Geology topics

Kim D. Klitgord

Publications and source records attributed to Kim D. Klitgord.

At least 37 records · Page 2Linked to original sources

USGS1990

Major off-axis hydrothermal activity on the northern Gorda Ridge

The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV Sea Cliff . The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on the east wall. Preliminary mapping and sampling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of elastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinites. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.

Gorda Ridge↗

USGS1988

The development of the continental margin of eastern North America-conjugate continental margin to West Africa

The continental margin of eastern North America was initiated when West Africa and North America were rifted apart in Triassic-Early Jurassic time. Cooling of the crust and its thinning by rifting and extension caused subsidence. Variation in amounts of subsidence led to formation of five basins. These are listed from south to north. (1) The Blake Plateau Basin, the southernmost, is the widest basin and the one in which the rift-stage basement took longest to form. Carbonate platform deposition was active and persisted until the end of Early Cretaceous. In Late Cretaceous, deposition slowed while subsidence persisted, so a deep water platform was formed. Since the Paleocene the region has undergone erosion. (2) The Carolina Trough is narrow and has relatively thin basement, on the basis of gravity modeling. The two basins with thin basement, the Carolina Trough and Scotian Basin, also show many salt diapirs indicating considerable deposition of salt during their early evolution. In the Carolina Trough, subsidence of a large block of strata above the flowing salt has resulted in a major, active normal fault on the landward side of the basin. (3) The Baltimore Canyon Trough has an extremely thick sedimentary section; synrift and postrift sediments exceed 18 km in thickness. A Jurassic reef is well developed on the basin's seaward side, but post-Jurassic deposition was mainly non-carbonate. In general the conversion from carbonate to terrigenous deposition, characteristics of North American Basins, occurred progressively earlier toward the north. (4) The Georges Bank Basin has a complicated deep structure of sub-basins filled with thick synrift deposits. This may have resulted from some shearing that occurred at this offset of the continental margin. Postrift sediments apparently are thin compared to other basins—only about 8 km. (5) The Scotian Basin, off Canada, contains Jurassic carbonate rocks, sandstone, shale and coal covered by deltaic deposits and Upper Cretaceous deeper water chalk and shale.

Journal of African Earth Sciences↗

USGS1987

Migration of mid-ocean-ridge volcanic segments

The propagation of small-offset volcanic spreading-centre segments along mid-ocean ridge crests may reflect absolute motion of the plate boundary relative to the underlying mesospheric frame. Such a relationship could be caused by a purely vertical flow of the mantle under spreading centres and would have value in constraining past plate motions from non-transform trends generated during along-ridge propagation and in linking the major-element variability of oceanic crust and upper mantle to the bulk composition and temperatures of mantle ascending under mid-ocean ridges.

Nature↗

USGS1987

Subsidence, crustal structure, and thermal evolution of Georges Bank basin

A geophysical study of Georges Bank basin defines a deep crustal structure that is interpreted in terms of the basin's tectonic and thermal history. Gravity models along three basin cross sections delineate two zones of crustal thinning at the basement hinge zone and oceanic crustal margins. These two zones bound rift-stage crust (about 25 km thick) which underlies the central portion of the basin. Subsidence analysis of the basin, using data from multichannel seismic reflection lines and two COST wells, suggests a rifting and (uniform) extensional origin. Two-dimensional finite difference modeling of the basin defines a crustal structure that concurs with the gravity and subsidence studies. The resulting isotherms show no major changes in the thermal structure since the ate Jurassic. In some areas of the basin, temperatures sufficient for oil generation are determined from maturation studies of Jurassic sediments. Hydrocarbon generation is questionable, however, because of the probable lack of proper and sufficient kerogen in the Jurassic deposits.

American Association of Petroleum Geologists Bulle↗

USGS1987

Geology of the Caribbean

The Venezuelan and Colombian basins are located on the Caribbean Plate whilst the Yucatan basin is on the North American Plate. The processes occurring at the boundaries between the Caribbean Plate and the adjacent North American, South American and Cocos Plates, and the resulting surface features and patterns of volcanic and earthquake activity are described. Most of the Caribbean area is floored by atypical oceanic crust and its most valuable main geologic resources identified so far are petroleum, together with sand and gravel. Geological research is being carried out with techniques for broad-range swath imaging of the seafloor, such as GLORIA, and for directly measuring the movement between plates. -J.G.Harvey

Oceanus↗

USGS1987

Passive margins: U.S. Geological Survey Line 19 across the Georges Bank basin

Georges Bank is a shallow part of the Atlantic continental shelf southeast of New England (Emery and Uchupi, 1972, 1984). This bank, however, is merely the upper surface of several sedimentary basins overlying a block-faulted basement of igneous and metamorphic crystalline rock. Sedimentary rock forms a seaward-thickening cover that has accumulated in one main depocenter and several ancillary depressions, adjacent to shallow basement platforms of paleozoic and older crystalline rock. Georges Bank basin contains a thickness of sedimentary rock greater than 10 km, whereas the basement platforms that flank the basin are areas of thin sediment accumulation (less than 5 km).

AAPG Studies in Geology↗

USGS1985

Segmentation of mid-ocean ridges

Studies of mid-ocean ridges in the Pacific and Atlantic oceans show that the volcanism that forms the oceanic crust along the spreading-plate boundaries is concentrated at regular intervals related to spreading rate. This observation and a new calculation for a Rayleigh-Taylor type of gravitational instability of a partially molten mantle region growing under spreading centres yield reasonable estimates of upper mantle viscosities.

Nature↗

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↗

USGS1982

The memory of the accreting plate boundary and the continuity of fracture zones

A detailed aeromagnetic anomaly map of the Mesozoic seafloor-spreading lineations southwest of Bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation. The magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone (flowline) trends. The linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones. During the period of Mesozoic geomagnetic polarity reversals (when 1200 km of central North Atlantic seafloor formed), the Atlantic accreting boundary consisted of stationary, elongate, spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells. Normal oceanic crustal structure was formed in the spreading center cells, but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries, which parallel flowlines of Mesozoic relative plate motion in the central North Atlantic. We suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest; here, each spreading center cell independently goes through its cylce of stress buildup, stress release, and crustal accretion, after which its memory is refreshed. The temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists.

Earth and Planetary Science Letters↗

USGS1982

Growth faulting and salt diapirism; their relationship and control in the Carolina Trough, eastern North America

The Carolina Trough is a long, linear, continental margin basin off eastern North America. Salt domes along the trough's seaward side show evidence of active diapirism and a normal growth fault along its landward side has been continually active at least since the end of the Jurassic. This steep fault extends to a strong reflection event at about 11 km depth that may represent the top of a salt layer. We infer that faulting is caused by seaward flow of salt from the deep part of the trough into domes, thereby removing support for the overlying block of sedimentary rock. Diapirs off eastern North America seem to be concentrated in the Carolina Trough and Scotian Basin, where basement seems to be thinner than in other basins off eastern North America, south of Newfo ndland. Thinner basement, probably due to greater stretching during rifing, may have resulted in earlier subsidence below sea level, a longer life for the salt evaporating pans in these basins, and thus a thicker salt layer, which would be more conducive to diapirism.

Book chapter↗

USGS1982

Deep structure and evolution of the Carolina Trough

Multichannel seismic-reflection data together with two-dimensional gravity and magnetic models suggest that the crustal structure off North Carolina consists of normal continental crust landward of the Brunswick magnetic anomaly (BMA), rift-stage crust in the 80-km-wide zone between the BMA and the East Coast magnetic anomaly (ECMA), and normal oceanic crust seaward of the ECMA.

Book chapter↗

USGS1980

High-sensitivity aeromagnetic survey of the U.S. Atlantic continental margin

The U.S. Geological Survey contracted a high-sensitivity, digital aeromagnetic survey that was flown over the U.S. Atlantic continental margin over a period of 15 months between 1974 and 1976. The 185,000 km of profile data have a relative accuracy approaching a few tenths of a nanotesla, which allowed compilation into maps at a scale of 1:250,000, with a contour interval of 2 nT. Automatic data processing using the Werner method allowed calculations of apparent depth to sources of the magnetic anomalies on all of the profiles, assuming a dike or interface as a source. Comparison of the computed depths to magnetic basement with multichannel seismic profiles across the survey area helped to reduce ambiguities in magnetic depth estimates and enabled interpolation of basement structures between seismic profiles. The resulting map showing depth to basement of the Atlantic continental margin is compatible with available multichannel seismic data, and we consider it a reasonable representation of the base of the sedimentary column.

Geophysics↗

USGS1980