HR: 1340h
AN: T13C-1467    [Abstracts]
TI: New K/Ar ages on Martinique Island: A Record of the Lesser Antilles Island Arc Evolution
AU: * GERMA, A
EM: aurelie.germa@u-psud.fr
AF: Laboratoire de geochronologie, Batiment 504, 1er etage Universite Paris Sud, ORSAY, 91405, France
AU: Quidelleur, X
EM: xavier.quidelleur@u-psud.fr
AF: Laboratoire de geochronologie, Batiment 504, 1er etage Universite Paris Sud, ORSAY, 91405, France
AU: LABANIEH, S
EM: shasa.labanieh@ujf-grenoble.fr
AF: Laboratoire de Geodynamique des Chaines Alpines, Universite Joseph Fourier, Maison des geosciences 1381, rue de la Piscine, Saint Martin d'Heres, 38400, France
AU: CHAUVEL, C
EM: Catherine.Chauvel@ujf-grenoble.fr
AF: Laboratoire de Geodynamique des Chaines Alpines, Universite Joseph Fourier, Maison des geosciences 1381, rue de la Piscine, Saint Martin d'Heres, 38400, France
AB: We present here a combined geochronology, geochemistry and geomorphology study of Martinique Island based on carefully selected lava flows and domes sampled during two field trips in spring 2006 and 2007. Our aim is to better constrain the whole volcanic evolution of the island, with a special emphasize on the timing of its initiation in Oligocene, and its westward migration during Miocene. The Lesser Antilles island arc results from the westward subduction of the Atlantic plate beneath that of the Caribbean. Whereas in the southern part of the arc volcanic activity occurred along a single SW-NE axis, the northern part, which experienced a westward jump of the volcanic front, is divided in two distinct branches. Due to its central position where the two northern arcs merge, Martinique is the Lesser Antilles island where the most complete history of the arc can be found. Volcanism has there been almost continuous and outcrops from east to west, without superimposition neither apparent hiatus such as observed for other islands of the arc. Our first results using the K-Ar Cassignol-Gillot technique, which has demonstrated its suitability for Antilles lavas at La Guadeloupe Island (Samper et al., 2007), show that the oldest products are older than 23 Ma. They are situated in the eastern and south-eastern peninsulas and interpreted as the onset of subaerial volcanism in the Lesser Antilles island arc. The NW-SE trending Vauclin- Pitault chain, in the central southern part, is constituted of hyaloclastites attesting for a submarine emplacement. Within the whole arc, it is though to be the only outcropping products emitted during the westward arc migration. Our ages constrain its activity between 17 and 7 Ma. During Miocene, volcanism pursued to the southwest with emplacement of small monogenetic volcanoes aligned along active faults between 6 Ma and 340 ka. In the meantime, the northern compartment has been constructed with the Morne Jacob volcano (5.5 – 1.5 Ma), Pitons du Carbet (1 Ma – 340 ka), Mont Conil (550 – 200 ka) and Mount Pelée, the active volcano. This northern compartment experienced flank collapses on the western flank of Mount Pelée at about 100 ka, 25 ka and 9 ka (Le Friant et al., 2003). Our new ages confirm that the western flank of Pitons du Carbet was affected by a collapse event at 337 ka, and that the eastern flank of Morne Jacob also, between 2.11 and 2.04 Ma, from dated lava flows sampled outside and inside the structure, respectively. Strong geochemical variations in major and trace elements occurred between pre and post collapse volcanism, suggesting that conditions within the superficial magmatic chamber was modified by this event. Finally our set of about 80 new ages, ranging between 23 Ma and 10 ka, allow us to revise the chronology of the different volcanic phases of Martinique island, and to identify episodes of high production rate magmatism associated with either regional geodynamic changes and/or flank collapse events.
DE: 1065 Major and trace element geochemistry
DE: 1115 Radioisotope geochronology
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 9325 Atlantic Ocean
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: 2007 Fall Meeting