Rotation of prismatic rigid porphyroblasts and development of internal foliation

Results from pixel-based modelling study

Youngdo Park, Jin-Han Lee, Won Sun Jung

Research output: Contribution to journalArticle

Abstract

We have modelled rigid-body rotation of growing prismatic porphyroblasts and development of internal foliation formed by capturing external foliation. Jefferey equations (1922) were used for the porphyroblast rotation with the assumptions that porphyroblasts are mechanically rigid objects embedded in a deforming ductile matrix. The growth rule applied in this model is a simple expansion of crystal faces with known Miller indices with the pre-assigned growth rate for each face. The external foliation is assumed to have constant orientation. Parts of external foliation within the calculated volume of a porphyroblast are captured during the growth and rotated with the porphyroblast once they are captured. During simple shear flow, prismatic porphyroblasts with every possible orientation with respect to the shear plane rotate constantly. The rate of rotation is determined as a function of strain rate and the shape and orientation of porphyroblasts. On the contrary, during pure shear flow, the longest axes of porphyroblasts approach toward the stretching direction. The observed patterns of the internal foliation within a porphyroblast are complicated in general, because the orientation of the rotation axis is not fixed with respect the kinematic reference frame. However, when there is pure shearing component in the flow geometry, porphyroblasts tend to have stable orientations and it is expected that Si patterns within a syntectonic porphyroblast can be straight. Thus, the straight Si patterns can be a good indicator for the flow geometry with some component of shear-direction-parallel stretching for syntectonic porphyroblasts. From the observations of model porphyroblasts, it is also proposed that central sections needs to be observed for the interpretation of internal foliations within prismatic porphyroblasts.

Original languageEnglish
JournalJournal of the Virtual Explorer
Volume15
Publication statusPublished - 2004 Dec 1

Fingerprint

porphyroblast
foliation
pixel
Pixels
pixels
flow geometry
Shear flow
Stretching
modeling
shear flow
Geometry
shear
Shearing
Strain rate
rigid structures
Kinematics
shearing
strain rate
kinematics
Crystals

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geology
  • Geophysics

Cite this

@article{a66b4ac570e24b4bae555d9978ccaea1,
title = "Rotation of prismatic rigid porphyroblasts and development of internal foliation: Results from pixel-based modelling study",
abstract = "We have modelled rigid-body rotation of growing prismatic porphyroblasts and development of internal foliation formed by capturing external foliation. Jefferey equations (1922) were used for the porphyroblast rotation with the assumptions that porphyroblasts are mechanically rigid objects embedded in a deforming ductile matrix. The growth rule applied in this model is a simple expansion of crystal faces with known Miller indices with the pre-assigned growth rate for each face. The external foliation is assumed to have constant orientation. Parts of external foliation within the calculated volume of a porphyroblast are captured during the growth and rotated with the porphyroblast once they are captured. During simple shear flow, prismatic porphyroblasts with every possible orientation with respect to the shear plane rotate constantly. The rate of rotation is determined as a function of strain rate and the shape and orientation of porphyroblasts. On the contrary, during pure shear flow, the longest axes of porphyroblasts approach toward the stretching direction. The observed patterns of the internal foliation within a porphyroblast are complicated in general, because the orientation of the rotation axis is not fixed with respect the kinematic reference frame. However, when there is pure shearing component in the flow geometry, porphyroblasts tend to have stable orientations and it is expected that Si patterns within a syntectonic porphyroblast can be straight. Thus, the straight Si patterns can be a good indicator for the flow geometry with some component of shear-direction-parallel stretching for syntectonic porphyroblasts. From the observations of model porphyroblasts, it is also proposed that central sections needs to be observed for the interpretation of internal foliations within prismatic porphyroblasts.",
keywords = "Foliation, Modelling, Porphyroblasts, Prismatic, Rigid",
author = "Youngdo Park and Jin-Han Lee and Jung, {Won Sun}",
year = "2004",
month = "12",
day = "1",
language = "English",
volume = "15",
journal = "Journal of the Virtual Explorer",
issn = "1441-8126",
publisher = "Virtual Explorer Pty. Ltd.",

}

TY - JOUR

T1 - Rotation of prismatic rigid porphyroblasts and development of internal foliation

T2 - Results from pixel-based modelling study

AU - Park, Youngdo

AU - Lee, Jin-Han

AU - Jung, Won Sun

PY - 2004/12/1

Y1 - 2004/12/1

N2 - We have modelled rigid-body rotation of growing prismatic porphyroblasts and development of internal foliation formed by capturing external foliation. Jefferey equations (1922) were used for the porphyroblast rotation with the assumptions that porphyroblasts are mechanically rigid objects embedded in a deforming ductile matrix. The growth rule applied in this model is a simple expansion of crystal faces with known Miller indices with the pre-assigned growth rate for each face. The external foliation is assumed to have constant orientation. Parts of external foliation within the calculated volume of a porphyroblast are captured during the growth and rotated with the porphyroblast once they are captured. During simple shear flow, prismatic porphyroblasts with every possible orientation with respect to the shear plane rotate constantly. The rate of rotation is determined as a function of strain rate and the shape and orientation of porphyroblasts. On the contrary, during pure shear flow, the longest axes of porphyroblasts approach toward the stretching direction. The observed patterns of the internal foliation within a porphyroblast are complicated in general, because the orientation of the rotation axis is not fixed with respect the kinematic reference frame. However, when there is pure shearing component in the flow geometry, porphyroblasts tend to have stable orientations and it is expected that Si patterns within a syntectonic porphyroblast can be straight. Thus, the straight Si patterns can be a good indicator for the flow geometry with some component of shear-direction-parallel stretching for syntectonic porphyroblasts. From the observations of model porphyroblasts, it is also proposed that central sections needs to be observed for the interpretation of internal foliations within prismatic porphyroblasts.

AB - We have modelled rigid-body rotation of growing prismatic porphyroblasts and development of internal foliation formed by capturing external foliation. Jefferey equations (1922) were used for the porphyroblast rotation with the assumptions that porphyroblasts are mechanically rigid objects embedded in a deforming ductile matrix. The growth rule applied in this model is a simple expansion of crystal faces with known Miller indices with the pre-assigned growth rate for each face. The external foliation is assumed to have constant orientation. Parts of external foliation within the calculated volume of a porphyroblast are captured during the growth and rotated with the porphyroblast once they are captured. During simple shear flow, prismatic porphyroblasts with every possible orientation with respect to the shear plane rotate constantly. The rate of rotation is determined as a function of strain rate and the shape and orientation of porphyroblasts. On the contrary, during pure shear flow, the longest axes of porphyroblasts approach toward the stretching direction. The observed patterns of the internal foliation within a porphyroblast are complicated in general, because the orientation of the rotation axis is not fixed with respect the kinematic reference frame. However, when there is pure shearing component in the flow geometry, porphyroblasts tend to have stable orientations and it is expected that Si patterns within a syntectonic porphyroblast can be straight. Thus, the straight Si patterns can be a good indicator for the flow geometry with some component of shear-direction-parallel stretching for syntectonic porphyroblasts. From the observations of model porphyroblasts, it is also proposed that central sections needs to be observed for the interpretation of internal foliations within prismatic porphyroblasts.

KW - Foliation

KW - Modelling

KW - Porphyroblasts

KW - Prismatic

KW - Rigid

UR - http://www.scopus.com/inward/record.url?scp=84883668147&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84883668147&partnerID=8YFLogxK

M3 - Article

VL - 15

JO - Journal of the Virtual Explorer

JF - Journal of the Virtual Explorer

SN - 1441-8126

ER -