中文摘要：

对华北板块东南缘蚌埠隆起区内凤阳县老山含石榴子石片麻状花岗岩进行了锆石SHRIMP U—Pb定年。阴极发光图像显示所研究样品中锆石通常具有核-幔-边结构。其中，核部年龄为新元古代（一个谐和年龄为673Ma±12Ma）、幔部年龄为三叠纪和具有岩浆结晶环带的边部年龄为159Ma±2Ma。锆石边部明显具有岩浆结晶环带以及高的Th／U比值（一般为0．14～0．45），其年龄代表该岩石的形成时代；幔部具有低的Th／U比值（一般为0．02～0．15），为变质成因；而核部常具有岩浆结晶环带，有时因重结晶等原因而模糊，其年龄应代表源区岩石的形成时代。由于继承锆石的形成时代为新元古代并经过印支期变质作用，这些年龄记录与大别山超高压岩石一致。因此，证明老山含石榴子石片麻状花岗岩为159Ma±2Ma，其为经历了三叠纪多期变质作用改造的华南俯；中陆壳物质发生部分熔融而形成即由华南三叠纪俯冲陆壳物质再循环的结果。而华北板块通东南缘深部存在华南俯冲陆壳岩石，进一步证实在中生代华南板块至少已俯冲至蚌埠地区。

英文摘要：

Garnet-bearing gneissic granite from Laoshan,Bengbu was dated by zircon SHRIMP U-Pb method. The CL images revealed that the zircon from the dated sample generally displayed core-mantle-rim structure. The age of the core domains was Neoproterozoic （a concordant age of 673 Ma±12 Ma）,the mantle yielded an age of 210 Ma±4 Ma-242 Ma±5 Ma with low Th/U values of 0.02-0.15, and the rims with oscillatory zoning gave a weighted mean ^206pb/^238U age of 159 Ma±2 Ma （MSWD=0.91,n=9）. The oscillatory zoning in CL imaging and high Th/U ratios （generally 0.14-0.45） suggested that the rim domains of zircon were magmatic in origin, hence the 159 Ma± 2 Ma was its formation age; the mantle domains with low Th/U ratios, formed in the metamorphic conditions;while the age of the weak oscillatory zoning core obscured by the metamorphic recrystallization should represent the age of source rock. The inherited cores formed in the Neoproterozoic and was overprinted by the Triassic multiple metamorphism which was consistent with the Dabie ultra-high pressure （UHP） rocks. Hence the Laoshan garnet-bearing gneissic granite was derived from the partial melting of the crustal materials of the South China Block （SCB）,which was suffered from the Triassic UHP metamorphism,or resulted from the recycling of the Triassic subducted continental crust of the SCB. The presence of the Triassic subducted continental materials from the SCB beneath southeastern margin of the North China Block indicated that the SCB subducted beneath the Bengbu region in the Mesozoic.