Gravity and Seismic Reflection Investigations into the Crustal Structure of the Aves Ridge, Eastern Caribbean

Abstract

Summary The results of bathymetric, gravimetric and seismic reflection surveys over the Aves Ridge and Grenada Trough (eastern Caribbean) are presented. The Aves Ridge is a submerged linear prominence typically formed of two flanking ridges enclosing a sediment filled trough in which occur seismic reflectors similar to those found in the Venezuela Basin and Grenada Trough. The short wavelength gravity anomalies of the Aves Ridge may be adequately explained in terms of structures in the sediment/basement interface. The Aves Ridge is underlain by a mass deficiency which may be interpreted in terms of a thickened crust with consequent depression of the Moho and lowest crustal layer. The positive Bouguer anomalies of the Grenada Trough are probably due to a relatively shallow Moho. The Aves Ridge and Grenada Trough typically exhibit negative isostatic anomalies and the Lesser Antilles define a linear belt of positive isostatic anomalies. These new results support the suggestion that the Aves Ridge is an ancient island arc.

Crustal structure of the Caribbean–northeastern South America arc‐continent collision zone

“…Crustal thickness in Figure 5b is ∼26 km at the Aves Ridge and ∼24 km at the Lesser Antilles arc; similar crustal thickness estimates of 26–28 km are observed on the eastern extension of these features near 64°W and 67°W [ Clark et al , 2008; M. B. Magnani et al, Crustal structure of the South America–Caribbean plate boundary at 67°W from controlled‐source seismic data, submitted to Journal of Geophysical Research , 2008]. These values are less than previous crustal thickness estimates of 30–35 km across the Lesser Antilles arc [ Westbrook , 1975; Boynton et al , 1979; Maury et al , 1990] and 30–40 km [ Kearey , 1974; Boynton et al , 1979] for the Aves Ridge. The differences in crustal thickness estimates may reflect spatial variability (previous experiments were farther to the north, Figure 1), or could be an artifact of the previous techniques which relied primarily on nonunique gravity modeling with some sparse seismic constraints [ Kearey , 1974; Westbrook , 1975; Boynton et al , 1979; Maury et al , 1990].…”

“…Most investigators have argued that the basin formed through back‐arc spreading, although extension orientation varies in these models from east‐west [ Tomblin , 1975; Bird et al , 1993, 1999], to north‐south [ Pindell and Barrett , 1990], to northeast‐southwest [ Bouysse , 1988]. An alternate model for Grenada Basin origin is that it is trapped oceanic crust or forearc that formed during an eastward jump or rollback of the subduction zone [ Bunce et al , 1970; Malfait and Dinkleman , 1972; Kearey , 1974]. The Tobago Basin may have formed as a consequence of uplift of the Barbados Ridge to its east [ Westbrook , 1975].…”

Evolution of the Grenada and Tobago basins and implications for arc migration

“…Previous workers have proposed various tectonic models for the origin of the Grenada basin (Bird et al, 1999;Bouysse, 1988;Kearey, 1974;Pindell and Barrett, 1990;Pinet et al, 1985;Smith, 1993;Tomblin, 1975). One model is that the Grenada basin is a trapped portion of Atlantic oceanic crust that formed as a result of an eastward jump in the subduction zone (Kearey, 1974); an alternative is that the Grenada basin formed as an oceanic backarc basin as the result of rifting of the Lesser Antilles arc away from the Aves Ridge (Bird et al, 1999;Bouysse, 1988;Pindell and Barrett, 1990).…”

“…One model is that the Grenada basin is a trapped portion of Atlantic oceanic crust that formed as a result of an eastward jump in the subduction zone (Kearey, 1974); an alternative is that the Grenada basin formed as an oceanic backarc basin as the result of rifting of the Lesser Antilles arc away from the Aves Ridge (Bird et al, 1999;Bouysse, 1988;Pindell and Barrett, 1990). …”

The Caribbean plate: Pulled, pushed, or dragged?

“…The Grenada basin is suggested to be either a Cretaceous‐Eocene back‐arc or fore‐arc basin, resulting from slab roll‐back [ Bird et al , 1993; Aitken et al , 2009] or a trapped piece of Atlantic lithosphere [ Kearey , 1974]. No active spreading is taking place at present, although Schellart et al [2007] suggest in their global compilation that trench migration still takes place at the Antilles.…”