加拿大圣方济各泽维尔大学J. Brendan Murphy团队研究了超含水岩浆、平坦俯冲和冷穿壳大陆弧岩基。2025年3月25日出版的《地质学》杂志发表了这项成果。

来自几个标志性大陆弧花岗岩岩基的压力-温度阵列定义了延伸至>60公里深度的凉爽、含水绝热上升路径，受5~15 wt%H₂O花岗岩液相线曲线的约束。这些路径与许多火山弧岩浆的路径明显不同，后者通常是在正常的陡峭俯冲过程中由地幔减压熔融形成的。新西兰白垩纪峡湾弧保留了一个由含水角闪辉长岩和闪长岩组成的深地壳热区（DCHZ），该热区在持续的岩浆作用中增厚，埋深50-60公里。

已发表的断层成像表明，这种地幔主导的（第1阶段）岩浆活动与从正常板块俯冲到平板俯冲的过渡相吻合，最终终止了峡湾岩浆活动。在其他大陆弧中，恢复正常俯冲模式（板块变陡）会恢复正常厚度（约30-35km）的弧壳。这一过程通过含水熔融破坏了增厚的DCHZ，在地壳主导的（第2阶段）耀斑期间产生了超含水花岗岩弧岩浆。致密的石榴石辉岩最初以残留物的形式形成，但随着地幔楔中剧烈的角流逐渐被移除。

一旦建立了下地壳含水熔融，上升的花岗岩岩浆就会保持凉爽，接近水饱和，因为随着压力的降低，水会逐渐脱气，这解释了许多电弧熔融包裹体中H₂O含量高的原因。这种含水熔融机制建立了凉爽的跨地壳大陆弧岩基，即使在地幔减压熔融过程中被热的含水镁铁质注入偶尔复活，当地幔楔在向正常模式俯冲过渡期间重新打开时，它再次主导地壳热传递（但不是花岗岩岩浆温度）。

附：英文原文

Title: Superhydrous magmas, flat subduction, and cool transcrustal continental arc batholiths

Author: William J. Collins, Nathan R. Daczko, J. Brendan Murphy

Issue&Volume: 2025-03-25

Abstract: Pressure-temperature arrays from several iconic continental arc granitoid batholiths define cool, hydrous adiabatic ascent paths extending to depths >60 km, constrained between the 5 and 15 wt% H2O granite liquidus curves. These paths differ significantly from those of many volcanic arc magmas, which typically form by mantle decompression melting during normal steep subduction. The Cretaceous Fiordland arc, New Zealand, preserves a deep crustal hot zone (DCHZ) of hydrous hornblende gabbros and diorites that was thickened during ongoing magmatism and burial to depths of 5060 km. Published tomographic imaging suggests that this mantle-dominated (stage 1) magmatic flareup coincided with a transition from normal to flat-slab subduction, which ultimately terminated Fiordland magmatism. In other continental arcs, the return to normal subduction mode (slab steepening) restores normal-thickness (～3035 km) arc crust. This process destroys the thickened DCHZ through hydrous fluxed melting, generating superhydrous granitoid arc magmas during a crust-dominated (stage 2) flareup. Dense garnet-pyroxenite initially forms as a residue but is progressively removed by vigorous corner flow in the mantle wedge. Once lower-crustal, hydrous fluxed melting is established, ascending granitoid magmas remain cool and near water saturated because water is incrementally degassed as pressure decreases, which explains the high H2O content in many arc melt inclusions. This hydrous melting mechanism establishes cool, transcrustal continental arc batholiths even when episodically rejuvenated by hot, hydrous mafic infusions during mantle decompression melting, which again dominates crustal heat transfer (but not granitoid magma temperature) as the mantle wedge reopens during the transition back to normal-mode subduction.

DOI: 10.1130/G53145.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G53145.1/653288/Superhydrous-magmas-flat-subduction-and-coolredirectedFrom=fulltext