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The geology of approximately 5000 sq km in central Dominican Republic has been mapped and described. Metamorphosed, pre-Middle Albian(P), volcanic rocks of the greenschist facies crop out in a belt that trends northwest-southeast across the mapped area. The metamorphosed rocks occur as two distinct rock types: metamorphosed mafic volcanic rocks (Duarte Formation and unnamed rocks northeast of Jarabacoa); and a unit composed predominantly of metamorphosed quartz keratophyre (Maimon Formation). A fault zone containing a large elongate body of serpentinized peridotite separates the two metamorphosed units. At the east end of the Cordillera Central, the trend of the peridotite and of the schistosity in the metamorphic rocks is approximately N. 40° W., but near La Vega in the northwest corner of the area studied the trend changes to N. 70° W. Unconformably overlying the metamorphosed Duarte Formation are vitric basalts of the Siete Cabezas Formation, and unconformably overlying the Maimon Formation are pyroxene andesite and tuff of the Peravillo Formation. The Siete Cabezas and Peravillo Formations are pre-Tertiary and probably also pre-Middle Albian.

The oldest dated rocks are Lower Cretaceous Middle Aptian-Middle Albian, and these occur at the base of the known Cretaceous section. The sequence began with the extrusion of various volcanic types that constitute the Los Ranchos Formation. Minor shallow-water sedimentary rocks and radiolarian tuff occur interlayered in the volcanic rocks. Deposition of the Hatillo Limestone of Early Cretaceous age followed the eruption of Los Ranchos rocks. Fine tuffs of the Las Lagunas Formation (Lower Cretaceous?) were deposited conformably upon the limestone.

Cenomanian to Lower Maestrichtian deposits of coarse tuff, fine tuff, lapillituff, and quartz keratophyre comprise the Tireo Formation. Uplift and erosion seem to have taken place in Late Campanian to Early Maestrichtian; and middle to late Maestrichtian(?) limestone and clastic deposits of the Las Canas Limestone, Don Juan Formation, and other unnamed formations were deposited unconformably upon older rocks. Deposition of the Las Canas Limestone (latest Cretaceous) was followed conformably by Paleocene to middle Eocene wacke, tuff, and algal limestone of the Loma Caballero Formation. Early Eocene tuff, mudstone, limestone, and limestone pebble conglomerate of the Los Banitos Formation occur south of the Loma Caballero Formation. Deposits of shale, siltstone, sandstone, and limestone were also accumulating in early Eocene time in a basin to the west on the south side of the present Cordillera Central. Eocene volcanism and uplift near central Dominican Republic are in marked contrast to Eocene limestone deposition in the northern and southern parts of the country and in Haiti.

Major faulting and northeastward thrusting occurred in late Eocene time. Oligocene and younger sections are dominated by clastic sedimentary rocks which fill deep basins north and south of the present Cordillera Central. An episode of deformation in late Oligocene time affected parts of the Dominican Republic.

Plutons of tonalite (foliated), hornblendite, and augite norite intrude the Duarte Formation and are considered pre-Middle Albian(?). The serpentinized peridotite mass appears to have been emplaced after these intrusive rocks and is also considered to be pre-Middle Albian(?). Unfoliated tonalite plutons (some batholiths) of Maestrichtian-middle Eocene age intrude rocks as young as Campanian. Stocks and sills of pyroxene diorite and gabbro were intruded in the late Eocene.

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