Cornelis Weemstra

Magmatism on rift flanks: Insights from ambient noise phase velocity in Afar region

During the breakup of continents in magmatic settings, the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis. Magmatic processes near the rift flanks are commonly ignored. We present phase velocity maps of the crust and uppermost mantle of the conjugate margins of the southern Red Sea (Afar and Yemen) using ambient noise tomography to constrain crustal modification during breakup. Our images show that the low seismic velocities characterize not only the upper crust beneath the axial volcanic systems but also both upper and lower crust beneath the rift flanks where ongoing volcanism and hydrothermal activity occur at the surface. Magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading.

Magmatism at continental passive margins inferred from Ambient-Noise Phase-velocity in the Gulf of Aden

Non-volcanic continental passive margins have traditionally been considered to be tectonically and magmatically inactive once continental breakup has occurred and seafloor spreading has commenced. We use ambient-noise tomography to constrain Rayleigh-wave phase-velocity maps beneath the eastern Gulf of Aden (eastern Yemen and southern Oman). In the crust, we image low velocities beneath the Jiza-Qamar (Yemen) and Ashawq-Salalah (Oman) basins, likely caused by the presence of partial melt associated with magmatic plumbing systems beneath the rifted margin. Our results provide strong evidence that magma intrusion persists after breakup, modifying the composition and thermal structure of the continental margin. The coincidence between zones of crustal intrusion and steep gradients in lithospheric thinning, as well as with transform faults, suggests that magmatism post-breakup may be driven by small-scale convection and enhanced by edge-driven flow at the juxtaposition of lithosphere of varying thickness and thermal age.

To: “Introduction to special section: Ambient noise,” Sjoerd de Ridder, Florent Brenguier, Farnoush Forghani, Erica Galetti, Nori Nakata, and Cornelis Weemstra, Interpretation, 4, no. 3, SJi, doi: 10.1190/INT-2016-0627-SPSEINTRO.1.

The author names for the following two summaries originally appeared as Pascal and Yuan and Pascal and Halliday , but they should have read: Edme and Yuan formulate a novel acquisition and processing technique to derive surface-wave dispersion curves from seismic ambient noise. The authors show

Introduction to special section: Ambient noise

Many efforts of geophysical processing have traditionally been devoted to the separation, attenuation, and elimination of noise from seismic acquisition data. However, one geophysicist’s noise is another geophysicist’s signal. [Aki (1957)][1] formulated the spatial autocorrelation method, which