The northern part of the island of Martinique in the Lesser Antilles consists of three overlapping volcanic cones: Mont Pelée, Pitons du Carbet, and Morne Jacob. The southern half of the island consists of a complex of older, smaller, more deeply dissected and weathered centers. The deposits of the island are largely volcaniclastic, originating as nuée ardente pyroclastic flows, air-fall material, explosion breccia, mudflow, and lahars. Many of the deposits cannot be grouped as above because of extensive reworking shortly after their eruption and deposition in an extremely friable and uncompacted state. Lava flows, domes, spines, and pitons compose only a small part of the exposed volume of the island. Chemically, the majority of rocks are close to 60 percent ±3 percent SiO2, but distinctly different abundances of alkali elements are present in the different centers. The older Morne Jacob lavas have more than double the K, Rb, Ba, and Th of the Mont Pelée rocks, whereas the latter have higher Na and Sr. Other element abundances are similar. Mont Pelée is thus one of the low-K andesite series typical of island arcs, whereas Morne Jacob tends toward the Andean type in alkali content, although still composed of calcic andesite.

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