Heterogeneous Neogene cooling and exhumation of the Los Cabos block, southern Baja California: Evidence from fission-track thermochronology

摘要: The Los Cabos block is a massif of Mesozoic crystalline basement at the southern tip Baja California Peninsula and has long been considered distinct tectonostratigraphic terrane separated from rest peninsula by La Paz fault along its western margin. Although region cut an extensive array active north-northwest–striking normal faults, none them correspond to proposed fault. largest in arguably one dominant Neogene structures Gulf extensional province San Jose del Cabo fault, which east-dipping that strike length ∼150 km, topographic escarpment excess 1000 m, forms eastern limit block. Apatite zircon fission-track data demonstrate marked difference tectonism between two margins Samples margin, footwall indicate rapid Paleocene cooling (∼20 °C/m.y.), followed essentially slow monotonic (∼2–3 °C/m.y.) through Tertiary. In contrast, samples record (to ∼45 related tectonic exhumation across commencing mid-Miocene (∼10–12 Ma), when sampled rocks were °C. accommodated ∼5.2–6.5 km rates as high ∼1.5–2 mm/yr, but averaged 0.4–0.7 mm/yr. Continental rifting postdated southward passage Rivera triple junction (ca. 12 implies driving forces likely dominated far-field plate kinematics coupling Pacific, Farallon, North America plates. This continental persisted many inferred reconfigurations motion: northward rotation relative-motion vector (8 eastward migration wrenching Pacific (6 onset sea-floor spreading (3.6 Ma).