Chemical Diversity of the Ueno Basalts, Central Japan: Identification of Mantle and Crustal Contributions to Arc Basalts
Chemical Diversity of the Ueno Basalts, Central Japan: Identification of Mantle and Crustal Contributions to Arc Basalts
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DOI：
10.1093/petrology/43.10.1923
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发表时间：
2002-10
影响因子：
3.9
通讯作者：
J. Kimura;W. Manton;C. Sun;S. Iizumi;Takeyoshi Yoshida;R. Stern
中科院分区：
文献类型：
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作者：
J. Kimura;W. Manton;C. Sun;S. Iizumi;Takeyoshi Yoshida;R. Stern
日本中部的上野玄武岩由一个单成因火山锥杂岩组成，其活动时间为2.76 ~ 1.34 Ma。玄武岩在14个以上的中心喷发，散布在直径40公里的区域内。碱性玄武岩最先喷发，次碱性玄武岩次之。准同心扩张的喷发中心，同时与隆起和碱性降低的熔岩表明，上野岩浆活动起源于地幔底辟，因为它如雨后春笋般出现在岩石圈的基础。亏损的软流圈地幔（碱性玄武岩）、富集的岩石圈地幔（亚碱性玄武岩）和地壳成分被确定为上野玄武岩成因的化学端员。不相容微量元素丰度表明，上野碱性玄武岩是典型的板内玄武岩，而亚碱性玄武岩显示出较强的亲和力与正常的弧熔岩。Sr-Nd-Pb同位素组成表明，碱性玄武岩的地幔源区比亚碱性玄武岩更亏损。石榴子石-二辉橄榄岩稳定场中约7%的软流圈地幔熔融产生原始碱性玄武岩，而陆下岩石圈内约12%的尖晶石二辉橄榄岩熔融产生原始亚碱性玄武岩。同位素组成和流体移动的/非移动的元素比值与SiO2含量在亚碱性套件中广泛地协变，并且增加的SiO2含量与更强的EMII（富集地幔II）同位素亲和力和流体移动的元素丰度相关。一个渐进的AFC（同化分离结晶）模型假设同化的低钾熔体再现的化学变化中观察到的亚碱性套件。在岩石圈底部的一个平坦的地幔底辟熔融是上野岩浆活动的主要原因，伴随着老弧地壳的同化。
The Ueno Basalts of central Japan comprise a monogenetic volcanic cone complex that was active between 2·76 and 1·34 Ma. Basalts were erupted at more than 14 centers scattered over a region 40 km in diameter. Alkali basalt was erupted first, followed by sub-alkaline basalt. Quasi-concentric expansion of eruption centers coinciding with uplift and with decreasing alkalinity of the lavas suggests that Ueno magmatism originated from a mantle diapir as it mushroomed at the base of the lithosphere. Depleted asthenospheric mantle (alkali basalt), enriched lithospheric mantle (sub-alkaline basalt), and crustal components are identified as chemical end-members in the petrogenesis of the Ueno Basalts. Incompatible trace element abundances indicate that the Ueno alkali basalts are typical within-plate basalts, whereas the sub-alkaline basalts show strong affinities with normal arc lavas. Sr–Nd–Pb isotopic compositions indicate that the mantle source of the alkali basalts was more depleted than that of the sub-alkaline basalts. About 7% melting of asthenospheric mantle in the garnet-lherzolite stability field produced the primitive alkali basalts and 12% melting of spinel lherzolite within the subcontinental lithosphere produced the primitive sub-alkaline basalts. Isotopic compositions and fluid mobile/immobile element ratios broadly covary with SiO2contents in the sub-alkaline suite, and increasing silica content is associated with stronger EMII (Enriched Mantle II) isotope affinities and fluid mobile element abundances. A progressive AFC (assimilation–fractional crystallization) model assuming assimilation of a low-K silicic melt reproduces the chemical variations observed in the sub-alkaline suite. Melting of a flattening mantle diapir at the base of the lithosphere is the dominant cause of Ueno magmatism, accompanied by the assimilation of older arc crust.