Abstract For as long as geologists have looked at deformed rocks, they have grappled to understand the mechanical origins of deformation. Natural systems are inherently complex so that, for many, purely geometric and kinematic approaches have sufficed. However, we know that stress within the brittle upper crust controls the nucleation, growth and reactivation of faults and fractures, induces seismic activity, affects the transport of magma and modulates structural permeability, thereby influencing the redistribution of hydrothermal and hydrocarbon fluids. An endeavour of structural geology and seismotectonics is therefore to reconstruct states of stress and their evolution over geological time from observations of the final products of rock deformation. Experimentalists endeavour to recreate structures observed in nature under controlled stress conditions. Earth scientists studying earthquakes attempt to monitor or deduce stress changes in the Earth as it actively deforms. All are building upon the pioneering researches and concepts of Ernest Masson Anderson dating back to the start of the 20th century. His insights, encapsulated in a small number of research papers and in the book The Dynamics of Faulting and Dyke Formation with Applications to Britain , continue to influence investigations in structural geology, seismology, rock mechanics, processes of hydrothermal mineralization and physical volcanology. This volume celebrates this legacy.

Deposits in the Gona Paleoanthropological Research Project (GPRP) area in east-central Ethiopia span most of the last ~6.4 m.y. and are among the longest and most complete paleoenvironmental and human fossil archives in East Africa. The 40 Ar/ 39 Ar and paleomagnetic dates and tephrostratigraphic correlations establish the time spans for the four formations present at Gona: the Adu-Asa (>6.4–5.2 Ma), Sagantole (>4.6–3.9 Ma), Hadar (3.8–2.9 Ma), and Busidima Formations (2.7 to <0.16 Ma). The volcano-sedimentary succession at Gona displays many classic tectono-sedimentary features of an evolving rift basin. The mixed volcanic and fluviolacustrine Adu-Asa Formation is the earliest expression of rifting at Gona, probably deposited in a small half-graben. The Sagantole and Hadar Formations were deposited in a much larger half-graben bounded to the E-NE by an as-yet-unidentified normal fault. The Sagantole and Hadar Formations are both fluvial and lacustrine, reflecting periodic shallow impoundment of a low-gradient paleo–Awash River, perhaps by an accommodation zone north of the Ledi-Geraru project area. Starting at 2.9–2.7 Ma, the character of sedimentation changed dramatically throughout the Awash Valley as bed load coarsened and the meandering paleo–Awash River cyclically cut and filled. Unlike the Hadar Formation, the Busidima Formation thickens westward, suggesting deposition in a half-graben of the opposite polarity compared to Sagantole/Hadar time. Sedimentation rates decreased 5-fold, from 0.25 mm/yr in the Hadar Formation to 0.05 mm/yr in the Busidima Formation, perhaps in response to slowing extension rates and/or opening of the half-graben north of Gona.

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Abstract An orogenic cycle (Wilson, 1963) in simplest form may be of long duration, and it includes rifting, subduction, and final closure by which an ocean basin is initiated and ultimately destroyed. In real orogens the cycle must be more complicated, being punctuated, possibly at several intervals, by such things as cessation of subduction, collision of microplates, or by obduction. The Acadian orogeny probably represents such a punctuation in an orogenic cycle that lasted through Paleozoic time. Where the Acadian orogeny is recognized in the Appalachians, it was in some places preceded by earlier punctuations (Penobscottian, Taconian), and was followed by a final collisional event (Alleghanian). In the context of the Acadian orogeny, only those geologic features that have a causal relationship to the Acadian will be considered in this chapter.

Ultramafites in the Piedmont of North Carolina and South Carolina occur mainly in four types of bodies. (1) In many parts of the Inner Piedmont, small pods and lenses of Alpine-type altered dunite and peridotite are typically less than 200 m long, and their emplacement predates the main regional deformation and metamorphism. (2) In the south-central Inner Piedmont of South Carolina, more than 100 bodies of potassic ultramafic rocks occur in an area of several hundred square kilometers; the bodies are probably metamorphosed lamproites. (3) In the western Charlotte and Kings Mountain belts, peridotite, clinopyroxenite, and hornblende-bearing ultramafites are gradational into gabbroic rocks in large complexes that extend over tens of square kilometers; the ultramafites are probably cumulates formed in the roots of a calc-alkaline magmatic arc. (4) Several occurrences of ultramafic and related rocks interpreted to be dismembered ophiolites or ophiolitic mélanges are located near the Inner Piedmont–Kings Mountain belt boundary, on the flanks of the Raleigh belt, and in the Kiokee belt.

Abstract The Carolina slate belt includes volcanic and sedimentary rocks of Late Precambrian and Cambrian age, metamorphosed to lower greenschist facies, that extend through the Piedmont from Georgia to Virginia. The segment in central North Carolina (Fig. 1) is probably the best-known part of the belt. Rocks in the Albemarle area are mildly deformed and metamorphosed; the dominant structures are open folds plunging southwest and the regional metamorphism is chlorite and biotite grade. The Albemarle region includes type localities for several stratigraphic units. The localities described here are on the Albemarle (Conley, 1962) and Denton (Stromquist, Choquette, and Sundelius, 1971) 15-minute quadrangles. The guidebook by Stromquist and Conley (1959) marked the beginning of modern studies in the central Carolina slate belt, as they demonstrated that stratigraphy and structure could be worked out on a regional basis. Conley and Bain (1965) applied formation names to the section in the Albemarle area (Fig. 2) and extended this stratigraphic nomenclature through most of the slate belt in North Carolina. In the Albemarle region, a thick, dominantly felsic volcanic unit (Uwharrie Formation) is overlain by a dominantly sedimentary sequence (Albemarle Group). The Morrow Mountain Rhyolite and Badin Greenstone of the Tater Top Group were interpreted to be the uppermost units and to lie with angular unconformity above folded older units (Conley and Bain, 1965). Stromquist and Sundelius (1969) reinterpreted part of the middle and upper stratigraphic sequence. They considered the Tater Tbp Group to be interlayered with other units of the Albemarle Group, rather than

Abstract Pilot Mountain State 52, 24 mi (38 km) north km) south of Mount Airy, Park is located just west of U.S. of Winston-Salem and 14 mi (22 Surry County, Pinnacle 7½-minute quadrangle (Fig. 1). The Pilot Mountain State Park exit from U.S. 52 leads directly to the park entrance. The field trip narrative begins at the parking lot on the mountain top (Fig. 2, Location A). No rock collecting is allowed in the park without special written permit.

Abstract One half mi (1 km) south of the Linville Falls parking area off Blue Ridge Parkway east of the town of Linville Falls, North Carolina, Linville Falls 7½-minute Quadrangle, North Carolina (Fig. 1). This locality is within the Blue Ridge Parkway National Park. Consequently, the collecting of samples and breaking of rocks is prohibited. The actual fault exposure is about 100 yd (90 m) above the falls at the end of the trail from the parking lot and is in the area indicated by a sign to not enter because of the dangerous rapids and the river. This area can be entered by walking carefully.

Abstract Two regionally important stratigraphic units in the Carolina slate belt are exposed along North Carolina 24-27 on both sides of Lake Tillery (Pee Dee River), about 7 mi (11 km) east of Albemarle, Stanly and Montgomery Counties, Morrow Mountain 7½-minute quadrangle (Fig. 1). Site A (Fig. 2) is 1.7 miles (2.7 km) east of the Lake Tillery bridge and 0.6 mile (1 km) east of the intersection of North Carolina 24-27 and State Road 1150. At Site B (Fig. 2), mudstone of the Tillery Formation and a metagabbro sill are exposed along North Carolina 24-270.3 mi (0.5 km) west of the Lake Tillery bridge. Since traffic conditions at Site B are dangerous, extreme caution must be used when stopping.

Abstract The Kings Mountain belt and spodumene Pegmatite district are located in Cherokee and York Counties, South Carolina, and Cleveland County, North Carolina, south of Kings Mountain, North Carolina (Fig. 1). This area includes the most complete stratigraphic section, the most productive mineral deposits, and the most intensively studied parts of the belt.

Abstract The large diabase dike and adjacent granite that it intruded are well exposed in road cuts along US Highway 601, about midway between Lancaster and Pageland in the northeastern South Carolina Piedmont (Figs. 1 and 2), about 50 mi (80 km) southeast of Charlotte, North Carolina. The outcrop is about 4,000 ft (1,200 m) south of Flat Creek and 0.9 mi (1.5 km) northeast of the village of Midway (intersection of US 601 and South Carolina 903). There is ample parking on the grassy shoulder of the highway just north of the outcrop, large enough even for several buses; in wet weather, be careful of soggy ground

Abstract The Brevard fault zone is exposed near Rosman, Transylvania County, North Carolina (Fig. 1), in the southwestern quadrant of the Rosman 7½-minute Quadrangle. The stops are along public roads and are accessible without special permission. Busloads of approximately 50 people have visited these outcrops in the past.

Major rock units of the central and eastern Beartooth Mountains are granitic gneiss, amphibolite, and biotite schist. Migmatitic interlayering and gradational sequences are common. In the western Beartooth Mountains, biotite schist and quartzite are dominant units and granitic gneiss is relatively minor. A summary of available data shows that amphibolite has a composition similar to tholeiitic basalt, and biotite schist is probably a metamorphosed pelitic rock. Granitic gneiss is similar in composition to magmatic granitic rocks. Summary data are evaluated by use of four basically different models for the origin of granitic gneiss: sedimentary-volcanic depositional, magmatic, anatectic, and metasomatic models. Combinations of processes are likely in nature; therefore, combined models such as the magmatic-metasomatic are also considered. Depositional and anatectic models are inadequate to explain field relationships and composition of major rock units. The magmatic model is plausible only if magma injection can take place over hundreds of square miles and vertical distance of thousands of feet without significantly disturbing the homogeneity of fabric and conformable nature of contacts. Rounded zircons in granitic gneiss are evidence against the magmatic model. If gradational sequences are explained by reaction between magma and country rock, there is a problem of disposal of elements, mainly aluminum, that are shown not to be needed in the reaction. The metasomatic model explains many of the observed relationships, but little evidence is available on source of material and transport mechanism. Some experimental evidence suggests that metasomatism under conditions of upper amphibolite facies may produce granitic rocks similar in composition to magmatic or anatectic granites. No single-process model can explain the observed relationships in the Beartooth Mountains. The author is most convinced by a theory of metasomatism as the dominant process, but the evidence can also be interpreted to favor other processes, particularly a combination of synkinematic magmatism and metasomatism.