High-Grade Crystalline
Basement of the Northwestern Wilson Terrane at Oates Coast: New
Petrological and Geochronological Data and Implications for Its
Tectonometamorphic Evolution
U. Schüssler1*, F. Henjes-Kunst2,
F. Talarico3 & T. Flöttmann4
1Institut für
Mineralogie der Universität Würzburg, Am Hubland, D-97074
Würzburg - Germany
2Bundesanstalt für Geowissenschaften und Rohstoffe,
Postfach 510153, D-30631 Hannover - Germany
3Dipartimento di Scienze della Terra, Via Laterina 8,
I-53100 Siena - Italy
4CBU Exploration/Corporate New Ventures, Santos Ltd., 60
Edward Street,
Brisbane QLD 4000 (GPO Box 1010) - Australia
Received 1 October 2003; accepted in revised form 18 May 2004
Abstract
- The high-grade basement of the northwestern Wilson Terrane at Oates
Coast is subdivided into three roughly north-south trending zones on
the basis of tectonic thrusting and differences in metamorphic
petrology. New results of detailed petrological investigations show
that metamorphic rocks of the central zone were formed in course of one
single, clockwise directed P-T evolution including a medium-pressure
and high-temperature granulite-facies stage at about 8 kbar and
>800°C, a subsequent isothermal decompression and a final stage
with retrograde formation of biotite + muscovite gneisses. In the
eastern and western zones the majority of metamorphic rocks experienced
clockwise oriented metamorphism at somewhat lower P-T conditions of
about 4-5.5 kbar and 700–800°C. While some rocks in both
zones did not reach the upper stability limit of muscovite + quartz,
granulite-facies rocks detected in parts of the western zone were
formed under P-T conditions similar to those of the central zone. New
SHRIMP data support an age for the metamorphic peak of 496-500 Ma in
the central zone (Henjes-Kunst et al., this volume). 40Ar-39Ar
dating of amphiboles and micas indicate a general trend to younger ages
from the west to the east of the basement complex, i.e. from 488–486 Ma to 472–469 Ma
for amphiboles and from 484–482 Ma to 466 Ma for micas. This is
explained by temporal differences in the retrograde metamorphic
evolution of the three zones in the course of the late-Ross-orogenic
thrust-related uplift of the basement complex, with the western zone
being exhumed earlier than the eastern zone.
*Corresponding author (uli.schuessler@mail.uni-wuerzburg.de)