The elusive Rivera-Cocos plate boundary: not diffuse
Román Alvarez, Vsevolod Yutsis, 2016. "The elusive Rivera-Cocos plate boundary: not diffuse", Magmatic Rifting and Active Volcanism, T. J. Wright, A. Ayele, D. J. Ferguson, T. Kidane, C. Vye-Brown
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Inland and offshore gravimetric determinations in the Southern Colima rift in western Mexico allowed for the construction of a Bouguer anomaly map of the area. Four submarine canyons of tectonic relevance are located in the offshore area. Gravimetric models of the oceanic subducting slab were calculated from the residual Bouguer anomaly along six trench-parallel lines and three trench-perpendicular lines including the area of the canyons. The former lines show considerable distortion of the slab that we attribute to compression, while the latter show distinct dipping angles of the oceanic slab at distances of around 75 km from the trench: the westernmost line shows a dip angle of 55° between depths of 20 and 70 km, while the easternmost shows a dip angle of 32° at depths between 18 and 50 km. We submit that the former represents a section of the subducting Rivera plate, and the latter represents a section of the Cocos plate. Extracting coordinates of representative points on the surface of the nine slab models allowed for a reconstruction of the slab surface: the transition from the Rivera to the Cocos plate is marked by topographic gradients in the modelled slab surface suggesting the trajectory of the boundary between the plates. We propose a tectonic model that includes a transpression zone involving the marine platform and the Southern Colima rift and a transtension zone in the Northern Colima rift: the Colima Volcanic Complex is located in the transition zone between them.
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A major rifting episode began in the Afar region of northern Ethiopia in September 2005. Over a ten-day period, c. 2.5 km3 of magma were intruded along a 60 km-long dyke separating the Arabian and Nubian plates. Over the next five years, a further 13 dyke intrusions caused continued extension, eruptions and seismicity. This activity led to a renewed international focus on the role of magmatism in rifting, with major international collaborative projects working in Afar and Ethiopia to study the ongoing activity and to place it in a broader context. This book brings together articles that explore the role of magmatism in rifting, from the initiation of continental break-up through to full seafloor spreading. We also explore the hazards related to rifting and the associated volcanism. This work has implications for our understanding of how continents break-up and the associated distribution of resources in rift basins and continental margins.