Raum Fault Zone (New Name)

Part of the Fluorspar Area Fault Complex
Old Name: Raum Fault

Location

T11S, R7E, Pope County to T14S, R3E, Massac County (pl. 2)

References

Baxter et al. 1967, Weibel et al. 1993

Description

The Raum Fault was named by Baxter et al. (1967), but it is a zone of several parallel faults and is renamed Raum Fault Zone. It strikes northeast and is parallel to the Lusk Creek Fault Zone, about 3 miles (5 km) northwest, and the Hobbs Creek Fault Zone, 2 to 3 miles (3-5 km) southeast. The Raum Fault Zone merges at its northeast end with faults radial and concentric to Hicks Dome. Southwestward, it has been mapped to the edge of the Mississippi Embayment and it probably continues beneath the embayment sediments. Several faults obliquely interconnect the southwestern Raum and Lusk Creek Fault Zones.

In Sections 13 and 14, T12S, R6E, Pope County, the Raum Fault Zone consists of two parallel faults a few hundred feet (approximately 100 m) apart at the surface. Pennsylvanian rocks crop out on both sides of the fault zone and display little or no relative displacement. Between the two faults is a narrow slice of Chesterian rock that is upthrown several hundred feet relative to rocks outside the fault zone. These strata and Pennsylvanian rocks adjacent to the faults dip steeply northwest (fig. 60). Surface exposures and test drilling for fluorspar indicate that the faults themselves also dip steeply toward the northwest (Weibel et al. 1993).

The configuration of the Raum Fault Zone is best explained by two opposing episodes of dip-slip motion. The first involved reverse faulting with the northwest side upthrown. The second was normal and nearly canceled the earlier reverse movement, returning the fault blocks nearly to their original positions. Narrow slices of Mississippian rock were sheared off the hanging wall in the second episode and were left stranded high within the fault zone. Thus, the Raum Fault Zone is virtually a mirror image of the adjacent Lusk Creek Fault Zone. A proprietary seismic reflection profile indicates that the Raum Fault Zone intersects the Lusk Creek Fault Zone in Upper Cambrian or Lower Ordovician strata, whereas the Lusk Creek Fault Zone continues into Precambrian basement (fig. 50). The Raum Fault Zone thus is antithetic to the Lusk Creek Fault Zone and shared its post-Pennsylvanian history.

Figure(s)

Figure 60   Cross section of the Raum Fault Zone, as interpreted from an outcrop study in SW NW, Section 13, T12S, R6E, Pope County. Test borings for fluorspar and a seismic reflection profile confirm the steep northwest dip of faults. Net displacement across the fault zone is slight, but the central slice of Mississippian rock is upthrown. Configuration of the fault zone indicates initial reverse movement followed by normal faulting, during which the northwest block dropped back to approximately its original position. Plate 2   Fluorspar Area Fault Complex and Shawneetown Fault Zone