Relative age dating inclusions

17-May-2015 03:16 by 10 Comments

Relative age dating inclusions

This combined X-ray elemental map shows Mg (red), Ca (green) and Al (blue) of the CR carbonaceous chondrite PCA 91082. Rocks like these preserve a record of the processes and timing of events in the solar nebula. This drawing depicts some of the processes that might have operated in the nebular disk surrounding the young Sun.There are two mechanisms proposed for CAI and chondrule formation: shock waves and jet flows. It shows the jet flow model of CAI and chondrule formation.

The young Sun emits vast quantities of energetic particles, which create winds in the nebula.

Rising plumes above the dashed lines are blown out to cooler parts of the disk.

According to Shu, powerful jets accelerate CAIs and chondrules to hundreds of kilometers per second, allowing them to reach the asteroid belt in only a day or two. Göpel (Paris Geophysical Institute) report an impressively precise Pb-Pb age of 4566±2 Ma for CAIs from the Allende CV chondrite. My colleague, Yuri Amelin, has developed an even more precise technique for determining Pb-Pb ages.

Al had an external stellar origin and was injected and homogenized in the solar nebula over a time scale shorter than its half-life. The key to improving the precision of the age determinations comes from Amelin's ability to analyze many small samples.

hondritic meteorites (chondrites), the oldest rocks in our solar system, provide a significant record of the processes that transformed a disk of gas and dust into a collection of planets, moons, asteroids, and comets.

They are considered to be the building blocks of the inner planets, Mercury, Venus, Earth, and Mars.

Chondrites are aggregates of three major components: refractory Ca-Al-rich inclusions (CAIs), less refractory ferromagnesian silicate spherules called chondrules, and a fine-grained matrix.We know that CAIs and chondrules formed at nearly the same time as the Sun (4.56 billion years ago), but we don't know the details of how or where the CAIs and chondrules formed.The timing and duration of their formation remains obscure.My colleagues, Yuri Amelin (Royal Ontario Museum), Ian Hutcheon (Lawrence Livermore National Laboratory), Alexander Ulyanov (Moscow State University), and I set out to resolve these unknowns by determining the absolute formation ages of CAIs and chondrules using lead isotopic analyses. (Kingsborough College-CUNY), chondrules and CAIs were heated by shock waves that originated in the asteroid belt region.ost meteorite experts believe that CAIs and chondrules formed in the solar nebula by high temperature processes. These shock waves moved through the dusty cloud at supersonic speeds, produced frictional heating, and melted the dust particles.These processes included condensation, evaporation, and, for all chondrules and many CAIs, subsequent melting during multiple brief heating episodes. According to the jet flow model developed by Frank Shu (University of California, Berkeley), chondrules and CAIs formed near the Sun (at ~0.04-0.08 AU) by sunlight and radiation associated with solar flares and were transported later to the asteroid belt region by a bipolar outflow [see articles Relicts from the Birth of the Solar System and The Oldest Metal in the Solar System for more information.] Ages (relative or absolute) of CAIs and chondrules can provide important constraints on their origin, but past calculations are either controversial or insufficiently precise.