Late Permian appinite-granite complex from northwestern Liaoning, North China Craton: Petrogenesis and tectonic implications
Late Permian appinite-granite complex from northwestern Liaoning, North China Craton: Petrogenesis and tectonic implications
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DOI：
10.1016/j.lithos.2012.09.002
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发表时间：
2012-12
期刊：
影响因子：
3.5
通讯作者：
Xiaohui Zhang;F. Xue;Lingling Yuan;Y. Ma;S. Wilde
中科院分区：
文献类型：
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作者：
Xiaohui Zhang;F. Xue;Lingling Yuan;Y. Ma;S. Wilde
在造山运动的最后阶段，appinite-granite套件通常出现在俯冲后的制度，因此持有关键的地球动力学和地壳演化过程的监测。本文通过锆石U-Pb定年和地球化学研究，证实了辽宁西北部晚二叠世辉长花岗岩杂岩的存在。富角闪岩的SiO2范围为41.8%至53.4%，碱含量中等至高，富集大离子亲石元素，亏损高场强元素，初始87 Sr/86 Sr比值为0.7066至0.7128，εNd（t）为−8.3至−13.3，锆石εHf（t）为−10.1至−18.7。这些特征表明，它们的产生最有可能涉及地幔橄榄岩的交代作用，由沉积物衍生的液体有关的俯冲和后来的部分熔融。相关的二长花岗岩的SiO2范围从72.6%到75.0%，并表现出高钾钙碱性的字符，具有高Sr-Ba丰度和升高的Sr/Y和La/Yb比值。这种钾质埃达克岩特征，加上它们演化的同位素组成（87 Sr/86 Sri =0.7063 ~ 0.7066，εNd（t）=−15.6 ~ −16.3，锆石εHf（t）=−16.5 ~ −18.8），与混合原岩的部分熔融相一致，包括新底侵富集的镁铁质下地壳和少量古老的下地壳物质。这种镁铁质和长英质岩浆组合不仅证明了华北北方陆下岩石圈地幔的不均匀富集，而且还表明了造山后岩石圈拆沉的平移机制的改造。目前的appinite花岗岩复杂的时间与区域横向断层活动的巧合导致进一步的建议，这种镁铁质长英质岩浆套件可以提供空间标志，监测重要的造山后构造和地球动力学过程。
The appinite–granite suite commonly occurs within post-subduction regimes during the final stage of an orogeny and thus holds the key to monitoring critical geodynamic and crustal evolutionary processes. The present zircon U–Pb dating and geochemical study documents the Late Permian appinite–granite complex from northwestern Liaoning, North China Craton. The hornblende-rich appinitic rocks have an SiO2range from 41.8 to 53.4%, moderate to high alkali contents, enrichment in large ion lithophile elements and depletion in high field strength elements, with initial87Sr/86Sr ratios of 0.7066 to 0.7128, εNd(t) of −8.3 to −13.3 and zircon εHf(t) from −10.1 to −18.7. These features suggest that their generation most likely involves metasomatism of mantle peridotites by sediment-derived liquids related to subduction and a later partial melting. The associated monzogranites range in SiO2from 72.6 to 75.0% and exhibit a high-K calc-alkaline character, with high Sr–Ba abundances and elevated Sr/Y and La/Yb ratios. Such potassic adakitic signatures, plus their evolved isotopic compositions (87Sr/86Sri=0.7063 to 0.7066, εNd(t)=−15.6 to −16.3, zircon εHf(t)=−16.5 to −18.8), are consistent with partial melting of mixed protoliths including newly underplated enriched mafic lower crust and minor old lower crustal materials. Such a mafic and felsic magma association not only attests to a heterogeneously enriched sub-continental lithospheric mantle beneath the northern North China Craton, but also indicates reworking within a post-orogenic transcurrent regime of lithospheric delamination. The temporal coincidence of the present appinite–granite complex with regional transcurrent fault activity leads to the further suggestion that such mafic–felsic magmatic suites could provide spatial markers for monitoring important post-orogenic structural and geodynamic processes.