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Magmatic Layering in the Nuptse S-type Granite, Himalaya

Roberto Weinberg, Monash University, Australia

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Copyright 2004-2011 by Roberto Weinberg. All rights reserved. Unlimited permission to copy or use is hereby granted for non-profit driven enterprise, subject to inclusion of this copyright notice and acknowledgment of the source URL: users.monash.edu.au/~weinberg.

 

I would very much appreciate an email stating how this material will be used: Roberto Weinberg, Monash University, Australia. Thanks, RW.

 

DISCLAIMER. The material on this website has not undergone the scrutiny of Monash University and does not conform to its corporate web design. It is entirely based on a free-spritied, curiosity-driven research effort by the author, and therefore in no way expresses the official position of the University.

 

"
Leucogranite
Ama Dablam peak 		This page illustrates the extensive magmatic layering developed in the tml-gnt-ms-bt leucogranites of the Nuptse area in the Khumbu valley in Nepal. Layering here is beautifully developed, and locally magmatic deformation deforms the original layering in systematic ways. Layering can be defined by tml, gnt or feldspar. Some beautiful comb layering (unidirectional structures) are also well-developed. Some but not all the images shown have been published in Weinberg and Searle (1999). The purpose here is to illustrate the structures and trigger discussions, ideas and potential collaborations. If you want to help expand this site or connect your own related page to this one please let me know.

Weinberg, R.F. and Searle, M.P. 1999, Volatile-assisted intrusion and autometasomatism of leucogranites in the Khumbu Himalaya, Nepal, J. Geol. 107, 27-48.

 

Leucogranite, Nuptse Pluton, Nuptse PeakNuptse Peak, Khumbu, close to Everest, Nepal.
The Nuptse pluton forms the two semi-circles.

 

 

Magmatic Structures

 

  • Magmatic Layering
  • Deformed layering
  • Comb Layering
  • Porphyroblasts relationship to melt
  • Pervasive intrusion

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    Magmatic layering in S-type tml-gnt-ms-bt Himalayan leucogranite

     

    All layering shown is 3D, as most features were photographed from blocks


     

    leucogranite, igneous layering
    A) Two different styles of layering nearly orthogonal    		 leucogranite, igneous layering
    B) Three types of layering at dm scale

     

    leucogranite, igneous layering
    C) Layering and flower texture    		 leucogranite, igneous layering, comb layering
    D) Comb layering (upper half)
    and flower texture (lower half)

     

    leucogranite
    E) 3D repetitive and distorted layering    		 leucogranite, igneous layering
    F) Layering and flower texture

     

    igneous layering
    G) Complex tourmaline layering     		igneouslayering
    H) Layering defined by coarse feldspar.
    Note angular relationships

     

     

    Deformed Layering

     

    igneous layering
    A)Leucogranite layering broken up and rotated ~20 o by deformation (thick black line).
    Notice small fold hinges filled with tml (arrow)    		 igneous leucogranite
    B) Magmatic fold and with weak axial planar foliation developed

     

     

     

    Comb Layering

    leucogranite, Comb Layering
    A)Comb layering

     

    		 leucogranite, Comb Layering
    B) Dyke: K-feldspar pointing inwards at an angle to the walls.
    Growth controlled by stresses

     

     

    Relationship between melt-country rock and porphyroblasts

     

    leucogranite and porphyroblast

    A) A finger of country rock in between magma lobes:
    2 cordierite grains (arrow) grew at the end of the tip    		 leucogranite
    B) Finger caught up within a magma whirl.
    Large tml at tip.
    leucogranite
    A)     		leucogranite
    B)

     

     

    Pervasive melt intrusion


    For more information see: Leitch, A.M.,and Weinberg, R.F. 2002, Mesoscale pervasive flow model for granite magma migration. Earth Planet. Sci. Lett. 200, 131-146.

     

     

    Liked the structures? Want to know more? Contact me on my email