The influence of H2O on mantle wedge melting
The influence of H2O on mantle wedge melting
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DOI：
10.1016/j.epsl.2006.06.043
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发表时间：
2006-09-15
影响因子：
5.3
通讯作者：
Medard, Etienne
中科院分区：
文献类型：
--
作者：
Grove, Timothy L.;Chatterjee, Nilanjan;Medard, Etienne
在1.2- 3.2GPa压力范围内，在H_2O饱和条件下，测定了一种原始未贫化橄榄岩组分的固相线和近固相线熔融行为。蒸气饱和熔化（在富含H2O的超临界流体存在下熔化）在1.2GPa下在940 ℃开始，固相线温度在2GPa下连续降低到860 ℃，在3.2GPa下降低到800 ℃。该固相线与先前研究的较低温度结果相似。早期研究中发现的温度差异可能是由于几项研究中使用的运行时间较短以及橄榄石与透辉石熔化的动力学较慢。固相线相包括橄榄石、斜方辉石、高钙单斜辉石和富铝相，在2 ~ 2.4GPa压力范围内，从尖晶石+角闪石（1.2- 1.8GPa）转变为尖晶石+角闪石（1.2- 1.8GPa）。在2.4GPa以上，固相线上沿着橄榄石+斜方辉石+单斜辉石分布着石榴子石+石榴子石+钛铁矿。绿泥石可能是地幔楔底部的稳定相，它可能在熔剂熔融的开始中起作用。钛铁矿可能在岩浆HFSE亏损的发展中发挥作用。俯冲洋壳上方地幔楔的通量熔融开始于从俯冲洋壳释放的富H2O组分（流体或熔体）在上覆地幔内上升。当它上升到地幔楔中时，H2O在比楔板界面浅的深度处的蒸汽饱和固相线处触发熔融。熔融继续上升到更浅，更热的覆盖地幔。在楔的这一部分熔融发生在蒸汽欠饱和的条件下，因为熔体中的H2O含量不断稀释，熔体上升通过楔，溶解和再平衡较浅，较热的地幔。与地幔楔的最终平衡发生在楔顶部附近的浅深度处。这个过程的模型开发使用的蒸汽饱和相关系作为出发点。(c)2006 Elsevier B.V保留所有权利。
The solidus and near-solidus melting behavior of a primitive undepleted peridotite composition has been determined over a pressure range of 1.2-3.2 GPa at H2O saturated conditions. Vapor-saturated melting (melting in the presence of an H2O-rich supercritical fluid) begins at 940 degrees C at 1.2 GPa and the solidus temperature decreases continuously to 860 degrees C at 2 GPa and 800 degrees C at 3.2 GPa. This solidus is similar to the lower temperature results of previous investigations. The temperature discrepancies found in earlier studies could be a result of short run times used in several studies and the slower kinetics of olivine vs. diopside melting. The solidus phases include olivine, orthopyroxene, high-Ca clinopyroxene and Al-rich phases that change from spinel + amphibole (1.2-1.8 GPa) to spinel + chlorite over the pressure range of 2-2.4 GPa. Above 2.4 GPa garnet + chlorite + ilmenite are present along with olivine + orthopyroxene + clinopyroxene on the solidus. Chlorite may be a stable phase at the base of the mantle wedge and it may play a role in the onset of flux melting. Ilmenite might play a role in the development of HFSE depletions in are magmas, Flux melting of the mantle wedge above the subducting oceanic lithosphere begins when an H2O-rich component (either fluid or melt) released from the stab ascends within the overlying mantle. As it ascends into the mantle wedge the H2O triggers melting at the vapor-saturated solidus at a depth shallower than the wedge-slab interface. Melting continues as the melt ascends into shallower, hotter overlying mantle. Melting in this part of the wedge occurs at vapor-undersaturated conditions because the H2O content of the melt is continually diluted as the melt ascends through the wedge, dissolving and re-equilibrating with shallower, hotter mantle. Final equilibration with the mantle wedge occurs at shallow depths near the top of the wedge. A model of this process is developed using the vapor-saturated phase relations as a starting point. (c) 2006 Elsevier B.V All rights reserved.