川滇菱形地块白垩纪古地磁学特征

PALEOMAGNETIC FEATURES OF CRETACEOUS SICHUAN_YUNNAN RHOMBOIDAL BLOCK

在位于川滇菱形地块的西昌西南大德里向斜两翼的白垩系红色砂岩内采集古地磁学定向样品９６个（１２个采点），进行了古地磁学研究．研究结果表明，西昌晚白垩世末期的古地磁偏角为５．９°，古地磁倾角为４５．８°，古地磁极位置为北纬８４．７°，东径１９３．３°．将该数据与作者前期研究结果对比，则可见自楚雄至元谋，进而至西昌，其古地磁偏角逐渐靠近正北，而古地磁极纬度渐次升高．这反映了川滇菱形地块内的断块呈自西南至东北逐渐减弱的顺时针旋转特征，而这一古地磁学特征又揭示了川滇菱形地块断裂的右行走滑性质．

Paleomagnetic study was carried out with the 96 samples (from 12 sites) collected from the Cretaceous red sandstone strata on the two wings of the Dadeli syncline, southwest of Xichang, in the Sichuan_Yunnan rhomboidal block. The study manifests that in Xichang in the Late Cretaceous the paleomagnetic declination and inclination were 5.9°, and 45.8° respectively, and that the paleomagnetic pole position was at 84.7°N and 193.3°E. The incorporation of these results into the data previously obtained indicates that from Chuxiong to Yuanmou and farther to Xichang the paleomagnetic declination is closer and closer to the due north and the latitude of the paleomagnetic pole position is higher and higher. This implies that the fractions in the Sichuan_Yunnan rhomboidal block experienced a clock_wise rotation, with the strength of the rotation tapering off from southwest to northeast. This paleomagnetic feature, in turn, reveals that the rifts in this rhomboidal block are characterised by the right_slip.