Post-collisional granitoids from the Dabie orogen in China: Zircon U–Pb age, element and O isotope evidence for recycling of subducted continental crust
Post-collisional granitoids from the Dabie orogen in China: Zircon U–Pb age, element and O isotope evidence for recycling of subducted continental crust
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DOI：
10.1016/j.lithos.2006.03.067
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发表时间：
2007-02
期刊：
影响因子：
3.5
通讯作者：
Zi‐Fu Zhao;Yong‐Fei Zheng;Chun-Sheng Wei;Y. Wu
中科院分区：
文献类型：
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作者：
Zi‐Fu Zhao;Yong‐Fei Zheng;Chun-Sheng Wei;Y. Wu
虽然人们普遍认为洋壳的俯冲再循环与洋岛、岛弧和与俯冲有关的埃达克岩岩浆活动有关，但俯冲陆壳的再循环是否发生在大陆碰撞带中尚不清楚。中国大别造山带早白垩世碰撞后花岗岩的锆石U-Pb定年、主微量元素地球化学和O同位素综合研究表明，它们可能是由俯冲大陆地壳的部分熔融作用产生的。大别造山带碰撞后花岗岩类包括含角闪石的中间岩和不含角闪石的花岗岩。这些花岗岩类具有REE分馏模式，REE含量低，HFSE负异常（Nb、Ta和Ti）。虽然锆石U-Pb测年结果显示岩浆结晶年龄为120 ~ 130 Ma，但通过CL成像和SHRIMP U-Pb测年确定了继承核的存在；部分锆石粒产年龄为739 ~ 749 Ma， 214 ~ 249 Ma，分别与UHP变质岩新元古代元岩年龄和大别-苏鲁造山带三叠纪构造变质事件相符。花岗岩类相对均匀，锆石δ18O值为4.14‰~ 6.11‰，平均为5.10‰±0.42‰（n=28），与正常地幔锆石相似。大部分同代基性-超基性岩石和侵入岩体的锆石δ18O值较低，排除了基性岩浆的亚铁化作用或基性岩浆与长英质岩浆混合作用作为花岗岩类岩石成因的可能机制。结合锆石U-Pb年龄和元素分析结果，推测花岗岩可能来源于中下地壳的部分熔融作用，而中下地壳中基性岩的角闪石脱水熔融作用以及岩浆侵位过程中的分异结晶作用。大别造山带的碰撞后花岗岩类解释为三叠纪大陆-大陆碰撞增厚的俯冲扬子陆壳的再循环。造山带岩石圈龙骨的部分熔融作用产生了具有相似地壳遗产的双峰火成岩。碰撞后拆离导致的地壳变薄，推迟了早白垩世由地幔超涌热脉冲引发的双峰岩浆活动的发生。
While recycling of subducted oceanic crust is widely proposed to be associated with oceanic island, island arc, and subduction-related adakite magmatism, it is less clear whether recycling of subducted continental crust takes place in continental collision belts. A combined study of zircon U–Pb dating, major and minor element geochemistry, and O isotopes in Early Cretaceous post-collisional granitoids from the Dabie orogen in China demonstrates that they may have been generated by partial melting of subducted continental crust. The post-collisional granitoids from the Dabie orogen comprise hornblende-bearing intermediate rocks and hornblende-free granitic rocks. These granitoids are characterized by fractionated REE patterns with low HREE contents and negative HFSE anomalies (Nb, Ta and Ti). Although zircon U–Pb dating gives consistent ages of 120 to 130 Ma for magma crystallization, occurrence of inherited cores is identified by CL imaging and SHRIMP U–Pb dating; some zircon grains yield ages of 739 to 749 Ma and 214 to 249 Ma, in agreement with Neoproterozoic protolith ages of UHP metaigneous rocks and a Triassic tectono-metamorphic event in the Dabie–Sulu orogenic belt, respectively. The granitoids have relatively homogeneous zircon δ18O values from 4.14‰ to 6.11‰ with an average of 5.10‰±0.42‰ (n=28) similar to normal mantle zircon. Systematically low zircon δ18O values for most of the coeval mafic–ultramafic rocks and intruded country rocks preclude an AFC process of mafic magma or mixing between mafic and felsic magma as potential mechanisms for the petrogenesis of the granitoids. Along with zircon U–Pb ages and element results, it is inferred that the granitic rocks were probably derived from partial melting of intermediate lower crust and the intermediate rocks were generated by amphibole-dehydration melting of mafic rocks in the thickened lower crust, coupled with fractional crystallization during magma emplacement. The post-collisional granitoids in the Dabie orogen are interpreted to originate from recycling of the subducted Yangtze continental crust that was thickened by the Triassic continent–continent collision. Partial melting of orogenic lithospheric keel is suggested to have generated the bimodal igneous rocks with the similar crustal heritage. Crustal thinning by post-collisional detachment postdated the onset of bimodal magmatism that was initiated by a thermal pulse related to mantle superwelling in Early Cretaceous.