Accommodation of opposite vergency between two detachments: Insights from the thermal history of the El Jaralito batholith (Mexico)

Abstract The El Jaralito batholith of Central Sonora is located in the footwall of two large-scale low-angle normal faults with opposite vergences. These faults structurally control the two southernmost metamorphic core complexes of the Basin and Range Province. To investigate the presence of previously proposed fracture zones that might dissect the range and to constrain the timing of rapid cooling and exhumation since the middle Miocene, we present new structural and thermochronological data. We integrate our results along with the previously published data by presenting new QTQt thermal history models for the El Jaralito batholith, enabling a refined interpretation of the timing of the extensional event responsible for its exhumation. Our models indicate that rapid cooling occurred between 25 Ma and 16 Ma along the southwest-dipping Mazatán–Puerta del Sol detachment, which we interpret as the active period of this detachment fault. In contrast, along the northeast-dipping El Amol low-angle normal fault, rapid cooling took place between ca. 25 Ma and 20 Ma and again from ca. 10 Ma to ca. 5 Ma. We attribute this younger cooling phase to renewed slip along high-angle normal faults and increased surface processes such as erosion. We also find no evidence supporting the existence of previously proposed E–W strike-slip transfer zones dissecting the range. Instead, our results reveal increasing metamorphic and exhumation gradients along both major normal faults—from southwest to northeast along the El Amol fault and from northeast to southwest along the Mazatán–Puerta del Sol fault. The lateral overlap of these fault tips defines a high-relief accommodation zone, which we interpret as the result of a scissor-like opening geometry during extension.