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Precambrian tectonicevolution
1.1Mainresearchcontents andprogress
1.1.1Precambrian tectonicevolution of North China Craton
The North Chinacratonconsists of the EasternBlock,WesternBlock,and the intervening Central Orogenic beltwhichcontainsat least two sutures.Significantprogress was made on theeasternmost circa 2.5GaZanhuang-Zunhua suture, focused mainly on thestructuralrelationships of differentgeological units,ages of plutons intruded into mélangeassociated with openingandclosing ofan Archean oceanalong this belt,andpetrogenesis of the Archean intrusive rocks thatcut the mélange.We proposed that the Eastern Blockandanarc terrane(Fuping terrane) in the COBcollided prior to 2.5 Ga, forming theextensive mélange belt.Asubduction polarity reversalevent followed thearc-continentcollision,causingadditional deformationand forming the intrusive rocks thatcutacross the mélangeand parts of the EasternBlock. Theocean that remainedopenbehindtheFupingarcclosedsometimebetween2.4and2.1Ga,causingadditional deformationandamalgamating theEasternandWesternBlocks.From 1.9-1.85 Ga thecratonexperienced acraton wide granulitefaciesevent.We relate this to acontinent-continentcollision on the north margin of thecraton, probably related to when the North China Cratoncollided with the Columbia (Nuna)Supercontinent. These research results have been published inLithos(2 papers,T2).WealsoinitiatedresearchontheDengfenggreenstonebeltand proposed that the sedimentary-volcanic rocks inthegreenstonebelt mayrepresent a Neoarchean subduction-accretionarycomplexcorrelative with theZanhuang Complex. The research results have been published inPrecambrian Research(1 paper,T2).
Contact:WangJunpeng, Deng Hao
Modelofinterpreted geodynamic origin ofthe ca.2.5Gamagmatic eventintheCentralOrogenic BeltoftheNCC. A new east-dipping reversed subduction happenedat 2.5Ga,followingthe collision betweenthe Eastern Block oftheNCC andtheintra-oceanic arcterranetothewest. This east-dippingsubduction polarityreversalevent resultsinthemelting oftheenrichedmantle, andthengivesrisetotheformation ofthe ca. 2.5Gamafic dikes and granites(includingtheWangjiazhuang granite) ofthe Eastern Block.
Inaddition, Kuskyand Mooney (U.S. GeologicalSurvey) studied thegeologicalandgeophysicalcharacters of OrdosBlockand foundS-waveanomaliesat different depths, incommon with theSichuanand TarimBasins thatarealso underlainbycratoniccrust.Seismic velocitysections show that the OrdosBlockhas thickcrust, with the Moho deeper than 40 km.It is underlainby adenser lowercrustal body with seismic velocities of 7.1 km/s which ischaracteristicof oceanic plateausglobally. Comparisons weremade directly with the southern CaspianSea,another trapped oceanic plateau inan orogenic belt,and theWrangellia terrane,an oceanic plateauaccreted to western North America.We proposed anhypothesis that the OrdosBasin hadan originasan oceanic plateau thataccreted to the NCC,and laterexperienced differentepisodesofdifferentiationassociatedwithlatersubductionandcollisions.The formation ofcratonic lithospherebyaccretionof oceanic plateaus may be one mechanism tocreate stablecratons. These research results havebeen published inEarthand PlanetaryScience Letters(1 paper,T1).
Contact: Tim Kusky,Walter Mooney
Mapoffree-air gravityanomaliesin SE Asia(modifiedfromYangand Liang, 2011).
Topography andfree-air gravitymapsofthe southernCaspian Sea and surrounding regions.DatatogeneratethetopographicmapisfromtheNationalGeophysicalDataCenter(NGDC; http://www.ngdc .noaa.gov/) andthefree air anomalywas calculatedviatheInternationalCentreforGlobalEarthModels(ICGEM; http://icgem.gfz-potsdam.de/ICGEM/ICGEM .html). Bothmapswere drawn usingGMT(GenericMapping Tools) software.
S-wave anomaliesat different depths(modifiedfromBao et al., 2015). TheOrdosCraton has aclearhigh-S-wave anomaly,in commonwiththe Sichuan and Tarim Basinsthatare also underlainby cratonic crust. Panelsa,b,canddcorrespondtothe depthsuppercrust(panela),mid-lower crust(panel b),Moho-100 km(panel c), and
100–150 km below surface(panel d).
1.1.2Precambrian tectonicevolution of the YangtzeCraton and Cathaysia Orogen
We documented Neoproterozoic (0.94-0.93Ga) metamorphicevents forthe first time in the Miaowan ophiolite onthe northern marginofthe Yangtzecraton, which provides importantevidence for the finalamalgamation of the basement of the Yangtzecraton.We identified two stagesof metabasite- ultrabasic rocks in the Miaowan ophioliticcomplex; latest Mesoproterozoic (1.12-1.1 Ga)and Neoproterozoic (1.0-0.97 Ga), formed in different tectonic settings.In Cenxi, southeastGuangxi,earlyPaleozoicophioliteremnantsandhigh-Mgbasalticandesiteandandesite has been recognized, which providescrucialevidence for theexistence ofPaleozoic oceancrust subduction-accretionaryandcollision-orogenesis inthe Cathaysian terranes.
We studied the Archean-Paleoproterozoic high-grade metamorphic rocks in thecore of theHuangling dome,thenorthernmarginofYangtzecratonthroughdetailedgeological mapping,geochronologyand geochemical methods.We found that thePaleoproterozoic mafic- ultramafic rocks in the volcano-sedimentary sequence formed inanarcenvironmentabove a subductionzoneand we proposed that records of aPaleoproterozoic subduction-collisioneventare preserved in the Huangling dome on the northern margin of Yangtzecraton. This research paper isaboutto be submitted to an internationalSCI journal (T2).
Inaddition, we describe the field relationships on the basis ofgeological mapping, then present detailedandsystematicgeochemical,geochronologyandSm-Nd isotopic investigations on these mafic-ultramafic rocks in theJiangnanorogenicbelt (JOB)between theYangtzecratonand Cathaysian terranes inSouth China. Geochemical signatures suggest that those rocks formed inanextensionalarcenvironment,and the subduction may havecontinued toca. 750 Ma in the westernJOB, implyingthat theamalgamationevent between the Yangtzecratonand Cathaysian terranes was later than 750 Ma. This researchhas been published inGondwana Research(T2).
Contact:PengSongbai
MapoftheYangtzecratonshowingareas discussed.
world
The presence orabsence of a thick lithospheric root beneath the Yangtze Craton has been debated.We integratedandanalyzedexisting geological,geophysicalandgeochemical data for the first time and the results indicate thatthe Yangtze Craton has lost theeastern half of its root, much like the North Chinacraton.Theprocesses of destructioncan be divided into Neo- proterozoicand Mesozoic stages. The majordecratonization occurred in the Mesozoic, which iscloselyrelatedtothesubductionandrollingbackofthePacificPlate.Resultshavebeen published inTectonophysics(T2).
Aftercomprehensiveandcomparativeanalysisof the Yilgarn Craton,Superior Cratonand NCC, it has been proposed that the lithospheric thinningat theedgesofcratons is acommon phenomenon,related to theeffects of orogenicevents oncratonicmargins.Inaddition, acomparison of the NCC withcratons that have lost parts of their roots via impingementby mantle plumes (Tanzania, North Atlantic) shows that plumescan interact with the Mid- lithospheric discontinuity,aiding in large-scalefoundering ofSCLM. Areview paper on this is in review. Otherrelated results have been published inCanadian Journal of EarthSciences(T4).
Contact: Tim Kusky, XiaoyongLi,ZhengshenWang
(a) SimplifiedtectonicmapoftheNCC and surrounding orogenic belts(modifiedfromKusky andLi 2003,Zhaiet al.2010, andKusky 2011).Notethatthe cratonis dividedintotwomain blocks(EasternandWestern) bytheCOB.Notethatknown Archean granulitesareconfinedtotheCOB,butthattheca. 1.9–1.8Ga granulites areconcentratedin a belt alongthe northernmargin ofthe cratonsouth oftheNorthHebeiOrogenic Belt, andonthe ShandongPeninsula.(b) SimplifiedtectonicmapoftheSlave craton(drawn afterHoffman 1989b) andits relationshipsto surrounding orogensand basins.NotethattheSlavecratonismuch smallerthanthe NCC.HP, high pressure;HT,hightemperature;UHT, ultra-hightemperature;GSLsz,GreatSlave Lake shear zone.
alongtwodifferent vertical profiles(a,b) andthe distribution ofthemantletransitionthickness ofthe Yangtze andNorthChina cratons(c, d).(a),(b) are Pwave velocityperturbations profiles along37°N and31°Nlatitude, respectively(ModifiedfromHuang andZhao, 2006,with permissions);(c)DistributionofthemantletransitionthicknessoftheNCC(Chen and Ai,2009,with
permissions);(d)Distribution ofthemantletransitionthickness oftheYangtze craton(ModifiedfromHuang et al., 2014a,with permissions). The redin a and b representsthe slow velocitieswhiletheblue representsthefast velocities. Thefast velocities outlinetheflat-lyingslabs beneath Eastern Asia. The areaswith bluein c and d are characterized bythickmantletransition zone(N250 km)whilethe areaswithredare characterized bythinmantletransitionzone(b250 km).
New comprehensivemodelforcraton destructionthroughflat slabdehydration, slab rollback,mantleinflux,melt-generation, andmelt SCLM peridotite reaction.
1.2Scientificresearchprojects
We have threeNational NaturalScienceFundProjects (41572203; 41172069; 41372075)
thisyearaboutPrecambrian tectonicevolution.
1.3 Researchpapers
We have published 1 paper in T1 journal, 5 papers in T2 journals, 1 paper in T3 journaland
3 papers in T4 journalsduring 2014-2015aboutthis research direction.