关键词: 敦煌杂岩, 古元古代, 构造变形, 变质温压, 碰撞造山

Abstract: The Dunhuang block is located at the southeastern margin of the Tarim Craton and is an important region where the
Precambrian rocks are exposed. The Dunhuang block includes the northern Altyn Tagh and the Dunhuang regions. The oldest rocks
exposed in both regions are known as the Milan complex and the Dunhuang complex respectively. While, the focus of this study is the
Dunhuang complex. TTG gneisses and metamorphic supracrustal rocks make up the Dunhuang complex mainly, and the dominant
rocks are composed of tonalitic gneiss, trondhjemitic gneiss, granodioritic gneiss, garnet amphibolite, garnet biotite schist and marble.
In this study, LA-ICP-MS U-Pb dating was performed on the zircons of granodioritic gneiss sample from the Gangou area and the
sample of garnet biotite schist was analyzed by electron probe, moreover, the structural deformation of the Dunhuang complex was
studied in order to reveal the geochronology, characteristics of structural deformation and P-T conditions of metamorphism of the
Dunhuang complex. We report that the crystallization age of the granodioritic gneiss sample was 2057±75 Ma. and also Two episodes of
metamorphism were recorded, the older one has the age of ~1.88 Ga representing the Palaeoproterozoic orogeny, whereas the younger
one with the age of ~400 Ma may relate to the Paleozoic orogenic event. The study of structural deformation has shown that the
Dunhuang complex underwent two episodes of deformation, namely the right-lateral ductile shearing (S1) and S-N-trending folding (S2),
and the right-lateral ductile shearing (S1) occurred at the same period of the ~400 Ma metamorphism. In addition, analysis of the garnet
biotite schist sample revealed that the metamorphic peak mineral assemblages of the ~400 Ma metamorphism were mainly composed of
garnet, biotite, plagioclase and quartz, and that the temperature and pressure conditions of metamorphism during the peak are 667~
690 ℃/0.88~0.89 GPa, which represent the high-temperature amphibolite-facies metamorphism.

Key words: words：Dunhuang complex, Paleoproterozoic, structural deformation, P-T conditions of metamorphism, collisional orogenesis