Paleomagnetic results from the TRiassic of the Yangtze Platform

Abstract

Two widely separated localities have been sampled from Triassic Formations of the Yangtze platforms. The first is from the border area between Sichuan and Guizhou provinces, where the Early Triassic Yelang Formation was sampled at 15 sites, located on both flanks of an anticline. Characteristic high‐temperature components were isolated from nine sites, the remainder were severely overprinted by a recent field. Two polarities are present, one directed toward the northeast with shallow positive inclinations, and the other to the southwest with almost horizontal inclinations. The northeast group passes the fold test at the 95% level. The second area of study was from the city of Nanjing, Jiangsu Province, where 19 sites were drilled from three formations ranging in age from the lower to upper Triassic. The samples are severely overprinted with a component that is almost vertical and whose origin is unclear. However, in 23 of the samples, a high‐temperature component was isolated directed to the northeast and positive and to the southwest and negative. The fold test is indeterminate. The pole positions from the two localities are Sichuan 46.3°N, 219.2°E, α95 = 10.9°; Nanjing 44.8°N, 223.6°E, α95 = 9.3°, which are not significantly different from each other and fall near two other recent studies of Triassic rocks from the Yangtze block. The pole positions given above are significantly different from the Triassic of Eurussia, Siberia, the North China block, and Thailand, indicating that these different components of eastern Asia were not sutured together in their present configuration until after the Triassic.