TY - JOUR
T1 - The New England batholith, eastern Australia
T2 - geochemical variations in time and space.
AU - Shaw, S. E.
AU - Flood, R. H.
PY - 1981
Y1 - 1981
N2 - The New England Batholith, Australia, is part of the Upper
Paleozoic New England Fold Belt, with most plutons intruded into the deformed
trench-complex metasedimetary rocks in the southeast part of the Fold Belt. The
Batholith was emplaced in two major periods of plutonism, the first during the
Upper Carboniferous and the second during the Upper Permian and Triassic, with
a major phase of metamorphism and deformation including westward overthrusting
of the trench-complex sedimentary rocks between the two periods. On the basis
of petrography, geochemistry and isotopic characteristics, the granitoids of
the Batholith are subdivided into five named intrusive suites and a group of
leucoadamellites. The differences between the six groups are considered to
reflect differences in their source-rock types. The Carboniferous granitoids
are peraluminous S-type and are divided into the Bundarra Plutonic Suite, a
belt of very coarse-grained adamellites with cordierite ± garnet, and the
Hillgrove Plutonic Suite, a belt of biotite-rich ± garnet deformed adamellites
and granodiorites. Both suites have δ 18O greater than 10, negative δ34S,
87Sr/86Sr initial ratios about 0.706, are ilmenite-bearing and have low FeO3
ratios. The Bundarra Plutonic Suite, however, is consistently SiO2-rich
(greater than 70%), contains cordierite and has higher δ 18O than the Hillgrove
Plutonic Suite. The two S-type suites are inferred to have formed by partial
melting of the deepest parts of a wedge of trench-complex sedimentary rocks
oceanwards of an ‘Andean’ volcanic chain to the west, analagous to the lower
Tertiary S-type plutons of the Sanak-Baranof plutonic belt of southern Alaska.
Of the remaining four groups of plutons emplaced during the Upper Permian and
Triassic, two are metaluminous I-type granitoids, one the Clarence River
Plutonic Suite (new name), a group of K-poor granodiorites and tonalites with
low 87Sr/86Sr initial ratios (average 0.7035), and the other the Moonbi
Plutonic Suite, a group of K-rich adamellites with low 87Sr/86Sr initial ratios
(average 0.7045), δ18O less than 10 and δ34S positive. The Clarence River
Plutonic Suite is inferred to have formed from the partial melting of a
large-ion lithophile element-poor (gabbro?) source region and the Moonbi
Plutonic Suite from a large-ion lithophile element-rich (shoshonite?) source
region. A third group, the Uralla Plutonic Suite, is less metaluminous, has
higher 87Sr/86Sr initial ratios (average 0.706), δ18O only just less than 10
and negative δ34S, and is considered to have formed in a region containing a
physical mixture of metaluminous and peraluminous source rocks (gabbro and
metasedimentary rocks?). Plutons of the fourth group are leucoadamellites,
largely emplaced after the other suites, with low δ18O indicating an I-type
source. It is argued that this group has resulted from low degrees of ‘dry’
partial metling of an I-type source region that had undergone an earlier
melting event. These four groups of plutons are largely confined to a narrow
belt parallel to, but 100 km west of, the present rifted margin of Australia.
Their origin may be related to crustal thickening attendant on the
overthrusting that occurred early in the Permian and/or a temperature increase
in the lower crust due to the recovery of normal continental geotherms following
the cessation of subduction.
AB - The New England Batholith, Australia, is part of the Upper
Paleozoic New England Fold Belt, with most plutons intruded into the deformed
trench-complex metasedimetary rocks in the southeast part of the Fold Belt. The
Batholith was emplaced in two major periods of plutonism, the first during the
Upper Carboniferous and the second during the Upper Permian and Triassic, with
a major phase of metamorphism and deformation including westward overthrusting
of the trench-complex sedimentary rocks between the two periods. On the basis
of petrography, geochemistry and isotopic characteristics, the granitoids of
the Batholith are subdivided into five named intrusive suites and a group of
leucoadamellites. The differences between the six groups are considered to
reflect differences in their source-rock types. The Carboniferous granitoids
are peraluminous S-type and are divided into the Bundarra Plutonic Suite, a
belt of very coarse-grained adamellites with cordierite ± garnet, and the
Hillgrove Plutonic Suite, a belt of biotite-rich ± garnet deformed adamellites
and granodiorites. Both suites have δ 18O greater than 10, negative δ34S,
87Sr/86Sr initial ratios about 0.706, are ilmenite-bearing and have low FeO3
ratios. The Bundarra Plutonic Suite, however, is consistently SiO2-rich
(greater than 70%), contains cordierite and has higher δ 18O than the Hillgrove
Plutonic Suite. The two S-type suites are inferred to have formed by partial
melting of the deepest parts of a wedge of trench-complex sedimentary rocks
oceanwards of an ‘Andean’ volcanic chain to the west, analagous to the lower
Tertiary S-type plutons of the Sanak-Baranof plutonic belt of southern Alaska.
Of the remaining four groups of plutons emplaced during the Upper Permian and
Triassic, two are metaluminous I-type granitoids, one the Clarence River
Plutonic Suite (new name), a group of K-poor granodiorites and tonalites with
low 87Sr/86Sr initial ratios (average 0.7035), and the other the Moonbi
Plutonic Suite, a group of K-rich adamellites with low 87Sr/86Sr initial ratios
(average 0.7045), δ18O less than 10 and δ34S positive. The Clarence River
Plutonic Suite is inferred to have formed from the partial melting of a
large-ion lithophile element-poor (gabbro?) source region and the Moonbi
Plutonic Suite from a large-ion lithophile element-rich (shoshonite?) source
region. A third group, the Uralla Plutonic Suite, is less metaluminous, has
higher 87Sr/86Sr initial ratios (average 0.706), δ18O only just less than 10
and negative δ34S, and is considered to have formed in a region containing a
physical mixture of metaluminous and peraluminous source rocks (gabbro and
metasedimentary rocks?). Plutons of the fourth group are leucoadamellites,
largely emplaced after the other suites, with low δ18O indicating an I-type
source. It is argued that this group has resulted from low degrees of ‘dry’
partial metling of an I-type source region that had undergone an earlier
melting event. These four groups of plutons are largely confined to a narrow
belt parallel to, but 100 km west of, the present rifted margin of Australia.
Their origin may be related to crustal thickening attendant on the
overthrusting that occurred early in the Permian and/or a temperature increase
in the lower crust due to the recovery of normal continental geotherms following
the cessation of subduction.
UR - http://www.scopus.com/inward/record.url?scp=0019677639&partnerID=8YFLogxK
U2 - 10.1029/JB086iB11p10530
DO - 10.1029/JB086iB11p10530
M3 - Article
AN - SCOPUS:0019677639
SN - 0148-0227
VL - 86
SP - 10530
EP - 10544
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
IS - B11
ER -