T174 Unravelling Timescales of Magmatism, Metamorphism, and Crustal Evolution (Posters)

Tuesday, 17 October 2023
8:00 AM - 5:30 PM
Hall B

KINEMATIC CONTROLS DURING INCREMENTAL PLUTON GROWTH, MCGONAGALL PLUTON, ALASKA RANGE, ALASKA

Paper number: T174-11
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The role lithospheric-scale strike-slip faults play during the transport and emplacement of plutonic systems is widely debated. The 2000 km long dextral strike-slip Denali fault hosts a suite of Eocene calc-alkaline plutons emplaced directly adjacent to the fault, including the 43-33 Ma structurally complex McGonagall pluton. Detailed mapping, petrographic analysis, geochemistry, and geochronology work was completed to determine the possible tectonic controls played on the emplacement of the McGonagall pluton. Mapping conducted perpendicular to strike of the Denali fault yielded two high resolution strip maps. Two major textural units were mapped: an equigranular biotite-hornblende-plagioclase granodiorite and a texturally heterogenous porphyritic hornblende-plagioclase granodiorite. Magmatic contacts between the two are broadly NE-SW oriented. We interpret the McGonagall pluton to have been emplaced shallowly based on crystallization textures. Geochemical analyses of the two units point to a common source, with textural variations originating from differing cooling histories. Field relationships paired with new and ongoing zircon U-Pb LASS and CA-ID-TIMS ages indicate that the McGonagall pluton was built incrementally, even within the same unit. Ti thermometry in zircon indicates crystallization temperatures ranging from 650-800°C. New data from the McGonagall pluton overlap with published geochronology and geochemistry data from the nearby Mt Galen volcanics, tentatively linking the two as an intrusive-extrusive system. The geometry of the internal contacts within the McGonagall pluton as well as the distribution of units are consistent with emplacement during dextral slip along the Denali fault. We interpret the McGonagall pluton to have formed along bookshelf faulting between dextral strike-slip faults during clockwise rotation. Given the asymmetric and systematic spatial distribution of major units, geochemistry, and geochronology results about the Denali fault, the McGonagall pluton is an example of a kinematically controlled pluton emplaced during active dextral deformation along the Denali Fault.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-394955

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