Based on the large-scale Late Triassic angular unconformity in northern Vietnam,French geologists proposed the Indosinian Movement in the early 20th century.The Song Chay tectonic belt in northern Vietnam,where the Indosinian orogeny was named,records a lot of information about the classical Indosinian orogenic belt and is the key area to understanding its tectonic evolution.According to our ten-year work on the Song Chay area and previous research results,this paper systematically reviews the geometry,kinematics,timing and evolution of the Song Chay tectonic belt.Detailed field work shows that the Song Chay tectonic belt can be divided into the Cenozoic Day Noi Con Voi unit,the Song Chay ophiolitic mélange unit and the NE Vietnam fold and thrust unit from SW to NE.In the ophiolitic mélange unit and the fold and thrust unit,NE-SW mineral and stretching lineations with top-to-the-NE kinematics indicate a SW-ward subduction and the corresponding NE-ward thrust of the Song Chay Ocean crust.Precise geochronological work shows that the crystallization age of the plagiogranite in the ophiolitic mélange unit is 356.4±2.9Ma,indicating that the Song Chay Ocean opened before the Early Carboniferous.The low-temperature geochronological data in the fold and thrust unit constrain the top-to-the-NE shearing between 250Ma and 245Ma,indicating the collision timing of 250～245Ma.In addition,the detrital zircons of the Song Chay ophiolitic mélange matrix were sourced from the downgoing South China block,and only a few ones were derived from the overriding Indochina block,so the Song Chay Ocean may be a very limited ocean basin.Structural analysis and detrital zircon dating suggest that the geometry and kinematics on both sides of the"Dian-Qion suture zone"are the same.Therefore,the"Dian-Qion suture zone"is hardly interpreted as a suture zone.Based on our and previous works in structural geology,petrology and geochronology,we proposed a tectonic evolution model of the Song Chay Ocean from Late Carboniferous to Middle Triassic:(1)310～270Ma,the Song Chay Ocean SW-ward subducted beneath the Indochina block,the magmatic arc was not developed at this time,and the ophiolitic mélange matrix was mainly sourced from the South China block;(2)270～250Ma,the Song Chay Ocean subduction continued,during which the magmatic arc developed well,and ophiolitic mélange received materials from both arc and South China block at the same time;(3)250～245Ma,the Song Chay Ocean closed and the South China block collided with the Indochina block;(4)245～230Ma,the Indochina orogenic belt entered the post-collision extension stage.
Indosinian MovementSong Chay tectonic beltStructural analysisDetrital zirconDian-Qiong suture zone
万方数据
维普
