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.

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.

Stratigraphy and tectonic significance of Cretaceous volcanism in the Queen Elizabeth Islands, Canadian Arctic Archipelago

1988 ◽  
Vol 25 (8) ◽  
pp. 1209-1219 ◽  
Author(s):  
Ashton F. Embry ◽  
Kirk G. Osadetz
Keyword(s):  
Hot Spot ◽  
Volcanic Rocks ◽  
Ellesmere Island ◽  
Canada Basin ◽  
Southern Limit ◽  
Sea Floor ◽  
Sverdrup Basin ◽  
Cretaceous Volcanism ◽  
Volcanic Succession ◽  
Sea Floor Spreading

Cretaceous volcanic rocks, which consist mainly of basalt flows and pyroclastic rocks, occur on northern Ellesmere Island, Axel Heiberg Island, and northernmost Amund Ringnes Island as part of the Sverdrup Basin succession. Volcanic rocks are associated with each of four regional transgressive–regressive (T–R) cycles that constitute the Cretaceous clastic succession of Sverdrup Basin and are of Valanginian – early Barremian, late Barremian – Aptian, latest Aptian – early Cenomanian, and late Cenomanian – Maastrichtian age; the volcanic component of each increases northward. The centre of volcanism appears to have been north of Ellesmere Island and is interpreted as the site of a mantle plume that was active throughout the Cretaceous.Most of the volcanic activity took place from Hauterivian to early Cenomanian (T–R cycles 1–3) and was accompanied by widespread sill and dyke intrusion. This activity coincided with the main rifting phase of the adjacent oceanic Canada Basin and with minor crustal extension in the Sverdrup Basin. From late Cenomanian to Campanian, volcanism was restricted to the extreme northeast, and trachytes and rhyolites were extruded along with basalts. This volcanic succession is interpreted as being the southern limit of Alpha Ridge, a major volcanic edifice that formed as a hot-spot track across Canada Basin during sea-floor spreading in Late Cretaceous.

Distribution of volcanic rocks about mid-ocean ridges and the Kenya Rift Valley

1970 ◽  
Vol 107 (2) ◽  
pp. 125-131 ◽  
Author(s):  
J. B. Wright
Keyword(s):  
Rift Valley ◽  
Volcanic Rocks ◽  
Pressure Relief ◽  
Kenya Rift ◽  
Sea Floor ◽  
Ocean Ridges ◽  
Volcanic Islands ◽  
Two Stages ◽  
Sea Floor Spreading ◽  
Kenya Rift Valley

SummaryQuartz-trachytic differentiates characterise volcanic islands on or near mid-ocean ridges, while phonolitic trends are found on islands rising from ocean basins. A large part of the Kenya Rift Valley is dominated by Plio-Pleistocene quartz-trachytes, which are underlain and flanked by variably nepheline-rich Miocene and Plio-Pleistocene lavas.Phonolitic and nephelinitic lavas dominate the assemblages of Miocene age, trachytes and olivine basalts those of Plio-Pleistocence age. This change in petrographic character with time is attributed to two stages of sub-crustal pressure relief corresponding to Lower Miocene and late Pliocene elevations of the Kenya dome. The result was a change in partial melting products from less to more silicic, especially along the axial rift valley.The doming movements and related vulcanism are believed to have originated because of lateral compression, induced by sea-floor spreading movements in the Atlantic and Indian oceans.

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.

Geophysical observations of the northern Juan de Fuca Ridge system: lessons in sea-floor spreading

1993 ◽  
Vol 30 (2) ◽  
pp. 278-300 ◽  
Author(s):  
E. E. Davis ◽  
R. G. Currie
Keyword(s):  
Oceanic Crust ◽  
Plate Tectonics ◽  
Hydrothermal Systems ◽  
Juan De Fuca Ridge ◽  
Plate Boundaries ◽  
Plate Motions ◽  
Sea Floor ◽  
Fuca Ridge ◽  
Juan De Fuca ◽  
Sea Floor Spreading

By virtue of its proximity to the coastline of North America and to numerous oceanographic institutions, the Juan de Fuca Ridge has been the focus of a large number of marine geological, geochemical, and geophysical investigations. Systematic studies began in the early 1960's with the geophysical survey of A. D. Raff and R. G. Mason, which provided much of the foundation for the development of the extraordinarily successful paradigms of sea-floor spreading and plate tectonics. Subsequent systematic and detailed studies of the plates and plate boundaries of the area by investigators from many academic, industrial, and government agencies, including the Geological Survey of Canada, have provided the basis for much of the fundamental understanding we now have of global plate motions and the processes that are involved in the creation of new oceanic crust at sea-floor spreading centres. Much of the success of these studies can be attributed to the geological diversity found along the Juan de Fuca Ridge. Clear examples are present of "normal" volcanically robust ridge segments, deep extensional rift valleys, stable and evolving transform faults, nontransform ridge offsets, propagating rifts, and off-axis seamount chains. Much has been learned about the nature of hydrothermal circulation through intensive studies of the many active hydrothermal systems and mature hydrothermal deposits that occur in both unsedimented and sedimented environments along the ridge. Better understanding of the way that oceanic crust chemically and physically "ages" is emerging from studies on the ridge and ridge flank. A clear history of the evolution of the ridge and of plate motions is provided by the magnetic anomalies mapped over the ridge and adjacent plates. From this history, lessons have been learned about the causes and consequences of plate motions, fragmentation, and internal deformation. Some of the success of these studies can be attributed to the rapidly evolving geophysical tools which provide ever increasing efficiency of operation and resolution. A new phase of study most recently begun involves the deployment of sea-floor geophysical "observatories" that provide a means by which temporal variations and events can be monitored over extended periods of time. These new studies are expected to yield yet another level of understanding of the processes that have produced two thirds of the Earth's surface as well as many important geologic formations in terrestrial settings.

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