Deformation, stirring and material transport in thermochemical plumes

[1] The deformation, stirring processes and transport structures for a series of numerical models of plume formation in axisymmetric spherical shell are examined to better understand the development of lateral heterogeneity in mantle plumes. In our models we find that under a wide range of conditions the surrounding material is heated and entrained. This indicates that plume sampling the ambient mantle material on its way to the base of the lithosphere cannot be ruled out. The deformation and convective stirring can be significantly enhanced in the thermochemical plumes and the dispersion of compositional heterogeneity can be much more effective than that in the purely thermal plumes. For models with episodic pulsations or with small-scale convection due to the interplay between the thermal and compositional buoyancy forces, material in the plume and the source region can undergo strong stretching and folding resulting in structures such as filaments, streaks, tendrils and well-mixed regions. Islands can be surrounded by highly deformed regions which may contribute to structures such as the coexistence of the compositional heterogeneity and relatively homogeneous matrix in Ocean Island Basalts (OIBs). These results may have implications for the interpretation of the lateral heterogeneities of the OIBs.

[1]  P. V. Keken.  Evolution of starting mantle plumes: a comparison between numerical and laboratory models , 1997 .

[2]  Ulrich R. Christensen,et al.  Dynamic Earth: Plates, Plumes and Mantle Convection , 2000 .

[3]  Sylvaine Ferrachat,et al.  Regular vs. chaotic mantle mixing , 1998 .

[4]  S. Hart,et al.  Mantle Plumes and Entrainment: Isotopic Evidence , 1992, Science.

[5]  J. Ottino,et al.  Kinematic considerations for mantle mixing , 1995 .

[6]  R. Hilst,et al.  Compositional heterogeneity in the bottom 1000 kilometers of Earth's mantle: toward a hybrid convection model , 1999, Science.

[7]  Shu-Chuan Lin,et al.  Dynamics of thermochemical plumes: 2. Complexity of plume structures and its implications for mapping mantle plumes , 2006 .

[8]  A. Hofmann,et al.  Segregation of subducted oceanic crust in the convecting mantle , 1994 .

[9]  G. Davies.  Stirring geochemistry in mantle convection models with stiff plates and slabs , 2002 .

[10]  Zhong‐Yuan Ren,et al.  The chemical structure of the Hawaiian mantle plume , 2004, Nature.

[11]  D. Yuen,et al.  Fractal features in mixing of non-Newtonian and Newtonian mantle convection , 1997 .

[12]  Peter E. van Keken,et al.  MANTLE MIXING: The Generation, Preservation, and Destruction of Chemical Heterogeneity , 2002 .

[13]  J. Schmalzl,et al.  Mixing in vigorous, time-dependent three-dimensional convection and application to Earth's mantle , 1996 .

[14]  Shu-Chuan Lin,et al.  Dynamics of thermochemical plumes: 1. Plume formation and entrainment of a dense layer , 2006 .

[15]  A. McBirney,et al.  Petrology and geochemistry of the Galápagos Islands: Portrait of a pathological mantle plume , 1993 .

[16]  J. Ottino.  The Kinematics of Mixing: Stretching, Chaos, and Transport , 1989 .

[17]  B. Legras,et al.  Mixing and deformations in mantle plumes , 2002 .

[18]  A. Davaille,et al.  Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle , 1999, Nature.

[19]  Louise H. Kellogg,et al.  Mixing and the distribution of heterogeneities in a chaotically convecting mantle , 1990 .

[20]  Paul J. Tackley,et al.  Testing the tracer ratio method for modeling active compositional fields in mantle convection simulations , 2003 .

[21]  Henri Samuel,et al.  Lagrangian structures and stirring in the Earth’s mantle , 2003 .

[22]  H. Samuel,et al.  Beyond the thermal plume paradigm , 2005 .

[23]  Shijie Zhong,et al.  Thermochemical structures beneath Africa and the Pacific Ocean , 2005, Nature.

[24]  S. Hart,et al.  Fluid dynamic and geochemical aspects of entrainment in mantle plumes , 1994 .

[25]  G. Davies,et al.  Dynamic Earth: Interior , 1999 .