Saut D'Eau And Thomazea
Two areas of alkaline lavas of about 18x2 km and 5x2 km are located some 30 km north-northeast and northeast of Port au Prince. They lie north of the Cul de Sac graben and overlie Eocene to Miocene sedimentary rocks.
Two areas of alkaline lavas of about 18x2 km and 5x2 km are located some 30 km north-northeast and northeast of Port au Prince. They lie north of the Cul de Sac graben and overlie Eocene to Miocene sedimentary rocks.
The Kaituma intrusion of peralkaline quartz syenite covers about 70 km2 and appears to grade westwards into biotite granite. It comprises microcline perthite, albite-oligoclase, quartz, aegirine, arfvedsonite, biotite and accessory sphene, orthite, magnetite and apatite.
Makarapan forms a mountain some 8 to 9 km in diameter and rising to 800 m. Two smaller hills, Urume and Wurumu, lie to the east, but all three areas probably belong to the same intrusion of riebeckite granite.
The Muri alkaline complex is centred on the Muri Mountains, which run along the Guyana-Brazil border, and is emplaced in Precambrian granodiorite and gneiss which are locally fenitized.
Sumaco is an active strato-volcano forming a lofty, symmetrical cone rising to 3828 m from a low elevation on the Amazonian plain. It has a crater within which lies a central cone with a smaller crater of 300x400 m and a depth of 100 m (in 1925); there is a small crater lake.
Limburgitic and alkali olivine basalt flows cover about 85 km2 in an area northwest of San Juan de la Maguana filling depressions in the underlying Tertiary Loro conglomerate.
In the vicinity of the village of Atenas along the Rio Grande de Tarcoles occurs a basanite flow associated with andesites, ignimbrites and tuffs.
In the area between the villages of Siquirres and Turrialba along the Rio Reventazon a number of teschenite sills outcrop which are associated with lavas of alkali basalt and basanite. The sills are up to 40 m thick and are emplaced in Tertiary marine sediments.
Along the northeastern side of the Cordillera de Talamanca, particularly on the Fila de Matama and in the Rio Chirripo, occur lavas of alkali basalt, basanite and nephelinite. The distribution is not known and no petrographic descriptions are available.
This is a prominant hill which is probably an intrusion of nepheline syenite. No details are available.