Emplacement conditions of igneous dikes in Ethiopian Traps

Abstract The emplacement conditions for 39 igneous dikes cutting basalts in northwestern Ethiopia are evaluated by analyzing their displacement–length scaling relations. Maximum opening displacements and lengths of the dikes demonstrate displacement–length scaling of the form D max  = 0.088 L 0.48 , consistent with other populations of dikes and veins and different than the power-law scaling relation typically found for faults. The dikes propagated through the thin Trap basalt sequence under conditions of constant fracture toughness, with values corrected for three-dimensional dike geometry of ~ 77–273 MPa m 1/2 . The large values of fracture toughness are likely associated with (1) the toughening effects of near-tip damage, (2) mixed-mode dike propagation, as shown by magma flow fabric analysis through anisotropy of magnetic susceptibility (AMS) and image analysis of thin sections, and (3) elevated temperature within the blocky and ductile basaltic host rock, evidence of which has been found in the field.

[1]  Peter Sammonds,et al.  Fracture toughness measurements on igneous rocks using a high-pressure, high-temperature rock fracture mechanics cell , 2004 .

[2]  H. Sheth,et al.  Structure and emplacement of the Nandurbar–Dhule mafic dyke swarm, Deccan Traps, and the tectonomagmatic evolution of flood basalts , 2007 .

[3]  Richard A. Schultz,et al.  Relative scale and the strength and deformability of rock masses , 1996 .

[4]  B. Henry,et al.  Tectonic applications of magnetic susceptibility and its anisotropy , 1997 .

[5]  G. Mandl.  Rock Joints: The Mechanical Genesis , 2005 .

[6]  Agust Gudmundsson,et al.  Geometry, structure and emplacement of mafic dykes in the Red Sea Hills, Sudan , 2004 .

[7]  G. Walker,et al.  Magma flow directions in dikes of the Koolau Complex, Oahu, determined from magnetic fabric studies , 1988 .

[8]  Patrick Launeau,et al.  Magmatic fabric acquisition mechanisms in a syenite: Results of a combined anisotropy of magnetic susceptibility and image analysis study , 1998 .

[9]  D. Reeves,et al.  Dependence of displacement-length scaling relations for fractures and deformation bands on the volumetric changes across them , 2008 .

[10]  D. Mège,et al.  Dyke swarm emplacement in the Ethiopian Large Igneous Province: not only a matter of stress , 2004 .

[11]  Patrick Launeau,et al.  Fabric analysis using the intercept method , 1996 .

[12]  B. Atkinson.  Fracture Mechanics of Rock , 1987 .

[13]  M. Perrin,et al.  Is this magnetic fabric normal? A review and case studies in volcanic formations , 1999 .

[14]  I. Main,et al.  Non-universal scaling of fracture length and opening displacement , 1994, Nature.

[15]  R. M. Clark,et al.  A modern regression approach to determining fault displacement-length scaling relationships , 1996 .

[16]  S. Hautot,et al.  The structure of a Mesozoic basin beneath the Lake Tana area, Ethiopia, revealed by magnetotelluric imaging , 2006 .

[17]  M. Klausen.  Similar dyke thickness variation across three volcanic rifts in the North Atlantic region: Implications for intrusion mechanisms , 2006 .

[18]  A. Aydin,et al.  Effect of thermal regime on growth increment and spacing of contraction joints in basaltic lava , 1993 .

[19]  Zhongmin Jin,et al.  Magma-Driven Multiple Dike Propagation and Fracture Toughness of Crustal Rocks , 2008 .

[20]  D. Mège,et al.  Fissure eruption of flood basalts from statistical analysis of dyke fracture length , 2004 .

[21]  D. Pollard,et al.  Origins of blade-like dikes in volcanic rift zones. , 1987 .

[22]  R. Schultz,et al.  Displacement-length scaling relations for faults on the terrestrial planets , 2006 .

[23]  Laura Marinoni,et al.  Injection and arrest of dykes: implications for volcanic hazards , 1999 .

[24]  E. Rivalta,et al.  Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface , 2006 .

[25]  E. P. Oliveira,et al.  Development of symmetrical and asymmetrical fabrics in sheet-like igneous bodies: the role of magma flow and wall-rock displacements in theoretical and natural cases , 2001 .

[26]  A. Ziv,et al.  Stability of dike intrusion along preexisting fractures , 2000 .

[27]  Agust Gudmundsson,et al.  Emplacement and arrest of sheets and dykes in central volcanoes , 2002 .

[28]  B. Atkinson,et al.  11 – EXPERIMENTAL FRACTURE MECHANICS DATA FOR ROCKS AND MINERALS , 1987 .

[29]  A. Gudmundsson.  Formation and growth of normal faults at the divergent plate boundary in Iceland , 1992 .

[30]  Patience A. Cowie,et al.  Physical explanation for the displacement-length relationship of faults using a post-yield fracture mechanics model , 1992 .

[31]  A. Allen,et al.  Geological setting and tectonic subdivision of the Neoproterozoic orogenic belt of Tuludimtu, western Ethiopia , 2003 .

[32]  Rolf V. Ackermann,et al.  Geometry and scaling relations of a population of very small rift-related normal faults , 1996 .

[33]  C. Scholz.  The Mechanics of Earthquakes and Faulting , 1990 .

[34]  V. Li,et al.  Fracture processes in concrete and fiber reinforced cementitious composites , 1986 .

[35]  D. Pollard,et al.  Deformation of host rocks and flow of magma during growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico , 1981 .

[36]  J. callot,et al.  Magnetic and plagioclase linear fabric discrepancy in dykes: a new way to define the flow vector using magnetic foliation , 2002 .

[37]  Agust Gudmundsson.  How local stresses control magma-chamber ruptures, dyke injections, and eruptions in composite volcanoes , 2006 .

[38]  Hervé Diot,et al.  Shape fabrics of particles in low concentration suspensions: 2D analogue experiments and application to tiling in magma , 1996 .

[39]  E. Parfitt.  The role of rift zone storage in controlling the site and timing of eruptions and intrusions of Kilauea Volcano, Hawaii , 1991 .

[40]  G. M Spink,et al.  Post Yield Fracture Mechanics , 2013 .

[41]  Jon E. Olson,et al.  Sublinear scaling of fracture aperture versus length: An exception or the rule? , 2003 .

[42]  Hervé Diot,et al.  Asymmetrical to symmetrical magnetic fabric of dikes: Paleo-flow orientations and Paleo-stresses recorded on feeder-bodies from the Motru Dike Swarm (Romania) , 2003 .

[43]  A. Rubin.  Tensile fracture of rock at high confining pressure: implications for dike propagation , 1993 .

[44]  R. Schultz.  Limits on strength and deformation properties of jointed basaltic rock masses , 1995 .

[45]  David A. Seal,et al.  The Shuttle Radar Topography Mission , 2007 .