科研之友
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摘要
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 (enjt)) the magmatic zircons can be subdivided into two groups, i.e., Group I with epsilon(Hf)(t)values of -16.1 similar to -18.4, including Nashan(130Ma)and Xilushan ( 130Ma)granites; and Group II with epsilon(Hf)(t)values of -21.1 similar to -2.1, including Caoshan(110Ma), Zhuishan(110Ma) monzonitic granites, Mayishan granite( 110Ma)and Huaiguang ( 130Ma) granodiorite. The low epsilon(Hf)( t) values of these magmatic zircons imply that they could come from the old lower continental crust. Combined with the epsilon(Hf)( t) values of 2. 3 similar to -7. 7 of the Early-Paleozoic and Neoproterozoic inherited zircons from Nushan and Xilushan granites, the SHIM Values 16.1 similar to -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 epsilon(Hf)( t) value:3 of the Paleoproterozoic inherited zircons and trapped zircons of 3400Ma from the Huaiguang pluton are - 5. 7 similar to -6. 8, - 0. 6 and - 0. 9, respectively. The corresponding Hf two-stage model ages are 2. 44Ga similar to 2. 80Ga and 3. 7Ga, respectively. Taken together with their strongly negative epsilon(Hf)( t) values of - 21. 1 similar to - 28. 1, these lines of evidence suggest that they could chiefly come from the North China Craton ( NCC) basement. The positive epsilon(Hf)(t) values of 0. 3 to 6. 7 of the Paleoproterozoic inherited zircons and the high positive epsilon(Hf)( t) values of 16. 9 to 21. 7 of the Neoarchean inherited zircons from Huaiguang and Nashan plutons suggest that the mantle materials could be involved in the magmatic sources when the inherited zircons were formed. The existence of the Yangtze Craton basement underlying the NCC Bengbu uplift implies that the subduction of the Yangtze Craton beneath the North China Craton took place along the Tan-Lu fault oriented in a E-W or NW direction in the early Mesozoic.
- 出版日期2007-2
- 单位吉林大学
