Age of the Wisconsin Range Batholith

The Middle Cambrian age and elevated initial Sr/ Sr ratio are typical of the Granite Harbor Intrusives of the Transantarctic Mountains. 

All specimens in this group are unfoliated (i.e., post-tectonic) and equigranular or porphyritic with euhedral phenocrysts of pink microcline. These 

The Rb-Sr date (494 5 Ma) and low initial Sr/ Sr ratio (0.7055 0.0014) indicate that the rocks of the post-tectonic facies of the Wisconsin Range Batholith crystallized during the Late Cambrian to Early Ordovician from magma that was not a derivative of the syntectonic magmas that formed the gneissic granitoids. Moreover, the wide distribution of the post-tectonic 

These insights concerning the history of magmatic activity in the Wisconsin Hills remind us that McLelland (1967) divided the Granite Harbor Intrusives in the southern part of the Nilsen Plateau into four distinctive facies (Section 6.3.1). Three of these facies are cata-clastically deformed (i.e., syntectonic), whereas the North Quartz Monzonite is not foliated (i.e., post-tectonic) and may be younger than the other facies. 

This result confirms that the aplite dikes began to retain in-situ produced radiogenic Sr during the Middle Ordovician (lUGS 2002) although they were 

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