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Do zircons form in sedimentary environments?

Do zircons form in sedimentary environments?

Zircon is a common accessory or trace mineral constituent of most granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands.

What is sedimentary provenance?

Provenance in geology, is the reconstruction of the origin of sediments. In the modern geological lexicon, “sediment provenance” specifically refers to the application of compositional analyses to determine the origin of sediments.

How is zircon used to date igneous rocks?

Since igneous rocks have no fossils, this makes zircon valuable in dating them. This means that any lead found in zircon minerals was made by radioactive decay, after the formation of the mineral. The ratio of lead versus uranium in the zircon is what is used to determine the age of the rock.

How old is detrital zircon?

Yavapai, Mazatzal, and Granite-Rhyolite ages dominate the Cambrian detrital-zircon populations, as well as the Devonian; however, the Devonian Temple Butte Formation has a few zircons with ages of 521–403 Ma.

What happens to some of the zircon atoms in a zircon crystal?

Zircons hold minute amounts of two naturally occurring uranium isotopes — isotopes are atoms of the same element with different numbers of neutrons. But as the uranium kicks out lead atoms, the radioactive decay releases alpha particles, which can damage the crystals, creating defects.

Why are zircon crystals important?

Originally formed by crystallization from a magma or in metamorphic rocks, zircons are so durable and resistant to chemical attack that they rarely go away. They may survive many geologic events, which can be recorded in rings of additional zircon that grow around the original crystal like tree rings.

What is a facies in geology?

1. n. [Geology] The overall characteristics of a rock unit that reflect its origin and differentiate the unit from others around it. Mineralogy and sedimentary source, fossil content, sedimentary structures and texture distinguish one facies from another. See: depositional environment, lithofacies.

Where does burial metamorphism occur?

Burial metamorphism commonly occurs in sedimentary basins, where rocks are buried deeply by overlying sediments. As an extension of diagenesis, a process that occurs during lithification (Chapter 5), burial metamorphism can cause clay minerals, such as smectite, in shales to change to another clay mineral illite.

How is zircon used?

Zircon is widely used in the foundry industry mainly for casting and refractory applications. Zircon’s properties make it ideal for use in sand casting, investment casting and as a mould coating in die casting processes. It is also used in refractory paints and washes to reduce wettability of other foundry sands.

Why is zircon important as a dating tool?

Second, zircon, once formed, is highly resistant to change and has the highest blocking temperature ever observed. Finally, with few predictable exceptions, zircon grows or regrows only in liquid rock or in solid rock reheated to approach its melting point.

What is the meaning of detrital?

1. adj. [Geology] Pertaining to particles of rock derived from the mechanical breakdown of preexisting rocks by weathering and erosion. Detrital fragments can be transported to recombine and, through the process of lithification, become sedimentary rocks.

What is depositional age?

1. Introduction. The age of a sedimentary deposit is no older than its youngest constituent. This fact, and the recent proliferation of detrital geochronology data to understand sedimentary provenance, have expanded the use of maximum depositional ages (MDAs) to constrain the ages of sedimentary deposits.

Are detrital zircons metamorphic?

Because of remarkable durability, detrital zircons may be reworked through multiple sedimentary cycles. A mixed sedimentary population of zircons will endure metamorphism, but younger metamorphic events may be recorded in overgrowths (rims) on cores that record initial crystallization.

What makes detrital-zircon geochronology useful for Provenance studies?

The combination of the ubiquity of detrital zircons, the precision of age determinations, and the opportunity to analyze large populations from a single sandstone sample has made detrital-zircon geochronology a powerful tool in provenance studies.

Are detrital zircons in the Grand Canyon evidence for provenance?

Detrital zircons in the Paleozoic succession in the Grand Canyon exhibit distinctive components of the age population, and those ages are used to identify a provenance ( Gehrels et al., 2011 ).

What is the earliest record of Alleghanian detrital zircons?

One zircon grain in Permian strata (Washington Formation) has a 314-Ma rim around an 1108-Ma core, constituting the earliest record of Alleghanian detrital zircons in the Appalachian foreland basin ( Becker et al., 2006 ).

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