The Eastern Iratsu body of the Sanbagawa metamorphic terrane in central Shikoku recorded an Early Jurassic metamorphic event older than the Sanbagawa metamorphic event. This study carried out the petrochronology of eclogitic high-pressure marble in the Eastern Iratsu body to determine the corresponding conditions of metamorphism and their variation in time. A combination of trace element (Zr) thermometry, host-inclusion mineral elastic barometry, and in-situ UPb dating was performed on the titanite in an eclogitic marble to reveal the metamorphic pressure/temperature conditions of 2.3–2.7 GPa and 1000–1200 °C high-temperature (HT) eclogite facies metamorphic conditions, which occurred at approximately 200 Ma. Moreover, certain titanite grains exhibited a distinctly younger age of 164 Ma with a similar Zr concentration. The 164 Ma domain of titanite is observed near the Na-enriched diopside, indicating the fluid-infiltration and corresponding titanite recrystallization. Some diopside in the matrix contains high-salinity aqueous fluid inclusions (freezing point depression = 3.6–3.7 °C) in the Na-enriched domain, which may infer the source of Na. Furthermore, titanite rims containing trace amounts of Zr yielded 126 Ma, which is comparable with that of early Sanbagawa metamorphism; however, no P-T estimation was available.

This newly identified Early Jurassic metamorphic event is much older than the previously reported metamorphic age of the Sanbagawa metamorphic belt, i.e., c. 120 Ma for early Sanbagawa metamorphism. Although the origin of the HP marble is unclear, the pre-Sanbagawa HT eclogite facies metamorphism reported here could provide a new insight for the subduction of the Izanagi plate and the corresponding geotectonic evolution of eastern Asia.

四国中部三叶川变质地体的东部伊拉津体记录了比三叶川变质事件更古老的早侏罗世变质事件。本研究对东伊拉津体中榴辉岩高压大理岩进行了岩石年代学研究，以确定相应的变质条件及其随时间的变化。微量元素 (Zr) 温度测量、宿主包裹体矿物弹性气压测量和原位 U 的组合对榴辉岩大理中的钛石进行 Pb 测年，揭示了 2.3-2.7 GPa 的变质压力/温度条件和 1000-1200°C 高温 (HT) 榴辉岩相变质条件，发生在大约 200 Ma。此外，某些钛铁矿颗粒显示出明显更年轻的 164 Ma，具有相似的 Zr 浓度。在富钠透辉石附近观察到钛铁矿的 164 Ma 域，表明流体渗透和相应的钛铁矿重结晶。基质中的一些透辉石在富钠域中含有高盐度水性流体包裹体（冰点降低 = 3.6–3.7 °C），这可能推断出 Na 的来源。此外，含有微量Zr的钛铁矿边缘产生了126 Ma，与早期三叶川变质作用相当；然而，

这个新发现的早侏罗纪变质事件比先前报道的三叶川变质带的变质时代更古老，即c。120 Ma 为早期三叶川变质作用。虽然 HP 大理岩的起源尚不清楚，但这里报道的前三波川 HT 榴辉岩相变质作用可以为伊邪那岐板块的俯冲和相应的东亚大地构造演化提供新的见解。