Crustal structure of the Colima rift, western Mexico: gravity models revisited

Abstract

Two 250 km and 280 km long gravity transects, across the southern (SCR) and central (CCR) sectors of the Colima rift are reinterpreted. Spectral analysis is used to estimate statistical depths to major interfaces. Gravity anomalies are reinterpreted as- suming: (1) that the gravity signal arises solely from deep sources at the crust-mantle boundary, and (2) that the signal arises from a combination of deep and shallow sources. We use vertical prisms or a polygon to model the Moho interface. The spectral depths and the Moho topography are combined with available seismic data to construct layered crustal models with Talwani-type polygo- nal source bodies. The crustal structure along the coast consists of an 80-90 km wide and 7-9 km deep graben, which constitutes the offshore continuation of a 100 km wide graben, extending from just NW of Manzanillo to SE of Tecoman. The Moho shoals under the graben to about 17-18 km depth. Previous interpretations proposed an offshore profile of two grabens. The shallow crustal structure inland features a 9-10 km deep asymmetric depression with a steep NW boundary. Granitic intrusions thicken towards the SE. The crust is 28-30 km thick along the CCR transect, and thins to 22 km beneath the western sector of the Colima graben.