科研之友
微信
新浪微博
Facebook
分享链接
摘要
Timing of fluid activity during diagenetic process keeps to be a difficult problem, notably in carbonate successions. The Lower Qiulitag Group dolomites of the Upper Cambrian in the Tarim Basin experienced extensive hydrothermal alteration through fracturing, crystallization and saddle dolomite precipitation; however, the timing of hydrothermal alteration was poorly constrained. To solve this problem, the extensive remagnetization data are used to constrain the timing of hydrothermal alteration on the Upper Qiulitag Group dolomites. We drilled 43 oriented plugs from saddle dolomite veins of the Lower Qiulitag Group in Keping and Yong'anba in the western flank of Tarim Basin, from which 64 samples were prepared for paleomagnetic analysis and 29 samples for rock maganetic studies. The magnetism of most samples cannot be washed out at a temperature over 580℃, and only some samples can yield saturation isothermal remanent magnetism in a high magnetic field, which resides in the high-coervicity, high-unblocking temperature magnetic carrier minerals, i.e., hematite. However, the other samples can rapidly reach saturation isothermal remanent magnetism in a low magnetic field, which is likely yielded by the low-coervicity, high-temperature magnetic carrier such as magnetite. Although many samples yield discrete demagnetization data, minor samples do yield bimodal fractions on the demagnetization curve. The paleomagnetic polar positions calculated from the characteristic high-temperature, remanent magnetism fractions from the two sampling sites (Keping and Yong'anba) agree well with those of the Early Permian and Late Permian in the study area, respectively. Considering that the measured samples are mainly obtained from hydrothermal dolomite veins, the high-temperature characteristic remanent magnetism fractions apparently resulted from chemical remagnetization induced by hydrothermal activity, which was temporally linked to the intense Permian large igneous province (LIP) activity in the Tarim block initiated in the Early Permian.
- 单位
