A Lower Cretaceous, syn-extensional magmatic source for a linear belt of positive magnetic anomalies: the Pacific Margin Anomaly (PMA), western Palmer Land, Antarctica
Ar–Ar laserprobe dating suggests that in western Palmer Land, plutons associated with a curvilinear belt of positive magnetic anomalies along the Pacific margin of the Antarctic Peninsula, the Pacific Margin Anomaly (PMA), are Early Cretaceous in age. The new ages, combined with published structural and geochemical studies, suggest that highly magnetically susceptible gabbroic to tonalitic–granodioritic rocks, the probable source of the Palmer Land segment of the PMA, were generated during Early Cretaceous extension when mantle-derived basaltic magma intruded mafic lower to middle crust. Continued extension uplifted newly generated, lower to middle crust through the Curie Isotherm (ca. 600°C) forming the magnetic anomaly. The PMA broadly tracks an arc-parallel band in western Palmer Land where crustal extension and uplift of lower crust were greatest. The close spatial relationship between the PMA and Early Cretaceous, syn-extensional plutons suggests that anomaly area can be used as a crude proxy for the volume of a related plutonic complex; the areal extent of the PMA indicates that a significant proportion of the arc crust was newly generated during the Early Cretaceous in western Palmer Land.
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