Experimental Study of the Stability of a Dolomite + Coesite Assemblage in Contact With Peridotite: Implications for Sediment–Mantle Interaction and Diamond Formation During Subduction
Experimental Study of the Stability of a Dolomite + Coesite Assemblage in Contact With Peridotite: Implications for Sediment–Mantle Interaction and Diamond Formation During Subduction
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DOI：
10.1093/petrology/egr066
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发表时间：
2012-02
影响因子：
3.9
通讯作者：
Audrey M. Martin;D. Laporte;K. Koga;T. Kawamoto;T. Hammouda
中科院分区：
文献类型：
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作者：
Audrey M. Martin;D. Laporte;K. Koga;T. Kawamoto;T. Hammouda
碳酸盐岩是大洋板块携带的沉积物或玄武岩蚀变产物，通过俯冲作用进入地幔，封闭体系中碳酸盐岩的高压、高温稳定性一直受到许多研究的限制，但俯冲碳酸盐岩与周围地幔的相互作用对碳酸盐岩稳定性的影响却知之甚少。然而，这些相互作用可能会影响俯冲物质的稳定深度、相互作用区的组成以及碳从板层向地幔的转移速率。为了确定俯冲的蓝绿柯石英组合与上覆地幔之间界面的交换机制，我们在6 GPa和9008 C和11008 C的多砧装置中进行了实验。在第一系列的实验中，我们研究了反应和迁移过程操作沿着之间的界面圆柱体的石榴石橄榄岩和石榴石柯石英。在第二个系列的实验中，均匀的混合物的milliterite柯石英和石榴石橄榄岩平衡在高压和高温下的（milliterite柯石英）/橄榄岩ratio.We的功能相关系的特征表明，俯冲milliterite柯石英组合的不稳定温度小于9008 ℃，在6 GPa时，在接触的石榴石二辉橄榄岩或方辉橄榄岩。在斜长岩-柯石英-橄榄岩的界面上产生了以单斜辉石-菱镁矿为主的反应带。以流体或碳酸岩熔体形式存在的碳也渗入石榴橄榄岩中形成菱镁矿和单斜辉石。此外，在两个实验中观察到石墨。我们认为，它是由氧化还原反应之间的橄榄岩中的含铁硅酸盐的界面处的铁云母柯石英。由于我们的实验条件处于金刚石的稳定性范围内，这表明金刚石可能是从俯冲的辉绿-柯石英中结晶出来的。
Carbonates carried by oceanic platescin the form of sediment or alteration products of basaltscare introduced into the mantle by subduction.The high-pressure^high-temperature stability of carbonates in a closed system has been constrained by a number of studies, but the effects of the interactions between subducted carbonates and the surrounding mantle on carbonate stability are poorly known. These interactions may, however, influence the stability depth of the subducted material, the composition of the interaction zone, and the rate of carbon transfer from the slab to the mantle. To determine the exchange mechanisms at the interface between a subducted dolomiteþ coesite assemblage and the overlying mantle, we performed experiments at 6 GPa and 9008C and 11008C in a multi-anvil apparatus. In a first series of experiments, we studied the reaction and migration processes operating along the interface between a cylinder of dolomiteþ coesite and a cylinder of garnet peridotite. In a second series of experiments, homogeneous mixtures of dolomiteþ coesite and garnet peridotite were equilibrated at high pressure and high temperature to characterize the phase relations as a function of the (dolomiteþ coesite)/peridotite ratio.We show that the destabilization temperature of a subducted dolomiteþ coesite assemblage is less than 9008C at 6 GPa when in contact with a garnet lherzolite or a harzburgite. A reaction zone composed mainly of clinopyroxene þmagnesite is produced at the interface between dolomiteþ coesite and peridotite. Carboncin the form of a fluid or in a carbonatitic meltcalso infiltrates the garnet peridotite to form magnesite and clinopyroxene. Moreover, graphite was observed in two experiments. We believe that it was produced by a redox reaction at the interface between dolomiteþ coesite and iron-bearing silicates in the peridotite. As our experimental conditions are in the stability field of diamond, this suggests a potential mechanism for diamond crystallization from subducted dolomiteþ coesite in contact with the mantle wedge.