TY - JOUR
T1 - Evolution of mantle-derived, augite-hypersthene granodiorites by crystal-liquid fractionation
T2 - Barrington Tops Batholith, eastern Australia
AU - Eggins, S.
AU - Hensen, B. J.
PY - 1987
Y1 - 1987
N2 - The Barrington Tops Batholith (BTB) is a shallow level intrusive complex of Permian age (262 Ma) in Zone A of the New England Fold Belt, northern New South Wales. It comprises a comagmatic suite of early pyroxene+plagioclase-phyric quartz diorite stocks and dykes (10% by area), augite-hypersthene granodiorite (75%), and aplite. Less voluminous hornblende-biotite granodiorite (15%) appears to be related to the augite-hypersthene granodiorite by the addition of minor amounts of an incompatible element rich component. The augite-hypersthene granodiorite plutons formed by fractional crystallisation of a dry (< 2 wt.% H20), high temperature (> 1000°C) liquid. Major element modelling, using analysed phenocryst compositions, closely reproduces the geochemical differentiation trends observed. Combined petrographic and mineral chemistry evidence indicates that parental liquids were of quartz dioritic and more mafic compositions, probably mantle-derived. Low initial 87Sr/86Sr (0.7036–0.7039) and high ∈Nd values (+ 5.6 to + 7.8), suggest these were produced from a geochemically depleted mantle source. The BTB may be regarded as an end-member of the spectrum of calc-alkaline granitic rocks that are formed by the mixing of variably fractionated melts of upper mantle origin with lower continental crust material. It is suggested that lower crustal mafic and ultramafic xenoliths found m Mesozoic to Cenozoic basalts represent cumulates complementary to the more evolved mantle-derived component of calc-alkaline magmatism. Crystal-liquid fractionation, aided by mixing of evolved mantle-derived magma with crustal material, appears to be the most important process giving rise to the diverse geochemical and isotopic continuum displayed by calc-alkaline magmatism m orogemc terrains.
AB - The Barrington Tops Batholith (BTB) is a shallow level intrusive complex of Permian age (262 Ma) in Zone A of the New England Fold Belt, northern New South Wales. It comprises a comagmatic suite of early pyroxene+plagioclase-phyric quartz diorite stocks and dykes (10% by area), augite-hypersthene granodiorite (75%), and aplite. Less voluminous hornblende-biotite granodiorite (15%) appears to be related to the augite-hypersthene granodiorite by the addition of minor amounts of an incompatible element rich component. The augite-hypersthene granodiorite plutons formed by fractional crystallisation of a dry (< 2 wt.% H20), high temperature (> 1000°C) liquid. Major element modelling, using analysed phenocryst compositions, closely reproduces the geochemical differentiation trends observed. Combined petrographic and mineral chemistry evidence indicates that parental liquids were of quartz dioritic and more mafic compositions, probably mantle-derived. Low initial 87Sr/86Sr (0.7036–0.7039) and high ∈Nd values (+ 5.6 to + 7.8), suggest these were produced from a geochemically depleted mantle source. The BTB may be regarded as an end-member of the spectrum of calc-alkaline granitic rocks that are formed by the mixing of variably fractionated melts of upper mantle origin with lower continental crust material. It is suggested that lower crustal mafic and ultramafic xenoliths found m Mesozoic to Cenozoic basalts represent cumulates complementary to the more evolved mantle-derived component of calc-alkaline magmatism. Crystal-liquid fractionation, aided by mixing of evolved mantle-derived magma with crustal material, appears to be the most important process giving rise to the diverse geochemical and isotopic continuum displayed by calc-alkaline magmatism m orogemc terrains.
UR - http://www.scopus.com/inward/record.url?scp=0023523137&partnerID=8YFLogxK
U2 - 10.1016/S0024-4937(87)80003-8
DO - 10.1016/S0024-4937(87)80003-8
M3 - Article
AN - SCOPUS:0023523137
SN - 0024-4937
VL - 20
SP - 295
EP - 310
JO - Lithos
JF - Lithos
IS - 4
ER -