Abstract

An active modern tectonic activities in the Sông Cả - Rào Nậy Area made this area be characterized by a complex structural subdivision. The strong uplift in western part of the Bắc Sông Cả Zone and surrounding areas formed ablock-shaped dome. In contrast, the strike-slip motion, and shearing together with relative subsidence have mainly occurred in southeastern part of Nam Sông Cả Zone, which are characterized by  the NW-SE oriented graben-horst structures. Based on modern tectonic manifestations observed in remote sensing images and tectono-geomorphological maps,  lithology and paleo-tectonics of the Sông Cả - Rào Nậy Area, the first-order structures of the area were divided into 2 blocks, which demonstrate different tectonic activities: The Bắc Sông Cả uplifted, differentiated orogenic Blockand the Nam Sông Cả uplifted, differentiated orogenic Block. The Sông Cả Fault Zone is the boundary between these two blocks. The higher order structures weredivided as follows:

- The Bắc Sông Cả uplifted, differentiated orogenic Zone was subdivided into: the weakly differentiated block associated with the Thanh Hóa Depression, the Phu Hoạt Dome, the Sông Cả River diferentiated Uplift Block, the weakly differentiated Sốp Cộp - Đồng TrầuUplift Block, the Đô Lương graben-shaped Depression.

- The Nam Sông Cả uplifted, differentiated orogenic Zone was subdivided into:: the Hương Sơnuplifted, differentiated Dome, the Con Cuông - Hà Tĩnh step-like Depression, the Hoành Sơn Horst, the Hương Khê - Tuyên Hóa Horst, the Tây Rào Nậy Dome, the Xuân Sơn uplifted block and the Long Đại differentiated Dome.