U-Pb zircon geochronology and field relations provide insights into metavolcanic and associated rocks in the Central Appalachian Piedmont of Maryland and northern Virginia. Ordovician ages were determined for volcanic-arc rocks of the James Run Formation (Churchville Gneiss Member, 458 ± 4 Ma; Carroll Gneiss Member, 462 ± 4 Ma), Relay Felsite (458 ± 4 Ma), Chopawamsic Formation (453 ± 4 Ma), and a Quantico Formation volcaniclastic layer (448 ± 4 Ma). A previously dated first phase of volcanism in the Chopawamsic Formation was followed by the second phase dated here. The latter suggests a possible source for contemporaneous volcanic-ash beds throughout eastern North America. Dates from the Chopawamsic and Quantico Formations constrain the transition from arc volcanism to successor-basin sedimentation. Ordovician metatonalites of the Franklinville (462 ± 5 Ma) and Perry Hall (461 ± 5 Ma) plutons are contemporaneous with the James Run Formation, whereas granitoids of the Bynum Run (434 ± 4 Ma) and Prince William Forest (434 ± 8 Ma) plutons indicate an Early Silurian plutonic event. The Popes Head Formation yielded Mesoproterozoic (1.0–1.25 Ga, 1.5–1.8 Ga) detrital zircons, and metamorphosed sedimentary mélange of the Sykesville Formation yielded Mesoproterozoic (1.0–1.8 Ga) detrital zircons plus a minor Archean (2.6 Ga) component. A few euhedral zircons (ca. 479 Ma) in the Sykesville Formation may be from granitic seams related to the Dalecarlia Intrusive Suite. A Potomac orogeny in the Central Appalachian Piedmont is not required, but the earliest Taconic orogenesis remains poorly constrained.

Abstract The Earth’s Moon is the largest natural satellite in the inner Solar System. The Moon is also witness to more than 4.5 Ga of Solar System history and is the only planetary body other than the Earth for which we have collected samples from known locations. Moreover, the lunar surface preserves a record of the cratering rate and the evolution of solar and galactic cosmic radiations throughout the history of the Solar System. Understanding the Moon is essential to understanding both the Earth and our Solar System. Consequently, the Moon was the prime target in Solar System exploration programs, before the pursuit of more distant targets such as Mars and beyond. Our knowledge about the Moon is based on telescopic observations from the Earth, observations by spacecraft from the lunar orbit, measurements on the lunar surface by manned and unmanned lander missions and the analyses of lunar samples in terrestrial laboratories. The knowledge gained from the Apollo and Luna programs of the 1960s and subsequent lunar missions, carried out over the last four decades, continues to demonstrate the value of the Moon in the understanding of our Solar System and the fundamental processes that drive planetary formation and evolution. Because of its restricted geological activity and relatively simple composition compared with the Earth, the Moon provides insights into elementary planetary processes. In comparison to the Earth, the Moon is depleted in both volatile elements, and iron and other siderophile elements. Recently, however, the presence of H2O and OH has been confirmed on the lunar surface as well as in lunar samples. While it has long been suspected that water-ice might be preserved in cold traps at the lunar poles, recent results indicate the presence of OH and H2O outside of these regions. This new discovery makes the Moon an extremely interesting target once again, both scientifically and as a potential resource. Although new data have helped to address some of our questions about the Earth-Moon system, major new questions have emerged and many existing ones remain unanswered.

Abstract Classically, the Old Red Sandstone (ORS) embraces the continental, predominantly siliciclastic deposits of Devonian age, being in part the terrestrial correlatives of the marine Devonian of SW England. Subsequent stratigraphical revision (e.g. House 1977 ) demonstrated that the base of the ORS is actually of Silurian age in many places. The ORS has long been of interest due to the presence of early vascular plants and vertebrate faunas. Studies of the ORS have spawned significant sedi-mentological advances, for example the now classic analysis of high-sinuosity fluvial channels ( Allen 1965a , 1970 ). Today, the ORS is a term applied to tectono-stratigraphic units of Upper Silurian–Carboniferous age bordering the North Atlantic Ocean ( Friend 1969 , Friend et al. 2000 ). It has long been seen as representing the syn- to post-orogenic depositional response (molasse) to the Caledonian Orogeny, being modified by synchronous tectonism and volcanicity. The influence of Variscan tectonics on basin formation and subsequent deformation has recently being highlighted ( Friend et al. 2000 ). Lithologically, it embraces a wide range of textural grades from mudrocks to conglomerates. Fluvial, lacustrine, aeolian, pedogenic and marginal marine deposits have been recognized. In England and Wales, the ORS crops out in four main areas ( Fig. 8.1 ): the Anglo-Welsh Basin, Anglesey, Edenside (Cumbria) and North Devon.

Cores recovered on Deep Sea Drilling Program leg 43 and on Bermuda itself, together with geophysical data (anomalies in basement depth, geoid, and heatflow) and modeling have long suggested that the uplift forming the Bermuda Rise, as well as the initial igneous activity that produced the Bermuda volcanoes, began ca. 47–40 Ma, during the early to middle part of the Middle Eocene. Some authors attribute 65 Ma igneous activity in Mississippi and 115 Ma activity in Kansas to a putative “Bermuda hotspot” or plume fixed in the mantle below a moving North America plate. While this is more or less consistent with hotspot traces computed from “absolute motion” models, the hotspot or plume must resemble a blob in a lava lamp that is turned off for up to 25 million years at a time, and/or be heavily influenced by lithosphere structure. Moreover, Cretaceous igneous activity in Texas and Eocene intrusions in Virginia then require separate mantle “blobs.” The pillow lavas forming the original Bermuda shield volcano have not been reliably dated, and the three associated smaller edifices have not been drilled or dated. A well-dated (ca. 33–34 Ma) episode of unusually titaniferous sheet intrusion in the Bermuda edifice was either triggered by platewide stress changes or reflects local volcanogenic events deep in the mantle source region. The high Ti and Fe of the Bermuda intrusive sheets probably relate to the very high-amplitude magnetic anomalies discovered on the islands. Numerical models constrained by available geophysical data attribute the Bermuda Rise to some combination of lithospheric reheating and dynamic uplift. While the relative contributions of these two processes cannot yet be wholly separated, three features of the rise clearly distinguish it from the Hawaiian swell: (1) the Bermuda Rise is elongated at right angles to the direction of plate motion; (2) there has been little or no subsidence of the rise and the volcanic edifice since its formation—in fact, rise uplift continued at the same site from the late Middle Eocene into the Miocene; and (3) the Bermuda Rise lacks a clear, age-progressive chain. We infer that the Bermuda Rise and other Atlantic midplate rises are supported by anomalous asthenosphere, upwelling or not, that penetrates the thermal boundary layer and travels with the overlying plate. The elongation along crustal isochrons of both the Bermuda volcanoes and the Bermuda Rise and rise development mostly within a belt of rougher, thinner crust and seismically “slower” upper mantle—implying retention of gabbroic melts at the ancient Mid-Atlantic Ridge axis—suggest that the mantle lithosphere may have helped localize rise development, in contradiction to plume models. The Bermuda Rise area is seismically more active than its oceanic surroundings, preferentially along old transform traces, possibly reflecting a weaker upper mantle lithosphere. We attribute the “Bermuda event” to a global plate kinematic reorganization triggered by the closing of the Tethys and/or the associated gravitational collapse into the lower mantle of subducted slabs that had been temporarily stagnant near the 660 km mantle discontinuity. The widespread onset of sinking slabs required simultaneous up-welling for mass balance. In addition, the global plate kinematic reorganization was accompanied by increased stress in some plate interiors, favoring magma ascent along fractures at structurally weak sites. We suggest that the Bermuda event and concomitant igneous activity in Virginia, West Antarctica, Africa, and other regions were among such upwellings, but structurally influenced by the lithosphere, and probably originated in the upper mantle. Drilling a transect of boreholes across and along the Bermuda Rise to elucidate turbidite offlap during rise formation might discriminate between a widely distributed mantle source (such as a previously subducted slab) and a narrow plume whose head (or melt root) spreads out quasi-radially over time, generating an upward and outward expanding swell.

The magnetic induced polarization (MIP) method determines the variation of the induced polarization and resistivity of the earth through measurements of the magnetic field associated with galvanic current flow in the earth, rather than the electric field, as in the traditional induced polarization (IP) or electrical induced polarization (EIP) method. Important differences between the MIP and EIP methods are evident in field practice, mathematical theory, and field results. For example, the MIP method is insensitive to horizontal layering in the earth and reflects only lateral variations in its electrical properties. MIP also provides an enhanced ability to detect the presence of bodies of anomalous electrical properties even through a highly conducting surface layer. For this reason the MIP methods primary application is in regions of highly conducting (e.g., saline) overburden or weathered rock, such as in Australia. MIP responses tend to be more complex and varied in pattern than responses normally encountered in EIP measurements. For example, polarity reversals are the rule in MIP but are rarely encountered in EIP. MIP employs high-sensitivity component magnetometers as basic sensors. These are small relative to the length of the electric dipole sensors normally employed in EIP, and, therefore, provide relatively higher geometric resolving power.