First posted March 18, 2022 For additional information, contact: Florence Bascom Geoscience CenterU.S. Geological SurveyMail Stop 926A12201 Sunrise Valley DriveReston, VA 20192Contact Pubs Warehouse This 1:100,000-scale geologic map of the South Boston 30' × 60' quadrangle, Virginia and North Carolina, provides geologic information for the Piedmont along the I–85 and U.S. Route 58 corridors and in the Roanoke River watershed, which includes the John H. Kerr Reservoir and Lake Gaston. The Raleigh terrane (located on the eastern side of the map) contains Neoproterozoic to early Paleozoic(?) polydeformed, amphibolite-facies gneisses and schists. The Carolina slate belt of the Carolina terrane (located in the central part of the map) contains Neoproterozoic metavolcanic and metasedimentary rocks at greenschist facies. Although locally complicated, the slate-belt structure mapped across the South Boston map area is generally a broad, complex anticlinorium of the Hyco Formation (here called the Chase City anticlinorium) and is flanked to the west and east by synclinoria, which are cored by the overlying Aaron and Virgilina Formations. The western flank of the Carolina terrane (located in the western-central part of the map) contains similar rocks at higher metamorphic grade. This terrane includes epidote-amphibolite-facies to amphibolite-facies gneisses of the Neoproterozoic Country Line complex, which extends north-northeastward across the map. The Milton terrane (located on the western side of the map) contains Ordovician amphibolite-facies metavolcanic and metasedimentary gneisses of the Cunningham complex.Crosscutting relations and fabrics in mafic to felsic plutonic rocks constrain the timing of Neoproterozoic to late Paleozoic deformations across the Piedmont. In the eastern part of the map, a 5- to 9-kilometer-wide band of tectonic elements that contains two late Paleozoic mylonite zones (Nutbush Creek and Lake Gordon) and syntectonic granite (Buggs Island pluton) separates the Raleigh and Carolina terranes. Amphibolite-facies, infrastructural metaigneous and metasedimentary rocks east of the Lake Gordon mylonite zone are generally assigned to the Raleigh terrane. In the western part of the map area, a 5- to 8-kilometer-wide band of late Paleozoic tectonic elements includes the Hyco and Clover shear zones, syntectonic granitic sheets, and amphibolite-facies gneisses along the western margin of the Carolina terrane at its boundary with the Milton terrane. This band of tectonic elements is also the locus for early Mesozoic extensional faults associated with the early Mesozoic Scottsburg, Randolph, and Roanoke Creek rift basins.The map shows fluvial terrace deposits of sand and gravel on hills and slopes near the Roanoke and Dan Rivers. The terrace deposits that are highest in altitude are the oldest. Saprolite regolith is spatially associated with geologic source units and is not shown separately on the map.Mineral resources in the area include gneiss and granite quarried for crushed stone, tungsten-bearing vein deposits of the Hamme district, and copper and gold deposits of the Virgilina district. Surface-water resources are abundant and include rivers, tributaries, the John H. Kerr Reservoir, and Lake Gaston. Groundwater flow is concentrated in saprolite regolith, along fractures in the crystalline bedrock, and along fractures and bedding-plane partings in the Mesozoic rift basins.

Temperature dependent magnetoelastic properties of Fe100-xGex(5 < x < 18) single crystals have been measured. Tetragonal magnetostriction (3/2)lambda(100) measurements at x = 5.7, 12.1, 14.9, and 17.7 were performed between 78 K and 426 K and resonant ultrasound spectroscopy measurements were used to determine the shear elastic constant c' from 5 K to 300 K for x = 6.4, 7.2, 10.8, 14.6, 17.7, and 17.9. A clear distinction was observed between the temperature dependencies of lambda(100) for the A2 and D0(3) phases of Fe100-xGex. The elastic constant c' displays a monotonic decrease with concentration through the different phases (6 < x < 18) and at all temperatures. Experimental values of the tetragonal magnetoelastic coupling constant -b(1) at 81 K were remarkably consistent with theoretical values determined by density functional calculations at 0 K.

Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U–Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153±6Ma), hornblende monzonite gneiss (1149±19Ma), porphyroblastic granite gneiss (1144±2Ma), coarse-grained metagranite (about 1140Ma), and charnockite (>1145Ma?). These gneisses contain three Proterozoic deformational fabrics. Because of complex U–Pb systematics due to extensive overgrowths on magmatic cores, zircons from hornblende monzonite gneiss were dated using the sensitive high-resolution ion microprobe (SHRIMP), whereas all other ages are based on conventional U–Pb geochronology. Group 2 rocks are leucocratic and biotitic varieties of Marshall Metagranite, dated at 1112±3Ma and 1111±2Ma respectively. Group 3 rocks are subdivided into two age groups: (1) garnetiferous metagranite (1077±4Ma) and quartz-plagioclase gneiss (1077±4Ma); (2) white leucocratic metagranite (1060±2Ma), pink leucocratic metagranite (1059±2), biotite granite gneiss (1055±4Ma), and megacrystic metagranite (1055±2Ma). Groups 2 and 3 gneisses contain only the two younger Proterozoic deformational fabrics. Ages of monazite, separated from seven samples, indicate growth during both igneous and metamorphic (thermal) events. However, ages obtained from individual grains may be mixtures of different age components, as suggested by backscatter electron (BSE) imaging of complexly zoned grains. Analyses of unzoned monazite (imaged by BSE and thought to contain only one age component) from porphyroblastic granite gneiss yield ages of 1070, 1060, and 1050Ma. The range of ages of monazite (not reset to a uniform date) indicates that the Grenville granulite event at about 1035Ma did not exceed about 750°C. Lack of evidence for 1110Ma growth of monazite in porphyroblastic granite gneiss suggests that the Short Hill fault might be a Grenvillian structure that was reactivated in the Paleozoic. The timing of Proterozoic deformations is constrained by crystallization ages of the gneissic rocks. D1 occurred between about 1145 and 1075Ma (or possibly between about 1145 and 1128Ma). D2 and D3 must be younger than about 1050Ma. Ages of Mesoproterozoic granitic rocks of the northern Blue Ridge are similar to rocks in other Grenville terranes of the eastern USA, including the Adirondacks and Hudson Highlands. However, comparisons with conventional U–Pb ages of granulite-grade rocks from the central and southern Appalachians may be specious because these ages may actually be mixtures of ages of cores and overgrowths.

U-Pb ages of zircon from rhyolites of the Catoctin and Mount Rogers Formations demonstrate that rifting of the Laurentian continent to form the Iapetus Ocean was a prolonged event spanning 200 my involving two important pulses of extrusive igneous activity. Rhyolitic flows of the non-fossiliferous Catoctin and Mount Rogers Formations, long correlated with one another on the basis of similar stratigraphic constraints, are dated at 564 +/- 9 Ma and 758 +/- 12 Ma, respectively. A hypabyssal felsic dike, intruding Middle Proterozoic (Grenville) granitic gneiss basement and presumed to feed the Catoctin flows, is dated at 572 +/- 5 Ma. These new data invalidate previous geochronology that combined U-Pb data from both units to derive an upper intercept age of about 810 Ma. Ages of anorogenic granitoids of the Crossnore Complex (760-740 Ma), Robertson River Igneous Suite (730-700 Ma), and the Bakersville mafic dike swarm (734 Ma) are bracketed by the new ages presented herein, but all are closer to the age of the Mount Rogers than the Catoctin. All these data suggest a history of rifting in the central and southern Appalachians spanning 200 my near the end of the Late Proterozoic. The earliest pulses, represented by the Mount Rogers Formation and by granitoids, did not proceed to continental separation and are not recorded north of the Potomac River. The later pulse or pulses, which produced the areally more extensive Catoctin Formation, affected the area from Newfoundland (ages of 617-590 Ma) to North Carolina and resulted in the opening of the Iapetus Ocean.

A newly recognized suite of trondhjemite–tonalite and dacitic gneiss forms a 10 km wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif of Vermont. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the Middle Proterozoic regional deformation that affected the Mount Holly Complex. U–Pb zircon dates indicate ages as great as 1.35 Ga for crystallization of the volcanic protoliths and for intrusion of crosscutting trondhjemite. Tonalitic plutonism continued until 1.31 Ga.Map-scale contacts between the trondhjemitic–tonalitic–dacitic gneisses and the paragneiss sequence of the Mount Holly Complex are sharp, suggesting that the volcanic rocks of the trondhjemite–tonalite suite underlie the paragneiss units and do not intrude them. These relationships suggest that the trondhjemite–tonalite suite is either considerably older than, and unconformable beneath, the paragneiss cover rocks or represents a volcanic edifice slightly older than the deposition of the sedimentary precursor to the paragneiss units. The paragneiss and tonalite–trondhjemite gneisses are both intruded by younger granitoids that were intruded at about 1.25 Ga during strong dynamothermal metamorphism.The trondhjemitic gneisses of the Mount Holly Complex of Vermont have high Al2O3 and low Yb contents and light rare-earth element enrichment patterns that are more characteristic of continental than oceanic volcanic arcs. The Mount Holly intrusives and volcanics may have formed during 1.35–1.31 Ga ensialic volcanic-arc activity, contemporaneous with ensimatic arc activity during the early part of the Elzevirian phase of the Grenville orogeny. In Vermont, later deformation and granite intrusion at about 1.25 Ga coincide with the major pulse of the Elzevirian orogeny and associated trondhjemitic plutonism in the Central Metasedimentary Belt of eastern Canada.

Low-angle 25° to 35° dips have been determined for the border fault of the Newark basin near Riegelsville, Pennsylvania, on the basis of a Vibroseis profile and two continuously cored drill holes across faults at the basin margin. A group of moderately strong planar reflections in a zone 0.5 km thick in gneiss and carbonate rocks of the footwall block coincides with the updip projection of imbricate fault slices and mylonites associated with the Musconetcong thrust system of Drake et al. (1967). Contrasts in acoustic impedance among mylonitic dolostone and mylonitic gneiss and their protoliths, determined from measurements on samples from a third cored hole, are sufficiently large to account for reflections seen in the footwall block. Analysis of drill core and surface outcrops supports the conclusion that low-angle extensional faulting in the early Mesozoic was localized by reactivation of Paleozoic imbricate thrust faults in the basement rocks. Extension in the northwest-southeast quadrant was approximately perpendicular to the strike of the ancient thrust faults in eastern Pennsylvania. The data presented here are the most explicit three-dimensional information obtained thus far in the eastern United States in support of the concept of fault reactivation in controlling formation of early Mesozoic extensional basins.

As reported previously, 1 mashed potato powder is subject to two types of deterioration‐‐‐the development of a brown colour and charred taste at high storage temperatures, and the development of an ' off' flavour. The present paper is concerned with the latter type.