Geochronology and Petrochemistry of Volcanic Rocks in the Xaignabouli Area, NW Laos
Geochronology and Petrochemistry of Volcanic Rocks in the Xaignabouli Area, NW Laos
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DOI：
10.1007/s12583-018-0863-8
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发表时间：
2019-02
影响因子：
3.3
通讯作者：
Meifeng Shi;Zhenbo Wu;Shusheng Liu;Zhimin Peng;Linnan Guo;F. Nie;Siwei Xu
中科院分区：
文献类型：
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作者：
Meifeng Shi;Zhenbo Wu;Shusheng Liu;Zhimin Peng;Linnan Guo;F. Nie;Siwei Xu
对西格纳布里地区南行组玄武岩-安山质凝灰岩和火山角砾岩以及西格纳布里地区芒南组玄武岩-安山质凝灰岩进行了锆石U-Pb年代学、岩石化学和锆石Lu-Hf同位素的综合研究。3个样品的锆石U-Pb测年加权平均年龄分别为235±2.6 Ma、232±1.4 Ma和278±2.8 Ma，表明南坑组形成于晚三叠世，芒南组形成于早二叠世。地球化学特征为高场强元素亏损(如Nb、Ta、Ti)和高LILE/HSE比值，锆石εHf(T)值为8.7~15.9时为正值，显示出大陆弧火山亲和性和俯冲洋板在岩浆源区的部分熔融作用。结合火山岩的空间产状和已有的地质年代学和地球化学资料，我们认为西格纳布利-琅勃拉邦火山岩带可以与洛伊-佩查布恩火山带联系起来。该带二叠-三叠纪火山岩可能是南弧后盆地向东俯冲的产物。
An integrated study of zircon U-Pb geochronology and petrochemistry, together with zircon Lu-Hf isotopes, has been carried out on the basaltic-andesitic tuff and volcanic breccia from the Nam Hang Formation and andesitic tuff from the Muang-Nan Formation in the Xaignabouli area, which had been mapped as the Permian-Early Triassic on the 1 : 1 000 000 geological map or Late Carboniferous on the 1 : 200 000 geological maps. Zircon U-Pb dating of three samples yielded weighted mean ages of 235±2.6, 232±1.4 and 278±2.8 Ma, respectively, suggesting a Late Triassic origin for the Nam Hang Formation and an Early Permian origin for the Muang-Nan Formation. Geochemically, they are characterized by depletions in HFSEs (e.g., Nb, Ta, Ti) and high LILE/HFSE ratios, and they have positive zirconεHf(t) values of 8.7-15.9, which exhibits the continental arc volcanic affinity and partial melting of subducting oceanic slab in the magma source. Combined with spatial occurrence of the volcanic rock and existing geochronological and geochemical data, we suggest that the Xaignabouli-Luang Prabang volcanic belt can be linked to the Loei-Phetchabun belt. The Permian-Triassic volcanic rocks in this belt might be a product of the Nan back-arc basin eastward subduction.