Mineralogy and geochemistry of serpentinized peridotites of the Northern Nubian Shield: The origin of compositionally banded olivine and implications for Neoproterozoic supra-subduction zone metasomatism
Mineralogy and geochemistry of serpentinized peridotites of the Northern Nubian Shield: The origin of compositionally banded olivine and implications for Neoproterozoic supra-subduction zone metasomatism
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努比亚地盾北部蛇纹石化橄榄岩的矿物学和地球化学：成分带状橄榄石的起源及其对新元古代俯冲带交代作用的影响
DOI：
10.1016/j.lithos.2022.106894
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发表时间：
2022
期刊：
影响因子：
3.5
通讯作者：
Selim, Hussam A.
中科院分区：
文献类型：
--
作者：
Ismail, Mohamad A.;Maurice, Ayman E.;Asimow, Paul D.;Gharib, Moustafa E.;Wilner, M.J.;Selim, Hussam A.
埃及沙漠东南部Wadi El-Mireiwa的新元古代超基性岩石序列——蛇纹岩化橄榄岩、蛇纹岩和斜辉石岩。它们代表了一个破碎蛇绿岩的地幔和最下端的地壳部分，通过在变质沉积岩和岛弧组合上的逆冲而就位，后来被花岗岩块侵入。在蛇纹橄榄岩样品中，橄榄石的背散射电子图像显示带状带，由典型镁质主晶体（Fo ~ 89）内的直线和平行富镁（Fo ~ 96）片层定义。斜辉石的存在、较低的全岩mg#（~ 88）、较低的橄榄石NiO含量（0.1 ~ 0.32 wt%）和较高的新鲜cr尖晶石tio2含量（~ 0.3 wt%）均与蛇纹化橄榄岩和蛇纹岩的堆积成因一致。另一方面，部分伴生蛇纹岩具有较高的全岩mg#（92）和低TiO2in cr尖晶石（~ 0.01 wt%），符合超俯冲带（SSZ）环境弧前区域高熔体萃取残余成因。橄榄石中富镁带的形成是由于高应变速率位错蠕变形成的亚晶界上，与高mg /Fe2+流体的交代Mg-Fe交换增强所致。这种高mg /Fe2+流体交代作用也解释了cr尖晶石中MgO的反向分带，而REE和其他微量元素的低全岩浓度排除了熔体-岩石相互作用的重要作用。高mg /Fe2+流体交代的证据表明，SSZ流体和高弧前应变率不仅影响地幔楔，而且影响上覆超镁铁质堆积。未交代（+2.48 ~ +2.67）和交代（+3.75 ~ +4.53）样品的氧逸度[ΔlogƒO2(FMQ)]值反映了新元古代SSZ岩浆的氧化性质和交代流体的氧化性。马里亚纳弧前橄榄岩和显生宙SSZ蛇绿岩的橄榄石也记录了带状分带；新元古代Wadi El-Mireiwa案例表明，快速的地幔流动是弧前蛇绿岩发育的构造环境的一个持续特征。
A sequence of Neoproterozoic ultramafic rocks — serpentinized peridotite, serpentinite, and clinopyroxenite — outcrop in Wadi El-Mireiwa in the south Eastern Desert of Egypt. They represent the mantle and lowermost crustal section of a fragmented ophiolite, emplaced by thrusting above metasedimentary rocks and an island arc assemblage and later intruded by a granite mass. In samples of the serpentinized peridotite, back-scattered electron images of olivine reveal banded zoning, defined by straight and parallel Mg-enriched (Fo ∼ 96) lamellae within typically magnesian host crystals (Fo ∼ 89). The presence of clinopyroxene, the relatively low whole-rock Mg# (∼88), the low NiO content of olivine (0.1–0.32 wt%), and the relatively high TiO2content of fresh Cr-spinel (∼0.3 wt%) are all consistent with a cumulate origin for the serpentinized peridotite and serpentinites. On the other hand, some associated serpentinite has higher whole-rock Mg# (92) and low TiO2in Cr-spinel (∼0.01 wt%), consistent with a residual origin by high-degree melt extraction in the fore-arc region of a supra-subduction zone (SSZ) environment. The formation of Mg-enriched bands in olivine is attributed to the enhancement of metasomatic Mg-Fe exchange with high-Mg/Fe2+fluids along crystallographically-oriented subgrain boundaries produced by high strain-rate dislocation creep. Such high-Mg/Fe2+fluid metasomatism also explains reverse zoning of MgO in Cr-spinel, whereas the low whole-rock concentrations of REE and other trace elements exclude a significant role for melt-rock interaction. The evidence for high-Mg/Fe2+fluid metasomatism in this suite indicates that SSZ fluids and high fore-arc strain rates affect not only the mantle wedge but also overlying ultramafic cumulates. The oxygen fugacity [ΔlogƒO2(FMQ)] values calculated from unmetasomatized (+2.48 to +2.67) and metasomatized (+3.75 to +4.53) samples reflect the oxidized nature of Neoproterozoic SSZ magma and the even more oxidizing character of the metasomatic fluids. Banded zoning has also been recorded in olivine from Mariana fore-arc peridotite and Phanerozoic SSZ ophiolites; the Neoproterozoic Wadi El-Mireiwa case shows that rapid mantle flow has been a persistent feature of the tectonic environment where fore-arc ophiolites develop.
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DOI：
--
发表时间：
1990
期刊：
影响因子：
--
作者：
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通讯作者：
B. Windley
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影响因子：
2.9
作者：
Maurice, Ayman E.;Azer, Mokhles K.;Asimow, Paul D.;Basta, Fawzy F.;Helmy, Hassan M.;Shibata, Tomoyuki
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Shibata, Tomoyuki
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影响因子：
3.5
作者：
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通讯作者：
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变质橄榄石记录了蛇纹岩脱水过程中的外部流体渗透
影响因子：
4.9
作者：
Clarke E
通讯作者：
Clarke E
直接观测橄榄石中的科特雷尔大气
DOI：
--
发表时间：
1986
期刊：
影响因子：
--
作者：
M. Kitamura;H. Matsuda;N. Morimoto
通讯作者：
N. Morimoto