The exhumation and cooling rates of high-grade metamorphic rocks are crucial for inferring orogenic processes and understanding the regimes of heat transport in Earth's crust. Quantification of these rates remains challenging for Precambrian terranes, because the temporal resolution of geochronology becomes coarser in deeper geologic time. This limitation is partly reflected by a striking lack of Proterozoic or older short-duration events (<10 Myr), most documented cases of fast metamorphism are confined to the Phanerozoic. In this study, we use garnet geospeedometry to explore the metamorphic rates of Paleoproterozoic high-grade rocks from two representative areas within the long-lived (1.95–1.80 Ga) Jiao-Liao-Ji orogenic belt, North China Craton. The pelitic granulites in the Taipingzhuang area record high-pressure granulite-facies (HPG) metamorphism of ∼12 kbar and ∼800 °C, followed by a fast decompression-cooling to ∼5 kbar and ∼600 °C within ∼5 Myr, at ca. 1.87 Ga. The pelitic granulites in the Rizhuang area document a brief (<1 Myr) thermal excursion to ultra-high-temperature (UHT) metamorphism of ∼8 kbar and ∼940 °C at ca. 1.85 Ga, followed by a fast cooling to ∼600 °C within 1–5 Myr. In light of available geological data, the fast decompression-cooling of HPG granulites is interpreted as the syn-collisional exhumation of thickened lower crustal segments at ca. 1.87 Ga, most likely through tectonic extrusion. The thermal excursion transiently reaching UHT conditions is inferred to be triggered by localized syn-metamorphic mafic intrusions in association with magmatic underplating during post-collisional extension at ca. 1.85 Ga. These metamorphic pulses were interspersed within the protracted Paleoproterozoic orogenesis and require geodynamic processes resembling modern plate tectonics. Notably, these ancient rapid events are beyond the temporal resolution of commonly-used in-situ geochronology that tends to yield apparent longer durations given errors and uncertainties. We therefore note that most ancient metamorphic rates might be underestimated using geochronological data, and recommend garnet geospeedometry as a promising alternative approach. The largely similar rates recorded by Paleoproterozoic and Phanerozoic orogens, as well as high-pressure metamorphism at 1.9–1.8 Ga, support the operation of modern plate tectonics in Paleoproterozoic time.

中文翻译：

---

长寿命古元古代造山运动中的局部快速发掘和快速冷却

高品位变质岩的发掘和冷却速率对于推断造山过程和了解地壳中的热传输方式至关重要。对于前寒武纪地层，这些速率的量化仍然具有挑战性，因为地质学的时间分辨率在更深的地质时间内变得越来越粗糙。这种局限性部分由元古代显着缺乏或较早的短时事件（<10 Myr）所反映，大多数文献记载的快速变质病例仅限于生代。在这项研究中，我们使用石榴石测速仪研究了华北克拉通长寿（1.95–1.80 Ga）胶辽-冀造山带中两个代表性区域的古元古代高品位岩石的变质速率。太平庄地区的泥质粒状花岗岩记录了约12 kbar和〜800°C的高压花岗质相（HPG）变质，随后在〜5 Myr处快速减压冷却至〜5 kbar和〜600°C。 ca. 1.87 Ga。日庄地区的黄泥质粒状岩记录了一个短暂的（<1 Myr）热变迁，到大约8 kbar和940°C的超高温（UHT）变质。1.85 Ga，然后在1–5 Myr内快速冷却至〜600°C。根据可用的地质数据，HPG颗粒的快速减压冷却被解释为大约在30℃时加厚下地壳段的同碰撞掘出。1.87 Ga，最有可能是通过构造挤压形成的。推断瞬时达到UHT条件的热偏移是由局部同形变质铁镁质岩侵入与岩浆后镀层在约200毫米处的伸展相关联的。1.85 Ga。这些变质脉冲散布在旷日持久的古元古代造山运动中，需要类似于现代板块构造的地球动力学过程。值得注意的是，这些古老的快速事件超出了常用时间分辨率的范围在存在误差和不确定性的情况下，往往会产生明显更长的持续时间的原位地球年代学。因此，我们注意到，使用年代学数据可能会低估大多数古代的变质率，并建议使用石榴石地球速度法作为一种有前途的替代方法。古元古生代和生元古代造山带记录的速率大体相似，以及在1.9–1.8 Ga的高压变质作用，支持了古元古代的现代板块构造。