摘要
对蚌埠隆起区中生代不同时期的花岗岩中6个岩体的锆石LA-MC-ICP MS原位Hf同位素的研究,据此限定它们的岩浆源区和重建华北克拉通东南部的构造格架。结果表明,中生代不同时期的花岗岩中岩浆锆石的初始Hf同位素组成(ε_(Hf)(t))可以分成两组:第一组的女山(130Ma)和西庐山花岗岩(130Ma)的ε_(Hf)(t)值分别为-18.4和-16.1;第二组的曹山(110Ma)、锥山二长花岗岩(110Ma)和蚂蚁山花岗岩(110Ma)以及淮光花岗闪长岩(130Ma)的ε_(Hf)(t)值分别为-22.3、-23.1和-21.1以及-28.1,这些岩浆锆石低的ε_(Hf)(t)值表明它们可能来源于古老的大陆下地壳。女山和西庐山岩体中早古生代—新元古代继承锆石具有低的ε_(Hf)(t)值(-2.3～-7.7)和1.52Ga～1.79Ga的Hf同位素两阶段模式年龄,表明它们的岩浆源区主要以扬子克拉通下地壳物质为主。曹山、锥山和蚂蚁山以及淮光岩体中岩浆锆石的Hf同位素两阶段模式年龄为1.89Ga～2.58Ga,结合淮光岩体中古元古代继承锆石和3400Ma捕获锆石中低的ε_(Hf)(t)值(-5.7～-6.8,-0.6、-0.9)和古老的Hf同位素两阶段模式年龄(2.44Ga～2.80Ga,3.7Ga),表明它们主要来源于华北克拉通下地壳物质的部分熔融。淮光和女山岩体中古元古代—新太古宙继承锆石中正的ε_(Hf)(t)值(0.3～6.7)以及高的ε_(Hf)(t)值(16.9～21.7)的存在,暗示形成这些古老继承锆石的初始物质中有幔源物质的涉入。蚌埠隆起区深部地壳中扬子克拉通基底物质的存在暗示扬子克拉通可能沿着郯庐断裂带向西或北西方向俯冲于华北克拉通之下。
Abstract Zircon Hf isotope analyses are carried out for the Mesozoic granitoids from six intrusions in Bengbu uplift on the basis of previous zircon U-Pb dating as a way to constrain their magmatic sources and to reconstruct the tectonic frame in the eastern North China Craton. Based on their initial Hf isotope ratios （БHf（t）） the magmatic zircons can be subdivided into two groups, i, e, , Group I with БHf（t）values of -16.1 ~ -18.4, including Nushan（130Ma） and Xilushan （130Ma）granites; and Group II with БHf（t）values of - 21.1 ~ - 28.1, including Caoshan（110Ma） , Zhuishan（110Ma） monzonitic granites, Mayishan granite（110Ma） and Huaiguang （130Ma） granodiorite. The low БHf（t） values of these magmatic zircons imply that they could come from the old lower continental crust. Combined with the БHf （t） values of -2.3 ~ - 7.7 of the Early-Paleozoic and Neoproterozoic inherited zircons from Nushan and Xilushan granites, the БHf（t）values（ -16. 1 - -18.4）of Group I magmatic zircons suggest that their magma sources are mainly composed of the Yangtze Craton（YC） basement, which is consistent with their Hf two-stage model ages of 1.52Ga to 1.79Ga. The Hf two-stage model ages of magmatic zircons from Caoshan, Zhuishan, Mayishan and Huaiguang plutons range from 1.89Ga to 2.58Ga. The БHf（t） values of the Paleoproterozoic inherited zircons and trapped zircons of 3400Ma from the Huaiguang pluton are - 5.7 ~ -6.8, -0.6 and -0.9, respectively. The corresponding Hf two-stage model ages are 2.44Ga ~2.80Ga and 3.7Ga, respectively. Taken together with their strongly negative БHf（t） values of -21.1 ~ -28.1, these lines of evidence suggest that they could chiefly come from the North China Craton（NCC） basement. The positive БHf（t） values of 0.3 to 6.7 of the Paleoproterozoic inherited zircons and the high positive БHf（t） values of 16.9 to 21.7 of the Neoarchean inherited zircons from Huaiguang and Nushan plutons suggest that the mantle materials could be
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第2期381-392,共12页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40472033)资助
