The Acasta gneiss: Earth’s oldest surface rock

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Discovery of world’s oldest rocks challenged

The Acasta River is kms sm north of the City of Yellowknife. You will get to experience flight in the north as so many prospectors, geologists, and adventures have in the past on board an iconic de Havilland Canada DHC-2 Beaver Floatplane. The Acasta Gneiss is a tonalite gneiss. The exposed rock body is the oldest known intact crustal fragment on Earth.

The rock deposit is believed to be 4.

The Hadean The Acasta Gneiss Evidence of what happened in the first Ma of Earth history is sparse, and rocks that provide Hadean dates.

Many studies link the presence of continents on Earth to the operation of plate tectonics. Radiogenic isotope data have, however, long consigned the bulk of crust generation and preservation to the murky realm of the Precambrian Earth, where the prevailing geodynamic systems are highly uncertain due to the sparse and complex nature of the geological record of these early eons.

The purpose of this paper is to examine the nature of this geological record, considering the biases and artefacts that may undermine its fidelity, and to assess what are the most robust lines of evidence from which meaningful geodynamic inferences can be drawn. This is pursued with reference to Hadean detrital zircons, Archean gneiss complexes and Archean granite—greenstone terranes, and by considering isotopic proxies of crust—mantle interaction.

The evidence reinforces long held views that the formation of some of the oldest continental nuclei involved a distinctive mode of planetary geodynamics that rests uneasily within definitions of modern style plate tectonics. A detailed interrogation of the oldest rocks, integrating multi-scale information from the best preserved whole-rock and mineral archives, and emphasizing careful selection at the sampling and analytical stages, will lead to the most robust input data for petrological and thermodynamic models of early Earth processes.


It falls within the Hadean Period, which started with the formation of the Earth 4. It is named after Hades, the Greek god of the underworld and the hellish conditions that prevailed on Earth at the time. Only a few geological traces from this period remain, with others in Western Greenland and Western Australia.

From the top: □ Acasta Gneiss The Acasta Gneiss, from Northwest Territories, The Acasta Gneiss was dated by uranium-lead radiometric anal- ysis using.

These rocks provide an opportunity to investigate the nature of continental crust formation on the early Earth. Because complexities in zircons and bulk rocks are characteristic of the early Earth record—including the AGC—strategies are needed to extract accurate and meaningful age and isotopic information. In order to evaluate the accuracy of the early Earth Hf isotope record, we examined AGC zircons from a range of lithologies using paired chemical abrasion isotope dilution U-Pb age and solution Lu-Hf isotope analysis and compared these with previous results obtained using laser ablation split-stream LASS analysis.

We describe an approach whereby LASS is used to identify rocks with the least complex zircons, and, when appropriate, solution methods are then used to refine the age and Hf isotopic composition to the highest precision. This two-pronged analytical approach results in a more robust determination of the age and Hf isotopic record of complex rocks and zircons and allows identification of complexity in the Hf isotopic record that would not be apparent by solution analysis alone, thereby refining the record of magmatic evolution on the early Earth.

Despite the better precision, solution techniques are unsuitable for rocks with complexly zoned zircons. This is attributable to the presence of later radiogenic overgrowths on the zircon grains which are incorporated in solution analyses but can be avoided using LASS. This provides important clarity to the AGC Hf isotope record. Despite the presence of ancient AGC crust, there is no record of corresponding mantle depletion. This implies that extraction of Hadean crust in this region did not happen in sufficient volume to result in widespread mantle depletion in the AGC source by the Eoarchean.

Our results underscore the importance of identifying different components in ancient zircons—and the rocks that contain them—and accurately determining the age and isotopic composition of those components. Unraveling the complexity of zircons from the 4. Bauer; Jeffrey D. Vervoort; Christopher M.

High-precision temporal resolution of planetary processes in the Proterozoic and Archean

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Isotopic dating gives absolute ages in years or millions of years. In contrast, the layered successions of rocks give only relative ages – older than.

Tags: geology , rock , paleogeology , geochronology. Objective s : Earth’s oldest rocks, the 4. An area to the west near Grant Lake contains rocks of similar appearance that have not been thoroughly investigated with respect to age and crustal history. The research team proposes to collect samples from this area and determine, using U-Pb geochronology, the age of various rock units.

If Acasta-aged rocks are present, the results will help to determine the extent and geological history of Earth’s oldest continental fragment. A demonstrated absence of these rocks will provide equally important information. In both cases, the results will contribute to a broader study of the nature and extent of a large, ancient continental fragment in which the Acasta gneisses occur. The collection of a specimen of Acasta gneiss for public display in the Earth Sciences Gallery of the Royal Ontario Museum will draw public attention to the remarkable geological history of the Northwest Territories.

Project Description: During the proposed study, transportation of the research team to the field will be by fixed-wing float plane from Yellowknife. From the base camp at Grant Lake, the research team will examine the study area immediately to the east on foot and by inflatable boat. Rock samples up to 20 kg 45 lbs will be collected for age dating. It is anticipated that only samples will be collected for dating.

Acasta gneiss

Johnson, Daniel J. Here we present a detailed geological map of the main area of the complex around the sample locality of the oldest known rocks and detailed sketch maps of critical geological outcrops. The geological map shows that the complex is divided, by a northeast-trending fault, into eastern and western domains.

The eastern area is comprised from quartz dioritic-gabbroic gneisses and multi-phase tonalitic-granitic gneisses. The western area is comprised of layered quartz dioritic-dioritic and tonalitic-granitic gneisses and younger foliated granitic intrusions.

The Acasta Gneiss Complex of northwestern Canada contains the out U-Pb dating combined with cathodoluminescence imagery on zircon.

The rock body is exposed on an island about kilometres north of Yellowknife. The rock of the outcrop was metamorphosed 3. It is the oldest known exposed rock in the world. The metamorphic rock exposed in the outcrop was previously a granitoid that formed 4. Acasta Gneiss was formed in the Basin Groups unofficial period of the Hadean eon, which came before the Archean: see Timetable of the Precambrian. In an age of 4. Mafic rocks from the Nuvvuagittuq Greenstone Belt have recorded isotopic compositions that can be produced only in the Hadean eon i.

From Wikipedia, the free encyclopedia. A rock that is among the oldest known crustal fragments on Earth. Priscoan 4. Contributions to Mineralogy and Petrology, v. Contributions to Mineralogy and Petrology. Precambrian Research. The Gazette.

Record-breaking rocks?

Bedrock along the northeast coast of Hudson Bay, Canada, has the oldest rock on Earth. 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. Canadian bedrock more than 4 billion years old may be the oldest known section of the Earth’s early crust.

These dating techniques, which are firmly grounded in physics and are The oldest rocks on Earth found so far are the Acasta Gneisses in.

During your visits to the Lizzadro Museum, you may have noticed a small rock in the Rocks display. A metamorphic rock, its protolith original, unmetamorphosed rock was a granite, an intrusive igneous rock. Using radiometric dating of zircon crystals found in the rock, scientists determined the age of the zircon crystals to be 4. That means, the zircons found in the Acasta Gneiss are almost as old as the earth itself! Zircons have been used to measure some of the oldest rocks on earth, including the Acasta Gneiss.

It is common in the crust of the earth and occurs in igneous rocks, although it is usually very small 0. It is resistant to heat and erosion, making it an ideal mineral for measuring ages of rocks. Additionally, it commonly contains trace elements, including uranium and thorium, elements that are radiogenic. Radiometric dating, using elements such as uranium that break down over time, is the main way scientists can estimate actual ages of rocks, within a few thousand years.

Half-lives are unchanging figures that have been tested repeatedly. Using mathematical analysis, scientists can determine how old a rock or mineral is using these half-lives. The most commonly known method is Carbon dating. However, the half-life of 14 C is only 5, years, definitely not helpful when trying to determine something as old as the Acasta Gneiss!

Acasta Gneiss

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