山东中侏罗世-早白垩世侵入岩的锆石Hf同位素组成及其意义
Zircon Hf isotope compositions of Middle Jurassic-Early Cretaceous intrusions in Shandong Province and its implications
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摘要: 对山东中侏罗世-早白垩世侵入岩中锆石的原位Hf同位素分析显示,形成于晚太古代(上交点年龄~2.5 Ga)的继承锆石具有正的εHf(t)值(+8~+1),Hf同位素模式年龄集中在2.6~2.8 Ga,与辽宁古生代金伯利岩中基性下地壳捕虏体中锆石Hf组成和Hf模式年龄十分一致,Hf模式年龄也与研究区变质岩和花岗岩的全岩Nd模式年龄相同,因此,这些继承锆石来自于晚太古代由岩浆底侵形成的基性下地壳.新生锆石出现在继承锆石周围或者以独立颗粒出现,其U-Pb年龄为177 Ma和132~126 Ma,εHf(t)值均为负值(-23~-1).山东中生代侵入岩的形成与富集岩石圈地幔,亏损地幔和地壳三个端员之间的相互作用有关.其中根据来源于晚太古代下地壳的侏罗纪铜石二长花岗岩限定的研究区下地壳εHf(t)平均值为-20,根据来源于富集岩石圈地幔的早白垩纪沂南辉长岩限定的富集地幔端员的εHf(t)为-16.部分样品锆石εHf(t)变化非常大(-20~-1),示踪了岩浆作用过程中亏损地幔物质的参与程度的逐渐增强.这种变化是华北晚中生代岩石圈大规模减薄作用的结果.
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Key words:
- Zircon Hf isotope /
- Middle Jurassic-Early Cretaceous /
- Intrusion /
- Lithospheric evolution /
- Petrogensis /
- Shandong
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