贵州碳酸盐岩红色风化壳次生石英的裂变径迹测年研究

Fission track dating of secondary quartz in red weathering crusts of carbonate rocks in Guizhou Province

贵州位于青藏高原东南缘,由于缺乏沉积记录其新生代的地质演化历史还不很明晰,而广泛分布于云贵高原的碳酸盐岩红色风化壳可能蕴涵着重要的地质演化信息。本文对贵州多个原位碳酸盐岩红色风化壳中产出的晶体形态较好的石英进行了裂变径迹方法测年。结果显示,石英的裂变径迹年龄数据呈现出较大的变化范围,从1Ma到25Ma,且远远地小于其三叠纪和寒武纪的母岩年龄;结合贵州25Ma到1Ma的区域地质演化历史,裂变径迹年龄值可以排除石英来源于母岩碎屑、成岩过程的次生形成以及火山活动产生的热水沉淀或交代形成的可能性,而只能推断为该晶体形态较好的石英于碳酸盐岩风化作用产生的富硅流体中沉淀形成;各剖面石英的年龄值与新生代的青藏高原夷平期、华南红土期、贵州构造稳定期乃至世界范围内的风化-气候期有着良好的对应关系,说明次生石英裂变径迹测年具有很好的可行性和可靠性。

The Cenozoic evolution history of Guizhou Province, which is locat ed on the southeastern flank of the Qinghai-Xizang Plateau, is unclear because of the lack of sedimentation records. The red weathering crusts widespread on the Yunnan-Guizhou Plateau may bear critical information about their evolution hist ory. This work firstly determined the ages of four red weathering crusts in east ern, central and northern Guizhou. The material used in fission track dating is well-crystallized quartz occurring in many in situ weathering crusts of carbona te rocks. The results showed that the fission track ages of quartz vary over a w ide range from 1 Ma to 25 Ma in the four profiles, significantly younger than th e ages of Triassic and Cambrian parent rocks. In combination with the regionally geological evolution history during the period from 25 Ma to 1 Ma, the ages of quartz can exclude the possibility that the origin of quartz has something to do with primary clastic minerals in parent rocks, secondary origin during diagenes is and hydrothermal precipitation or replacement by volcanic activities. It is d educed that the well-crystallized quartz was precipitated from Si-rich weather ing fluids during weathering processes of carbonate rocks. The recorded ages of quartz from the four profiles are consistent with the episodes of planation surf aces on the Qinghai-Xizang Plateau, the stages of red soil in the tropics of So uth China, the tectonically stable periods in Guizhou, and the ages of weatherin g in other parts of the world during the Cenozoic era. That is to say, the ages of secondary quartz dated by the fission track method are well feasible and cred ible.