Textural and chemical consequences of interaction between hydrous mafic and felsic magmas: an experimental study
Textural and chemical consequences of interaction between hydrous mafic and felsic magmas: an experimental study
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DOI：
10.1007/s00410-015-1218-4
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发表时间：
2015
影响因子：
3.5
通讯作者：
M. Pistone;J. Blundy;R. Brooker;Eimf
中科院分区：
文献类型：
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作者：
M. Pistone;J. Blundy;R. Brooker;Eimf
源自地幔的含水镁铁质岩浆经常被用作将热量、质量和挥发物传递到地壳中的长英质岩体的机制。现场观察表明，镁铁质、富含水的岩浆经常侵入富含粘性长英质晶体的糊状物。这种情况可以将水从正在结晶的镁铁质岩浆平流到长英质岩浆，导致长英质糊状物中的熔体分数增加并随后流动，同时镁铁质岩浆通过冷却和失水的组合而被淬火。为了研究这种情况，我们对水不饱和（填隙熔体中含有 4 wt% H2O）英安岩晶体糊（50–80 vol% 石英晶体）进行了实验，该晶体糊状物在 950 °C 和 4 kbar 下由水饱和（≥6 wt% H2O）安山岩岩浆提供挥发性供应。我们的实验产品显示出单向凝固织构（即梳状分层），因为晶体在镁铁质-长英质界面成核并生长成镁铁质端元。该过程是由等温和等压过冷驱动的，该过冷是由于水从镁铁质迁移到长英质岩浆时液相线温度的变化而引起的。我们将这个过程称为“化学淬火”，并认为与天然镁铁质-长英质相互作用相关的一些纹理在起源上不仅仅是冷却驱动的，而且可能是由邻近界面的挥发物的溶出引起的，无论是水不饱和的长英质岩浆（如我们的实验）还是裂缝。
Mantle-derived, hydrous mafic magmas are often invoked as a mechanism to transfer heat, mass and volatiles to felsic plutons in the Earth’s crust. Field observations suggest that mafic, water-rich magmas often intrude viscous felsic crystal-rich mushes. This scenario can advect water from the crystallising mafic magma to the felsic magma, leading to an increase in melt fraction in the felsic mush and subsequent mobilisation, at the same time as the mafic magma becomes quenched through a combination of cooling and water loss. To investigate such a scenario, we conducted experiments on a water-undersaturated (4 wt% H2O in the interstitial melt) dacitic crystal mush (50–80 vol% quartz crystals) subject to volatile supply from a water-saturated (≥6 wt% H2O) andesite magma at 950 °C and 4 kbar. Our experimental run products show unidirectional solidification textures (i.e. comb layering) as crystals nucleate at the mafic–felsic interface and grow into the mafic end-member. This process is driven by isothermal and isobaric undercooling resulting from a change in liquidus temperature as water migrates from the mafic to the felsic magma. We refer to this process as “chemical quenching” and suggest that some textures associated with natural mafic–felsic interactions are not simply cooling-driven in origin, but can be caused by exsolution of volatiles adjacent to an interface, whether a water-undersaturated felsic magma (as in our experiments) or a fracture.