Zircon U／Pb Dating of Cretaceous Adakitic Volcanic Rocks in the Eastern Part of North Dabie Mountains

1IntroductionMostgeologistshaveacceptedthattheQinling Dabieorogenicbeltistheproductofcontinentaldeepsubduction (Okayetal.,1993;Cong ,B .etal.,1995 ;Hackeretal.,1995 ;DongShuwenetal.,1993) .Butasthebiggest scaleUHPmetamorphicbeltintheworld ,thereactionbetweenthecrustandthemantleatthepost orogenicstageandtheexhumation ,upliftinganddenudationoftheorogenicbeltarethecomplexdynamicprocesses .ItwasreportedpreviouslythatsomeCretaceousvolcanicrocksexistinthemiddleoftheDabieMountains (GuanYuncaiet…

Zircon U/Pb dating of Cretaceous adakitic volcanic rocks in the eastern part of North Dabie Mountains

Mesozoic volcanic rocks in the eastern part of the North Dabi e Mountains are rich in Na (Na\-2O=\{4.03%\}, Na\-2O/K\-2O=\{1.31\}), Sr and Ba , and high in Sr/Y ratio but low in Nb, Y and H REE. They have experienced strong fractionation of REE \, and are similar to adakite in geochemical characteristics. The U-Pb dating of zircon from the volcanic rocks is Ma, belonging to Early Cretaceous. These rocks are similar to the volcanic rocks of North Huaiyang not only in age and rare-earth element and trace element geochemistry, but also in the formati on temperature and pressure of the minerals. The results indicated that the dela mination of mountain root and underplating of mafic-ultramafic magma had happen ed in the Dabie orogen before Early Cretaceous. Mesozoic magmatism was intense i n the North Dabie Mountains, including the intrusion of mafic-ultramafic magma, uplifting of gneiss dome, explosion of volcanic rocks and intrusion of granitic magma. The Mesozoic volcanic rocks in the eastern part of the North Dabie Mount ains may be one part of the Mesozoic volcano-intrusive complex belt of North Hu aiyang. The existence of Mesozoic volcanic remnant cap means the denudation of t he Dabie orogenic belt was not very strong since Early Cretaceous.