Compositional Dependence of Potassium-Argon Ages and Hydrogren and Oxygen Stable Isotopes in Hornblendes From Connemara, Western Ireland

Geology, Geochemistry

Jappy, Trevor George

University:University of Glasgow

关键词: Geology, Geochemistry;   

Others  :  http://theses.gla.ac.uk/75407/1/13815590.pdf

来源: University of Glasgow

【 摘 要 】

The work of this thesis set out to investigate the relationship between K-Ar age, hydrogen isotope values, oxygen isotope values and mineral composition in samples collected from the Dalradian rocks of the Connemara region of western Ireland. Previous studies by Elias et al. (1988) and Miller et al. (1991) found no evidence for a connection between hornblende K-Ar ages and compositions on hornblendes ranging from ~490Ma to ~390Ma. The hornblendes are believed to have cooled through their 40Ar* closure temperature between 490Ma and 463Ma (Cliff et al., 1994; Friedrich et al., 1997), therefore the younger ages are not explainable by conventional understanding of 40Ar* loss. Miller et al. (1991) found a relationship of increasing hornblende 5D values (from -750/00 to -610/00) with decreasing age and excess water contents in hornblendes. This was interpreted as being due to the hornblende being infiltrated by a retrogressive, convecting meteoric fluid (RGF) at sub-40Ar* closure temperatures (~275