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A geochemical perspective on the genesis of Cenozoic basic volcanism in northeastern Turkey:an overview of metasomatism and heterogeneity of the sub-continental lithospheric mantle in a post-collisional setting

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Acta Geochimica 2024年第3期43卷 489-506页

作者： Mehmet Arslan Irfan Temizel Department of Geological Engineering Karadeniz Technical University61080 TrabzonTurkey

The post-collisional Cenozoic basic volcanic rocks in NE Turkey show temporal variations in whole-rock lithophile element and highly siderophile element(HSE)systematics that are mainly associated with the nature of sub-continental lithospheric mantle(SCLM)sources and parental melt generation.So far,the traditional whole-rock lithophile geochemical data of these basic volcanic rocks have provided important constraints on the nature of SCLM sources.Integrated lithophile element and HSE geochemical data of these basic volcanic rocks also reveal the heterogeneity of the SCLM source,which is principally related to variable metasomatism resulting from previous subduction(s)and post-collisional mantle-crust interactions in an extensional setting.Lithophile element geochemical features suggest that the parental magmas have derived from metasomatized spinel-to garnet-bearing SCLM sources for Eocene and Miocene basic volcanic rocks with subduction signatures whereas originated from spinel-to garnet-bearing SCLM sources for Mio-Pliocene and Plio-Quaternary basaltic volcanic rocks without the subduction signature.Lithophile element and HSE geo-chemistry also reveal that Eocene and Miocene basic vol-canic rocks were affected by more pronounced crustal contamination than the basaltic volcanic rocks of Mio-Pliocene and Quaternary.Furthermore,the integrated lithophile element and HSE compositions of these basic volcanic rocks,together with the regional asymmetric lithospheric delamination model,reveal that the compositional variation(especially due to metasomatism)was significant temporally in the heterogeneity of the SCLM sources from which parental magmas formed during the Cenozoic era.

关键词： Basalt Lithospheric mantle Metasomatism mantle heterogeneity Cenozoic volcanics NE Turkey

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Dupal Anomaly and Identification using Nd-Hf Isotopes

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Acta Geologica Sinica(English Edition) 2022年第2期96卷 416-429页

作者： TIAN Ye XU Jifeng LIU Xijun School of Earth Science and Resources and State Key Laboratory of Geological Processes and Mineral ResourcesChina University of GeosciencesBeijing 100083China Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration College of Earth SciencesGuilin University of TechnologyGuilinGuangxi 541004China

The Dupal anomaly has attracted widespread attention since being discovered and is regarded as the most direct manifestation of mantle inhomogeneity at present. From the initially defined anomalies limited to the southern hemisphere to the global scale, the criteria for identifying anomalies defined by Pb isotopes have also been adjusted, providing an important method and reference for the study of the mantle evolution. Pearce and Peate(1995) proposed the method of NdHf isotope and element ratio to identify the Dupal anomaly. The Nd-Hf method also offers a possible way to discriminate the mantle region of arc magmatism through the correction of Nd in the subduction process. This paper introduces the concepts and determination methods of the Dupal anomaly, and reports new Hf isotopic data of MORB-type rocks with Dupal signature in the several Tethys ophiolites. Our results of Nd-Hf method are in good agreement with those of previous Pb isotope identification. Moreover, origins and their controversy of Dupal anomaly are reviewed, and possible internal connections between Dupal anomalies and the two Large Low Shear Velocity Provinces(LLSVPs) in the lower mantle are discussed in depth. Further studies on origin and evolution of the Dupal anomaly are suggested, especially using integrated approach of Hf-Nd and Pb isotopes.

关键词： Dupal anomaly LLSVPs Pb isotope Nd-Hf isotope mantle heterogeneity

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Subduction-induced mantle heterogeneity beneath Eastern Tianshan and Beishan:Insights from Nd-Sr-Hf-0 isotopic mapping of Late Paleozoic mafic-ultramafic complexes

Subduction-induced mantle heterogeneity beneath Eastern Tian...

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中国科学院地质与地球物理研究所2012年度（第12届）...

作者： Ben-Xun Su Ke-Zhang Qin He Sun Dong-Mei Tang Patrick Asamoah Sakyi Zhu-Yin Chu Ping-Ping Liu Qing-Hua Xiao Key Laboratory of Mineral Resources Institute of Geology and GeophysicsChinese Academy of Sciences State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences Department of Earth Science University of GhanaP.O.Box LG 58Legon-AccraGhana Department of Earth Sciences the University of Hong Kong

Extensive late Paleozoic mafic-ultramafic complexes in the Eastern Tianshan and Beishan regions in the southern Central Asian Orogenic Belt(CAOB) represent an ideal opportunity to assess the characteristics of the mantle in this area.Whole-rock Nd-Sr and zircon Hf-O isotopic data from the mafic-ultramafic complexes of the Jueluotage Belt,Middle Tianshan Massif and Beishan Rift were compiled for isotopic mapping.ε(t) and(Sr/Sr) values range from +5.5 to +9.5 and 0.702 to 0.706 respectively in the Jueluotage Belt,and from- 2 to + 11 and 0.703 to 0.710 respectively in the Middle Tianshan and Beishan.Zirconε(t) andεO values are in the range of +6.0-+17.0 and 4.14‰-8.00‰respectively in the Jueluotage Belt,+1-+8 and 5.17‰-6.30‰respectively in the Middle Tianshan,and show large variations of -1- + 17 and 4‰-12‰respectively in the Beishan.Spatially,the(Sr/Sr) ratios of mafic-ultramafic complexes increase from Lhe Jueluotage Belt and Beishan to the Middle Tianshan,while theε(t) values show an opposite trend and reflect a mixing character between depleted mantle and EM-Ⅱreservoirs.Zirconε (t) andδO values exhibit an apparent southward decreasing and increasing trends respectively,from the Jueluotage Belt,through Middle Tianshan,to Beishan Rift.Their corresponding Hf model ages increase continuously from north to south.These observations demonstrate that the mantle sources beneath the Eastern Tianshan and Beishan are compositionally heterogeneous,which presumably result from significant and variable degrees of subduction-related modification.We therefore suggest that the late Paleozoic subcontinental lithospheric mantle beneath the Jueluotage Belt was modified by slab-derived melts and fluids during the subduction of the Junggar Ocean,whereas the mantle beneath the Beishan Rift was influenced mainly by slab-derived fluids during the subduction of the South Tianshan Ocean.The unique similarities of the Middle Tianshan mafic-ultramafic complexes reflect a two-stage modification of their mantle source,namely the sequential sub

关键词： Central Asian Orogenic Belt Mafic-ultramafic complex mantle heterogeneity Md-Sr-Hf-O isotopes Subduction

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Implications of the melting depth and temperature of the Atlantic mid-ocean ridge basalts

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Acta Oceanologica Sinica 2019年第12期38卷 35-42页

作者： Yili Guan Xuefa Shi Quanshu Yan Xun Wei Yan Zhang Xiaoping Xia Haoda Zhou Key Laboratory of Marine Sedimentology and Environmental Geology First Institute of OceanographyMinistry of Natural ResourcesQingdao 266061China Laboratory for Marine Geology Pilot National Laboratory for Marine Science and Technology(Qingdao)Qingdao 266061China State Key Laboratory of Isotope Geochemistry Guangzhou Institute of GeochemistryChinese Academy of SciencesGuangzhou 510640China Zhuhai Central Station of Marine Environmental Monitoring State Oceanic AdministrationZhuhai 519015China

Mid-ocean ridge basalts(MORBs) are characterized by large variations in trace element compositions and isotopic ratios, which are difficult to be interpreted solely by using magmatic process such as partial melting of a peridotitic mantle and subsequently fractional crystallization. Geochemical diversity of MORBs have been attributed to large-scale heterogeneity within the underlying mantle, and the heterogeneity might have been caused by addition of recycled crustal component, subcontinental lithosphere, metasomatized lithosphere and outer core contribution. In this study, we investigated the MORBs along the Mid-Atlantic Ridge(MAR) by estimating the temperature and pressure of partial melting, and comprehensively comparing trace element and isotope ratios. The data for MORBs from areas close to mantle plumes show large variations. mantle plumes can affect mid-oceanic ridges 1 400 km away, but plume effects did not cover all of the ridge segments, and those segments without plume effects did not have any abnormalities in temperature, trace element or isotope ratios.We ascribed the above phenomena to result from the shapes of the plume flow, which we categorized as "pipelike channels" and "pancake-like channels". The "pancake-like channels" plumes affected the ambient mantle nondirectionally, but the range of the mantle affected by the "pipe-like channels" plumes were selective. Element ratios of MORBs reveal that the mantle source of the MORBs along the MAR is highly heterogeneous. We suggest that most of source heterogeneities of the MORBs may be due to the presence of subducted slab and delaminated lower crust in the source. In addition, the plume that carried materials from the core-mantle boundary may affect some of the segments.

关键词： Mid-Atlantic Ridge MORB mantle heterogeneity plume-ridge interaction

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Holocene volcanic rocks in Jingbo Lake region --Diversity of magmatism

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Progress in Natural Science:Materials International 2006年第1期16卷 65-71页

作者： FAN Qicheng, SUN Qian, LI Ni and WANG Tuanhua (Institute of Geology, China Seismologieal Bureau, Beijing 100029, China) Institute of Geology China Seismological Bureau Beijing 100029 China

During the time from 5500 a to 5200 a BP more than 10 Holocene volcanoes in Jingbo Lake region erupted and the volcanic rocks covered an area of about 500 km2. Holocene volcanic rocks in Jingbo Lake region belong to the potassium-rich rocks and contain three rock types: trachybasalts, basanites and phonotephrites. Various types of magmatism formed in a small area and in a short period of time came from partial melting of potassically-metasomatised lithospheric mantle. The diversity of magmatism can be explained by that Jingbo Lake is situated in the back-arc extensional region of East Asian continent subducted by the Pacific Ocean, and potassic fluid derived from mantle wedge or dehydration of subducted slab can result in a high heterogeneity of the mantle beneath this region. Based on the pressure estimation of clinopyroxene megacrysts, we estimate that phonotephrite magma fractionally crystallize at ca . 52-54 km down the earth.

关键词： magma diversity mantle heterogeneity Holocene volcano Jingbo Lake.

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Scale lengths of heterogeneities under Tibet

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Earthquake Science 2012年第5期25卷 409-414页

作者： Yingcai Zheng Department of Earth Atmospheric and Planetary SciencesMassachusetts Institute of Technology

Important information about small-scale heterogeneities is hardly accessible by the traditional deterministic seismic tomography. Fluctuations of the phase and the logarithmic amplitude of direct teleseismic plane P waves can be used to characterize small-scale heterogeneities. Seismic data recorded by the Hi-CLIMB array are used to analyze the average power spectrum of the small-scale velocity heterogeneities under Tibet. Coherence functions of the logarithmic amplitude and the phase fluctuations due to different earthquakes from different back azimuths show consistent characteristics, indicating that fluctuations are due to heterogeneities under the stations. Assuming that the heterogeneities are statistically stationary and distributed within a layer, we invert for the average heterogeneity spectrum by fitting both the logarithmic amplitude and the phase coherence data. Multiscale nature of the heterogeneity is evident. The inverted power spectrum is ＂red＂ at the large-scale end, meaning that the power spectrum decreases as the length scale decreases. Such a decreasing trend stops at smaller scales -20-50 km and 10 km. This may indicate that mantle convection is not effective in destroying smaller heterogeneities.

关键词： seismic tomography mantle heterogeneity scattering coherence function

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溢流玄武岩成因过程中的岩浆补给作用:同位素证据（英文）

溢流玄武岩成因过程中的岩浆补给作用:同位素证据（英文）

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2016中国地球科学联合学术年会

作者：俞恂陈立辉曾罡南京大学地球科学与工程学院同济大学海洋地质国家重点实验室

Continental flood basalts are thought to be the volcanic manifestations of large volumes of magma derived from Earth’s mantle including mantle compositions with variable elemental and isotopic compositions(Zhang et al., 2006;Hooper et al., 2007;Sobolev et al., 2009, 2011). Understanding the compositional record of continental flood basalts is thus crucial for a better understanding of mantle compositional variations and ultimately the dynamics that lead to these variations. Radiogenic isotope systematics of melts derived from a mantle source may provide clues on the formation mechanisms(e.g., plume versus nonplume) of continental flood basalts. Isotopic compositions of continental flood basalts are essential to understand their genesis and to constrain the character of their mantle sources. Because of potential crustal contamination, it needs to be evaluated if and to which degree these basalts record primitive isotopic signals of their mantle sources and/or crustal signatures. This study examines the Sr, Nd, Hf, and Pb isotopic compositions of the late Cenozoic Xinchang-Shengzhou(XS) flood basalts, a small-scale continental flood basalt field in eastern China. The basalts show positive correlations between 87Sr/86 Sr and 143Nd/144 Nd, and negative correlations between 143Nd/144 Nd and 176Hf/177 Hf, which deviate from compositional arrays of crustal contamination and instead highlight variations in magmatic recharge intensity and mantle source compositions. The lava samples formed by high-volume magmatic recharge recorded signals of recycled sediments in the mantle source, which are characterized by moderate Ba/Th(91.9–106.5), excess 208Pb/204 Pb relative to 206Pb/204 Pb, and excess 176Hf/177 Hf relative to 143Nd/144 Nd. Thus, we propose that magmatic recharge buffers the original isotopic compositions of magmas against crustal contamination. Identifying and utilizing the isotope systematics of continental flood basalts generated by high volumes of magmatic recharge is thus crucial to trace their mantle sources.

关键词： Continental flood basalts mantle heterogeneity magmatic recharge crustal contamination

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