| Summary: | 碩士 === 國立臺灣師範大學 === 地球科學系 === 97 === The Cenozoic collision of the Indian and Eurasia plate had controlled the East Asian tectonic movement, and the uplift of the Himalaya Mountains and the Tibet plateau. One of the major shear zones formed due to this plate collision is the Red River shear zone (RRSZ). However, the deformation mechanism is still under heavy debate. This research focus on the Diancang Shan metamorphic belt. Reconstruction of the structural evolution, strain pattern and thermal history of the Diancang Shan Metamorphic Belt via field work, numerous strain analysis with 40Ar/39Ar geochronology was performed in order to gain insite into the structural and strain history of the Diancang Shan metamorphic belt, and their tectonic significance.
Field data analysis revealed the Diancang Shan had experienced 5 deformation events. The first deformation event (D1) forms upright fold with N-S striking (~N10°), steep dipping (63°), axial planes probably during the Triassic Indosinian orogeny. The second deformation event (D2) forms recumbent fold with NW-SE striking (~N19°), shallow to subhorizontal dipping( 20°) axial plane. The third deformation event (D3) forms upright fold with NW-SE striking (~N29°), inclined dipping (55°) axial planes, possibly resulted from the left-lateral strike-slip movement of the RRSZ during the early Miocene (21 ~ ? Ma), As suggeated by the first rapid cooling event according to the decides the dating by this research 40Ar/39Ar dating result . The fourth deformation event (D4) forms upright fold with E-W striking (~N88°), inclined dipping (43°) to ward south axial plane is only observed in the Diancang shan south section, and the strain pattern suggested a right-lateral shear regime; that I correlated the D4 event to the right-lateral shearing of the ASRR. The D4 event possibly formed during 5 Ma as the second cooling event of the 40Ar/39Ar dating result. The uplifting continued under the right-lateral shear regine, which the Diancang Shan metamorphic belt (D5) are mostly normal fault with right-lateral displacement.
Of the Rf/φ, Fry, and center to center strain analysis methods applied in this research. The Rf/φ is the most suitable method or strain analysis for med to high grade metamorphic rocks. As the foliation orientation calculated base on the Rf/φ analysis method better corrects with the actual foliation orientation. The strain pattern calculated
from the N-S and E-W sections suggested that the Diancang Shan recorded a right lateral shear event with thrusting component. further more, the mineral lineation distribute a concentric circle pattern, which suggests the southern portion of Diancang shan metamorphic belt might have decoupled tectonic activity between the upper crust from the lower crust, and the deformation activity is driven by a lower crustal flow.
|
|---|
