SUMMARY

Ar-Ar age of mylonite and geodynamic signification of Trà Bồng shear zone, Middle Trung Bộ

Vũ Văn Tích, Nguyễn Văn Vượng,
Phan Trường Thị, Henri Maluski, Claude Lepvrier

The Trà Bồng shear zone is situated in Middle Trung Bộ and extends approximately 100 km from Khâm Đức Town to East Việt Nam Sea in E-W direction. Along this shear zone, all rocks are deformed into microgneiss, mylonite and ultramylonite. Tectonic criteria observed in field show that this zone is affected by left-lateral shear. Two mylonitic samples of granodioritic and dioritic composition from this shear zone were dated by ⁴⁰Ar - ³⁹Ar method on their syn-kinematic biotite. The results indicated an Indosinian age between 223-243 Ma with more than 85% accumulated argon. The lower temperature steps indicated an Yenshan age between 70-100 Ma. The results of the study show that the Trà Bồng shear zone is a complex one and plays a role of an important boundary between Khâm Đức and Ngọc Linh Formations in Indosinian orogeny. The lower temperature steps may be related to magmatic activity in Yenshan orogeny.

Ngày nhận bài : 30-7-2004

Người biên tập : Nguyễn Khắc Vinh