Extremely high-Na adakite-like magmas derived from alkali-rich basaltic underplate:The Late Cretaceous Zhantang andesites in the Huichang Basin,SE China
Extremely high-Na adakite-like magmas derived from alkali-rich basaltic underplate:The Late Cretaceous Zhantang andesites in the Huichang Basin,SE China
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DOI：
10.2343/geochemj.37.233
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发表时间：
2003-04
影响因子：
0.8
通讯作者：
Xiaolin Xiong;Xian‐Hua Li;Ji‐Feng Xu;Wu-Xian Li;Zhenhua Zhao;Qiang Wang;Xiaoming Chen
中科院分区：
文献类型：
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作者：
Xiaolin Xiong;Xian‐Hua Li;Ji‐Feng Xu;Wu-Xian Li;Zhenhua Zhao;Qiang Wang;Xiaoming Chen
中国东南会昌晚白垩世盆地中的詹堂安山岩与晚中生代岩石圈伸展和玄武质底侵作用有关。它们是高Na（6.59- 8.46wt%Na_2 O）、高Al的奥长花岗岩类岩石，具有高Sr、Ba、低Y、低HREE、高Sr/Y、La/Yb比值，与现代埃达克岩相似。然而，它们比埃达克岩的Na_2 O含量高得多，而CaO含量低得多。它们的eNd（T）值为-2.3 ~-3.8，初始87 Sr/86 Sr比值为0.707 ~ 0.708，也明显不同于具有类MORB同位素组成的埃达克岩。这些化学和同位素特征，沿着构造环境，表明它们不是俯冲板片部分熔融的产物。詹塘类埃达克岩岩浆可能来源于底侵玄武质下地壳，但其高Na、低Ca的特征需要一种成分特殊的玄武质原岩来解释。它们的成分相媲美的实验产生的富碱玄武岩的部分熔体。因此，我们将它们解释为富碱玄武岩熔融的产物。
The Zhantang andesites, which erupted in the Late Cretaceous Huichang Basin of SE China interior, were associated with the Late Mesozoic lithospheric extension and basaltic underplating. They are high-Na (6.59-8.46 wt% Na2O), high-Al trondhjemitic rocks with high Sr and Ba, low Y and HREE, and high Sr/Y and La/Yb ratios, similar to modern adakites. However, they are much higher in Na2O but lower in CaO than adakites. Their eNd(T) values of -2.3 to -3.8 and initial 87Sr/86Sr ratios of 0.707 to 0.708 are also significantly different from those of adakites with MORB-like isotopic compositions. These chemical and isotopic features, along with the tectonic setting, suggest that they were not produced by partial melting of subducting slab. The Zhantang adakite-like magmas may be derived from underplated basaltic lower crust, but require a compositionally peculiar basaltic protolith to account for their extremely high-Na and low-Ca feature. They are compositionally comparable to the experimentally produced partial melts of alkali-rich basalt. We therefore interpret them as the products of melting of an alkali-rich basaltic rock.