Amphibolite retrograded from high-pressure (HP) mafic granulite can provide valuable insight into exhumation of deeply buried crust in orogenic belts. In the north Hengshan terrane of the North China Craton, amphibolite occurs as rims of HP mafic granulite block or as smaller homogeneous boudins representing retrograde products of the granulite. Three amphibolite samples were selected. The rocks are mainly composed of hornblende + plagioclase + quartz + biotite + ilmenite with or without garnet pseudomorph consisting of plagioclase + hornblende + ilmenite and symplectite of hornblende + plagioclase ± clinopyroxene. The pseudomorph-, symplectite-bearing sample experienced a post-peak isothermal decompression at >800 °C that was accompanied by breakdown of garnet and clinopyroxene. Isopleths of the maximum An in plagioclase and Ti in hornblende were used to constrain the Tmax stage of ca. 6 kbar/825–850 °C, which was followed by cooling and post-cooling decompression. For the sample showing an “equilibrated” mineral assemblage, a medium-temperature decompression from >6.8 kbar/685 °C to 3.6–4.8 kbar/640–660 °C was inferred. P-T evolution of the north Hengshan terrane is characterized by two discrete (post-peak and post-cooling) decompression processes. Zircon U-Pb dating of amphibolite yields a metamorphic age of 1868 ± 15 Ma, which is interpreted to record the timing of late amphibolization. Synthesized metamorphic P-T-t data in the Hengshan-Wutai area indicate a complicated tectonic evolution that includes an older collisional orogeny at ca. 1.95 Ga and a younger metamorphism at ca. 1.85 Ga. The post-cooling decompression path of the amphibolite may reflect final exhumation of the north Hengshan terrane through the late deformation/metamorphism of the Zhujiafang shear zone.

中文翻译：

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华北克拉通衡山北部角闪岩变质PTt演化: 对晚古元古代从初始碰撞到最终折返的构造过程的洞察

从高压 (HP) 镁铁质麻粒岩回生的角闪岩可以为造山带中深埋地壳的挖掘提供有价值的见解。在华北克拉通的衡山北部，角闪岩以高压镁铁质麻粒岩块体的边缘或较小的均质布丁形式出现，代表麻粒岩的逆行产物。选择了三个角闪石样品。岩石主要由角闪石+斜长石+石英+黑云母+钛铁矿组成，有或无石榴石假晶，由斜长石+角闪石+钛铁矿和角闪石+斜长石±单斜辉石的辛辉石组成。含假晶质、辛辉石的样品在 > 800 °C 时经历了峰后等温减压，伴随着石榴石和单斜辉石的分解。斜长石中最大 An 和角闪石中 Ti 的等值线被用来限制约 1 的 Tmax 阶段。6 kbar/825–850 °C，然后进行冷却和后冷却减压。对于显示“平衡”矿物组合的样品，推断中温减压从 >6.8 kbar/685 °C 到 3.6–4.8 kbar/640–660 °C。北衡山地体的 PT 演化具有两个离散的（峰后和冷却后）减压过程。角闪石的锆石 U-Pb 测年产生 1868 ± 15 Ma 的变质年龄，这被解释为记录晚期角闪石化的时间。横山-五台地区的综合变质 PTt 数据表明复杂的构造演化包括约 约 1.95 Ga 和较年轻的变质作用。1.85 加仑。