Ancient oceanic crust in island arc lower crust: Evidence from oxygen isotopes in zircons from the Tanzawa Tonalitic Pluton
Ancient oceanic crust in island arc lower crust: Evidence from oxygen isotopes in zircons from the Tanzawa Tonalitic Pluton
复制标题
DOI：
10.1016/j.lithos.2015.04.005
复制
发表时间：
2014-10
期刊：
影响因子：
3.5
通讯作者：
Kazue Suzuki;K. Kitajima;Y. Sawaki;Kentaro Hattori;T. Hirata;S. Maruyama
中科院分区：
文献类型：
--
作者：
Kazue Suzuki;K. Kitajima;Y. Sawaki;Kentaro Hattori;T. Hirata;S. Maruyama
了解岛弧地壳的岩性变异性和成因对认识大陆生长具有重要意义。虽然岛弧的火山结构相对较为人所知，但由于暴露有限，岛弧中地壳和下地壳的性质仍然不确定。解释岛弧系统演化的最佳目标之一是伊豆-小笠原-马里亚纳岛弧内的Tanzawa Tonalites（4-9 Ma）。这些占据中地壳位置的音调是由下地壳的部分熔融产生的。为确定岛弧下地壳深成岩的原岩来源，利用IMS-1280二次离子质谱仪对丹泽英云闪长岩中4个深成岩中的202个锆石颗粒进行了原位同位素分析。锆石的δ 18 O值为4.1‰ ~ 5.5‰，部分锆石的δ 18 O值略低于地幔范围。丹泽英云闪长岩的锆石δ 18 O值较低，表明其原岩中的物质δ 18 O值低于地幔物质。大洋下地壳中的热液蚀变辉长岩的δ 18 O值往往低于地幔，是弧下地壳的主要成分。Tanzawa英云闪长岩被解释为岛弧下地壳部分熔融形成。因此，丹泽英云闪长岩中锆石的低δ 18 O值可能是热液蚀变辉长岩熔融的结果。古海洋地壳物质可能存在于伊豆-小笠原-马里亚纳弧下地壳，在形成丹泽英云闪长岩的时候。
Knowledge of the lithological variability and genesis of island arc crust is important for understanding continental growth. Although the volcanic architecture of island arcs is comparatively well known, the nature of island arc middle- and lower-crust remains uncertain owing to limited exposure. One of the best targets for deciphering the evolution of an island arc system is the Tanzawa Tonalites (4–9 Ma), in the intra-oceanic Izu–Bonin–Mariana arc. These tonalities which occupied a mid-crustal position were generated by partial melting of lower crust. To constrain protoliths of the plutonic rocks in the island arc lower crust,in-situO-isotopic analysis using an IMS-1280 Secondary Ion Mass Spectrometer was carried out on 202 zircon grains separated from 4 plutons in the Tanzawa Tonalite. δ18O value of the zircons ranges from 4.1‰ to 5.5‰ and some zircons have δ18O slightly lower than the mantle range. The low zircon δ18O values from the Tanzawa Tonalite suggest that their protoliths involved materials with lower δ18O values than those of the mantle. Hydrothermally altered gabbros in the lower oceanic crust often have lower δ18O values than mantle and can be primary components of arc lower crust. The Tanzawa Tonalite is interpreted to have been formed by partial melting of island arc lower crust. Thus the low δ18O values in zircons from the Tanzawa Tonalites may originate by melting of the hydrothermally altered gabbro. Ancient oceanic crustal material was likely present in the Izu–Bonin–Mariana arc lower crust, at the time of formation of the Tanzawa Tonalites.