三江北段晚三叠世构造-岩浆作用和几个相关的科学问题

Late Triassic tectono-magmatism of northern Sanjiang and associated several scientific problems

关键词:  松潘-甘孜褶皱带  义敦地体  甘孜-理塘洋  金沙江洋  晚三叠世岩浆作用

Key words:  Songpan-Garze Fold Belt  Yidun Terrane  Garze-Litang Ocean  Jinshajiang Ocean  late Triassic magmatism

摘要:

中国西南三江北段的松潘-甘孜褶皱带和义敦地体以强烈的晚三叠世构造-岩浆活动为特征。松潘-甘孜褶皱带的岩浆活动主要发生在228~190 Ma（峰期时代为约210 Ma），略晚于义敦地体的岩浆活动（236~200 Ma，峰期时代为约216 Ma）。金沙江洋可能经历了西向和东向的双向俯冲，于晚二叠世末—早三叠世初闭合，甘孜-理塘洋可能是金沙江洋东向俯冲背景下形成的弧后盆地，在217 Ma以前已经闭合。松潘-甘孜褶皱带和义敦地体晚三叠世岩浆岩均属于碰撞后岩浆作用的产物，可能分别与岩石圈拆沉和东向俯冲的金沙江洋俯冲板片的断离有关。这些晚三叠世碰撞后岩浆活动记录了地幔物质的贡献，幔源镁铁质岩浆的结晶分异作用在中酸性岩浆岩的形成过程中起到了重要作用，反映了地壳的净生长。三叠纪不同地体之间的碰撞导致了明显造山作用，造成了具有空间差异性的地壳增厚和山脉隆升。

Abstract:

The Songpan-Ganzi fold belt and Yidun Terrane in northern Sanjiang, Southwest China are characterized by intensive Late Triassic tectono-magmatism. The magmatism in Songpan-Ganzi fold belt occurred mainly at 228-190 Ma (peaking at 210 Ma), slightly younger than the magmatism in the Yidun Terrane (236-200 Ma, peaking at 216 Ma). The Jinshajiang Ocean may have experienced divergent subduction to the west and east and closed at the end of Late Permian to the beginning of Early Triassic. The Ganzi-Litang Ocean might be a back-arc basin associated with the eastward subduction of the Jinshajiang Ocean and closed before ca. 217 Ma. The Late Triassic magmatism in the Songpan-Garze fold belt and Yidun Terrane is assigned to post-collisional magmatism and most likely related to lithospheric delamination and the slab break-off of the Jinshajiang Ocean, respectively. Mantle components have contributed to the Late Triassic post-collisional magmatism. Fractional crystallization of mantle-derived mafic magmas played an important role in the formation of Late Triassic intermediate to felsic magmas, suggesting net crustal growth. The Triassic collisional events occurred among terranes resulted in orogenesis, and spatially varied crustal thickening and mountain uplift.