Evidence for focused magmatic accretion at segment centers from lateral dike injections captured beneath the Red Sea rift in Afar

Continental breakup occurs through repeated episodes of mechanical stretching and dike injection within discrete, narrow rift segments. However, the time and length scales of the dike intrusions, along with the source regions of melt within continental and oceanic rifts, are poorly constrained. We present measurements of spatial and temporal variability in deformation from the currently active 60-km-long Dabbahu segment of the Red Sea rift in Afar, using satellite radar, global positioning system, and seismicity data sets, that capture emplacement of two ~10-km-long, ~1–2-m-wide dike intrusions in June and July 2006. Our observations show that the majority of strain is accommodated by dikes that propagate laterally over ~4–5 h time scales along the rift axis and are sourced from a reservoir in the middle to lower crust, or upper mantle, beneath the center of the rift segment. New intrusions during the ongoing rifting episode in Afar show that the injection of lateral dikes fed from magma reservoirs beneath rift segment centers is a key component in creating and maintaining regular along-axis rift segmentation during the final stages of continental breakup. Our observations also provide evidence that the focused magmatic accretion at segment centers observed in slow-spreading mid-ocean ridges occurs prior to the onset of seafloor spreading.

[1]  R. Pik,et al.  Timing of the Ethiopian flood basalt event and implications for plume birth and global change , 1997, Nature.

[2]  R. C. Kerr,et al.  Fluid‐mechanical models of crack propagation and their application to magma transport in dykes , 1991 .

[3]  P. Einarsson,et al.  Seismological evidence for Lateral magma intrusion during the July 1978 deflation of the Krafla volcano in NE-Iceland , 1978 .

[4]  C. Ebinger,et al.  Variations in the along‐axis segmentation of the Afar Rift system , 1996 .

[5]  H. Schouten,et al.  A mechanism for magmatic accretion under spreading centres , 1984, Nature.

[6]  R. Armijo,et al.  Propagation of rifting along the Arabia-Somalia plate boundary: , 1998 .

[7]  P. Lahitte,et al.  New age constraints on the timing of volcanism in central Afar, in the presence of propagating rifts , 2003 .

[8]  K. Cashman,et al.  The origin of volcano-tectonic earthquake swarms , 2006 .

[9]  T. Wright,et al.  Fault growth at a nascent slow-spreading ridge: 2005 Dabbahu rifting episode, Afar , 2007 .

[10]  T. Wright,et al.  Postdiking Deformation following the September 2005 Afar Tectono-Magmatic Event , 2006 .

[11]  Tim J. Wright,et al.  Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode , 2006, Nature.

[12]  C. Ebinger,et al.  Strain accommodation by magmatism and faulting as rifting proceeds to breakup: Seismicity of the northern Ethiopian rift , 2006 .

[13]  J. Makris,et al.  The Afar Depression: transition between continental rifting and sea-floor spreading , 1987 .

[14]  J. Sempere,et al.  Evidence from gravity data for focused magmatic accretion along the Mid-Atlantic Ridge , 1990, Nature.

[15]  T. Wright,et al.  Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift , 2008 .

[16]  E. Engdahl,et al.  Finite-Frequency Tomography Reveals a Variety of Plumes in the Mantle , 2004, Science.

[17]  E. Jacques,et al.  The volcano–seismic crisis in Afar, Ethiopia, starting September 2005 , 2007 .

[18]  K. Grönvold,et al.  Current rifting episode in north Iceland , 1977, Nature.

[19]  M. Lilley,et al.  The quantum event of oceanic crustal accretion: impacts of diking at mid-ocean ridges. , 1998, Science.

[20]  P. Einarsson,et al.  Tectonic stress and magma chamber size as controls on dike propagation : Constraints from the 1975-1984 Krafla rifting episode , 2006 .

[21]  C. Vigny,et al.  Confirmation of Arabia plate slow motion by new GPS data in Yemen , 2006 .

[22]  Deborah K. Smith,et al.  Constructing the upper crust of the Mid-Atlantic Ridge : A reinterpretation based on the Puna Ridge, Kilauea Volcano , 1999 .

[23]  N. Driscoll,et al.  1. Consequences of Asthenospheric Variability on Continental Rifting , 2004 .

[24]  A. Tarantola,et al.  Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries , 1979, Nature.

[25]  J. Escartín,et al.  Discovery of a magma chamber and faults beneath a Mid-Atlantic Ridge hydrothermal field , 2006, Nature.

[26]  A. Rubin,et al.  Dike‐induced earthquakes: Theoretical considerations , 1998 .

[27]  P. Segall,et al.  Magma compressibility and the missing source for some dike intrusions , 2008 .

[28]  Kenneth H. Rubin,et al.  A Sea-Floor Spreading Event Captured by Seismometers , 2006, Science.

[29]  Y. Fialko,et al.  Thermodynamics of lateral dike propagation: Implications for crustal accretion at slow spreading mid‐ocean ridges , 1998 .

[30]  M. Tolstoy,et al.  Crustal Thickness on the Mid-Atlantic Ridge: Bull's-Eye Gravity Anomalies and Focused Accretion , 1993, Science.

[31]  R. Taylor,et al.  Geochemistry of basalts from Manda Hararo, Ethiopia: LREE-depleted basalts in Central Afar , 2003 .