RhymeZone: Sentences that use geochronology
Example sentences from Wikipedia that use the word geochronology: Geomorphologists may rely on geochronology, using dating methods to measure the monazite is used for monazite geochronology to study geological events, such as. Monazite dating methods wiki. Monazite geochronology is another example of U –Pb dating, employed for dating metamorphism in particular. Uranium–lead. Isotopic dating and chemical dating are the two typical dating approaches used in monazite geochronology. Both methods.
The temperature in the reactor rises due to heat released from the exothermic reactions. The product reacts for 3 to 4 hours.
It is then removed from the digester before the solution hardens. The ratio of sulfuric acid to sand removed is 1.
A ratio of 10 parts water to mass of ore originally added is used. This leaching process continues for 12 to 15 hours. All solids from step three are filtered off.
The resulting solution is called monazite sulfate. Add NH3 aq to neutralize to a pH of 1. Collect thorium phosphate precipitate during filtration of neutralized monazite solution. Add NH3 aq to remaining monazite solution to create rare-earth-metal precipitate at a pH of 2. Filtrate out the RE precipitate to yield the concentrated rare-earth metal hydroxides. Add NH3 aq to remaining filtrate to a pH of 6.
This creates a uranium concentrated precipitate. Yet as reaction proceeds, dissolving phase and the fluid are separated by the solid precipitating phase, blocking the transport of reactants. Therefore, there must be some inter-connected porosity in the precipitating phase, which allows the fluid to infiltrate and fuel the reaction front.
Once they are subject to a temperature higher than Tc, all age information will be reset, losing information of the past geological events.
In contrast, since monazite has a high Tc, even it experiences younger high-grade metamorphism with high temperatures, it is likely that the previous geological history is preserved. Furthermore, dissolution-precipitation is usually triggered by geological events such as metamorphismdeformation and hydrothermal alternation below Tc.
Each of these events writes a new age information by precipitating a new domain without erasing the older information. Therefore, it is likely that monazite preserves a complete history of generations. However, they behave differently throughout the geological history.
Zircon is not as reactive as monazite during metamorphism reaction and better in recording igneous events cooling ages. A single monazite grain can contain domains of distinctively different compositions and ages. These domains are widely accepted to represent episodes in geological history during monazite growth or recrystallisation. The age of the event is thus represented by the domain age.
The ideal formula of monazite is [LREE PO4 ], the variation in composition is mainly due to the chemical substitutions of light rare earth elements REE in monazite by other elements. Since all three minerals share the same chemical structure, they are the three endmembers in their solid solutionmeaning that they appear in a same solid phase where substitutions happen. It is important to note that the composition zonation pattern may not be the same when we are considering different elements.
And age zonation may have no relationship with composition zonation at all. The method[ edit ] If there is no lead in the zircon originally, and if no lead or uranium has been added or subtracted to the zircon since its formation, then the following formula will hold: It is possible to refine this date still further.
If we suspect that the zircon, despite its chemical properties, still managed to incorporate a little lead at or after its formation, then since all lead isotopes are chemically the same, we can measure the amount of Pb the zircon contains. Since we know the ratios in which the various lead isotopes are usually found, we can then apply the same sort of correction we used to account for atmospheric argon in the K-Ar method.
While zircon has been the most popular mineral for U-Pb dating, other minerals have been employed, including apatite, monazite, titanite, allanite and, most interesting of all, xenotime.
Xenotime[ edit ] There is a difficulty in using radiometric dating to put an age on sedimentary rock.
Monazite dating methods. Radiometric dating - Wikipedia
The problem is that sediment is made up of clasts of some parent rockand when we date these clastswe are in effect dating the parent rock rather than the sediment as such. If, for example, we apply U-Pb dating to a grain of zircon found in sandstonewe aren't dating the formation of the sandstone, we're dating the formation of the granite that the zircon came from; all we could say about the sandstone is that it must be younger than that.
However, it is possible to put a date on some sedimentary rocks using the mineral xenotime Y P O 4. Uranium can and often does substitute for the element yttrium, whereas lead cannot, making xenotime suitable for radiometric dating.Rare-earth element - Wikipedia audio article
The key fact about xenotime is that since it has the same crystal structure as zircon, it can grow on zircon crystalsforming a crust; and this process, of course, cannot begin to take place while the zircon crystal is still locked inside its parent rock.
The zircon will only start acquiring its xenotime crust after weathering and erosion have freed it from its parent rock and it becomes sediment.
So by dating the xenotime crust, we can find out when the zircon it's growing on became sediment ; dating the zircon itself would tell you the age of the parent rock. Speleothems[ edit ] A cave with speleothems.
A speleothem, more colloquially known as a cave formation, is formed when minerals dissolved in water precipitate out of the water as it drips, seeps, or flows into a cave. The reader will probably be familiar with stalagmites and stalagtites; more speleothems are shown in the photograph to the right. Now, compounds of uranium are often highly soluble in water this, indeed, is one of the major problems with U-Pb isochron dating whereas compounds of lead are stubbornly insoluble.
- Historical Geology/U-Pb, Pb-Pb, and fission track dating
As a result, we expect speleothems when they are first formed to contain some uranium but little or no lead — just like zircons. So we can apply the same technique to speleothems as we do to zircons.