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Late Cretaceous to Paleogene contractional deformation in the southern U.S. Cordillera is commonly attributed to the Laramide Orogeny, in part because of the prevalence of moderate- to high-angle, basement-involved reverse faults. However, it is unclear if the tectonic models developed for the archetypal Laramide foreland belt in the U.S. Rocky Mountain region are applicable to the southern U.S. Cordillera. New geologic mapping of the northern Chiricahua Mountains in southeast Arizona, USA, indicates the presence of an originally sub-horizontal thrust fault, the Fort Bowie fault, and a thin-skinned ramp-flat thrust system that is offset by a younger thrust fault, the Apache Pass fault, that carries basement rocks. Cross-cutting relationships and new geochronologic data indicate deformation on both faults occurred between 60 Ma and 35 Ma. A biotite 40Ar/39Ar plateau age of 48 Ma from the hanging wall of the basement-involved Apache Pass fault is interpreted to record erosion related to reverse fault movement and rock uplift. The presence of thrust faults in southeast Arizona raises the possibility of a latest Cretaceous−Eocene retroarc orogenic wedge that linked the Sevier and Mexican thrust belts to the north and south, respectively. Basement-involved deformation does not rule out the presence of a retroarc wedge, and many Cordilleran orogenic systems include basement-involved thrusting. 

Granitic rocks, interpreted to be related to crustal melting, were emplaced into regions of thickened crust in southern Arizona during the Laramide orogeny (80–40 Ma). Laramide-age anatectic rocks are exposed as plutons, sills, and dike networks that are commonly found in the exhumed footwalls of metamorphic core complexes. This study investigates newly discovered exposures of granodioritic–leucogranitic rocks from three intrusive phases in the footwall of the Pinaleño–Jackson Mountain metamorphic core complex of southeastern Arizona, called the Relleno suite. Zircon U–Pb geochronology indicates that the suite was emplaced from 58 to 52 Ma. Zircon Lu/Hf isotope geochemistry, whole-rock Sr and Nd isotope geochemistry, and mineral O isotope geochemistry were used to investigate the source of these rocks and evaluate whether they are related to crustal anatexis. Average zircon εHf(t) values of the suite range from −4.7 to −7.9, whole-rock εNd(i) and 87Sr/86Sr(i) values range from −9.4 to −11.8 and 0.7064 to 0.7094 respectively, and quartz δ18OVSMOW values range from 6.8 to 9.4 ‰. Isotopic and geochemical data of these rocks are consistent with derivation from and assimilation of intermediate–mafic (meta)igneous rocks, at deep crustal levels, and are supported by thermodynamic melt models of Proterozoic igneous rocks equivalent to those exposed in the Pinaleño Mountains. In comparison with other Laramide-age anatectic granites in SE Arizona, those exposed in the Pinaleño Mountains are temporally similar but present compositional and isotopic differences that reflect melting and assimilation of different lithologies, producing distinct mineralogical and isotopic characteristics. The results suggest that crustal melting during this interval was not limited to metasedimentary protoliths and may have affected large portions of the deep crust. The early Paleogene Relleno suite in the Pinaleño Mountains strengthens the relationship between crustal melting and regions of thickened crust associated with the Sevier and Laramide orogenies. 

Abstract The Pinaleño Mountains of southeastern Arizona is the eastern‐most metamorphic core complex in the southern U.S. and northern Mexican Cordillera. This study investigates the thermal history and exhumation record of the Pinaleño core complex using mica⁴⁰Ar/³⁹Ar, apatite and zircon (U‐Th)/He, and apatite fission‐track thermochronometers. The Pinaleño Mountains experienced two periods of rapid cooling during the Cenozoic. The first period, from ca. 27 to 21 Ma, records tectonic exhumation related to the development of the core complex and extensional shear zone. This period was followed by a relatively quiescent interval from 21 to 13.5 Ma that records little to no exhumation. The second period of rapid cooling, from 13.5 to 11 Ma, records tectonic exhumation related to high‐angle normal faulting, characteristic of the Basin and Range province. The exhumation timing of the Pinaleño core complex matches previously recognized spatiotemporal trends in the southern Basin and Range province and indicates that core complex exhumation in this region started in southeastern Arizona (ca. 32–33°N) and migrated both northward and southward. These trends correlate well with the latitude and timing of subduction of the Pacific‐Farallon spreading ridge and the migration of the Mendocino (northward) and Rivera (southward) triple junctions. Spatiotemporal core complex exhumation trends also correlate well with regional magmatism associated with the mid‐Cenozoic flare‐up, including syn‐extensional intrusive rocks found in the footwalls of core complexes.