The East Coast Magnetic Anomaly

Alsop, L. E.; Talwani, Manik

doi:10.1126/science.226.4679.1189

Cited by 41 publications

(21 citation statements)

References 9 publications

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“…It can be traced laterally for 600 km before terminating against or merging with the East Coast Magnetic Anomaly (ECMA), which is a 48-km-wide, through going magnetic high along the rifted Atlantic margin of Laurentia (e.g., Vogt, 1986;Klitgord and Schouten, 1986, and references therein). The ECMA, which can be traced for more than 3000 km, has been interpreted variously: as an edge effect; as a dike suite; as a series of seaward-dipping reflectors containing tilted basalt flows; and as a deep-seated mafic intrusion (e.g., Alsop and Talwani, 1984;Keen, 1969;Keller et al, 1954;Oh et al, 1995) along or near the continent-ocean transition (Vogt, 1973;Vogt and Einwich, 1979)) Nelson et al (1985a,b) and McBride and Nelson (1988) suggested the ECMA may represent a Paleozoic suture. Thus the ECMA was probably emplaced 175-190 Ma (Vogt and Einwich, 1979;Klitgord and Grow, 1980;Sheridan, 1983;Alsop and Talwani, 1984) possibly along or near the relict suture during early rifting leading to successful opening of the Atlantic Ocean.…”

Section: Introductionmentioning

confidence: 99%

The Grenville orogenic cycle of southern Laurentia: Unraveling sutures, rifts, and shear zones as potential piercing points for Amazonia

Bartholomew¹,

Hatcher²

2010

Journal of South American Earth Sciences

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Section: Introductionmentioning

confidence: 99%

The Grenville orogenic cycle of southern Laurentia: Unraveling sutures, rifts, and shear zones as potential piercing points for Amazonia

Bartholomew¹,

Hatcher²

2010

Journal of South American Earth Sciences

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“…The ECMA is a distinct magnetic high running parallel to the margin from the Blake Spur fracture zone (FZ) to Nova Scotia and is often taken to mark the continent-ocean boundary. Hypothesized sources for the ECMA include a highly magnetized ridge or intrabasement dike [Klitgord and Behrendt, 1979], faulting associated with rifting [Alsop and Talwani, 1984], an edge effect between transitional and oceanic crust [Hutchinson et al, 1983], and rift-related volcanics [Austin et al, 1990]. However, recent magnetics modeling of across-margin seismic refraction profiles strongly support the last mechanism as the source of the ECMA [Austin et al, 1990;Talwani et al, 1995].…”

Section: Geologic Settingmentioning

confidence: 99%

Segmentation in gravity and magnetic anomalies along the U.S. East Coast passive margin: Implications for incipient structure of the oceanic lithosphere

Behn¹,

Lin²

2000

J. Geophys. Res.

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Abstract. Segmentation is a characteristic feature of seafloor spreading along the global midocean ridge system. While segmentation of active spreading centers has been the focus of much recent research, the process by which a rifted continental margin develops into a segmented midocean ridge is still poorly understood. In this study we investigate the segmentation character of the U.S. East Coast margin through a modeling study of the margin basement structure, magnetics, and gravity anomalies. The East Coast margin is of particular interest because it is one of several rifted continental margins that display thick sequences of high seismic velocity igneous crust, presumably formed during rifting. The East Coast Magnetic Anomaly (ECMA), a distinct total field magnetic high running offshore along the margin, is commonly located seaward of the thickest sections of the high-velocity crust and displays segmentation on length scales (100-120 km) similar to the segmentation observed at the Mid-Atlantic Ridge (MAR). Isostatic gravity anomalies were calculated by removing from free-air gravity the predicted effects of seafloor, sediments, and a crust-mantle model assuming local isostatic compensation. The resultant residuals show a corridor of high anomaly running along the margin, situated close to the maximum thickness of the high seismic velocity crust as determined from the two available seismic refraction lines. Reduction to the pole (R-T-P) of the total field magnetic anomaly shows that after the removal of skewness from the ECMA, the location of the isostatic gravity high is closely correlated to the ECMA. The isostatic gravity high is also segmented but in two distinct wave bands: 100-150 km and 300-500 km. The short-wavelength (100-150 km) segmentation in the R-T-P magnetic and isostatic gravity anomalies is similar in wavelength to segmentation in magnetization and mantle Bouguer anomaly observed along the present-day MAR. The 300-500 km segmentation in the along-margin isostatic gravity anomaly is similar in length scale to both intermediate-wavelength tectonic segmentation observed in the South Atlantic and variations in lithospheric strength observed along the African margin. Furthermore, two of the intermediatewavelength (300-500 km) isostatic gravity lows correspond to the early traces of the Kane and Atlantis fracture zones, suggesting that these two fracture zones may define boundaries of a single tectonic corridor in the North Atlantic. We hypothesize that the direct cause of the intermediatewavelength segmentation may be along-margin variations in both the amount of underplated igneous crust and the strength of the lithosphere, although the relative importance of these two effects remains unresolved. Our results imply that segmentation is an important feature of margin development and that segmentation at mature oceanic spreading centers may be directly linked to segmentation during continental rifting.

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“…A steep hinge zone and landward-dipping block faults are characteristic of the western edge of the northern basin (Klitgord and others, 1988). The postrift unconformity is at a depth of over 13 km, and the seaward end of this surface terminates at a fault known as the East Coast boundary fault that is coincident with the ECMA (Alsop and Talwani, 1984;Klitgord and others, 1988). The carbonate bankpaleoshelf edge complex migrated seaward of this boundary fault during Jurassic time and masks the deeper structure over the zone corresponding to where salt diapirs and seaward-dipping reflectors are observed off Georges Bank.…”

Section: Multichannel Seismic Reflection Datamentioning

confidence: 96%

“…It has variously been interpreted to result from dikes (Emery and others, 1970;Alsop and Talwani, 1984), to be an edge effect due to the juxtaposition of continental crust and sedimentary units (Keen, 1969;Alsop and Talwani, 1984), or to be an edge effect due to the juxtaposition of oceanic crust and sedimentary units (Taylor and others, 1968;Klitgord and Behrendt, 1979;Hutchinson and others, 1983). The ability of different models to reproduce the shape of the anomaly reflects the nonuniqueness of the magnetic data.…”

Section: Magnetic Datamentioning

confidence: 96%

“…North of the Blake Plateau, the seaward margin of these basins is marked by the East Coast magnetic anomaly (ECMA) (Klitgord and Behrendt, 1979). Although this prominent linear magnetic anomaly is generally thought to be near the landward edge of oceanic crust (Keen, 1969;Emery and others, 1970;Klitgord and Behrendt, 1979;Sheridan and others, 1979;Hutchinson and others, 1983;Alsop and Talwani, 1984), the details of its origin remain controversial (Klitgord and others, 1988). Why a similar anomaly is not present along the seaward edge of the Blake Plateau or along the southern edge of the U.S. Gulf of Mexico margin also remains a question.…”

Section: Atlantic Continental Marginmentioning

confidence: 97%

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Chapter 17: Atlantic and Gulf of Mexico continental margins

Tréhu¹,

Klitgord²,

Sawyer³

et al. 1989

Geological Society of America Memoirs

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The U.S. Atlantic and Gulf of Mexico continental margins are thickly sedimented passive margins that formed when Pangea split apart during Middle Jurassic time to create the Atlantic Ocean and Gulf of Mexico. Keys to understanding the process of continental breakup and its relation to preexisting structure are found in the structure of the crust beneath the sediment-filled basins and adjacent platforms and embayments that outline the margins. Because of the great thickness of post-rift sedimentary rock in the basins and the presence of massive reef carbonates and salt layers and diapirs, the crustal structure beneath the basins in the region of the transition between oceanic and continental crust is poorly known at present. Recent advances in seismic reflection and refraction data collection techniques (both sources and receivers), however, are just beginning to yield new data to look at the crustal structure in this important region. One of the most important results on the deep structure of continental margins obtained in recent years is recognition of a thick, high-velocity (7.2 to 7.5 km/sec) layer at the base of the crust beneath the U.S. Atlantic continental margin as well as beneath several other margins worldwide. This layer is observed beneath both extended continental crust and early oceanic crust and has been interpreted to indicate that extensive intrusive magmatism was associated with the late stage of rifting and early sea-floor spreading. Only a weak suggestion of such a layer has been observed beneath the Gulf of Mexico margin, although this may be in part due to the difficulty of observing lower crustal arrivals because of the extensive presence of salt in the shallow section.

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The East Coast Magnetic Anomaly

Cited by 41 publications

References 9 publications

The Grenville orogenic cycle of southern Laurentia: Unraveling sutures, rifts, and shear zones as potential piercing points for Amazonia

The Grenville orogenic cycle of southern Laurentia: Unraveling sutures, rifts, and shear zones as potential piercing points for Amazonia

Segmentation in gravity and magnetic anomalies along the U.S. East Coast passive margin: Implications for incipient structure of the oceanic lithosphere

Chapter 17: Atlantic and Gulf of Mexico continental margins

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