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西大别山浒湾高压变质带是研究秦岭-大别山-苏鲁造山带演化的关键区域,但是该地区榴辉岩相变质时间还存在较大争议.本文通过对浒湾变质带熊店附近的一个变沉积岩样品进行LA-ICPMS锆石U-Pb定年和微量元素分析,来确定该地区榴辉岩相变质作用和碎屑锆石的年龄,并确定该变质带的演化历史.该样品的变质锆石具有弱分带或无分带、低Th/U比值、重稀土含量低且相对平坦以及无明显的Eu负异常等特征.反映这些变质锆石形成时有石榴石,而缺乏长石,其形成对应于榴辉岩相变质作用条件.该样品中变质锆石的206Pb/238U加权平均值为310±3Ma,这一年龄代表了该地区榴辉岩相峰期变质作用的时间,因此浒湾地区榴辉岩相变质作用时间为石炭纪.碎屑岩浆锆石得到了3组近谐和的U-Pb年龄,其206Pb/238U年龄变化范围分别为:400±5Ma～419±5Ma、426±5Ma～449±5Ma以及496±5Ma～524±7Ma,还有1个颗粒给出了580±7Ma的较老年龄.这些结果表明变沉积岩中的碎屑锆石可能大部分来自于华北板块南缘,少量来自于扬子板块.
The high pressure metamorphic belt in Xibashan Bay is a key area for studying the evolution of the Qinling-Dabie-Sulu orogenic belt, but there is still much controversy over the metamorphic time of eclogite in this area. Sedimentary rock samples were analyzed by LA-ICPMS zircon U-Pb dating and trace element analysis to determine eclogite facies metamorphism and age of detrital zircons and to determine the evolutionary history of the metamorphic belt. The metamorphic zircons With weak or no band, low Th / U ratio, low heavy rare earth content and relatively flat, and no obvious Eu negative anomalies and other characteristics of these metamorphic zircons garnet formation, lack of feldspar, the formation of Corresponding to eclogitic facies metamorphism conditions.The 206Pb / 238U weighted average of the metamorphic zircons in this sample is 310 ± 3Ma, which represents the period of peak metamorphism of the eclogite facies in this area. Therefore, The eclogitic metamorphism of the eclogite is Carboniferous.The clastic magmatic zircons have three groups of near-harmonic U-Pb ages with 206Pb / 238U ages ranging from 400 ± 5Ma to 419 ± 5Ma and 426 ± 5Ma ~ 449 ± 5Ma and 496 ± 5Ma ~ 524 ± 7Ma, as well as 1 Particles gives the older age of 580 ± 7Ma These results indicate that detrital zircons in metasedimentary rocks may mostly from the southern margin of the North China plate, a small amount from the Yangtze plate.