J. Morales et al., A rock-magnetic and paleointensity study of some Mexican volcanic lava flows during the Latest Pleistocene to the Holocene, EARTH PL SP, 53(9), 2001, pp. 893-902
Eleven Late Quaternary lava flows were sampled in the Chichinautzin volcani
c field of central Mexico to determine their magnetic characteristics and a
bsolute paleointensity. The samples studied cover a geological time interva
l of approximately 0.39 My to 2000 years. Several rock-magnetic experiments
were carried out in order to identify the magnetic carriers and to obtain
information about their paleomagnetic stability. Continuous susceptibility
measurements with temperature in most cases yield reasonably reversible cur
ves with Curie points close to that of almost pure magnetite, which is comp
atible with low-Ti titanomagnetite resulting from oxi-exsolution. Judging f
rom the ratios of hysteresis parameters, it seems that all samples fall wit
hin the pseudo-single domain grain size region, probably indicating a mixtu
re of multidomain and a significant amount of single domain grains. Forty-t
wo samples belonging to six independent cooling units yielded acceptable ab
solute paleointensity estimates. The NRM fractions used for paleointensity
determination range from 0.34 to 0.97 and the quality factors varies betwee
n 4.5 and 97.8, being normally greater than 5. The obtained virtual dipole
moment values are higher than those recently reported for the past 5 My and
to the present day geomagnetic field strength. Individual paleointensity o
f around 2000 BP is substantially higher than the present day intensity, wh
ich is in broad agreement with worldwide archeomagnetic results.