U–Pb ion-microprobe zircon geochronology from the basement inliers of eastern Graham Land, Antarctic Peninsula
T. R. Riley
M. J. Flowerdew
M. J. Whitehouse
10.6084/m9.figshare.3453059.v1
https://geolsoc.figshare.com/articles/dataset/U_Pb_ion-microprobe_zircon_geochronology_from_the_basement_inliers_of_eastern_Graham_Land_Antarctic_Peninsula/3453059
<p>New geological mapping combined with U–Pb ion microprobe zircon geochronology on the isolated but locally extensive exposures
of crystalline basement inliers of eastern Graham Land has greatly improved our understanding of the region’s early crustal
evolution and has allowed a more thorough evaluation of Patagonia–Antarctic Peninsula connections prior to Gondwana break-up.
At Eden Glacier, diorite gneisses yield Early Ordovician protolith ages of 487 ± 3 and 485 ± 3 Ma and represent the oldest
<em>in situ</em> rocks recorded on the Antarctic Peninsula, and indicate a significant spatial extension of Famatinian-age magmatism of Patagonia.
Zircon overgrowths in the Early Ordovician protoliths and granitic leucosomes developed within them record two phases of Permian
metamorphism at <em>c</em>. 275 and <em>c</em>. 257 Ma, coincident in part with diorite plutonism of the area at 272 ± 2 Ma. At Adie Inlet, granitic leucosomes from paragneiss
have been dated at 276 ± 3 Ma, and these are in turn cut by 257 ± 3 Ma xenolith-rich diorite gneiss. The diorite intruded
during a second phase of deformation, which folded the paragneiss leucosomes into tight folds. This whole assembly is cut
by intensely brecciated megacrystic granodiorite, which yielded a 259 ± 3 Ma age. South of Cabinet Inlet a very different
sequence of events is evident, with Triassic magmatism at <em>c</em>. 236 Ma extensive along the Joerg Peninsula. Migmatitic leucosomes are dated at <em>c</em>. 224 Ma and magmatism and deformation events apparently continued to <em>c</em>. 209 Ma at Cape Casey. Our data indicate that the Devonian and Carboniferous magmatism at Target Hill, considered to represent
the ‘classic’ basement complex of the Antarctic Peninsula, is not representative regionally. The Target Hill crustal block
contains a major break along Cabinet Inlet; to the north, Ordovician and Permian protoliths were variably migmatized during
two episodes of Permian deformation and metamorphism, whereas to the south, Triassic protoliths and Triassic metamorphism
are encountered.
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2016-06-21 11:06:22
Ordovician protolith ages
Antarctic Peninsula
Graham Land
magmatism
Target Hill crustal block
basement inliers
Ma
brecciated megacrystic granodiorite
Cabinet Inlet
Antarctic Peninsula New
granitic leucosomes
Geology