Widespread arc-related melting in the mantle section of the northern Oman ophiolite as inferred from detrital chromian spinels
Widespread arc-related melting in the mantle section of the northern Oman ophiolite as inferred from detrital chromian spinels
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DOI：
10.1144/0016-76492005-057
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发表时间：
2006-09
影响因子：
2.7
通讯作者：
S. Arai;K. Kadoshima;T. Morishita
中科院分区：
文献类型：
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作者：
S. Arai;K. Kadoshima;T. Morishita
我们研究了现代河床中来自地幔剖面的碎屑铬尖晶石，以确定阿曼北部蛇绿岩的地幔橄榄岩是洋源还是弧源。碎屑状铬尖晶石的铬数(=Cr/(Cr+Al)原子比)大多在0.4~0.8之间，其中60%以上的铬数大于0.6。这在很大程度上表明了岛弧性质，因为在海底岩石中，铬尖晶石的铬数很少高于0.6。高铬尖晶石(>；0.6)，也是低含量的二氧化钛(<；0.3wt%)，可能来自于弧形环境。除剖面底部外，无尖晶石二辉橄榄岩。高铬碎屑的铬尖晶石在地幔剖面中更加丰富，具有更频繁的不协调的纯橄榄石豆荚。变形后不协调的纯橄榄岩和相邻的方辉橄榄岩包括露头中的高铬尖晶石。阿曼北部蛇绿岩的上地幔形成于快速扩张的山脊，后来在俯冲带环境中受到岛弧岩浆作用的改造。这种从大洋中脊到岛弧的构造环境转换是解释大洋岩石圈切片作为蛇绿岩向大陆边缘俯冲的关键。
We examined detrital chromian spinels, in recent river beds, derived from the mantle section to deterrmine whether the mantle peridotite of the northern Oman ophiolite is of oceanic or arc origin. The Cr-number (= Cr/(Cr + Al) atomic ratio) of the detrital chromian spinels mostly ranges from 0.4 to 0.8, and more than 60% of them have Cr-numbers higher than 0.6. This indicates a significant extent of island-arc nature because chromian spinels seldom have Cr-numbers higher than 0.6 in ocean-floor rocks. The high-Cr-number (>0.6) spinels, which are also low in TiO2 (<0.3 wt%), are probably derived from an arc setting. Lherzolite with spinel Cr-numbers <0.2 is absent except near the base of the section. The high-Cr-number detrital chromian spinels are more abundant from the mantle section with more frequent discordant dunite pods. Post-deformational discordant dunite and adjacent harzburgite include the high-Cr-number spinels in outcrops. The upper mantle of the northern Oman ophiolite was formed at a fast-spreading ridge and was later modified by island-arc magmatism in a subduction-zone environment. This switch of tectonic setting from a mid-oceanic ridge to an island arc is essential in the explanation of obduction of a slice of oceanic lithosphere onto a continental margin as an ophiolite.