkaline feldspar and quartz. (2) The helium source rocks are classified into distinct temporal intervals: 2.60–2.45 Ga, 2.45–2.30 Ga and 1.95–1.80 Ga, respectively. 2.60–2.45 Ga granitoids exhibit compositional signatures of I-type granites, consistent with magmatic arc tectonic settings linked to subduction zones. 2.45–2.30 Ga granitoids display both A-type and I-type granitic affinities, indicating long live continental magmatic arc environment characteristics.1.95–1.80 Ga granitoids exhibit both A-type and S-type characteristics, suggesting formation in an extensional tectonic regime following continental collision. (3) 2.60–2.45 Ga period is late Archean subduction-accretion and arc magmatism, followed by arc-continent collision; 2.45–2.30 Ga period is a long-time arc-continental accretion process with multiple arc magmatism; 1.95–1.80 Ga period represents continent-continent collision to post-collisional extension setting. Thus, the long-term arc-continental accretion and multistage crustal recycling of terrigenous sediments with high U and Th content, comparable to Phanerozoic subduction-accretionary orogens, explain why effective helium source rocks are enriched in the northern Ordos Block. By the comparison of Khondalite Belts in North China Craton with global Khondalite Belts, global Khondalite belts could be favorable areas for predicting the worldwide distribution of helium source rocks.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107905"},"PeriodicalIF":3.2,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145050237","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":"Temporal and magmatic evolution of the Neoproterozoic ultramafic and mafic Ougda arc complex and associated granitoids (Western Tuareg Shield, Algeria)","authors":"Chaouki Djallel Eddine Bendimerad ,&nbsp;Abderrahmane Bendaoud ,&nbsp;Julien Berger ,&nbsp;Renaud Caby ,&nbsp;Gaston Godard ,&nbsp;Karel Schulmann","doi":"10.1016/j.precamres.2025.107903","DOIUrl":"10.1016/j.precamres.2025.107903","url":null,"abstract":"<div><div>The Ougda area, located within the Tassendjanet terrane of the Western Tuareg Shield, hosts a large (ultra)mafic complex associated with granitoid intrusions. This magmatic complex represents a Neoproterozoic continental arc, active between 749 ± 2 Ma and 653 ± 4 Ma ago; during this time, various ultramafic and mafic (meta)cumulates (serpentinites, hornblendites, garnet amphibolites, amphibolites and leucogabbros) and non-cumulates (amphibole gabbros, quartz diorites, diorites) were emplaced. The latter exhibit a calc-alkaline affinity. Sr-Nd isotope data reveal a distinct contrast between North and South Ougda ultramafic and mafic units. The North Ougda units have a more juvenile signature (<em>ε_Nd</em> = +6.3 to +9.4, <em>ISr</em> = 0.70248–0.70377) than the South Ougda units (<em>ε_Nd</em> = +5.3 to +6.3, <em>ISr</em> = 0.70267–0.70400). Early arc construction is represented by the emplacement of the South Ougda units into a thinned juvenile crust at shallow crustal levels. In contrast, the younger and more juvenile North Ougda units were emplaced at deeper crustal levels, likely at the base of the arc crust.</div><div>Syn-collisional granitoids, dated at 626 ± 5 Ma and 627 ± 4 Ma, intruded the Tassendjanet terrane and show a hybrid juvenile-crustal signature (<em>ε_Nd</em> = +2.68 to −8.04, <em>ISr</em> = 0.70296–0.70743), interpreted as resulting from the partial melting of juvenile basaltic rocks in the lower crust of the Ougda arc, followed by the crustal contamination of primitive magmas. In addition, aplitic dykes crosscutting these granitoids display geochemical characteristics similar to those of the post-collisional granites that sealed the Panafrican orogeny in the Tuareg Shield. The Ougda continental arc complex is believed to have formed during the closure of an oceanic basin, leading to the amalgamation of West Gondwana and ultimately to the Pan-African orogeny observed across the Neoproterozoic NW African provinces.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"430 ","pages":"Article 107903"},"PeriodicalIF":3.2,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145027881","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":"Paired metamorphic belts in the Usagaran Orogen of Tanzania: evidence for one-sided oceanic subduction in the Palaeoproterozoic","authors":"V. Schenk ,&nbsp;T. Sarkar ,&nbsp;D. Wiemer","doi":"10.1016/j.precamres.2025.107891","DOIUrl":"10.1016/j.precamres.2025.107891","url":null,"abstract":"<div><div>Paired metamorphic belts (PMB) are the tectono-metamorphic expression of the one-sided subduction of oceanic lithosphere beneath continental margins and island arcs, which represents a key characteristic of terrestrial plate tectonics. PMB that are spatially and timely paired are mainly known from Phanerozoic orogenic belts, although the metamorphic rock record points to a duality of thermal regimes since the Palaeoproterozoic. Here we describe the tectono-metamorphic evolution of the Usagaran Orogen at the SE-margin of the Tanzania Craton, which includes PMB of Palaeoproterozoic age. The orogen’s lithological inventory reflects a Wilson cycle: (1) The passive margin sequence (Konse Group) was deposited during the Lomagundi carbon isotope excursion (2.22–2.06 Ga) and metamorphosed at 2.03 Ga during the Usagaran orogeny. (2) The precursors of most eclogites were ocean-floor basalts, but those of the Ky- and Opx-eclogites of boninite chemistry were related to subduction-initiation. Peak eclogite metamorphism at mantle depths (850–880 °C/18–19 kbar) was followed by transient granulite-facies conditions during exhumation (750–800 °C/6–10 kbar). High-<em>T-P</em> shear zones in Opx-eclogites and felsic mylonites formed at P &lt; 15 &gt; 10 kbar are related to exhumation. (3) High-P amphibolite-facies metamorphism of metasediments enveloping the eclogite belt (770 °C/13.2 kbar at 2.0 Ga) is attributed to an accretionary wedge setting. The concurrent evolutions and the preserved growth zonations in garnet of both units point to a shared short-lived metamorphism. (4) Low-P Grt-Crd-Sil-granulites, which overlie the accretionary wedge metasediments as a nappe, experienced a counter-clockwise <em>P-T</em> path at ca. 2.06 Ga (peak 820 °C/7.2 kbar) in an arc setting that predates the orogeny for 50–60 Myr. We attribute their protomylonitic texture to post-peak NW-thrusting towards the orogenic foreland during collision. Late-stage <em>P-T</em> paths of all units in the nappe stack (isobaric cooling at 20 km depth) are interrelated. Other Palaeoproterozoic PMB in orogens around the Congo Craton and in the Yangtze Craton, in addition to subduction-related eclogites in the Trans-North China Orogen, indicate that subduction of oceanic lithosphere and its partial exhumation after slab breakoff at mantle depths were already viable tectonic processes. Pre-Neoproterozoic eclogites representing exhumed oceanic crust are dominantly known from a short time interval (2.1–1.8 Ga), during which warm (12–14 °C/km) and cold (&lt;11 °C/km) subduction zones existed, which both show the tectono-metamorphic characteristics akin to modern asymmetric one-sided oceanic subduction.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"429 ","pages":"Article 107891"},"PeriodicalIF":3.2,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020962","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}