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The Devonian connection between the Brooks Range of Alaska, USA, with the continental margin of Arctic Canada and its subsequent Jurassic–Cretaceous counterclockwise rotation to form the Amerasian Basin, is a highly debated topic in Arctic tectonics. This resource-rich region was assembled from terranes that formed part of Laurentia or Baltica, or were juvenile oceanic arcs in the early Paleozoic that were brought together during Caledonian Orogenesis and the subsequent collision that formed Pangea (Uralide Orogeny). Elements of these orogens, as well as older ones, are predicted to occur in the Brooks Range of Arctic Alaska. This study presents the first combined zircon U-Pb and oxygen data from six Brooks Range metasedimentary units with assumed Neoproterozoic to Devonian ages. Three distinct detrital zircon patterns are identified in these units: (1) those with Neoproterozoic maximum depositional ages characteristic of the Timanide Orogen of northern Baltica and adjacent parts of Siberia, (2) an almost unimodal Siluro–Ordovician (443.5 ± 2.3 Ma) detrital zircon population consistent with the oceanic Apoon arc believed to have existed off shore of northern Laurentia and to have accreted to the North Slope subterrane during the Caledonian event, and (3) those with Middle Devonian maximum depositional ages consistent with post-accretion extension during the final (Scandian) phase of Caledonian Orogenesis. Oxygen isotopes from the same zircons reveal minor to significant crustal contamination with approximately two thirds (n = 255/405) having δ18O values >5.9‰ (above the mantle field of 5.3 ± 0.6‰). Pattern 1 units exhibit a progressive increase in δ18O values throughout the Proterozoic (5.99 to 9.29‰) indicative of increasing crustal growth and Timanide age zircons yield average δ18O values of 7.18 ± 0.64‰ (n = 26) suggestive of more crustal influence than Caledonian age zircons, possibly reflecting northern Baltica signatures. The unimodal population in Pattern 2 yields average δ18O values of 5.49 ± 0.66‰ (n = 17) and 6.02 ± 0.27‰ (n = 23) prior to and during, respectively, the main Caledonian event and suggest derivation from Devonian juvenile arc sources possibly representing the initiation of the collision between Laurentia and Baltica. Similar to Pattern 1, the δ18O values associated with Pattern 3 show a progressive increase in δ18O values throughout the Proterozoic (5.00 to 9.39‰). However, Pattern 3 also exhibits a distinct juvenile fingerprint (6.13 ± 0.24‰, n = 51) during the main Caledonian event and a slight increase to 7.12 ± 1‰ (n = 7) in post-Caledonian zircons possibly suggest correlating with a post-accretion phase in which proximally sourced zircon-bearing detritus was deposited in extension-related basins marking the joining of Laurentia and Baltica.

A B S T R A C TArabian Shield granitic zircon geochemistry provides insight into the petrogenetic processes involved in generating one of the planet's largest tracts of juvenile Neoproterozoic crust. New zircon geochemistry supports previous U-Pb and whole-rock data that defined four magmatic groups: (1) ∼870-675 Ma island arc and synorogenic I-type granitoids (IA1Syn), (2) ∼640-585 Ma I-and A-type granitoids from the Nabitah and Halaban Suture (NHSG), (3) ∼610-600 Ma postorogenic perthitic (hypersolvus) A-type granitoids (POPG), and (4) !600 Ma anorogenic aegirine-bearing perthitic (hypersolvus) A-type granitoids (AAPG). The low Nb (∼1-300 ppm) and intrasuite rare earth element variation in IA1Syn and NHSG zircons indicates that these suites are derivatives of contaminated mantle followed by fractionation. AAPG suites, however, have higher Nb content (∼10-400 ppm) and are derived from limited crust-enriched mantle interaction. Each of the IA, Syn, and NHSG suites have discrete granite subsuites distinguished using zircon morphology and geochemistry whose U-Pb ages in each case form three groups. The IA subgroups are ∼867, ∼847, and ∼829 Ma; the Syn subgroups are ∼730, 716, and 696 Ma; and the NHSG subgroups are ∼636, ∼610, and ∼594 Ma. This apparent subevent repetition suggests some form of magmatic pulsing in the Arabian Shield. It is suggested that IA1Syn suites reflect typical volcanic arc granite settings and incremental subduction/accretion of eastward-migrating oceanic fragments of the East African Orogen. The appearance of ∼636 Ma A-type magmatism within suture zones (NHSG) is possibly derived from a long-lived (∼50 m.yr.) melting, assimilation, storage, and homogenization (MASH) zone resulting from an ∼640 Ma slab tear. These A-types are distinguished from more-enriched anorogenic (!600 Ma) A-types, possibly associated with lithospheric delamination.

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