SUMMARY

Cenozoic deformation and thermodynamic evolution of Phan Si Pan zone

Phan Trọng Trịnh, Hoàng Quang Vinh,
 Herve Leloup, Paul Tapponnier

We present here the Tertiary deformation and thermodynamic evolution of the Phan Si Pan zone located SW of Dãy Núi Con Voi Shear Zone. Steep NW-SE foliation and nearly horizontal stretching lineation are observed in both sides of the Po Sen granite batholith. The Yê Yên Sun granite batholith locally shows a crude NW-SE trending foliation. This foliation can be seen in the landscape along the left-lateral fault that displaces the granite by 20 km. Field observation has been suggesting the syntectonic emplacement of Yê Yên Sun granite. At Bát Xát, from K-feldspar modelling, the best cooling model shows two rapid cooling phases of 41 and 25 Ma ages separated by an isothermal period at 285⁰C. In the SW margin of the Po Sen granite batholith, K-feldspar shows an age spectrum of 22±0.4 Ma and 26.7±0.5 Ma. Biotite giving an inverse isochron of 34.2 ±0.7 Ma suggests the temperatures of  300 ⁰C at 34 Ma. After this date the sample suffered two rapid cooling periods of 27 and 22 Ma in Yê Yên Sun granite. A major cooling event affected the entire Phan Si Pan range at 35 Ma. Rapid cooling resumed at 28 Ma in Yê Yên Sun granite, 27 Ma in the  SW margin of Po Sen granite and 25 Ma at Bát Xát. These cooling ages increase from NE to SW along the section perpendicular to the Red River shear zone.

Ngày nhận bài: 30-7-2004

Người biên tập: Trần Văn Trị