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Discovery of the Proterozoic low-grade metamorphicsubmarine carbonatite lavas in China

Chinese Science Bulletin 1998年第5期43卷 416-420页

作者： Yongbei Zhang Qirong Wei Chengyan Xiu Hao Wang China Univ Geosci Fac Earth Sci Wuhan 430074 Peoples R China

The carbonatite lavas found in the Kunyang Group were formed in submarine extrusive environment. Many igneous features (e.g. colors, textures, structures, minerals, inclusions) are clear. But most of their petrologic characteristics are different from typical carbonatites over the world. Most petrologic details of the rocks are given by comparison with other carbonatites and adjacent sedimentary dolomites. The discovery of the lavas proves that the carbonatite volcano also existed in Kunyang rift.

关键词： carbonatite lavas submarine extrusion Proterozoic low-grade metamorphic rock Kunyang rift.

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The geochemical variations of mid-Cretaceous lavas across western Shandong Province,China and their tectonic implications

The geochemical variations of mid-Cretaceous lavas across we...

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中国科学院地质与地球物理研究所2006学术年会

作者： Jifeng Ying,Xinhua Zhou and Hongfu Zhang State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,P.O.Box 9825,Beijing,100029,China

Major and trace element as well as Sr-Nd isotopic compositions of mid-Cretaceous lavas across western Shandong Province,China have been *** lavas can be generally divided into southern Shandong group(including Pingyi and Mengyin) and northern Shandong group(including Laiwu and Zouping) based on their *** southern group lavas are characterized by extreme enrichment in LREE,large ion lithophile elements(LILE),and depletion in HFSE along with EMII-like Sr-Nd isotopic compositions,suggesting that the crustal involvements play a significant role in their *** studies with Fangcheng basalts reveal that the Triassic continent-continent collision between the Yangtze craton(YC) and the North China craton(NCC),and subsequent extensive modification of the sub-continental lithospheric mantle(SCLM) beneath the south part of the NCC by silicic melts released from the subducted Yangtze lower crust,formed an enriched lithospheric mantle which was the source of the southern Shandong group *** contrast,the northern Shandong group lavas are mildly enriched in LREE and LILE relative to those of the southern group *** isotope compositions are also distinctive in that the Sr isotopic ratios are very *** geochemical evidence and comparing studies with spatially closed related mafic intrusions suggest that the SCLM feeding the northern group lavas seems to be linked to carbonatitic metasomatism and changed modal proportion of phlogopite and clinopyroxene in the mantle rather than subduction-related *** contrasting geochemical characters of the mid-Cretaceous lavas across western Shangdong suggest that the SCLM of the NCC is spatially heterogeneous in Mesozoic.

关键词： China Shandong Province Geochemistry Mid-Cretaceous lavas

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Mantle plume activity and melting conditions： Evidence from olivines in picritic-komatiitic rocks from the Emeishan Large Igneous Province, southwestern China

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Episodes 2005年第3期28卷 171-176页

作者： Zhaochong Zhang Jingwen Mao Fusheng Wang Yanli Hao John J. Mahoney Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China China University of Geosciences Beijing 100083 China Institute of Mineral Resources Chinese Academy of Geological Sciences Beijing 100037 China School of Ocean and Earth Science and Technology University of Hawaii Honolulu HI 96822 USA

Olivine phenocryst compositions and whole-rock chemical compositions are used to identify primitive picrite basalts from the early part of flood basalt successions in the western part of the Emeishan large igneous province （ELIP）, southwestern China. The Fo contents of olivine phenocrysts of komatiites with MgO-21.79 wt% range from 85.2% to 91.4%. The composition of unerupted parental melts is calculated from the compositions of the most Fo-rich olivine phenocrysts. These melts had -22 wt% MgO, and originated in mantle with a potential temperature of -1600℃ and at about 4.2 GPa pressure, supporting the conclusion that the generation of ELIP can be attributed to melting of a plume head beginning at -138 km depth.

关键词： PERMIAN-TRIASSIC BOUNDARY FLOOD BASALTS SW CHINA GEOCHEMICALCONSTRAINTS HAWAIIAN VOLCANISM PERIDOTITE KLB-1 ICELAND PLUME HIGH-MG MAGMAS lavas

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Petrology of the Volcanic Rocks from Bioko Island(“Cameroon Hot Line”)

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International Journal of Geosciences 2015年第3期6卷 247-255页

作者： Fadimatou Ngounouno Yamgouot Bernard Deruelle Isaac Bertrand Gambie Mbowou Ismaila Ngounouno Departement des Sciences de la Terre Facultedes SciencesUniversite de NgaoundereNgaoundereCameroun Laboratoire de Magmatologie et Géochimie Inorganique et Expérimentale(MAGIE) Institut de Physique du Globe de ParisUniversite Pierre et Marie CurieParisFrance Département des Mines et de la Géologie Ecole de Geologie et d’Exploitation Minière(EGEM)Universite de NgaoundéréMeigangaCameroun

Bioko island (3008 m a.s.l.), is composed of the alkaline basaltic lavas (basalts and hawaiites) with xenoliths. These lavas have a microlitic textureand consisted of euhedral to subhedral phenocrysts?(>1 mm) of olivine (0.83 lavas increase and Fe2O3, MgO and CaO decrease with increasing differentiation from basalts to hawaiites. The compatible elements Ni, Cr and V decrease strongly in basalts and remain at low levels in hawaiites. Basaltic lavas from Bioko lavas have low Hf contents (4.2 - 9.2 ppm) and consequently higher Hf/Zr ratios (50 - 90) than those (lavas from other volcanoes of the Cameroon Hot Line. Such high ratios are commonly observed in alkaline basaltic lavas associated with carbonatitic and/or nephelinitic magmatism. The Sr and Nd isotopic compositions point to a slightly depleted mantle source.

关键词： Petrology Geochemistry lavas Bioko Cameroon Hot Line

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Evidence for weak geomagnetic field intensity prior to the Cretaceous normal superchron

Evidence for weak geomagnetic field intensity prior to the C...

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中国科学院地质与地球物理研究所2003学术年会

作者： Kenneth A.Hoffman Physics Department California Polytechnic State UniversitySan Luis ObispoCA 93407USA

A palaeomagnetic and geochronologic investigation has been carried out on a sequence of 19 lava flows at Sihetun in northeastern *** determinations by K/Ar dating indicate that the sequence spans 124-133 Ma,that is,the time just prior to Cretaceous normal superchron(CNS).Rock magnetic measurements of thermomagnetic curves and hysteresis loops show the primary carrier of remanence to be pseudo-single domain *** thermal demagnetization successfully isolated a well-defined direction of characteristic magnetization(ChRM) in all the *** mean palaeodirection determined is D/I = 5.4°/58.7°(α= 2.4°) and D/I = 175.9°/-60.0°(α = 6.4°) for 15 normally magnetized flows and 3 reversely magnetized flows,*** lava was found to possess an intermediate direction of *** inferred palaeolatitude of the sampling site is very similar to the present-day position,supporting the contention that suturing between the Mongolia and north China plates was probably completed by the Late Jurassic,and that subsequently little rotation or translation occurred in the region west of the Tanlu fault ***-Thellier palaeointensity experiments with systematic partial thermoremanent magnetization(pTRM) checks were conducted on 66 samples from 13 lava *** from the 29 samples(44%) which met strict reliability criteria indicate a range of virtual dipole moments(VDMs) from 2.83 to 4.17×10 A m with an average of(3.53±0.02)×10 A *** finding helps confirm that a weak geomagnetic field probably occurred just prior to the CNS.

关键词： Palaeointensities Cretaceous normal superchron China lavas Thellier method

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