HR: 0800h
AN: V41D-0822    [Abstracts]
TI: Implications for the Indosinian Orogeny and closure of eastern Paleo-Tethys: A perspective from the Song Ma suture
AU: * LIn, T
EM: f90224101@ntu.edu.tw
AF: Dept. Geosciences, Natl. Taiwan Univ., No. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Chung, S
AF: Dept. Geosciences, Natl. Taiwan Univ., No. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Lo, C
AF: Dept. Geosciences, Natl. Taiwan Univ., No. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Lan, C
AF: Inst. Earth Sci., Acad. Sinica, 128 Sec. 2, Academia Rd., Nankang, Taipei, 115, Taiwan
AU: Wang, P
AF: Inst. Oceanography, Natl. Taiwan Univ., No. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Lee, T
AF: Dept. Earth Sci., Natl. Taiwan Normal Univ., 162, He-ping East Road, Section 1, Taipei, 106, Taiwan
AU: Tran, T
AF: Inst. Geol. Sci., NCNST, 38 Ngo Quyen Street, Hanoi, 10000, Viet Nam
AU: Hoang, H
AF: Inst. Geol. Sci., NCNST, 38 Ngo Quyen Street, Hanoi, 10000, Viet Nam
AU: Tran, T
AF: Inst. Geol. Sci., NCNST, 38 Ngo Quyen Street, Hanoi, 10000, Viet Nam
AB: The eastern paleo-Tethys was consumed by amalgamation/collision between the South China, Indochina and Simbumasu blocks, a process also widely considered responsible for the Indosinian Orogeny. Here we report a detailed study of ophiolitic and associated granitic rocks from the Song Ma suture between the South China and Indochina blocks. The ophiolite consists of mafic (now exposed as amphibolites) and ultramafic (as serpentinites) members. The mafic rocks show basaltic compositions, marked with depleted light rare earth elements [(La/Sm)_N= 0.44 to 0.99] and high Nd isotope ratios [εNd (0)= +10 to +6], and without apparent depletion in the high field strength elements (Nb, Ta and Ti), thus representing the Paleo-Tethyan oceanic crust. Besides, the so-called plagiogranites previously reported from the Chieng Khoung complex, now exposed in the Song Ma belt, are actually felsic rocks with adakitic geochemical signatures. These Chieng Khoung rocks, dated at 255 +/- 2 Ma by single zircon U-Pb method, exhibit low Nd [εNd(0)= -1 to -2] and relative high Sr (ISr= 0.7050 to 0.7056) isotope ratios that, together with trace element constraints, imply an origin from partial melting of garnet-amphibolites in a thickened lower continental crust above the mantle wedge related to the Paleo-Tethyan subduction. In addition to the adakitic rocks in the Chieng Khoung complex, this subduction resulted in a late Permian-early Triassic (~274-240 Ma) magmatic arc that extends south of and parallel to the Song Ma suture through central Vietnam. Our study is consistent with the notion that the continental collision between the South China and Indochina blocks along the Song Ma suture took place around 245 Ma, thus reiterating the issue of existence of an early phase of the Indosinian Orogeny.
DE: 1065 Major and trace element geochemistry
DE: 1115 Radioisotope geochronology
DE: 8178 Tectonics and magmatism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting