A hybrid origin for the Qianshan A-type granite, northeast China: Geochemical and Sr–Nd–Hf isotopic evidence
A hybrid origin for the Qianshan A-type granite, northeast China: Geochemical and Sr–Nd–Hf isotopic evidence
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DOI：
10.1016/j.lithos.2005.10.002
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发表时间：
2006-06
期刊：
影响因子：
3.5
通讯作者：
Jin-Hui Yang;Fu-Yuan Wu;Sun‐Lin Chung;S. Wilde;M. Chu
中科院分区：
文献类型：
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作者：
Jin-Hui Yang;Fu-Yuan Wu;Sun‐Lin Chung;S. Wilde;M. Chu
报道了辽东半岛前山岩体早白垩世（126±2 Ma）一套A型花岗岩和镁铁质微粒包体的主量元素、微量元素、全岩Sr、Nd同位素和锆石Hf同位素数据，探讨了A型花岗岩的物质来源和岩石成因。潜山岩体包括角闪石型碱长花岗岩、图形黑云母花岗岩和镁铁质微粒包体。角闪岩型碱长花岗岩具有高SiO2、Fe 2 O3 T/MgO、K2 O + Na 2 O、Rb、Zr和LREE含量，低Ba、Sr含量，具强烈的Eu负异常。它们的高Rb/Sr（87 Rb/86 Sr =16.76-24.15）和初始87 Sr/86 Sr比值（0.7215 - 0.7283）、负εNd（t）值（−14.1-−16.5）和负εHf（t）值（−18.9-−11.5）表明它们主要来源于地壳，但也有高εNd（t）和εHf（t）物质的参与。图解黑云母花岗岩具有与包体相似的地球化学特征和Sr-Nd-Hf同位素组成，表明它们是演化的镁铁质岩浆结晶分异的结果，但有低εNd（t）和εHf（t）物质的参与。镁铁质包体具有火成结构，并含有针状磷灰石，表明与寄主花岗岩混合的镁铁质岩浆淬火。它们具有较低的87 Sr/86 Sr比值（0.7097-0.7148）、负εNd（t）（−14.5 ~ −11.9）和负εHf（t）（−17.1 ~ −6.9），富集大离子亲石和轻稀土元素，亏损高场强元素。当与高MgO（Mg#高达54），这表明来自富集的岩石圈地幔源，但地壳物质的污染。地球化学和Sr-，Nd-和锆石Hf-同位素组成排除了简单的晶体-液体分馏或restite unmixing作为包体和寄主岩石之间的主要成因联系。相反，幔源镁铁质岩浆和壳源岩浆混合，再加上晶体分馏，是兼容的数据。该实例表明，至少有一些A型花岗岩是通过幔源和壳源岩浆混合、晶体分异和壳内熔融等复杂过程形成的。
Major and trace element, whole rock Sr and Nd isotope and zircon Hf isotope data are reported for a suite of A-type granites and mafic microgranular enclaves from the Early Cretaceous (126±2 Ma) Qianshan pluton, Liaodong Peninsula, northeast China, with the aim of investigating the sources and petrogenesis of A-type granites. The Qianshan pluton includes hornblende alkali-feldspar granite, graphic biotite granite and mafic microgranular enclaves. The hornblende alkali-feldspar granites have high SiO2, Fe2O3T/MgO, K2O+Na2O, Rb, Zr and LREE contents and low Ba and Sr concentrations with strongly negative Eu anomalies. Their high Rb/Sr (87Rb/86Sr=16.76–24.15) and initial87Sr/86Sr ratios (0.7215 to 0.7283), negative εNd(t) values (−14.1 to −16.5) and zircon εHf(t) values (−18.9 to −11.5) indicate they were mainly derived from a crustal source, but with involvement of high εNd(t) and εHf(t) materials. Graphic biotite granites have similar geochemical features and Sr–Nd–Hf isotopic compositions to enclaves, indicating they were the result of crystal fractionation of evolved mafic magmas, but with involvement of low εNd(t) and εHf(t) materials. The mafic enclaves have an igneous texture and contain acicular apatite, suggesting quenching of mafic magmas that have co-mingled with the host granites. They have low initial87Sr/86Sr ratios (0.7097–0.7148), negative εNd(t) (−14.5 to −11.9) and zircon εHf(t) (−17.1 to −6.9) values, and are enriched in LILEs and LREEs and depleted in HFSEs. When coupled with the high MgO (Mg# up to 54), this indicates derivation from an enriched lithospheric mantle source, but contaminated by crustal materials. Geochemical and Sr-, Nd- and zircon Hf-isotopic compositions rule out simple crystal–liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead, magma mixing of mantle-derived mafic and crustal-derived magmas, coupled with crystal fractionation, is compatible with the data. This example shows that at least some A-type granites formed through a complex process involving mantle- and crustal-derived magma mixing, crystal fractionation and infracrustal melting.