TY - JOUR
T1 - Magma evolution in the primitive, intra-oceanic tonga arc
T2 - Petrogenesis of basaltic andesites at Tofua volcano
AU - Caulfield, J. T.
AU - Turner, S. P.
AU - Smith, I. E M
AU - Cooper, L. B.
AU - Jenner, G. A.
N1 - Corrigendum exists for this article and can be found in Journal of Petrology, volume 56, issue 3, 1 March 2015, pp. 641–644, doi:10.1093/petrology/egv009
PY - 2012/6
Y1 - 2012/6
N2 - Tofua volcano is situated midway along the Tonga oceanic arc and has undergone two phases of ignimbrite-forming activity. The eruptive products are almost entirely basaltic andesites (52·5-57 wt % SiO 2) with the exception of a volumetrically minor pre-caldera dacite. The suite displays a strong tholeiitic trend with K 2O <1 wt %. Phenocryst assemblages typically comprise plagioclase + clinopyroxene ± orthopyroxene with microlites of Ti-magnetite. Olivine (Fo 83-88) is rare and believed to be dominantly antecrystic. An increase in the extent and frequency of reverse zoning in phenocrysts, sieve-textured plagioclase and the occurrence of antecrystic phases in post-caldera lavas record a shift to dynamic conditions, allowing the interaction of magma batches that were previously distinct. Pyroxene thermobarometry suggests crystallization at 950-1200°C and 0·8-1·8 kbar. Volatile measurements of glassy melt inclusions indicate a maximum H 2O content of 4·16 wt % H 2O, and CO 2-H 2O saturation curves indicate that crystallization occurred at two levels, at depths of 4-5·5 km and 1·5-2·5 km. Major and trace element models suggest that the compositions of the majority of the samples represent a differentiation trend whereby the dacite was produced by 65% fractional crystallization of the most primitive basaltic andesite. Trace element models suggest that the sub-arc mantle source is the residuum of depleted Indian mid-ocean ridge basalt mantle (IDMM-1% melt), whereas radiogenic isotope data imply addition of 0·2% average Tongan sediment melt and a fluid component derived from the subducted altered Pacific oceanic crust. A horizontal array on the U-Th equiline diagram and Ra excesses of up to 500% suggest fluid addition to the mantle wedge within the last few thousand years. Time-integrated ( 226Ra/ 230Th) vs Sr/Th and Ba/Th fractionation models imply differentiation timescales of up to 4500 years for the dacitic magma compositions at Tofua.
AB - Tofua volcano is situated midway along the Tonga oceanic arc and has undergone two phases of ignimbrite-forming activity. The eruptive products are almost entirely basaltic andesites (52·5-57 wt % SiO 2) with the exception of a volumetrically minor pre-caldera dacite. The suite displays a strong tholeiitic trend with K 2O <1 wt %. Phenocryst assemblages typically comprise plagioclase + clinopyroxene ± orthopyroxene with microlites of Ti-magnetite. Olivine (Fo 83-88) is rare and believed to be dominantly antecrystic. An increase in the extent and frequency of reverse zoning in phenocrysts, sieve-textured plagioclase and the occurrence of antecrystic phases in post-caldera lavas record a shift to dynamic conditions, allowing the interaction of magma batches that were previously distinct. Pyroxene thermobarometry suggests crystallization at 950-1200°C and 0·8-1·8 kbar. Volatile measurements of glassy melt inclusions indicate a maximum H 2O content of 4·16 wt % H 2O, and CO 2-H 2O saturation curves indicate that crystallization occurred at two levels, at depths of 4-5·5 km and 1·5-2·5 km. Major and trace element models suggest that the compositions of the majority of the samples represent a differentiation trend whereby the dacite was produced by 65% fractional crystallization of the most primitive basaltic andesite. Trace element models suggest that the sub-arc mantle source is the residuum of depleted Indian mid-ocean ridge basalt mantle (IDMM-1% melt), whereas radiogenic isotope data imply addition of 0·2% average Tongan sediment melt and a fluid component derived from the subducted altered Pacific oceanic crust. A horizontal array on the U-Th equiline diagram and Ra excesses of up to 500% suggest fluid addition to the mantle wedge within the last few thousand years. Time-integrated ( 226Ra/ 230Th) vs Sr/Th and Ba/Th fractionation models imply differentiation timescales of up to 4500 years for the dacitic magma compositions at Tofua.
UR - http://www.scopus.com/inward/record.url?scp=84861820439&partnerID=8YFLogxK
UR - https://doi.org/10.1093/petrology/egv009
U2 - 10.1093/petrology/egs013
DO - 10.1093/petrology/egs013
M3 - Article
AN - SCOPUS:84861820439
VL - 53
SP - 1197
EP - 1230
JO - Journal of Petrology
JF - Journal of Petrology
SN - 0022-3530
IS - 6
ER -