Geochronology of ultra-high-pressure metamorphic rocks is able to constrain the timing and rates of subduction-zone processes. Lu–Hf garnet dating has the potential to yield information about the timing of the prograde evolution of subducting rocks under increasing pressure. In combination with other methods, it thus allows constraining the complete P–T–t path with high precision. Ultra-high-pressure eclogites from the Tromsø Nappe, the structurally highest tectonic unit of the Scandinavian Caledonides in northern Norway, were dated using Lu–Hf geochronology on garnet. A sample from Tromsdalstind yielded an age of 448.3 ± 3.6 Ma, interpreted as dating prograde garnet growth due to preserved zoning in the major-element and Lu contents of garnet grains. A sample from the diamond-bearing locality Tønsvika yielded an identical age of 449.4 ± 3.3 Ma. Garnet from this sample shows a weak zoning in Ca content and near-homogeneous Lu content. These ages are identical within error among each other and with published U–Pb ages of peak-eclogite-facies zircon and rutile/titanite from exhumation-related leucosome veins. Consequently, the entire subduction–exhumation cycle leading to the ultra-high-pressure eclogites lasted only very few millions of years during the Late Ordovician.

超高压变质岩的地球年代学能够限制俯冲带过程的时间和速度。Lu-Hf石榴石测年法有可能产生有关俯冲岩石在压力增加时进行前移演化时间的信息。因此，与其他方法结合使用时，它可以高精度地约束完整的Pt-t路径。TromsøNappe是挪威北部斯堪的纳维亚喀里多尼德群岛上构造最高的构造单元，其超高压榴辉岩是用石榴石上的Lu-Hf年代学年代确定的。Tromsdalstind的一个样品的年龄为448.3±3.6 Ma，这被解释为由于石榴石主要元素和Lu含量的保留区划而使石榴石的生长定年。来自钻石产地Tønsvika的样本的年龄相同，为449.4±3.3 Ma。该样品中的石榴石在Ca含量和接近均质的Lu含量方面显示出较弱的分区。这些年龄彼此之间是有误差的，并且与从发掘相关的白血球静脉中出现的峰榴辉岩相锆石和金红石/钛铁矿的U–Pb年龄相同。因此，在奥陶纪晚期，导致超高压榴辉岩的整个俯冲-发掘循环仅持续了几百万年。