Swinford and Harker plutons : a study in late-orogenic magmatism, Southern Victoria Land, Antarctica
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The Swinford and Harker granite plutons crop out on the eastern side of the St Johns Range and intrude all other lithology's except for scattered mafic dykes and aplite dykes. The Harker Pluton truncates and has cooled against the Swinford Pluton and both were passively emplaced at around 1 Okm depth in the crust.
Major element, trace element and Rb-Sr isotopes indicate that the two plutons have evolved by differentiation from a common magma. The Swinford Pluton ranges from 64.31 to 72.33 wt% Si02 and its evolution was dominated by fractional crystallisation of predominantly plagioclase. The Barker Pluton ranges from 73.45 to 76.98 wt% Si02. Up to 76% Si02 the Harker displays 'normal' chemical trends and has evolved by similar processes to the Swinford Pluton. Beyond 76% Si02 chemical trends are 'anomalous' with massive enrichment's in Nb, Y, Ga, Rb, Pb and Th, indicative of evolution by thermogravitational diffusion (TGD) processes. Evolution of the two plutons probably occurred within a single parent chamber within which TGD processes established a quasi-stagnant 'enriched' cap. The rest of the convecting chamber was dominated by fractional crystallisation. The Swinford Pluton magma was tapped from near the bottom of the chamber while the Barker Pluton magma was tapped from the chambers middle and top regions.
Microgranitoid enclaves and spatially and temporally associated primitive dykes indicate that melting was initiated by intrusion and ponding of mantle derived basic magmas in the lower crust. Enclaves within the plutons represent incorporated globules of the progressively differentiated basic magma. Major and trace element data, mineral chemistry and petrography indicate that these enclaves have undergone hybridisation within the host granites by mechanical mixing and interdiffusional chemical exchange.
Granitoids in the Dry Valleys region have been subdivided into DV la, DVlb and DV2 suites (Alii bone et al. in press) on the basis of field relationships and chemistry. The Swinford and Barker plutons belong in the DV2 suite. A review of dating carried out in the Dry Valleys area seems to iildicate that DVla plutons did not close with respect to the Rb-Sr sytem until emplacement of the main DVlb plutons at around 490 My implying that uplift in the area began at around this time. Rb-Sr dating indicates that emplacement of the Swinford and Barker plutons occurred at around 480My. Textural variations indicate that uplift has occurred between the emplacement of the two plutons, implying that orogenic processes were still active. The Swinford and Barker plutons are thought to have been emplaced in a locally extensional environment in an overall transpressional tectonic regime during the late stages of the CambroOrdovician Ross Orogeny.
Major element, trace element and Rb-Sr isotopes indicate that the two plutons have evolved by differentiation from a common magma. The Swinford Pluton ranges from 64.31 to 72.33 wt% Si02 and its evolution was dominated by fractional crystallisation of predominantly plagioclase. The Barker Pluton ranges from 73.45 to 76.98 wt% Si02. Up to 76% Si02 the Harker displays 'normal' chemical trends and has evolved by similar processes to the Swinford Pluton. Beyond 76% Si02 chemical trends are 'anomalous' with massive enrichment's in Nb, Y, Ga, Rb, Pb and Th, indicative of evolution by thermogravitational diffusion (TGD) processes. Evolution of the two plutons probably occurred within a single parent chamber within which TGD processes established a quasi-stagnant 'enriched' cap. The rest of the convecting chamber was dominated by fractional crystallisation. The Swinford Pluton magma was tapped from near the bottom of the chamber while the Barker Pluton magma was tapped from the chambers middle and top regions.
Microgranitoid enclaves and spatially and temporally associated primitive dykes indicate that melting was initiated by intrusion and ponding of mantle derived basic magmas in the lower crust. Enclaves within the plutons represent incorporated globules of the progressively differentiated basic magma. Major and trace element data, mineral chemistry and petrography indicate that these enclaves have undergone hybridisation within the host granites by mechanical mixing and interdiffusional chemical exchange.
Granitoids in the Dry Valleys region have been subdivided into DV la, DVlb and DV2 suites (Alii bone et al. in press) on the basis of field relationships and chemistry. The Swinford and Barker plutons belong in the DV2 suite. A review of dating carried out in the Dry Valleys area seems to iildicate that DVla plutons did not close with respect to the Rb-Sr sytem until emplacement of the main DVlb plutons at around 490 My implying that uplift in the area began at around this time. Rb-Sr dating indicates that emplacement of the Swinford and Barker plutons occurred at around 480My. Textural variations indicate that uplift has occurred between the emplacement of the two plutons, implying that orogenic processes were still active. The Swinford and Barker plutons are thought to have been emplaced in a locally extensional environment in an overall transpressional tectonic regime during the late stages of the CambroOrdovician Ross Orogeny.
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1 v. (various pagings) : col. ill., maps ; 30 cm.
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1993Waters
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Waters, Alex Sean., “Swinford and Harker plutons : a study in late-orogenic magmatism, Southern Victoria Land, Antarctica,” Otago Geology Theses, accessed March 23, 2025, https://theses.otagogeology.org.nz/items/show/293.