The Petrology of Oceanic Crust across Fracture Zones in the Atlantic Ocean: Evidence of a New Kind of Sea-Floor Spreading

1972 ◽  
Vol 80 (5) ◽  
pp. 526-538 ◽  
Author(s):  
Geoffrey Thompson ◽  
William G. Melson
Keyword(s):  
Atlantic Ocean ◽  
Oceanic Crust ◽  
Fracture Zones ◽  
Sea Floor ◽  
Sea Floor Spreading

The role of fracture zones in sea floor spreading

1973 ◽  
Vol 78 (32) ◽  
pp. 7776-7785 ◽  
Author(s):  
Christopher G. A. Harrison ◽  
Mahlon M. Ball
Keyword(s):  
Fracture Zones ◽  
Sea Floor ◽  
Sea Floor Spreading

Early Paleozoic Volcanism and Metamorphism of the Moretons Harbour–Twillingate Area, Newfoundland

1973 ◽  
Vol 10 (9) ◽  
pp. 1363-1379 ◽  
Author(s):  
D. F. Strong ◽  
J. G. Payne
Keyword(s):  
Oceanic Crust ◽  
Volcanic Rocks ◽  
Metal Sulfides ◽  
Early Paleozoic ◽  
Extensive Area ◽  
Sea Floor ◽  
Pillow Lavas ◽  
Intense Deformation ◽  
Sea Floor Spreading ◽  
Harbour Area

In the Moretons Harbour area, at the eastern end of the Lushs Bight terrane of central Newfoundland, the volcanic rocks of the "Lushs Bight Supergroup" are divided into two new groups, viz, the Moretons Harbour Group and the Chanceport Group. The former is separable into four formations, consisting primarily of variable proportions of basaltic pillow lavas and volcanoclastic sediments, with a composite thickness in excess of 6 km, or around 8 km including an extensive area of 'sheeted' diabase dikes. These formations are steeply dipping and face southwest; they are separated by the Chanceport fault from the Chanceport Group to the south. The latter consists of interbedded basaltic pillow lavas with graywackes and banded red and green cherts, all facing north and steeply dipping to overturned, with a composite thickness of approximately 3 km.The Moretons Harbour Group has been intruded by the Twillingate trondhjemitic granite–granodiorite pluton and abundant basic dikes intrude the granite, indicating that the mafic and felsic magmatism were coeval. Both have undergone intense deformation and the volcanics show a change from greenschist to amphibolite facies mineralogy within a distance of 2 km on approaching the pluton, a result of buttressing by the pluton during deformation, and not an intrusive effect.Base metal sulfides are common throughout the area, but the main occurrences of Cu, As, Sb, and Au are concentrated in the Little Harbour Formation, a 2600 m thick sequence of volcanoclastic rocks within the Moretons Harbour Group.The great thickness of volcanic rocks is interpreted as having formed in an island arc environment, although it is possible that the lowermost parts of the sequence represent oceanic crust. It is unlikely that the sheeted diabases of the Moretons Harbour area were produced by sea-floor spreading.

A Discussion on volcanism and the structure of the Earth - Proposals concerning the variation of volcanic products and processes within the oceanic environment

1972 ◽  
Vol 271 (1213) ◽  
pp. 131-140 ◽  
Keyword(s):  
Structural Model ◽  
Early Stage ◽  
Volcanic Rocks ◽  
Fracture Zones ◽  
Sea Floor ◽  
Stage Of Development ◽  
Incompatible Elements ◽  
The Earth ◽  
Sea Floor Spreading ◽  
Low Pressures

An attempt is made to fit available petrochemical data on oceanic volcanic rocks into the structural model for the ocean basins presented by the plate tectonic theory. It is suggested that there are three major volcanic regimes: (i) the low-potassic olivine tholeiite association of the axial zones of the oceanic ridges where magmatic liquids are generated at low pressures high in the mantle, (ii) the alkalic (Na > K) associations along linear fractures where liquids generated at greater depth gain easy egress to the surface, (iii) those alkalic associations, rich in incompatible elements, of island groups, remote from fracture zones, where magmas created at depth proceed slowly to the surface and in consequence suffer intense fractionation. There are certain discrepancies in this pattern, notably that there is no apparent relation between rate of sea-floor spreading and degree of over-saturation of the axial zone basalts and that certain areas, such as Iceland, are characterized by excess volcanism. Explanation of these anomalies is sought by examining an oceanic area in an early stage of development—the Red Sea. It is tentatively suggested that the initial split of a contiguous continent might be brought about by the linking of profound fractures, caused by domal uplift related to rising isolated lithothermal systems, and that the present anomalies in oceanic volcanism may reflect the variation in rate of thermal convection within the original isolated lithothermal plumes.

Amplitudes of oceanic magnetic anomalies and the chemistry of oceanic crust: Synthesis and review of 'magnetic telechemistry'

1979 ◽  
Vol 16 (12) ◽  
pp. 2236-2262 ◽  
Author(s):  
P. R. Vogt
Keyword(s):  
Oceanic Crust ◽  
Fracture Zone ◽  
Hot Spots ◽  
Hot Spot ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Fracture Zones ◽  
Juan De Fuca ◽  
Sea Floor Spreading ◽  
Ocean Ridge

A growing body of evidence suggests that certain areas of high-amplitude (H) sea-floor spreading-type magnetic anomalies reflect FeTi-enriched basalts of high remanent magnetization. A worldwide tabulation of these 'H-zones' is presented, together with a review of pertinent geochemical, rock magnetic, and deep-tow data relevant to the hypothesis of magnetic telechemistry.' H-zones are found in two tectonic settings: (1) along 102–103 km long sections of spreading axis close to hot spots; and (2) in narrow bands extending a few hundred kilometres along the edges of some fracture zones. Amplitudes in both provinces are 1.5 to 5, typically 2 to 3 times normal, and the hot spot H-zones are known from spreading half-rates of 0.6 to 3.7 cm yr−1 The highest amplitudes, magnetizations, and FeTi enrichment (up to 15–18% FeOT and 2–3% TiO2) seem to occur where both provinces overlap, i.e., where fracture zones occur near hot spots, for example along the Blanco Fracture Zone south of the Juan de Fuca hot spot and along the Inca Fracture Zone east of the Galapagos hot spot. The FeTi enrichment appears to reflect shallow-depth crystal fractionation (plagioclase, augite, and olivine), which is more extensive near hot spots, and more generally for fast-spreading ridges. H-zones presently affect at least 2.6 × 103 km, or 6.5% of the Mid-Ocean Ridge axis. However, the total known H-area of 8.5 × 105 km2 represents only 0.3% of oceanic crust. This suggests that older H-zones remain to be discovered, or/and that conditions favoring the formation of FeTi basalt and H-anomalies are more prevalent now than they have been on the average for the last 108 years. Evidence for the latter is provided by the known expansion of the magnetically well surveyed Juan de Fuca, Galapagos, and Yermak (Arctic) H-zones in the last 5 million years.

Thermal aspects of sea-floor spreading and the nature of the oceanic crust

1973 ◽  
Vol 18 (1-2) ◽  
pp. 1-17 ◽  
Author(s):  
Y. Bottinga ◽  
C.J. Allegre
Keyword(s):  
Oceanic Crust ◽  
Sea Floor ◽  
Sea Floor Spreading

The structure of the oceanic lithosphere

1971 ◽  
Vol 268 (1192) ◽  
pp. 619-619
Keyword(s):  
Oceanic Crust ◽  
Upper Mantle ◽  
Oceanic Lithosphere ◽  
Ocean Floor ◽  
Mass Motion ◽  
Sea Floor ◽  
Ocean Ridges ◽  
Velocity Gradients ◽  
The Earth ◽  
Sea Floor Spreading

Sea-floor spreading requires that new ocean floor be generated at mid-ocean ridges and that along with the underlying oceanic crust it move laterally away from its site of generation. In so far as it is unlikely that the 5 km thick oceanic crust moves independently of the underlying upper mantle, the horizontal mass motion associated with spreading extends at least some way into the mantle. The lithosphere is the crust and that part of the upper mantle to which it is mechanically coupled; together they form the brittle and relatively ‘strong’ outermost part of the Earth; velocity gradients within the lithosphere are negligible.

The Canadian Cordillera, the Hellenides, and the Sea-Floor Spreading Theory

1972 ◽  
Vol 9 (6) ◽  
pp. 709-743 ◽  
Author(s):  
Jean Dercourt
Keyword(s):  
Pacific Ocean ◽  
Oceanic Crust ◽  
Continental Margin ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Late Triassic ◽  
Canadian Cordillera ◽  
Transform Faults ◽  
Sea Floor ◽  
Sea Floor Spreading

The theory of plate tectonics is applied to the tectonic evolution of the Hellenides and the Canadian Cordillera. In the Hellenides a Tethyan zone of sea-floor spreading developed within the continental crust during Triassic time and functioned until the end of the Middle Jurassic. It led to the formation of two plates, each with continental and oceanic segments, that were separated in some places by accreting plate margins and in others by transform faults. In Late Jurassic time the mid-Tethyan ridge became inactive as new ridges developed in the Atlantic Ocean. From Late Jurassic to Recent time, Tethyan oceanic crust largely disappeared under one of the cratons. The chronology of tectonic events in the Hellenides corresponds well with that of sea-floor spreading in the Atlantic.Four periods of sea-floor spreading were involved in the formation of the Canadian Cordillera: (1) a Silurian? to Early Devonian period when an Archeo-Pacific Ocean separated the Canadian craton with a stable sedimentary margin from a volcanic archipelago; (2) a Middle Devonian to Permian period when the extinct volcanic archipelago was bounded to the west by a spreading Paleo-Pacific Ocean, and to the east by a tectonic contact which was consuming Archeo-Pacific oceanic crust; part of this crust was obducted over the continental margin; (3) a Late Triassic to Middle Jurassic period when a second volcanic archipelago separated a spreading Neo-Pacific Ocean from the continental margin; and (4) a Late Jurassic to Recent period where spreading occurred in both the Atlantic and Pacific Oceans, subjecting the second volcanic archipelago and the continental margin to major tectonism; since the Paleocene, the Cordillera has slid towards the NNW along transform faults.

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