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Deborah R. Hutchinson

Publications and source records attributed to Deborah R. Hutchinson.

46 records · Page 3Linked to original sources
USGS1988

U.S. Geological Survey deep seismic reflection profile across the Gulf of Maine

Deep seismic reflection and magnetic data suggest that the Gulf of Maine is underlain by four crustal blocks of differing reflection and magnetic character. Two of these blocks, the Gulf of Maine fault zone and adjacent central plutonic zone, can be correlated with Avalonian rocks in southern New England and New Brunswick. The boundary between them, the Fundy fault, projects onshore near the Ponkapoag fault in southeastern Massachusetts in a region where no major crustal boundary has (yet) been identified. A third block, called the southern plutonic zone, is interpreted as Avalonian, although the reflection and magnetic data are ambiguous. The fourth block, along the rifted continental margin, is correlated with Meguma rocks of Nova Scotia. The late Paleozoic Variscan front crosses the Gulf of Maine within the Gulf of Maine fault zone and indicates significant compressional movement rather than strike-slip. The Moho surface throughout the region is essentially flat and may have been produced by Mesozoic crustal extension. Associated modification of the lower crust was minimal in the northern Gulf and may have been moderate in the central and southern Gulf. The Franklin rift basin formed by reactivation of the inferred Avalon-Meguma boundary beneath Georges Bank as a low-angle detachment.

Gulf of Maine↗
USGS1985

New York Bight fault

High-resolution, single-channel and multichannel seismic-reflection profiles in the New York Bight provide 7 crossings of a 50-km-long fault that trends north-northeast for 30 km from its southern end, then bends northeast, and may continue northward beneath Long Island. Displacement, which is consistently down to the west, decreases upsection and suggests a growth fault. Dip of the fault is near vertical. Its maximum offset of 109 m is the largest offset at the base of the Coastal Plain known for any Cretaceous and younger fault along the East Coast. Seismic stratigraphic controls constrain motion on the fault between Late Cretaceous (95 m.y. B.P.) and middle Oligocene (30 m.y. B.P.). The evidence for Quaternary activity is ambiguous. The fault parallels a magnetic low to the east, interpreted as a buried Mesozoic rift basin from seismic-reflection data, and a gravity low to the west, interpreted as a structure within Paleozoic rocks from well data. Whether these structures control the location of, or movement on, the fault is not clear.

New Jersey, New York↗
USGS1985

Block Island fault: A Paleozoic crustal boundary on the Long Island platform

A major fault cutting through most of the crust can be identified and mapped on the Long Island platform using multichannel seismic reflection profiles and magnetic data. The fault, here called the Block Island fault (BIF), strikes north-northeast, dips westward at low angle, and does not resemble the thin-skinned thrust faulting observed in the foreland of the Appalachians. The BIF is located within the hinterland of the Appalachian mountain belt in the collision zone between Africa and North America. We present several interpretations but favor one in which the fault originated as an east-verging mid–late Paleozoic thrust fault, possibly related to the collision of Avalon or Meguma with North America. It was probably reactivated during early Mesozoic continental breakup and again in the Late Cretaceous and Tertiary, causing the steeply dipping postrift New Shoreham fault to form, either as an antithetic (normal) or splay (reverse) fault.

Long Island platform↗
USGS1983

Crustal structure beneath the southern Appalachians: Nonuniqueness of gravity modeling

Gravity models computed for a profile across the long-wavelength paired negative-positive Bouguer anomalies of the southern Appalachian Mountains show that the large negative anomaly can be explained by a crustal root zone, whereas the steep gradient and positive anomaly east of the root may be explained equally well by three different geometries: a suture zone, a mantle upwarp, or a shallow body. Seismic data support the existence of a mountain root but are inadequate to resolve differences among the three possible geometries for the positive anomaly. The presence of outcropping mafic and ultramafic rocks in the southern Appalachians and the inferred tectonic history of the Appalachian orogen are most consistent with the suture-zone model. Crust similar to continental crust probably exists beneath the Coastal Plain and inner continental shelf where the gravity anomalies return to near-zero values.

Appalachian Mountains↗
USGS1979

The gravity field of the U.S. Atlantic continental margin

Approximately 39,000 km of marine gravity data collected during 1975 and 1976 have been integrated with U.S. Navy and other available data over the U.S. Atlantic continental margin between Florida and Maine to obtain a 10 mgal contour free-air gravity anomaly map. A maximum typically ranging from 0 to +70 mgal occurs along the edge of the shelf and Blake Plateau, while a minimum typically ranging from −20 to −80 mgal occurs along the base of the continental slope, except for a −140 mgal minimum at the base of the Blake Escarpment. Although the maximum and minimum free-air gravity values are strongly influenced by continental slope topography and by the abrupt change in crustal thickness across the margin, the peaks and troughs in the anomalies terminate abruptly at discrete transverse zones along the margin. These zones appear to mark major NW—SE fractures in the subsided continental margin and adjacent deep ocean basin, which separate the margin into a series of segmented basins and platforms. Rapid differential subsidence of crustal blocks on either side of these fractures during the early stages after separation of North America and Africa (Jurassic and Early Cretaceous) is inferred to be the cause of most of the gravity transitions along the length of margin. The major transverse zones are southeast of Charleston, east of Cape Hatteras, near Norfolk Canyon, off Delaware Bay, just south of Hudson Canyon and south of Cape Cod. Local Airy isostatic anomaly profiles (two-dimensional, without sediment corrections) were computed along eight multichannel seismic profiles. The isostatic anomaly values over major basins beneath the shelf and rise are generally between −10 and −30 mgal while those over the platform areas are typically 0 to +20 mgal. While a few isostatic anomaly profiles show local 10–20 mgal increases seaward of the East Coast Magnetic Anomaly (ECMA: inferred to mark the ocean-continent boundary), the lack of a consistent correlation indicates that the relationship of isostatic gravity anomalies to the magnetic anomalies and the ocean—continent transition is variable. Two-dimensional gravity models have been computed for two profiles off Cape Cod, Massachusetts and Cape May, New Jersey, where excellent reflection, refraction and magnetic control appear to define 10 and 12 km deep sedimentary basins beneath the shelf, respectively and 10 km deep basins beneath the rise. The basins are separated by a 6–8 km deep basement ridge which underlies the ECMA and appears to mark the landward edge of oceanic crust. The gravity models suggest that the oceanic crust is between 11 and 18 km thick beneath the ECMA, but decreases to a thickness of less than 8 km within the first 20–90 km to the southeast. In both profiles, the derived crustal thickness variations support the interpretation that the ECMA occurs over the ocean-continent boundary. The crust underlying the sedimentary cover appears to be 12 to 15 km thick on the landward side of the ECMA and gradually thickens to normal continental values of greater than 25 km within the first 60 to 110 km to the northwest. Multichannel seismic profiles across platform areas, such as Cape Hatteras and Cape Cod, indicate the ocean-continent transition zones there are much narrower than profiles across major sedimentary basins, such as the one off New Jersey.

Tectonophysics↗
USGS1979

Lake Ontario geological and geophysical data sources

A bibliography of various geological and geophysical data sources was compiled as part of an overall effort to evaluate the status of research on the Great Lakes. We hope that such a summary will be a catalyst for additional work and be an aid in planning future work. Our presentation has two forms: maps showing the locations of the different data types and a bibliography which lists the references from the maps and additional relevant papers. The charts shown in this map summarize the data source for Lake Ontario.

Lake Ontario↗