Magnetic fabrics and rock magnetism of the Xaltianguis intrusive, southern Mexico: Implications for the emplacement mode

Abstract

Rock-magnetic and magnetic fabric studies provide constraints on the emplacement mode of the 1-type, magnetitebearing Xaltianguis pluton, southern Mexico. Rock-magnetic measurements include AF coercivity and unblocking temperature spectra, IRM acquisition curves, comparison of NRM and saturation IRM coercivity spectra, Curie point determination, low-field susceptibility variation at low temperatures, room temperature and liquid nitrogen temperature determinations of hysteresis curves and ore microscopy observations. Pure magnetite and iron-rich titanomagnetites with dominantly multidomain state behaviour were found. Two distinct sectors (north and south) feature high and low NRM intensities and susceptibilities, respectively. These variations are also present in other rock-magnetic parameters and may be related to spatial petrographic zonation or to post-emplacement alterations. A single transect across the pluton was sampled, and it is not possible to document any spatial patterns such as concentric zonation. The magnetic fabric is well defined, predominantly oblate, with almost horizontal foliation planes which are consistent through the measured transect, suggesting emplacement of this part of the body as a large sill-type intrusion possibly associated with a WNWESE trending crustal fracture.