Epidote eclogites embedded in paragneisses from the Austrian Eastern Alps host rare, decimetre- to metre-sized planar pegmatitic segregations (‘pegmatoids’) that consist of a hornblende–plagioclase–epidote–titanite–quartz assemblage. The pegmatoids cut the primary eclogite foliation at a high angle, show abrupt terminations and exhibit numerous microtextures indicating the former presence of melt, whereas the surrounding eclogites and paragneisses lack evidence for dehydration melting. We interpret the pegmatoids as crystallised hydrous melts of intermediate composition derived from a nearby eclogitic source, similar to the eclogite host rock. The host eclogite preserves high-pressure assemblages of garnet–omphacite–epidote–quartz–rutile ± phengite that yield peak P–T estimates of 21 ± 2 kbar and 700 ± 20 ^∘C calculated via pseudosection modelling and Zr-in-rutile thermometry. Subsequent near-isothermal decompression occurred in a closed system under fluid-absent conditions that favoured the preservation of garnet–omphacite assemblages in eclogites. Thermodynamic modelling of the metapelitic country rock indicates that the paragneisses remained fluid-absent during early exhumation, but became fluid-saturated at mid-crustal conditions of 7.5–9 kbar and 680–690 ^∘C. We suggest that, as the metapelites dehydrated, minor aqueous fluid was released and infiltrated the enclosed eclogites along discordant fractures that formed in response to unloading, further facilitated by steep gradients in μ_H2O between the fluid-saturated pelitic country rock and fluid-absent eclogite lenses. Eclogite distal from fluid sources/pathways experienced limited retrogression, whereas localised re-equilibration and H₂O-fluxed melting is inferred for eclogite affected by extensive fluid infiltration. Zr-in-titanite thermometry on crystals from pegmatoids yields a crystallisation temperature of 697 ± 10 ^∘C at 8.5 ± 1.5 kbar, similar to retrograde conditions recorded by the regionally dominant metapelites. Oxygen- and hydrogen isotopic data for eclogite, pegmatoids and paragneiss are consistent with hydrous fluid transfer from paragneisses to eclogites and a small fluid/rock ratio. We suggest that, at conditions that preclude dehydration-melting, even small-scale melting of eclogite requires addition of fluid from a suitable near-field source.

奥地利东部阿尔卑斯山的石棺中埋有的埃迪奥德榴辉岩具有稀有的，十米至米大小的平面角砾岩偏析（“ pegmatoids”），由角闪石-斜长石-斜辉石-钛铁矿-石英组合组成。仿生岩以高角度切开主要榴辉岩的叶面，显示出突然的终止，并显示出许多微纹理，表明以前存在熔体，而周围的榴辉岩和石蜡缺乏脱水融化的证据。我们将类钉岩解释为来自附近辉闪岩岩浆的中间成分的结晶含水熔融物，类似于榴辉岩主岩。主体榴辉岩保留了石榴石-辉石-闪石-石英-金红石型±锂铁矿的高压组合，产生峰值P - T通过伪截面建模和Zr-in-金红石测温法计算得出的估计值为21±2 kbar和700± ^20∘C。随后的近等温减压发生在一个封闭的系统中，在没有流体的条件下，有利于保存榴辉岩中的石榴石-斜辉石组合。在泥质围岩的热力学模型表明，早期副片麻岩折返过程中保持流体缺席，但成为流体饱和的条件中地壳7.5-9千巴和680-690 ^∘ C.我们认为，作为脱水泥质，次要含水流体被释放并渗入沿着形成响应于卸载不和谐骨折封闭榴辉，进一步通过陡梯度促进μ _{ħ 2 ö}在饱和流体的胶粉岩乡村岩石和不存在流体的榴辉岩晶状体之间。远离流体源/途径的榴辉岩经历了有限的倒退，而对于受大量流体渗透影响的榴辉岩，则推断出局部重新平衡和H ₂ O助熔。锆在-榍从pegmatoids晶体测温得到的697±10结晶温度^∘C在8.5±1.5 kbar处，类似于区域优势变质岩记录的逆行条件。榴辉岩，类钉状岩和长石岩的氧和氢同位素数据与从长石岩到榴辉岩的含水流体转移以及较小的流体/岩石比率是一致的。我们建议，在避免脱水熔融的条件下，即使榴辉岩的小规模熔融也需要从合适的近场源中补充流体。