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Palaeomagnetic, 40Ar/39Ar, and stratigraphical correlation of Miocene–Pliocene basalts in the Brandy Bay area, James Ross Island, Antarctica

Published online by Cambridge University Press:  17 August 2005

LEÓ KRISTJÁNSSON ,
MAGNÚS T. GUDMUNDSSON ,
JOHN L. SMELLIE ,
WILLIAM C. MCINTOSH  and
RICHARD ESSER
LEÓ KRISTJÁNSSON
Affiliation:
Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
MAGNÚS T. GUDMUNDSSON
Affiliation:
Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
JOHN L. SMELLIE
Affiliation:
British Antarctic Survey, NERC, High Cross, Madingley Rd, Cambridge CB3 0ET, UK
WILLIAM C. MCINTOSH
Affiliation:
New Mexico Geochronology Research Laboratory, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA
RICHARD ESSER
Affiliation:
New Mexico Geochronology Research Laboratory, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA
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Abstract

A revised stratigraphy of Cenozoic volcanic outcrops in the Brandy Bay area on James Ross Island is obtained by combining palaeomagnetic and stratigraphical anlysis with 40Ar/39Ar dating. The fieldwork was carried out between January and March 2002. Oriented palaeomagnetic samples were obtained from 17 volcanic units, the majority of samples being from lava-fed deltas. Individually the deltas are a few to several hundred metres thick and were formed during voluminous basaltic eruptions within an ice sheet or in a marine setting. Out of the sampled units, 15 carry a stable primary magnetization; six were of normal polarity and nine were reversely magnetized. Our 40Ar/39Ar dating constrains the emplacement of most of the Brandy Bay basalts to the Gilbert chron, with the youngest dated unit having an age of 3.95 Ma and the oldest 6.16 Ma. The mean palaeomagnetic field direction from 14 units has an inclination I = −76° and declination D = 352°, α95 = 7°. The results further suggest that the lava caps on some of the deltas have high remanent intensity and should generate recognizable aeromagnetic anomalies. The combination of palaeomagnetic and isotopic analysis with field mapping methods in a single field area is unique in Antarctica so far and demonstrates that the combination can yield rigorous local stratigraphy in a geographically remote volcanic terrain having discontinuous outcrops.

Keywords

lava-fed deltasNeogeneradiometric datingvolcanics
Type
Research Article
Information
Antarctic Science , Volume 17 , Issue 3 , September 2005 , pp. 409 - 417
Copyright
© Antarctic Science Ltd 2005

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