1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
2. Department of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
3. Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA
4. Department of Geology, Centro de Invest. Científica y de Educación Superior de Ensenada, Ensenada C.P. 22860, Mexico
5. Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, California 92037, USA
6. Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011, USA
7. BP Exploration Operating Company Ltd, Sunbury-on-Thames TW16 7LN, UK

Correspondence to: Daniel Lizarralde¹ Correspondence and requests for materials should be addressed to D.L. (Email: danl@whoi.edu).

Abstract

Constraints on the structure of rifted continental margins and the magmatism resulting from such rifting can help refine our understanding of the strength of the lithosphere, the state of the underlying mantle and the transition from rifting to seafloor spreading. An important structural classification of rifts is by width¹, with narrow rifts thought to form as necking instabilities² (where extension rates outpace thermal diffusion³) and wide rifts thought to require a mechanism to inhibit localization, such as lower-crustal flow in high heat-flow settings^{1, 4}. Observations of the magmatism that results from rifting range from volcanic margins with two to three times the magmatism predicted from melting models⁵ to non-volcanic margins with almost no rift or post-rift magmatism. Such variations in magmatic activity are commonly attributed to variations in mantle temperature. Here we describe results from the PESCADOR seismic experiment in the southern Gulf of California and present crustal-scale images across three rift segments. Over short lateral distances, we observe large differences in rifting style and magmatism—from wide rifting with minor synchronous magmatism to narrow rifting in magmatically robust segments. But many of the factors believed to control structural evolution and magmatism during rifting (extension rate, mantle potential temperature and heat flow) tend to vary over larger length scales. We conclude instead that mantle depletion, rather than low mantle temperature, accounts for the observed wide, magma-poor margins, and that mantle fertility and possibly sedimentary insulation, rather than high mantle temperature, account for the observed robust rift and post-rift magmatism.

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