中文摘要：

对出露于华北南缘小秦岭-熊耳山地区的中基性岩墙的Sr、Nd、Pb同位素研究显示：岩墙的（^87Sr/^86Sr）i变化于0.712310～0.735100,平均值0.722117,（^143Nd/^144Nd）i变化于0.511160～0.512066,平均值0.511436。用t=130Ma计算的岩墙的εSr（t）变化于113.06～436.61,εNd（t）变化于-7.9～-25.57,岩墙的Sr、Nd同位素组成显示出极端富集特征。岩墙的^206Pb/^204Pb变化于16.1921～19.8149,平均17.7067,207Pb/204Pb变化于15.3245～15.7540,平均15.6638,208Pb/204Pb变化于36.8607～41.6251,平均38.9494,其铅同位素比值显示出明显的富放射性成因铅的特征。通过对岩墙与区域太华群、熊耳群地层和中生代花岗岩的对比示踪研究表明,岩墙岩浆源区显示出与洋壳和深海沉积物质混染有关的特征,形成岩墙的岩浆物质与扬子陆块具有更大的亲缘性,由此证明秦岭造山带是由扬子陆块俯冲于华北陆块南缘之下造山的大陆动力学演化过程。结合现今的秦岭造山带深部地球物理资料,认为中生代时期太平洋构造域的兴起是导致秦岭造山带地区由陆陆碰撞向岩石圈拉张伸展构造体制转化的根本原因,从而造成小秦岭-熊耳山地区燕山期大规模花岗岩体和中基性岩墙的浅成侵位活动。

英文摘要：

Research of Sr, Nd, Pb isotope compositions of the meso-basic dykes in the Xiaoqinling and Xiong＇ ershan area in the southern edge of North China Craton, shows that （^87Sr/^86Sr）i and （^143Nd/^144Nd）i of the dykes is 0. 712310-0. 735100 and 0. 511160--0. 512066, respectively, with an average value of 0. 722117 and 0. 511436 separately. The dykes have εSr（t）and εNd （t）value in 113.06-436.61 and -7.9--25.57 in the time scale of 130Ma calculated. Sr, Nd isotope compositon show the characteristics of extremely enriched magma sources, ^206Pb/^204 Pb, ^207Pb/^204 Pb, ^208Pb/^204Pb of the dykes vary betweem 16. 1921 19. 8149, 15. 3245 -15. 7540, and 36. 8607-41. 6251,respectively, with averaging 17. 7067, 15. 6638 and 38. 9494, indicating a distinct radiogentic lead feature. Comparsion of dykes with regional Taihua Formation and Xiong＇er strata as well as Mesozoic granite shows that the source of dyke magma is of mixing features of crustal and deep sea sediments, and magatic material for dykes is of affinity to the Yangtze Plate. So it is proved that the Qinling orogenic belt stands for a geodynamic evolution process in which the Yangtze Plate subducted towards the southern margin of North China Craton. Combined with deep geophysical information in the Qinling orogen, the authors think that activation of the Pacific tectonic domain is a fundamental factor for tectonic regime transition from intraplate collision to lithospheric extension in the Qinling orogenic belt in late Mesizoic, thus resulting in the emplacement of large scale granite and meso-basic dikes in the Xiaoqinling and Xiong＇ershan mountains area.