锆石U-Pb年龄及Lu-Hf模式年龄对印支地块基底的限定

印支地块的板块构造归属不仅对特提斯演化研究有重要意义, 对探讨新生代青藏高原及周缘板块的陆内变形同样至关重要.我们近期的研究工作表明, 本区的花岗岩主要是印支期旧特提斯闭合的产物, 少数花岗岩与加里东期的构造活动有关.花岗岩内锆石Lu-Hf二阶段模式年龄主要聚集在1.8~1.6 Ga, 此外在1.4~1.2 Ga有另一峰值区.老挝北部花岗岩峰值区与印支地块内其它地区的锆石U-Pb年龄及Lu-Hf二阶段模式年龄峰值相似, 表明印支地块内部有稳定的基底组成.老挝花岗岩年龄峰值与昌都-思茅地块的年龄峰值近于一致, 同时, 由于奠边府构造带不具有缝合带的属性且两个地块有相似的古生代暖水动物群, 我们认为印支地块与昌都-思茅地块可能为同一陆块, 这个联合陆块与华南陆块在Rodinia超大陆时期可能是一体的, 因为他们的峰值区在4.0~3.5 Ga, 2.0~1.8 Ga, 1.4~1.2 Ga的3个峰值区完全重合.

Zircon U-Pb age and Lu-Hf ratios constraint the basement of the Indochina block

Nature of the Indochina blocks is not only important to Tethys study but also important to the Cenozoic deformation style of the Tibetan Plateau. There is little knowledge from the North Laos which locates inner of the Indochina. Our study shows most of the granites in North Laos are related to the closure of the Tethys, a few related to Caledonian orogeny. T_DM^C ages of zircon Lu-Hf in North Laos cluster around 1.8~1.6 Ga, other ages cluster around 1.4~1.2 Ga. The zircon U-Pb and T_DM^C age peaks in North Laos are similar to the ages got in other areas of Indochina block, indicating the same basement in the Indochina block. The age peaks are also similar to that of the Changdu-Simao peaks, indicating the possibility of the same basement of the Indochina-Simao untied block if the Dien Bien Phu belt between the blocks is not ophiolite suites. The united block should be the same basement with the Yangtze block in Rodinia era due to the same age peaks around 4.0~3.5 Ga, 2.0~1.8 Ga, and 1.4~1.2 Ga.