K-Ar ages of four mafic lavas from the Central Jalisco Volcanic Lineament: Supporting evidence for a NW migration of volcanism within the Jalisco block, western Mexico

Abstract

Four of 14 Plio-Quaternary mafic rock samples collected along the Central Jalisco Volcanic Lineament (CJVL) were dated by the K-Ar method to verify the existence of a systematic decrease in the age of volcanism northwestward along the lineament, as suggested by previous geological and geophysical observations. The results are in agreement with the proposed age progression. Specifically, these results support the contention that the volcanism along the southeastern most segment of the CJVL (located between the Ayutla and Atenguillo volcanic fields) occurred at about 3.0 Ma, volcanism along the segment to the NW (between the Atenguillo and Mascota grabens) at 1.8 to 1.9 Ma, and from 0.5 to 0.06 Ma within the Mascota graben. The lack of observed volcanism along the northwestern most segment of the lineament (between the Mascota graben and San Sebastián) is also consistent with the proposed age progression. A geochemical analysis was performed on all 14 samples and a rare earth element analysis was performed on the four dated samples. These analyses, in conjunction with the results of previous studies, indicate that the volcanism along the CJVL exhibits a varied composition similar to that exhibited by the Plio-Quaternary volcanic rocks located within the main volcanic fields. Additionally, the outcrop from which the Mascota sample (dated as 0.166 ± 0.038 Ma) was obtained is cut by a northwest oriented strike-slip fault (tentatively identified from striation roughness to be right-lateral) indicating that recent strike-slip deformation has occurred in the Mascota graben.