| Summary: | 碩士 === 國立東華大學 === 自然資源與環境學系 === 106 === Rare serpentinite and meta-igneous rocks are distributed as exotic blocks in the metasedimentary Yuli belt of the Tananao Metamorphic Complex, eastern Taiwan. The discovery of high-pressure (HP) minerals (glaucophane and omphacite) in some of the meta-igneous blocks and preliminary geochronological studies indicate a Late-Miocene subduction metamorphism. These serpentinites and meta-igneous rocks were regarded as fragments of a dismembered ophiolite in previous studies, however, their origin is still controversial. In the Chinshuichi area of Yuli belt, HP minerals such as sodic amphibole, omphacite and aegirine-augite occur in some meta-plagiogranites. In this study recently discovered a new occurrence of veinlets crosscuting meta-plagiogranite. Based on the field relations, the meta-plagiogranite and associated meta-igneous rocks (meta-gabbro, meta-diorite and meta-microdiorite) probably represent a section of oceanic crust. These meta-igneous rocks showing relative Nb-Ta-Ti depletion in whole-rock composition. Zircon 206Pb/238U dates of meta-plagiogranite yield ca. 15 Ma. On the basis of zircon petrographic features and the Th/U ratios, these dates are interpreted as the timing of magmatic crystallization of the meta-plagiogranites. The protolith of these meta-igneous rocks in Chinshuichi area were probably formed in a young fore-arc crust while the South China Sea Plate initially sinked down below the Philippine Sea Plate. Then newly formed fore-arc crust was dismembered as pieces into sediments during subduction, subsequently metamorphosed and exhumed at arc-continent collision.
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