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Murfreesboro
Topographic Controls on the Duration of Sinkhole Flooding in Central Tennessee, USA
Mesoscale faults, macroscale folds, and inferred basement structures, Nashville dome, central Tennessee
ABSTRACT This guide explores relationships among macroscale folds, mesoscale structures, the Nashville dome, and an inferred Precambrian or Cambrian rift in the basement beneath the dome. The Nashville dome, central Tennessee, is an ~12,000 km 2 north-northeast–trending, elliptical cratonic uplift. A published crustal density model shows that a previously undescribed Precambrian or Cambrian rift, herein named the Nashville rift, probably runs from northwestern Alabama through the Nashville dome to southern Kentucky. Within the Nashville dome, macroscale folds and mesoscale structures of the Stones River and Harpeth River fault zones have been interpreted previously as the surface manifestation of subsurface normal faults. This road guide describes two previously undescribed inferred subsurface fault zones: the Marshall Knobs fault zone and the Northern Highland Rim fault zone. The Marshall Knobs fault zone, which is ~16.3 km long, is associated with ~35 m of structural relief, trends east-southeast, is down on the north side, and is inside the geophysically defined rift. The Northern Highland Rim fault zone consists of east-northeast–striking minor normal and reverse faults and a minor strike-slip fault exposed above the western margin of the geophysically defined rift. The authors hypothesize that the Northern Highland Rim fault zone may be the surface manifestation of the subsurface continuation of a macroscale fault previously mapped at the surface 25 km to the southwest. All of the inferred faults fit into a tectonic model in which they originally formed within a rift and later reactivated, accommodating extension of the uppermost crust during uplift of the Nashville dome.
A road guide to the Harpeth River and Stones River fault zones on the northwest flank of the Nashville dome, central Tennessee
Abstract The authors use mesoscale structures and existing 1:24,000 scale geologic maps to infer the locations of four macroscale NNW-striking blind normal faults on the northwest flank of the Nashville dome ~30 km south of downtown Nashville. The Harpeth River fault zone has an across-strike width of ~6 km, and, from west to east, includes the Peytonsville, Arno, McClory Creek, and McDaniel fault zones. All of the fault zones are east-side-down except for the west-side-down Peytonsville fault zone. Mesoscale structures are exposed within each fault zone and are observed at three stops along Tennessee State Route (S.R.)-840 and at an additional stop 1.8 km south of the highway. These structures include minor normal faults (maximum dip separation 3.8 m), non-vertical joints, and mesoscale folds. No faults are depicted on existing geologic maps of the zone, but these maps reveal macroscale folding of the contact between the Ordovician Carters Formation and the overlying Hermitage Formation. The authors use the orientation and amplitude of these folds to constrain the orientation and length of the inferred blind fault zones and the amount of structural relief across the zones. The longest fault zones are the Arno (13.2 km long) and McDaniel (11.6 km) fault zones, and the amount of structural relief across these zones peaks at 27 m and 24 m, respectively. The authors also use existing geologic maps to hypothesize that a second east-side-down blind normal fault zone (Stones River fault zone) is located ~27 km northeast of the Harpeth River fault zone. The authors interpret non-vertical joints at one stop as fault-related, and they interpret joints at a second stop as related to a hanging wall syncline. Both of these stops are within 4 km of S.R.-840.
Cuspidine-sodalite natrocarbonatite from Oldoinyo Lengai, Tanzania: a novel hybrid carbonatite formed by assimilation of ijolite
FORAMINIFERA OF HYDROCARBON SEEPS, GULF OF MEXICO
Permian-Triassic sequence in northwest Utah
The Twin Knobs #1 diatreme (TK1), delineated in 1981, is located 3.8 km southeast of Murfreesboro, Pike County, Arkansas and is within the northeast-trending group of pipes, plugs, and dikes that comprise the Murfreesboro district. TK1 is an elongate, bilobate pipe, oriented north-south, and approximately 0.05 km 2 in surface area. The diatreme penetrated the Lower Cretaceous Trinity Formation, whereas the Upper Cretaceous Tokio Formation overlies portions of the pipe. These relationships suggest an emplacement age of early Late Cretaceous, which is contemporaneous with isotopic ages obtained at the Prairie Creek lamproite complex (97 to 106 Ma; Gogineni and others, 1978). Rock types at TK1 include magmatic lamproites, sandy tuffs and breccias, and epiclastics. The magmatic breccias are porphyritic, with euhedral olivine, plus pyroxene and phlogopite phenocrysts set in a cryptocrystalline or glassy groundmass that also contains priderite, perovskite, and chromite. The sandy tuffs and epiclastics contain up to 30 percent quartz grains, in addition to lamproite and sedimentary rock fragments, set in a matrix of calcite, sericite, or fine-grained to cryptocrystalline glass. The average diamond grade from bulk sampling of the phases is 0.17 carats per 100 metric tons. Diamond crystal habits include octahedra, tetrahexahedra, macles, and fragments. Megacrysts of picroilmenite, chrome spinel, clinopyroxene, orthopyroxene, garnet, and nodules of eclogite, peridotite, Iherzolite, websterite, as well as crustal xenoliths, were recovered during sampling. Whole-rock and trace element geochemistry strongly suggests that Twin Knobs #1 has more affinities to olivine lamproite than to kimberlite.
Stratigraphy of the Lower Middle Ordovician of Tazewell County, Virginia
(A) Location of areas subject to sinkhole flooding in relation to the easte...
Lower Ordovician Sandy Zones (“St. Peter”) in Middle Tennessee
Geology of the Elmwood and Gordonsville Mines, Central Tennessee Zinc District – An Update
Abstract Major known sphalerite deposits of the Central Tennessee zinc district are localized in upper Lower Ordovician carbonate rocks of the Knox Group along the crest of the Cincinnati Arch, a broad northeast-trending regional uplift with gentle dips of only a few meters per kilometer (Figs. 1 and 2). Some deposits occur at the northeast edge of the Nashville Dome, the southern extension of the Cincinnati Arch (Fig. 3). Other deposits extend north and northeastward into the Cumberland Saddle, which separates the Nashville Dome from the Jessamine Dome of north-central Kentucky. The district occupies the northeast part of the Central Basin, and adjacent parts of the Eastern and Western Highland Rim physiographic provinces of north-central Tennessee and south-central Kentucky (Fig. 2). The crest of the Nashville Dome, from its apex near Murfreesboro, plunges gently northeastward into the Cumberland Saddle. Consequently, dips in the Elmwood-Gordonsville area are toward the northeast at about six meters per kilometer. Pre-Middle Ordovician erosional thinning of the upper Knox Group from west to east across the crest of the Nashville Dome indicates the pre-existence of a paleoarch with a crest east of the present crest of the dome (Stagg and Fischer, 1970; Fischer, 1977). A reconstruction of the crest of the dome as it existed during early Middle Ordovician time is shown in Figure 3, and illustrates this relationship.
The DeQueen Formation at the old Highland Quarry, Arkansas
Abstract To reach the Highland Quarry, start at the junction of Arkansas 24 and 27 at the north edge of Nashville, Arkansas. Drive north on Arkansas 27 (toward Murfreesboro) for 8.6 mi (13.9 km) and turn left (west) on Arkansas 26 (Fig. 1). The gravels at this junction are units of the Tokio Formation (Upper Cretace- US). Drive 1.6 mi (2.6 km) to the west on Arkansas 26 to the entrance of the quarry. Enter the quarry and ask permission at the mine office. The most convenient exposures are on the west wall of the quarry (Figs. 2, 3). This end of the quarry has been inactive for several years, but if you follow the road through the quarry for 2 mi (3.2 km) or so you will reach more recently developed pits.