Structure Of Piton De La Fournaise Volcano (La Reunion Island, Indian Ocean) From Magnetic Investigations, An Illustration Of The Analysis Of Magnetic Data In A Volcanic Area

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Journal Article: Structure Of Piton De La Fournaise Volcano (La Reunion Island, Indian Ocean) From Magnetic Investigations, An Illustration Of The Analysis Of Magnetic Data In A Volcanic Area

Abstract
The active Piton de la Fournaise volcano (La Reunion Island, western Indian Ocean) is a basaltic shield built on the flank of the larger and older Piton des Neiges volcano whose early activity was basaltic but ended with eruption of differentiated alkaline lavas. Previously, few data were available to define the internal and deep structure of Piton de la Fournaise. This report contains interpretation of magnetic data that take the first steps into this domain. The data consist of an aeromagnetic survey at a constant elevation of 3048 m - 10 000 ft - (Piton de la Fournaise rises to a height of 2637 m) and a shipborne magnetic survey in the eastern coastal area of the Island. A first model shows that the island does not behave as a uniformly magnetized body. In order to enhance the effects of the internal magnetic contrasts, a correction of the topographic effects has been attempted. To this purpose, it has been possible to make a good estimation of the superficial terrain magnetization in the following way: main features of the relief, such as caldera ramparts and deep valleys, induce short-wavelength anomalies, analysis of which provides the apparent magnetization of the whole formations exposed in the cliffs. These determinations are used to compute a realistic magnetic model of the topography, the effect of which is removed from the observed data to obtain a map of the residual anomalies related to internal magnetic variations. The main magnetic contrasts are attributed to the differences in intensity of magnetization between the dikes and the surrounding lava flows. Under volcanic vent areas, such as rift zones, dikes cluster at depth in complexes and are the sources of high-amplitude magnetic anomalies. In the Piton de la Fournaise area, dike complexes can be located in the central and eastern parts of the summit caldera and on northeastern and southeastern rift zones. A third, northwestern rift zone, oriented in the direction of Piton des Neiges, is well developed south and southeast of the Palmistes Plain graben. In the northeast part of the caldera, the circular depression of the Osmondes Plain corresponds to the convergence zone of the structural trends of the northeastern rift, the caldera dike complex and the northwestern rift. The attenuation of anomalies observed above the summit area of Piton de la Fournaise may be related to the presence of rocks at a temperature above the Curie point. The orientation of the caldera dike complex may possibly be controlled by the gravitational stresses of the island. The intrusion of dikes in that highly active part of the volcano will then displace the unbuttressed east flank seaward, much in the manner of Kilauea volcano (Swanson et al., 1976), thus explaining the origin of the broad landslide of Grand Brule. Further less active northeast and southeast rift zones may control the southward and northward extension of the Grand Brule structure. The formation of the Palmistes Plain graben may be related to similar phenomena

Authors 
Jean-Francois Lenat and Maurice Aubert








Published Journal 
Journal of Volcanology and Geothermal Research, 1982





DOI 
Not Provided
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Citation

Jean-Francois Lenat,Maurice Aubert. 1982. Structure Of Piton De La Fournaise Volcano (La Reunion Island, Indian Ocean) From Magnetic Investigations, An Illustration Of The Analysis Of Magnetic Data In A Volcanic Area. Journal of Volcanology and Geothermal Research. (!) .