17:15 〜 19:15
[SMP28-P05] Synthesis on the Metamorphism along Chingshui River:
Deciphering the Geologic History of Yuli Belt, Eastern Taiwan
キーワード：Yuli Belt, Chingshui River, geochronology, metamorphic temperature, mineralogy, structural geology
The Yuli Belt in eastern Taiwan comprises autochthonous and allochthonous high-pressure, low-temperature metamorphic blocks, representing the deeper zones of an accretionary prism formed by the arc-continent collision between the Eurasian Plate and the Philippine Sea Plate. This study integrates metamorphic temperature estimates, U-Pb age dating, and structural data to provide a comprehensive understanding of the Yuli Belt’s tectonic evolution.
Metamorphic temperatures were estimated using carbonaceous materials and garnet compositional isopleths in meta-sedimentary rocks, as well as calcic amphibole and plagioclase in meta-igneous rocks. Detailed petrographic, mineralogical, and geochronological analyses, including U-Pb age dating and Th/U ratio measurements of zircons, were employed to constrain pressure-temperature conditions. Zircons from meta-igneous rocks reveal a two-stage thermal history, with magmatic zones dated to ~17–19 Ma and metamorphic overgrowths at ~6–9 Ma, reflecting low-temperature, high-pressure conditions during the arc-continent collision.
Metamorphic temperatures along the Chingshui River increase from east to west, outlining a west-verging antiform. Meta-igneous and adjacent meta-sedimentary rocks exhibit temperatures of ~488–517°C and ~500–520°C, respectively, and display isoclinal folding. Phengite, formed during the prograde subduction phase, is marked by S1 foliation, while muscovite, which developed during retrograde exhumation, is associated with S2 foliation. Garnet internal foliations reflect distinct deformation stages, and calcic amphibole compositions in metaplagiogranites suggest that pressures did not exceed ~10 kbar.
These findings indicate that the metamorphic conditions were lower than previous estimates of ~13–17 kbar/550°C, suggesting that metamorphism occurred at shallower depths than previously thought. This study refines our understanding of the Yuli Metamorphic Belt and highlights variations in metamorphic conditions.
Metamorphic temperatures were estimated using carbonaceous materials and garnet compositional isopleths in meta-sedimentary rocks, as well as calcic amphibole and plagioclase in meta-igneous rocks. Detailed petrographic, mineralogical, and geochronological analyses, including U-Pb age dating and Th/U ratio measurements of zircons, were employed to constrain pressure-temperature conditions. Zircons from meta-igneous rocks reveal a two-stage thermal history, with magmatic zones dated to ~17–19 Ma and metamorphic overgrowths at ~6–9 Ma, reflecting low-temperature, high-pressure conditions during the arc-continent collision.
Metamorphic temperatures along the Chingshui River increase from east to west, outlining a west-verging antiform. Meta-igneous and adjacent meta-sedimentary rocks exhibit temperatures of ~488–517°C and ~500–520°C, respectively, and display isoclinal folding. Phengite, formed during the prograde subduction phase, is marked by S1 foliation, while muscovite, which developed during retrograde exhumation, is associated with S2 foliation. Garnet internal foliations reflect distinct deformation stages, and calcic amphibole compositions in metaplagiogranites suggest that pressures did not exceed ~10 kbar.
These findings indicate that the metamorphic conditions were lower than previous estimates of ~13–17 kbar/550°C, suggesting that metamorphism occurred at shallower depths than previously thought. This study refines our understanding of the Yuli Metamorphic Belt and highlights variations in metamorphic conditions.