Devonian A-type granitic magmatism on the northern margin of the North China Craton: SHRIMP U–Pb zircon dating and Hf-isotopes of the Hongshan granite at Chifeng, Inner Mongolia, China
Devonian A-type granitic magmatism on the northern margin of the North China Craton: SHRIMP U–Pb zircon dating and Hf-isotopes of the Hongshan granite at Chifeng, Inner Mongolia, China
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DOI：
10.1016/j.gr.2009.11.011
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发表时间：
2010-05
影响因子：
6.1
通讯作者：
Yuruo Shi;Dunyi Liu;L. Miao;Fuqin Zhang;P. Jian;Wei Zhang;K. Hou;Junyu Xu
中科院分区：
文献类型：
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作者：
Yuruo Shi;Dunyi Liu;L. Miao;Fuqin Zhang;P. Jian;Wei Zhang;K. Hou;Junyu Xu
首次报道了华北前寒武纪陆缘北方泥盆系红山A型花岗岩沿着的资料。花岗岩富含二氧化硅（SiO2=76.07-77.62wt.%）碱（Na 2 O + K 2 O =8.45-8.78wt.%），但钙含量低（CaO=0.28-0.70wt.%）和镁（MgO=0.08- 0.20wt%）。红山花岗岩样品的球粒陨石标准化稀土配分模式显示出明显的负Eu异常（Eu/Eu*=0.13-0.19）。它们富含Rb、Ga、Y、Nb、Zn，而Ba、Sr含量较低，在原始地幔标准化的多元素蛛网图上，表现出与A型花岗岩相似的Ba、Nb、Ta、Sr、P、Ti负异常。地球化学图也显示出与A型花岗岩的亲和力，并建议后造山环境（A2型花岗岩）。锆石SHRIMP U-Pb定年获得206 Pb/238 U加权平均年龄为387± 4 Ma，确定了泥盆纪岩浆事件。锆石的εHf（t）为负，为-8.4 ~-11.5，给出了TDM 2 =2548- 2820 Ma（平均2667 Ma）的古老Hf模式年龄。大部分176 Hf/177 Hf和ε Hf值显示了下陆壳Hf同位素演化线。这些结果表明，红山花岗岩是泥盆纪后造山伸展环境下华北陆下陆壳熔融的产物。
We report first data for the Devonian Hongshan A-type granite along the northern margin of the Precambrian North China Craton. The granite is rich in silica (SiO2=76.07–77.62wt.%) and alkalis (Na2O+K2O=8.45–8.78wt.%), but poor in calcium (CaO=0.28–0.70wt.%) and magnesium (MgO=0.08–0.20wt.%). Chondrite-normalized REE patterns for the samples from the Hongshan granite show significant negative Eu anomalies (Eu/Eu*=0.13–0.19). They contain high Rb, Ga, Y, Nb, and Zn, but low Ba and Sr contents, and in the multi-element spider diagrams normalized to primitive mantle, they show a similar pattern to that of A-type granites, such as negative Ba, Nb, Ta, Sr, P and Ti anomalies. Geochemical plots also show an affinity with A-type granites and suggest a post-orogenic setting (A2type granite). SHRIMP U–Pb zircon dating yielded a concordant weighted mean206Pb/238U age of 387±4Ma, which defines a Devonian magmatic event. The zircons have negative εHf(t) of −8.4 to −11.5 and give old Hf model ages of TDM2=2548–2820Ma (mean 2667Ma). Most176Hf/177Hf and εHfvalues display Hf-isotope evolutional line of the lower continental crust. These results suggest that the Hongshan granite originated from melting of Archaean lower crust beneath the North China Craton in a post-orogenic extensional setting during the Devonian.