Abstract

Detailed analysis of two deep – water mass – transport deposit (DWMTD) sections (Quang Trach, Huong Son) and two siliceous microfossil – bearing sections (Minh Hoa, Duc Tho) in Central Vietnam’s Truong Son Fold Belt (TSFB) (Northeastern Indochina Terrane) reveals a NW – trending deep – water continental slope system existed throughout the Upper Devonian–Lower Carboniferous. Radiolarians and tentaculitoids from Ngoc Lam Formation (Minh Hoa section) constrain deposition to the Upper Devonian, while cherts from Thien Nhan Formation (Duc Tho section) yield Tournaisian – early Visean radiolarians. Geochemical and lithological data indicate Minh Hoa cherts formed near the continental rise, while Duc Tho cherts accumulated on the continental slope. Two DWMTDs further confirm a continental margin setting. This system extends into Central Laos; however, it contrasts with the Loei Fold Belt (Western Indochina),  NE Thailand – where an oceanic crust existed during the Late Devonian – Early Carboniferous period, and arc – related subduction volcanism occurred in the Carboniferous. At the TSFB, the absence of true oceanic crust likely prevented Carboniferous–age subduction and magmatic arc activity.