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North-Central Section (44th Annual) and South-Central Section (44th Annual) Joint Meeting (11–13 April 2010)

Paper No. 2
Presentation Time: 8:30 AM-12:00 PM

DATING RHYOLITE FLOWS IN THE NOUMEA BASIN, NEW CALEDONIA IN ORDER TO CONSTRAIN THE BREAKUP OF THE EASTERN GONDWANA MARGIN


ALEXANDER, Aaron M., Department of Geological Sciences, Ball State University, Ball State University AR 117, Muncie, IN 47306, NICHOLSON, Kirsten N., Geology, Ball State University, Muncie, IN 47306, SIMONETTI, Antonio, Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, MAURIZOT, P., BRGM-BGNC, Service des Mines et de l'Energie, BP 56, Noumea Cedek, 98845, New Caledonia and CLUZEL, D., Insititue des Sciences de la Terre d'Orleans, Institut des Sciences de la Terre, BP 6759, Orleans cedex 2, 45067, France, amalexander@bsu.edu

North of the city of Noumea, New Caledonia, lays the geologic terrain known as the Noumea Basin. The Noumea Basin is one of a few in-situ examples of late Cretaceous volcanism in the region. It is significant because few rocks are preserved and accessible that were formed during the break-up of the eastern Gondwana margin. Hence the chemistry and age of these rocks helps to constrain the tectonic configuration during this time period.

The Noumea Basin itself contains various types of sediments, along with numerous igneous features of basaltic and rhyolitic flows. These igneous features are lens shaped, have a general southeast-northwest trend, and have a tendency to follow the ridges of the mountains and hills. The rhyolite lavas generally overlie the basaltic lavas, forming large hills, however in some instances there are rhyolite flows interbedded within the basaltic flows. There are volcanic conglomerates and baked zones immediately surrounding the majority of the flows and a consistent pattern of flow orientations, which indicate the flows are in situ.

The Noumea Basin lavas are thought to be around 100 million years old, based primarily on limited paleontological evidence. Dating the basalts has been hindered by the fine grain size and the pervasive lower greenschist alteration. Therefore we have begun a study of the interbedded and overlying rhyolitic lavas in order to constrain the age of volcanism within the basin.

The petrographic analyses show that the rhyolite lavas contain phenocrysts of quartz (60%), plagioclase (25%), and sanidine (15%). The ground mass mostly consisted mostly of both K and Na feldspars, micas, and some hornblend. The rocks were pervasively metamorphosed and contained a significant amount of clay minerals and chlorite.

Preliminary analyses, using LA-ICPMS has only provided one sample with large enough zircons for dating. This sample yielded 4 zircons with ages of 88.4 million years. Within the next two months we plan to analyze more samples in hopes of further constraining the age of volcanism within the Noumea Basin, and therefore the processes active along the eastern Gondwana margin during the late Cretaceous.

Session No. 45--Booth# 36

Tectonics, Volcanology, Petrology (Posters)
Tuesday, 13 April 2010: 8:30 AM-12:00 PM
Taneycomo A (Branson Convention Center)
Geological Society of America Abstracts with Programs. Vol. 42, No. 2, p.105
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