Effects of a large pulse of magmatism on the crustal evolution of a continental magmatic ARC: mapping the west-central exhumed north cascades ARC, washington project period: 6/15/2026 through…

Effects of a large pulse of magmatism on the crustal evolution of a continental magmatic ARC: mapping the west-central exhumed north cascades ARC, washington project period: 6/15/2026 through 3/15/2028 abstract high-flux magmatism impacts the mechanical and rheological properties of continental ARC crust. In the north cascades range, washington, structural and temporal relationships among exhumed plutons, orthogneisses, and metasedimentary rocks document the effects of multiple high-flux magmatic events within a late cretaceous?eocene ARC system. The first two events (CA. 96?88 MA and CA. 75?65 MA) were related to normal subduction-driven magmatism, while the third (CA. 50?45 MA) likely resulted from slab-tearing. The eldorado pluton, associated with the first event, was intruded at shallow crustal levels (4?5 kbar) where andalusite was stable. The presence of kyanite overprinting andalusite in adjacent metasedimentary rocks suggests a pressure increase. This indicates either a burial of both units during crustal thickening or that a structure separates the host rock from the pluton, and only the host rock was buried after the pluton was intruded. A younger, CA. 73 MA pluton recently identified east of the eldorado pluton suggests there are two adjacent plutons from different magmatic events. Adjacent to that are upper-amphibolite facies paragneisses of a second supracrustal unit. The extent of the newly recognized pluton and whether IT is directly adjacent to the kyanite?andalusite-bearing rocks remain unclear. Therefore, a reevaluation of the dimensions of the CA. 90 MA eldorado pluton, the CA. 73 MA pluton, and the metamorphic mineral assemblages in the adjacent supracrustal rocks is required. The recipient will test whether the eldorado pluton stayed at a shallow crustal level after emplacement and how plutons of different high-flux magmatic events interact: are they separated by a shear zone? Is there any interaction along the contact? In addition, if kyanite?andalusite-bearing metasedimentary rocks are linked to the CA. 73 MA pluton, metamorphism likely corresponds to the second high-flux event, similar to what is observed for other supracrustal rocks to the east. Three 1:24,000 strip maps spanning the forbidden peak, goode mountain, agnes mountain, and mount lyall quads in the west?central exhumed ARC crystalline core will be prepared. Limited geochronology will also be completed to understand the timing of emplacement and metamorphism of the rock units.