Resumé
U-Th-Ra disequilibria of basanites, tephrites, and phonolites from the A.D. 1585 eruption on La Palma, Canary Islands, constrain magma differentiation times in an ocean-island rift zone. The insignificant difference in (230Th)/(232Th) implies differentiation from basanite to phonolite in <15 k.y. 226Ra has a half-life of 1600 yr, however, and permits higher temporal resolution; (226Ra)/(230Th) disequilibria are highest in the phonolites (46%-54%) and basanites (44%-47%) and lowest in the tephrites (38%-41%). The higher 226Ra excesses in the end-member compositions model basanite-phonolite differentiation within 1550-1750 yr at a rate of 0.04% fractional crystallization per year. Such a short time interval is in sharp contrast to the ∼200 k.y. proposed for phonolite differentiation on the neighboring island of Tenerife and could reflect different volcanic systems, with a mantle-fed rift system on La Palma versus a crustal magma reservoir on Tenerife.
Originalsprog | Engelsk |
---|---|
Sider (fra-til) | 897-900 |
Antal sider | 4 |
Tidsskrift | Geology |
Vol/bind | 33 |
Udgave nummer | 11 |
DOI | |
Status | Udgivet - nov. 2005 |
Udgivet eksternt | Ja |
Emneord
- La Palma
- Canary Islands
- Volcanic activity
- Magma differentiation
- Geochemistry and petrology
- U-series disequilibria
Programområde
- Programområde 4: Mineralske råstoffer