TY - JOUR
T1 - Oriented growth of sillimanite in andalusite, Placitas-Juan Tabo area, New Mexico, U.S.A
AU - Vernon, R. H.
PY - 1987
Y1 - 1987
N2 - In metapelitic schists near the Sandia granite in this area of New Mexico, nucleation sites for sillimanite are very variable, but growth of sillimanite in andalusite is common, either as bundles of fibrous sillimanite crystals or as coarser-grained parallel prisms or dendritic crystals of sillimanite. Optical relationships indicate a coaxial relationship between andalusite and sillimanite but with a and b axes interchanged. Stacking faults formed by dissociated screw locations in the andalusite may have provided nucleation sites for sillimanite. Some large sillimanite grains appear to have formed by coarsening of fibrous sillimanite, but others show no evidence of such coarsening. Some fibrous sillimanite occurs in folia in zones of inferred non-coaxial strain accumulation, and some occurs in radiating or crystallographically controlled aggregrates in low-strain zones between sillimanite folia. These aggregates do not necessarily indicate post-deformation growth, except on a very small scale, and many of the fibrous sillimanite aggregates have been deformed. Hence, the sillimanite is a product of syn-deformational rather than post-deformational metamorphism, although regional metamorphism and granite emplacement may have been broadly synchronous. The andalusite-sillimanite microstructural relationships indicate a prograde P-T-time path similar to those in other low-P (andalusite-sillimanite) metamorphic areas.-P.Br.
AB - In metapelitic schists near the Sandia granite in this area of New Mexico, nucleation sites for sillimanite are very variable, but growth of sillimanite in andalusite is common, either as bundles of fibrous sillimanite crystals or as coarser-grained parallel prisms or dendritic crystals of sillimanite. Optical relationships indicate a coaxial relationship between andalusite and sillimanite but with a and b axes interchanged. Stacking faults formed by dissociated screw locations in the andalusite may have provided nucleation sites for sillimanite. Some large sillimanite grains appear to have formed by coarsening of fibrous sillimanite, but others show no evidence of such coarsening. Some fibrous sillimanite occurs in folia in zones of inferred non-coaxial strain accumulation, and some occurs in radiating or crystallographically controlled aggregrates in low-strain zones between sillimanite folia. These aggregates do not necessarily indicate post-deformation growth, except on a very small scale, and many of the fibrous sillimanite aggregates have been deformed. Hence, the sillimanite is a product of syn-deformational rather than post-deformational metamorphism, although regional metamorphism and granite emplacement may have been broadly synchronous. The andalusite-sillimanite microstructural relationships indicate a prograde P-T-time path similar to those in other low-P (andalusite-sillimanite) metamorphic areas.-P.Br.
UR - http://www.scopus.com/inward/record.url?scp=0023104313&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0023104313
SN - 0008-4077
VL - 24
SP - 580
EP - 590
JO - Canadian Journal of Earth Sciences
JF - Canadian Journal of Earth Sciences
IS - 3
ER -