Detrital Zircon U-Pb Age Distribution And Hf Isotopic Constraints From The Terrigenous Sediments Of The Song Chay Suture Zone (Ne Vietnam) And Their Paleogeographic Implications On The Eastern Paleo-Tethys Evolution

The location of the suture zone between the South China Block (SCB) and the Indochina Block (IB) is disputed. Recently, along the Song Chay (Chay river) belt, a melange zone was proposed as a potential suture zone of the SCB and IB. However, the provenance and age of the Song Chay melange is poorly known. In order to better constrain the age and provenance of the elements forming the Song Chay melange, nine samples of detrital material, and one orthogneiss were subjected to zircon U-Pb and Hf isotope analysis. Detrital zircons from the silty matrix of the Song Chay melange record three major Neoproterozoic age clusters at 580-650, 700-800, and 900-1,000 Ma, which correspond well to the substratum of the SCB. Two minor Late and Early Paleozoic age groups at 270-330, and 420-500 Ma, with mainly negative epsilon(Hf)(t) values were also recovered. We consider that the zircons in the matrix of the melange were mainly derived from the subducting plate, namely the SCB. This interpretation is supported by the occurrence of lensoid sandstone blocks, representing the substratum of the SCB, included into the melange. The deposition age of the Song Chay melange is between 310 and 250 Ma. Our results demonstrate that in an ophiolitic melange, the detrital material does not invariably come from the overriding plate, but at the onset of the collision, the subducting continental plate may also supply the terrigenous material.