PALEOINTENSITY STUDIES OF A LATE PERMIAN LAVA SUCCESSION FROM GUIZHOUPROVINCE, SOUTH CHINA - IMPLICATIONS FOR POST-KIAMAN DIPOLE FIELD BEHAVIOR

Palaeomagnetic results are presented from a volcanic sequence in Zhiji n County, Guizhou Province, Southern China. The lavas and associated v olcanic breccias comprising the sequence represent a southern extensio n of the Emeishan volcanic province. Biostratigraphic dating of interb edded limestone units and stratigraphic constraints indicate that the section formed during the late Permian (similar to 263-255 Ma), and is thus somewhat older than the Emei stratotype section in Sichuan Provi nce, and close in age to reported estimates of the termination of the Permo-Carboniferous (Kiaman) reverse superchron. Rock magnetic analyse s and reflected light microscopy indicate that the magnetic mineralogy of the lava units is dominated by fresh, primary magnetites containin g a significant fraction of single-domain grains. Thermal demagnetizat ion behaviour of the breccia units is poor, but most lava samples have one or two components of remanence above 250 degrees C. The normal po larity characteristic remanence held by the lavas implies a post-Kiama n age for this succession and suggests that the termination of the Kia man occurred prior to 263 Ma, supporting recently published estimates. According to standard criteria, Thellier palaeointensity results from the lavas are of good quality and reveal that the dipole field streng th was comparatively low shortly after the termination of the superchr on. 80 per cent of samples record relative VDM values in the range 42- 52 per cent of the present-day value, supporting recent studies of mid -Kiaman field intensity. This suggests that a low-energy dipole existe d at least between 300 and 255 Ma and does not appear to have been con fined to the stable reverse polarity interval.