Metasomatism and Intrusion in Jamaica

Abstract

The nearest known pre-Cretaceous rocks to Jamaica are Jurassic in Western Cuba, and Carboniferous in Colombia, Venezuela, and Honduras, all about 500 miles away. The evolution of Jamaica seems to have been somewhat as follows. Andine (?) orogenesis on or near the site took place, accompanied by magmatic invasion; the rocks are nowhere seen “in situ”, but they have supplied pebbles of granite, granodiorite, porphyry, hornfels, vein stuff, and limestones, more or less foliated or marmorized, but not gneisses nor schists. There is no evidence that any of them are older than Cretaceous, but they go to form the oldest beds of the island, the massive Blue Mountain purple conglomerates whose composition varies from place to place and of which no natural base is seen. Interbedded with these conglomerates are fossiliferous shales and Rudist limestones of Upper Senonian to Maestrichtian age. Low down, however, there is in Eastern Jamaica a bed of algal and foraminiferal limestone, without Rudistae, which was partly torn up and incorporated as rolled pebbles in the conglomerate. Some of these pebbles contain Camerina dickersoni Palmer, a foraminifer of Upper Cretaceous age, so the pebbles are but little older than the conglomerate containing them. Laramide orogenesis took place and this series was invaded by granodiorite and other intrusions. The uplifted area was eroded and some of the igneous and associated Cretaceous rocks exposed to denudation. Depression occurred and Lower or Lower Middle Eocene Carbonaceous shale or Richmond Beds, a Flysch-like series of limestones, shales, and conglomerates, were deposited.