i. Abstract Numerous extinct spreading centres are found within the world’s ocean basins and these record instances of spreading cessation or migration that provide valuable insights into the mechanism of heat-loss from the mantle and plate tectonic behaviour. This study presents the first comprehensive review of all reported extinct ridges and investigates their characteristics and regional distribution and frequency of occurrence over the last ~170 Myr as recorded in present-day preserved oceanic crust. The axial morphology, gravity signal and crustal structure of extinct ridges are evaluated by generating across-axis profiles through global datasets (IHO - IOC 2014; Sandwell et al. 2014) for individual ridge segments. Information on the spreading-rates, time of cessation and duration of spreading prior to cessation was collating information from previous studies. The potential geodynamic influences on the lifespan and activity of mid-ocean ridges were investigated by evaluating the relationship of extinct ridges to hotspots at their time of extinction using GPlates (Boyden et al. 2011) and a global reconstruction (Seton et al. 2012). Global examples are investigated to assess similarities or differences and to determine the ‘characteristic’ signal of extinct ridges. Ridges were classified according to the quality of constraints into a primary, secondary or tertiary tier that dictated their inclusion in the quantitative analysis undertaken. Spreading centre subtype is
This lab uses earthquake data to construct profiles of two convergent boundaries: the Tonga Trench and the Peru-Chile Trench. Where two tectonic plates converge, if one or both of the plates is an oceanic lithosphere, a subduction zone will form. When crust is formed at a mid-ocean ridge, it is hot and buoyant meaning it has a low density. As it spreads away from the ridge and cools and contracts, or becomes denser, it is able to sink into the hotter underlying mantle. When two oceanic plates collide, the younger of the two plates, because it is less dense will ride over the edge of the older plate. The density of the
One evidence of this theory is molten material. Molten Material is magma erupting from mid-ocean ridges. Alvin the submarine found weird rocks shaped like pillows or toothpaste. This tells us this magma cools quickly underwater. Another type of evidence are magnetic stripes. Magnetic stripes are patterns in the ocean floor to prove Earth’s magnetic field has reversed itself in history. Scientist also looked at the “magnetic memory” of the rocks. Scientist drilled pipes through water to drill holes into the ocean floor. Scientists discovered that the older rocks were further away and younger rocks were closer. Those were the three types of evidence that scientist used to support the theory of Sea Floor Spreading.
The Slate Belt bioregion is nested within the Great Valley Section of the Valley and Ridge Province that was formed by thrust and fault folding during the Late Ordovician period through and Late Paleozoic era.(Bailey,1992; Geyer, 1979;Van Diver, 1990). During this time Taconian
There are three distinct types of plate boundaries existing, which are supported by geological observation, geophysical data, and theoretical considerations. Their names and categories are based on if adjacent plates move apart from each other (divergent plate margins), toward one another (convergent plate margins), or slip past one another in a direction parallel to their common boundary (transform plate margins) (Pitman, W.C., 2007).
The heavier oceanic plate is being pushed under and melted so that it will rise up the lithosphere as magma and gasses to cause an
To support the theory of continental drift is through topography, surveying the floors of oceans, charts of rock magnetism, and statistics on rock ages (Trefil & Hazen, 2010). At one time scientist believed that the deep ocean floors were flat; accumulating the sediment that progressively wore away from the prehistoric landmasses (Trefil & Hazen, 2010). However, they discovered steep-walled valleys and elevated highlands. This was evidences that just as the continents are transformed and are active, so to is the seafloor (Trefil & Hazen, 2010). The Mid- Atlantic Ridge, positioned in the central part of the Atlantic Ocean, is recorded to be the longest mountain range on this planet. Volcanoes, lava flow, and earthquakes are a source of
The creation of the Ring of Fire is very interesting too, it is the result of plate tectonics. These are huge slabs of Earth’s crust that fit together like the pieces of a puzzle. These plates can collide, stay apart, or move up right next to each other. The convergent plate boundaries are formed by plates colliding into each other. The heavier plates slide under the lighter plates causing a deep trench in the ocean floor, as we talked about earlier. If you went down into the ocean you’d be able to see a bunch of trenches in the ocean floor running parallel to corresponding volcanic arcs like the Ring of Fire. This allows islands and continental mountain ranges to be created. A divergent boundary is formed by
The youngest oceanic crust is located along the mid-ocean ridges where new crust is formed when the old crust is pushed away from mid – ocean ridges as a result of the seafloor spreading.
8.18 What explains the shrinking of ocean crust as the crust moves away from volcanoes?
The western Cordilleran orogenic belt had been depicted as a passive margin after Neoproterozoic to Early Cambrian rifting. Afterwards, the passive margin converted to an active margin most probably about Late Devonian to Late Cretaceous through the subduction of the exotic allochthons beneath the North American plate. The late Jurassic to Cretaceous subduction of (Sevier and Laramide Orogeny) representing as a period of the back thrust, intraplate thrusting, behind a magmatic arc on the upper plate near or on its westernmost margin from the latest
However, if you travel away from the ridges you will encounter rocks with reverse polarity and then rocks of normal polarity which are followed by reverse polarity rocks, etc. Vine and Matthews observed that there were symmetrical bands of rocks with similar polarities on each side of every mid-ocean ridge. They hypothesized that the reverse polarized rocks formed at the ridges during the geologic past when the earth's magnetic field had reverse polarization. Their work provided rather elegant proof that the seafloor spreading actually occurs.
Another rifting phase started in the early Jurassic around Pliensbachian or Toarcian (Chongzhi et al., 2013; Geoscience, 2014; Tindale, Newell, Keall, & Smith, 1998). Exmouth, Barrow, Dampier and Beagle Sub-basins were created until Middle Jurassic (He, 2002; Tortopoglu, 2015) and oceanic crust was laid down to form the Argo Abyssal Plain in Late Jurassic around 164-160 Ma during the Callovian to Oxfordian then followed by the Gascoyne and Cuvier Abyssal Plain in Early Cretaceous around 125 Ma (Fullerton, Sager, & Handschumacher, 1989; Müller, Mihut, & Baldwin, 1998). Passive margin was established in North West Shelf. Rifting phase of the basin transformed into sagging phase post breakup thermal subsidence when Gondwana breakup took place during Valanginian early Cretaceous around 134Ma. During the Campanian late Cretaceous, rifting along the Australian southern margin triggered the basin inversions and wrench reactivation of basin structures on NW Shelf. These movements arose the Barrow Island above sea level and formed Novara, Resolution and Exmouth Plateau Arch in Barrow, Dampier Sub-Basins and Investigator Sub-Basin (Figure 1) (Longley et al., 2002; Sinhabaedya,
7. What is the relationship between plate tectonics and the ocean floor—seafloor spreading, for example?
Another cause is the formation of submarine, volcanic ranges, which would cause transgression. The subsequent subsidence of the submerged volcanic ranges would result in regression. Since the ocean floor over 200 million years old has been removed through plate tectonic subduction, the remnants of those marine volcanoes, if they formed during the P-T transition , would not be observable today.
Crustal shortening is the primary result of a continent-continent collision in the orogenic thrust belts. Several techniques have been applied to understand the shortening rates in active collisional belts like the Himalayas. These estimates have been derived by Global Positioning System (GPS) for shorter timescales and balanced cross sections for longer time scales (Long et al., 2012). The preliminary studies conducted in the eastern Himalayas using GPS states that modern shortening rates are in the order of ~15-20 mm/yr to 20-12 mm/yr (Bilhan et al., 1997; Larson et al., 1999; Banerjee and Burgmann, 2002; Zhang et al., 2004). Using balanced cross section techniques DeCelles et al., (2002) and Long et al., (2011b) estimated that close to 400-670 km of crustal shortening has been accommodated in eastern thrust belt during 23-25 Ma range, giving the shortening rate of 16-29 mm/yr. Both of these techniques provides shortening rates that are quite similar and shows the motion along basal dècollement have been constant through time (Herman et al., 2010).