关键词: 碧口块体, 花岗质岩体, 锆石U-Pb年龄, Hf同位素, 扬子西北缘, 岩石学

Abstract:

The Baiquesi and Daan granitic plutons on the northwestern margin of the Yangtze block have been investigated by zircon U-Pb dating and Hf isotope analysis. Research results indicate that U-Pb ages of zircons in the Baiquesi pluton can be divided into two groups: (855±6) Ma (n=23) and (917±14) Ma (n=3).The ε_Hf(t) values of the former are 3.8-10.4, and the one-stage Hf isotope model age varies from 1.00 to 1.27 Ga; The ε_Hf(t) values of the latter are 2.0-8.1, and the one-stage Hf isotope model are 1.14-1.40 Ga. However, the ages of the Daan pluton can be divided into six groups: (854±10) Ma (n=3), (801±7) Ma (n=3), (702±10) Ma (n=3), (565±6) Ma (n=1), (246±7) Ma (n=1) and (207±2) Ma (n=1). The ε_Hf(t) values of the Daan pluton are -12.6-11.4 (t=854 Ma), and the one-stage Hf isotope model ages and the two-stage Hf isotope model ages are 0.95-1.90 Ga and 1.02-2.55 Ga. The Baiquesi and Daan plutons were emplaced at (855±6) Ma and (854±10) Ma, respectively, which reflect a significant magmatic event in Bikou terrane, northwestern margin of Yangtze block, and the former was mainly derived from the Mesoproterozoic juvenile crustal source, while the latter was products of two end-member mixing magmas respectively sourced from the Mesoproterozoic juvenile crustal and the Neoarchean old crustal. In addition, the (917±14) Ma which is larger than the intruding age of the Baiquesi pluton represents the record of the Early Neoproterozoic magmatism. Ages which are smaller than the intruding age of Daan pluton probably record the subsequent modifications of other thermal events.

Key words: Bikou terrane, granitic plutons, zircon U-Pb age, Hf isotope, northwestern of Yangtze block, lithology