| Abstract: |
The Song Ma-Song Da region of northern Vietnam contains the Song Ma Anticlinorium, a polydeformed, polymetamorphosed, early Palaeozoic island arc/forearc terrane accreted to the South China plate in Siluro-Devonian times. The Song Ma Anticlinorium is not an Indosinian subduction zone and nor is its southern boundary, the Song Ma Fault. The Song Ma Fault is merely one of many northwest-trending, post-Cretaceous, high-angle reverse oblique-split faults and thrusts responsible for Cenozoic shortening and strike-slip transposition of northern Vietnam. Folds penecontemporaneous with this faulting include the Song Ma Anticlinorium, which is formed probably of thrust-ramp folds. Faulting and Penecontemporaneous regional folding occurred during Oligocene sinistral strike-slip on the Song Hong Fault and was reactivated during Pliocene-Quarternary times. The present plate boundary is a broad deformation zone between Da Nang and the Song Hong and parts of the South China plate extend into and beyond the Song Ma Anticlinorium.
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