Geochemistry of the Caledonian Basic Volcanic Rocks at the South Margin of the Qinling Orogenc Belt,and Its Tectonic Implications

(整期优先)网络出版时间:1999-03-13
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ThegeochemistryofthebasicvolcanicrocksatthesouthmarginoftheQinlingorogenicbelt(SMQOB)suggeststhattheywereformedinanintraplatetectonicsetting.TheREEdistributionpatternsshowtheserocksarestronglyenrichedinLREEwithhigh∑REE,andtheirtraceelementsgeochemistryissimilartothatofcontimentalfloodbasalt.AlltheaboveevidencesuggeststhattheCaledonianbasicvolcanicrocksintheSMQOBweretholeiiticbasaltsformedinanintraplatespreading-initialrifttectonicsetting.Thecharacteristicsofregionalgeologyandgeochemistryindicatethattherewasanintraplatespreading-rifttectonicsettingbetweentheSouthQinglingblockandtheYangtzeblockintheCaledonianepoch.ThedynamicspreadinginthisdistrictbeganintheEarlyCaledonianandthentheintraplatespreadinginitialriftswereformedintheLateCaledonian.AsaresultofspreadingoftheTethysandgeodynamicprocessesindeepmantle,theMianlue-HuashanoceanicbasinwasformedbetweentheQinlingblockandtheYangtzeblockinDevonian,andtheQinlingmicroplatewasseparatedfromthenorthernpartoftheYangtzeplate.