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Abstract:
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Con Voi range in Vietnam was a southeastward continuity of the Red River Ailaoshan
tertiary shear zone, a boundary between Indochina and south China blocks during the
southeastward extrusion of Indochina block. It composed of high grade metamorphic and strongly
deformed rocks with various protoliths. The foliation and schistosity folded to produce a large
antiform structure during the late phase of ductile deformation and exhumation. Together with the
Ailaoshan, Diancangshan, Con Voi range suffered from an intensively sheared and metamorphosed
during the collision of Indian with Eurasian plates. The published radiochronological data
indicated that the cooling age took place from 28 to 17 m.y. (millions years). Those data did not
reflect the timing of peak metamorphic event and associated ductile deformation. New Sm/Nd
isochron age on single garnet extracted from biotite-garnet-silimanite bearing gneiss rock within
Con Voi range evidenced that the timing of metamorphic culmination and ductile deformation
occurred as early as c.a 36 m.y. ago. This implied that the earliest stage of deformation along the
Red River-Ailaoshan shear zone could be at least absorbed partially by the opening of Bac Bo basin. |