Back to Abstract Index
Paper Number: 129
Geological
mapping and U-Pb and Sm-Nd chronology of the Rauer Group Islands (East
Antarctica)
Alexeev
N.L.1, Kamenev I. A.1, Yegorov
M.S.1, Kapitonov I.N.2, Bogomolov
Ye.S.2, Sergeev S.A.2
1Polar
Marine Geological Research Expedition, St-Petersburg, Russia, nikola.alekseev@gmail.com
2All
Russian Geological Institute (VSEGEI), St-Petersburg, Russia
_____________________________________________________________________________________________
The Rauer Group are a series of ice free islands and peninsulas
located adjacent to the Archaean block of the Vestfold Hills. Commonly,
they interpreted to consist of mainly high-temperature orthogneiss with
minor sediments incorporated into Mather and Filla series. Geological
mapping of northern part of Rauer Group accompanied with U-Pb zircon and
Sm-Nd whole-rock-garnet dating provide a new insight on geology and
chronology of the Rauer Group.
On Efremova Island the garnet- biotite (±orthopyroxene) orthogneiss
were found to intrude the layered orthopyroxene-bearing gneisses.
Orthogneisses contains igneous zircons given an age of about 1400 Ma
that thought to date a time of their igneous protolith crystallization.
A sample of garnet-spinel bearing metasediments from Mather series
contains detrital zircons given an age of about 2435±99 Ma. That is
interpreted to date a maximum time of sedimentation. A model
T(DM)Nd= 3.23 Ga and presence of detrital zircons of c. 3.21
Ga and c. 2.8 Ga suggests that protolith of these rocks were formed
mainly on expense of Archaean material.
The Filla series is thought to incorporate the three sequences.
Sequence I involves mainly two- pyroxene bearing mafic gneisses of
apparently volcanic (basalts) origin. They were deposited within a time
interval of 1342±19 Ma - 1156±21 Ma. Sequence II consists mainly of
garnet-biotite (±orthopyroxene) metasediments with rare mafic and
intermediate gneisses. A lens of clinopyroxene bearing leucocratic
schist within this sequence contains detrital zircon with an age of
1748±24 Ma dating a maximum time of sedimentation. Sequence III involves
mainly sillimanite-garnet bearing gneisses and quartzite-like rocks.
Detrital zircons given an age of 1630±74 provide a maximum limit of
sediments deposition. Model T(DM)Nd=3.4 Ga and detrital
zircon with an age of c. 3.2 Ga suggest mainly Archaean age of their
protolith. Because both c. 2.8 Ga and c. 3.2 Ga orthogneisses are
widespread at the Rauer Islands [1] we may suggest that they were a main
source of Mather and Filla sediments protolith.
An Archaean rocks at Scherbinina Island were intruded by series of
two pyroxene-hornblende bearing mafic dykes. They contain igneous zircon
given an age of c. 1.7 Ga that is interpreted to date a maximum time of
the dyke injection.
A major impulse of igneous and probably tectonic activity of the
region occurred between c. 1156 Ma and c. 960 Ma. This has led to
emplacement of series intrusions and development of ductile shear
zones.
Intrusive rocks were incorporated in two association: an older
diorite-tonalite-plagiogranite association emplaced between c. 1156-1143
Ma and younger gabbronorite-diorite association injected between c.
1143- 960 Ma ago. Both association contain pods of deformed Filla series
rocks and were deformed by E-W trending ductile shear zones. On Filla
and Efremova Islands the rocks a intruded by numerous mafic dykes
injected after c. 1400 and c. 1143 Ma. Sm-Nd whole rock-garnet dating
provides a limit for high-temperature thermal event which is within
523.7±2.8 Ma- 511.6±2.8 Ma time space.
[1] Kinny P.D. et al. (1993) Antarctic Science 5 (2): 193-206.
