Seismic refraction and reflection measurements-Puerto Rico Outer Ridge

Bunce, Elizabeth T.; Fahlquist, Davis A.; Clough, John W.

doi:10.1029/jb074i012p03082

Cited by 8 publications

(8 citation statements)

References 11 publications

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“…In addition, an attempt has been made to assign a sea floor age to each site on the basis of magnetic anomalies and deep-sea drilling results, to clasgify each site in terms of tectonic province (e.g., median valley, ridge flank, back arc basin), and finally, for studies of seismic anisotropy and structure, to determine the azimuth of each profile with respect to nearby fracture zones and magnetic anomaly orientations or, for back arc,basins, with respect to the axial trends of nearby island arcs and behind-arc ridges. Although extensive use will be made of this compilation below, compressional wave velocity data will be presented here in summary form only, since they can, for the most part, be found elsewhere in the literature ; Francis and Shot, 1966;Keen and Loncarevic, 1966;Ludwig et al, 1966Ludwig et al, , 1968Ludwig et al, , 1971Ludwig et al, , 1973Francis and Raitt, 1967;Fenwick et al, 1968;Furumoto et al, 1968Furumoto et al, , 1971Murauchi et al, 1968Murauchi et al, , 1973Shor et al, 1968Shor et al, , 1971Bunce et al, 1969;Den et al, 1969Den et al, , 1971Ewing and Houtz, 1969;Helmberger and Morris, 1969;Matthews et al, 1969;Bosshard and MacFarlane, 1970;Ewing et al, 1970Ewing et al, , 1971Houtz et al, 1970;Sutton et al, 1971;Talwani et al, 1971;Yoshii et al, 1973].…”

Section: Oceanic Refraction Datamentioning

confidence: 99%

Structure and constitution of the lower oceanic crust

Christensen¹,

Salisbury²

1975

Reviews of Geophysics

485

312

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Any petrologic model of the lower oceanic crust must be consistent with three sets of data: (1) the seismic structure of the oceanic crust, (2) the petrology of oceanic dredge samples, and (3) laboratory measurements of seismic velocity through such samples. A review of these data indicates that within the framework of earlier three‐layer models of oceanic seismic structure the crust is internally complex and varies markedly with age, azimuth, and tectonic province. Mantle compressional wave velocities Vp are anomalously low under the ridge (7.2–7.7 km/s) but increase to 8.0–8.3 km/s beyond 15 m.y.; layer 3 thickens by 2 km within 40 m.y. of formation and decreases in Vp from 6.8 to 6.5 km/s within 80 m.y.; both the mantle and layer 3 are statistically anisotropic. Dredge lithologies consist predominantly of serpentinized ultramafics and mafic igneous rocks ranging from basalt to gabbro, the gabbro often showing evidence of fractionation. Metamorphism of mafic rocks from zeolite to amphibolite facies grade is common. Velocities in oceanic serpentinites and basalts are generally lower than layer 3 refraction velocities. Unaltered gabbros have compressional wave velocities of approximately 7.0 km/s, which is high for layer 3, together with shear wave velocities Vs of 3.8 km/s and values of Poisson's ratio σ of 0.30. Metabasites containing hornblende and plagioclase have values of Vp = 6.8 km/s, Vs = 3.8 km/s, and σ = 0.28, in good agreement with those of layer 3. On the basis of petrology and velocity it is suggested that layer 3 is composed of hornblende metagabbro underlain by normal gabbro. In a model consistent with geophysical observations of heat flow, seismicity, gravity, and seismic structure at the ridge it is proposed that layer 2 and the upper levels of layer 3 form near the median valley but that deeper levels of layer 3 thicken for 40 m.y. by intermittent offridge intrusion fed from the underlying anomalous mantle. Ophiolites in such a model represent segments of thin immature ridge crest obducted onto continental margins during subduction of a spreading ridge.

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Section: Oceanic Refraction Datamentioning

confidence: 99%

Structure and constitution of the lower oceanic crust

Christensen¹,

Salisbury²

1975

Reviews of Geophysics

485

312

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“…Seismic refraction data used in this study were compiled from: Bowin (1968), Bunce and Fahlquist (1962), Bunce et al. (1969), Ebeniro et al. (1986), Edgar et al.…”

Section: Data Availability Statementmentioning

confidence: 99%

“…Over 400 reversed and unreversed seismic refraction stations were compiled for this study from: Bunce et al (1969), Bunce and Fahlquist (1962), Dillon et al (1972), Ebeniro et al (1986), Edgar et al (1971), J. I. Ewing et al (1960), M. Ewing and Worzel (1954), Hersey et al (1959), Houtz and Ewing (1964), Houtz and Ludwig (1977), Ibrahim et al (1981), Ladd et al (1977Ladd et al ( , 1981, Ludwig et al (1975), Mauffret and Leroy (1997), Officer et al (1959), Rosencrantz (1993), Sheridan et al (1966), andSun et al (2020).…”

Section: Rodríguezmentioning

confidence: 99%

Crustal Structure, Deformational History, and Tectonic Origin of the Bahamas Carbonate Platform

Shipper,

Mann

2024

Geochem Geophys Geosyst

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The 2–10‐km‐thick, mainly carbonate cap of the 14,000 km2 Bahamas carbonate platform (BCP) has impeded imaging of its underlying crustal structure. The deeper structure of the BCP records both its Mesozoic rift and hotspot history and its later deformation related to its Paleogene collision with the Great Arc of the Caribbean (GAC). We use regional gravity data to model the crustal structure, type, and deformational processes of the BCP by: (a) integrating publicly available seismic data; (b) inverting the Moho along 2D regional gravity transects across the collisional zone; (c) modeling flexural uplift of a forebulge that reflects the attempted subduction of the BCP beneath the GAC; and (d) using downhole temperatures and radiogenic heat production in 1D basin models to differentiate crustal types related to the Mesozoic rift history. We interpret three crustal domains underlying the BCP: (a) 27–12‐km‐thick, rifted, and thinned continental crust of the northern Bahamas between the Blake Plateau and Exuma Sound; (b) 24–12‐km‐thick, volcanically‐thickened oceanic crust related to the Triassic‐Jurassic Bahamas hotspot in the central Bahamas southeast of Long Island; and (c) 20–12‐km‐thick, thickened oceanic crust north of Hispaniola. We propose that these crustal types reflect northwest‐southeastward, Triassic‐Jurassic rifting of the Bahamas region during the breakup of Pangea and accompanying magmatic activity related to the Triassic‐Jurassic Bahamas hotspot and early oceanic spreading. Growth of the BCP during the Cretaceous in this area was followed by Late Cretaceous‐Paleogene subduction‐related flexure and terminal Paleogene collision between the GAC and the BCP.

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“…I have used the refraction data implying thicker sediments in the Caribbean than in the Atlantic Ocean (Edgar, Ewing & Hennion 1971 ; Talwani et QZ. 1959b), but partly for the reason given above I have ignored the refraction data suggesting a more subtle thinning of the crust beneath the outer rise (Bunce & Fahlquist 1962 ;Bunce et al 1969).…”

Section: Analysis Of Gravity Datamentioning

confidence: 99%

“…The Puerto Rico Trench is a peculiar feature in that it displays many features of island arcs but without a major component of active subduction. The trench trends east-west and north-south profdes show an outer rise (Bunce & Hersey 1966;Bunce, Fahlquist & Clough 1969;Bunce, Phillips & Chase 1974) with an outer gravity high (Bowin 1971(Bowin ,1972(Bowin ,1976Talwani, Sutton & Worzel 1959b), a gentle slope on the seaward side into the trench, and a steeper slope on the landward side. A large negative free-air gravity anomaly corresponds well with the position of the trench (Bowin 1971(Bowin , 1972(Bowin , 1976Talwani et ul.…”

Section: Introductionmentioning

confidence: 99%

Gravity anomalies and the origin of the Puerto Rico Trench

Molnár¹

1977

Geophysical Journal International

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The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The gravitational body force that acts on a flap of lithosphere, hanging in the aesthenosphere and more dense than it, pulls the lithosphere down at the trench. Gravity anomalies are modelled assuming that the crustal thicknesses of the Atlantic and Caribbean Oceans are constant (but different) and that the Atlantic Ocean floor seaward of the outer rise, Puerto Rico, and the Caribbean Sea floor are each in isostatic equlibrium. The residual gravity anomalies are then consistent with the existence of a subcrustal dense mass, that could be the hanging slab of lithosphere. The value of this excess mass depends upon more arbitrary .assumptions for the crustal mass in the Puerto Rico Trench and its landward wall, but if the other assumptions above are realistic, the dense mass is required and is adequate to bend the surface down at the trench.

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Seismic refraction and reflection measurements-Puerto Rico Outer Ridge

Cited by 8 publications

References 11 publications

Structure and constitution of the lower oceanic crust

Structure and constitution of the lower oceanic crust

Crustal Structure, Deformational History, and Tectonic Origin of the Bahamas Carbonate Platform

Gravity anomalies and the origin of the Puerto Rico Trench

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