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Zircon Xenocrysts from the Shaka Ridge Record Ancient Continental Crust:New U-Pb Geochronological and Oxygen Isotopic Data

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Journal of Earth Science 2022年第1期33卷 5-16页

作者： Sergey G.Skublov Natalia A.Rumyantseva qiuli li Boris G.Vanshtein Dmitriy I.Rezvukhin Xianhua li Institute of Precambrian Geology and Geochronology of Russian Academy of Sciences St.Petersburg 199034Russia Saint Petersburg Mining University St.Petersburg 199106Russia Institute for Geology and Mineral Resources of the World Ocean(VNIIOkeangeologia) St.Petersburg 190121Russia State Key Laboratory of lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of SciencesNovosibirsk 630090Russia

Over the past two decades, a significant number of discoveries of ancient zircon xenocrysts in ocean-floor magmatic rocks have been reported. These findings provide compelling evidence for the presence of ancient continental crust within young oceanic lithosphere. Almost all finds of ancient zircon xenocrysts within oceanic crust are from the Mid-Atlantic Ridge. For other localities, however, similar data are very limited. This report presents the first age determinations(U-Pb, SHRIMPII) and isotope-geochemical data(oxygen, trace and rare earth elements) for zircon xenocrysts from gabbro-diorites of the Shaka Ridge, in the vicinity of the Shaka fracture zone, near the western end of the Southwest Indian Ridge. The work is based on a study of bottom rock material dredged during expeditionary research on the R/V"Akademik Fedorov"(Russia) in 2016. The U-Pb isotope system of the zircon xenocrysts recorded a crystallization age of ~2.8 Ga at an upper discordia intercept and an age of ~600 Ma interpreted as the timing of a superimposed thermal event at a lower discordia *** zircon xenocrysts show geochemical signatures of magmatic origin, i.e., fractionated REE distribution spectra with an increase in chondrite-normalized values from light to heavy REE, positive Ce anomalies and negative Eu anomalies, and high Th/U ratios(0.59-7.77). In discrimination diagrams based on a series of inter-element relationships, zircon compositions fall into the fields of zircons from rocks of continental crust, mostly granitoids. The li content of the zircons is high(1.8 ppm-50 ppm),adding further evidence to their derivation from rocks of continental crust. During their residence within young oceanic crust, the zircon xenocrysts experienced alterations under the influence of submarine high-temperature hydrothermal fluids, which selectively affected the distribution of trace elements in the zircons and reduced the δ;O values to 1.75‰-3.15‰. The presence of obviously older zircons

关键词： zircon U-Pb geochronology oxygen isotopes trace elements rare earth elements Shaka Ridge South Atlantic Southwest Indian Ridge

Decoupling between Oxygen and Radiogenic Isotopes: Evidence for Generation of Juvenile Continental Crust by Partial Melting of Subducted Oceanic Crust

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Journal of Earth Science 2021年第5期32卷 1212-1225页

作者： Xuan-Ce Wang qiuli li Simon A.Wilde Zheng-Xiang li Chaofeng li Kai Lei Shao-Jie li linlin li Manoj K.Pandit School of Earth Sciences Yunnan UniversityKunming 650500China School of Earth Science and Resources Chang1 an UniversityXi'an 710054China State Key Laboratory of lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China ARC Centre of Excellence for Core to Crust Fluid Systems and The Institute for Geoscience Research Department of Applied GeologyCurtin UniversityPerth 6845Australia Department of Geology University of RajasthanJaipur 302004India

There is increasing evidence indicating that melts derived from subducted oceanic crust and sediments may have played a key role in building continental crust. This mechanism predicts that juvenile arc crust should have oxygen isotope characteristics ranging from mantle-like to supracrustal, but consistent mantle-like radiogenic(Nd-Hf) isotopic signatures. Here we present in-situ zircon U-Pb dating, Hf-O isotope analyses, and whole rock major-trace element and Nd isotope analyses of a granitoid from NW India. In-situ secondary ion mass spectrometry(SIMS) zircon U-Pb dating yields a weighted mean ^(207)Pb/^(206)Pb age of 873±6 Ma for the granitoid. It displays mantle-like zircon εHf(εHf(873 Ma)= +9.3 to +10.9) and whole-rock Nd(εNd(873 Ma)= +3.5) values but supracrustal δ^(18)O values, the latter mostly varying between 9‰ and 10‰. The calculated whole-rock δ^(18)O value of 11.3‰±0.6‰ matches well with those of hydrothermally-altered pillow lavas and sheeted dykes from ophiolites. The major and trace element composition of the granitoid is similar to petrological experimental melts derived from a mixture of MORB+sediments. Thus, the granitoid most likely represents the product of partial melting of the uppermost oceanic crust(MORB+sediments). We propose that the decoupling between Hf-Nd and O isotopes as observed in this granitoid can be used as a powerful tool for the identification of slab melting contributing to juvenile continental crustal growth. Such isotopic decoupling can also account for high δ^(18)O values observed in ancient juvenile continental crust, such as Archean tonalitetrondhjemite-granodiorite suites.

关键词： zircon Hf-Nd and O isotopes decoupling slab melting Neoproterozoic continental crustal growth

Rutile U-Pb age for the ultra-high pressure eclogite from the Dabie Mountains, central China: Evidence for rapid cooling

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Chinese Science Bulletin 2002年第1期47卷 62-65页

作者： li qiuli li Shuguang ZHOU Hongying li Huimin HONG Ji’an WANG Qingchen H.J.Massonne Department of Earth and Space Science University of Science and Technology of ChinaHefei 230026China Tianjin Institute of Geology and Mineral Resources Institule of Geology and Geophysics Chinese Academy of SciencesBeijing 100029China Institut fur Mineraloie&Kristallechemie Universitat StuttgartAzenbergster.1870174 StuttgartGermany

The U-Pb isotope compositions of rutile, om-phacite and garnet in the eclogite from the Jinheqiao area in the Southern Dabie ultrahigh-pressure metamorphic zonewere analyzed. The consistent high precision U-Pb age (218± 1.2) Ma of rutile in eclogite from the Dabie Mountains was obtained by two ways of isochron and common Pb correction based on the composition of omphacite. This proves that the omphacite in eclogite has a U/Pb ratio (μ = 2.8) low enough to be used for common Pb correction in the analyses of rutile. Under the rapid cooling condition (40℃/Ma) the closure temperature for U-Pb diffusion in rutile is about 470℃. Thus, this U-Pb age of rutile proves that 218 Ma should be the cooling age of eclogite at 470℃ instead of the peak meta-morphic age.

关键词： U-Pb dating of rutile eclogite Dabie Mountains.

SIMS U-Pb dating of rutile within eclogitic xenoliths in the Early Cretaceous adakitic rocks of the Xuzhou-Huaibei area, China: Constraints on the timing of crustal thickening of the eastern North China Craton

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Science China Earth Sciences 2015年第5期58卷 1100-1106页

作者： XIONG BoQin XU Wenliang li qiuli YANG DeBin ZHOU QunJun College of Earth Sciences Jilin University State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences State Key Laboratory of lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences

This paper reports the results of secondary ion mass spectrometry （SIMS） U-Pb dating of rutile within eclogitic xenoliths from the Early Cretaceous adakitic rocks in the Xuzhou-Huaibei area of China and discusses the geological significance of these new dates. The dating of rutile from pargasite-bearing eclogite and garnet clinopyroxenite （retrograde eclogite） yielded ages of 209 ± 25 and 132 ± 7 Ma, respectively. The former is consistent with the timing of the first stage of exhumation of the Dabie-Sulu orogenic belt and provides evidence of crustal thickening within the southeastern margin of the North China Cra- ton during the early Mesozoic, related to subduction and collision between the Yangtze and North China cratons. The latter age is similar to the timing of emplacement of the hosting intrusion and indicates that the rutile U-Pb system was triggered after uplifting by the intrusion of the hosting magmas. It implies that garnet clinopyroxenite was previously at the depth where the temperature was above the futile U-Pb closure temperature.

关键词： North China Craton crustal thickening eclogitic xenoliths rutile SIMS U-Pb dating

Accessary Minerals SIMS U-Th-Pb Dating for Kimberlite and Lamproite

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Acta Geologica Sinica(English Edition) 2016年第S1期90卷 74-75页

作者： li qiuli li Xianhua WU Fuyuan liU Yu TANG Guoqiang State Key Laboratory of lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences

Kimberlite and lamproite,the major source of diamonds,are volatile-rich potassic ultramafic rocks that originate from the deep lithospheric *** rocks are important for deciphering the composition and

关键词： SIMS Pb Accessary Minerals SIMS U-Th-Pb Dating for Kimberlite and Lamproite Th

Qinghu zircon:A working reference for microbeam analysis of U-Pb age and Hf and O isotopes

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Chinese Science Bulletin 2013年第20期58卷 4647-4654页

作者： li XianHua TANG GuoQiang GONG Bing YANG YueHeng HOU KeJun HU ZhaoChu li qiuli liU Yu li WuXian State Key Laboratory of lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences CAS Key Laboratory of Crust-Mantle Materials and Environments School of Earth and Space Sciences University of Science and Technology of China Institute of Mineral Resources Chinese Academy of Geological Sciences State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences State Key Laboratory of Isotope Geochemistry Guangzhou Institute of Geochemistry Chinese Academy of Sciences

Zircon is the most useful mineral for studies in U-Pb geochronology and Hf and O isotope *** effect is a major problem of the microbeam techniques such as SIMS and LA-(MC)-***,external standardization using well-characterized natural zircon standards is fundamental for accurate microbeam *** the isotopic geochronology and geochemistry laboratories equipped with microbeam analytical facilities have been increasingly established in China during the past decade,applications of the isotopic microanalysis are still limited due to shortage of available *** report here the Qinghu zircon as a potential new working reference for microbeam analysis of zircon U-Pb age and O-Hf *** zircon was separated from the Qinghu quartz monzonite from the western Nanling Range,Southeast *** is fairly homogeneous in U-Pb age and Hf and O isotopes in terms of large amounts of mircobeam measurements by LA-MC-ICPMS and SIMS at the scales of 20–60 *** measurements yield consistent206Pb/238U age within analytical uncertainties with that obtained by *** determinations of O isotopes by IRMS and Hf isotopes by solution MC-ICPMS are in good agreement with the statistical mean of microbeam *** recommend U-Pb age of=159.5±0.2 Ma(2SE),18O=5.4‰±0.2‰(2SD)and176Hf/177Hf=0.283002±0.000004(2SD)as the best reference values for the Qinghu zircon.

关键词：锆石U-Pb年龄 Hf同位素微束分析天然锆石 O同位素 MC-ICPMS U-Pb年代学中国东南部

METHODS TO IMPROVE PRECISION FOR OXYGEN ISOTOPE ANALYSIS USING CAMECA IMS-1280 SIMS

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METHODS TO IMPROVE PRECISION FOR OXYGEN ISOTOPE ANALYSIS USI...

Metamorphic Isotope Chronology and Collisional Process between North China and South China Blocks

第十四届北京分析测试学术报告会暨展览会(BCEIA 2011)

作者： Guoqiang TANG Xianhua li qiuli li Yu liU State Key Laboratory of lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Science

High precision and accuracy oxygen isotope analysis is important in geochemistry research ***(secondary ion mass spectrometry)is a powerful in situ analysis technique which could get information from micrometer scale ...

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Bulletin of the Chinese Academy of Sciences 2011年第2期25卷 140-141页

作者： li Shuguang liU Yican XIAO Yilin SUN Weidong li qiuli University of Science and Technology of China

Intercrossing several research realms including geochronology, isotope geochemistry and petrogeochemistry, the studies on continental collision processes and ultrahigh-pressure (UHP) metamorphism have remained one of the hottest and most interesting fields in continental dynamics research since the early 1980s, which constantly provide important knowledge and scientific ideas for developing and improving the plate tectonic *** Qinling-Dabie-Sulu metamorphic belt, one of the largest UHP metamorphic terrains

关键词：同位素年代学碰撞过程中国北方变质同位素地球化学大陆动力学陆块南方

New age determination of the Cenozoic Lunpola basin,central Tibet

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New age determination of the Cenozoic Lunpola basin,central ...