Origin and evolution of the Bainaimiao arc belt: Implications for crustal growth in the southern Central Asian orogenic belt

摘要

Recent results show that evolution of the huge Central Asian orogenic belt can be explained in terms of southwest Pacific-style accretion of arcs and microcontinents. A better understanding of the origin and evolution of arcs and microcontinents will enhance our knowledge on the evolution of the Central Asian orogenic belt. As one of the most important early Paleozoic arc systems south to the Solonker suture zone, the origin and evolution of the Bainaimiao arc belt are still not well constrained. New zircon U-Pb geochronological and geochemical results on magmatic rocks in the Bainaimiao arc belt indicate that the arc was active from 0.52 Ga to 0.42 Ga and can extend to east Siping in NE China. Zircon U-Pb geochronological results of metasedimentary rocks in the Bainaimiao arc belt indicate that they are early Paleozoic in age, not Precambrian as previously regarded. Detrital zircon analysis of metasedimentary rocks and Sr-Nd-Hf geochemical results of magmatic rocks indicate the existence of some Proterozoic basement rocks beneath the Bainaimiao arc, and it was built upon a Precambrian microcontinent that has a tectonic affinity to the Tarim or Yangtze cratons. The Bainaimiao arc is an ensialic island arc characterized by different evolution history and basement compositions from the northern North China craton. It was separated by a wide ocean from the northern North China craton during the Cambrian-Ordovician period. Successive northward subduction resulted in contraction of the ocean and final accretion of the Bainaimiao arc to the northern North China craton during the Late Silurian-earliest Devonian by arc-continent collision. Arc-continent collision could be an important mechanism for continental crustal growth and formation of the huge Central Asian orogenic belt.