“海南陆缘弧”体系的构建与“特提斯南海”的识别:一个关于“古南海”演化新模式的探讨

A new model on the Mesozoic “South China Sea”(SCS):Reconstructing the Hainan marginal arc and recognizing the Tethyan SCS

应用近期在琼南、广东、湘南和越南芽庄、大叻等地的研究成果,综合区域地质资料,从岩浆岩性质、组合与地化特征、沉积序列特征和碎屑岩组分、年代学和地层学等方面进行分析,构建起以海南岛中南部的岩浆-沉积组合为典型标志、以东西向延伸为基本特征、演化过程与浙闽活动陆缘带明显有别的海南陆缘弧体系。该陆缘弧晚中生代处于华南大陆的南端,在构造地理格局上从属于特提斯域。笔者主张向北俯冲于海南陆缘弧下的"古南海"应正名为"特提斯南海",它是特提斯多岛洋北部的边缘海,西段可能与缅、马等地的海域沟通,东段则与太平洋域相接。海南陆缘弧具有广阔的弧后区,各弧后盆地的演化进程可以对比。该弧最初似发育于晚侏罗世,早白垩世晚期和晚白垩世初期岩浆弧与俯冲造山活动达到高峰,晚白垩世发生弧后拉张,但近弧地带挤压条件下的岩浆-沉积作用一直延续至晚白垩世后期(约70 Ma)。海南陆缘弧的活动时间表实际上是特提斯南海消减过程的真实反映。由于消减过程及随后发生的中南半岛在早新生代的挤出逃逸运动和现代南海的扩张作用,特提斯南海的地质记录受到极其严重的破坏,恢复特提斯南海的原貌仍是一项有待开展的艰巨工作。

Showing the results gained newly from the southern Hainan,Guangdong,southern Hunan and Vietnamese Nhatrang-Dalat areas,in this paper we use the regional data and analyze them in magmatic petrology and geochemistry,sedimentary sequence and detrital composition,stratigraphy and geochronology.In the light of the above analyses,we constitute the Hainan arc system,which is based on the magmatosedimentary association outcropping in the central and south parts of the Hainan Island,characterized geographically by its extension in E-W direction,differed tectonically from the Zhejiang-Fujian active margin overlooking the west Pacific.Lying to the south China land,the Hainan Arc was actually at the Tethyan realm.Consequently we suggest that the proto-South China Sea subducting northward to the Hainan Arc should be named the Tethyan South China Sea（TSCS）.It was one of the marginal seas of the Tethys Archipelago,whose west part may connect with the Burmese and Malaysian waters while east part led to the Pacific.There was a large back-arc area occurring north of the Hainan marginal arc and the basins in the area can be tectonically correlated and show a common evolutionary tendency.The arc developed probably since the late Jurassic.Its magmatism and subduction-related orogeny reached an all time high during the transition from the early Cretaceous to the late Cretaceous.A large-scale retroarc extension took place in the late Cretaceous but the compression and arc-related magmato-sedimentary activities did not fade away till the last stage of the Cretaceous（~70 Ma）at the arc ridge or the near arc.The above schedule reflected the fact of the convergence process of the TSCS.The TSCS＇s records were strongly destroyed because of a series of great tectonic events happening from the late Mesozoic to the early Cenozoic such as the TSCS＇s subducion,southeastward escape of the Indo-China Massif and spreading of the South China Sea of today.It is a hard work to reconstruct the original framework of the TSCS.