Transition zone origin of potassic basalts from Wudalianchi volcano, northeast China
Transition zone origin of potassic basalts from Wudalianchi volcano, northeast China
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DOI：
10.1016/j.lithos.2012.10.010
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发表时间：
2012-12
期刊：
影响因子：
3.5
通讯作者：
T. Kuritani;J. Kimura;E. Ohtani;H. Miyamoto;K. Furuyama
中科院分区：
文献类型：
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作者：
T. Kuritani;J. Kimura;E. Ohtani;H. Miyamoto;K. Furuyama
研究了中国东北五大连池火山田1719 ~ 1721年火山喷发时期历史钾质玄武岩的成因。本研究中检测的样品是干燥的，含有~5vol。%橄榄石微晶。对样品的地球化学分析，以及从公元1719年到1721年喷发的已发表的材料数据，表明玄武岩在全岩变化图中表现出线性的成分趋势，并具有K2O富集（>4wt.%）和类似em1的同位素特征。利用热力学计算和观察到的玄武岩岩石学特征，估计岩浆喷发前的温度为~1250℃，岩浆深处的含水量为bb0 ~1.1wt.%。由于估计温度明显高于五大连池火山场岩石圈地幔的预测最高温度，岩浆可能来自软流圈地幔。我们认为玄武岩的钾质和em1类性质都起源于地幔过渡带，大约1.5Ga以前通过古板块的停滞被富钾沉积流体交代。玄武岩的线性全岩组成趋势主要反映了地幔过渡带的地球化学非均质性，古停滞板块的~1.5Ga沉积物和太平洋停滞板块的近期沉积物和橄榄岩的贡献是可变的但耦合的。我们推测，五大连池岩浆活动是由地幔过渡带的含水地幔柱上涌引起的，该地幔柱通过古代俯冲板块和近代太平洋板块的停滞而水化。
The origin of historic potassic basalts (from the 1719 to 1721AD eruption) from the Wudalianchi volcanic field, northeast China, is investigated. The samples examined in this study are aphyric, and contain ~5vol.% olivine microphenocrysts. Geochemical analyses of the samples, along with published data for material from the 1719 to 1721AD eruption, show that the basalts exhibit linear compositional trends in whole-rock variation diagrams, and are characterized by K2O enrichment (>4wt.%) and an EM1-like isotopic signature. Using thermodynamic calculations and the observed petrological features of the basalts, the temperature of the magmas shortly before eruption is estimated to have been ~1250°C, and the water content of the magma at depth is estimated to have been >~1.1wt.%. Because the estimated temperatures are significantly higher than the projected maximum temperature of the lithospheric mantle beneath the Wudalianchi volcanic field, the magmas were likely derived from the asthenospheric mantle. We suggest that both the potassic- and EM1-like natures of the basalts originated from the mantle transition zone, metasomatized by K-rich sediment fluids ~1.5Ga ago through a stagnation of an ancient slab. The linear whole-rock compositional trends of the basalts primarily reflect the geochemical heterogeneity in the mantle transition zone, with variable but coupled contributions of ~1.5Ga sediments in the ancient stagnant slab, and recent sediments and peridotites in the stagnant Pacific slab. We infer that the Wudalianchi magmatism was caused by an upwelling of a hydrous mantle plume from the mantle transition zone, which was hydrated through the stagnation of the ancient subducted slab and the recent Pacific slab.