HR: 1330h
AN: T12C-0468    [PDF]
TI: Preliminary $^{40}$Ar-$^{39}$Ar thermochronological study of Dien Bien Phu Fault, northern Vietnam
AU: * Lin, T
EM: f90224101@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, 245, Choushan Rd, Taipei, 106 Taiwan
AU: Lo, C
EM: loch@ccms.ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, 245, Choushan Rd, Taipei, 106 Taiwan
AU: Wang, P
EM: p.wang@gl.ciw.edu
AF: Department of Geosciences, National Taiwan University, 245, Choushan Rd, Taipei, 106 Taiwan
AU: Lee, T
EM: t44001@cc.ntnu.edu.tw
AF: Department of Earth Science, Naitonal Taiwan Normal University, 88, Sec.4, Tingjou Rd, Taipei, 116 Taiwan
AU: Chung, S
EM: sunlin@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, 245, Choushan Rd, Taipei, 106 Taiwan
AU: Lan, C
EM: kyanite@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128, Sec.2, Academia Rd, Nankang, Taipei, 115 Taiwan
AB: The Song Ma belt, located along the suture zone between the South China and Indochina blocks, was offset by the Dien Bien Phu Fault (DBF) in northern Vietnam. Many previous studies suggested that the Dien Bien Phu Fault is one of the Tertiary shear zones, resulted from the Cenozoic extrusion tectonics due to the Eurasian-Indian collision. However, the timing of the movement of DBF is remained unclear due to lacking of age data. In the present study, schists and mylonitic granites from DBF, and undeformed granites from the granitic belt along the south China block, were analysed by $^{40}$Ar-$^{39}$Ar method. K-feldspar, hornblende, and biotite samples form granite plutons along south edge of South China block displayed different age ranges between opposite sides of DBF. Samples from plutonic body which is located in west side exhibit plateau ages ranging form 207Ma to 229Ma. Whereas, hornblende separates from granites on the west side exhibit much older plateau dates at around 277Ma. More detail studies were required to get better understand about the discrepancy of dating results between granitic masses located in different sides of DBF. On the other hand, Laser $^{40}$Ar-$^{39}$Ar single-grain analyses conducted on deformed biotites and muscovites separated from the schists in DBF, show $^{40}$Ar-$^{39}$Ar ages ranging form 185Ma to 205Ma, which are much younger than the plateau dates of those undeformed granitic samples. In summary, K-feldspar, hornblende and biotite samples from the undeformed granites, exhibit plateau dates in the range of 207- 277Ma, reflecting the ages of plutonism during the Indosinian orogeny. Whereas, muscovites and biotites extracted from schists and deformed granites in DBF, display young $^{40}$Ar-$^{39}$Ar ages in the range of 205-185 Ma. This may suggest that although the DBF might have been reactivated during the Cenozoic extrusion tectonics, but it was in fact active in the Mesozoic.
DE: 8110 Continental tectonics--general (0905)
DE: 9320 Asia
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: 2003 Fall Meeting