Tectonophysics最新文献_第4页

Seismic lithospheric model across Ukrainian Shield from the Carpathians to the Dnieper-Donets Basin and its tectonic interpretation 从喀尔巴阡山脉到第聂伯河-顿涅茨盆地的整个乌克兰地盾的地震岩石圈模型及其构造解释

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-24 DOI: 10.1016/j.tecto.2024.230540

V. Starostenko , T. Janik , A. Murovskaya , W. Czuba , P. Środa , T. Yegorova , P. Aleksandrowski , O. Verpakhovska , K. Kolomiyets , D. Lysynchuk , T. Amashukeli , T. Burakhovych , D. Wójcik , V. Omelchenko , O. Legostaeva , D. Gryn , S. Chulkov

The SW-NE directed wide-angle reflection-refraction (WARR) SHIELD’21 profile crosses entire width of Ukraine. It targeted the structure of the crust and uppermost mantle in the southwestern part of the East European Craton (EEC), between Carpathians and Voronezh Massif, across Ukrainian Shield and Dnieper-Donets Basin. The ∼660 km-long profile is an extension of the RomUkrSeis profile in Romania and Ukraine. SHIELD’21 experiment, using TEXAN and DATA-CUBE short-period seismic stations, provided high-quality seismic sections from 10 shot points. This allowed construction of a ray-tracing P-wave velocity model, supplemented by V_p/V_s ratio, for the upper part of the lithosphere in the Sarmatia segment of the EEC and constraining geodynamic processes that led to the formation of the Ukrainian Shield and its margins since Archean times.

The velocity distribution in the crystalline crust indicates a rather uniform structure, with velocity changing from 6.0 km/s near the surface to 6.8 km/s at the Moho. The entire section shows the lack of a high-velocity lower crust (V_p > 6.8 km/s), presumably resulting from delamination of the primitive mafic lower crust during early evolution of a juvenile continental crust. The seismic boundaries in the upper crust reflect a Paleoproterozoic extensional detachment system below the SW flank of Dnieper-Donets rift basin, initiated in the Devonian. At larger depths, a wide dome of the lower crust with velocities of 6.5–6.8 km/s in the SW-central segment of the profile, probably represents an enormous Palaeoproterozoic(?) granitoid batholith. In the southwesternmost part of the profile, the crystalline crust shows exclusively low velocities. The prominent Moho is undulating and varies in depth between 32 and 50 km. It is underlain by high-velocity bodies (V_p: 8.36–8.40 km/s), against the background of 8.16–8.25 km/s in the mantle. The velocity model corresponds with the anomalies of potential fields and zones of high electric conductivity.

西南-东北定向广角反射-折射（WARR）SHIELD'21剖面横跨乌克兰全境。它的目标是东欧克拉通（EEC）西南部，喀尔巴阡山脉和沃罗涅日山丘之间，横跨乌克兰地盾和第聂伯河-顿涅茨盆地的地壳和最上层地幔的结构。该剖面长达 660 公里，是 RomUkrSeis 剖面在罗马尼亚和乌克兰的延伸。SHIELD'21 试验使用 TEXAN 和 DATA-CUBE 短周期地震台，提供了 10 个测点的高质量地震剖面。这就为欧洲经济共同体萨尔马特区段岩石圈上部构建了一个射线追踪 P 波速度模型，并辅以 Vp/Vs 比值，从而对自 Archean 时代以来导致乌克兰地盾及其边缘形成的地球动力过程进行了约束。整个剖面显示缺乏高速的下地壳（Vp > 6.8 km/s），这可能是在幼年大陆地壳早期演化过程中原始岩浆下地壳分层的结果。上地壳的地震边界反映了第聂伯河-顿涅茨河断裂盆地西南侧下方的古新生代延伸剥离系统，该系统始于泥盆纪。在剖面的中西南部，下地壳有一个宽大的圆顶，其速度为 6.5-6.8 公里/秒，这可能是一块巨大的古新生代（？）花岗岩熔岩。在剖面的最西南部，结晶地壳只显示出较低的速度。突出的莫霍面起伏不定，深度在 32 至 50 千米之间。其下是高速岩体（Vp：8.36-8.40 千米/秒），而地幔的背景速度为 8.16-8.25 千米/秒。该速度模型与电位场异常和高电导率区相吻合。

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引用次数: 0

Present-day incipient fault coalescence at a relay zone (Jiloca extensional basin, Spain): Evidence from instrumental seismicity 中继带（西班牙吉洛卡伸展盆地）现今萌生的断层凝聚：来自仪器地震的证据

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-22 DOI: 10.1016/j.tecto.2024.230541

Alba Peiro , Lucía Lozano , Luis E. Arlegui , Juan V. Cantavella , Sandra Ruiz-Barajas , José L. Simón

The relay zones between NW-SE to NNW-SSE striking faults of the Jiloca graben (Iberian Chain) mostly show distributed along-strike fault and fracture patterns. The latter are chiefly controlled by the Late Pliocene-Quaternary regional stress field, and secondarily respond to local controls from inherited structures. Such fracture patterns contrast with the classical models of transverse connecting faults controlled by relay kinematics. North of the Concud fault trace, at the relay zone with the Sierra Palomera fault, an unusually high seismic activity has been noticed since 2014, with magnitudes up to M = 3.5. Upgrading of the National Seismic Network allowed obtaining such new detailed records, while the installation of a new seismometer by the IGN within the study area has improved the reliability of focal depth data since 2017. A high-precision absolute relocation of seismicity from 01/01/2000 to 30/05/2022 has been carried out. The results show that (i) the epicentres are significantly clustered along a nearly N-S trending band, and (ii) the focal depths range from 0 to 14 km, in good agreement with the thickness of the brittle crust. This 3D spatial distribution of seismicity is interpreted as a consequence of activation of either a single fault or a fault zone, nearly vertical and N-S striking. Such structural setting is consistent with the surficial fracture patterns observed at both map and outcrop scale: NNW-SSE and NNE-SSW oriented faults and fractures, orthogonal to the ENE-WSW to ESE-WNW regional σ₃ trajectories, together with NW-SE trending ones controlled by inherited contractive faults. The present-day seismic activity suggests that along-strike, incipient fault propagation at the relay zone between the Concud and Sierra Palomera faults is currently operating under the control of the remote stress field.

吉洛卡地堑（伊比利亚地链）西北-东南至西北-东南走向断层之间的中继带大多呈现分布式沿走向断层和断裂形态。后者主要受晚渐新世-第四纪区域应力场的控制，其次是受继承结构的局部控制。这种断裂模式与由中继运动学控制的横向连接断层的经典模式形成鲜明对比。Concud 断层以北，在与 Sierra Palomera 断层的中继区，自 2014 年以来，地震活动异常频繁，震级最高达 M = 3.5。国家地震台网的升级使我们得以获得这些新的详细记录，而 IGN 在研究区域内安装的新地震仪则提高了自 2017 年以来焦点深度数据的可靠性。对 2000 年 1 月 1 日至 2022 年 5 月 30 日的地震活动进行了高精度的绝对重新定位。结果表明：(i) 震中明显集中在近南北走向的带状区域；(ii) 震源深度在 0 至 14 千米之间，与脆性地壳的厚度十分吻合。这种地震的三维空间分布被解释为一个近乎垂直和 N-S 走向的单一断层或断层带被激活的结果。这种结构设置与在地图和露头尺度上观察到的表层断裂模式一致：NNW-SSE 和 NNE-SSW 走向的断层和断裂与 ENE-WSW 至 ESE-WNW 的区域 σ3 轨迹正交，同时还有由继承性收缩断层控制的 NW-SE 走向的断层和断裂。目前的地震活动表明，Concud 断层和 Sierra Palomera 断层之间中继带的沿走向、初生断层扩展目前正在远程应力场的控制下运行。

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引用次数: 0

Upper mantle shear velocity structure of the Cathaysia Block and surrounding areas: New insight into deep geodynamics 国泰岛地块及周边地区的上地幔剪切速度结构：对深部地球动力学的新认识

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-22 DOI: 10.1016/j.tecto.2024.230542

Yao Xu , Qingtian Lü , Dapeng Zhao , Jiayong Yan , Danian Shi , Yongqian Zhang , Shuai Ruan , Zhiwu Xu , Changxin Chen , Wenwen Zhang , Xu Wang

The Cathaysia Block (CAB) and its surrounding areas experienced intensive magmatism and mineralization in the Yanshanian period (ca. 200–90 Ma), but their mechanism and deep geodynamics are still debated. In addition, the origin and structures of the Hainan mantle plume are still unclear. To resolve these issues and investigate the large-scale lithospheric thinning and extension in the eastern South China Block, we determine a detailed 3-D S-wave velocity (Vs) model down to 700 km depth by collecting 24,190 S-wave teleseismic data recorded at 164 permanent stations and 125 portable stations deployed in the CAB and surrounding areas. Our results show that high-Vs anomalies exist separately in the study volume. Two high-Vs anomalies appear in the shallow upper mantle and the mantle transition zone, which may reflect the present thin lithosphere and the stagnant Paleo-Pacific slab, respectively. Two other high-Vs anomalies exist in the upper mantle, which may reflect the detached lithosphere and subducting slabs. In contrast, low-Vs anomalies appear widely beneath the CAB, which reflect a tilting magmatic conduit beneath the Wuyishan metallogenic belt (WYMB) and magmatic chambers beneath the Nanling metallogenic belt (NLMB). In addition, our results show that the Hainan plume has a double-layered appearance. Combining our tomographic results with previous multidisciplinary findings, we consider that (1) the subduction and rollback of the Paleo-Pacific Plate may have played different roles in the Yanshanian mineralization of the WYMB and the NLMB; (2) the double-layered appearance of the Hainan plume may be formed due to the influence of plume self-evolution dynamics and pre-existing deep structures; and (3) lithospheric delamination triggered by gravity instability may have occurred beneath the Xuefengshan Mountain in the late Mesozoic.

在燕山期（约200-90Ma），华夏地块（Cathaysia Block）及其周边地区经历了密集的岩浆活动和成矿作用，但其机制和深部地球动力学仍存在争议。此外，海南地幔羽流的起源和结构仍不清楚。为了解决这些问题并研究华南东部块体的大尺度岩石圈减薄和延伸，我们通过收集部署在CAB及周边地区的164个永久台站和125个便携式台站记录的24190个S波远震数据，确定了一个详细的三维S波速度（Vs）模型，其深度可达700千米。结果表明，研究区内分别存在高 Vs 异常。两个高 Vs 异常点出现在浅上地幔和地幔过渡带，可能分别反映了目前较薄的岩石圈和停滞的古太平洋板块。另外两个高 Vs 异常出现在上地幔，可能反映了脱离的岩石圈和俯冲板块。相反，低Vs异常广泛出现在CAB下方，反映了武夷山成矿带下方的倾斜岩浆导管和南岭成矿带下方的岩浆腔。此外，我们的研究结果表明，海南羽流具有双层外观。结合我们的层析成像结果和之前的多学科研究结果，我们认为：（1）古太平洋板块的俯冲和回滚可能在西洋大洋带和南岭成矿带的燕山期成矿过程中扮演了不同的角色；(2)海南羽流的双层外观可能是由于羽流自我演化动力学和原有深部构造的影响而形成的；(3)雪峰山下可能在中生代晚期发生过重力不稳定引发的岩石圈分层。

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引用次数: 0

Tectonomagmatic evolution of Pune – Nasik Deccan Dykes: Insights from structure and dimension scaling 普纳-纳西克德干堤坝的构造地貌演化：从结构和尺寸缩放中获得的启示

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-19 DOI: 10.1016/j.tecto.2024.230539

Ragini Kumari, Jyotirmoy Mallik, Garima Shukla

The Deccan Continental Flood Basalt of the Indian Peninsula is characterized by extensive basaltic eruptions ornamented with three spectacular distinct dyke swarms: the Pune – Nasik, Narmada – Tapi, and Western Coastal dyke swarms. Our study area is the Pune – Nasik dyke swarm, which has ∼465 mappable dykes. These dykes exhibit different orientations with a predominant trend of N101° and vary in length from less than 1 km to ∼64 km. These dykes are massively jointed and occasionally contain vesicles filled with secondary minerals like quartz and calcite. The host rock is weathered basalt of various older Deccan flows. In this study, we have calculated magmatic overpressures and magma chamber depths using the aspect ratios (length/thickness) of the dykes. The average estimated source depth is ∼13 km, based on an average Young's modulus for the host rock basalt (E_avg, 7.5 GPa). Additionally, we compared the inferred magma source depths of the Pune – Nasik, and Narmada-Tapi dyke swarms which include the Nandurbar – Dhule, and Pachmarhi dykes of the Deccan Flood Basalt Province. Our findings indicate that the magma chamber source depth is greater in the Pune – Nasik dyke swarm compared with other dyke swarms. The variation in strike distribution of the Pune-Nasik dyke swarm may be attributed to several factors, including a larger magma chamber, local stress fields generated by shallow magma chamber, or the superimposition of tectonic stress fields (N-S and E-W extension) during the emplacement of dykes. This contrasts with the commonly held belief that the dykes are solely connected to a central edifice of the Reunion hotspot.

印度半岛德干大陆洪积玄武岩的特点是广泛的玄武岩喷发，并以三个壮观独特的堤坝群为装饰：普纳-纳西克堤坝群、纳尔马达-塔皮堤坝群和西部海岸堤坝群。我们的研究区域是普纳-纳西克堤坝群，该堤坝群有 465 个可标注的堤坝。这些堤坝的走向各不相同，主要走向为 N101°，长度从不足 1 千米到 64 千米不等。这些堤坝具有大量节理，偶尔含有充满石英和方解石等次生矿物的囊泡。主岩是各种较古老的德干岩流的风化玄武岩。在这项研究中，我们利用堤坝的长宽比（长度/厚度）计算了岩浆超压和岩浆腔深度。根据主岩玄武岩的平均杨氏模量（Eavg，7.5 GPa），估计岩浆源的平均深度为 13 千米。此外，我们还比较了推断的普纳-纳西克和纳尔马达-塔皮堤群（包括德干洪水玄武岩省的南杜尔巴尔-杜勒和帕赫马希堤群）的岩浆源深度。我们的研究结果表明，与其他堤群相比，普纳-纳西克堤群的岩浆室源深度更大。普纳-纳西克堤坝群走向分布的变化可归因于多种因素，包括岩浆腔较大、浅岩浆腔产生的局部应力场或堤坝形成过程中构造应力场（N-S 和 E-W 向延伸）的叠加。这与人们普遍认为堤坝仅与留尼汪热点的中心结构有关的观点形成了鲜明对比。

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引用次数: 0

Remagnetisation of the Caerfai Group (lower Cambrian, SW Wales) in hot geothermal fluids during Caledonian (pre-Acadian) metamorphism 在喀里多尼亚（前阿卡迪亚）变质过程中，热地热流体对 Caerfai 组（下寒武统，威尔士西南部）的重磁作用

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-18 DOI: 10.1016/j.tecto.2024.230532

Peter Turner , Rob Ixer , Duncan Pirrie , Matthew Power

Palaeomagnetic data from the Lower Cambrian red beds of the Caerfai Group in Pembrokeshire, South Wales have been revisited. Original studies all produced closely similar directional data with the combined results yielding a palaeomagnetic pole at 21.8^oS; 355.5°E corresponding to a time of ∼430 Ma when compared with the APWP of Stable Europe and Baltica. The results of this study indicate that remagnetisation occurred during Caledonian metamorphism, prior to Acadian deformation in the area. The magnetic remanence is carried by fine grained hematite distributed throughout the sequence and which appears to have been acquired during the duration of a single chron. This time zone is traditional early Silurian (late Llandovery) and corresponds to the docking of Baltica and east Avalonia with the Laurentian continent. The proposed age of the remagnetisation event is consistent with radiometric ages from epizonal authigenic illites in overlying Middle Cambrian bentonites at Porth-y-Rhaw and elsewhere in the Welsh Basin and other parts of Avalonia including Charnwood block and Brabantia. The Caerfai Group comprises texturally immature litharenites with a mineral assemblage including chlorite, biotite, muscovite, graphite, and epidote consistent with a greenschist facies source area which remains unidentified. A key component of the Caerfai mineral assemblage are magnetite crystals (typically 30–60 μm) deposited during contemporaneous volcanic activity. Deep burial during the drift of Avalonia, indicated by clay transformations and overpressure in the Caerfai Bay Mudstone, was associated with the alteration of iron-bearing minerals and the dissolution of magnetite. During collision of Avalonia/Baltica with Laurentia a geothermal cell with epizonal metamorphic conditions (>300 °C) and fluids enriched in iron, probably in the form of iron chloride complexes was established. The remagnetisation event was triggered when the geothermal cell was cooled, most likely by the infiltration of meteoric water, and the reaction of iron chloride with water produced the widespread precipitation of fine-grained hematite and the formation of a chemical remanent magnetisation (CRM).

我们重新研究了南威尔士彭布罗克郡凯尔法伊组下寒武统红色岩床的古地磁数据。最初的研究都得出了非常相似的方向数据，综合结果得出古地磁极位于 21.8oS; 355.5°E 与稳定的欧洲和波罗的海的 APWP 相比，对应的时间为 ∼430 Ma。这项研究的结果表明，在该地区阿卡迪亚变形之前的喀里多尼亚变质过程中发生了再磁化。磁性剩磁由分布在整个序列中的细粒赤铁矿携带，似乎是在一个纪元期间获得的。该时区是传统的志留纪早期（兰德发现晚期），与波罗的海和东阿瓦隆尼亚与劳伦大陆的对接相吻合。所提出的再磁化事件的年龄与 Porth-y-Rhaw 和威尔士盆地其他地方以及阿瓦鲁尼亚其他地区（包括 Charnwood 区块和 Brabantia）上覆中寒武纪膨润土中的外生自生伊利石的放射性年龄一致。Caerfai 组由质地不成熟的石英岩组成，矿物组合包括绿泥石、黑云母、白云母、石墨和绿帘石，与绿帘石面源区一致，该源区仍未确定。凯尔法伊矿物组合的一个重要组成部分是在同期火山活动中沉积的磁铁矿晶体（通常为 30-60 μm）。阿瓦隆尼亚漂移期间的深埋（由卡埃尔费湾泥岩中的粘土转化和超压表明）与含铁矿物的蚀变和磁铁矿的溶解有关。在阿瓦鲁尼亚/波罗的海与劳伦提亚碰撞期间，建立了一个地热单元，该单元具有表层变质条件（>300 °C）和富含铁的流体，可能以氯化铁复合物的形式存在。地热池冷却时（很可能是流星水的渗入）引发了再磁化事件，氯化铁与水的反应产生了细粒赤铁矿的广泛沉淀，并形成了化学剩磁（CRM）。

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引用次数: 0

Crustal imaging and characterization of active faults with a large-N nodal deployment - Application to the Chaînons Béarnais region (western Pyrenees foothills, France) 利用大 N 节点部署对活动断层进行地壳成像和特征描述--在 Chaînons Béarnais 地区（法国比利牛斯山麓西部）的应用

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-18 DOI: 10.1016/j.tecto.2024.230531

Sébastien Chevrot , Matthieu Sylvander , Nicolas Saspiturry , Amine Ourabah , Sébastien Benahmed , Benoît Derode , Frank Grimaud , Jean Letort , Hélène Pauchet , Guy Sénéchal , Antonio Villaseñor , Jean-Baptiste Ammirati

Understanding the driving forces and nature of intraplate seismicity remains a major unsolved problem in seismology. In the western Pyrénées, seismicity is concentrated in a narrow region that follows the boundary between the Axial Zone and the North Pyrenean Zone. Despite the presence of a permanent network in the region, the geometry of active faults, and their relationship with crustal structures, remain elusive, owing to significant earthquake location uncertainties. Here, we exploit data recorded by a large-N nodal array deployed in the Chaînons Béarnais region during four weeks of 2022 in order to image crustal structures and characterize active faults. We automatically detected and picked P and S waves with PhaseNet, resulting in a catalog of over 500 events, half of which are located beneath the temporary deployment. Tomographic images obtained from the inversion of P and S arrival times provide detailed insight into the geometry of folds and thrusts in the sedimentary cover, as well as the presence of a main fault in the basement which dips northward with an angle of 65° (Chaînons Béarnais normal fault). Seismicity relocation within the 3D model obtained by tomography shows that earthquakes are concentrated along this main active fault, extending from the top of the basement to a depth of approximately 16 km. These results demonstrate that passive imaging approaches can offer cost-effective alternatives to traditional controlled source imaging for seismotectonic studies and natural resource exploration in regions with active seismicity.

了解板内地震的驱动力和性质仍然是地震学中一个尚未解决的重大问题。在比利牛斯西部，地震活动集中在轴心带和北比利牛斯带交界处的一个狭窄区域。尽管该地区存在永久性地震网络，但由于地震定位存在很大的不确定性，活动断层的几何形状及其与地壳结构的关系仍然难以确定。在此，我们利用 2022 年四周期间部署在谢农-贝阿尔奈地区的大 N 节点阵列记录的数据，对地壳结构进行成像，并描述活动断层的特征。我们利用PhaseNet自动检测和挑选P波和S波，得到了500多个事件的目录，其中一半位于临时部署的阵列下方。通过反演 P 波和 S 波的到达时间获得的层析成像可以详细了解沉积覆盖层中褶皱和推力的几何形状，以及基底中存在的向北倾 65° 角的主断层（Chaînons Béarnais 正断层）。层析成像法获得的三维模型中的地震活动重新定位显示，地震主要集中在这一主要活动断层沿线，从基底顶部一直延伸到约 16 千米深处。这些结果表明，被动成像方法可替代传统的受控震源成像方法，为地震构造研究和活跃地震地区的自然资源勘探提供具有成本效益的方法。

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引用次数: 0

Insight into intracontinental deformation and crustal reworking of ancient continents implied by crustal structure imaging of the Yangtze Craton 长江克拉通地壳结构成像对古代大陆内部变形和地壳再加工的启示

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-18 DOI: 10.1016/j.tecto.2024.230537

Mingming Jiang , Tianyu Zheng , Yumei He

The crustal imprints from multistage tectonic activities in cratons offer valuable insights into continental evolution. Utilizing seismic data from two densely deployed, nearly perpendicular linear arrays, and a newly developed stepwise joint inversion of depth-domain receiver function and surface wave dispersion, we constructed a detailed crustal layering model for the Yangtze Craton. Our analysis revealed elongated double velocity reversal zones as salient features of the crust, which likely record ancient crustal reworking and juvenile crustal growth associated with Neoproterozoic rift-related magmatic processes. The interlayering of low- and high-velocity structures may contribute to the enduring stability of the Yangtze Craton. Additionally, superimposed layers separated by east-dipping interfaces and abrupt changes in crustal thickness in the boundary belts surrounding the Yangtze Craton document the crust's structural responses to intracontinental deformation during continent assembly.

环形山多期构造活动的地壳印记为了解大陆演化提供了宝贵的信息。利用两个密集布设、几乎垂直的线性阵列的地震数据，以及新开发的深域接收函数和面波频散联合逐步反演，我们构建了长江克拉通的详细地壳分层模型。我们的分析揭示了拉长的双速度反转带是地壳的显著特征，它可能记录了与新近纪断裂相关的岩浆过程有关的古代地壳再加工和幼年地壳生长。低速和高速构造的相互叠加可能有助于长江克拉通的持久稳定。此外，长江克拉通周围边界带被东倾界面分隔的叠加层和地壳厚度的突然变化，记录了大陆组装期间地壳对大陆内部变形的结构反应。

引用次数: 0

Structural evolution of the Horoman peridotite complex in conjunction with the formation of the Hidaka Metamorphic Belt, Hokkaido 与北海道日高变质带的形成有关的幌满橄榄岩复合体的构造演化

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-18 DOI: 10.1016/j.tecto.2024.230535

Kazuki Matsuyama , Katsuyoshi Michibayashi

We conducted crystal-fabric analyses of peridotites within the Horoman peridotite complex in the Hidaka metamorphic belt, Hokkaido, Japan. Over fifty oriented peridotite samples were collected and analyzed for olivine fabric strength (J-index) and crystallographic preferred orientations (CPOs). The peridotites contained four olivine CPOs: A, E, D, and AG types. We confirmed that olivine CPOs presented a transitional distribution from E to A to AG type from south to north. Previous experimental studies have demonstrated that E type CPO can merge under hydrous conditions. In addition, magnetotelluric observations suggested that the subducting oceanic plate supplies pore fluid to the basal thrust in the region (the Hidaka Main Thrust). Therefore, we infer that the E type CPO was originated from a local water infiltration event. AG type CPO, on the other hand, was considered as a secondary product enhanced by the synkinematic melts in the northern (geological upper) part, combined with the pressure-temperature path inferred by previous petrological studies. Furthermore, we reconstructed the senses of shear strain using the microstructure and olivine crystal-fabrics. Then we built the tectonic history of the Horoman peridotite complex integrating the structural development of the Hidaka metamorphic belt.

我们对日本北海道日高变质带霍罗曼橄榄岩群中的橄榄岩进行了晶体构造分析。我们收集了五十多个取向橄榄岩样本，并对其橄榄石结构强度（J-指数）和晶体学优选取向（CPO）进行了分析。橄榄岩包含四种橄榄石 CPO：A、E、D 和 AG 型。我们证实橄榄石 CPOs 从南到北呈现出从 E 型到 A 型再到 AG 型的过渡分布。之前的实验研究表明，E 型 CPO 在水合条件下可以合并。此外，磁强计观测表明，俯冲的大洋板块为该地区的基底推力（日高主推力）提供了孔隙流体。因此，我们推断 E 型 CPO 起源于当地的水渗透事件。另一方面，AG 型 CPO 被认为是北部（地质上部）同步熔融强化的次生产物，与之前岩石学研究推断的压力-温度路径相结合。此外，我们还利用微观结构和橄榄石晶格重建了剪切应变的感应。然后，我们结合日高变质带的构造发展，构建了霍罗曼橄榄岩群的构造史。

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引用次数: 0

New insight into the velocity and anisotropy structures of the subduction zone in northern Sumatra 对苏门答腊岛北部俯冲带速度和各向异性结构的新认识

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-18 DOI: 10.1016/j.tecto.2024.230534

Xueyuan Huang , Ping Tong

In this study, we conducted seismic tomographic inversions to investigate the velocity and anisotropy structures of northern Sumatra, using 9774 P-wave and 8405 S-wave arrivals from regional earthquakes. Isotropic P-wave velocity, isotropic S-wave velocity, P-wave azimuthal anisotropy, and P-wave radial anisotropy models were generated using eikonal equation-based traveltime tomography methods. The study identified low-velocity zones beneath the Toba and Sinabung volcanoes, potentially indicating the presence of magma reservoirs. Furthermore, low-velocity anomalies above the subduction slab were detected, which were likely caused by the dehydration of the slab and interpreted as channels of upwelling flow. The tomographic results revealed a trench-parallel high-velocity belt in the uppermost mantle, representing the subducting slab of the India-Australian plate. The trench-parallel fast velocity directions in the slab suggested that the subducted oceanic slab retains its frozen-in anisotropy formed at the mid-ocean ridge, or that the anisotropy is induced by the lattice-preferred orientation of the B-type olivine. Negative radial anisotropy in the mantle wedge was observed, reflecting hot upwelling flows and transitions of olivine fabrics in the presence of water due to slab dehydration. The results also indicated a multilevel magma plumbing system beneath the Toba Caldera. In summary, the results of this study provided new insights into the structure and dynamic processes of the northern Sumatra subduction zone.

在这项研究中，我们利用来自区域地震的 9774 个 P 波和 8405 个 S 波到达数据进行了地震层析反演，以研究苏门答腊岛北部的速度和各向异性结构。利用基于 eikonal 方程的行进时间层析成像方法生成了各向同性 P 波速度、各向同性 S 波速度、P 波方位各向异性和 P 波径向各向异性模型。研究确定了多巴火山和西那榜火山下方的低速区，这可能表明存在岩浆储层。此外，还探测到俯冲板块上方的低速异常，这可能是板块脱水造成的，被解释为上升流通道。层析成像结果表明，在最上层地幔中有一条沟槽平行高速带，代表印度-澳大利亚板块的俯冲板块。板块中与海沟平行的快速速度方向表明，俯冲的大洋板块保留了在大洋中脊形成的冻结各向异性，或者说该各向异性是由 B 型橄榄石的晶格偏好取向引起的。在地幔楔中观察到了负径向各向异性，反映了板块脱水导致的热上升流和橄榄石结构在有水的情况下的转变。研究结果还表明，鸟羽破火山口下方存在多级岩浆管道系统。总之，这项研究的结果为了解苏门答腊岛北部俯冲带的结构和动态过程提供了新的视角。

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引用次数: 0

Deep plutonic bodies over low-frequency earthquakes revealed from receiver-side Green's functions 从接收方格林函数揭示低频地震上方的深成岩体

IF 2.7 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Tectonophysics

Pub Date : 2024-10-18 DOI: 10.1016/j.tecto.2024.230536

Yasunori Sawaki , Yoshihiro Ito , Emmanuel Soliman M. Garcia , Ayumu Miyakawa , Takuo Shibutani

Seismological heterogeneity in subduction zones provides insights into slow earthquakes and potential megathrust earthquakes. Studies at the Kii Peninsula in the Nankai subduction zone suggest that there are high-density and high-velocity plutonic bodies in the accretionary prism over the subducting slab, potentially influencing megathrust earthquakes. The lateral variation of heterogeneity and the spatial extent of plutonic bodies remain to be investigated well. Our passive-source imaging of receiver-side Green's functions, from widely distributed campaign seismic observations, reveals a sharp negative S-wave velocity contrast on the top surface of the subducting Philippine Sea plate common to all along-dip profiles and a positive phase tilted upward in the forearc crust. The low permeability of the forearc crust prevents the infiltration of slab-dehydrated fluid further into the upper crust. In the western area, we also found positive phases tilted upward in the forearc crust. The negative phase extends towards the deeper extent of slow-earthquake sources. Meanwhile, the positive phase likely represents the top surface of plutonic rocks of the Kumano and Ohmine plutons that span all the way down to the plate interface. Together with observations of gravity anomaly, intraslab seismicity, and seismic tomography, our interpretation supports the presence of plutonic bodies which extend deep beneath the forearc crust as well as laterally over the subducting PHS slab, rather than a serpentinized mantle wedge. The upper plate is generally low in permeability, but areas with localized high permeability may exist on the updip side of tremor sources. This condition, wherein fluid can infiltrate upwards locally, may maintain the relatively less active slow earthquakes in the western area. The lateral variation of the upper-plate lithology likely influences fluid processes and slow earthquake activities.

俯冲带的地震异质性提供了对慢速地震和潜在大地震的洞察力。对南海俯冲带纪伊半岛的研究表明，在俯冲板块上方的增生棱柱中存在高密度和高速度的柱状体，可能对特大推覆地震产生影响。异质性的横向变化和柱状体的空间范围仍有待深入研究。我们从广泛分布的活动地震观测资料中获得的接收方格林函数的被动源成像显示，在俯冲菲律宾海板块的顶面，所有沿倾角剖面都有一个尖锐的负S波速度对比，而在前弧地壳则有一个向上倾斜的正相位。弧前地壳的低渗透性阻止了板块脱水流体进一步渗入上地壳。在西部地区，我们也在前弧地壳中发现了向上倾斜的正相位。负相向慢震源的深部延伸。与此同时，正相位可能代表了熊野和大峰岩浆岩的顶面，一直延伸到板块界面。结合重力异常、板块内地震和地震层析成像的观测结果，我们的解释支持了在前弧地壳深处以及俯冲的 PHS 板块横向上存在着延伸的深成岩体，而不是蛇化的地幔楔。上层板块的渗透率一般较低，但在震源的上升侧可能存在局部渗透率较高的区域。在这种情况下，流体可以在局部向上渗透，这可能会使西部地区的慢地震相对不那么活跃。上盘岩性的横向变化可能会影响流体过程和缓震活动。

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引用次数: 0