Geophysical studies of the continental margin northeast of Newfoundland

1968 ◽  
Vol 5 (3) ◽  
pp. 483-500 ◽  
Author(s):  
D. K. B. Fenwick ◽  
M. J. Keen ◽  
Charlotte Keen ◽  
A. Lambert
Keyword(s):  
Continental Crust ◽  
Continental Margin ◽  
Magnetic Anomalies ◽  
Ocean Basin ◽  
Labrador Sea ◽  
Mobile Belt ◽  
Magnetic Survey ◽  
Continental Plate ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

A seismic and magnetic survey has been made of an area that straddles the continental margin northeast of Newfoundland from the edge of the shelf to the ocean basin of the Labrador Sea. The results bear on the question of the extension of the mobile belt of the Appalachian System in Newfoundland to the margin. Our seismic studies show that the crust is approximately 30 km thick beneath the edge of the shelf northeast of Newfoundland, and thins to approximately 12 km at the foot of the slope. Seismic studies by Lamont Geological Observatory suggest that the mobile belt continues to the upper part of the slope; our studies support this. Large magnetic anomalies run nearly parallel to the edge of the shelf over the slope and rise, at right angles to the strike of the Appalachian System. Their amplitude is 1400 gammas and the belt of anomalies is 180 km wide. It runs continuously for at least 220 km. One interpretation is that the anomalies owe their origin to the juxtaposition of a magnetic continental plate 30 km thick against a thinner magnetic oceanic plate 10 to 12 km thick. We suggest that the continental crust is particularly magnetic, and the 'shelf-edge' anomalies particularly large, because it represents the basic mobile belt of the Appalachian System terminating beneath the lower part of the continental slope. The contrast in magnetization between non-magnetic oceanic mantle and magnetic continental crust is due to this, and perhaps also to higher temperatures in the oceanic mantle. They could be particularly high if the Labrador Sea is the site of a mid-ocean ridge. Some evidence from the magnetic survey suggests that a fault with dextral slip runs on the continent side of the margin in a northeasterly direction. It does not continue into the ocean basin.

First mid-ocean ridge-type ophiolite from the Meso-Tethys suture zone in the north-central Tibetan plateau

2020 ◽  
Vol 132 (9-10) ◽  
pp. 2202-2220 ◽  
Author(s):  
Yue Tang ◽  
Qing-Guo Zhai ◽  
Sun-Lin Chung ◽  
Pei-Yuan Hu ◽  
Jun Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Ocean Basin ◽  
Suture Zone ◽  
The Tibetan Plateau ◽  
Spreading Ridge ◽  
North Central ◽  
The North ◽  
Central Tibetan Plateau ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Abstract The Meso-Tethys was a late Paleozoic to Mesozoic ocean basin between the Cimmerian continent and Gondwana. Part of its relicts is exposed in the Bangong–Nujiang suture zone, in the north-central Tibetan Plateau, that played a key role in the evolution of the Tibetan plateau before the India-Asia collision. A Penrose-type ophiolitic sequence was newly discovered in the Ren Co area in the middle of the Bangong–Nujiang suture zone, which comprises serpentinized peridotites, layered and isotropic gabbros, sheeted dikes, pillow and massive basalts, and red cherts. Zircon U-Pb dating of gabbros and plagiogranites yielded 206Pb/238U ages of 169–147 Ma, constraining the timing of formation of the Ren Co ophiolite. The mafic rocks (i.e., basalt, diabase, and gabbro) in the ophiolite have uniform geochemical compositions, coupled with normal mid-ocean ridge basalt-type trace element patterns. Moreover, the samples have positive whole-rock εNd(t) [+9.2 to +8.3], zircon εHf(t) [+17 to +13], and mantle-like δ18O (5.8–4.3‰) values. These features suggest that the Ren Co ophiolite is typical of mid-ocean ridge-type ophiolite that is identified for the first time in the Bangong–Nujiang suture zone. We argue that the Ren Co ophiolite is the relic of a fast-spreading ridge that occurred in the main oceanic basin of the Bangong–Nujiang segment of Meso-Tethys. Here the Meso-Tethyan orogeny involves a continuous history of oceanic subduction, accretion, and continental assembly from the Early Jurassic to Early Cretaceous.

A Silurian U–Pb age for the Cape St. Mary's sills, Avalon Peninsula, Newfoundland, Canada: implications for Silurian orogenesis in the Avalon Zone

1993 ◽  
Vol 30 (8) ◽  
pp. 1607-1612 ◽  
Author(s):  
John D. Greenough ◽  
Sandra L. Kamo ◽  
Thomas E. Krogh
Keyword(s):  
Sedimentary Rocks ◽  
Geochemical Data ◽  
Mobile Belt ◽  
Ridge Basalt ◽  
Tectonic Environment ◽  
Mid Ocean Ridge ◽  
Mafic Magmas ◽  
Ocean Ridge ◽  
Avalon Peninsula ◽  
Orogenic Events

Mafic sills from Cape St. Mary's on the Avalon Peninsula of Newfoundland give an U–Pb baddeleyite age of 441 ± 2 Ma. This age corresponds with the earliest ages recorded for the climactic Silurian orogenic event that dominantly affected rocks of the Central Mobile Belt in Newfoundland. The age is consistent with but in no way necessitates that the Avalon and Gander zones were juxtaposed during the Silurian. Because sills tend to form in poorly lithified and undeformed sedimentary rocks, it is unlikely that Cambrian sediments hosting the sills were affected by Ordovician orogenic events that strongly affected central Newfoundland. Negative Nb and Ti anomalies on mid-ocean-ridge basalt normalized diagrams show that the sill geochemistry is consistent with formation in a transpressional tectonic environment. Mafic magmas clearly associated with the Silurian event share these chemical and tectonic affinities. Thus both the age and geochemical data are consistent with but do not require a link between the Gander and Avalon zones during the Silurian. If the two zones were joined prior to the Silurian then the Avalon must have been distal to both the Ordovician and Silurian orogenic activity. Further, considerable post-Silurian movement would have had to occur along the bounding Hermitage–Dover fault to account for contrasts in the intensity of metamorphism, plutonism, and deformation between the Gander and Avalon zones.

CONTINENTAL MARGIN TECTONICS AND THE EVOLUTION OF SOUTH EAST AUSTRALIA

1971 ◽  
Vol 11 (1) ◽  
pp. 75 ◽  
Author(s):  
J. R. Griffiths
Keyword(s):  
Continental Margin ◽  
Rift Valley ◽  
Structural Evolution ◽  
Initial Crack ◽  
Alkali Basalts ◽  
Australian Plate ◽  
Differential Movement ◽  
Mid Ocean Ridge ◽  
Regional Tectonic ◽  
Ocean Ridge

Following recent advances in geotectonics, a new approach can be applied to the study of the development of continental margins.A continental margin begins to form as an older continental craton breaks up. The initial crack develops into a rift valley, which becomes filled with thick clastic and volcanic deposits. As separation continues a new mid-ocean ridge is formed, and the two plates begin to drift apart more rapidly. At this stage the structural evolution of the margins is virtually complete, and marine sediments are deposited unconformably across the fault troughs.The continental fragments in the south west Pacific can be reassembled as a part of the ancient continent of Gondwanaland. Gondwanaland began to break up in the mid-Jurassic. A rift valley developed along the line of the present southern coast of Australia, through the Otway Basin. Two subsidiary tensional splays gave rise to the Elliston and Robe-Penola Troughs. Clastic sediments stripped from the cratonic highlands, and alkali basalts, occur in the rift grabens. Faulting and deposition continued throughout the Lower Cretaceous. About mid-Cretaceous a marine transgression from the west entered the subdividing rift valley. In the Eocene a new mid-ocean ridge formed and the Australian and Antarctic plates began to separate more rapidly. After this, quiet marine sedimentation occurred on the continental shelf and slope.The Bass and Gippsland Basins began to develop in the Cretaceous as differential movement occurred between the main Australian plate and a partially detached Tasmanian sub-plate. In the Upper Cretaceous the Gippsland Basin became open towards the evolving Tasman Sea, as New Zealand detached. The Tasmanian sub-plate ceased fo exist after the Eocene, becoming firmly fixed to the Australian plate. Later readjustments have occurred giving rise to further limited movements, mainly in the Gippsland Basin.The integration of detailed geological work and a regional tectonic analysis has been successfully applied to south east Australia and it is probable that a similar approach would yield fruitful results applied elsewhere.

Movements of thick evaporites on the flanks of a mid-ocean ridge: the central Red Sea Miocene evaporites

2020 ◽  
Author(s):  
Neil Mitchell ◽  
Wen Shi ◽  
Ay Izzeldin ◽  
Ian Stewart
Keyword(s):  
Red Sea ◽  
North Atlantic ◽  
Ocean Basin ◽  
Vertical Movements ◽  
Oceanic Spreading ◽  
Mid Ocean Ridge ◽  
History Of ◽  
Global Sea Level ◽  
Ocean Ridge ◽  
Thermal Subsidence

<p>Thick evaporites ("salt") were deposited in the South and North Atlantic, and Gulf of Mexico basins, in some parts deposited onto the flanks of nascent oceanic spreading centres.  Unfortunately, knowledge of the history of evaporite movements is complicated in such places by their inaccessibility and subsequent diapirism.  This is less of a problem in the Red Sea, a young rift basin that is transitioning to an ocean basin and where the evaporites are less affected by diapirism.  In this study, we explore the vertical movements of the evaporite surface imaged with deep seismic profiling.  The evaporites have moved towards the spreading axis of the basin during and after their deposition, which ended at the 5.3 Ma Miocene-Pliocene boundary.  We quantify the evaporite surface deflation needed to balance the volume of evaporites overflowing oceanic crust of 5.3 Ma age, thermal subsidence of the lithosphere and loss of halite through pore water diffusion, allowing for isostatic effects.  The reconstructed evaporite surface lies within the range of estimated global sea level towards the end of the Miocene.  Therefore, the evaporites appear to have filled the basin almost completely at the end of the Miocene.  Effects of shunting by terrigenous sediments and carbonates near the coast and contributions of hydrothermal salt are too small to be resolved by this reconstruction.</p>

Mid-ocean-ridge basalt of Indian type in the northwest Pacific Ocean basin

2009 ◽  
Vol 2 (4) ◽  
pp. 286-289 ◽  
Author(s):  
Susanne M. Straub ◽  
Steven L. Goldstein ◽  
Cornelia Class ◽  
Angelika Schmidt
Keyword(s):  
Pacific Ocean ◽  
Ocean Basin ◽  
Northwest Pacific ◽  
Northwest Pacific Ocean ◽  
Ridge Basalt ◽  
Mid Ocean Ridge ◽  
The Northwest Pacific Ocean ◽  
Ocean Ridge

Copper Systematics in Arc Magmas and Implications for Crust-Mantle Differentiation

Science ◽  
2012 ◽  
Vol 336 (6077) ◽  
pp. 64-68 ◽  
Author(s):  
Cin-Ty A. Lee ◽  
Peter Luffi ◽  
Emily J. Chin ◽  
Romain Bouchet ◽  
Rajdeep Dasgupta ◽  
...  
Keyword(s):  
Continental Crust ◽  
Redox State ◽  
Building Blocks ◽  
Magmatic Differentiation ◽  
Redox States ◽  
Cu Content ◽  
Arc Magmas ◽  
Reducing Conditions ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Arc magmas are important building blocks of the continental crust. Because many arc lavas are oxidized, continent formation is thought to be associated with oxidizing conditions. On the basis of copper’s (Cu’s) affinity for reduced sulfur phases, we tracked the redox state of arc magmas from mantle source to emplacement in the crust. Primary arc and mid-ocean ridge basalts have identical Cu contents, indicating that the redox states of primitive arc magmas are indistinguishable from that of mid-ocean ridge basalts. During magmatic differentiation, the Cu content of most arc magmas decreases markedly because of sulfide segregation. Because a similar depletion in Cu characterizes global continental crust, the formation of sulfide-bearing cumulates under reducing conditions may be a critical step in continent formation.

scholarly journals Ridge Jumps and Mantle Exhumation in Back-Arc Basins

Geosciences ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 475
Author(s):  
Valentina Magni ◽  
John Naliboff ◽  
Manel Prada ◽  
Carmen Gaina
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Numerical Models ◽  
Spreading Ridge ◽  
Transient Nature ◽  
Mid Ocean Ridge ◽  
Thinned Continental Crust ◽  
Mantle Exhumation ◽  
Back Arc ◽  
Ocean Ridge

Back-arc basins in continental settings can develop into oceanic basins, when extension lasts long enough to break up the continental lithosphere and allow mantle melting that generates new oceanic crust. Often, the basement of these basins is not only composed of oceanic crust, but also of exhumed mantle, fragments of continental crust, intrusive magmatic bodies, and a complex mid-ocean ridge system characterised by distinct relocations of the spreading centre. To better understand the dynamics that lead to these characteristic structures in back-arc basins, we performed 2D numerical models of continental extension with asymmetric and time-dependent boundary conditions that simulate episodic trench retreat. We find that, in all models, episodic extension leads to rift and/or ridge jumps. In our parameter space, the length of the jump ranges between 1 and 65 km and the timing necessary to produce a new spreading ridge varies between 0.4 and 7 Myr. With the shortest duration of the first extensional phase, we observe a strong asymmetry in the margins of the basin, with the margin further from trench being characterised by outcropping lithospheric mantle and a long section of thinned continental crust. In other cases, ridge jump creates two consecutive oceanic basins, leaving a continental fragment and exhumed mantle in between the two basins. Finally, when the first extensional phase is long enough to form a well-developed oceanic basin (>35 km long), we observe a very short intra-oceanic ridge jump. Our models are able to reproduce many of the structures observed in back-arc basins today, showing that the transient nature of trench retreat that leads to episodes of fast and slow extension is the cause of ridge jumps, mantle exhumation, and continental fragments formation.

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