Il. Millar et al., The role of crustal and mantle sources in the genesis of granitoids of theAntarctic Peninsula and adjacent crustal blocks, J GEOL SOC, 158, 2001, pp. 855-867
Magmatic rocks from the Antarctic Peninsula show marked variations in isoto
pe composition, which reflect changes in the geodynamic evolution of the pe
ninsula through time. Most Antarctic Peninsula granitoids formed as a resul
t of subduction: they fall on well-defined trends on plots of Nd, Pb-207/Pb
-204 and delta O-18 against Sr-87/Sr-86(i). between a component derived fro
m subduction-modified mantle or juvenile basaltic underplate (epsilon Nd-i>
6, Pb-207/Pb-204=15.61, delta O-18=5.5 parts per thousand, Sr-87/Sr-86 <0.7
04) and an end-member interpreted as a melt of Proterozoic lower crust (eps
ilon Nd=-7, Pb-207/Pb-204=15.67, delta O-18=10 parts per thousand, Sr-87/Sr
-86=0.709). A small group of granitoids. emplaced before or during Gondwana
break-up, plot on distinct trends towards high Sr-87/Sr-86(i) compositions
. reflecting mixing between melts derived from Proterozoic lower crust and
melts of middle-upper crustal rocks (epsilon Nd-i=-9, Pb-207/Pb-204=15.64,
delta O-18=10 parts per thousand, Sr-87/Sr-86=0.726). with little or no inp
ut of new material derived from the mantle or from juvenile basaltic underp
late. These granitoids are thought to have formed as a result of crustal at
tenuation during the initial rifting phase of Gondwana break-up. Similar tr
ends are shown by data from granitoids of the adjacent crustal blocks of We
st Antarctica, The isotope data suggest that an enriched Ferrar/Karoo-type
lithosphere was not involved in the genesis of granitoids of the Antarctic
Peninsula or of the Ellsworth-Whitmore Mountains crustal block.