A paleomagnetic study was carried out on a total of 122 oriented cores from Daye Formation of the Huangben section, Guangdong Province. Rock magnetic investigations show that low-titanium magnetite is a dominant carrier. Detailed progressive thermal demagnetization isolated 2―3 components. The low temperature component clusters around the present geomagnetic field direction. An intermediate temperature component is isolated at 100―400℃ and is interpreted as a Yanshanian remagnetization. A high-temperature characteristic remanent mag- netization (ChRM) is obtained at 400―530℃ with D = 51.1°,I = 15.3°,α95 = 5.0° and passes generalized fold test and reversal test, suggesting high tempera- ture component is a primary remanence. Its corre- spondent pole position is 38.5°N, 212.7°E (dp = 2.6, dm = 5.1), which overlaps contemporaneous pole of Yangtze Block at 95% confidence level. Therefore, we believe that Huanan and Yangtze blocks were not separated in the Early Triassic. Compared to other published Early Triassic paleomagnetic data from Huanan Block, the inclinations are very close but the declinations are greatly variable. In stereo-projection, all the Early Triassic poles from Huanan Block lie along a small circle around the Huanan Block, im- plying that local micro-blocks rotations lead to the inconsistence of Early Triassic paleomagnetic direc- tions.
SHEN Zhongyue DING Jinghai YE Changhe WEN Junwei WANG Zhaoliang CHEN Zhifei
Measurements of anisotropy of magnetic susceptibility (AMS) were performed on a gabbro pluton and 7 diabase dykes in the Wanning area, southeast Hainan Island. Rock magnetism showed that pseudo-single domain (PSD) to multidomain (MD) Ti-poor magnetite carries the magnetic fabric in the gabbro pluton whereas MD Ti-poor magnetite carries the magnetic fabric in the diabase dykes. The corrected anisotropy degree (Pj ) in most specimens was found to be less than 1.2 which is indicative of a possible flow-related magnetic fabric. The AMS eigenvectors within each site are generally well grouped. The maximum susceptibility axes (K1 ) of the gabbro pluton are inclined towards the north at low angles (< 30°). K1 axes of the diabase dykes are inclined towards the NNW and SSE with dip angles of ≤ 30°. From this study, it appears that the emplacement mode of the gabbro pluton was characterized by intrusion from the north to the south at a low angle whereas the diabase dykes were emplaced from the NNW to the SSE at low to moderate angles. This was verified by comparison of the rock fabric to the magnetic fabric. All of this evidence leads to the conclusion that the Wanning gabbro pluton and diabase dykes were the products of pulsative intrusion from the same magma chamber in the area far to the north of Wanning, which suggests that basic rocks may exist beneath the Indosin- ian granite in the area to the north of Wanning.
PAN XiaoQingSHEN ZhongYueDONG ChuanWanCHEN HanLinCHENG XiaoGanYANG ShuFengZHANG ZhiLiang
