Melt extraction and metasomatism recorded in basal peridotites above the metamorphic sole of the northern Fizh massif, Oman ophiolite
Melt extraction and metasomatism recorded in basal peridotites above the metamorphic sole of the northern Fizh massif, Oman ophiolite
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阿曼蛇绿岩 Fizh 地块北部变质底上方基底橄榄岩中记录的熔体提取和交代作用
DOI：
10.1016/j.tecto.2014.12.004
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发表时间：
2015
期刊：
影响因子：
2.9
通讯作者：
A.
中科院分区：
文献类型：
--
作者：
Yoshikawa;M.;Python;M.;Tamura;A.;Arai;S.;Takazawa;E.;Shibata;T.;Ueda;A.;Sato;A.
阿曼蛇绿岩是世界上保存最完好的海洋地壳和上地幔部分之一，由多个地块组成，沿着400多公里的阿拉伯海岸。在最北端的地块，海洋地壳保存了从洋中脊到俯冲相关阶段的多成因岩浆活动记录。菲什地块的辉橄榄岩和富斜辉石（Cpx）的辉橄榄岩位于蛇绿岩变质底之上几十~ 100米处，这些富含Cpx的橄榄岩的地球化学特征为海洋壳幔之间的成因联系提供了证据。这些富含cpx的橄榄岩中含有橄榄石，橄榄石含量范围有限（90-91），但Cr-尖晶石的Cr# （Cr/(Cr + Al)原子比）值变化较大（0.12-0.33），表明这些富含cpx的橄榄岩经历了不同程度的熔融萃取。富含cpx的橄榄岩中的cpx具有球粒正态化的微量元素变化模式，在重稀土元素（ree）和中稀土元素（(Sm/Yb)N= 0.08-0.55，其中N球粒正态化）之间平缓或陡峭地倾斜，富含Rb、Ba和Nb等高度不相容的元素。这种Cpx化学可以用多成因演化来解释，即在地幔与俯冲起始和逆冲过程中变质底脱水产生的流体相互作用交代之前，最初4-12%的熔体是从枯竭的地幔源中提取出来的。菲什基性富Cpx橄榄岩中Cpx的143nd /144Nd与147sm /144Nd的对比以及同一地块辉长岩的矿物-全岩Sm-Nd等时线的对比表明，该区地壳和地幔岩石之间存在成因联系。此外，基底富含cpx的橄榄岩中的cpx具有高度变化的Sr同位素组成，这表明来自变质底的海水的重要贡献，最初来自俯冲的海洋地壳物质。
The Oman ophiolite is one of the best preserved sections of oceanic crust and upper mantle worldwide, and consists of multiple massifs that lie along more than 400 km of the Arabian coast. In the northernmost massifs, the oceanic crust preserves a record of polygenetic magmatism from mid-ocean ridge to subduction-related stages. The lherzolites and clinopyroxene (Cpx)-rich harzburgites of the Fizh block are located a few tens to a hundred meters above the metamorphic sole of the ophiolite and the geochemistry of these Cpx-rich peridotites provides evidence of a genetic link between oceanic crust and mantle. These Cpx-rich peridotites contain olivine with a restricted range of forsterite contents (90–91), but variable Cr-spinel Cr# (Cr/(Cr + Al) atomic ratio) values (0.12–0.33), suggesting that these Cpx-rich peridotites have undergone variable degrees of melt extraction. Cpxs within the Cpx-rich peridotites have chondrite-normalised trace element variation patterns that slope either gently or steeply between the heavy rare earth elements (REEs) and the middle REEs ((Sm/Yb)N= 0.08–0.55, where N chondrite-normalised) and are enriched in highly incompatible elements such as Rb, Ba and Nb. This Cpx chemistry can be explained by a polygenetic evolution whereby an initial 4–12% of melt was extracted from the depleted mantle source before this mantle was metasomatised by interaction with fluids derived from dehydration of the metamorphic sole during subduction initiation and obduction. A comparison between143Nd/144Nd versus147Sm/144Nd for Cpx in the Fizh basal Cpx-rich peridotites and a mineral–whole rock Sm–Nd isochron for a gabbro from the same massif suggests a genetic link between crustal and mantle rocks in this area. In addition, Cpxs within the basal Cpx-rich peridotites have highly variable Sr isotopic compositions that are indicative of a significant contribution of seawater from the metamorphic sole, originally derived from subducted oceanic crustal material.