三江中段两古陆铅同位素地球化学边界的厘定

Determination of Pb isotopic geochemical boundary between Yangtze and Gondwana continental blocks in the middle part of Sanjiang region, southwestern China

根据三江中段及周边邻区火成岩铅同位素数据 ,确认了三江中段扬子陆块与冈瓦纳古陆的边界。两古陆的铅同位素地球化学边界为2 0 6Pb/2 0 4Pb =18.5 83、2 0 8Pb/2 0 4Pb =38.5 75和V1=6 0、V2 =5 2 ,低于界线值的属扬子陆块 ,高于界线值的属冈瓦纳古陆。三江中段两古陆的铅同位素地球化学边界在地理上对应于德钦鲁春 -红坡牛场一线 ,以东属扬子陆块 ,以西为冈瓦纳古陆 ;在构造上对应于德钦 -字呷断裂带 ;在构造 -岩浆带上对应于金沙江构造岩浆带与澜沧江构造岩浆带的分界线 ;在成矿上则对应于德钦羊拉 -鲁春 -红坡牛场铜多金属成矿带。

Based on Pb isotopic data of volcanic rocks from the middle part of Sanjiang ( Nujiang, Lancangjiang and Jinshajiang) and adjacent areas, the authors have determined the Pb isotopic geochemical boundary between Yangtze and Gondwana continental blocks in the middle part of Sanjiang region, southwestern China. The geochemical boundary has the values of 206 Pb/ 204 Pb = 18.583, 208 Pb/ 204 Pb = 38.575 and V 1 = 60, V 2 = 52. Compared with standard geochemical boundary values, Yangtze and Gangwana blocks have lower and higher values, respectively. The Pb isotopic geochemical boundary separates Yangtze block in the east from Gangwana block in the west, it corresponds to Luchun-Hongponiuchang belt geographically, to Deqin-Ziga fault tectonically, to the boundary between Jinshajiang and Lancangjiang in terms of tectonic-magmatic belt, and to the Yangla-Luchun-Hongponiuchang polymetallic ore_forming belt metallogenetically.