Magmatic processes occurring in the deepest parts of sub-volcanic plumbing systems remain poorly constrained. However, crystal mush fragments incorporated into ascending magmas can provide valuable insights into the processes and conditions of transcrustal magma transport, storage and differentiation. Here we use lava samples drilled from Tamu Massif, Shatsky Rise, to understand the magmatic processes taking place in a region of thickened oceanic crust. We observe correlations between crystal textures and compositional zones in plagioclase that reveal relationships between mechanisms of magmatic differentiation and the crustal depths at which they occurred. When combined with geothermobarometric models, our observations indicate that deep crustal crystal storage took place in high-crystallinity mushes at two discrete levels (∼17 and ∼27 km depth). Diffusive constraints from crystal zoning lengthscales indicate that the lifetime of crystals within the mushes exceeded several thousand years. Magmatic recharge was frequent and produced various dissolution textures in plagioclase. In contrast, shallow crystal storage (∼2·4 km depth) took place in a liquid-dominated domain where crystal residence times were much shorter. Crystal zoning patterns indicate that magmas transporting crystals from the deepest environment to the surface sometimes accumulated additional crystals from mid-crustal storage regions and sometimes did not, highlighting the complexity of magma assembly processes. Temperature contrasts in the lower crust at Shatsky Rise are probably low, owing to extensive magma input and a paucity of hydrothermal cooling at depth. Crystal growth morphologies are consequently relatively simple. Crystallization in thick and thermally mature crusts may therefore lead to less complexity in crystal textures than crystallization in thinner crusts where temperature contrasts are higher. Our observations indicate that combining thermobarometry with studies of crystal textures and crystal compositions is a powerful approach for improving our understanding of magmatic differentiation and magma ascent paths.

中文翻译：

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跨壳岩浆运输，储存和分化的分区晶体记录：来自沙茨基崛起的海洋高原的见解

在次火山岩管道系统的最深部发生的岩浆过程仍然受约束较弱。但是，合并到上升岩浆中的水晶糊状碎片可以提供有关跨壳岩浆运输，储存和分化过程和条件的宝贵见解。在这里，我们使用从Shatsky Rise的Tamu Massif钻出的熔岩样本来了解在增厚的洋壳区域发生的岩浆作用过程。我们观察到斜长石的晶体纹理与组成区域之间的相关性揭示了岩浆分化机制与它们发生的地壳深度之间的关系。当与地热气压模型结合使用时，我们的观察结果表明，深地壳晶体的储藏发生在两个离散水平（深度约17和约27 km）的高结晶度麝香中。来自晶体分区长度尺度的扩散约束表明，在麝香内的晶体寿命超过了数千年。岩浆补给频繁，并在斜长石中产生各种溶解质地。相比之下，浅晶体存储（约2·4 km的深度）发生在一个以液体为主的区域，其晶体停留时间要短得多。晶体分区模式表明，将岩浆从最深处的环境转移到地表的岩浆有时会积聚来自中地壳储藏区域的额外晶体，有时却不会，这突出了岩浆组装过程的复杂性。Shatsky Rise下部地壳的温度差异可能很低，这是由于大量的岩浆输入和缺乏深度的热液冷却所致。因此晶体生长形态相对简单。因此，与在温度差较高的较薄的外壳中结晶相比，在较厚且热成熟的外壳中结晶可能导致晶体结构的复杂性降低。我们的观察结果表明，将热压法与对晶体纹理和晶体组成的研究相结合，是提高我们对岩浆分化和岩浆上升路径的理解的有力方法。