S1.xlsx

The Song Chay suture zone has been proposed as the boundary of South China Block (SCB) and Indochina Block (IB). However<b>,</b> the Song Chay ophiolitic mélange remains poorly studied. In order to better constrain the structure, and age of the Song Chay ophiolitic mélange, nine samples of terrigenous material, and one Orthogneiss from this mélange and recent unit, were carried out for detrital zircon U-Pb dating, and in-situ Hf isotope investigations. Detrital zircons from the silty matrix of the Song Chay ophiolitic mélange show three major Neoproterozoic age clusters at 580-650 Ma, 700-800 Ma and 900-1000 Ma, which correspond well to the substratum of the SCB. Two minor Late and Early Paleozoic age groups at 270-330 Ma, and 420-500 Ma, with mainly negative εHf(t) values are also recovered. We consider the zircons in the matrix of the mélange mainly derived from the SCB. This hypothesis is supported by the occurrence of lensoid sandstone blocks, representing the substratum of W margin of SCB, included into the matrix of the mélange. The deposition age of the Song Chay ophiolitic mélange is no younger than 254 Ma ± 1 Ma that represents the age of a granitic intrusion in the mélange. Very limited Late Paleozoic detrital zircons were detected, and considered to originate from IB. Our results demonstrate that in an ophiolitic mélange, the detrital material does not always come from the overriding plate, but at the onset of the collision, the continental lower plate may also supply the terrigenous material.