Resumo

ALVA VALDIVIA, Luis Manuel et al. Paleomagnetism in the determination of the emplacement temperature of Panalillo Ignimbrite, Juchín, San Luis Potosí, Mexico. Rev. mex. cienc. geol [online]. 2012, vol.29, n.3, pp.619-638. ISSN 2007-2902.

We report paleomagnetic results of thermoremanent magnetization of the lithic clasts and matrix of the Lower Panalillo ignimbrite in the San Luis Potosi Volcanic Field (CVSLP), that provide quantitative estimation of emplacement temperature range of the lithic-rich proximal facies in the Arroyo El Juachín, from which we sampled 78 specimens of lithic fragments (from 40 cm to less than about 10 cm in size) of the matrix which contains them. The results of the saturation isothermal remanent magnetization, the magnetic susceptibility vs. high temperature curves (k-T) and hysteresis loops suggest that the main magnetic carriers are titanomagnetite, titanohematite and hematite. The k-T curves in rare cases show two different thermomagnetic phases during heating, and the cooling curves show irreversibility indicating the presence of titanomagnetite and titanomaghemite. This study shows two emplacement temperatures for this ignimbrite: one of low temperature (280-360 °C and 440 C, samples showing that we have two or more components) and another of high temperature (560 °C - 680 °C, samples which have in general only one component). This wide range of emplacement temperature could be related to the composite thermal history of the lithic clasts incorporated in the pyroclastic flow.

Palavras-chave : paleotemperature; paleomagnetism; Panalillo ignimbrite; San Luis Potosí; Mexico.

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