Precise U-Pb Zircon Ages and Geochemistry of Jurassic Granites, Ellsworth-Whitmore Terrane, Central Antarctica
The Ellsworth-Whitmore Mountain terrane of central Antarctica was part of the early Paleozoic amalgamation of Gondwana, including a 13,000 m section of Cambrian– Permian sediments in the Ellsworth Mountains deposited on Grenville-age crust. The Jurassic breakup of Gondwana involved a regional, bimod...
| Published in: | Geological Society of America Bulletin |
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| Main Authors: | , , |
| Format: | Text |
| Language: | unknown |
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ScholarWorks
2017
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| Subjects: | |
| Online Access: | https://scholarworks.boisestate.edu/geo_facpubs/345 https://doi.org/10.1130/B31485.1 |
| Summary: | The Ellsworth-Whitmore Mountain terrane of central Antarctica was part of the early Paleozoic amalgamation of Gondwana, including a 13,000 m section of Cambrian– Permian sediments in the Ellsworth Mountains deposited on Grenville-age crust. The Jurassic breakup of Gondwana involved a regional, bimodal magmatic event during which the Ellsworth-Whitmore terrane was intruded by intraplate granites before translation of the terrane to its present location in central Antarctica. Five widely separated granitic plutons in the Ellsworth-Whitmore terrane were analyzed for their whole-rock geochemistry (X-ray fluorescence), Sr, Nd, and Pb isotopic compositions, and U-Pb zircon ages to investigate the origins of the terrane magmas and their relationships to mafic magmatism of the 183 Ma Karoo-Ferrar large igneous province (LIP). We report high-precision (±0.1 m.y.) isotope dilution– thermal ionization mass spectrometry (IDTIMS) U-Pb zircon ages from granitic rocks from the Whitmore Mountains (208.0 Ma), Nash Hills (177.4–177.3 Ma), Linck Nunatak (175.3 Ma), Pagano Nunatak (174.8 Ma), and the Pirrit Hills (174.3–173.9 Ma), and U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages from the Whitmore Mountains (200 ± 5 Ma), Linck Nunatak (180 ± 4 Ma), Pagano Nunatak (174 ± 4 Ma), and the Pirrit Hills (168 ± 4 Ma). We then compared these results with existing K-Ar ages and Nd model ages, and used initial Sr, Nd, and Pb isotope ratios, combined with xenocrystic zircon U-Pb inheritance, to infer characteristics of the source(s) of the parent magmas. We conclude that the Jurassic plutons were not derived exclusively from crustal melts, but rather they are hybridized magmas composed of convecting mantle, subcontinental lithospheric mantle, and lower continental crustal contributions. The mantle contributions to the granites share isotopic similarities to the sources of other Jurassic LIP mafic magmas, including radiogenic 87Sr/86Sr (0.706–0.708), unradiogenic 143Nd/144Nd (εNd < –5), and Pb isotopes consistent with a low-µ ... |
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