Geology, age and origin of the Mount Willing area (Prince Charles Mountains, East Antarctica)

Mount Willing in the Prince Charles Mountains (East Antarctica) is part of the Fisher Volcanoplutonic complex which formed as part of the global-scale Grenvillian mobile belt system. Mount Willing is composed of four rock com plexes: 1) a metamorphic sequence, 2) gabbro intrusions, 3) deformed felsic intrusives, and 4) abundant post-metamorphic dykes and veins. Three rock t ypes constitute the metamorphic sequence: amphibole-biotite felsic plagiogn eiss, mafic to intermediate biotite-amphihole schist, and biotite paragneis s. The bulk composition of the mafic schists classifies them as tholeiitic basalts, and rarely as basaltic andesites or andesites. Index mg ranges wid ely from 47 to 71. Concentrations of TiO2, P2O5, and high-field strength el ements are high in some rocks. These rocks are thought to have been derived from enriched (subcontinental) mantle sources. Sm-Nd and U-Pb isotopic dat a indicate a series of Mesoproterozoic thermal events between 1100 and 1300 Ma. In particular, these events occurred at 1289 +/- 10 Ma (volcanic activ ity), at 1177 +/- 16 Ma (tonalite intrusion), at 1112.7 +/- 2.4 and at 1009 +/- 54 Ma (amphibolite facies metamorphic events). Rb-Sr systematics also indicates a thermal overprint at 636 +/- 13 Ma. Mafic schists show low init ial Sr-87/Sr-86 ratios between 0.7024 and 0.7030. Felsic rocks show higher Sr-1 values between 0.7037 and 0.7061. Basaltic andesite metavolcanic and p lutonic rocks form a calc-alkaline evolutionary trend, and probably origina ted from subduction-modified mantle sources in a convergent plate margin en vironment. An oceanic basin may have existed in central Prince Charles Moun tains about 1300 Ma ago and was closed as a result of continental collision around 1000 to 800 Ma.