Low‐temperature thermochronology of northern Baja California, Mexico: Decoupled slip‐exhumation gradients and delayed onset of oblique rifting across the Gulf of California

Abstract

The northern Gulf Extensional Province displays key structural relationships that characterize the magnitude, direction, and timing of Neogene rift‐related transtension during the opening of the Gulf of California. Apatite fission track and (U‐Th)/He thermochronology from the Sierra San Felipe document moderate cooling (4°C/Myr–7°C/Myr) during the early Paleogene associated with progressive unroofing caused by erosional downwearing of the ancestral Peninsular Ranges. Beginning at ∼45–35 Ma, a period of tectonic quiescence with low cooling rates (≤1°C/Myr) marks the development of a regional Oligocene‐Miocene peneplain. Rift‐related exhumation began at ∼9–7 Ma and attains ∼2.5 km in the hinges of two antiformal megamullions. Decoupling between exhumation and finite displacement in certain fault segments is explained by vertical deflections associated with extension‐perpendicular folding of the fault surfaces. The main faults of the detachment system were active contemporaneously, thus forming a mechanically linked array of large‐displacement normal faults in the hanging wall of the Main Gulf Escarpment. The Late Miocene onset of transtension in the Sierra San Felipe suggests that widespread deformation may only have localized in the Gulf Extensional Province between ∼9 and 7 Ma, some ∼3–5 Ma after a major plate reorganization associated with cessation of subduction in the trench to the west. Between ∼12 Ma and ∼9–7 Ma, plate boundary shearing was likely distributed between the continental borderland west of Baja California and the southern Basin and Range province in Mexico.

Eocene-Early Miocene paleotopography of the Sierra Nevada-Great Basin-Nevadaplano based on widespread ash-flow tuffs and paleovalleys

“…45 Ma, and exhumation related to rifting in the Gulf of California in the Late Miocene (Seiler et al, 2011). The cooling history and interpreted exhumation is similar to but displaced slightly younger than those for the Sierra Nevada (Cecil et al, 2006;Seiler et al, 2011). The thermochronology suggests that paleodrainages across the Peninsular Ranges were established at least by ca.…”

Timing of rifting in the southern Gulf of California and its conjugate margins: Insights from the plutonic record

“…For the Gulf of California, a late Miocene onset of rifting is supported by structural and thermochronology studies, mostly along the narrow onshore part of the Baja California margin and Tiburón Island in the northern Gulf of California (e.g., Stock and Hodges, 1989;Martín-Barajas et al, 1995;Oskin et al, 2001;Umhoefer et al, 2002;Oskin and Stock, 2003;Seiler et al, 2011;Mark et al, 2014). For the Gulf of California, a late Miocene onset of rifting is supported by structural and thermochronology studies, mostly along the narrow onshore part of the Baja California margin and Tiburón Island in the northern Gulf of California (e.g., Stock and Hodges, 1989;Martín-Barajas et al, 1995;Oskin et al, 2001;Umhoefer et al, 2002;Oskin and Stock, 2003;Seiler et al, 2011;Mark et al, 2014).…”

“…4E-4F). (Seiler et al, 2011). 3.7 Ma linked the northeast end of the Alarcón spreading axis to actual or incipient spreading centers in Farallón Basin before opening of the Pescadero Basin.…”

Transtensional rifting in the proto-Gulf of California near Bahia Kino, Sonora, Mexico

“…Structural mapping and thermo chronology in northeastern Baja California indicate that transtensional faulting initiated ca. 9-8 Ma (Seiler et al, 2010(Seiler et al, , 2011. Gans (1997) documented that the majority of NE-SW extension in the Mexican Basin and Range Province of central and eastern Sonora occurred from 27 Ma to 12 Ma, prior to proto-Gulf of California time.…”