西南“三江”造山带大地构造相

Tectonic facies along the Nujiang-Lancangjiang-Jinshajiang orogenic belt in southwestern China

西南“三江”造山带由多条缝合带及其间多个大小不等的中间陆块构成,其大地构造属性与划分方案历来受地学界关注与争论。本文以大地构造相理论为切入点,将西南“三江”造山带划分出11个一级及其若干二级大地构造相,包括俯冲、消减杂岩、仰冲等一级大地构造相以及与其相伴的后造山及走滑大地构造相。俯冲大地构造相类包括块体变质相、前陆褶冲相、前陆盆地相;消减杂岩大地构造相包括洋壳残片相、陆壳残片相、增生变质杂岩相、活化基底相、侵入岩相、上叠磨拉石相;仰冲板块大地构造相包括弧前盆地相、岛弧相、弧后及弧间盆地相。特提斯洋向北消减,使泛华夏大陆群各块体先拼接,其后弧后扩张、闭合、造山,从而形成了“三江”造山带“多缝合带”、“多陆体”特征。

The Nujiang-Lancangjiang-Jinshajiang orogenic belt in southwestern China displays the mosaic tectonic framework of alternating suture zones and continental masses. The tectonic attributes and division of the orogenic belt have long been much debated. In this study, eleven first-order tectonic facies and several second-order tectonic facies are recognized for this orogenic belt. The first-order tectonic facies include subduction, subduction complex and obduction tectonic faces, and associated post-orogenic and strike-slip tectonic facies. The subduction tectonic facies may be subdivided into mass metamorphic facies, foreland fold-thrust facies, foreland basin facies; the subduction complex tectonic facies into oceanic crust relicts facies, continental crust relicts facies, accretionary metamorphic complex facies, activiated basement facies, intrusive facies and superimposed molasse facies, and obduction tectonic faces into fore-arc basin facies, island-arc facies, back-arc basin facies and inter-arc basin facies. The northward subduction of the Tethyan Ocean led to the collage of the Pan-Cathysian continental masses, and following back-arc spreading, closure and mountain building, thus resulting in the formation of the tectonic features of ＂ multiple suture zones＂ and ＂multiple continental masses＂.