Pyroxenite melting at subduction zones
Pyroxenite melting at subduction zones
复制标题
俯冲带辉石岩熔融
DOI：
10.1130/g50929.1
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发表时间：
2023
期刊：
影响因子：
5.8
通讯作者：
Ducea, Mihai N.
中科院分区：
文献类型：
--
作者：
Bowman, Emilie E.;Ducea, Mihai N.
弧形岩浆作用被认为是由地幔楔形中的橄榄岩熔融驱动的。然而，辉石岩在岩浆弧下的熔融区无处不在。与橄榄岩相比，辉石岩通常具有较低的固相温度和较高的熔体生产率，因此辉石岩可能在岩浆生成中发挥重要作用。这里，我们利用全球上新世-全新世原始弧岩浆数据库的锌/铁比值来表明，随着上覆板块地壳厚度的增加，辉石岩来源的熔体相对于橄榄岩来源的熔体的比例也增加。事实上，在地壳厚度为40公里的弧处，大多数岩浆来自辉石岩。辉石岩熔体的常量元素和微量元素地球化学与地幔中冻结的镁铁质岩浆的来源是一致的。我们假设，随着大陆地壳厚度的增加，地幔楔体向更高的压力和更低的温度移动，从而降低橄榄岩熔融的程度，使来自辉石岩的地幔的岩浆主导弧预算。
Arc magmatism is thought to be driven by peridotite melting in the mantle wedge. Yet pyroxenites are ubiquitous in the melting region beneath magmatic arcs. Because they typically have lower solidi temperatures and higher melt productivities compared to peridotite, pyroxenites likely play a significant role in magma generation. Here, we use the Zn/Fe ratios of a global database of Pliocene–Holocene primitive arc magmas to show that, as the crustal thickness of the overlying plate increases, so does the proportion of pyroxenite-derived melts relative to peridotite-derived melts. In fact, at arcs with crustal thicknesses >40 km, the majority of magmas are sourced from pyroxenite. Major and trace element geochemistry of pyroxenite melts is consistent with derivation from mafic magmas frozen in the mantle en route to the surface. We hypothesize that, as the thickness of the continental crust increases, the mantle wedge is displaced toward higher pressures and cooler temperatures, thereby lowering the extent of peridotite melting and allowing magmas sourced from the pyroxeniteveined mantle to dominate the arc budget.