Figures 2 and 3 show the generalized lithology and structure of the Florida basement, respectively (see Part Two for further discussion). A comparison of these figures with Figure 1 reveals that intrusions of basalt and diabase most commonly occur in the Mesozoic basins of Florida and are least common in the igneous terrane of central Florida. The exact intrusive form of each tholeiitic body is unknown. In general, these rocks occur as dikes, sills (or sheets) and flows, but detailed core descriptions, additional petrographic analyses and geophysical data are required in order to be more specific.
The variation in depth to these mafic rocks is predominantly controlled by their geographical position relative to the Peninsular Arch. For example, diabase is encountered at a depth of approximately 3,500 feet in Columbia County, whereas in Wakulla and Hardee Counties, diabase or basalt is present at a depth of approximately 12,000 feet (Figure 3 and Table 4). The position (depth) of these rocks relative to
............
N
...............
EXPLANATION
V::: Triassic red-beds and diabase intrusions
Early to Middle Mesozoic hypabyssal and extrusive mafic rocks Ordovician-Devonian sedimentary rocks Late Precambrian-Early Cambrian felsic intrusive rocks
--1 Late Precambrian-Early Cambrian felsic extrusive rocks
Approximate contact
9 Denotes areas for which there are conflicting descriptions or a lack of data
U
0 25 50 MILES
0 40 80 KILOMETERS
Figure 2. Lithology of the pre-Middle Jurassic Florida basement surface.
9