305 Subduction Zone Processes: Insights from Geology, Geochemistry, and Petrochronology (Posters)

We invite contributions that explore the geologic processes of subduction zones from new field observations, analytical methodologies, and numerical modeling of metamorphic rocks along the subduction interface or try to integrate or reconcile the rocks record with geophysical observations.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

New geochronology constraints on the evolution of the high-pressure belt of the Brooks Range, northern Alaska: the early years

Paper number: 305-6
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Brooks Range (northern Alaska) formed from Jurassic(?)-Cretaceous convergence between a passive margin and the oceanic Angayucham terrane. The Schist belt of the southern Brooks Range records an early blueschist/eclogite metamorphism in rocks that represent the continental margin. With a strike-length of over 600 km, the Schist belt is one of the world’s largest blueschist belts and shares many characteristics with other high-pressure terranes. Many key aspects of tectono-metamorphic evolution of the Brooks Range, however, remain poorly understood, resulting in diverse orogenic models. Central to the poor understanding is the lack of direct constraints on the timing of high-pressure metamorphism and subsequent exhumation. To address this, we obtained new ages from Lu-Hf dating of garnet and in-situ U-Pb LA-ICP-MS dating of zircon and titanite from the two eclogite bodies within the Schist belt. Garnet from the Clara Creek eclogite (near the Dalton Highway) yielded an age of 136 ± 1.0 Ma, which we interpret as the age of high-pressure metamorphism. U-Pb dating of texturally late titanite from the eclogite yielded ages that overlap with or are slightly younger than the garnet age suggesting rapid(?) decompression immediately following attainment of peak pressures. Zircon ages suggest that zircon may have grown both during high-pressure metamorphism and exhumation. The Cosmos Hills eclogite (250 kilometers to the west) yielded Lu-Hf garnet age of 130.5 ± 0.5 Ma, indicating that the age of high-P metamorphism might vary slightly along strike. Published data show that formation of the Brooks Range ophiolites and thrusting to produce the metamorphic sole occurred at 173-160 Ma period representing the initial of subduction. Thus, our new geochronology implies that there was ca. 20 million years of intra-oceanic thrusting and seamount accretion between ophiolite formation and high-pressure metamorphism. Furthermore, our garnet ages suggest that syn-orogenic sedimentation beginning around 145 Ma occurred during or immediately prior to subduction of the Schist belt.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412649

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