Postgraduate Report
2007 ANNUAL AMERICA GEOPHYSICAL UNION FALL MEETING
Matthew De Paoli
University of Sydney, NSW
2007 AIG Postgraduate Bursary Winner
In December 2007, I travelled to the United States from Australia for the 2007 Annual
American Geophysical Union (AGU) Fall meeting held at the Moscone Centre, San
Francisco. The AGU meeting is viewed as a major gathering on the geophysical and
geological community calendars. Every year the meeting attracts a large number of
international delegates and is seen as an excellent opportunity to present recent results
and to initiate new collaborations and networks with North American and European
colleagues in a vast variety of fields in Earth and physical sciences.
The AIG Postgraduate bursary contributed towards my flight from Australia to the US
and provided dearly needed funds to assist my attendance at the AGU meeting. The
bursary funds enabled me to present a poster on my postgraduate research dealing with
the high-pressure geology of Breaksea Sound, Fiordland, New Zealand. In particular,
the poster detailed the unusual occurrence of interlayered granulites and eclogites,
including in-depth research on the petrological and textural relationships of these
diverse assemblages and their preliminary thermobarometric results. The uniqueness of
these assemblages and their intimate existence together, along with the significantly
higher pressure and temperature estimates obtained in the current research attracted
significant attention in the metamorphic petrology session of the meeting, enabling me
to gain valuable critical feedback from my fellow researchers.
I wish to convey my sincere thanks to the Australian Institute of Geoscientists for their
generous support without which I would not have been able to make the long and
arduous journey to attend, what was, an excellent meeting.
ABSTRACT: Interlayered High-P Granulites and Eclogites, Fiordland, New Zealand
As lithospheric plates are subducted and thickened, rocks are metamorphosed under
high-P and UHP conditions to produce granulite and eclogite facies metamorphic rocks.
Serendipitous circumstances may facilitate chemical equilibrium at such conditions, but
it is rarely entirely achieved. Granulites and eclogites can preserve, in their distinctive
mineral assemblages and textures, a record of the pressure, temperature and deformation
conditions experienced during subduction, crustal thickening, and subsequent
exhumation.
Granulite facies rocks reflect the highest temperature conditions, whereas eclogite facies
rocks are most commonly associated with subduction and reflect highest-pressure
conditions associated for orogenic metamorphism. Eclogite facies assemblages may also
reflect upper mantle conditions. Rocks that record assemblages from both the granuilte
and eclogite facies, evidence of the garnulite-eclogite facies transition, are extremely
rare. These types of rocks are of interest as they represent the deepest parts of Earth’s
crust affected by orogenesis and encapsulate processes related to nascent crust and
lower crust – upper mantle interaction.
Fiordland, New Zealand, offers a unique cross-section through the lower crust root of a
Cretaceous magmatic arc. We have recently identified a suite of unusual rocks that
contain interlayered eclogite and granulite facies assemblages. On the basis of published
literature, rocks with assemblages similar to those occur in relatively few localities – the
Bohemian massif (Czech Republic) and the Western Gneiss Region (Norway). Peak
metamorphic conditions accompanied by the formation of penetrative gneissic textures
displaying interstitial partitions of mafic to felsic bearing assemblages – garnetomphacite-rutile (mafic) and antiperthite-plagioclase-quartz-rutile-kyanite (felsic).
Preliminary thermobarometric results for these uncommonly well preserved high-P
high-T orthopyroxene-bearing rocks indicate P≈17–19kbar, and T≈ 850–920°C.
This abstract has been published in a modified form as:
De Paoli M.C., Clarke, G.L., Klepeis , K.A., and Turbull, I., 2007. Interlayered high-P
Granulites & Eclogites, Fiordland, New Zealand. , Eos Trans. AGU, 88(52), Fall Meet.
Suppl., Abstract