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The northeastern Brooks Range (NEBR) in the Arctic National Wildlife Refuge of Alaska (ANWR) is a complex Mesozoic to Cenozoic northward-verging fold-and-thrust belt. Shortening in the upper crust occurred through the duplexing of thrust sheets and formation of associated fault-bend folds. Regional deformation in the NEBR has extended farther to the north than elsewhere in the Brooks Range and is among the youngest in the region.
Apatite fission track analyses (AFTATM) of Permian to Paleogene clastic rock sequences in four areas in the NEBR document the northward younging of uplift and erosion attending the duplexing of thrust sheets. AFTA data on the Permian to Albian Bathtub Ridge section indicate rapid (<3-5 m.y.) cooling through 110-60°C and a minimum of 2 km of uplift and erosion during the Paleocene at about 62 Ma, assuming reasonable geothermal gradients of about 20-30°C/km. This was followed by a second cooling phase which occurred after the Paleocene (<50 Ma). AFTA data from Albian sedimentary rocks at Arctic Creek suggest slower (<5-10 m.y.) cooling through 110-60°C due to uplift and erosion during the late Eocene-middle Oligocene between ^sim40 and 30 Ma. AFTA data on Neocomian to Eocene sandstones, exposed along the Canning River west of the Sadlerochit Mountains, and Upper Cretaceous to Paleocene sandstones, exposed at Sabbath Creek near the Jago River east of the Sadlerochit Mountains, suggest two phases of rapid (<3-5 m.y.) cooling due to uplift and erosion at about 45 and about 23 Ma. In contrast, AFTA data on Late Cretaceous to Tertiary sediments from the Arctic coastal plain show that these rocks have not been subjected to temperatures greater than about 60°C for longer than 1 m.y. since their deposition. Their fission track ages reflect the thermal, uplift, and erosion histories of their provenance terranes (i.e., the NEBR). Therefore, four major regional cooling (uplift and erosion) phases are recognized (^sim62 Ma, ^sim45 Ma, ^sim 0-30 Ma, and ^sim23 Ma). These phases progressively young to the north across a 100-km transect in the NEBR and are interpreted as periods of major compression, effectively dating periods of thrusting in the NEBR and constraining the timing of formation of possible oil-bearing structures on the coastal plain.
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