The Wiley Glacier complex, Antarctic Peninsula: pluton growth by pulsing of granitoid magmas

Early Cretaceous gabbro, quartz-diorite-granodiorite, and tonalite-granodiorite plutons of the Wiley Glacier complex, in the Antarctic Peninsula magmatic arc, were emplaced in a zone of syn-magmatic extensional shearing. The oldest component pluton is the Creswick Gap quartz-diorite-granodiorite pluton and this is cut by slightly younger hornblende gabbro of the Moore Point pluton. These plutons form the wall rock to the Burns Bluff tonalite-granodiorite pluton, the youngest component of the complex. The Burns Bluff pluton comprises tonalite-granodiorite sheets which, at the plutons margins, are interleaved with screens of mylonite wall rock. The Moore Point hornblende gabbro has ϵNd141 of ca. +4 and ϵSr141 of ca. +1. It is predominantly mantle in origin, although its parent magma assimilated some continental crust during emplacement. The Creswick Gap pluton has ϵNd141 between ca. +4 (quartz-diorite) and ca. −1 (granodiorite) and ϵSr141 from ca. −1 (quartz-diorite) to ca. +22 (granodiorite). This pluton contains both mantle and crustal components. We suggest that the quartz-diorite facies fractionated from a similar parent magma to that of the Moore Point gabbro, whilst the granodiorite fractionated from a gabbro-quartz-diorite magma during continued crustal assimilation. Geochemical variations within the Creswick Gap pluton cannot be generated by AFC models. Some of the granodiorite samples have chemical characteristics which typify partial melts of amphibole ± garnet-bearing crust. We conclude that the pluton comprises fractionates of basaltic magma and crustal partial melt. The Burns Bluff tonalite-granodiorite sheets have ϵNd141 between ca. +4 and ca. −2 and ϵSr141 from ca. +5 to ca. +31. Their isotopic and chemical compositions suggest that some are fractionates of basalt-gabbro magma, others are predominantly partial melts of amphibole ± garnet-bearing crust, and some are mixtures of these two magma types. The chemical and isotopic compositions of the Burns Bluff plutons constituent tonalite sheets and its dyke-like internal structure suggest that it grew incrementally via the addition of melt batches from a variety of crustal and mantle sources. The growth of this pluton, via dyking, may reflect magma pulsing associated with transtensional movement along the Creswick Gap shear zone. Moreover, the Burns Bluff pluton may be a ‘frozen’ conduit system for structurally higher plutons in the Antarctic Peninsula batholith.

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