青藏高原羌塘中部本松错花岗质片麻岩锆石U-Pb年龄、Hf同位素特征及地质意义
摘要
The Bunsumco granitic batholith in the Longmu Co-Shuanghu suture zone is the product of intermediate-acidic intrusive magmatism over several periods. Using zircon U-Pb dating by laser-ablation inductively coupled mass spectrometry of granitic gneiss from the batholith, we obtained weighted mean <sup>206</sup>Pb/<sup>238</sup>U ages of 496.2±3.9 and 497.1±3.0 Ma. These are the oldest and most reliable dates for the chronological record of magmatism in the Qiangtang Basin of the Qinghai-Tibet Plateau. These dates provide new clues to solve the key geological problems in this area. The negative <italic>ε</italic>Hf(t) values (averages of -2.9 and -4.1) imply a crustal source for the granite, with Hf two-stage model ages of 1648 and 1723 Ma. The Bunsumco granite is the product of partial melting of old crust, initiated by the subduction of the proto-Tethys in an Andean-type orogenic zone after Gondwana assembly, but does not represent a Pan-African orogen during continental collision within the Gondwana terranes. This suggests that the northern Gondwana margin extends northward to the Qiangtang Basin and is represented by the Longmu Co-Shuanghu suture zone.