TY - JOUR
T1 - Titanite petrochronology linked to phase equilibrium modelling constrains tectono-thermal events in the Akia Terrane, West Greenland
AU - Kirkland, C.L.
AU - Yakymchuk, C.
AU - Gardiner, N. J.
AU - Szilas, K.
AU - Hollis, J.
AU - Olierook, H.
AU - Steenfelt, A.
N1 - GeoHistory Facility instruments (part of the John de Laeter Centre) were funded via an Australian Geophysical Observing System (AGOS) grant provided to AuScope by the AQ44 Australian Education Investment Fund.
PY - 2020/3/20
Y1 - 2020/3/20
N2 - The Mesoarchean Akia Terrane in West Greenland contains a detailed
magmatic and metamorphic mineral growth record from 3.2 Ga to at least
c. 2.5 Ga. This time span makes this region an important case study in
the quest to track secular changes in geodynamic style which may
ultimately inform on the development of plate tectonics as a globally
linked system of lateral rigid plate motions. The common accessory
mineral titanite has recently become recognised as a powerful high
temperature geochronometer whose chemistry may chart the thermal
conditions of its growth. Furthermore, titanite offers the potential to
record the time-temperature history of mafic lithologies, which may lack
zircon. Although titanite suffers from higher levels of common Pb than
many other UPb chronometers, we show how measurement of 207Pb/206Pb
in texturally coeval biotite may assist in the characterization of the
appropriate common Pb composition in titanite. Titanite extracted from
two samples of mafic gneisses from the Akia Terrane both yield UPb
ages of c. 2.54 Ga. Although coeval, their chemistry implies growth
under two distinctly different processes. In one case, the titanite has
elevated total REE, high Th/U and grew from an in-situ partial melt,
consistent with an identical date to granite dyke zircon. In contrast,
the second titanite sample contains greater common Pb, lower total REE,
lower Th/U, and grew from dominantly hydrothermal fluids. Zr-in-titanite
thermometry for partial melt-derived titanite, with activities
constrained by phase equilibrium modelling, indicates maxima of c.
690 °C. Elsewhere in the Akia Terrane, coeval metamorphism linked to
growth of hydrothermal titanite is estimated at temperatures of c.
670 °C. These new results when coupled with existing findings indicate
punctuated, repeated metamorphic events in the Akia Terrane, in which
high temperature conditions (re)occurred at least three times between
3.0 and 2.5 Ga, but crucially changed in style across a c. 3.0 Ga change
point. We interpret this change in metamorphism as reflecting a
fundamental shift in geodynamic style in West Greenland at 3.0 Ga,
consistent with other estimates for the onset of widespread plate
tectonic-type processes.
AB - The Mesoarchean Akia Terrane in West Greenland contains a detailed
magmatic and metamorphic mineral growth record from 3.2 Ga to at least
c. 2.5 Ga. This time span makes this region an important case study in
the quest to track secular changes in geodynamic style which may
ultimately inform on the development of plate tectonics as a globally
linked system of lateral rigid plate motions. The common accessory
mineral titanite has recently become recognised as a powerful high
temperature geochronometer whose chemistry may chart the thermal
conditions of its growth. Furthermore, titanite offers the potential to
record the time-temperature history of mafic lithologies, which may lack
zircon. Although titanite suffers from higher levels of common Pb than
many other UPb chronometers, we show how measurement of 207Pb/206Pb
in texturally coeval biotite may assist in the characterization of the
appropriate common Pb composition in titanite. Titanite extracted from
two samples of mafic gneisses from the Akia Terrane both yield UPb
ages of c. 2.54 Ga. Although coeval, their chemistry implies growth
under two distinctly different processes. In one case, the titanite has
elevated total REE, high Th/U and grew from an in-situ partial melt,
consistent with an identical date to granite dyke zircon. In contrast,
the second titanite sample contains greater common Pb, lower total REE,
lower Th/U, and grew from dominantly hydrothermal fluids. Zr-in-titanite
thermometry for partial melt-derived titanite, with activities
constrained by phase equilibrium modelling, indicates maxima of c.
690 °C. Elsewhere in the Akia Terrane, coeval metamorphism linked to
growth of hydrothermal titanite is estimated at temperatures of c.
670 °C. These new results when coupled with existing findings indicate
punctuated, repeated metamorphic events in the Akia Terrane, in which
high temperature conditions (re)occurred at least three times between
3.0 and 2.5 Ga, but crucially changed in style across a c. 3.0 Ga change
point. We interpret this change in metamorphism as reflecting a
fundamental shift in geodynamic style in West Greenland at 3.0 Ga,
consistent with other estimates for the onset of widespread plate
tectonic-type processes.
KW - Titanite
KW - Geochronology
KW - Phase equilibrium
KW - Ti-in-zircon
KW - Petrochronology
U2 - 10.1016/j.chemgeo.2020.119467
DO - 10.1016/j.chemgeo.2020.119467
M3 - Article
SN - 0009-2541
VL - 536
JO - Chemical Geology
JF - Chemical Geology
M1 - 119467
ER -