Porphyroblast Textural Sector-zoning and Matrix Displacement

A. H. N. Rice and J. I. Mitchell
Geologisch-Paläontologisches Institut, Ruprecht-Karls Universität, Im Neuenheimer Feld 234, D-6900 Heidelberg, Germany
9 St Peters Street, Roath, Cardiff CF2 3BA, Wales, U.K.

Abstract: There is an association between the development of cleavage domes, a texture reflecting the displacement of insoluble matrix grains by porphyroblasts growing under a bulk hydrostatic stress, and textural sector-zoning. This has been found in garnet, staurolite, chiastolite, pyrite and possibly emerald porphyroblasts. Sector-zoned porphyroblasts form by lineage growth normal to the crystal faces. This causes several distinctive textures (type 1 inclusions and type 2 intergrowths, inclusion bands, growth prongs), all of which are directly or indirectly related to displacement growth. Graphite or other carbonaceous material is ubiquitous in samples showing textural sector-zoning.

Keywords: graphite • cleavage dome • matrix displacement • porphyroblasts • sector-zoning • textures • garnet • staurolite • chiastolite • pyrite • emerald

Mineralogical Magazine; September 1991 v. 55; no. 380; p. 379-396; DOI: 10.1180/minmag.1991.055.380.08
© 1991, The Mineralogical Society
Mineralogical Society (www.minersoc.org)