Location The basalt flows of the Hartford Basin crop out as prominent topographic ridges extending from Amherst in central Massachusetts, to New Haven in Connecticut. Only two streams traverse the ridge: the Westfield and the Farmington Rivers. The Farmington enters the basin near Bristol but makes a 9-mi (15km) detour north to the Tariffville Gorge before crossing the basalt ridges. Tariffville is located in north-central Connecticut at the junctions of Connecticut Routes 189, 187, and 315. The sites discussed below are located by number in Figure 1. Outcrops along the roads are easily accessible. Access to the exposures on the banks of the Farmington River is more difficult but well worth the visit.

High-grade metamorphic rocks and migmatites in the Farmington Canyon Complex were derived from igneous and sedimentary rocks possibly, as old as 3000 m.y. They were probably metamorphosed about 2600 m.y. ago, and they were severely metamorphosed, migmatized, and intruded by quartz monzonite 1790 m.y. ago. A very high initial Sr 87 /Sr 86 ratio of 0.769 indicates that the quartz monzonite magma was derived by melting of the more leucocratic parts of the layered gneisses. On and just west of Antelope Island, plutons of granite were emplaced 2020 m.y. ago.

ABSTRACT Synthesis of the Ordovician Taconic orogeny in the northern Appalachians has been hindered by along-strike variations in Laurentian, Gondwanan, and arc-generated tectonic elements. The Dashwoods terrane in Newfoundland has been interpreted as a peri-Laurentian arc terrane that collided with the Laurentian margin at the onset of the Taconic orogeny, whereas along strike in New England, the Moretown terrane marks the leading edge of peri-Gondwanan arcs. The peri-Laurentian affinity of the Dashwoods terrane hinges on the correlation of its oldest metasedimentary rocks with upper Ediacaran to Lower Ordovician rift-drift deposits of the Laurentian Humber margin in western Newfoundland. Here, we report U-Pb dates and trace-element geochemistry on detrital zircons from metasedimentary rocks in the southern Dashwoods terrane that challenge this correlation and provide new insights into the Taconic orogeny. Based on age and trace-element geochemistry of detrital zircons analyzed by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS), we identified ca. 462–445 Ma sedimentary packages with a mixed provenance consisting of Laurentian, Gondwanan, and arc-derived Cambrian–Ordovician sources. These deposits overlap in age with Upper Ordovician strata of the Badger Group of the Exploits subzone, which also contain Laurentian detritus. We infer dominantly east-directed transport of Laurentian detritus from the Taconic collision zone across a postcollisional arc–back-arc complex at ca. 462–455 Ma followed by dominantly west-directed transport of detritus from the Red Indian Lake arc at ca. 455–445 Ma. Our analysis of zircon inheritance from Dashwoods igneous rocks suggests that 1500–900 Ma Laurentian crystalline basement of the Humber margin is an unlikely source of Dashwoods inherited zircon. Instead, a more cosmopolitan Laurentian inheritance may be best explained as sourced from subducted Laurentian sediment. Our results demonstrate that the sampled metasedimentary units from the southern Dashwoods terrane do not correlate with rift-drift strata of the Humber margin as previously proposed, nor with the basement of the Moretown terrane; yet, these Middle to Upper Ordovician successions suggest the potential for an alternative plate-tectonic model in which the Taconic orogeny may have been initiated by collision of Gondwanan arc terranes that closed the main tract of the Iapetus Ocean along the Baie Verte–Brompton Line.

Abstract Weaponry can be conveniently and safely concealed in enemy underground bedrock facilities (UGF). The bedrock environment surrounding UGF offers a high degree of protection for the assets contained within. Physical characteristics of the surrounding bedrock constrain the effects of conventional and even nuclear weapons. Brittle structures in the bedrock such as fracture systems have anisotropic characteristics and present a formidable obstacle to the survival of penetrating weapons. Knowledge of the three-dimensional (3-D) characteristics of bedrock fracture systems in enemy UGF, which may be covered by soil or vegetation, is of paramount importance to the weapons development community in its quest to penetrate anisotropic environments. We utilize rigorous methodologies to predict fracture characteristics in overburden-covered regions from outcrop, core, borehole, and remote sensing data. We have established digital scanline and scangrid methodologies to characterize fracture geometries. The digital data allow us to easily analyze the fractures in terms of fractal and more advanced geostatistical techniques. We have developed theoretical and practical guidelines for determining the two-dimentional (2-D) density of fractures from one-dimentional (1-D) (scanline) data. Additionally, we have developed theoretical relationships between 2-D and 3-D fracture densities. Integration of digital field data with density and spatial structure of the fracture networks allows us to predict the distribution of fractures in areas removed from the outcrop. These methodologies, once refined, fully tested, and verified, will allow us to characterize three-dimensional fracture systems in potential target areas worldwide by remote sensing means alone.

Abstract The area discussed here is in San Juan County, New Mexico, approximately 30 mi (48 km) south of Farmington and 20 mi(32 km) northwest of Chaco Canyon National Monument (Fig. 1). The small settlement of Bisti is most conveniently reached by traveling south on New Mexico 371 from Farmington or north on New Mexico 57 and New Mexico 371 from Thoreau, which is about 73 mi (117 km) east of Gallup on 1-40. Both of these routesare paved to within a few miles of Bisti. From New Mexico 44 atHuerfano an improved dirt road (County Road 15) runs southwest about 25 mi (40 km) to intersect New Mexico 371 about 9 mi (14 km) south of Bisti. All of the stops indicated on Figure 1 are accessible by two-wheel drive vehicles, but many of the side roads into the badlands and arroyo areas require four-wheel drive. Viewing of areas off the main roads is best done on foot. The nearest gasoline, food, and water are in Farmington and several stores along New Mexico 44. Most of the area under consideration is within recently established federal wilderness areas, managed by the U.S. Bureau of Land Management (BLM). A few sections are owned by the State of New Mexico or the Navajo Nation, but no part of the area is within the Navajo Reservation. Permission is not required to examine exposures on federal or state land (a permit from the BLMis required to collect fossils), but permission should be obtained from the few