NEW KINEMATIC CONSTRAINTS OF BASIN EVOLUTION IN THE NORTHERN GULF OF 
CALIFORNIA RIFT

Manuel Aragon
CICESE

The Northern Gulf of California (NGC) records the transition from a narrow 
oceanic-type transform domain in the southern gulf, to a diffuse, continental-
type transform domain in southern California.  Interpretation of ~ 3,600 km 
of marine multichannel-seismic reflection and well data from PEMEX indicates 
the diachronous development of two basin systems since late Miocene within 
the NGC. The now-inactive Tiburon and Tepoca basin system (TTB) extends 
~ 70x220 km, and is characterized by sigmoidal- shaped basins controlled by 
large NW-striking, right-stepping faults that cut the basement in an en-echelon 
pattern. Due to the relay geometry of the faults, the axis of the basins are 
oriented N-NE, ~ 45 degrees clockwise to the rift orientation, consistent with 
transtensional strain.  These basins evolved contemporaneously and contain 
~ 6 and 4.5 km of sediments, respectively, transported by the Colorado River 
and western Sonora drainages. The currently active Wagner and Delfin basin 
system (WDB), to the NW, has similar orientation and dimensions as the TTB. 
Here subsidence occurs along coalescing depocenters controlled by a broad 
deformation zone.  Sedimentation reaches > 4 km, with the Colorado River as 
the main source. Recent andesitic to rhyolitic volcanics, and extensive high 
impedance signal, interpreted as shallow magmatism, are restricted to the axis 
of the Delfin basin and the Baja California margin.  

The active WDB and inactive TTB are separated by an anticline accommodation 
zone parallel to both systems.  Seismostratigraphic analysis shows good lateral 
continuity of the lower sequence in the WDB and the uppermost sequence of the 
TTB. This reveals the older age of basins along the Sonora margin, suggesting 
that strain and subsidence migrated to the NW. We conclude that oblique rifting 
in the NGC started with the localization of strain along the TTB and the 
subsequent re-localization of strain to the NW, likely controlled by the thermal
conditions of the crust. The conspicuous localization of igneous activity in the
Delfin basin and the Baja California margin, along with the broad deformation 
zone suggests an ongoing process of crustal thining partially compensated by 
magmatic intrusions and rapid sedimentation.