Continental and Oceanic Crust Recycling-induced Melt-Peridotite Interactions in the Trans-North China Orogen: U-Pb Dating, Hf Isotopes and Trace Elements in Zircons from Mantle Xenoliths
Continental and Oceanic Crust Recycling-induced Melt-Peridotite Interactions in the Trans-North China Orogen: U-Pb Dating, Hf Isotopes and Trace Elements in Zircons from Mantle Xenoliths
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华北造山带大陆和洋壳再循环引起的熔体-橄榄岩相互作用：U-Pb定年、Hf同位素和地幔捕虏体锆石中的微量元素
DOI：
10.1093/petrology/egp082
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发表时间：
2010-01-01
影响因子：
3.9
通讯作者：
Wang, Dongbing
中科院分区：
文献类型：
--
作者：
Liu, Yongsheng;Gao, Shan;Wang, Dongbing
本文首次在华北造山带中部新近纪汉诺坝玄武岩携带的地幔捕虏体中的石榴子石/尖晶石辉石岩脉中发现了前寒武纪陆壳源锆石。岩石学和地球化学特征表明，这些幔源复合捕虏体是由地幔熔体与二辉橄榄岩相互作用形成的。前寒武纪锆石年龄可划分为2中心点4-2中心点5Ga、1中心点6-2中心点2Ga和0中心点6-1中心点2Ga三个年龄组，与华北克拉通的主要地质事件相吻合。这些前寒武纪锆石在U/Yb与Hf、Y的关系图上属于大陆花岗岩类。它们的岩浆型稀土配分模式和变质锆石型CL图像表明，它们在熔体-橄榄岩相互作用和随后的高压变质作用中没有结晶。与2中心点相似的5 Ga锆石具有正Hf（t）值（2中心点9-10中心点6），而较年轻的前寒武纪锆石以负Hf（t）值为主，表明其起源于古老的大陆地壳。这些观察结果表明，前寒武纪的锆石捕虏晶，幸存下来的熔融回收大陆地壳岩石，然后注入硅酸盐熔体到主机橄榄岩。除了前寒武纪锆石外，还从石榴石/尖晶石辉石岩脉中分离出315 +/- 3 Ma（2 Sigma）、80-170 Ma和48-64 Ma的火成锆石;这些为下陆壳和洋壳再循环导致的NCC中心带多幕熔体-橄榄岩相互作用提供了证据。315 Ma锆石的Hf（t）正值（2个中心点91-24个中心点6）与华北克拉通北方边缘罕见的302-324 Ma俯冲相关闪长花岗岩岩体的组合表明，315 Ma岩浆锆石可能记录了古亚洲洋壳俯冲引起的岩石圈地幔熔体-橄榄岩相互作用。80-170 Ma的岩浆锆石一般与前寒武纪变质锆石共存，具有较低的Ce/Yb和Th/U比值，较高的U/Yb比值和较大的Eu负异常。这些锆石的Hf（t）值从-47中心点6到24中心点6变化很大。170-110 Ma锆石的Hf（t）值一般为负值，而110-100 Ma锆石的Hf（t）值一般为正值。这些观察结果表明，熔体橄榄岩相互作用在80-170 Ma的诱导部分熔融的再循环大陆地壳。48-64 Ma岩浆锆石的Ce异常可忽略不计，稀土元素、U、Th含量异常高，Hf（t）值为正值。这些特征意味着48-64 Ma的熔体-橄榄岩相互作用可能与亏损的幔源碳酸盐熔体或流体有关。
We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC). Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt-lherzolite interaction. The Precambrian zircon ages can be classified into three age groups of 2 center dot 4-2 center dot 5 Ga, 1 center dot 6-2 center dot 2 Ga and 0 center dot 6-1 center dot 2 Ga, coinciding with major geological events in the NCC. These Precambrian zircons fall in the field of continental granitoid rocks in plots of U/Yb vs Hf and Y. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt-peridotite interaction and subsequent high-pressure metamorphism. The similar to 2 center dot 5 Ga zircons have positive epsilon(Hf(t)) values (2 center dot 9-10 center dot 6), whereas the younger Precambrian zircons are dominated by negative epsilon(Hf(t)) values, indicating an ancient continental crustal origin. These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite. In addition to the Precambrian zircons, igneous zircons of 315 +/- 3 Ma (2 Sigma), 80-170 Ma and 48-64 Ma were separated from the garnet/spinel pyroxenite veins; these provide evidence for lower continental crust and oceanic crust recycling-induced multi-episodic melt-peridotite interactions in the central zone of the NCC. The combination of the positive epsilon(Hf(t)) values (2 center dot 91-24 center dot 6) of the 315 Ma zircons with the rare occurrence of 302-324 Ma subduction-related diorite-granite plutons in the northern margin of the NCC implies that the 315 Ma igneous zircons might record melt-peridotite interactions in the lithospheric mantle induced by Palaeo-Asian oceanic crust subduction. Igneous zircons of age 80-170 Ma generally coexist with the Precambrian metamorphic zircons and have lower Ce/Yb and Th/U ratios, higher U/Yb ratios and greater negative Eu anomalies. The epsilon(Hf(t)) values of these zircons vary greatly from -47 center dot 6 to 24 center dot 6. The 170-110 Ma zircons are generally characterized by negative epsilon(Hf(t)) values, whereas the 110-100 Ma zircons have positive epsilon(Hf(t)) values. These observations suggest that melt-peridotite interactions at 80-170 Ma were induced by partial melting of recycled continental crust. The 48-64 Ma igneous zircons are characterized by negligible Ce anomalies, unusually high REE, U and Th contents, and positive epsilon(Hf(t)) values. These features imply that the melt-peridotite interactions at 48-64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid.