Date of Award
8-17-2024
Document Type
Thesis
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 33-43 Ma structurally complex McGonagall pluton. Detailed mapping, petrographic analysis, geochemistry, and geochronology work was completed to determine the role tectonic control 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 (Eogd) and a texturally heterogeneous porphyritic hornblende-plagioclase granodiorite (Eogdp). Contacts between these units occur along SW striking faults/shear zones preserving sinistral asymmetric unit displacement. The McGonagall pluton was emplaced shallowly, evident from fine-grained crystallization textures and the presence of volcanic rocks in faulted contact within the pluton. Geochemical analyses of the two units indicate a common origin, with textural variations controlled by differing cooling histories. Field relationships paired with new zircon U-Pb LA- ICP-MS and CA-ID-TIMS ages indicate that the McGonagall pluton was built incrementally, even within the same unit. Analyses from the McGonagall pluton overlap with published geochronology and geochemistry data from the nearby Mt Galen volcanics, establishing them 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. The McGonagall pluton was emplaced via dilational bookshelf faulting between dextral strike-slip faults during strain partitioning through clockwise rotation. Given the asymmetric 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.
Recommended Citation
Marble, Sean, "Tectonic controls on the emplacement of the McGonagall Pluton, Alaska Range, Alaska" (2024). Geosciences . 324.
https://ualaska.researchcommons.org/uaf_grad_geosci/324
Handle
http://hdl.handle.net/11122/15517