Age dating of basalt

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This is essentially the same as the so-called model ages of the formation of KREEP (a chemical component enriched in potassium, rare earth elements, and phosphorous) and of the formation of the deep source regions that melted to produce mare basalts.

The numerous ages close to 4370 million years suggests a complicated and protracted cooling of the primordial lunar magma ocean or a widespread vigorous period of magmatic activity in the Moon.

Reference: Knowing precisely when major rock types formed during construction of the lunar crust builds a quantitative framework for understanding the origin and geochemical evolution of the lunar highlands.

For example, a cherished idea in lunar science is that the Moon melted when it formed.

As this ocean of magma crystallized, plagioclase feldspar floated to the top, accumulating in large masses of a rock type called anorthosite (also abbreviated FAN, for ferroan anorthosite).

The anorthosite primary crust was then invaded by magmas formed by partial melting of the lunar mantle, which formed substantially by dense minerals sinking in the magma ocean.

The rock has a distinctively fragmental appearance, not an igneous texture, although in places in other pieces of 60025 a good igneous texture is seen easily.

The rock has been affected by one or more impacts, but in spite of its fragmentation it is possible to extract a reliable age from it. In fact, geochronologists can determine the time when the metamorphism took place if the temperature was hot enough for long enough to reset chronometers.

Essentially all the variation in elevation is associated with impact craters.

Lars Borg and Amy Gaffney (Lawrence Livermore National Laboratory), and Charles Shearer (University of New Mexico) have devised a set of guidelines to apply to geochronological data that leads to a relative ranking of the reliability of the age determined for a sample.

Applying their guidelines to existing data for lunar highland rocks shows an upper limit on rock ages between 43 million years.

On the Moon, however, the main metamorphic process is impact, which damages mineral crystals as the shock wave passes through the target rock.

The shock also heats the rock, sometimes imparting a transient heat pulse, other times surrounding a chunk of rock in impact melt that might cool slowly, but not necessarily slow enough to reset the age.

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