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Discovery of a Miocene Mafic Dyke from the Western Hills of Beijing and its Geological Implications

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Acta Geologica Sinica(English Edition) 2009年第3期83卷 640-647页

作者： ZhanG Zhicheng han baofu WU Tairan Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of Education School of Earth and Space Sciences Peking University Beijing 100871 China

The present study is the first report of a Miocene mafic dyke from the Dahuichang, in the Western Hills of Beijing. The dyke cuts the fossil-dated Changxindian Formation of Eocene sequences and yields K-Ar ages of 14-15 Ma. The dyke is fine-grained diabase and has 49.84%-50.81% SiO2 and 3.56-3.97% Na2O＋K2O, high TiO2 （1.65%-1.93%） and MgO （7.36%-9.85%）, and low K2O （〈1.22%） contents, with Na2O〉K2O and slightly varied magnesium numbers （Mg#=55.54-62.74）. In trace elements geochemistry, the dyke is very similar to the Miocene basalts from Jining and hanuoba. The enrichment of light rare earth elements （[La/Yb]N=5.03-6.12） and large ion lithophile elements （LILEs）, no negative Eu anomalies, relatively high Cr （265-326 ppm） and Ni （155-262 ppm）, and almost constant V concentrations （194-213 ppm） reveal that the composition close to the primary basaltic magma from an enriched-mantle source, with little crustal contamination and fractional crystallization. The basaltic magma was possibly derived from the upwelling asthenosphere mantle beneath eastern China during the Miocene lithospheric thinning.

关键词： Miocene mafic dyke Dahuichang Western Hills of Beijing

The Middle Devonian Bimodal Association of Volcanic Rocks in the Northern Area of East Junggar, Xinjiang

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Acta Geologica Sinica(English Edition) 1992年第2期66卷 141-153页

作者： han baofu Department of Geology, Peking University, Beijing Department of Geology Peking University Beijing

The Middle Devonian volcanic rocks in the northern area of East Junggar, located between the Ertix andUlungur rivers of northern Xinjiang, may be divided into basic and acid ones. It is evident that a compositionalgap exists between the two groups so that the volcanic rocks are not in line with a calc-alkaline series becausethe intermediate rocks are absent in the area. The fact shows that the volcanic rocks are a typical bimodal asso-ciation. The formation of the bimodal association of volcanic rocks in the area was closely related to continen-tal rifting or continental extension in the Middle Devonian. In such a tectonic setting, magmas were first pro-duced by partial melting of the mantle. Where crustal thinning was greater, the magmas ascended and eruptedon the surface directly so that the basic volcanic rocks formed, but olivine and/or partial pyroxenefractionation occurred in the magmas during their ascent through the thinning crust. On the other hand, wherecrustal thinning was less, ascending mantle-derived magmas reached the lower crust and accumulated there, re-sulting in partial melting of the lower crust and thus giving rise to the contaminated magma which was consoli-dated as acid volcanic rocks on the surface.

关键词： rock REE area The Middle Devonian Bimodal Association of Volcanic Rocks in the Northern Area of East Junggar Xinjiang

Chronological constraints on multi-staged rapid cooling of the Tianshan Mountains inferred from apatite fission track analysis of modern river sands

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Science China Earth Sciences 2015年第8期58卷 1305-1319,1-5页

作者： WANG LiNing JI JianQing SUN DongXia XU QinQin han baofu Research Institute of Petroleum Exploration and Development Laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space Sciences Peking University

The extreme modern elevation of the Tianshan Mountains reflects the Cenozoic deformation. Apatite Fission Track （AFI） chronometry is widely used to study the latest cooling stages caused by tectonic process or by exhumation in the uppermost crust. However, uncertainties remain over timing constraints on thermal history of the Tianshan Mountains since the Cenozoic though a great mount of dating work had been done in this area. To address this issue, modern river sands from the drainage basin on the piedmont of the Tianshan Mountains were sampled to integrate regional information. Single grains were dated with the AFT method, and then different grain-age components were identified to provide thermochronological constraints of their sources. Combined with discussion of previous dataset, our results show the multi-staged rapid cooling cluster at 46-32, 25-24, 19-13, 8-6, and -3 Ma, respectively. We interpreted these cooling events as a result of interplays between the Cenozo- ic tectonic uplift of the mountains and regional climate change.

关键词： Tianshan Mountains detrital apatite fission track cooling stages exhumation thermal history

Petrogenesis and Tectonic Implications of Middle Ordovician Ocean Island Basalts from the Chagantaolegai Ophiolitic Mélange in Junggar,NW China

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Acta Geologica Sinica(English Edition) 2021年第4期95卷 1099-1111页

作者： CHEN Jiafu LI Rongyan MA Haitao han baofu LIU Junlai Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines Department of GeologyNortheastern UniversityShenyang 110819China Department of Earth Planetaryand Space SciencesUniversity of CaliforniaLos Angeles 90095USA Ministry of Education Key Laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space SciencesPeking UniversityBeijing 100871China State Key Laboratory of Geological Process and Mineral Resources School of Earth Sciences and ResourcesChina University of Geosciences(Beijing)Beijing 100083China

Seamount accretion is one of the most significant accretionary orogenic processes in the Central Asian Orogenic Belt,but there are few paleo-seamounts reported from and debate on the tectonic evolution of the Junggar Ocean still *** this study,we present geochronological,mineralogical,geochemical and isotopic data for basalts from the Chagantaolegai ophiolitic mélanges in *** U-Pb dating on one basalt yielded a weighted mean^(206)Pb/^(238)U age of 469±7 Ma,which suggests that it formed in the Middle *** rock samples belong to alkaline basalt and show similar geochemical characteristics,displaying high TiO_(2)(~3 wt%),(La/Yb)N(17.6–19.0),ΣREE(232–289 ppm)and enrichment in Nb and Ta,which implies an ocean island basalt(OIB)*** upon positiveεN d(t)(+4.16 to+4.23),ΔNb(0.20–0.22)and low initial^(87)Sr/^(86)Sr(0.70425 to 0.70452)and Zr/Nb(3.35–3.57),we suggest that the Chagantaolegai OIB samples were likely derived from a fertile mantle source related to *** OIB rock assemblage,chert and marble in the southern part of the Chagantaolegai ophiolitic mélange indicates that a Middle Ordovician seamount was accreted to the Boshchekul-Chingiz arc due to the northward subduction of the Junggar-Balkhash Ocean.

关键词： ocean island basalt seamount Middle Ordovician CAOB West Junggar

A rare zigzag mud crack

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Chinese Science Bulletin 1999年第4期44卷 380-381页

作者： Tairan Wu Guoqi He baofu han Peking Univ Dept Geol Beijing 100871 Peoples R China

MUD crack is a common bedding-plane structure, but the zigzag mud cracks (figs. 1 and 2) are rare phenomena that were found beside G314 highway from Kaxgar to Taxkorgan in Xin-jiang, China. From the photographs we can find that there are footprints of a small animal at every top of zigzag. The zigzag cracks were controlled admittedly by the animal slightly disturbing just when they were breaking. There is a phenomenon worth researching further (fig. 1 ). Distributing equality of zigzags, the horizontal crack (F1) is cracked along the footprints strictly. The vertical one (F2) was not cracked regularly and confined by F1. The crack was

关键词： A rare zigzag mud crack

Geochemical characteristics of the metapelites from the Xingxingxia group in the Eastern Segment of the Central Tianshan:Implications for the provenance and paleoweathering

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Science China Earth Sciences 2005年第10期48卷 1637-1648页

作者： LI Qiugen LIU Shuwen han baofu WANG Yueran DANG Qingning The Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of EducationSchool of Earth and Space SciencesPeking UniversityBeijing 100871China

Metapelites from the Mesoproterozoic Xingxingxia group in the Eastern Segment of the Central Tianshan,Northwestern China,were analyzed for major and trace elements,includ-ing rare earth *** with post-Archean shales,the metapelites are enriched in Sr,Hf and *** other elements are similar to the compositions of the Phanerozoic North American Shale Composite and the Post-Archean Australian average Shale(PAAS).The characteristics of Al_(2)O_(3)/TiO_(2),Cr/Zr,Cr/Th,Th/Sc and high Zr concentration suggest that these pelites could be derived from a significant proportion of felsic and a few proportion of participation of mafic mate-rials in *** rocks display highly fractionated REE patterns,and average(La/Yb)_(n)=*** samples have slightly negative Eu anomalies(Eu/Eu^(*)=0.7―0.84)in comparison with PAAS(Eu/Eu^(*)=0.65),indicating contribution from young immature *** low K_(2)O/Al_(2)O_(3) values of these metapelites suggest that their source materials could contain minimal alkali *** the A-CN-K triangular diagram,the sample data array intersects the feldspar join,indicating that the source had a plagioclase:K-feldspar ratio of approximately 5:1,repre-senting weathered products from components that could approximately correspond to granodio-rites and *** low Chemical Index of Alteration(CIA)and high Index of Compositional Variability(ICV)values suggest low degrees of weathering of the source and low compositional maturity of the sediments,*** geochemical characteristics of the metapelites from the Xingxingxia group also demonstrate that these sediments were deposited in a back-arc background within a continental-arc system.

关键词： Eastern Segment of the Central Tianshan metapelites from the Xingxingxia group geochemistry provenance paleoweathering tectonic setting.

Platinum-group element geochemistry of Cenozoic basalts from the North China Craton: Implications for mantle heterogeneity

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Science China Earth Sciences 2015年第6期58卷 881-895页

作者： ZhanG WenHui ZhanG HongFu SUN YaLi FAN WeiMing han baofu TANG YanJie School of Zijin Mining Fuzhou University State Key Laboratory of Lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences Guangzhou Institute of Geochemistry Chinese Academy of Sciences Department of Earth Sciences Peking University

Forty-two Cenozoic （mostly Miocene） basalt samples from Jining, Chifeng, Fansi, Xiyang, and Zuoquan areas of the North China Craton （the NCC basalts hereafter） were analyzed for platinum-group elements （PGE, including Os, It, Ru, Rh, Pt, and Pd）. Most of them are alkaline basalts and tholeiites and all of them display little crustal contamination. The total PGE contents of the NCC basalts vary from 0.1 to 0.9 ppb, much lower than those of the primitive mantle values of 23.5 ppb. Primitive man- tie-normalized PGE patterns of these basalts define positive slopes and Pd/Ir ratios vary from 1.2 to 25. In terms of both PGE contents and Pd/Ir ratios, they are quite similar to the mid-ocean ridge basalts. There are no obvious negative correlations be- tween PGE vs. MgO, Ni, and Cu in the NCC basalts, indicating that fractional crystallization of olivine, pyroxene, and/or sul- fides during magmatic process cannot be the controlling factor for the observed PGE variation. The observed Pd/Ir variations of the NCC basalts require involvement of non-chondritic heterogeneous mantle sources. Based on Sr-Nd-Pb-Hf isotopic sys- tematics and incompatible-element signatures, a mixing of partial melts from both asthenospheric peridotites and enclosed mantle eclogites at the top of asthenosphere was proposed for the origin of these NCC basalts. The lenses of eclogites are de- rived from upwelling of recycled continental crust during the westward subduction of the Pacific plate from the -600 km dis- continuity zone. The PGE geochemistry of these basalts provides independent evidence to support this conclusion and the ob- served Pd/Ir variations may reflect variations in proportions of tapped peridotitic and eclogitic melts.

关键词： Continental basalts platinum group elements geochemistry North China Craton

Structural,Kinematic and Geochronological Study of the Main Tianshan Shear Zone in the Borohoro Ranges,NW China

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Acta Geologica Sinica(English Edition) 2021年第5期95卷 1431-1455页

作者： LIU Tianlun CHEN Siyu ZhanG Bo CAI Keda han baofu QU Junfeng GUO Lei WANG Meng The Key Laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space SciencesPeking UniversityBeijing 100871China School of Earth Sciences and Resources China University of Geosciences(Beijing)Beijing 100083China Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits MNRSchool of Earth Science and ResourcesChang'an UniversityXi'an 710054China

The western segment of the Main Tianshan shear zone(MTSZ)branches into three major dextral strike-slip shear zones in the Borohoro Ranges,northwestern *** rocks within these zones exhibit vertical foliations,subhorizontal lineations,and dextral *** microstructures and CPO patterns of calcite and quartz in the tectonites suggest shearing at temperatures of 200℃ to 500℃ or *** amount of dextral displacement along the zones is less than 100 ***-ICP-MS U-Pb dating of zircons from some pre-kinematic granites gave ages of 364-325 Ma and 316 Ma,and zircons from a syn-kinematic leucogranite gave an age of 291 *** propose that dextral shearing along the MTSZ started in the earliest *** data indicate that collision between the Yili and Junggar plates might have finished before 325 Ma or 316 Ma,with a tectonic transformation from 325 Ma to 300 Ma,resulting in intracontinental transpression from 300 Ma or 291 *** suggest that the formation of the Kazakhstan orocline(KO)took place in two stages,with the early stage of bending driven by convergence related to oblique subduction,and the late stage possibly associated with lateral disarticulation as a result of the dextral strike-slip shear zones.

关键词： structural geology geochronology dextral shearing CPO pattern Late Paleozoic Main Tianshan Shear Zone Yili-North Tianshan

Post-Entrainment Mineral-Magma Interaction in Mantle Xenoliths from Inner Mongolia,Western North China Craton

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Journal of Earth Science 2012年第1期23卷 54-76页

作者： Yamei Wang baofu han William L Griffin Lei Zhang Guiming Shu Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of EducationPeking UniversityBeijing 100871China School of Earth and Space Sciences Peking UniversityBeijing 100871China GEMOC ARC National Key Centre Department of Earth and Planetary SciencesMacquarie UniversityNSW 2109Australia CSIRO Exploration and Mining North RydeNSW 2113Australia

In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sieve-textured, and reaction rims on mineral grains of mantle xenoliths in the Cenozoic basalts from the western North China craton. The spongy rims on primary clinopyroxene show neither obvious compositional zoning nor preferential development towards the host basalt and probably suggest an origin via partial melting within the lithospheric mantle or pressure release as the xenoliths were carried upwards. The sieve-textured rims on primary spinel show clear chemical zoning with increasing Cr# and decreasing AI towards the host basalt. They are interpreted as the result of partial melting due to heating of the host basaltic magma and decreasing pressure during ascent proc- ess. Post-entrainment reaction mainly generated secondary minerals at contacts between the host ba- saltic melt and xenoliths. The secondary clinopyroxene in reaction rims develops on primary clinopy- roxene and has higher Ti, Ca, and Fe contents and lower Mg# and Si contents than primary one, while the secondary spinel on primary Cr-AI spinel is titanomagnetite. The secondary olivine and clinopy- roxene in the reaction rims on primary orthopyroxene are enriched in Fe, Al, and Ti. The occurrence of reaction rims in mantle xenoliths reflects disequilibrium processes after xenolith entrainment in the basaltic melt. The spongy rims on primary clinopyroxene may not be related to the interaction with thehost basaltic melt, while the sieve-textured rims on primary spinel and reactions rims on primary clinopyroxene, spinel, and orthopyroxene may result from post-entrainment reaction between the host basaltic melt and xenolith minerals.

关键词： mantle xenolith interaction,spongy rim sieve-textured rim reaction rim.