Fission track dating solid earth sciences library
Based on magmatic variation, the Andes can be divided into four zones: 1) the northern volcanic zone which includes Venezuela, Colombia and Ecuador, 2) the central plutonic zone in Peru, 3) the central volcanic zone which includes Bolivia and northern Chile, 4) the southern plutonic zone in central Chile (Mc Nulty et.
al.,n and are exposed over 4.4 km of vertical relief.
Usable concentrations can range anywhere from approximately 1-1000 ppm over geologic time scales of 1-500 Ma.
The whole arc is formed by the subduction of oceanic crust under the continent, but magma genesis varies dramatically from north to south.
It soon became apparent that, after etching, fission tracks could be used as a dating method.
The only difference is that physical damage is the product of the fission process instead of a daughter element.
The main rock component of the batholith is granodiorite, which makes up ~80 to 90 % of the exposed intrusive rock.
The remainder of the rocks are mostly tonalite and diorite (Mc Nulty et. Exhumation of the batholith and adjacent metamorphic rocks has occurred along the Cordillera Blanca Normal Fault (CBNF) that extends for some 210 km along the margin of the mountain range (Schwartz, 1988).
The tracks formed on the mica are from uranium present in the sample (U), and close enough to the etched surface to create a track in the mica. The external detector method allows each individual grain or parts of each grain to have its uranium concentration determined, avoiding the assumption of uniform distribution inherent in the population method (Gallagher Fission tracks are not stable and can shorten or even disappear if the sample spends considerable time at elevated temperatures.