Rift flank uplift at the Gulf of California: No requirement for asthenospheric upwelling

Continental rifts are commonly flanked by zones of high elevation, but the cause of uplift remains controversial. Proposed uplift mechanisms include active and induced asthenospheric upwelling, and isostatically driven lithospheric flexure. Discrimination between these hypotheses requires close constraint of the timing of rift flank uplift and crustal extension. Here, we focus on the well-preserved Neogene Gulf of California rift. The western rift margin is characterized by a prominent east-facing kilometer-scale escarpment, which bounds a west-tilted, topographically asymmetric rift flank. We exploit west-draining canyons incised into the rift flank to constrain the timing of uplift to between ca. 5.6 and 3.2 Ma using 40Ar/39Ar dating of lavas, which show cut-and-fill relationships to the canyons. Rift flank uplift closely followed the onset of slip on the principal fault of the Loreto rift segment at ca. 8–6 Ma, the age of which we obtain from apatite (U-Th)/He and fission-track thermochronologic analysis of rift escarpment exhumation. Uplift was therefore coeval with lithospheric rupture and the onset of oceanic spreading between ca. 6 and 3 Ma, but post-dates a proposed asthenospheric upwelling event by ∼8–10 Ma. The timing of uplift is inconsistent with either active or induced upwelling as uplift mechanisms, and we conclude that rift flank uplift was driven by the flexural response to lithospheric unloading.

[1]  L. Solari,et al.  Late Oligocene to Middle Miocene rifting and synextensional magmatism in the southwestern Sierra Madre Occidental, Mexico: The beginning of the Gulf of California rift , 2013 .

[2]  H. Paulssen,et al.  Geodynamics of the Gulf of California from surface wave tomography , 2012 .

[3]  B. Kohn,et al.  Low‐temperature thermochronology of northern Baja California, Mexico: Decoupled slip‐exhumation gradients and delayed onset of oblique rifting across the Gulf of California , 2011 .

[4]  I. Bindeman,et al.  Plio-Pleistocene climate change and timing of Peninsular Ranges uplift in southern California: Evidence from paleosols and stable isotopes in the Fish Creek-Vallecito basin , 2011 .

[5]  D. May,et al.  Numerical modelling of spontaneous slab breakoff and subsequent topographic response , 2011 .

[6]  D. Hilton,et al.  Petrology and Sr‐Nd‐Pb‐He isotope geochemistry of postspreading lavas on fossil spreading axes off Baja California Sur, Mexico , 2011 .

[7]  M. Benoit,et al.  Volcanic Markers of the Post-Subduction Evolution of Baja California and Sonora, Mexico: Slab Tearing Versus Lithospheric Rupture of the Gulf of California , 2011 .

[8]  R. Negrete-Aranda,et al.  Post-subduction volcanism in the Baja California Peninsula, Mexico: The effects of tectonic reconfiguration in volcanic systems , 2008 .

[9]  G. Gehrels,et al.  Ridge-trench interactions and the Neogene tectonic evolution of the Magdalena shelf and southern Gulf of California: Insights from detrital zircon U-Pb ages from the Magdalena fan and adjacent areas , 2007 .

[10]  G. Kent,et al.  Variation in styles of rifting in the Gulf of California , 2007, Nature.

[11]  K. Whipple,et al.  Uplift of the western margin of the Andean plateau revealed from canyon incision history, southern Peru , 2007 .

[12]  S. Scott,et al.  Arc to rift transitional volcanism in the Santa Rosalía Region, Baja California Sur, Mexico , 2005 .

[13]  Richard A. Ketcham,et al.  Forward and Inverse Modeling of Low-Temperature Thermochronometry Data , 2005 .

[14]  P. A. Ziegler,et al.  Dynamic processes controlling evolution of rifted basins , 2004 .

[15]  Michael Oskin,et al.  Marine incursion synchronous with plate-boundary localization in the Gulf of California , 2003 .

[16]  L. Mayer,et al.  Evolution of the margin of the Gulf of California near Loreto, Baja California Peninsula, Mexico , 2002 .

[17]  P. Renne,et al.  Stratigraphy and geochronology of the Comondú Group near Loreto, Baja California sur, Mexico , 2001 .

[18]  L. Mayer,et al.  Late Miocene to Pliocene stratigraphic evolution of northeast Carmen Island, Gulf of California: implications for oblique-rifting tectonics , 2001 .

[19]  Y. Podladchikov,et al.  Transition from passive to active rifting: Relative importance of asthenospheric doming and passive extension of the lithosphere , 2001 .

[20]  K. Farley,et al.  Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite , 2000 .

[21]  A. Gleadow,et al.  Heterogeneous Neogene cooling and exhumation of the Los Cabos block, southern Baja California: Evidence from fission-track thermochronology , 2000 .

[22]  R. Dorsey,et al.  Tectonic and eustatic controls on sequence stratigraphy of the Pliocene Loreto basin, Baja California Sur, Mexico , 2000 .

[23]  Richard A. Ketcham,et al.  Variability of apatite fission-track annealing kinetics: III. Extrapolation to geological time scales , 1999 .

[24]  Christopher J. Johnson,et al.  FISSION TRACK ANALYSIS AND ITS APPLICATIONS TO GEOLOGICAL PROBLEMS , 1998 .

[25]  T. Parsons,et al.  Tectonic implications of post–30 Ma Pacific and North American relative plate motions , 1995 .

[26]  K. G. Cox.  The role of mantle plumes in the development of continental drainage patterns , 1989, Nature.

[27]  J. Weissel,et al.  Flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension , 1989 .

[28]  J. O’Connor,et al.  Uplift of the Sierra San Pedro Mártir Baja California, Mexico , 1989 .

[29]  C. Beaumont,et al.  A physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins , 1989 .

[30]  W. R. Buck,et al.  Small scale convection induced by passive rifting: the cause for uplift of rift shoulders , 1986 .

[31]  R. Ballog,et al.  Neogene Palynology from the Southern California Continental Borderland, Site 467, Deep Sea Drilling Project Leg 63 , 1981 .