TY - JOUR
T1 - Brine Infiltration in the Middle to Lower Crust in a Collision Zone
T2 - Mass Transfer and Microtexture Development Through Wet Grain-Boundary Diffusion
AU - Higashino, Fumiko
AU - Kawakami, Tetsuo
AU - Tsuchiya, Noriyoshi
AU - Satish-Kumar, M.
AU - Ishikawa, Masahiro
AU - Grantham, Geoffrey
AU - Sakata, Shuhei
AU - Hirata, Takafumi
N1 - Publisher Copyright:
© © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: [email protected].
PY - 2019/2/1
Y1 - 2019/2/1
N2 - Brine-induced microtexture formation in upper amphibolite to granulite facies lower crust is investigated using a garnet-hornblende (Grt-Hbl) selvage developed along a planar crack discordantly cutting the gneissic structure of an orthopyroxene-bearing gneiss (central Sør Rondane Mountains, East Antarctica). The Cl contents of hornblende and biotite, K contents of hornblende and the thickness of relatively Na-rich rims of plagioclase decrease with distance from the center of the Grt-Hbl selvage (inferred position of the crack). Biotite and hornblende arrangement defining the gneissic structure can be traced into the selvage, suggesting that the wall-rock was overprinted by the selvage formation. Addition and loss of elements to the wall-rock was examined using Zr as an immobile element. Trace elements that tend to be mobile in brines rather than in melts are added to the wall-rock, indicating that the Grt-Hbl selvage was formed by the advection of NaCl-KCl brine into a thin crack. Plagioclase in the wall-rock shows a discontinuous drop of anorthite content at the rim, indicating that coupled dissolution-reprecipitation took place and the grain boundaries were once wet. Trace element concentrations in the wall-rock minerals decrease with distance from the crack, and, in most cases show exponentially decreasing/increasing profiles depending on the elements. These profiles are best modelled by a diffusion equation, suggesting that the wet grain-boundary diffusion in the wall-rock minerals controlled the observed mass transfer and resulted in dissolution-reprecipitation of mineral rims.
AB - Brine-induced microtexture formation in upper amphibolite to granulite facies lower crust is investigated using a garnet-hornblende (Grt-Hbl) selvage developed along a planar crack discordantly cutting the gneissic structure of an orthopyroxene-bearing gneiss (central Sør Rondane Mountains, East Antarctica). The Cl contents of hornblende and biotite, K contents of hornblende and the thickness of relatively Na-rich rims of plagioclase decrease with distance from the center of the Grt-Hbl selvage (inferred position of the crack). Biotite and hornblende arrangement defining the gneissic structure can be traced into the selvage, suggesting that the wall-rock was overprinted by the selvage formation. Addition and loss of elements to the wall-rock was examined using Zr as an immobile element. Trace elements that tend to be mobile in brines rather than in melts are added to the wall-rock, indicating that the Grt-Hbl selvage was formed by the advection of NaCl-KCl brine into a thin crack. Plagioclase in the wall-rock shows a discontinuous drop of anorthite content at the rim, indicating that coupled dissolution-reprecipitation took place and the grain boundaries were once wet. Trace element concentrations in the wall-rock minerals decrease with distance from the crack, and, in most cases show exponentially decreasing/increasing profiles depending on the elements. These profiles are best modelled by a diffusion equation, suggesting that the wet grain-boundary diffusion in the wall-rock minerals controlled the observed mass transfer and resulted in dissolution-reprecipitation of mineral rims.
KW - brine
KW - continental collision zone
KW - diffusion
KW - microtexture
KW - trace element
UR - http://www.scopus.com/inward/record.url?scp=85062527193&partnerID=8YFLogxK
U2 - 10.1093/petrology/egy116
DO - 10.1093/petrology/egy116
M3 - Article
AN - SCOPUS:85062527193
SN - 0022-3530
VL - 60
SP - 329
EP - 358
JO - Journal of Petrology
JF - Journal of Petrology
IS - 2
ER -