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1、2011年9月地球学报Sep.2011第32卷第5期:523-532ActaGeoscienticaSinicaVol.32No.5:523-532www.cagsbulletin.comwww.地球学报.com皖北地区新元古代构造背景的转换:来自碎屑岩地球化学的证据孙林华,桂和荣宿州学院地球科学与工程学院,安徽宿州234000摘要:在对安徽省北部宿州新元古代史家组砂岩地球化学特征分析的基础上,结合前人发表的淮南和凤阳新元古代刘老碑组页岩的地球化学数据,对它们的物源和构造背景进行了对比讨论。结果表明:刘老碑组页岩的地球化学特征表明其来自于中-酸性火成岩高程
2、度的首次风化,而史家组砂岩则来自于经历了再循环的古老地壳物质较低程度的风化。刘老碑组页岩相对史家组砂岩具有高(MgO+Fe2O3)、TiO2含量和Al2O3/SiO2比值的特征,结合La-Th-Sc和Th-Sc-Zr/10判别图解,表明二者可能沉积于不同的构造背景,其中前者属于大陆岛弧(也可能是弧后盆地),而后者则形成于相对稳定的被动大陆边缘或者板内。结合前人关于皖北新元古代研究的相关进展,证实了华北板块东南缘构造背景在新元古代时期经历了从活动向稳定的转变。关键词:地球化学;碎屑岩;新元古代;构造背景;皖北中图分类号:P595;P588.21;P542.4
3、文献标志码:Adoi:10.3975/cagsb.2011.05.02TransitionofNeoproterozoicTectonicBackgroundinNorthernAnhuiProvince:EvidencefromGeochemistryofClasticRocksSUNLin-hua,GUIHe-rongSchoolofEarthScienceandEngineering,SuzhouUniversity,Suzhou,Anhui234000Abstract:Basedonageochemicalanalysisofsandstoneso
4、fNeoproterozoicShijiaFormationinSuzhouofnorthernAnhuiProvince,incombinationwithpreviouslypublishedgeochemicaldataofshalesofNeoproterozoicLiulaobeiFormation,theauthorsmadeacomparativelyCAGSstudyoftheprovenanceandtectonicsettingofthesetwosuitesofclasticrocks.Theresultsindicatethatth
5、eshalesofLiulaobeiFormationmighthaveoriginatedfromthefirstcycleofintermediate-felsicvolcanicrockswithintenseweathering,whereassandstonesofShijiaFormationwereprobablygeneratedbylow-intenseweatheringoftherecycledoldcrustmaterial.TheshalesofLiulaobeiFormationarecharacterizedbyhigh(Mg
6、O+Fe2O3)andTiO2contentandAl2O3/SiO2ratiosrelativetothesandstonesofShijiaFormation.Thesedata,togetherwithLa-Th-ScandTh-Sc-Zr/10discriminationdiagrams,implythattheyweredepositedindifferentsettings,i.e.,theformerwasdepositedinacontinentalislandarc(probablyback-arcbasin),whereasthelat
7、terwasinapassivecontinentalmarginorintra-plateenvironment.IncombinationwithpreviousstudiesoftheNeoproterozoicevolutioninnorthernAnhuiProvince,theseresultsdemonstratethatthetectonicbackgroundofthesoutheastmarginofNorthChinaCratonunderwenttransitionfromactivetopassiveduringNeoproter
8、ozoic.Keywords:geochemistry;clast
