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Precambrian Tectonic Affinity of the Southern Langshan Area, Northeastern Margin of the alxa block: Evidence from Zircon U-Pb Dating and Lu-Hf Isotopes

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Acta Geologica Sinica(English Edition) 2022年第5期96卷 1516-1533页

作者： NIU Pengfei QU Junfeng ZHANG Jin ZHANG Beihang ZHAO Heng Key Laboratory of Deep-Earth Dynamics Ministry of Natural Resources of GeologyInstitute of GeologyChinese Academy of Geological SciencesBeijing 100037China

The alxa block is the westernmost part of the North China Craton(NCC), and is regarded as one of the basement components of the NCC. Its geological evolution is of great significance for the understanding of the NCC.However, the Precambrian basement of the alxa block is still poorly studied. In this study, we present new in situ LA-ICPMS zircon U-Pb and Lu-Hf isotope data from the Diebusige Metamorphic Complex(DMC) which located in the eastern alxa block. Field and petrological studies show that the DMC consists mainly of metamorphic supracrustal rocks and minor metamorphic plutonic rocks and has experienced amphibolite-granulite facies metamorphism. Zircon U-Pb dating results suggested that the amphibolite sample yields a crystallization age of 2636 ± 14 Ma and metamorphic ages of 2517–2454 Ma and 1988–1952 Ma, proving the existence of exposed Archean rocks in the Langshan area and indicating that late Neoarchean to Paleoproterozoic metamorphic events existed in the alxa block. Two paragneiss samples show that the magmatic detrital zircons from the DMC yield 207Pb/206Pb ages ranging from 2.48 Ga to 2.10 Ga with two youngest peaks at 2.13 Ga and 2.16 Ga, respectively, and they were also overprinted by metamorphic events at 1.97–1.90 Ga and 1.89–1.79Ga. Compilation of U-Pb ages of magmatic detrital and metamorphic zircons suggested that the main part of the DMC may have been formed at 2.1–2.0 Ga. Zircon Lu-Hf isotope data show that the source materials of the main part of the DMC were originated from the reworking of ancient Archean crust(3.45–2.78 Ga). The Hf isotope characteristics and the tectonothermal event records exhibit different evolution history with the Khondalite Belt and the Yinshan block and the other basements of the alxa block, indicating that the Langshan was likely an independent terrain before the middle Paleoproterozoic and was subjected to the middle to late Paleoproterozoic tectonothermal events with the Khondalite Belt as a whole.

关键词： zircon U-Pb dating Hf isotop Paleoproterozoic Neoarchean Diebusige Metamorphic Complex alxa block North China Craton

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Magma Generation of Magnetite-Rich Intermediate-Mafic Rocks and Its Mantle Processes in the Southwestern alxa block,NW China

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Journal of Earth Science 2022年第1期33卷 161-176页

作者： Lu Tao Hongfei Zhang Jing Wu Xiaochun Zhou Liqi Zhang State Key Laboratory of Geological Processes and Mineral Resources China University of GeosciencesWuhan 430074China School of Earth Sciences China University of GeosciencesWuhan 430074China Gemmological Institute China University of GeosciencesWuhan 430074China Faculty of Earth Resources China University of GeosciencesWuhan 430074China

Many studies focus on mineralization of huge magnetite ore deposits and petrogenesis of their large-volume host rocks.However,magma generation of those small-scale intrusions with enrichment of magnetite is poorly reported and paid attention to.We here carry out an integrated study of magnetite chemistry,U-Pb zircon dating,geochemistry,and Sr-Nd-Hf isotopes for the magnetite-rich intermediate-mafic rocks from the Helishan pluton in the southwestern alxa block,Northwest China.This,together with several previously reported magnetite/iron-rich intrusions nearby,is capable of providing some constraints on magma generation of magnetite/iron-rich intrusive rocks.The Helishan pluton,dated at ca.290 Ma,consists of hornblende gabbro,diorite,and quartz monzodiorite with~3%-5%magnetite in all the lithologies.Study on magnetite chemistry manifests a magmatic origin for them.All the lithologies display high TFeO/MgO ratio (1.71-1.89),weakly fractionated REE patterns((La/Yb)_(N)=1.82-10.17),enrichment of Rb,Sr,and Pb,and depletion of high field strength elements.They have (^(87)Sr/^(86)Sr)_(i) values of 0.705 2 to 0.705 8,ε_(Nd)(t) values of+0.03 to+0.64,and zircon ε_(Hf)(t) values of +6.5 to+12.0.We propose that they were derived from partial melting of iron-rich metasomatized lithospheric mantle.The systematic variations of Sr/Y ratios and Nd-Hf isotopic compositions with time for the Paleozoic igneous rocks at the southwestern alxa block indicate ever existence of thinning and rebirth of lithospheric mantle.This geodynamic process could be the potential mechanism to give rise to the iron-rich signature of the reborn mantle sources of the Helishan pluton.For intermediatemafic intrusions at subduction zones,they are unlikely to form considerable magnetite ore deposits since their modest magmatic flux and early fractional crystallization of magnetite at a high oxygen fugacity and H_(2)O condition.

关键词： geochemishtry magnetite-rich intrusion mantle source petrogenesis lithospheric process alxa block Northwest China

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Multiple Deformation in the Northeastern alxa block: Implications for the Southern Central Asian Orogeny and Its Subsequent Intraplate Evolution

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Acta Geologica Sinica(English Edition) 2020年第S1期94卷 84-85页

作者： ZHANG Jin QU Junfeng ZHANG Beihang ZHAO Heng ZHENG Rongguo Institute of Geology Chinese Academy of Geological SciencesBeijing100037China

As an important tectonic unit in the middle part of the southern Central Asian Orogeny, the alxa block was affected by multiple deformational events occurring in the Central Asian tectonic regime during the Paleozoic and Mesozoic. The record of deformation in the alxa block represents the entire evolutionary process from a continental margin to an intraplate setting. In the Langshan region of the northeastern alxa block, four important Paleozoic-early Mesozoic deformation events have been distinguished:(1) nearly north-south-striking ductile thrusting along the eastern alxa block in the Late Devonian;(2) nearly east-west-trending brittle top-to-the-south thrusting in the Mid-Late Permian;(3) nearly east-west-trending initially ductile then brittle dextral transtension with 30-40 km of displacement in the Late Permian;and(4) northeast-trending ductile sinistral shearing with 120-125 km of displacement in the Mid-Late Triassic. The ductile thrusting in the Late Devonian may have resulted from the interaction between the North China Craton and the alxa Black, which was a peri-eastern Gondwana block. Parallel east-west-trending thrusts and related folds formed in the Neoproterozoic Langshan Group due to the closure of the PaleoAsian Ocean in the Mid-Late Permian. The Late Permian eastwest-trending and dextrally ductile transtension may have resulted from intraplate adjustment after the Central Asian Orogeny and the formation of the Ural Orogenic Belt to the west;this shear zone may have been part of a huge ductile tectonic belt developed along the whole southern Central Asian Orogenic Belt(CAOB). During the Early Triassic, the subduction of oceanic crust along the southern central CAOB terminated then the eastern alxa block was affected by the collision between the North China Craton and the Yangtze Craton to the south. Since the late Mesozoic, the Langshan region has experienced another five important deformation events, which were all far-field tectonic effects related to plate margin tectonic activities(e.g., the

关键词： alxa block Langshan Central Asian Orogenic Belt North China Craton multi-stage deformation

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NEOPROTEROZOIC S-TYPE GRANITES IN THE alxa block,WESTERNMOST NORTH CHINA AND TECTONIC IMPLICATIONS:IN SITU ZIRCON U-Pb-Hf-O ISOTOPIC AND GEOCHEMICAL CONSTRAINTS

NEOPROTEROZOIC S-TYPE GRANITES IN THE ALXA BLOCK,WESTERNMOST...

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中国科学院地质与地球物理研究所2014年度（第14届）...

作者： WEI DAN XIAN-HUA LI QIANG WANG XUAN-CE WANG YU LIU State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences State Key Laboratory of Isotope Geochemistry Guangzhou Institute of GeochemistryChinese Academy of Sciences

The alxa block in northern China has been traditionally considered as the westernmost part of the Archean North China Craton(NCC).However,recent studies revealed that there are few Archean rocks exposed in the alxa block,and the Paleoproterozoic geology of this block is different from that of the western part of the NCC.Thus,the tectonic affinity of the alxa block to the NCC and/or other Precambrian blocks needs further investigations.In this study,we carry out integrated analyses of in situ zircon U–Pb age and Hf–O isotopes as well as whole-rock geochemistry and Nd isotopes for the Neoproterozoic Dabusushan and Naimumaodao granites from central alxa block.Secondary ion mass spectrometry(SIMS)U–Pb zircon dating results indicate that the Naimumaodao and Dabusushan granite plutons were formed at ca.930 Ma and ca.910 Ma,respectively.These granites are peraluminous(A/CNK value>1.0),and contain peraluminous minerals such as muscovite and tourmaline,similar to those of S-type granites.They are characterized by high zircon 18O values of ca.8.2 to 12.1 permil,corresponding to a calculated magmatic 18O value of ca.10.5 to14.3 permil,variable zircon Hf(t)values of 6.2 to 3.8(corresponding to Hf model ages of 2.2 to 1.6 Ga)and whole-rock Nd(t)values of 10.1 to 4.5(corresponding to Nd model ages of 2.4-1.9 Ga).The petrological and Nd–Hf–O isotopic study indicated that these granites were most probably generated by remelting of dominant(meta)sedimentary rocks in an orogenesis-related compressional environment.There is a clear contrast in the Precambrian geological evolution,including basement rock age data,Precambrian magmatism and detrital zircon age patterns,between the alxa block and the NCC.Furthermore,the new in-situ detrital zircon ages on Neoproterozoic(meta)sedimentary rock suggest that alxa block is likely related to the Cathaysia block of South China during the Neoproterozoic,and amalgamated with the NCC since the Early Paleozoic.Thus,our new data suggest that the alxa block is most likely a separated Precambrian te

关键词： North China Craton alxa block Neoproterozoic S-type granite zircon Hf-O isotopes

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Paleoproterozoic evolution of the eastern alxa block,westernmost North China:Evidence from in situ zircon U-Pb dating and Hf-0 isotopes

Paleoproterozoic evolution of the eastern Alxa Block,western...

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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： Wei Dan Xian-Hua Li Jinghui Guo Yu Liu Xuan-Ce Wang State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences Graduate School of Chinese Academy of Sciences State Key Laboratory of Geological Processes and Mineral Resources.China University of Geosciences

The alxa block is the westernmost part of the North China Craton(NCC).In the past,it has been considered to be part of the Archean NCC.However,formation and evolution of this block remain poorly understood,and this has hampered a broader understanding of the NCC.In this study we analyzed the in situ zircon U-Pb age and Hf-0 isotopes for the two oldest rock units in the eastern alxa block,namely the Bayanwulashan and Diebusige Complexes.The Bayanwulashan Complex consists mainly of metamorphic rocks with mafic and felsic protoliths.SIMS U-Pb zircon dating results indicate that the primary magmatic ages of the mafic and felsic igneous rocks are ca.2.34 Ga and ca.2.32-2.30 Ga,respectively,and both sets of rocks were overprinted by two metamorphic events at ca.1.89 Ga and ca.1.79 Ga.Geochemical and zircon Hf-0 isotopic data suggest that the ca.2.34 Ga amphibolites within the Bayanwulashan Complex are characteristically high in TiO(up to 3.2%),Zr(up to 394 ppm) and Ti/V(>30),resembling the basaltic rocks formed within continental rifts.The ca.2.32-2.30 Ga felsic rocks were generated by remelting of dominant meta-igneous rocks that have zircon Hf model ages of 2.92-2.81 Ga.The Diebusige Complex is composed of amphibolites,mafic gneisses and paragneisses.It was intruded by granites dated at ca.1.97-1.98 Ga,and subjected to high grade metamorphic events at ca.1,89 Ga and ca.1.79 Ga.Re-examination of U-Pb ages for detrital and metamorphic zircons indicate that the depositional ages of protoliths of the Diebusige paragneisses may be considered to be between ca.2.45 and 2.0 Ga.These U-Pb zircon age data do not support the existence of exposed Archean rocks in the eastern alxa block,although the possibility of Archean rocks at deeper crustal levels cannot be ruled out entirely. The eastern alxa block contrasts to the neighboring Yinshan block and Khondlite Belt,as well as the Trans-North China Orogen,in terms of the timing and evolution of magmatism and metamorphism.Thus,we conclude that the alxa block is a separated Paleopro

关键词： North China Craton alxa block Paleoproterozoic U-Pb zircon age Zircon Hf-O isotopes

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Deformation at the Easternmost Altyn Tagh Fault: Constraints on the Growth of the Northern Qinghai–Tibetan Plateau

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Acta Geologica Sinica(English Edition) 2020年第4期94卷 988-1006页

作者： ZHANG Jin YUN Long ZHANG Beihang QU Junfeng ZHAO Heng HUI Jie WANG Yannan ZHANG Yiping Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources Institute of GeologyChinese Academy of Geological SciencesBeijing 100037China Key Laboratory on Geological Disposal of High-level Radioactive Waste Beijing Research Institute of Uranium GeologyCNNCBeijing 100029China University of Chinese Academy of Sciences Beijing 100049China Hebei University of Engineering School of Earth Science and EngineeringHandanHebei 056038China Chinese Academy of Geological Sciences Beijing 100037China

How the Altyn Tagh fault(ATF) extends eastwards is one of the key questions in the study of the growth of the Qinghai–Tibetan Plateau. Detailed fieldwork at the easternmost part of the ATF shows that the ATF extends eastward and bypasses the Kuantan Mountain;it does not stop at the Kuantan Mountain, but connects with the northern Heishan fault in the east. The ATF does not enter the alxa block but extends eastward along the southern alxa block to the Jintanan Mountain. The Heishan fault is not a thrust fault but a sinistral strike-slip fault with a component of thrusting and is a part of the ATF. Further to the east, the Heishan fault may connect with the Jintananshan fault. A typical strike-slip duplex develops in the easternmost part of the ATF. The cut and deformed Quaternary sediments and displaced present gullies along the easternmost ATF indicate that it is an active fault. The local highest Mountain(i.e., the Kuantan Mountain) in the region forms in a restraining bend of the ATF due to the thrusting and uplifting. The northward growth of the Qinghai–Tibetan Plateau and the active deformation in South Mongolia are realized by sinistral strike-slipping on a series of NE–SW-trending faults and thrusting in restraining bends along the strike-slip faults with the northeastward motion of blocks between these faults.

关键词： sinistral strike-slip fault Altyn Tagh fault alxa block Late Cenozoic Qinghai–Tibetan Plateau

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Provenance and paleogeography of Carboniferous-Permian strata in the Bayanhot Basin:Constraints from sedimentary records and detrital zircon geochronology

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Geoscience Frontiers 2021年第3期12卷 113-131页

作者： Junfeng Zhao Yijun Zhou KeWang Xuan Li Zhanrong Ma Zhengzhong Ruan DongWang Rui Xue State Key Laboratory of Continental Dynamics Department of GeologyNorthwest UniversityXi'an710069China Changqing Branch of Geophysical Research Institute BGPCNPCXi'an 710021China Exploration and Development Research Institute Changqing Oilfield Company of PetroChinaXi'an 710021China Twelfth Oil Production Plant Changqing Oil Field Company of PetroChinaHeshui 745400China

The Bayanhot Basin is a superimposed basin that experienced multiple-staged tectonic movements;it is in the eastern alxa block,adjacent to the North China Craton(NCC)and the North Qilian Orogenic Belt(NQOB).There are well-developed Paleozoic-Cenozoic strata in this basin,and these provide a crucial window to a greater understanding of the amalgamation process and source-to-sink relationships between the alxa block and surrounding tectonic units.However,due to intensive post-depositional modification,and lack of subsurface data,several fundamental issues-including the distribution and evolution of the depositional systems,provenance supplies and source-to-sink relationships during the Carboniferous-Permian remain unclear and thus hinder hydrocarbon exploration and limit the geological understanding of this basin.Employing integrated outcrop surveys,new drilling data,and detrital zircon dating,this study examines the paleogeographic distribution and evolution,and provenance characteristics of the Carboniferous-Permian strata in the Bayanhot Basin.Our results show that the Bayanhot Basin experienced a long-term depositional evolution process from transgression to retrogression during the Carboniferous-late Permian.The transgression extent could reach the central basin in the early Carboniferous.The maximum regional transgression occurred in the early Permian and might connect the Qilian and North China seas with each other.Subsequently,a gradual regression followed until the end of the Permian.The northwestern NCC appeared as a paleo-uplift area and served as a sediments provenance area for the alxa block at that time.The NCC,Bayanwula Mountain,and NQOB jointly served as major provenances during the Carboniferous-Permian.There was no ocean separation,nor was there an orogenic belt between the alxa block and the NCC that provided sediments for both sides during the Carboniferous-Permian.The accretion of the alxa and North China blocks should have been completed before the Carboniferous period.

关键词： Carboniferous-Permian Detrital zircon geochronology Paleogeography Bayanhot Basin alxa block North China Craton

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