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Amato, J.M., 1995

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Bibliographic Reference

Amato, J.M., 1995, Tectonic evolution and petrogenesis of the Kigluaik gneiss dome, Seward Peninsula, Alaska: An integrated structural and geochemical study of extensional processes in mid-crustal rocks: Palo Alto, California, Stanford University, Ph.D. dissertation, 150 p., illust., maps.


New structural, petrologic, geochemical, and geochronologic data from the Kigluaik gneiss dome on Seward Peninsula, Alaska, help constrain its Late Cretaceous tectonic and magmatic evolution. Upper-amphibolite facies metamorphism that followed a pre-120 Ma blueschist-facies metamorphic event was induced by mafic magmatism during Late Cretaceous time. Zircon from the mafic root of the Kigluaik pluton was dated at 90 +/- 1 Ma. This mafic root is genetically related to its large-volume granitic cap. U-Pb analyses of metamorphic monazite yields an estimate of 91 +/- 1 Ma for the attainment of peak temperatures in the country rock. The relationships favor a magmatically driven metamorphic event. The mafic root has high-K compositions. Sr and Nd isotopic analyses yield an array from values from the mafic root of (~0.706, 0) to values from the granitic cap of (0.712, -2.5). Assimilation and fractional crystallization processes best explain this array. Trace element abundances are similar to subduction-related continental volcanic rocks and mafic potassic plutons throughout the world. The Cretaceous tectonic setting of the Seward Peninsula was likely characterized by a continental arc undergoing extension over a north-dipping subducting slab which was retreating to the south. The most intriguing aspect of the fabrics in the Kigluaik Mountains is an apparent rotation with structural depth of stretching lineations. Comparison the Ruby Mountains suggests that lower crustal E-W flow was compensating for differential crustal thinning associated with N-S extension, possibly related to the extension of lower crustal material from Alaska into a region of N-S extension in the Bering Straits. Coeval magmatism, metamorphism, and deformation at ~90 Ma within the core of the Kigluaik Mountains indicates that the western Seward Peninsula was tectonically active during the Late Cretaceous. The genesis of gneiss domes such as those on the Seward Peninsula are common in regions that have experienced large-magnitude crustal extension, and the favored interpretation is that the Seward Peninsula gneiss domes developed in a similar extensional setting.

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