Ji-Lei Li

Subduction advance or retreat results in an erosional or accretional plate boundary, and strong orogen‐parallel heterogeneity in large suture zones, but their identification of these processes is challenging. Blueschist is a proxy that can archive these tectonic processes in ancient subduction zones. Within NW Türkiye, the Tavşanlı zone preserves blueschist‐facies rocks, and documents a succession of subduction events that preceded the closure of the Neo‐Tethys Ocean. Here, we report for the first time the occurrence of Triassic blueschist blocks within the Late Cretaceous Tavşanlı zone. These blueschists and marbles have abundant HP minerals such as winchite, jadeite, and lawsonite, and yield zircon U‐Pb age at ca. 228 Ma, resembling the Karakaya HP metamorphic rocks of the overlying Eurasian plate. The available block‐matrix relationships record strong later deformation, but do not preserve the diagnostic textures required to determine whether the Triassic rocks were incorporated into the younger complex by tectonic or sedimentary processes. Regionally, the extensive low‐angle geometry of the İzmir‐Ankara‐Erzincan suture, the scarcity of Jurassic‐Early Cretaceous arc and ophiolitic remnants, the landward migration of the magmatic arc front, and provenance links between the Tavşanlı and Sakarya zones, are compatible with significant forearc removal during Neo‐Tethys evolution. In this context, the Triassic HP rocks may have been either redeposited into trench‐fill deposits and resubducted, or tectonically entrained along the erosive plate interface and accreted downdip. These results highlight the importance of multi‐stage tectonic reworking in assembling age‐disparate HP terranes along the Tethyan suture system.

Sulfur is a key volatile that influences Earth's redox state, climate, and deep geochemical cycles. Subduction zones are the primary pathways carrying sulfur from the surface into the mantle, yet the global sulfur budget and recycling efficiency remain uncertain. Here, we compile a trench-by-trench inventory of subducting sulfur using sediment compositions from ocean drilling programs collected near major trenches, integrated with spatially resolved estimates of oceanic crustal and serpentinite thicknesses derived from seismic data. Our results reveal pronounced spatial heterogeneity in sulfur fluxes, driven by large variations in sedimentary sulfur contents and fundamental tectonic differences between erosive and accretionary margins. Slab-to-arc sulfur recycling efficiency averages 37% globally but varies markedly among individual subduction systems. Despite this heterogeneity, the global sulfur cycle appears balanced on the modern Earth: Sulfur input into the mantle via slab subduction (57 ± 3 Mt y^-1) is matched within uncertainty by mantle output (~60 ± 14 Mt y^-1) through mid-ocean ridges, volcanic arcs, and intraplate magmatism. This balance suggests that Earth's deep sulfur cycle operates in a steady state today. Sulfur isotopes reveal a systematic decoupling, with subducted sulfur carrying negative δ³⁴S values, whereas arc sulfur output is consistently positive. The strong spatial variability in sulfur inputs and recycling efficiency underscores the individuality of Earth's subduction zones, but the balanced input-output fluxes highlight its capacity for self-regulation. These findings have important implications for atmospheric chemistry, surface environments, and the long-term evolution of the deep Earth's sulfur cycle.

俯冲带作为地球最大的物质循环系统,通过板块俯冲将地表物质/元素输送至深部地幔,同时通过熔流体迁移、火山/地幔柱作用等将深俯冲物质/元素重新循环回地表,深刻影响地球多圈层物质循环、岩浆活动、成矿作用及宜居性演化。本文系统综述了俯冲带挥发分(H₂O、C、S、N、卤素)、主量元素(Si、Ca、Mg、P)、微量元素(LILE、REE、HFSE)、金属元素(Cu、Au、Os、Mo、W)及轻元素(Li、Be、B)的循环规律,具体如下:H₂O通过含水矿物俯冲脱水引发弧岩浆作用,部分进入地幔过渡带甚至核幔边界,调控地幔熔融与火山活动;碳循环以多机制协同为特征,岛弧火山CO₂释放仅占板片脱碳量的40%~70%,未释放碳通过深俯冲形成金刚石或地幔柱重返地表,构成跨圈层闭环;硫循环受流体氧化还原状态控制,冷俯冲以还原性流体(HS^-、H₂S)主导,热俯冲可能释放SO^2-₄,硫海沟输入通量显著高于岛弧输出,循环效率不足10%;氮循环受载体矿物(如云母)稳定性与氧逸度调控,俯冲板片-岛弧循环效率低于50%;卤素中Cl、Br优先进入流体,而F滞留固相,反映流体-矿物分配差异。主微量元素迁移受流体类型与矿物残留制约:富水流体迁移LILE,超临界流体可携带HFSE及HREE,高效迁移这些传统不活动性元素。金属元素中Cu、Au通过硫络合物迁移,Os同位素揭示地壳物质再循环,Mo-W同位素分馏为示踪板片熔/流体氧化还原提供新工具。轻元素循环中Li同位素动力学分馏、¹⁰Be示踪年轻沉积物俯冲、B同位素分馏均揭示流体-岩石相互作用特征。此外,还整合了天然样品解析、高温高压实验、同位素示踪及数值模拟等多学科成果,阐述了俯冲带元素循环的综合框架。最后,本文提出俯冲带元素循环研究未来需聚焦超临界流体性质识别、挥发分资源-环境效应、地球物理成像技术创新及深时循环与宜居性关联,通过多学科交叉深化俯冲带元素循环理论,为全球物质通量评估与行星宜居性研究提供基础支撑。

俯冲带是全球最大的物质循环系统,控制着壳幔相互作用、岛弧岩浆作用、成矿物质聚集和全球元素循环等诸多重要的地质过程。俯冲带流体作为板片向上覆地幔楔进行物质传输的重要媒介,在上述地质过程中扮演着关键角色。基于岛弧火山岩地球化学特征、高温高压实验、相平衡模拟,以及高压-超高压变质岩的研究,我们对俯冲带流体基本特征及其地球化学行为已经有了较为深刻的认识,然而,目前对俯冲带流体作用的复杂性,如多期流体作用,还缺少深入的理解。本文对西南天山高压-超高压变质带榴辉岩中一条含石英-绿帘石-铁白云石-硫化物的高压脉开展了详细的岩石学、地球化学研究。脉体中有绿辉石、铁白云石、金红石等特征高压矿物的产出,暗示其代表的流体作用发生于高压条件下。脉体与主岩榴辉岩界线截然,之间无蚀变带/过渡带/交代晕产出,说明主岩榴辉岩与迁移流体之间没有发生显著的水-岩交换反应。脉体矿物(如绿帘石、铁白云石、黄铁矿等)的多期生长特征及其成分差异研究揭示出至少三期流体作用。前两期流体作用均发生于高压条件下,特征如下:(1)两期流体分别以两期矿物组合(Ep¹-Dol¹-Py¹组合以及Ep²-Dol²-Py²组合)为代表,在第二期流体作用下,第一期流体沉淀的矿物(如Dol¹等)发生了明显的溶解-再沉淀作用;(2)两期流体性质均以富Ca、Si,含CO₂、S为特征,第一期流体较第二期流体富Fe贫Mg,富Ni贫Co,富轻稀土元素(LREE);(3)两期黄铁矿的δ³⁴S值分别为-8‰和-5‰,暗示这两期流体均主要来源于俯冲沉积物,且第二期流体可能有更多俯冲洋壳或蛇纹岩脱水流体的参与;(4)两期流体作用下,碳酸盐矿物和硫化物显示出耦合共生的特点,暗示C、S在流体作用下可能具有协同演化(如溶解-迁移-沉淀)的关系。第三期流体作用以绿帘石+铁白云石反应生成方解石+绿泥石、绿帘石边部(与黄铁矿相邻处)发生成分改造为特征,流体作用发生在高压岩石折返的退变质阶段,记录了退变质流体的信息。本研究通过榴辉岩高压脉体中多期矿物生长的特征,揭示了俯冲带内多期流体作用,对深入理解俯冲带流体性质、流体来源、以及俯冲带关键挥发分元素的耦合演化信息,具有重要的科学意义。

Carbon release during continental rifting is thought to regulate atmospheric CO₂ levels. Supercontinent dispersal‐induced extensional tectonics is similar during the Late Ediacaran and Jurassic, while they exhibit different increases in atmospheric CO₂ concentration. The underlying mechanism of distinct CO₂ emissions remains to be understood. Here, we conduct petrological‐thermomechanical modeling to show that metamorphic decarbonation and melting of carbonates that are derived from subducted sediments are ubiquitous during continental extension. We find that the hotter lithosphere and deeper storage of these carbonates cause more significant amounts of rift‐related CO₂ release through volcanoes and faults. They may cause ∼12%–77% larger decarbonation efficiency, providing an efficient driving mechanism for a ∼31% larger increase in atmospheric CO₂ levels during the Late Ediacaran than throughout the Jurassic. The rapid eruption and deposition of recycled carbonatite volcanic ash may contribute to the production of Late Ediacaran marine carbonates with the largest negative δ¹³C (−12‰).

Metamorphic devolatilization of subducted slabs generates aqueous fluids that ascend into the mantle wedge, driving the partial melting that produces arc magmas. These magmas have oxygen fugacities some 10–1,000 times higher than magmas generated at mid-ocean ridges. Whether this oxidized magmatic character is imparted by slab fluids or is acquired during ascent and interaction with the surrounding mantle or crust is debated. Here we study the petrology of metasedimentary rocks from two Tertiary Aegean subduction complexes in combination with reactive transport modelling to investigate the oxidative potential of the sedimentary rocks that cover slabs. We find that the metasedimentary rocks preserve evidence for fluid-mediated redox reactions and could be highly oxidized. Furthermore, the modelling demonstrates that layers of these oxidized rocks less than about 200 m thick have the capacity to oxidize the ascending slab dehydration flux via redox reactions that remove H₂, CH₄and/or H₂S from the fluids. These fluids can then oxidize the overlying mantle wedge at rates comparable to arc magma generation rates, primarily via reactions involving sulfur species. Oxidized metasedimentary rocks need not generate large amounts of fluid themselves but could instead oxidize slab dehydration fluids ascending through them. Proposed Phanerozoic increases in arc magma oxygen fugacity may reflect the recycling of oxidative weathering products following Neoproterozoic–Palaeozoic marine and atmospheric oxygenation.

Accretionary complexes are a major component of the Central Asian Orogenic Belt (CAOB) and are important for understanding its architecture and evolution. The Wuwamen accretionary complex in the Chinese South Tianshan contains a tectonic mélange that witnessed the dynamic evolution from early accretion to final collision of the western CAOB with the Tarim Craton. We present geochronological and geochemical studies on the exotic blocks and metasedimentary matrix of the tectonic mélange in order to refine the subduction‐accretion processes in the CAOB. Geochemical and age data reveal that the exotic blocks are of diverse origins, including arc‐related granite and arc basalt‐like garnet amphibolite from the upper plate, and MORB‐like amphibolite from the subducting slab. The blocks underwent subduction‐related high‐temperature metamorphism between ca. 397 and 340 Ma. Detrital zircons in the metasedimentary matrix are dominated by Paleozoic ages corresponding to the continuous arc magmatism in the Yili‐Central Tianshan Block. This finding is consistent with the accretion of the Wuwamen complex on the southern margin of the Yili‐Central Tianshan Block above the northward subducting South Tianshan Ocean. A ca. 307 Ma post‐accretion granite dyke intruded the Wuwamen complex, thereby providing a minimum age limit for its terminal accretion. In conjunction with subduction‐related magmatism, metamorphism, and sedimentation, the accretion of the Wuwamen accretionary complex was active during the early Ordovician to the late Carboniferous. Our new results reiterate that long‐lasting accretionary processes in the South Tianshan Ocean and the terminal collision due to its closure exert a major control on the architecture of the southwestern CAOB.

The effects of buoyant ridge subduction have been researched for decades. However, it remains unclear how this process influences magma chemistry. Here we use a compilation of geochemical data, well‐established geochemical proxies (i.e., Ba/Nb, Th/Nb) and mantle redox modeling (i.e., V/Sc, Cu) to propose that the subduction of a ridge underneath the central portion of the Vanuatu arc causes shallow‐angle subduction and the development of a slab tear. We suggest that the shallow slab pinches out the asthenospheric mantle and bulldozes ancient metasomatized lithospheric mantle from the forearc toward the main‐arc. Slab‐fluxed melting of this bulldozed material could account for the along‐arc ⁸⁷Sr/⁸⁶Sr‐¹⁴³Nd/¹⁴⁴Nd variations of the Vanuatu magmas. The influx of hot sub‐slab material into the Vanuatu arc mantle wedge through a slab tear produces magmatism within the forearc. Modeling of V/Sc and Cu systematics suggest that the mantle source of the forearc magmas has a higher fO₂ and Cu content than the source of the main‐arc and rear‐arc samples. The main‐arc and rear‐arc mantles were metasomatized by both slab‐derived fluids and melts. Whereas release of high Cu‐SO₂ slab‐derived fluids caused oxidation and Cu enrichment of the forearc mantle. These systematics indicate a decrease in the fO₂ of slab fluxes with increasing depth‐to‐slab and distance‐from‐trench. Our findings highlight the role of ridge subduction in controlling the along‐arc and across‐arc variations in the chemistry of Vanuatu arc magmas. This updated geodynamic model, based on geochemistry, is consistent with recent geophysical constraints and 3D numerical modeling.

俯冲带是全球最大的物质循环系统，控制着硫(S)在地球内部圈层及表层的循环，影响着大气圈、水圈、生物圈、岩石圈的稳定性以及地球的宜居性。厘清S在俯冲带中的地球化学行为和循环特征对理解地球各储库的氧化还原状态、岩浆作用与演化、成矿物质聚集、以及地球大气成分等具有重要意义。本文首先总结了进入俯冲带之前的大洋岩石圈的S结构模型，对S在大洋板片中的分布状态和地球化学特征进行了系统归纳。随后，系统阐述了俯冲带高压-超高压变质岩记录的板片变质及脱水过程中硫的地球化学行为。岩石学研究表明俯冲板片中的S多以硫化物相存在，硫酸盐矿物在弧前深度就已被释放或分解。相较于熔体，俯冲带流体中S的溶解度更高，是运移硫的更有效方式。DEW模型计算结果显示，流体中S含量总体较低，但在俯冲板片~90km处其含量有一个峰值(浓度0.5%~1.0%)。岩相学证据、地球化学测试结果、磷灰石S近边吸收结构(S-XANES)特征以及模拟结果都显示俯冲深部流体中S多以HS^-及H₂S形式存在，不含大量的SO₄^2-及硫酸盐；中f_S2流体有利于S迁移出俯冲板片，从而促进俯冲带大规模S循环，而高f_S2流体在流-岩交换过程沿流体通道发生S的锁固作用而不利于俯冲带S循环。质量平衡计算显示全球俯冲带S输入通量为4.65×10¹³g/yr，弧下深度板片S输出通量为2.91×10¹²g/yr，板片-岛弧S循环效率仅6.3%。俯冲板片在弧下深度可能存在一个短暂高效的S释放窗口，释放流体的δ³⁴S值为-2.1±3.0‰。基于高压-超高压变质岩中硫化物的研究，初步厘清了俯冲板片中S的地球化学行为，首次从板片角度全面、定量地限定了俯冲带的脱硫通量、效率、种型和同位素特征，提出俯冲带循环的S不是岛弧岩浆的氧化剂，与岛弧环境的正δ³⁴S值也无直接因果联系，对解析俯冲带S循环和理解地球长期的S循环具有重要意义。最后，本文还展望了俯冲带S循环的未来发展方向，应在俯冲带流体氧化还原性质(硫酸盐的命运)、俯冲沉积物对S循环的制约、俯冲带环境下多硫同位素的分馏效应、S循环与其它挥发分(如C等)循环之间的耦合关系、地球历史上深部S循环等方向做出探索，更深入地理解俯冲带及全球S循环过程。