Precambrian Research最新文献_第10页

Mesoproterozoic Pb loss in the 1.67 Ga Davis Dam Granite, northern Colorado River Extensional Corridor, USA 美国科罗拉多河伸展走廊北部1.67 Ga Davis坝花岗岩中元古代铅损失

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-11-01 Epub Date: 2025-09-12 DOI: 10.1016/j.precamres.2025.107917

Elizabeth A. Bell

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 > 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.

美国西南部科罗拉多河伸展走廊的大部分元古代地壳在盆地和山脉伸展过程中被广泛加热。然而，大部分的热年代学研究都集中在走廊的南部和最延伸的部分，有限的结果表明北部走廊的加热强度较小，因此可能在某些地方保留了前新生代的中温Pb损失。本文报道了古元古代戴维斯坝花岗岩东部地区的锆石和磷灰石U-Pb定年。本研究在靠近中新世火山侵入和断裂的地区寻找结晶后铅损失的证据。虽然3个样品的锆石平均年龄总体上在误差范围内相似，总体平均年龄为1665±30 Ma，但其中一个样品中的少量>； 1.7 Ga锆石可能是异晶锆石。在所有单元中，较年轻的和谐锆石的尾巴显示了1.65-1.58 Ga的Pb损失，可能反映了马扎扎造山运动期间的变质蚀变。3个样品在锆石不一致行为、叠印/蚀变阴极发光分带以及锆石颗粒中充填裂隙和空隙的次生矿物组合等方面的差异表明，花岗岩在结晶后蚀变过程中存在地理差异。磷灰石年龄在1.7 ~ 1.2 Ga之间，平均年龄为1440±132 Ma。戴维斯大坝花岗岩保存了莫哈韦省东部的一个或多个后伊凡帕和后马扎扎尔变质事件，没有在科罗拉多河北部伸展走廊的新生代盆地和山脉扩展期间被加热覆盖。对古花岗岩类及其附属矿物的类似研究可以更好地阐明北科罗拉多河伸展走廊的中元古代历史、与更广泛的区域中元古代构造的关系以及新生代复盖作用的程度。

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引用次数: 0

Sedimentology, petrography, and carbon isotopes of the ∼2.2 Ga Randville Dolomite, Upper Peninsula of Michigan 密歇根上半岛~ 2.2 Ga Randville白云岩的沉积学、岩石学和碳同位素

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-11-01 Epub Date: 2025-09-16 DOI: 10.1016/j.precamres.2025.107916

Garrett D. Brown , Maya L. Giannecchini , Cory M. Redman , Ian Z. Winkelstern , Dylan T. Wilmeth

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.

Lomagundi-Jatuli事件（LJE）是地球上最长（2.3 ~ 2.0 Ga）和最大（+5 ~ +30‰）的正δ13C偏移。LJE的确切原因仍然不确定，有各种各样的假设，包括增加有机碳埋藏或限制沉积相。虽然许多LJE碳酸盐岩具有丰富的δ13C特征，但有几个位置更接近地球历史上的平均值（~ 0‰），为测试沉积模型提供了机会。例如，密歇根州上半岛的~ 2.2 Ga Randville白云岩的δ13C含量（0 ~ +3‰）低于邻近的Kona白云岩（+5 ~ +10‰）。Randville年龄限制较宽，但落在LJE （2.3-2.1 Ga）范围内，与Kona矿床（2.17 Ga）大致相同。Randville白云岩包含广泛的平面层，具有较小的冲冲充填结构，滑坡和砾岩，表明在外部碳酸盐台地上，相对平静的沉积环境被风暴和斜坡破坏所打断。Randville矿床包含各种微生物岩，包括穹状、斜状、结节状和锥形叠层石，以及可能记录的最古老的树突岩。兰德维尔白云岩和科纳白云岩之间δ13C差异最可能的解释与沉积环境有关。许多富集的Kona矿床代表了一个蒸发海相盆地，而Randville相几乎没有证据表明地面暴露或蒸发。Randville和Kona白云岩之间的相依赖模式反映在整个苏必利尔湖地区的LJE碳酸盐岩中：与其他地区相比，具有蒸发岩的地层始终富含δ 13c。这些数据集支持了先前的研究，表明至少在某些时间间隔内，LJE的漂移在所有海洋环境中并不普遍。

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引用次数: 0

The role of environmental pressures on stromatolite morphology: Insights from the Ediacaran Salitre Formation, Irecê Basin, Brazil 环境压力对叠层石形态的影响：来自巴西Irecê盆地埃迪卡拉纪盐层组的启示

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-11-01 Epub Date: 2025-09-20 DOI: 10.1016/j.precamres.2025.107924

Jhon Willy Lopes Afonso , Carolina Bedoya-Rueda , Sergio Caetano-Filho , Cristian Guacaneme , Guilherme Raffaelli , Mariane Candido , Kamilla Borges Amorim , Gustavo Macedo Paula-Santos , Marly Babinski , Ricardo Ivan Ferreira Trindade

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.

叠层石是层状生物沉积结构，记录了环境条件和共同进化的微生物生命之间长期的相互作用。虽然它们是地球上最古老和最持久的生命形式之一，但环境参数对其形态和分布的影响程度仍然知之甚少。本研究以巴西Irecê盆地埃迪卡拉系盐层组的叠层石为研究对象，探讨了物理沉积过程和早期岩化动力学如何控制叠层石的生长和形成。通过综合沉积学和岩石学分析，我们记录了地层形态从层状到柱状的转变，这与水动力能、沉积物流入和局部起伏的变化密切相关。我们的研究结果表明，增加的水动力能量和碎屑输入促进了柱状结构的发展，通常是倾斜或分支形式，而低能量条件允许层状结构的发展，特别是在受保护的冲刷洼地内。斜而完整的叠层石柱的出现及其与古流动指示物的排列表明，叠层石是在动态、高能条件下生长的，同沉积岩化作用弱或不完全。尽管处于高能量环境，但颗粒只集中在柱间空间内，叠层石层叠层中几乎没有颗粒，这表明层叠主要是由微生物碳酸盐沉淀而不是沉积物捕获造成的。此外，叠层石内部的层压模式和碎屑物质分布反映了幕式沉积和微生物席破坏，进一步强调了叠层石形态对环境变化的敏感性。我们的研究结果强调，盐层组的叠层石为新元古代末期物理参数与生物活动之间复杂的相互作用提供了有价值的快照。

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引用次数: 0

Dynamics of Marinoan-age glaciers in NW Tarim, China 塔里木盆地西北部马里诺世冰川动力学

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-11-01 Epub Date: 2025-09-26 DOI: 10.1016/j.precamres.2025.107933

Xiaoshuai Chen , Hongwei Kuang , Yongqing Liu , Daniel Paul Le Heron , Yuchong Wang , Nan Peng , Mingming Cui , Kening Qi

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.

冰川是通过侵蚀和沉积过程塑造低温期景观的关键因素。冰下侵蚀形式是冰川动力学和热状态的重要档案，为古环境解释和古地理重建提供了见解。全球有7个克拉通保存着冰冻期冰下侵蚀形态，中国塔里木克拉通西北部的阿克苏-乌什地区就是一个很好的例子。一系列保存完好的冰下成因侵蚀特征显露出来，迄今为止还没有得到系统的描述和解释。本文对这一问题进行了解决，并对8个地点进行了详细调查，使人们对阻碍低温期冰川动力学研究的问题有了更深入的了解。在阿克苏-乌什地区，条痕、沟槽、p形、岩洞和冰川撕裂形态证明了冰-基岩界面的磨损和融水作用。确定了一个西南方向的冰流，并逐渐向南偏转。研究记录的冰下侵蚀形态和上覆沉积序列共同揭示了Yuermeinak组从冰下-冰前-冰后海侵的沉积环境演化，形成了完整的大陆冰盖进退过程记录。马里诺冰川的动力模式和热状态进一步为古地理重建提供了关键的约束条件。塔里木的Yuermeinak组和澳大利亚的Walsh组一致的冰流方向和沉积演化表明塔里木在冰川期可能与澳大利亚相邻。阿克苏-乌什地区的冰下侵蚀形态和条纹碎屑显示了雪球地球事件后期的温带冰川热环境，与中低纬度古地理环境相适应。大块含砾石的砂岩和粉砂岩，其落石介于基底二晶岩和上覆埃迪卡拉盖帽白云岩之间，代表了温带冰川末期大规模的化学风化作用。因此，古冰川学可以在深时古地理重建中发挥重要作用。

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引用次数: 0

Rhyacian (2218–2066 Ma) subduction-related volcanosedimentary accretion in the Western Bahia Orogenic Domain (São Francisco Craton, Brazil), and tectonic implications 西巴伊亚造山带（巴西<s:1>奥弗朗西斯科克拉通）的Rhyacian （2218-2066 Ma）俯冲相关火山-沉积增生及其构造意义

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-11-01 Epub Date: 2025-09-26 DOI: 10.1016/j.precamres.2025.107925

Michel Macedo Meira , Simone Cerqueira Pereira Cruz , Elson Paiva Oliveira , Joseneusa Brilhante Rodrigues , Angela Beatriz de Menezes Leal , Cristiano Lana

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.

来自西北弗朗西斯科克拉通的新证据揭示了米纳斯-巴伊亚造山带的古元古代构造演化。boqueir o de Baixo组和Chapada Grande组两个变质火山-沉积层序记录了一个流纹造山系的阶段，通过综合地层、岩石学、地球化学、年代学和同位素数据进行了表征。boqueir o de Baixo组变质火山岩主要为细粒拉斑闪长岩，锆石ƐHf(t)值为+3.78 ~ + 5.6，在2218±18 Ma结晶，在2020±7 Ma变质。查帕达大组由变质沉积岩和钙碱性-超经典基性-中变质火山岩组成，结晶年龄在2096±20 Ma ~ 2066±6 Ma之间，演化的同位素特征为ƐHf(t)−18.5 ~−8.84。这些地层发育于Bom Jesus da Lapa地体东部边缘的大陆弧环境中，其变质沉积岩记录了弧前、弧内和被动边缘沉积。碰撞后的左旋走滑剪切带形成了拉分盆地，有利于沉积和瓜南壁正长岩套的侵位。该研究细化了米纳斯-巴伊亚造山系的构造演化，为研究流-奥造山带和哥伦比亚超大陆的早期组装提供了新的认识。

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引用次数: 0

Temporal and magmatic evolution of the Neoproterozoic ultramafic and mafic Ougda arc complex and associated granitoids (Western Tuareg Shield, Algeria) 阿尔及利亚西图阿雷格地盾新元古代超基性和基性奥格达弧杂岩及其花岗岩类的时间和岩浆演化

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-11-01 Epub Date: 2025-09-10 DOI: 10.1016/j.precamres.2025.107903

Chaouki Djallel Eddine Bendimerad , Abderrahmane Bendaoud , Julien Berger , Renaud Caby , Gaston Godard , Karel Schulmann

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 (ε_Nd = +6.3 to +9.4, ISr = 0.70248–0.70377) than the South Ougda units (ε_Nd = +5.3 to +6.3, ISr = 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.

Syn-collisional granitoids, dated at 626 ± 5 Ma and 627 ± 4 Ma, intruded the Tassendjanet terrane and show a hybrid juvenile-crustal signature (ε_Nd = +2.68 to −8.04, ISr = 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.

奥格达地区位于西图阿雷格地盾的塔森珍妮特地块内，拥有一个与花岗岩类侵入有关的大型（超）基性复杂岩体。该岩浆杂岩为新元古代大陆弧，活动时间为749±2 Ma ~ 653±4 Ma；在此期间，各种超镁铁质和基性（变）堆积物（蛇纹岩、角闪岩、石榴石角闪岩、角闪岩和浅辉长岩）和非堆积物（角闪岩、石英闪长岩、闪长岩）被侵位。后者表现出钙碱性亲和力。Sr-Nd同位素数据揭示了南北奥格达超镁铁和基性单元的明显对比。北奥格达单元（εNd = +6.3 ~ +9.4, ISr = 0.70248 ~ 0.70377）比南奥格达单元（εNd = +5.3 ~ +6.3, ISr = 0.70267 ~ 0.70400）具有更明显的幼化特征。早期弧的构造表现为南奥格达单元在地壳浅层进入一个变薄的幼年地壳。相比之下，更年轻和更年轻的北奥格达单元位于更深的地壳水平，可能在弧壳的底部。同碰撞花岗岩类（626±5 Ma和627±4 Ma）侵入Tassendjanet地体，表现出幼体-地壳混合特征（εNd = +2.68 ~−8.04,ISr = 0.70296 ~ 0.70743），解释为奥格达弧下地壳幼体玄武岩部分熔融，然后是原始岩浆的地壳污染。此外，横切这些花岗岩的胶结脉显示出与图阿雷格地盾中封闭泛非造山作用的碰撞后花岗岩相似的地球化学特征。奥格达大陆弧复合体被认为是在一个海洋盆地闭合期间形成的，导致了西冈瓦纳的合并，并最终形成了横跨新元古代西北非洲省的泛非造山运动。

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引用次数: 0

U–Pb zircon geochronology and geochemistry of Um Genud layered mafic intrusion in the northern tip of the Arabian-nubian shield: implications for the genesis of the plutonic crust of neoproterozoic immature intra-oceanic arc 阿拉伯-努比亚盾北端Um Genud层状基性侵入体的U-Pb锆石年代学和地球化学：对新元古代未成熟洋内弧深部地壳成因的启示

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-10-01 Epub Date: 2025-09-05 DOI: 10.1016/j.precamres.2025.107915

Tarek H. Abu El-Kheir , Keda Cai , Ayman E. Maurice , Kai Wang , Hairuo Wang , Maher Dawoud

The Um Genud Neoproterozoic layered mafic intrusion, located in the South Eastern Desert of Egypt, represents the northwestern tip of the juvenile crust of the Arabian-Nubian Shield (ANS). This intrusion is composed of olivine gabbro, gabbro, noritic-gabbro and hornblende gabbro. Zircon U–Pb data constrain the emplacement age of the intrusion to 718 Ma, coinciding with the island arc stages of the ANS. The trace element patterns of pyroxenes, amphiboles, whole-rock samples and calculated melts in equilibrium with clinopyroxene and amphibole show marked Nb-Ta and Zr-Hf troughs and prominent peak of Pb. These features, along with the trace element abundances and ratios in zircon, suggest that the parental magma was generated in an intra-oceanic island arc setting from a depleted mantle source metasomatized by subducted slab-derived aqueous fluids. Textural features, mineral compositions of olivine, pyroxene and plagioclase, whole-rock geochemical characteristics, the calculated ƒO₂ values (FMQ + 1 – FMQ + 1.6), and the estimated water content (5.9 – 9.1 wt%) of melt indicate that the Um Genud gabbroic rocks represent cumulates differentiated from oxidized hydrous low-K tholeiitic magma, essentially by fractional crystallization. The estimated pressure of crystallization (∼3 to ∼ 3.5 kbar; ∼10 km depth), the low-K tholeiitic nature of parental magma and the relative abundance of the exposed gabbroic and granitic arc rocks in the study area are consistent with intrusion emplacement within the lower crust of an immature oceanic arc. This implies that even arcs with thin crust can develop considerable plutonic layers and contribute to continental crust growth through vertical accretion.

位于埃及沙漠东南部的Um Genud新元古代层状基性侵入岩，代表了阿拉伯-努比亚盾（ANS）幼壳的西北端。该侵入岩由橄榄辉长岩、辉长岩、北辉长岩和角闪辉长岩组成。锆石U-Pb资料限定了该岩体的侵位年龄为718 Ma，与ANS的岛弧阶段一致，辉石、角闪石、整岩样品以及与斜辉石和角闪孔平衡的计算熔体微量元素模式显示出明显的Nb-Ta和Zr-Hf槽，Pb峰明显。这些特征以及锆石中微量元素的丰度和比值表明，母岩浆是在洋内岛弧背景下由俯冲板源水交代的衰竭地幔源形成的。构造特征、橄榄石、辉石和斜长石矿物组成、全岩地球化学特征、熔体ƒO2值（FMQ + 1 ~ FMQ + 1.6）计算和熔体含水量（5.9 ~ 9.1 wt%）估算表明，Um Genud辉长岩主要是由氧化含水低钾拉斑岩浆分异而成。估计结晶压力（~ 3 ~ ~ 3.5 kbar； ~ 10 km深度）、母岩浆的低钾拉斑性质以及研究区内暴露的辉长岩和花岗质弧岩的相对丰度与未成熟洋弧下地壳的侵入侵位一致。这意味着即使是地壳薄的弧也可以发育相当大的深成层，并通过垂直增生促进大陆地壳的增长。

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引用次数: 0

Kilometer-scale hook-shaped Type2/Type3 folds due to refolding and transpressional strike-slip reversal in the Egyptian Nubian Shield, east African orogenic belt 东非造山带埃及-努比亚盾逆转走滑作用下的千米尺度钩状2/ 3型褶皱

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-10-01 Epub Date: 2025-09-05 DOI: 10.1016/j.precamres.2025.107912

Mohamed A. Abd El‑Wahed , Ahmed M. Eldosouky , Osama M.K. Kassem , Ahmed Abdelhady Abo-Rayan , Mohamed Attia

This study combines remote sensing, aeromagnetic data, and field investigations to provide the initial identification of hook-shaped Type 2/Type 3 folds within the Egyptian Nubian Shield. The Western Allaqi shear belt (WASB) exhibits remarkable refolded structures that are distinctly observable from space. This belt primarily comprises ophiolite slices, metavolcanics, and volcanoclastic metasediments, which have been intruded by syn- (729–635 Ma) and post-tectonic granites (610–543 Ma). The WASB region experienced significant compression during the N-S shortening (830–720 Ma), leading to the formation of east–west oriented folds and foliation and N-dipping thrust imbrications. The interference patterns of the folds predominantly display Type 2 and Type 3 refolds characterized by wavelengths on the order of kilometers. The geological observation reveals a complex history of deformation, with refolded folds linked to dextral shear zones, ductile and brittle fabrics, and opposing movement directions. The fold interference structures were formed through the reactivation of NW-trending sinistral strike-slip shear zones, combined with shear-related folding of the initial F₁ folds, and NE-SE compression (625–565 Ma). The subsequent development of NW-trending Haseierbah folds (F₂) was accompanied by a shift in stress orientation from NE-SW to E-W (620–580), resulting in a reversal of shear sense and the reactivation of NW-trending shear zones into dextral strike-slip shear zones, which in turn formed the N-trending El-Quleib fold (F₃) and the NE-trending Haimur and Shilman folds (F₄). This reversal in shear sense contributes to the formation of Type 2 and Type 3 fold interference patterns and the distinctive hook-shaped fold structures observed within the WASB. This study provides a detailed description of refolding and transpressional strike-slip reversal in the WASB, highlighting the innovative tectonic evolution and urging a reassessment of the entire Allaqi-Heinai suture and the major shear zones in the Egyptian Nubian Shield.

该研究结合了遥感、航磁数据和实地调查，初步确定了埃及努比亚盾内的2/ 3型钩形褶皱。西阿拉奇剪切带（WASB）表现出非凡的折叠式结构，从太空中可以清楚地观察到。该带主要由蛇绿岩片、变质火山和火山碎屑沉积组成，曾被syn- (729-635 Ma)和后构造花岗岩（610-543 Ma）侵入。830 ~ 720ma南北向缩短期，WASB区域经历了明显的挤压作用，形成了东西向的褶皱、片理和向n倾斜的逆冲叠瓦构造。褶皱的干涉图案主要显示波长在千米量级的2型和3型折痕。地质观测揭示了一个复杂的变形历史，与右旋剪切带、韧性和脆性织物以及相反的运动方向有关的再折叠褶皱。褶皱干涉构造是由北西向左旋走滑剪切带的重新激活、F1初始褶皱的剪切相关褶皱和NE-SE挤压作用（625 ~ 565 Ma）共同形成的。随着北西向Haseierbah褶皱（F2）的发育，应力方向由NE-SW向E-W转变（620-580），导致剪切意义逆转，北西向剪切带重新活化为右旋走滑剪切带，进而形成n向El-Quleib褶皱（F3）和ne向Haimur和Shilman褶皱（F4）。这种剪切意义上的反转有助于形成2型和3型褶皱干涉模式，并在WASB内观察到独特的钩状褶皱结构。该研究详细描述了WASB的折叠式走滑反转和转压式走滑反转，强调了构造演化的创新性，并敦促对整个Allaqi-Heinai缝合带和埃及努比亚盾的主要剪切带进行重新评估。

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引用次数: 0

Paired metamorphic belts in the Usagaran Orogen of Tanzania: evidence for one-sided oceanic subduction in the Palaeoproterozoic 坦桑尼亚乌萨加兰造山带的成对变质带：古元古代单侧大洋俯冲的证据

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-10-01 Epub Date: 2025-09-09 DOI: 10.1016/j.precamres.2025.107891

V. Schenk , T. Sarkar , D. Wiemer

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-T-P shear zones in Opx-eclogites and felsic mylonites formed at P < 15 > 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 P-T 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 P-T 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 (<11 °C/km) subduction zones existed, which both show the tectono-metamorphic characteristics akin to modern asymmetric one-sided oceanic subduction.

对变质带（PMB）是大洋岩石圈在大陆边缘和岛弧下单向俯冲的构造变质表现，是陆地板块构造的一个重要特征。虽然变质岩记录显示了古元古代以来的二元热机制，但在空间和时间上配对的PMB主要来自显生宙造山带。本文描述了坦桑尼亚克拉通东南缘Usagaran造山带的构造变质演化，其中包括古元古代的PMB。(1)被动边缘层序（Konse群）在Lomagundi碳同位素漂移时期（2.22 ~ 2.06 Ga）沉积，在Usagaran造山带2.03 Ga变质。(2)大部分榴辉岩的前体为海底玄武岩，而宝钢化学的Ky-和opx -榴辉岩的前体则与俯冲起生有关。在地幔深度（850-880°C/ 18-19 kbar）的榴辉岩变质作用达到峰值，随后是挖掘过程中（750-800°C/ 6-10 kbar）的瞬态麻粒岩相条件。在P <； 15 >； 10 kbar形成的opx榴辉岩和长英质糜棱岩的高t -P剪切带与发掘有关。(3)包裹榴辉岩带的变质沉积物（770℃/13.2 kbar, 2.0 Ga）的高磷角闪岩相变质作用属于楔形增生环境。这两个单位在石榴石中的同步演化和保存下来的生长带表明它们共同经历了短暂的变质作用。(4)低磷grt - crd - si -麻粒岩在约2.06 Ga（峰值820°C/7.2 kbar）的弧形环境中经历了逆时针P-T路径，早于50-60 Myr的造山运动。其原糜棱岩结构是碰撞过程中造山前陆向北西逆冲的峰后构造。推覆层各单元的后期P-T路径（20 km深度等压冷却）是相互关联的。刚果克拉通和扬子克拉通周围造山带的其他古元古代PMB，以及跨华北造山带中与俯冲有关的榴辉岩，表明大洋岩石圈的俯冲及其在地幔深处板块断裂后的部分掘出已经是可行的构造过程。前新元古代榴辉岩主要是在短时间间隔（2.1 ~ 1.8 Ga）内发现的，在此期间存在温暖（12 ~ 14℃/km）和寒冷（<11℃/km）的俯冲带，具有类似于现代不对称单边海洋俯冲的构造变质特征。

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引用次数: 0

Late Mesoproterozoic mafic magmatism in the southwestern Yangtze Block and its implications for reconstructing the Rodinia supercontinent 扬子地块西南晚中元古代基性岩浆活动及其对罗迪尼亚超大陆重建的意义

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research

Pub Date : 2025-10-01 Epub Date: 2025-09-09 DOI: 10.1016/j.precamres.2025.107904

Dongxue Li , Mingguo Zhai , Lu Xiang , Hailong He , Junping Liu , Hanlin Chen

Late Mesoproterozoic igneous rocks are traditionally considered a key hallmark of the Grenvillian Orogeny and have been widely utilized in reconstructing the Rodinia supercontinent. Despite increasing attention to Late Mesoproterozoic magmatism in the southwestern Yangtze Block, the tectonic evolution of this region during that time still remains unresolved, leading to ongoing debate regarding the role of the Yangtze Block in Rodinia assembly. Here, we report two suites of ca. 1085 Ma mafic rocks from the Dongchuan area in the SW Yangtze Block to investigate their petrogenesis and assess their implications for reconstructing the Yangtze Block in the Rodinia supercontinent. The studied mafic rocks are characterized by high TiO₂ content (1.49–4.49 wt%) and low Mg^# values (22–56), exhibiting slight enrichment in light rare earth elements, with (La/Yb)_N ratios ranging from 1.65 to 5.24, and displaying trace element patterns analogous to E-MORB, without significant Nb-Ta or Zr-Hf anomalies. Their zircon ε_Hf(t) and whole-rock ε_Nd(t) values range from 1.9 to 9.4 and 0.7 to 4.9, respectively, indicating that their primary magmas were derived from the partial melting of a depleted mantle source. In contrast, their zircon δ¹⁸O values vary from 5.50 ± 0.29 ‰ to 6.78 ± 0.39 ‰, likely reflecting the involvement of subducted oceanic mafic crust in the magma source. Moreover, their geochemical characteristics, such as high Zr/Y ratios and elevated Ti concentrations, are consistent with formation in an intra-continental rifting environment. Integrated with the presence of other 1.2–1.0 Ga intraplate magmatism in the SW Yangtze Block, we propose that the block most possibly remained an independent landmass during 1.2–1.1 Ga and began drifting toward Rodinia between 1.1 and 1.0 Ga, ultimately positioning itself on the periphery rather than at the core of the supercontinent.

中元古代晚期火成岩被认为是格林尼治造山运动的重要标志，并被广泛用于重建罗丁尼亚超大陆。尽管人们对扬子地块西南部晚中元古代岩浆活动的关注越来越多，但该地区在这一时期的构造演化仍未得到解决，因此关于扬子地块在Rodinia组合中的作用的争论仍在继续。本文报道了西南扬子地块东川地区两套约1085 Ma的基性岩，探讨了它们的成因，并评价了它们对Rodinia超大陆扬子地块重建的意义。研究的基性岩石具有TiO2含量高（1.49 ~ 4.49 wt%）、Mg#值低（22 ~ 56）的特征，轻稀土元素轻度富集，（La/Yb）N比值在1.65 ~ 5.24之间，微量元素模式与E-MORB相似，Nb-Ta和Zr-Hf无明显异常。锆石εHf(t)和全岩εNd(t)值分别在1.9 ~ 9.4和0.7 ~ 4.9之间，表明其原生岩浆来源于衰竭地幔源的部分熔融作用。锆石δ18O值变化范围为5.50±0.29‰~ 6.78±0.39‰，可能反映了洋基俯冲地壳参与岩浆源作用。高Zr/Y比值、高Ti浓度等地球化学特征与陆内裂陷环境相一致。结合扬子地块西南段1.2 ~ 1.0 Ga板块内岩浆活动的存在，我们认为该地块在1.2 ~ 1.1 Ga期间很可能是一个独立的陆块，并在1.1 ~ 1.0 Ga之间开始向Rodinia漂移，最终定位于超大陆的外围而非核心。

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