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出露于扬子克拉通北缘大洪山地区的打鼓石群一直被认为是一套中元古代沉积地层,其上被花山群不整合覆盖。但是由于缺少可靠的年龄依据,打鼓石群与同属扬子克拉通北缘的神农架群以及其他相关地层的对比关系一直存有争议。本文作者利用高精度高分辨率离子探针质谱仪(SHRIMP)测定了打鼓石群中凝灰岩的锆石U-Pb年龄,并利用激光烧蚀多接收器电感耦合等离子体质谱仪(LA-MC-ICPMS)测定了打鼓石群凝灰岩和基本同时代的神农架地区神农架群上亚群凝灰岩的锆石Lu-Hf同位素。这是迄今为止第一次测得了打鼓石群罗汉岭组凝灰岩年龄(1 225±19)Ma和(1 239±23)Ma;锆石Lu-Hf同位素结果显示打鼓石群罗汉岭组凝灰岩与神农架群上亚群野马河组凝灰岩具有相似的Lu-Hf同位素特征:~(176) Hf/~(177) Hf初始值介于0.282 172~0.282 397,ε_(Hf)(t)值为4.9~12.0,T_(DM)~C=1 150~1 943Ma。结合现有区域地质资料,我们认为打鼓石群与神农架群上亚群属于同时期沉积物,形成于超级地幔柱主导的哥伦比亚超大陆裂解背景。
The Kwupuk Group, exposed in the Dahongshan area on the northern margin of the Yangtze craton, has long been considered as a set of Mesoproterozoic sedimentary formations overlaid by the unconformity of Huashan Group. However, due to the lack of a reliable age basis, the contrast between the Taigu Formation and the Shennongjia Group and other related formations in the northern margin of the Yangtze craton has been controversial. The author has used the high-resolution, high-resolution ion-probe mass spectrometer (SHRIMP) to determine the zircon U-Pb ages of tuffs in the tundulid cluster. Laser ablation of multi-receiver inductively coupled plasma mass spectrometry (LA-MC- ICP-MS) were used to determine the zircon Lu-Hf isotopes of the Tuogu Group tuff and the basic contemporaneous Shennongjia Group upper subfacies tuff. This is the first time so far measured the tuffstone age (1 225 ± 19) Ma and (1 239 ± 23) Ma of the Lohanling Formation in the Taiguogroup. The Lu-Hf isotopic results of the zircons show that the tuff rocks of the Luohanling Formation and the Shennongjia The tuffs in the Mauhang Group Mahe Formation have similar Lu-Hf isotope characteristics: initial values of ~ (176) Hf / ~ (177) Hf ranged from 0.282 172 ~ 0.282 397 and ε_ (Hf) (t) values ranged from 4.9 ~ 12.0 , T_ (DM) ~ C = 1 150 ~ 1 943Ma. Combined with the existing regional geological data, we believe that the Taigu Group and the Shennongjia Group belong to the same period of sediments, formed in the supercontinental plume dominated by the super mantle plume.