Petrogenesis of the middle Jurassic appinite and coeval granitoids in the Eastern Hebei area of North China Craton
Petrogenesis of the middle Jurassic appinite and coeval granitoids in the Eastern Hebei area of North China Craton
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华北克拉通冀东地区中侏罗统平岩及同时期花岗岩岩石成因
DOI：
10.1016/j.lithos.2017.01.030
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发表时间：
2017-05
期刊：
影响因子：
3.5
通讯作者：
Zong K.Q.
中科院分区：
文献类型：
--
作者：
Fan W.B.;Jiang N.;Xu X.Y.;Hu J.;Zong K.Q.
对华北克拉通冀东地区3个岩性多样的中侏罗统岩体进行了锆石U-Pb年龄、Hf-O同位素组成、全岩元素和Sr-Nd同位素地球化学综合研究，以揭示它们的岩石成因和可能的构造亲和力。3个岩体的岩浆锆石U-Pb年龄在167±1 Ma ~ 173±1 Ma之间，具有一致性。年子峪岩体具有低SiO2（43.7 ~ 52.6%）、高Ca、Mg、Fe、H2O含量的典型斜长石特征。具有与俯冲相关的微量元素模式、富集的Nd-Hf同位素特征和较高的锆石δ18O值（6.2‰~ 7.2‰），表明其为俯冲相关流体交代的富集地幔源。水胡同二长花岗岩硅、碱含量高（SiO2= 75.4 ~ 75.9%）， Ca含量低，Ba、Sr、Eu呈负异常。岩体样品的Nd-Hf同位素值较为演化，认为极有可能来自古代下大陆地壳的深熔岩。白家店基性微细粒包体花岗岩具有幔源岩浆和古下地壳岩浆的杂化作用，其εNd (t)和εHf(t)值具有变化特征。结合区域地质历史，认为三个中侏罗统岩体的形成与古太平洋板块的俯冲作用有关。它们的岩石成因差异反映了俯冲背景下复杂的岩浆过程，包括多源熔融作用，部分原因可能是流体交代作用和富水岩浆注入，并伴有不同程度的岩浆混合作用。中侏罗统扁屑岩的出现使我们认为，由于古太平洋板块的俯冲作用，岩石圈地幔水化后的减弱，促进和控制了北陆盆地的破坏和岩石圈的减薄。同时，克拉通的下地壳由于俯冲作用也被重新激活。
An integrated study of zircon U–Pb ages and Hf–O isotopic compositions, whole rock elemental and Sr–Nd isotope geochemistry was conducted on three lithologically diverse middle Jurassic plutons from the Eastern Hebei area of the North China Craton (NCC), in order to reveal both their petrogenesis and possible tectonic affinity. The three plutons have consistent magmatic zircon U–Pb ages from 167 ± 1 Ma to 173 ± 1 Ma. The Nianziyu pluton has typical characteristics of appinite with low SiO2(43.7–52.6%), high Ca, Mg, Fe and H2O contents. It possesses subduction-related trace element patterns, enriched Nd–Hf isotopic signatures as well as elevated zircon δ18O values (6.2–7.2‰), arguing for an enriched mantle source metasomatized by fluids related to subduction. The Shuihutong monzogranites have high silica (SiO2= 75.4–75.9%) and alkali contents, low Ca contents and striking negative Ba, Sr and Eu anomalies. Samples from the pluton have more evolved Nd–Hf isotopic values and are considered to be most likely derived from anatexis of ancient lower continental crust. Hybridization between mantle- and ancient lower crust-derived magmas is proposed for the mafic microgranular enclave-bearing Baijiadian granitoids, which are characterized by variable εNd (t)and εHf(t)values. Integrated with the regional geologic history, we suggest that the formation of the three middle Jurassic plutons were related to the subduction of the Paleo-Pacific ocean plate beneath the NCC. Their petrogenetic differences reflect complex magmatic processes in subduction settings involving melting of multiple sources, possible partly facilitated by fluid metasomatism and water-rich magma injection, accompanied with various degrees of magma mixing. The appearance of middle Jurassic appinitic rocks leads us to propose that the NCC destruction and lithosphere thinning were facilitated and controlled by the weakening of the lithospheric mantle after hydration because of the subduction of the paleo-Pacific ocean plate. The lower crust of the craton was also reactivated at the same time due to the subduction.
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