In orogens worldwide and throughout geologic time, large volumes of deep continental crust have been exhumed in domal structures. Extension‐driven ascent of bodies of deep, hot crust is a very efficient mechanism for rapid heat and mass transfer from deep to shallow crustal levels and is therefore an important mechanism in the evolution of continents. The dominant rock type in exhumed domes is quartzofeldspathic gneiss (typically migmatitic) that does not record its former high‐pressure (HP) conditions in its equilibrium mineral assemblage; rather, it records the conditions of emplacement and cooling in the mid/shallow crust. Mafic rocks included in gneiss may, however, contain a fragmentary record of a HP history, and are evidence that their host rocks were also deeply sourced. An excellent example of exhumed deep crust that retains a partial HP record is in the Montagne Noire dome, French Massif Central, which contains well‐preserved eclogite (garnet+omphacite+rutile+quartz) in migmatite in two locations: one in the dome core and the other at the dome margin. Both eclogites record P ~ 1.5 ± 0.2 GPa at T ~ 700 ± 20°C, but differ from each other in whole‐rock and mineral composition, deformation features (shape and crystallographic preferred orientation, CPO), extent of record of prograde metamorphism in garnet and zircon, and degree of preservation of inherited zircon. Rim ages of zircon in both eclogites overlap with the oldest crystallization ages of host gneiss at c. 310 Ma, interpreted based on zircon rare earth element abundance in eclogite zircon as the age of HP metamorphism. Dome‐margin eclogite zircon retains a widespread record of protolith age (c. 470–450 Ma, the same as host gneiss protolith age), whereas dome‐core eclogite zircon has more scarce preservation of inherited zircon. Possible explanations for differences in the two eclogites relate to differences in the protolith mafic magma composition and history and/or the duration of metamorphic heating and extent of interaction with aqueous fluid, affecting zircon crystallization. Differences in HP deformation fabrics may relate to the position of the eclogite facies rocks relative to zones of transpression and transtension at an early stage of dome development. Regardless of differences, both eclogites experienced HP metamorphism and deformation in the deep crust at c. 310 Ma and were exhumed by lithospheric extension—with their host migmatite—near the end of the Variscan orogeny. The deep crust in this region was rapidly exhumed from ~50 to <10 km, where it equilibrated under low‐P/high‐T conditions, leaving a sparse but compelling record of the deep origin of most of the crust now exposed in the dome.

中文翻译：

---

混合岩中榴辉岩揭示片麻岩穹顶的深地壳来源（Montagne Noire，法国地块中部）

在世界各地的造山带和整个地质时期，大量深部大陆地壳在穹窿结构中被挖掘出来。深部热地壳体的伸展驱动上升是一种非常有效的热量和质量从深部地壳层向浅部地壳传递的机制，因此是大陆演化的重要机制。挖出的圆顶中的主要岩石类型是石英长石片麻岩（通常是混合岩），在其平衡矿物组合中没有记录其以前的高压 (HP) 条件；相反，它记录了中/浅地壳的就位和冷却条件。然而，包含在片麻岩中的镁铁质岩石可能包含 HP 历史的零碎记录，并且证明它们的主岩来源也很深。保留部分 HP 记录的挖掘深层地壳的一个很好的例子是在法国地块中部的 Montagne Noire 圆顶，它在两个位置的混合岩中包含保存完好的榴辉岩（石榴石+绿辉石+金红石+石英）：一个在圆顶核心另一个在圆顶边缘。两种榴辉岩在 T ~ 700 ± 20°C 均记录 P ~ 1.5 ± 0.2 GPa，但在全岩和矿物组成、变形特征（形状和晶体择优取向，CPO）、顺变质作用记录范围等方面各不相同。石榴石和锆石，以及继承锆石的保存程度。两种榴辉岩中锆石的边缘年龄与 c. 的寄主片麻岩最古老的结晶年龄重叠。310 Ma，根据榴辉岩锆石中的锆石稀土元素丰度解释为HP变质作用年龄。圆顶边缘榴辉岩锆石保留了广泛的原岩年龄记录（约 470-450 Ma，与寄主片麻岩原岩时代相同），而圆顶榴辉岩锆石对继承锆石的保存更为稀少。两种榴辉岩差异的可能解释与原岩基性岩浆成分和历史和/或变质加热持续时间和与含水流体相互作用的程度的差异有关，影响锆石结晶。HP 变形结构的差异可能与榴辉岩相岩石在穹窿发育早期相对于受压和受拉带的位置有关。不管差异如何，两种榴辉岩都在 c. 的深地壳中经历了 HP 变质和变形。310 Ma，并在瓦里斯坎造山运动结束时被岩石圈伸展（连同它们的寄主混合岩）挖掘出来。该地区的深部地壳从约 50 公里迅速挖掘到 <10 公里，在低 P/高 T 条件下达到平衡，留下了现在暴露在穹顶中的大部分地壳深部起源的稀疏但引人注目的记录.