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滇西南团梁子岩组是南澜沧江构造带内重要的构造岩石单元之一,与兰坪-思茅盆地演化有密切联系。由于层序恢复困难和缺乏标志生物化石,该套岩石地层的时代归属缺乏有效约束。江桥团梁子岩组中基性脉岩和构造分异石英脉岩较为发育,在岩石学观察基础上,以绿片岩、辉长(绿)岩及与区域面理(S2)同期的构造分异石英脉岩为研究对象,借助激光剥蚀等离子体质谱(LA-ICP-MS)技术,对其中分选出的锆石开展了精确的U-Pb年龄测定。2件绿片岩样品31个锆石测点中存在4组206Pb/238U年龄,分别为1816~1542 Ma(加权平均为1630±210 Ma,N=6)、850~832 Ma(加权平均为844±95 Ma,N=2)、517~422 Ma(加权平均为438±26 Ma,N=4)和292~188Ma(加权平均为219.7±8.5 Ma,N=19)。2件辉长(绿)岩样品31个锆石测点中也存在4组206Pb/238U年龄,分别为2256~1357 Ma(加权平均为1646±160 Ma,N=16)、861~750 Ma(加权平均为773±92 Ma,N=2)、484~388 Ma(加权平均为433±38 Ma,N=6)和320~233 Ma(加权平均为253±16 Ma,N=7)。1件构造分异石英脉岩样品20个锆石测点中有3组206Pb/238U年龄,分别为1244±19 Ma(N=1)、430±5 Ma(N=1)和312~212 Ma(加权平均为229.6±6.7 Ma,N=18)。不同类型岩石中的各组锆石206Pb/238U加权平均年龄极为接近,代表了不同的地质意义,其中1646~1630 Ma可能代表了团梁子岩组原岩的形成年龄,而253~219 Ma可能代表了团梁子岩组在此时期受到构造热事件影响,该事件可能与古特提斯洋盆由西向东的俯冲消减作用有关。本次获得的绿片岩、基性脉岩及构造分异石英脉岩锆石U-Pb年龄将团梁子岩组时代约束为老于1630 Ma,即中元古代,可能属澜沧岩群的一部分。
The Liangziyan Formation in southwestern Yunnan is one of the important tectonic units in the southern Lancangjiang structural belt and is closely related to the evolution of the Lanping-Simao Basin. Due to the difficulty of sequence recovery and the lack of biological fossils, the age of the set of lithostratigraphic rocks lacks an effective constraint. Basal veins and tectonic-differentiated quartz veins of the Liangziyan Formation in Jiangqiao Formation are well developed. Based on the petrological observations, the green schist, gabbro (green) rock and the tectonic component of the same period (S2) Different quartz vein rocks were studied by laser ablation ICP-MS, and the zircon U-Pb dating of these zircons was determined accurately. There are 4 groups of 206Pb / 238U ages in 18 zircons from 2 greenschist samples, ranging from 1816 to 1542 Ma (weighted average 1630 ± 210 Ma, N = 6) and 850 to 832 Ma (weighted average 844 ± 95 Ma, N = 2), 517-422 Ma (weighted mean 438 ± 26 Ma, N = 4) and 292-188 Ma (weighted average 219.7 ± 8.5 Ma, N = 19). There are also four 206Pb / 238U ages in 22 zircons from 2 gabbros (green rock) samples, ranging from 2256 to 1357 Ma (weighted average 1646 ± 160 Ma and N = 16) and 861 to 750 Ma Weighted average 773 ± 92 Ma, N = 2), 484-388 Ma (weighted mean 433 ± 38 Ma, N = 6) and 320-233 Ma (weighted average 253 ± 16 Ma, N = 7). There are three 206Pb / 238U ages of 20 zircons in one tectonic-differentiated quartz vein sample, which are 1244 ± 19 Ma (N = 1), 430 ± 5 Ma (N = 1) and 312 ~ 212 Ma (Weighted average 229.6 ± 6.7 Ma, N = 18). The 206Pb / 238U weighted average ages of zircons from different types of rocks are very close and represent different geological significance. Among them, 1646 ~ 1630 Ma may represent the formation age of protolith in Tuanliangzi Formation, while 253 ~ 219 Ma may represent The Tuanliangziyan Formation was affected by the tectono-thermal event at this period, which may be related to the subduction and abatement of the paleo-Tethys ocean basin from west to east. The zircon U-Pb ages of the greenschist, basic veins and structurally differentiated quartz veins obtained in this time constrain the age of the Tuanliangziyan Formation to be older than 1630 Ma, that is, Mesoproterozoic and may be part of the Lancang Group .