UPb Geochronology

1
U-Pb Geochronology

• Dave Rodriguez
• Carlos Villa
• Pat Wagner

2
Our Area of Exploration
North Central New Mexico
3
Our Samples

• Conglomerate rock samples brought back from New
  Mexico.
• Tres Piedras, NM located in the foothills of the
  Sangre de Cristo Mountains.
• The Sangre de Cristo Mountains are the longest
  (350 km), straightest and highest chain of
  mountains in America.
• They were formed about 27 million years ago.
• Area was about 60 million years old.
• There are ten peaks over 4,200 m high in the
  range.

4
Crushing the Rocks

• Machine would crush rocks down to pebble sized.

5
Size Comparison

• Original Sample

• Pebbles

Football Sized
Pea Sized
6
Grinding the Pebbles

• Pebbles were then ground into a thin powder.

7
Using the Super Panner

• Side to side motion of panner allows lighter
  minerals to flow away while heavier minerals sink
  and are then picked up.

8
Purifying the Sample

• Remaining sample in water filled a 10 ml beaker.
• Sample was then dried in an oven.
• Dried sample was purified by running a wand
  magnet over and removing Iron fillings.

9
Heavy Liquid Separation

• Heavy liquids are dense fluids or solutions used
  to separate materials of different density
  through their buoyancy. Quartz, feldspar, and
  mica floated while our zircons sank and were
  separated.

10
Isodynamic Separation

• Many minerals have a certain magnetic
  susceptibility. By varying the magnetic flux (and
  thus the size of the magnetic field) it is
  possible to make different fractions. Garnets and
  Hornblende were separated.

11
Picking Zircons

• Microscope time consisted of patient sittings
  separating zircons from other minerals.

12
Size Comparison 2
One Millimeter
Mineral Field
13
Size Comparison 2 (cont.)
Wire used to separate zircons.
One Millimeter
Human Hair
14
Zircon Field
Viewing range four millimeters across
Zircon field
15
Dissolution and Baking

• Zircons are dissolved in several acid solutions.
• The solution is then baked in an oven for three
  days.
• Heat and pressure contribute to dissolving the
  zircons into an ion solution.

16
Ion Column Separation

• Pb and U ions are separated from the solution
  and prepared for the spectrometer.

17
Spectrometer

• Sample is placed into mass spectrometer for
  analysis.
• The mass spectrometer will analyze ratio of U and
  Pb ions.
• The ratio will then give us the age of the rock.

18
Acknowledgments

• Wed like to thank Dr. Roy Odom and the
  Geochemistry department for their help in making
  this experience possible.
• Thanks also go out to Pat Dixon, Karl Hook, and
  Gina Hickey for supervising the program.
• A special thanks to Paula Crone, Gayla Sanders,
  and Ann Spangler for all their assistance.