Paleomagnetic study of the upper Devonian and Lower Carboniferous carbonates near JiangYou, Sichuan,South China Block
|Course||Mineral prospecting and exploration|
|Keywords||Paleomagnetic Upper Devonian Jiangyou Yangtze Block Lower Carboniferous Geographic coordinate system Polar wander Magnetic mineral Primary remanence Fold test|
The northern Sichuan Jiangyou - Beichuan Devonian limestone the paleomagnetism experimental studies have shown that in a step-by-step thermal demagnetization process, most of the specimens remanent magnetization first increases and then decreases; usually when the heating temperature reaches 500 ° C, remanent magnetization decay to the the impatient sound level of the instrument. Most specimens remanence dual-component, low-temperature component (100 to 300 ° C) in the geographic coordinate system is consistent with modern geomagnetic field; component temperature (300 to 480 ° C) in the formation coordinate system has a high negative rake angle The characteristics; Some specimens have the characteristics of the three-component, high-temperature component isolated from the 62 gray-black creature micritic limestone and light gray calcarenite (400 to 520 ° C) at 95% confidence level by the reversal test and 99% fold test should be representative of the the primary remanence rock formation, corresponding paleomagnetic pole position 46.50N, 188.30E (dp = 6.30, dm = 10.10), the Yangtze block located in existing polar wander, the corresponding the ancient latitude 26.10, indicating that the Late Devonian Yangtze block is located in the northern hemisphere mid-latitudes. The area of ??the Carboniferous limestone specimens paleomagnetism experimental research show that the specimen remanence dual-component, low temperature (100 to 300 ° C) component in the geographic coordinate system is consistent with the Earth magnetic field and can not fold inspection, should be re-magnetization of the modern geomagnetic field, temperature (300 to 480 ° C) anti-polar component in the formation coordinate system has the characteristics of high negative rake angle, the same magnetic components with the Late Devonian temperature reverse polarity component system, the may be related to the Early Jurassic strata fold bending. Rock magnetic studies show that the Lower Carboniferous limestone samples: Upper Devonian three-component samples of the main magnetic mineral magnetite, and pseudo-single domain, multi-domain and a small amount of single-domain state exists, the main magnetic mineral It is a mixture of pseudo-single domain and multi-domain magnetite. Separated from the sample temperature component by the pseudo-single domain and multi-domain magnetite carry, Upper Devonian three-component samples by high-temperature component recorded rock primary remanence of single-domain magnetite carry. The principle of measurement and isolated the the core deposition remanence (DRM), the direction of the geomagnetic field based on its level coordinate system in the direction of rock formation, by reference to published block paleomagnetic pole shift curve (APWP ) can be calculated concealed occurrence core of stratum. For those who had not take into account the directional drilling, and now an urgent need to redirect coring, the proposed algorithm is very useful.