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305-7 New geochronology constraints on the evolution of the high-pressure belt of the Brooks Range, northern Alaska: the early years

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

Poster Booth No.: 196

Presenting Author:

Minh Pham

Authors:

Pham, Minh¹, Vogl, James J.², Baker, Peter Louis³, Vervoort, Jeff David⁴, Williams, Samuel⁵

(1) Department of Geological Sciences, University of Florida, Gainesville, FL, USA, (2) Department of Geological Sciences, University of Florida, Gainesville, FL, USA, (3) School of the Environment, Washington State University, Pullman, WA, USA, (4) School of the Environment, Washington State University, Pullman, WA, USA, (5) Department of Geosciences, The Pennsylvania State University, University Park, PA, USA,

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 Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7290

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

Description

Session Format: Poster

Presentation Date: 10/22/2025

Presentation Room: HBGCC, Hall 1

Poster Booth No.: 196

Author Availability: 3:30–5:30 p.m.

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