Multiple Episodes of Rock-Melt Reaction at the Slab-Mantle Interface: Formation of High Silica Primary Magmas in Intermediate to Hot Subduction Zones
Multiple Episodes of Rock-Melt Reaction at the Slab-Mantle Interface: Formation of High Silica Primary Magmas in Intermediate to Hot Subduction Zones
复制标题
板幔界面多期熔岩反应：中热俯冲带高硅质原生岩浆的形成
DOI：
10.1093/petrology/egad011
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发表时间：
2023
影响因子：
3.9
通讯作者：
Straub, Susanne M
中科院分区：
文献类型：
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作者：
Rebaza, Anna M;Mallik, Ananya;Straub, Susanne M
硅质板片来源的部分熔融物渗入弧下地幔并引起岩石熔融反应，控制了不同的原生弧岩浆和岩性不均一性的形成。先前的研究已经研究了在亚弧条件下的岩石熔体反应的散装水含量，反应物的组成，和熔体渗透（多孔与通道化）的性质的影响。然而，在这种情况下，岩石熔融反应的多个情节的效果还没有被调查过。在这里，我们探讨地幔楔修改通过一系列的补充水螅状岩板部分熔体，以及这样的过程是否可以最终解释的起源高镁安山岩在弧世界各地。一系列活塞-圆筒实验模拟了在3 GPa和800-1050°C下，使用75-25和50-50的岩石熔体比例，在多达三个阶段（I至III）连续添加板坯熔体。合成的KLB-1和天然流纹岩（JR-1）分别代表地幔和板片成分。从第一次岩石-熔体相互作用开始，橄榄岩地幔转变为无橄榄石富云母辉石岩±角闪石±石英/柯石英，与流纹岩-含水熔体（72-80 wt% SiO2和40-90 Mg#）平衡。无橄榄石辉石岩的形成似乎是由复杂的功能控制的T，P，岩熔体比，楔成分，和硅的活动的板熔体。值得注意的是，辉石岩接近熔融缓冲状态与岩石熔融反应的渐进阶段，其中这些流纹岩熔体继承和保存的主要（碱金属，铁，镁，钙）和微量元素板签名。我们的研究结果表明，岩石的不均匀性，如辉石岩形成的岩石熔融反应的产物，在弧下地幔可能会作为熔体的“使能者”，这意味着他们可能会作为途径，使渗透熔体保留其板签名，而不进行修改。此外，岩石熔融反应的产物（熔体和残留物）和平均地幔楔（~150至400 kg/m3）之间的密度差异可能有助于形成不稳定性和底辟上升的板块成分到地幔楔。然而，原始板片熔体的命运似乎与地幔相互作用的路径的长度，这解释了明显的宽岩浆谱，以及他们的程度板片石榴石签名稀释。这项工作和高镁#墨西哥trondhjemites的存在表明，几乎原始板熔体可以使他们的方式到地壳水平，并有助于弧岩浆的多样性。
Siliceous slab-derived partial melts infiltrate the sub-arc mantle and cause rock-melt reactions, which govern the formation of diverse primary arc magmas and lithological heterogeneities. The effect of bulk water content, composition of reactants, and nature of melt infiltration (porous versus channelized) on the rock-melt reactions at sub-arc conditions have been investigated by previous studies. However, the effect of multiple episodes of rock-melt reactions in such scenarios has not been investigated before. Here, we explore mantle wedge modifications through serial additions of hydrous-silicic slab partial melts and whether such a process may ultimately explain the origin of high-Mg# andesites found in arcs worldwide. A series of piston-cylinder experiments simulate a serial addition of silicic slab melts in up to three stages (I through III) at 3 GPa and 800–1050°C, using rock-melt proportions of 75–25 and 50–50. A synthetic KLB-1 and a natural rhyolite (JR-1) represented the mantle and the slab components, respectively. Right from the first rock-melt interaction, the peridotite mantle transforms into olivine-free mica-rich pyroxenites ± amphibole ± quartz/coesite in equilibrium with rhyolitic-hydrous melts (72–80 wt% SiO2and 40–90 Mg#). The formation of olivine-free pyroxenite seems to be controlled by complex functions ofT,P, rock-melt ratio, wedge composition, and silica activity of the slab-melt. Remarkably, the pyroxenites approach a melt-buffered state with progressive stages of rock-melt reactions, where those rhyolitic melts inherit and preserve the major (alkalis, Fe, Mg, Ca) and trace element slab-signature. Our results demonstrate that lithological heterogeneities such as pyroxenites formed as products of rock-melt reactions in the sub-arc mantle may function as melt ‘enablers,’ implying that they may act as pathways that enable the infiltrating melt to retain their slab signature without undergoing modification. Moreover, the density contrast between the products of rock-melt reaction (melts and residues) and the average mantle wedge (~150 to 400 kg/m3) may help forming instabilities and diapiric rise of the slab components into the mantle wedge. However, the fate of the primitive slab-melts seems to be associated with the length of the pathway of mantle interaction which explains the evident wide magma spectrum as well as their degree of slab garnet-signature dilution. This work and the existence of high-Mg# Mexican-trondhjemites indicates that almost pristine slab-melts can make their way up to crustal levels and contribute to the arc magma diversity.