Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica
The Cambrian-Ordovician Ross Orogeny in Antarctica produced a voluminous magmatic belt composed mainly of post-orogenic granitoids. This magmatic belt has strong calc-alkaline characteristics reflecting a convergent-margin origin associated with subduction of paleo-Pacific oceanic lithosphere beneat...
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ftanucanberra:oai:digitalcollections.anu.edu.au:1885/67004 2023-05-15T13:36:32+02:00 Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica Goodge, John W Fanning, Christopher Norman, Marc Bennett, Victoria 2015-12-10T23:23:52Z http://hdl.handle.net/1885/67004 unknown Oxford University Press 0022-3530 http://hdl.handle.net/1885/67004 Journal of Petrology Journal article 2015 ftanucanberra 2015-12-28T23:33:46Z The Cambrian-Ordovician Ross Orogeny in Antarctica produced a voluminous magmatic belt composed mainly of post-orogenic granitoids. This magmatic belt has strong calc-alkaline characteristics reflecting a convergent-margin origin associated with subduction of paleo-Pacific oceanic lithosphere beneath cratonic East Antarctica. However, it is unclear how and when magmatism began, and to what degree magmatism was associated with syn-orogenic deformation and intra-arc extension. New U-Pb zircon ages, and whole-rock geochemical and Sr-Nd isotope data for granitoids sampled along a transect across the Ross Orogen in the Nimrod Glacier area of the central Transantarctic Mountains provide constraints on the timing, spatial variation, and origin of the magmatism in this area. This transect is one of the few places where the orogenic arc extends into the East Antarctic cratonic basement, thus helping to constrain both craton and arc evolution. New U-Pb ages show that magmatism was initiated as early as ∼590 Ma following latest Neoproterozoic rifting, that the magmatic belt is long-lived, lasting over about 100 Myr, and that the locus of magmatism shifted oceanward over time. Early syn-orogenic magmatism was focused within the leading edge of the cratonic basement, perhaps guided by strain partitioning during oblique subduction; younger magmas intruded a forearc sedimentary molasse basin, itself eroded from the earlier established arc system. Broadening of the arc during the later phases of Ross convergence indicates rollback of the subducting plate hinge and thickening of the developing forearc during continuing orogenic contraction. The granitoids mainly have calc-alkaline geochemical characteristics, but they show some similarity to adakitic compositions indicative of melt fractionation from the subducting slab; they do not show the alkaline signatures attributed in other areas to crustal extension. Inherited zircon components are compatible with melting of lower crust similar to that exposed at present in the Nimrod Group; however, the paucity of older cores suggests that melt production involved relatively large degrees of fractional melting at high temperature. Whole-rock Sr and Nd isotopic compositions vary systematically across the belt, as expected in a convergent-margin arc setting, and they show significant cratonic influence, with initial. 87Sr/. 86Sr compositions as high as 0·750 and e{open}Nd values as low as -15 for granitoids intruding Nimrod Group basement. Although there is an isotopic discontinuity associated with the inferred cratonic rifted margin, the later phase of magmatism is characterized by uniformly low. 87Sr/. 86Sr and high e{open}Nd, indicating that melt compositions are controlled more by subduction processes than by assimilation of existing crust in the cratonic upper plate. Article in Journal/Newspaper Antarc* Antarctic Antarctica East Antarctica Nimrod Glacier Australian National University: ANU Digital Collections Antarctic East Antarctica Nimrod ENVELOPE(165.750,165.750,-85.417,-85.417) Nimrod Glacier ENVELOPE(163.000,163.000,-82.350,-82.350) Pacific Transantarctic Mountains |
institution |
Open Polar |
collection |
Australian National University: ANU Digital Collections |
op_collection_id |
ftanucanberra |
language |
unknown |
description |
The Cambrian-Ordovician Ross Orogeny in Antarctica produced a voluminous magmatic belt composed mainly of post-orogenic granitoids. This magmatic belt has strong calc-alkaline characteristics reflecting a convergent-margin origin associated with subduction of paleo-Pacific oceanic lithosphere beneath cratonic East Antarctica. However, it is unclear how and when magmatism began, and to what degree magmatism was associated with syn-orogenic deformation and intra-arc extension. New U-Pb zircon ages, and whole-rock geochemical and Sr-Nd isotope data for granitoids sampled along a transect across the Ross Orogen in the Nimrod Glacier area of the central Transantarctic Mountains provide constraints on the timing, spatial variation, and origin of the magmatism in this area. This transect is one of the few places where the orogenic arc extends into the East Antarctic cratonic basement, thus helping to constrain both craton and arc evolution. New U-Pb ages show that magmatism was initiated as early as ∼590 Ma following latest Neoproterozoic rifting, that the magmatic belt is long-lived, lasting over about 100 Myr, and that the locus of magmatism shifted oceanward over time. Early syn-orogenic magmatism was focused within the leading edge of the cratonic basement, perhaps guided by strain partitioning during oblique subduction; younger magmas intruded a forearc sedimentary molasse basin, itself eroded from the earlier established arc system. Broadening of the arc during the later phases of Ross convergence indicates rollback of the subducting plate hinge and thickening of the developing forearc during continuing orogenic contraction. The granitoids mainly have calc-alkaline geochemical characteristics, but they show some similarity to adakitic compositions indicative of melt fractionation from the subducting slab; they do not show the alkaline signatures attributed in other areas to crustal extension. Inherited zircon components are compatible with melting of lower crust similar to that exposed at present in the Nimrod Group; however, the paucity of older cores suggests that melt production involved relatively large degrees of fractional melting at high temperature. Whole-rock Sr and Nd isotopic compositions vary systematically across the belt, as expected in a convergent-margin arc setting, and they show significant cratonic influence, with initial. 87Sr/. 86Sr compositions as high as 0·750 and e{open}Nd values as low as -15 for granitoids intruding Nimrod Group basement. Although there is an isotopic discontinuity associated with the inferred cratonic rifted margin, the later phase of magmatism is characterized by uniformly low. 87Sr/. 86Sr and high e{open}Nd, indicating that melt compositions are controlled more by subduction processes than by assimilation of existing crust in the cratonic upper plate. |
format |
Article in Journal/Newspaper |
author |
Goodge, John W Fanning, Christopher Norman, Marc Bennett, Victoria |
spellingShingle |
Goodge, John W Fanning, Christopher Norman, Marc Bennett, Victoria Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica |
author_facet |
Goodge, John W Fanning, Christopher Norman, Marc Bennett, Victoria |
author_sort |
Goodge, John W |
title |
Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica |
title_short |
Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica |
title_full |
Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica |
title_fullStr |
Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica |
title_full_unstemmed |
Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica |
title_sort |
temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, central transantarctic mountains, antarctica |
publisher |
Oxford University Press |
publishDate |
2015 |
url |
http://hdl.handle.net/1885/67004 |
long_lat |
ENVELOPE(165.750,165.750,-85.417,-85.417) ENVELOPE(163.000,163.000,-82.350,-82.350) |
geographic |
Antarctic East Antarctica Nimrod Nimrod Glacier Pacific Transantarctic Mountains |
geographic_facet |
Antarctic East Antarctica Nimrod Nimrod Glacier Pacific Transantarctic Mountains |
genre |
Antarc* Antarctic Antarctica East Antarctica Nimrod Glacier |
genre_facet |
Antarc* Antarctic Antarctica East Antarctica Nimrod Glacier |
op_source |
Journal of Petrology |
op_relation |
0022-3530 http://hdl.handle.net/1885/67004 |
_version_ |
1766080238633091072 |