Volcanism and Curie Isotherm Distribution in the Jalisco Block, Mexico

 A suitable combination of magnetic field determinations is assembled in the whole area of the Jalisco block in central-western Mexico; it serves as the basis for calculations of the Curie Point Isotherm by means of Spectral Analysis. The Jalisco block contains numerous volcanic manifestations; an attempt is made at correlating the Curie Isotherm (CI) with volcanic manifestations and its implicit risk to nearby populated regions. A preliminary analysis of this isotherm is carried out using areas of 60 × 60 km2, where the volcanic regions at the NW and SE portions of the Tepic-Zacoalco (T-Z) rift coincide with shallow layers of the CI. Results show an unexpected region in the middle of the T-Z rift, where the isotherm deepens to 12 km depth and volcanism appears to be missing. The authors argue that this phenomenon may be associated with a flare up episode occurring at 5-3 Ma along the rift. Varying the area used for the calculation of the CI, from 30 × 30 km2 to 120 × 120 km2, illustrates how the concomitant changes in volume affect the depth of penetration. The authors find exceptional regions in which the CI shows shallow depths at all area sizes used in the calculations; this consistency is interpreted as a magnetic alteration of the crust originating at mid-crustal depths. These regions also correspond to high values of the Bouguer anomaly reported elsewhere. Six magneto-stratigraphic profiles are presented for the results of the 60 × 60 km2 calculations, where geologic, topographic, and magnetic properties are displayed along their length.