Tectonics: Detrital Zircon U-Pb Age Distribution and Hf Isotopic Constraints From the Terrigenous Sediments of the Song Chay Suture Zone (NE Vietnam)

发布时间:2021-09-15 放大 缩小

Abstract: 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 mélange zone was proposed as  a potential suture zone of the SCB and IB. However, the provenance and age of the Song Chay mélange  is poorly known. In order to better constrain the age and provenance of the elements forming the Song  Chay mélange, 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 mélange 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 εHf(t) values were also recovered. We consider that the zircons in the matrix of the  mélange 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 mélange. The deposition age of the Song Chay mélange is between 310 and 250 Ma. Our results  demonstrate that in an ophiolitic mélange, 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.