Enrichment of HFSE in chlorite‐harzburgite produced by high‐pressure dehydration of antigorite‐serpentinite: Implications for subduction magmatism
Enrichment of HFSE in chlorite‐harzburgite produced by high‐pressure dehydration of antigorite‐serpentinite: Implications for subduction magmatism
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DOI：
10.1029/2004gc000791
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发表时间：
2005-01
期刊：
影响因子：
3.7
通讯作者：
C. Garrido;V. López Sánchez‐Vizcaíno;M. T. Gomez-Pugnaire;V. Trommsdorff;O. Alard;J. Bodinier;M. Godard
中科院分区：
文献类型：
--
作者：
C. Garrido;V. López Sánchez‐Vizcaíno;M. T. Gomez-Pugnaire;V. Trommsdorff;O. Alard;J. Bodinier;M. Godard
高场强微量元素（HFSE）相对于正常洋中玄武岩（N-MORB）的亏损是俯冲岩浆活动最独特的地球化学指纹。提出的假说主张，这种“俯冲”的签名是在熔融和/或流体转移过程中获得的地幔楔或在地壳中的俯冲洋板块。在这里，我们提供了基于野外和地球化学的证据，表明叶蛇纹石-蛇纹岩的高压脱水产生了相对富集HFSE的斜方辉石，这是由于F-OH-Ti-斜腐植岩共生体与橄榄石的稳定性。现有的实验数据表明，在水化的、中间到温暖的俯冲带中，斜腐镁石-橄榄石共生体可以在弧下深度稳定地存在于斜腐镁石-哈氏橄榄石中。在这些环境中，沙漠化可能作为流体的来源，从上覆地壳和沉积物中浸出大离子亲石元素（LILE），Pb和Sr，并将其带到地幔楔。另一方面，在地幔楔中斜辉橄榄岩-橄榄石共生体的稳定作用，通过选择性地将它们与来自板片的流体中的其他不相容微量元素分离，充当HFSE的汇。由此产生的弧流体与楔状体平衡，在HFSE中强烈亏损，并将这种亏损转移到上覆的热地幔楔中，在那里产生俯冲岩浆。
Depletion of high‐field‐strength trace elements (HFSE) relative to normal mid‐ocean basalts (N‐MORB) is the most distinctive geochemical fingerprint of subduction magmatism. Proposed hypotheses advocate that this “subduction” signature is acquired during melting and/or fluid transfer either in the mantle wedge or in the crust of the subducting oceanic plate. Here we provide field‐based and geochemical evidence showing that high‐pressure dehydration of antigorite‐serpentinite produces chlorite‐harzburgite relatively enriched in HFSE due to the stabilization of F‐OH‐Ti‐clinohumite intergrowths with prograde olivine. Available experimental data indicate that in hydrated, intermediate to warm subduction zones, clinohumite‐olivine intergrowths can be stable in prograde chlorite‐harzburgite olivine at subarc depths. In these settings, deserpentinization may act as a source of fluids leaching large‐ion lithophile elements (LILE), Pb, and Sr from the overlying crust and sediments on their way up to the mantle wedge. Stabilization of chlorite‐harzburgites with clinohumite‐olivine intergrowths in the mantle wedge, on the other hand, acts as a sink of HFSE by selectively fractionating them from other incompatible trace elements in fluids emanating from the slab. Resulting arc fluids in equilibrium with wedge chlorite‐harzburgite are strongly depleted in HFSE and transfer this depletion to the overlying hot mantle wedge, where subduction magmas are generated.