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Kinetic studies in contact metamorphic zones


, : Kinetic studies in contact metamorphic zones. Geochimica et Cosmochimica Acta 31(7): 1119-1153

Rubidium-strontium and K/Ar ages of biotite, muscovite, and potassium feldspar and K/Ar ages of hornblende from a granitic stock (2600 m.y.) near the contact with a gabbro (1050 m.y.), and Rb/Sr and K/Ar ages of biotite and K/Ar ages of hornblende from amphibolite (metamorphosed at 2600 m.y.) near the contact with a quartz dolerite dike (800 m.y.) were determined to study the effects of thermal metamorphism on mineral ages. Volume diffusion and zero- and first-order chemical reaction-rate models are used to describe the rate of loss of radiogenic Sr and Ar from these minerals: the chemical reaction-rate models may apply if the rate of loss is controlled by recrystallization. The different models give activation energies ranging from 30 to 75 kcal/mole. The loss of Ar from hornblende took place at higher temperatures than for biotite and the activation energies also may be higher. The relative stability of mineral ages in a contact zone is hornblende K/Ar > muscovite Rb/Sr > muscovite K/Ar > biotite Rb/Sr > biotite K/Ar, although for the micas the Rb/Sr and K/Ar ages are essentially concordant.

US$19.90

DOI: 10.1016/s0016-7037(67)80053-x


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