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Dating oceanic crust

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October 31, A newly developed method that detects tiny bits of zircon in rock reliably predicts the age of ocean crust more than 99 percent of the time, making the technique the most accurate so far. Image: Tiny crystals called zircons, used to date oceanic crust, are relatively common in rocks known as gabbros. About 25 percent of the samples were 2.

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Oceanic crust

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This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts. A newly developed method that detects tiny bits of zircon in rock reliably predicts the age of ocean crust more than 99 percent of the time, making the technique the most accurate so far.

About 25 percent of the samples were 2. Zircons are widely regarded as providing the best basis for finding the absolute age of rocks on land, according to Cheadle's coworker, Barbara John, who is also geologist at UW. The zircon dating technique has been used extensively to answer questions such as when and how fast the Earth's continental crust forms. But until now, scientists have relied on geophysical methods based on magnetism to date ocean crust.

As the Earth's tectonic plates separate over time, new crust is created at mid-ocean ridges, says John. Minerals in the rocks that make up the crust are magnetized in the direction of the Earth's magnetic field as they cool and freeze. Because the field reverses polarity over time, the rocks record the polarity, creating alternating stripes on either side of a mid-ocean ridge.

Traditionally, instruments aboard ships have predicted the age of the ocean's crust by mapping these magnetic stripes, and then calculating an age using distance and time between polarity reversals within the crust, says Rodey Batiza, program director in the National Science Foundation NSF 's Division of Ocean Sciences, which funded the research.

But that method does not reveal the entire process involved in the growth of ocean crust, he says. Joshua Schwartz, the paper's first author and a UW Ph. Adds Cheadle, "Findings about today's ocean ridges help us to better understand how the Earth has worked in the past.

Other co-authors of the paper are affiliated with the U. Geological Survey in Menlo Park, Calif. Media Contacts Cheryl L. Dybas, NSF, , email: cdybas nsf. The U. National Science Foundation propels the nation forward by advancing fundamental research in all fields of science and engineering. NSF supports research and people by providing facilities, instruments and funding to support their ingenuity and sustain the U.

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Home News. Email Print Share. Tiny crystals called zircons are used to date oceanic crust. Credit and Larger Version.

Scientists Discover Accurate Method to Date Oceanic Crust

Dating , in geology , determining a chronology or calendar of events in the history of Earth , using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques. These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events. Radiometric dating and certain other approaches are used to provide absolute chronologies in terms of years before the present. The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere.

A newly developed method that detects tiny bits of zircon in rock reliably predicts the age of ocean crust more than 99 percent of the time, making the technique the most accurate so far. About 25 percent of the samples were 2. Zircons are widely regarded as providing the best basis for finding the absolute age of rocks on land, according to Cheadle's coworker, Barbara John, who is also geologist at UW.

This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts. A newly developed method that detects tiny bits of zircon in rock reliably predicts the age of ocean crust more than 99 percent of the time, making the technique the most accurate so far. About 25 percent of the samples were 2. Zircons are widely regarded as providing the best basis for finding the absolute age of rocks on land, according to Cheadle's coworker, Barbara John, who is also geologist at UW.

New Method Of Dating Oceanic Crust Is Most Accurate So Far

Scientists can determine the age of the seafloor thanks to the changing magnetic field of our planet. This has happened many times throughout Earth's history. When scientists studied the magnetic properties of the seafloor, they discovered normal and reversed magnetic stripes with different widths. These magnetic patterns are parallel to the mid-ocean ridges and symmetrical on both sides. As rocks crystallize from lava at the ridges, they literally record the magnetic field of the Earth at the time of their creation. These stripes of normal and reverse magnetic fields with different sizes can be matched with the geomagnetic reversals records obtained from continental rocks already dated: this is how scientists get the age of the seafloor. To confirm the ages obtained with magnetic records, and get an absolute age of the seafloor, scientists use the radioactive dating technique. When the lava solidifies at the ridges to form the new seafloor, radioactive elements coming from the mantle are trapped in it. These elements, like U Uranium or 40 K Potassium are unstable, and decay with a very precise rate to become what is called daughter products: P Lead for Uranium and 40 Ar Argon for Potassium.

New Method of Dating Oceanic Crust Is Most Accurate So Far

The youngest crust of the ocean floor can be found near the seafloor spreading centers or mid-ocean ridges. As the plates split apart, magma rises from below the Earth's surface to fill in the empty void. The magma hardens and crystallizes as it latches onto the moving plate and continues to cool over millions of years as it moves farther away from the divergent boundary. Like any rock, the plates of basaltic composition become less thick and denser as they cool. When an old, cold and dense oceanic plate comes into contact with a thick, buoyant continental crust or younger and thus warmer and thicker oceanic crust, it will always subduct.

Michael J.

Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust , composed of troctolite , gabbro and ultramafic cumulates. The crust and the solid mantle layer together constitute oceanic lithosphere.

New Ocean Crust May Form Slower Than Thought

The crust that makes up the bottom of the world's oceans is constantly being generated along mid-ocean ridges, mountain ranges that look like the seams of a baseball on the seafloor. A new study that examined some of the minerals that make up new ocean crust suggests that the formation process may be slower and less uniform than previously thought. Mid-ocean ridges are the boundaries between tectonic plates and are the place where the plates spread apart from each other. Magma from the underlying mantle erupts at the edges, then cools and solidifies to form new ocean crust.

Oceanic crust is about 6 km 4 miles thick. It is composed of several layers, not including the overlying sediment. The topmost layer, about metres 1, feet thick, includes lavas made of basalt that is, rock material consisting largely of plagioclase [ feldspar ] and pyroxene. Oceanic crust differs from continental crust in several ways: it is thinner, denser, younger, and of different chemical composition. Like continental crust, however, oceanic crust is destroyed in subduction zones. The lavas are generally of two types: pillow lavas and sheet flows.

Lower oceanic crust

The lower oceanic crust is the lower part of the oceanic crust and represents the major part of it volumetrically biggest part. And the recycling of this part of the oceanic crust, together with the upper mantle has been suggested as a significant source component for tholeiitic magmas in Hawaiian volcanoes. The three main processes happening in this region of the oceanic crust are partial melting of the earth's mantle, melt accumulation at various depths and the chemical modification of this melts during ascent,. The mantle melts are most commonly modified by fractional crystallisation due to cooling [7] and by assimilation of crustal rocks. The most important parameter controlling the processes operating in the lower oceanic crust is the magma supply, this is further controlled by the spreading rate, and therefore, spreading rate is a critical variable in models for the formation of the lower oceanic crust. Intensive search spanning over three decades of seismic imaging have shown that the ridge axis is underlain by a crystal mush containing a small percentage of melt , [10] capped by a thin melt lens containing a generally high, but variable melt fraction.

Mar 4, - Therefore, seafloor dating isn't that useful for studying plate motions beyond the Cretaceous. For that, geologists date and study continental crust.

The basic granulite, which is considered to be the MORB based on geochemistry and isotopic characteristics [1] , has been discovered recently as the enclaves in the Yingjiang islandarc magmatic suite on the border of Burma and west Yunnan, east of Myitkyina suture in the eastern Burma. The laser micro-area 40 Ar- 39 Ar technique is used to date the age of garnet and cliopyroxene that is the result of the early metamorphic event. The discovery of the high-grade or high-pressure metamophic rocks in the island-arc magmatic suite by the way of studying its P-T-t paths can provide a good way to study the age and process of oceanic crust subduction, slab break-off, metamorphic terrain exhumation and the evolution of paleoocean basin. This is a preview of subscription content, log in to check access.

The Age of the Ocean Floor

Она ждала чего угодно, но только не. - Внешний файл. Вы не шутите.

Dating the growth of oceanic crust at a slow-spreading ridge.

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Люди на подиуме с нетерпением ждали, когда на экране появится их бывший сослуживец Энсей Танкадо.

За Цифровую крепость, волнения из-за Дэвида, зато, что не поехала в Смоуки-Маунтинс, - хотя он был ко всему этому не причастен. Единственная его вина заключалась в том, что она испытывала к нему неприязнь. Сьюзан важно было ощущать свое старшинство. В ее обязанности в качестве главного криптографа входило поддерживать в шифровалке мирную атмосферу - воспитывать .

Лучше всего - Нетскейп. Сьюзан сжала ее руку. - Давайте скорее. Попробуем порыскать. ГЛАВА 125 - Сколько у нас времени? - крикнул Джабба. Техники в задней части комнаты не откликнулись.

Наконец-то, черт возьми. Бринкерхофф поднял трубку: - Канцелярия директора. Фонтейн протянул руку.

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