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北大别东部中生代火山岩以富Na(Na2O=4.03%,Na2O/K2O=1.31)、高Al2O3(15.30%)、高Sr(865μg/g)和Ba(1361μg/g)含量及高Sr/Y比值(66.1),贫Nb、Y和HREE,轻、重稀土元素的分馏程度强犤(La/Yb)N=26.6犦为特征,岩石地球化学的特征类似于埃达克岩。火山岩中锆石的U-Pb年龄为(129.2±2.6)Ma,属早白垩世。这套火山岩与北淮阳地区中生代的火山岩不仅形成时代相近,地球化学性质相似,而且其中矿物形成的温度压力条件也很类似。结果表明:(1)大别造山带早白垩世前曾发生过山根的拆沉和镁铁质-超镁铁质岩浆的底侵作用;(2)北大别地区早白垩世岩浆作用比较强烈,不仅有超镁铁-镁铁质岩浆的侵入、片麻岩穹隆的侵位,还有一定规模的火山喷发和花岗质岩浆的侵入;(3)北大别东部中生代火山岩可能属北淮阳中生代火山-侵入岩带的一部分;(4)北大别中生代火山岩残留顶盖的存在说明至少早白垩世以来大别造山带的剥蚀规模不会很大。
The Mesozoic volcanic rocks in the eastern part of the North Dabie are rich in Na (Na2O = 4.03%, Na2O / K2O = 1.31), high Al2O3 (15.30%), high Sr (865μg / g) and Ba (1361μg / g) 66.1), depleted in Nb, Y and HREE, characterized by strong fractionation of light and heavy rare earth elements (La / Yb) N = 26.6,, with geochemical characteristics similar to adakites. The zircon U-Pb ages of volcanic rocks are (129.2 ± 2.6) Ma, belonging to the Early Cretaceous. The volcanic rocks and the Mesozoic volcanic rocks in the northern Huaiyang area are not only similar in age but similar in geochemical characteristics, and the temperature and pressure conditions for the formation of minerals are also very similar. The results show that: (1) Decomposition of marsh roots and underplating of mafic-ultramafic magma took place before the Early Cretaceous in the Dabie orogenic belt; (2) Early Cretaceous magmatism was relatively strong in the North Dabie area, Not only the invasion of ultramafic-mafic magma, the emplacement of gneiss dome, but also the volcanic eruption of a certain scale and the intrusion of granitic magma; (3) The Mesozoic volcanic rocks in the eastern part of North Dabie may belong to the Mesozoic Volcanic-intrusive rock belt; (4) The existence of the remaining cap rocks of the Mesozoic volcanic rocks in the North Dabie shows that the scale of erosion of the Dabie orogen is not large at least since the Early Cretaceous.