The Ozark region of the United States midcontinent is host
for the largest Mississippi Valleytype (MVT) lead-zinc province
in the world. This region, located north of the Ouachita foldbelt
and covering more than 240,000 km2, includes the world-class
MVT districts of Old Lead Belt, Viburnum Trend, and Tri-State,
and the smaller Northern Arkansas, Central Missouri, and Southeast
Missouri barite districts (fig. 1). Leach and Rowan (1986) presented
evidence that brine migration from the Arkoma foredeep (fig.
1), in response to Late PennsylvanianEarly Permian orogenesis
in the Ouachita foldbelt, was responsible for the formation of
MVT deposits in the Ozark region. However, we are becoming increasingly
convinced that a major component of fluid flow for the lead-rich
deposits in the Viburnum Trend and Old Lead Belt in southeast
Missouri was from the Reelfoot rift zone (Farr and Land, 1985;
Farr, 1989a, 1989b; Erickson and others, 1988; Diehl and others,
1991; Goldhaber and Mosier, 1989; Viets and Leach, 1988, 1990;
Horrall and others, 1993). In addition, Shelton, Bauer, and Gregg
(1992) suggested the possibility of brine migration from the
We report herein a reconnaissance fluid inclusion study of
epigenetic sparry dolomite from Upper Cambrian and Lower Ordovician
strata in two drill cores located in the Reelfoot rift complex,
drill cores along the southeastern flank of the Ozark dome and
the western flank of the Nashville dome, and samples from a rock
quarry in northern Arkansas. In addition, conodont thermal-alteration
studies were conducted where possible to provide additional thermal
constraints. The fluid inclusion data, combined with conodont
thermal-alteration studies, indicate that hot and highly saline
brines were present in the Reelfoot rift complex during the Paleozoic.
Cathodoluminescent (CL) zoning in sparry dolomite from the Reelfoot
rift is similar to zoning in sparry dolomite in the Ozark region
that is closely associated with MVT sulfide deposition. If the
sparry dolomite studied in this report is temporally related
to sparry dolomite in the Ozark region, then these data provide
insights into the possible ore-fluid migration with respect to
the tectonic history of the rift complex. Because many of our
interpretations are based on previous studies of fluid inclusions
and sparry dolomite in the Ozark region, we summarize the most
important aspects of these earlier reports. In addition, we present
a brief overview of the complex geology and tectonics of the
Reelfoot rift to provide insight into possible tectonic implications
of our data.
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