On the significance of magnetic anomalies from the Baja California Peninsula: its relationship with IOCG deposits and the deep crustal magnetic layer

Abstract

A regional-residual separation process has been applied to aeromagnetic data observed over southern California and the Baja California Peninsula. The 3D analytic signal amplitude computed from the residual magnetic anomalies is intense and delineates a strip ~60 km wide and ~1200 km long characterized by short-wavelength and high amplitude anomalies, that extends from southern California southward nearly to the tip of the Baja California Peninsula. Known iron-oxide-copper-gold (IOCG) ore deposits are for the most part located in the northern portion of the strip, and its eastern boundary closely follows the magnetite-ilmenite boundary. The amplitude and continuity of regional magnetic anomalies, which suggests an almost continuous belt of magnetized rocks, supports a hypothesis suggesting that the western margin of the Baja California Peninsula evolved as an island arc that was accreted to the western margin of North America in Cretaceous time. Inverse modeling of the long-wavelength regional magnetic anomalies indicates that two nearly continuous belts of magnetized rocks, of mafic to intermediate composition, extend from southern California to the La Paz fault. The boundary between these two belts is located near the Bahía de Sebastián Vizcaíno, in a region where magnetization abruptly decreases.