Crust–mantle interaction in the central North China Craton during the Mesozoic: Evidence from zircon U–Pb chronology, Hf isotope and geochemistry of syenitic–monzonitic intrusions from Shanxi province
Crust–mantle interaction in the central North China Craton during the Mesozoic: Evidence from zircon U–Pb chronology, Hf isotope and geochemistry of syenitic–monzonitic intrusions from Shanxi province
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DOI：
10.1016/j.lithos.2011.03.004
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发表时间：
2011-07
期刊：
影响因子：
3.5
通讯作者：
Jifeng Ying;Hong‐fu Zhang;Yanjie Tang
中科院分区：
文献类型：
--
作者：
Jifeng Ying;Hong‐fu Zhang;Yanjie Tang
本文报道了华北中部山西三个中生代正长-二长岩体的锆石U-Pb年龄、Hf同位素组成、全岩地球化学和Sr-Nd同位素组成。这些侵入体中的锆石都显示出核-边结构，振荡边记录了它们的侵入年龄，而核则被解释为捕虏晶。最北的滴水岩二长岩侵位于241 Ma，而虎岩山和二峰山正长-二长杂岩侵位于130 Ma和128- 134 Ma。滴水岩二长岩岩石学和地球化学均一，表现为LREE富集、HFSE亏损，Sr、Nd同位素组成富集，（87 Sr/86 Sr）i=0.7065，εNd（t）=−8.3-−7.9。滴水岩二长岩中的锆石边缘显示出高度变化的Hf同位素组成，εHf（t）=−27.8-−6.4。不同的Hf同位素组成和富集的Sr-Nd同位素组成，以及普遍存在的捕晶锆石核，表明滴水岩二长岩是由富集的岩石圈地幔和下地壳熔融物混合而成。虎岩山杂岩中的二长岩和正长岩具有不同的地球化学特征。正长岩的εNd（t）值高于二长岩，类似于富集的岩石圈地幔，结合正长岩中锆石的缺失，我们认为正长岩是富集的岩石圈地幔部分熔融的产物。虎岩山和二峰山的二长岩具有相似的岩石学和地球化学特征，富集轻稀土，亏损高场强元素，εNd（t）值较低，介于−18.2和−13.9之间。与滴水岩二长岩中的锆石边相似，虎岩山和二峰山二长岩中的锆石边也具有高度变化的Hf同位素组成。二长岩中的捕虏晶锆石与北CC下地壳基底岩石的年龄一致，表明下地壳对二长岩的形成有重要贡献。我们认为，虎岩山和二峰山的二长岩是由富集的岩石圈幔源岩浆和下地壳岩浆混合而成的。山西中生代正长-二长岩体形成于不同的地球动力学背景下的拉张环境。三叠纪滴水岩二长岩是碰撞后岩石圈伸展作用的产物，与古亚洲洋板块向北俯冲及随后的板片断裂有关，而白垩纪虎岩山和二峰山正长岩二长岩则是弧后伸展作用的产物，与古太平洋板片向东亚俯冲有关。
In-situ zircon U–Pb ages, Hf isotopic compositions and whole rock geochemical and Sr–Nd isotopic compositions are presented for three Mesozoic syenitic–monzonitic intrusions from Shanxi province, central North China Craton. Zircons from these intrusions all show core–rim structures in that the oscillatory rims recorded their intrusive ages, whereas the cores are interpreted as xenocrysts. The U–Pb age data reveal that the northernmost Dishuiyan monzonite was emplaced at 241Ma, while the Huyanshan and Erfengshan syenitic–monzonitic complexes were emplaced at 130Ma and 128–134Ma, respectively. The Dishuiyan monzonite is petrologically and geochemically uniform, it shows LREE enrichment and HFSE depletion and exhibits enriched Sr and Nd isotopic compositions with (87Sr/86Sr)i=0.7065 and εNd(t)=−8.3–−7.9. The zircon rims in the Dishuiyan monzonite show highly varied Hf isotopic compositions with εHf(t)=−27.8–−6.4. The varied Hf isotopic compositions and enriched Sr–Nd isotopic compositions, together with the ubiquitous xenocrystic zircon cores, suggest the Dishuiyan monzonite was produced by the mixing of melts from enriched lithospheric mantle and lower crust. The monzonite and syenite from the Huyanshan complexes exhibit different geochemical features. The εNd(t) values of syenite, which are higher than those of monzonite resemble the enriched lithospheric mantle, and together with the absence of zircon in the syenite, we propose that it was originated by partial melting of enriched lithospheric mantle. Monzonites from Huyanshan and Erfengshan share similar petrological and geochemical characteristics, being enriched in LREE and depleted in HFSE, and they show low εNd(t) values between −18.2 and −13.9. Similar to zircon rims in the Dishuiyan monzonite, those in the Huyanshan and Erfengshan monzonites also exhibit highly varied Hf isotopic compositions. The consistent ages between the xenocrystic zircons in monzonites and the lower crustal basement rocks of the NCC reveal a significant contribution from the lower crust in the formation of the monzonites. We propose that the monzonites from Huyanshan and Erfengshan were formed through hybridization of enriched lithospheric mantle-derived and lower crust-derived magmas. The Mesozoic syenitic–monzonitic intrusions in Shanxi province were produced under extensional environments which linked to different geodynamic settings. The Triassic Dishuiyan monzonite is a product of post-collisional lithospheric extension related to the subduction of the paleo-Asian oceanic plate under the NCC and subsequent slab break-off in the north, while the Cretaceous Huyanshan and Erfengshan syenite–monzonite was produced under a back-arc extensional regime linked to the subduction of the paleo-Pacific slab beneath East Asia.