TY - JOUR T1 - Middle Miocene to early Pliocene oblique extension in the southern Gulf of California JF - Geosphere Y1 - 2012 A1 - Sutherland, Fiona H. A1 - Kent, Graham M. A1 - Harding, Alistair J. A1 - Umhoefer, Paul J. A1 - Driscoll, Neal W. A1 - Lizarralde, Daniel A1 - Fletcher, John M. A1 - Axen, Gary J. A1 - Holbrook, W. Steven A1 - González-Fernández, Antonio A1 - Lonsdale, Peter AB - A multichannel seismic (MCS) experiment spanning 600 km across the Alarcón Rise and its conjugate rifted margins in the southern Gulf of California (western North America) provides insight into the spatial and temporal evolution of extension between Baja California and the mainland (Mexico). Stratigraphic analysis of multiple rift basins within the Alarcón spreading corridor indicates an initial stage of oblique extension starting ca. 14–12 Ma. This initial phase of extension was characterized by the formation of several large basins in the center of the gulf and on the southeast margin with negligible synrift sedimentation. A second phase of oblique extension, likely synchronous with large-scale basin opening in the central and northern Gulf of California, began ca. 8–5 Ma and was characterized by the formation of smaller half-grabens distributed across the conjugate margins that contain both synrift and postrift deposits. A key feature imaged within the MCS data is a highly reflective, ropey layer at the top of basement, interpreted to be either volcanic rocks from the 25–12 Ma Comondú Group, and/or early rifting volcanic rocks that are between 11 and 9 Ma, or younger. This volcanic layer is extensively faulted, suggesting that it predates the episode of early extension. Upper crustal extension appears to be equally distributed across conjugate margins, forming a symmetrical continental rift. Two styles of rifted basin are observed; older basins (estimated as 14–11 Ma using sedimentation rates) show distributed extension with extensive basement faulting. In contrast, the younger basins (likely post–6 Ma) are asymmetrical with synrift deposits thickening into the basin-bounding faults. The northeast-southwest geomorphic expression of the Tamayo bank and trough and other features provides additional evidence that northwest-southeast oblique extension began ca. 12 Ma. These new spatial and temporal constraints, when combined with a crustal thickness profile obtained across the entire Alarcón corridor, suggest that significant northwest-southeast oblique extension within the Gulf of California started well before 6 Ma, in contrast to earlier models. VL - 8 UR - https://doi.org/10.1130/GES00770.1 ER - TY - JOUR T1 - Variation in styles of rifting in the Gulf of California JF - Nature Y1 - 2007 A1 - Lizarralde, Daniel A1 - Axen, Gary J. A1 - Brown, Hillary E. A1 - Fletcher, John M. A1 - González-Fernández, Antonio A1 - Harding, Alistair J. A1 - Holbrook, W. Steven A1 - Kent, Graham M. A1 - Paramo, Pedro A1 - Sutherland, Fiona A1 - Umhoefer, Paul J. KW - Humanities and Social Sciences KW - multidisciplinary KW - Science AB - Results from the PESCADOR seismic experiment in the Gulf of California provide new insight into rifting — the process that ruptures continents and forms new ocean basins. Unpredicted variations in magmatic activity in continental rifts are commonly attributed to variations in mantle temperature, but such thermal variations tend to occur over large length scales. The new results reveal large differences in rifting style and magmatism over short lateral distances. This suggests that the observed range in magmatism is caused not by variation in temperature, but rather by variability in mantle composition and fertility — the intrinsic capacity of the underlying mantle to produce melt. VL - 448 UR - https://www.nature.com/articles/nature06035 N1 - Number: 7152 Publisher: Nature Publishing Group ER -