陕西地区岩浆岩Nd、Sr同位素特征及其与大地构造发展的联系

岩浆岩Nd、Sr同位素特征表明,扬子地块基底有着和华北地块很不相同的早期演变历史。这意味着华北和扬子两地块在历史上曾经是相互独立的,后来才拼合在一起。Nd、Sr同位素研究还表明,华北和扬子两地块的会聚在泥盆纪以前就已经在进行中,它是通过位於两地块之间的古秦岭海洋壳俯冲消亡在华北地块之下实现;华北和扬子两陆块最终相碰撞至少发生在二叠纪以前。

Nd-Sr ISOTOPES OF GRANITOIDS FROM SHAANXI PROVINCE AND THEIR SIGNIFICANCE FOR TECTONIC EVOLUTION

This paper deals with the ages of basements of North China terrene and Yangzi terrene, and the convergent history of the two terrenes during middle-late Palaeozoic, It also deals with the felting events happened at the Southern margin of North China terrene during middle Proterozoie and at the north margin of Yangzi terrene during late Proterozoic. Sm-Nd model ages and Rb-Sr, Sm-Nd isochron chronology suggest that the creation of North China craton be in Late Archean, while the creation of Yangzi creaton be in early-middle Proterozoic (Fig. 2). With regard to the convergence of North China terrene and Yangzi terrene, Nd-Sr isotopes suggest that before Devonian or even before Late Silurian, the Qinglin palaeocean floor, which was situated between North China terrene and Yangzi terrene, and had been subducting underneath and consummed beneath the southern margin of North China terrerne, where a kind of magmatism of mostly mantle sources occurred (Table 5, Fig.4). Moreover, before late Permian the Qinling palaeocean basin had closed. Consequently, The North China and the Yangzi terrenes became convergent and compressed each other. This resulted in the formation of fold belts and the intrusion of granitoids of mostly crustal sources during the periods of late Permian,Triassic, and early Jurassic in the both sides of the suture (Table 5, Fig.3,4). As to the rifting events, according to the Nd-Sr isotopes,the ocean basin formed by rifting at the northern margin of Yangzi terrene during late Proterozoic was more developed than that at the southern margin of North China terrene during middle Proterozoic (Table 2).