Rocks, aging

The Silver Bell Mine area consists of dipping units that are composed of dacite porphyry, alaskite and monazite. The rock ages span the Paleozoic, Mesozoic and Cenozoic periods. The Paleozoic wall rocks consist of quartzite, siltstone and altered limestone. The carbonate rocks are exposed along the contact between the host rock and intrusions, and host the... 

Uz - U-Pb zircon age Rw s Rb-Sr whole-rock age Ab = Ar-Ar blotile age Kb - K-Ar biotite age A Location of granite- related mlnereiizetlon " Othe r Mo-W loca tlons... 

A specific example of applications in the second category is the dating of rocks. Age determination is an inverse problem of radioactive decay, which is a first-order reaction (described later). Because radioactive decay follows a specific law relating concentration and time, and the decay rate is independent of temperature and pressure, the extent of decay is a measure of time passed since the radioactive element is entrapped in a crystal, hence its age. In addition to the age, the initial conditions (such as initial isotopic ratios) may also be inferred, which is another example of inverse problems. 

Fairbairn, H. W., P. M. Hurley, and W. H. Pinson The relation of discordant Rb—Sr mineral and whole-rock ages in an igneous rock to its time of crystallization and to the time of subsequent Sr87/Sr metamorphism. Geochim. cosmochim. Acta 23, 135 (1961). 

Soil Samples Rock ages in b.y. (40Ar/36Ar)tr range average Number of measurements... 

The data in Table 2 are from groundwaters found in a variety of crystalline rock environments on several different continents. The ages and size of the rock complexes vary. The oldest are billions of years, the youngest tens of millions. Some are individual plutons or batholiths others are massive complexes composed of many rock types of variable age. To attempt to subdivide the data based on crystalline rock type, size of rock complex or rock age would result in so many subdivisions that any discussion of origin and evolution would be unnecessarily cumbersome. 

Fig. 1. Relative probability histograms of Slave craton detrital zircons (continuous curve with black infill below based on data from Sircombe et al. 2001), Ar/ Ar ages of impact spherules in lunar soil samples (dash-dot curve after Culler et al. 2000), and Ar/ Ar ages of impact glasses in lunar meteorites (dashed curve after Cohen et al. 2000). Time interval spans from 4500 Ma, the approximate age of formation of the Moon, to 2500 Ma, the defined Archaean-Proterozoic boundary. Vertical scales of the three curves are independent. Shaded age bars with roman numerals represent main events in basement of the Slave craton that were initially defined on the basis of individual rock age and their inheritance (see Bleeker Davis 1999). The detrital zircon data represent c. 300 zircon grains from five widely distributed samples of a c. 2800 Ma quartzite unit overlying the Mesoarchaean to Hadean-age basement complex of the Slave craton. These data represent a least-biased record of pre-2.8 Ga components of the Slave craton. The broad complementarity in the datasets should be noted. With the first major peak in Slave crustal ages (event V 3100-3200 Ma) immediately following the last major peak in the lunar spherule data. Both lunar soil and meteorite data sets support a lunar cataclysm or late heavy bombardment that appears to have erased or swamped out the pre-4.0Ga lunar record.

Walraven, R and Pape, J., 1994. Pb-Pb whole-rock ages for the Pongola supergroup and the Usushwana Complex, South Africa. J. Afr. Earth Sci., 18, 297-308. 

As mentioned in Section 1.3.1, the first indirect (carbon isotopic) evidence for life appears in rocks aged some 3.8Ga, and there are also structures dating from 3.5 Ga that have been interpreted as the counterparts of modern microbial mats, primarily formed by large... 

Fig. 5. 27 Variations over geological time in sterane C-number distributions in oils from marine source rocks (age refers to inferred source after Grantham Wakefield 1988).

The interpreta- Whole-rock systems are more likely than mineral ages to determine the timing of tion of jphole- crystaUization of an igneous rock or the timing of the metamorphic peak during rock ages metamorphism. Sometimes it may be possible to determine the time of crustal formation. 

Inferred source rock age based on geology. Geochemical analyses discussed below suggest that the Dome oil sample originated mainly from Devonian source rock. 

Glucose, galactose, and mannose have been identified as the principal monosaccharides in sedimentary rocks aged 200 million years.The oligosaccharides... 

Nature has a history—for a long time the ideal of physics was geometry, as implied in Einstein s general relatively. Relativity is certainly one of the great achievement of the human mind. But the geometrical view is incomplete. Now we see that narrative elements also play a basic role. This leads to a different concept of nature in which the arrow of time is essential. After all, this arrow appears as the feature which is common to all objects in the expanding bubble which is our universe. We all age in the same direction all stars, all rocks age in the same direction even if the mechanism of aging is different in each case. 

Though some lead is easily lost from zircons as a result of geologic events such as metamorphism, complete resetting rarely occurs and the concordia-discordia treatment furnishes a powerful eye to see through metamorphic events to determine rock ages. 

Rock Age Locality 206pb/204pb 207pb/204 Pb Reference ... 

Rock Age Locality Pb/ Pb 207pb/204pb 208pb/204pb Type of Reference analysis... 

Lovtsyus, a. V. Rock age of Taromskoe quarry according to data of... 

In this chapter all poles whose magnetisation age is not the same as the rock age are rejected. However, strict application of additional selection criteria (Van der Voo, 1988,1990), such as the application of certain magnetic tests, results in too few poles for making reconstructions. 

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