美国华盛顿大学Eirini Poulaki团队取得一项新突破。他们的最新研究揭示了滑石在俯冲界面的形成，Mg同位素表明Mg损失大于Si增益。相关论文发表在2025年2月13日出版的《地质学》杂志上。

俯冲界面剪切带中富滑石交代岩，对地震活动和弧岩浆活动有着深远的影响，但其成因仍存在争议。美国加利福尼亚卡塔利娜片岩俯冲界面岩镁同位素组成，记录了镁从超镁质到碳酸盐岩的交换。蛇纹岩中同位素轻Mg的优先损失，产生同位素重的富滑石交代岩。这些同位素轻的Mg分别被添加到邻近的变质沉积岩和变质岩中，形成了富含放光石和绿泥石的交代岩，相对于它们的原岩具有收敛的δ26Mg值。

超镁质和变质沉积岩衍生的交代岩中Ca的添加，反映了变质岩衍生流体的渗透作用。富滑石岩是镁向相邻镁汇流失过程中，蛇纹岩中硅被动富集形成的。这些结果和全球已出土古俯冲地体的汇编表明，滑石是俯冲界面的共同组成部分，通常独立于硅交代作用而形成。滑石很可能沿着地幔楔角到亚弧的界面分布，只要超镁质物质与镁汇接触，滑石就会影响现代俯冲带的慢滑事件、俯冲界面流变学和弧岩浆活动。

附：英文原文

Title: Formation of talc in the subduction interface: Mg isotopes demonstrate Mg loss over Si gain

Author: Griffin Easthouse, William Hoover, Fang-Zhen Teng, Cailey Condit, Courteney Pike, Ze-Zhou Wang, Anna Berg, Peter Wynn, Lauren Woods, Eirini Poulaki

Issue&Volume: 2025-02-13

Abstract: Talc-rich metasomatic rocks in subduction interface shear zones profoundly influence seismicity and arc magmatism, but their petrogenesis remains controversial. Magnesium isotope compositions of exhumed subduction interface rocks from the Catalina Schist (California, USA) record Mg exchange from ultramafic to crustal rocks. Preferential loss of isotopically light Mg from serpentinite produces isotopically heavy talc-rich metasomatic rocks. Addition of this isotopically light Mg to adjacent metasedimentary and metamafic rocks from the slab produces actinolite- and chlorite-rich metasomatic rocks, respectively, with convergent δ26Mg values relative to their protoliths. The addition of Ca to ultramafic- and metasedimentary-derived metasomatic rocks reflects a separate contribution from infiltrating metabasalt-derived fluids. Talc-rich rocks are formed by passive enrichment of Si in serpentinite during Mg loss to adjacent Mg sinks. These results and a global compilation of exhumed paleosubduction terranes suggest that talc is a common component of the subduction interface and often forms independent of Si metasomatism. Talc is likely prevalent along the interface from mantle wedge corner to subarc wherever ultramafic material is in contact with a Mg sink and where it could influence slow slip events, subduction interface rheology, and arc magmatism in modern subduction zones.

DOI: 10.1130/G52538.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52538.1/652085/Formation-of-talc-in-the-subduction-interface-Mg