A series of granites crop out to the northeast of Erenhot City,near the China-Mongolian border.Zircon U-Pb dating and whole-rock elemental and Sr-Nd isotopic analysis were performed for four granitic plutons.The Halatumiao syenogranite intruded into the Middle-Devonian strata,showing geochemical features of aluminous to weakly peraluminous A-type granite,with A/CNK of 0.98～1.04,and its LA-ICP-MS zircon U-Pb age is 317.5 ± 2.8 Ma (the Late Carboniferous).The Saiyinwusu,Yaguoaobao,and Gancihuduge plutons intruded into the Carboniferous strata,and their LA-ICP-MS zircon U-Pb ages range from 270.1 ± 2.7 Ma to 273.8 ± 1.6 Ma (the Early Permian).The Saiyinwusu pluton consists of biotite monzogranites,granodiorite,and svenogranite,while the Gancihuduge pluton is biotite monzogranites,and both plutons show transitional characteristics of I-and A-type granites.All the four granitic plutons are characterized by positive εNd(t) values ranging from + 3.2 to + 5.8 and variable ISr values from 0.703 58 to 0.709 92.Sr-Nd isotopic characteristics show that these granites are juvenile and thus are indicative of crustal growth.Combined with regional data,the study area probably have been subjected to an extensional setting during the Late Carboniferous to the Early Permian.%在靠近中蒙边界的内蒙古二连浩特市东北部,出露一系列花岗岩岩体.本文对其中的赛音乌苏、雅果敖包、干次呼都格和哈拉图庙等4个岩体进行了锆石U-Pb定年、全岩主微量元素和Sr-Nd同位素分析.哈拉图庙正长花岗岩体侵入于中泥盆统,具有A型花岗岩的特征,其A/CNK值在0.98～1.04之间,显示铝质到弱过铝质特征,LA-ICP-MS锆石206pb/238U年龄的加权平均值为317.5±2.8 Ma,相当于晚石炭世.赛音乌苏、雅果敖包和干次呼都格岩体均侵入于石炭系中,它们的年龄集中在270.1±2.7 Ma到273.8±1.6 Ma之间,相当于早二叠世.其中赛音乌苏岩体岩性变化较大,包括黑云二长花岗岩、花岗闪长岩和正长花岗岩,干次呼都格岩体为黑云二长花岗岩,它们具有I-A型过渡的花岗岩地球化学特征.这些花岗岩的εNd(t)值介于+3.2～+5.8之间,JSr值在0.703 58～0.709 92之间.Sr-Nd同位素特征表明这些花岗质岩石属于新生地壳物质,指示了地壳的生长.结合区域地质资料,研究区在晚石炭世到早二叠世之间很可能处于伸展的构造背景.
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