Mesozoic–Paleogene structural evolution of the southern U.S. Cordillera as revealed in the Little and Big Hatchet Mountains, southwest New Mexico, USA
A Mesozoic to Paleogene polyphase tectonic model presented here for the southern United States (U.S.) Cordillera provides new insight into style and timing of Mesozoic–Paleogene deformation and basin formation in the region south of the Colorado Plateau and Mogollon-Datil volcanic field. The model proposes reverse reactivation of Jurassic normal faults during Late Cretaceous Laramide shortening. It also recognizes late Paleogene east-west– and northwest-southeast–trending normal faults formed during a north-south extensional event that postdated Laramide shortening and preceded Neogene Basin and Range extension.
Late Jurassic to Early Cretaceous extension generated northwest-southeast normal faults that formed part of the Border rift system that extended from southern California to the northwestern Gulf of Mexico. The normal faults cut Mesoproterozoic basement rocks, and localized subsequent uplift of basement rocks during Late Cretaceous fault reactivation that formed northwest-southeast–trending Laramide uplifts of southwest New Mexico and southeastern Arizona. The Hidalgo uplift, reconstructed here from structural relations in the Little Hatchet and Big Hatchet Mountains of southwestern New Mexico, is bound by bivergent reverse faults that resulted from tectonic inversion of a Jurassic–Early Cretaceous graben. The Hidalgo uplift is flanked to the north by the Campanian to earliest Maastrichtian Ringbone basin, which accumulated synorogenic continental strata and basaltic andesite flows from ca. 75 to 70 Ma. The Ringbone basin was converted from a subsiding basin in the Little Hatchet Mountains to a volcanic center by ca. 69 Ma, the emplacement age of an assemblage of shallow, subvolcanic intrusions termed the Sylvanite plutonic complex. The basement-involved structural style and yoked intermontane basin resemble other Laramide uplifts and basins in the Rocky Mountain Cordillera and refute alternative Laramide models of strike-slip faulting or regionally extensive horizontal thrust faults in southwestern New Mexico, the latter of which fail to account for basement-cored uplifts. A significant difference with the Rocky Mountain Laramide province is the size of the uplifts and basins and the close association of southern U.S. Cordilleran structures to nearby Late Cretaceous magmatic centers, which contributed to interstratified volcanic and volcaniclastic rocks in the basin fill.
Upper Eocene–Oligocene ignimbrites and volcaniclastic rocks of the Boot Heel volcanic field of southwestern New Mexico unconformably overlie Laramide syntectonic strata and bury eroded Laramide structures. The distribution of the Paleogene volcanic rocks in the Little Hatchet and Big Hatchet Mountains is in part controlled by synmagmatic east-west and northwest-southeast normal faults active from ca. 34 to 27 Ma, the age range of rhyolite dikes intruded along the faults. Two generations of intrusive rocks occupy these normal faults in the Little Hatchet Mountains: (1) older (ca. 34 Ma) phaneritic stocks and dikes in the central and southern parts of the range, and (2) younger (31–27 Ma) aphanitic latite and rhyolite dikes. East-west–trending faults and dikes are cut by north-south faults formed during Basin and Range extension. The late Eocene–early Oligocene north-south extension provides an important minimum age limit for Laramide shortening, which ended prior to ca. 34 Ma.
Figure 12. Structural restoration of the Little and Big Hatchet Mountains with preserved formation thicknesses and line length. Formation labels as in Figures 5 and 10 (v.e.— vertical exaggeration). (A) Present-day structure with dip tadpoles and projected contacts based on field relations. Line of section is identical to Figure 7A and location is shown as A-A’ in Figure 5. (B) Paleogene extension and magmatism restored. Fault offset on the Big Tank and Mojado faults is restored to simplify section. Section illustrates the asymmetry of the bivergent Hidalgo uplift. The Laramide unconformity represents a conceptual erosional base over the main uplift that existed during Laramide short- ening. This line of section does not intersect Laramide synorogenic strata directly north of the Copper Dick fault; however, Laramide synorogenic rocks are only preserved in the northern hanging wall.
Geosphere (2017) DOI: https://doi.org/10.1130/GES01539.1 Published: December 20, 2017