Uplift of the Sierra San Pedro Mártir Baja California, Mexico

Abstract

The Sierra San Pedro Mártir of Baja California is the highest of the Peninsular Ranges and has undergone rapid Cenozoic uplift. Recent uplift can be explained as a result of flexural isostasy driven by a previously suppressed crustal root. Two‐dimensional modeling of topography and Bouguer gravity data for present and preuplift conditions indicates that a flexural isostatic mechanism for uplift is consistent with the available topographic, geologic, and geophysical data. The crustal root underlying the batholithic rocks of the Sierra San Pedro Mártir was probably emplaced during Cretaceous magmatic arc activity. However, existence of a vast, low‐relief and low‐elevation erosion surface mantled with deposits of fluvial systems originating far to the east suggests that by the early Tertiary the plutons were unroofed, and there was only subtle topographic expression of this crustal thickening. We model the remnant crustal root as regionally compensated (suppressed) beneath a strengthened and continuous elastic plate and topographically expressed as a broad dome. The regional distribution of Tertiary sediments and preserved drainage patterns are geologic evidence of such doming. Since the late Miocene there has been rapid uplift and apparent drainage reversal near the dome apex. The present topography approximates the predicted isostatic response of a doubly broken elastic plate to the previously suppressed root. Several lines of evidence indicate that a major component of uplift of the Sierra San Pedro Mártir has occurred during the Pliocene‐Quaternary and that the crustal scale faulting that has allowed the range to rise rapidly toward local isostasy is related to full development of the San Andreas‐Gulf of California transform system.