Magma emplacement into the Lemptégy scoria cone C

Authors: M S Petronis A Delcamp B van Wyk de Vries

Publish Date: 2013/09/13

Volume: 75, Issue: 10, Pages: 753-

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Abstract

The Lemptégy volcano is a small monogenetic scoria cone located in the Chaîne des Puys Auvergne France which erupted about 32000 years ago A first edifice Lemptégy 1 formed during a trachybasalt eruption as a group of satellite vents of the Puy de Gouttes scoria cone A second trachyandesitic edifice Lemptégy 2 formed soon after and completely covered Lemptégy 1 with an 80mhigh breached cone Since 1946 the Lemptégy volcano has been quarried for scoria and today offers unprecedented threedimensional exposure of the subvolcanic plumbing system To map the internal flow architecture of the plumbing system and to study the subvolcanic deformation of Lemptégy 2 structural mapping petrographic observations anisotropy of magnetic susceptibility AMS rock magnetic and paleomagnetic data were collected Field structural mapping and thin section study of tension gashes Riedel shears striations as well as ductile shear zones and bubbles allow the direction and sense of the magma flow to be determined Twenty AMS sites were established in ten dikes one to four sites in each dike with 504 specimens analyzed and 479 specimens used to infer magma flow patterns Structural data the maximum susceptibility axis K 1 and the imbrication of the magnetic foliation K 1–K 2 planes indicate both upward and downward sense of flow as well as flow toward and away from the central vent Rock magnetic experiments reveal that a cubic Fe–Ti oxide phase likely lowTi titanomagnetite is the principal magnetic phase carrying both the remanence and anisotropy Paleomagnetic data from some sites yield statistically distinct at the 95  confidence level remanence directions while at other sites the data are indistinguishable at the 95  confidence level The paleomagnetic results observed steeply tilted scoria layers internal unconformities and faults show that as each dike was emplaced it displaced earlier dikes evidencing subvolcanic deformation The Lemptégy 2 volcano shares similarities in terms of inferred eruption style and structures with other scoria cones such as Cerro Negro Nicaragua and thus provides an excellent field laboratory to investigate active scoria cones worldwidePartial support provided by the National Geographic grantsinaidof research 810606 BPClermont International Visiting Professor Award Petronis et al 2004 and the support from all the personnel at the Lemptegy volcano http//wwwvolvictourismecom/HTML/sites/volcan de lemptegy gbhtm are acknowledged The authors also acknowledge the efforts of the associate editor and an anonymous reviewer for constructive comments on the manuscript Observations at Cerro Negro were done with Pedro Perez “El Caminante” while working with INETER LiDAR image used for figures was generated by Stéphane Petit at GEOLAB UMR6042 at http//wwwveodis3dcom

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