Abstract
New paleomagnetic results from the Permian Emeishan basalts in the Zhaotong area, NE Yunnan province, China show four natural remanent magnetization components. Detailed stepwise thermal demagnetization of basaltic samples from 16 flows from the Dadi section, which represent basalt units III and IV, isolated two groups of characteristic remanent magnetizations. Samples in unit IV (five flows) record a southwest declination and a moderate downward inclination that is considered to be a partial remagnetized remanence. The bottom flows from unit III (11 flows) record a normal polarity direction, interpreted as a remagnetization, which yields a tilt-corrected mean direction of Ds/Is= 8.8°/31.6° (N = 9, ks= 39.7,α95= 8.3°), with a corresponding paleomagnetic pole at 77.1°N, 240.0°E (K = 49.2, A95= 7.4°). The secondary directions have steeper inclinations than primary ones that have been successfully recovered from other studies in this area of the Emeishan basalts. By comparison with the Phanerozoic paleomagnetic poles of the South China Block, the preferred timing of remagnetization is the Lower-Middle Jurassic. Field relationships suggest that the remagnetization of the Emeishan basalts is coeval with the spatially related, but localized, copper mineralization. Thus the timing of the main copper mineralization hosted in the Emeishan basalts is hypothesized to occur in the Early-Middle Jurassic.
Highlights
The Emeishan flood basalts form a large igneous province (LIP) that covers an area of around 2.5 × 105 km2 in southwestern China, and is considered to have originated from a mantle plume (Xu et al, 2001; He et al, 2003; He et al, 2007)
The room temperature hysteresis loops of specimens from the flows DD7-22 are closed by ≤ 0.2 T and have low coercivity (Hc) values range from 3.8 to 11.7 mT with a mean of 6.4 ± 2.2 mT (n 27; Figure 2)
We suggest that the hydrothermal fluids migrated through the Emeishan basalts using the large tuff unit separating units III and IV of the basalts and the fault systems as pathways diverting laterally, reducing, but not stopping, the upward flow into unit IV
Summary
The Emeishan flood basalts form a large igneous province (LIP) that covers an area of around 2.5 × 105 km in southwestern China, and is considered to have originated from a mantle plume (Xu et al, 2001; He et al, 2003; He et al, 2007). A series of paleomagnetic studies on the Emeishan basalts have been conducted for more than three decades It was noted in early studies that both north-northeast shallow-up (normal) and southwest down (reverse) directions are primary remanent magnetizations (Huang and Opdyke, 1998; Zheng et al, 2010; Liu et al, 2012). The potential causes of remagnetization, have not been established
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
