Ultrahigh-temperature (UHT) granulites, a prominent feature of Paleoproterozoic orogenic belts, preserve a record of geodynamic processes during the Precambrian (Archean–Paleoproterozoic). Quantitative pressure–temperature–time (P–T–t) paths of these UHT granulites can constrain the tectonic processes and metamorphic evolution in such a tectonic regime. Here, UHT mafic granulites with a high-pressure (HP) prograde path are first reported in the Diebusige Complex in the Alxa Block, western part of the Khondalite Belt (KB), North China Craton (NCC). The detailed petrographic studies show that two mafic granulite samples preserve corona textures around relict garnet or garnet pseudomorphs (completely replaced by plagioclase), and a third mafic granulite sample has a relatively simple mineralogy with a granoblastic-polygonal texture. These mafic granulites have similar peak (T_max) assemblages of clinopyroxene + orthopyroxene + plagioclase + ilmenite ± garnet ± amphibole ± quartz + melt. Phase equilibrium modelling and Ti-in-amphibole and rare earth element (REE)-based thermometries all constrain similar peak conditions of ~880–950°C/~8.5–10 kbar implying an ~100°C/kbar apparent geothermal gradient for these mafic granulites. Based on the corona textures or pseudomorphs of garnet and mineral assemblages, we identified a P_max (~14 kbar) prograde stage before the T_max stage. Thus, a clockwise P–T path with heating and decompression followed by near-isobaric cooling (IBC) is recorded from these UHT mafic granulites. In addition, zircon and apatite SHRIMP or LA–ICP–MS U–Pb dating yields an age interval of ~1.81–1.7 Ga, which is interpreted as representing the cooling time from ~900–800°C to ~575°C at the middle-upper crustal levels (<25 km deep) for these mafic granulites, with an ~1.5–2.5°C/Myr cooling rate. The new P–T–t path of these rocks includes high-pressure prograde, UHT peak, and slow cooling retrograde processes, which implicates a post-collisional tectonic setting for UHT metamorphism in the KB and the processes of collision, exhumation, and cooling of the KB.

中文翻译：

---

阿拉善地块高压前进路径的古元古代超高温镁铁质麻粒岩：对华北克拉通孔兹岩带构造演化的启示

超高温（UHT）麻粒岩是古元古代造山带的一个显着特征，保存了前寒武纪（太古代-古元古代）地球动力学过程的记录。这些超高温麻粒岩的定量压力-温度-时间（P - T - t）路径可以约束这种构造体制中的构造过程和变质演化。在此，华北克拉通（NCC）孔兹岩带（KB）西部阿拉善地块的迭布斯格杂岩中首次报道了具有高压（HP）顺进路径的超高温镁铁质麻粒岩。详细的岩相研究表明，两个镁铁质麻粒岩样本保留了残石榴石或石榴石假晶（完全被斜长石取代）周围的日冕纹理，第三个镁铁质麻粒岩样本具有相对简单的矿物学，具有花岗质多边形纹理。这些镁铁质麻粒岩具有相似的峰（T _max）组合：单斜辉石 + 斜方辉石 + 斜长石 + 钛铁矿 ± 石榴石 ± 角闪石 ± 石英 + 熔体。相平衡模型以及角闪石中的钛和基于稀土元素 (REE) 的测温都限制了 ~880–950°C/~8.5–10 kbar 的相似峰值条件，这意味着这些材料的表观地温梯度约为 100°C/kbar镁铁质麻粒岩。根据石榴石和矿物组合的日冕结构或假晶，我们在T _{max阶段之前确定了}P _max (~14 kbar) 顺行阶段。因此，从这些 UHT 镁铁质麻粒岩中记录了一条顺时针P - T路径，包括加热和减压，然后是近等压冷却 (IBC)。此外，锆石和磷灰石 SHRIMP 或 LA-ICP-MS U-Pb 测年得出~1.81-1.7 Ga 的年龄区间，这被解释为代表在这些镁铁质麻粒岩位于中上地壳层（<25 公里深），冷却速率约为 1.5–2.5°C/Myr。这些岩石的新P - T - t路径包括高压顺行、UHT峰值和缓慢冷却逆行过程，这暗示了KB中UHT变质作用的碰撞后构造背景以及碰撞、折返和冷却过程知识库的。