Computer Science
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998e%26psl.160...49h&link_type=abstract
Earth and Planetary Science Letters, vol. 160, Issue 1-2, pp.49-63
Computer Science
22
Soufriere, Saint Vincent, Lesser Antilles, U-238/Th-230, Isochrons, Th/U, Phase Equilibria, Magmas, Residence Time
Scientific paper
High-precision (TIMS) measurements of U and Th isotope concentrations have been determined on whole rocks and mineral separates from Soufriere volcano on St. Vincent in the Lesser Antilles island arc. The whole rocks display relatively constant U/Th ratios (~0.5), and are characterised by excess 238 U relative to 230 Th which is attributed to the addition of U-rich fluids from the subducting slab to the mantle source of the magmas. Mineral isochrons for four recently erupted (<4 ka) rocks yield ages of 46-77 ka and the combined data have an age of ka with an initial ( 230 Th/ 230 Th) ratio of 1.05. Mixing of young magmas, or magma-cumulate mixing, are unlikely to be responsible for these isochronous relationships. Contamination of young, phenocrystic magmas with previously crystallised magma could produce the isochrons, in which case the ages provide maximum and minimum ages, respectively, for these two components. However, no lavas with ( 230 Th/ 230 Th) ratios of 1.054 have been found and there is no petrographic evidence for mixing or phenocryst-magma disequilibrium. Our preferred interpretation is that the isochrons reflect long magma residence times within the arc crust. Following initial crystallisation, due to heat loss to the wall rocks, the magmas were maintained at a temperature close to their liquidus while 230 Th-ingrowth occurred in both the magma and the crystals. Maintenance of a relatively constant temperature requires good insulation by cumulate layers and probably heating from below by influxes of fresh magma which either did not mix with the resident magma or else had an essentially indistinguishable composition. Subtraction of the residence times from the ~90 ka inferred to have elapsed since fluid addition to the mantle wedge leaves ~30 ka for transfer through the wedge. Long residence times may typify more evolved lavas that develop in thicker arc crust whereas tholeiitic arc lavas are inferred to have trivial crustal residence times but similar transfer times through the mantle wedge.
Hawkesworth Chris J.
Heath Emily
MacDonald Rachel
Turner Peter S.
van Calsteren Peter
No associations
LandOfFree
Long magma residence times at an island arc volcano (Soufriere, St. Vincent) in the Lesser Antilles: evidence from 238 U- 230 Th isochron dating does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Long magma residence times at an island arc volcano (Soufriere, St. Vincent) in the Lesser Antilles: evidence from 238 U- 230 Th isochron dating, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Long magma residence times at an island arc volcano (Soufriere, St. Vincent) in the Lesser Antilles: evidence from 238 U- 230 Th isochron dating will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1344777