For the following mark whether it is an example of absolute time (A) or relative
ID: 283747 • Letter: F
Question
For the following mark whether it is an example of absolute time (A) or relative time (R) (ie write "A" or "R" after the six following examples). The high-pressure metamorphic sole of the Palawan ophiolite of the western Philippines give 34 million years old Ar-Ar ages which makes these rocks younger than similar rocks of the Franciscan Complex of California that give Lu-Hf and Ar-Ar ages of 155-170 million years U-Pb zircon and Lu-Hf garnet ages of eclogite in the Sanbagawa Belt of Japan are 120 million years and 89 million years old, respectively, giving rise to controversy over the age of eclogitic metamorphism in those rocks. In a rock a hornblende crystal is rimmed by glaucophane indicating that the glaucophane grew after the hornblende. the Feather River canyon is incised (ie the canyon was cut) into granitic and metamorphic rocks. This shows that the development of the canyon is younger than those rocks. Folds in Franciscan Complex rocks are displaced (cut off) by the Rodgers Creek fault indicating that movement on the Rodgers Creek fault is younger than the folds of the Franciscan Complex. The Modesto Formation overlies the Riverbank Formation in Fresno indicating that the Riverbank Formation is older than the Modesto Formation. The U-Pb ages of the youngest granites in the Sierra Nevada is 85 million years old, whereas the youngest zircons in some units of the Franciscan Complex have U-Pb ages of 34 million years indicating that the youngest zircons in those Franciscan rocks could not have been derived from Sierra Nevada granites.Explanation / Answer
a)absolute time(A): the dates obtained from radiometric dating are compared to form the sequence.They provide absolute time.
b)absolute time(A): the dating of Zircon and Garnet are absolute and gives absolute time.HEnce the age of the Eclogites that given though controversial will be absolute time as it will be derived from dating.
c)relative time(R):Reaction rim textures defines the time of minerals .Glaucophane forms after from reaction with Hornblende with addition of calcium and Iron by replacing Sodium .
d)relative time(R): The feather River during its course cuts rocks to form canyon.Based on law of geochronology the time derived is always relative.
e)relative time(R):Folds cut off by faulting and disposition of layers owing to it provides reltaive time.
f)relative time(R:law of superposition states that if the sequence is undisturbed then the youngest layer will be on the top and the oldest at the bottom but it does not provide the absolute time.