Harzburgite-dunite-orthopyroxenite suite as a record of supra-subduction zone setting for the Oman ophiolite mantle
Harzburgite-dunite-orthopyroxenite suite as a record of supra-subduction zone setting for the Oman ophiolite mantle
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DOI：
10.1016/j.lithos.2005.12.012
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发表时间：
2006-08
期刊：
影响因子：
3.5
通讯作者：
A. Tamura;S. Arai
中科院分区：
文献类型：
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作者：
A. Tamura;S. Arai
我们在阿曼北部蛇绿岩的西吉子地块中发现了一套方辉橄榄岩-纯橄榄岩-斜方辉石岩套，记录了地幔中的超俯冲带岩浆活动。斜方辉石岩具有平行岩脉的特征，每个岩脉厚度10-30厘米，与寄主方辉橄榄岩直接接触。斜方辉石由斜方辉石(>；95vol.%)、单斜辉石(<；5vol.%)和微量尖晶石(<；1vol.%)组成，不含橄榄石。该套岩石均具有较高的尖晶石Cr#[=Cr/(Cr+Al)原子比](Cr#≥0.65)。方辉橄榄石和纯橄榄石中橄榄石的Fo含量较低，为89.9~91.1。单斜辉石的不相容元素含量很低，在斜方辉石岩和寄主方辉橄榄岩中表现出LREE的富集性。方辉橄榄岩和斜方辉石岩中单斜辉石的微量元素含量相似，表明它们之间存在遗传联系：方辉橄榄岩是部分熔融的残留物，其提取的熔体形成了斜方辉石岩脉。与单斜辉石平衡的熔体在微量元素特征上与玻安岩相似。矿物化学研究表明，方辉橄榄岩的部分熔融程度高于深海橄榄岩。富LREE熔体和/或流体促进了高熔度熔融。这些证据表明，弧岩浆参与了岩套的成因，即阿曼蛇绿岩地幔经历的超俯冲带背景。
We found a harzburgite–dunite–orthopyroxenite suite from the West Jizi block in the northern Oman ophiolite as a record of supra-subduction zone magmatism in the mantle. The orthopyroxenite has features of parallel dikes, each dike being 10–30 cm thick and in direct contact with the host harzburgite. The orthopyroxenite is composed of orthopyroxene (>95 vol.%), clinopyroxene (<5 vol.%) and trace spinel (<1 vol.%), and is free from olivine. All rocks from the suite are characterized by high Cr# [=Cr/(Cr+Al) atomic ratio] of spinel (Cr#≥0.65). The Fo content of olivine is relatively low, 89.9 to 91.1, in harzburgite and dunite. Clinopyroxenes are very low in incompatible elements and show LREE enrichment in orthopyroxenite and host harzburgite. Similar trace element concentrations of clinopyroxenes in the harzburgite and orthopyroxenite suggest their genetic linkage: the harzburgite is a residue of a partial melting, and its extracted melt formed orthopyroxenite dike. The melt in equilibrium with clinopyroxene is similar in trace-element characteristics to boninite. The mineral chemistries indicate that the harzburgite experienced higher degree of partial melting than abyssal peridotite. LREE-enriched melt and/or fluid assisted the high-degree melting. These lines of evidence indicate an involvement of arc magma in the rock suite genesis, i.e. a supra-subduction zone setting experienced by the Oman ophiolite mantle.